The evaluation of the equilibria of displacement reactions involving slags

New relations for the evaluation of displacement reactions in ternary slags,e.g. FeO?CoO?SiO₂, CaO?CaS?Al₂O₃, and CaO?CaS?SiO₂ are derived. In addition, equations for the quarternary system CaO?CaS?MnO?MnS?SiO₂ and analogous systems are derived.     

Activity determinations in the CaF2−CaO−SiO2 system at 1450°C

The silica activities of slags in the CaF₂?CaO?SiO₂ system (N_CaO∶N_{SiO 2}>3∶2) have been determined at 1450°C by measuring the equilibrium partial pressure of carbon monoxide for the reaction (SiO₂)+3C _(s) =SiC _(s) +2CO _(g) The results have been correlated with phase diagram determinations and are not consistent with other activity measurements in the literature. Lime activities have been determined using the ternary Gibbs-Duhem relationship.     

Rate of change of oxygen chemical potential in liquid PbO−SiO2 binary solution

The rate of the chemical potential change of oxygen in a liquid PbO?SiO₂ binary solution, with SiO₂ contents of 10, 20, and 30 mol pct, and in pure PbO, has been measured at temperatures of 900°, 950°, 1000°, 1050°, and 1100°C. The rate increased with temperature according to the Arrhenius type relation and decreased with the increase of the silica content. It is suggested that the rate-controlling step is the counter diffusion rate of Pb²⁺ and Pb⁴⁺ ions, which are considered to be the most easily movable ions in the PbO?SiO₂ solution. The relation between the rate of oxygen chemical potential change and the electrical conductivity is also discussed for the liquid PbO?SiO₂ system.     

Distribution of Boron Between Silicon and CaO-MgO-Al2O3-SiO2 Slags

Production of solar-grade silicon through metallurgical refining methods can be less expensive than current production methods both in terms of energy use and capital cost. Slag refining is a potential metallurgical refining method for removal of boron from silicon. The distribution of boron between silicon and binary CaO-SiO₂ and MgO-SiO₂ slags, and between silicon and ternary CaO-MgO-SiO₂ and CaO-Al₂O₃-SiO₂ slags has been investigated in this work at 1873 K (1600 °C). The distribution coefficient of boron has been found to be between 2 and 2.5 in the binary CaO-SiO₂ and MgO-SiO₂ systems. It has also been found to be in the same range across the entire CaO-MgO-SiO₂ system. In these systems the distribution coefficient is unaffected by slag composition. The distribution coefficient has been found to decrease with increasing Al₂O₃ content in the slag in the ternary CaO-Al₂O₃-SiO₂ system.     

The Wear Behavior of In-Situ Al–AlN Metal Matrix Composites

Al–AlN composites are synthesized using NH₄Cl + CaO powder as a nitrogenation precursor in the melt of pure aluminum. In-situ formation of AlN to varying volume fraction is attempted using different proportion of NH₄Cl + CaO precursor into the aluminum melt held at 700 °C. Mechanical properties of synthesized metal matrix composites are evaluated for different volume fraction and distribution of AlN particles in aluminum matrix. Agglomeration of AlN is noticed with increasing precursor addition and synthesis time into the aluminum matrix. Due to heterogeneous distribution of AlN particles in aluminum matrix, marginal changes in hardness are observed. Pin on disc, dry sliding wear of metal matrix composites is carried to study wear behavior of synthesized composites. Composite with good dispersion of AlN particulates has shown higher hardness and wear resistance. Present paper discusses wear behavior of composites with different weight fraction of AlN tested under load and sliding distance as wear parameters. The shearing mechanism of agglomerate due to friction and its correlation with the wear loss is also highlighted in the present paper.     

The Structure of the Molten FeO-SiO2 System

A structural study of the molten FeO-SiO₂ system has been carried out by means of a high temperature X-ray diffraction technique. The composition range studied was from 0 to 44 mole pct SiO₂. From an analysis of the scattering intensity, the radial distribution function was calculated from which interionic distances and coordination numbers were estimated. The following characteristic features emerge from these results. A constant coordination number of about four is obtained for Si-O pairs in the composition range between 17 and 44 mole pct SiO₂. This supports the existence of SiO₄ tetrahedra in the basic region. The Si-Si distance, which corresponds to the inter SiO₄ distance, gradually decreases as the composition increases from 20 mole pct SiO₂ and then shows a nearly constant value at compositions beyond 39 mole pet SiO₂. This constant value is comparable with the value of the Si-O-Si distance with an angle of less than 180 deg. This indicates that some of the SiO₄ tetrahedra polymerize to form silicate anions. The distance of the Fe-Si and Fe-O varies in a similar manner with the Si-Si correlation.     

