前驱体组成对钛酸钡形成特性的影响

O. Kovalenko
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引用次数: 0

摘要

在Pechini法制备钛酸钡的过程中,建立了配合物沉淀条件与其热分解性质之间的联系。热分解前驱体的x射线物相分析表明,前驱体沉积过程中,在高试剂浓度和低溶液pH下,Ba/Ti比为0.96 ~ 1.01的范围内,可以形成以钛酸钡为主的单相体系。在热重分析的基础上,提出了前驱体分解及其组成的可能机理。结果表明,结构中氢氧根基团的数量影响结晶机理、总质量损失和表面吸附水量。特别是,在低溶液pH下获得的样品具有最少的羟基,并且根据草酸钛钡热分解的典型四步机制分解。其他样品中含有氢和碳基团,这导致最终分解温度在770℃以上升高,由于不同相成核活化能的差异,导致了多阶段分解过程。与纯草酸分解的产物相比,这反过来又可以确定成核过程在小晶的生长和成核过程中占主导地位。一方面,低pH下氯离子的高含量促进了产物的结晶和非晶态二氧化钛相附加成核中心的形成;另一方面,在低浓度溶液条件下,由于没有明显的颗粒碰撞,形成较小的晶体。热重分析表明,在高浓度下,草酸钛钡主要以生成中间碳酸氧化物的方式分解,而不是以碳酸钡和二氧化钛的方式分解。因此,对前驱体沉淀参数的优化和钛酸钡形成机理的研究,可以更好地调控最终产物的组成和晶粒尺寸。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
THE INFLUENCE OF THE PRECURSOR COMPOSITION ON THE PECULIARITIES OF THE BARIUM TITANATE FORMATION
In the process of obtaining barium titanate by the Pechini method, a connection between the conditions of complexes precipitation and the nature of their thermal decomposition was established. X-ray phase analysis of thermally decomposed precursors showed that the formation of a single-phase system based on barium titanate can be achieved in the range of Ba/Ti ratio 0.96-1.01 at high reagent concentration and low solution pH during the precursor deposition process. On the basis of thermogravimetric analysis, a possible mechanism of precursor decomposition and its composition is assumed. It is shown that the number of hydroxide groups in the structure affects the crystallization mechanism, total mass loss, and the amount of water adsorbed on the surface. In particular, samples obtained at low solution pH have a minimal amount of hydroxyl groups and decompose according to a typical four-step mechanism of thermal decomposition of barium titanyl oxalate. Other samples contain hydro and carbo groups, which leads to an increase in the final decomposition temperature above 770 °C and a multistage decomposition process due to the difference in the activation energy of the nucleation of different phases. This, in turn, may determine the dominance of the nucleation process over the growth and nucleation of smaller crystallites, compared to the product of pure oxalate decomposition. On the one hand, the high content of chloride ions at the lowest pH promotes the crystallization of the product and the formation of additional nucleation centers from the phase of amorphous titanium dioxide. On the other hand, the formation of smaller crystallites occurs due to the absence of significant particle collisions in conditions of low concentration of the solution. On the basis of thermogravimetric analysis, it is shown that at high concentration, barium titanyl oxalate decomposes mainly by the mechanism of formation of intermediate oxycarbonates, and not barium carbonate and titanium dioxide. Thus, the optimization of the precursor precipitation parameters and the study of the barium titanate formation mechanism allow for better regulation of the composition and crystallite size of the final product.
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