Heterogeneous nucleation of Pb Particles Embedded in a Zn Matrix

Zinc-10 and 20 wt pct Pb alloys have been rapidly solidified by melt spinning to obtain a very fine scale dispersion of nanometer-sized Pb particles embedded in Zn matrix. The microstructure and crystallography of the Pb particles have been studied using transmission electron microscopy (TEM). Each embedded Pb particle is a single crystal, with a truncated hexagonal biprism shape with the 6/mmm Zn matrix point group symmetry surrounded by {0001},\(\left\{ {10\bar 10} \right\}\) and\(\left\{ {10\bar 11} \right\}\) facets. The Pb particles solidify with a well-defined orientation relationship with the Zn matrix of (0001)_zn‖(111)_pb and\([11\bar 20]_{Zn} ||[1\bar 10]_{Pb} \). The melting and solidification behavior of the Pb par- ticle have been studied using differential scanning calorimetry (DSC). The Pb particles solidify with an undercooling of approximately 30 K, by heterogeneous nucleation on the {0001} facets of the surrounding Zn matrix, with an apparent contact angle of 23 deg.     

Kinetics of deoxidation of liquid Cu-O alloys by rotating graphite cylinders under argon

The rate of deoxidation of liquid Cu-O alloys by graphite cylinders rotating at about 250, 580, and 860 rpm was studied at 1400, 1482, and 1582 K under argon at 30, 58, and 99 kPa. Those at 1400 and 1482 K with about 580 and 860 rpm and at 1582 K do not depend on rotational speed. Under each argon pressure with these rotational speeds, at 1400 K, the apparent deoxidation-rate constantK _e defined by first order kinetics increases and then approaches a constant value with a decrease in the concentration of oxygen in the melt and at 1482 K,K _e is constant. At 1582 K,K _e is approximately constant. A plot of log₁₀ K _e at 1482 K and in very low oxygen concentration at 1400 and 1582 Kvs 1/T gives an apparent activation energy of 146 kJ · mol⁻¹. The dependence ofK _e on the concentration of oxygen can qualitatively be explained on the basis of a mechanism involving the chemisorption of oxygen from liquid copper onto the graphite surface, the release of carbon monoxide from the surface, and the interfacial reaction between oxygen in the melt and the carbon monoxide. This mechanism indicates that the activation energy is that for the chemisorption. The rate of deoxidation of liquid Cu-O alloys in graphite crucibles also was studied at 1473, 1573, and 1673 K under argon at 100 or 60 kPa by use of an induction furnace and is much smaller than that by the rotating graphite cylinders. The values ofK _e under both pressures of argon at 1473 K appear not to differ from each other and are close to theK _e value at 1573 K under argon at 100 kPa.     

Vacuum distillation of copper matte to remove lead,arsenic, bismuth,and antimony

Vacuum-refining experiments were carried out on copper matte melts, containing 35 to 73 pct Cu, to measure the removal rates of lead, bismuth, arsenic, and antimony over the temperature range of 1373 to 1523 K under pressures in the range of 50 to 130 Pa. High rates of refining, controlled by mass transport in the liquid phase, were achieved for all impurities in melts containing up to 65 pct Cu and for chamber pressures less than 100 Pa. After 40 to 60 minutes of treatment, lead elimination was between 70 and 96 pct, bismuth elimination was between 88 and 98 pct, arsenic, elimination was between 60 and 93 pct, and antimony elimination was between 40 and 92 pct. The overall mass transfer coefficients for vacuum refining for the impurities considered fell in the range of 5×10⁻⁵ to 2×10⁻⁴ m s⁻¹. The values were insensitive to small changes in melt temperature but decreased with increasing pressure above 250 Pa. Also, the rates of refining were seen to be influenced by the sulfur and oxygen activity in the melt. The evaporation and subsequent elimination of the impurities were mathematically modeled by extending previously published models beyond consideration only of evaporation of monomers to consideration of the evaporation of monomers and dimer compounds. The model showed that due to the contributions to the refining by evaporation of each of the metallic, oxide, or sulfide vapor species, arsenic and antimony exhibited a maximum in refining rates atP _{o 2} andP _{s 2} potentials corresponding to matte grades of about 55 pct copper, whereas lead showed a minimum at about the same matte grade, and bismuth showed a continuously decreasing rate of refining with increasing matte grade. The model was also used to simulate the refining behavior of copper matte melts. An example of a commercial-scale operation is given.     

