Showing papers in "Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science in 1988"

Surface tension of binary metal—surface active solute systems under conditions relevant to welding metallurgy

Abstract: Since the fluid flow, heat transfer, and the resulting weld properties are significantly affected by interfacial tension driven flow, the variation of interfacial tension in dilute binary solutions is studied as a function of both composition and temperature. Entropy and enthalpy of adsorption of surface active components such as oxygen, sulfur, selenium, and tellurium in Fe-O, Fe-S, Fe-Se, Cu-O, Cu-S, Cu-Se, Cu-Te, Ag-O, and Sn-Te systems were calculated from the analysis of the published data on interfacial tension of these systems. For these calculations, a formalism based on the combination of Gibbs and Langmuir adsorption isotherms was used. Interfacial tensions in Cr-O, Co-S, and Ni-S systems, where the data are scarce, were predicted by using certain approximations. The computed values were found to be in reasonable agreement with the data available in the literature. Temperature coefficients of interfacial tensions were calculated for several binary systems. It was demonstrated that in dilute solutions, the temperature coefficient of interfacial tension is strongly influenced by the heat of adsorption which, in turn, is influenced by the difference in electronegativity between the solute and solvent ions.

Fluid dynamics in bubble stirred ladles: Part II. Mathematical modeling

Abstract: A mathematical model which describes the fluid flow in a bubble stirred ladle is presented. The model predicts mean flow, turbulent characteristics, bubble dispersion, and gas-liquid interaction from fundamental principles. Numerical predictions for a water model of a ladle show very satisfactory quantitative agreement with experimental results for all regions of the ladle. The model is applied to the study of refractory wear and yields results that are in qualitative agreement with practical experience.

Free surface flow and heat transfer in conduction mode laser welding

Abstract: Temperature profiles and fluid flow fields in a weld pool are simulated through numerical solutions of Navier-Stokes equation and the equation of conservation of energy for low power laser welding in conduction mode. Experimentally determined weld pool surface topography, peak temperature, and the secondary dendrite arm spacings are found to be in fair agreement with the corresponding theoretically calculated values.

On the weldability, composition, and hardness of pulsed and continuous Nd:YAG laser welds in aluminum alloys 6061,5456, and 5086

Abstract: The effect of Nd:YAG laser welding aluminum alloys 6061, 5456, and 5086 was studied from a perspective of alloying element vaporization, hot cracking susceptibility, and resultant mechanical properties. Both continuous wave and pulsed Nd.YAG laser welds were investigated. It was found that Mg was vaporized during welding, the extent of which was a function of the weld travel speed. Calculations based upon evaporation theory, and assuming a regular solution model, resulted in an estimation of weld pool surface temperatures from 1080 to 1970 K for the continuous wave welds. Pulsed Nd:YAG laser welds were observed to be extremely susceptible to weld metal hot cracking whereas continuous wave Nd:YAG laser welds were crack-free. The hardness of 6061 welds was affected by the Mg vaporization such that base metal strengths could not be achieved by subsequent re-heat treatment to the T6 condition. This loss in hardness was attributed to a reduced ability of the alloy to precipitation harden due to a lower Mg concentration. In the cases of 5456 and 5086, when samples containing welds were processed to the O condition, the weld metal had reduced hardness relative to the base metal. This loss of hardness was also attributed to the loss of Mg in these welds, resulting in reduced solid solution strengthening.

Fluid dynamics in bubble stirred ladles: Part I. experiments

Abstract: Air is supplied through a porous plug placed in the center axis of a cylindrical perspex-water model of a ladle. A Laser-Doppler system is employed to measure radial and axial mean and fluctuating velocities. Velocities in the two-phase bubbly region can also be determined. Velocities are measured near the bottom, half-way up, and near the free surface. It is shown that the bubbles contribute to production of turbulence. The ladle has recirculation zones near the bottom, where the mean velocities are very low. Close to the free surface the radial mean and turbulent velocities are high, promoting mass transfer through the interface. The present measured velocity profiles cannot be reduced to a single profile by employing similarity scaling.

