Cu, The Influence Of Bi On The Microstructure And Properties Of Synthetic The Agsno <sub> 2 </ Sub> Composite Response

In the present study, both the oxidation behavior of AgSn AgSnCu AgSnBi alloys and the reactive synthesis of AgSnO₂CuO and AgSnO₂Bi₂O₃ composites are investigated.Hence, the effect of Cu Bi additive to fabriacte the AgSnO₂ composites is analysed by means of thermodynamic and kinetics.Also, microstructure and physical property of AgSnO₂CuO and AgSnO₂Bi₂O₃ composites at the different stage of process are detail studied.In this case , three conclusions are concluded by thermodynamic computation: l)The chemical affinity (Oxygen potential) of tin is stronger than bismuth, and bismuth stronger than copper. 2) The SnO₂ is more stable than SnO, and CuO more stable than Cu₂O. 3)From high to low, the order of chemical potential is Cu, Ag, Sn, Bi.It's easy to form thick external oxide layer for AgSn alloy during the internal oxidation process.The internal oxidation mechanism in AgSnCu alloy has much common with the AgSn alloys.When copper gets oxidation, tin captures the oxygen from the copper oxide.The key point temperatures for tin to overcome energy barrier to capture the Oxygen belong to copper oxide is 350℃ .Bismuth has low cohesive affinity to oxygen.So, at first, the present of bismuth decreases the oxidation rate of the tin in the AgSnBi alloy.Tin is easy to fix oxygen and makes excessive oxygen in the matrix.Later, bismuth depends on tin oxide to form new oxide, such as Bi₂Sn₂O₇.At last, tin snatches oxygen from this new bismuth oxide at the 250℃.During the reactive synthesis of AgSnO₂CuO(SnO₂7.42wt% , CuO6.21wt%) and AgSnO₂Bi₂O₃(SnO₂ 7.79wt% , Bi₂O₃5.44wt%) composites, the activation energy of AgSnBiO system is higher than the AgSnCuO system.The activation energy to decompose for AgSnCuO system is about 229kJ/mole, AgSnBiO system about 235kJ/mole.The decompose temperature for AgSnCuO system is 350℃ , which is lower than AgSnBiO system about 20℃.During the reactive synthesis process: 1) The higher concentration ofcopper is, the higher ability for AgSnCu alloy to absorb oxygen.As for the bismuth in the AgSnBi alloy, quite the reverse. 2) The chemical reaction in the AgSnCuO or AgSnBiO system can be divided into two parts: One is displacement reactions between alloys and Ag₂O.The other is alloys reacting with active oxygen.Displacement reaction happens at the low temperature(<352℃) for the AgSnCuO system.Because of large quantity of copper oxide apperance, the density of matrix obviously decreases. 3) Bismuth is condensed at the grain boundary and decreases the property of the boundary.The SnO₂ particle uniformly disperses at the matrix and segregates at the grain boundary. The appearance of Bi₂Sn₂O₇ decreases the density of matrix.