Gaseous complexes formed between trichlorides (A1C13 and FeC13) and dichlorides

It has been found that in general the volatility of dichlorides is much enhanced in the presence of gaseous A1C1₃ and FeCl₃, and the existence of the complexes MA1₂C1₈, MAl₃Cl₁₁, and MFe₂Cl₈ is postulated. ΔH _T, ΔS _T, andT for MCl₂(s) + 2AlCl₃(g) = MAl₂Cl₈(g) are CaCl₂: −17.8 kcal, −25.7 cal K⁻¹ at 900 °K; CoCl₂: −15.2, −19.4 at 750°K; MgCl₂: −13.8, −17.9 at 800°K; MnCl₂: −15.8, −20.9 at 750°K; NiCl₂: −16.3, −24.2 at 750°K. For MCl₂(s) + 3AlCl₃(g) = MAl₃Cl₁₁(g) − CaCl₂: −30.0, −40.5 at 900°K; CoCl₂: −36.6, −47.4 at 700°K; MgCl₂: −42.6, −55.4 at 750°K; MnCl₂: −33.3, −42.0 at 750°K. For MCl₂(s) + 2FeCl₃(g) = MFe₂Cl₈(g) − CdCl₂: −19.4, −20.9 at 700°K: CoCl₂: −16.5, −17.2 at 800°K, MnCl₂: −19.1, −21.2 at 750°K; NiCl₂: −19.7, −24.4 at 800°K. Enhanced volatility was also found for ZnCl₂, PbCl₂, and CuCl, but since the condensed phase was liquid of unknown composition no calculations could be made. Owing to the interplay of the above equilibria with the dimerization equilibria for A1C1₃ and FeCl₃ the effective vapor pressures of the dichlorides in the presence of the trichlorides pass through maxima in the region 600° to 700°C.     

The thermal capacity and enthalpy of gadolinium sesquiselenide over a wide temperature range

Measurements have been made on the thermal capacity of γ-Gd₂Se₃ at 58.88–298.34 K. Values have been obtained for the thermal capacity, entropy, reduced Gibbs energy, and enthalpy under standard conditions: C°_p = 125.87 ± 0.5 J· mole⁻¹ · K⁻¹; S°(298.15 K) = 196.5 · 1.6 J · mole⁻¹ · K⁻¹; Φ°(298.15 K) = 103.6 ± 1.6 J · mole⁻¹ · K⁻¹; H°(298.15 K)-H°(0) = 27681 ± 138 J · mole⁻¹. The enthalpy of Gd₂Se₃ has been measured and the major thermodynamic functions have been calculated for the solid and liquid states over the temperature range 450–2300 K. The temperature dependence of the enthalpy in the ranges 300–1800 K and 2000–2300 K are represented: H°(T)-H°(298.15 K) = = 1.1949 · 10⁻² · T² + 122.38 · T + 347402 · T⁻¹ − 38716 and H°(T)-H°(298.15 K) = 262.81 · T-− 196047, respectively. The calculated temperature, enthalpy, and entropy of melting for Gd₂Se₃ are: T_m = 1925 ± 40 K, Δ_mH° (Gd₂Se₃) = 68.5 kJ · mole^-1, Δ_mS°(Gd₂Se₃) = 35.6 J · mole⁻¹ · K⁻¹. __________ Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 56–61, March–April, 2006.     

A generalized approach to the flood-knapp structure based model for binary liquid silicates: Application and update for the PbO-SiO2 System

