Note: Descriptions are shown in the official language in which they were submitted.
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PLATINUM ALLOY AND METHOD OF PRODUCTION THEREOF
FIELD OF THE INVENTION
The present invention relates to a platinum alloy and a method of
production thereof. In particular, the 'present invention relates to platinum
alloys
that are suitable for the fabrication of ornamental articles such as rings,
necklaces,
-bracelets, earrings, watch bands, watch bodies and other jewelry.
Furthermore, the
present invention relates to an ornamental article made from the
platinum.alloy
and a method bf production thereof.
BACKGROUND OF THE INVENTION
Platinum is a precious metal and is relatively expensive. In recent years
platinum has come into increasing prominence -as a metal used for jewelry
fabrication. Platinum for fine, jewelry is commonly sold in high
concentrations of
.20 over 85 percent by weight.
;Pure platinum metal (Pt1000) is soft and does not have the mechanical
strength for most jewelry applications. For this reason, in most jewelry
applications various kinds of platinum alloys are employed. Platinum alloys
are
desirable for 'their neutral color when combined with gems, they are -hypo-
allergenic, they have high tensile strength, and a.pleasurable heft due to
their high-
density.
The jewelry industry uses three main classes of platinum alloys. These
classes are Pt950, Pt90D and Pt850. These alloys have~ a platinum content of
95, 90
and 85 wt.%, respectively. Commercially available alloys frequently used in
the
CONFIRMATION COPY
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fabrication of jewelry include Pt/Ir 900/100 (90 wt.% platinum and 10 wt.%
iridium), PtCu950 (95 wt.%4 of platinum and 5 wt.% of copper) and PtCo950 (95
wt..% of platinum and 5 wt.% of cobalt).
Various high platinum content jewelry materials are known in the art. The
term "high platinum. content" as used herein refers to platinum alloys having
a
platinum content equal or greater than85 wt.%.
For example, U.S. Patent. 4;165,983 describes an alloy for fabricating
jewelry containing at least 95 wt.% platinum, 1.5 to 3.5 wt.% gallium,. and a
balance of at least one of indium, gold, palladium, silver, copper, cobalt,
nickel,
ruthenium, iridium and rhodium. U.S. Patent 5,846,352 describes a heat-treated
platinum-gallium alloy for fabricating jewelry containing 1 to 9 wt.% gallium
and
a small amount of palladium. Japanese published patent application JP 61-
133340
describes an alloy for fabricating jewelry consisting of 84 to 96 wt.%
platinum, 1
to.10 wt.% gallium, 0.5 to 10 wt.% copper, and 0.01 to 5 wt.% cobalt. Japanese
published patent application JP 61-034133 describes an alloy for fabricating
jewelry containing 84-to 96 wt.% platinum, 0.5 to 10 wt.% cobalt, 0.5 to 10
wt.%
copper and 0.01 to 0.5 Y, B, CaB mischmetal.
Although such alloys have satisfactory mechanical and optical -properties
that make them suitable for jewelry fabrication, these alloys are expensive to
- produce due to their high, platinum content.
There are also a number of low platinum content jewelry materials known
in the art. The term "low platinum content" as used herein refers to platinum
alloys
having aplatinum content smaller than 85 wt.%.
U.S. Patent No. 6,048,492 describes a platinum alloy composition for use
in jewelry.products containing about 58.5 wt.% of platinum, 26.5 to 36.5 wt.%
of
palladium and 5 to 15 wt.% of either iridium, copper or ruthenium. U.S. Patent
2,279;763 describes a ductile platinum alloy containing 10 to 80 wt.% of
platinum,
12 to 90 wt.%- of palladium, and 1 to 15 wt.% of ruthenium.
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W02004/059019 Al describes PT-base bulk solidifying amorphous alloys
utilizing platinum and other ingredients and requiring the presence of
phosphorous. The amorphous alloys described in this document are prepared by
quenching the molten alloy from above the melt temperature to ambient
temperatures and thus achieving a substantially (i.e. non-crystalline)
structure of
the alloy and .requiring more than 50% to be in the amorphous state.
A disadvantage of known low platinum content jewelry materials is that
they often have inferior mechanical and physical properties compared to the
high
platinum content jewelry materials. In particular, the castability of known
low
platinum content jewelry materials is not as good as that of high platinum
content
alloys. Also, the color of known low platinum content jewelry materials
differs
from the typical "platinum, color" of Pt950 alloys that is desired by most
customers
of fine jewelry. Hence, low platinum content jewelry materials are often
rejected
by customers for aesthetical reasons. In fact, it is very difficult to produce
a low
platinum content jewelry material that combines both the mechanical strength
and
workability as well as the optical properties of high platinum content
materials.
Due to the potential improvements in properties and performance of such
alloys, there is a need for additional alloys suitable for use in jewelry and
art
applications.
Accordingly, it would be desirable to provide a platinum alloy composition
suitable for jewelry that is less expensive than the platinum that, is
presently
available, yet still provides a platinum jewelry item with desirable
technological
and optical properties.
SUMMARY OF THE INVENTION
According to the present invention there is provided an improved low platinum
content alloy composition that contains 63.01 to 69.99 wt.% of platinum, 1.5
to 10
wt:% of cobalt and 20.01 to 35.49 wt.% of copper. The alloys according to the
present invention are particularly well suited for the fabrication of
ornamental
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articles, such as rings, necklaces, earrings, watch bands, watch bodies and
other
jewelry.
Surprisingly, it was found that despite of their relatively low platinum
content the alloys of the present invention exhibit excellent mechanical and
optical
properties that make them extremely suitable for the manufacturing of
ornamental
products such as jewelry of any kind. Due to the lower density of the alloys
of the
present invention it is possible to manufacture thinner, lighter constructions
and
castings at considerable less cost than with high platinum content alloys.
(e.g.
Pt850, Pt900, Pt950).
The platinum alloys of the present invention have a lower melting range
compared to known low platinum content alloys as described in, for example,
U.S.
Patent 6,048,492. Due to their relatively low melting temperature they cast
easier
than previously known platinum alloys and are more energy efficient. This
lower
temperature alloy also allows a lower mold temperature, decreasing defect rate
due
to shrinkage porosity, investment cracking, inclusions, and contaminations
that
occur more readily at highly-elevated temperatures.
The alloys according to the present invention are particularly well suited
for the fabrication of jewelry due to their improved hardness, workability,
castability, deformability, wear and abrasion properties, and resistance to
corrosion. The platinum alloy composition of the invention appears and looks
no
different than 95 percent platinum, but is substantially lighter, less dense,
and thus,
less expensive to produce. In fact, the platinum alloy composition of the
present
invention has essentially the same color and appearance as PtCu950 alloy.
The invention further relates -to a method of preparing the alloys of the
present invention by formulating and mix.ing the components of the alloy in
the
specified amounts and melting them together.
The alloy may be formed into a desired shape. Such operations are many
and include casting or fabricating. Some examples of fabrication can be by
rolling
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of the alloy into a sheet, drawing a wire, molding, casting, forging, stamping
or
constructing the object or shape useful as a jewelry component.
Accordingly, the invention also relates to a method of manufacturing an
ornamental article, which comprises formulating one of the platinum alloys
described above and then utilizing the alloy as a component of jewelry.
Further, the invention also relates to the use of such alloys in the
production of ornamental articles such as jewelry. Still further, the
invention
relates to ornamental articles comprising such alloys.
Accordingly, it is an object of the invention to provide an improved low
platinum content platinum alloy composition.
Still another object of the invention is to provide an improved platinum
alloy composition that is suitable for use in jewelry for the mass commercial
market.
A further object of the invention is to provide an improved platinum alloy
composition which is substantially lighter and less dense than conventional
-platinum-alloy compositions.
Still further it is an object of the invention to provide platinum alloys
which
may be cast more readily than known platinum alloys.
Still other objects and 'advantages of the invention will in part be obvious,
and will in part be apparent from the following description.
DETAILED DESCRIPTION
The platinum alloy compositions of~ the invention include platinum in an
amount of 63.01 to 69.99 wt.%. -The platinum content of the alloy compositions
of
the invention is significantly lower than that of conventional Pt850, Pt900
and
Pt950 platinum alloys commonly used in the jewelry industry.
According to one embodiment of the invention the platinum alloy
comprises:
63.01 to 69.99 wt.% of platinum;
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1.5 to 10 wt.% of cobalt; and
22.01 to 35.49 wt.% of copper.
Preferably, the platinum content of this alloy is from 63.5 to 66.5 wt.% , in
particular from 64 to 66 wt.%, based on the total alloy composition. If the
platinum
content of the alloy is smaller than about 63 wt.% the workability and
stampability
of the alloy decrease significantly and the alloy loses its platinum-like
color. If the
platinum content of the alloy is greater than about 70 wt.%, the costs for the
production of the alloy increase significantly while, at the same time, the
mechanical and chemical properties of the alloy do not improve significantly.
