Phase equilibria of Co−Mo−Zn ternary system

To experimentally determine the isothermal sections of Co−Mo−Zn ternary system at 600 and 450 °C, the equilibrated alloy and diffusion couple methods were adopted by using scanning electron microscopy coupled with energy-dispersive spectrometry, X-ray diffractometry and electron probe microanalysis. Experimental results show that there are six three-phase regions on the Co−Mo−Zn isothermal section at 600 °C and nine three-phase regions on the Co−Mo−Zn isothermal section at 450 °C. No ternary compound is found in these two isothermal sections. Both the maximum solubilities of Mo in the Co−Zn compounds (γ-Co₅Zn₂₁, γ₁-CoZn₇, γ₂-CoZn₁₃ and β₁-CoZn) and that of Zn in ε-Co₃Mo are no more than 1.5 at.%. The maximum solubilities of Zn in μ-Co₇Mo₆ are determined to be 2.1 at.% and 2.7 at.% at 600 and 450 °C, respectively. In addition, the maximum solubilities of Co in MoZn₇ and MoZn₂₂ are 0.5 at.% and 4.7 at.% at 450 °C, respectively.     

Converting jarosite residues into compact hematite products

Sodium jarosite is readily converted into hematite by hydrothermal reaction at temperatures greater than 220°C. Although the initial acid and ferric ion concentrations must be kept low to avoid the unwanted formation of Fe(SO₄)(OH), the conversion reaction is unaffected by modest concentrations of ZnSO₄, FeSO₄ or Na₂SO₄. Hematite seeding is desirable to promote the reaction and to stabilize the reaction system. The hematite conversion product will likely contain ～0.5% Zn and ～2% SO₄; most of the arsenic in the jarosite will remain with the hematite.     

Effect of rolling reduction and annealing process on microstructure and corrosion behavior of LZ91 alloy sheet

The effect of rolling reduction and annealing process on the microstructure and corrosion behavior of Mg−9Li−1Zn (LZ91) alloy was investigated. The test alloy sheets were cold rolled with the reduction of 50% and 75%, respectively, and then were annealed at 200 °C for 1 h. The microstructure of test alloys was observed by OM and SEM while the phase composition was determined by XRD. The corrosion property was evaluated by electrochemical measurements and immersion tests. The results show that LZ91 alloy sheet consists of α-Mg, β-Li and precipitated Mg−Li−Zn compounds (MgLi₂Zn and MgLiZn phases). Dynamic recrystallization grains appear in β-Li phase during annealing process, leading to grain refinement. The results indicate that the increasing rolling reduction and performing the annealing process can enhance the corrosion resistance of LZ91 alloy. The 75% cold-rolled and annealed LZ91 alloy shows the best corrosion resistance.     

Evolution of precipitates in Mg−7Gd−3Y−1Nd−1Zn−0.5Zr alloy with fine plate-like 14H-LPSO structures aged at 240 °C

The morphology and crystal structure of the precipitates in Mg−7Gd−3Y−1Nd−1Zn−0.5Zr (wt.%) alloy with fine plate-like 14H-LPSO structures aged at 240 °C were investigated using transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Fine plate-like 14H-LPSO structures precipitate after heat treatment at 500 °C for 2 h, and β-type phases precipitate after the alloy is aged at 240 °C. The long-period atomic stacking sequence of 14H-LPSO structures along the [0001]_α direction is ABABCACACACBABA. After being aged at 240 °C for 2 h, the β-type phases are the ordered solution clusters, zig-zag GP zones, and a small number of β′ phases. The peak hardness is obtained at 240 °C for 18 h with a Brinell hardness of 112, the β-type phases are β’ phases and local RE-rich structures. After being aged at 240 °C for 100 h, the β-type phases are β’, β₁ and β’_F phases. β′ phases nucleate from the zig-zag GP zones directly without β″ phases, and then transform into β₁ phase by β’→β’_F→β₁ transformations. The Zn not only can form LPSO structure, but also is the constituent element of β₁ phases. LPSO structures have a certain hindrance to the coarsening of β’ and β₁ along 〈0001〉_α.     

