Mol Pct Research Articles

EXPERIMENTAL STUDY OF PHASE EQUILIBRIA IN THE Fe-Sn-Zn-O SYSTEM IN AIR

The four-component Fe-Sn-Zn-O system was studied experimentally in the range of temperatures from 1100 to 1400 °C in air using high temperature equilibration and quenching techniques followed by electron probe X-ray microanalysis (EPMA). Phase equilibrium relations and the extent of solid solutions among the phases cassiterite (Sn,Zn)O2, hematite (Fe,Sn,Zn)2 O3, spinel (Fe,Sn,Zn)3 O4 and zincite (Zn,Fe,Sn)O are reported. Phase equilibria in the pseudo-binary systems Fe2 O3 -SnO2 and SnO2 -ZnO are reported in air in the temperature ranges from 1100 to 1400 °C and 1200 to 1400 °C, respectively.On a étudié expérimentalement le système Fe-Sn-Zn-O à quatre constituants dans la gamme de températures de 1100 à 1400 °C, dans l’air, en utilisant des techniques d’équilibration à haute température et de trempe suivies par une analyse par microsonde électronique (EPMA). On décrit les relations d’équilibre de phases et le degré de solutions solides entre les phases cassitérite (Sn,Zn)O2, hématite (Fe,Sn,Zn)2 O3, spinelle (Fe,Sn,Zn)3 O4 et zincite (Zn,Fe,Sn)O. On décrit les équilibres de phases des systèmes pseudo-binaires Fe2 O3 -SnO2 et SnO2 -ZnO, dans l’air, dans les gammes de température de 1100 à 1400 °C et de 1200 à 1400 °C, respectivement.

Discussion of “synthesis of ultrafine particles of intermetallic compounds by the vapor-phase magnesium reduction of chloride mixtures: Part I. Titanium aluminides”

A new chemical synthesis process for the preparation of intermetallic compounds has been developed. It involves the vapor-phase reduction of mixtures of constituent metal chlorides by magnesium vapor to produce intermetallic compounds in the form of fine powder. The advantages of the process include (a) the use of inexpensive raw materials, (b) low reaction temperatures, and (c) products in the form of fine particles. Part I describes the synthesis of titanium aluminide particles by this method, whereas Part II presents the synthesis of nickel aluminides particles. Although nickel aluminides can also be prepared by the hydrogen reduction of nickel chloride and aluminum chloride vapor mixtures, titanium aluminides cannot be produced by hydrogen reduction because of unfavorable thermodynamics. The effect of AlCl3/TiCl3 partial pressure ratio on the formation of different titanium aluminides was studied. A two-phase mixture containing 80 mol pct of TiAl+20 mol pct of TiAl3 formed at an AlCl3/TiCl3 ratio of 10. The amount of TiAl3 was maximized to 72 mol pct at an AlCl3/TiCl3 ratio of 16. The maximum conversion of the limiting chloride TiCl3 was 94 pct. The product particles were very fine in the size range of 0.2 to 0.3 µm.

Temperature dependence of the refractive index of Al2O3-Na2O-SiO2 melts: Role of electronic polarizability of oxygon controlled by network structure

Refractive indexes for the Al2O3-Na2O-SiO2 system have been measured using an ellipsometer for a wavelength of 632.8 nm over a wide temperature range (1100 to 1800 K). Two kinds of sample were used: xAl2O3-(40-x)Na2O-60SiO2 and yAl2O3-yNa2O-(100-2y)SiO2, where x ranged between 6 and 20 mol pct and y between 12.5 and 25 mol pct. In the former samples, the temperature coefficient of refractive indexes changed from negative to positive on increasing the concentration of Al2O3. In the latter samples, the refractive indexes increased monotonically with decreasing concentration of SiO2, and the temperature coefficient was always positive. It has been found that the temperature dependence of refractive indexes in these melts is determined by the coefficient of thermal expansion, which would be relevant to the degree of polymerization of the melts. In addition, the electronic polarizability of oxygen derived from the refractive indexes increased with increasing temperature in each melt. This suggests that the basicity of the alumino-silicate melts increases as temperature increases. The positive temperature coefficient of the electronic polarizability of oxygen can be attributed to an increase in the distance between cation and oxygen ion due to thermal expansion. The dependence of the electronic polarizability of oxygen on the concentration of Al2O3 has also been discussed in terms of the electronic polarizabilities of three types of oxygen contained in the melts.

