U.S. patent application number 09/037145 was filed with the patent office on 2002-03-21 for method and apparatus for the nondestructive determination of the purity of precious metals and the composition of an unknown material sample.
Invention is credited to BARATTA, FRANCIS I..
Application Number | 20020034211 09/037145 |
Document ID | / |
Family ID | 21892689 |
Filed Date | 2002-03-21 |
United States Patent
Application |
20020034211 |
Kind Code |
A1 |
BARATTA, FRANCIS I. |
March 21, 2002 |
METHOD AND APPARATUS FOR THE NONDESTRUCTIVE DETERMINATION OF THE
PURITY OF PRECIOUS METALS AND THE COMPOSITION OF AN UNKNOWN
MATERIAL SAMPLE
Abstract
This invention will provide a method of determining
nondestructively, the purity or composition of an unknown material
sample, such as, for example a sample of gold or silver of unknown
purity. Their forms can be a: casting, bullion, coupon or disc (a
coin), as well as some jewelry, such as gold or silver rings with
signet surfaces. The method involves subjecting one of the large
surfaces of the sample of known thickness to an elevated or a cold
temperature, relative to the initial temperature of the sample, and
comparing the time-varying temperature pattern during finite
lengths of time at the same surface thereof, or at the opposite
surface, with that of a known and identically-sized standard
subjected to the equivalent conditions. The temperature of said
surfaces or opposite surfaces can be monitored during the time the
heat or cold pulse, or constant temperature is applied and/or after
withdrawal. The test specimens are such that their areal dimensions
are large compared to their thicknesses, thus qualifying as
`slabs`. In order to detect a particular adulterant the method may
require a dual-test procedure: The first is an application of a
pulse of constant heat and the second, if necessary, is an
application of constant temperature. Furthermore, during the time
the conditions are applied the slopes of the time-varying
temperature patterns can be determined, the decay curves, after
such conditions are removed, and their slopes can also be realized.
Such information will provide a further check on the authenticity
of the test item.
Inventors: |
BARATTA, FRANCIS I.;
(ARLINGTON, MA) |
Correspondence
Address: |
FRANCIS I BARATTA
138 RIDGE STREET
ARLINGTON
MA
021741737
|
Family ID: |
21892689 |
Appl. No.: |
09/037145 |
Filed: |
March 9, 1998 |
Current U.S.
Class: |
374/45 ;
374/5 |
Current CPC
Class: |
G01N 33/2028 20190101;
G01N 25/18 20130101 |
Class at
Publication: |
374/45 ;
374/5 |
International
Class: |
G01N 025/00 |
Claims
I claim as protected by U.S. Letters Patent:
1. A method for determining nondestructively the purity of a test
object of unknown purity, the method comprising: providing a test
object of unknown purity with a given geometric configuration;
providing a means for applying a temperature variation to the test
object; applying a temperature variation to the test object for a
defined time whereby a temperature change is effected at a spot on
the test object; providing a means for measuring a temperature-time
signature of the test object at the spot on the test object;
measuring a temperature-time signature of the test object at the
spot on the test object; providing a temperature-time signature of
a standard object of known purity; providing a means for comparing
the temperature-time signature of the test object to the
temperature-time signature of the standard object; comparing the
temperature-time signature of the test object to the
temperature-time signature of the standard object; and determining
the relative purity of the test object relative to the standard
object based on a comparison between the temperature-time signature
of the test object relative to the temperature-time signature of
the standard object.
2. The method of claim 1 wherein the step of providing a
temperature-time signature of a standard object of known purity
comprises providing a standard object of known purity with a
geometric configuration that is similar to the geometric
configuration of the test object; providing a means for applying a
temperature variation to the standard object; applying a
temperature variation to the standard object for a defined time
whereby a temperature change is effected at a spot on the standard
object, and providing a means for measuring a temperature-time
signature of the standard object at the spot on the standard
object; and measuring a temperature-time signature of the standard
object at the spot on the standard object.
3. The method of claim 1 wherein the step of providing a means for
measuring a temperature-time signature of the test object comprises
providing a focused infrared temperature sensor.
4. The method of claim 2 wherein the step of providing a means for
measuring a temperature-time signature of the standard object
comprises providing a focused infrared temperature sensor.
5. The method of claim 2 wherein the step of providing a means for
applying a temperature variation to the test object of unknown
purity comprises providing a means for applying a temperature
increase above ambient temperature to the test object for a defined
time whereby a temperature increase is effected at a spot on the
test object and wherein the step of providing a means for applying
a temperature variation to the standard object of known purity
comprises providing a means for applying a temperature increase
above ambient temperature to the standard object for a defined time
whereby a temperature increase is effected at a spot on the
standard object.
6. The method of claim 5 wherein the step of providing a means for
applying a temperature increase above ambient temperature to the
test object for a defined time comprises providing an object heated
above ambient temperature, wherein the step of providing a means
for applying a temperature increase above ambient temperature to
the standard object comprises providing an object heated above
ambient temperature, wherein the step of applying a temperature
variation to the test object comprises placing the object heated
above ambient temperature in contact with the test object for a
defined time, and wherein the step of applying a temperature
variation to the standard object comprises placing the object
heated above ambient temperature in contact with the standard
object for a defined time.
7. The method of claim 5 wherein the step of providing a means for
applying a temperature increase above ambient temperature for a
defined time to the test object and the step of providing a means
for applying a temperature increase above ambient temperature for a
defined time to the standard object each comprise providing a means
for applying constant energy inputs of the same constant heat flux
for a defined time to create set temperature changes above ambient
temperature in the test object and the standard object.
8. The method of claim 5 wherein the step of providing a means for
applying a temperature increase above ambient temperature for a
defined time to the test object and the step of providing a means
for applying a temperature increase above ambient temperature for a
defined time to the standard object each comprise providing a means
for applying inputs of constant temperature for a defined time to
create set temperature changes above ambient temperature in the
test object and the standard object.
9. The method of claim 7 wherein the step of providing a means for
applying constant energy inputs of the same constant heat flux for
a defined time to create set temperature changes above ambient
temperature in the test object and the standard object comprise
providing a single heating coil and wherein the steps of applying a
temperature variation to the test object and applying a temperature
variation to the standard object comprise applying the single
heating coil to a surface of the test object for a defined time and
to a surface of the standard object for a defined time to create
set temperature changes above ambient temperature in the test
object and the standard object.
10. The method of claim 7 wherein the step of providing a means for
applying constant energy inputs of the same constant heat flux for
a defined time to create set temperature changes above ambient
temperature in the test object and the standard object comprise
providing a focused laser for applying an input of electromagnetic
energy and wherein the steps of applying a temperature variation to
the test object and applying a temperature variation to the
standard object comprise applying the focused laser on a spot on
the test object for a defined time and then on a spot on the
standard object for a defined time to create set temperature
changes above ambient temperature in the test object and the
standard object.
11. The method of claim 7 wherein the step of providing a means for
applying constant energy inputs of the same constant heat flux for
a defined time to create set temperature changes above ambient
temperature in the test object and the standard object comprise
providing a single heat sink and wherein the steps of applying a
temperature variation to the test object and applying a temperature
variation to the standard object comprise applying the heat sink to
a surface of the test object for a defined time and to a surface of
the standard object for a defined time to create set temperature
changes above ambient temperature in the test object and the
standard object.
12. The method of claim 2 wherein the step of providing a means for
applying a temperature variation to the test object of unknown
purity comprises providing a means for applying a temperature
decrease below ambient temperature for a defined time whereby a
temperature decrease is effected at a spot on the test object and
wherein the step of providing a means for applying a temperature
variation to the standard object of known purity comprises
providing a means for applying a temperature decrease below ambient
temperature for a defined time whereby a temperature decrease is
effected at a spot on the standard object.
13. The method of claim 12 wherein the step of providing a means
for applying a temperature decrease below ambient temperature to
the test object for a defined time comprises providing an object,
liquid, or liquified gas chilled below ambient temperature, wherein
the step of providing a means for applying a temperature decrease
below ambient temperature to the standard object comprises
providing an object, liquid, or liquified gas chilled below ambient
temperature, wherein the step of applying a temperature variation
to the test object comprises placing the object, liquid, or
liquified gas chilled below ambient temperature in contact with the
test object for a defined time, and wherein the step of applying a
temperature variation to the standard object comprises placing the
object, liquid, or liquified gas chilled below ambient temperature
in contact with the standard object for a defined time.
14. The method of claim 1 wherein the step of measuring a
temperature-time signature of the test object is performed during
the defined time over which the temperature variation is applied to
the test object whereby the temperature-time signature of the test
object is a compilation of temperature versus time data taken
during the defined time over which the temperature variation is
applied to the test object.
15. The method of claim 1 further comprising ceasing applying the
temperature variation to the test object and wherein the step of
measuring a temperature-time signature of the test object is
performed after the step of ceasing applying the temperature
variation to the test object whereby the temperature-time signature
of the test object comprises a compilation of
temperature-versus-time data taken during a temperature decay time
after the temperature variation has ceased being applied to the
test object.
