U.S. patent application number 14/760545 was filed with the patent office on 2015-12-10 for master alloy composition for producing gold alloys and gold alloy.
This patent application is currently assigned to LEGOR GROUP S.P.A.. The applicant listed for this patent is LEGOR GROUP S.P.A.. Invention is credited to Andrea BASSO, Massimo POLIERO.
Application Number | 20150354029 14/760545 |
Document ID | / |
Family ID | 47722367 |
Filed Date | 2015-12-10 |
United States Patent
Application |
20150354029 |
Kind Code |
A1 |
POLIERO; Massimo ; et
al. |
December 10, 2015 |
MASTER ALLOY COMPOSITION FOR PRODUCING GOLD ALLOYS AND GOLD
ALLOY
Abstract
A master alloy composition for producing gold alloys with
innovative refiners system comprising iridium (Ir): 0.01/0.8% by
weight, ruthenium (Ru): 0.002/0.9% by weight, rhodium (Rh):
0.002/0.8% by weight, and copper (Cu): 20/99.965% by weight,
wherein iridium (Ir), ruthenium (Ru) and rhodium (Rh) are the grain
refiners.
Inventors: |
POLIERO; Massimo; (Vicenza,
IT) ; BASSO; Andrea; (Santa Giustina in Colle (PD),
IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LEGOR GROUP S.P.A. |
Bressanvido (vi) |
|
IT |
|
|
Assignee: |
LEGOR GROUP S.P.A.
BRESSANVIDO (VI)
IT
|
Family ID: |
47722367 |
Appl. No.: |
14/760545 |
Filed: |
January 9, 2014 |
PCT Filed: |
January 9, 2014 |
PCT NO: |
PCT/IB2014/058152 |
371 Date: |
July 13, 2015 |
Current U.S.
Class: |
420/483 ;
420/485; 420/497; 420/503; 420/507 |
Current CPC
Class: |
C22C 1/00 20130101; C22C
9/04 20130101; C22C 5/02 20130101; C22C 5/08 20130101; C22C 9/00
20130101; C22C 1/03 20130101; C22C 9/05 20130101; C22C 1/02
20130101; C22C 5/04 20130101 |
International
Class: |
C22C 9/04 20060101
C22C009/04; C22C 5/08 20060101 C22C005/08; C22C 9/00 20060101
C22C009/00; C22C 5/02 20060101 C22C005/02; C22C 1/00 20060101
C22C001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 11, 2013 |
IT |
PD2013A000003 |
Claims
1. Master alloy composition for producing gold alloys with
innovative refiners system comprising: iridium (Ir): 0.01 to 0.8%
by weight; ruthenium (Ru): 0.002 to 0.9% by weight; rhodium (Rh):
0.002 to 0.8% by weight; copper (Cu): 20 to 99.965% by weight.
2. Master alloy composition according to claim 1, wherein the
iridium (Ir) weight percentage is in the range between 0.03% and
0.17%.
3. Master alloy composition according to claim 2, wherein the
iridium (Ir) weight percentage is in the range between 0.03% and
0.06% for yellow gold alloys and in the range between 0.1% and
0.16% for white gold alloys.
4. Master alloy composition according to claim 1, wherein the
ruthenium (Ru) weight percentage is in the range between 0.03% and
0.09%.
5. Master alloy composition according to claim 4, wherein ruthenium
(Ru) weight percentage is in the range between 0.0045% and 0.04%
for yellow gold alloys and in the range between 0.01% and 0.08% for
white gold alloys.
6. Master alloy composition according to claim 1, wherein the
rhodium (Rh) weight percentage is in the range between 0.05% and
0.15%.
7. Master alloy composition according to claim 1, further
comprising zinc (Zn) wherein the zinc(Zn) weight percentage is in
the range between 1 and 25%.
8. Master alloy composition according to claim 7, wherein the zinc
(Zn) weight percentage is in the range between 1% and 18%.
9. Master alloy composition according to claim 8, wherein the zinc
(Zn) weight percentage is in the range between 1% and 12% for
yellow gold and in the range between 7% and 14% white gold
alloys.
10. Master alloy composition according to claim 1, further
comprising silver (Ag) wherein the silver (Ag) weight percentage is
in the range between 20 and 64%.
