Preparation of ZrB_(2)-ZrO_(2)-SiC Composite Powder by Carbothermal Reduction from Zircon

Using zircon,boric acid and carbon black as starting materials,ZrB_(2)-ZrO_(2)-SiC composite powder was synthesized by calcining at 1500℃in flowing argon atmosphere.The effects of the soaking time(3,6 and 9 h)and the addition of additive AlF_(3)(0,0.5%,1.0%,1.5%,2.0%and 2.5%,by mass)on the phase composition and the microstructure of the synthesized products were investigated.The results show that:(1)ZrB_(2)-ZrO_(2)-SiC composite powder can be synthesized by carbothermal reduction at 1500℃in flowing argon atmosphere;ZrB_(2) and ZrO_(2) are granular-like,and SiC crystals are fiberous;(2)with the soaking time increasing,the amount of ZrB_(2) increases,the amounts of m-ZrO_(2) and SiC decrease,and the total amount of non-oxides ZrB_(2),SiC and ZrC gradually increases;the optimal soaking time is 3 h;(3)compared with the sample without AlF_(3),the sample with 0.5% AlF_(3) has decreased m-ZrO_(2)amount,noticeably increased ZrB_(2) amount but decreased SiC amount;however,when the addition of AlF_(3) increases from 0.5%to 2.5%,the m-ZrO_(2) amount increases,the ZrB_(2)amount decreases,and the SiC amount changes slightly;the optimum AlF_(3)addition is 0.5%.

Investigation of β-Ga_(2)O_(3) thick films grown on c-plane sapphire via carbothermal reduction

We investigated the influence of the growth temperature, O_(2) flow, molar ratio between Ga_(2)O_(3) powder and graphite powder on the structure and morphology of the films grown on the c-plane sapphire(0001) substrates by a carbothermal reduction method. Experimental results for the heteroepitaxial growth of β-Ga_(2)O_(3) illustrate that β-Ga_(2)O_(3) growth by the carbothermal reduction method can be controlled. The optimal result was obtained at a growth temperature of 1050 °C. The fastest growth rate of β-Ga_(2)O_(3) films was produced when the O_(2) flow was 20 sccm. To guarantee that β-Ga_(2)O_(3) films with both high-quality crystal and morphology properties, the ideal molar ratio between graphite powder and Ga_(2)O_(3) powder should be set at 10 : 1.

Mineralogy and carbothermal reduction behaviour of vanadium-bearing titaniferous magnetite ore in Eastern India

Vanadium-beaxing titaniferous magnetite bands hosted by Precambrian gabbro-norite-anorthositic rocks or their metamorphic equivalents were discovered in some parts of Eastern Indian Shield, containing 48%-49% Fe （total）, 10%-25% TiO2, and 0.3%-2.20% V2O5 by mass. Mineralogical and petrological study, composition, and characterization of the vanadium-bearing titaniferous magnetite ore were carried out by scanning electron microscopy-energy dispersive X-ray （SEM-EDX）, wave length X-ray florescence （WDXRF）, inductively coupled plasma-atomic emission spectroscopy （ICP-AES）, X-ray diffraction （XRD）, etc. Chemical beneficiation for valuable metals, such as Fe, Ti, andV, was performed by reduction roasting. The direct and indirect reduction were investigated by mixing the lump ore with solid activated charcoal in a closed reactor and purging the reducing gas mixture in standard reducibility index apparatus at different temperatures and time intervals. The reduction roasting parameters were optimized. Finally, the reduced samples were crushed and upgraded by magnetic separation. The results show that, the maximum mass fractions of magnetic and nonmagnetic parts achieved axe 69.36% and 30.64%, respectively, which contain 10.6% TiO2 and 0.84% V205 in the magnetic part and 36.5% TiO2 and 0.22% V205 in the nonmagnetic part.

