Electrotransport of carbon,nitrogen, and oxygen in zirconium

The electrotransport velocities of carbon, nitrogen, and oxygen in zirconium were determined at 1625°, 1700°, and 1800°C. Diffusion coefficients and effective charges were calculated for each of these elements at the same temperatures. The diffusion coefficients in combination with the migration velocities were used to predict the mean concentration profile of zirconium rods after various time intervals. The removal of nitrogen and oxygen from zirconium was in good agreement with the predicted values after a 5 day run. In conjunction with this investigation the specific resistivity of β zirconium was measured and the solid solubility of carbon determined.     

Electrotransport of carbon,nitrogen, and oxygen in hafnium metal

The electrotransport velocities of carbon, nitrogen, and oxygen in alpha and beta hafnium were determined for the temperature range of 1650 to 2130°C. Diffusion coefficients and effective valences were also obtained for each solute. These data were used to predict the degree of purification achievable in a hafnium rod after electrotransport at 2000°C for different times. A comparison was made between the predicted and experimentally observed results. Formerly Graduate Assistant, Department of Metallurgy, Iowa State University     

Leaching of molybdenum and arsenic from uranium ore and mill tailings

A sequential, selective extraction procedure was used to assess the effects of sulfuric acid milling on the geochemical associations of molybdenum and arsenic in a uranium ore blend, and the tailings derived therefrom. The milling process removed about 21% of the molybdenum and 53% of the arsenic initially present in the ore. While about one-half of the molybdenum in the ore was water soluble, only about 14% existed in this form in the tailings. The major portion of the extractable molybdenum in the tailings appears to be associated with hydrous oxides of iron, and with alkaline earth sulfate precipitates. In contrast with the pattern seen for molybdenum, the partitioning of arsenic into the various extractable fractions differs little between the ore and the tailings.     

Contact carbon impregnation of molybdenum and niobium castings

Conclusions The results are presented of a metallographic study of the surface zone of castings from niobium and molybdenum poured into graphite molds. Differences in the character of carbon diffusion into molybdenum and niobium castings are examined. The characteristics of the diffusion processes investigated are explained in the light of information on the electronic structure of the molybdenum, niobium, and carbon atoms.Translated from Poroshkovaya Metallurgiya, No. 11(71), pp. 39–41, November, 1968.     

Electrotransport and thermotransport of oxygen and nitrogen in vanadium metal

The effective valence of oxygen in vanadium was measured by a steady state electrotransport technique at six different temperatures in the range of 1500 to 2060 K. A temperature dependence inZ∗ was observed decreasing from 1.51 at 1500 to 1.15 at 2060 K. In thermotransport experiments the heats of transport were measured for oxygen and nitrogen in vanadium as a function of solute concentration. Positive values ofQ* were obtained for both solutes at all concentrations which, in view of their positive sign ofZ* in vanadium, is somewhat anomalous. The heat of transport of oxygen increases from 4.6 kcal/mole at 0.25 at. pct oxygen to 7.6 kcal/mole at 2.0 at. pct oxygen and above. Nitrogen shows a similar trend. This work was done while O. N. Carlson was a visiting scientist with the Max-Planck Institut.     

Electrotransport and diffusion of iron and silver in α-yttrium

The electrotransport mobilities and diffusion coefficients were determined for iron and silver impurities in yttrium. The mobility of iron increased from 1.2 x10^-4 cm²/V-s at 900°C to 7.4X10^-4 cm²/V-s at 1330°C. The silver mobility ranged from 8.1X10^-6 cm²/V-s at 905°C to 6.4 x 10^-5 cm²/V-s at 1095°C. The iron movement was anode-directed, and the silver movement was cathode-directed. The diffusion coefficients obtained fit an Arrhenius equationD = D₀e-ΔH/RT with the following values: Fe:D ₀ = 1.8 x 10^-2 cm²/s ΔH = 85 kJ/mol (20 kcal/mol); Ag:D ₀ = 5.4 x 10^-3 cm²/s ΔH = 77 kJ/mol (18 kcal/mol). A substitutional-interstitial mechanism previously proposed for anomalously high diffusion rates of impurities in cerium and lanthanum is also proposed for yttrium.     

The diffusion of carbon into tungsten and molybdenum at low carbon concentrations

Summary The principal diffusion constants of carbon — the preexponential factor D₀ and the energy of activation of the process, Q — have been determined with the aid of the isotope C¹⁴.As a result of annealing for 3.5 h in the temperature range 1100–1450°C, carbon was found to penetrate into tungsten and molybdenum to depths of 5 and 40 , respectively.     

Electrotransport and thermotransport of oxygen and nitrogen in vanadium metal

The effective valence of oxygen in vanadium was measured by a steady state electrotransport technique at six different temperatures in the range of 1500 to 2060 K. A temperature dependence inZ? was observed decreasing from 1.51 at 1500 to 1.15 at 2060 K. In thermotransport experiments the heats of transport were measured for oxygen and nitrogen in vanadium as a function of solute concentration. Positive values ofQ* were obtained for both solutes at all concentrations which, in view of their positive sign ofZ* in vanadium, is somewhat anomalous. The heat of transport of oxygen increases from 4.6 kcal/mole at 0.25 at. pct oxygen to 7.6 kcal/mole at 2.0 at. pct oxygen and above. Nitrogen shows a similar trend.     