11. Master alloy composition according to claim 1, further
comprising nickel (Ni) wherein the nickel weight percentage is in
the range between 5 and 40%.
12. Gold alloy with innovative refiners system comprising: gold
(Au): 333.33.Salinity. (8 k) to 958.33.Salinity. (23 k) by weight;
master alloy composition according to claim 1, for the remaining
part by weight.
13-14. (canceled)
15. A method of making a gold alloy which comprises adding an
amount of a master alloy composition of claim 1 to gold to form a
gold alloy having 333.33.Salinity. (8 k) to 958.33.Salinity. (23 k)
by weight of gold.
Description
TECHNICAL FIELD
[0001] The present invention concerns a master alloy composition
for producing gold alloys with innovative refiners system.
[0002] Furthermore, the current invention concerns a gold alloy
comprising the aforesaid master alloy composition and used to
produce precious jewelry, goldsmith, costume jewelry items (or
jewels), coins and/or medals, both through a micro-casting process
and through a mechanical working.
PRIOR ART
[0003] Usefulness of grain refiners as improving chemical elements
of the performances of gold alloys as a whole has been long known
in producing goldsmith and/or jewelry alloys. In particular, main
benefits observed by reducing the size of the crystalline grain
(refining) in gold alloys which follows the introduction of these
refiners may be summarized as follows: [0004] improvement of
physico-mechanical properties in general, in particular
deformability and elongation (physical properties which can be
summarized in the term "ductility" or ability to withstand plastic
deformation); [0005] increase of the resistance to corrosion
understood, for example, as decrease in the release of nickel in
white gold alloys or as resistance to acidic emptying solutions in
the processes of production of hollow objects (crimped process,
hollow tube, etc.).
[0006] Among the better known, used and most effective grain
refiners for gold alloys, iridium (Ir) and ruthenium (Ru) are
included.
[0007] The same Applicant has described, in European Patent
application published with N. EP1266974 A1, master alloys
compositions to obtain gold alloys comprising at least (percentages
by weight): iridium .ltoreq.0.4%, germanium .ltoreq.4% and copper
for the difference to 100%. Said compositions may also include
silver .ltoreq.72%, nickel .ltoreq.41%, zinc .ltoreq.25%, ruthenium
.ltoreq.0.96%. These compositions, due to the germanium that is
present in particular as fluidifying element, possess excellent
fluidity in the molten state and reduced tendency to oxidation even
in absence of silicon and also, thanks to the small size of the
crystalline grain, are normally able to not require the use of
other refining elements.
[0008] As it is well known, iridium (Ir) is a transition metallic
element belonging to the so-called platinum group metals (PGMs,
otherwise also known as platinoids): it has atomic number equal to
77, molecular weight equal to 192 and melts at 2,466.degree. C.
[0009] Being a precious element, the cost of this grain refiner is
particularly high (about 26/28/g, at the time of filing of the
present patent application).
[0010] Even ruthenium (Ru) is a transition metallic element of the
group of platinoids: it possesses atomic number equal to 44,
molecular weight equal to 101 and melts at 2,334.degree. C. Its
cost, however, is considerably lower than that one of iridium
(about 2.5/3 /g at the time of filing of the present patent
application).
[0011] Since both of these metallic elements have a high melting
point and have limited solubility in gold, it is conceivable that
they are already present as precipitates (separated compounds,
because little soluble in a given liquid solution) upon reaching
the liquidus temperature of the gold alloy (including fine gold and
master alloy), acting as "impurities" or nucleation (or
crystallization) centres for the formation and growth of the
crystalline grains.
[0012] Their addition in the gold alloys or master alloys for
producing the first ones is carried out in small amounts, generally
not exceeding a few hundred of parts per million (ppm) on the final
gold alloy.
[0013] Furthermore, the established practice commonly followed and
the current state of the art in the field of production of gold
alloys provides that these crystalline grain refiners are added
individually, never in combination each other, therefore addition
of iridium (Ir) is entirely alternative to addition of ruthenium
(Ru).
[0014] The addition of only iridium (Ir) or, alternatively, of only
ruthenium (Ru) in a master alloy (or in a gold alloy using such a
master alloy) involves a significant but still even presumably
improvable reduction in the sizes of the crystalline grain compared
to those ones of a gold alloy missing these refiners, although the
reduction which can be obtained with the addition of iridium (Ir)
is greater than that one achievable with the addition of ruthenium
(Ru).
