PHASE-DIAGRAM OF THE SYSTEM BI2O3-MO03

The phase diagram of the Bi2O3MoO3 system was studied by X-ray diffraction and differential thermal analysis, in particular in the range Bi Mo = 2 1 ~ 2 3 of interest for catalysis. X-Ray diffraction identified the following eight compounds: 7Bi2O3 · MoO3, 3Bi2O3 · MoO3, low and high temperature forms of 3Bi2O3 · 2MoO3, koechlinite, and high temperature forms of Bi2O3 · MoO3, Bi2O3 · 2MoO3, and Bi2O3 · 3MoO3. The low temperature form of 3Bi2O3 · 2MoO3 is a new modification of the Bi Mo = 3 compound, while 7Bi2O3 · MoO3 corresponds to that reported hitherto as ~10Bi2O3 · MoO3, and others are identical to those found before. Bi2O3 · 3MoO3 forms eutectics with MoO3 at 615°C and with Bi2O3 · 2MoO3 at 640 °C. Bi2O3 · 2MoO3 is generated by the peritectic reaction of the liquid phase and the high temperature phase of Bi2O3 · MoO3 at 665 °C. Bi2O3 · 2MoO3 is stable in the range from 665 to 540 °C, below which it disproportionates into Bi2O3 · 3MoO3 and the koechlinite form of Bi2O3 · MoO3. The high temperature form of Bi2O3 · MoO3 is also formed by the peritectic reaction of the liquid and the high temperature phase of 3Bi2O3 · 2MoO3. The transition temperatures between two modifications in Bi2O3 · MoO3 and in 3Bi2O3 · 2MoO3 are supposed to be 600 and 750 °C, respectively. 3Bi2O3 · MoO3 forms a eutectic with 3Bi2O3 · 2MoO3 at 950 °C, and a solid solution with Bi2O3. © 1979.