Extraction of molybdenum from weak acid rhenium-containing solutions

The possibility of extracting molybdenum from weak acid (pH 2 to 3) rhenium-containing solutions with the non-specific extractant Aliquat 336 is studied. A mechanism for the temperature influence on extraction and in particular for the extraction of molybdenum and rhenium is proposed. It is shown that the selectivity coefficient (β = D_Mo/D_Re) depends on the concentrations of both elements and also on the NO₃^? concentration in solution. When the concentration of molybdenum and nitrate ions increases, β increases. Increasing temperature has the same effect. A modifier is essential. At low rhenium concentrations it is better to use high molecular weight alcohols (as modifier), and at high concentrations it is better to use acetophenone. The authors believe that the investigations can be generalized and that analogous results can be expected if trialkylamine (for example, trioctylamine) is used.     

The diffusivity and solubility of oxygen in liquid tin and solid silver and the diffusivity

The diffusivity and solubility of oxygen in liquid tin and solid silver in the temperature range of about 750° to 950°C (1023 to 1223 K) and the diffusivity of oxygen in solid nickel at 1393°C (1666 K) were determined using the electrochemical cell arrangement of cylindrical geometry: Liquid or Solid Metal + O (dissolved) | ZrO₂ + (3 to 4%)CaO | Pt, air The diffusivity and solubility of oxygen in liquid tin are given by:D _O(Sn) = 9.9 × 10⁻⁴ exp(−6300/RT) cm²/s (9.9 × 10⁻⁸ exp − 6300/RT m²/s) andN _O ^S (Sn) = 1.3 × 10⁵ exp(−30,000/RT) at. pct The diffusivity and solubility of oxygen in solid silver follow the relations:D _O(Ag) = 4.9 × 10⁻³ exp (−11,600/RT) cm²/s ( 4.9 × 10⁻⁷ exp − 11,600/RT m²/s) andN _O ^S (Ag) = 7.2 exp (−11,500/RT) at. pct The experimental value for the preexponential in the expression forD _O(Ag) is lower than the value calculated according to Zener’s theory of interstitial diffusion by a factor of 11. The diffusivity of oxygen in solid nickel at 1393°C (1666 K) was found to be 1.3 × 10⁻⁶ cm²/s (1.3 × 10⁻¹⁰ m²/s). Formerly Graduate Student, Department Formerly Graduate Student, Department Formerly Graduate Student, Department This paper is based upon a This paper is based upon a This paper is based upon a This paper is based upon a     

Oxygen diffusion in alpha and beta titanium in the temperature range of 932° to 1142°C

An attempt is made to determine the diffusion coefficient of oxygen in α-Ti from oxidation studies of oxygen-unsaturated and oxygen-saturated β-Ti. Knowledge about the rates of movements of the α/β interface permits evaluation of oxygen diffusivity in α-Ti. The results conform to the relationship:D _α=0.778 exp (?48,600/RT), sq cm per sec, for the temperature range of 932° to 1142°C. From microhardness measurements, the diffusion coefficient of oxygen in β-Ti can be expressed as:D _β=3.30×10² exp (?58,800/RT), sq cm per soc, for the same temperature range.     

The nitridation of chromium and Cr-Ti alloys

Reaction zones and growth kinetics were studied after exposing high-purity chromium and alloys containing 0.5, 3.0, and 5.0 wt pct Ti to 1 atm of nitrogen between 1000° and 1400°C. Outer layers of Cr₂N and regions of internal nitridation, containing dispersed TiN particles, grew in a parabolic manner. An exact solution of Maak’s simplified analysis for internal oxidation provided calculations of nitrogen diffusion in the internal-nitride zone of each alloy. Extrapolation gave the relationshipD = 9.6 × 10^-3 exp (-28,500/RT) cm² sec^-1 for nitrogen diffusion in high-purity chromium. Increasing titanium to 5.0 wt. pct gaveD = 2.5 × 10^-3 exp (-24,000/RT) cm² sec^-1.     

