低压ZnO压敏陶瓷增长晶粒法制备工艺及性能研究

【作者】 肖胜根；

【导师】 甘国友；

【作者基本信息】 昆明理工大学 ， 材料学， 2007， 硕士

【摘要】 实现ZnO压敏陶瓷低压化的途径主要有三条：减小ZnO压敏陶瓷片的厚度、降低ZnO压敏陶瓷中单晶界层击穿电压、增大ZnO晶粒的平均尺寸，而且，亦可把各途径适当地结合起来。本论文主要创新性地对低压ZnO压敏陶瓷增长晶粒法制备工艺及性能进行了较为深入和系统的研究。通过做大量的试验和借助大型万能光学显微镜、X射线衍射仪、能谱仪、扫描电镜等先进测试分析仪器，不仅得到了一些比较理想的试验结果，而且得到了具有一定价值的理论收获，这将能够为工厂中试生产提供有益的直接参考。具体如下：找到了适当的籽晶制备方法，即以99.5mol％ZnO+0.5m01％BaCO₃的配方组成，按与典型电子陶瓷制备工艺相似的工艺在1420℃下保温10h，然后用沸水煮解足够长时间，利用240目、300目及400目标准分样筛进行粒径分级便可制备出粒径范围分别为38μm～48μm和48μm～61μm的ZnO籽晶；该ZnO籽晶具有六方纤维锌矿结构。参照欧盟RollS指令设计配方，通过按正交表L₁₆（4⁵）来安排并进行试验，用极差分析法对试验结果进行合理的处理分析，找到了对于压敏瓷片的低压化要求而言较优的工艺条件，并较稳定地制得了电学性能较理想的低压ZnO压敏陶瓷，其压敏电压为11V／mm、漏电流为0.018mA、非线性系数为15.6。借助能谱仪对瓷片进行测试分析，了解了瓷片的微观组成分布，发现在瓷片内部不仅主要存在Bi富集晶界层、Bi贫化晶界层、晶粒直接接触晶界层等三种晶界层，而且可能存在一种等效晶界层——残留有Bi的闭口气孔，这四种晶界层对瓷片压敏效应的贡献不同，换言之，这四种晶界层的有效性程度不同，瓷片的压敏效应应该是瓷片内部所有这四种晶界层对压敏效应贡献的统计平均。借助扫描电镜获得瓷片断口形貌的背散射电子像，通过科学合理的对比分析，基本上印证了高烧结温度、长保温时间、TiO₂及籽晶对ZnO晶粒的助长作用，并且有单独TiO₂的助长作用小于单独籽晶的助长作用、单独籽晶的助长作用又小于TiO₂+籽晶的合助长作用。得到了如下规律：在瓷片内部单晶界层击穿电压可以近似地认为是一个常数的前提下，随着瓷片内部晶粒平均尺寸的增大（当然，晶粒尺寸分布也要较均匀），瓷片将变得更加低压化；按理，当晶粒平均尺寸很大时，压敏电压应很低，但由于这时晶粒内部将具有更多的等效晶界层，故压敏电压不是继续降低，而是略有升高。更多还原

【Abstract】 We can prepare low-voltage ZnO varistor by three main methods such as diminishing the thickness of the ZnO voltage-sensitive ceramic disc, reducing the breakthrough voltage of the single grain boundary layer in ZnO voltage-sensitive ceramic and augmenting the average size of the ZnO grains. What’s more, those methods mentioned above can be combined each other properly to be applied to prepare low-voltage ZnO varistor. In this thesis, the preparation process of augmenting the ZnO grains’ average size and properties of low-voltage ZnO varistor is investigated originally and systematically. By virtue of advanced test&analysis apparatus such as good-sized omnipotent optical microscope, XRD instrument, EDS instrument and SEM, not only quite a few relatively ideal test results have been obtained, but also some theoretical fruits of a considerable value have been acquired after extensive tests. The above achievement can contribute helpful reference to large-scale industrialization production. They are as follows:The appropriate preparation process of seed crystal has been found. In detail, the formula for seed crystal consists of 99.5% ZnO and 0.5%BaCO₃. First, lasting for ten hours at the temperature of 1420℃according to the process like the typical preparation process of electronic ceramic, secondly, to be poached by boiling distilled water for enough time, thirdly, ZnO seed crystal with the sizes of 38μm～48μm and 48μm～61μm are attained through classifying grains by size depending on sieves of 240, 300 and 400mesh.The above ZnO seed crystal possesses hexagonal wurtzite structure.The formulas for low-voltage ZnO varistor are designed according to the RoHS instructions instituted by Europe Union. These tests in this thesis are arranged and carried out on the basis of L16（4⁵） orthogonal experiment table. And then, the relatively ideal process to voltage-sensitive ceramic discs’ demand for lower-voltage has been found and the ZnO voltage-sensitive ceramic of relatively fine electrical properties has been also prepared stably after the test data&results were dealt with and analyzed by polar margin analysis method rationally, which has breakdown voltage of 11V/mm, leakage current of 0.018mA and nonlinear coefficient of 15.6.By dint of EDS instrument, the constituent micro-distribution of ceramic disc is realized and it can be found that not only there are chiefly bismuth accumulation grain boundary layer, bismuth sparsity grain boundary layer and direct contact grain boundary layer, but also there is possibly a equivalent grain boundary layer named close pore containing residual bismuth. In fact, the four kinds of grain boundary layers can have different contribution to the voltage-sensitive effect of ceramic disc. In other words, the four kinds of grain boundary layers have different efficacy, the voltage-sensitive effect of ceramic disc should be statistical average of the different contribution of the four kinds of grain boundary layers in ceramic disc.By dint of SEM, the transect BSEI of ceramic disc can be acquired. Through rational comparison and analysis of the transect BSEI, that high sintering temperature, long soaking time, titanium dioxide and seed crystal are beneficial to the size increase of ZnO grain is confirmed basically. In addition, the conclusion can be drawn from the comparison and analysis that the effect of single titanium dioxide is less than single seed crystal for the size increase of ZnO grain and the effect of single seed crystal is less than titanium dioxide plus seed crystal.What’s more, the law can be found that as the average size of the ZnO grains gets smaller the breakdown voltage gets lower when the breakthrough voltage of the single grain boundary layer in ZnO voltage-sensitive ceramic could be approximatively regarded as a constant and the grain size distribution is relatively uniform; As grain average size becomesbigger breakdown voltage gets lower in principle, whereas breakdown voltage gets higher little by little because many equivalent grain boundary layers exist in the grains at the same time.更多还原