D.R. Fredrickson

Enthalpy of uranium dioxide and sapphire to 1500 K by drop calorimetry

Abstract A high-precision drop calorimetric system has been used to measure the enthalpy of UO2 and National Bureau of Standards sapphire in the temperature range 500 to 1500 K, relative to 298.15 K. All temperatures are based on IPTS-48. The UO2 results can be represented by the equation: H°(T) − H°(298.15 K) = {19.7614( T K ) + 5.49053 × 10 −4 ( T K ) 2 + 6.96890 × 10 6 ( T K ) −1 − 7951.68} cal mol −1 Values of Cpo, Ho(T) − Ho(298.15 K), So, and {G o − H o (298.15 K )} T are tabulated. The sapphire results can be represented by the equation: H°(T) − H°(298.15 K) = {27.6002( T K ) + 1.61393 × 10 −3 ( T K ) 2 + 9.65836 × 10 5 ( T K ) −1 − 11554.31} cal mol −1

The enthalpy of sodium oxide Na2O to 1300 K by drop calorimetry

A high-precision drop-calorimetric system has been used to measure the enthalpy (relative to 298.15 K) of Na 2 O in the temperature range 500 to 1300 K. A rapid rise in the derived C p ( T ) is observed about 900 K, which may be attributed to the onset of a diffuse transition in Na 2 O and a disordering of the Na + ions. The results are therefore represented by two equations, one for temperatures below 900 K and another for temperatures above 900 K. In the range 298 to 900 K: { H o ( T ) − H o ( 298.15 K ) } / c a l t h m o l − 1 = 13.8814 ( T / K ) + 4.4249 × 10 − 3 ( T / K ) 2 − 4532.09. In the range 900 to 1300 K: { H o ( T ) − H o ( 298.15 K ) } / c a l t h m o l − 1 = 35.4157 ( T / K ) − 2.80046 × 10 − 2 ( T / K ) 2 + + 1.42549 × 10 − 5 ( T / K ) 3 − 8036.87. All temperatures are based on IPTS-68. Values of { H o ( T )− H o (298.15 K)}, C o p ( T ), { S o ( T ) − S o (298.15 K)}, Δ H o f ( T ), Δ G o f ( T ), and log K o p ( T ) are tabulated.

Thermodynamic investigation of trisodium uranium(V) oxide (Na3UO4) III. Enthalpy to 1200 K by drop calorimetry

Abstract The enthalpy (relative to 298.15 K) of Na3UO4 was measured from 500 to 1200 K using a high-precision drop-calorimetric system. The following equation represents the enthalpy of Na3UO4 in the temperature range 298 to 1200 K. All temperatures are based on IPTS-68. Values of Cpo(T), {Ho(T)−Ho(298.15 K)}, So(T), and {G o (T)−H o (298.15 K)} T are tabulated.

Cesium chromate, Cs2CrO4: high-temperature enthalpy increments and other thermodynamic properties

Abstract High-temperature enthalpy increments and derived heat capacities are reported for Cs 2 CrO 4 . There is a solid-to-solid transition at (1031 ± 3) K and the melting temperature is (1236 ± 5) K. The enthalpies of transition and fusion are (2.9 ± 0.6) and (35.3 ± 0.7) kJ mol −1 , respectively, and the entropies of transition and fusion are (2.8 ± 0.6) and (28.6 ± 0.5) J K −1 mol −1 , respectively. Results obtained in this study are combined with other recent data to produce a table of the thermodynamic functions of Cs 2 CrO 4 to 1500 K.

The enthalpy of molybdenum disulfide to 1200 K by drop calorimetry

A high-precision drop-calorimetric system has been used to measure the enthalpy (relative to 298.15 K) of MoS2 in the temperature range 500 to 1200 K. All temperatures are based on IPTS-48. The results can be represented by the following equation, which should be used only over the experimental range: H o ( T ) − H o ( 298.15 K ) = { 16.8278 ( T / K ) + 9.4045 × 10 − 4 ( T / K ) 2 + 5.1881 × 10 4 ( T / K ) − 1 − 5495.38 } cal mol − 1 . Values of Cop(T), Ho(T) − Ho(298.15 K), So(T), and {Go(T) − Ho(298.15 K)}/T are tabulated.

