U.S. patent number 3,742,226 [Application Number 05/143,462] was granted by the patent office on 1973-06-26 for liquid cell for x-ray fluorescence analysis.
This patent grant is currently assigned to Applied Research Laboratories, Inc.. Invention is credited to Allan H. Smallbone.
United States Patent |
3,742,226 |
Smallbone |
June 26, 1973 |
LIQUID CELL FOR X-RAY FLUORESCENCE ANALYSIS
Abstract
Solids in a slurry batch or batch mixtures of liquids of
different densities the upper surfaces of which are presented in a
liquid cell for X-ray analysis are prevented from separating by an
impeller causing rotary movement of the slurry or liquid mixture
within the cell; the liquid surface being maintained substantially
planar by baffles which inhibit the creation of a vortical
cavity.
Inventors: |
Smallbone; Allan H. (La
Crescenta, CA) |
Assignee: |
Applied Research Laboratories,
Inc. (Sunland, CA)
|
Family
ID: |
22504187 |
Appl.
No.: |
05/143,462 |
Filed: |
May 14, 1971 |
Current U.S.
Class: |
378/47;
250/432R |
Current CPC
Class: |
G01N
23/2204 (20130101); G01N 23/223 (20130101); G01N
2223/076 (20130101) |
Current International
Class: |
G01N
23/223 (20060101); G01N 23/22 (20060101); G01n
021/00 () |
Field of
Search: |
;250/51.5,46,49,48 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"An X-Ray Fluorescence Slurry Presenter Which is Insensitive to
Solid Concentration" by Carr-Brion, J. Sci. Instru. 1965, Vol. 42,
No. 11, pp. 817, 818..
|
Primary Examiner: Lawrence; James W.
Assistant Examiner: Dixon; Harold A.
Claims
I claim:
1. A liquid cell for X-ray fluorescence analysis comprising a
receptacle having a window opening adjacent the top thereof, means
including an impeller in said receptacle adjacent the bottom
thereof for imparting rotary motion to liquid in said receptacle,
baffle means within said receptacle disposed sufficiently below the
upper end thereof to permit said baffle means to be covered by
liquid in said receptacle whereby continuous mixing of liquids and
other materials in said receptacle may be achieved while
maintaining a substantially planar liquid surface below said window
opening, a removable cover for said window opening having an X-ray
translucent portion and a depending lip defining a pocket in said
receptacle above the level of said portion, and a vent to
atmosphere communicating with said pocket.
2. A "window up" type liquid cell for X-ray fluorescence analysis
comprising a walled receptacle having a top and bottom, a window
opening adjacent the top of said receptacle, means for imparting
rotary motion to liquid contents of said receptacle, and means for
inhibiting creation of a vortical cavity in the liquid contents of
said receptacle during operation of said rotary motion imparting
means comprising baffle plate means in said receptacle extending
from the center of said receptacle toward its walls and from
adjacent said window opening toward the bottom of said
receptacle.
3. A liquid cell according to claim 2 in which said baffle plate
means comprises a pair of plates interlocking at the center of said
receptacle and extending into engagement with the walls
thereof.
4. A "window up" type liquid cell for X-ray fluorescence analysis
comprising a walled receptacle having a top and bottom, a window
opening adjacent the top of said receptacle, means for imparting
rotary motion to liquid contents of said receptacle comprising an
impeller in said receptacle and means including a motor drive unit
outside said receptacle for rotating said impeller; and means for
inhibiting creation of a vortical cavity in the liquid contents of
said receptacle during rotation of said impeller comprising baffle
plate means in said receptacle extending from the center of said
receptacle toward its walls and from adjacent said window opening
toward the bottom of said receptacle.
5. A liquid cell according to claim 4 in which said impeller
comprises a free bar magnet and said motor drive unit includes
means for producing a rotating magnetic field encompassing said bar
magnet, whereby said bar magnet may be rotated within said
receptacle.