16. The method of claim 15 further comprising determining a slope
of the temperature-time signature of the test object during the
temperature decay time, providing a slope of the temperature-time
signature of a standard object during a temperature decay time,
providing a means for comparing the slope of the temperature-time
signature of the test object during the temperature decay time with
the slope of the temperature-time signature of the standard object
during the temperature decay time, comparing the slope of the
temperature-time signature of the test object during the
temperature decay time to the slope of the temperature-time
signature of a standard object during the temperature decay time,
and determining the relative purity of the test object relative to
the standard object based on a comparison between the slope of the
temperature-time signature of the test object during the
temperature decay time relative to the slope of the
temperature-time signature of the standard object during the
temperature decay time.
17. The method of claim 14 further comprising ceasing applying the
temperature variation to the test object and wherein the step of
measuring a temperature-time signature of the test object is
further performed after the step of ceasing applying the
temperature variation to the test object whereby the
temperature-time signature of the test object is a compilation of
temperature-versus-time data taken during the defined time over
which the temperature variation is applied to the test object and
during a temperature decay time after the temperature variation has
ceased being applied to the test object.
18. The method of claim 1 wherein the temperature variation is
applied and the temperature-time signature is measured at a single
spot on the test object.
19. The method of claim 1 wherein the temperature-time signature of
the test object is measured at a spot on the test object distant
from a spot on the test object at which the temperature variation
is applied to the test object.
20. The method of claim 1 further comprising determining a slope of
the temperature-time signature of the test object, providing a
slope of the temperature-time signature of a standard object,
providing a means for comparing the slope of the temperature-time
signature of the test object with the slope of the temperature-time
signature of the standard object, comparing the slope of the
temperature-time signature of the test object to the slope of the
temperature-time signature of a standard object, and determining
the relative purity of the test object relative to the standard
object based on a comparison between the slope of the
temperature-time signature of the test object relative to the slope
of the temperature-time signature of the standard object.
21. The method of claim 20 wherein the step of providing a slope of
the temperature-time signature of a standard object comprises
providing a mathematically-calculated temperature-time signature of
a standard object of known purity.
22. The method of claim 21 wherein the slope of the
temperature-time signature of a standard object of known purity is
calculated by a computer.
23. The method of claim 20 wherein the step of providing a slope of
the temperature-time signature of a standard object of known purity
comprises providing a computer-recorded slope of the
temperature-time signature of a standard object of known
purity.
24. The method of claim 1 wherein the step of providing a
temperature-time signature of a standard object of known purity
comprises providing a mathematically-calculated temperature-time
signature of a standard object of known purity.
25. The method of claim 24 wherein the temperature-time signature
of a standard object of known purity is calculated by a
computer.
26. The method of claim 24 wherein the step of providing a
temperature-time signature of a standard object of known purity
comprises providing a computer-recorded temperature-time signature
of a standard object of known purity.
27. The method of claim 2 wherein the step of applying a
temperature variation to the test object for a defined time and the
step of applying a temperature variation to the standard object for
a defined time are performed substantially concomitantly and
wherein the step of measuring a temperature-time signature of the
test object and the step of measuring a temperature-time signature
of the standard object are performed substantially
concomitantly.
28. A method for determining nondestructively the purity of a test
object of unknown purity, the method comprising: providing a test
object of unknown purity with a given geometric configuration;
providing a means for applying a constant energy input to the test
object; applying a constant energy input to the test object for a
defined time whereby a temperature change is effected at a given
spot on the test object; providing a means for measuring a
temperature-time signature of the test object at the given spot on
the test object; measuring a constant-energy-input temperature-time
signature of the test object at the given spot on the test object;
providing a means for applying a constant temperature input to the
test object; applying a constant temperature input to the test
object for a set time whereby a temperature change is effected at a
given spot on the test object; measuring a
constant-temperature-input temperature-time signature of the test
object at the given spot on the test object providing a
constant-energy-input temperature-time signature of a corresponding
spot on a geometrically similar standard object of known purity;
providing a constant-temperature-input temperature-time signature
of a corresponding spot on a geometrically similar object of known
purity; providing a means for comparing the constant-energy-input
temperature-time signature of the test object to the
constant-energy-input temperature-time signature of the standard
object; providing a means for comparing the
constant-temperature-input temperature-time signature of the test
object to the constant-temperature-input temperature-time signature
of the standard object; comparing the constant-energy-input
temperature-time signature of the test object to the
constant-energy-input temperature-time signature of the standard
object; comparing the constant-temperature-input temperature-time
signature of the test object to the constant-temperature-input
temperature-time signature of the standard object; and determining
the relative purity of the test object relative to the standard
object based on a comparison between the temperature-time
signatures of the test object relative to the temperature-time
signatures of the standard object.
29. The method of claim 28 wherein the step of providing a
constant-energy-input temperature-time signature of a corresponding
spot on a geometrically similar standard object of known purity
comprises providing a standard object of known purity that is
geometrically similar to the test object, providing a means for
applying a constant energy input to the standard object, applying a
constant energy input to the standard object for the defined time
whereby a temperature change is effected at a corresponding spot on
the standard object that corresponds to the given spot on the test
object, providing a means for measuring a constant-energy-input
temperature-time signature of the standard object at the
corresponding spot on the standard object, and measuring a
constant-energy-input temperature-time signature of the standard
object at the corresponding spot on the standard object and wherein
the step of providing a constant-temperature-input temperature-time
signature of a corresponding spot on a geometrically similar
standard object of known purity comprises providing a means for
applying a constant temperature input to the standard object
applying a constant temperature input to the standard object for
the set time whereby a temperature change is effected at a
corresponding spot on the standard object that corresponds to the
given spot on the test object, providing a means for measuring a
constant-temperature-input temperature-time signature of the
standard object at the corresponding spot on the standard object,
and measuring a constant-temperature-input temperature-time
signature of the standard object at the corresponding spot on the
standard object
30. The method of claim 28 wherein the step of providing a means
for measuring a temperature-time signature of the test object at
the given spot on the test object comprises providing a non-contact
temperature sensor.
31. The method of claim 30 wherein the step of providing a
non-contact temperature sensor comprises providing a focused
infrared temperature sensor.
32. The method of claim 29 wherein the step of providing a means
for applying a constant energy input to the test object comprises
providing an object heated above ambient temperature and wherein
the step of applying a constant energy input to the test object
comprises placing the object heated above ambient temperature in
contact with the test object.
33. The method of claim 29 wherein the step of providing a means
for applying a constant energy input to the test object comprises
providing a non-contact focused input of constant energy of a given
constant heat flux and wherein the step of applying a constant
energy input to the test object comprises focusing the non-contact
focused input of constant energy on a given spot on the test
object.
34. The method of claim 33 wherein the step of providing a
non-contact focused input of constant energy of a given constant
heat flux comprises providing focused lasers for applying
electromagnetic energy to the given spot on the test object.
35. The method of claim 30 wherein the step of providing a means
for applying a constant energy input to the test object comprises
providing a heating coil, wherein the step of providing a means for
applying a constant energy input to the standard object comprises
providing the same heating coil, and wherein the step of applying a
constant energy input to the test object and the step of applying a
constant energy input to the standard object comprise applying the
heating coil to a surface of the test object and to a corresponding
surface on the standard object.
36. The method of claim 30 wherein the step of providing a means
for applying a constant energy input to the test object comprises
providing a heat sink, wherein the step of providing a means for
applying a constant energy input to the standard object comprises
providing the same heat sink, and wherein the step of applying a
constant energy input to the test object and the step of applying a
constant energy input to the standard object comprise applying the
heat sink to a surface of the test object and to a corresponding
surface on the standard object.
37. An apparatus for determining nondestructively the purity of a
test object of unknown purity, the apparatus comprising: a means
for applying a temperature variation to a test object of unknown
purity; a means for measuring a temperature-time signature of the
test object; a means for providing a temperature-time signature of
a standard object of known purity; and a means for comparing the
temperature-time signature of the test object to the
temperature-time signature of the standard object; whereby a user
can employ the apparatus to determine the relative purity of the
test object relative to the standard object based on a comparison
between the temperature-time signature of the test object relative
to the temperature-time signature of the standard object.
38. The apparatus of claim 37 wherein the means for providing a
reference temperature-time signature of a standard object of known
purity comprises a means for applying a temperature variation to
the standard object and a means for measuring a temperature-time
signature of the standard object.
39. The apparatus of claim 37 wherein the means for measuring a
temperature-time signature of the test object comprises a focused
infrared temperature sensor.
40. The apparatus of claim 38 wherein the means for measuring a
temperature-time signature of the standard object comprises a
focused infrared temperature sensor.
41. The apparatus of claim 38 wherein the means for applying a
temperature variation to the test object of unknown purity
comprises a means for applying a temperature increase above ambient
temperature to the test object for a defined time and wherein the
means for applying a temperature variation to the standard object
of known purity comprises a means for applying a temperature
increase above ambient temperature to the standard object for a
defined time.
42. The apparatus of claim 41 wherein the means for applying a
temperature increase above ambient temperature to the test object
for a defined time comprises an object heated above ambient
temperature and wherein the means for applying a temperature
increase above ambient temperature to the standard object comprises
an object heated above ambient temperature.
43. The apparatus of claim 41 wherein the means for applying a
temperature increase above ambient temperature for a defined time
to the test object and the means for applying a temperature
increase above ambient temperature for a defined time to the
standard object each comprise a means for applying constant energy
inputs of the same constant heat flux for a defined time to create
set temperature changes above ambient temperature in the test
object and the standard object.