Modeling of infiltration kinetics for liquid metal processing of composites

Abstract: An equation for modeling the kinetics of liquid-metal infiltration into a porous compact has been developed. The model is based on considering a bundle of capillary tubes as an analog for the porous compact. A solution which describes a limiting form of behavior has been shown to be valid for small extents of infiltration relative to a hypothetical static state. The numerical solutions of the dimensionless infiltration-equation have been used to delineate conditions for which limiting solutions are valid. A dimensionless group λ has been shown to be capable of classifying the behavior into two limiting cases: either “inviscid-flow“, λ 10-2, or “viscous-flow“, λ > 102. It would appear that for capillary-tube (pore) radii less than 100 µ-m and for conditions where the compact is wetted by the liquid metal, A is likely to be >100 and therefore correspond to a “viscous-flow system“. Also, an infiltration-rate parameter, ϕ, has been selected which can be used to assess the effects of alloying additions to the liquid-metal infiltrant. This parameter can therefore provide for the selection of alloy infiltrants, surface preparation modification, and processing parameters such as temperature, time of infiltration, and pore size of compact in regard to the processing of composites. Although the model concept (capillary-tube bundle) is recognized as being deficient in not treating the compact as what it really is (a porous medium), the work presented was intended to quantify the limiting behavior of the capillary-tube-bundle approach which has been used in the past.

Mathematical modeling of meniscus profile and melt flow in electromagnetic casters

Abstract: The paper describes a mathematical model which predicts the meniscus shape and melt flow in an electromagnetic caster. Computations were carried out for the two types of caster (with and without a screen to shape the magnetic field) in commercial use. The dependence of meniscus shape on parameters such as inductor geometry, placement, current, and frequency, as well as screen properties and placement, was determined. Calculated velocities showed agreement with measurements of other investigators on a physical model and an actual caster. The effect of an auxiliary low frequency inductor on melt flow was also computed.

Speciation and reduction potentials of metal ions in concentrated chloride and sulfate solutions relevant to processing base metal sulfides

Abstract: The speciation, Eh-pH and Eh-log aCl- dependence of Fe(III), Fe(II), Cu(II), Cu(I), Ag(I), Pb(II), Zn(II), Ni(II), As(III), Sb(III), and Bi(III) ions in practical (high ionic strength) sulfate and chloride solutions are discussed. The emphasis is placed on those ions which form strong sulfato-, chloro-, and hydroxo-complex species. Measured potentials are compared with potentials calculated from reported association and stability constants to test the applicability of these constants in nonideal solutions and to characterize predominant species.

Correlations of electrical conductivity to slag composition and temperature

Abstract: The electrical conductivity of slags is an important factor in the design of electric smelting furnaces. Although there are many experimental studies on this subject, as yet there are no quantitative correlations of conductivity to slag composition and temperature. The objective of this work was to develop such correlations, on the basis of the experimental data by various other authors. The results show that in the concentration range of industrial-type SiO2-CaO-MgO-MnO slags the slag conductivity can be expressed as a linear function of the molar concentrations of the basic oxides; in the concentration range of industrial nonferrous slags, where the iron oxide content is usually over 20 pct, the slag conductivity can be expressed as an exponential function of the molar concentrations of the iron and basic oxides. The effect of temperature on slag conductivity, in the industrial range of interest, can be accounted for by means of an Arrhenius-type of equation.

Flow fields in electromagnetic stirring of rectangular strands with linear inductors: Part I. theory and experiments with cold models

Abstract: A model is presented to compute the electromagnetic force fields and fluid flow fields in electromagnetic stirring of continuously cast strands with rectangular cross-section. The model involves the solution of the Maxwell equations, the Navier-Stokes equations, and the transport equations for the turbulence characteristicsk and e. The procedure of depth-averaging is applied in the treatment of several three-dimensional flows. Experiments were performed to check the computations using mercury as fluid. The spatial distribution of the magnetic induction and of the force density was determined for the laboratory inductor used in the stirring experiments. The flow velocity was measured photographically or with a drag probe, respectively. The agreement between experimental and theoretical data was found to be within 25 pct. It is concluded that the theory is sufficiently reliable to predict the flow fields in electromagnetic stirring of steel strands. In Part II of this paper the model is applied to analyze stirring situations in continuous casting of steel.

