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.     

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.     

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.     

Corrosion Inhibition and Adsorption Behavior of Gentian Violet on AISI 4130 Alloy Steel in HCl Solution

The inhibition ability of hexamethyl pararosaniline chloride (gentian violet) on the corrosion resistance of AISI 4130 steel in 1 M HCl solution was studied by potentiodynamic polarization (Tafel), electrochemical impedance spectroscopy and scanning electron microscopy (SEM). Polarization studies indicated that the inhibition efficiency increases with the increase in inhibitor concentration and inhibitor retards both the cathodic and anodic reactions, so are classified as mixed type inhibitors. The effect of temperature on the corrosion behavior of steel in HCl with the addition of the inhibitor was studied in the temperature range from 25 to 65 °C. The experimentally obtained adsorption isotherms follow the Langmuir equation. Activation parameters and thermodynamic adsorption parameters of the corrosion process such as E _a , ΔH, ΔS, K _ads and ΔG _ads were calculated at different temperatures and using the adsorption isotherm. The morphology of steel surface after its exposure to HCl solution in the absence and presence of inhibitor was examined by SEM images.     

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.     

Synthesis and Characterization of Polyaniline–Mn3O4 Nanocomposite: Electrical Conductivity and Magnetic Studies

Polyaniline (PANI)–Mn₃O₄ nanocomposites (NCs) have been synthesized by in situ chemical oxidative polymerization of aniline with different molar ratios of aniline:Mn₃O₄ (3.3:1 and 2.5:1) using ammonium per sulfate as an oxidant in an aqueous solution of sodium dodecyl benzene sulfonic acid, as surfactant and dopant at 5 °C under N₂ atmosphere. The structural components and the crystalline phase of the Mn₃O₄ nanoparticles (NPs) and PANI–Mn₃O₄ NCs were identified from Fourier transform infrared spectroscopy and X-ray diffraction. The result of FTIR and TGA shows that the interaction between Mn₃O₄ particles and PANI matrix could improve the thermal stability of NCs. The room temperature electrical conductivity of the synthesized PANI, PANI-Mn₃O₄ NCs (3.3:1) and (2.5:1) was found to be 3.26 × 10^?4, 8.11 × 10^?7 and 3.93 × 10^?7 S/cm respectively, indicating the decrease of conductivity with an increase of Mn₃O₄ content in PANI. The magnetic behavior of composite was studied at 5 K. The coercive force (H_c) and remnant magnetization (M_r) increases with increase in addition of Mn₃O₄ NPs in PANI matrix.     

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.     

Diffusional creep and creep-degradation in dispersion-strengthened Ni-Cr base alloys

Dispersoid-free regions were observed in the dispersion-strengthened alloy TD-NiCr (Ni-20 Cr-2 ThO₂) after, slow strain rate testing (stress rupture, creep, and fatigue) in air from 1145 to 1590 K. Formation of the dispersoid-free regions appears to be the result of diffusional creep. The net effect of creep in TD-NiCr is the degradation of the alloy to a duplex microstructure. Creep degradation of TD-NiCr is further enhanced by the formation of voids and intergranular oxidation in the dispersoid-free bands. Void formation was observed after as litte as 0.13 pct creep deformation at 1255 K. The dispersoid-free regions apparently provide sites for void formation and oxide growth since the strength and oxidation resistance of Ni-20 Cr is much less than Ni-20 Cr-2 ThO₂. This localized oxidation does not appear to reduce the static load bearing capacity of TD-NiCr since long stress-rupture lives were observed even with heavily oxidized microstructures, but this oxidation does significantly reduce the ductility and impact resistance of the material. Dispersoid-free bands and voids also were observed in two other dispersion-strengthened alloys, TD-NiCrAl (Ni-16Cr-4 Al-2 ThO₂) and IN-853 (Ni-20 Cr-2.5 Ti-1.5 Al-1.3 Y₂O₃). Thus, it appears that diffusional creep is characteristic of dispersion-strengthened alloys and can play a major role in the creep degradation of these materials.     

