GB2279967A - Platinum alloy - Google Patents

Abstract

A platinum alloy, which is a hard, high-purity platinum alloy, contains 10 - 100 ppm of cerium. The alloy has good hardness, luster and perspiration resistance, thereby allowing the fabrication of jewelry products having both high quality and suitable strength characteristics. The alloy generally contains at least about 99% by weight of platinum.

Description

PLATINUM ALLOY The present invention relates to a high-purity platinum alloy, and more particularly, to a hard platinum alloy used as a material in the field of jewelry, incllldinFr rings, necklaces, broaches, necktie pins, cufflinks, watch cases, watch frames, lighters, writing instruments, eyeglass frames and earrings.

Platinum is widely used in the field of jewelry because it closely matches the color of precious gems such as diamonds and pearls. However, since platinum is not suited for manufacture of accessories because it is excessively soft in pure form, it is necessary to form platinum into an alloy with small amounts of other metals to give it suitable hardness, strength and elasticity.

Consequently, platinum has been conventionally used in the form of an alloy in which palladium, gold, copper, nickel, cobalt, ruthenium and so forth are added to platinum. In particular, although palladium does not impair corrosion resistance and oxidation resistance, adequate hardness will not be obtained unless at least 10% by weight is added, and palladium alloys having a platinum grade of 900, namely those containing 90 by weight or more of platinum, are not considered to be practical.

In addition, although alloys blended with copper, ruthenium and so forth have greater hardness than palladium alloys, it is necessary to blend roughly 3-4% by weight of these alloy components in order to be practical, and alloys having a grade of 950, namely those containing 95% by weight of platinum, are considered to be the limit of practical use. Thus, these metals were frequently used to form ternary alloys in which a portion of the palladium is substituted with a different metal in order to increase hardness and improve polishability of platinum-palladium alloys.

As explained above, platinum alloys having high purity, as in the case of those containing 95% by weight of platinum or more, have been considered to be difficult to use for alloy materials having strength and hardness suitable for use in the field of jewelry.

The present invention seeks to provide a platinum alloy containing preferably at least 99% by weight of platinum and having hardness suitable for use in jewelry.

Accordingly the present invention provides a hard, high-purity platinum alloy containing 10-100 ppm of cerium.

The cerium contained in the platinum alloy of the present invention is a rare earth element which is a metal that oxidizes easily at high temperatures. Consequently, although methods in which the metals are melted by heating in air may be used when blending cerium with platinum to form an alloy, since the amount of cerium formed into an alloy becomes less than half of the amount added due to oxidation of a considerable amount of cerium, it is desirable to use a method that prevents the cerium from being subjected to oxidation as much as possible.Examples of method which can be used to obtain an alloy with platinum while preventing oxidation of cerium include a method wherein melting is performed in a vacuum, a method wherein melting is performed in an inert gas atmosphere such as nitrogen or argon, and a method wherein cerium is melted with platinum after sealing the cerium in a platinum capsule.

When the cerium content of the platinum alloy is excessively low, the hardness of the alloy decreases. When said cerium content is excessively high, the hardness of the alloy av be too high. Thus, the cerium content should be appropriately selected within a range of 10-100 ppm corresponding to the purpose of use of the target platinum alloy. Furthermore, the cerium content of the platinum alloy can be measured by, for example, a physical analytical technique such as plasma mass spectrometry.

Although conventional, commonly known methods can be used for casting the platinum alloy of the present invention, in the case of performing precision casting, the use of centrifugal casting is preferable. At this time, it is preferable to, for example, attach a sand mold, heated in advance in a separate kiln, to the casting machine, and perform casting after drawing a vacuum and replacing the air with an inert gas such as argon as necessary. If the amount of air contained in the sand mold is decreased by this method, oxidation loss of cerium during the casting procedure can be suppressed, thereby allowing the obtaining of a cast article of the platinum alloy of greater hardness. However, the above-mentioned performing of casting in the presence of an inert gas is not essential.If an alloy is used in which the cerium content is relatively high before casting, casting may be performed in air without this impairing in any way the obtaining of a cast article having improved hardness.