Preferably, the cobalt content of the alloys of the present invention is from
1.5 to 10 wt.%, in particular 2.0 to,8.0 wt.% or 2.0 to 6.0 wt.%, based on the
total
alloy composition. If the cobalt content of the alloy is smaller than about
1.5 wt.%,
the mechanical properties and the workability of the alloy decrease
significantly
and the alloy loses its platinum-like color. If the cobalt content of the
alloy is
greater than about 8 wt.% the alloy becomes too hard.
Preferably, any balance in the alloys of the present invention is made up by
copper.
.The platinum alloys of the present invention may further comprise 0.00 1 to
2 wt.% of at least one first metal selected from the group consisting of
iridium and
ruthenium. A combination of these -elements may also be added, so long as the
total amount does not exceed 2 wt.% of the alloy composition. Iridium and/or
ruthenium can be added as metal hardeners in order to improve the hardriess of
the
alloy, with iridium being the preferred hardener since it offers gradual
hardness
improvements over a wide range of concentrations, with. no deterioration of
alloy
properties.
The platinum alloys of the present invention may further comprise 0.001 to
2 wt.% of at least one second metal selected from the group consisting of
indium
and gallium. A combination of these elements may also be added, so long as the
total amount does not exceed 2 wt.% of the alloy composition. Indium and
gallium
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may be added to improve the precipitation hardening of the alloy. The platinum
alloys of the present invention may further comprise palladium in an amount of
0.001 to 5 wt.%, preferably 0.25 to 2.5 wt.%. An addition of palladium is
useful in
order to vary the color of the alloy.
The platinum alloys of the present invention may further comprise silicon
in an amount of 0.001 to 0.5 wt.%, preferably in an amount of 0.1 to 0.3 wt.%.
It
was found that an addition of silicon in the specified amount improves the
casting
properties of the alloy and results in a smoother surface of the casted
article. This
effect is particularly desirable when the alloy of the present invention is
used for
the manufacture of an ornamental article where excellent casting properties
are
required. It was found that silicon in the amounts specified is soluble in the
Pt-Co-
Cu alloys of the present invention and results in the aforementioned effect.
In
contrast thereto, addition of silicon to high content platinum alloys
generally
results in inhomogeneous low melting phases and is thus undesirable.
The platinum alloys of the present invention may further comprise
zirconium in an amount of 0.001 to 0.5 wt.%, preferably in an amount of 0.1 to
0.3
wt.%. It was found that an addition of zirconium in the specified amount
improves
the workability of the alloys.
According to -a preferred embodiment of the present invention, the total
amount of other elements present in the platinum alloy besides Pt, Cu, and Co
does
not-exceed about 10 wt.%, preferably about 7.5 wt.%, even more preferably
about
5 wt.%, and most preferably about 4 wt.%, 'based on the total weight of the
platinum alloy.
The platinum alloy of the present invention may be present in a crystalline
state .or in an amorphous state. Preferably, the platinum alloy of the present
invention is present in a substantially crystalline state. The term
"substantially
crystalline state" as used herein means that the platinum alloy is greater
than fifty
percent crystalline by volume. Preferably, the platinum alloy is at least
about
ninety percent crystalline by volume, more preferably at least ninety five
percent
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crystalline by volume and most preferably about one hundred percent
crystalline
by volume.
While phosphorous can be used as..an additive in some platinum alloys to
make the alloy more brittle and/or amorphous, the addition of phosphorous to
the
alloy of the present invention is not particularly preferred since it is not
desired to
produce an amorphous alloy. Therefore, if.phosphorous is added to the platinum
alloy of the present invention, such an addition should be done in moderate
amounts. Preferably, the amount of phosphorous contained in the platinum alloy
of
the present invention is less than 4.2 wt.%, more preferably less than 3.4
wt.%,
even more preferably less than 2.3 wt.% and most preferably less than about
1.5
wt.% of phosphorous, based on the total alloy composition. According to
another
preferred embodiment the platinum alloy of the present invention contains less
than about 2.0 wt.% and more preferably less than about 1- wt.% of
phosphorous,
based on the total alloy composition.
Advantageously, the alloy can include any one of a number of property
enhancing agents, including a deoxidizing agent, grain reducing agent, a
viscosity
decreasing agent or a color variation agent. The number and amount of the
other
additives may vary depending on the desired mechanical properties of the alloy
and can readily be determined by a person of ordinary skill in the art by
means of
routine experiments.
According to another embodiment of the invention, the platinum alloy
consists essentially of, apart from impurities,
63.5 to 67.5 wt.% of platinum,
1.5 to 8 wt.% of cobalt, and
24.5 to 35 wt.% of -copper,
wherein copper may be substituted by one or more of the following elements in
the
amounts specified:
0.001 to 2wt.% of at least one of said first metals;
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0.001 to 2 wt.% of at least one of said second metals;
0.001 to 5 wt.% of palladium;
0.001 to 0.5 wt.% of silicon; and/or
0.001 to 0.5 wt.% of zirconium.
