Low T heat capacity measurements and new entropy data for titanite (sphene): implications for thermobarometry of high-pressure rocks

Accurate heat capacity measurements on powdered samples using a Quantum Design physical property measurement system

“…As stated earlier, previous studies [9][10][11][12][13][14][15][16][17][18][19][20][21] using the heat capacity option on the PPMS may have significant errors because of the poor thermal contact between the sample and the platform or because of the poor thermal conductivity of the samples. However, using our new method on powdered samples, we can obtain an accuracy of ±1% from (20 to 300) K and ±2% to ±5% below 20 K for both insulating and conducting samples.…”

“…Recently, heat capacity measurements using the PPMS have been reported [9][10][11][12][13][14] for a series of powdered inorganic samples which were sealed in an Al pan following the method of Dachs et al [7]. As discussed above, this method is likely to produce unreliable results for insulating samples at low temperatures.…”

An improved technique for accurate heat capacity measurements on powdered samples using a commercial relaxation calorimeter

“…Generally, four approaches are used to obtain measurements on these powdered samples using the PPMS: (a) compress or sinter a sample into a pellet that is suitable to sit on the PPMS platform [11,[16][17][18][19][20][21][22][23], (b) introduce another supporting substance, such as, mix a powdered sample with an Apiezon N high-vacuum grease (ANG) and transfer the mixtures to the platform [7], (c) use an encapsulation procedure that encloses the sample in an adhesive such as Stycast Ò 2850 FT [9], and (d) put the sample into a container and measure the total heat capacity of the sample and the container [8,[24][25][26][27][28][29][30]. Approach (a) is likely to achieve an accurate measurement if and only if the sample is a good thermal conductor, but it tends to give precise but inaccurate results for insulating samples because of poor thermal conductivity throughout the pellet [11].…”

The influence of glass composition on crystalline phase stability in glass-ceramic wasteforms

“…As the alumina content of the glass matrix increased with x, the amount of sphene, zircon and rutile decreased until at x = 0.8 and x = 1.0 zircon was present only as a trace, and sphene and rutile were absent based on XRD traces. Hence, based on the observed phases it is suggested that there is an equilibrium: ZrSiO 4 = À1919.7 kJ mol À1 [7] CaTiSiO 5 = À2456.2 kJ mol À1 [8] It is recognised that these data are for a temperature of 298.15 K, but in the absence of high temperature data it is necessary to make the assumption that they will remain essentially invariant with temperature. Inspection of a wider range of data for the formation of mixed oxides from their parent oxides indicates this approximation is reasonable [9].…”