Synthesis of High Purity Lithium Sulfide for Sulfide Solid Electrolyte Applications through Hydrogen Reduction of Lithium Sulfate

This paper is aimed to present a clean,inexpensive and sustainable method to synthesize high purity lithium sulfide(Li_(2)S)powder through hydrogen reduction of lithium sulfate(Li_(2)SO_(4)).A three-step reduction process has been successfully developed to synthesize well-crystallized and single-phase Li_(2)S powder by investigating the melting,sintering and reduction behavior of the mixtures of Li_(2)SO_(4)-Li_(2)S.High purity alumina was found to be the most suitable crucible material for producing high purity Li_(2)S,because it was not attacked by the Li_(2)SO_(4)-Li_(2)S melt during heating,as compared with other materials,such as carbon,mullite,quartz,boron nitride and stainless steel.The use of synthesized LizS resulted in higher purity and substantially higher room temperature ionic conductivity(2.77 mS·cm^(-1))for the argyrodite sulfide electrolyte Li_(6)PS_(5)Cl than commercial Li_(2)S(1.12 mS·cm^(-1)).This novel method offers a great opportunity to produce battery grade Li_(2)S for sulfide solid electrolyte applications.

Investigation of Refractory Bricks and Oxide Materials Heated in Hydrogen Reduction Conditions

This study aims to provide the basic knowledge for furnace refractory design by investigating refractory property changes occurred in a hydrogen atmosphere.Since refractory bricks are thermodynamically stable in a hydrogen atmosphere at 1100°C,we tried to find out the minute changes.In this experiment,a refractory brick was prepared by andalusite,mullite chamotte,and clay as raw materials and heated to 1100°C in a 100%hydrogen atmosphere for 72 h.It was found that the strength of the brick was decreased and the color was changed to black by the reduction of impurities.And in addition,this study covered research on the slaking risk of MgO raw materials because the minimum temperature is expected to 400°C in fluidized reduction furnaces unlike shaft furnaces.

Industrial application prospects and key issues of the pure-hydrogen reduction process

The industrial application prospect and key issues in basic theory and application are discussed by the methods of theoretical analysis and calculation to promote the development of the pure-hydrogen reduction process.According to the discussion of thermodynamics and kinetics of pure-hydrogen reduction reaction,the reduction reaction of iron oxide by pure hydrogen is an endothermic reaction,and the reaction rate of hydrogen reduction is significantly faster than that of carbon reduction.To explore the feasibility of the industrial applications of pure-hydrogen reduction,we design the hydrogen reduction reactor and process with reference to the industrialized hydrogen-rich reduction process and put forward the methods of appropriately increasing the reduction temperature,pressure,and temperature of iron ore into the furnace to accelerate the reaction rate and promote the reduction of iron oxide.The key technical parameters in engineering applications,such as hydrogen consumption,circulating gas volume,and heat balance,are discussed by theoretical calculations,and the optimized parameter values are proposed.The process parameters,cost,advantages,and disadvantages of various current hydrogen production methods are compared,and the results show that hydrogen production by natural gas reforming has a good development prospect.Through the discussion of the corrosion mechanism of high-temperature and high-pressure hydrogen on heat-resistant steel materials and the corrosion mechanism of H_2S in the hydrogen gas on steel,the technical ideas of developing new metal temperature-resistant materials,metal coating materials,and controlling gas composition are put forward to provide guidance for the selection of heater and reactor materials.Finally,the key factors affecting the smooth operation of the hydrogen reduction process in engineering applications are analyzed,offering a reference for the industrial application of the purehydrogen reduction process.

