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 system NaF-AlF3. Part IV: The cryolite liquidus curve

The theory of the variation of activity of a binary compoundAXB with composition in a $$a_{A_x B} = {\text{ }}K \cdot a_A^x \cdot a_B $$ the activity coefficient should be defined as $$\gamma _{A_x B} {\text{ = }}K \cdot \gamma _A^x {\text{ }} \cdot {\text{ }}\gamma _B {\text{ = }}a_{A_x B} {\text{/(}}n_A^x {\text{ }} \cdot {\text{ }}n_B {\text{)}}$$ K is chosen so that^aA_xb is unity in the stoichiometric liquid (or, if preferred, so that γA_XB is unity). Such an activity coefficient possesses the property of approaching a limiting value at the stoichiometric composition, and the analog of Raoult’s law is^aA_xB∝ n_A ^x nB From this it follows that a plot of log (n_A ^x nB) against 1/T should show the same limiting tangent for points on both sides of the liquidus curve. Data for Na₃AlF₆ do not pass this test. With the aid of previously measured activities the discrepancy can be resolved if it be assumed that the solid material separating has a composition (2.824 ±0.005)NaF A1F₃; the calculated enthalpy of fusion of this material is 24,270 cal/gfw, and the standard deviation of the liquidus points from the least-squares line is ±2.3 deg.     

Thermodynamics of the system NaF-AlF3: Part VII. Non-stoichiometric solid cryolite

Earlier data are recalculated to give the boundaries of the homogeneous field of solid cryolite. The equilibrium constant

Na3AlF6 -Al2O3二元系熔度与熔盐结构

采用热分析与相平衡相结合的方法研究了Na3AlF6-Al2O3二元系的熔度,发现了此体系是一简单共晶系,共晶组成位于含Al2O3质量分数为10.2%处.加入不同量的Al2O3,根据凝固点降低公式,推算出Na3AlF6-Al2O3熔体的熔盐质点结构并且研究了氧化铝在冰晶石熔体中溶解的机理及带来的影响.     

Na3AlF6-Al2O3二元系熔度与熔盐结构

采用热分析与相平衡相结合的方法研究了Na3AlF6-A2lO3二元系的熔度，发现了此体系是一简单共晶系，共晶组成位于含Al2O3质量分数为10.2％处。加入不同量的AlO3根据凝固点降低公式，推算出Na3AlF6-Al2O3熔体的熔盐质点结构并且研究了氧化铝在冰晶石熔体中溶解的机理及带来的影响．     

Phase stability investigations of the palladium-cadmium system: part ii. structural studies

The crystal structure and the precise lattice parameters of palladium-cadmium alloys containing 33 to 60 at. pct Cd were determined by X-ray diffraction at 294 K, using samples quenched from 1073 K. The results indicate that at 1073 K the β₁(Ll₀) phase extends from 33 to 55 at. pct Cd while the β′(B2) phase is stable from 56 to 60 at. pct Cd. No evidence for the existence of a separate high-temperature phase between the β, and β′ phase fields was found. A modification of the currently accepted Pd-Cd phase diagram near the equiatomic composition is proposed. The lattice parameters of the fct β₁ - phase have the following values at the stoichiometric composition:a = 0.4 2817 nm,c = 0.3 6310 nm. The molar volume of the β₁-phase is a linear function of composition from 33 to 50 at. pct Cd. The partial molar volumes of Pd and Cd have the following values in this range: V_Pd = 8.87 cm³/g-atom, V_Cd = 11.18 cm³/g-atom. An analysis of Pd-and Pt-based Ll₀ phases indicates that the c/a ratio of these phases is related to their enthalpy of formation. Phases with a small enthalpy of formation have a high c/a ratio while phases with a large enthalpy of formation exhibit a small c/a ratio. Y. A. CHANG, formerly Professor of Materials Engineering and Associate Dean for Research, Graduate School, University of Wisconsin-Milwaukee     

The nature of the FeAl3 liquid-(FeMn)Al6 reaction in the Al-Fe-Mn system

Crystallization studies using an invertedL pattern of liquid aluminum alloys of compositions just to the right of the ternary point, and the application of a theoretical analysis of the behavior of a hypothetical system, show that the FeAl₃-(FeMn)Al₆-liquid reaction is peritectic close to the ternary point, and that the invariant reaction is eutectic,i.e., L = FeAl₃ + (FeMn)Al₆ + Al_(C).     

Use of (NH4)3AlF6 in the synthesis of aluminum nitride powder

Conclusions A study was made of the kinetics of formation of aluminum nitride in a charge consisting initially of aluminum mixed with ammonium hexafluoroaluminate. It was established that the addition of (NH₄)₃AlF₆ increases the rate of nitriding of aluminum and decreases the energy of activation of the process. Details are given of a new method for the preparation of aluminum nitride of improved quality.Translated from Poroshkovaya Metallurgiya, No. 3 (147), pp. 11–14, March, 1975.     

