Papers by Keyword: Hydrogen Reduction

Abstract: This study develops a fast and simple way to produce high purity magnetite (Fe₃O₄) microparticles from mill scale by using hydrogen reduction with the addition of vapour as a retarding agent. By optimising the reduction temperature and gas flow rate, the characterisations by X-ray diffractometry technique shown that the Fe₃O₄ fraction of over 93 wt.-% is shown at the reduction temperature of 550 – 650 oC with the flow rate of the 4.5-5.5 mol%H₂ + Ar gas + H₂O gas mixture from 100 – 200 ml/min. The highest Fe₃O₄ fraction of over 99 wt.-% can be achieved from the reduction with the mixed gas at 650 oC and the flow rate of 200 ml/min for 4 hour.

Abstract: As a key material for microchannel plate, the lead silicate glasses doped with different content of Bi₂O₃ was prepared by melt-quenching method. The effect of Bi₂O₃ content on thermal properties, chemical stability, and resistivity before and after hydrogen reduction of the prepared glasses were studied. The results show that the coefficient of thermal expansion increases with the increasing of Bi₂O₃ content, while the transition temperature and softening temperature, the acid and alkali resistance, the volume and surface resistivity decrease gradually. Glass with 10% Bi₂O₃ and without PbO was used to prepare MCP, which has a resistance of 70MΩ and gain of 4,200 at 900V.

Abstract: Fine tungsten powder is prepared with blue tungsten oxide (BTO) through the hydrogen reduction. The samples were characterized with the scanning electron microscope (SEM), fisher sub-sieve sizer (FSSS) and the particulate size description analyzer (PSDA). Fine tungsten powder is easily obtained when the reduction temperature is low. With the increasement of the reduction temperature, the grain size of tungsten powder becomes coarse. The increase of the weight of BTO in the ceramic boat leads to the increasement of the thickness of its bed. Therefore, the weight of BTO in the ceramic boat ought to reduce if fine tungsten powder is prepared. Fine tungsten powder can be obtained when the hydrogen flow increases.

Abstract: Reduction of iron oxide by hydrogen is important in the production of direct reduced iron. This method of iron production is gaining increasing significance as an alternative route to the blast furnace technology with the many difficult issues facing the latter, the most important being the problem related to environmental. In order to reduce the emission of greenhouse gases CO₂, particularly for iron making, the production of Direct Reduced Iron (DRI) using hydrogen as the reducing gas instead of carbon monoxide is being considered. Reduction of pure hematite by hydrogen was studied at the laboratory scale, varying the experimental conditions like temperature (700oC and 800oC) and porosity (20% and 40%). Then, a Kinetic Modelling was conducted using Matlab software based on independently measured physical and thermodynamic properties of the reaction system and experimentally measured properties of the reactant solid (Fe₂O₃), gas phase (H₂) and reactant product (Fe). There is a gap that occurs between the predicted result and the experimental result although the model explicated the trend and the behaviour of the reduction rate of Ferric Oxide and indicated a good homogeneity to the experimental conditions used in this research.

Abstract: With the processes of solution doping and hydrogen reduction process, the raw materials APT powder was converted into the tungsten with calcium additive. Micro-morphology, micro-structure, the existing form of element calcium and their distribution were examined by SEM, HRTEM and EDS. The results show that Element calcium is mainly in the form of CaWO₄ in tungsten oxide powder and has two calcium tungstate forms which are CaWO₄ and Ca_4.26W₁₀O₃₀ in reducing tungsten powder. The Ca-W-O particles are embedding in the tungsten powder particles; the rest distribute between the tungsten powder particles.