Preparation of titanium mineral from vanadium titanomagnetite concentrates by hydrogen reduction and acid leaching

Titanium mineral was prepared from vanadium titanomagnetite concentrates by hydrogen reduction and acid leaching.The leaching behaviors of elements like Fe,V,Mn,Al,Mg,Ca,and Si were highly related to the reduction degree.The phase compositions of the reduced materials and the leached residues were analyzed by XRD to identify the effect of reduction degree on the leaching mechanisms.The results showed that the concentrates were reduced to iron metal and titanomagnetite at 800-1000°C for 0.5 h,and the above elements of Fe and impurities were easily leached.Deeper reduction led to the formation of ilmenite and Mg-Al spinel,which hindered leaching.Mg-bearing anosovite appeared in the further reduced materials,and the leaching rates of impurities became much lower.An upgraded titanium mineral with a normalized TiO_(2) grade of 70.3%was achieved by H_(2) reduction at 850°C for 0.5 h and acid leaching,which is a satisfactory Ti resource for the preparation of titanium oxide by sulfate process.

Preparation of spherical ultrafine copper powder via hydrogen reduction-densification of Mg(OH)_2-coated Cu_2O powder

A novel process was developed to produce spherical copper powder for multilayer ceramic capacitors （MLCC）. Spherical ultrafine cuprous oxide （Cu20） powder was prepared by glucose reduction of Cu（OH）2. The Cu20 particles were coated by Mg（OH）2 and reduced to metallic copper particles. At last, the copper particles were densified by high-temperature heat treatment. The products were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, tap density, and thermogravimetry （TG）. It is found that the shape and size distribution of the copper powder are determined by the Cu20 powder and the copper particles do not agglomerate during high-temperature heat treatment because of the existence of Mg（OH）2 coating. After densification at high temperature, the particle tap density increases from 3.30 to 4.18 g/cm3 and the initial oxidation temperature rises from 125 to 150~C.

φ-pH diagrams and kinetics of V_(2)O_(3) prepared by solution-phase hydrogen reduction

Solution-phase hydrogen reduction(Sp HR)was introduced into V_(2)O_(3)preparation to overcome disadvantages of traditional reduction roasting,which include a long process,high energy consumption,and generation of pollution.The research mainly focuses onφ-pH diagrams and kinetics of SpHR.Thermodynamic analysis ofφ-pH diagrams for the V-H_(2)O system demonstrates that V_(2)O_(3)preparation via Sp HR requires a high temperature,a high vanadium concentration,and sufficient hydrogen in acidic solution.Kinetic analyses show that the activation energy of V_(2)O_(3)preparation via SpHR is 38.0679 k J/mol,indicating that the reduction is controlled by a combination of interfacial chemical reaction and internal diffusion.Effects of H;partial pressure(slope K=0.05246)on the reaction rate is not as significant as the vanadium concentration(K=1.58872).V_(2)O_(3)crystals with a purity of 99.59%and a vanadium precipitation rate of 99.83%were obtained under the following conditions:pH=5-6,c(V_(2)O_(3))=0.5 mol/L,p(H;)=4 MPa,m(PdCl;)=10 mg,T=250℃,and t=2.5 h.

Effect of Hydrogen Reduction of Silver Ions on the Performance and Structure of New Solid Polymer Electrolyte PEI/Pebax2533/AgBF4 Composite Membranes

In this paper, the effect of hydrogen reduction of silver ions on the performance and structure of new solid polymer electrolyte polyetherimide （PEI）/Pebax2533 （Polynylonl2/tetramethylene oxide block copolymer, PA12-PTMO）/AgBF4 composite membranes is investigated. For PEI/Pebax2533/AgBF4 composite membranesprepared with dillerent AgBF4 concentration, the permeances of propylene and ethylene increase with the increase of AgBF4 concentration due to the carrier-facilitated transport, resulting in a high selectivity. But for propyl- ene/propane mixture, the mixed-gas selectivity is lower than its ideal selectivity. The hydrogen reduction strongly influences the membrane performance, which causes the decrease of propylene permeance and the increase of pro-pane permeance. With the increase of hydrogen reduction time, the membranes show a clearly color change from white to brown, yielding a great selectivity loss. The data of X-ray diffraction and FT-IR prove that silver ions are reduced to Ago after hydrogen reduction, and aggregated on the surface of PEI/Pebax2533/AgBF4 composite mem- branes.

