【作者】 刘颖；

【导师】 徐建中；

【作者基本信息】 河北大学 ， 应用化学， 2009， 硕士

【摘要】 负热膨胀材料是指在一定的温度范围内材料的线膨胀系数(αT)或体膨胀系数(βT)为负值(NTE)。根据材料的结晶学特征和负热膨胀性能可将其分为三种类型：各向同性负热膨胀材料、各向异性负热膨胀材料和无定型材料。自1995年Sleight研究小组报道了负热膨胀材料ZrW2O8以来,负热膨胀材料受到广泛关注,已成为材料科学中一枝奇葩。ZrW2O8为各向同性负热膨胀材料,通过与其他元素复合,可制备在-273℃到777℃温度范围都具有强负热膨胀特性的材料,且可与多种其他材料复合、制备膨胀系数可控的复合材料,具有广阔的应用前景。稀土钨酸盐负热膨胀材料在精密仪器制造、航空、航天、航海、通讯等高精尖技术领域有极其重要的用途。稀土和钨都是我国优势资源,开展此项目研究对于促进优势资源综合利用具有积极意义。近年来,关于钨酸锆与重稀土元素复合的研究已有所报道,而钨酸锆与轻稀土元素复合制备负热膨胀材料的研究未见报道。首先,本文对负热膨胀材料ZrW2O8合成进行了研究,并研究了反应物组分含量和反应条件对产物的影响,用X射线衍射、扫描电子显微镜等分析手段对合成产物进行了表征。其次,本文通过钨酸锆与轻稀土元素进行复合制备出可控负热膨胀材料Zr1-XLaXW2O8-X/2(X=0.00、0.01、0.02)。通过X射线粉末衍射、扫描电子显微镜分别对粉体进行物相分析和形貌观测,用热膨胀仪测定了样品从室温到700℃的膨胀行为。结果表明合成产物为立方结构,室温到200℃复合负热膨胀材料Zr1-XLaXW2O8-X/2(X=0.00.0.01.0.02)的平均线性热膨胀系数分别为-2.594×10-6K-1、-2.309×10-6K-1、-2.298×10-6K-1,200℃到700℃的平均线性热膨胀系数分别为-5.002×10-6K-1、-4.810×10-6K-1、-4.730×10-6K-1,在150℃到220℃,Zr1-XLaXW2O8-X/2(X=0.00.0.01.0.02)发生相变且其负热膨胀性能随X值增加而略有减弱。更多还原

【Abstract】 Negative thermal expansion(NTE),i.e.a decrease in length as temperature increases, Materials which demonstrate NTE can be divided into three classes:isotropic, anisotropic and amorphous.Materials that exhibit negative thermal expansion (NTE) have been of considerable interest, since Sleight et al.reported ZrW2O8 shows NTE in 1996.Due to ZrW2O8′s relatively large isotropic, unusual negative thermal expansion over a wide range of temperature from 0 to 1050k,and Zr cation position could be partly substituted by various cations,the thermal expansion coefficients could be adjusted to a desired value. Rare earth tungstate negative thermal expansion materials in precision instruments manufacturing, aviation,aerospace, marine, communications and other high-technology has an extremely important purposes.Rare earth and tungsten resources are the advantages of our country, to carry out this project for the comprehensive utilization of resources to promote the advantages of positive significance.Synthesis and properties of negative thermal expansion materials Zr1-XLaXW2O8-X/2 substituted for Zr(IV) sites by the heavy rare earth ions have been recently reported while no paper has been written on the preparation of Zr1-XLaxW2O8-X/2 (M was lighter rare earth ions).Firstly, the synthesis of ZrW2O8 were reported.The products were characterized by X-ray powder diffraction and scanning electric microscope.Secondly, Synthesis and properties of negative thermal expansion materials Zr1-XLaXW2O8-X/2 substituted for Zr(IV) sites by the light rare earth ions were reported. The structure and morphology of the resulting powders were characterized by powder X-ray diffraction (XRD) and scanning electron microscope(SEM) respectively. The thermal expansion coefficient of the samples were measured by dilatometer at room temperature to 700℃.The results showed that samples were single cubic phase.The average thermal expansion coefficients of ZrW2O8 Zr0.99La0.01W2O7.995 and Zr0.98La0.02W2O7.99 were-2.594×10-6K-1,-2.309×10-6K-1,and-2.298×10-6K-1 in the temperature range from room temperature to 200℃,-5.002×10-6K-1,-4.810×10-6K-1, and-4.730×10-6K-1 from 200℃to 700℃respectively. The phase transition temperature of the samples were between 150℃to 220℃.There were slightly decrease in the thermal expansion property of the samples with the increase in substitution fraction X.更多还原