Influence of rare earth metals on the nucleation and solidification behavior of iron and 1045 steel

Abstract: Two series of experiments have been conducted to determine the influence of rare earth additions on the nucleation and crystallization behavior of pure iron and 1045 steel In the first series, additions of rare earth suicide or cerium dioxide powder to two-Kg 1045 steel ingots indicated that rare earth suicide can refine the as-cast structure of such ingots However, if the holding time after rare earth silicide addition is over two minutes, the grain refinement decreases With cerium dioxide additions, a relatively large columnar zone was obtained In the second series, the effects of cerium metal or cerium dioxide powder additions on the degree of undercooling obtainable in pure iron and 1045 steel were examined by the levitation melting method Surface tension measurements of the levitated droplets were carried out at the same time to investigate the possible effects of surface tension variations on the nucleation and crystallization behavior of the metals The experimental data show that rare earth inclusions can greatly reduce the degree of undercooling of iron and steel, and that a small amount of dissolved cerium can further reduce the degree of undercooling of levitated droplets The structure and reaction products obtained with Fe-Ce levitated droplets were examined with both optical and scanning electron microscopy as well as X-ray diffraction analysis The experimental results clearly indicated that cerium solute redistribution during solidification is the dominant factor in refining the as-cast structure A nucleation and solidification model for the Fe-Ce levitated droplets has been developed, which can successfully explain the experimental results

Effects of Oxygen and Sulfur on Alloying Element Vaporization Rates during Laser Welding

Abstract: Inadequate control of weld metal composition due to vaporization of volatile alloying elements is a serious problem in the welding of many important engineering alloys. Effectiveness of surface active elements such as oxygen or sulfur in blocking vaporization sites on the weld pool surface was investigated. Several iron samples doped with oxygen or sulfur were exposed to a carbon dioxide laser beam in pulsed mode. The time average metal vaporization rates and the emission spectra were compared with those obtained from ultra pure iron samples. Since the weld pool surface area and temperature distribution are affected by oxygen and sulfur, the true effects of these elements on metal vaporization rates cannot be easily evaluated from welding data. Therefore, rates of isothermal vaporization of iron and copper drops doped with oxygen or sulfur were determined both in the presence and the absence of low pressure argon plasma. These rates were compared with the rates of vaporization of ultrapure metal drops. Presence of sulfur or oxygen in metals always resulted in increased metal vaporization rates. The results are analyzed on the basis of interfacial phenomena.

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

Abstract: 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.

Experimental Investigation of Mixing Phenomena in a Gas Stirred Liquid Bath

Abstract: Mixing phenomena in a room temperature water bath, agitated by injecting air through a straight circular nozzle fitted axially at the bottom of the vessel, were characterized by experimentally measuring mixing time(t mix) by electrical conductivity technique. It was found thatt mix defined at 99.5 pct homogenization did not depend on location and size of conductivity probe, location of tracer injection, and the amount of tracer injected. tpet decreased with increasing gas flow rate and bath height, but decreasing nozzle diameter. Visual observations of the two-phase plume and flow conditions in the bath revealed that the plume swirled above a certain gas flow rate which enhanced the mixing rates in the bath. The transitions in Int mix vs In eb curves were found to correspond to onset of swirling; eb is the rate of buoyancy energy input per unit bath volume. Systematic analysis of experimental data revealed that a fraction of gas kinetic energy contributed to mixing in the bath. It was a function of bath height, being negligible at lower bath heights and almost 1 at larger bath heights. Further, it was experimentally found thatt mix decreased with increasing bath height only up to a certain value, beyond which it started increasing. Visual observations of the bath revealed that the height at whicht mix started increasing corresponded to a transition in which the bath was converted into a bubble column. The experimental data, for a particular bath height, were fitted into two separate straight lines of the formt mix =ce −n wherec andn are empirical constants and e is the rate of energy input per unit bath volume.