[0015] Such a situation, according to which the iridium (Ir) is
preferable to the ruthenium (Ru) as grain refiner in terms of the
improvement of the mechanical properties of the alloy, however,
must be weighted at the light of the significantly higher
commercial cost of the first one than the second one, which however
makes not always convenient its use.
[0016] It follows that, in the field concerned, the need to use or
add crystalline grain refiners of master alloys or related gold
alloys is now strongly felt which are able to further reduce the
sizes of the crystalline grain of the gold alloy, thus resulting in
a marked improvement of the physical-mechanical properties (in
particular, ductility) of the alloy compared to equivalent alloys
of known type provided with refiners.
[0017] At the same time, at the state of the art the need to use
refiners which have not only high performances in terms of the
mechanical features but also able to affect the production costs of
the gold alloy to a lesser extent than the refiners used in the
prior art is felt.
[0018] In short, at the current state of the technique of the field
of the for jewelry and/or goldsmith alloys a need to produce a
master alloy composition for the production of gold alloys remains
which exploits a refiners system alternative to that one
constituted by the single use of the most widespread refiners, that
is iridium (Ir) and ruthenium (Ru), while trying to exploit or
enhancing the merits of both the latter.
PURPOSES AND BRIEF DESCRIPTION OF THE INVENTION
[0019] Starting, therefore, from the knowledge of the drawbacks
mentioned above of the current state of the art, the present
invention seeks to give concretely solution to them.
[0020] In particular, primary purpose of the present invention is
to provide a master alloy composition for the production of gold
alloys which, by using a special and innovative system of refiners,
allows to get sizes of the crystalline grain of the gold alloys
themselves better than those ones of equivalent gold alloys of
known type, including refiners.
[0021] It is a second purpose of the invention to improve the
physical-mechanical properties, in particular ductility, of a gold
alloy compared to similar gold alloys of the known technique.
[0022] It is another purpose of the present invention to devise a
master alloy that provides a refiners system cheaper than that one
of similar known master alloys, degree of crystalline grain
refining reached being equal.
[0023] It is a last but not least purpose of the invention to make
available a gold alloy comprising refiners which, generally, while
achieving the above purposes in terms of mechanical performance,
presents a cost lower than that one of prior art gold alloys
equivalent to it.
[0024] During several laboratory tests, the Applicant has
surprisingly found that a system of crystalline grain refiners for
gold alloys where iridium (Ir), ruthenium (Ru) and rhodium (Rh) are
added simultaneously in the master alloy, then combined by fusion
with fine gold to form the gold alloy, is quite beneficial and
effective and able to reach the purposes set above. The invention,
indeed, highlights how the combined use of iridium (Ir), ruthenium
(Ru) and rhodium (Rh) causes a synergic effect of the grain
refining properties, and related properties, by these refining
metals, in respect to the separated and alternative use of only
iridium (Ir) and ruthenium (Ru) in a given master alloy
composition, as it typically happens in prior art. Even more: such
a synergic effect is associated with an overall reduction of the
cost of the refiners used in the master alloy, because the refining
system composed of iridium (Ir), ruthenium (Ru) and rhodium (Rh)
allows to get a qualitative level of the physico-mechanical
properties listed above even better than that one of the known gold
alloys but without increasing the content of iridium (Ir), as said
metal significantly and notoriously more expensive than ruthenium
(Ru).
[0025] On the other hand, the combination of refiners according to
the technical concept expressed by the current invention
surprisingly allows to exploit the rhodium (Rh) as innovative and
new grain refiner (never used in the prior art for similar
purposes), without causing significant increases of cost since it
is added in small quantities (less than 1%).
[0026] As known, rhodium (Rh) is a transition metallic element of
the group of platinoids: it has atomic number equal to 45,
molecular weight equal 102.9 and melts at 1,964.degree. C. Its
cost, very high in the past, has drastically declined in recent
times (about 30 /g at the time of filing of the present patent
application).
[0027] In detail, the combination of a date, however small, amount
by weight of ruthenium (Ru) and rhodium (Rh) to iridium
(Ir)--without changing the quantity of the latter--surprisingly and
advantageously involves a not negligible reduction of the
crystalline grain size of the gold alloy and an equally noticeable
increase in the ductility of the same.
