Na2SO4-induced accelerated oxidation (hot corrosion) of nickel

The Na₂SO₄-induced accelerated oxidation of nickel has been studied at 1000°C. It has been found that low oxygen activities in the Na₂SO₄, which are produced by the formation of NiO, cause the sulfur activity of the Na₂SO₄ to be increased. Nickel and sulfur from the Na₂SO₄ combine to form nickel sulfide and the oxide ion activity of the Na₂SO₄ is increased. The accelerated oxidation of nickel occurs because oxide ions react with NiO to form a nonprotective oxide scale. The accelerated oxidation of nickel is not self-sustaining since oxide ions are not produced when conditions in the Na₂SO₄ are no longer favorable for the formation of nickel sulfide.     

Solvent extraction of cobalt and nickel by organophosphorus acids I. Comparison of phosphoric,phosphonic and phosphonic acid systems

The solvent extraction of cobalt(II) and nickel(II) by xylene solutions of commercial dialkyl-phosphoric (D2EHPA), phosphonic (Shell RD 577) and phosphinic acids (Cyanex CNX) has been investigated. In each case, cobalt is extracted at lower pH values than nickel; under comparable conditions, the cobalt-nickel separation increases in the order phosphoric < phosphonic < phosphinic acids. Application of the slope analysis technique indicates stoichiometries of Co(HA₂)₂ and NiHA₂)₂(H₂A₂)_x(H₂O)2?x for the cobalt and nickel complexes, respectively, where H₂A₂ represents the dimerized extractant molecule and x = 0, 1, or2. The effect of a range of organic phase additives has been examined. Typical emulsion inhibiting reagents such as isodecanol and tributyl phosphate cause the cobalt—nickel separations to decrease significantly. A novel synergistic effect has been found with mixtures of D2EHPA and 2-ethylhexanal oxime (EHO); the synergism is so marked in the case of nickel as to reverse the selectivity for cobalt over nickel shown by D2EHPA alone. The electronic spectra of the organic extracts show that the organophosphorus acids examined from complexes of tetrahedral structure with cobalt and octahedral structure with nickel. In the D2EHPA—EHO system, however, the deep blue tetrahedral cobalt-D2EHPA complex is transformed into a pink octahedral complex, presumably of the type Co(HA₂)₂(EHO)₂, whilst the green octahedral nicke—D2EHPA complex is converted to a bright blue species of similar geometry, in which the neutral oxygen-donor ligands (H₂A₂ and/or H₂O) have been displaced by the nitrogen-donor oxime ligands.     

Leaching of nickel from supported nickel waste catalyst using aqueous sulfur dioxide solution

Waste nickel catalyst is an important secondary source for recovery of nickel. Nickel from the waste has been leached out using aqueous SO₂ solution. The initial leaching kinetics is controlled by reaction at the surface involving the adsorption of SO₂ and H⁺ resulting in the formation of product species. A kinetic model based on the above scheme has been presented. The X-ray photoelectron spectroscopy (XPS) studies indicate that easily soluble Ni(OH)₂ or NiO is initially leached out, leaving behind the other nickel species which dissolves at a slower rate.     

Thermodynamics of oxygen behaviour in cobalt-nickel alloys

In this study the concentration and chemical potential of oxygen in liquid Co-Ni alloys equilibrated with cobalt-nickel aluminate spinel solid solutions and alumina have been determined at 1773, 1823 and 1873K as a function of nickel concentration. The oxygen content of the melt has been measured by suction sampling and inert gas fusion analysis. The corresponding oxygen potential has been determined with the following solid state cell: Mo, Mo+MoO₂ | (MgO)ZrO₂ | (Co, Ni) melt + AI₂O₃ + (Co, Ni)O·(1+x)Al₂O₃, Mo. The effect of nickel on the activity coefficient of oxygen in Co-Ni alloys has been determined. The results for the activity coefficient have been modelled with Wagner's interaction parameters and also the more recent exponential method of St. Pierre et al. at the three temperatures.     

