Controlled Gas Atmospheres Research Articles

Development of a new laboratory-scale reduction facility for the hydrogen plasma smelting reduction of iron ore based on a multi-electrode arc furnace concept

Steel production accounts for a significant share of industrial CO2 emissions. The HPSR process is a possible alternative to reduce these emissions massively if not completely negate them. In principle, Fe-ore is reduced at high temperatures in the plasma of a DC electric arc. hydrogen reacts with the oxidic melt at the gas-liquid interface. Various concepts for the hydrogen plasma reduction of iron ore have been investigated, but the process technology has not yet surpassed the demonstration scale (TRL5). Experimental setups for charging masses from a few grams to a few hundred kilograms have been realized. Further investigations on the process stability and the reaction kinetics are still necessary. An improved laboratory-scale furnace concept shall provide the basis for the fundamental research. An existing laboratory facility is the starting point for designing and constructing the new plasma furnace. There are several problems with this experimental setup. Mainly, the reactor’s dimensions and power supply limitations restrict the arc’s length. The first leads to problems with excessive refractory wear, while the latter limits the variation of process parameters. Strong cooling when using Fe crucibles and the unstable nature of the arc complicate the process control. A promising concept to deal with the problem of arc stability is the use of multiple electrodes in a direct current arc furnace. Together with an optimized furnace geometry, new potential for further investigations can open. Using a multi-cathode furnace is also promising to further explore ferroalloy production via hydrogen plasma reduction. An electric arc furnace was designed based on the requirements for the planned plasma reduction facility. The energy requirement was based on assumptions for heat transfer from the arc to the melt, walls, and lid and continuous transfer through the individual furnace parts. Considerations of power supply, hearth dimensions, refractory design, controlled gas atmosphere, and the implementation of auxiliary equipment were central to creating an ideal basis for various experimental setups.

In situ cell for grazing-incidence x-ray diffraction on thin films in thermal catalysis.

A cell for synchrotron-based grazing-incidence x-ray diffraction at ambient pressures and moderate temperatures in a controlled gas atmosphere is presented. The cell is suited for the in situ study of thin film samples under catalytically relevant conditions. To some extent, in addition to diffraction, the cell can be simultaneously applied for x-ray reflectometry and fluorescence studies. Different domes enclosing the sample have been studied and selected to ensure minimum contribution to the diffraction patterns. The applicability of the cell is demonstrated using synchrotron radiation by monitoring structural changes of a 3nm Pd thin film upon interaction with gas-phase hydrogen and during acetylene semihydrogenation at 150 °C. The cell allows investigation of very thin films under catalytically relevant conditions.

Integrated Experimental Phase Equilibria and Thermodynamic Modelling Research and Implementation in support of progress of process pyrometallurgy towards sustainability

Responding to the many sustainability challenges facing the metallurgical industry, we report progress that has been made on the development of predictive tools that can be applied to a wide range of technologies. The aim is to provide accurate, fundamentally-based thermodynamic tools that can be used by industry to improve process efficiencies, metal recoveries and productivities, and reduce energy requirements of pyrometallurgical systems. The program involves an integrated experimental and thermodynamic modelling research on phase equilibria in complex multi-component, multi-phase gas-slag-matte-speiss-metal-solids system with the Cu2O-PbO-ZnO-FeO-Fe2O3-CaO-Al2O3-MgO-SiO2-S major and As-Sn-Sb-Bi-Ag-Au-Ni-Co-Cr-Na minor elements. The experiments involve high temperature equilibration in controlled gas atmospheres, rapid quenching and direct measurement of equilibrium phase compositions with quantitative microanalytical techniques, including electron probe X-ray microanalysis and Laser Ablation ICP-MS. The thermodynamic modelling is undertaken using FactSage software package with advanced thermodynamic solution models. The continuing development of analytical and research methodologies has resulted in significant advances in predictive capability. Implementation of the results of fundamental studies involves ongoing collaboration of researchers and industry technologists, and the provision of advanced professional training. An overview of recent progress in research, implementation and applications in industrial practice will be presented in the paper.