[0028] Said purposes are achieved by a master alloy composition for
the production of gold alloys with innovative refiners system and a
gold alloy using such a master alloy composition, respectively
according to the appended claims 1 and 12, as hereinafter referred
for the sake of exhibition brevity.
[0029] Integral part of the invention is also the use of iridium
(Ir), ruthenium (Ru) and rhodium (Rh) as refiners in the production
of a master alloy composition for the production of gold alloys,
according to claim 13 attached, as hereinafter referred for the
sake of exposure brevity.
[0030] Object of the present invention is also the use of iridium
(Ir), ruthenium (Ru) and rhodium (Rh) as synergic refiners of the
crystalline grain of gold alloys according to claim 14 attached, as
still hereinafter referred for the sake of exhibition brevity.
[0031] It is, therefore, a first objective of the present
invention, possibly independent and usable autonomously with
respect to the other aspects of the invention, a master alloy
composition for the production of gold alloys with innovative
refiners system, represented particularly by the simultaneous
presence of iridium (Ir), ruthenium (Ru) and rhodium (Rh) as
refiners of the crystalline grain size of the final gold alloy
obtained through such a master alloy composition.
[0032] It is a second purpose of the invention a master alloy
composition for the production of gold alloys, comprising
simultaneously iridium (Ir), ruthenium (Ru) and rhodium (Rh), able
to improve, compared to the known technique, the mechanical
properties, and in particular the ductility, of the final gold
alloy obtained through such a master alloy composition.
[0033] It is, therefore, another purpose of the present invention,
possibly independent and usable autonomously with respect to the
other aspects of the invention, a master alloy composition for the
production of gold alloys, comprising simultaneously iridium (Ir),
ruthenium (Ru) and rhodium (Rh), able to improve, compared to the
prior art, the properties of resistance to corrosion--for example
by reducing the release of nickel in white gold alloys--of the gold
alloy obtained through such a master alloy composition.
[0034] It is, therefore, another purpose of the invention, possibly
independent and usable autonomously in relation to the other
aspects of the invention, the combined and simultaneous use of
iridium (Ir), ruthenium (Ru) and rhodium (Rh) as refiners in the
production of a master alloy composition for the production of gold
alloys.
[0035] It is, then, a further purpose of the invention, possibly
independent and usable autonomously in relation to the other
aspects of the invention, the combined and simultaneous use of
iridium (Ir), ruthenium (Ru) and rhodium (Rh) as synergic
crystalline grain refiners of gold alloys.
[0036] Other technical features of detail of the master alloy
composition for the production of gold alloys with innovative
refiners system, and the corresponding gold alloy, as well as the
simultaneous use of iridium (Ir), ruthenium (Ru) and rhodium (Rh)
for the production of a master alloy composition, and related gold
alloy, according to the present invention, are described in the
corresponding dependent claims.
[0037] The claims, hereinafter specifically and concretely defined,
are considered an integral part of the present description.
DESCRIPTION OF THE FIGURES
[0038] Further features and specificities of the present invention
will appear to a greater extent from the detailed description which
follows, relating to preferred embodiments of the master alloy
composition, gold alloy and uses claimed herein by exclusive, given
by indicative and illustrative, but not limitative, way with
reference to the enclosed drawing tables, also provided only by way
of example, in which the FIGS. 1-3 are three distinct images of the
section of a master alloy composition of the invention, captured
using a backscattered electrons beam (QBSD) of an electronic
scanning microscope equipped with a microprobe (SEM/EDX), at three
different levels of enlargement (680.times., 2080.times. and
5670.times., respectively).
DETAILED DESCRIPTION OF THE INVENTION
[0039] While the invention is susceptible to various alternative
modifications and implementations, some embodiments thereof will be
described below in detail, in particular by means of some
illustrative examples.
[0040] It should be understood, however, that there is no intention
to limit the present invention to the specific embodiments
described but, on the contrary, the invention itself intends to
cover all the further alternative and equivalents modifications and
implementations that fall within the scope of protection as defined
in the appended claims.
[0041] In the following description, therefore, use of "for
example", "etc." and "or" indicates a non-exclusive alternatives
without any limitation, unless otherwise stated.
