| 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 -272.7℃to 777℃, the thermal expansion coefficient is -8.7×10-6℃-1. Due to the excellent properties and potential applications of ZrW2O8, the synthesis of ZrW2O8 powders and film were reported, and the NTE property of the obtained products were also studied in this paper.ZrW2O8 powders were synthesized using co-precipitation, Sol-Gel and hydrothermal method using ZrO(NO3)2·5H2O and N5H37W6O24·H2O as raw materials. In order to control the particle size and morphology, different additions were added in the experiment, such as polyethylene glycol (PEG), sodium dodecyl benzene sulfonate (SDBS), cetyltrimethylammonium bromide (CTAB), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP) et al. The influence of the additions on particle size and morphology was investigated and the mechanism was also discussed. Influece of particle size on NTE coefficient was studied. Sol-Gel method and hydrothermal method were used to synthesize the film with different addition, such as citric acid, tartaric acid, polyvinyl alcohol (PVA) et al. The reaction conditions, growth mechanism of film and the property of negative thermal expansion were investigated.The precursors of ZrW2O8 powders 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 products was characterized by Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Atomic force microscope (AFM). The NTE coefficient was calculated using the lattice constants obtained by Powder X and Material Studio software using the data collected at different temperatures by in Situ X-ray measurement. The chemical composition and state were tested by X-ray phptoelectron Spectroscopy (XPS).The results were following:ZrW2O8 powders (1) Cubic ZrW2O8 powders were synthesized by co-precipitaiton method. When different additions were used, the particle size reduced. Among them, When the value of nPEG(20000)/nmetal iron was 0.032, due to the steric effect, the smallest particle with an average dimension of 0.4×0.4um was obtained and the average thermal expansion coefficient was -6.00×10-6℃-1 from room temperature to 500℃. (2) Only HCl and HNO3 can used to synthesize single cubic phase ZrW2O8 powders by Sol-Gel method. The morphology of resulting powders changed from nano-particles to rod-like. The NTE coefficient decreased with the decreasing of particle size from room temperature to 500℃. (3) Cubic ZrW2O8 powders were synthesized by hydrothermal method heated at 570℃for 6h with the shape of rod-like and an average dimension of 1.2×1.2×10μm. The average thermal expansion coefficient of resulting powders was -6.30×10-6℃-1 from room temperature to 500℃. HNO3 was also used in hydrothermal method, when reaction temperature reduced to 160℃, nano-sphere with an average diameter of 30nm was obtained. When SDBS was added, with increasing the amount of SDBS, morphology and particle size changed from rod-like with an average dimension of 1.2μm×1.2μm×10μm to layered column with an average diameter of 0.4μm and the amount of SDBS had no influence on the average thermal expansion coefficients. The thermal expansion coefficients were about similar with an average value of -5.80×10-6℃-1 from room temperature to 500℃.ZrW2O8 film (1) Citric acid was used as addition to prepare ZrW2O8 film by Sol-Gel method. With the increasing amount of citric acid, the quality of resulting film was improved and the resulting film had no obvious holes and cracks, whereas the surface was roughness and the film-substrate cohesion was improved to 9.01N. ZrW2O8 film had strong NTE property and the thermal expansion coefficient changed from -12.82×10-6℃-1 to -9.84×10-6℃-1at the temperature range from room temperature to 500℃. (2) In-situ hydrothermal method was used to prepare ZrW2O8 film and the resulting film was discontinuous and formed by inhomogeneous particles. When citric acid and tartaric acid were used as additions, ZrW2O8 film was obtained and formed by network structure rod-like particles with no obvious cracks. ZrW2O8 film had strong NTE property and the thermal expansion coefficient was -10.76×10-6℃-1 and -12.24×10-6℃-1 respectively from room temperature to 500℃. (3) All the ZrW2O8 films were completely light transmission in visible band. Compared with powders, the temperature range of the structure transition fromαtoβstructure reduced from 150℃-175℃to 100℃-150℃.
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