S.K.Sadrnezhaad
,
S.Badakhshan Raz
材料科学技术（英文）
Losses of the alloying elements during vacuum induction melting of the binary NiTi alloys were evaluated by visual observation and chemical analysis of the NiTi melted specimens and the scalp formed on the internal surface of the crucible. The results indicated that the major sources of the losses were (a) evaporation of the metals, (b) formation of the NiTi scalp and (c) the sprinkling drops splashed out of the melt due to the exothermic reactions occurring between Ni and Ti to form the NiTi parent phase. Quantitative evaluations were made for the metallic losses by holding the molten alloy for 0.5, 3, 5, 10 and 15 min at around 100℃ above the melting point inside the crucible. Chemical analysis showed that there existed an optimum holding time of 3 min during which the alloying elements were only dropped to a predictable limit. Microstructure, chemical composition, shape memory and mechanical properties of the cast metal ingots were determined to indicate the appropriate achievements with the specified 3 min optimum holding time.
关键词:
Shape memory alloy (SMA)
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S.K.Sadrnezhaad
,
E.Ahmadi
,
M.Mozammel
材料科学技术（英文）
Kinetics of dissolution of silver present in precious metal scraps in HNO3 was studied in temperature range of 26~85℃. Dissolution rate of silver was much faster than that of copper at all temperatures. Effects of particle size, stirring speed, acid concentration and temperature on the rate of dissolving of silver were evaluated. Dissolution rate decreases with particle size and increases with temperature. Dissolving was accelerated with acid concentrations less than 10 mol/L. Concentrations greater than 10 mol/L resulted in slowing down of the dissolution rate. Shrinking core model with internal diffusion equation t/τ=1-3(1-x)2/3+2(1-x) could be used to explain the mechanism of the reaction. Silver extraction resulted in activation energies of 33.95 kJ/mol for Ag-Au0:04-Cu0:10 and 68.87 kJ/mol for Ag-Cu0:23 particles. Inter-diffusion of silver and nitrate ions through the porous region of the insoluble alloying layer was the main resistance to the dissolving process. Results were tangible for applications in recycling of the material from electronic silver-bearing scraps, dental alloys, jewelry, silverware and anodic slime precious metal recovery.
关键词:
Silver
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