The alloys of the present invention exhibit excellent mechanical and
physical properties such as tensile. strength, Vickers hardness and elongation
at
break. The tensile strength of the platinum alloys of the present invention.
is in the
range of 450 to 800 N/mm2. The Vickers hardness of the platinum alloys of the
present invention, measured at softened state, is in the range of 130 to 210
HV 10.
The elongation at break of the platinum alloys of the present invention is at
least
about 20 %.
A further advantage of the present invention is -that the color tone of the
platinum alloy corresponds essentially to the platinum white color tone of a
PtCu950 alloy, which is aesthetically very appealing.
The alloys of the present invention may be prepared by conventional
alloying methods that are well known in the art. The preparation of the alloy
generally includes the step of melting platinum, cobalt and copper and any
other
component in the specified amounts. The method may further include the step of
hardening the alloy by cold working or heat treatment.
The method may include the steps of annealing and then quenching the
alloy, before hardening the alloy.
The alloys are usually cast from melts under a shielding gas and then
shaped. After shaping, they may be subjected to heat treatment, possibly under
a
shielding gas, to improve their mechanical properties.
In order to prepare the platinum alloy composition of the invention, a high
temperature melting process is carried out. This can achieved using induction
melting equipment, as is well known in the art. At all times, extreme care
should
be exercised - in order to limit metal contamination, as platinum is easily
contaminated by many elements routinely present in the environment. Such care
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can be achieved by melting the metals in either a vacuum or an inert gas
atmosphere, by preventing contact with other metals, and by preventing mixing
with silica-based products.
The platinum alloy is preferably melted and blended together by induction
heating.in appropriate crucibles for platinum alloys. After melting, the alloy
can be
poured through water to create grain-shot and can then be dried, weighed and
used
for casting.
For the preparation of the alloy of the present invention, the components of
the inventive composition are preferably melted in a silica crucible (for
small, fast
melts) or a zirconium oxide (for large, slow melts) crucible in an induction
oven. It
is preferred to use a vacuum or inert gas in the melting process and to place
all
components of the alloy composition in the crucible~ at the same time. In the
melting of the alloy, the molten metals should preferably be "turned"
(utilizing
medium to low frequency induction fields) in order to obtain an appropriate
mixing of the metals.
Following the melting step, the resulting alloy nugget elements can be
subjected to cold rolling and/or annealing in order to improve mechanical
qualities
of the mix. Thereafter, the mixed metal composition can optionally be re-
melted
as before, and a shot or plate be produced.
The preparation of the platinum alloys of the present invention can further
comprise -an annealing step. Annealing can be carried out either in a furnace
or
with a torch, as'is well known in the art. The annealing temperature depends
on the
platinum content and the melting point of the alloy and will readily be
determined
by a person of ordinary skill by routine experiments. Preferably, the
annealing is
done in a furnace that is atmosphere.controlled with shielding gas.
The shielding gas can be any of the non-oxidizing inert gasses, such as
argon, nitrogen, or mixtures thereof; anti-oxidizing gasses such as hydrogen,
carbon monoxide, or "forming" or "cracked ammonia" gas (nitrogen with a few
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percent of hydrogen). The piece can also be protected from oxidation by
enveloping them with commercially available heat-treating wraps:
The alloys can be used for a wide variety of jewelry components, such as
rings, clasps, spring parts, even compression-spring settings for gemstones,
and the
like.
Furthermore, the alloys can be repeatedly annealed and heat-trea.ted/age-
hardened, if desired.
As. used herein, the term "age-hardening" is essentially synonymous with
the term "precipitation hardening" which results from the formation of tiny
particles of a new constituent (phase) within a solid solution. The presence
of these
particles create stress within the alloy and increase its yield strength and
hardness.
See, B. A. Rogers, "The Nature of Metals", p.320 (Iowa State University Press,
1964); H. W. Polock, "Materials Science and Metallurgy", p. 266 (Reston Pub.
Inc. 1981) and "The Metals Handbook", pp.l-2 (Am. Soc'y Metals, 1986).
In their annealed/softened state the alloys can be worked by standard
jewelry-making techniques: they can be rolled, drawn, soldered to, shaped,
bent,
stamped, etc. These alloys can be applied to a variety of designs for springs,
gemstone mountings in rings, pendants, bracelets, chains, precious metal art
objects, and the like.
It should be noted that in designing for structure of the jewelry or art
object, the smallest cross-sectional area and shape of a component is taken
into
account. It is possible to adapt the design of the alloy to almost any
configuration.
