【作者】 徐桂芳；

【导师】 程晓农；

【作者基本信息】 江苏大学 ， 材料学， 2008， 博士

【摘要】 负热膨胀（Negative thermal expansion简称NTE）材料是近年来兴起的一个研究热点,其中的ZrW₂O₈由于负热膨胀温度范围宽（-273-777℃）、热膨胀系数小(-8.9×10^-6K^-1)且各向同性而备受关注。该材料及其复合材料在微电子、微机械、光学、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。根据ZrW₂O₈常温下亚稳态、在770℃分解的特性,选择其与环氧树脂、ZrO₂、Cu复合制备可控热膨胀电子封装用复合材料,并对所制备复合材性能作了基础性探讨。采用固相化学分步法合成了粒径介于0.5-1μm、平均线膨胀系数为-5.33×10^-6/K的高纯度ZrW₂O₈粉体。将ZrW₂O₈粉体与环氧树脂（E-51）复合制备了电子封装材料,采用超声波处理能提高粉体在基体中的均匀性;增大ZrW₂O₈粉体在复合材料中的比例能提高玻璃化转变温度、降低线膨胀系数与介质损耗、但介电常数增加;阻温特性表明在室温-163℃范围内,E-51/ZrW₂O₈复合材料的电阻率稳定在3.03×10⁶Ω·m;室温下,封装材料击穿场强均大于10KV/m,满足于微电子器件封装材料的实际应用。E-51/ZrW₂O₈封装材料的拉伸、弯曲强度、显微硬度随ZrW₂O₈含量得到增加而增大,当E-51:ZrW₂O₈=1:1时封装材料的拉伸、弯曲强度分别达到99MPa、158MPa,而显微硬度则在E-51:ZrW₂O₈=1:0.7时达到了最佳;所制备的封装材料耐湿性较好。以分析纯ZrO₂、WO₃为原料,采用分步焙烧-原位反应固相法合成不同比例ZrO₂-ZrW₂O₈复合材料,此法能在1125-1200℃之间经6小时烧结合成高纯度ZrO₂/ZrW₂O₈复合材料。与直接原位反应固相法相比,降低了合成温度和反应时间,减小样品的颗粒尺寸。当复合材料中含25wt%ZrW₂O₈时,在30-600℃的平均热膨胀系数为0.2153×10^-6K^-1,近似为零。添加0.5wt%Al₂O₃可以提高ZrO₂/25wt%ZrW₂O₈复合材料的致密度,达到理论致密度的96.1%。以分析纯[ZrO（NO₃）₂·5H₂O]和[H₄₀N₁₀O₄₁W₁₂·xH₂O]为原料,采用化学共沉淀法合成不同比例的ZrO₂/ZrW₂O₈复合材料,此法在1150℃烧结2h得到结晶完全、颗粒细小的ZrO₂/ZrW₂O₈复合材料,且有效提高两物相混合均匀度和样品的致密度。随着烧结时间的延长,ZrO₂/ZrW₂O₈陶瓷的结晶越来越致密化,但颗粒相应增大。随着ZrW₂O₈质量分数增加,复合材料的热膨胀系数减小,其中ZrO₂/26wt%ZrW₂O₈复合材料在30-600℃的平均热膨胀系数为-0.5897×10^-6K^-1,近似为零。添加0.3wt%Al（NO₃）₃·9H₂O使得ZrO₂/26wt%ZrW₂O₈复合材料致密度提高到理论致密度的98.67%。Al₂O₃促进烧结的机理可以归结于晶界形成的低熔点液相物质Al₂（WO₄）₃,起着消除气孔促进致密化的作用。固相法和化学共沉淀法合成的近零膨胀ZrO₂/ZrW₂O₈复合材料的介电常数≥11.61,其介电损耗正切值在10^-2-10^-1之间,维氏硬度≥453HV,加入适量烧结助剂后可以提高复合材料的性能。机械混合法制备的ZrO₂/ZrW₂O₈复合材料体积电阻率100-500℃内表现出较强的电阻负温度变化效应,变化的幅度达到3-5个数量级;室温下近零膨胀ZrO₂/ZrW₂O₈复合材料的导热系数为14.11W/（m·K）,随温度的升高,导热系数呈下降趋势。在超声波的辅助作用下,采用化学镀的方法在ZrW₂O₈颗粒表面进行金属Cu的包覆,用X射线衍射仪（XRD）确定复合粉体的物相组成,用扫描电镜（SEM）观察包覆效果,通过TG-DSC技术分析复合粉体在加热过程中的热量和重量的变化。结果表明,在化学镀液中添加2-2’联毗啶和亚铁氰化钾双稳定剂,显著抑制了氧化亚铜（Cu₂O）的产生。在pH值为12.5,硫酸铜（CuSO₄·5H₂O）含量为3.5g/0.2L,甲醛（HCHO）含量为2.4ml/0.2L,以及适量络合剂稳定剂共同作用下,ZrW₂O₈颗粒表面均匀包覆一层纳米级Cu。随pH值,主盐及甲醛按比例的增加,反应速度增加,包覆在ZrW₂O₈颗粒表面的Cu颗粒粒径变大。讨论了渡液成分配比对镀速、粉体增重的影响。探讨了化学镀过程中Cu₂O产生机理及消除方法。采用粉末冶金法制备了Cu/ZrW₂O₈复合材料,分析不同压力下复合材料的物相组成,观察了不同体积分数复合材料的显微组织及断面形貌。测试了不同压力不同体积分数Cu/ZrW₂O₈复合材料的密度、致密度,结果表明:随着压力的提高和Cu含量的增加,复合材料的密度致密度相应提高。ZrW₂O₈颗粒体积分数为45%、55%、65%的Cu/ZrW₂O₈复合材料在35-200℃之间的平均线性膨胀系数分别为9.21×10^-6K^-1、7.35×10^-6K^-1、4.85×10^-6K^-1。复合材料的热导率随着Cu含量的增加而增加,随温度的升高,复合材料的热导率降低。更多还原

【Abstract】 Negative thermal expansion （NTE） material becomes one of the most interesting research field in recent years, Among them,ZrW₂O₈ with excellent isotropic NTE property and low thermal expansion coefficient (-8.9×10^-6K^-1) over a wide temperature range has been dramatically studied. NTE materials and its composites have potential applications in microelectronic, micromechanic, optics, medicine materials, low temperature sensor, electric thermal couple daily necessaries and so on.According to the characteristics of ZrW₂O₈ that is metastable at room temperature and will decompose at 770℃,epoxy resin, ZrO₂ and Cu were chosen as matrix to fabricate electronic packing composite materials with controllable thermal expansion coefficient in this thesis and the