The nonideal activity of a metal oxide in a molten binary silicate system is described by treating the liquid as an ideal solution and by considering the formation of a few complexes. Application of this approach to the binary system PbO-SiO₂ shows that the experimentally determined activity of PbO(l) can be modeled by considering the lead silicate melt as an ideal solution of Pb²⁺ and O²⁻,SiO ₄ ⁴⁻ , Si₂O ₇ ⁶⁻ , Si₁₂O ₃₇ ²⁶⁻ , and Si₄O ₁₀ ⁴⁻ . The calculated Gibbs free energy values for the formation of the anionic complexes from O²⁻ and SiO ₄ ⁴⁻ are: ΔGℴ(Si₂O ₇ ⁶⁻ )/J · mol⁻¹ = 38977 − 30.909(T/K); ΔGℴ(Si₁₂O ₃₇ ²⁶⁻ )/J · mol⁻¹ = 200158 − 121.813(T/K); Δℴ(Si₄O ₁₀ ⁴⁻ )/J · mol⁻¹ = 104627 − 28.094(T/K). Values of Gibbs free energy of formation of the solid phases PbO, Pb₄Si0₆, Pb₂SiO₄, PbSiO₃, and SiO₂ which, together with the melt model data, give the best fit to experimental phase relations in the system PbO-SiO₂ were calculated. These values are all in good agreement with literature data.     

The thermodynamic behavior of sulfur in molten nickel and nickel-base alloys

The thermodynamic properties of dilute solutions of sulfur in pure liquid nickel were investigated at 1500, 1550, and 1575°C for sulfur concentrations up to 0.7 wt pct. Based on the infinitely dilute, wt pct standard state, the equilibrium data obtained for the reaction: H₂(g) + S = H₂S(g) were fitted by the equations: logK = − 1489/T − 1.772, and ΔG° = 6812 + 8.11T, cal/mole. For the solution ofS ₂(g) in pure Ni according to the reaction: 1/2S ₂(g) = S (in Ni), the standard free energy of solution is found to be: ΔG° = - 28,342 + 3.62T, cal/mole. For the very dilute solutions of sulfur normally encountered in nickel-base melting, the activity coefficient of sulfur in pure Ni at 1575°C is given by: log f_S= -0.035 (pct S). The effects of alloying elements normally used in nickel-base alloys on the activity coefficient of sulfur in molten nickel were investigated. The activity coefficient of sulfur is increased by all of the alloying elements studied, as evidenced by the interaction parameters: e_S ^fe = +0.005, e_S ^Cr = +0.030, e_S ^Mo = +0.053, e_S ^Ti = +0.160, and e_S ^A1 = +0.133. Measured values of the activity coefficient of sulfur in the quaternary system Ni-S-Cr-Fe agreed reasonably well with those predicted from binary and ternary data. This work constitutes a portion of the work performed by W. F. VENAL for the Ph.D. degree from the University of Illinois at Chicago Circle. Formerly Professor of Metallurgical Engineering at UICC.     

On the Gibbs energy of formation of wustite

Gibbs energy change for the reactionxFe_(s) + 1/2O_2(g) = Fe _x O_(s) has been redetermined using the galvanic cell (−) Fe_(s), Fe _x O_(s)∥ZrO₂ − CaO∥NiO_(s), Ni_(s)(+) in the temperature range 866 to 1340 K. The results are at variance with earlier works in that they reflect the transformations occurring in the iron phase. The Gibbs energy function is represented by two nonlinear equations,viz., ΔG° (866 to 1184 K) = −251480 − 18.100T + 10.187T lnT ± 210 J/mol and ΔG° (1184 to 1340 K) = −286248 + 181.419T - 13.858T lnT ± 210 J/mol. Formerly Research Assistant at the Department of Theoretical Metallurgy, The Royal Institute of Technology, Stockholm     

Thermodynamic properties of Ni-S melts between 700° and 1100°c

The vapor pressure of sulfur over Ni-S melts of various compositions was calculated from the equilibrium weight of the melt in gas streams of known H₂S-H₂ composition. The Gibbs-Duhem equation was used to calculate the activity of nickel and other thermodynamic properties. For the reaction: 3Ni(S) + S₂(g) ⇌ Ni₃S₂(l) the suggested free energy rslationship is: ΔG° = -57,910 + 15.89T (800° to 1100°C). The Calculations were extrapolated to predict that for the reaction: Ni(s) + 1/2S₂(g) ⇌ NiS(l), ΔG° = -26.730 + 10.5T (1000° to 1100°C)     

