【作者】 霍伟荣；

【导师】 曲远方；

【作者基本信息】 天津大学 ， 材料学， 2007， 博士

【摘要】 为了研制无铅化的高居里温度PTC材料以及低室温电阻率的PTC材料,本文对多种BaTiO₃基复合材料进行了研究,通过阻温测试、介温曲线、XRD分析以及微观结构分析等方法,研究了复合材料的性能特点及其影响因素,并取得了一定的成果。在BaTiO₃基PTC陶瓷材料中复合具有高居里温度的NBT,可以提高材料的居里温度。当NBT加入量为1.0mol%时,居里温度提高了近30℃,而NBT加入量为1.5mol%时,居里温度提高了近50℃。这主要是因为NBT的引入,加强了Ti-O键,使材料的四方性加强。同时由于从NBT中挥发出来的Bi2O₃有抑制晶粒长大的作用,并且易与MnO₂形成电子捕获的中心,提高了试样的PTC效应:升阻比提高了近两个数量级,而温度系数由原来的8.1%oC-1提高到了21.9%oC-1。当NBT加入量为8.0mol%时,尽管试样的PTC效应较差,但试样的居里温度由原来的97℃升高到了230℃附近,这使制备高居里温度的无铅化的BaTiO₃基PTC材料成为可能。但随着NBT加入量的增加,试样越难半导化。复合NBT后,试样的室温电阻率提高,为降低室温电阻率,在复合1.0mol%NBT的BaTiO₃基PTC材料中加入适量金属Ni,当Ni粉的加入量为12wt%时,采用弱还原气氛热处理,并在C粉中加入微量的NBT,900℃下保温50min,可得到室温电阻率为15.56Ω·cm,升阻比为169.82的材料。研究发现在预合成的BaTiO₃粉料中加入金属Cu粉,可以有效的降低材料的室温电阻率,金属Cu粉的最佳加入量范围为2mol%⁴mol%,约为Ni粉加入量十分之一。在BaTiO₃基础料中加入4mol%的Cu粉,1275℃烧结并保温20min,再在弱还原气氛下800℃热处理60min后,可得到室温电阻率为101.12Ω·cm,升阻比为102.58的PTC材料。研究还发现CuO和SiO₂的加入都能提高试样的居里温度,说明对B位进行掺杂也能加强B-O键而提高相变温度,但加入量有限。本文还研究了不同A位施主掺杂剂对材料性能的影响,结果表明,与Sb2O₃、Y2O₃相比,以Bi2O₃为A位施主掺杂剂时,得到的试样的温度系数最大,高达46.42%oC-1。当升温速度较慢为200℃/h时,尽管试样的室温电阻率有所上升,但试样的PTC效应得到了明显的改善,同时,试样的居里温度也均向高温方向发生了不同程度的移动。更多还原

【Abstract】 In order to prepare the lead-free PTC ceramics with high Curie Tempreture（TC）and low room temperature resistivity, some BaTiO₃-based PTC composites werestudied in this paper. The properties and influence factor of this composite ceramicswere investigated through many test methods such asρ-t curve measuring,ε-t curvemeasuring, XRD, SEM and so on. The research achievements were as follows:The TC of PTC ceramics could be increased by compounding NBT with high TCinto the BaTiO₃-based PTC composites. When the content of NBT amounted to1.0mol%, the TC of PTC ceramics increased 30°C, and when the content of NBT wasup to 1.5mol%, the TC increased about 50°C, the reason was that introduce of NBTstrengthened Ti-O bond and then enhanced the tetragonality of the ceramic crystallattice. At the same time, the PTC effects were also meliorated which attributed tovast electron capture centers formed by Bi2O₃ acting with MnO and grain growthrestrained by Bi2O₃ volatilized from NBT: The magnitude had been improved greatlyfrom 104to106, and the resistivity temperature factor increased from 8.1%°C-1 to21.9%°C-1. When the content of NBT amounted to 8.0mol%, the Curie point increasedfrom 30°C to 230°C, so it was possible to prepare the lead-free BaTiO₃-based PTCceramics with high TC. However, it was quite difficult to form semiconductingmaterials with the increase of NBT content.Compounding NBT into the BaTiO₃-based PTC composites increased the roomtemperature resistivity of samples. In order to decrease the room temperatureresistance, an amount of Ni powder was added into BaTiO₃-based PTC compositeswith 1.0mol% NBT. The composites with low room temperature resistivity（15.56Ω·cm） and resistance jump （169.82） were obtained by adding 12wt% Nisintered in reducing atmosphere, then heat-treated at 900°C in weak reducingatmosphere with some NBT for 50min.It was found that adding copper powder into the pre-synthesized BaTiO₃ powdercould impactfully reduce the room temperature resistance of composites. Theoptimize content of copper powder was from 2mol% to 4mol% which was about tenthof the content of Ni powder. The Cu/BaTiO₃ PTC composites with low roomtemperature resistivity （101.12Ω·cm ） and resistance jump （102.58 ） were obtained when the amount of added Cu was 4mol%, and the samples were sintered at 1275°C for20min in reducing atmosphere, then heat-treated at 800°C for 60min in weak reducingatmosphere.The results showed that adding CuO and SiO2 into the BaTiO3-based PTCceramics could increase TC, It illustrated that dopping on B site could also strengthenTi-O bond and enhance the phase-transition temperature, but the quantity of thedopant was limited.The influences of different donor dopants at A site on the properties of PTCceramics were investigated. Compared with Sb2O3 and Y2O3, Bi2O3 as A site donormade the materials have the maximum temperature coefficient 46.42%oC-1. When theheating rate was 200oC/h which was slow, the room temperature resistance of samplesincreased in some short, but the PTC effects were improved obviously. At the sametime, the TC of samples shifted to the high temperature to some certain extent.更多还原