Calciothermic reduction of titanium oxide and in-situ electrolysis in molten CaCl2

A concept for calciothermic direct reduction of titanium dioxide in molten CaCl2 is proposed and experimentally tested. This production process consists of a single cell, where both the thermochemical reaction of the calciothermic reduction and the electrochemical reaction for recovery of the reducing agent, Ca, coexist in the same molten CaCl2 bath. A few molar percentages of Ca dissolve in the melt, which gives the media a strong reducing power. Using a carbon anode and a Ti basket-type cathode in which anatase-type TiO2 powder was filled, a metallic titanium sponge containing 2000 ppm oxygen was produced after 10.8 ks at 1173 K in the CaCl2 bath. The optimum concentration of CaO in the molten CaCl2 was 0.5 to 1 mol pct, to shorten the operating time and to achieve a lower oxygen content in Ti.

Calciothermic reduction of titanium oxide in molten CaCl2

Titanium oxides were reduced to metallic titanium using the liquid calcium floating on the molten CaCl2. A part of Ca dissolved into CaCl2 and reacted with TiO2 settled below CaCl2. The by-product CaO also dissolved by about 20 mol pct into CaCl2, which was effective in reducing the oxygen concentration in the obtained Ti particles. The compositional region in the Ca-CaCl2-CaO system was examined for the less oxygen contamination in Ti and the better handling in leaching. A large amount of the residual calcium oxidized the titanium powder in leaching. The metallic Ti powder less than 1000 mass ppm oxygen could be obtained only for 3.6 ks using 5 to 7 mol pct Ca-CaCl2 at 1173 K. The powder was slightly sintered like sponge, and contained approximately 1500 ppm Ca. The anatase phae, the intermediate product in the refining process of TiO2, could be also supplied as raw material as well as rutile.

Mechanical properties of As-cast and directionally solidified Nb-Mo-W-Ti-Si in-situ composites at high temperatures

To improve the high-temperature strength of Nb-Mo-Ti-Si in-situ composites, alloying with W and a directional solidification technique were employed. The alloy composition of Nb-xMo-10Ti-18Si (x=10 or 20) was used as the base, and Nb was further replaced by 0, 5, 10 and 15 mol pct W. For samples without W, the as-cast microstructure was a eutectic mixture of fine Nb solid solution (NbSS) and (Nb, Me)5 Si3 silicide (Me = Mo, W, or Ti), while large primary NbSS particles appeared besides the eutectic mixture as a result of replacing Nb by W. The directionally solidified samples consisted of coarse NbSS and (Nb,Me)5 Si3 silicides, and the microstructure showed a slight orientation in the direction of growth. The maximum compressive ductility (ɛmax) at room temperature decreased with increasing W content and was in the range of 0.8 to 2.3 pct, in contrast to the Vickers hardness (HV), which increased with W content. The 0.2 pct yield compressive strength (σ0.2) and the specific 0.2 pct yield compressive strength (σ0.2S) (σ0.2 divided by the density of sample) at elevated temperatures were markedly improved by the W addition. The directionally solidified samples always showed higher σ0.2 and σ0.2S values than the as-cast samples. At elevated temperatures, the directionally solidified sample with 10 mol pct Mo and 15 mol pct W had the highest σ0.2 and σ0.2S values; even at 1770 K, σ0.2 was as high as 650 MPa. The directionally solidified materials alloyed with W exhibited excellent compressive creep performance. The sample with 10 mol pct Mo and 15 mol pct W had a minimum creep rate \((\dot \varepsilon _m )\) of 1.4×10−7s−1 and retained steady creep deformation at 1670 K and an initial stress of 200 MPa. Under compression, the damage and failure of these in-situ composites were dominated by decohesion of interfaces between the NbSS and silicide matrix.

