【作者】 张晨；

【导师】 沈毅；

【作者基本信息】 河北理工学院 ， 材料学， 2004， 硕士

【摘要】 近几年,随着各类保护元件保护功能应用的空前发展,制备具有低电阻、高升阻比及高耐压耐流强度的PTC陶瓷,已成为该领域的工作重点。本研究采用柠檬酸盐溶胶-凝胶法,以Y₂O₃ +Nb₂O₅双施主掺杂,AST+BN复合烧结,采用二次合成工艺制备了室温电阻为22Ω、升阻比为2.6×10⁵的PTC陶瓷材料。利用XRD、SEM、TEM、FAM等测试方法,研究了PTC粉体的合成,掺杂物的掺杂方式和烧成制度对PTC性能的影响。在粉体制备过程种,采用了柠檬酸盐溶胶-凝胶二步合成法和草酸盐共沉淀法来制备PTC陶瓷粉体,对溶液的pH值、反应中溶液的含水量、凝胶化温度、共沉淀反应物的加入顺序等因素进行了分析。研究结果表明:采用柠檬酸盐溶胶-凝胶二步合成法,在600℃即可得到粒径分布在30-70nm之间的施主掺杂BaTiO₃粉体,通过二次合成掺杂受主杂质和烧结助剂,不但使粉体的“软团聚”状态得以分散,而且还有利于二次掺杂物均匀地分布在晶界上。在溶胶化反应中,金属离子与柠檬酸充分反应的pH值区间为6.5< pH <7.5;在凝胶化反应中,使溶胶凝胶反应充分进行的溶液含水量范围R=[H₂O]/[[Ba²⁺]（mol）在70～80,使凝胶化络合反应充分进行的温度在80℃左右。采用草酸盐共沉淀法,控制共沉淀反应的pH值范围在2.5-3.5之间,在800℃煅烧可获得粒径分布在200-300nm之间的PTC粉体。与草酸盐共沉淀法相比,柠檬酸盐溶胶-凝胶二次合成法得到的PTC粉体化学组成更为均匀、晶型发育更为完全的PTC粉体。因此,采用柠檬酸盐溶胶-凝胶二步合成法更容易获得性能优良的PTC陶瓷材料。在瓷体的制备过程中,采用二次掺杂和双施主技术,来降低PTC陶瓷的室温电阻率;引入AST+BN复合掺杂作为烧结助剂来降低瓷体的烧结温度、宽化烧结范围,进而改善材料的PTC效应。结果表明,采用Y₂O₃ +Nb₂O₅双施主掺杂,二次合成掺入0.8mol%左右的Nb₂O₅,可以使R25降低到22Ω;采用AST+BN复合掺杂,可以使烧结温度降低80℃达到1120℃,烧结温度范围宽化30℃左右。更多还原

【Abstract】 The PTC material which have lower resistivity at room temperature, higher PTCR jumps and higher PTC effect have been prepared with citrate sol-gel twice-through method. Some effecting factors e.g. the preparation of PTC powder, the doping method and the doped value of every dopant and sinteriong schedule have been studied by means of XRD, SEM, TEM, FAM. The work has been stressed on the development of a new high performance PTC material.In the work, two kind of wet chemical method, oxalate-coprecipition method and citrate sol-gel twice-through method, have been applied in the preparation of PTC powder. Some factors e.g. the pH value, the concentration, the temperature of gelation, the added method of coprecipitating reactor were analysized. The results have shown that: The donor-doped BaTiO₃ powder having a particle size of 30-70 nm can be prepared at 600℃by citrate sol-gel method. Through the adding of receivers and fluxs as sintering aid with twice-through method, the powder has shown only a weak agglomeration, the dopants can also be well distributed on the grain boundary.At the process of citrate sol-gel method, the range of pH value was 6.5-7.5, the water-content value (R=[H₂O]/[Ba²⁺]（mol）) was 70-80,and the temperature of gelation was 80℃. With oxalate-coprecipition method, the PTC powder which particle size was 200-300 nm can be prepared at 800℃, and the range of pH value was fixed at 2.5-3.5. To obtain a PTC powder of more uniform in chemical composition and well developed magnetite, it can be prepared by citrate sol-gel twice-through method. Compared with oxalate-coprecipitation method, this method is more ideal. This imparity is mainly due to the difference between the two mechanism of crystal formation.The process of specimen preparation, the seconed-doped method and twe donor-doped had been used to decrease the resistivity of the product at room temperature. By adding AST+BN fluxs as sintering aid, the sintering temperature can be decreased and the sintering temperature range can be widen. On these bases, the mechanism of thermoluminescence the dynamic and the microstructure of the final products have been discussed. The results have shown that, by Y₂O₃ +Nb₂O₅ doped method and twice-through method, when the amount of Nb₂O₅ was 0.08mol%, R25 can reach 21Ω, through adding AST+BN the sintering temperature can be decreased 80℃and the sintering range can be widen up to 30℃approximately.更多还原