Preparation And Performance Research Of CePO₄/ZrO₂ Composite Ceramics With Structure Design

For CePO₄/ZrO₂ composite ceramics, suitable and machinable CePO₄ is the main factor. Currently, the large amount of CePO₄ is needed, leading to serious degradation of the composite strength. In order to avoid such disadvantage, machinable CePO₄/ZrO₂ composite ceramics are designed and investigated, including preparation of CePO₄ and preparation of CePO₄ coated ZrO₂ powders. Two different ways are used to prepare CePO₄/ZrO₂ composite ceramics by the traditional mechanical ball milling method and powder coating method. The mechanical and machinable properties of the materials are analyzed and compared. The machinable mechanism of materials has also been researched. Our purpose is improving this materials'machinability as well as maintaining outstanding mechanical properties.Firstly, two different routes are used to synthesize CePO₄ by the chemical precipitation method and the hydro-themal method. The morphology, phase structure of the products are characterized by XRD, SEM, TEM, TG-DTA and Zeta potential measurements. The experimental results indicated that hexagonal CePO₄ with the morphology urchin sphere is synthesized by the chemical precipitation method at room temperature. Hexagonal and monoclinic CePO₄ nanowires about 5-50nm in diameter and up to several micrometers long are prepared through hydro-thermal reaction in 100℃and 200℃, respectively.The CePO₄ coated ZrO₂ powders are synthesized using the heterogeneous nucleation method and the hydro-themal method, respectively. The effect of pH values, reaction product concentration, hot water temperature and calcining temperatures are investigated to explore the best coating process. The coated powders are characterized through XRD, TEM, DTA and Zeta potential measurements.The results show that the CePO₄ coated ZrO₂ powders are successfully synthesized through heterogeneous nucleation method and the hydro-themal method,respectively. When using the heterogeneous nucleation method, the best coating condition is acidic suspension, 0.05mol/L of Ce³⁺ and PO₄^3-, room temperature. The homogeneous coating with different thickness is coated on the ZrO₂ powder surface. When using the hydro-themal method, the hexagonal CePO₄ with rod-like and monoclinic CePO₄ with needle-like coated ZrO₂ composite powders can be obtained. When the concentration of Ce³⁺ and PO₄^3- is 0.05mol/L and the bathing temperature is 100℃, the coating effect is the best. The morphology of the coated powders calcined at 1000℃was also investigated.The coated powders with 20% CePO₄ are prepared CePO₄/ZrO₂ composite ceramics by pressureless sintering process. In addition, with the same content of CePO₄, the CePO₄/ZrO₂ composite ceramics are made by the traditional mechanical ball milling method. By the comparison of the mechanical and machinable results of the two CePO₄/ZrO₂ composite ceramics, we conclude that the CePO₄/ZrO₂ composite ceramics which made by coating method have higher relative density, mechanical and machinable properties. The layered crack of CePO₄ and the weak combination with CePO₄ and ZrO₂ are the main reasons resulting in CePO₄/ZrO₂ composite ceramics can be easily machined.