Abstract: Electroless plating was used to coat Fe layers on the hard magnetic Nd-Fe-B powders to fabricate Nd-Fe-B/α-Fe heterostructured magnetic powders. The heat treatment was performed to study the property evolution of the heterostructured magnetic powders. The results show that Fe coating was oxidized to Fe₂O₃ while drying; through the hydrogen reduction annealing, Fe₂O₃ was reduced to α-Fe. The coercivity of the heterostructured magnetic powders increased from 111.3 kA/m (1.4 kOe) to 524.7 kA/m (6.6 kOe) after annealing at 650°C. However, the demagnetization curve of powders presents a kink due to un-ideal coupling between hard and soft magnetic phases because of the aggregation of α-Fe. The magnetization processes of the heterostructured powders transferred from the dominant nucleation mechanism to domain wall pinning mechanism after the heat treatment.

Abstract: The effect of doping different content of Mn into ammonium paratungstate (APT) on the production of tungsten products was studied systematically. The calcination of APT, reduction of WO₃ and carbonization of W were studied in sequence.The phase composition, powder morphology, existence form and distribution of Mn were analyzed by X-ray diffraction, scanning electron microscope and transmission electron microscope, respectively. The results showed that Mn converted from MnCl₂ to Mn²⁺WO₄ during reduction process. And then Mn²⁺WO₄ converted to Mn₅C₂ in the process of carbonization. Besides, Mn finally existed as the form of (Mn, W) C solid solution and Mn₅C₂. The distribution of Mn was always in the low contrast areas.

Abstract: Tungsten-copper(W-Cu) alloy is employed for manufacturing heavy duty contactors, relays,switches etc. During production of such components, W-Cu turnings/borings aregenerated. At CSIR-NML, a process for recovering tungsten and copper fromtungsten-copper borings containing 46.01% W, 53.78% Cu, 0.13% Fe and otherminor metals as high purity tungsten powder and copper powder has beendeveloped. In the present work, a detailed investigation on reduction ofammonium paratungstate (APT) having purity 99.95% by hydrogen gas to produce highpurity tungsten powder is presented. The various process parameters such astemperature, time and flow rate of hydrogen gas have been optimized. At the temperatureof 800°C and 0.1 lpm flow rate a reduction of 77.78% was observed upto 2h time. At 900°C, with increase in flow rate from 0.1 lpm to 0.3lpm the increase in reduction was found to be from 63.88% to 99.99% at 1h time.At still high temperature of 1000°C, almost complete reduction was obtainedat 0.1 lpm flow rate in 1h time. The effect of bed-depth was also carried out. Atall temperatures chemical reaction was the rate determining step.

Abstract: Ni-based superalloys are used extensively in the hot section of gas turbine engines owing to their inherent elevated temperature strength and creep resistance. As such, aircraft engine manufactures are continually striving to push the envelope of the capabilities of such high temperature structure materials in order to increase both engine performance and efficiency [1,2].

Abstract: nickel and iron was recovered as ferronickel from sodium jarosite residue containing nickel, the processes include alkaline decomposing residue, hydrogen reducing precipitations produced in alkaline decomposition process and magnetic separating reduced precipitations. The effects of alkaline decomposition temperature, the concentration of NaOH solution and solid/liquid ratio on the process of alkaline decomposing residue were examined. Meanwhile, the influence of hydrogen reduction temperature on the reduced products was studied, too. The results shown the natrojarosite in residue can be near completely decomposed to form hydroxide precipitations in the process of alkaline decomposition. In the process of hydrogen reduction, the rise of reduction temperature can increase the percent reduction for both nickel and iron in reduced results. But it is easier to reduce nickel than to reduce iron at the range of 750°C-950°C. When hydrogen reduction temperature was 950 °C, the percent reduction for nickel and iron in hydrogen reduction process was 95.81% and 94.4%, respectively. XRD tests indicated, except for ferronickel, there were still some impurities such as barium sulfate and barium oxide in reduced product. SEM test indicated the particles of precipitations will become fused together during hydrogen reduction process, so it is difficult to magnetic separate ferronickel purely from reduced results. The content of nickel and iron in magnetic separating product was only 11.64% and 62.40%.