In situ/operando plug-flow fixed-bed cell for synchrotron PXRD and XAFS investigations at high temperature, pressure, controlled gas atmosphere and ultra-fast heating.

A plug-flow fixed-bed cell for synchrotron powder X-ray diffraction (PXRD) and X-ray absorption fine structure (XAFS) idoneous for the study of heterogeneous catalysts at high temperature, pressure and under gas flow is designed, constructed and demonstrated. The operating conditions up to 1000°C and 50 bar are ensured by a set of mass flow controllers, pressure regulators and two infra-red lamps that constitute a robust and ultra-fast heating and cooling method. The performance of the system and cell for carbon dioxide hydrogenation reactions under specified temperatures, gas flows and pressures is demonstrated both for PXRD and XAFS at the P02.1 (PXRD) and the P64 (XAFS) beamlines of the Deutsches Elektronen-Synchrotron (DESY).

Influence of elevated temperature and gas atmosphere on coke abrasion resistance. Part one: Pilot oven cokes

A novel approach was developed to examine coke abrasion resistance in-situ at temperatures of up to 950 °C and in a controlled gas atmosphere using rotational tribological testing. The originality of this approach lay in the ability to apply tribological testing to the porous coke surface at elevated temperatures under a controlled inert or CO2 reactive atmosphere. Coke wear characteristics were quantified via (i) the application of advanced microscopy and image analysis techniques, and (ii) analysis of the coefficient of friction (COF) during tribological testing.Two pilot oven cokes were examined in this study, which were generated from single coking coals of similar rank but different petrographic composition. The cokes tested showed a deterioration in abrasion resistance even at 400 °C, and this was accentuated at 950 °C.The COF and the severity of the wear as a function of temperature and gas atmosphere were markedly different between the two cokes. Coke C396 from a mid-to-low vol, medium vitrinite coal showed no statistically significant differences between the wear severity results recorded following room temperature testing and high temperature testing in a CO2 environment. Conversely, the more reactive coke C426 with a higher parent coal inertinite content showed clear differences in the extent of abrasive wear at room temperature and at high temperature in both inert and reactive gas atmospheres.This suggests that the reduction in abrasion resistance at elevated temperatures is accentuated in the coke with the highest coke reactivity index (CRI) and the highest content of inertinite maceral derived components (IMDC). Our research has shown that at room temperature, the IMDC show greater resistance to abrasion than the reactive maceral derived components (RMDC). This has implications for understanding the relevance of room temperature testing to the abrasion resistance of coke under practical blast furnace operation conditions. For example, a coke from a coal or blend with a comparatively high inertinite content may show lower resistance to abrasion in the blast furnace than would be expected from tumble drum indices. Larger sample numbers and cokes from a variety of single coals need to be tested in further work to verify these assertions.Finally, a novel method using micro-CT image analysis was developed to examine the wear path generated at the coke surface during tribological testing. The purpose of this was to assess the extent of the abrasive wear by comparing the rendered micro-CT images before and after tribological testing. A colour gradient scale was used to facilitate the quantitative assessment, whereby the colour of each voxel was based on the distance from the nearest voxel that is associated with solid phase.As expected, the specific surface area (SSA) calculated for the upper 1 mm of each sample decreased following tribological testing due to the generation of a wear track which is smoother than the initially rough, porous coke surface. In the C426 coke type examined, the SSA decreased the most for the sample tested in an argon atmosphere at 950 °C, matching the COF and quantified wear severity results, which showed there was a notable increase in abrasive wear to this coke as the temperature was raised from room to elevated temperature.Coupling this method of analysis with 3D visualisation techniques in further work would provide a powerful approach to examine and quantify mechanisms of coke surface breakage and the microstructural and/or microtextural features responsible for the breakage.

