Determination of Liquidus Ranges

Each of the above three methods employs a different data base. Most of the property values required for the evaluation of in Equations 7-9 have been experimentally determined for III—V systems and these three relationships can be used as a test for thermodynamic consistency. The first method, Equation 7, is most reliable at or near the binary compound melting temperature. As the temperature is lowered below the melting one, uncertainties in the extrapolated stoichiometric liquid heat capacity and component activity coefficients become important. The second method, Equation 8, is limited to the temperature range in which an experimental determination of AG. is feasible (e.g., high temperature galvanic cell). Method II is also valuable for "pinning down" the low temperature values of 0yp. Method III is the preferred procedure when estimating solution model parameters from liquidus data. Since the activity coefficients of the stochiometric liquid... 

Solidification studies at fast (150-200°C-min ) and slow (50-100°C min ) and very slow (10-20°C-min ) cooling of alloys in the region Fe, Fc2B, FcsC. Determination of the solid solution range of FesBi. , in solidified alloys. Determination of isothermal sections at 900, 1000, 1080°C and of the liquidus surface for the Fe rich part. Conditions for stability/metastability of the Fe23(B,C)e phase. Techniques used were XPD and metallography. 

The required reaction or fusion temperature is determined from the phase diagram. As a minimum, this temperature must be higher than the liquidus point of the alloy product. Preferably, however, it should exceed the meltii points of all the reacting metals. The best temperature is one which exceeds the liquidus point by 30-50 °C over the entire range of compositions of the system. Such a temperature will certainly ensure proper reaction conditions. 

For systems with mutual miscibility in the solid phase - so-called solid solutions - Eq. (8.9) has to be used instead Eq. (8.10). In the case of ideal systems (y, = 1) the concentrations and of the liquidus and solidus line in the whole concentration range can directly be determined from the melting temperatures Tmj and the enthalpies of fusion Ahm.i of the compounds involved. For compounds 1 and 2 of a binary system the following expressions are obtained ... 

Binary systems have been studied by the DTA technique (heating curves) in the range -40t+30 C. The reproducibility near the liquidus curve maximum is 0.02o. jhe density of the crystals has been determined by the flotation technique. X-ray investigations have been carried out by means of Laue and oscillation technique on CuKa radiation (-10 0. 

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