Preparation of Mn−Zn ferrite from spent zinc-carbon batteries by alkali leaching,acid leaching and Co-precipitation

The treatment of spent zinc-carbon batteries for the recovery of valuable metals followed by conversion to Mn−Zn ferrite has been conducted employing two-stage alkali and acid leaching and co-precipitation method. In the first stage, leaching process was carried out with 4 M NaOH, which resulted in a recovery of 63.4 %Zn and 0.1% Mn. Electrowinning of alkali leaching solution containing 12.75 g/L Zn at a current density of 0.2 A/cm² produced Zn metal of 15 nm to 30 nm size and 99.9% purity. The second stage leaching of residue with 3 M H₂SO₄ and 6 vol.% H₂O₂ at a solid/liquid ratio of 1∶10 indicated the leaching efficiency of 98.0% Zn, 97.9% Mn and 55.2% Fe. The obtained leaching solution was finally adjusted to suitable mole ratios of Mn∶Zn∶Fe (1∶1∶4) by the addition of Zn and Fe sulfate salts followed by pH control to produce Mn−Zn ferrite powder. The characterization of the ferrite powder showed uniform nano-crystalline particles of about 20 nm size with spinel structure.     

Hydrometallurgical recovery of zinc from industrial hot dipping top ash

Top ash from hot-dip galvanizing plant was investigated as a source of secondary zinc to be returned to galvanizing bath. The waste material contained 63% Zn as metallic, oxide and hydroxychloride phases. It was leached in H₂SO₄ solutions (20% and 25%) at various bath loadings (100−300 g/L). Leaching behaviors of zinc, manganese, iron and chloride ions were investigated. A few strategies of iron elimination from leaching liquors were examined. Flocculant addition was harmful for subsequent filtration of iron precipitates due to increased viscosity of solution, while a combination of zinc oxide and calcium carbonate for rising pH resulted in the formation of dense suspension unenforceable to separate from zinc sulphate solution. Zinc electrowinning was carried out at different pH (from −0.5 to 2.8) using a range of current densities (3−10 A/dm²). Optimal conditions for pure metal recovery were: leaching in 20% H₂SO₄ solution at zinc ash content 100−150 g/L, Fe₂O₃·xH₂O precipitation using H₂O₂ and CaCO₃, zinc electrowinning at pH of 0.1−1.0 at 3−6 A/dm². Correlations between pH and free H₂SO₄ concentration in electrolyte solutions were also discussed. pH−acid concentration dependence for zinc electrolyte was between experimental and calculated curves for pure H₂SO₄ solutions, while the curve was shifted towards lower pH if ferric ions were in the solution.     

Electrochemical behavior and electrolytic preparation of lead in eutectic NaCl−KCl melts

A novel molten salt extraction process consisting of chlorination roasting and molten salt electrolysis was proposed to develop a more efficient and environmental friendly technology for recovering lead from spent lead acid batteries (LABs). The feasibility of this process was firstly assessed based on thermodynamics fundamentals. The electrochemical behavior of Pb(II) on a tungsten electrode in the eutectic NaCl−KCl melts at 700 °C was then investigated in detail by transient electrochemical techniques. The results indicated that the reduction reaction of Pb(II) in NaCl−KCl melts was a one-step process exchanging two electrons, and it was determined to be a quasi-reversible diffusion-controlled process. Finally, potentiostatic electrolysis was carried out at −0.6 V (vs Ag/AgCl) in the NaCl−KCl−PbCl₂ melts, and the obtained cathodic product was identified as pure Pb by X-ray diffraction analysis. This investigation demonstrated that it is practically feasible to produce pure Pb metal by electrochemical reduction of PbCl₂ in eutectic NaCl−KCl melts, and has provided important fundamental for the further study on lead recovery from spent LABs via molten salt extraction process.     

