【摘要】 近零及负热膨胀材料有诸多的潜在应用领域,而具有负热膨胀效应的A2M3O12系列材料在较宽的温度范围,易于通过组份变化调整其热膨胀系数.本文首次使用共沉淀法合成了Al2-xYxW3O12(x=0-2)系列粉体材料.经X射线衍射分析证明Al2W3O12和Y2W3O12能完全固溶形成二元固溶体,采用PowderX软件对Al2-xYxW3O12的晶胞参数进行计算,结果表明室温下随着稀土钇(Y)含量的增加,晶体的晶胞参数与晶胞体积逐渐增加.高温X射线衍射结果表明,随着稀土钇(Y)含量的增加,Al2-xYxW3O12的本征热膨胀系数逐渐由正到负变化.热机械分析(TMA)压缩法测定其宏观热膨胀系数,发现通过调整材料的组成,可以将其热膨胀系数控制为一定的正值、负值或零.但是由于其结构的各向异性,多晶陶瓷内部存在的微裂纹使热膨胀曲线出现较大的滞后环.更多还原

【Abstract】 Near zero and negative thermal expansion materials have a number of important potential applications including circuit boards, optical substrates, dental restorations and so on. In this article, Al2-xYxW3O12 powder was synthesized by co -precipitate method. The X-ray diffraction (XRD) analysis indicates that the compounds are orthorhombic structure, and the lattice constant increase with the x value due to the different atom radius between Al3+ and Y3 +. The high temperature X - ray diffraction analysis exhibits that the intrinsic linear expansion coefficients of Al1.5Y0.5W3O12 and Al0.7 Y1.3W3O12 are +0. 85 × 10-6/℃ (20 -900℃) , -2. 6 × 10-6/℃ (20 -800℃), respectively. The compacts were sintered at temperature from 900 to 1100℃ for 10h. Their average thermal expansion coefficients from room temperature to 840℃ and their thermal expansion curves during heating (r. t. - 840 ℃) and cooling (840 - 400℃) were measured by thermal mechanic analysis (TMA) compressing method. The results indicate that the thermal expansion coefficient of Al2-x YxW3O12 can be adjusted to the desired values such as near zero and negative by changing the composition. The thermal expansion curves show hysteresis loops due to micro - cracks resulting from structure anisotropy.更多还原