Measured Enthalpy and Derived Thermodynamic Properties of Crystalline and Liquid Potassium Chloride, KCl, from 273 to 1174 K.

The enthalpy of KCl relative to that at 273.15 K was precisely measured by drop calorimetry from 273 to 1174 K, and smooth thermodynamic functions were derived for this temperature range. The heat capacities found for the crystalline phase join smoothly the most precise published data for lower temperatures; those for the liquid phase are temperature-independent within the precision of measurement over the 120° range covered.

An Experimental Search for Gaseous Reactivity Between AlF and HF Near 1200 K.

Using an accurate transpiration method, AlF was sublimed near 1200 K into argon containing 0, 0.02, and 0.76 atm of HF, but no reaction between AlF and the HF was detected within the precision (about 1%).

An Alternative to Accurate Pyrometry in Distinguishing Concurrent Vaporization Reactions. Postulated Results Using the Vaporization of Gold in Analyzing the Vaporization of Beryllium Oxide in Water Vapor.

For the transpiration determination of vaporization properties whose interconsistency is critical, the simultaneous vaporization of a reference substance such as uncontaminated gold is suggested as an alternative to accurate pyrometry. Calculations suggest that gold would be superior to all but the most accurate pyrometry in the temperature range 1700 to 2300 K. An application to seeking unreported gaseous hydrates of beryllia is illustrated by calculations based on estimated thermodynamic parameters.

Measurement of the Relative Enthalpy of Pure α-AIO (NBS Heat Capacity and Enthalpy Standard Reference Material No. 720) from 273 to 1173 K.

The relative enthalpy of NBS Standard Reference Material No. 720 (99.98 percent pure, single-crystal α-AlO, a calorimetrie heat-capacity standard) was measured over the range 273 to 1173 K by the drop method using a highly precise Bunsen ice calorimeter.

Measured Enthalpy and Derived Thermodynamic Properties of Solid and Liquid Lithium Tetrafluoroberyllate, LiBeF, from 273 to 900 K.

The enthalpy of a sample of lithium tetrafluoroberyllate, LiBeF, of 98.6 percent purity was measured relative to 273 K at eleven temperatures from 323 to 873 K. Corrections were applied for the impurities and for extensive premelting below the melting point (745 K).

Measured Enthalpy and Derived Thermodynamic Properties of Alpha Beryllium Nitride, BeN, from 273 to 1200 K.

The relative enthalpy of a sample of alpha beryllium nitride, BeN, of 95 percent purity was precisely measured over the temperature range 273 to 1173 K using a drop calorimetric method. Corrections were applied for the impurities, and the resulting heat capacity-temperature function was required to join smoothly that from recent precise NBS adiabatic calorimetry which covered the range 20 to 315 K. The enthalpy, heat capacity, entropy, and Gibbs free-energy function were computed from empirical functions of temperature and tabulated from 273 to 1200 K.

Conversion of Existing Calorimetrically Determined Thermodynamic Properties to the Basis of the International Practical Temperature Scale of 1968.

Formulas are derived for converting the relative enthalpy, heat capacity, entropy, and Gibbs energy from the basis of one practical temperature scale to the basis of another, when these properties on either scale have been derived from calorimetric measurements of enthalpy as though that scale were the thermodynamic one. These formulas are directly applicable for converting certain other properties as well. The conversion relates the values of the property at the same numerical temperature on both scales.

Measured Relative Enthalpy of Anhydrous Crystalline Aluminum Trifluoride, AlF, from 273 to 1173 °K and Derived Thermodynamic Properties from 273 to 1600 K.

The enthalpy of a high-purity sample of anhydrous crystalline aluminum trifluoride, AlF, relative to that at 0 °C (273.15 °K), was precisely measured with an ice calorimeter and a "drop" method at 18 temperatures starting at 50 °C and proceeding in 50-deg steps to 900 °C (1173.15 °K).

Relative Enthalpy of Beryllium 1:3-Aluminate, BeO · 3AIO, from 273 to 1173 °K. Thermodynamic Properties from 273 to 2150 °K.

The relative enthalpy of beryllium 1:3-aluminate, BeO · 3AlO, was measured from 273 to 1173 °K. Thermodynamic properties were calculated up to 2150 °K (near the melting point) by extrapolating the present measurements and making them consistent with existing low-temperature data.

Relative Enthalpy of Beryllium 1:1-Aluminate, BeO · AlO, from 273 to 1173 °K. Thermodynamic Properties from 273 to 2150 °K.

The relative enthalpy of the beryllium aluminate BeO · AlO was measured by "drop" calorimetry from 273 to 1173 °K. The thermodynamic properties were calculated up to 2150 °K (approximately the melting point). For this calculation, the data were extrapolated above 1173 °K and the entropy at 273 °K, previously determined at the NBS, was used.

Heat Capacity and Enthalpy Measurements on Aluminum Carbide (AlC) From 15 to 1173 °K. Thermodynamic Properties From 0 to 2000 °K.

Measurements of the heat capacity and relative enthalpy were made on aluminum carbide (AlC) from 15 to 1173 °K. The thermodynamic properties were calculated up to 2000 °K from the data by judicious extrapolation above 1173 °K. In conjunction with the heat-of-formation data on AlC obtained by King and Armstrong and by Mah, second- and third-law analyses have been made of the thermodynamics of several high-temperature vapor-equilibrium reactions involving AlC.

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.