自蔓延高温合成技术法合成La_(0.7)Sr_(0.3)MnO_3过程的热力学分析

Thermodynamics Analysis on SHS Process of La_(0.7)Sr_(0.3)MnO_3

通过热力学计算研究自蔓延高温合成技术合成La0.7Sr0.3MnO3反应机制。结果表明:对于Mn,La2O3,SrCO3,NaClO4组成的自蔓延高温合成La0.7Sr0.3MnO3反应体系,理论上Mn粉优先与La2O3反应生成LaMnO3,低温下Mn粉优先与O2反应生成少量MnOx,大部分剩余的Mn粉高温(>1417 K)下优先与O2反应生成SrMnO3;同时,少量低温(<1417 K)时形成的MnOx与SrCO3反应生成SrMnO3。高温下,SrMnO3与LaMnO3反应生成La0.7Sr0.3MnO3,这是SHS法合成La0.7Sr0.3MnO3的主要途径。另外,当温度大于1235 K时,少量La2O3与SrCO3反应生成La2SrOx,La2SrOx再与LaMnO3反应生成La0.7Sr0.3MnO3。

The reaction mechanism of the SHS system was explored through thermodynamic calculation method. It is found that in the reaction system consisted of Mn, La2O3, SrCO3, NaClO4, firstly, Mn prefers to react with La2O3 and O2 to produce LaMnO3. Then the remainder prefers to be reacted with O2 to produce MnOx. Howerer, SHS is a quick process and at high temperature （above 1417 K）, most residual Mn reacts with SrCO3 to produce SrMnO3. At the same time,MnOx produced at low temperature （bellow 1417 K） reacts with SrCO3 to produce SrMnO3. The high temperature way is predominant. Finally, La, Sr1-xMnO3 is prepared by SrMnO3 and LaMnO3. Nevertheless, when the temperature was above 1235 K, some La2O3 reacts with SrCO3 to produce La2SrOx, then the La2SrOx will react with LaMnO3 to produce La0.7Sr0.3MnO3, but it is much less than that produced by SrMnO3-LaMnO3 reaction.