Rare earth extraction and separation from mixed bastnaesite-monazite concentrate by stepwise carbochlorination-chemical vapor transport

A stepwise carbochlorination-chemical vapor transport (SC-CVT) process is proposed for the rare earth extraction and separation from a mixed bastnaesite-monazite concentrate based on thermodynamic and kinetic analysis using carbon as reductant, chlorine gas as chlorination agent, SiCl4 as defluorination agent, and AlCl3 as vapor complex former. Between 500 °C and 800 °C, apparent activation energy of the carbochlorination within 2 hours changed from 22 to 16 kJ/mol roughly for the initial half hour and final 1 hour, respectively, in the absence of SiCl4; but these values reduced to 15 and 2.1 kJ/mole under 2 kPa of SiCl4 gas. The rare earth chloride yield for 2 hours was 56 to 88 mol pct in the absence of SiCl4 and 92 to 99 mol pct in the presence of SiCl4; but carbochlorination at above 1000 °C yielded a large amount of acid-insoluble residue. This, together with the negligible equilibrium vapor pressure of ThCl4 at below 600 °C, suggests that carbochlorination of the mixed concentrate at temperatures as low as 500 °C in the (Cl2 + SiCl4) atmosphere is suitable for rare earth extraction and thorium-free volatile by-product release, which is different from the conventional Goldschmidt process at 1000 °C to 1200 °C. The CVT reaction of the carbochlorination product was performed at 800 °C for 0.5 hours in the (Cl2 + SiCl4 + AlCl3) atmosphere and then at 1000 °C for 6 hours in the (Cl2 + AlCl3) atmosphere along different temperature gradients, leading to complete thorium removal and efficient rare earth separation, respectively. Their combination allows an efficient and environmentally conscious extraction and separation of rare earth elements from the mixed concentrate.

Thermodynamic behavior of nickel in CaO-SiO2-FetO slag

The distribution ratio of nickel between Ag-Ni alloy and CaO-SiO2-FetO slag at high temperatures was measured to clarify the dissolution mechanism of nickel in this melt. Also, the nickel oxide capacity was suggested and was compared to phosphate and sulfide capacities. The dissolution mechanism of nickel into the CaO-SiO2-FetO slags could be described by the following equation from the effect of oxygen potential and slag basicity on nickel dissolution behavior: $$Ni(1) + \frac{1}{2}O_2 (g) + O^{2 - } (slag) = NiO_2^{2 - } (slag)$$ The nickel oxide capacity increases with increasing CaO/SiO2 ratio at a fixed FetO content. When the ratio of XCaO to \(X_{SiO_2 } \) (C/S) is about 1.1 to 1.3, log \(C_{NiO_2^{2 - } } \) increases with increasing FetO content up to about 35 mol pct, followed by a nearly constant value of \(C_{NiO_2^{2 - } } \cong 10^3 \). In the composition of C/S=0.5 to 0.7, log \(C_{NiO_2^{2 - } } \) exhibits a maximum value at about 50 mol pct FetO. From the iso-\(C_{NiO_2^{2 - } } \) trends in ternary phase diagram, nickel oxide capacity dominantly depends on FetO content in slags; it exhibits a maximum value of \(C_{NiO_2^{2 - } } \cong 10^3 \) at \(X_{Fe_t O} \cong 0.5\). The relationship between nickel oxide capacity and phosphate (sulfide) capacities exhibit linear correlations, as expected from theoretical equations.

Thermodynamic observations of the molten FeS-FeO system and its vicinity at 1473 K

The Fe-S-O melts were equilibrated with the CO-CO2-SO2 gases at 1473 K under a S2 (g) partial pressure of 0.0004 atm (=0.041 kPa). This S2 isobar runs on both sides of the pseudobinary FeS-FeO system, thus adding a continuous extension to the isobaric network of S2 and O2 in the literature. The activities of S2 (g), O2 (g), Fe (γ), FeS (L), FeO (L), FeO1.33 (s), and FeO1.5 (s) were calculated in the vicinity of the pseudobinary FeS-FeO melt. The activity of magnetite FeO1.33 (s) was observed to be greater than that of FeO (L) in the ferrous binary FeS-FeO melts containing 35 to 55 mol pct FeO.