6. A liquid cell according to claim 4 in which said motor drive
unit includes a drive shaft extending through the bottom of said
receptacle and connected to said impeller.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
In X-ray fluorescence analysis, or fluorescent X-ray spectroscopy,
primary X-rays from an X-ray source, such as the target of an X-ray
tube, are directed against the surface of a specimen which may be
either in gaseous, liquid or solid form. Characteristic lines of
the elements contained in the specimen emerge in all directions and
a beam of this radiation separated by diffraction or dispersion
into characteristic wavelengths is directed against a detector.
Analysis is accomplished by relating each characteristic wavelength
to the chemical composition of the material.
There are two ways of discriminating the characteristic wavelengths
for measurement: (1) crystal diffraction, in which only one
wavelength is diffracted for a given setting of the crystal, and
(2) energy dispersion, in which at a given setting the detector
circuitry passes only a selected X-ray energy corresponding to a
particular characteristic wavelength. Energy dispersion is
sometimes referred to as "non-dispersive optics" because various
characteristic X-rays are distinguished without an analyzing
crystal to disperse them according to wavelength. Various
arrangements for crystal diffraction are described in "Electron
Probe Microanalysis" by L. S. Birks, published by Interscience
Publishers, a division of John Wiley & Sons in 1963, at Chapter
6, while detectors and energy dispersion are treated in Chapter
7.
Liquids, including slurries some of which may contain as much as 60
percent solid particles, are presented for analysis in apparatus
for X-ray fluorescence analysis either by flowing the liquid in a
continuous stream past an X-ray translucent surface through which
radiation from the primary X-ray source can be directed, or by
placing a batch of the liquid in a cell, through an X-ray
translucent surface of which such radiation can be directed. The
present invention is directed to the improvement of liquid cells of
the latter type, which are called static liquid analysis cells and
which must be employed when the quantities of materials available
for analysis are limited.
2. Description of the Prior Art
Previously known static liquid analysis cells have been of two
general types designated as "window up" and "window down,"
respectively, but each has had a number of disadvantages.
In the "window up" type, the upper surface of a static body of
liquid is exposed to X-ray radiation and the radiation produced by
the resulting fluorescence emerges from that surface through an
X-ray translucent membrane. In such cells, however, the settling of
solid particles and/or the separation of mixtures of liquids of
different densities introduces inaccuracies into the results of
analyses, as do bubbles, either introduced during filling or
evolved or enlarged by the heat generated by the X-ray tubes, since
such bubbles collect in the area under the window.
In the "window down" type, the lower surface of the liquid, through
a similar membrane, is exposed to X-rays; the resulting
fluorescence emerging through the same membrane. Bubbles rise away
from the membrane in this type of cell and therefore create no
problem, but solid particles settle onto the membrane, and mixtures
of liquids separate; these occurrences introducing inaccuracies in
an inverse sense as compared with those introduced by settling and
liquid separation in "window up" cells. Additionally, because very
thin membranes must be used, they tend to bulge so that the liquid
surface is no longer substantially planar. Also, the membrane may
rupture, causing damage to the equipment and requiring lengthy
clean-up operations.
SUMMARY OF THE INVENTION
According to the present invention a liquid analysis cell having a
window opening is provided with an impeller driven by a variable
speed motor, whereby rotary motion is imparted to a slurry or a
mixture of liquids in the cell. In order to inhibit distortion of
the substantially planar liquid surface by creation of a vortical
cavity in the liquid, baffles are disposed within the cell so as to
cause the liquid to move in a continuous serpentine path, portions
of which are tangent to the surface presented adjacent the window
opening for analysis. The cell is designed for operation in "window
up" position so that that surface can be inspected visually without
inconvenience. It can be operated without any membrane covering its
upper opening, without spilling any liquid, although preferably an
X-ray transparent membrane is employed.
