Silver ternary alloy

a silver alloy and ternary alloy technology, applied in the field of ternary alloys, can solve the problems of alloy sagging and contributing to brittleness, and achieve the effect of enhancing tarnish resistan

Inactive Publication Date: 2010-09-23
ARGENTIUM INT
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0069]Example 3 is repeated for the ternary alloy samples except that instead of buffing with cotton wool after the mercaptan treatment, the samples are ultrasonically degreased in EnSolv 765 for 2 minutes. The samples are then tarnish tested as described in Example 3 and all show enhanced tarnish resistance. The ability of the protective effect of the stearyl mercapta

Problems solved by technology

In particular, the applicants have become aware of the desirability of reducing or avoiding the formation and/or melting of the above mentioned binary copper-germanium eutectic which melts at 554° C. During the production of e.g. 925 Argentium silver alloys, the formation of this phase can be avoided by careful control of the casting conditions since under equilibrium cooling conditions the crystallisation is complete at below 640° C. However, this binary phase can create problems during subsequent thermal treatment of the allo

Method used

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  • Silver ternary alloy

Examples

Experimental program
Comparison scheme
Effect test

example 2

Production and Properties of Investment Cast Strip

[0065]The molten alloy of Example 1 is formed into strip by investment casting. The resulting strip is substantially free of “hot short” defects and brittleness, and has a hardness of 63.5 HV.

example 3

Solvent Dip Cleaning

Solvent Degreased Samples

[0066]Solutions are made up containing stearyl mercaptan (0.1, 0.5 and 1.0 gram) in EnSolv 765 (100 ml). Samples of the rolled annealed ternary alloy sheet of Example 1 which have been polished and ultrasonically degreased in EnSolv 765 for 2 minutes are each immersed in one of the stearyl mercaptan solutions for periods of 2 minutes, 5 minutes and 15 minutes. The samples are then buffed with clean cotton wool.[0067]In order to evaluate tarnish resistance, the alloy samples are supported on a glass slide in a fume cupboard about 25 mm above the surface of 20% ammonium polysulphide solution so as to be exposed to the hydrogen sulphide that arises from that solution. All of the samples demonstrate good tarnish resistance during a one-hour test, with very slight yellowing after 45 minutes exposure to the hydrogen sulphide. The light film on the samples is easily removed with a cleaning cloth impregnated with stearyl mercaptan.

[0068]By way of...

example 4

Effect of Post-Treatment Solvent Cleaning

[0069]Example 3 is repeated for the ternary alloy samples except that instead of buffing with cotton wool after the mercaptan treatment, the samples are ultrasonically degreased in EnSolv 765 for 2 minutes. The samples are then tarnish tested as described in Example 3 and all show enhanced tarnish resistance. The ability of the protective effect of the stearyl mercaptan treatment to survive ultrasonic cleaning in EnSolv suggests that the tarnish resistance is achieved by a surface reaction involving the stearyl mercaptan and possibly the germanium in the present alloy, and not by formation of a grease or oil layer on the surface of the present alloy.

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Abstract

A firestain and tarnish-resistant ternary alloy of silver, copper and germanium contains from more than 93.5 wt % to 95.5 wt % Ag, from 0.5 to 3 wt % Ge, optionally 0.5 wt % Zn and the remainder, apart from incidental ingredients (if any), impurities and grain refiner, copper. In order to further protect an article made from the alloy, it may be surface treated with an alkanethiol, alkyl thioglycollate, dialkyl sulphide or dialkyl disulphide. Embodiments of the above alloy exhibit relatively low elution of copper when subjected to a simulated sweat test.

Description

REFERENCE TO PRIOR APPLICATIONS[0001]This application is a continuation-in-part application of U.S. patent application Ser. No. 10 / 559,092 filed Nov. 22, 2005 which claims priority from International patent application PCT / GB2004 / 002317 filed Jun. 1, 2004 (Publication No. WO 2004 / 106567) which claims priority from UK Patent Application 03 12693.5 filed Jun. 3, 2003 and issued as a patent GB 2402399, which disclosures are herein incorporated by reference in their entirety.FIELD OF THE INVENTION[0002]The present invention relates to a ternary alloy of silver, copper and germanium, to finished or semi-finished shaped articles made from the alloy, and to the use for the surface treatment of the alloy with alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide.BACKGROUND TO THE INVENTION[0003]Since ancient times it has been appreciated that unalloyed ‘fine’ silver is too soft to withstand normal use, and it has been the practice to add a proportion of a base metal to inc...

Claims

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Application Information

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IPC IPC(8): C22C5/08
CPCC22C5/06C22C5/08C23F11/161C23F11/16C23C22/02
InventorJOHNS, PETER GAMON
OwnerARGENTIUM INT