Determination of standard gibbs energies of formation of Cr2N and CrN

The standard Gibbs energies of formation of Cr₂N and CrN have been measured by an equilibration technique and by using thermogravimetry and differential thermal analysis (TG-DTA) at temperatures ranging from 1232 to 1523 K. The results are expressed as follows:

Determination of standard gibbs energies of formation of MgO,SrO, and BaO

The standard Gibbs energy of formation of MgO was determined from the measurement of the ΔG° for the reaction ; by equilibrating Mg and Nb with a magnesia crucible and is expressed as follows: Mg(l)+ l/2O₂(g) = MgO(s) ΔG° = −657,000(±5000) + 141(±13)T [J/mol] (973 to 1323 K) The standard Gibbs energies of formation of SrO and BaO were determined by equilibrating silver and MO(M: Sr, and Ba) in a graphite crucible on the basis of the reactionM(in Ag) + CO (g) = MO (s) + C (s), yielding the following results:

Determination of the standard gibbs energies of formation of Ca3As2, Ca3Sb2, and Ca3Bi2

The standard Gibbs energies of formation of Ca₃As₂, Ca₃Sb₂, and Ca₃Bi₂ were determined by a chemical equilibration technique yielding the following results: 3Ca(1)+2As(1)=Ca₃As₂ (s) ΔG°=−723,800+172.8T (±23,700)(J/mol) 1273 to 1573 K 3Ca(1)+2Sb(1)=Ca₃Sb₂(s) ΔG°=−726,300+159.3T(±24,600) (J/mol) 1273 to 1573K 3Ca(1)+2Bi(1)=Ca₃Bi₂(s) ΔG°=−696,400+195.6T(±23,200) (J/mol) 1148 to 1323 K The thermodynamic data for removal of arsenic, antimony, and bismuth by other experimental investigations were discussed in terms of the activity coefficients of these compounds in slags. The stabilities of these compounds were also discussed by using the critical oxygen partial pressures calculated from the above equations. D.J. MIN, formerly Graduate Student, Department of Metallurgy, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan     

Determination of the standard gibbs energies of formation of Ba3P2 and Ba3(PO4)2

The standard Gibbs energies of formation of barium phosphide and barium orthophosphate were determined by a chemical equilibration technique yielding the following results: 3Ba(1)+P₂(g)=Ba₃P₂ (s) ΔG°=−732,000+156.1T(±12,800) (J/mol) 3BaO (s)+P₂(g)+5/2O₂(g)=Ba₃(PO₄)₂(s) ΔG°=−2,523,000+580.0T(±16,600) (J/mol) The stability and the thermodynamic behavior of barium compounds as reaction products of dephosphorization of steel were discussed in terms of the oxygen partial pressure and the activity coefficient of Ba_1.5P in molten Ba saturated with CaO. D.J. MIN, formerly Graduate Student, Department of Metallurgy, The University of Tokyo, Bunkyo-ku, Tokyo 113, Japan     

Determination of standard free energies of formation of Ca3P2 and Ca2Sn at high temperatures

The standard free energies of formation of calcium phosphide and calcium stannide were determined by a chemical equilibration technique, yielding the following results: 3Ca(1) + P₂(g) = Ca₃P₂(s) ΔG° = −653,460(±7110) + 144.01(±4.98)T (J/mol)1000 °C to 1300 °C2Ca(1) + Sn(1) = Ca₂Sn(s) ΔG° = −353,970(±1670) + 79.28(±1.26)T (J/mol)1000 °C to 1300 °C 1120 °C The experimental data to express the thermodynamics for removal of phosphorus and tin from molten iron by calcium based slags by other investigators were discussed in terms of the activity co-efficients of Ca₃P₂ and Ca₂Sn in slag melts by using the present results described above.     

Standard gibbs energies of formation of the carbides of chromium by emf measurements

The standard Gibbs energies of formation of Cr₃C₂, Cr₇C₃, and Cr₂₃C₆ have been determined by electromotive force (emf) measurements using galvanic cells of the type (−) Cr, CrF₂, CaF₂ // CaF₂ // CaF₂, CrF₂, ‘Cr−C’ (+) The measurements have been carried out in the temperature range 1002 to 1176 K. The ΔG° values obtained in the present work are generally in agreement with some of the earlier emf measurements but differ significantly from those obtained by Cr₂O₃−CO equilibrium studies.     