Thermodynamics of the system NaF-AIF3: Part VI. revision

Literature data are reviewed to derive enthalpies and entropies of Na₃AlF₆ and NaF, and they are combined with electrochemical and equilibrium data to yield free energies of formation of Na₃AlF₆ from the constituent fluorides. Liquidus data and measurements of the Na content of Al in equilibrium with the melts then enable the calculation of the free energy of formation, enthalpy, and entropy of all mixtures liquid at 1293 K. In stoichiometric Na₃AlF₆ at 1293 K, a_NaF =0.37 and a_{AlF 3} = 4.9 × 10⁻⁴. The activity coefficient of Na in dilute solution in Al is given byRT ln γ_Na = (40 967 + 9.480 T) J. At 1293 K the partial pressure of NaAlF₄ is given by pNaA1F₄/bar = 27a_NaF . a_{Aif 3}- A heavier species— suggested to be NaAl₃F₁₀—is present in the vapor above AlF₃-rich melts.     

H2SiF6—Fe2（SiF6）3—H2O系中方铅矿的浸出热力学

对Fe2(SiF6)3酸性浸出剂浸出方铅矿的可行性做了热力学分析,提供了PbSiF6的溶解度图,利用热力学数据计算并绘制了H2SiF6-H2O和PbS-H2O系的E－pH图以及Fe－F电位图。结果分析表明：在Fe2(SiF6)3酸性溶液中,H2SiF6-H2O体系的氧化还原性质是稳定的;SiF6^2-离子稳定的pH计算值范围约在－0．97－－4．86之间;pH值大小可能对PbS的两种氧化机制产生影响;随着F^-浓度的增加,Fe^3 的氧化电位下降。     

Computer analysis of phase diagrams and thermodynamic properties of cryolite based systems: I. The AIF3-LiF-NaF system

Calculations of the phase diagram of the AlF₃-LiF-NaF system up to 35 mol pct A1F₃ and of the binary subsystems are presented. For the binary LiF-NaF, AlF₃-NaF, AlF₃-LiF, and the quasibinary Li₃AlF₆-Na₃AlF₆ systems, thermodynamic properties of the unary and binary phases are used to numerically generate the corresponding phase diagram. The calculated and measured values are in good agreement. The broad data base thus constructed is used with equations from the conformai ionic solution theory to derivea priori phase equilibria of the AlF₃-LiF-NaF system. Ternary liquidus temperatures are calculated covering compo-sitions outside the range of measurements.     

Discussion of “On the free energy of formation of TiC and Al4C3”

Several years ago, Banerji and Reif^[1] reported some very interesting studies on a process to react Ti and C in molten Al to form particles of TiC. The process was used to prepare a master alloy with a fine dispersion of TiC to inoculate Al for grain refinement. Approximately 2 wt pct of preheated graphite particles were stirred into the Al-5 to 10 pct Ti melts. The authors explained that the melts needed to be superheated above 1000 °C to avoid the undesirable formation of A1₄C₃ and Ti₃AlC at the TiC/melt interface. Their explanation for this phenomenon was based on thermodynamics. They observed that the standard free energy of formation curves for AI4C3 and TiC cross near 1175 °C, with A1₄C₃ having the lower free energy of formation below this temperature. There are several aspects of this work which merit further discussion.     

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     

Conduction properties of condensed lanthanum phosphates:La(PO3)3 and LaP5O14

Single crystals of LaP3O9·3H2O were prepared using a classical method of aqueous chemistry whereas those of the ultraphosphate LaP5O14 were obtained by flux method.Thermal treatment of LaP3O9·3H2O up to 700 °C allowed us to obtain the lanthanum polyphosphate La(PO3)3.The conductivity as well as the vibrational study of the lanthanum ultraphosphate and polyphosphate were analysed in order to explain the mechanism of conduction.Activation energies of 0.45 and 0.84 eV,deduced from the Arrhenius relation,were respectively found for the polyphosphate and the ultraphosphate.Taking into account the structural features of these materials we linked the origin of their electrical properties to the incorporation of atmospheric humidity.Thus,it was a proton conduction phenomenon which took place as a result of the establishment of hydrogen bonds as well as the reorganisation of water molecules already incorporated into these structures.Referring to the Grotthuss mechanism,a proton transfer model inside the polyphosphate's structure was suggested.     

Characterization and Thermodynamics of Al2O3-MnO-SiO2 (-MnS)Inclusion Formation in Carbon Steel Billet

A method to extract inclusion particles from solid steel by electrolysis with organic electrolyte solution was introduced;meanwhile,thermodynamics of inclusion formation was calculated using FactSage software.The results showed that there were two kinds of inclusions in the billet,i.e.Al2O3-MnO-SiO2-MnS(AMS-MnS)and Al2O3-MnO-SiO2(AMS).Most of AMS-MnS inclusion particles,with diameter of 10-30μm,showed three-layer structures:SiO2-rich core with a small quantity of Mn,intermediate AMS layer,and MnS outer layer containing small quantities of Al and O.Most AMS inclusion particles were 50-90μm and exhibited homogeneous composition.Thermodynamic results indicated that SiO2-rich core could form firstly by Si reacting with O in molten steel at temperatures above 1 923 Kduring Si-Fe alloy addition,and then,the SiO2-rich core could react with Mn and Al to form liquid AMS enveloping the SiO2-rich core at 1 823-1 873 K.MnS began to precipitate from AMS when temperature reached 1 728 K.Liquid AMS could form by coupled reaction among Si,Mn,Al and O in molten steel.     

