【作者】 孙秀娟；

【导师】 程晓农；

【作者基本信息】 江苏大学 ， 材料学， 2009， 博士

【摘要】 负热膨胀（Negative thermal expansion,简称NTE）材料研究是材料科学中近年来新兴的学科分支,其中负热膨胀性金属氧化物具有负热膨胀系数大、响应温度范围宽等优点,在光学平面镜、光纤通信领域、医用材料、低温传感器、热电偶及日常生活等方面有巨大的潜在应用价值。特别是新型氧化物ZrW₂O₈材料,在很宽的温度范围内（-272.7-777℃）表现为良好的各向同性负热膨胀特性,热膨胀系数达到-8.7×10^-6℃^-1。鉴于ZrW₂O₈的独特性质,本文围绕着ZrW₂O₈粉体、薄膜的制备及其负热膨胀特性开展了相关的研究工作。以硝酸氧锆[ZrO（NO₃）₂·5H₂O]和钨酸铵[N₅H₃₇W₆O₂₄·H₂O]为原料,分别通过共沉淀法、溶胶凝胶法和水热合成法制备ZrW₂O₈粉体,考察不同反应条件、添加剂种类,如聚乙二醇（PEG）、十二烷基苯磺酸钠（SDBS）、十六烷基三甲基溴化铵（CTAB）、聚乙烯醇（PVA）、聚乙烯吡咯烷酮（PVP）等对粉体粒径及形貌的影响并探讨其作用机理,进而考察负热膨胀特性与粉体粒径的关系。采用溶胶凝胶和水热法制备ZrW₂O₈薄膜,以柠檬酸、酒石酸、PVA等为添加剂,并通过旋涂法进行镀膜,考察薄膜的形成工艺、初步探索薄膜的形成机理以及负热膨胀特性,揭示薄膜制备工艺关键因素对薄膜化学组成及结构的影响规律。对所得粉体的前驱体进行热重一差热（TG-DSC）分析:以X射线衍射仪（XRD）对所得粉体及薄膜进行物相分析;以扫描电子显微镜（SEM）、透射电子显微镜（TEM）以及原子力显微镜（AFM）对粉体及薄膜的形貌进行表征。利用变温X射线衍射仪精确收集粉体在不同温度下的XRD数据,以Powder X、Material Studio软件分别计算在不同温度下的晶胞参数,进而计算其负热膨胀系数。以X射线光电子能谱仪（XPS）对薄膜的化学组成和状态进行分析。所得结果如下:ZrW₂O₈粉体:（1）采用共沉淀法制备得到单一立方相ZrW₂O₈粉体,加入不同类型的添加剂后,有效的减小粉体颗粒尺寸。其中PEG（20000）当加入量为n_PEG/n_{metal iron}=0.032时,由于单层吸附提供的空间位阻效应得到平均尺寸约为0.4×0.4μm的超细ZrW₂O₈粉体。添加剂对热膨胀系数的影响较小,从室温到500℃范围内平均热膨胀系数约为-6.00×10^-6℃^-1。（2）只有HCl和HNO₃才能提供用于溶胶-凝胶法制备ZrW₂O₈粉体合成的酸性介质,所得粉体形貌从纳米颗粒变为棒状且负热膨胀系数随颗粒的减小而减小。（3）采用水热法在570℃保温6h制备得到ZrW₂O₈粉体。所得粉体为规则的棒状,平均尺寸约为1.2×1.2×10μm。粉体具有良好的负热膨胀特性,从室温到500℃,热膨胀系数约为-6.30×10^-6℃^-1。采用HNO₃为介质时,当将水热温度降至160℃时,所得粉体的颗粒尺寸降至纳米级,呈现纳米球形状。加入添加剂SDBS后,粉体颗粒尺寸从原来的1.2×1.2×10μm减小至0.4μm,形状逐渐由棒状转变为类球形、层状圆盘。SDBS的加入对粉体整体的负热膨胀性能无影响,从室温到500℃的平均热膨胀系数约为-5.8×10^-6℃^-1。ZrW₂O₈薄膜:（1）采用溶胶凝胶法制备薄膜时,以柠檬酸为添加剂,随着柠檬酸量的增加,改善了ZrW₂O₈薄膜的开裂现象,所得薄膜致密、无明显的裂纹和孔洞,但表面较粗糙。薄膜和基片的结合力提高至9.01N。薄膜表现为良好的负热膨胀性能,从室温到500℃范围内的平均热膨胀系数随着柠檬酸量的增加从-12.82×10^-6℃^-1变为-9.84×10^-6℃^-1。（2）采用原位水热法制备得到的ZrW₂O₈薄膜由棒状颗粒组成,没有形成连续的薄膜。当以柠檬酸和酒石酸为添加剂时,均能制备得到连续ZrW₂O₈薄膜,薄膜由相互交叠,形成网状结构的纳米棒颗粒组成。所得薄膜具有良好的负热膨胀性能,两者从室温到500℃范围内平均热膨胀系数分别约为-10.76×10^-6℃^-1和-12.24×10^-6℃^-1。（3）所有ZrW₂O₈薄膜在可见光区域完全透光。与粉体相比,ZrW₂O₈薄膜α-ZrW₂O₈向β-ZrW₂O₈相转变的温度区间降低至100℃到150℃温度范围内。更多还原

【Abstract】 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 n_PEG（20000）/n_{metal 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℃.更多还原