properties of the obtained composites were studied.Pure ZrW₂O₈ powders with linear thermal expansion coefficient of -5.33×10^-6/K and average particle size of 0.5-1μm were synthesized via step-by-step solid state reaction method. ZrW₂O₈ and epoxy resin were used as raw materials to prepare electronic packing material, the uniformity of ZrW₂O₈ powders in the matrix was enhanced by ultrasonic wave treatment. The glass transition temperature and dielectric constant were increased with the increasing of the ratio of ZrW₂O₈ powders in the composite while the linear thermal expansion coefficient and dielectric loss were decreased. Electric resistant property was also studied and the results showed that the electrical resistivity of E-51/ZrW₂O₈ was stabilized at about 3.03×10⁶Ω·m in the temperature range from room temperature to 163####.The breakdown strength of the obtained packing material was greater than 10KV/m at room temperature which meets the practical requirements of microelectronic packing material. The tensile strength,flexural strength and the microhardness of E-51/ZrW₂O₈ packing material have been enhanced with the increasing content of ZrW₂O₈.The tensile strength and flexural strength were 99MPa and 158Mpa, respectively, when the ratio of E-51 to ZrW₂O₈ was 1 to 1, while the optimal microhardness was obtained when the ratio of E-51 to ZrW₂O₈ was fixed at 1 to 0.7. The obtained packing materials have good waterlogging tolerance property.ZrO₂/ZrW₂O₈ composite materials with different ratios were prepared by step-by-step in-situ solid-state reaction using analytically ZrO₂ and WO₃ as starting materials. ZrO₂/ZrW₂O₈ composite with high purity can be obtained by sintering at 1125 to 1200℃for 6 hours Compared to the direct in-situ solid-state reaction, the reaction temperature was decreased, reaction time was reduced, and the average grain size of the sample was also decreased. The average thermal expansion coefficient of the composite with 25wt% ZrW₂O₈ was 0.2153×10^-6K^-1 （nearly zero） at the temperature range 30-600℃.The density of ZrO₂/25wt%ZrW₂O₈ composite can be enhanced to 96.1% of the theoretical density when 0.5wt% Al₂O₃ was added.ZrO₂/ZrW₂O₈ composites were also prepared by chemical co-precipitation method using analytically [ZrO（NO₃）₂·5H₂O] and [H₄₀N₁₀O₄₁W₁₂·xH₂O] as starting material. ZrO₂/ZrW₂O₈ composite with good crystallinity and smallgrain size can be obtianed by sintering at 1150℃for 2 hours.The homogeneity and density of the sample were efficiently enhanced by using chemical co-precipitation method.By prolonging the sintering time, the density of the composite was improved and the particle size was increased. The average thermal expansion coefficient of ZrO₂/26wt%ZrW₂O₈ composite was -0.5897×10^-6K^-1,approximate to zero, in the temperature range from 30 to 600℃.When 0.3wt % Al（NO₃）₃·9H₂O was added into ZrO₂/26wt% ZrW₂O₈ composite, the density was reached 98.67% of the theoretical density. The mechanism of the