Thermodynamic studies of some Fe‐Pt alloys by the solid electrolyte galvanic cell method

In the present investigation, the thermodynamic activities of iron in iron‐platinum solid alloys were measured by the solid electrolyte galvanic cell method in the temperature range 1073–1273 K. The galvanic cell employed can be represented as(−) Pt, Fe(s), FetO(s) // ZrO2(11 mol pct CaO) //FetO(s), Fe‐Pt alloys, Pt(+)The experimental set‐up as well as the satisfactory performance of the galvanic cell were validated by measuring the standard Gibbs energy of formation of CoO in equilibrium with Co in the same temperature range by replacing the working electrode by a Co, CoO mixture. 6 different Fe‐Pt alloys covering the entire composition range were studied and the results are compared with earlier thermodynamic studies available in the literature. The present experimental results are found to be in general agreement with those of Alcock and Kubik. The values were fitted into a regular solution description in order to estimate the enthalpies of mixing Pt and Fe in the solid alloys.

Thermodynamic behavior of Na2O-B2O3 melt

The activity of Na2O in a Na2O-B2O3 melt was measured at 1373 K by a chemical equilibration technique to understand the thermodynamic behavior of this slag system. Also, the activity coefficient of Na in Ag was preliminarily measured as fundamental thermodynamic data, to estimate the activity of Na2O in the slag. Sodium in the silver melt, within the present concentration range, exhibits the Henrian behavior, and the Henrian activity coefficient of Na in Ag (γ 0 Na) is estimated to be 37.5 at 1373 K, indicating a positive deviation from ideality. The activity of Na2O in the slag varies from 1.86×10−6 to 4.99×10−4 when its content is increased from 11.0 to 64.9 mol pct; this indicates a significant negative deviation from ideality. The excess stability does not exhibit any pronounced peak, despite being drastically changed at specific slag compositions. Comparing the molar Gibbs free energy of mixing in various binary slags, Na2O was considered to be more basic than BaO (CaO) was, followed next by MgO; also, P2O5 would be significantly more acidic than SiO2 would be, followed next by B2O3. Comparing the heats of formation of solid compounds in binary slags, the larger the differences in the electronegativity values between slag components, the more the relative ionic characters of the melts seemed to be.

Solubilities and raman spectra of NdOCl in some chloride melts of interest for the electrowinning of magnesium from its oxide

Some fundamental data related to the solvent proposed for a new technical electrolytic process for magnesium production based on MgO as the raw material are presented. Liquidus data are obtained for MgCl2-rich melts in the MgCl2-NdOCl system. The solubility of MgO and NdOCl in pure liquid NdCl3, MgO in NdCl3-MgCl2 and in MgCl2-NdCl3-NaCl liquid mixtures, and NdOCl in CaCl2 and Cs2MgCl4 have also been studied. The solubility of MgO decreases when MgCl2 is added to the pure NdCl3 and further by additions of NaCl as expected. A so far unidentified compound having the composition MgxNdyOCl2x-3y-2 where x and y are larger than 1 seems to be formed in very small amounts in these melts. This compound seems to precipitate at temperatures higher than 910 °C in the NdCl3-MgO quasi-binary system containing about 8 mol pct MgO and seems to remain suspended in the melt in small quantities. The first liquid-solid phase transition observed, however, was the NdCl3 (1)=NdCl3 (s) transition <758 °C. X-ray diffraction (XRD) data of filtered samples of this solid show new X-ray lines not detected in MgCl2, NdCl3, NaCl, MgO, and NdOCl. The published phase diagram of the quasi binary system MgCl2-NdOCl is, according to the present work, not correct because the solubility of MgO seems to be much less than previously reported. Raman spectroscopic data of NdCl3-MgCl2-NdOCl melts show the known features of the NdCl3-MgCl2 and NdCl3-NdOCl melts. Raman bands due to dissolved species of the unidentified compound were not detected. In view of the obvious small concentration of this species in the liquid phase, this was reasonable.