The impeller may be in the form of a bar magnet within the cell
coated with chemically inert material and rotated by another bar
magnet outside the cell driven by a small motor; a thin plastic
bottom wall of the cell separating the two bar magnets. Where,
however, slurries containing magnetic particles are to be analyzed,
a non-magnetic impeller driven by a shaft passing through the
bottom wall of the cell is provided in order to insure against
concentration of the particles of magnetic material adjacent the
impeller.
Liquid analysis cells constructed in accordance with the present
invention, therefore, present a planar liquid surface for analysis
and at the same time maintain a uniform temperature in the material
under analysis and prevent the separation of liquids of different
densities and the settling of solid particles in liquids and
slurries presented for such X-ray fluorescence analysis. Bubbles
entrained in such liquids or slurries are moved away from the
surface presented for analysis, as is material heated by the X-ray
tube, and any pressure build-up which might bulge a covering
membrane is avoided by the provision of a suitable vent. When the
cell is oriented in the preferred "window up" position, a very thin
membrane or none at all may be employed to cover the surface
presented for analysis, which can be visually inspected without
inconvenience.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic view of a typical arrangement for
wavelength diffractive fluorescent X-ray spectroscopy employing
curved crystal X-ray optics;
FIGS. 2 and 3 are diagrammatic views of typical alternative
arrangements for energy dispersive fluorescent X-ray
spectroscopy;
FIG. 4 is an elevational view in vertical section of a liquid
analysis cell embodying the present invention;
FIG. 5 is a plan view in section taken on the line 5--5 of FIG.
4;
FIG. 6 is a plan view in section taken on the line 6--6 of FIG.
4;
FIG. 7 is a detail view of the impeller employed in the cell
illustrated in FIGS. 4 to 6;
FIG. 8 is an exploded perspective view in detail of the baffles
employed in both embodiments of the liquid cell of the present
invention;
FIG. 9 is an elevational view in vertical section of an alternative
embodiment of the present invention; and
FIG. 10 is a plan view in section taken on the line 10--10 of FIG.
9.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the typical arrangement for wavelength dispersive fluorescent
X-ray spectroscopy illustrated diagrammatically in FIG. 1, primary
X-rays from the target of a sealed off X-ray tube 11 emerge through
the window 12 of the tube and strike the surface 14 of the material
to be analyzed. X-rays characteristic of the elements contained in
the specimen emerge in all directions and are focused by X-ray
optics including slits 16 and 17 so that a focused beam of
radiation strikes an angularly adjustable curved crystal 18. At
each of a range of positions of the crystal on the focal circle 19
a single wavelength will be diffracted and pass on to a detector 20
which must always be positioned the proper angle on the same focal
circle 19 to be in a proper position to intersect the diffracted
radiation. Analysis is accomplished by relating each characteristic
line to the composition of the material.
In a typical arrangement for energy dispersive fluorescent X-ray
spectroscopy illustrated diagrammatically in FIG. 2, radiation from
a source 22, such as a radioactive material, contained in a
shielding housing 24 strike the surface 26 of the material to be
analyzed. X-rays characteristic of the elements contained in the
specimen surface 26 are collimated by the opening 28 in the housing
24 through which opening they pass to a detector 30 such as a gas
proportional or scintillation counter which gives an electrical
pulse the amplitude of which is proportional to the X-ray quantum
energy.
The energy of each characteristic X-ray quantum is invariable; each
CuK quantum, for instance, having an energy of 8,000 v. The number
of quanta is a measure of the relative number of atoms of an
element in the specimen, and the different elements in it are
distinguished by the different pulse amplitudes associated with
their characteristic X-ray quantum energies.
In another typical energy dispersive arrangement illustrated
diagrammatically in FIG. 3, radiation from a similar source 32
shielded by a lip 34 of a housing 36 from the surface 38 of the
material to be analyzed, strikes a target 40 secured within the
housing 36. X-rays emitted by the target 40 under such bombardment,
which are selectively controlled as to wavelength by selection of
the target material, strike the surface 38 of the material to be
analyzed, and X-rays characteristic of the elements contained in
the specimen surface 38 are collimated by an opening 36a in the
housing 36 through which opening they pass to a detector 30
identical with the detector 30 of the arrangement illustrated in
FIG. 2.