Potentiometric determination of the gibbs energies of formation of SrZrO3 and BaZrO3

The Gibbs free energies of formation of strontium and barium zirconates have been determined in the temperature range 960 to 1210 K using electrochemical cells incorporating the respective alkaline-earth fluoride single crystals as solid electrolytes. Pure strontium and barium monoxides were used in the reference electrodes. During measurements on barium zirconate, the oxygen partial pressure in the gas phase over the electrodes was maintained at a low value of 18.7 Pa to minimize the solubility of barium peroxide in the monoxide phase. Strontium zirconate was found to undergo a phase transition from orthorhombic perovskite (o) with space groupCmcm; D _2h ¹⁷ to tetragonal perovskite (t) having the space group 14/mcm;D _4h ¹⁸ at 1123 (/+- 10) K. Barium zirconate does not appear to undergo a phase transition in the temperature range of measurement. It has the cubic perovskite (c) structure. The standard free energies of formation of the zirconates from their component binary oxidesAO (A = Sr, Ba) with rock salt (rs) and ZrO₂ with monoclinic (m) structures can be expressed by the following relations: SrO (rs) + ZrO₂ (m) → SrZrO₃ (o) ΔG° = -74,880 - 14.2T (/+-200) J mol^-1 SrO (rs) + ZrO₂ (m) → SrZrO₃ (t) ΔG° = -73,645 - 15.37T (/+-200) J mol^-1 BaO (rs) + ZrO₂ (m) → BaZrO₄ (c) ΔG° = -127,760-1.79T (/+-250) J mol^-1 The results of this study are in reasonable agreement with calorimetric measurements reported in the literature. Systematic trends in the stability of alkaline-earth zirconates having the stoichiometry AZrO₃ are discussed.     

Standard gibbs energies of formation of the carbides of manganese by emf measurements

The standard Gibbs energies of formation of Mn₇C₃, Mn₅C₂, Mn₁₅C₄, and Mn₂₃C₆ have been obtained from emf measurements using galvanic cells of the type (-)Mn, MnF₂, CaF₂//CaF₂//CaF₂, MnF₂, ‘Mn-C’(+) The measurements have been carried out in the temperature range 909 to 1247 K. In the case of measurements with Mn-C alloy containing 12.9 wt pct C (Mn₇C₃-C two-phase region at room temperature), the slope change in the emf-temperature curve at 1181 K suggests the formation of a hitherto unidentified phase above this temperature.     

Standard gibbs energies of formation of the carbides of vanadium by emf measurements

The relative partial molar Gibbs energies of vanadium in the vanadium-carbon system have been determined for the V-C alloys containing 36.7, 41.2, 43.1, 44.8, 45.5, 46.8, 50.5, and 54.0 at. pct carbon by using galvanic cells of the type (−) V, VF₃, CaF₂ // CaF₂ // CaF₂, VF₃, ‘V-C’ (+) The measurements were carried out in the temperature range of 816 to 1008 K. The relative partial molar Gibbs energies of carbon have been calculated in the same composition range. The relative integral molar Gibbs energy in the VC single-phase region can be expressed asG ^M = −98,850 + 72,242X_C + (24.81 −37.23X _C)TJ/mol The standard Gibbs energies of formation of V₄C_3-x and V₂CC can be represented as ΔG° = −67,208 + 9.37T J/mol of V_0.60C_0.40 and ΔGδ = −62,581 + 7.10T J/mol of Va66Co.34 respectively.     

Calculation and evaluation of the gibbs energies of formation of Cr3C2, Cr7C3, and Cr23C6

A thermodynamic analysis of chemical composition data for a series of iron alloys containing chromium and carbon has been completed. These data were obtained from literature compilations for alloys equilibrated for extended times at 700 °C under neutral atmospheres. The results of this analysis, when supplemented with thermochemical data from the literature, permitted the calculation of the standard Gibbs energies of formation for the chromium carbides Cr₇C₃ and Cr₂₃C₆ over the range 600 to 1000 °C. These standard Gibbs energies were compared to data for these carbides from other sources. Available Gibbs energy data for the third pure chromium carbide, Cr₃C₂, were also evaluated. For each of these three compounds, a separation of the values for the Gibbs energy of formation into two distinct groups was observed. Each of these groups can be classed according to the nature of the experimental study used, whether it be a high temperature solid-gas equilibration involving a system of a carbide-chromic oxide-carbon (or chromium) with carbon monoxide, on one hand, or a series of investigations concerned mainly with electrolytic cell measurements, plus the work on which the present study is based. It is suggested that the differences in the Gibbs energies of formation for the respective carbides are associated with 1) the nonstoichiometric nature of these carbides and 2) possible dissolution of oxygen in the carbides during the equilibration studies.     

