Preparation And Characterization Of ZrW₂O₈/ZrSiO₄Near-zero Expansion Composite Materials

NTE-ZrW2O8, which has an isotropic property and is often used as the keyrepresentative of NTE material, is of a unique combination of properties of thermalstability over a wide temperature range and large negative CTE over a broad range oftemperatures (-8.8ppm/K,0.3～1050K) etc. So it has drawn great interest forscientific researcher from all over the world and a lot of very broad potentialapplication prospect. This study is mainly aimed at the mismatch of coefficient of thethermal expansion (CTE) in the process of practical application of composite. In thiswork, the purpose is research on the preparation and the thermal expansion propertiesof NTE-ZrW2O8and ZrW2O8/ZrSiO4composites. Throughout the first section work,cubic ZrW2O8was synthesized by the method, which combined with thecharacteristics of solid phase synthesis and co-precipitation. We researched on thesynthesis process of precursor, and analyzed the impact on the preparation of thequench medium and heat treatment time. Using the NTE-ZrW2O8ceramic materialsand commercially ZrSiO4powder as the raw materials, the low expansion of ZrW2O8-ZrSiO4ceramic composites were prepared. And the optimal synthesis route wasdetermined. The theoretical models of the CTE of the ZrW2O8-ZrSiO4compositeswere predicted, and the best model for prediction was determined by compared withthe experimental value.In this work, the samples of the negative-thermal-expansion materials ZrW2O8were prepared from zirconium oxychloride and ammonium tungstate by high-temperature sintering at1200°C for1~8h and being quenched in the air or liquidnitrogen. Effects of rapid quenching process on the crystal structure, cross-sectionmorphology and thermal expansion properties of the sample were characterized byway of X-ray Powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) and thermal mechanical analysis (TMA).The experimental results show that the final product is a single cubic phase α-ZrW2O8during the liquid nitrogen quenching process after being sintered at1200°Cfor6h. Under the air and liquid nitrogen quenching process, the average coefficientof thermal expansion of the samples are-8.02×10-6K-1and-9.12×10-6K-1respectively,from25°C to400°C.ZrW2O8-ZrSiO4ceramic composites with low coefficient of the thermal expansion were successfully prepared by conventional solid phase process. Weadopted four different sintering temperatures. By means of SEM and XRD analysismethods, it demonstated that the optimum sintering temperature of preparation ofcomposite materials are1473K. Based on the previous experimental results, thespecimens were processed at1473K with different sintering time (0~10h,respectively). Fracture surface analysis and the relative density of the samplesrevealed that the results were very similar of the sintering time8h and10h. Theexperimental results showed that, when ZrW2O8volume percentage of90%,75%,50%,25%and10%, the coefficient of thermal expansion of composites are-7.013ppm/K,-4.193ppm/K,-0.613ppm/K,3.814ppm/K and3.874ppm/K, respectively.The average coefficient of thermal expansion of the composite is demonstrated to benear-zero (-0.613×10-6K-1) when the ZrW2O8content of50vol%. The Schapery’smodel gave a good prediction of CTEs for ZrW2O8-ZrSiO4ceramic composites bycomparison of the experimental CTE data of ZrW2O8-ZrSiO4composites withdifferent model theoretical predictions.