accelerating of the sintering process by adding Al₂O₃ is that liquid Al₂（WO₄）₃ with low-melting point is formed at the grain boundary, which would remove stomata to improve the density.The dielectric constant of the nearly zero thermal expansion ZrO₂/ZrW₂O₈ composite prepared by solid-state method and chemical co-precipitation is greater than 11.61,while its dielectric loss is between 10^-2and 10^-1 and the Vickers hardness is greater than 453HV,the property of the composite can be improved by adding proper amount of sintering assistant. The volume electrical resistivity of ZrO₂/ZrW₂O₈ composite prepared by mechanical mixing method shows strong negative temperature changing property between 100 and 500℃,the changing amplitude can reach 3 to 5 of the order of magnitude. The thermal conductivity coefficient of the zero thermal expansion ZrO₂/ZrW₂O₈ composite is 14.11 W/（m·K） and the thermal conductivity coefficient will decrease with increasing temperature.Cu is coated on the surface of the ZrW₂O₈ particles by electroless plating method with the auxiliary action of ultrasonic wave, the phase structure of the composite powders was characterized by Powder X-ray diffraction （XRD）, and the coating results were observed by scanning electron microscope （SEM） and the heat and weight change in the heating process of the composite was studied by TG-DSC method. The creation of Cu₂O was inhibited by using 2-2’bipyridine and potassium ferrocyanide as double stabilizing agent . Nano Cu can be coated on the surface on the condition that the pH value was 12.5,the content of CuSO₄·5H₂O and HCHO were 3.5g/0.2L and 2.4ml/0.2L,respectively, and proper complexing agent was added. The increasing of pH value and the ratio of salt to HCHO would enhance the reaction speed and the grain size of Cu on the surface of ZrW₂O₈ will be further increased . Effects of component ratio of plating liquid on the speed of plating and weight gain are discussed. The mechanism of the creation of Cu₂O during the electroless plating process and its elimination method is also studied.Cu/ZrW₂O₈ composite material was prepared by powder metallurgy method, the phase component of the composite material obtained under different pressures was analyzed, the microscopic structure and the fracture surface morphology of the composite material prepared with different volume percentage were observed. The density of the Cu/ZrW₂O₈ composite material with different volume percentage obtained under different pressures were also measured. The results showed that the density would increase with the increasing of the pressure and the content of Cu. The average linear thermal expansion coefficient of Cu/ZrW_O8 composite are 9.21×10^-6K^-1,7.35×10^-6K^-1,4.85×10^-6K^-1 in the temperature range of 35-200℃with 45vol % ,55vol % and 65vol % ZrW₂O₈ in the composites. The thermal conductivity would increase with the increasing of the content of Cu and decrease with the increasing of the temperature.更多还原