Nitridation kinetics of niobium in the temperature range of 873 to 1273 K

The kinetics of Nb (Cb) nitridation and ε-NbN growth obey a parabolic relationship and their temperature dependence can be expressed ask _p = 5.19 × 10⁻⁷ exp (−125,500/RT) and (k _{p ξ} = 1.15 × 10⁻⁴ exp (−61,500/RT), respectively, with the activation energies in joules/mole. The nitrogen diffusion coefficient in niobium, obtained from microhardness traverses, is given byD = 1.02 × 10⁻⁵ exp (−77,000/RT). A diffusion model accounting for the partition of nitrogen between ε-NbN and Nb is proposed. The total nitrogen uptake calculated from the model is compared to that obtained experimentally.     

The interdiffusivity matrix of Fe2O3-CaO-SiO2 melt at 1693 to 1773 K

The diffusion couple method was used at 1693 to 1773 °K on liquid slags with their average compositon of 20 wt pct Fe₂O −₃−35 wt pct CaO-45 wt pet SiO₂. After diffusion runs for 40 min, the samples have been quenched to glassy state. The samples were sectioned, polished, and analyzed by a X-ray micro analyzer. The diffusivities matrix obtained from the penetration curves can be expressed by the following equations,D ³⁰ ₁₀₋₁₀ = 3.27 exp (−50000―RT)(cm²/s)D ³⁰ ₁₀₋₂₀ = -11.1 exp (−50000―RT)(cm²/s)D ³⁰ ₂₀₋₁₀ = 8.30 exp (−56300―RT)(cm²/s)D ³⁰ ₂₀₋₂₀ = 11.5 exp (−56200―RT)(cm²/s) where 10, 20, and 30 mean Fe₂O₃, CaO and SiO₃, respectively and the activation energies are in Cal per mol. The elements obtained satisfy the restriction derived from the second law of thermodynamics. The diffusion-composition paths obtained are consistent with the Cooper's parallelogram.     

Diffusion of managenese and silicon in liquid iron over the whole range of composition

The measurement of the diffusivities of manganese and silicon in molten binary ferroalloys over the whole range of composition was undertaken to clarify existing but conflicting data at lower concentrations, to present new data at higher concentrations and to indirectly confirm the behavior of both systems observed in thermodynamic studies. The experiments were carried out under argon atmosphere in a Tammann furnace. The diffusion couples were held in 5 mm ID alumina tubes (98 pct Al₂O₃). Electron probe microanalysis of the samples led to a diffusion-penetration curve for the system under consideration. Results obtained over the whole range of composition showed a slight negative deviation for the Fe−Mn system and a very large positive deviation for the Fe−Si system. At lower concentrations (0 to 4 pct Mn), the temperature dependence of managanese diffusivity for the Fe−Mn binary alloy in the temperature range 1550° to 1700°C is as follows:D _Fe−Mn=1.8×10⁻³ exp (−13,000/RT) cm²/sec The concentration dependence of manganese diffusivity for the same system at 1600°C may be expressed asD _Fe−Mn={5.48−0.0137 (%Mn)+0.000276 (%Mn)²}×10⁻⁵ cm²/sec The temperature dependence of silicon diffusivity for the Fe−Si binary system in the temperature range 1550° to 1725°C at various concentrations is as follows:D _Fe−Si=2.8×10⁻³ exp (−11,900/RT) cm²/sec at 20 pct SiD _Fe−Si=2.1×10⁻³ exp (−13,200/RT) cm²/sec at 12.5 pct SiD _Fe−Si=5.1×10⁻⁴ exp (−9,150/RT) cm²/sec at 2.2 pct Si FELIPE P. CALDERON, formerly Graduate Student. University of Tokyo, Tokyo, Japan. This paper is based on a portion of a thesis submitted by FELIPE P. CALDERON in partial fulfillment of the requirements for the degree of Doctor of Engineering at University of Tokyo.     