44. The apparatus of claim 41 wherein the means for applying a
temperature increase above ambient temperature for a defined time
to the test object and the means for applying a temperature
increase above ambient temperature for a defined time to the
standard object each comprise a means for applying inputs of
constant temperature for a defined time to create set temperature
changes above ambient temperature in the test object and the
standard object.
45. The apparatus of claim 43 wherein the means for applying
constant energy inputs of the same constant heat flux for a defined
time to create set temperature changes above ambient temperature in
the test object and the standard object comprise a single heating
coil.
46. The apparatus of claim 43 wherein the means for applying
constant energy inputs of the same constant heat flux for a defined
time to create set temperature changes above ambient temperature in
the test object and the standard object comprise a focused laser
for applying an input of electromagnetic energy.
47. The apparatus of claim 43 wherein the means for applying
constant energy inputs of the same constant heat flux for a defined
time to create set temperature changes above ambient temperature in
the test object and the standard object comprise a single heat
sink.
48. The apparatus of claim 38 wherein the means for applying a
temperature variation to the test object of unknown purity
comprises a means for applying a temperature decrease below ambient
temperature for a defined time whereby a temperature decrease may
be effected at a spot on the test object and wherein the means for
applying a temperature variation to the standard object of known
purity comprises a means for applying a temperature decrease below
ambient temperature for a defined time whereby a temperature
decrease may be effected at a spot on the standard object.
49. The apparatus of claim 48 wherein the means for applying a
temperature decrease below ambient temperature to the test object
for a defined time comprises an object, liquid, or liquified gas
chilled below ambient temperature and wherein the means for
applying a temperature decrease below ambient temperature to the
standard object comprises an object, liquid, or liquified gas
chilled below ambient temperature.
50. The apparatus of claim 37 further comprising a means for
determining a slope of the temperature-time signature of the test
object, a means for providing a slope of the temperature-time
signature of a standard object and a means for comparing the slope
of the temperature-time signature of the test object to the slope
of the temperature-time signature of the standard object to
determine the relative purity of the test object relative to the
standard object based on a comparison between the slope of the
temperature-time signature of the test object relative to the slope
of the temperature-time signature of the standard object.
51. The apparatus of claim 50 wherein the means for providing a
slope of the temperature-time signature of a standard object
comprises a means for providing a mathematically-calculated
temperature-time signature of a standard object of known
purity.
52. The apparatus of claim 50 wherein the means for providing a
slope of the temperature-time signature of a standard object of
known purity comprises a computer.
53. The apparatus of claim 52 wherein the means for providing a
slope of the temperature-time signature of a standard object of
known purity comprises a means for providing a computer-recorded
slope of the temperature-time signature of a standard object of
known purity.
54. The apparatus of claim 37 wherein the means for providing a
temperature-time signature of a standard object of known purity
comprises a means for providing a mathematically-calculated
temperature-time signature of a standard object of known
purity.
55. The apparatus of claim 54 wherein the means for providing a
temperature-time signature of a standard object of known purity
comprises a means for providing a computer-recorded
temperature-time signature of a standard object of known
purity.
56. The apparatus of claim 37 wherein the means for applying a
constant energy its input to the test object comprises focused
lasers for applying electromagnetic energy to the test object and
wherein the means for measuring a temperature-time signature of the
test object comprises a focused infrared temperature sensor.
57. An apparatus for determining nondestructively the purity of a
test object of unknown purity, the apparatus comprising: a means
for applying a constant energy input to a test object of unknown
purity; a means for applying a constant temperature input to the
test object; a means for measuring a temperature-time signature of
the test object at the given spot on the test object; a means for
providing a constant-energy-input temperature-time signature of a
corresponding spot on a geometrically similar standard object of
known purity, a means for providing a constant-temperature-input
temperature-time signature of a corresponding spot on a
geometrically similar object of known purity; a means for comparing
the constant-energy-input temperature-time signature of the test
object to the constant-energy-input temperature-time signature of
the standard object; and a means for comparing the
constant-temperature-input temperature-time signature of the test
object to the constant-temperature-input reference temperature-time
signature of the standard object; whereby a user can determine the
relative purity of the test object relative to the standard object
based on a dual comparison between the temperature-time signatures
of the test object relative to the temperature-time signatures of
the standard object.
58. The apparatus of claim 57 wherein the means for providing a
constant-energy-input temperature-time signature of a corresponding
spot on a geometrically similar standard object of known purity
comprises a means for providing a standard object of known purity
that is geometrically similar to the test object, a means for
applying a constant energy input to the standard object whereby a
temperature change may be effected at a corresponding spot on the
standard object that corresponds to the given spot on the test
object, and a means for measuring a constant-energy-input
temperature-time signature of the standard object at the
corresponding spot on the standard object and wherein the means for
providing a constant-temperature-input temperature-time signature
of a corresponding spot on a geometrically similar standard object
of known purity comprises a means for applying a constant
temperature input to the standard object whereby a temperature
change may be effected at a corresponding spot on the standard
object that corresponds to the given spot on the test object and a
means for measuring a constant-temperature-input temperature-time
signature of the standard object at the corresponding spot on the
standard object.
59. The apparatus of claim 58 wherein the means for measuring a
temperature-time signature of the test object at the given spot on
the test object comprises a non-contact temperature sensor.
60. The apparatus of claim 59 wherein the non-contact temperature
sensor comprises a focused infrared temperature sensor.
61. The apparatus of claim 57 wherein the means for applying a
constant energy input to the test object comprises an object heated
above ambient temperature.
62. The apparatus of claim 57 wherein the means for applying a
constant energy input to the test object comprises a means for
applying a non-contact focused input of constant energy of a given
constant heat flux.
63. The apparatus of claim 62 wherein the means for applying a
non-contact focused input of constant energy of a given constant
heat flux comprises focused lasers for applying electromagnetic
energy to the given spot on the test object.
64. The apparatus of claim 58 wherein the means for applying a
constant energy input to the test object comprises a heating coil
and wherein the means for applying a constant energy input to the
standard object comprises the same heating coil.
65. The apparatus of claim 58 wherein the means for applying a
constant energy input to the test object comprises a heat sink and
wherein the means for applying a constant energy input to the
standard object comprises the same heat sink.
66. The apparatus of claim 57 wherein the means for applying a
constant energy input to the test object comprises focused lasers
for applying electromagnetic energy to the given spot on the test
object and wherein the means for measuring a temperature-time
signature of the test object at the given spot on the test object
comprises a focused infrared temperature sensor.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the nondestructive
determination of the composition of a material when comparing the
thermal properties of a sample of the material with the thermal
properties of a standard of a similar material, said standard or
substitute having a desired composition.
[0002] The invention herein described has use for nondestructive
qualitative determination of composition of a variety of materials
and its use is discussed mostly with reference to precious metals,
such as gold and silver.
BACKGROUND OF THE INVENTION AND PRIOR ART
Background
[0003] The rise in trading in recent years of precious metals, such
as gold and silver, as commodities, and the rise in their unit
prices has increased the need for an economical, fail-safe
mechanism for determining nondestructively, the purity of such
materials. Since gold, like silver, is often transferred or sold by
persons not particularly knowledgeable about such precious metals
to one of greater knowledge, it is important that some way be found
to detect forgeries and ascertain the purity of such precious
metals that avoids the costly and time consuming methods, several
of which are outlined below, a way that is nondestructive, fast and
accurate. By way of background, much of what follows was
paraphrased from The collector's Dictionary of the Silver and Gold
of Great Britain and North America, Michael Clayton, World
Publishing Company, 1971.
[0004] Pure gold is extremely heavy in proportion to its cubic
volume and also very soft (malleable), and if pure, is referred to
as `24 carat`. Silver is not so malleable and only approximately
half the weight of a piece of gold of similar cubic measurement.
Both are too soft to use in their pure form and must be hardened by
the admixture of base metals, usually copper, though silver may be
used with gold. If both silver and copper are added to gold it
becomes pale and green in color. The fact that adding a 50 percent
alloy of copper to silver retains a silvery appearance can easily
lead to fraud without protection. In general, the best proportions
of gold and alloy are 22 parts pure gold to 2 parts alloy, but this
can be varied so that 18, 15, 12, or 9 carats (or parts) are
balanced by an alloy making up 24 parts. These balanced fractions
of pure gold and alloys are legally used and obviously the less
pure gold parts, the cheaper the finished product. With silver,
only two standards are permitted in Great Britain, 925 parts out of
1000 as normal Sterling standard and 958.3 parts as the higher
Britannia standard. By the same measurement, 18 carat gold is the
equivalent of 750 parts fine gold to 1000 (24 carats). For most of
the English gold coinage and all since 1672, the fineness has never
been below 22 carats (916.66 parts gold to the 1000). Since the
nineteenth century in the United States, the coin standard is 900
parts pure silver to 100 parts alloy.
[0005] In order to protect the buyer of gold and silver, a system
of testing, or assaying, and checking the quality and standards of
an object is necessary. This can be done by comparison (touch),
weight, or chemical means. The first demands considerable visual
skill as the object to be tested and a piece of known quality have
both to be stroked across a piece of basanite, a hard flint-like
slate, and the resulting streaks compared. In the second test,
weight, small portions of the object to be assayed are scraped from
each piece, wrapped in lead (lead and silver are also used to wrap
gold) and heated in a bone-ash crucible. As the heat is applied
lead and other base metals oxidize and are absorbed by the
crucible, known as a `cupel`; the balance is then weighed and
compared with the weight of the original scrapings.