Effects of oxygen atmosphere,FeOx and basicity on mineralogical phases of CaO–SiO2–MgO–Al2O3–FetO–P2O5 steelmaking slag

ABSTRACT

The mineralogical phase of slag after crystallisation is essential to utilisation of steelmaking slag. The mineralogical phases of cooled multicomponent CaO–SiO₂–MgO–Al₂O₃–Fe_tO–P₂O₅ slag with different iron oxide contents and basicities (defined as the ratio of mass percentage of CaO to mass percentage of SiO₂ (w(CaO)/w(SiO₂))) in different atmospheres were investigated in the present work by scanning electronic microscopy and energy dispersed spectroscopy analysis and X-ray diffraction. The mineralogical phases in steelmaking slag cooled in argon are mainly nCa₂SiO₄-Ca₃(PO₄)₂ (thereafter nC₂S-C₃P) solid solution, (Fe, Mn, Mg)O (RO) phase. Some CaMgSiO₄ phases could be found in slag with lower basicity. The mineralogical phases in steelmaking slag cooled in air are mainly nC₂S-C₃P solid solution, spinel phase. The overall crystallisation of slag cooled in both argon and air was enhanced with increasing basicity. However, the crystal sizes become smaller in sample with high basicity. The Fe-enriched phases were transformed from non-faceted RO phase in sample cooled in argon to faceted spinel phases in sample cooled in air. The crystallisation of slag cooled in both argon and air was promoted with increasing FeO_x content. The phosphorus content in solid solution was elevated with decreasing basicity and increasing FeO_x content. It was implied by the present work that appropriate basicity and air oxidation would be beneficial to magnetic separation and phosphorus utilisation.     

Solubility of Zn and Pb in liquid iron and their partition between liquid iron and selected steelmaking slag systems

The use of Zn- and Pb-contaminated scrap in steelmaking has led to a significant increase of the zinc and lead contents in dusts and sludges, especially produced in the electric arc furnace melting shops. To understand the behaviour of Zn and Pb, fundamental research on the thermodynamics and kinetics of zinc and lead reactions under steelmaking conditions is helpful. In the first part of the present work, the solubilities of lead and zinc in iron are discussed. Furthermore, the influence of several alloying elements, such as carbon, oxygen, sulfur and chromium on the dissolution behaviour of Zn and Pb was examined and compared with former studies. Measurements of the solubility of lead in liquid iron were made at elevated temperatures in the systems Fe-Pb-O, Fe-Pb-C and Fe-Pb-Cr under argon in a gas-tight Tammann furnace. An increase of lead solubility was found with increasing temperature and increasing oxygen content. On the other hand, higher contents of carbon and chromium led to lower solubilities of lead in liquid iron. In the second part, the partition ratios of zinc and lead between liquid iron and various selected slag compositions were investigated. It is shown that zinc partition is determined by oxygen activity and slag basicity. In SiO₂-saturated slags, the partition ratio of zinc is considerably higher than in CaO-saturated slags. In comparison, the partition ratio of lead is significantly lower under the same experimental conditions.     

Evaporation behavior of aluminum during the cold crucible induction skull melting of titanium aluminum alloys

Taking the Ti-Al binary alloy as an example, this article studied the evaporation behavior of Al during the cold crucible induction skull melting (ISM) process of titanium alloys. A formula was deduced to predict the activity of Al in a molten Ti-Al binary system. The calculated activity of Al negatively deviates from an ideal solution. A model was established to judge the evaporation controlling mode and, on this basis, several conclusions were obtained. (1) The evaporation controlling mode of Al in molten Ti-Al transfers from the evaporation reaction controlling mode to the double controlling mode (diffusion and evaporation reaction) with increasing melt temperature (T _ms) and/or Al content (x _Al) and/or decreasing pressure (P) in the melting chamber. (2) The expression P≤P _crit (P _crit≈0.44 P _e(Al)) is a criterion used to judge whether the evaporation is in the state of free evaporation. (3) The term P _impe (P _impe=(3.5 to 4) P _e(Al)) is a critical value which impedes the evaporation loss. Almost all of common used ternary additions could enhance the activity of Al in molten Ti-Al and, accordingly, aggravate the evaporation of Al, except for Zr. The enhancing sequence is Y, Ni, Nb, Mn, V, Fe, Cr, Mo, Cu, Si, W, Mg, B, and Sn. The Al evaporation mass-transfer losses, measured from the melting experiments of several titanium aluminum alloys, were in reasonable agreement with the calculated results.     