The embodiment of the liquid cell of the present invention
illustrated in FIGS. 4 to 8, which is useful in all of the types of
arrangements described above, comprises a cell body 25 of
non-magnetic and chemically inert plastic material, such as
polypropylene, a vertically oriented sample receptacle 27 having a
window opening 29 at its upper end is formed in the upper end of
the body 25; the lower end of the sample receptacle 27 being closed
by a wall 31 separating the sample receptacle 27 from a cavity 33
formed in the lower portion of the cell body 25.
An X-ray translucent membrane 35 which may be of polyimide film
such as that marketed under the trademark "Kapton" which may be of
a thickness of up to 25 .mu.m. (0.000025 m.), is secured to a cover
member 37 adapted to be frictionally secured in position over the
upper end of the cell body 25; a liquid tight seal between the cell
body 25 and the cover member 37 being effected by an O-ring 39.
It is important in systems of the character illustrated in FIGS. 1,
2 and 3 that the surface of the sample to be analyzed be maintained
substantially planar during analysis in order to make possible
proper focusing or collimation of the X-ray optics. Therefore, in
order to prevent bulging of the membrane 35 due to the expansion of
liquid materials in the sample receptacle 27 or the formation of
bubbles in such materials, either of which would affect the
planarity of the liquid surface, a vent 41 connecting an annular
pocket 42 in the sample receptacle 27 with an overflow cavity 43 in
communication with the atmosphere is provided in the wall of the
cell body 25. The annular pocket 42 is defined by a depending lip
44 of the cover member 37 and lies above the normal liquid level
which is defined by the free edge of that lip, so that any bubbles
in the liquid will tend to move into the pocket and thence out
through vent 41.
Disposed within the sample receptacle 27 is an impeller 45
illustrated in detail in FIG. 7. The impeller 45 comprises a bar
magnet having north and south poles at its opposite ends, as
indicated in FIG. 7, and a coating of an inert material such as
polytetrafluoroethylene, marketed under the trademark "Teflon." The
impeller 45 is also provided with a diametrical belt 47 of the
material with which it is coated, the belt being disposed at the
center of the impeller and thus serving to space the main body of
the impeller 45 from the wall 31 so as to facilitate rotation of
the impeller by the means hereinafter described.
Driving means for the impeller 45 are provided in the form of a
motor unit 47 which comprises an electric motor which may be
connected to a source of power by leads not shown and the speed of
which is variable according to the voltage supplied, together with
speed reduction gearing through which the motor drives an output
shaft 49. The motor unit 47 is removably retained in a conforming
recess 51 in an adapter 53 by cementing with a cement which may be
dissolved for the purpose of removing the unit 47 from the adapter
53. The adapter 53 is, in turn, retained in position in the cavity
33 of the cell body 25 by a shouldered set screw 55 screwed into a
threaded bore 57 of the cell body 25 and provided with a portion of
reduced diameter adapted to engage in a bore 59 in the adapter
53.
The cell body 25 is mounted on a base 61 secured to the cell body
25 by a plurality of nylon screws 63 spaced equidistantly around
the ring shaped base 61; the screws 63 passing through an
insulating ring 65 and a spacer 67 into the threaded bores 69 in
the cell body 25.
Secured to the upper end of the motor unit output shaft 49 is a
magnet holder 71. At its opposite ends the magnet holder 71 carries
bar magnets 73 and 75, respectively, the magnet 73 being oppositely
oriented with respect to the magnet 75 as to polarity. For example,
with the magnet of the impeller 45 having the polarity orientation
indicated in FIG. 4, the magnet 73 should have its south pole
uppermost and its north pole lowermost, while the magnet 75 should
have its north pole uppermost and its south pole lowermost. A third
permanent magnet 77 U-shaped in cross-section as shown in FIG. 4
but of cylindrical configuration in plan as shown in FIG. 6, is
secured to the magnet holder 71 centrally thereof and is
magnetically oriented with its north pole toward the magnet 73 and
its south pole toward the magnet 75. The magnets 73, 75 and 77 are
secured to the magnet holder 71 by an adhesive material such as an
epoxy resin.
