Growth of a layer of W6Co7 phase in systems with participation of phases containing cobalt

Growth kinetics for a layer of W₆Co₇ at the interfaces tungsten-cobalt and tungsten-melts based on copper and tin containing cobalt at 1200 °C are studied. It is established that rate constant for growth of this layer in the system with participation of tin (k_Sn) is much greater than in the system with copper (k_Cu). Dependences are determined for these constants on cobalt activity in the melt (a_Co): k_Cu(m²/sec) = = 1.72 · 10^?15(a_Co ? 0.221) + 2.99 · 10^?14 (a_Co ? 0.221)²; k_Sn(m²/sec) = 1.8 · 10^?14 (a_Co ? 0.221) + + 9.077 · 10^?12 (a_Co ? 0.221)³.     

Phase formation in the nickel—Zinc reaction couple

Annealing of Ni’MZn reaction couples at 400°C for 1–25 h results in the formation of intermetallic layers of the γ- and δ-phases at the interface between nickel and zinc. The width of the homogeneity region for the γ-phase is 73.0–86.0 at. % Zn, while that for the δ-phase is 87.5–89.0 at. % Zn. The chemical formula for the γ-phase is thus NiZn_3–6, while that for the δ-phase is NiZn_7–8. The γ-phase growth kinetics is described by a parabolic equation x _i ² ’Mx ₀ ² =2k₁t_i (x_i and x₀ are the thicknesses of the layer at times t_i and t₀=0, k₁ is the growth rate constant): k₁=(4.4±0.2)·10^’M14 m²/sec. The δ-phase shows a deviation from the parabolic law since its growth rate constant decreases from 9.6·10^’M14 m²/sec at t=1 h to 6.9·10^’M14 m²/sec at t=25 h. The thickness ratio for the layers in this time interval chages by about 13%.     

The solubility of copper in lime-saturated and calcium ferrite-saturated liquid iron oxide

The solubility of copper in lime-saturated and calcium ferrite-saturated liquid iron oxide has been measured at 1300 °C by equilibrating copper-gold alloys with the melts in CO-CO₂ atmospheres of oxygen potentials 10^?7, 10^?8, 10^?9, and 10^?10 atm. It was found that copper exhibits Henrian behavior in the oxide melts and that the solubility is given by $$wt pct Cu = 17.6a_{CuO_{0.5} } $$ The copper capacity of the melts, 17.6, is approximately one-half of that of silica-saturated iron silicate melts at the same temperature. The results are compared with those of previous studies, and the difference between the solubilities of copper in silica-saturated and lime-saturated melts are discussed in terms of ionic interactions in the melts.     

Effect of low hydrostatic pressures on the diffusional phase transformation in dispersed multilayered systems

The effect of low hydrostatic pressures on the growth kinetics of phases in two-layer and multilayer Ni-Al diffusion specimen was studied by x-ray diffractometric, microprobe, optical and electron microscopic methods at temperatures T=0.4–0.6 T_m (T_m=melting temperature of the principal Ni₂Al₃ phase). Two types of specimens were investigated: massive two-layer, consisting of ∽3·10^?3 m thick sheets of nickel and aluminum presintered together, and finely dispersed multilayered, consisting of alternating layers of 10^?7-5·10^?7 m thick nickel and aluminum sheets. It was found that theapplication of pressure accelerated the formation of the Ni₂Al₃ and NiAl phases in both types of diffusion specimens. This effect is attributed to the action of pressure in preventing the formation of diffusional porosity at phase interfaces, and improving diffusional contact between adjoining layers.     

Reaction of Tungsten with Melts in the Cu - Co System

We have studied the solubility at 1200°C of tungsten in Cu - Co melts and the growth kinetics of a W₆Co₇ layer at the tungsten — melt interface. We have established the composition of the melt in the three-phase equilibrium tungsten — W₆Co₇ — melt: 0.0195 Co, 4.8 · 10⁻⁵ W, the rest is Cu (in atomic fractions). In the studied composition range for the melt, the solubility of tungsten is described well by the expression: lgX_W = −7.117 + 25.7 · X_Co ^1/2 − 41.06 · X_Co, where X_W and X_Co are the atomic fractions of the corresponding elements in the melt. We have determined the correlation between the growth rate for a layer of tungsten-containing phase at the tungsten — melt interface and the thermodynamic characteristics of the melt. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 81–86, May–June, 2005.     