The thermodynamic activity of ZnO in silicate melts

The activity of ZnO in ZnO-SiO₂ and CaO-ZnO-SiO₂ melts has been measured at 1560 °C using a transpiration technique with CO-CO₂ mixtures as the carrier gas. The activities of ZnO in dilute solution in 42 wt pct SiO₂?38 wt pct CaO-20 wt pct A1₂O₃ in the range 1400° to 1550 °C and in 62 wt pct SiO₂?23.3 wt pct CaO?14.7 wt pct A1₂O₃ at 1550 °C have also been measured. The measured free energies of formation of ZnO-SiO₂ melts are significantly more negative than published estimated values and this, together with the behavior observed in the system CaO-Al₂O₃-SiO₂, indicate that ZnO is a relatively basic oxide. The results are discussed in terms of the polymerization model of binary silicate melts and ideal silicate mixing in ternary silicate melts. The behavior of ZnO in dilute solution in CaO-Al₂O₃-SiO₂ melts is discussed in terms of the possibility of the fluxing of ZnO by iron blast furnace slags.     

Desulfurization of liquid steel containing aluminum or silicon with lime

The reaction mechanisms for the desulfurization of iron containing from 0.04 to 1.5 pct aluminum or 1.1 to 3.7 pct silicon by CaO at 1600° have been examined. The desulfurization of Fe-Al by CaO is considerably faster than that of Fe-Si. The basic difference between the two processes is that Fe-Al alloys can be desulfurized by the formation of AI₂O₃, whereas for Fe-Si melts it is necessary to form Ca₂SiO₄. The rate of desulfurization of Fe-Si alloys by CaO is controlled by the formation of the gaseous intermediates, SiS and S, and is the same as that for desulfurization in vacuum. The rate of desulfurization of Fe-Al melts is fast, and is apparently controlled by the diffusion of sulfur to the liquid metal—CaO interface. Experiments were also conducted to demonstrate that sulfur could be transferred to CaO by the gaseous intermediates SiS and S.     

Thermodynamic activity of Na2O in Na2O-CaO-SiO2, Na2O-MgO-SiO2, and Na2O-CaO-SiO2-Al2O3 melts at 1400°C

A gas phase equilibration technique was used to generate Na₂O isoactivity data at high-silica compositions in the systems Na₂O-CaO-SiO₂, Na₂O-MgO-SiO₂, and Na₂O-CaO-SiO₂-(10 and 20 wt pct) A1₂O₃ at 1400 °. Loga _{Na 2 O} values referenced to pure liquid Na₂O at 1400 ° as standard state ranged from about ?8.0 to ?7.0. Silica activities were calculated in the Na₂O-CaO-SiO₂ system using the Gibbs-Duhem equation. Richardson’s model for ideal mixing of basic oxides in silica was applied to the Na₂O-CaO-SiO₂ system. The model shows best fit when cationic mixing is assumed to occur on divalent sites. The alkali retention in slags has been described using a defined “sodium capacity”. The temperature variation of alkali retention was estimated, and the resulting sodium capacity was used to evaluate alkali stability in blast furnace slags.     

Phase Relations in CaO-SiO2-Al2O3-15 mass pct CaF2 System at 1523 K (1250 °C)

CaO-SiO₂-Al₂O₃-CaF₂ is a base system of mold flux for high Al steels. Phase equilibrium in CaO-SiO₂-Al₂O₃-15 mass pct CaF₂ system at 1523 K (1250 °C) was investigated using quenching method followed by X-ray diffraction and Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. Isothermal section in this system at 1523 K (1250 °C) with Al₂O₃ being less than 25 mass pct and CaO/SiO₂ (mass pct) being between 0.43 and 1.25 was experimentally constructed. The liquidus composition and seven solid-liquid coexistence regions at 1523 K (1250 °C) were determined.     