Preparation of titanium oxycarbide from various titanium raw materials:Part I.Carbothermal reduction

Carbothermal reduction was performed at temperatures up to 1600°C for vanadium-bearing titanomagnetite,ilmenite concentrate,and high titania slag.The possibility of selective carbothermal reduction was discussed in detail from the viewpoint of thermodynamics,and also tested.The products were analyzed by X-ray diffraction,scanning electron microscopy,and chemical analysis.The results show that it is possible to reduce all iron oxide to metallic iron,and titania to oxycarbide（TiCxOy）,without the reduction of other oxides like silica and magnesia.

Carbothermal reduction process of the Fe-Cr-O system

Understanding the reduction behaviors and characteristics of the end products of Fe-Cr-O systems is very important not only for maximizing the recovery of metals from stainless steel dust but also for the subsequent reuse in metallurgical process. The present work first predicted the possible products thermodynamically when FeCr204 was reduced by C. The reduction behaviors by graphite of three kinds of Fe-Cr-O systems, i.e., FeCr204, Fe203q-Cr203, and Feq-Cr203, were then investigated in 1350-1550℃. Further, the microstructures of final products and element distribution conditions were examined. The results suggest that, thermodynamically, the mass of products for the carbothermal reduction of FeCr204 is a strong function of temperature, and the initial carbon content is used. More Fe-Cr-C solution and less residual carbon content are obtained at higher temperatures and lower no：no ratios （the initial molar ratio of C to O in the sample）. Experimental data show that the sample amount tends to affect the reduction rate, and the residual carbon content strongly depends on nc：no. With regard to the phases present in products during the reaction process, metal carbides tend to form in the initial stage, whereas Fe-Cr-C solution forms when the degree of reduction is sufficiently high.

Production of magnesium during carbothermal reduction of magnesium oxide by differential condensation of magnesium and alkali vapours

Most of researchers believed that the developments on the condensation of magnesium produced by carbothermic reduction just concentrated on two process routes:the“quench”route and the“solvent”route.But this paper will briefly analyzes the major challenges in magnesium vapor condensation during the vacuum carbothermic reduction of calcined dolomite,on equipment upgrade,heat transfers alter,to achieve condensation control and production collection.Solutions are then proposed using theoretical calculations and experiment results.Comparative analysis of the experiment results shows that the burning and even explosion of condensation products during the vacuum carbothermic reduction of calcined dolomite are mainly due to the burning of crystallized powder magnesium,which results from the self-ignition of alkali metals.Finally,this paper proposes a multistage condensation solution to improve traditional vacuum condensation equipment.And result show that the condensation equipment can effectively mitigate the burning and loss during condensation,also the morphology of the condensation products clearly improved,the grain size increased,and the oxidation rate decreased.The potassium/sodium vapor and the magnesium vapor were separately condensed.

Effects of Technological Parameters on Carbothermal Reduction and Nitridation of Zircon

Carbothermal reduction and nitridation （CRN） of zircon （ ZrSiO4 ） permits obtaining diffbrent composites of oxides and nitrides such as ZrO2 -Si2N2O and ZrN - Si3N4. The effects tf technological parameters （ carbon source, reaction temperature, and carbon con.tent ） on the reaction rate and product phase composition of CRN of zircon were investigated by TGA and XRD. The resuhs show that： （1） carbon source is an important factor for a rapid reaction, and actiwtted carbon is chosen as the carbon source considering the expect products and reaction rate ; （ 2 ） reaction tetnperature has vital effect on reaction rate and product. In, case of carbon content above 20% , the zircon phase and m-ZrO2 phase decrease with increasing temperature, while the ZF7N8O4 phase increases firstly and then decreases, and the ZrN phase increases continually; （3） different carbon contents result in different reaction products. The higher the carbon content, the lower the starting temperature for the CRN of zircon.