Iron redox equilibria in CaO-Al2O3-SiO2 and MgO-CaO-Al2O3-SiO2 slags

Measurements have been made of the ratio of ferric to ferrous iron in CaO-Al2O3-SiO2 and MgO-CaO-Al2O3-SiO2 slags at oxygen activities ranging from equilibrium with pCO2/pCO≈0.01 to as high as air at temperatures of 1573 to 1773 K. At 1773 K, values are given by $$\begin{gathered} \log {\text{ }}\left( {\frac{{Fe^{3 + } }}{{Fe^{2 + } }}} \right) = 0.3( \pm {\text{ }}0.02){\text{ }}Y + {\text{ }}0.45( \pm {\text{ }}0.01){\text{ }}\log \hfill \\ \left( {\frac{{pCO_2 }}{{pCO}}} \right) - 1.24( \pm {\text{ }}0.01) \hfill \\ \end{gathered} $$ where Y=(CaO+MgO)/SiO2, for melts with the molar ratio of CaO/SiO2=0.45 to 1.52, 10 to 15 mol pct Al2O3, up to 12 mol pct MgO (at CaO/SiO2≈1.5), and with 3 to 10 wt pct total Fe. Available evidence suggests that, to a good approximation, these redox equilibria are independent of temperature when expressed with respect to pCO2/pCO, probably from about 1573 to 1873 K. Limited studies have also been carried out on melts containing about 40 mol pct Al2O3, up to 12 mol pct MgO (at CaO/SiO2≈1.5), and 3.6 to 4.7 wt pct Fe. These show a strongly nonideal behavior for the iron redox equilibrium, with $$\frac{{Fe^{3 + } }}{{Fe^{2 + } }} \propto \left( {\frac{{pCO_2 }}{{pCO}}} \right)^{0.37} $$ The nonideal behavior and the effects of basicity and Al2O3 concentration on the redox equilibria are discussed in terms of the charge balance model of alumino-silicates and the published structural information from Mossbauer and NMR (Nuclear Magnetic Resonance) spectroscopy of quenched melts.

Experimental study of phase equilibria in the systems PbO x -CaO and PbO x -CaO-SiO2

The reported experimental work on the systems PbOx-CaO and PbOx-CaO-SiO2 in air is part of a wider research program that combines experimental and thermodynamic computer modeling techniques to characterize zinc/lead industrial slags. Extensive experimental investigation by high-temperature equilibration and quenching techniques followed by electron probe microanalysis was carried out in the temperature range 640 °C to 1500 °C (913 to 1773 K) and in the composition ranges 0 to 65 mol pct SiO2 and 0 to 42 mol pct CaO. Liquidus and solidus data were reported for most of the primary phase fields. Liquidus surfaces in the systems CaO-Pb-O and PbOx-CaO-SiO2 in air were completely reconstructed. Extensive solid solutions of PbO in α′ dicalcium silicate and Ca2Pb3Si3O11 were measured.

The effect of surfactants on the interfacial rates of reaction of CO2 and CO with liquid iron oxide

The 14CO2-CO isotope exchange technique has been used to measure the rates of dissociation of CO2 on liquid iron oxide containing the surface active components P2O5 or Na2O, principally at 1673 K. The apparent first-order rate constant is found to decrease monotonically with small additions of P2O5 up to a factor of about 4 at 3.5 mol pct. Vaporization losses prevented detailed studies of the effect of Na2O, but it is shown that there is probably a twofold increase in the rate constant at a concentration of about 0.2 wt pct and a fivefold increase at a concentration between 0.5 and 1.6 wt pct. A smoothed surface potential model, based upon the Vol’kenshtein model for catalysis by semiconductors, is developed, and it is shown that the required surface potential changes due to the segregation of P2O5 and Na2O are physically reasonable.