The kinetics of the exchange of cobalt(II) ions between NaCl and Na2O-SiO2-Fe2O3 melts in the temperature range 1200 to 1400 K

Studies of the equilibria and kinetics of the Co²⁺ ion exchange in the Na₂O-SiO₂-Fe₂O₃/NaCl system were performed over the 1200 to 1400 K temperature range by measuring the emf of galvanic cells of the following composition: $$( - )Co\left| {\frac{{NaCl - CoCl_2 }}{{Na_2 O - SiO_2 - Fe_2 O3}}} \right.\left| {NaCl - CoCl_2 } \right.\left| {Co( + )} \right.$$ Distribution coefficients α of the Co²⁺ ions between the salt phase and silicate melt are of the l0^?2 order. Differential equations describing the transfer process of the Co²⁺ ions from the salt phase to the silicate phase were solved. The diffusion coefficients D_Co ²⁺ in the Na₂O-SiO₂-Fe₂O₃ melt were determined by substituting the Co²⁺ ion concentration change in fused NaCI into the differential equations. The values of D_Co ²⁺ are about 10^?5 cm²S^?1 and they decrease with decreasing temperature and increasing Fe_?2O_?3 content in slags. The diffusion coefficient of the cobalt (II) ions in slags determined in this way is consistent with that determined by the otating disk method.     

Electrolytic recovery of molybdenum from molybdic oxide and molybenum sesquisulfide

An electrolytic process for molybdenum extraction in a KCl?K₃MoCl₄ electrolyte (containing approximately 7.5 wt pct molybdenum) was investigated using three types of anode feed —namely, molybdic oxide-graphite, molybdenum sesquisulfide-graphite, and molybdenum sesquisulfide without graphite. In the case of molybdic oxide-graphite anode, a maximum current efficiency of 99 pct was achieved at an operating voltage of 0.35V, a cathode current density of 5000 A/m² (450 A/f²) and a bath temperature of 1223 K. Electrolysis with molybdenum sesquisulfide-graphite, at an operating voltage of 1.2V, a cathode current density of 13,900 A/m² (1250 A/f²) and a bath temperature of 1173 K, yielded a maximum current efficiency of 84 pct. Electrolysis of molybdenum sesquisulfide without graphite incorporation, yielded under almost similar conditions, a maximum current efficiency of 87 pct. Extended electrolysis was carried out using molybdic oxide-graphite and molybdenum sesquisulfide cell charges and yielded metal with purity over 99.9 pct.     

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.     

Epitaxial formation of AlNi on Al3Ni during electropolishing

Electron micrographs are presented which are interpreted as evidence of the surface dealloying of Al₃Ni to AlNi during electropolishing. The epitaxial relationships between the AlNi films and the Al₃Ni substrate have been studied. Moiré fringes arising from AlNi films on both surfaces of thinned foils have been observed.     

The effect of grain size and retained austenite on the ductile-brittle transition of a titanium-gettered iron alloy

The effect of microstructural changes on the ductile-brittle transition temperature (DBTT) was studied in a titanium-getter ed Fe-8Ni-2 Mn-0.15 Ti alloy. A fairly strong grain size dependence of the transition temperature, 8°C/mm^?1/2, was found. Grain size refinement from 38 μm (ASTM #6.5) to 1.5 μm (ASTM #15.5) through a four-step thermal treatment lowered the transition temperature by 162°C. A small amount of retained austenite was introduced into this grain-refined microstructure, and the transition temperature was reduced by an additional 120 ~ 150°C. The reduction of the DBTT due to retained austenite was smaller when the austenite was in a large-grained structure (64°C). The distribution and stability of retained austenite were also studied.     

Grain boundary segregation in Ni and binary Ni alloys doped with sulfur

The kinetics and temperature dependence of sulfur segregation in Ni and binary alloys of Ni with Cu, Al, Cr, Mo, W, and Hf, all containing between 70 and 100 atomic ppm sulfur, have been measured using Auger spectroscopy over the temperature range 500 to 1000 °C. No evidence for cosegregation of these alloying elements with sulfur is found. The alloying elements do influence the precipitation of sulfides, however, and this influences the amount of segregation which occurs. Comparison with theoretical models of grain boundary segregation allows the sulfur solubility in the various alloys to be determined.     

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.     

Initial Kinetics of Tungsten Carburization by Methane

The initial kinetics of the gas-phase carburization of tungsten by methane were studied and found to be controlled by the surface adsorption of methane. It was observed that W₂C was formed as the initial carbide phase. Carburization rates were explained by a topochemical model and an equation was developed which predicts the initial reaction rate for a variety of experimental conditions. The activation enthalpy for the initial gas-phase reaction was determined to be 12.4 kcal/mole.     

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.     

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.     

Microstructural effects on the stress corrosion cracking behavior of medium and high strength steels

The effects of variations in microstructure and strength level on the stress corrosion cracking susceptibility of three medium to high strength steels, H13, 300M, and HY-130, in 3.5 pct NaCl have been systematically studied. Superimposed on the expected inverse dependence of K_ISCC on yield strength was more than an order of magnitude reduction in crack growth rate, with no strength penalty. These results have been analyzed in terms of the possible relative roles of different microstructural features, in particular retained austenite, whose detailed behavior is the subject of a companion paper.