Effect of water content in powder mixture on mechanochemical reaction of LaMnO3 fine powder

Effect of water content in starting powder mixture of La2O3 and Mn3O4 on mechanochemical reaction of lanthanum manganite (LaMnO3) fine powder was investigated. The water content was controlled to be <0.5, 2 and 8% mass fraction in the powder mixture. An attrition-type milling apparatus was employed. This mechanochemical method has several advantages including the use of low cost raw materials, simplicity of the process and the ability to obtain fine powder. When the water content was 2% mass fraction, the single phase LaMnO3 fine powder was obtained after milling only for 30 min. On the other hand, the reaction was not completed on the drier condition (<0.5% mass fraction) and the wetter condition (8% mass fraction). For the powder mixture with the water content of 2% mass fraction, the increase of specific surface area (SSA) with structural defects (forming an activated matrix) occurred in the early stage of the milling, and then solid-state reaction proceeded in the activated matrix, which led to the synthesis of crystalline LaMnO3 phase. The SSA did not change drastically with increasing milling time for the drier powder mixture. The SSA rather decreased for the wetter powder mixture. The results indicated that the water content in starting materials influenced significantly their grinding behavior and thereby the reaction rate for LaMnO3 formation.