Determination of thermodynamic activity of carbon in alloyed molybdenum carbide

Conclusions It is demonstrated that the thermodynamic properties of carbon in the carbide {ie736-01}. and {ie736-02}, vary greatly under the action of alloying, and that the effect shows up at concentrations of alloying elements less than 1%.The complex nature of the concentration dependence of carbon bond energy in alloyed carbides is due to the simultaneous effect of a variety of factors. The contribution of a particular factor to the overall bond energy differs with different concentrations.Translated from Poroshkovaya Metallurgiya, No. 9, pp. 64–70, September, 1967.     

Electrotransport purification and some characterization studies of vanadium metal

High-purity vanadium metal having an interstitial impurity content of <5 wt ppm and a resistance ratio,R _{300 K}/R _{4.2 K}, of >1880 has been prepared by an electrotransport technique. The lattice parameter of vanadium of this purity is 3.0269 +- 3Å. An extrapolated value for the room temperature resolved flow stress of vanadium free of C, O, and N was determined to be 0.41 kg/mm² on this material.     

Electrotransport and diffusion of Co,Fe, and Ag in γ-Cerium

Electrotransport mobilities and diffusion coefficients were obtained for radiotracer impurities of Fe, Co, and Ag in Ce. The iron and cobalt moved toward the anode with mobilities of ～10^?3 cm²/v-s in the range of 550° to 650°C. The silver moved to the cathode with mobilities of ～10^?5 cm²/v-s in the range of 600° to 700°C. The, diffusion coefficients obtained fit an Arrhenius equationD=D _o e ^?ΔH/RT with the following parameters: Fe:D _o=3.3×10^?4, ΔH=4.6 kcal/mole Co:D _o=10^?2, ΔH=11 kcal/mole Ag:D _o=1.4, ΔH=28 kcal/mole The results are compared with other rare-earth diffusion data, and the possibility of a substitutional-interstitial diffusion mechanism, is considered.     

Effect of molybdenum on tempered martensite embrittlement of medium carbon Si-Mn steels

This paper reports a study of the effects of molybdenum on tempered martensite embrittlement (TME) of medium carbon Si-Mn steels. The study employed standard U-notch impact tests, scanning electron fractography, transmission electron microscopy, Auger electron spectroscopy, and dilatometric measurements. It is shown that the addition of molybdenum to Si-Mn steels does not eliminate TME, but molybdenum acts to decrease the ductile-brittle transition temperature (DBTT), thus making the impact test temperature for revealing TME lowered. Furthermore, the deferring role of molybdenum on TME is observed. In the molybdenum doped steels the TME embrittlement trough is displaced to a higher tempering temperature. The embrittlement is found to be concurrent with the replacement of ?-carbide by cementite during tempering. In the molybdenum doped steels the displacement of TME to a higher tempering temperature is seen to be associated with the role of molybdenum retarding cementite precipitation.     

Free energy of formation of Mo2C and the thermodynamic properties of carbon in solid molybdenum

The activity of C in the two-phase region Mo+Mo₂C has been obtained from the C content of iron rods equilibrated with metal+carbide powder mixtures. From this activity data the free energy of formation of α-Mo₂C has been determined as ΔG _f ^o (α-Mo₂C) (1270 to 1573 K)=−47,530−9.46T±920 J/mol. This is in good agreement with the expression obtained from gas-equilibration studies by Gleiser and Chipman, ΔG _f ^o (α-Mo₂C) (1200 to 1340 K)=−48,770−7.57 J/mol, but both our and Gleiser and Chipman's values are about 10 pct lower than those of Pankratz, Weller and King calculated from ΔH _f,298 ^o andC _p vs T data. With the aid of available data for the solid solubility of C in Mo, the thermodynamic properties of C in the terminal solid solution have been calculated as J/mol, J/mol and , the excess entropy ofC in the solid solution assumingC is in the octahedral interstices =43.4±8.2 J/deg.-mol.     

Influence of carbon,silicon and molybdenum on the separating and emulsifying behaviour of steel and slag

The influence of C, Si, and Mo on the surface tension of Armco iron, and on the interfacial tension between Armco iron and a 40%CaO/40%SiO₂/20%Al₂O₃ slag at 1550°C has been investigated. Surface tension was determined according to the drop weight method, and the interfacial tension by the drop detachment method. Based on these measurements, ternary interfacial tension diagrams are set up, which enable the separating and emulsifying tendencies of the related steel/slag/gas systems to be predicted. This is followed by the calculation of the meniscus radius as a function of interfacial tension in continuous casting, together with the assessment of its effect on lubrication.