Synthesis of titanium oxycarbonitride by carbothermal reduction and nitridation of ilmenite with recycling of polyethylene terephthalate (PET)

An innovative and sustainable carbothermal reduction and nitridation(CTRN) process of ilmenite(FeTiO_3) using a mixture of polyethylene terephthalate(PET) and coal as the primary reductant under an H_2–N_2 atmosphere was proposed. The use of PET as an alternative source of carbon not only enhances the porosity of the pellets but also results in the separation of Fe from titanium oxycarbonitride(TiOxCyNz) particles because of the differences in surface tension. The experiments were carried out at 1250°C for 3 h using four different PET contents ranging from 25wt% to 100wt% in the reductant. X-ray diffraction(XRD),scanning electron microscopy(SEM) in conjunction with energy-dispersive X-ray spectroscopy(EDX),and LECO elemental analysis were used to study the phases and microstructures of the reduced samples. In the case of 75wt% PET,iron distinctly separated from the synthesized Ti OxCyNz phase. With increasing PET content in the sample,the reduction and nitridation rates substantially increased. The synthesis of an oxycarbonitride with stoichiometry of TiO_(0.02)C_(0.13)N_(0.85) with minimal intermediate titanium sub-oxides was achieved. The results also showed that the iron particles formed from CTRN of FeTiO_3 exhibited a spherical morphology,which is conducive for Fe removal via the Becher process.

SYNTHESIS OF TiN BY MICROWAVE CARBOTHERMAL REDUCTION OF TiO_2

Titanium nitride powder was synthesized by microwave carbothermal reduction of titanium oxide. The mechanism and thermal dynamics of the reaction process were studied. The results show that the microwave carbothermal reduction technology has unique advantages over the conventional reduction methods. It can not only lower the reaction temperature, shorten the synthesis cycle, but also refine the product particles,as well as improving the reactivity of the powder.

Synthesis of ZrO_2-SiC Composite by Carbothermal Reduction of Zircon

Zircon （mesh size ≤ 44μm ） and carbon black （mesh size ≤30μm ） were used as the starting materials, weighed with re（zircon） ： re（carbon black） of 100 ： 20 and mixed fully. The specimens with the diameter of 20ram and length of 5ram were prepared by pressing at 100 MPa, then dried at 120℃ for 12h, put into a furnace with 1. 5L ·min^-1 argon gas and fired at 1450℃, 1500℃, 1550℃, 1600℃ and 1650℃ for 4h, respectively. The chemical composition, phase composition and microstructure of the specimens were studied by chemical analysis, X-ray diffraction and scanning electronic microscope, and the carbothermal reduction reaction process was discussed by thermodynamic analysis. The results showed that the ZrO2-SiC composite could be synthesized by carbothermal reduction reaction using zircon and carbon black as the starting materials in argon atmosphere. The composite with different composition was obtained by controlling the firing temperature and partial pressure of CO gas. The proper temperature to synthesize ZrO2-SiC composite was 1600℃ in this experiment.

Preparation of ZrB_2-SiC Powders via Carbothermal Reduction of Zircon and Prediction of Product Composition by Back-Propagation Artificial Neural Network

Phase pure ZrB2-SiC composite powders were prepared after 1 450℃/3 h via carbothermal reduction route,by using ZrSiO4,B2O3 and carbon as the raw materials.The influences of firing temperature as well as the type and amount of additive on the phase composition of final products were detailedly investigated.The results indicated that the onset formation temperature of ZrB2-SiC was reduced to 1 400℃by the present conditions,and oxide additive（including CoSO4·7H2O,Y2O3 and TiO2）was effective in enhancing the decomposition of raw ZrSiO4,therefore accelerating the synthesis of ZrB2-SiC.Moreover,microstructural observation showed that the as-prepared ZrB2 and SiC respectively had well-defined hexagonal columnar and fibrous morphology.Furthermore,the methodology of back-propagation artificial neural networks（BP-ANNs）was adopted to establish a model for predicting the reaction extent（e g,the content of ZrB2-SiC in final product）in terms of various processing conditions.The results predicted by the as-established BP-ANNs model matched well with that of testing experiment（with a mean square error in 10^（-3） degree）,verifying good effectiveness of the proposed strategy.

