AN080 – Thermodynamic properties of strontium and barium feldspars-zh

REFERENCE

M. GAMBINO, P. GAUNE and J.P. BROS
Thermochimica Acta, Vol 175 (1991) p 119-127

INTRODUCTION

The molar heat capacities of two synthetic Sr and Ba compounds were measured by differential scanning calorimetry between 312 an d 712 K. In addition, heat capacities were calculated from a model of the vibrational spectra u sing optical frequencies measured by IR spectroscopy.

Plot of the heat capacity of BaAl2Si2O8 against temperature
computed from model of vibrational spectrum.

EXPERIMENTAL

All heat capacity measurements were performed under purified argon flow using stainless steel calorimetric cells (6mm in diameter, 12 mm in length). These gas tight containers were closed
by a nickel O-ring pressed between the cell and the lid.

RESULTS

The measured and calculated heat capacity values we re used to calculate the standard entropies :

S298.15 (SrAl2Si2O8) = 218.5 ±4.0 J.K-1.mol-1 and
S298.15 (BaAl2Si2O8)= 231.5 ± 4.0 J.K-1 .mol-1

and also to propose the recommended equations :
Cp SrAl2Si2O8 = 269.59 + 5.784 x 10-2T – 5.833 x 106T-2J.K-1.mol-1
Cp BaAl2Si2O8= 261.05 + 6.640 x 10-2T – 5.256 x 106T-2J.K-1.mol-1
for 250 < T/K < 1000 (eqn. (4) )

The results are given with an accuracy of about 3 % for Cp and ± 0.5K for T.

For more details ask for publication B0733