Research on Transformation Mechanism of Oxide Inclusion in Tire Cord Steel

In order to investigate the relation and transformation mechanism of two type oxide inclusions (MnO–Al₂O₃–SiO₂ and CaO–Al₂O₃–SiO₂ system) in tire cord steel the experiment was carried out. It’s found that oxide inclusions’ transformation has experienced MnO–Al₂O₃–SiO₂ type at RH stage, CaO–Al₂O₃–SiO₂ type at LF stage and soft blow argon stage, and finally MnO–Al₂O₃–SiO₂ type in casting blank and billet during the production process of test steel. According to the analysis of reaction among slag/steel/inclusion it’s found that Ca content in steel is a major factor for transformation of inclusion composition. With the rising of Ca content in liquid steel the formation of CaO becomes easier and it is good for the formation of CaO–Al₂O₃–SiO₂ complex inclusion. When the [O] content in steel is less than 0.002 %, the Al₂O₃–CaO–2SiO₂ inclusions may be generated if Ca content in steel is more than 0.0001 %.     

Moiré patterns in electron transmission through Au-Ni alloys

Moiré patterns were developed in the transmission electron microscopy of thinned Au-Ni alloys as a consequence of the deposition of very thin layers of gold during the thinning process. The transmission photographs showed striated patterns, and the wavelength of the striations, which were in the range 20 to 100Å, corresponded closely to the predicted Moiré spacings. The striations are not related to the true composition modulations which occur in some of these alloys as a result of the decomposition of the solid solution. The true lattice modulations are of the order 6 to 13Å. The Moiré patterns arise from gold layers which are much thinner than the alloy layer. The electron diffraction spots of the gold are thus elongated in reciprocal space in a direction normal to the surface, and this feature can greatly affect the spacing of the Moiré striations. It is shown that Moiré spacings can be useful in determining with good precision the small changes in lattice parameter which occur on the aging of the alloys, thus providing a new tool for the study of small lattice strains.     

Structure and properties of rapidly solidified dispersion-strengthened titanium alloys: Part I. Characterization of dispersoid distribution,structure, and chemistry

The feasibility of developing dispersion-strengthened powder metallurgy Ti alloys was determined in Ti-RE (RE = Ce, Dy, Er, Gd, La, Nd, or Y) alloys prepared by rapid solidification processing. The alloys were produced by electron-beam melting and splat quenching. Dispersoid precipitation and growth were studied as functions of annealing temperature, 700 to 1000 °C, for annealing times between 5 and 50,000 minutes. Dispersoid diameters, spacings, compositions, and crystal structures were characterized by transmission and scanning electron microscopy, X-ray and electron diffraction, energy-dispersive X-ray analysis, and scanning Auger microscopy. Two classes of dispersoid coarsening behavior at temperatures below theβ-transus were identified. In Ti-Ce, Ti-Gd, and Ti-Nd alloys, equilibrium rare earth sesquioxide (RE₂O₃) dispersoids form early in the annealing process and coarsen rapidly to > 1 μm diameter. The Ti-Nd alloys additionally contain large volume fractions of small (< 100 nm diameter) dispersoids. In the other Ti-RE alloys, dispersoids identified as Ti-RE-O-C compounds coarsen relatively slowly. Ti-Er is the most promising of the investigated systems for application in a multicomponent dispersion-strengthened alloy because long-time annealing at 700 to 800 °C produces stable dispersoids of 50 to 150 nm average diameter and 300 to 600 nm inter-particle spacing.     

Study on Quantification of Oxide Phases in Ex-situ AlN/Al Metal Matrix Nanocomposites

Al based metal matrix nanocomposite (MMNC) is synthesized by dispersing nanocrystalline aluminium nitride (AlN) particles in Aluminum matrix using ex-situ melt metallurgy method. The entrapment of atmospheric oxygen along with ex-situ particulate has been a long standing issue during fabrication of metal matrix composites. In the present investigation, presence of oxygen has been quantified in synthesized Al-AlN MMNCs with varying AlN content. The high resolution scanning electron microscopy is used to study morphology and distribution of AlN in Al matrix. Energy dispersive spectroscopy analysis is used to quantify in situ oxide phases along with AlN particles in the synthesized MMNCs using thermodynamic mass balance calculations. Present study also attempts to understand the role of in-situ oxide phases on the mechanical properties of MMNCs using microindentation hardness and nanoindentation test.     

Thermodynamic consistency of the interaction parameter formalism

The apparent contradiction between the exact nature of the interaction parameter formalism as presented by Lupis and Elliott and the inconsistencies discussed recently by Pelton and Bale arise from the truncation of the Maclaurin series in the latter treatment. The truncation removes the exactness of the expression for the logarithm of the activity coefficient of a solute in a multi-component system. The integrals are therefore path dependent. Formulae for integration along paths of constant X_i,or X _i/X_j are presented. The expression for In γ_solvent given by Pelton and Bale is valid only in the limit that the mole fraction of solvent tends to one. The truncation also destroys the general relations between interaction parameters derived by Lupis and Elliott. For each specific choice of parameters special relationships are obtained between interaction parameters.     