This arrangement is such that upon rotation of the shaft 49 by the
motor unit 47, the magnets carried by the rotating magnet holder 71
attract the respectively opposite poles of the magnet forming a
part of the impeller 45 and thus cause rotation of the impeller 45
upon its central belt 47 as a pivot, thus imparting rotary motion
to any liquid contained in the sample receptacle 27.
In applications involving the employment of fluorescent X-ray
spectroscopy for the analysis of materials such as slurries
containing iron oxide or other magnetic particles, which would be
attracted to a magnetic impeller, the use of the modified
embodiment of the present invention illustrated in FIGS. 9 and 10
eliminates any possibility of concentration of such magnetic
particles at the bottom of the sample receptacle 27.
All of the elements illustrated in the embodiments shown in FIGS. 9
and 10 to which the same numbers have been applied are identical
with the elements to which those numbers have been applied in FIGS.
4 to 8, inclusive, so that a detailed description of them need not
be repeated.
In the embodiment of the liquid cell of the present invention
illustrated in FIGS. 9 and 10, the lower end of the sample
receptacle 27 is only partially closed by a wall 100 having a
central opening 102 closed by a threaded sleeve 104 the threads of
which are engaged by a nut 106; the margin of the opening 102 being
clamped between an enlarged upper portion of the sleeve 104 and the
nut 106.
A shaft 110 is rotatably received in a central opening in a sleeve
104 extending beyond the ends thereof and retained by a fluid-tight
seal. Secured to the upper end of the shaft 110 is an impeller 112
disposed within the sample receptacle 27, and secured to the lower
end of the shaft 110 is a disc 114 having peripheral slots 116 for
the reception of driving pins 118 fixed in a disc 120 secured to an
output shaft 122 of the drive unit 47.
In order to maintain the surface presented for analysis
substantially planar, for the reasons previously explained, means
are provided in both embodiments of the invention for preventing
the formation of a vortical cavity in such liquid as an incident to
the rotary motion imparted to it by either the impeller 45 or the
impeller 112. The surface of the liquid presented for analysis is
maintained closely adjacent the window opening 29 of the sample
receptacle 27 at all times. This means comprises a pair of
interlocked baffle plates 81 and 83 shown in detail in FIG. 8,
which are disposed within the sample receptacle 27 as shown in
FIGS. 4 and 5. The lower portion of each of the plates 81, 83 is
cut away as at 85 in order to provide ample clearance for
rotational movement of the impeller 45 or the impeller 112, and
each is formed with an upper edge having an arcuate portion, as at
87, for the purpose of leaving a space 89 between the upper edge of
the plates 81, 83 and the window opening 29 for the circulation of
liquid in a horizontal plane at the window opening, whether or not
the membrane 35 carried by the cover member 37 is in place.
This arrangement is such that the rotary motion imparted to the
liquid within the sample receptacle 27 by the impeller 45 is caused
to move in a continuous serpentine path extending vertically along
the sides of the baffle plates 81, 83 and tangent to the surface
presented for analysis before returning to the area being agitated
by the impeller 45. This arrangement insures that solid particles
contained in a liquid placed in the sample receptacle 27 will be
maintained in suspension in the liquid by the motion imparted to
the liquid by the impeller 45; that the temperature of the liquid
and any entrained solid particles presented for analysis is
maintained substantially uniform by circulation of the liquid
produced by the impeller 45; that bubbles, whether initially
introduced or formed due to heating of the liquid, are continuously
removed by circulation of the liquid under the annular pocket 42
and thence into the vent 41 and to atmosphere; and that at the same
time the surface of the liquid presented for analysis is maintained
substantially planar at the window opening 29 without any vortical
cavity.
* * * * *