Kyanite Melting temperatures

The pressure inside the heated chamber may also vary as a result of the local density changes produced by thermal expansion or phase changes resulting from the heating. For example NaCl may expand, melt, and thereby increase the local pressure, while pyrophyllite, a layer-lattice-type aluminum silicate, may transform into a denser assembly of coesite and kyanite, thereby reducing the local pressure. It follows that experimental results in high-pressure, high-temperature work must be interpreted with care. 

The heat of the reaction Al OgCcr, a) + Si02(quartz) Al2S10g(cr, kyanite) has been determined at 968 K by Holm and Kleppa (, 2) to be -2.37 0,15 kcal mol". This value was obtained from heat of solution measurements in a high temperature oxide melt calorimeter. Using the JANAP functions, this reduces to Aj,H"(298.15 K) -1.96 kcal mol", which is used to calculate the adopted value for the heat of formation of kyanite. 

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