|Author||Ackermann, R. J. ♦ Rauh, E. G.|
|Source||United States Department of Energy Office of Scientific and Technical Information|
|Subject Keyword||METALS, CERAMICS, AND OTHER MATERIALS ♦ DIFFRACTION ♦ EVAPORATION ♦ HIGH TEMPERATURE ♦ MASS SPECTROMETERS ♦ MEASURED VALUES ♦ OXYGEN ♦ QUALITATIVE ANALYSIS ♦ SOLID SOLUTIONS ♦ SOLIDIFICATION ♦ THERMODYNAMICS ♦ TUNGSTEN ♦ TUNGSTEN OXIDES ♦ VACUUM ♦ VAPORS ♦ X RADIATION|
|Abstract||The sublimation behavior of the tungsten- oxygen system was investigated over the temperature range 1300 to 1600 deg K by means of mass effusion studies, mass spectrometric observations, chemical analyses, and x-ray diffraction examination of the condensed phases. Measurements were carried out on compositions ranging from WO<sub>1.80</sub> to WO<sub>3</sub>. In all cases the thermodynamically important vapor species are W<sub>4</sub>O<sub>12</sub>, W<sub>3</sub>O<sub>9</sub> , W<sub>3</sub>O<sub>8</sub>, and W<sub>2</sub>O<sub>6</sub>. Univariant behavior was observed for the solid phases W = WO<sub>2</sub>, WO<sub>2</sub>- W<sub>28</sub>O<sub>49</sub>, W<sub>18</sub>O<sub>49</sub>- W<sub>20</sub>O<sub>58</sub>, W<sub>20</sub>O<sub>58</sub> - W<sub>20</sub>O<sub>2.96</sub> and WO<sub>2.96</sub> . The composition WO<sub>2.96</sub>probably represents the azeotropic composition of the WO<sub>3-x</sub> solid solution produced by the vacuum and is the only single phase that evaporates congruently below 1550 deg K. Except for the W<sub>20</sub>O<sub>58</sub>-WO<sub>2.96</sub> mixture in which the composition of the vapor phase is between those of the solid phases, all other phases and mixtures of two solid phases evaporate incongruently, since the vapor phase is richer in oxygen than the condensed phase. Above 1550 deg K there are no congruently evaporating compositions. Standard free energies, enthalpies, and entropies of formation for the four major vapor species and for the W<sub>18</sub>O<sub>49</sub>, W<sub>20</sub>O<sub>58</sub>, and WO<sub>2.96</sub> solid phases are given.|
|Learning Resource Type||Article|
|Publisher Department||Argonne National Lab., Ill.|
|Journal||Journal of Physical Chemistry|
|Organization||Argonne National Lab., Ill.|
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