Enthalpy increments for α- and β-Na2UO4 and Cs2UO4 by drop calorimetry The enthalpy of the α to β transition in Na2UO4☆

A high-precision drop-calorimetric system has been used to measure the enthalpies (relative to 298.15 K) of α- and β-Na2UO4 to 1300 K, and of Cs2UO4 to 1100 K. In the range 298 to 1193 K the enthalpy increments for α-Na2UO4 can be represented by the equation: H°(T)−H°(298.15 K={38.8476(T/K)+3.09342×10−3(T/K)2+5.01109×105(T/K)−1−13538.12}calthmol−1. In the range 1193 to 1300 K the enthalpy increments of β-Na2UO4 can be represented by: H°(T)−H°(298.15K={53.69844(T/K)−23824.88} calthmol−1. Enthalpy increments for Cs2UO4 are represented over the temperature range 298 to 1100 K by: H°(T)−H°(298.15K)={39.4076(T/K+2.03432×10−3(T/K)2+3.65323×105(T/K)−1−13155.51} calth mole−1. Values of Cpo(T), {Ho(T) − Ho(298.15 K), So(T), and {Go(T) − Ho(298.15 K)}T are tabulated. For the α to β transition in Na2UO4, a value of ΔHtr = 5.9 kcalth mol−1 at 1193 K has been deduced.

Thermochemistry of uranium compounds IX. Standard enthalpy of formation and high-temperature thermodynamic functions of magnesium uranate (MgUO4) A comment on the non-existence of beryllium uranate☆

Solution and drop-calorimetric studies of magnesium uranate are described. From the solution experiments, the standard enthalpy of formation, ΔHfo(MgUO4, c, 298.15 K) was found to be −(1857.0 ± 1.3) kJ mol−1. The drop-calorimetric experiments gave values for the enthalpy increment {Ho(T) − Ho(298.15 K)} and heat capacity Cpo(T), which, over the temperature range 298.15 to 1400 K, are best represented by the equations: {H°(T) − H°(298.15K}J mol−1 = 110.268(TK + 3.3398 × 10−2(TK)2 −7.8127×10−6(TK3 − 35638; C°p(T)J K−1mol−1 = 110.268 + 6.6796 x 10−2(TK) −2.3438 × 10−6(TK)2 The complete thermodynamic functions of MgUO4 are tabulated from 298.15 to 1400 K. The spontaneity of the decomposition of BeUO4 to its component oxides is advanced as an explanation for the non-existence of this compound.

Heat capacity and thermodynamic properties of triuranium silicide from 1 to 1203 K

Abstract The heat capacity of triuranium silicide, U 3 Si, has been measured from 1 to 350 K and its enthalpy determined from 298 to 1160 K. The coefficient γ for the heat capacity contribution of the conduction electrons ( γT ) is (39.3 ± 0.4) mJ K −2 mol −1 . Thermodynamic functions are tabulated at selected temperatures between 1 and 1203 K. At 298.15 K, the values determined for the heat capacity C p o , the entropy S o , the enthalpy { H o (298.15 K) − H o (0)}, and the function {G o (298.15 K ) − H o (0)} 298.15 K are (107.90 ± 0.43) J K −1 mol −1 , (174.02 ± 0.70) J K −1 mol −1 , (23297 ± 93) J mol −1 , and −(95.88 ± 0.38) J K −1 mol −1 , respectively. The standard Gibbs energy of formation ΔG f o (U 3 Si, c, 298.15 K) = −(105.6 ± 19.2) kJ mol −1 was derived.

The enthalpy of liquid sodium to 1505 K by drop calorimetry

Abstract The enthalpy (relative to 298.15 K) of liquid sodium was measured to 1505 K, using a high-precision drop-calorimetric system. The following equation represents the enthalpy of liquid sodium in the temperature range from 554 to 1505 K: H o (T)−H o (298.15 K ={4.62436( T K )+8.4442 × 10 −4 ( T K ) 2 −5.92445×10 5 ( T K )×10 5 ( T K ) −1 +731.931} cal th mol − All temperatures are based on IPTS-68. Values of {Ho(T) − Ho(298.15 K)}, Cpo(T), and {So(T) − So(298.15 K} are tabulated.