Catalytic reduction of SO2 by CO over CeO2–TiO2 mixed oxides

The structure and catalytic desulfurization characteristics of CeO₂–TiO₂ mixed oxides were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and catalytic activity tests. According to the results, a CeO₂–TiO₂ solid solution is formed when the mole ratio of cerium to titanium n(Ce):n(Ti) is 5:5 or greater, and the most suitable n(Ce):n(Ti) is determined as 7:3, over which the conversion rate of SO₂ and the yield of sulfur at 500 °C reach 93% and 99%, respectively. According to the activity testing curve, Ce_0.7Ti_0.3O₂ (n(Ce):n(Ti)=7:3) without any pretreatment can be gradually activated by reagent gas after about 10 min, and reaches a steady activation status 60 min later. The XPS results of Ce_0.7Ti_0.3O₂ after different time of SO₂+CO reaction show that CeO₂ is the active component that offers the redox couple Ce⁴⁺/Ce³⁺ and the labile oxygen vacancies, and TiO₂ only functions as a catalyst structure stabilizer during the catalytic reaction process. After 48 h of catalytic reaction at 500 °C, Ce_0.7Ti_0.3O₂ still maintains a stable structure without being vulcanized, demonstrating its good anti-sulfur poisoning performance.     

Application limits of Ta and Ta-2.5% W for sulfur acid handling

Long term corrosion test with welded coupons were carried out to determine the application limits of Ta and Ta-2.5% W in sulfuric acid (H₂SO₄). The program included the following two fields of investigation:

• • Determination of corrosion behavior in 90 through 100% H₂SO₄ at temperatures up to 200°C.
• •Determination of corrosion behavior in 96 wt % H₂SO₄ comparing recovered nitration-spent acid and technical grade between 150 and 230°C.

Mainly immersion tests were performed. A comparison of Ta and Ta-2.5 % W showed that in technical H₂SO₄ the alloy performed better than the metal. Regardless of which material was considered, the higher the H₂SO₄ concentration, the lower the temperature necessary to achieve acceptable corrosion behavior. In technical H₂SO₄, the following application limits were revealed: Ta: 96 wt %/200°C – 97 wt %/150°C Ta-2.5% W: 96 wt %/210°C – 97.5 wt %/175°C. Above 97.5 wt % the corrosion resistance decreased rapidly. The recovered nitration-spent acid led to remarkably lower corrosion rates due to small amounts of nitric acid. In these types of acidcontaining oxidizing compounds. 230°C seemed to be satisfactory, provided the wall of the heat exchanger was sufficiently thick.     

Separation and recovery of Cu and As from copper electrolyte through electrowinning and SO2 reduction

Cu and As were separated and recovered from copper electrolyte by multiple stage electrowinning, reduction with SO₂ and evaporative crystallization. Experimental results showed that when the current density was 200 A/m², the electrolyte temperature was 55 °C, the electrolyte circulation rate was about 10 mL/min and the final Cu concentration was higher than 25.88 g/L, the pure copper cathode was recovered. By adjusting the current density to 100 A/m² and the electrolyte temperature to 65 °C, the removal rate of As was 18.25% when the Cu concentration decreased from 24.69 g/L to 0.42 g/L. After As(V) in Cu-depleted electrolyte was fully reduced to As(III) by SO₂, the resultant solution was subjected to evaporative crystallization, then As₂O₃ was produced, and the recovery rate of As was 59.76%. The cathodic polarization curves demonstrated that both Cu²⁺ concentration and As(V) affect the limiting current of Cu²⁺ deposition.     