Activities of oxygen in liquid Bi,Sn, and Ge from electrochemical measurements

Modified coulometric titrations on the galvanic cell: O in liquid Bi, Sn or Ge/ZrO₂( + CaO)/Air, Pt, were performed to determine the oxygen activities in liquid bismuth and tin at 973, 1073 and 1173 and in liquid germanium at 1233 and 1373 K. The standard Gibbs energy of solution of oxygen in liquid bismuth, tin and germanium for 1/2 O₂ (1 atm) →O (1 at. pct) were determined respectively to be ΔG° (in Bi) = −24450 + 3.42T (±200), cal· g-atom⁻¹ = − 102310 + 14.29T (±900), J·g-atom⁻¹, ΔG° (in Sn) = −42140 + 4.90T (±350), cal· g-aton⁻¹ = −176300 + 20.52T (± 1500), J-g-atom⁻¹, ΔG° (inGe) = −42310 + 5.31 7 (±300), cal·g-atom⁻¹ = −177020 + 22.21T(± 1300), J· g-atom⁻¹, where the reference state for dissolved oxygen was an infinitely dilute solution. It was reconfirmed that the modified coulometric titration method proposed previously by two of the present authors produced far more reliable results than those reported by other investigators. TOYOKAZU SANO, formerly a Graduate Student, Osaka University     

Desulfurization of iron alloys in vacuo-free energy of formation of SiS (v)

The rate of desulfurization of Fe-C-Si-S meltsin vacua (10 ώm pressure) has been investigated using 15 kg alloys melted by induction heating. For the sulfur contents from 0.008 to 0.1 pct investigated, the rate is a first-order type with respect to sulfur. Over this sulfur concentration range and in the presence of carbon up to saturation and silicon from 0 to 5 pct, the sulfur activity is sufficiently high that the fractional surface coverage by adsorbed sulfur is within 0.75 < θ_S < 1. The rate equation derived to satisfy the experimental findings for the limiting case of θ_S → 1 indicates that sulfur is evolved primarily via two activated reactions involving (SiS₂)° and (S₂)°. These complexes then produce SiS and S vapor species. At 1600°C the rates of formation of these volatile species are about one fourth of those for free vaporization of SiS and sulfur, respectively. The apparent heats of activation are ∼47 kcal for SiS and ∼37 kcal for sulfur vapor. Using an apparatus involving a Knudsen cell and the Bendix mass spectrometer, the enthalpy of reaction SiS₂(s) + Si(s) = 2SiS(v) has been measured, giving 102.2 kcal. Combining this with other thermodynamic data, the free energy of formation of SiS vapor is evaluated as Si(s) + 1/2S₂(v) = SiS(v) δF° = 15,500-19.5T from 1000° to 1686°K Si(l)+ 1/2S₂(v)= SiS(v) δF°= 3500 -12.4T above 1686°K     

Quantitative differential thermal analysis of polymorphic transformations in LaGe1.8 and SmSi2

The possibility of using quantitative differential thermal analysis to investigate phase transformations is examined. The temperature, enthalpy, and entropy of polymorphic transformations in LaGe_1.8 and SmSi₂ are determined: T_tr = 724 K, Δ_trH = 1635 ± 79 J · mole⁻¹, Δ_trS = 2.3 ± 0.1 J · mole⁻¹ · K⁻¹ (LaGe_1.8); T_tr = 658 K, Δ_trH = 1384 ± 69 J · mole⁻¹, Δ_trS = 2.1 ± 0.1 J · mole⁻¹ · K⁻¹ (SmSi₂). __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 72–78, 2007.     

Standard enthalpies of formation of TiSi2 and VSi2 by high-temperature calorimetry

The standard enthalpies of formation of TiSi₂ and VSi₂ have been measured by a new calorimetric method. The following results are reported: ΔH _f ^° (TiSi₂) = −(170.9 ± 8.3) kJ mol⁻¹ and ΔH _{f ^°} (VSi₂) = −(112.4 ± 6.0) kJ mol⁻¹. These results are compared with experimental, assessed, and predicted values reported in the literature and with our own data for the corresponding borides. Estimates are given for the enthalpies of formation of the silicides of scandium and chromium.     

