Synthesis Mechanism Of The Reaction Of Synthesis Of Silver Tin Oxide Composite And Performance

In present thesis, AgSnO2 composite fabricated by reactive synthesis was considered as a research object. By means of composite fabrication, analysis in microstructure and properties, microstructure homogenization and its finite element analysis, electric contact properties and its molecular dynamics simulation, and the reactive synthesizable mechanism analyzed by first principle calculation. The thesis had been studied systemic both in experimental and theoretically in microstructure analysis and its forming mechanism, relation between microstructure homogeneity and properties, the electric contact properties, and the reactive synthesizable mechanism for AgSnO2 composite fabricated by reactive synthesis. The mainly results could be concluded as follows.1. Technology of AgSnO2 composite fabricated by reactive synthesisAgSnO2 composite with 10wt% SnO2 could be fabricated by reactive synthesis with Ag-15wt% Sn, Ag2O, and Ag powder as initial materials. The composite posse the features in fresh interface and bind firmly between matrix and reinforcement.2. Microstructure ofAgSnO2 composite fabricated by reactive synthesisSnO2 particles with fine and conglomeration existed in sintered bulks for AgSnO2 composite fabricated by reactive synthesis. By serving plastic deformation process, when the true strain reached to 11.7, the conglomerated SnO2 particles could be dispersed into silver matrix.It is shown that some more fine Ag6O2 particles dispersed into SnO2 particles in AgSnO2 composite fabricated by reactive synthesis and the orientation relation (OR) between Ag6O2 and SnO2 are that: (110)SnO2//(101)Ag6O2 [001]SnO2//[010]Ag6O2The Ag/SnO2 interface is very clear, and there is not any other resultant formed in the interface. After microstructure homogenization, there is not any certainly OR relation in the Ag/SnO2 interface. 3. Microstructure homogenization and its properties of AgSnO2 composite fabricated by reactive synthesisIt is shown that by finite element analysis to microstructure homogenization for the composite, with the cumulative extruded plastic deformation, the larger shear stress formed in the inner of composite for the reason that non-harmony of strain and stress produced both in surface layer and inside in AgSnO2 composite. With the act of shear stress, the SnO2 particles distributed in round and conglomeration in the composite will be dispersed in silver matrix along with the flow of matrix. It is the key for the serve plastic deformation technology applied to homogenize the microstructure of AgSnO2 composite fabricated by reactive synthesis.4. Electric contact features ofAgSnO2 composite fabricated by reactive synthesisThe electric contact critical current for AgSnO2 composite fabricated by reactive synthesis were varied to true strain of the composite in deformation, when contact current is lower than 25A, which means the composite possessed a better arc erosion resistance.Anode transfer occurs when current below to a critical value under the electric contacting condition of 18V for AgSnO2 composite fabricated by reactive synthesis. While the current over critical value, the transfer ways of composite will reversed to cathode transfer. The cathode transfer only occurred when electric contacting condition is 8.5V. The composite presents a better welding resistance feature under the condition of 18V and the current value less than 20A. While current value is larger than 20A, the feature of better welding resistance will lost. The experimental results confirmed thatⅠ-Ⅴcharacteristics of the arc it self will influenced the transfer ways for AgSnO2 composite fabricated by reactive synthesis, and it was the most factor to effect the composite transfer ways.In the operation ranges of 18V and≤20A, the composite presented a better weld resistance for the small undulation and lower values. As the current was lager than 20A, the weld resistance of the composite will reduce markedly.As the anode transfer occurs on anode of AgSnO2 composite fabricated by reactive synthesis, some structural objection such as pores, cracks, melting beads and reticular structure present on the surface of anode. The molecular dynamics simulation showed, when the temperature located between the melt point of silver and SnO2 caused by arc acted on contacts of composite, the conglomeration SnO2 particles were dispersed by melting silver flow, and then the viscosity of melting pool increased, this is the mainly reason to the lower transfer for the composite. While the temperature of melting pool is higher than that sublimation temperature of silver, silver vaporization and tin oxide decomposition will occurred, both of the two processes need energy consumption, and it would consume the arc energy; extinguished arc is an important factor to reduce the transfer of the composite.5. Mechanism ofAgSnO2 composite fabricated by reactive reactionAccording to the calculation results from the thermal dynamics, it could be seen most reactive Gibbs free energy is far less than zero for AgSnO2 composite fabricated by reactive synthesis with Ag-15wt%Sn, Ag2O, and Ag powder as initial materials. It was proved that the reactions could be realized, but the thermal dynamics was hard to estimate the stability of resultants and reactive direction exactly.The crystal cell for reactants, resultants, transition phases, and their reacted with oxygen were be built according to Ag-Sn diagram and relative lattice parameters in AgSnO2 composite synthesis.The mechanism of reactive synthesis for AgSnO2 composite was studied theoretically by first principle calculation. It is shown that that the direction to form the SnO2 occurs in Tin rich zone indicated by Ag-Sn diagram. The sequence to complete the reaction is that Ag4Sn→Ag4Sn+Ag3Sn→Ag3Sn→Ag3Sn+Sn(Ag) solid solution→Sn(Ag) solid solution.Compared with Ag6O2/SnO2 and Ag/SnO2 in binding energy, Ag6O2/SnO2 has a lower energy than Ag/SnO2, that means Ag6O2 has more stability in SnO2 crystals b, its vary fit with experimental analysis.According to the formation enthalpy and population came from the calculation, the stability of phases in AgSnO2 composite could be obtained, that is, SnO2> Ag6O2>SnO>Ag2O.As Ag-Sn alloy reacted with oxygen, Ag2O decomposed and released free oxygen atoms, the diffusion mechanism of oxygen atom is interstitial mechanism, and Sn atom is substitutional mechanism.With the studies mentioned above, results the thesis not only clarify theoretically in mechanism of microstructure forming, the principle of microstructure homogeneity, relation of microstructure and properties of composite, mechanism of reactive synthesis, enriches and perfects the fundamental theory in metal matrix composite, but that also can be used in application practice of AgSnO2 composite.