A dynamic mathematical model of the complete grate/kiln iron–ore pellet induration process

Abstract: Induration (drying and hardening) of iron ore pellets is an energy-intensive feed preparation step for both the blast furnace and direct reduction routes to iron. It is commonly carried out by a ‘grate/kiln’ process. A mathematical model of the process is described, in which mechanistic models of the grate furnace, kiln, and cooler are linked to enable simulation of the entire process. The model includes equations for the gas stream pressure balances and process controller responses, and provides dynamic solutions. The validation of the model for an operating plant is discussed and steady-state solutions are compared with data from the plant.

Thermodynamics of nitrogen in CaO-SiO2-AI2O3 slags and its reaction with Fe-Csat. melts

Abstract: The solubility of nitrogen as the nitride ion in CaO-SiO2-Al2O3 slags in equilibrium with N2-CO gas mixtures and carbon was measured at 1823 K. The nitride capacity (C N3-) was calculated to compare the nitrogen contents measured under different nitrogen and oxygen potentials.C N3- decreased with increasing basicity and by replacing SiO2 with A12O3. The nitrogen partition ratio between carbon saturated iron and the slag was measured in CO gas at one atmosphere at 1823 K. By comparing the partition ratios with the corresponding nitride capacities measured by the gas-slag experiments, it was concluded that the oxygen partial pressure at the slag-metal interface was controlled by the Fe-FeO reaction. A new definition of nitride capacity was proposed based on the reaction between nitrogen and the network former,i.e., SiO2 or A12O3. This capacity could consistently explain the experimental results. Empirical equations were derived to estimate the activity coefficients of silicon and aluminum nitrides in the slags.

The calcium-phosphorus and the simultaneous calcium-oxygen and calcium-sulfur equilibria in liquid iron

Abstract: The equilibrium Ca3P2(s) = 3[Ca] + 2[P] was studied at 1600 ° by equilibrating liquid iron, saturated with Ca3P2, and contained in a TiN crucible, with Ca vapor. The source of Ca was liquid Ca contained in an Mo crucible, and the vapor pressure of Ca was varied by varying the position of the Mo crucible in the temperature gradient of a vertical tube furnace. A least-squares analysis of the data gave $$K_{Ca_3 P_2 } = 7.0 \times 10^{--14} $$ and $$e_P^{Ca} = - 3.1$$ . The simultaneous equilibria CaO(s) = [Ca] + [O] and CaS(s) = [Ca] + [S] were studied at 1600 ° by equilibrating liquid iron, contained in a pressed and sintered CaO-CaS crucible with Ca vapor. The advantage of this technique is that two equilibrium constants,K cas andK cao, and two interaction coefficients, $$e_S^{Ca} $$ and $$e_O^{Ca} $$ can be determined from one set of experiments. It was determined that, at 1600 °,K cas = 5.9 × 10−8 K cao = 5.5 × 10−9, $$e_S^{Ca} = - 106$$ , and $$e_O^{Ca} = - 475$$ .

Determination of the diffusion coefficients of CuSO4, ZnSO4, and NiSO4 in aqueous solution

Abstract: The diffusion coefficients of CuSO4, ZnSO4, and NiSO4 in the aqueous solution systems of MSO4 and MSO4-H2SO4 were measured at 298 K using a diaphragm-cell method, and are listed as a function of molar concentrations of MSO4 and H2SO4. It was found that the concentration dependencies of the diffusion coefficients for CuSO4, ZnSO4, and NiSO4 in each single metal sulfate solution are very similar. The presence of H2SO4 generally causes a less significant concentration dependency of the diffusion coefficients of MSO4. The concentration dependencies of the diffusion coefficients of CuSO4 in aqueous solutions of CuSO4 and CuSO4-H2SO4 are attributed to the changes in the mean activity coefficient of CuSO4 and the viscosity of the solutions.