[0042] Use of the term "also" means "among which, but not limiting
to," unless otherwise indicated. In accordance with the invention,
the master alloy composition for the production of gold alloys with
innovative refiners system includes: [0043] iridium (Ir): 0.01/0.8%
by weight; [0044] ruthenium (Ru): 0.002/0.9% by weight; [0045]
rhodium (Rh): 0.002/0.8% by weight; [0046] copper (Cu): 20/99.965%
by weight, wherein iridium (Ir), ruthenium (Ru) and rhodium (Ru)
are added as the refining elements of the crystalline grain.
[0047] In particular, the percentage by weight of iridium (Ir) is
preferably in the range between 0.03% and 0.17%.
[0048] Still more in particular, the percentage by weight of
iridium (Ir) is in the range between 0.03% and 0.06% for yellow
gold alloys, while it is in the range between 0.1% and 0.16% for
white gold alloys.
[0049] Preferably, the weight percentage of ruthenium (Ru) is in
the range between 0.003% and 0.09%.
[0050] In further preferred but not exclusive manner, the
percentage by weight of ruthenium (Ru) is in the range between
0.0045% and 0.04% for yellow gold alloys, while it is in the range
between 0.01% and 0.08% for white gold alloys.
[0051] Preferably, also, the percentage by weight of rhodium (Rh)
is in the range between 0.05% and 0.15% and for example it is equal
to 0.1% by weight.
[0052] Preferably but not necessarily, the master alloy composition
concerned further comprises zinc (Zn): 1/25% by weight.
[0053] In a preferred but not binding way, the percentage by weight
of zinc (Zn) is in the range between 1% and 18%.
[0054] Even more in detail, the percentage by weight of zinc (Zn)
is in the range between 1% and 12% for yellow gold alloys and in
the range between 7% and 14% in case of white gold alloys; this
depending on the title (carat) of the final gold alloy to be
obtained.
[0055] As mentioned above, it is also possible to provide master
alloy compositions deprived of zinc (so-called "zinc-free"), as it
will be shown in the examples below; the absence of this element,
while not compromising the mechanical features and resistance to
corrosion nor the performances in terms of color and workability,
especially in case of yellow or red alloys, allows to stabilize the
weight of the casting and consequently the title of the alloy.
[0056] In case of yellow gold alloys, preferably, the master alloy
composition of the invention further includes silver (Ag): 20/64%
by weight.
[0057] If, instead, the final alloy to be produced provides white
gold, preferably the master alloy composition further comprises
nickel (Ni): 5/40% by weight.
[0058] As already mentioned, another integral aspect of the
invention concerns a gold alloy with innovative refiners system
which includes: [0059] gold (Au): 333.33.Salinity. (8
k)/958.33.Salinity. (23 k) by weight; [0060] a master alloy
composition as just identified and described, for the remaining
part by weight.
[0061] According to a preferred embodiment of the gold alloy of the
invention, the percentage by weight of gold (Au) is equal to
750.Salinity. (18 k) and the percentage by weight of the master
alloy composition is equal to 250.Salinity..
[0062] In accordance with another preferred and alternative
embodiment of the gold alloy of the invention, the percentage by
weight of gold (Au) is equal to 585.Salinity. (14 k) and the
percentage by weight of the master alloy composition is equal to
415.Salinity..
[0063] By way of preferred but not exclusive example, the above
gold alloy of the invention provides that the metals of the master
alloy composition are bonded together in order to form an
intermediate, separated and distinct, compound, subsequently
combined to the fine gold (Au) to obtain precisely the final gold
alloy.
[0064] This does not exclude, however, that in other embodiments of
the gold alloy of the invention, the metals of the master alloy
composition are bonded directly to gold (Au) during the production
phase of the final gold alloy, i.e. without creating an
intermediate compound.
[0065] Another aspect of the present invention relates to the use
of iridium (Ir), ruthenium (Ru) and rhodium (Rh) as refiners in the
production of a master alloy composition for the production of gold
alloys, wherein iridium (Ir), ruthenium (Ru) and rhodium (Rh) are
used simultaneously and in combination each other.
[0066] A further aspect of the present invention refers to the use
of iridium (Ir), ruthenium (Ru) and rhodium (Rh) as synergic
refiners of the crystalline grain of gold alloys, wherein, again,
iridium (Ir), ruthenium (Ru) and rhodium (Rh) are used
simultaneously and in combination each other.