Solvent extraction of nickel and cobalt by mixtures of carboxylic acids and non-chelating oximes

The effect of non-chelating oximes on the solvent extraction of nickel(II) and cobalt(II) by solutions of carboxylic acids (H₂A₂) in xylene has been studied. Synergistic enhancements of extraction were found with aldoximes, but not with ketoximes. The synergistic effects are larger for nickel than for cobalt, with the result that the selectivities of the carboxylic acids for nickel over cobalt are considerably enhanced in the presence of aldoximes. The influence of the molecular structure of the oxime and carboxylic acid components upon the synergistic effects is rationalized in terms of the prevailing stereochemical and electronic effects. The extracted complexes were shown to be octahedral in structure, with the compositions NiA₂(oxime)₄ and CoA₂(oxime)₄.The mixed reagent systems may prove useful for the selective extraction of nickel in the presence of cobalt.     

An approach for the development of protective coatings for the novel magnetostrictive material Tb0.3Dy0.7Fe1.92

A logical approach towards the development of protective metallic coatings for the newly developed pseudo-binary rare earth magnetostrictive material Tb_0.3Dy_0.7Fe_1.92 has been put forth. Based on the proposal, experimental trials were conducted on nickel-based coatings, produced by electrodeposition and electroless plating techniques. Direct current electrodeposition of nickel was conducted using both aqueous and non-aqueous plating baths. Non-aqueous electrodeposition produced adherent nickel deposits unlike aqueous electrodeposition and electroless plating methods. The main cause of poor coating adherence in aqueous electrodeposition and electroless plating has been identified as excessive hydrogen evolution. The physical disintegration of the substrate due to hydrogen embrittlement has been briefly addressed.     

A thermodynamic model of nickel smelting and direct high-grade nickel matte smelting processes: Part II. distribution behaviors of Ni, Cu, Co, Fe, As, Sb, and Bi

A thermodynamic model has been developed to predict the distribution behavior of Ni, Cu, Co, Fe, S, As, Sb, and Bi in nickel smelting and direct high-grade nickel matte smelting processes. The model has been validated by numerous experimental data and industrial data with a wide range of operating conditions. The effect of operating conditions on the distributions of Ni, Cu, Co, As, Sb, and Bi among the gas, matte, and slag phases has been investigated. It was found that the distribution behavior of Ni, Co, Cu, As, Sb, and Bi in the nickel smelting furnace depends on process parameters such as the smelting temperature, matte grade, oxygen enrichment, Fe/SiO₂ ratio in the slag, Cu/Ni ratio in charge, and oil/air ratio. The parameters also have an influence on the behavior of Fe₃O₄ in the slag.     

Simultaneous sulfidation-oxidation of nickel at 603°c in argon-so2 atmospheres

The simultaneous oxidation-sulfidation rate of nickel has been measured as a function of SO₂ pressure (0.04 to 1 atm) in Ar-SO₂ gas mixtures at 603°C. The observed corrosion rates are about 10⁷ times faster than the oxidation rate of nickel in oxygen at 1 atm. The product scale consists of an inner Ni₃S₂ layer and an outer two-phase layer of NiO and Ni₃S₂. A linear rate law is observed during an initial time period, and the most probable rate-controlling step is dissociation of SO₂. An increase in the scale-gas interfacial area increases the corrosion rate during intermediate time periods. With increasing time, parabolic corrosion rates are measured for SO₂ pressures of 0.25 and 1 atm. Values of the nickel diffusivity in Ni₃S₂ calculated from our measured parabolic-rate constants are in good agreement with recently reported values. This agreement indicates that an interconnected Ni₃S₂ phase in the outer two-phase layer provides rapid transport paths for nickel diffusion through the scale. Formerly a Graduate Student in the Department of Metallurgy and Materials Science at the University of Pennsylvania, Philadelphia, PA     

Structure of martensites in Fe-Ni-Ti alloys

The morphology, internal structure and crystal structure of martensites in three Fe-Ni-6 pct Ti alloys containing 10, 20, and 25 pct by weight of nickel have been studied. The 10 and 20 pct nickel alloys transform to lath martensite with a dislocated sub-structure, and are not tetragonal. The 25 pct nickel alloy forms martensite plates on transformation, with a substructure of dislocations and twins. This alloy is tetragonal in both twinned and dislocated regions with ac/a ratio of 1.017. Electron diffraction evidence for a tetragonal phase produced by the Bain strain of Ni₃Ti has also been obtained. The observations support the hypothesis that the tatragonality results from the formation of an ordered Ni₃Ti phase in austenite prior to transformation to martensite.     