Room temperature compressive properties and strengthening mechanism of Mg_(96.17)Zn_(3.15)Y_(0.50)Zr_(0.18) alloy solidified under high pressure

The microstructures of Mg_(96.17)Zn_(3.15)Y_(0.50)Zr_(0.18) alloys solidified under 2-6 GPa high pressure were investigated by employing SEM(EDS) and TEM.The strengthening mechanism of experimental alloy solidified under high pressure is also discussed by analyzing the compressive properties and compression fracture morphology.The results show that the microstructure of experimental alloy becomes significantly fine-grained with increasing GPa level high pressure during solidification process,and the secondary dendrite arm spacing reduces from 40 μm at atmospheric pressure to 10 μm at 6 GPa pressure.The morphology of the second phases changes from the net structure by the lamellar-type eutectic structure at atmospheric pressure to discontinuous thin rods or particles at 6 GPa pressure.Besides,the solid solubility of Zn in the Mg matrix is improved with the increase of the solidification pressure.Compared with atmospheric-pressure solidification,high-pressure solidification can improve the strength of the experimental alloy.The compressive stre ngth is improved from 263 to 437 MPa at 6 GPa.The fracture mechanism of the experimental alloy changes from cleavage fracture at atmospheric pressure to quasi-cleavage fracture at high pressure.The main mechanism of the strength improvement of the experimental alloy includes the grain refinement strengthening caused by the refinement of the solidification microstructure,the second phase strengthening caused by the improvement of the morphology and distribution of the second phases,and solid solution strengthening caused by the increase of the solid solubility of Zn in the Mg matrix.     

An observation on microstructure of a casting Zn-40 Wt pct al alloy

The microstructure of a casting Zn-40 wt pct Al alloy was studied by transmission electron microscopy (TEM). The results show that primary α’ dendrites decompose into η-Zn phases and an aluminum matrix during cooling and at ambient aging. There are three typical morphologies corresponding to the different microcompositions or cooling conditions: coherent platelike η-Zn phases, spherical η-Zn phases coexisting with the platelike η-Zn phases, and the full equilibrium structure of spherical η-Zn phases and an aluminum matrix. The formation mechanism of these three kinds of microstructures is discussed. On the surface of the α’ dendrite, there is a cell with fcc structure, which should be β-Zn phase by the peritectic reaction. In the interdendritic regions, there are proeutectic β-Zn phases with equiaxed grains and lamellar colonies which are ternary eutectic β-Zn, η-Zn, and ε-CuZn₄ phases, with the orientation relationships of

Effect of strontium on the microstructure, mechanical properties, and fracture behavior of AZ31 magnesium alloy

The effect of strontium (Sr) on the microstructure, mechanical properties, and fracture behavior of AZ31 magnesium alloy and its sensitivity to cooling rate are investigated. Three phases—blocky-shaped Mg₁₇Al₁₂, acicular Mg₂₀Al₂₀Mn₅Sr, and insular Mg₁₆(Al,Zn)₂Sr—are identified in the Sr-containing AZ31 alloys. With increasing cooling rate, the blocky-shaped Mg₁₇Al₁₂ phase increases, the acicular Mg₂₀Al₂₀Mn₅Sr phase diminishes, and the insular Mg₁₆(Al,Zn)₂Sr phase is refined and granulated. The study suggests that the grain size decreases with increasing cooling rate for a given composition. However, the grain size decreases first, then increases, and finally decreases again with increasing Sr for a given cooling rate. The yield strength (σ _y ) of AZ31 magnesium alloy can be improved by grain refinement and expressed as σ _y =35.88+279.13d ^−1/2 according to the Hall-Petch relationship. The elongation increases when Sr is added up to 0.01 pct and then decreases with increasing Sr addition. Grain refinement changes the fracture behavior from quasicleavage failure for the original AZ31 alloy to mixed features of quasicleavage and microvoid coalescence fracture.     