[0067] Some preferred but not limiting examples of the master alloy
composition, and the resulting gold alloy with innovative refiners
system, object of the invention, are described below.
Example 1
750.Salinity. Yellow Gold Alloy
[0068] Table I below compares four master alloy compositions with
different refining systems of the crystalline grain, three of these
master alloy compositions are of known and traditional type
(indicated with the reference "A", "C" and "D"), while the
remaining master alloy composition is designed according to the
teachings of the invention (reference "B" in bold). It is also
stated precisely that, in the following Table I, the term "bal" for
copper (Cu) stands for "balanced" and indicates that this element
is present in an amount by weight necessary to complete the master
alloy composition to 100%.
[0069] In the lower part of Table I the main physico-mechanical
properties related to the corresponding gold alloy, having in this
case a title of 750.Salinity. (18 k), comprising the directly above
master alloy composition reported in Table I, are reported.
[0070] Master alloy compositions "A" and "C" of the prior art
provide different types of refiners inserted individually, while
the master alloy composition "B" of the invention provides three
different types of refiners inserted simultaneously.
[0071] The master alloy composition indicated by the reference "D"
is, instead, a traditional version without any kind of grain
refiner.
[0072] It can be clearly seen that the composition of the master
alloy "B" according to the invention, in which the triple refiner
system (Ir+Ru+Rh) is inserted holds crystalline grain having sizes
about 35% lower than the refined alloy only with Iridium (Ir).
[0073] It is also stressed how the triple refiner system (Ir+Ru+Rh)
produce a significant improvement in the ductility of the alloy
(indicated with A %), amounting to 22%.
TABLE-US-00001 TABLE I Composition (% by weight on master alloy) A
B C D Zn 9 9 9 9 Ag 45 45 45 45 Ir 0.04 0.04 -- -- Ru -- 0.0045
0.0045 -- Rh -- 0.1 -- -- Cu bal bal bal bal Measured properties
(750%.sub.0 - 18k gold alloy) Grain (.mu.m) 120 70 85 700 A% 38 47
39 38
[0074] In FIGS. 1, 2 and 3 attached, referring to the sample of
master alloy composition "B" of the present invention shown in
Table I, it can be observed some surveys carried out by means of
backscattered electrons beam (QBSD) with electronic scanning
microscope with microprobe (SEM/EDX), at three different levels of
enlargement (FIG. 1=680x; FIG. 2=2080x; FIG. 3=5670x).
[0075] From the images of these FIGS. 1-3 at the origin of the
dendrites, the presence of a nucleus consisting of elements of high
molecular weight (light color) appears clearly visible.
Example 2
750.Salinity. Yellow Gold Alloy
[0076] The second favourite, although not binding, example of
master alloy composition (and corresponding gold alloy) of the
invention presented herein is derived from Table II below, which
compares three master alloys compositions having different grain
refining systems. In particular, Table II shows two master alloy
compositions of the known and traditional type, (indicated
respectively with the reference "E" and "G", each having a single
refiner different from that one of the other), and a master alloy
composition designed according to the concept of the invention
(indicated with the reference "F" in bold), i.e. with triple
refiner. "Bal" term for copper (Cu) used in Table II means again
"balanced" and indicates that this element is present in an amount
by weight necessary to complete the master alloy composition to
100%.
[0077] Moreover, at the bottom of Table II the main
physico-mechanical properties related to the corresponding
750.Salinity. gold alloy are shown.
TABLE-US-00002 TABLE II Composition (% by weight on master alloy) E
F G Zn 8 8 8 Ag 47 47 47 Ir 0.04 0.04 -- Ru -- 0.04 0.04 Rh -- 0.04
-- Cu bal bal Bal Measured properties (750%.sub.0 - 18k gold alloy)
A% 29 34 30
[0078] Also in this case it can be observed how by including in the
master alloy composition the triple refiner system according to the
invention (iridium (Ir)+ruthenium (Ru)+rhodium (Rh)) produces an
increase of ductility (parameter A %) more than proportional to the
addition of the individual refiners in a given master alloy
composition.
Example 3
750.Salinity. White Gold Alloy
[0079] Another important novelty introduced by the invention is the
ability of the crystalline grain refining system--that involves the
simultaneous addition of iridium (Ir), ruthenium (Ru) and rhodium
(Rh)--to increase the properties of resistance to corrosion in
white gold alloys.