Non-contact non-resonant atomic force microscopy method for measurements of highly mobile molecules and nanoparticles

Atomic force microscopy (AFM) is nowadays indispensable versatile scanning probe method widely employed for fundamental and applied research in physics, chemistry, biology as well as industrial metrology. Conventional AFM systems can operate in various environments such as ultra-high vacuum, electrolyte solutions, or controlled gas atmosphere. Measurements in ambient air are prevalent due to their technical simplicity; however, there are drawbacks such as formation of water meniscus that greatly increases attractive interaction (adhesion) between the tip and the sample, reduced spatial resolution, and too strong interactions leading to tip and/or sample modifications. Here we show how the attractive forces in AFM under ambient conditions can be used with advantage to probe surface properties in a very sensitive way even on highly mobile molecules and nanoparticles. We introduce a stable non-contact non-resonant (NCNR) AFM method which enables to reliably perform measurements in the attractive force regime even in air by controlling the tip position in the intimate surface vicinity without touching it. We demonstrate proof-of-concept results on helicene-based macrocycles, DNA on mica, and nanodiamonds on SiO2. We compare the results with other conventional AFM regimes, showing NCNR advantages such as higher spatial resolution, reduced tip contamination, and negligible sample modification. We analyze principle physical and chemical mechanisms influencing the measurements, discuss issues of stability and various possible method implementations. We explain how the NCNR method can be applied in any AFM system by a mere software modification. The method thus opens a new research field for measurements of highly sensitive and mobile nanoscale objects under air and other environments.

Experimental Study of the Combined Effects of Al2O3, CaO and MgO on Gas/Slag/Matte/Spinel Equilibria in the Cu–Fe–O–S–Si–Al–Ca–Mg System at 1473 K (1200ºC) and p(SO2) = 0.25 atm

The combined effects of Al2O3, CaO and MgO slagging components on phase equilibria and thermodynamics in the basic Cu–Fe–O–S–Si system have been evaluated at 1473 K (1200 ºC) and p(SO2) = 0.25 atm for a range of oxygen partial pressures and matte compositions. The experimental technique included high-temperature equilibration of the samples on a spinel substrate under controlled gas atmosphere (CO/CO2/SO2/Ar), followed by rapid quenching and subsequent measurement of the equilibrium phase compositions using Electron Probe X-ray Microanalysis (EPMA). The experimental data have been compared with the results of thermodynamic calculations undertaken using FactSage software and an internal thermodynamic database. Both the experimental results and the calculations results revealed that the presence of Al2O3, CaO and MgO reduced both the sulphur and copper concentrations in the slag phase for a given set of process conditions. The data have been used for further optimisation of the parameters of the thermodynamic database describing multicomponent metallurgical systems. The resulting thermodynamic database is capable of predicting, with high accuracy, the phase equilibria and the distribution of all elements between the phases in the Cu–Fe–O–S–Si–(Al, Ca, Mg) system.Graphical

CO2 Capture and Low-Temperature Release by Poly(aminoethyl methacrylate) and Derivatives.

Poly(aminoethyl methacrylate) (PAEMA), poly(ethylene oxide)-block-(aminoethyl methacrylate) (PEO–PAEMA), and their guanidinylated derivates, poly(guanidine ethyl methacrylate) (PGEMA) and poly(ethylene oxide)-block-(guanidine ethyl methacrylate) (PEO–PGEMA), were prepared to study their capabilities for CO2 adsorption and release. The polymers of different forms or degree of guanidinylation were thoroughly characterized, and their interaction with CO2 was studied by NMR and calorimetry. The extent and kinetics of adsorption and desorption of N2 and CO2 were investigated by thermogravimetry under controlled gas atmospheres. The materials did not adsorb N2, whereas CO2 could be reversibly adsorbed at room temperature and released by an elevated temperature. The most promising polymer was PGEMA with a guanidinylation degree of 7% showing a CO2 adsorption capacity of 2.4 mmol/g at room temperature and a desorption temperature of 72 °C. The study also revealed relations between the polymer chemical composition and CO2 adsorption and release characteristics that are useful in future formulations for CO2 adsorbent polymer materials.