Hydrogen Reduction of Tungsten Oxides Part Ⅰ:Reduction of WO_(2.90),W_(20)O_(58) and WO_3

The hydrogen reduction of tungsten oxides WO_(2.90),W_(20)O_(58) and WO_3 were directly studied using high temperature X-ray diffraction analysis.The differences between tetragonal WO_(2.90) and monoclinic W_(20)O_(58) were discussed.Pure β-W was obtained from oxide WO_(2.90),while there appears small amount of WO_2 during the reduction of W_(20)O_(58) to β-W.

Hydrogen Reduction of Tungsten Oxides Part Ⅱ:Reduction of WO_(2.72) and WO_2,Transformation of β-W

The hydrogen reduction of tungsten oxides WO_(272)and WO_2 were studied directly using high-temperature X-ray diffraction analysis,The pure β-W was obtained from the reduction of WO_(272)The transformation of β-W to x-W was also studied in both hydrogen and nitrogen.The forming condition of β-W from WO_2 was discussed.Finally.a complete schematic diagram of reduction of tungsten oxides was given in this paper.

Production of nanocrystalline silver particles by hydrogen reduction of silver nitrate aerosol droplets

Nanocrystalline silver particles were produced by hydrogen reduction of silver nitrate aerosol droplets formed by high frequency ultrasonic generator.The dependences of the particle size,morphology and crystallite size on the precursor concentration and the reaction temperature were investigated.Ultrasonic spray pyrolysis process was combined with hydrogen reduction to research the effects on the silver particle production.Nanocrystalline silver particles including slight oxide structure were prepared at temperature as low as 200 ℃ from silver nitrate under hydrogen atmosphere.X-ray diffraction（XRD） studies showed that pure silver particles were obtained above 200 ℃ reaction temperature.The crystallite sizes of the samples ranged from 29 to 47 nm.The results indicate that the crystallite sizes hardly ever depended on the reaction temperature.Crystallites slightly enlarged by increasing precursor concentration.SEM observations showed that particles were obtained in spherical morphology with particle sizes between 210 and 525 nm.Reaction temperature and precursor concentration strongly influenced the particle size.

Synthesis and Characterization of Ultra-fine Cr_2O_3 from Hydrogen Reduction of K_2CrO_4

As a part of the green process for manufacturing chromium compounds, two steps are involved in the synthesis of ultra-fine Cr2O3 powders： the first is the hydrogen reduction of K2CrO4 into intermediate trivalent （Cr^3＋） or tetravalent （Cr^4＋） chromium compounds; the second is the decomposing of the intermediate into Cr2O3 by heat treating. The intermediate is well characterized by means of SEM, XRD, and XPS. The possible reaction mechanism of the process is analyzed.

Kinetics of hydrogen reduction and the influence of gas composition on hot- rolled steel scale after temper rolling

For replacing the presently employed pickling method with a more environmentally friendly descaling method, hydrogen reduction of oxide scale formed during hot rolling was studied at 800℃ under a varied atmosphere. The hydrogen level and water vapor content in the reducing atmosphere were found to influence the reduction rate wherein increasing hydrogen level as well as decreasing water vapor content resulted in faster oxide reduction. The reduction reaction substantially obeyed a parabolic rate law. Oxide scale of a usual thickness （approximately 7 micrometer） could be reduced almost completely in an atmosphere of 20 vol. % hydrogen with a water vapor content corresponding to a -40℃ dew point at 800℃. When lowering the hydrogen level to 10% and increasing the water vapor content to a 10℃ dew point,quite a large extent of the oxide scale was retained,which might be attributable to the formation of an outermost dense layer of pure iron at the early stage of reduction.