Thermodynamics of the system NaF-Alf3. part ii: The free energies of formation of cryolite (Na3AlF6) and chiolite (Na5Al3F14)

The theory of the solid-electrolyte cells is given, and it is shown that cryolite itself with Ca²⁺ in solid solution is a suitable Na⁺-ion conductor. Experimental electromotive forces for the ranges 570° to 725°C and 570° to 670°C, r − 18,960 cal with a standard deviation of ±36 cal (based on a third-law calculation). For 5NaF(s) + 3AlF₃(s) = Na₅Al₃F₁₄(s), ΔG° = −38,560 − 7.081T with a standard deviation of ±130 cal. Combination of these results with recent values for Al + 3/2 F₂ = A1F₃ and for 6NaF + Al = Na₃AlF₆ + 3Na gives ΔH°_f298(Na₃AlF₆) = −792,400 cal and ΔH°_f298(NaF) = −137,530 cal. The latter is in excellent agreement with the most recent critical assessment.     

Gibbs energies of formation of intermetallic phases in the systems Pt-Mg,Pt-Ca,and Pt-Ba and some applications

The standard Gibbs energies of formation of platinum-rich intermetallic compounds in the systems Pt-Mg, Pt-Ca, and Pt-Ba have been measured in the temperature range of 950 to 1200 K using solid-state galvanic cells based on MgF2, CaF2, and BaF2 as solid electrolytes. The results are summarized by the following equations: ΔG° (MgPt₇) = −256,100 + 16.5T (±2000) J/mol ΔG° (MgPt₃) = −217,400 + 10.7T (±2000) J/mol ΔG° (CaPt₅) = −297,500 + 13.0T (±5000) J/mol ΔG° (Ca₂Pt₇) = −551,800 + 22.3T (±5000) J/mol ΔG° (CaPt₂) = −245,400 + 9.3T (±5000) J/mol ΔG° (BaPt₅) = −238,700 + 8.1T (±4000) J/mol ΔG° (BaPt₂) = −197,300 + 4.0T (±4000) J/mol where solid platinum and liquid alkaline earth metals are selected as the standard states. The relatively large error estimates reflect the uncertainties in the auxiliary thermodynamic data used in the calculation. Because of the strong interaction between platinum and alkaline earth metals, it is possible to reduce oxides of Group ILA metals by hydrogen at high temperature in the presence of platinum. The alkaline earth metals can be recovered from the resulting intermetallic compounds by distillation, regenerating platinum for recycling. The platinum-slag-gas equilibration technique for the study of the activities of FeO, MnO, or Cr₂O₃ in slags containing MgO, CaO, or BaO is feasible provided oxygen partial pressure in the gas is maintained above that corresponding to the coexistence of Fe and “FeO.” Formerly Professor and Chairman, Department of Metallurgy, Indian Institute of Science Formerly Visiting Scientist, Department of Metallurgy, Indian Institute of Science     

Enthalpies of formation of liquid and solid (gallium + palladium) alloys

The enthalpies of formation of liquid (Ga + Pd) alloys were determined by direct reaction calorimetry in the temperature range 1322 <T/K < 1761 and the molar fraction range 0 <x _Pd < 0.87. The enthalpies are very negative with a minimum Δ_mix H _m = −70.4 ± 3.0 kJ mol_-1 atx _Pd = 0.6, independent of the temperature. Limiting partial molar enthalpies of palladium and gallium were calculated as Δh _m (Ga liquid in ∞liquid Pd) = −265 ± 10 kJ mol₋₁ and Δh _m (Pd liquid in ∞liquid Ga) = -144 ± 5 kJ mol₋₁. The integral molar enthalpy is given by Δ_mix H _m =x(1-x) (-143.73 -232.47x + 985.77x ²-4457.8.x ³ + 6161.1x ⁴ + 2577.4x ⁵), wherex = x _Pd. Moreover, values for the enthalpies of formation and fusion of PdGa, Pd₂Ga, and the solid solution (withx _Pd = 0.8571) have been proposed. These results have been discussed taking into account the equilibrium phase diagram. Formerly Ph.D. student, Université de Provence     