[0006] In the case of gold, which is also wrapped in silver, a
further process is required whereby the silver is finally removed
by placing it in hot nitric acid. This method was first recorded in
1495. If on completion of these tests, the gold or the silver are
found to be below the lowest permitted standards, the marks which
would guarantee their quality, `hall-marks`, as they are known, are
withheld and the objects under examination are crushed and returned
to the maker. The third is a simple method and applicable only to
silver, but requires some reasonable idea of the quality of the
metal being tested. This involves the dissolving of the weighed
scrapings, also known as `diet`, in nitric acid and the addition of
a standard solution of sodium chloride (common salt); at a certain
point the cloudy liquid clears and silver chloride is precipitated.
A comparison of the original weight of the silver sample and the
quantity of saline solution required to do this, enables the
fineness of the metal to be assessed.
[0007] Historically, as indicated above there are a number of
methods used to determine the composition of metallic materials
that can be classified as comparative as well as destructive. A
comparative method is one, as the name implies, that requires a
comparison to a known reference material. A destructive test is as
the name implies and needs no explanation. The descriptions of
pertinent testing methods that follows are all comparative tests
and are categorized as `destructive` or `nondestructive`. The
following paragraphs, under the heading "Prior Art", discuss
appropriate examples of these.
Prior Art
[0008] Destructive Tests
[0009] Some of the more modern methods, than those described above,
that have been developed and in use today to determine alloy
content of metallic materials are: optical emission spectrography,
spectrometry, x-ray fluorescence spectrometry, atomic absorption
spectrometry, plasma emission spectrometry and combustometric
analysis to determine particular elements. Such methods usually
require a sample from the test piece, and thus are somewhat
destructive.
[0010] A primary example of a destructive test is the standard
prescribed by the American Society for Testing and Materials,
(ASTM) Test Method B 562-95, "Standard Specification for Refined
Gold". This test method examines samples taken from the melt before
pouring the casting of gold. The standard utilizes, for 99.5
percent purity, a test method for chemical analysis by cupellation
fire assay. If there is a disagreement between the manufacturer and
the purchaser the specified test will then be in accordance with
ASTM Test Method E 1446, "Test method for Chemical Analysis of
Refined Gold by Direct Current Plasma Emission Spectroscopy."
[0011] The standard for testing silver, which is also destructive,
is that given by the ASTM Test Method B 413-89, "Standard
Specification for Refined Silver". This method requires that the
samples be taken from bars by drilling six holes and the chemical
composition is determined in accordance with ASTM Test Method E 378
"Test Method for Spectrographic Analysis of Silver by the Powder
Technique".
[0012] Portable electronic gold testers that measure the carat
value of gold are also available, such as those described in U.S.
Pat. Nos. 4,799,999 and 5,218,303, authored by Medvinsky and
Radomyshelsky. These patents describe a method for determining the
assay of gold alloy, utilizing an electrochemical process. The
specimen gold is wetted by an electrolyte, and a small current
anodizes the surface of the specimen for a metered period of time.
A potential sensing device is then applied to the charged surface,
and a potential decay is observed. The potential decay information
is compared with empirical data and by interpolating the potential
with the empirical data a determination of the carat quality of the
gold alloy may be determined. This same method may be used for
other precious metals, employing different electrolytes, empirical
standards, and potentiometers.
[0013] There are two additional patents, U.S. Pat. Nos. 5,128,016
and 5,080,766, authored by Moment and Nelson, that essentially
utilize the same technique with some variation as those indicated
above.
[0014] The criticism of these gold testing devices are that they
are slightly destructive, are surface sensitive only, will not
detect plating or gold overlay, and will leave a mark on items that
are of 14 carat or less.
[0015] Nondestructive Tests
[0016] There are several methods of nondestructively discriminating
between bodies having similar appearances but of slightly different
composition or even of different material. In one instance the
relatively old technique of eddy current testing is utilized to
attempt to separate higher grade from lower grade materials. This
method principally compares the subsurface electrical conductivity,
synonymous with thermal conductivity, and magnetic permeability of
a resulting read-out wave form of the higher grade standard
material to that of the sample. The conductivity of gold and a
mixture of gold with an adulterant will be very similar, as will
silver and a mixture of silver with an adulterant, and thus the
sensitivity of the eddy current technique will not be sufficient to
separate such forgeries. Also, if a tungsten body, which has the
same density as gold, is gold plated at a surface depth deeper than
the subsurface penetration of the eddy current, then this test
method will not discriminate between pure gold and the forgery.
[0017] In another instance U.S. Pat. No. 4,255,962, issued to
Ashman, teaches a method of distinguishing a simulated diamond from
a natural diamond by utilizing a probe which applies a pulse of
heat to the surface of the sample in an air environment and during
the occurrence of thermal equilibrium the same probe detects the
change in temperature. This change in temperature is related to the
thermal conductivity of the sample. Since the thermal conductivity
of natural diamond is at least an order of magnitude greater than a
simulated diamond, such as cubic zirconia, it is readily detected.
This method, however, is not sensitive enough to detect the slight
change in thermal conductivity between: pure gold and a forgery or
pure silver and a forgery.
[0018] Another example of a nondestructive test method is described
in U.S. Pat. No. 3,981,175, which was issued to Hammond, III and
Baratta. In accordance with that patent, the device is a
nondestructive counterfeit gold bar and silver bar detection system
based upon heat transfer principles. Regarding the testing of gold
the principle entails the application of identical finite suddenly
applied controlled heat pulses at a first region which is one end
of an elongated gold bar of specific dimensions and of known
purity, used as a standard, and a geometrically identical test bar.
The system is completely enclosed in an insulating medium. The
temperatures, which are measured at a second region at the far end
of each bar are not only dependent upon the thermal properties of
each bar, but upon its length and the length of the test time.
Those thermal properties, which in gold are unique, are specific
heat, thermal conductivity and density; the combination of these
properties is defined as thermal diffusivity. Since these
properties in gold are singular, the temperature at the second
region, i.e., the end opposite from that which is suddenly pulsed
by a quantity of heat, will usually be at a higher temperature in a
given time than that of a bar of a particular length less pure than
the standard gold bar of the same length. Because of the large
differences in thermal properties of gold and an alloyed gold
sample, temperature measurements conducted at the far end will
reveal differences.
[0019] The general heat transfer equation for the aforementioned
situation is given in the following:
[0020] If heat (e.g., a square wave pulse of indefinite duration)
is applied to one end of a gold bar, at x=L, the general equation
given in U.S. Pat. No. 3,981,175 for the temperature T(x,t) at any
distance x along the bar's length is:
T(x,t)=QL/k{.alpha.t/L.sup.2+(3x.sup.2-L.sup.2)/6L.sup.2-2/.pi..sup.2.SIGM-
A..sub.m=1.sup..infin.(-1).sup.m/m.sup.2[exp(-.alpha.m.sup.2.pi..sup.2t/L.-
sup.2)]cos(m.pi.x/L)} (1)
[0021] Where: Q is the suddenly applied constant heat flux applied
over an area BTU/sec-ft.sup.2) of the bar, at x=L, L is length in
feet, k is the thermal conductivity (BTU/sec-ft-F),
.alpha.=k/.rho.c, and is the thermal diffusivity in ft.sup.2/sec, c
is the specific heat (BTU/lb-F), .rho. is the density in
lbs/ft.sup.3, t is time in seconds, x is the distance in feet along
the length of the sample and T(x,t) is temperature in degrees F.
Note at x=0, at the far end there is no flow of heat because of the
insulation, See Carslaw and Jaeger conduction Heat in Solids,
Oxford Press, 1950.
[0022] The nondestructive testing of silver bars described in U.S.
Pat. No. 3,981,175 is essentially the same as that indicated above
except rather than employing a pulse of heat a constant temperature
source is applied. Silver has the highest thermal diffusivity of
any known material and the equation for the temperature along the
bar length is dependent upon thermal diffusivity. Therefore, as a
function of time, the silver bar will attain a higher far end
temperature than any other material. The equation for the
temperature at the far end is given in the following: 1 T ( t ) = 2
T 0 n = 0 .infin. ( - 1 ) n { 1 - erf [ ( 2 n + 1 ) / 2 ( t / L 2 )
1 / 2 ] } ( 2 )
[0023] Where T.sub.0 is the applied constant temperature above
ambient and erf is the standard definition of the error function;
well tabulated in many references.
[0024] The method of U.S. Pat. No. 3,981,175 requires that the
standard and test sample be completely insulated and the further
restrictions are that: The standard and test sample must be
elongated bars of the same particular length, and temperatures at
the far end of each bar must be taken over same particular time
interval after the heat is applied, depending on the length of the
bar.
[0025] Yet another example of a nondestructive test method to
detect fraudulent precious metal bars is revealed in U.S. Pat. No.
4,381,154, issued to Hammond, III. It was found that of all
possible forgeries, a non-alloyed tungsten forgery of gold, i.e.,
an insert of tungsten within the gold bar, is the most difficult to
detect because the density and heat-capacity of tungsten and gold
are virtually identical (a less difficult forgery to detect is an
alloyed forgery wherein its composition is generally uniform
throughout). Thus, an improvement in accuracy over the previous
U.S. Pat. No. 3,981,175 was required at that time. This improvement
consists mainly of increasing the accuracy of the detection system
by providing and controlling heat into the test chamber resulting
in equilibrium, termed "dynamic insulation" by the author; accurate
heater control and using a compensated infrared sensor to measure
the temperature at the far end opposite the heated end of the
sample. Also the author claimed that this method allowed the
determination of the density, thermal conductivity and and heat
capacity of a given material.
[0026] Although the improved techniques adopted in U.S. Pat. No.
4,381,154 will enhance the the sensitivity of this test method, it
still requires that the test piece be an elongated bar of specific
dimensions and additional temperature sensors, controls and
electronic instrumentation compared to the method of prescribed in
U.S. Pat. No. 3,981,175. It is also noted that the present day
infrared temperature sensors can readily determine temperatures to
an accuracy within 0.10 C. over a wide range of temperatures (see
the paper by J. M. Looney, JR., and F. Pompei, Medical Electronics,
1989), thus superseding the method proposed in U.S. Pat. No.
4,381,154.
[0027] An additional improvement is described in U.S. Pat. No.
4,385,843 granted to Hammond, III, whereby an induction heater is
employed to provide a pulse of heat to a bar of precious metal to
determine if it has the purity of composition within a given range
of variance. Heat is induced at one end of the bar using an
induction heater powered by a high frequency power source, and the
time versus temperature response at the other end of the bar is
monitored. This device was employed, according to the author, to
circumvent the problems associated with contact heaters. However,
present day lasers or infrared heat sources will accomplish the
same goal.
[0028] A more recent U.S. Pat. No. 5,052,819, was issued to
Baratta; this document taught a method of nondestructively
identifying materials and fraudulent carbon steel fasteners. This
invention compared the characteristic temperature-time curve of a
standard fastener to a test fastener by simultaneously providing a
pulse of heat to both fasteners and measuring the temperatures at
their heated ends. However this patent required an insulated
receptacle and specified that the standard and test sample be
restricted to elongated bars.
SUMMARY
[0029] The device will provide, broadly, a method of determining
nondestructively, the purity or composition of an unknown material
sample, such as, for example a sample of gold or silver of unknown
purity. The form of the sample can be the shape of a casting, a
bullion, a coupon or a disc (a coin). The procedure involves first
subjecting one of the large surfaces of the sample of known
thickness to an elevated or a cold temperature relative to the
initial temperature of the sample and comparing the time-varying
temperature pattern at the same surface thereof, or at the opposite
surface during finite lengths of time with that of a known and
identically-sized standard subjected to the equivalent or the same
conditions for an interval of time of the same finite length. The
temperature of said surface or the opposite surface can be
monitored during the time the heat or cold pulse, or constant
temperature is applied and/or after withdrawal. A second test in
the form of the application of constant temperature may be
required, dependent upon a particular adulterant; this is referred
to as a dual test. In addition, the slopes of the time-varying
temperature patterns during the time the condition is applied
and/or after it is withdrawn can also be determined.
[0030] Several shapes of jewelry, such as gold or silver rings with
partially flat surfaces, such as signets, can also be tested using
the same processes as those indicated above.
[0031] The objects of the present invention are to provide
improvements over U.S. Pat. No. 3,981,175 by Hammond, III and
Baratta for the nondestructive comparison of the composition of an
unknown material sample to the composition of a known material
sample and provide a mechanism for such a nondestructive comparison
determination, and one that can be operated by persons with only a
small amount of technical training.
[0032] Such improvements over the present state-of-the art consist
of eliminating the need for a specified sample shape such as an
elongated bar, as well as a completely insulated environment and
allowing testing of samples whose surfaces are exposed to a medium,
and the use of both contacting and non-contacting heating units;
and noncontacting temperature sensing elements. Further improvement
is realized by examining: the slope of the temperature-time curves,
the decay of the temperature-time curves after the heat or cold
pulse, or constant temperature is removed, as well as the slope of
the decay curve. Such improvements are applicable to field
operations.
[0033] The improved invention described herein allows for the
temperature measurements at either the large surfaces at which the
heat or cold pulse, or constant temperature is applied or at the
opposite surfaces of the standard and the sample. In this way, a
comparison of temperature differences between the standard and the
test sample definitively reveals the temperature differences such
that the fraudulent bullion, coupons, coins, and certain shaped
jewelry can be determined.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Other and further objects, advantages and features of the
invention will be apparent to those skilled in the art from the
following description thereof, taken in connection with
accompanying drawings, in which:
[0035] FIG. 1 is a diagrammatic representation, partly block
diagram in form and the portions of the apparatus shown being
partly cut away, of a system adapted to effect nondestructive
determination of the composition of a material sample in the form
of bullion, a coupon, or a disc;
[0036] FIG. 2 shows in block diagram form a part of the system of
FIG. 1, but slightly modified;
[0037] FIG. 3 shows in block diagram form another modified version
of a part of the system of FIG. 1;
[0038] FIG. 4 shows a modification of the system shown in FIG.
1:
[0039] FIG. 5 shows a modification of the system shown in FIG.
4;
[0040] FIG. 6 shows a modification of the system shown in FIG.
5;
[0041] FIG. 7 schematically shows a partly cut-away system to
determine the purity of a material sample in the form of a
ring;
[0042] FIG. 8 shows a modification of the system shown in FIG. 5;
and
[0043] FIG. 9 shows a modification of FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] In the description of the preferred embodiments that now
follows, the invention is first discussed with reference to a
system for determining nondestructively the composition of an
unknown sample in various forms and, to simplify the explanation,
the samples taken up are precious metals, gold and silver, but it
will be kept in mind that most aspects of the system discussed with
respect to such materials may also apply to other materials not
having unique thermal properties as those of gold or silver.
[0045] It is noted that in the descriptions that follow where
reference is made to the application or discontinuance of heat to
the various bodies, it is understood to be equally applicable to
cryogenic operations as well, which can be accomplished, for
example, by the application of chilled objects of defined sizes or
with liquids or liquified gases in contact with the sample and the
standard for comparison. However, this is not repeated in each case
for the sake of brevity.
[0046] As previously mentioned in the discussion of U.S. Pat. No.
3,981,175 in the prior art, the shapes of the standard and the
sample were required to be in the form of an elongated bars of
specific dimensions where both were insulated. The formulation in
the aforementioned patent is given by Carslaw and Jaeger supra.
These authors, as well as A. B. Newman and L. Green in their paper
entitled "The Temperature History and Rate of Heat loss of an
Electrically Heated Slab," in Transactions of the Electrochemical
Society, Vol. LXVI, 1934, also indicate that if the four edges of a
slab are large compared to their thickness, then heat flow toward
the edges may be neglected. Therefore, if these dimensions are so
large compared to the thickness, such as bullion, coupons and discs
(coins), and most importantly, these cases can be considered from
the view of thermodynamic analysis as approaching slabs, then the
general aforementioned heat transfer equations, equations (1) and
(2), can also be applied to the bodies of interest here, e.g.,
bullion, coupons, discs (coins), as well as certain shapes of
jewelry, which will be discussed later.
[0047] Turning now to FIG. 1, which is a partly cut-away schematic
of the apparatus for such nondestructive determination of gold
bullion, a coupon, or a coin sample. Gold bullion, including gold
coupons, have large width and length dimensions and gold coins have
large diameters compared to their thicknesses. To qualify as a
`slab` the ratio of the edge dimensions, i.e., length, width or
diameter, to the thickness can be approximately 3/1 or greater.
Sample 1 is of unknown composition which is compared with a
standard gold bullion, coupon or coin 2 of known composition.
Although in FIG. 1 and subsequent figures, the sample and standard
are shown as bullion, it is understood that the concepts as now
explained are equally applicable to coupons, discs (coins) and in
some instances jewelry. An electric-resistance heater 3, making
contact over the full bottom surface of sample 1, which is
insulated from the environment by insulation 13, applies a sudden
pulse of constant energy and at the same time an identical
electric-resistance heater 4, which is insulated from the
environment by insulation 14, applies a sudden pulse of constant
energy over the full bottom surface of the standard 2, thereby
providing the same time-varying temperature patterns in the sample
and the standard. Simultaneously, with or at a predetermined time
after the heat is applied and for a predetermined time interval, or
after the heat has been shut off and for a predetermined time
interval, the temperature or time-varying temperature patterns of
the sample, and the standard are sensed or noted and compared. The
sensing functions are provided by infrared temperature sensor 9
focused on a spot 15 located at the middle of the top surface of
sample 1 by a focal lens 5 and an infrared temperature sensor 10
located at the middle of the top surface of standard 2 focused on a
spot 16 by a focal lens 7, both operatively disposed to sense the
time-varying temperatures of the sample and the standard, thus
providing as output an electrical signal that is a function of the
time-varying temperature. Rather than utilize contacting
temperature sensors as in U.S. Pat. No. 3,981,175, non-contacting
infrared temperature sensors 9 and 10 are employed; a further
improvement.