A new procedure for measuring the thermal diffusivity of non-metallic melts at high temperatures

A new procedure for measuring the thermal diffusivity of non-metallic melts at high temperatures has been developed, and a measuring set up based on thermography and the use of a CO₂ laser has been constructed. The working efficiency of the measuring procedure, together with the accuracy and reproducibility of the measured values have been checked by measurements on synthetic slags. The thermal diffusivities of synthetic slag (38% CaO – 38% SiO₂ – 19% Al₂O₃ – 5% Fe₂CO₃) at temperatures from 1648 to 1740 K lie between 2.6×10^?7 and 3.0×10^?7 m²s^?1. The mean deviation of measured values is about ±6%. The advantages of this new procedure are compared with usual laser flash methods and possible error sources are discussed.     

Thermodynamic properties of holmium monogermanide

The heat capacity and enthalpy of HoGe is investigated for the first time over a temperature range between 51.62 and 2096 K. The values of heat capacity, entropy, reduced Gibbs energy (J · mole^?1 × × K^?1), and enthalpy (J · mole^?1) are determined at 298.15 K: C °_P(T) = 49.63 ± 0.20; S °(T) = 89.1 ± 0.7; Φ′(T) = 50.9 ± 0.8; H °(T) ? H °(0 K) = 11391 ± 57. Temperature dependences of enthalpy (J · mole^?1) for holmium monogermanide are determined as follows: H °(T) ? H °(298.15 K) = 8.474 × × 10^?3 · T² + 47.13 · T + 226747 · T^?1 ? 15565 and H °(T) ? H °(298.15 K) = 88.91 · T ? 26507, for 298.15–1765 K and 1951–2096 K, respectively. The enthalpy and entropy of HoGe melting are calculated: T_m = 1765 ± 35 K, ΔH_m = 36.3 ± 2.9 kJ · mole^?1, ΔS_m = 20.5 ± 1.6 J · mole^?1 · K^?1.     

STUDIES ON THE ACTIVATION-SINTERING OF IRON POWDER

Abstract

A study of the sintering behaviour of iron compacts containing additions of tin up to 1 wt.-% has been made. A tensile strength of 234 MN/m² (34 x 10³ lbf/in²) has been achieved with an optimum tin addition of 0·5 wt.-%, sintering being carried out for 10 min at 1100°C (1373 K) in a reactive halide atmosphere. Combination of the two ‘activating’ techniques (addition of tin and sintering in a reactive atmosphere) permits current properties to be attained at considerably lower sintering temperatures or sintered densities, and is much more effective than when they are applied individually. A tensile strength of 165·3 MN/m² (24 x 10³lbf/in²), achieved by sintering at 1200°C (1473 K) for 10 min with an addition of 0·5 wt.-% tin can be obtained by reactive-sintering the same composition at 900°C (1173 K) for 10 min. Alternatively, the density of the part can be reduced from 6·7 to 6·2 g/cm³ with no loss of strength or elongation. Tin in excess of 0·5 wt.-% causes deterioration in properties under the sintering conditions studied and a reason for this is cited. The improvements in properties are lost also if admixed lubricant is used in the compactionprocess.     

The distribution of silver,gold, platinum and palladium in metal-matte systems

The distribution of silver between molten metal and matte was determined at temperatures of 1150 to 1250°C. The partition coefficient (K_Ag-ratio of wt pct silver in matte to wt pct silver in metal) was 0.46 and was essentially independent of silver concentration, temperature, iron content and oxygen and SO₂ partial pressures over the ranges studied. Only the presence of nickel significantly affected K_Ag, causing it to rise from 0.46 to 1.16 within the region of liquid immiscibility. Outside this region all silver was intimately associated with chalcocite, rather than the heazel woodite or metallics, formed during solidification. Studies on other precious metals showed that K_Au=8×10^?3, K_Pd=6×10^?3 and K_Pt=4×10^?4 in the Cu?S system at 1200°C. Application of these results to actual operations is discussed, as is the chemical behavior of precious metals during matte smelting.     