Standard enthalpy of formation of Sc5Si3

The standard enthalpy of formation of Sc₅Si₃ has been determined by solute-solvent drop calorimetry at (1473±2) K. The following value is reported: ΔH _f ^o (mean)=−(719.1±34.0) kJ mol⁻¹. This result is compared with corresponding published values for the enthalpies of formation of Me₅Si₃, with Me=Mn, Cr, V, Ti. This comparison shows regularly increasing negative enthalpies of formation from Mn₅Si₃ to Sc₅Si₃. LETTTIA TOPOR, formerly Senior Research Associate, The James Franck Institute, The University of Chicago,     

Thermodynamics of the Ca-S-O,Mg-S-O,and La-S-O systems at high temperatures

High temperature thermodynamic data for equilibria in the Ca-S-O, Mg-S-O, and La-S-0 systems were determined by a galvanic cell technique using calcia stabilized zirconia (CSZ) solid electrolytes. The measured emf data were used to calculate the standard free energy changes of the following reactions: [1] CaO(s) + 1/2S₂(g) → CaS(s) + 1/2O₂(g) 1000 to 1350 K ΔG° = 21906.9 − 0.8T(K)(±400 cal) = 91658 − 3.37 (±1700 J) [2] CaS(s) + 2O₂(g) → CaSO₄(s) 1050 to 1450 K ΔG° = -227530.7 + 80.632T(K) (±400 cal) = -951988.5 + 337.4T (±1700 J) [3] CaO(s) + 3/2O₂(g) + 1/2S₂(g) → CaSO₄(s) 1050 to 1340 K ΔG° = -204892.7 + 79.83T(K)(±400 cal) = -857271.1 + 334.0T (±1700 J) [4] MgO(s) + 1/2S₂(g) → MgS(s) + 5O₂(g) 1000 to 1150 K ΔG° = 45708.6 − 2.897(K)(±500 cal) = 191244.8 − 12.1T (±2100 J) [5] La₂O₃(s) + 1/2S₂(g) → La₂O₂S(s) + 1/2O₂(g) 1080 to 1350 K ΔG° = 17507 − 2.32T(K)(±380 cal) = 73249.3 − 9.7T (±1600 J) [6] La₂O₃S(s) + S₂(g) → La₂S₃(s) + O₂(g) 950 to 1120 K ΔG° = 70940 + 2.25T(K)(±500 cal) = 296812.9 + 9.47 (±2100 J) The ΔG° values of reaction [5] were combined with the literature data for ΔG°_f(La₂O₃) to obtain the standard free energy of formation of La₂O₂S at high temperatures. The values of ΔG°_f thus calculated for La₂O₂S were combined with the ΔG° data for reaction [6] to obtain the standard free energy of formation of La₂S₃ at high temperatures.     

The Decomposition equilibria of platinum di- and mono-chlorides by the simultaneous torque-knudsen technique

The decomposition equilibria of platinum dichloride have been found to consist of two decomposition steps, with chlorine molecules being the vapor species for both steps. An intermediate metastable PtCl solid is formed in the first step in addition to platinum metal and chlorine molecules. The platinum dichloride decomposes incongruently, the stepwise decomposition being PtCl₂ → PtCl → Pt. The PtCl₂ decomposition reactions consist of PtCl₂(s) = PtCl (metastables) + 1/2 Cl₂ (g) and PtCl₂(s) = Pt(s) + Cl₂ (g). The sum of the third lawΔH _{D, 298} K for the above two reactions is 214.637 ± 1.963 kJ/mole, in very good agreement with the second law ΔH_{D, 298 K} = 215.107 ± 13.062 kJ/mole. The second decomposition step is given by the reaction 2PtCl (metastables) = 2Pt(s) + Cl₂ (g) with a third law ΔH_{D, 298 K} = 127.356 ± 0.791 kJ/mole, in excellent agreement with the second law ΔH_{D, 298 K} = 127.509 ± 6.154 kJ/mole. The calculated heat of formation of PtCl₂ is -139 ± 2 kJ/mole and that of PtCl is -63 ± 1 kJ/mole. Formerly Graduate Assistant. Formerly Undergraduate Research Helper,     