Dissolution kinetics of particulate graphite injected into iron/carbon melts

Abstract: An experimental investigation was undertaken to study the kinetics of graphite dissolution in gasstirred iron/carbon melts. Laboratory apparatus was developed to allow the injection of closely sized graphite into the bottom of a 1 kg scale reactor with nitrogen as a carrier gas. The effects of gas flow, particle loading, particle size, bath sulfur, and temperature on the rate of dissolution were assessed. It was found under the experimental conditions used that the graphite dissolution rate kept pace with the injection rate up to approximately 85 pct of carbon saturation, except when sulfur is present in the bath, in which case the dissolution rate is retarded. Modeling the rate of graphite particle dissolution supports the experimental results in that particle dissolution occurs quickly and under mass transport limitations. Computer generated gas-stirred flow field diagrams for the experimental reactor indicate that conditions exist for particle entrainment in the bath, and hence complete contact with the melt at all times during dissolution.

The nucleation of iron on dense wustite: A morphological study

Abstract: Dense wustite was reduced at temperatures from 430 to 1100 °C in CO-A, CO-CO2, H2-A, and H2-H2O mixtures. Most of the experiments were conducted on a hot stage microscope, providing a clear record of the sequence of events. The morphology of phases was further studied on the optical and the scanning electron microscopes. Two types of nuclei were identified: (1) dense nuclei, ranging from regular whiskers to simple protrusions, around which flat bases develop to form a protective film, and (2) porous nuclei with lenticular shapes, which remain level with the sample surface as they grow (both radially and into the wustite) to form a porous layer. Mild gases and moderate temperatures favor dense iron, whereas strong gases and extreme temperatures (either low or high) favor porous iron. The domains of the two types are represented in morphology maps. They overlap in transition zones where mixed nuclei are found; in this case the porous nuclei appear later than the dense ones but they grow much faster. The morphology maps support the view that sponge iron in iron ore reduction does not originate from porous iron nuclei but develops as a maze of dense iron growths. Experiments with cold-worked and annealed samples indicate that dislocations are essential to the growth of whiskers.

Effect of temperature on magnetizing reduction of agbaja iron ore

Abstract: Agbaja oolitic iron ore, which has not been responsive to such beneficiation processes as froth flotation, gravity concentration, magnetic separation, and electrostatic separation, has been concentrated to 60 pct Fe grade and 87.3 pet Fe recovery (starting from a crude assaying 45.6 pct Fe) by the magnetizing reduction technique. The main parameter investigated was the effect of temperature on the magnetizing reduction process, and 600 °C was established as the optimum temperature for the reduction step. X-ray diffraction studies of the reduction products showed that the iron oxides were converted to magnetite, to wustite, or to metallic iron, depending on the temperature of reduction. The results from the subsequent magnetic concentration step were, in the main, dependent on the observed reduction products.

A Microscopic study of the transformation of sphalerite particles during the roasting of zinc concentrate

Abstract: The formation of zinc ferrite (ZnFe2O4) during the roasting of iron-bearing zinc concentrates requires substantial additional processing to recover the zinc from this compound by leaching and to eliminate the iron from the leachate. The phase changes that occur in the particles of a typical industrial zinc sulfide concentrate during roasting in a fluidized bed at 1223 K were investigated by the use of light microscopy, electron microprobe analysis, and SEM with EDS. The processes which the iron undergoes during its eventual transformation into ferrite have been clarified by examination of the phases and the morphology of partially roasted marmatitic sphalerite particles (Zn, Fe)S, and by reference to the known phase equilibria involved in the Zn-Fe-S-0 system. The oxidation of ironbearing sphalerite occurs in three stages. The first involves the selective diffusion of most of the iron to the particle surface resulting in the formation of an iron oxide shell enclosing a largely unreacted zinc sulfide kernel. In the second stage, this kernel is oxidized to form a solid solution of zinc oxide and iron oxide. The iron is initially present in the ferrous state but, with the disappearance of the sulfide kernel, is oxidized to ferric iron. In the final stage, this dissolved iron oxide and the iron oxide shell react with the surrounding zinc oxide to form the refractory spinel zinc ferrite.

