Preparation Of Al₂(WO₄)₃ Powders And Thin-Film And Study Of The Thermal Expansion Performance

Negative thermal expansion (NTE) material becomes a new branch of materials science in recent years. The NTE dysphasia have the characteristic of large coefficient of NTE and wide range of response temperature. Their potential uses in products, voyage and livelihood vastly. As one kind of the NTE material, Al(WO) have NTE capability in large range of temperature. The synthesis of Al(WO) is simple and it retain stability at high temperature and stress, so it is good NTE material. Due to the strange properties and potential applications of Al(WO), the synthesis of Al(WO) powders and thin-film and the NTE property were studied in this paper.Two methods were used to synthesize the powders in this paper. The one, Al(WO) powders were prepared using the solid state reaction. AlO and WO powders, which were used as raw materials, were mixed at 1:3 ratios and milled, and then sintered at 1000℃for 30h to prepare Al(WO) powders. The other, Al(WO) powders were also synthesized using co-precipitation method. In this method, Al(NO)·9HO and NHWO·HO, which were used as raw materials, were mixed at certain ratios and stirred, and then they produced the white sedimentations which were sintered at 800℃for 10h to prepare Al(WO) powders.In this paper, the Al(WO) film were prepared using two-butt-rotating magnetron sputtering method by ZrO and WO which were used as butts. The heat treatment temperature was 1000℃and the time was 10min.The Al(WO) powders which were synthesize by solid state method and the precursors of Al(WO) which were synthesize by co-precipitation method were studied by Thermo gravimetric and differential scanning calorimetric (TG-DSC), and it used to research heat stability of Al(WO) powders and thermodynamic property of the precursors. The structure of the powders and thin film was studied by Powder X-ray diffraction (XRD) and the morphology of the resulting powders and thin film 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 the data collected at different temperatures by in Situ X-ray measurement. The thermal expansion characteristic of column sample, which was sintered by the powders of two method, was determinate by NETZSCH thermal expansion instrument and the coefficient of thermal expansion was calculated using the resulting data.The results showed that pure Al(WO) powders were synthesized by both solid state method and co-precipitation method. The granule of Al(WO) powders by solid state method was rectangle and ellipse and the average size was 0．6×0．4μm. The granule of Al(WO) powders by co-precipitation method was ellipse and the average size was 0．2×0．1μm. The lattice constants of powders by two method both showed anisotropic thermal expansion characteristic. The a and c axis showed NTE character that shrink when temperature rose. The b axis showed strong positive thermal expansive character when temperature rose. The macro performance of thermal expansion that were showed by the powders synthesized by two method was difference. The powders synthesized by solid state method showed NTE at the range of room temperature to 900℃. The powders synthesized by co-precipitation method first showed positive thermal expansion at the range of room temperature to 520℃and then showed NTE at the range of 520℃to 900℃. The average coefficient of thermal expansion of the powders by two method were-1．56×10Kand-1．13×10K respectively. The Al(WO) powders was no decomposition and no phase transition in the range of room temperature to melting point.The pure Al(WO) thin-film was synthesized by magnetron sputtering method and the growth of film showed the character of pick-direction. The film well distribute on the matrix. The lattice constants of thin-film also showed anisotropic thermal expansion characteristic. However, compared to powders, the negative thermal expansion character of a and c axis was not stabilization and the b axis also showed positive thermal expansive character.