Wt Pct Oxygen Research Articles

Correlation of Oxygen and Aluminum Contents of Molten Titanium-Aluminum Alloys in Alumina and Calcia Crucibles

As a key part of investigating a new proposed Ti-alloy production process, Ti-Al alloys were produced by aluminothermic reduction experiments at 1973 K in Al2O3 crucibles. Besides, pure Ti and Al were melted inside CaO crucibles at 1973 K to investigate the possibility of melt refining in equilibrium with CaO. The experiments were carried out in a vacuum induction furnace under argon gas at atmospheric pressure. The experimental results were proved by thermodynamic evaluations including also literature data. The correlation of oxygen and aluminum in Ti melt with 11 to 23 wt pct Al in contact with Al2O3 was assessed as $$ 3\ln X_{\text{O}} = -\,2\ln X_{\text{Al}} - 9.1 \pm 0.4. $$ This correlation in Ti melt with 3 to 10 wt pct Al in contact with CaO was $$ 3\ln X_{\text{O}} = - \,2\ln X_{\text{Al}} - 14.9 \pm 0.3. $$ Partial molar excess Gibbs free energies of mixing and combinations thereof in Ti-rich Ti-Al-O-Ca melt were assessed as $$ RT \ln (\gamma_{\text{Al}}^{2} \cdot \gamma_{\text{O}}^{3} ) = - 894 \pm 6\,({\text{kJ}}/{\text{mol}}) $$ , $$ RT \ln \left( {\gamma_{\text{Ca}} \cdot \gamma_{\text{O}} } \right) = - 195 \pm 4\,({\text{kJ}}/{\text{mol}}) $$ , $$ RT \ln \gamma_{\text{O}} = - 258 \pm 6\,({\text{kJ}}/{\text{mol}}) $$ , $$ RT \ln \gamma_{\text{Ca}} = 62 \pm 7\,({\text{kJ}}/{\text{mol}}). $$ The activity of Al2O3 in CaO-saturated slag was assessed as 0.003 ± 0.001. The changes of Gibbs free energy for the dissolution of 1 wt pct oxygen and 1 wt pct calcium in Ti-Al melt were estimated as −630 ± 6 and −11 ± 7 (kJ/mol), respectively. A model was developed and applied to calculate the basic data for refining Ti-Al alloy.

Direct electrolytic preparation of chromium powder

Chromium oxide powder (Cr2O3) was slip cast or pressed into small cylindrical pellets which were then sintered in air. The sintered pellets were attached to a current collector to form an assembled cathode. Constant-voltage (2.7 to 2.8 V) electrolysis, with a graphite anode, was performed in molten CaCl2 (950 °C). After electrolysis, the pellets were removed from the molten salt and washed in water. Scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, and fusion elemental analysis all confirmed that, when electrolyzed for a period longer than 4 hours, the Cr2O3 pellets were fully reduced to Cr metal. The oxygen content in the product depended on electrolysis time. Typically, for a 6-hour electrolysis, less than 0.2 wt pct oxygen was found in the product, with the current efficiency and energy consumption being 75 pct and 5 kWh/kg, respectively. The fully reduced pellet had a friable strength and could be manually crushed into a powder composed of cubic crystallites, very uniform in size, that grew with the electrolysis time, up to 50 μm (15 hours). The unique product morphology (cubic crystallites) differs drastically from the nodular morphology observed in other metals prepared by similar methods and is rarely seen among various commercial metal powders. A reduction mechanism is proposed, emphasizing the surface metallization at the early stage of electrolysis through the propagation of the metal-oxide-electrolyte three-phase interline (3PI).

Deoxidation of molybdenum during vacuum sintering

Molybdenum is usually fabricated through the powder metallurgy (P/M) process, using fine powders with a relatively high oxygen content. Oxygen, however, is one of the main elements causing embrittlement during the deformation processing of molybdenum, such as rolling, extrusion, and forging. Thus, how to deoxidize the compact as completely as possible is critical in the P/M process. This study shows that, as an alternative to hydrogen reduction, molybdenum oxides can be reduced by adding organic lubricants to the compact and by sintering the compact under high vacuum with long sintering times. After 10 hours of sintering at 1750 °C and a 0.03 torr vacuum, the oxygen content decreased from 0.927 wt pct of the green compact to 0.017 wt pct. The ductility also improved significantly compared to compacts sintered for 5 hours, which contained 0.218 wt pct oxygen. The morphology evolution, weight changes, and the X-ray analysis indicated that the oxide was first present in the form of MoO3. It was then transformed into MoO2 before deoxidation was completed. Two deoxidation mechanisms were identified: evaporation and decomposition of MoO3 and MoO2, with evaporation being dominant in the early-stage sintering and decomposition being dominant in the later stage.