Biological method based on track membranes to form controlled gaseous media for fruit cold storage

The article proposes a biological method based on the use of gas-selective track membranes to form a modified gas atmosphere, considering the respiration rate of fruit. The work aims to study the change in the respiration rate of apples depending on the variety and storage time to substantiate the formation of the gas medium composition depending on the respiration rate of the fruit and the area of track membranes, and to study the kinetics of oxidation reactions of biologically active substances during cold storage of apples. The research is based on autumn apple varieties: Grushovka Yudicheva, Kordonovka and Pepin Shafranny. We have obtained the kinetic curves of changes in the content of mono- and disaccharides, ascorbic and organic acids in autumn apple varieties depending on the gas composition in terms of oxygen and carbon dioxide content, as well as the duration of fruit storage using track membranes. For maximum quality preservation, nutritional and biological value of the studied apple varieties at t = (3 ± 1) °C, we have determined a recommended composition of the controlled gas atmosphere: oxygen concentration - (5.2 ± 0.1%), carbon dioxide - (3.6 ± 0.1%). Controlled atmosphere is created using a gas-selective composite membrane with an area of 14-22 cm2/kg, depending on the variety and respiration rate.

Infrared furnace for in situ neutron single-crystal diffraction studies in controlled gas atmospheres at high temperatures

To understand oxygen diffusion mechanisms in non-stoichiometric oxides, the possibility to explore structural changes as a function of the oxygen partial pressure with temperature and related oxygen bulk stoichiometry is mandatory. This article reports on the realization of a high-temperature furnace, suitable for single-crystal neutron diffraction, working continuously at temperatures of up to 1000°C at different and adjustable partial gas pressures of up to 2 bar (1 bar = 100 kPa). This allows exploration of the phase diagrams of non-stoichiometric oxides under in situ conditions and controlled oxygen partial pressure. As a pilot study, the structural changes of Pr2NiO4+δ were explored at room temperature (δ ≃ 0.24) and at 900°C under 1 bar P(O2) (δ ≃ 0.13) as well as under secondary vacuum (approximately 10−5 mbar) conditions yielding a δ close to zero. The strong anharmonic displacements of the apical oxygen atoms along the [110] shallow diffusion pathway, which were previously observed at room temperature and 400°C, become more isotropic at 900°C. The study shows that the anisotropic oxygen displacements, here related to lattice instabilities, play a major role in understanding oxygen diffusion pathways and related activation energies at moderate temperatures. This also shows the importance of the availability of reaction cells for single-crystal neutron diffraction to explore the phase diagram and associated structural changes of non-stoichiometric oxygen ion conductors and respective diffusion mechanisms.

Reversible engineering of spin-orbit splitting in monolayer MoS2via laser irradiation under controlled gas atmospheres.

Monolayer transition metal dichalcogenides, manifesting strong spin-orbit coupling combined with broken inversion symmetry, lead to coupling of spin and valley degrees of freedom. These unique features make them highly interesting for potential spintronic and valleytronic applications. However, engineering spin-orbit coupling at room temperature as demanded after device fabrication is still a great challenge for their practical applications. Here we reversibly engineer the spin-orbit coupling of monolayer MoS2 by laser irradiation under controlled gas environments, where the spin-orbit splitting has been effectively regulated within 140 meV to 200 meV. Furthermore, the photoluminescence intensity of the B exciton can be reversibly manipulated over 2 orders of magnitude. We attribute the engineering of spin-orbit splitting to the reduction of binding energy combined with band renormalization, originating from the enhanced absorption coefficient of monolayer MoS2 under inert gases and subsequently the significantly boosted carrier concentrations. Reflectance contrast spectra during the engineering stages provide unambiguous proof to support our interpretation. Our approach offers a new avenue to actively control the spin-orbit splitting in transition metal dichalcogenide materials at room temperature and paves the way for designing innovative spintronic devices.