[0048] The top surface of sample 1 is insulated from the
environment by insulation 11, which also encloses temperature
sensor 9 and focal lens 5. Also, the upper surface of the standard
2 is insulated from the environment by insulation 12, which also
encloses temperature sensor 10 and focal lens 7. As previously
explained, the edges of the sample and the standard need not be
insulated because they behave thermodynamically as heated slabs;
this is an important embodiment. Each pair of heating means, as
well as the sample 1 and standard 2 are well distanced from each
other so as to eliminate thermodynamic interference between the two
systems. The two electrical signals are connected as inputs to a
difference amplifier 20 which notes any difference between the two
electrical signals due to a temperature differential and amplifies
the same.
[0049] In FIG. 2, a comparator 21 is connected to receive an output
from the difference amplifier 20A and is connected to an alarm 22
which is activated in those instances in which the content of
sample 1 varies from that of the standard 2, or to a recorder 23.
As FIG. 1 shows, and to complete the electric circuitry of FIG. 1
by which sample purity is evaluated or analyzed, the heaters 3 and
4 are electrically energized through a switch 24 from an electrical
power supply 25. The sequencing and timing of the events in the
system are provided by a timer means 26.
[0050] In the apparatus shown by FIG. 1, the heating elements 3 and
4 are in contact with the bottom of sample 1 and sample 2,
respectively, and temperature sensors 9 and 10 are focused on the
top surfaces of the unknown sample 1 and the standard 2,
respectively, as noted above. The thickness of the the sample 1 and
the standard 2 must be known. This can be readily accomplished
through exterior means by physical measurement, or for example done
through additional instrumentation and sensors built into the
testing apparatus (this is not shown in FIG. 1 since it is not
necessary to the understanding of the concept).
[0051] Each heater means 3 and 4 should be of a type that provides,
in this instance, controlled constant heat input to the sample 1 of
unknown purity and to the gold standard 2, as opposed to a constant
temperature source (the later case is subsequently discussed); the
heat thus applied is a controlled amount and the heating elements 3
and 4, by their physical nature, each have low heat capacity so
that all of the heat generated therein is transferred to the sample
1 and the standard 2.
[0052] If the temperature is measured at x=0, the surface opposite
from the heated surface, equation (1) becomes:
T(t)=QL/k{.alpha.t/L.sup.2-1/6-2/.pi..sup.2.SIGMA..sub.m=1.sup..infin.(-1)-
.sup.m/m.sup.2[exp(-.alpha.m.sup.2.pi..sup.2t/L.sup.2)]} (1A)
[0053] If an attempt is made to counterfeit a sample, the weight W
in pounds and the thickness L in feet, would be dependent upon its
size. Thus, equation (1A) becomes:
T(t)=q/W{t/c-L.sup.2.rho./6k-2L.sup.2.rho./.pi..sup.2k.SIGMA..sub.m=1.sup.-
.infin.(-1).sup.m/m.sup.2[exp(-.alpha.m.sup.2.pi..sup.2t/L.sup.2)]}
(1B)
[0054] Where: q is the suddenly applied constant heat flux in
BTU/sec and all other terms are as previously defined.
[0055] For proof of the purity of the sample it is sufficient that
at all times during the test interval, the measured temperature of
the suspected counterfeit bullion, or coupon, or coin sample be as
high as that of the known gold standard (or a recording thereof).
If the sample in question has the same purity as the standard, then
it will be as hot as or hotter than the standard for comparison.
This is subject to several restrictions and possible errors which
are taken up in the next paragraph.
[0056] Use of equation (1B) requires that the ratio
q.sub.sa/W.sub.sa=q.sub.st/W.sub.st (wherein q.sub.sa and q.sub.st
are the heat inputs to the sample and standard of respective
weights W.sub.sa and W.sub.st) must be kept within acceptable
tolerance. The test is as good as the exactitude with which the
thicknesses and weights are known. It may be impracticable to match
thicknesses and weights of the test sample and the standard for
comparison. However, neither is it necessary that the standard
actually be present at the time the sample is tested nor is it
necessary that a difference amplifier be employed since present day
computers can readily discriminate between the temperature-time
signatures and determine differences. Thus, in FIG. 3, one input to
the computer 27 allows the measured thickness and weight of the
sample and has stored within it the signatures of an equivalent
standard, see Senturia et al, U.S. Pat. No. 3,747,755, which is
incorporated by reference. Note the measurement of thickness and
weight can be integral to the test device (for simplicity this is
not shown in FIG. 1) and automatically programmed into the computer
27, as shown in FIG. 3, or be manually programmed. The second
input, the time-varying temperature patterns of the sample, are
converted to electric signals as before and are fed to a sensor
amplifier 28 and thence to an analog-to-digital converter 29, the
output of the converter being connected as the second input back to
the computer 27. The two signatures, one from the standard and the
other from the sample, are compared by the computer; filed and
recorded for viewing, and connected to an alarm 22A.
[0057] The embodiment indicated in the partly cut-away schematic,
FIG. 4, shows as before the heating element 3A, within the
insulation 13A, in full contact with the bottom surface of the test
sample 1A and the top surface of the sample 1A is insulated by
insulation 11A from the environment. If the temperature is measured
at the middle of the heated surface at x=L of the sample, as
indicated by the sensor 9A with focusing element 5A focused on a
spot 17, then equation (1) becomes:
T(x,t)=QL/k{.alpha.t/L.sup.2+1/3-2/.pi..sup.2
.SIGMA..sub.m=1.sup..infin.(-
-1).sup.m/m.sup.2[exp(-.alpha.m.sup.2.pi..sup.2t/L.sup.2)]cos(m.pi.)}
(1C)
[0058] The temperature sensor 9A is operatively disposed to sense
the time-varying temperatures at the lower surface of sample 1A and
thus provide as an output an electrical signal that is a function
of the time-varying temperature. For this situation, only the
thicknesses of test sample 1A is needed and its weight need not be
known. As before, the thickness of the test sample 1A can be
predetermined by physical measurement or a sensor built into the
system with supplementary instrumentation. This is neither shown
nor discussed here and is not further mentioned with reference to
subsequently described systems, because it is not necessary to the
understanding of the present concepts.
[0059] It is noted that the heating element 3A, shown in FIG. 4,
can easily be replaced by either a focused laser or a focused
infrared heater and equation 1C above will still be applicable. The
definition of Q is defined by the knowledge of the area of the spot
at which the heater is focused.
[0060] Note also, that the physical system associated with the
standard is not shown in FIG. 4, nor need it be, because as already
explained in the description of FIG. 1, an electronic signal
representative of the standard's temperature-time signature, i.e.,
temperature-time curve, can readily be built into the electronics
of the system; this was included in the discussions of FIGS. 2 and
3. Therefore, subsequent discussions of related embodiments and
figures will include only the physical system associated with the
sample to be tested.
[0061] As stated in U.S. Pat. No. 3,981,175 most adulterated
samples will be cooler than the pure gold standard at the far end
when x=0 (also at the heated end at x=L), but not always. In the
course of the work leading to and arising from the aforementioned
patent it was necessary to adjust the length of the sample and
standard, which were in the form of rods, and the time of the test
in order that an adulterated sample would always be cooler than the
standard. In this work that choice is not available because the
thickness, L, for bullion, coupons and discs (coins) are all
different and fixed. For example, Handy and Harmon Corporation
produce gold bullion that range from a thickness of {fraction
(3/16)} inch (4.76 mm) to 11/2 inches (38.10 mm) and gold coupons
that range from 0.039 inch (0.99 mm) to {fraction (1/16)} inch
(1.59 mm). Consequently, not all adulterated gold samples, when
applying either Equation (1A), (1B) or (1C) were cooler than the
gold standard after applying a pulse of heat for a given time
interval.
[0062] The reason for this is that there appears to be an optimum
combination of thermal properties as they occur in equation (1),
and related equations (1A), (1B) and (1C), as a function of
thickness and length of test time. These properties, important in
controlling the transmission of heat through the body and thus the
temperature, are: thermal conductivity, k, and thermal diffusivity,
.alpha.; where .alpha. is defined as k/.rho.c, .rho. being the
density and c the specific heat. The thermal properties of gold and
those elements most likely to be used as adulterants are presented
in Table I below:
1TABLE I .rho. c k .alpha. Elements lb/ft.sup.3 BTU/lb-F
BTU/hr-ft-F ft.sup.2/hr Gold (Au) 1204.860 0.031 183.159 4.936
Copper (Cu) 559.355 0.092 231.693 4.483 Silver (Ag) 655.494 0.056
247.872 6.729 Lead (Pb) 705.436 0.031 20.396 0.948 Tungsten (W)
1204.860 0.032 100.535 2.591
[0063] Ratios of from 50% gold (Au) and 50% adulterants, each of:
copper (Cu), silver (Ag), lead (Pb) or tungsten (W), to ratios of
99.5% Au and 0.5% adulterants, each of Cu, Ag, Pb or W in bullion
thicknesses from {fraction (3/16)} inch (4.76 mm) to 11/2 inches
(38.10 mm) and coupons and coin of from 0.039 inch (0.95 mm) to
{fraction (1/16)} inch (1.67 mm) were examined. A linear
relationship was used to estimate the thermal properties of the
various ratios of adulterants examined. White and yellow gold
samples of 14, 15, 18 and 22 carats were also tested and compared
to pure gold (24 carat).
[0064] The samples that defeated the test set forth in equation
(1), because of their particular combination of thermal properties
and required thicknesses, were composed of the adulterant Pb.
