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Representation des courbes de vaporus dans les systemes binaires a tension de vapeur non negligeable
Application au système As2Se3-As
Influence de la tension de vapeur sur une transition de phases et un equilibre peritectoide
ReprésentationT-V-x applicable au système As2Se3-As
RepresentationT-V-x des systemes binaires a tension de vapeur non negligeable
I. Règle des phases, règle du levier et description d'un équilibre eutectique
Binary systems with non-negligible vapour pressure may be described by theT-V-x diagram. The use of the volumeV as an independent variable makes it possible to show the part played by the vapour phase in binary systems. This first part deals with the experimental connection betweenT, V andx data measured by DTA with sealed silica ampoules. As an example the eutectic composition is used: the theoretical isothermal, isochoric and isoplethal sections are presented and compared to those of some former works.
RepresentationT-V-x des systemes binaires a tension de vapeur non negligeable
II.-Influence du volume massique sur les courbes d'ATD lors de l'étude du système NdAs-As
Representation T-V-x des systemes binaires a tension de vapeur non negligeable
III. — Etude expérimentale par ATD du système NdAs-As
The effect of the variableV/m on the appearance of DTA endotherms has been used to obtain quantitative data on theT-V-x representation of the NdAs-As system.
The heat capacities of Bi.4Te. 6 in the solid and liquid states are calculated from the results of the experimental “drop calorimetric” method, and the heat of fusion of the compound is deduced.
For DTA studies, arsenic samples are placed in silica ampoules which are evacuated and sealed. Since the arsenic sample does not fill the whole inner volume of the ampoule, theV/m ratio (whereV is the inner volume andm is the weight of the sample) can be varied. Depending on theV/m value, two kinds of curves are obtained. The distribution of phase regions in theT vs.V/m space is described. This distribution makes it possible to determine the specific volume of arsenic vapor at the triple point. The result obtained (7.90 mm3 mg−1) is consistent with As4 molecules in the vapor phase. From the DTA curves obtained, the heat of fusion of arsenic is estimated. The result (24.2 kJ mol−1) is consistent with the values reported in the literature.