Phase Equilibria and Thermodynamic Studies in the System CaO−FeO−Fe2O3−SiO2

Phase equilibria and thermodynamic properties of the system CaO?FeO?Fe₂O₃?SiO₂ were studied at 1450° and 1550°C, over a range ofpO₂ from 1 to about 10^?11 atm. Isothermal phase diagrams and activity-composition diagrams were constructed for 0, 5, 10, 20, and 30 wt pct SiO₂ sections. The data are applicable to further understanding the behavior of simple BOF steelmaking slags.     

Removal of phosphorus from synthetic oxide melts

The behavior of phosphorus in FeO-Fe₂O₃-CaO-MgO-SiO₂-Al₂O₃-P₂O₅ oxide melts is experimentally studied. To determine the factors affecting the removal of phosphorus from the oxide melt to the gas phase, experiments are conducted with different melt basicity (CaO/SiO₂) and with different CO/CO₂ ratios in injection. The removal of phosphorus is greatest when the basicity is 0.5. At higher basicity, thermodynamic factors hinder the removal of phosphorus; at lower basicity, the viscosity of the melt is a hindrance. In kinetic calculations, the apparent activation energy of the process is found to be E = 140 ± 56 kJ/mol. That suggests that the process is limited by the diffusional mass transfer of phosphorus pentoxide in the liquid phase.     

Radiochemical measurement of diffusion in the cesium chloride-tin and barium-sodium systems

Diffusion coefficients for cesium chloride in molten tin from 308 to 396°C and for barium in liquid sodium from 290 to 396°C were measured radiochemically. Cesium chloride coefficients were determined by measurement of nonsteady state surface concentrations of cesium chloride deposited on the surface of cylindrical specimens. Cesium chloride traced with cesium-137 was deposited on the specimens from a supersaturated solution dispersed in the molten tin and measured by gamma spectroscopy after removal of the specimen from the solution. Diffusion coefficients for barium in sodium were measured by a unique method in which radioactive cesium-137 (half-life of 33 yrs) dissolved in the sodium served as a volumetric source for its short-lived barium-137 daughter (half-life of 2.6 min). Since barium deposited on the surface of the specimen, measurement of the equilibrium barium-137m gamma activity on the specimen surfaces after removal from the solution yielded barium diffusion coefficients. The equations for these diffusion coefficients with 95 pct confidence limits are: Cesium chloride in tin (308 to 396°C):D=[(4.84±0.14)×10^?4] exp [?6720±6400)/RT] Barium in sodium (290 to 496°C):D=[(4.27±0.05)×10^?4] exp [?4600±990)/RT]     

Carbosilisiothermic Reduction of Rutile to Produce Nano-Sized Particles of TiC and Its Composite with SiO2

Ceramic nanoparticles of TiC were successfully synthesized in a matrix of SiO₂ by high-energy ball milling with subsequent heat treatment. The milling procedure includes milling of a mixture of TiO₂, Si, and graphite powders at ambient temperature in an inert gas (Ar) atmosphere. The structural evaluation of powder particles has been accomplished by XRD, TEM, SEM, EDX, and DSC. XRD results suggest that the TiC-SiO₂ nonocomposite was produced after 10 hours of mechanical activation with subsequent heat treatment at 1473 K (1200 °C) for 7 minutes. TEM images reveal that the TiC and SiO₂ crystallites are <14 and 12 nm in size, respectively. The fracture toughness, and Vickers hardness values of the TiC-SiO₂ nanocomposite are measured to be 3.82 MPa m^1/2 and 19.9 GPa, respectively. Dimethylsulfoxide is used to eliminate SiO₂ from the final products.     

Thermodynamic properties of molten PbO−SiO2 systems

Thermodynamic properties of the molten PbO?SiO₂ systems were determined by electromotive force measurements employing solid electrolytes. The experiments were carried out in the temperature range 900° to 1000°C on the galvanic cells \(Pb_{(l)} + PbO_{(l)} \left| \begin{gathered} Electrolyte \\ ZrO_2 \times CaO \\ \end{gathered} \right|Pb_{(l)} + PbO - SiO_{2(l)} \) From the results the activities of PbO and SiO₂, the partial and integral free energies, entropies, and heats of mixing were determined. These experimental results are interpreted and compared with previous experimental data. Based on the present data and according to the model of Toop and Samis,¹the activity coefficients of the free oxygen ion O^2? concentration is reduced.