La_2CuO_4前驱物粉体的自蔓延燃烧合成及其晶化

PREPARTION OF La_2CuO_4 PRECURSOR POWDERS BY SELF-PROPAGATING COMBUSTION SYNTHESIS AND THEIR CRYSTALLIZATION

分别采用硝酸盐自蔓延燃烧法和醋酸盐／硝酸盐自蔓延燃烧法低温合成了Ｌａ_２ＣｕＯ_４前驱物粉体，研究了在不同条件下制备的前驱物粉体的晶化行为．在硝酸盐自蔓延燃烧法合成前驱物粉体时，燃烧反应十分剧烈，在前驱物粉体中发现有Ｃｕ单质存在，Ｃｕ单质的存在不利于在低温合成单一相Ｌａ_２ＣｕＯ_４粉体在硝酸盐自蔓延燃烧法基础上，以醋酸盐部分取代硝酸盐，大幅度降低了自蔓延燃烧温度，可以通过调整尿素的用量来改变氧化剂的总氧化价Ｏ与还原剂的总还原价Ｆ之比，使自蔓延燃烧温度连续可调．用醋酸盐／硝酸盐自蔓延燃烧法合成的前驱物粉体在较低温度焙烧处理，得到了单一相Ｌａ_２ＣｕＯ_４粉体自蔓延燃烧温度对前驱物的组成和焙烧产物的组成和显微形貌有显著影响．

Two self-propagating combustion synthesis (SPCS) methods, nitrate SPCS method and acetate/nitrate SPCS method, were used, respectively, to synthesize La2CuO4 precursor powders at relatively low temperatures, and the crystallization behaviors of the as-prepared precursor powders were investigated. In the case of nitrate SPCS method, combustion reaction was extremely strong, and metal copper was found in the as-prepared precursor powder. The existence of metal copper in the as-prepared precursor powder was deleterious to the synthesizing mono-phase La2CuO4 powders. Based on the nitrate SPCS method, a novel acetate/nitrate SPCS method in which acetate substituted partially for nitrate in the initial solution was developed. This novel method exhibits two advantages. 1) it decreases the combustion temperatures profoundly, and 2) it is possible to control the combustion temperatures precisely through adjusting the ratio of total oxidation valence of oxidizer (O) with respect to total reduction valence of reducer (F) by varying the amounts of urea used in the initial solution. Mono-phase La2CuO4 powders can be obtained after calcination of the as-prepared precursor powders synthesized by acetate/nitrate SPCS method at low temperatures. Combustion temperatures strongly influenced the compositions of the as-prepared precursors and the calcined products, as well as the morphologies of the calcined products. The gradual adjustment of combustion temperatures made it possible to obtain products with controlled morphology.