However, when these same samples were tested in accordance with
equation (2), where a constant temperature T.sub.0 was applied for
a given time period, they were cooler than the gold standard. The
basic reason for this is that pure gold has a higher thermal
diffusivity, .alpha., than any of the aforementioned admixtures of
gold samples with the exception of a silver admixture. Therefore,
with the use of the two tests, referred here as the dual test
method, i.e., application of both general equations (1) and (2),
discrimination between the pure standard and the adulterated sample
of at least 99.5 percent purity will be realized.
[0065] With further reference to equation (2); pure silver has the
highest thermal diffusivity of any known metallic material, and
thus as a function of time, fine silver bullion of up to 31/4 inch
(82.55 mm), including coin of up to 99.5 percent purity will attain
a higher far end temperature than any other admixture. The U.S.
Standard of 90 percent silver, the Sterling Standard of 92.5
percent purity and the Britannia Standard of 95.83 percent purity,
can also be used as successful paradigms for comparison. Therefore,
it is sufficient that at any time during the test, the temperature
of the known silver bullion, coupon or coin (or a recording
thereof) be as low as or lower than that of the suspected forgery,
for certainty that the sample in question is either as pure or
purer than the standard. This is subject to restrictions and
several possible errors, as now discussed.
[0066] The constant temperature T.sub.0 in equation (2), which can
be applied by the use of a heat sink for a defined time, must be
identical for the sample and the standard. The test is as good as
the exactitude with which the thicknesses of the bullion, coupons
and discs (coins) are known. The thermal diffusivity of silver is
very high compared to most materials, as shown in Table I. (Those
elements shown in Table I as possible adulterants of gold are also
candidates likely to be used as forgeries of silver.) As in the
case of the gold test, the thickness of the sample L in equation
(2), is very important for the sensitivity of the test.
Nevertheless, lower thickness values can be compensated for by more
sensitive instrumentation and amplification of temperature
differences.
[0067] Further embodiments can be realized by determining the
slopes of the temperature-time curves; these objectives can readily
obtained by taking the first derivative of the various appropriate
equations. This is accomplished in the following:
[0068] Differentiating equation (1), the general equation
applicable to FIGS. 1 and 4, we obtain:
dT/dt=Q/.rho.cL{1+2.SIGMA..sub.m=1.sup..infin.(-1).sup.m
exp(-.alpha.m.sup.2.pi..sup.2t/L.sup.2t)cos(m.pi.x/L)} (3)
[0069] However, at both x=0 and x=L equation (3) reduces to:
dT/dt=Q/.rho.cL (3A)
[0070] Similarly, equation (1B) reduces to:
dT/dt=q/Wc (3B)
[0071] To determine the slope of a system where constant
temperature is applied and where the system is completely enclosed
in an insulated medium or as shown in FIG. 1, differentiation of
equation (2), with x=0, will result in the following:
dT/dt=T.sub.0L/(.pi..alpha.t.sup.3).sup.1/2.SIGMA..sub.n=0.sup..infin.(-1)-
.sup.n(2n+1)exp[-(2n+1).sup.2/4.alpha.t/L.sup.2] (4)
[0072] If in the system shown in FIGS. 1 and 4 the heat is turned
off, referred here as the decay rate, the temperature of the slab
becomes:
T=Qt/.rho.cL (5)
[0073] Differentiating equation (5) gives the slope of the decay
rate as:
dT/dt=Q/.rho.cL (5A)
[0074] Equations (3), (3A), (3B), (5) and (5A) provide a further
check on the authenticity of the previously described gold and
silver bullion, coupons, and discs. Using the dual test method
indicated by equations (3A) and (4), the slopes for the constant
heat and constant temperature applications, respectively, will
provide a further check on the authenticity of the sample. Although
the formulations for the decay rate and its slope for the constant
temperature application are not presented here, nevertheless, such
tests appropriately combined with those indicated by equations (5)
and (5A), will provide a further check on the authenticity of the
previously described gold and silver bullion, coupons, and
discs.
[0075] Appropriate instrumentation can be employed with the use of
the above mentioned tests and equations providing guidelines. For
example, additional instrumentation, such as a differentiator (not
shown), can be added between the sensor amplifier 28 and the A/D
convertor 29 to the circuitry in FIG. 3 to differentiate the
temperature-time signal from the sample transducer to obtain slope
versus time signals analogous to equations (3A), (3B) and (4).
These signatures can then be compared to the appropriately stored
data in the computer 27; filed and recorded for viewing, and
connected to the alarm 22A. Alternatively, rather than include a
differentiator in the circuitry, the computer can numerically
differentiate the digitized temperature-time signal from the A/D
converter 29 and thus the process will proceed as
aforementioned.
[0076] The decay rate versus time signatures can also be obtained
by simply retaining the electric signal from the sample transducer
9 after the heating element 3 in FIG. 1 has been shut off. The
process for the attainment of the decay rate versus time signatures
will proceed as aforementioned and the slope of same would then
proceed as previously described in the above paragraph.
[0077] If the areal dimensions of the test item are relatively
large compared to its thickness, then another embodiment and
improvement, schematically shown in FIGS. 5 and 6, is realized,
i.e., exposure of the sample at x=0 to the environment.
[0078] The general heat transfer equation for the body shown in
FIGS. 5 and 6, i.e., constant heat flux Q applied at x=L and whose
opposite surface is exposed to a medium, is:
T(x,t)=Q/k{1/h+x-2 .SIGMA..sub.n=1.sup..infin.
exp(-.alpha..beta..sup.2.su-
b.nt)cos[(L-x).beta..sub.n](.beta..sup.2.sub.n+h.sup.2)/(.beta..sup.2.sub.-
n[h+L(.beta..sup.2.sub.n+h.sup.2)])} (6)
[0079] Where the thermal constants are as previously defined and
h=H/k; H is the coefficient of heat transfer as a function of
temperature in BTU/sec- ft.sup.2-F and .beta..sub.n, n=1, 2, 3 . .
. , are the positive roots of the transcendental equation .beta.
tan .beta.L=h. (See Carslaw and Jaeger conduction Heat in Solids,
Oxford Press, 1950).
[0080] Returning to FIG. 5, the sample 1B being testing has its
upper surface free of insulation. The sample 1B is placed on an
insulated bed 13B enclosing a non-contacting heat source such as a
laser or infrared heat source 30 and a focusing means 31, which is
concentrated on a known small area 32 at the mid-lower surface of a
bullion, coupon or a coin 1B. The sensing function is provided by
infrared temperature sensor 9B focused by a focusing means 5B on a
spot 15A directly in line with spot 32. The temperature sensor 9B
is operatively disposed to sense the time-varying temperatures at
the upper surface of sample 1B and thus provide as an output an
electrical signal that is a function of the time-varying
temperature. For this situation, only the thicknesses of test
sample is needed and its weight need not be known.
[0081] When the temperature is measured at x=0, as indicated in
FIG. 5, equation (6) becomes:
T(x,t)=Q/k{1/h-2.SIGMA..sub.n=1.sup..infin.
exp(-.alpha..beta..sup.2.sub.n-
t)cos(L.beta..sub.n)(.beta..sup.2.sub.n+h.sup.2)/(.beta..sup.2.sub.n[h+L(.-
beta..sup.2.sub.n+h.sup.2)])} (6A)
[0082] A variation of FIG. 5 shows a partly cut-away schematic,
FIG. 6, where again the sample 1C is placed on an insulated bed 13C
with the noncontacting laser or infrared heater 30A being focused
by focusing means 31A which is concentrated on a small known area
32A at the mid-lower surface of a bullion, coupon or a coin. The
sample being tested has its upper surface free of insulation and
the temperature is sensed by an infrared temperature sensor 9C
focused by a focusing means 5C at the lower surface on the spot
32A.
[0083] When the temperature is measured at x=L, the same surface at
which the heat is applied, as depicted in FIG. 6, equation (6)
becomes:
T(x,t)=Q/k{1/h+L-2.SIGMA..sub.n=1.sup..infin.
exp(-.alpha..beta..sup.2.sub-
.nt)(.beta..sup.2.sub.n+h.sup.2)/(.beta..sup.2.sub.n[h+L(.beta..sup.2.sub.-
n+h.sup.2)])} (6B)
[0084] A similar situation as that described above for FIG. 5,
where instead of a sudden pulse of heat, a constant temperature
source T(t) is applied to silver bullion or disc (coin); the
formula for this case, given by the same authors, is:
T=T.sub.0{1/(1+hL)-2.SIGMA..sub.n=1.sup..infin.
exp(-.alpha..gamma..sup.2.-
sub.nt)sin(L.gamma..sub.n)(.gamma..sub.n.sup.2+h.sup.2)/(.gamma..sub.n[h+L-
(.gamma..sup.2.sub.n+h.sup.2]) (7)
[0085] Where .gamma..sub.n, n=1, 2, 3 . . . , are the positive
roots of the transcendental equation .gamma. cot .gamma.L+h=0.