The effect of hydrogen reduction of α-MnO_(2) on formaldehyde oxidation: The roles of oxygen vacancies

A series of α-MnO_(2) catalysts with various Mn valence states were treated by hydrogen reduction for different periods of time. Their catalytic capacity for formaldehyde(HCHO) oxidation was evaluated. The results indicated that hydrogen reduction dramatically improves the catalytic performance of α-MnO_(2) in HCHO oxidation. The α-MnO_(2) sample reduced by hydrogen for 2 h possessed superior activity and could completely oxidize 150 ppm HCHO to CO_(2) and H_(2)O at 70℃. Multiple characterization results illustrated that hydrogen reduction contributed to the production of more oxygen vacancies. The oxygen vacancies on the catalyst surface enhanced the adsorption, activation and mobility of O_(2) molecules, and thereby enhanced HCHO catalytic oxidation. This study provides novel insight into the design of outstanding MnO_x catalysts for HCHO oxidation at low temperature.

Study on Kinetics of Iron Oxide Reduction by Hydrogen

Kinetics parameters of iron oxide reduction by hydrogen were evaluated by the isothermal method in a differential micro-packed bed. Influence of external diffusion, internal diffusion and heat transfer on the intrinsic reaction rate was investigated and the conditions free of internal and external diffusion resistance have been determined. In the experiments, in order to correctly evaluate the intrinsic kinetics parameters for reducing Fe203 to Fe3O4, the reaction temperatures were set between 440 ℃ and 490 ℃. However, in order to distinguish the reduction of Fe304 to FeO from that of FeO to Fe, the reaction temperature in the experiment was set to be greater than 570 ℃. Intrinsic kinetics of iron oxide reduction by hydrogen was established and the newly established kinetic models were validated by the experimental data.

Fluidization behavior and reduction kinetics of pre-oxidized magnetite-based iron ore in a hydrogen-induced fluidized bed

The influence of different pre-oxidation temperatures and pre-oxidation degrees on the reduction and fluidization behaviors of magnetite-based iron ore was investigated in a hydrogen-induced fluidized bed.The raw magnetite-based iron ore was pre-oxidized at 800 and1000℃ for a certain time to reach a partly oxidation and deeply oxidation state.The structure and morphology of the reduced particles were analyzed via optical microscope and scanning electron microscopy(SEM).The reaction kinetic mechanism was determined based on the double-logarithm analysis.The results indicate that the materials with higher oxidation temperature and wider particle size range show better fluidization behaviors.The lower oxidation temperature is more beneficial for the reduction rate,especially in the later reduction stage.The pre-oxidation degree shows no obvious influence on the fluidization and reduction behaviors.Based on the kinetic analysis,the reduction progress can be divided into three stages.The reduction mechanism was discussed combing the surface morphology and phase structure.

Reductive kinetics of Panzhihua ilmenite with hydrogen

The hydrogen reduction of Panzhihua ilmenite concentrate in the temperature range of 900?1050 °C was systematicallyinvestigated by thermogravimetric analysis (TG), X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods. It wasshown that the products of the Panzhihua ilmenite reduced at 900 °C were metallic iron and rutile. Above 1000 °C, ferrouspseudobrookite solid solution was generated. During the reduction process, element Mg gradually concentrated to form Mg-rich zonewhich can influence the metallization process. The reduction reaction proceeded topochemically and its related reduction kineticswere also discussed. The kinetics of the reduction indicated that the rate-controlling step was the diffusion process. The apparentactivation energy of the hydrogen reduction of Panzhihua ilmenite was calculated to be 117.56 kJ/mol, which was larger than that ofsynthetic ilmenite under the same reduction condition.

