【作者】 王华涛；

【导师】 曲远方；

【作者基本信息】 天津大学 ， 材料学， 2003， 硕士

【摘要】 本文研究了金属Ni/陶瓷复合PTCR材料的机理、数学模型和影响因素。根据数学模型,重点讨论了工艺过程对复合材料性能的影响,分析了提高复合材料性能的有效途径。并研究了一种能够降低复合材料的室温电阻率,提高其升阻比的玻璃添加剂。初步研究了一种NiO代替金属Ni的新工艺。通过研究复合材料的电阻率和金属的体积分数的关系,得到如下结论:金属Ni和(Ba,Sr)TiO3陶瓷的复合属于两相物质颗粒态的均匀混合,其电阻混合方式是混联模式,符合GEM方程,电阻率可通过下式近似的估算:。通过该式可推导出复合材料升阻比的计算公式。复合材料的升阻比由陶瓷基质的电阻率和升阻比、金属的体积分数和电阻率、结构因子决定。由该式可知,通过调节金属的体积分数能够实现复合材料的低阻化;复合材料的电阻率随陶瓷基质电阻率的升高而变大,这是复合材料具有PTC效应的主要原因。通过相关的计算可知:降低陶瓷基质的电阻率、提高陶瓷基质的升阻比,防止金属的氧化、降低结构因子有利于获得低室温电阻率、大升阻比的PTC复合材料。工艺条件对复合材料性能的影响是复杂的。还原烧成过程中,陶瓷的室温电阻率降低,PTC效应消失;烧成温度越高,陶瓷颗粒之间的接触电阻越小。氧化过程中,O2的扩散使陶瓷的电阻增加、PTC效应得到部分恢复,也使部分金属Ni被氧化。本实验工作条件下,烧成温度提高、保温时间适当延长复合材料的室温电阻率降低;氧化温度提高、氧化时间适当延长复合材料的室温电阻率增大、升阻比提高;成型压力适当增大,复合材料的室温电阻率降低、升阻比减小。适量的玻璃添加剂在烧结过程中,产生液相,促进了烧结,降低了试样的室温电阻率,提高了试样的PTC效应。采用NiO代替金属Ni的新工艺具有可以控制金属粉的粒度、金属颗粒在复合PTC材料中的分布更加均匀的优点。为获得性能优良的复合PTC材料提供了新途径。更多还原

【Abstract】 In this paper, the mechanism, mathematic model and influencing factors of Ni/(Ba,Sr)TiO3 PTC composites are present. According GEM theory, the influence of processing on the properties of composites and the useful ways to improve the properties are discussed. And some glass additives which can lower the room-temperature resistivity and improve the resistivity-jump are investigated. At last, a novel process in which NiO is introduced instead of Ni is explored. This process has potential to excellent performance PTCR. By research on the relation between resistivity and metal volume fraction of composites, it is concluded that Ni particles and (Ba,Sr)TiO3 particles are even distributed in composites which resistance pattern is series & parallel one and agrees with GEM equation. The resistivity of composites can be approximately calculated according to. Deducing from above formula, we get the resistivity-jump formula. The resistivity-jump of composites is dominated by the resistivity and resistivity-jump of ceramic matrix, the resistivity and volume fraction of Ni and structural factor. By analyzing related formula, it is concluded that the resistivity of composites can be controlled by the volume fraction of Ni, and the PTC effect of composites originates the PTC effect of ceramic matrix. And it will improve the properties of composites such as lowering the resistivity of ceramic matrix and Ni, increasing the resistivity-jump of ceramic matrix, decreasing the structural factor.The influence of processing on the properties of composites is complicated. In reducing phase, the room-temperature resistivity of ceramic matrix is lowered and the PTC effect is diminished, and the contact-resistance of composites decreases with the increasing sintering temperature. In oxidizing phase, oxygen diffuse in ceramic and metal particles which causes the ceramic matrix resistivity increased and a little amount of metal oxidized and the PTC effect of ceramic matrix restored.A suitable amount of glass-additives can lower the room-temperature resistivity and enhance the PTC effect which forms liquid phase that aids the solution and diffusion of solid atoms.This novel process has the following advantages: the uniform distribution and the good control over the particle size of metal material, and the high reactivity. This process supplies a new way to metal/ceramic PTC composites with good performance.更多还原