[0086] Equations (6A) and (6B) were employed to determine the
temperature differences between the idealized gold standard and
adulterated gold samples at the surfaces opposite the application
of constant heat at x=0 and at the heated surfaces at x=L,
respectively. The value of H used was 1.30 to 1.70
BTU/hr-ft.sup.2-F, obtained from Heat Transmission, McGraw-Hill,
2nd ed., 1942, for polished surfaces in still air with small
temperature differences. The thermal properties of the elements
used were those given in Table I, as well as the same percent
variation previously utilized when applying equation (1). Results
of testing the samples according to equations (6A) and (6B), again
indicated only the sample containing Pb defeated the test comprised
of the previously mentioned thicknesses of bullion, coupon and coin
at both x=0 and x=L. Nevertheless, when these samples containing
variations of Pb were tested in accordance to equation (7), where
constant temperature was applied for a given time period at x=L and
the temperature measured at x=0, they were cooler than the
idealized pure gold standard tested under the same circumstances.
Thus the dual method, wherein the first test will generally
discriminate between an idealized gold standard and most
adulterated samples; those compositions comprised of gold and lead
that defeat the first test can be retested, as indicated, and
successfully determined to be less than the idealized gold
standard.
[0087] Additional embodiments can be realized by determining the
slopes of the temperature-time curves; again these objectives can
readily be obtained by taking the first derivative of the various
appropriate equations. This is accomplished in the following:
[0088] Again by differentiating equation (6A), which is applicable
to FIG. 5 when x=0:
dT/dt=2Q/.rho.c.SIGMA..sub.n=1.sup..infin.
exp(-.alpha..beta..sup.2.sub.nt-
)cos(L.beta..sub.n)(.beta..sup.2.sub.n+h.sup.2)/[h+L(.beta..sup.2.sub.n+h.-
sup.2)], (8)
[0089] and differentiating equation (6B), where x=L, which is
appropriate for FIG. 6:
dT/dt=2Q/.rho.c .SIGMA..sub.n=1.sup..infin.
exp(-.alpha..beta..sup.2.sub.n-
t)(.beta..sup.2.sub.n+h.sup.2)/[h+L(.beta..sup.2.sub.n+h.sup.2)]
(9)
[0090] The slope at x=0 opposite to the surface which is exposed to
the environment and at which a constant application of temperature
is applied, analogous to FIG. 5, is obtained by differentiating
equation (7):
dT/dt=2 T.sub.0 .alpha..SIGMA..sub.n=1.sup..infin..gamma..sub.n
exp(-.alpha..gamma..sup.2.sub.nt)sin(L.gamma..sub.n)(.gamma..sub.n.sup.2+-
h.sup.2)/[h+L(.gamma..sup.2.sub.n+h.sup.2)] (10)
[0091] Equations (8), (9) and (10) with the use of the dual test
method, also provide a further check on the authenticity where
appropriately applied to the previously described gold and silver
bullion, coupons, and discs.
[0092] The formulations are not presented for the decay rates and
their slopes after the removal of the sudden heat pulse application
and after the removal of constant temperature application,
appropriate to FIGS. 5 and 6. Nevertheless, such tests along with
the use of the dual test method and the suitable instrumentation,
previously described, can be employed to provide a further check on
the authenticity of the gold and silver bullion, coupons, and
discs.
[0093] Heretofore, there has been no simple, viable method of
nondestructively determining the purity of gold or silver jewelry,
such as rings or other shapes. Jewelry items, whose shapes are
analogous to bullion already depicted, for example FIGS. 4 or 5,
i.e., signets of gold or silver rings, or other shapes that conform
to the ratio previously mentioned of unknown fineness for which it
is desired to know their carat or silver purity can also be
examined by the method already described. If the gold or silver
rings have signet portions or even other shapes in which their
dimensions, such as widths and lengths or diameters that are a
ratio of approximately 3/1 or greater compared to their
thicknesses, then these test items can be considered as slabs when
pulsed by a suddenly applied constant heat source or the
application of a constant temperature and compared to a standard
tested under the same circumstances.
[0094] The calibration of the standard can be attained by simply
fabricating the jewel item from the desired fineness for
comparison. A gold standard, being considered either 24, 22, 18, 14
or even 9 carat gold, or a Sterling or Britannia Standard from
which the temperature-time signature of the exact replica of the
test sample having already been attained. As indicated previously
the temperature-time signature of the standard can readily be built
into the system instrumentation and need not be discussed
further.
[0095] Analogous to the systems shown in FIGS. 1 and 5, is the
aforementioned gold or silver ring sample 40, shown in FIG. 7,
which can be slipped over an insulated semi-tapered mandrel 41. The
sample being tested has its upper surface and edges free of
insulation. The heating function can be supplied by a laser or an
infrared heater (30B) focused by a focusing means (31B) on to a
small known area 32B at the mid-lower surface of the signet and the
sensing function is provided by an infrared temperature sensor 9D
and a focusing means 5D. The temperature sensor is operatively
disposed to sense the time-varying temperatures at the small known
area 32B of the signet; the signet being exposed to the environment
and thus provides as output an electrical signal that is a function
of the time-varying temperature. For this situation, only the
thicknesses of the signet portion of the test sample is needed, but
its weight need not be known.
[0096] Additional variations of FIG. 7 can be envisioned: With the
heating function within the insulated semi-tapered mandrel and
focused on the mid-inside surface of the signet and measure the
temperature at the same location, similar to FIG. 6, or the heating
function focused on the mid-outside surface of the signet and the
temperature measured at the same location or on the inside
mid-surface of the signet.
[0097] It was found that the dual test according to equations (6A)
and (6B), as well as equation (7), as described above, were
successfully applied to a gold ring, such as that shown in FIG. 7,
having 14, 18 and 24 carat alloys, which were used as standards to
discriminate between such alloys and determine their carat content.
Also in all cases, the adulterants of silver tested according to
equation (7) showed lower temperature-time responses than those of
pure silver and the U.S., Sterling and Britannia Standards.
[0098] Equations (8), (9) and (10), with the use of the dual test
method, also provide a further check on the authenticity where
appropriately applied to the above described gold and silver
jewelry.
[0099] Again as previously mentioned, the formulations are not
presented for the decay rates and their slopes after the removal of
the sudden heat pulse application and after the removal of constant
temperature application, appropriate to FIG. 7. Nevertheless, such
tests along with the use of the dual test method and the suitable
instrumentation, previously described, can be employed to provide a
further check on the authenticity of the above described gold and
silver jewelry.
[0100] Test samples that are not insulated, as schematically
depicted in FIGS. 8 and 9, can also be tested even though the
formulation is not presented here. Nevertheless, the results will
be similar to those cases already described but the magnitudes of
the resulting temperatures will be mitigated. However, with present
day instrumentation the signals can be readily amplified such that
the difference between the standard and the test sample will 3be
measurable. Turning to FIG. 8, the test sample 1D is place on
supports 33 with the noncontacting laser or infrared heater 30C
being focused by focusing means 31C which are concentrated on a
small known area 32C at the mid-lower surface of a bullion, coupon
or a coin 1D. The sample 1D has at its upper surface an infrared
temperature sensor 9E and focusing means 5E focused on a spot 15B
opposite 32C, and as before the temperature sensor 9E and its
focusing means 5E detect the temperature-time response of the
sample which is compared to the temperature-time signature of the
standard having been tested under the exact conditions as the test
sample 1D for comparison.
[0101] Now turning to FIG. 9, the test sample 1E is place on
supports 33A with the noncontacting laser or infrared heater 30D
being focused by focusing means 31D which are concentrated on a
small known area 32D at the mid-upper surface of a bullion, coupon
or a coin 1E. The sample 1E being testing also has at its upper
surface an infrared temperature sensor 9F and focusing means 5F and
the temperature sensor is focused on the small area 32D and it
detects the temperature-time response of the test sample 1E which
is compared to the temperature-time response signature of the
standard having been tested under the exact conditions as the test
sample for comparison.
[0102] Again, other embodiments can be described as jewelry
samples, whose shapes are analogous to the bullion depicted in
FIGS. 8 and 9, i.e., the signets of gold rings or silver rings of
unknown fineness for which it is desired to know their carat or
silver purity. The aforementioned gold or silver ring samples are
suspended in air by gripping them at locations opposite from the
signets. The sample being tested has at its lower surface,
analogous to FIG. 8, an infrared heater or laser focused on a spot
of known area in the middle of the signet and the sensing function
is provided by an infrared temperature sensor focused on the top
surface of the signet opposite to the focused heater. The
alternative system, which is analogous to FIG. 9, would have the
sample being tested at its upper surface with an infrared heater or
laser focused on a spot of known area at the middle of the signet
and the sensing function, provided by an infrared temperature
sensor and is focused on a the same spot on the upper surface. The
temperature sensors are operatively disposed to sense the
time-varying temperatures at their respective surfaces of the
signets, which is exposed to the environment and thus provides as
output electrical signals that are a function of the time-varying
temperature which is compared to the temperature-time signature of
the standard having been tested under the exact conditions as the
test sample for comparison.
[0103] For the situations described above, i.,e., FIGS. 8 and 9,
and the similar systems such as the jewelry test sample, only the
thicknesses of the bullion and signet portion of the rings are
needed, but their weights need not be known. It is further noted
that even though the formulation, i.e., temperature-time
signatures, slopes versus time signatures, decay rate and slopes of
the decay rate versus time signatures for both sudden heat pulse
application and for constant temperature application are not
presented, nevertheless, such tests along with with the use of the
dual test method and the suitable instrumentation previously
described can be employed to provide a further check on the
authenticity of the previously described gold and silver bullion,
coupons, discs and jewelry.
* * * * *