An investigation of toughening in NiAl composites reinforced with yttria-partially stabilized zirconia particles

The results of an investigation of toughening mechanisms in NiAl composites reinforced with yttria-partially stabilized zirconia polycrystals are presented. Different yttria stabilization levels in the zirconia, between 0 and 6 mole pct are employed. It is shown that substantial improvements in fracture toughness are obtained in all the composites reinforced with partially stabilized zirconia particles. The phase contents and microstructures of the composite systems are characterized by X-ray diffraction and transmission electron microscopy (TEM) techniques. Crack tip deformation was also studied using crack tip TEM analysis, and laser Raman spectroscopy was used to estimate the size of the transformation zone. The results show that transformation toughening is significant only in the 2 mole pct yttria-stabilized zirconia composite. Toughening is also shown to occur via slip phenomena within the NiAl grains in the near-tip regions of the composites reinforced with 2, 4, or 6 mole pct yttria-stabilized zirconia particles.

Thermodynamics and phase equilibria in the Al-In-Sb system

As part of a program for determination of the thermodynamic properties of the group III and V alloys and assessment of the phase equilibria, the activities of aluminum in the liquid Al-In-Sb system have been measured using a concentration cell of the type $$Al (1)\left| {NaCl + KCl + 3 mole pct AlCl_3 } \right|Al - In - Sb(1)$$ The measurements are carried out along the constant compositional paths of x Sb=0.1 and 0.2 over a temperature range of 1073 to 1273 K. The measured activity data in the system exhibit positive deviations from ideality. The deviations increase progressively with the In content of the alloys for a constant compositional path of Sb. The magnitude of the a A1 as a function of In is found to decrease significantly with the increase in the Sb content of the alloys. The behavior is consistent with the existence of the liquid-liquid immiscibility in the system.

Effect of MgO and BaO on Fe3+/Fe2+ Equilibrium in a Candidate Glass for Immobilization of High Level Nuclear Waste

For better understanding of the behaviors of MgO and BaO within glass frit PF798, which is a candidate for use in immobilization of radioactive nuclear waste and consisted of 63.6SiO 2 , 16.8B 2 O 3 , 4Al 2 O 3 , 3ZnO, 4.4CaO and 8.2Li 2 O in mole pct, oxidation-reduction equilibrium experiments for Fe 3+ /Fe 2+ couple were conducted with the melts of (PF798+MgO) and (PF798+BaO) at 1473 K and under a stream of pure CO 2 of 1 atm.

Galvanic cell measurements on supersaturated activities of oxygen in Fe-Al-M (M=C, Te, Mn, Cr, Si, Ti, Zr, and Ce) melts

Using a mullite (3Al2O3 · 2SiO2)-tube and ZrO2-9 mol pct MgO-plug type solid electrolyte galvanic cells, the activities of supersaturated oxygen in Fe-0.0017 to 0.41 mass pct Al-M (M=C, Te, Mn, Cr, Si, Ti, Zr, and Ce) alloys were measured as a function of total Al or M contents at 1873 K in an alumina crucible. Based on these results, the effects of alloying elements on the supersaturated oxygen activity with respect to alumina precipitation were studied. In the Fe-Al-M (M=C, Te, Mn, Cr, and Si) alloys, the supersaturated oxygen activities for a given Al level approach the equilibrium values with increasing contents of alloying elements. However, the oxygen activities for a given Al level are still supersaturated in the Fe-Al-M (M=Ti, Zr, and Ce) alloys even in the presence of considerable amounts of the alloying elements.

Viscosity of PbO-SiO2 melts

Viscosities (η) of PbO-SiO2 melts that contained 25.0 to 48.8 mole pct SiO2 were measured at temperatures 928 to 1273 K by a rotating cylinder method. The data were analyzed in terms of the conventional polymer theory. The results followed Arrhenius behavior in the different temperature ranges despite the general belief of non-Arrhenius behavior of viscosity in slag melts. The calculated activation energies were a function of temperature and composition of the melts. The activation energies for viscous flow, in general, at above approximately 850 °C were lower than those below 850 °C and varied between 25 and 150 kJ per mole.