Electrical Conductivity and Water Effects in Phosphoric Acid Solutions for Doping of Membranes in Polymer Electrolyte Fuel Cells

Abstract Fuel cells (FCs) are among the more efficient solutions to limit the emission of greenhouse gases. Based on the conversion of the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electrical energy, a typical FC produces a voltage of 0.7 V under load. The potential is highly increased by placing the cells in series to obtain a stacked cell. Among the types of FCs, the polymer electrolyte membrane FCs (PEMFCs) are developed mainly for transport applications, because of their low impact on the environment, high power density and light weight compared with other types of FCs. Phosphoric acid (H3PO4) doped polybenzimidazole (PBI) membranes are widely used as efficient electrolytes. The performance of a (high temperature, 130–200 °C) HT-PEMFC depends mainly on the amount of H3PO4 in the solid polymer membrane. The strong autoprotolysis of H3PO4 is responsible for the high proton conductivity also in the anhydrous state. In this study, the H2OH3PO4 system is investigated in the temperature range 60–150 °C with varying water vapour activity at constant atmospheric pressure. Main purpose is to gain more insights into the kinetics of the equilibria in the H2O-H3PO4 system, which influence the fuel cell performance. Density, water content, electrical conductivity and activation energy are determined by exposing H3PO4 solutions for sufficiently long periods to controlled gas atmosphere in order to reach near-equilibrium conditions. The coexistence of ortho- and pyrophosphoric acid is analysed and higher condensed species are also considered. A new setup fully made in quartz is designed and developed to mix the phosphoric acid solutions in a climate chamber. The experimental results are compared to literature data to validate the developed setup and the methodology.

High-temperature creep of magnetite and ilmenite single crystals

We performed deformation experiments on dry natural single crystals of magnetite and ilmenite to determine the rheological behavior of these oxide minerals as a function of temperature, orientation, and oxygen fugacity. Samples were deformed at temperatures of 825–1150 ,^{circ }C to axial strains of up to 15–24% under approximately constant stress conditions up to 120 MPa in a dead-load-type creep rig at ambient pressure in a controlled gas atmosphere. Oxygen fugacity ranged from 10^{-9.4} to 10^{-4} atm. Ilmenite creep was insensitive to oxygen fugacity, while magnetite displayed a strong, non-monotonic oxygen fugacity dependence, with creep rates varying as f_{O_{2}}^{-0.7} and f_{O_{2}}^{0.4} at more reducing and more oxidizing conditions, respectively. Dislocation creep rates of magnetite single crystals were weakly dependent on crystallographic orientation with stress exponents that varied between 2.8 and 4.3 (mean 3.5 ± 0.4). Magnetite compressed parallel to <100>, <110>, and <111> axes exhibited apparent activation energies of 315±5, 345±30, and 290±5 kJ/mol, respectively. We estimated {f_O}_2-independent magnetite activation energies of 715 ± 150, 725 ± 145, and 690 ± 150 kJ/mol for <100>, <110>, and <111> orientations, respectively, in the region of negative {f_O}_2-dependence. Ilmenite single crystals were compressed parallel, normal, and inclined to the c-axis. Stress exponents of 3.4, 4.3, and 3.9 indicate dislocation creep with activation energies of 420 ± 35, 345 ± 30, and 360 ± 40 kJ/mol, respectively, for these orientations. Mechanical anisotropy in ilmenite is notably higher than in magnetite, as expected from its lower crystal symmetry. Constitutive equations were formulated for ilmenite and magnetite creep.