Influence of anions on the formation of artificial steel rust particles prepared from acidic aqueous Fe(III) solution

For simulation of atmospheric corrosion of steels, artificial steel rust particles were prepared in acidic aqueous solutions containing FeCl₃, Fe(NO₃)₃ and Fe₂(SO₄)₃. A single phase α-FeOOH was formed in only Fe(NO₃)₃ system. The β-FeOOH was formed by added Cl⁻ in FeCl₃–Fe(NO₃)₃ system. Adding SO₄²⁻ in Fe(NO₃)₃, FeCl₃ and a mixture of FeCl₃–Fe(NO₃)₃ solutions turned the products following as α- or β-FeOOH → Schwertmannite (Fe₈O₈(OH)₆(SO₄)·nH₂O). Further, increasing the added SO₄²⁻ suppressed the formation of steel rust particles. Accordingly, the influence of anions on the formation of steel rust particles was to be suggested in order of SO₄²⁻ ≫ Cl⁻ > NO₃⁻.     

Use of pre-oxidation to improve reactive wetting of high manganese alloyed steel during hot-dip galvanizing

The present study discusses hot-dip galvanizing of a Fe–23% Mn–0.6% C–0.3% Si steel using a Zn–0.22%Al bath. The paper concentrates on reactive Zn wetting on top a covering external oxide layer occurring after in-line annealing. Annealing was performed by soaking at 800 °C/60 s in 5% H₂–N₂ at different dewpoints. In-line pre-oxidation at 600 °C/10 s in 1.8% O₂–N₂ was further performed and the impact on selective oxidation as well as reactive Zn wetting was examined. After conventional annealing Zn wetting turns to increase if a roughly globular MnO layer appears on the external steel surface and Si is internally oxidized. Reactive wetting including the formation of Fe₂Al₅ crystals occurs on top of the MnO layer, because metallic-bond Fe exists incorporated within this MnO layer (→MnO·Fe_metall layer). The amount of metallic-bond Fe within the MnO·Fe_metall layer increases considerably if pre-oxidation is conducted. This results in an intensified Fe₂Al₅ formation on top of a MnO·Fe_metall, which improves liquid Zn wetting. Brittle Fe–Zn intermetallics were absent in all trials. These results offer a new way for hot-dip galvanizing (high) Mn alloyed steels. The absence of Fe–Zn intermetallics and (partial) MnO reduction implies that the currently discussed model of aluminothermic MnO reduction during hot-dip galvanizing Mn alloyed steel seems not to be dominating in the present case of reactive Zn wetting on top of a covering MnO·Fe_metall layer.     

Intermolecular interactions in the structure of new molecular semiconductor [Pd(dddt)2]2CF3SO3

An X-ray structural investigation of a new molecular semiconductor, [Pd(dddt)₂]₂CF₃SO₃ (1), where dddt²⁻ is 5,6-dihydro-1,4-dithiin-2,3-dithiolate, is made. Crystal data of 1:a = 6.521(7) Å, b = 8.354(4) Å, c = 16.113(6) Å, α = 87.12(4)°, β = 85.51(6)°, γ = 67.94(7)°, V = 811(1) ų, triclinic, space group P. Crystal structure 1 is characterized by layers of [Pd(dddt)₂]^1/2+ radical cations, with [CF₃SO₃]⁻ anions located between them. In these layers, [Pd(dddt)²]^1/2+ cations form dimers with strongly shortened intermolecular contacts Pd…Pd 3.031 (2) Å. The [CF₃SO₃]⁻ anion in the structure of 1 is disordered.     

Effect of Al addition on microstructure and mechanical properties of Mg−Zn−Sn−Mn alloy