[0080] It follows that in white gold alloys which provide the
simultaneous presence of iridium (Ir), ruthenium (Ru) and rhodium
(Rh) as refiners it has been observed a further reduction of the
values of nickel release compared to what has been observed in
alloys of equal composition in which the grain refiners, such as
typically iridium (Ir) and ruthenium (Ru), are included as
individual elements, not in combination.
[0081] Such a property is particularly important when it is
considered that from the next April 2013 will come into force the
new revision EN1811:2011 of the European standard on the nickel
release, which provides the adoption of limits of nickel release by
goldsmith, jewelry and costume jewelry articles much more
restrictive than the current ones.
[0082] As known, nickel is a low cost metal, used in jewelry as
whitening element of gold.
[0083] The problem of allergies (contact dermatitis) caused by the
release of nickel on the skin of people who are particularly
subject has been well known for many years. The public has shown an
increasing level of concern about the issue of the release of
nickel, to the point of pushing the European Union to adopt a
Community regulatory directive on the use of such a metal, formed
in particular by the legislation on the nickel EN1811 whose first
publication dates back to 1994.
[0084] With the entry into force of the new revision of the
regulation EN1811:2011, nickel release values actually determined
shall not exceed the values of 0.28 g/cm.sup.2/week--for objects in
long contact with the skin--and 0.11 g/cm.sup.2/week--for objects
to be inserted into pierced parts of the body--.
[0085] Compared to the previous version of the legislation, the new
standard EN1811:2011 de facto determines the reduction of the
maximum release limit of more than 18 times with respect to the
release limit allowed by the previous version of the legislation
concerned.
[0086] The entry into force of the new standard will result,
therefore, in heavy restrictions with respect to the availability
of nickel-based alloys which can be still used by
manufacturers.
[0087] The metallurgical implications that will follow the
introduction of the new standard are extremely important.
[0088] That being stated, the present invention demonstrates that
through the use of the triple refiner system iridium (Ir),
ruthenium (Ru) and rhodium (Rh) release values can be further
reduced, leading them to a safe range, well below the maximum limit
allowed by the new regulations EN1811:2011, as shown by table III
below.
[0089] In such a Table III, comparative tests among master alloy
compositions with different types of crystalline grain refining
systems are shown.
[0090] More in detail, master alloy compositions indicated with "H"
and "L" are of traditional type and each provide a single refiner
(either iridium (Ir) or ruthenium (Ru), alternative each other),
while the master alloy composition indicated with "I" (highlighted
in bold), is designed according to the invention, using a triple
refiner system (Ir+Ru+Rh).
[0091] The term "bal" for copper (Cu) always stands to shorten the
word "balanced" and provides that this element is present in an
amount by weight necessary to complete the master alloy composition
to 100%.
[0092] The lower part of Table III shows the main
physico-mechanical properties related to the corresponding white
gold alloy, having in the specific case a title equal to
750.Salinity. (18 k).
[0093] The example of Table III compares the crystalline grain
sizes, and the related nickel release values, of white gold alloys
having a master alloy composition with single grain refiner (only
iridium (Ir) for the master alloy composition "H" and only
ruthenium (Ru) for the master alloy composition "L"), with the
relevant parameters of white gold alloys having a master alloy
composition with triple refiner system, comprising, in particular,
iridium (Ir), ruthenium (Ru) and rhodium (Rh)) (master alloy
composition "I").
[0094] It can be clearly appreciated the synergic effect determined
by the simultaneous addition of the three refiners iridium (Ir),
ruthenium (Ru) and rhodium (Rh) [cf. master alloy composition "I"]
not only in refining the crystalline grain but also in reducing the
nickel release value, which is conveniently much lower than the
limit prescribed by the new standard EN1811:2011 (0.28
g/cm.sup.2/week), with the obvious advantages that this
entails.
TABLE-US-00003 Table III Composition (% by weight on master alloy)
H I L Zn 16 16 16 Ni 17 17 17 Ir 0.14 0.14 -- Ru -- 0.04 0.04 Rh --
0.1 -- Cu bal bal bal Measured properties (750%.sub.0 - 18k gold
alloy) Grain (.mu.m) 185 .+-. 15 64 .+-. 17 95 .+-. 20 Nichel
release (.mu.g/cm.sup.2/week) 0.203 0.065 0.103
Example 4
750.Salinity. White Gold Alloy
[0095] Even Table IV below shows comparative tests, carried out by
the Applicant, including alloys compositions with different grain
refining systems, intended to form white gold alloys.