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     

Uranium sorption from phosphoric acid solutions using selective ion exchange resins: Part II. Kinetic studies

Experiments have shown that the sorption of uranium from strong phosphoric acid solutions onto four D2EHPA/TOPO based ion exchange resins and one aminophosphonic acid resin is particle diffusion controlled in the uranium concentration range 42–780 μM. Interdiffusion coefficients of about 10^?12 m²s^?1 were obtained for D2EHPA/TOPO resins and 0.14 × 10^?12 m²s^?1 with the aminophosphonic acid exchanger at 20°C in 3 M H₃PO₄. Both homogeneous particle diffusion, based on Fick's Law, and the ash layer diffusion model fitted the kinetic measurements.     

Copper diffusion in iron during high-temperature tensile creep

The diffusion of liquid copper in iron from a notched surface has been studied by metallographic, microanalysis, and sessile drop techniques. The diffusivity of copper was found to be 0.59×10^?6 sq cm per sec at 1100°C and 0.97×10^?6 sq cm per sec at 1130°C. The diffusion factor,D ₀ was 0.78×10^?3 sq cm per sec and the activation energy 19.0 kcal per mole. The predominant mode of copper penetration was along grain boundaries, but when larger volumes of copper at the iron surface were used, surface diffusion increased and grain boundary penetration remained constant. The most frequently occurring dihedral angle for liquid copper was 34 deg at 1100° and 1130°C. The liquid copper/austenite interfacial energy was found to be 444 ergs per sq cm between 1100 and 1130°C. From sessile drop measurements, the contact angle was determined as 35 deg at 1100°C and 28 deg at 1130°C, from which values the respective interfacial energies were calculated to be 387 ergs per sq cm and 301 ergs per sq cm.     

On the thermodynamics of oxygen in molten copper,Cu-Sn,and Cu-Ag alloys

Measurements of oxygen activity in molten copper, Cu-Sn, and Cu-Ag alloys at 1135°C have been made utilizing the solid-state electrolyte technique. The activity coefficient of oxygen in molten copper at low oxygen levels (<0.1 pet) was found to be 0.12. The interaction parameters of silver and tin on oxygen were found to be ε _O ^Ag = 4.52 and ε _O ^Sn =-10.5. Comparison of experimental data with solution models revealed that the behavior of oxygen in Cu-O-Ag alloys is in accordance with predictions of Alcock and Richardson’s quasichemical model when a coordination number between 1 and 4 is assumed, depending on the silver and oxygen content. Furthermore, agreement with Belton’s quasichemical model based on the assumption of Ag-O dipoles serves to strengthen the evidence for the existence of Ag-O species in solution. The behavior of oxygen in the Cu-O-Sn system also shows better agreement with the quasichemical model than with the random model, with low coordination numbers favored in dilute tin solutions, increasing to larger values in Cu-60 Sn solutions.     

Oxidation of liquid alloys of tin with silver

Kinetic regularities of oxidation of Sn-Ag liquid alloys at T = 1273 K in air are investigated. The so-called catastrophic oxidation of melts containing 70 and 80 at % Ag is found. X-ray powder diffraction analysis of the scale forming on all Sn-Ag alloys, including such oxidation, showed that it consists of SnO₂ and silver metal. It is found that, in the range T = 1234–1303 K, the limiting wetting angle of liquid silver on tin dioxide is invariable and amounts to 72.4° ± 4.3°.     

Measurement of tracer diffusivities of Ca45 and Fe59 in silica saturated FeO-CaO-SiO2 melts with the porous frit technique

The tracer diffusivities of Ca⁴⁵ and Fe⁵⁹ in silica saturated FeO-CaO-SiO₂ melts have been determined, at 1600 °C, using the porous frit technique. The frits were made by sintering silica powder into quartz tubing. Diffusion occurred in a semi-infinite medium from a plane source of doped material with the same chemical composition. The tortuosity of each frit was determined by calibration with a resistivity cell. The diffusivity values obtained are about 2.0 · 10^?6 cm² s^?1 for Ca⁴⁵ and 1.0 · 10^?5 cm² s^?1 for Fe⁵⁹. The higher diffusivity of iron is possibly due to the different bonding by oxygen which causes a transition state in the jumps of Fe²⁺ ions from one site to the next.     

