MoO_3-MoO_2-H_2O-H_2系平衡及400—700℃Mo-O系相图

EQUILIBRIA OF SYSTEM MoO_3-MoO_2-H_2O-H_2 AND PHASE DIAGRAM FOR SYSTEM Mo-O BETWEEN 400 AND 700℃

使用自行设计的受控气氛热重装置研究了MoO_3—MoO_2-H_2O—H_2系平衡.在P_(H_2O)/P_(H_2)从0.412至0.609,温度从400至534℃范围内直接测定了反应:MoO_3+H_2=MoO_2+H_2O(g)的平衡常数与温度间的关系为1gK_p=0.702-739.8/T获得298.15K下MoO_3标准生成焓及绝对熵分别为:-845.75kJmole^(-1)及78.1 J·K^(-1)mole^(-1) 实验表明,存在于MoO_2-MoO_3系中的一些Magneli相在本研究条件下不能作为热力学稳定相而存在.并绘制了400-700℃下Mo-O系相图.

The equilibria of the system MoO_3-MoO_2-H_2O-H_2 were investigated usinga specially designed thermogravimetric apparatus under the control of atmospheres. The equi-librium constants for the reaction MoO_3+H_2=MoO_2+H_2O(g) were measured at P_(H_2O)/p_(H_2) ratio between 0.412 and 0.609 and in the temperature range of 400 to 534℃ as follows:lg(p_(H_2O)/ P_(H_2)=0.702-739.8/T.The standard enthalpy of formation and absoluteentropy forMoO_3 at 298.15 K have been evaluated as-854.75kJ/mole and 78.16 J/Kmole respectively. The experimental results show that the magneli phases in theMoO_3-MoO_2 system cannot exist as the thermodynamically stable phases under the condi-tions studied. The phase diagram of the system Mo-O between 400 and 700℃ has also beengiven.