The treatment of lateritic nickel ores — a further study of the caron process and other possible improvements. Part I. Effect of reduction conditions

An investigation of the reduction roast and ammonia leach method of treating lateritic nickel ore (Caron process) is reported. The effect of the CO₂/CO and H₂O/H₂ couples, both separately and in combination, upon the extraction of nickel from both serpentinic and limonitic ores has been studied as a function of reduction time and temperature, gas composition and particle size.In Part I leaching was carried out with ammoniacal liquors and the influence of aeration and reduction conditions upon the formation of ferric hydroxide which absorbs nickel from the leach liquor was studied. It was found that effective reduction required a minimum partial pressure of p_H2 or p_CO of at least 0.15 atm regardless of the type of ore; Partial pressures of reductant above 0.2 atm did not affect the reduction materially. Both the CO₂/CO and H₂O/H₂ couples could be used for selective reduction, but mixtures of the two were less effective than the reductants on their own. The presence of water vapour in the reducing gas appeared to have a deleterious effect upon nickel extraction.In Part II the effect of different leaching agents is reported.     

Phase equilibrium and minor-element distribution between Ni3S2-FeS matte and calcium ferrite slag under high partial pressures of SO2

Calcium ferrite slag has been successfully used in the copper smelting process, but no attempt has been made to use it in the nickel smelting process. The phase equilibrium and the distribution of minor elements between the Ni₃S₂-FeS matte and the CaO-FeO_x-based slag (containing about 2 wt pct MgO) in a magnesia crucible were investigated at 1523 K under controlled partial pressures of S₂, O₂, and SO₂ of 10.1, 50.7, and 101.3 kPa, respectively. The results were compared with those for the iron-silicate-based slag, and the following conclusions were obtained: (1) there is no significant difference in the solubility of nickel between both slags in the high-matte-grade range, (2) the dissolution of cobalt in the calcium ferrite slag is clearly smaller than that in the iron silicate slag, (3) detrimental arsenic, antimony, and bismuth are preferentially collected and fixed in the calcium ferrite slag rather than in the iron silicate slag, and (4) it is considered, with regard to technical feasibility, that the use of the calcium ferrite slag in a converting process of the Bessemer matte will have a prominent future for the nickel converting stage.     

Analysis of hydrogen-induced subcritical intergranular crack growth of iron and nickel

Hydrogen-induced subcritical crack growth of iron and nickel alloys has been shown to occur in both gaseous and aqueous environments and is a concern in a variety of applications. Identification of the mechanisms by which hydrogen induces crack growth in these materials remains an unsettled issue, with hydrogen-enhanced shear and hydrogen-induced decohesion the primary mechanisms under consideration. The purpose of this paper is to report on subcritical crack growth tests of iron and nickel conducted at catholic potentials under conditions in which the crack growth mode was predominantly intergranular. Subcritical crack growth tests were conducted using compact tension samples with thicknesses of 2, 5, and 10 mm at cathodic potentials ranging from −0.6 to −1.25 V for iron and −0.3 to −1.0 V for nickel in 1 N H₂SO₄. Crack growth thresholds and crack velocities were determined as a function of sample thickness and test potential. Plastic zone sizes for iron and nickel were determined using electron channeling patterns, microhardness, and transmission electron microscopy. Comparisons between plastic zone size and crack growth behaviour were made. The hydrogen-induced intergranular subcritical crack growth behavior of iron and nickel were found to exhibit several similarities including K_th and stage I crack growth kinetics. Nickel exhibited stage II behavior with a limiting velocity of about 10⁻⁴ mm/s; iron did not. This limiting velocity was consistent with the rate limiting process being hydrogen diffusion in nickel.     

The effect of temperature on nickel solubility in silica saturated fayalite slags from 1523 to 1623 K

The solubility of nickel in silica saturated fayalite slags has been measured at 1523 K and 1623 K through equilibration with liquid Ni-Au-Fe alloys and CO₂/CO gas. Solubility in weight percent is expressed as a function of oxygen pressure and activity of nickel and the data combined with previous measurements at 1573 K to quantify the effect of temperature on nickel solubility and to estimate the heat of solution of NiO in silica saturated slags.     

The effect of temperature on nickel solubility in silica saturated fayalite slags from 1523 to 1623 K

The solubility of nickel in silica saturated fayalite slags has been measured at 1523 K and 1623 K through equilibration with liquid Ni-Au-Fe alloys and CO₂/CO gas. Solubility in weight percent is expressed as a function of oxygen pressure and activity of nickel and the data combined with previous measurements at 1573 K to quantify the effect of temperature on nickel solubility and to estimate the heat of solution of NiO in silica saturated slags.     

A mass spectrometric study of nickel tetracarbonyl,iron pentacarbonyl and binary mixtures of these compounds

The mass spectra and appearance potentials for the major singly charged ions from iron pentacarbonyl, nickel tetracarbonyl and binary mixtures of these carbonyls have been determined. Enthalpies of formation of the ions have been calculated and the mechanism of formation of the ions is shown to be one of successive removal of CO groups from the molecule or ion (as indicated by previous workers). Mean metal-carbon bond dissociation energies have been calculated for the neutral molecules to be 156.5 and 129.0 kJ mole^-1 for nickel tetracarbonyl and iron pentacarbonyl respectively. No evidence has been found in the mass spectra of the carbonyl mixtures to substantiate the existence of the molecule FeNi(CO)₉ which has been proposed to account for nonideality in the binary carbonyl system.     

Kinetics of chloridization of nickel-bearing lateritic iron ore by hydrogen chloride gas

The selective chloridization of nickel in a lateritic iron ore by gaseous HCl is based on the principle of relative thermal stability of iron and nickel chlorides. This aspect has been discussed with differential thermal analysis (DTA) and thermogravimetric (TG) data of the hydrated chlorides of iron and nickel. The kinetics of chloridization of nickel in a lateritic nickel ore from Orissa, India, have been studied by using both pure HCl (g) and the HCl (g) + N₂ mixture. The sharp decrease in the rate of chloridization of nickel at temperatures above 250 °C is attributed to the rapid decomposition of molten ferric chloride hydrate (FeCl₃ · 3H₂O), which blocks the pores of the reactant solid. Therefore, kinetics of chloridization follow both the pore-blocking model (logarithmic rate law) and diffusion-controlled mechanisms. Very low values of apparent activation energy and effective diffusivity derived from the rate constants of the diffusion-controlled process suggest that diffusion of HCl (g) takes place either in a dissolved state in the molten ferric chloride (at 100 °C to 150 °C) or through cracks and fissures formed on the surface due to rapid decomposition of ferric chloride at 200 °C to 250 °C. Because of the complexity of the reaction system, the rate of chloridization of nickel is almost independent of grain size.     

Synthesis of ultrafine particles of intermetallic compounds by the vapor-phase magnesium reduction of chloride mixtures: Part I. Titanium aluminides

A new chemical synthesis process for the preparation of intermetallic compounds has been developed. It involves the vapor-phase reduction of mixtures of constituent metal chlorides by magnesium vapor to produce intermetallic compounds in the form of fine powder. The advantages of the process include (a) the use of inexpensive raw materials, (b) low reaction temperatures, and (c) products in the form of fine particles. Part I describes the synthesis of titanium aluminide particles by this method, whereas Part II presents the synthesis of nickel aluminides particles. Although nickel aluminides can also be prepared by the hydrogen reduction of nickel chloride and aluminum chloride vapor mixtures, titanium aluminides cannot be produced by hydrogen reduction because of unfavorable thermodynamics. The effect of AlCl₃/TiCl₃ partial pressure ratio on the formation of different titanium aluminides was studied. A two-phase mixture containing 80 mol pct of TiAl+20 mol pct of TiAl₃ formed at an AlCl₃/TiCl₃ ratio of 10. The amount of TiAl₃ was maximized to 72 mol pct at an AlCl₃/TiCl₃ ratio of 16. The maximum conversion of the limiting chloride TiCl₃ was 94 pct. The product particles were very fine in the size range of 0.2 to 0.3 μm.     

