利用柠檬酸-硝酸盐溶-胶凝胶自蔓延燃烧法,在室温下制备了NiFe_2O_4纳米粉体.通过调节氨水在前驱体溶液中的用量,获得了不同类型的干凝胶,并制备了相应的自燃烧粉体.借助XRD、TEM、IR、TG-DTA技术,研究了自燃烧粉体结晶度的变化规律,干凝胶的性质及热分解过程,进而分析了柠檬酸-硝酸盐自蔓延燃烧的机理.研究表明,自燃烧粉体的主要物相为NiFe_2O_4,但含有少量α-Fe_2O_3与FeNi_3杂相.随着氨水用量的增加,合成粉体的结晶度逐渐提高.干凝胶内含有无定形非晶相与NH_4NO_3结晶相,氨水用量对NH_4NO_3含量及干凝胶的性质有显著的影响.自蔓延燃烧的本质是NH_4NO_3分解与柠檬酸燃烧相互促进而形成的链式反应.
Nanocrystalline NiFe_2O_4 powders were synthesized by citrate. Nitrate Sol-Gel auto combustion method at room temperature. Various xerogels were obtained by adding different amounts of ammonia into precursor solution. The corresponding auto combustion powders were prepared through subsequent auto com-bustion process. The variation regularity of crystallinity of auto combustion powders, properties and thermal decomposition process of xerogel were investigated by XRD, TEM, IR and TG-DTA techniques. The mecha-nism of auto combustion method was further studied. The results indicate that auto combustion powders are mainly composed of NiFe_2O_4 phase with small amout impurity phase of α-Fe_2O_3 and FeNi_3. The crystallinity of auto combustion powders are enhanced with increasing the amount of ammonia. The xerogel contains amor-phous phase and NH_4NO_3 crystallization phase. The amount of ammonia exerts appreciable effects on the quantity of NH_4NO_3 and properties of xerogel. The mechanism of auto combustion is a chain reaction which is formed by mutual promotion of NH_4NO_3 decomposition and citric acid combustion.
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