Reaction mechanism for the CaO-Al and CaO-CaF2 desulfurization of carbon-saturated iron

Abstract: The desulfurization of carbon-saturated iron with CaO is inefficient due to the formation of solid reaction products on the CaO particles which inhibit sulfur transfer. It has been shown in full scale and pilot plant studies that Al improves desulfurization with CaO. The present results indicate that Al affects the rate at 1450 °C, but not at 1350 °C, and that zirconium, which has a stronger affinity for oxygen than Al, does not increase the rate as much as aluminum. Alternate methods of producing a liquid reaction surface, such as desulfurization with CaO-CaF2 or a premelted calcium aluminate flux, also increase the rate. From these results, it is concluded that it is critical to have a liquid reaction surface for effective desulfurization. Aluminum in the metal, reacting with oxygen and CaO, provides a liquid calcium aluminate surface. An optimum aluminum level of about 0.1 to 0.3 pct was found. At lower levels, the Al is consumed and eventually solid calcium silicate forms, and at higher levels, possibly an alumina-rich solid phase forms.

Flow fields in electromagnetic stirring of rectangular strands with linear inductors: Part II. computation of flow fields in billets, blooms, and slabs of steel

Abstract: The model presented in Part I of this series of papers is used to compute flow velocities in the longitudinal stirring of steel blooms and billets, and in the horizontal stirring of steel slabs. In longitudinal stirring of blooms and billets the reverse flow is on the side of the strand opposite to the inductor. The effects of penetration depth of the electromagnetic force, of the force itself, of the length of the stirrer, and of the width of the liquid core were determined. In horizontal stirring of slabs the reverse flow takes place outside of the stirrer region, forming the so-called butterfly stirring pattern. The characteristics of this flow field depend to a considerable extent on the width of the stirrer. The effects of stirrer width, of thickness of the liquid core, of force and of width of the slab were elucidated. The maximum velocities in both types of stirring are represented as simple formulae.

On the interfacial rate of reaction of CO 2 with a calcium ferrite melt

Abstract: Measurements of the rate of dissociation of CO2 have been made by the14CO2-CO isotope exchange technique on calcium ferrite melts with Ca/Fe = 0.30 at 1300 °C. Studies have also been made of the interfacial rates of oxidation of calcium ferrite melts with an average CaO content of 19.45 wt pct (CaJFe ≃0.33) in CO2-CO atmospheres at 1362 °C. It is shown that the rates of oxidation are consistent with the rates of isotope exchange, indicating a common rate determining step. Measurements of the equilibrium Fe3+/Fe2+ ratio as a function of the CO2/CO ratio for 19.3 wt pct CaO melts at 1360 °C and for 28.7 and 18.6 wt pct CaO melts at 1300 °C are found to be in close agreement with the deductions of Takeda, Nakazawa, and Yazawa. Combination of the equilibrium data with the results of the isotope exchange studies indicate that the apparent first order rate constant for the dissociation of CO2 is inversely proportional to the square of the Fe3+JFe2+ ratio of the melt, as has been previously found for liquid iron oxide, lime-saturated calcium ferrites, silicasaturated iron silicates, and an equimolar “FeO”-CaO-SiO2 melt.