Effect of salt-assisted reduction method on morphologies and size of metallic tungsten particles

A simple method was proposed to produce tungsten(W)particles with controllable shape and size by employing the salt-assisted hydrogen reduction.W particles with controlled shape and size were prepared by adjusting the amount of chlorine salts and the temperature.After adding salt additives,the dispersibility of final particles was obviously improved and more adequate growth of particles was obtained.It was found that the effect of NaCl and LiCl is particularly significant.The average sizes of the obtained W particles at 1038 K after adding 0.1 wt.%NaCl and 0.1 wt.%LiCl were 0.924 and 1.128μm,respectively.With the increase of temperature and amount of chlorine salts,the dispersity of the produced W particles became much better,the size of W sub-particles was increased,and the shape of W sub-particles was changed from spherical to polyhedral.At 1349 K,the addition of chlorine salts even multiplied the particle size,and the average sizes of W particles with 1 wt.%NaCl and 1 wt.%LiCl were raised up to 21.367 and 29.665μm,respectively.Based on the conventional pseudomorphic transformation and chemical vapor transport mechanisms,the effects of adding salts on the reaction mechanism were investigated in detail as well.

Hydrogen reduced sodium vanadate nanowire arrays as electrode material of lithium-ion battery

Vanadates and vanadium oxides are potential lithium-ion electrode materials because of their easy preparation and high capacity properties.This paper reports the electrochemical lithium-storage performance of VO2 and NaV2O5 composite nanowire arrays.Firstly,Na5V12O32 nanowire arrays are fabricated by a hydrothermal method,and then VO2 and NaV2O5 composite nanowire arrays are prepared by a reduction reaction of Na5V12O32 nanowire arrays in hydrogen atmosphere.Crystal structure,chemical composition and morphology of the prepared samples are characterized in detail.The obtained composite is used as an electrode of a lithium-ion battery,which exhibits high reversible capacity and good cycle stability.The composite obtained at 500℃presents a specific discharge capacity up to 345.1 mA·h/g after 50 cycles at a current density of 30 mA/g.

Simultaneous recovery of carbon and sulfur resources from reduction of CO_2 with H_2S using catalysts

An approach to the simultaneous reclamation of carbon and sulfur resources from CO2 and H2S has been proposed and effectively implemented with the aid of catalysts. A brief thermodynamic study reveals the potential of direct reduction of CO2 with H2S（15：15 mol% balanced with N2） for selective production of CO and elemental sulfur. The experiments carried out in a fixed-bed flow reactor over the temperature range of 400–800 °C give evidence of the importance of the employment of catalysts. Both the conversions of the reactants and the selectivities of the target products can be substantially promoted over most catalysts studied. Nevertheless, little difference appears among their catalytic performance. The results also prove that the presence of CO2 can remarkably enhance H2S conversion and the sulfur yield in comparison with H2S direct decomposition. A longtime reaction test on Mg O catalyst manifests its superior durability at high temperature（700 °C） and huge gas hourly space velocity（100,000 h-1）. Free radicals initiated by catalysts are supposed to dominate the reactions between CO2 and H2S.

Preparation of high pure tellurium from raw tellurium containing Cu and Se by chemical method

High pure tellurium was prepared from raw tellurium containing copper and selenium by chemical method containing oxidation with concentrated nitric acid, leaching with hydrochloric acid, reducing with sulfur dioxide and treating in hydrogen atmosphere at high temperature. Removal ratio of Cu in raw tellurium reaches 99% after raw tellurium is oxidized and leached with HNO3（69%） under the following conditions： 0.96 times stoichiometric quantity of concentrated nitric acid, 4：1 of ratio of liquid to solid, 20 °C of reaction temperature and 30 min of reaction time. Leaching ratio of Te reaches 99% after Te is leached with hydrochloric acid under the following conditions： 1.67 times stoichiometric quantity of hydrochloric acid, 4：1 of ratio of liquid to solid, 20 °C of reaction temperature and 30 min of reaction time. Tellurium powder（99.95%） is obtained when Te（IV） in leachate is reduced with sulfur dioxide. The purity of tellurium increases from 99.954% to 99.999 6% after tellurium（99.95%） is treated in hydrogen atmosphere at 723.15 K for 30 min.