Solution calorimetric investigation of fluor-chlorapatite crystalline solutions

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Solution calorimetric investigation of fluor-chlorapatite crystalline solutions

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Title: Solution calorimetric investigation of fluor-chlorapatite crystalline solutions
Author: Hovis, Guy L.; Harlov, D. E.
Abstract: Solution calorimetric measurements have been made on 17 synthetic fluorapatite-chlorapatite crystalline solutions at 50 degrees C in 20.0 wt% HCl under isoperibolic conditions. Analysis of the calorimetric data indicates that heats of mixing across the series may reach values as high as 8.3 kJ/mol. Normally such a high degree of thermodynamic nonideality would be associated with immiscibility, yet no such miscibility gap is indicated by either synthetic or natural fluor-chlorapatite specimens. Based on full chemical analyses, all Cl-rich samples (X(Cl) > 0.65) of this study have halogen deficiencies that imply the presence of 4-11 mol% vacancies in the anion sites, which are interpreted to be associated with oxyapatite substitution. Separate analysis of data for the vacancy-free samples produces a linear fit for enthalpy of solution vs. composition, which yields an alternative interpretation of thermodynamic ideality. Together these models define the limits of enthalpy behavior for the fluor-chlorapatite system.
URI: http://hdl.handle.net/10385/884
Date: 2010

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