The physical chemistry of thermal decomposition of South African chromite minerals

Natural chromite minerals form extended solid solutions with binary spinels of FeCr₂O₄, MgCr₂O₄, FeAl₂O₄, and MgAl₂O₄. The decomposition of natural spinels strongly depends upon the chemical potential imposed in the forms of temperature, pressure, and pH difference in aqueous media (e.g., during natural weathering). In this investigation, we studied the thermal decomposition behavior of South African chromite ores in order to relate the influence of oxygen potential with the likely product phases formed. The decomposition is also a generic step in the understanding of the formation of sodium chromate during soda-ash roasting and the reduction of chromite ores for ferrochrome alloy making. The phase equilibria in South African chromite minerals were investigated by isochronal thermal analysis and isothermal heat treatment of chromite mineral in air, argon, and Ar-5 pct H₂ atmospheres over a temperature range from 473 to 1473 K. The effects of the oxygen partial pressure and temperature on the phase constituents of the heat-treated product are discussed by referring to the results of X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray detector (EDX), and electron probe microanalysis (EPMA). The structure of phases formed and the morphology of phase-separated regions in chromite appear to be strongly dependent on the oxygen partial pressure. The mechanism of the decomposition of complex spinel phases is described under the influence of oxygen partial pressure and temperature.     

Effect of heat treatment on the structure and properties of extruded P/M alloy 718

The structure and mechanical properties of alloy 718 prepared from argon atomized powder have been investigated for a wide range of extrusion ratios and temperatures. The tensile and stress-rupture properties of extruded bar are sensitive to heat treatment. Notch ductility can be conferred through appropriate combination of solution anneal and intermediate temperature age. Structural evaluation shows that such treatment provides a uniform grain structure together with a coarseγ′’ precipitate dispersion and small amounts of δ Ni₃Cb phase at grain boundaries.     

Elimination of copper from the molten steel by NH3 blowing under reduced pressure

Based on the finding that blowing of NH₃ gas onto molten pure copper at atmospheric pressure causes an evaporation of an enormously high rate, attempts have been made to eliminate copper dissolved in molten steel by NH₃ gas blowing under reduced pressure. Typical behaviours of molten steel when attacked by NH₃ gas are boiling, splashing and, in a violent case, slopping from the crucible. These phenomena are accompanied by an immense increase in the surface area from which volatile species are able to evaporate and may be useful for vacuum metallurgical processes. In this investigation, the decuprization experiments have been conducted to measure the rate at which the copper level in the molten steel is reduced using a vacuum induction furnace and blowing NH₃ gas through a vertical water-cooled copper nozzle. The data were represented in terms of the amount of copper transferred from the melt to the gaseous phase per unit surface area and time. According to these experiments, complete decuprization was attainable confirming selective evaporation of copper from molten steel under reduced pressure. So far as the mechanism of copper elimination by NH₃ gas, besides the enhanced vacuum evaporation of metal by the cooling effect of endothermic decomposition of NH₃, the formation of volatile copper compound was suggested from the fact that the copper could be removed down to an extra-low level of several ppm, even under a residual gas pressure of the order of 10 Torr.     

Vacuum Evaporation of Pure Metals

Theories on the evaporation of pure substances are reviewed and applied to study vacuum evaporation of pure metals. It is shown that there is good agreement between different theories for weak evaporation, whereas there are differences under intensive evaporation conditions. For weak evaporation, the evaporation coefficient in Hertz-Knudsen equation is 1.66. Vapor velocity as a function of the pressure is calculated applying several theories. If a condensing surface is less than one collision length from the evaporating surface, the Hertz-Knudsen equation applies. For a case where the condensing surface is not close to the evaporating surface, a pressure criterion for intensive evaporation is introduced, called the effective vacuum pressure, p _eff. It is a fraction of the vapor pressure of the pure metal. The vacuum evaporation rate should not be affected by pressure changes below p _eff, so that in lower pressures below p _eff, the evaporation flux is constant and equal to a fraction of the maximum evaporation flux given by Hertz-Knudsen equation as 0.844 $ \dot{n}_{\hbox{Max} } $ . Experimental data on the evaporation of liquid and solid metals are included.     

