纳米钛酸钡前体热分解反应动力学及颗粒演化机理

Thermal decomposition kinetics and particle evolution characteristics of nano barium titanate precursor

钛酸钡具有介电常数高、介电损耗低等优良性能,是制备多层陶瓷电容器等元件的基础原料。以草酸盐共沉淀法制备的纳米钛酸钡前体为原料,采用热重-质谱联用分析仪研究了其热分解特性和气体析出特性,揭示了纳米钛酸钡前体热分解反应的机理,利用kissinger-akahira-sunose(KAS)法和flynn-wall-ozawa(FWO)法进行了反应动力学计算,并采用扫描电子显微镜(SEM)观察了热分解产物的微观形貌,分析了颗粒的演化机理。结果显示:纳米钛酸钡前体热分解过程可分为4个失重阶段,第一阶段为水分析出,第二阶段的析出气体为CO和CO_(2),第三和第四阶段的析出气体为CO_(2),据此推导出了各阶段涉及的反应式;随着升温速率的提高,各失重阶段对应的最大失重速率温度均向高温区移动,第四阶段向高温区移动的幅度最大,达到113℃,但该阶段在30℃/min条件下的失重速率最快、反应得到强化;FWO模型更适用于描述纳米钛酸钡前体的热分解过程,四个阶段的平均反应活化能分别为67.89kJ/mol、208.92kJ/mol、494.04kJ/mol和195.11kJ/mol,第三阶段的反应活化能最高、反应较难发生;在纳米钛酸钡前体热分解过程中,宏观大颗粒会演化成微观小颗粒的聚集体,较高的恒温温度会导致颗粒粒径变大,因此恒温温度不宜超过900℃。研究结果为纳米钛酸钡前体热分解工艺参数的选择提供了理论依据。

Barium titanate has excellent properties such as high dielectric constant and low dielectric loss,and is the main raw material for preparing multilayer ceramic capacitors and other components.The thermal decomposition and gas precipitation characteristics of nano barium titanate precursor prepared by oxalate co-precipitation method were studied using a thermogravimetric-mass spectrometry analyzer,and the mechanism of thermal decomposition reaction of nano barium titanate precursor was revealed.The kinetic calculations were carried out using kissinger-akahira-sunose(KAS)method and flynn-wallozawa(FWO)method.The microstructure of the thermal decomposition products was observed using scanning electron microscopy(SEM),and the evolution mechanism of particles was analyzed.The results showed that the thermal decomposition process of nano barium titanate precursor could be divided into four weight-loss stages.The first stage was the release of water,the second stage produced CO and CO_(2),and the third and fourth stages produced CO_(2).Based on these results,the reactions involved in each stage were derived.As the heating rate increased,the maximum weight loss rate temperature corresponding to each weight loss stage moved towards the high-temperature zone.The fourth stage had the largest displacement towards the high-temperature zone,reaching 113℃.However,this stage had the fastest weight-loss rate and the reactions had been strengthened under the condition of 30℃/min.The FWO model was more suitable for describing the thermal decomposition process of nano barium titanate precursors.The average activation energies of the four stages were 67.89 kJ/mol,208.92 kJ/mol,494.04 kJ/mol and 195.11 kJ/mol,respectively.The activation energy of the third stage was the highest and the reaction was difficult to occur.During the thermal decomposition process of nano barium titanate,macroscopic large particles would evolve into aggregates of microscopic small particles.A higher constant temperature would lead to an increase in particle size.Therefore,the recommended constant temperature should not exceed 900℃.This research provided a theoretical basis for the selection of thermal decomposition process parameters for nano barium titanate precursors.