Phase relations and gibbs energies in the system Mn-Rh-O

Phase relations in the system Mn-Rh-O are established at 1273 K by equilibrating different compositions either in evacuated quartz ampules or in pure oxygen at a pressure of 1.01 × 10⁵ Pa. The quenched samples are examined by optical microscopy, X-ray diffraction, and energy-dispersive X-ray analysis (EDAX). The alloys and intermetallics in the binary Mn-Rh system are found to be in equilibrium with MnO. There is only one ternary compound, MnRh₂O₄, with normal spinel structure in the system. The compound Mn₃O₄ has a tetragonal structure at 1273 K. A solid solution is formed between MnRh₂O₄ and Mn₃O₄. The solid solution has the cubic structure over a large range of composition and coexists with metallic rhodium. The partial pressure of oxygen corresponding to this two-phase equilibrium is measured as a function of the composition of the spinel solid solution and temperature. A new solid-state cell, with three separate electrode compartments, is designed to measure accurately the chemical potential of oxygen in the two-phase mixture, Rh + Mn_3−2xRh_2xO₄, which has 1 degree of freedom at constant temperature. From the electromotive force (emf), thermodynamic mixing properties of the Mn₃O₄-MnRh₂O₄ solid solution and Gibbs energy of formation of MnRh₂O₄ are deduced. The activities exhibit negative deviations from Raoult’s law for most of the composition range, except near Mn₃O₄, where a two-phase region exists. In the cubic phase, the entropy of mixing of the two Rh³⁺ and Mn³⁺ ions on the octahedral site of the spinel is ideal, and the enthalpy of mixing is positive and symmetric with respect to composition. For the formation of the spinel (sp) from component oxides with rock salt (rs) and orthorhombic (orth) structures according to the reaction, MnO (rs) + Rh₂O₃ (orth) → MnRh₂O₄ (sp),ΔG° = -49,680 + 1.56T (±500)J mol⁻¹ The oxygen potentials corresponding to MnO + Mn₃O₄ and Rh + Rh₂O₃ equilibria are also obtained from potentiometric measurements on galvanic cells incorporating yttria-stabilized zirconia as the solid electrolyte. From these results, an oxygen potential diagram for the ternary system is developed.     

The standard gibbs energy of formation of CeF3 and its activity coefficient in cryolite

Literature data are analyzed to give the activity coefficient (γ_Ce) of Ce in dilute solution in Al as log₁₀γ_Ce = −11 356/T + 4.261 referred to liquid Ce as standard state. Measurements were made in the range of 977 to 1288 K of the equilibrium Al (1) + CeF₃ (s) = AlF₃ (s) + Ce(Al) and give, by a third-law calculation, °G ^o = 183 360 + 19.456T joules, and Δ _{fH 298} ^o of CeF₃ = −1701 kJ mol⁻¹. Values of the partition coefficient of Ce between Al and molten cryolite then give activity coefficients of CeF₃ in solution. These activity coefficients decrease as the NaF/AlF₃ ratio is raised, showing acid behavior of CeF₃. It appears to dissolve mainly in the form of Na₂CeF₅.     

Determination of standard free energies of formation of Ca3P2 and Ca2Sn at high temperatures

The standard free energies of formation of calcium phosphide and calcium stannide were determined by a chemical equilibration technique, yielding the following results: 3Ca(1) + P₂(g) = Ca₃P₂(s) ΔG° = −653,460(±7110) + 144.01(±4.98)T (J/mol)1000 °C to 1300 °C2Ca(1) + Sn(1) = Ca₂Sn(s) ΔG° = −353,970(±1670) + 79.28(±1.26)T (J/mol)1000 °C to 1300 °C 1120 °C The experimental data to express the thermodynamics for removal of phosphorus and tin from molten iron by calcium based slags by other investigators were discussed in terms of the activity co-efficients of Ca₃P₂ and Ca₂Sn in slag melts by using the present results described above.     

EDTA滴定法测定新型复合脱氧剂中的CaC2和CaF2

利用碳化钙易溶解于稀醋酸,而氟化钙不溶解于稀醋酸的特性,以稀醋酸处理试样,用滤纸过滤不溶物后,滤液加氢氧化钾溶液调节pH值≥13,用EDTA滴定法测定CaC2含量。不溶物连同滤纸放在铂金坩锅中灰化、灼烧,加含有硼酸的混合熔剂,于950℃左右熔融,酸化浸取后,加氢氧化钾溶液调节试液至pH值≥13,用EDTA滴定法测定CaF2含量。测定结果表明,CaC2RSD为0.0645%～0.1016%,CaF2RSD为0.6285%～0.8357%。     

Determination of gibbs energy of formation of Ni-B-O system by electromotive force measurement using solid electrolyte

The standard Gibbs energies of formation of Ni₃B, Ni₂B, o-Ni₄B₃(Ni_0.586B_0.414), m-Ni₄B₃(Ni_0.564B_0.436), NiB, and Ni₃B₂O₆ of the Ni-B-O system have been determined by measuring electromotive forces of galvanic cells using a Y₂O₃-stabilized ZrO₂ solid oxide electrolyte. The results are as follows:

Phase equilibria in the system NiO-CaO-SiO2 and gibbs energy of formation of CaNiSi2O6

Phase relations in the pseudoternary system NiO-CaO-SiO₂ at 1373 K are established. The coexisting phases are identified by X-ray diffraction and energy-dispersive X-ray analysis of equilibrated samples. There is only one quaternary oxide CaNiSi2O6 with clinopyroxene structure. The Gibbs energy of formation of CaNiSi₂O₆ is measured using a solid state galvanic cell incorporating stabilized zirconia as the solid electrolyte in the temperature range of 1000 to 1400 K: From the electromotive force (emf) of the cell, the Gibbs energy of formation of CaNiSi₂O₆ from NiO, SiO₂, and CaSiO₃ is obtained. To derive the Gibbs energy of formation of the quaternary oxide from component binary oxides, the free energy of formation of CaSiO₃ is determined separately using a solid state cell based on single crystal CaF₂ as the electrolyte: The results can be expressed by the following equations: