THE JOURNAL OF
PHYSICAL CHEMISTRY
f
(Registered in
VOLUME62
U. 8. Patent Office)
(0Copyright, 1958,by the American Chemical Society)
NUMBER 7
JULY 30, 1958
THE VAPORIZATION OF MOLYBDENUM AND TUNGSTEN OXIDES’ BY PAULE. BLACKBURN, MICHAEL H O C HAND ~ HERRICK L. JOHNSTON Contribution from the Department of Chemistry, Ohio State University, Columbus, Ohio Received July 17, 1967
The vapor pressures above Mooa, Mo4OI1,Mooz, W03 and WOZhave been measured by the Knudsen effusion method. MoOs(s) vaporizes to (MoOa),(g) while Mo4OlI(s)disproportionates to (MoOa)s(g) and MoOz(s), the heats of vaporization of MOO&) and of decomposition of MorOll(s)being AHwo = 79.7 kcal./mole of (Moos), and AH900 = 68.7 kcal./mole of (MOO&, respectively. Some Mo02(s) vaporizes to MoOz(g) with AH: = 129.8 kcal./mole, but most of the MOOZ(S)disproportionates to MoOa(g) and Mo(s) with AH; = 133.6 kcal./mole of MOO& woa(s)va orizes to (WOa)s( ) with AH~aoo= 108.0 kcal./mole of (Wo!), and WOz(s) dis ropoFtionates to (WO& g) and W(s) with L&IS~O = 90.2 kcal.$mole of (WO& The calculated heat of dissociation for Mo&(g) IS 0 8 = 284.6 kcal./mole and for MoO,(g) is DE = 410.3 kcal./mole. The heat of decomposition of (MoOa)a(g) to the monomer MoOa(g) is AH = 220.9 kcal./mole of the trimer.
This research is concerned with the investigation of the vapor or dissociation pressures of Moo3, Of the Moo% w039 woz, and the mediate compounds. There has been substantial disarrreement among molybdenum trioxide vaDOr pressure data obtal‘led 6y the Knudsen effuGon r n e t h ~ d ,by ~ transpiration measurements,‘ and by the rate of evaporation method.s WOs vapor pressures have been investigated by U e n ~ . Calcula~ tions using KelleyW and Brewer’s? data show that Mooz and WOZshould decompose to the metal and the trioxide. No measurements are available on the lower oxides of either metal. Apparatus and Experimental Procedure --
inter-
I 1
,
The heating was done entirely by induction, using a Genera1 Electric or a Westinghouse 20 kilowatt electronic heater. Three furnaces were used for the research. A furnace for temperatures below the optical range was used for vapor pressure measurements on molybuenum trioxide and molybdenum dioxidemolybdenum trioxide mixtures. The remaining measurements were made in either the high ternperature Pyrex glass furnace or the metal furnace previously described.* The only change made on the high (1) This work wassupported in part by the Officeof Naval Research under contract with the Ohio State University Research Foundation. (2) Department of Metallurgical Engineering, University of Cincinnati, Cincinnati 21, Ohio. (3) K. Ueno, J . Chem. Soc. Japan, 62,990 (1941). (4) S. M. Ariya, S. A. Shchukarev and V. B. Glushkova, Zhur. Obshchei K h i m , 2S, 2063 (19.53). (5) J. Feiser, MetaEZ. Evz., 28, 297 (1931). (6) K. I