Experimental Study of the Individual Effects of Al2O3, CaO and MgO on Gas/Slag/Matte/Spinel Equilibria in Cu-Fe-O-S-Si-Al-Ca-Mg System at 1473 K (1200 °C) and p(SO2) = 0.25 atm

The individual effects of Al2O3, CaO and MgO on gas/slag/matte/spinel equilibria in the Cu-Fe-O-S-Si-(Al, Ca, Mg) system at 1473 K (1200 °C) and p(SO2) = 0.25 atm. have been experimentally measured for a range of oxygen partial pressures and matte compositions. The experimental methodology has included the high temperature equilibration of individual samples on a spinel primary phase substrate under controlled gas atmospheres (CO/CO2/SO2/Ar), followed by rapid quenching of the equilibrium condensed phases and direct measurement of the phase compositions using electron probe x-ray microanalysis. The experimental results show that the presence of Al2O3, CaO and MgO reduce the iron, sulphur and copper concentrations in the slag phase. Present study is undertaken as part of an integrated approach involving thermodynamic modelling and experimental measurements. The experimental data are compared with predictions obtained using the current thermodynamic database for the Cu-Fe-O-S-Si-(Al, Ca, Mg) system in order to further improve thermodynamic parameters.

Experimental Investigation of Gas/Slag/Matte/Tridymite Equilibria in the Cu-Fe-O-S-Si-Al-Ca-Mg System in Controlled Gas Atmosphere: Experimental Results at 1473 K (1200 °C), 1573 K (1300 °C) and p(SO2) = 0.25 atm

The effect of temperature, CaO, MgO and AlO on important technological copper smelting parameters, such as the chemically dissolved copper in slag and the composition of the liquid phase in equilibrium with tridymite, are experimentally characterised as a function of copper concentration in matte. Two series of experiments for the gas/slag/matte/tridymite equilibria in the Cu-Fe-O-S-Si system at p(SO) = 0.25 atm have been carried out. The effect of CaO at 1573 K (1300 °C), and the combined effect of AlO + CaO + MgO at 1473 K (1200 °C) and 1573 K (1300 °C) have been measured in the first and second series of experiments respectively. The experimental methodology involves high temperature equilibration of samples on a substrate made from the primary phase under controlled gas atmosphere (CO/CO/SO/Ar), followed by rapid quenching of the equilibrium condensed phases and direct measurement of the phase compositions using the Electron Probe x-ray Microanalysis. The resulting data are used in the optimization of the thermodynamic database for the copper-containing systems.

The effect of Al2O3 on fayalite-based copper smelting slags in equilibrium with matte and tridymite at 1 2008C and P(SO2) = 0.25 atm

Abstract Experimental investigations have been undertaken to determine the effect of Al2O3in slag on the gas/slag/matte/tridymite equilibria in the multi-component Cu-Fe-O-S-Si-Al system at 1 200 8C, and P(SO2) = 0.25 atm. The experimental technique involves high temperature equilibration of synthetic samples on the open silica substrate in controlled gas atmospheres (CO/CO2/SO2/Ar), rapid quenching after a designated equilibration time followed by the compositional analysis of the condensed phases with electron probe X-ray microanalyzer. The experimental data of the present study provide information on the effect of alumina on the slag composition, such as the chemically dissolved copper, dissolved sulphur, and Fe/SiO2 ratio in slag at tridymite saturation at different Cu in matte. The new data have been used as inputs for the optimization of the thermodynamic databases for the copper-containing systems and can also be used to evaluate the fluxing strategy in the copper smelting operation.