Standard molar enthalpies of formation of MeAl (Me = Ru,Rh, Os,Ir)

The standard molar enthalpies of formation of RuAl, RhAl, and IrAl have been determined by the direct combination method using a high-temperature calorimeter operated at (1473 ±2) K. The following values are reported: ΔH _f ^o (RuAl) = −(124.1 ± 3.3) kJ/mol; ΔH _f ^o (RhAl) =-(212.6 ± 3.2) kJ/mol; and ΔH _f ^o (IrAl) = -(185.5 ± 3.5) kJ/mol. For OsAl, an approximate value is −77 kJ/mol. The results are compared with available data for related alloys and with predicted values.     

A solid state emf study of the pyrrhotite-magnetite equilibrium in the temperature interval 850 to 1275 K

The equilibrium 3/(1 −x)Fe_1−x S(s) + (5 − 2x)/(1 −x)O₂(g) Fe₃O₄(s) + 3/(1 −x)SO₂(g) was studied in the temperature interval 850 to 1275 K by measuring oxygen potentials in a galvanic cell containing calcia stabilized zirconia as solid electrolyte. The SO₂ activity was controlled by equilibrating the solid phases pyrrhotite and magnetite with a continuously flowing SO₂-Ar gas mixture of known composition. Formation of S₂ gas was taken into account and a recently published thermodynamic model for the pyrrhotite phase⁴ was used to derive the Gibbs energy change for the pyrrhotite-magnetite equilibrium and for the formation of Fe_1−x S as a function of the variables temperature and pyrrhotite composition.     

Thermodynamics of the system NaF-AlF3 Part I: The equilibrium 6NaF(s) + Al = Na3AlF6(s) + 3Na

The pressure of sodium existing over a mixture of aluminum and NaF has been measured by a gas-transference method over the range 635° to 816°C. The results (corrected for the presence of Na₂) give for the reaction 6NaF(s) + A1(l) =Na₃AlF₆(s) + 3Na(g) ΔH°₂₉₈ = +107,970 ± 220 cal (standard deviation) or ±60 cal (standard error). The corresponding activities of Na(l) may be expressed by log a_Na = −2,854/T − 0.853 log T + 4.303 The sodium content of aluminum in equilibrium with NaF(s) and Na₃AlF₆(s) has been determined over the range 679° to 876°C. The activity coefficient of sodium in aluminum is given byRT In γ_Na/n ₂ ^Al = 8290 + 3.73 T The present results are not consistent with the suggestion that Na₂F is an important gaseous species in this system.     

Thermodynamics of the Mn-P system

The free energy of mixing in the Mn-P melts in the composition range ofX _p = 0.0 to 0.333 was estimated by coupling the phase boundary information with reliable ΔG° formation for the Mn2P phase. This information was used to obtain the dilute solution properties of P in Mn. P_(l,pure) = P_{(l,Henrian, Mn)} ΔG ^°(Joules) = -203,611.39 + 41.003T The free energy is shown to be more negative than in the Fe system, reflecting a stronger interaction between Mn and P atoms than between Fe and P atoms. Presenting the activity coefficient of P with the expression used by Lupis and Elliott, the first and second interaction coefficients are obtained as follows: ε _P ^P (Mn) = 10.538 + 9728.14/T ρ _P ^P (Mn) = 28.148 + 9101.83/T The Gibbs free energy of formation for Mn₃P was estimated in the temperature range of {dy1233} to {dy1378} K to be 3Mn _l + P_(l = Mn₃P_(s ΔG ^°(Joules) = -241,461.65 + 65.031T