Thermodynamic properties and high-temperature behavior of lanthanum selenides La3Se4-La2Se3

The enthalpy of the La₃Se₄ and La₂Se₃ boundary compositions of the La_3?xSe₄ phase (0 ≤ x ≤ 1/3) at temperatures from 370 to 2260 K is studied calorimetrically. The values obtained are used and the equilibria of the La-Se system are analyzed to establish, for the first time, the temperature-concentration relationships for the thermodynamic properties of La_3?xSe₄ selenides in the homogeneity region at 298 K ≤ T ≤ 2123 K. The enthalpy function (J/mole) of La^3?xSe₄ is given by H(T) ? (298 K) = (3837 · 10³T^?1 ? 85852 + 266.925 · T ? 8.7503 · 10^?2 T² + 3.437 · 10^?5 T³) · e^?0.2869x. The formation and melting enthalpies of La₃Se₄ are determined: Δ_fH °(298 K) = ?1340 ± ± 28 kJ/mole), Δ_mH = 147.5 ± 9.6 kJ/mole. It is shown that the high-temperature stability of different La_3?xSe₄ compositions is strongly dependent on pressure: as pressure decreases and temperature increases, the selenium content is reduced and the composition tends to La₃Se₄.     

CREEP OF SILICON CARBIDE

Abstract

The creep behaviour of high-density silicon carbide has been examined under four-point transverse bending in air at temperatures from 1000 to 1300°C. Stresses in the range 0·207 GN m^?2 (30 000 Ib in^?2) to 0·496 GN m^?2 (72000 lb in^?2) were applied.

In tests lasting up to 3·6 Msec (1000 h) the creep strain (?_p) increased with time (t) as ?_p = At^k where k was between 0·2 and 0·5. The dependence of A on stress (σ) and absolute temperature (T) was found to be with n between 1 and 2 and Q～230 kJ mole^?1 (55 kcal mole^?1).

These results are compared with estimates of creep in SiC obtained by extrapolation of steady-state creep data from higher temperatures.     

Effect of changing slag composition on spinel inclusion dissolution

Abstract

The rate of MgAl₂O₄ spinel inclusion dissolution in CaO–SiO₂–Al₂O₃ slags at 1504°C has been measured using a laser scanning confocal microscope. It was found that the mechanism of spinel inclusion dissolution was at least in part controlled by mass transfer in the slag phase for the slag compositions used. Evidence in support of this finding was that the calculated diffusion coefficient was inversely proportional to the slag viscosity and that the diffusion coefficients were in reasonable agreement with those obtained in a separate study on alumina dissolution. The diffusion coefficients obtained were in the range of 0·76–2·2 × 10^?10 m² s^?1.     

Generation of small batch high quality metal powder

Abstract

As part of a project to develop a small batch metal atomisation system, based on free fall atomisation and close-coupled atomisation, the influence of the process parameters on various powder quality features has been investigated, using copper–tin alloys as feedstock material. Particle size distribution, appearance of satellite particles, particle circularity and the flowability were recorded as criteria of particle quality. From the data obtained in these experiments, the effects of the main process parameters (atomisation pressure, mass melt flow, and height of the spray chamber as well as the atomiser system) have been evaluated with respect to powder quality features. The atomisation system was optimised to produce high quality powder with narrow particle distributions (d_84·3/d_50·3?=?1·6 for free fall) and high circularity with mass melt flows in the range of 100 kg h^?1 using melt volume between 100 and 1000 mL.     

The influence of growth rate and temperature on high cycle fatigue of Al−Al3Ni

High-cycle fatigue tests have been conducted on specimens of an Al?Al₃Ni eutectic alloy, unidirectionally solidified at selected rates from 1.39×10^?4 cm/s to 0.3 cm/s. Tests were conducted in air at 298, 458 and 683 K. Room temperature fatigue lives were independent of growth rate at low solidification rates (1.39×10^?4–8.33×10^?3 cm/s, but were markedly improved in samples grown at 0.3 cm/s. Materials grown at 8.33 × 10^?3 cm/s exhibited fatigue lives similar to those of the lower growth rates, despite gross misalignment due to cellular growth. At 0.5T _m (458 K) and 0.75T _m (683 K), the fatigue lives of the material grown at low solidification rates were dependent on growth rate. The dependence of fatigue life on growth rate at elevated temperatures appears to be due primarily to differences in cyclic creep rates as a result of varying interfiber spacings. Crack initiation and propagation mechanisms were established by metallographic and fractographic examination. Dislocation substructure-fiber interactions were studied by transmission electron microscopy.