Preparation of fine copper powders from organic media by reaction with hydrogen under pressure: Part I. Experimental study

In this work, a novel method of preparing copper powder having the required properties for thick film applications was investigated. This method involves the precipitation of copper powder by hydrogen reduction under pressure from Kelex 100-decanol-Versatic 10-kerosene media. The parameters studied were temperature (453 to 573 K), hydrogen pressure (1.03 to 3.79 MPa) time, use of additives, solvent composition,etc. Powders with the following excellent properties were produced:d 50 = 1 μm; 80 pct spread −1.3 + 0.7 μm; specific surface area = 1 ±0.2 m2/g, spheroidal shape; and 0.056 wt pct oxygen content.

Spreading and interlayer formation at the copper-copper oxide/polycrystalline alumina interface

Spreadability and reaction layer growth rates of copper-oxygen alloys on polycrystalline alumina were measured above the melting point of copper to better understand the direct bonding process. Spreading was measured as a function of composition and temperature by monitoring the diameter of molten droplets as a function of time. As the oxygen content of the melt increased from 0 to 3 wt pct, the spreading diameter increased linearly, at fixed time and temperature. Constant diameters were observed for oxygen compositions between approximately 3 and 6 wt pct. The diameters again increased linearly for oxygen concentrations greater than 7 wt pct. This behavior was explained by reference to the copper-oxygen binary phase equilibrium. An interfacial product was identified to be the complex oxide, CuA102. A detailed investigation of the interlayer growth kinetics was performed to understand the fundamental phenomena controlling the spreading rates. The growth rate of the CuAlO2 phase and the spreading rate were simultaneously measured for alumina in contact with a copper-2 wt pct oxygen alloy drop as a function of temperature. The reaction layer thickening was found to be diffusion controlled, with an apparent activation energy of 309 kJ/mol, and the spreading rate did not correlate with the thickening rate.

Deoxidation of molten titanium by electron-beam remelting technique

The deoxidation of molten titanium was attempted by aluminum suboxide evolution in an electron-beam remelting furnace. Titanium aluminum alloy was deoxidized to about 0.05 to 0.01 wt pct oxygen in a few minutes by adding aluminum to the melt. Aluminum activity in the alloy was estimated by the evaporation rate of aluminum.

A fundamental study on the preparation of niobium aluminide powders by calciothermic reduction

Fine niobium aluminide powders such as NbAl3 were produced directly from mixtures of Nb2O5 and aluminum powder by calciothermic reduction. Prior to the reduction experiment, phase equilibria between Nb-Al and Ca-Al alloys were studied. Isothermal annealing of the specimens in the Nb-Al-Ca system at 1273 K showed that NbAl3 is in equilibrium with CaAl2 and Al-rich Ca-Al liquid alloys and that Nb3Al and Nb2Al equilibrate with Ca-Al alloys containing around 9 to 18 and 18 to 36 mol pct Al, respectively. Based on these experimental phase equilibria and on reported thermodynamic data of the Al-Ca system, the activities of Al in Nb-Al alloys were evaluated. This information is necessary in determining suitable compositions and conditions for the coreduction and ultimate production of single-phase niobium aluminide. The procedure for preparation of niobium aluminide powders by calciothermic reduction of Nb2O5 consists of three steps: (1) blending of starting materials (Nb2O5 + Al); (2) high-temperature reaction with calcium; and (3) acid leaching. After the reduction of Nb2O5 with calcium and aluminum to produce niobium aluminide powders, by-products of Ca-Al alloy, CaAl2, and CaO were formed. These were removed by leaching in aqueous acid solution. The NbAl3 particles obtained were a few micrometers in size and contained about 0.15 wt pct oxygen.

Preparation of submicron titanium nitride powder by vapor-phase reactions

The United States Bureau of Mines continued research on the preparation of titanium nitride powder for potential use as a substitute for imported tungsten used in metal cutting tools and wear-resistant applications. Major emphasis was directed toward improving the purity of the powder produced by vapor-phase reaction of titanium tetrachloride with magnesium in the presence of nitrogen or anhydrous ammonia at 1000 °C. Modifications were made in powder collection, handling, and purification procedures that significantly reduced the oxygen content of the product from > >5 wt pct to <<1 wt pct oxygen. Powder samples contained oxygen contents as low as 0.23 wt pct and exhibited a median particle size of 0.28 micrometer.