The diffusion of hydrogen in liquid Ni,Cu, Ag,and Sn

The rates of absorption of hydrogen in stagnant liquid Ni, Cu, Ag, and Sn have been measured using 1) an unsteady-state gas-liquid metal diffusion cell technique similar to that used by El-Tayeb and Parlee for iron and 2) a steady-state diffusion cell technique recently developed in this laboratory. The rates of absorption are considered to be controlled by diffusion in the liquid. On this basis the chemical diffusion coefficients of hydrogen (D _H) in liquid Ni, Cu, and Ag, calculated from the rate data, can be described by:D _H ^Ni =7.47×10^?3 exp(?8550±1114/RT) cm²/secD _H ^Cu =10.91×10^?3 exp(?2148±349/RT) cm²/secD _H ^Ag =4.54×10^?2 exp(?1359±207/RT) cm²/sec In the above equations, the uncertainty in the activation energy (Q _H) corresponds to the 90 pct confidence level. No reliable Arrhenius equation could be obtained forD _H ^Sn , but theD _H values in tin are greater than for the other three metals. The following interesting and possibly significant correlations are observed betweenD _H,Q _H, and the hydrogen solubility (S _H):D _H ^Ni <D _H ^Fe <D _H ^Cu <D _H ^Ag <D _H ^Sn , andQ _H ^Ni >Q _H ^Fe >Q _H ^Cu >Q _H ^Ag , andS _H ^Ni >S _H ^Fe >S _H ^Cu >S _H ^Ag >S _H ^Sn .     

Anelasticity study on mobility of interstitial oxygen in niobium

The mobility of oxygen in niobium has been studied by means of a strain relaxation technique at temperatures from 348 to 368 K. Careful analysis of the relaxation curve shows that a summed exponentials model fits very well to the experimental data, while a conventional lognormal model fails to fit. The curves are separated into four relaxation processes using an approximation of neglecting a minor process with the longest relaxation time. For a process with the shortest relaxation time (process I), which is newly found in the present study, the diffusivity D is given by D = 4.2 ± 0.3 × 10⁻⁷(m²/s)exp(−107.2 ± 0.4kJ/mol)/RT.A linear Arrhenius relationship of the diffusivity is found on this alloy system, covering currently available diffusion data measured by mass flow and internal friction techniques at high temperatures where diffusion occurs by jumps of single oxygen atoms. Therefore, it is concluded that the present new process I arises from the stress-induced ordering of single oxygen atoms and the other processes from oxygen clusters and impurity-oxygen complexes.     

Diffusion of vanadium,chromium, and manganese in copper

The diffusion coefficients of vanadium, chromium and manaanese in copper have been determined by the residual activity method with radioactive tracers V⁴⁸, Cr⁵¹ and Mn⁵⁴ in the temperature ranges between 955 and 1342 K, between 999 and 1338 K and between 971 and 1253 K, respectively. The temperature dependence of the diffusion coefficients is expressed by the following Arrhenius equations along with the probable errors:D _V/Cu = (2.48 _-0.44 ^+0.53 ) x 10⁻⁴ exp [-(215 ± 2) kJ mol⁻¹/RT] m² per s,D _Cr/Cu = (0.337 _-0.090 ^+0.124 ) x 10⁻⁴ exp [-(195 ± 3) kJ mol⁻¹/RT] m² per s,D _Mn/Cu = (1.02 _-0.18 ^+0.22 ) x 10⁻⁴ exp [-(200 ± 2) kJ mol⁻¹/RT] m² per s. Anomalous penetration profiles for the diffusion of Cr⁵¹ and Mn⁵⁴ in the present results suggest that experimental results onD _Cr/Cu andD _Mn/Cu in the past have been influenced by oxidation and evaporation of the chemically active radiotracers during annealing for diffusion. formerly Graduate Student, Tohoku University     

Interdiffusion in the body cubic centered β-phase of titanium-hafnium alloys

Interdiffusion in the β-phase of Ti-Hf alloys has been studied between 1000 and 2000°C. The concentration dependence of the interdiffusion coefficients is small. With temperature, they show an “anomalous” behavior, caracteristic of the diffusion in b.c.c. metals and alloys: the high temperature activation energy (~ 175 kJ/mol) is greater than the low-temperature one, near the β → α transformation (~ 120 kJ/mol). Diffusion coefficients at infinite dilution D^o_Hf(Ti) and D^o_ti(hf) and the influence of zirconium impurities are specified. No Kirkendall effect was seen during experiments of diffusion in these alloys.     