The effect of Al2O3 on fayalite-based copper smelting slags in equilibrium with matte and tridymite at 1 2008C and P(SO2) = 0.25 atm

Abstract Experimental investigations have been undertaken to determine the effect of Al2O3in slag on the gas/slag/matte/tridymite equilibria in the multi-component Cu-Fe-O-S-Si-Al system at 1 200 8C, and P(SO2) = 0.25 atm. The experimental technique involves high temperature equilibration of synthetic samples on the open silica substrate in controlled gas atmospheres (CO/CO2/SO2/Ar), rapid quenching after a designated equilibration time followed by the compositional analysis of the condensed phases with electron probe X-ray microanalyzer. The experimental data of the present study provide information on the effect of alumina on the slag composition, such as the chemically dissolved copper, dissolved sulphur, and Fe/SiO2 ratio in slag at tridymite saturation at different Cu in matte. The new data have been used as inputs for the optimization of the thermodynamic databases for the copper-containing systems and can also be used to evaluate the fluxing strategy in the copper smelting operation.

The Influence of Temperature on the Gas/Slag/Matte/Spinel Equilibria in the Cu-Fe-O-S-Si System at Fixed P(SO2) = 0.25 atm

Equilibria between gas/slag/matte/spinel phases in the Cu-Fe-O-S-Si system have been experimentally studied at 1523 K (1250 °C), P(SO2) = 0.25 atm, and a range of oxygen partial pressures. The experimental technique involved high temperature equilibration using spinel substrates in controlled gas atmospheres (CO/CO2/SO2/Ar), rapid quenching of the equilibrated phases, and direct measurement of phase compositions using Electron Probe X-ray Microanalysis. The influence of temperature on the gas/slag/matte/spinel equilibria has been analyzed. Comparisons with previous studies on the gas/slag/matte/tridymite equilibria and the most recent thermodynamic database have been provided. This is the first systematic study on the influence of temperature on the gas/slag/matte/spinel equilibria in the Cu-Fe-O-S-Si system at P(SO2) = 0.25 atm.

Direct laser hardening of AISI 1020 steel under controlled gas atmosphere

Laser hardening is usually performed in air. Use of a controlled gas atmosphere might produce a direct reaction of the gas with surface and thus provide an opportunity to engineer the surface microstructures. However, few studies are reported on direct gas-assisted laser hardening process. In this paper, a direct gas-assisted laser hardening is demonstrated on AISI 1020 steel using an ytterbium-doped fiber laser in presence of four different gases – air, argon, carbon dioxide and propane. All hardening trials were conducted at same laser parameters and only the gas was changed to evaluate its effect on hardness and microstructure of the steel. Results show that argon had slightly higher hardening effect than air as it prevents surface oxidation. Propane produced a very high surface hardness (914 HV) compared to conventional laser hardening process (395 HV). The ultrahigh hardness is due to diffusion of carbon into steel from decomposed propane. Increasing the concentration of propane contributed to an increment in hardness primarily due to large amount of carbides in near surface region. Contrarily, carbon dioxide yielded a lower surface hardness (350 HV) despite its high carbon content. This is attributed to the oxidizing effect of carbon dioxide, which produces decarburization during laser processing. The study reveals the potential of using direct gas-assisted laser hardening technique to alter surface mechanical properties of steel.

Distribution of Co, Fe, Ni, and precious metals between blister copper and white metal

ABSTRACT The distribution coefficients of Co, Ni, Ag, Au, Pd, and Fe at low concentrations between liquid copper and molten white metal (low-iron copper matte, ‘Cu2S’) were investigated experimentally as a function of temperature (1250–1350°C) and SO2 partial pressure (0.01–1 atm). The experimental technique involved samples equilibration at controlled temperature and gas atmosphere, followed by quenching and subsequent elemental analysis of equilibrium phases with electron probe X-ray microanalysis and laser ablation-inductively coupled plasma-mass spectrometry. The distribution coefficient of silver, nickel, gold and palladium between liquid copper and white metal indicated that they favour the blister copper whereas cobalt and iron distribute more to the white metal. The distribution coefficient of nickel, e.g. increased from 2.1 at 0.1–1.0 atm PSO2 and 1250°C to 3.2 at 1350°C. The distribution coefficients were only slightly dependent on temperature. The relatively strong dependence of the distribution coefficient of cobalt on PSO2 was discussed.