Synthesis And Particle Size Control Study On Negative Thermal Expansion ZrW₂O₈ Powders

Negative thermal expansion (NTE) material becomes a new branch of materials science in recent years. Their potential uses include electronic, optics, fuel cell, oxygen sensors, thermostats and dental filling products. Particularly, ZrW₂O₈ exhibits large isotropic NTE property over its entire stability range from 0.3K to 1050K, the thermal expansion coefficient is -8.7×10^-6K^-1. Due to the strange properties and potential applications of ZrW₂O₈, the synthesis of ZrW₂O₈ powders and the NTE property were studied in this paper.Three methods were used to synthesize the powders: solid state method, Sol-Gel method and co-precipitaiton method. First, ZrW₂O₈ powders were prepared using the improved solid state reaction by ZrO₂ and WO₃ powders which were used as raw materials. The influence of reaction temperature on the particle size and the negative thermal coefficient were studied. ZrW₂O₈ powders were also synthesized using Sol-Gel route and co-precipitation method using ZrO(NO₃)₂·5H₂O and N₅H₃₇W₆O₂₄-H₂O as raw materials and the reaction conditions and negative thermal expansion coefficient were investigated. In order to decrease the particle size, polyethylene glycol (PEG) was used as dispersant and the influence of the amount of PEG on the particle size and negative thermal expansion coefficient were also studied.The precursors of ZrW₂O₈ were studied by Thermogravimetric and differential scanning calorimetry (TG-DSC). The structure of the products was studied by Powder X-ray diffraction (XRD) and the morphology of the resulting powders was characterized by Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). The negative thermal expansion coefficient was calculated using the lattice constants obtained by Powder X software using the data collected at different temperatures by in Situ X-ray measurement.The results showed that samples obtained at 1220℃ synthesized by improved solid state reaction were single phase with average size of 1.5×1.0μm. Compared with conventional solid state reaction, the pure powders with small particle size were obtained with shorter reaction time. The resulting powders had strong NTE property and the thermal expansion coefficient was -6.31×10^-6K^-1 at the temperature range from room temperature to 500℃. Pure ZrW₂O₈ powders with average dimension of...