Hematite single crystal reduction into magnetite with CO-CO 2

Abstract: In view of the striking discrepancies among previous authors as regards the transition between porous and lamellar magnetites, we have carried out a wide series of experiments with single crystals prepared by chemical vapor transport In addition to the classical temperature and CO pct parameters, which varied over a large range (400 ≤T ≤ 1000 ≤C and 2 ≤ CO pct ≤ 50), we also investigated the influence of the crystal size and of the fractional weight change Through observation of a great number of cross-sections of partially reduced crystals, we established that lamellar magnetite is favored by high temperature and low CO pct This is explained by consideration of the conditions governing the competition between cation diffusion in the semi-coherent hematite-magnetite interface and chemical reaction rate At low temperatures, the crystals are severely fractured, because hematite is not plastic enough, especially at a high CO2 pct The kinetic data are analyzed with the shrinking-core model, where the reaction interface is topochemical The chemical rate constant thus obtained is ϕ = 69 exp(−8950/T), in mol(CO) · m−2 · s−1, for crystals in the range 50 to 150 μm andT varying from 500 to 900 °C Bigger crystals yield a slightly higher preexponential term, confirming that porous diffusion does not rule the kinetics The nucleation frequency has also been evaluated; it tends toward a kind of saturation at around 700 °C with a value of 10 to 109 s−1 The nuclei growth rate is in reasonable agreement with direct measurements

Melting metal powder particles in an inductively coupled r.f. plasma torch

Abstract: A numerical model is developed for the prediction of melting metal powder particles in an inductively coupled r.f. plasma torch. The model is developed for dilute spray conditions where the gas phase flow is not affected by the loading condition. The governing equation for the gas phase flow contains the source terms from the electromagnetic field. The theoretical calculations have shown that particle thermal history and its velocity are greatly affected by the plasma operating conditions (i.e., carrier gas flow rate, injector location, and power level,etc.). Without the proper control of particle trajectories, particles may bounce around the fireball and exit the torch as unmelted or resolidified solid particles. With the insertion of an injector or injecting particles with a high carrier gas flow rate, the predictions show that even relatively small size particles can be directed into the fireball and maintained in the molten state before they impact on the substrate. Consequently, more uniform and dense deposits can be achieved.

An ionic diffusion mechanism of chromite reduction

Abstract: The occurrence of the various phases that form during the solid-state carbothermic reduction of chromite is explained by the use of a point-defect model. In this model each chromite particle is considered to be comprised of concentric layers of spinel unit cells (Fe2+and Mg2+ occupy tetrahedral sites, Cr3+, Al3+, and Fe3+ occupy octahedral sites). The phases that form are a result of the interchange of cations between unit cells within the particle effected by the presence of carbon monoxide at the surface of the particle. Four stages of reduction are identified: (1) the formation of a slightly iron-enriched core comprising distorted spinel unit cells surrounded by a region of normal spinel unit cells, effected by the reduction of Fe3+ to Fe2+; (2) the formation of Cr-Al sesquioxide and Mg-Cr-Al spinel phases effected by the metallization of Fe2+ ions and subsequent production of Cr2+ ions; (3) reduction of Fe2+ interstitials in the spinel core; and (4) metallization of chromium ionsvia the Cr2+ intermediate. The non-appearance of the sesquioxide phase at high temperatures is explained by considering the effect of temperature on the magnitudes of the diffusion coefficients of Cr2+, Mg2+, and interstitial Fe2+ ions.

The solubility of hydrogen in liquid binary Al-Li alloys

Abstract: The solubility of hydrogen in liquid binary aluminum alloys with 1, 2, and 3 wt pct lithium has been determined for the temperature range of 913 to 1073 K and pressure 5.3 × 104 to 10.7 × 104 Pa, using an appropriate version of Sieverts’ method. The results fit the Van’t Hoff isobar and Sieverts’ isotherm and the solubility,S, is given by: Al-1 pct Li: log(S/S°) − 1/2 log(P/P°) = −2113/T/k + 2.568 Al-1 pct Li: log(S/S°) − 1/2 log(P/P°) = −2797/T/k + 3.329 Al-1 pct Li: log(S/S°) − 1/2 log(P/P°) = −2889/T/k + 3.508 whereS° is a standard value of solubility equal to 1 cm3 of diatomic hydrogen measured at 273 K and 101,325 Pa per 100 g of metal, andP° is a standard pressure equal to 101,325 Pa. Added lithium progressively increases the solubility of hydrogen in liquid aluminum, due more to its effect on the entropy of solution of hydrogen, through its influence on the liquid metal structure than to an increase in the solute hydrogen atom binding enthalpy.