摘要
通过影响锆盐的水解-缩聚及其产物的Ostwald熟化(溶解-沉淀)过程,ZrO(NO3)2×2H2O-CO(NH2)2-CH3OH-H2O体系组成会对溶剂热产物的晶化行为产生显著影响。在非贫水(甲醇与水体积比不高于65:10)条件下,尿素通过其水解作用可有效促进锆盐水解-缩聚形成[ZrOy(OH)2+x-2y×z H2O]n聚合体的过程;表现为相同溶剂组成条件下,产物晶化程度显著提高。此外,随体系醇水比增加,混合溶剂对聚合体的溶解能力下降,Ostwald熟化过程受到抑制,使得热力学支持的四方向单斜相的转化几率降低;表现为溶剂热产物中四方与无定型相增加,热处理后粉体中四方相含量增加。在贫水(甲醇与水体积比高于65:10)条件下,甲氧基部分取代羟基与Zr^4+发生亲核取代、甲醇取代水参与配位,形成[ZrOz(OH)p(OCH3)q×r CH3OH]n聚合体,经中等温度焙烧形成碳掺杂ZrO2材料,从而稳定了ZrO2的四方相。同时,尿素水解对水与羟基的竞争作用使得相同溶剂组成条件下,聚合体中的甲氧基含量增加,产物中碳掺杂量增加,对四方相的稳定作用增强,表现为有尿素参与的贫水体系能在较宽的溶剂组成范围内获得四方纯相ZrO2结构。
The composition of ZrO(NO3)2×2H2O-CO(NH2)2-CH3OH-H2O system could have an effect on the crystallization behavior of the solvothermal products in the hydrolysis-condensation process of zirconium salts and the dissolution-precipitation process of the condensation products.In the system with water at a volume ratio of methanol to water of 65:10,urea can effectively promote the hydrolysis and condensation of zirconium salt to form[ZrOy(OH)2(10)x-2y×z H2O]n polymers.As a result,the introduction of urea greatly improves the crystallization degree of both the solvothermal products and calcined powders,compared to their counterparts prepared with the same solvent composition.Moreover,the solubility of mixed solvents to the polymers decreases with the increase of volume ratio of methanol to water,hence inhibiting the Ostwald process and reducing the probability of thermodynamically supported phase transformation from tetragonal to monoclinic ZrO2.Consequently,the proportion of tetragonal and amorphous phases in solvothermal products increases,resulting in an increasing amount of tetragonal phase in the calcined powders.Under water-poor conditions,methanol is obliged to take part in the nucleophilic substitution with Zr^4+ through its methoxy group and coordinated as molecules to form[ZrOz(OH)p(OCH3)q×r CH3OH]n polymers.After calcination at moderate temperatures,carbon-doped ZrO2 is formed,which stabilizes the tetragonal phase of ZrO2.In addition,the competition to hydroxyl groups and water between urea and zirconium salt results in more methoxyl groups in the polymers and subsequently more carbon doping in powder under the same solvent composition.This is probably since pure tetragonal phase can be obtained in a comparatively wide range of solvent composition for the water-poor system with urea addition.
作者
刘鹏
孟员员
乔彪
李腾
梁丽萍
LIU Peng;MENG Yuanyuan;Qiao Biao;Li Teng;LIANG Liping(Institute of Materials Science and Engineering,Taiyuan University of Science and Technology,Taiyuan 030024,China)
出处
《硅酸盐学报》
EI
CAS
CSCD
北大核心
2019年第12期1752-1759,共8页
Journal of The Chinese Ceramic Society
基金
山西省研究生联合培养基地人才培养项目(2017JD33)
山西省研究生联合培养基地人才培养项目(2018JD34)资助
关键词
二氧化锆
单斜相
四方相
溶剂热合成
碳掺杂二氧化锆
zirconia
monoclinic phase
tetragonal phase
solvothermal synthesis
carbon-doped zirconium dioxide
