【作者】 王卫民；

【导师】 田长生；

【作者基本信息】 西北工业大学 ， 材料学， 2006， 博士

【摘要】 具有尖晶石结构的Mn-Co-Ni基氧化物是NTC热敏电阻主要的材料体系；多层片式化技术是NTC热敏电阻领域的研究热点，陶瓷低温烧结是其中最为关键的技术。 本文选择Mn-Co-Ni基氧化物为研究对象；以降低材料的烧结温度为主要研究目标；把先进的粉体材料合成工艺、添加烧结助熔剂以及掺杂改性作为主要技术途径，开展了一系列的研究工作。揭示了形成溶胶凝胶体系的一般规律；研究了干凝胶自蔓延形成目标粉体的反应机理；揭示了多种掺杂、助熔剂对Mn-Co-Ni-O基半导体陶瓷烧结特性、显微结构以及电性能的影响；最终将Ni₁Co_0.2Mn_1.8O₄系半导体陶瓷的致密化烧结温度降低至950℃，且保持了良好的电性能。 首先，按照传统固相法工艺制备Mn-Co-Ni-O基半导体陶瓷，研究组成对其相结构与电性能的影响。结果表明：获得具有单一尖晶石结构的Mn-Co-Ni-O系半导体陶瓷，是保持其良好电性能的前提。为获得单一尖晶石结构的固溶体，控制Mn元素的含量最为重要。基于上述原则，选择了组成为A_1-1.2Mn_2-1.8O₄（其中A为其它金属离子的总和）的材料体系作为本文研究对象；Cu虽然可以降低Mn-Co-Ni-Cu-O系半导体陶瓷的烧结温度至1100℃，但却同时降低了材料的电阻率和材料常数B。作为有潜质的低温烧结体系，将在保持其低温烧结的同时，试图改善材料的电性能。 探索了溶胶凝胶自蔓延法合成Ni₁Co_0.2Mn_1.8O₄纳米粉体的工艺。分别制备出了硝酸盐-柠檬酸-乙二醇体系和油酸-硝酸盐体系的溶胶凝胶，经干燥得到干凝胶，干凝胶自蔓延后经800℃煅烧可以得到平均粒径～40nm的Ni₁Co_0.2Mn_1.8O₄粉体，该粉体具有较高的烧结活性以及均匀的化学组成，经1100℃烧结陶瓷致密度大于95％，比传统固相法合成粉体的烧结温度降低了100～150℃。研究发现：乙二醇与柠檬酸之间形成的网络结构以及金属离子与柠檬酸之间稳定配位键的形成是保持溶胶凝胶体系稳定的两个重要条件；提出了“非晶态羧酸盐前驱体的结构模型”。该模型既解释了硝酸盐．油酸体系中形成稳定溶胶凝胶前驱体的条件，同时也有助于探明该干凝胶燃烧分解的反应机理；揭示了干凝胶自蔓延形成目标粉体的反应机理；其反应过程为：（1）干凝胶前驱体的燃烧与分解；（2）形成具有尖晶石结构的中间粉体；（3）完成相转变中间过程并合成出目标组成的纳米粉体。初步探明了不同稳定剂对纳米粉体团聚以及烧结活性的影响；探索了溶胶凝胶的脱水工艺、粉体的后期处理工艺、粉体的成型技术等工艺因素对粉体烧结活性的影响。 以降低半导体陶瓷的烧结温度和提高电性能为目的，研究了多种掺杂、助熔剂（V₂O₅、Bi₂O₃、B₂O₃、SiO₂、CuO等）对Mn-Co-Ni-O基半导体陶瓷烧结特性、更多还原

【Abstract】 Mn-Co-Ni-O based ceramics with spinel structure are the most important materials for NTC thermistors. The technique of multilayer components is hotspot of NTC thermistors. To prepare the multilayer components, the low-temperature sintering is the pivotal technique.The Mn-Co-Ni-O based ceramics were used as main materials. The aim of our work is to decrease the sintering temperature. Synthesis of high active nano-powders and doping were used as main techniques. A series of works have been done in our study. We can explain the general rule about the formation of stable sol-gel. The reactive mechanism about the auto-combustion of dried gel was also studied. The effects of various additives on the microstructure, sintering characters and electric properties of Mn-Co-Ni-O based ceramics were shown in the paper. At last, the sintering temperature of Ni₁Co_0.2Mn_1.8O₄ baseed ceramics was decreased to 950℃, while it kept excellent electric properties.According to the traditional technique, the Mn-Co-Ni-O based ceramics were prepared. It can be concluded that single spinel structure is important factor for NTC materials to keep perfect electric properties. The compositions of Mn-Co-Ni based oxides with single spinel structure have been given as follows: A_1-1.2Mn_2-1.8O₄ （A: the others cations in the oxides）, which were studied in whole paper. In the same time, the effects of Cu contents on the microstructure, electric properties and sintering temperature of Mn-Co-Ni-Cu-O based ceramics were also studied. It is conclude that Cu in the Mn-Co-Ni-Cu-O can decrease the sintering temperature to 1100℃, but also decrease the material constant B obviously. So, we tried to improve the electric properties of Mn-Co-Ni-Cu-O based ceramics.We have explored the technique about synthesis of nano-powder via sol-gel methods. The sol-gels were prepared from nitrate-citric acid-EG system and nitrate-oleic acid system respectively. The dried-gels were obtained, and had auto-combustion in air, then were calcined in oven at 800℃. Finally, the Ni₁Co_0.2Mn_1.8O₄ powders with 40 nm crystallite were prepared, which have high sintering activities and uniform compositions. The powders were sintered at 1100℃ to form compact ceramics with more then 95% relative densities. Meanwhile the sintering temperature of samples prepared via traditional technique is 1200-1250℃. The main factors which have effects on the stability of sol-gel have been given as follows: one is the formation of network between citric acid and EG, the other is the formation of chemical bond between citric acid and cations. The model of Non-Crystalloid Precursors has been set up. The model can tell us how to obtain the stable non-crystalloid precursors in nitrate-oleic acid systems, and it is also useful to discuss the reactive mechanism of gels auto-combustions. Using the DSC and XRD techniques, the reactive mechanism from dried gels to nano-powders have更多还原