Literature Survey on Diffusivities of Oxygen, Aluminum, and Vanadium in Alpha Titanium, Beta Titanium, and in Rutile

A survey of diffusion data of interstitial oxygen and of the substitutional elements aluminum and vanadium is presented for alpha and beta titanium. It is based on a survey of literature. Oxygen is an important interstitial element in titanium alloys. Oxygen’s large chemical affinity to titanium is indicated by Ti—O bond energy of 2.12 eV,1 comparable to the Ti—Ti bond energy of 2.56 eV.2 Oxygen is difficult to eliminate completely from titanium, and commercial titanium alloys usually contain from 0.10 to 0.20 wt pct oxygen. Oxygen significantly affects the mechanical properties of titanium alloys1,3 and is sometimes used as an alloying element. The effects of oxygen on phase transformation ,4,5,6 Youngs modulus,7,8 hardness,9,10 fracture toughness,11 and other mechanical properties12 have been amply documented. Aluminum and vanadium are the most frequently used substitutional alloying elements. Aluminum is an alpha stabilizer and vanadium is a beta stabilizer.

Effects of oxygen and heat treatment on the mechanical properties of alpha and beta titanium alloys

Two alloys, Ti-6Al-2V and Ti-2Al-16V, simulating the alpha and beta phases of Ti-6A1-4V, respectively, were prepared with oxygen concentrations from 0.07 to 0.65 wt pct (0.20 to 1.83 at. pct). Their microstructure, deformation behavior, and strength were investigated with X-ray diffraction, microscopy, and mechanical tests to determine the effects of oxygen concentration and heat treatment. In both alloys the hardness increases in identical fashion with the square root of oxygen concentration. The alloys' strengths also depend on heat treatment, but in different ways. Whereas the alpha alloy is non-age-hardenable, the beta alloy's strength can be doubled by aging. The hardening effect of oxygen is generally unaffected by heat treatment, except for the alloys with the highest oxygen concentrations. During aging of the alpha a small amount of Ti3Al can form, and slight age-hardening occurs. The ductility of the alpha alloy is little affected by aging. On the other hand, oxygen causes a change from good ductility at low oxygen concentration (0.07 wt pct) to total brittleness at 0.65 wt pct oxygen, independent of heat treatment. In the beta alloy there are complex phase transformations depending on heat treatment. Its deformation behavior varies from very ductile in solutiontreated and quenched (STQ) condition to totally brittle in aged conditions. The aging embrittlement appears to be caused by alpha and some omega precipitation. Decoration of the beta grain boundaries with precipitates accounts for the intergranular brittle fracture. Oxygen, on the other hand, is not an embrittler, although it reduces the ductility of the beta alloy.

The solubility of the liquid oxysulfide phase in liquid Fe-O-S alloys

The solubility of the liquid oxide phase in liquid Fe-O alloys has been measured for the temperature range of 1378 to 1740 °C. Also the solubility of the liquid oxysulfide phase in liquid Fe-O-S alloys has been determined for the composition range of 0.08 to 0.30 wt pct oxygen and 0 to 0.5 wt pct sulfur. The oxygen content of liquid iron saturated with the liquid oxide phase is log O = −6358/T + 2.76. The standard free energy for the formation of the oxide phase is: xFe(l) + O(pct) = FexO(l); ΔG° = 242.4 − 0.0829T + 166,990/T(kJ). The equation for the standard free energy in the temperature range of 1550 to 1650 °C may be written as: −117.5 + 0.0496T (kJ). The effect of composition on temperature of saturation of liquid Fe-O-S alloys with the oxysulfide phase is:T(K) = −6358/(log pct O − 2.76) - (pct S)x [554 + 135.0(log O − 2.77)]. The relationship applies for the composition range of 0.15 to 0.30 wt pct oxygen and 0.0 to 0.5 wt pct sulfur and temperatures from 1480 to 1680 °C.

The rates of desulfurization of liquid iron by solid CaO and CaO-saturated liquid iron oxide at 1600‡c

The rates of desulfurization of Fe-O-S melts by CaO crucibles and by CaO-saturated liquid iron oxide have been measured at 1600 ‡C. It was found that irons containing 1.62 wt pct and 0.64 wt pct sulfur and 0.070 wt pct oxygen are desulfurized by a reaction with the containing CaO crucible which does not involve the formation of a CaS product layer. The rate of desulfurization reaction is controlled by diffusion of sulfur in the iron melt, and a value of 6.7 ±1.7 × 10-5 cm2 per second was obtained for the diffusion coefficient of sulfur in liquid iron. Iron containing 0.088 wt pct sulfur and 0.070 wt pct oxygen is not desulfurized by solid CaO. The rate of desulfurization of liquid iron containing 0.088 wt pct sulfur and 0.070 wt pct oxygen by CaO-saturated liquid iron oxide is significantly greater than that calculated on the assumption of diffusion control in the metal phase, and evidence is presented in support of speculation that the reaction rate is enhanced by Marangoni turbulence at the slag-metal interface. The addition of 4 wt pct CaF2 to the CaO-saturated liquid iron oxide has no influence on the rate of desulfurization of the melt.