Mechanism And Process Of Explosive Synthesis Of Al₂O₃ /ZrO₂ Eutectic Ceramics

Eutectic ceramics, with a new micro-structure, have very good mechanical and thermal properties. In this paper, Al₂O₃/ZrO₂ composite ceramics were prepared by explosive synthesis. Using the exothermal reaction between Al and Zr(NO3)4, the Al₂O₃ and ZrO₂ phases in reaction system were heated up to above the melting point, and then the Al₂O₃/ZrO₂ eutectic ceramics were formed through quick cooling, solidification and crystallization. By adding Al₂O₃ and ZrO₂ as diluents, the reaction temperature and velocity of the explosive combustion can be controlled, and these make sure of the reaction safety. Through the control of the ratio of Al₂O₃ to ZrO₂, eutectic or quasi-eutectic phase was obtained. Reaction temperature was calculated by thermodynamic analysis. The relationship between reactant and temperature was adjusted by the reaction temperature measured by W-Re thermocouples. The value of the molar enthalpy of formation of the Zr(NO3)4 was calculated at last.Through the mechanism of crystal growth analysis, the microstructure of the Al₂O₃/ ZrO₂ composite ceramics shows the eutectic structure with Al₂O₃ as the matrix and ZrO₂ rod as the reinforcement. Al₂O₃/ZrO₂ composite ceramics prepared by explosion synthesis, through XRD analysis, presented high purity of Al₂O₃/ZrO₂ eutectic. Eutectic structure content, observed by SEM, is not much as the theoretical analysis, which is due to the difference between the two-phase growth kinetics parameter. And the different particle size of the raw materials also affects the mutual solution between the Al₂O₃ and ZrO₂.By adjusting the dilution ratio of Al₂O₃ and ZrO₂, a deviation from the theoretical ratio between Al₂O₃ and ZrO₂ in the products can promote the precipitation of primary phase and completely dissolve between Al₂O₃ and ZrO₂. Samples show a large uniform area of eutectic phase by SEM. Microhardness of the samples increases with the increasing content of Al₂O₃ by the measurement of microhardness test.Through the adding Ti into the above reaction system, the reaction between Ti and nitrogen, which form TiN, can effectively reduce the release gas of the reaction and decrease the reaction pressure obviously. The SEM analysis shows that very little eutectic phase formed in the product. Simple substance of Ti, Al and Zr occurred through EDS analysis. This was due to the incompletely reaction between Ti and nitrogen in reactant, and some Al and Zr were replaced by the excess Ti because of the stronger reducibility of Ti under elevated temperature.