[0096] More specifically, master alloy compositions indicated with
"M" and "O" are of conventional and well known type, each providing
a single refiner (either iridium (Ir) or ruthenium (Ru),
alternative to each other), while master alloy composition
indicated with "N" (highlighted in bold) is designed according to
the invention, using simultaneously iridium (Ir), ruthenium (Ru)
and rhodium (Rh) as refining elements of the crystalline grain
(triple refiner system).
[0097] As usual in this paper, the term "bal" for copper (Cu)
abbreviates the word "balanced" and indicates that this element is
present in an amount by weight necessary to complete the master
alloy composition to 100%.
[0098] The lower part of the table shows the main physical and
mechanical properties (grain size and ductility) referred to the
corresponding 750.Salinity. (18 k) gold alloy.
[0099] In the example of Table IV the sizes of crystalline grain,
and their nickel release values, of white gold alloys whose
corresponding master alloy includes a single grain refiner (only
iridium (Ir), master alloy composition "M", and only ruthenium
(Ru), master alloy composition "O"), are compared with the same
parameters of white gold alloys whose related master alloy
composition "N" includes three grain refiners, in this case iridium
(Ir), ruthenium (Ru) and rhodium (Rh).
[0100] It should be clearly observed the synergic effect of the
triple refiner system, particularly iridium (Ir), ruthenium (Ru)
and rhodium (Rh), [master alloy composition indicated with "N"] in
refining the crystalline grain and reducing the nickel release
value that is, advantageously, well below the limit prescribed by
the new standard EN1811:2011 (0.28 g/cm.sup.2/week).
TABLE-US-00004 TABLE IV Composition (% by weight on master alloy) M
N O Zn 17 17 17 Ni 18.5 18.5 18.5 Ir 0.16 0.16 -- Ru -- 0.08 0.08
Rh -- 0.08 -- Cu bal bal bal Measured properties (750%.sub.0 - 18k
gold alloy) Grain (.mu.m) 170 .+-. 19 60 .+-. 21 102 .+-. 20 Nichel
release (.mu.g/cm.sup.2/week) 0.215 0.055 0.120
Example 5
750.Salinity. White Gold Alloy
[0101] It is, finally, considered useful to provide, in Table V
below, some additional comparative data between two traditional
master alloy compositions (respectively indicated with "P" and "R")
and a master alloy composition according to the present invention,
indicated with "Q". As usual, the term "bal" for copper (Cu)
abbreviates the word "balanced" and indicates that it is present in
an amount by weight useful to complete to 100% the master alloy
composition.
TABLE-US-00005 TABLE V Composition (% by weight on master alloy) P
Q R Ir 0.15 0.15 0.15 Ru -- 0.1 0.1 Rh -- 0.1 -- Cu bal bal bal
Measured properties (750%.sub.0 - 18k gold alloy) Grain (.mu.m) 140
70 115
[0102] As it can be easily noted, the composition according to the
present invention allows to get a crystalline grain having a size
reduced up to about the half compared to that one of the
traditional compositions of the prior art, this resulting from the
simultaneous and combined use of iridium, ruthenium and
rhodium.
[0103] On the basis of the description just given, it is
understood, therefore, that the master alloy composition for the
production of gold alloys with innovative refiners system, the gold
alloy using such a master alloy composition and the uses of the
present invention reach the purposes and achieve the advantages
previously mentioned.
[0104] It is, finally, clear that several other changes could be
made to the invention concerned, without departing from the
principle of novelty intrinsic in the inventive idea expressed
herein, as it is clear that, in the practical implementation of the
invention, materials, shapes and sizes of the illustrated details
could be changed, as needed, and replaced with others technically
equivalent.
[0105] Where the constructive features and techniques mentioned in
the following claims are followed by reference numbers or signs,
those reference signs have been introduced with the sole objective
of increasing the intelligibility of the claims themselves and
therefore they have no limiting effect on the interpretation of
each element identified, by way of example only, by these reference
signs.
* * * * *