Synthesis of high-purity ultrafine tungsten and tungsten carbide powders

High-purity ultrafine W or WC powder was prepared via a two-step process composed of the carbothermic pre-reduction of WO2.9 and the following deep reduction with H2 or carbonization with CH4+H2 mixed gases. The effects of C/WO2.9 molar ratio and temperature on phase composition, morphology, particle size, and impurity content of products were investigated. The results revealed that when the C/WO2.9ratio was in the range from 2.1:1 to 2.5:1, the carbothermic pre-reduction products consisted of W and a small amount of WO2. With changing C/WO2.9 ratio from 2.1:1 to 2.5:1, the particle sizes were gradually decreased. In order to prepare ultrafine W or WC powder, a relatively high C/WO2.9 ratio and a lower reaction temperature at this stage were preferred. After the second reaction, the final products of ultrafine W and WC powders with a high purity could be obtained, respectively.

Direct reduction of carburized pre-reduced pellets by microwave heating

A new iron-making process using carburized pre-reduced iron ore pellets and microwave heating is investigated. The pre-reduced pellets, with a porous structure, and fine particles are carburized homogeneously at 400-650 ℃ in a CO atmosphere. The carburized carbon not only acts reaction as a reduction agent, but also absorbs microwave in the reduction process. Hence, the carburized pre-reduced pellets can be rapidly reduced by microwave heating. There are three procedures involved in the process, namely, gas-based pre-reduction, low-temperatttre carburization and deep reduction by microwave heating. Carburized pre-reduced iron ore pellets show a rapid temperature rise that is twice as fast as the results for pre-reduced pellets in the laboratory. This not only improves the efficiency of the microwave heating, but also accelerates the reduction of iron oxides. The temperature of the pre-reduced pellets rises to 1050 ℃ in 45 min when the carburization rate is 2.02%, and the metallization rate and compressive strength reach 94.24% and 1725 N/pellet, respectively.

The removal of inevitable NOx species in catalysts and the selection of appropriate membrane for measuring electrocatalytic ammonia synthesis accurately

Ammonia synthesis by electrocatalytic nitrogen reduction reaction(NRR)is considered as a promising alternative to the Haber−Bosch process.However,due to the extremely low ammonia yield and easily accessible extraneous contamination in the laboratory,NRR study always suffers from fluctuation and variability.Finding and eliminating all kinds of possible extraneous contamination is crucial to evaluate the performance of electrocatalytic ammonia synthesis accurately.In this work,we systematically explored two factors that affect NRR results but are easy to be ignored:the selection of membrane for NRR and the unconscious N-source in NRR catalysts.After series of experiments,we proposed a low-cost and almost pollution-free Celgard 3501 membrane as the separator for NRR to avoid the adsorption and release of ammonia by the membrane.In addition,we proposed a pre-reduction strategy to remove residual or adsorbed NOx contaminants in catalysts.These two solutions will help the community to evaluate the NRR activity more accurately.

Two-stage reduction for the preparation of ferronickel alloy from nickel laterite ore with low Co and high MgO contents

The preparation of ferronickel alloy from the nickel laterite ore with low Co and high MgO contents was studied by using a pre-reduction-smelting method. The effects of reduction time, calcination temperature, quantity of reductant and calcium oxide (CaO), and pellet diameter on the reduction ratio of Fe and on the pellet strength were investigated. The results show that, for a roasting temperature > 800 A degrees C, a roasting time > 30 min, 1.5wt% added anthracite coal, 5wt% added CaO, and a pellet size of similar to 10 mm, the reduction ratio of Fe exceeds 70% and the compressive strength of the pellets exceeds 10 kg per pellet. Reduction smelting experiments were performed by varying the smelting time, temperature, quantity of reductant and CaO, and reduction ratio of Fe in the pellets. Optimal conditions for the reduction smelting process are as follows: smelting time, 30-45 min; smelting temperature, 1550A degrees C; quantity of reductant, 4wt%-5wt%; and quantity of CaO, 5wt%; leading to an Fe reduction ratio of 75% in the pellets. In addition, the mineral composition of the raw ore and that during the reduction process were investigated by process mineralogy.

Melting of Pre-Reduced Chromite Pellet Bearing Carbon

As the raw material for hot metal containing chromium from 20% to 40%, carbon-beared chromite pellets made from three kinds of typical chromite were reduced at 1 300 ℃ for 30 min and then kept at 1 550-1 600 ℃ for 10 min. The effect of Cr 2O 3/FeO mass ratio in pellets on chromium content in hot metal and the yield of chromium were investigated. The results indicated that the highest chromium content is in hot metal produced from South African UG2 ore, but slag volume produced with Indian chromite is the smallest. The yield of chromium is only 60% to 75%, due to short melting time, high melting point and large surface tension of the slag with high Al 2O 3 and MgO content, which influences the separation between metal and slag.

Reduction Behavior With CO Under Micro-Fluidized Bed Conditions

To process optimization and improve the degree of reduction, a two-step experiment was designed. The experiment was carried out in the micro-fluidized bed. The reactor in the micro-fluidized bed is operated as a differential reactor to ensure an equal temperature and residence time with the reactor volume. The experiment used Brazilian iron ore and reducing gas of CO. The operating temperature was 400 to 800 ℃ and the residence time was between 10 and 60 min. In correspondence with experiment, microscopic technique was applied too. The test shows that temperature and residence time of the pre-reduction stage have an important effect on the degree of reduction. By using two-step experiment, the maximum value of reduction degree increases by 44.1% compared with the maximum value of traditional reduction experiment. Microscopic analysis shows that the specific surface area, surface morphology and texture of reduced iron ore after pre-reduction stage have an important effect on the degree of final reduction too.