Since the platinum alloy of the present invention has a high degree of hardness despite having a low content of cerium, while also demonstrating adequate hardness even after casting only, there is no need to perform procedures for increasing hardness by secondary processing and so forth.

Embodiments of the invention are illustrated by the following Examples.

EXAMPLES A crucible containing 60 g of platinum and 0.04 g of cerium was placed in a high sreauency electric furnace having a secondary side output of a kw. After melting by heating for 11.5 minutes, 60 g of platinum and C.54 g of cerium were placed in the crucible followed by melting by heating for an additional 0.5-l minute. 0.04 g of cerium were then additionally added, the furnace was sealed and the air inside the furnace was evacuated with a vacuum pump. When the pressure in the furnace reached 1 atmosphere, heating was stopped and the molten metal was centrifugal cast into the shape of a ring at a casting o o temperature of 1900 C in a sand cast at a temperature of 800 C made according to the lost wax process.

In addition, platinum alloy rings were also cast using a method similar to that described above to obtain rings having cerium contents of 0.03, 0.05, 0.1, 0.2 and 0.3 parts by weight to 100 parts by weight of platinum, respectively, by changing the amount of cerium added to the platinum. Together with measuring the hardness of each of these rings, the rings were bluffed and observed for luster.

In addition, the rings were also examined for resistance to perspiration by immersing in an artificial perspiration solution at pH 4.7 containing 15.5 g/l of ammonium chloride, 120 g/l of sodium chloride, 2.5 g/l of acetic acid, 5 g/l of urea and 15 g/l o of lactic acid for 240 hours at 40 C. All the rings demonstrated excellent resistance to perspiration.

Moreover, after dissolving 1 mg of each of these alloys with nitrohydrochloric acid, the dissolved alloys were dried, additionally dissolved in dilute nitrohydrochloric acid and diluted to 10 ml to prepare test solutions. Analysis of the cerium content of each alloy was then performed by applying the test solutions to an inductive coupling plasma mass spectrometer (Yokogawa Electric, Model PMS200).

Those results are shown in Table 1.

COMPARATIVE EXAMPLES Furthermore, the hardness and luster of platinum alloy containing 0.29% by weight of ruthenium, platinum alloy containing 0.27 by weight of copper, platinum alloy containing 0.27% by weight of cobalt, platinum alloy containing 9.958 by weight of palladium and pure platinum were examined in the same manner as the alloy of the present invention. Those results are also shown in Table 1.

[Table 1] Alloy Composition Content Hardness Hv Luster 0.03% cerium 10 ppm 60.9 Good 0.05% cerium ia ppm 69.4 Good 0.1 cerium 34 ppm 75.1 Good 0.2 cerium 66 ppm 86.4 Good 0.3% cerium 98 ppm 101.6 Good 0.3% ruthenium 0.29% 66.3 Good 0.3% copper 0.27 71.6 Good 0.3% cobalt 0.27% 70.4 Good 11% palladium 9.95% 71.1 Good Pure platinum ---- 40 Poor In looking at these results, in contrast to pure platinum having low hardness and preventing the obtaining of adequate luster even when polished, the platinum alloy of the present invention can be seen to demonstrate hardness and luster not inferior to commonly known platinum alloys in practical use while still maintaining high purity.

The hard, high-purity platinum alloy of the present invention is able to provide a high degree of hardness while only containing an extremely small amount of dissimilar metal. Since it therefore has properties that are suitable for use as jewelry, it allows jewelry such as rings and so forth to be made extremely efficiently, while also adequately satisfying the requirements of customers desiring high grade jewelry products.

Claims (9)

1. A platinum alloy containing from 10 to 100 ppm of cerium.

2. An alloy according to Claim 1 containing at least 99% by weight of platinum.

3. An alloy according to Claim 2 which consists essentially of platinum and cerium.

4. An alloy according to any preceding claim which contains at least 18 ppm cerium.

5. An alloy according to Claim 4 which contains at least 34 ppm cerium.

6. An alloy according to Claim 4 which contains at least 66 ppm cerium.

7. An alloy according to Claim 4 which contains at least 98 ppm cerium.

8. An alloy according to Claim 1 substantially as hereinbefore described with reference to the accompanying Examples.

9. An article of jewelry comprising a platinum alloy as claimed in any preceding claim.