The basic forms of these designs can vary, from simple sheet, to ring-shapes
and
more complex helixes, v-shapes, and the like. Objects can be wire, sheet,
springs
of all types, pendants, chain-links, brooches, and a multitude of others.
Standard
jewelry soldering techniques can be applied and repairs requiring heat can be
carried out. The alloys can be shaped, bent, built onto, annealed, and when
the
piece is done, the spring power and hardness can be regained by heat-
treatment.
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The ornamental product can be made by casting. The hardness of the alloys
may also be further increased by heat treatment. The.heat treatment may be
carried
out in a range of from 300 to 950 C with a suitable value being in the range
of
from 600 to 950 C, and typically of the order of 800 C. The alloys can be
softened by standard annealing procedures, typically at about 1000 C to 1030
C,
or higher.
The alloys may be used in the form of wire, sheet or other manufactured
article and may be. given intricate shapes and forms due to their great
hardness
combined with great ductility.
The alloys according to the present invention can be used, for example, in
the fabrication of wedding bands. Such weddings bands are generally produced
by
sawing blanks from tubes and then further working the blanks by suitable
measures, such as milling, drawing, forging, and polishing.
Other jewelry articles that can be manufactured from the alloys according
to the present invention include, for example, rings, necklaces, bracelets,
earrings,
bangles, stickpins, watch bands, watch bodies, wristwatches, tooth picks as
well as
other decorative articles such as ballpoint pens, letter openers, pocket knife
handles, and the like.
The following Examples are provided to illustrate certain aspects of the
invention and it is understood. that such an Example does not limit the scope
of the
invention as defined in the appended claims.
EXAMPLE
An alloy of the composition as specified in the following table was
weighted and molten under vacuum in a zirconia crucible in a vacuum induction
furnace .at a temperature of 1480 to 1500 C to obtain a homogeneous melt. The
alloy was cast into a steel mold to form -blocks having a dimension of 20 x
140
mm.
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In the following table, the physical properties of the alloy specimens thus
formed are specified. The melting range was determined by rneasuring the
cooling
curve of the alloy with a Degussa resistance furnace HR1/Pt/PtRH10 equipped
with a Linseis thermo element and a temperature-time-plotter L250. The Vickers
hardness was determined according to DIN 50133 using a Wolpert V-Testor 4521
instrument. The tensile strength, elongation at break and yield stress were
determined according to DIN 50145 using a Zwick ZO10 instrument. The color
was determined visually.
COMPARISON EXAMPLE
A commercially available Pt/Cu 950/50 a11oy was weighted and molten
under vacuum in a zirconia crucible in a vacuum induction furnace to obtain a
homogeneous melt. The alloy was cast into a steel. mold to form blocks
having.a
dimension of 20 x 140 mm.
The physical properties of the alloy specimens thus formed were tested as
described above and are specified in the following table.
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TABLE
EXAMPLE 1 EXAMPLE 2 COMPARATIVE
EXAMPLE
Composition Pt 65 wt.% Pt 65 wt.% Pt 95 wt.%
Cu 31.5 wt.% Cu 31.25 wt.% Cu 5 wt.%
Co 3.5 wt.% Co 3.5 wt.%
Si 0.25 wt.%
Density 14.4 14.4 20.3
Color platinum white platinum white platinum white
Melting Range 1390 -1450 1390 =1450 1730 -1745
Castability very good excellent fair
Workability good good good
Hardness [HV]
softened state 120 120 110
20 % cold roiled 190 190 185
40 % cold rolled 230 230 210
60 % cold rolled 260 260 235
Tensile Strength
[N/mm2]
softened state .600 600 320
60 % cold rolled -1000 ~ 1000 -800
Yield-Stress 350 350 130
[N/mmz]
Elongation at >35 >35 > 30 .
Break [%]
The experimental results indicate that the alloy according to the present
invention
exhibits superior casting, wear and abrasion properties when compared to a
conventional Pt/Cu 950/50 alloy. The results of Example 1 further indicate
that the
castability of the alloy of the present invention is enhanced by addition of
small
amounts of silicon. Furthermore, the. experimental results indicate that the
forming
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properties and the color tone of the alloy according to the present invention
are
comparable to those of a conventional Pt/Cu 950/50 alloy. The alloy according
to
the present invention was found to be an excellent material for the
manufacture of
jewelry articles such as rings, bracelets or necklaces
The principle of the invention and the best mode contemplated for applying
that principle have been described. It is to be understood that the foregoing
is
illustrative only and that other means and techniques can be employed without
departing from the true scope of the invention defined in the following
claims.