The microstructure and properties of the as-cast, as-homogenized and as-extruded Mg−6Zn−4Sn−1Mn (ZTM641) alloy with various Al contents (0, 0.5, 1, 2, 3 and 4 wt.%) were investigated by OM, XRD, DSC, SEM, TEM and uniaxial tensile tests. The results show that when the Al content is not higher than 0.5%, the alloys are mainly composed of α-Mg, Mg₂Sn, Al₈Mn₅ and Mg₇Zn₃ phases_. When the Al content is higher than 0.5%, the alloys mainly consist of α-Mg, Mg₂Sn, MgZn, Mg₃₂(Al,Zn)₄₉, Al₂Mg₅Zn₂, Al₁₁Mn₄ and Al₈Mn₅ phases. A small amount of Al (≤1%) can increase the proportion of fine dynamic recrystallized (DRXed) grains during hot-extrusion process. The room- temperature tensile test results show that the ZTM641−1Al alloy has the best comprehensive mechanical properties, in which the ultimate tensile strength is 332 MPa, yield strength is 221 MPa and the elongation is 15%. Elevated- temperature tensile test results at 150 and 200 °C show that ZTM641−2Al alloy has the best comprehensive mechanical properties.     

Influence of sulfur on the solubility of graphite in Fe–C–S melts: optimization of interaction parameters

We report a Monte Carlo simulation study of a molten Fe–C–S system at 1600°C with the aim of developing an atomic model with optimum interaction parameters. This model should account for key features of the system, e.g., homogenous nature of Fe–FeS solution, separation of Fe–C–S liquid in two immiscible layers and a decrease in solubility of graphite in iron melts with the addition of sulfur. The atoms in the ternary Fe–C–S system were arranged on a graphitic hexagonal lattice and pair-wise interactions between them were assumed to be short ranged. The simulations were carried out using a combination of canonical and grand canonical ensembles for a range of interaction strengths, carbon and sulfur concentrations. The strength of ionic Fe–S interaction was one of the significant parameters and could lead to electronic distortions around the Fe atom. Local modifications to various interactions due to these distortions were represented by three parameters: ε (Fe–Fe), δ (Fe–S) and δ (Fe–C) and their effect on the Fe–C–S system was systematically analyzed. Optimum modulation parameters for this system, which simultaneously simulate key features of a molten Fe–C–S system are: ε (Fe−Fe)=1.0, δ (Fe−S)=1.0, δ (Fe−C)=1.0 and 1.5. Even though a slight increase in Fe–C repulsion gives optimum results, our high temperature simulation results clearly show that electronic distortions around Fe due to strong Fe–S bond do not play a significant role in the molten Fe–C–S system.     

Microstructure and shear strength of γ-TiAl/GH536 joints brazed with Ti−Zr−Cu−Ni−Fe−Co−Mo filler alloy

The influence of brazing temperature and brazing time on the microstructure and shear strength of γ-TiAl/GH536 joints brazed with Ti−Zr−Cu−Ni−Fe−Co−Mo filler was investigated using SEM, EDS, XRD and universal testing machine. Results show that all the brazed joints mainly consist of four reaction layers regardless of the brazing temperature and brazing time. The thickness of the brazed seam and the average shear strength of the joint increase firstly and then decrease with brazing temperature in the range of 1090−1170 °C and brazing time varying from 0 to 20 min. The maximum shear strength of 262 MPa is obtained at 1150 °C for 10 min. The brittle Al₃NiTi₂ and TiNi₃ intermetallics are the main controlling factors for the crack generation and deterioration of joint strength. The fracture surface is characterized as typical cleavage fracture and it mainly consists of massive brittle Al₃NiTi₂ intermetallics.     

Combustion synthesis of FeAl−Al2O3 composites with TiB2 and TiC additions via metallothermic reduction of Fe2O3 and TiO2