Kinetics of Na2O evaporation from CaO–Al2O3–SiO2–MgO–TiO2–Na2O slags

The present work is carried out to study the evaporation of Na₂O from CaO–Al₂O₃–SiO₂–TiO₂–MgO–Na₂O slags with high basicity and high alumina in the temperature range of 1500–1560°C. The ratio of evaporation was determined by monitoring the Na₂O content change of the slag melt under isothermal reduction conditions. The results show that the evaporation ratio increases with increasing the temperature. Higher basicity and increasing concentrations of Na₂O, Al₂O₃ are also found to increase the evaporation ratio of Na₂O, while MgO addition only slightly enhances the evaporation ratio. With TiO₂ content increasing, the evaporation ratio first increases and then decreases. The evaporation rate of Na₂O appears to be controlled by chemical reaction at the slag/gas interface in the beginning, followed by a mixed reaction-mass transfer regime, and finally a liquid-phase mass transport step. The apparent activation energy is 134.74?kJ?mol^?1 for the chemical reaction regime and 268.53?kJ?mol^?1 for the liquid-phase mass diffusion step.     

Magnesium silicide intermetallic alloys

Methods of induction melting an ultra-low-density magnesium silicide (Mg₂Si) intermetallic and its alloys and the resulting microstructure and microhardness were studied. The highest quality ingots of Mg₂Si alloys were obtained by triple melting in a graphite crucible coated with boron nitride to eliminate reactivity, under overpressure of high-purity argon (1.3 X 10⁵ Pa), at a temperature close to but not exceeding 1105 °C ± 5 °C to avoid excessive evaporation of Mg. After establishing the proper induction-melting conditions, the Mg-Si binary alloys and several Mg₂Si alloys macroalloyed with 1 at. pct of Al, Ni, Co, Cu, Ag, Zn, Mn, Cr, and Fe were induction melted and, after solidification, investigated by optical microscopy and quantitative X-ray energy dispersive spectroscopy (EDS). Both the Mg-rich and Si-rich eutectic in the binary alloys exhibited a small but systematic increase in the Si content as the overall composition of the binary alloy moved closer toward the Mg₂Si line compound. The Vickers microhardness (VHN) of the as-solidified Mg-rich and Si-rich eutectics in the Mg-Si binary alloys decreased with increasing Mg (decreasing Si) content in the eutectic. This behavior persisted even after annealing for 75 hours at 0.89 pct of the respective eutectic temperature. The Mg-rich eutectic in the Mg₂Si + Al, Ni, Co, Cu, Ag, and Zn alloys contained sections exhibiting a different optical contrast and chemical composition than the rest of the eutectic. Some particles dispersed in the Mg₂Si matrix were found in the Mg₂Si + Cr, Mn, and Fe alloys. The EDS results are presented and discussed and compared with the VHN data. Formerly Formerly     

Kinetics of the F,F2/Gd(s,v) reactions

The reaction of gadolinium with fluorine was studied in a low pressure, transonic flow reactor. Atomic fluorine reactant was generated by microwave discharge dissociation of F₂ in argon. Kinetic measurements included the rate of change of the electrical resistance of isothermal gadolinium filaments due to reaction with atomic and molecular fluorine and the intensity of chemiluminescence from the vapor phase Gd/F₂ reactionvs time, temperature, and F₂ partial pressure. The surfaces of reacted Gd specimens were examined by scanning electron microscopy, polished specimen cross sections were viewed under the optical microscope, and the Gd/F₂ chemiluminescent emission spectrum was obtained. A nonpassivating, metal rich, high melting and involatile fluoride, GdF_x, forms on the metal at temperatures above 1180 K. An orthorhombic, passivating GdF₃ forms at lower temperatures. The surface Gd activity remains high at the GdF_x/fluorine interface, and F-atom reaction is first order with a reaction probability approximately 0.28. Rapid reaction atT < 1180 K is followed by an abrupt transition to passivated behavior. This change in reactivity is attributed to a phase transition from GdF_x to orthorhombic GdF₃ that occurs as the oxygen impurity concentration of the reacting metal decreases from its value near the original specimen surface to that of the bulk material.     

Microstructural studies of a Cu-Zn-Al shape-memory alloy with manganese and zirconium addition

Mn and Zr were added to improve the shape-memory characteristics of a Cu-Zn-Al shape-memory alloy (SMA). The microstructure of a Cu-19.0Zn-13.1Al-1.1Mn-0.3Zr (at. pct) alloy was examined using a transmission electron microscope (TEM). The structure of the parent phase and martensite phase are DO₃ (or L2₁) and M18R₁, respectively. Two kinds of Zr-rich precipitates formed in the alloy. Energy-dispersive X-ray spectroscopy (EDXS) analysis with a TEM indicates that the two precipitates are all new phases and have the compositions of Cu_50.2Zr_24.6Al_17.3Zn_7.9 (at. pct) (Z ₁ phase) and Cu_57.4Zr_20.4Zn_10.3Al_11.9 (at. pct) (Z ₂ phase), respectively. The volume ratio of Z ₁ phase in the alloy is about 70 pct of the total precipitate volume. The structure of Z ₁ phase was studied in detail using TEM electron diffraction analyses. The lattice parameter of fcc Z ₁ phase is a=1.24 nm, and the space group of the phase is F432 (No. 209). The Z ₁ phase possesses an incoherent interface with the parent-phase matrix. The lattice correspondence of the Z ₁ phase and parent-phase matrix is as follows:

The inert gas effect on the rate of evaporation of zinc and cadmium

An experimental study has been made to investigate the effect of argon and helium on the rate of evaporation of zinc and cadmium under one atmosphere pressure at temperatures ranging from 500 to 850°C. The experimental results were compared with the maximum rates calculated using the effusion formula as well as with values obtained using two different types of equations based on kinetic theory, diffusion theory, and empirical data. Equations have been derived for expressing the rate of evaporation of zinc and cadmium in both argon and helium as functions of temperature of the liquid zinc and cadmium. It was found that the rates of evaporation of zinc and cadmium were higher in helium than in argon, with the difference increasing with increasing temperature. It was also found that the experimental results obtained in argon agree with the calculated values better than those obtained in helium.     

Pressureless Infiltration and Resulting Mechanical Properties of Al-AlN Preforms Fabricated by Selective Laser Sintering and Partial Nitridation

A novel manufacturing process has recently been developed for the fabrication of intricate Al-AlN composite parts. The process involves green shape formation by selective laser sintering, preform development by nitridation, and net shape forming by pressureless infiltration. The infiltration atmosphere has an important influence on the final fabrication and mechanical properties. This work presents a detailed investigation on the infiltration of Al-AlN preforms with AA 6061 at various temperatures above its liquidus under nitrogen, vacuum, and argon. The green shapes are formed by selective laser sintering of a premix of AA 6061-2Mg-1Sn-3Nylon (wt pct) powders. They are then partially nitrided to create a rigid, 2- to 3-μm-thick AlN skeleton for subsequent infiltration. Nitrogen infiltration results in the highest density (2.4 gcm⁻³) and best tensile properties (UTS: 214 MPa; elongation: 2.5 pct), while argon infiltration gives the lowest density. Fractographs confirmed the difference in density arising from the use of different atmospheres where small pores are evident on the fracture surfaces of both argon and vacuum-infiltrated samples. The molten AA 6061 infiltrant reacts with nitrogen during infiltration leading to a 5-μm-thick AlN skeleton compared to the original 2- to 3-μm-thick skeleton in both argon and vacuum-infiltrated samples. Transmission electron microscope (TEM) examination revealed inclusions of Mg₂Si and Mg₂Si _x Sn_1−x in both nitrogen- and argon-infiltrated samples but not in vacuum-infiltrated samples. Vacuum infiltration is slower than nitrogen and argon infiltration. The mechanisms that affect each infiltration process are discussed. Infiltration under nitrogen is preferred.     

The co-precipitation of copper and zinc with lead jarosite

The formation of lead jarosite, Pb_0.5Fe₃(SO₄)₂(OH)₆, in the presence of dissolved copper and/or zinc results in a significant substitution of these metals in the jarosite phase; the co-precipitation is most pronounced in sulphate media but also occurs, to a lesser degree, in chloride solutions. The copper and/or zinc substitute for iron, and under extreme conditions the product approaches beaverite, Pb(Cu,Zn)Fe₂(SO₄)₂(OH)₆, in structure and composition. The extent of co-precipitation increases sharply with increasing concentrations of dissolved CuSO₄ or ZnSO₄ and slightly with either an increasing stoichiometric ratio of PbSO₄/Fe³⁺ or increasing ionic strength. The co-precipitation of copper or zinc is not significantly affected by acid concentration although the yield of product declines with increasing concentration of H₂SO₄. The extent of reaction is relatively insensitive to reaction temperatures in the range 130–180°C and to reaction times in excess of 2 h. Copper is strongly co-precipitated in preference to zinc from solutions containing both metals. Other divalent base metals such as Co, Ni and Mn are also co-precipitated with lead jarosite although not to the same degree as copper or zinc.