Relative Enthalpy of Polytetrafluoroethylene From 0 to 440 °C.

Using a drop method and an ice calorimeter, precise measurements of enthalpy relative to 0 °C were made on a sample of granular polytetrafluoroethylene which was initially 95 percent crystalline. The measurements were at temperatures every 50 degrees from 50 to 300 °C (both before and after melting and quenching); and also at 340, 400, and 440 °C in the liquid range, where it appeared that structural equilibrium of the polymer was reached only slowly. Marked upturns in the heat capacity-temperature curves of the crystalline and quenched polymer above about 200 °C were treated as corresponding to gradual but reversible fusion of the type commonly caused by impurity components ("premelting").

High-Temperature Thermodynamic Functions for Zirconium and Unsaturated Zirconium Hydrides.

Giving greatest weight to the experimentally measured highest decomposition pressures and the enthalpies in one-phase fields, thermodynamically interconsistent integral and differential enthalpies (heat contents), heat capacities, entropies, and Gibbs free energies are derived for the crystalline one- and two-phase fields of the zirconium-hydrogen system for all stoichiometric compositions from Zr to ZrH and over the temperature range 298.15 to 1,200 °K. These properties are derived in analytical form, and in most cases are represented by numerical equations, with tabulation for zirconium and H/Zr atom ratios of 0.

Thermodynamic Properties of Magnesium Oxide and Beryllium Oxide from 298 to 1,200 °K.

As a step in developing new standards of high-temperature heat capacity and in determining accurate thermodynamic data for simple substances, the enthalpy (heat content) relative to 273 °K, of high purity fused magnesium oxide, MgO, and of sintered beryllium oxide, BeO, was measured up to 1,173 °K. A Bunsen ice calorimeter and the drop method were used. The two samples of BeO measured had surface-to-volume ratios differing by a factor of 15 or 20, yet agreed with each other closely enough to preclude appreciable error attributable to the considerable surface area.

Thermodynamic Properties of Thorium Dioxide From 298 to 1,200 °K.

As a step in developing new standards of heat capacity applicable up to very high temperatures, the heat content (enthalpy) of thorium dioxide, ThO, relative to 273 °K, was accurately measured at ten temperatures from 323 to 1,173 °K. A Bunsen ice calorimeter and a drop method were used to make the measurements on two samples of widely different bulk densities. The corresponding heat-capacity values for the higher density sample are represented within their uncertainty (estimated to be ±0.