Silver ternary alloy

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 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.

1 - 19 . (canceled)  
   
   
       20 . A ternary alloy of silver, copper and germanium comprising from more than 93.5 wt % to 95.5 wt % silver, from 0.5 wt % to 3 wt % germanium, 1-40 ppm of boron, optionally 0.5 wt % of any of zinc, cadmium and tin, optionally 0.1-1 wt % silicon, and the remainder, apart from impurities, copper, wherein the weight ratio of copper to germanium is from 4:1 to 3:1.  
   
   
       21 . The alloy of  claim 20 , wherein the weight ratio of copper to germanium is about 3.5:1.  
   
   
       22 . The alloy of  claim 20 , containing from 1.0 wt % to 1.5 wt % germanium.  
   
   
       23 . The alloy of  claim 22 , containing about 94.5 wt % silver, about 4.3 wt % copper, and about 1.2 wt % germanium.  
   
   
       24 . The alloy of  claim 20 , containing 5-20 ppm of boron.  
   
   
       25 . A finished or semi-finished shaped article of the alloy of  claim 20 .  
   
   
       26 . The article of  claim 25 , which is formed by casting.  
   
   
       27 . The article of  claim 25 , which is at least partly produced from sheet or strip.  
   
   
       28 . The article of  claim 25 , which is surface treated with an alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide.  
   
   
       29 . The article of  claim 28 , wherein the alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide comprise C 12 -C 24  alkyl groups.  
   
   
       30 . The article of  claim 28 , wherein the alkanethiol or alkylthioglycolate comprise a stearyl mercaptan, cetyl mercaptan (octadecyl mercaptan), stearyl thioglycollate and/or cetyl thioglycollate.  
   
   
       31 . A method for preventing tarnish of an alloy as claimed in  claim 20 , comprising surface treating the alloy with an alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide.