The Fe-P (iron-phosphorus) system

The Fe-Si system has been studied extensively due to its importance in steelmaking and electrical-magnetic applications. Thermodynamic and phase diagram data of the Fe-Si system available in the literature were critically evaluated and re-optimized to improve the thermodynamic description of this system. Two sets of optimized model parameters were obtained to reproduce the available and reliable literature data. In each set of parameters, the liquid phase was described using the modified quasi-chemical model or the Bragg-Williams random mixing model. The A2/B2 and B2/D03 order-disorder transitions were also taken into account in the present study.

Critical reassessment of the Fe-Si system

A data base of thermochemical parameters for liquid iron-base alloys containing C, N, Ti, Si, Mn, S, and P is presented. A matrix of linear inequalities describing the experimental data among these elements was constructed. A set of internally consistent thermochemical data permitted by the uncertainties of the experiments was evaluated by means of a linear programming algorithm. Expressions for the interaction parameters of the solutes and the Gibbs energies of formation of the carbides, nitrides, carbonitrides, and sulfides of titanium were simultaneously optimized. It is shown that the resulting thermochemical data base reproduces the experimental data satisfactorily.

Simultaneous optimization of thermochemical data for liquid iron alloys containing C, N, Ti, Si, Mn, S, and P

Differential scanning calorimetry (DSC) has been used to measure the heat capacities of iron phosphides Fe3P, Fe2P and FeP in the temperature range 113–873 K. Simultaneously a Knudsen effusion method with mass-spectrometric analysis of the gaseous phase has been applied to investigate the thermodynamic properties of iron phosphides (1041–1549 K), bcc solid solutions Fe–P (1384–1619 K) and Fe–P liquid alloys (1349–1811 K). ΔfS of the iron phosphides calculated according to the second and third laws of thermodynamics agree within the limits of experimental error. ΔfG of the phosphides produced from γ-Fe and P2 gas have been approximated with the following equations (in J mol–1): ΔfGFe3 P=–(239 076 ± 2269)+(80.44 ± 1.70)T, ΔfGFe2 P=–(231 728 ± 1110)+(79.95 ± 0.81)T, ΔfGFeP=–(193 892 ± 2700)+(82.10 ± 2.30)T. The thermodynamic behaviour of P diluted in α-Fe obeys Henry's law, the non-magnetic part of the excess Gibbs energy of mixing of the bcc solid solution being equal to (standard states: α-Fe and white P)ΔfGex(nm)=(–280.4T+ 0.195T2–3.70 × 10–5T3)XPXFe J mol–1. The thermodynamic properties of liquid solutions have been described with the ideal associated-solution model assuming that Fe3P, Fe2P and FeP complexes exist in the melt. The phase diagram computed with the help of the thermodynamic data agrees with the published information.

Thermodynamic properties and phase equilibria in the Fe–P system

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.

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

Mass Spectrometric Determination of Activities of Phosphorus in Liquid Fe-P-Si, Al, Ti, V, Cr, Co, Ni, Nb, and Mo Alloys

The interaction coefficients for phosphorus have been determined in the Fe-P-i systems at 1600°C. A Knudsen cell-mass spectrometer combination was used, and the interaction coefficients were computed from the ratio of the intensities of P+ and Fe+. The measured systems are Fe-P-Si, Fe-P-Ti, Fe-P-Al, Fe-P-V, Fe-P-Cr, Fe-P-Co, Fe-P-Ni, Fe-P-Nb and Fe-P-Mo.The experimental results show that the interaction coefficients for phosphorus with the elements in the fourth and fifth periods increase with the atomic number of the elements.The results obtained are summarized as follows; eSiP=11.9±0.6 eAlP=4.6±0.7 eTiP=-8±2 evp=-4.9±0.7 eCrp=-3.8±0.7 eCoP=0.9±0.7 eNiP=0.7±0.7 eNbP=-5.4±1.2 eMoP=-0.4±0.7

Effect of Dilute Concentrations of Si, Al, Ti, V, Cr, Co, Ni, Nb and Mo on the Activity Coefficient of P in Liquid Iron

The vapor pressures of phosphorus gases, P and P2, above Fe-P alloys have been determined by a newly developed experimental method. In this experimental method, phosphorus in the deposit film obtained by the Knudsen effusion method with collection technique was determined by a secondary ion mass spectrometer. The vapor pressures of P and P2 have been obtained from these determined values and the ratio of the ion currents of P+ to those of P+2 which had been obtained by the ordinary Knudsen cell-mass spectrometer combination. The standard free energy changes of the reactions for liquid Fe-P alloy system were calculated from these vapor pressures, and the following values have been obtained.P(g)=P(wt%)ΔG°=-95.3+1.55×10-2T(±2.2)(kcal/mol)1/2P2(g)=P(wt%)ΔG°=-37.7+0.13×10-2T(±1.1)(kcal/mol)P(g)=1/2P2(g)ΔG°=-57.6+1.42×10-2T(±1.1)(kcal/mol)(1-3wt% P, 1590-1650°C)

https://www.jstage.jst.go.jp/article/tetsutohagane1955/66/14/66_14_2032/_pdf

Keisaku Yamada

Papers

Mass Spectrometric Determination of Activities of Phosphorus in Liquid Fe-P-Si, Al, Ti, V, Cr, Co, Ni, Nb, and Mo Alloys

Effect of Dilute Concentrations of Si, Al, Ti, V, Cr, Co, Ni, Nb and Mo on the Activity Coefficient of P in Liquid Iron

The Standard Free Energies of Dissolution of Phosphorus Gases in Liquid Iron

Mass Spectrometric Determination of Activity of Phosphorus in Liquid Fe-P Alloy

The Standard Free Energies of Dissolution of Phosphorus Gases in Liquid Iron