Combustion synthesis involving metallothermic reduction of Fe₂O₃ and TiO₂ was conducted in the mode of self-propagating high-temperature synthesis (SHS) to fabricate FeAl-based composites with dual ceramic phases, TiB₂/Al₂O₃ and TiC/Al₂O₃. The reactant mixture included thermite reagents of 0.6Fe₂O₃+0.6TiO₂+2Al, and elemental Fe, Al, boron, and carbon powders. The formation of xFeAl−0.6TiB₂−Al₂O₃ composites with x=2.0−3.6 and yFeAl−0.6TiC−Al₂O₃ composites with y=1.8−2.75 was studied. The increase of FeAl causes a decrease in the reaction exothermicity, thus resulting in the existence of flammability limits of x=3.6 and y=2.75 for the SHS reactions. Based on combustion wave kinetics, the activation energies of E_a=97.1 and 101.1 kJ/mol are deduced for the metallothermic SHS reactions. XRD analyses confirm in situ formation of FeAl/TiB₂/Al₂O₃ and FeAl/TiC/Al₂O₃ composites. SEM micrographs exhibit that FeAl is formed with a dense polycrystalline structure, and the ceramic phases, TiB₂, TiC, and Al₂O₃, are micro-sized discrete particles. The synthesized FeAl−TiB₂−Al₂O₃ and FeAl−TiC−Al₂O₃ composites exhibit the hardness ranging from 12.8 to 16.6 GPa and fracture toughness from 7.93 to 9.84 MPa·m^1/2.     

Effect of Fe/SiO2 and CaO/SiO2 mass ratios on metal recovery rate and metal content in slag in oxygen-enriched direct smelting of jamesonite concentrate

The oxygen-enriched direct smelting of jamesonite concentrate was carried out at 1250 °C by changing the slag composition. The effects of Fe/SiO₂ and CaO/SiO₂ mass ratios on the metal recovery rate as well as metal content in slag were investigated. Experimental results indicated that the metal (Pb+Sb) recovery rate was up to 88.30%, and metal (Pb+Sb) content in slag was below 1 wt.% under the condition of slag composition of 21−22 wt.% Fe, 19−20 wt.% SiO₂ and 17−18 wt.% CaO with Fe/SiO₂ mass ratio of 1.1:1 and CaO/SiO₂ mass ratio of 0.9:1. The microanalysis of the alloy and slag demonstrated that the main phases in the alloy contained metallic Pb, metallic Sb and a small amount of Cu₂Sb and FeSb₂ intermetallic compounds. The slag was mainly composed of kirschsteinite and fayalite. Zinc in the raw material was mainly oxidized into the slag phase in the form of zinc oxide.     

Extraction of valuable metals from low nickel matte by calcified roasting−acid leaching process

A calcified roasting−acid leaching process was developed as a highly effective method for the extraction of valuable metals from low nickel matte in the presence of CaO additive. The influences of process parameters on the metal extraction were studied, including the roasting temperature, roasting time, addition of CaO, H₂SO₄ concentration and liquid−solid ratio. Under the optimum condition, 94.2% of Ni, 98.1% of Cu, 92.2% of Co and 89.3% of Fe were recovered. Additionally, 99.6% of Fe was removed from the leachate as goethite by a subsequent goethite iron precipitation process. The behavior and mechanism of CaO additive in the roasting process was clarified. The role of CaO is to prevent the formation of nonferrous metal ferrite phases by a preferential reaction with Fe₂O₃ during the roasting process. The metal oxides (CuO and Ni_xCu_1−xO) remained stable during high-temperature roasting and were subsequently efficiently leached using a sulfuric acid solution.     

The Fe–Ni–Al phase diagram in the Al-rich (>50 at.% Al) corner

The ternary Fe–Ni–Al phase diagram between 50 and 100 at.% Al was investigated by a combination of powder X-ray diffraction (XRD), differential thermal analysis (DTA) and electron probe microanalysis (EPMA). Ternary phase equilibria and accurate phase compositions of the respective equilibrium phases were determined within the isothermal section at 850 °C. The crystal structure of τ1 (Fe_4−xNi_xAl₁₀) and τ2 (Fe_2−xNi_xAl₉) was determined by means of single crystal X-ray diffraction. The decagonal quasi-crystalline phase q (Fe_4.9Ni_23.4Al_71.7) was found to be stable between 850 °C and 930 °C. All experimental data were combined to yield a ternary reaction scheme (Scheil diagram) involving 10 ternary invariant reactions in the investigated composition range, and a liquidus surface projection was constructed based on DTA results.