Microstructural Characterization and Properties Evaluation of Ni-Based Hardfaced Coating on AISI 304 Stainless Steel by High Velocity Oxyfuel Coating Technique

The present study concerns a detailed investigation of microstructural evolution of nickel based hardfaced coating on AISI 304 stainless steel by high velocity oxy-fuel (HVOF) deposition technique. The work has also been extended to study the effect of coating on microhardness, wear resistance and corrosion resistance of the surface. Deposition has been conducted on sand blasted AISI 304 stainless steel by HVOF spraying technique using nickel (Ni)-based alloy [Ni: 68.4 wt pct, chromium (Cr): 17 wt pct, boron (B): 3.9 wt pct, silicon (Si): 4.9 wt pct and iron (Fe): 5.8 wt pct] of particle size 45 to 60 ??m as precursor powder. Under the optimum process parameters, deposition leads to development of nano-borides (of chromium, Cr₂B and nickel, Ni₃B) dispersion in metastable and partly amorphous gamma nickel (??-Ni) matrix. The microhardness of the coating was significantly enhanced to 935 VHN as compared to 215 VHN of as-received substrate due to dispersion of nano-borides in grain refined and partly amorphous nickel matrix. Wear resistance property under fretting wear condition against WC indenter was improved in as-deposited layer (wear rate of 4.65 × 10^?7 mm³/mm) as compared to as-received substrate (wear rate of 20.81 × 10^?7 mm³/mm). The corrosion resistance property in a 3.56 wt pct NaCl solution was also improved.     

Fracture toughness of f.c.c. nickel and strain ageing b.c.c. iron in the temperature range 77–773 K

Ductile initiation fracture toughness J_IC of b.c.c. Armco iron and f.c.c. nickel has been measured in the temperature range 77–773 K. Armco iron exhibits dynamic strain ageing (DSA) in the temperature range 383–573 K while nickel of the purity used does not evince DSA. Load vs load line displacement (LLD) plots during fracture toughness testing of Armco iron show serrations in the temperature range 383–573 K similar to those observed in the tensile stress-strain curves. DSA is found to have a beneficial effect on the fracture toughness J_IC. A marked increase in tensile strength and fracture toughness occurs in Armco iron in the DSA regime. The strain hardening exponent, known to have a bearing on the plastic zone size and the void growth rate, seems a clear parameter in terms of which the observed J_IC variation with temperature can be understood. Remarkably, the variation of n with temperature is found to closely follow the observed trend in _IC. However, the slope of the J-R curve, dJ/da, decreases in the DSA regime with a minimum at 423 K. The decrease has been related to the fracture propagation process which is shown to occur by an alternate fast fracture and the ductile dimpled mode in the DSA regime. In the case of nickel, free from DSA, J_IC or dJ/da are found to be largely unaffected by the test temperature. At room temperature f.c.c. nickel, at closely matching strength levels, possesses higher fracture toughness as compared to b.c.c. Armco iron. The crystal structure effect is more pronounced at temperatures below the ambient. At 77 K, the fracture toughness of iron is drastically reduced due to the onset of cleavage while nickel, not prone to a change in the fracture mode, maintains the same level of J_IC, as at the ambient.     

Synergic extraction of nickel and cobalt by LIX63-dinonylnaphthalene sulfonic acid mixtures

The extraction of nickel and cobalt by mixtures of 5,8-diethyl-7-hydroxy-6-dodecanone oxime (H₂Ox, active extractant in LIX63, a product of Henkel Corp.) and dinonylnaphthalene sulfonic acid (HDNNS or HD) has been studied by using the methods of slope analysis and continuous variation. On the basis of distribution and spectrophotometric data, the observed synergic extraction of nickel and cobalt by H₂Ox-HDNNS mixtures is attributed to the formation of a mixed ligand complex with the stoichiometry: Me/H₂Ox/HDNNS = 1/3/2. In the absence of H₂Ox, log D versus log [HDNNS] plots give straight lines with slopes of unity for both nickel and cobalt extraction, thus indicating that the active extractant is the HDNNS micelle. In the presence of H₂Ox the log D versus log [HDNNS] plots go through a maximum and a minimum. It is proposed that the active extractant under these conditions is a mixed HDNNS-H₂Ox micelle of the form (HD)_p·3H₂Ox, and that the shape of the metal distribution curve, as a function of HDNNS concentration, follows the organic-phase concentration of this mixed micelle.