Preparation And Properties Of Zr₂P₂WO₁₂ And Its Composites

Negative expansion materials refers to the materials with negative mean thermalexpansion coefficient within a certain temperature range. This kind of material, withwide application in electronics, optics and Aerospace aviation, has received theattention of the researchers since it has been found. In general, instead of beingindependently applied to a certain field, it is usually composited with other materialsfor the purpose of reducing the CET of the basis material, improve their performanceand resolve the issues related to the mismatching of thermal expansion coefficientwithin the materials and the large thermal stress.Zr2P2WO12(abbreviated as ZWP) is an important part of A2(MO4)3seriesnegative expansion materials. With the maintenance of orthorhombic phase, resistanceto enormous pressure and incomparable stability without water absorption or phasechange within wide temperature span (25℃to800℃), it will not be subject to phasechange, melting or decomposition, thus being deservedly regarded as the idealcomposite materials. At present, the existing few reports about this material mainlyfocus on the investigation of the preparation method of solid phase method. Onaverage, the powder prepared by solid phase method is not pure with large particles,which fail to meet the basic requirements of the composite materials. To prepare pureand nano-grade fines, this paper adopts the hydrothermal method to prepareZr2P2WO12powder, which succeeds in generating the TiNi/ZWP and Cu/ZWPcomposite materials through being compounded with TiNi alloy and Cu. The powdergenerated and composite materials are characterized by XRD and SEM with thehardness and compactness of the composite materials investigated. The researchresults and conclusions are listed as follows:1. The influence of different pH value, reaction temperature and time on theappearance and phase of the pure Zr2P2WO12powder prepared by hydrothermalmethod is investigated. The results show that at the pH value of7, temperature of130℃and reaction time of48h, the phase is single and particles regular, togetherwith the size of40-100nm and mean negative thermal expansion coefficient of2.515×10-6K-1.2. The TiNi/ZWP composite materials are prepared through hot-pressed sinter.The sintering process is that, it is sintered for3hours at the pressure of25MPa and the temperature of1100℃in vacuum environment and then annealed for1hour atthe temperature of500℃. The results reveal that ZWP does not react with TiNi andgenerates no new substance. Its density, compactness and coefficient of thermalexpansion descends while its Vickers hardness increases along with the increase inZWP.3. The Cu/ZWP composite materials are prepared by hot-pressed sinter. Thesintering process is that, it is sintered for3hours at the pressure of25MPa and thetemperature of950℃in vacuum environment and then annealed for1hour at thetemperature of500℃. The results indicate that ZWP does not react with Cu andgenerates no new substance. Its density, compactness and coefficient of thermalexpansion descends while its Vickers hardness increases along with the increase inZWP.