Thermodynamics of titanium alloys: I. Development of a triple Knudsen cell and its use to study the activity of copper in the Ti−Cu system

A new experimental technique for the determination of thermodynamic activity of alloys has been developed utilizing a triple Knudsen cell with a pure enriched natural isotope as the standard reference state. The alloy for which activity is to be determined is placed in one of the two effusion chambers of the triple cell and the pure isotopic standard in the other. The molecular beams from each chamber effuse into a third upper chamber and through a collimating hole into the ion source of a Bendix time-of-flight mass spectrometer. Since the recorded intensities are proportional to the vapor pressures within the chambers, a simple calculation based upon their ratio gives a direct determination of the activity of the solute in the alloy. The accuracy of the triple cell technique for the experimental determination of activities was checked by the measurement of the copper activity in a Ni?Cu alloy containing 30.6 wt pct Cu. A value ofRT γ_Cu=1778±142 cal per g-atom at 1450°K was obtained, which is in excellent agreement with values in the literature. The activity of copper in the bcc β phase when then determined for four Ti?Cu alloys (X _Cu=0.033 to 0.085), using pure enriched Cu⁶⁵ as the standard reference state. The composition range investigated was limited to alloys belowX _Cu=0.10, the maximum solubility within the experimental temperature range between 1423° and 1573°K, the activity of copper in the bcc β phase can be expressed using pure liquid copper as the standard state by the following equation:RT Ina _Cu=RT InX _Cu+X _Ti ² (1.92±0.30) in kcal per g-atom. The activity of titanium is given byRT Ina _Ti=RT InX _Ti+X _Cu ² (1.92±0.30) in kcal per g-atom.     

Tracer diffusion of63Ni in Fe-17 wt pct Cr-12 wt pct Ni

The tracer diffusion of⁶³Ni in Fe-17 Cr-12 Ni by both volume and grain boundary transport has been studied from 600° to 1250°C. The use of an RF sputtering technique for serial sectioning allowed the determination of very small volume diffusion coefficients at the lower temperatures. Volume diffusion of nickel in this alloy was observed to be much slower than in pure iron or austenitic stainless steel at comparable temperatures. The volume diffusion coefficient is described byD _v =8.8 exp (−60,000/RT) cm²/s and grain boundary diffusion is described by σD _gb =3.7×10⁻⁹ exp (−32,000/RT) cm³/s. R. A. PERKINS, formerly Presidential Intern, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak, Ridge, Tenn. 37830, is     

Electrotransport of carbon in molybdenum and uranium

The electrotransport velocity of carbon in molybdenum and uranium was measured over a temperature range slightly below their melting points. Carbon was found to have a positive effective valence of 2.26 to 1.74 in molybdenum over the temperature range of 1890 to 2320°C and a negative value of - 5.0 in γ-uranium between 850 and 1000°C. The effective valences of nitrogen and oxygen were also observed to be positive in molybdenum and negative in uranium but their magnitudes were not determined. The diffusion coefficients for carbon in both metals were determined over the same temperature ranges.¹⁴Carbon was used as a tracer in the molybdenum work. The diffusion coefficient for carbon in molybdenum is described by the equationD = D ₀ exp (-†H/RT) whereD ₀ and †H are 0.033 cm²/s and 153 kJ/mole (36.60 kcal/mole), respectively. The values forD ₀ and †H for carbon in γ-uranium were determined as 0.218 cm₂/s and 123 kJ/mole (29.40 kcal/mole), respectively. Electrotransport was shown to be an effective method of purifying a small amount of each metal with regard to carbon as indicated by resistance ratio measurements and chemical analysis. A correlation is also presented showing the relationship between the atomic size of the solvent metal and the sign of the effective charge of the migrating solute.     

Grain-boundary diffusion of germanium in copper and Cu-Ge and Cu-Fe alloys

The grain-boundary diffusion (GBD) of germanium in copper and its alloys Cu-2% Ge and Cu-0.5% Fe is investigated in the temperature range of 500?C590°C by means of electron-probe microanalysis. The GBD parameters (triple product P = s??D _GB and effective activation energy E) are found. The temperature dependence of the triple product for germanium GBD in pure copper can be described by equation P = 3 × 10¹⁵exp[?80 kJ mol^?1/(RT)] m³ s^?1. It is shown that the addition of Ge has almost no effect on the GBD parameters in copper, while doping with iron leads to a considerable reduction in the triple product.     

