The heat capacities at low temperatures and entropies at 298.15 K of low albite, analbite, microline, and high sanidine
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Abstract
The heat capacities of low albite and analbite, NaAlSi3O8, and of microcline and high sanidine, KAlSi3Og, have been measured from 15 to 375 K using an adiabatic calorimeter. Tables of the thermodynamic functions C°p, (H°T–H°0)/T, (G°T–H°0)/T, and S°T–S°0 are presented for these four feldspars from 0 to 370 K. At 298.15 K (25.0°C) the values for S°T S°0 for low albite, analbite, microcline, and high sanidine are 207.4±0.4, 207.7±0.4, 214.2±0.4, and 214.2±0.4 J/(mol.K), respectively.
The effect of the state of Al/Si order upon the heat capacity is quite small. The difference, ΔC°p, between albite-analbite and microcline-sanidine never exceeds 0.5 percent at temperatures below 400 K.
With the exception of microcline, the heat capacities of these four feldspars follow a smooth S-shaped curve between 15 and 375 K, with no indication of transitions or anomalous behavior. Above 250 K, the heat capacity of microcline shows a form of thermal hysteresis. In the temperature range 250 to 375 K, the heat capacity of microcline is dependent upon its past thermal history. At 375 K, microcline which had been cooled to 230 K before the measurement of C°p has a heat capacity greater by approximately 1.2 percent than microcline which had not been previously cooled below 295 K. After a day of annealing at about 300 K, C°p of the previously cooled microcline decreases to essentially the same value as the microcline which had never been at a temperature below 300 K.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | The heat capacities at low temperatures and entropies at 298.15 K of low albite, analbite, microline, and high sanidine |
| Series title | Journal of Research of the U.S. Geological Survey |
| Edition | 195 |
| Volume | 4 |
| Issue | 2 |
| Year Published | 1976 |
| Language | English |
| Publisher | U.S. Geological Survey |
| Description | 10 p. |
| First page | 204 |
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