Thermodynamics of the system NaF-AlF3. Part III: Activities in liquid mixtures

Measurements have been made of a) the sodium content of aluminum in contact with NaF-AlF₃ melts at 1020° and 1080°C, and in contact with liquid-solid mixtures along the cryolite liquidus, b) the position of the A1F₃ liquidus line, and c) the electromotive force of solid-electrolyte cells with one side in the NaF-Na₃AlF₆ two-phase region and the other on the cryolite liquidus. With previously determined data for the activity coefficient of sodium in aluminum and for ΔH°_298f for cryolite, activities of NaF and A1F₃ are calculated. As a limiting condition the melts conform to a regular solution model withRTlnγ’₁ = ∔12,200(1 − n’₁)² cal where γ’₁=a₁/n’₁ and n’₁ the molar fraction of either NaF or NaAlF₄ calculated with them as species. This model breaks down progressively as the NaAlF₄ composition is approached, the deviations starting earlier at higher temperatures. The most plausible explanation is the disproportionation equilibrium 2A1F-₄ ⇌ A1₂F-₇ + F^-, stoichiometric NaAlF₄ containing about 70 pct AlF^- ₄ at 1020° to 1080°C. The hypothetical undisproportionated NaAlF₄ has a free energy of formation from NaF(I) and AlF₃(s) of ΔG° = •101,235 + 32.085T + 5.929 × 10⁷/T. This equation, together with that above for γ’NaAlF₄, defines α AlF₃ in all regions where the regular solution model holds. Solutions of sodium in aluminum are found to conform to Henry’s law in the range 100 to 2 ppm, contrary to recent suggestions.     

Electrolytic deposition of silicon and of silicon alloys Part II: Decomposition voltages of components and current efficiency in the electrolysis of the Na3AlF6-Al2O3-SiO2 mixtures

Abstract

The decomposition voltages E_d of SiO₂ and Al₂O₃, dissolved in molten cryolite, were measured using the I-E curve method. Several series of experiments were carried out using a graphite anode and graphite, aluminum and Al-Si cathodes alternatively. The E_d values for SiO₂ ranged between 1.00 – 1.25 V according to the experimental conditions. For Al₂O₃, the values were 1.25 – 1.45 V.

In the second part, the current efficiency (CE) in the electrolysis of Na₃AlF₆ - Al₂O₃-SiO₂ mixtures was studied. On the basis of the experimental results, CE was estimated to be around 90%.

Résumé

Les tensions E_d de décomposition du SiO₂ et de Al₂O₃ dissouts dans de la cryotite fondue ont été mesurées par la méthode de la courbe I-E. Plusieurs séries d'expériences ont été faites en utilisant comme anode du graphite et comme cathode, du graphite, de l'aluminium et du Al-Si. Les valeurs de E_d pour le SiO₂ varient de 1.00 à 1.25 V, selon les conditions expérimentales. Pour Al₂O₃ ces valeurs sont de 1.25 – 1.45 V.

Dans la seconde partie, le rendement en courant CE lors de l'électrolyse de mélanges Na₃AlF₆-Al₂O₃-SiO₂ a été étudié. D'après nos expériences, CE est d'environ 90%.     

The metabolism of 22:5(-6) and of docosahexaenoic acid [22:6(-3)] compared in rat hepatocytes

BACKGROUND: Between January 1985 and June 1995, more than 1800 consecutive patients underwent implantation of a new permanent cardiac pacemaker at our institution. Thirty-six patients (0.02%) had 45 reinterventions for infected pacemaker systems. METHODS: in group A, 24 of 27 patients received simultaneous implantation of a new pacemaker. One had reimplantation of the same pacemaker in the same pocket, and two did not require reimplantation. The leads were retained in 19 (70%) of the patients. In group B, nine patients underwent cardiopulmonary bypass or pursestring surgery for removal of an infected pacemaker; a new epicardial pacemaker system was simultaneously implanted in seven patients. RESULTS: Identification of an infectious agent failed in 17 patients (47%), and Staphylococci were found in 15 patients (42%). The time from pacemaker implantation to onset of infection ranged from 1 month to 11 years (mean 31 months; median 19 months) and the time from onset of infection to surgical treatment from 1 month to 7 years (mean 7 months; median 2 months). The mean follow-up time is 74 months (range, 1 month to 10 years; median 5 years). There were 9 reoperations in 3 patients (16%) of group A for recurrent infection of their retained leads ultimately necessitating the use of open cardiac surgery. There was no early death; six patients died late due to unrelated causes. CONCLUSIONS: Complete removal of all pacemaker leads is recommended; open heart surgery with the use of cardiopulmonary bypass is indicated in selected cases and is effective and safe.