Mass transfer mechanisms in CoO

In order to identify the diffusing species and to establish the diffusion mechanisms, the growth kinetics of grain boundary grooves have been investigated in high purity cobalt oxide over a temperature range from 1084° to 1408°C. The rate of mass transfer was determined interferometrically from a specimen annealed in air for various times. The controlling mechanism of mass transport was deduced from the morphological change of the groove profiles. At temperatures below 1100°C, surface diffusion was the controlling mass transport mechanism, and at temperatures above 1140°C, volume diffusion was the dominant mechanism. The mass transfer volume diffusion coefficient,D _m , is given byD _m =D _o exp(?Q/RT) whereD _o=3.94×10^?3 sq cm per sec andQ=38,420±2110 cal per mole. TheD _o value is based on an estimated value for the surface free energy of 500 ergs per sq cm. The measured activation energy is in good agreement with the activation energy for cation self-diffusion determined recently by Chen, Peterson, and Reeves using tracer-sectioning techniques. TheD _o value agrees with their results within a factor of two, depending on the surface free energy value that is chosen. Reducing the oxygen partial pressure results in a decrease inD _m , similar to the decrease in the cobalt self-diffusion coefficient at 1309°C.     

A model for the applied stress effects on the Intergranular Phosphorus Segregation in ferrous materials

A model has been presented in terms of which the facts observed in a previous paper can be successfully explained. It is based on the assumption that phosphorus atoms migrate along grain boundaries so as to decrease the strain energy in the grain boundaries more stressed under normal traction. The change in the intergranular phosphorus concentration (IPC) due to this solute migration during the first aging of At, at a grain boundry normal to the applied stress, is given by ∼ φχ_p⁰D_p^gVσΔt/s²RT, where χ_p⁰ is the initial value of IPC prior to stress aging, D_p^p the diffusion coefficient of P along grain boundaries, V the specific volume of the alloy, s half the grain diameter, φ a numerical factor of the order of unity, RT has the usual meaning and σ is an apparent traction at the grain boundary, being more than 4 ∼ 5 times as large as the applied stress.     

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.     

Solute diffusion in alpha- and gamma-iron

The diffusion rates of chromium, vanadium, and hafnium in α- and γ-Fe have been determined by radiotracer techniques. The results are (in sq cm sec⁻¹): α-Fe γ-Fe ChromiumD = 8.52 exp (−59,900/RT)D = 10.80 exp(−69,700/RT) VanadiumD = 3.92 exp (−57,600/RT)D = 0.25 exp (−63,100/RT) HafniumD = 1.31 exp (−69,300/RT)D = 3600 exp (−97,300/RT) The differences in diffusion rates are discussed in terms of the compressibility of the diffusing atom. Diffusion of chromium in γ-Fe was also measured by a microprobe analysis technique. The result is:D = 4.08 exp (−68,500/RT) Comparison is made between diffusion analysis by tracer techniques and by electron probe microanalysis. Formerly with Department of Metallurgy, University of Manchester, Manchester, England     

Fast diffusion of cobalt along stationary and moving grain boundaries in niobium

⁵⁷Co diffusion along grain boundaries (GBs) in high-purity Nb has been studied in the temperature range 823–1471 K by the serial sectioning technique. As it was not possible to fully stabilize the grain size by any pre-diffusion annealing, part of the GBs could migrate during the diffusion anneals. Using the earlier proposed method [Z. Metallk. 84, 584 (1993)], the product P = sD_GBδ [s being the 7GB-segregation factor, D_GB the GB-diffusion (GBD) coefficient, δ the GB width] for stationary GBs and the velocity V of moving GBs were deduced from the diffusion profiles. The P-values follow an Arrhenius dependence P = (4.84_−2.68^5.99) × 10⁻¹³ exp[-(14.5 +- 7.2) kJ mol⁻¹/RT] m³ s⁻¹ and are 4–2 orders of magnitude higher in the measured temperature range than the expected P-values for GB self-diffusion in Nb. This observation is well consistent with the known fact of fast lattice diffusion of Co in Nb and provides evidence for a combined vacancy-interstitial GBD mechanism. From the temperature dependence of V an activation enthalpy of GB motion in Nb H_m ≅ 182 kJ mol⁻¹ is estimated.