Study On Formation Mechanism And Properties Of Cubic Copper Oxide In AgCuO Composites Synthesized By In Situ Reaction

Silver copper oxide(AgCuO) electrical contact materials is a new type of environmentally friendly particulate reinforced metal matrix composites(MMCs). On the one hand, it has the high electric and thermal conductivity, easy workability of silver(Ag); On the other hand, it has the good stability, well interface combination with Ag, excellent substrate wetting and anti-welding of copper oxide(CuO); and so on. Therefore AgCuO electrical contact materials has attracted much attention.Previous experiments showed that there were two types of CuO particles both cubic and monoclinic crystal structure in AgCuO by in-situ reaction synthesis method, and the cubic CuO particles easy to deformation, formed fiber phase of CuO as reinforcement on the subsequent processing using large plastic deformation, it is beneficial to improve the performance of AgCuO electrical contact materials. But the formation mechanism of cubic CuO crystal structure is not clear, the preparation of fibrous reinforced phase and the number of cubic CuO control is very important. Therefore, this paper uses the first principles calculation, calculation and analysis of thermodynamics and combined with the experimental verification to studied the thermodynamic conditions, formation mechanism and properties of cubic CuO in AgCuO composite materials by in-situ reaction synthesis method. The final conclusions are as follows:Based on the first principle, the thermodynamic properties for two types of CuO particles both cubic and monoclinic crystal structure were calculated, the phonon spectrum analysis found that the thermodynamic instability for two types of CuO both cubic and monoclinic crystal structure is caused mainly by the O atom.the thermodynamic properties of monoclinic CuO is dominated by Cu atom and O atom at low temperature and high temperature, whereas the thermodynamic properties of cubic CuO is dominated by Cu at low and by O atoms at high temperature. Meanwhile, there were gained the thermodynamic properties (including entropy(S), enthalpy(H), free energy(G), heat capacity(Cp)) and the relationship between the thermodynamic properties and temperature for two types of CuO both cubic and monoclinic crystal structure. According to the Gibbs free energy difference, the thermodynamic temperature of the phase shift between cubic CuO and monoclinic CuO was obtained at 1013.28K(740.13℃).According to the thermodynamic calculation and analysis of the CuO reaction in AgCuO by in-situ reaction synthesis method, the formation manner of the cubic CuO in AgCuO can be drawn with the following three ways:a) The cubic CuO could synthesize directly by the reaction of Cu and O2, and the synthesis temperature should be lower than 883K(609.85℃);b) The cubic CuO could synthesize by the reaction of CuO2 and O2 during the sintering processof AgCuO, and the reaction temperature should be lower than 742.99K(469.84℃).c) The cubic CuO could generate at 1048.49K(775.3℃) from the phase transition of monoclinic CuO which could synthesis directly by the reaction of Cu and O2.A series of experiments demonstrate that the possibility of the synthesized cubic CuO by the first way((a))and the second way((b)) are very small, or never happen. The formation of the cubic CuO through the third way((c)) is mainly manner to get the cubic CuO in AgCuO by in-situ reaction synthesis method. And the experiment also confirmed that the temperature roughly 1048K(775℃) is the phase transition temperature between monoclinic CuO and cubic CuO, the phase transition temperature is very close to the simulation and theoretical calculation temperature. the existence of the Ag has a certain influence on phase transformation and the amount of cubic CuO.Finally, the mechanical property and microstructure of two types of CuO both cubic and monoclinic crystal structure were studied in this dissertation.. The results showed that the ductility of the cubic CuO is better than monoclinic CuO; and the cubic CuO is an indirect band gap semiconductor, monoclinic CuO is a direct band gap semiconductor. Furthermore, there was no obviously interaction between Cu and O atoms in cubic CuO; but the interaction is significant between Cu and 0 atoms in monoclinic CuO. Besides cubic CuO has better electrical conductivity than the monoclinic CuO, and the electrical conductivity mainly come from Cu atom 3d10 orbital contribution.