วิทยานิพนธ์ (วศ.ม.)--จุฬาลงกรณ์มหาวิทยาลัย, 2547

The objective of this research is to investigate the effect of calcium and silicon in 92.5%Ag – Cu alloys on their microstructure, mechanical properties, surface color, and tarnish and corrosion resistance. This is ultimately to determine the suitable calcium and silicon content of sterling silver alloy for the jewelry industry. The experimental alloys are divided into 3 groups, first group is contain only calcium, second group is contain only silicon and the last one is contain both of calcium and silicon. The microstructure of 92.5%Ag – Cu alloys consists of both silver – rich solid solution, as a matrix, and eutectic structure. The amount of calcium found in the matrix is higher than those in the eutectic structure but the amount of silicon found in Cu – rich phase. By increasing calcium content, the amount of eutectic structure, and therefore, tensile and yield strength and hardness of the alloys were decreasing. The tarnish resistance was found to be improved when the amount of calcium was small (0.012%Ca) and the tarnish films were studied quantitatively using a spectrophotometer. Potentiodynamic anodic polarization technique was applied to measure the corrosion potentials (E[subscript corr]) and corrosion current density (I[subscript corr]) In 1% sodium chloride solution saturated with hydrogen sulfide (H₂S), the amount of calcium at 0.012%Ca not only promoted the noble shift in corrosion potentials but also reduced corrosion current density.