Preparation of primary Al-Si alloy from bauxite tailings by carbothermal reduction process

Effects of various reaction parameters such as atmospheric pressure, treating temperature, sintering time and bituminite content on the preparation of primary Al-Si alloy by carbothermal reduction of bauxite tailings were investigated by XRD,XRF, infrared absorption carbon-sulfur analysis unit and SEM coupled with EDS. Meanwhile, the mechanism of carbothermal reduction of Al2O3 and SiO2 was discussed. It is found that pressure and temperature are major factors that influence the carbothermal reduction of bauxite tailings. The appropriate conditions for preparation of primary Al-Si alloy are as follows: atmospheric pressure of 0.1 MPa, heating temperature of 1 900 ℃,bituminite content of 95% (mass fraction) of theoretic bituminite content and sintering time of 1 h. Among four mechanisms of carbothermal reduction of Al2O3 and SiO2, the theory of the formation and decomposition of carbides might be the best one to interpret the reaction process.

Carbothermal reduction characteristics of oxidized Mn ore through conventional heating and microwave heating

For the purpose of exploring a potential process to produce FeMn,the effects of microwave heating on the carbothermal reduction characteristics of oxidized Mn ore was investigated.The microwave heating curve of the mixture of oxidized Mn ore and coke was analyzed in association with the characterization of dielectric properties.The comparative experiments were conducted on the carbothermal reductions through conventional and microwave heatings at temperatures ranging from 973 to 1373 K.The thermogravimetric analysis showed that carbothermal reactions under microwave heating proceeded to a greater extent and at a faster pace compared with those under conventional heating.The metal phases were observed in the microstructures only under microwave heating.The carbothermal reduction process under microwave heating was discussed.The electric and magnetic susceptibility differences were introduced into the thermodynamics analysis for the formation of metal Mn.The developed thermodynamics considered that microwave heating could make the reduction of MnO to Mn more accessible and increase the reduction extent.

Comparative evaluation of energy and resource consumption for vacuum carbothermal reduction and Pidgeon process used in magnesium production

With the fast development of the application of magnesium based alloys,the demand for primary magnesium is increasing dramatically all over the world.The Pidgeon process is the most widely used process for producing magnesium in China,but suffers from problems such as high energy,resource consumption and environmental pollution.While the process of vacuum carbothermal reduction to produce magnesium(VCTRM)has attracted more and more attention as its advantages,but it has not been well-practiced in industrial applications and there also is no comprehensive and quantitative analysis of this process.This study quantified the flows of resource and energy for the Pidgeon process and the VCTRM process,then compared and analyzed these two processes with each other from three aspects.The VCTRM process results in 63.14%and 69.16%lower of non-renewable mineral resources and energy consumptions when compared to the Pidgeon process,respectively.Moreover,the low energy consumption(2.675 tce vs.8.681 tce)and material to magnesium ratio(2.953:1 vs.6.429:1)of the VCTRM process,which lead to lower greenhouse gas(GHG)emissions(8.777 t vs.26.337 t)and solid waste generation(0.522 t vs.5.465 t)with a decrease of 66.67%and 90.45%,respectively.Results indicate that the VCTRM process is a more environmentally friendly process for magnesium production with high efficiency but low cost and low pollution,and it shows a good potential to be industrialized in the future after solving the bottleneck problem of the reverse reaction.

Microwave permittivity of SiC-Al_2O_3 composite powder prepared by sol-gel and carbothermal reduction

SiC-Al2O3 composite powder was prepared by sol-gel and carbothermal reduction method. The powder synthesized was characterized by X-ray diffraction(XRD) and scanning electron microscopy(SEM) to confirm the phase formation, and the thermodynamic analysis was performed systematically. Moreover, the variation of its microwave permittivity with different atomic ratio of Al/Si was investigated in the frequency range of 8.2-12.4 GHz. The results show that, the powder obtained consists of spherical particles of 300-400 nm in diameter, which are composed of SiC and Al2O3 microcrystal with the grain size of approximately 45 nm. The results of XRD accord with those of the thermodynamic analysis. It is impossible for Al atoms to dissolve in the lattice of SiC during the carbothermal reduction process. Along with the increase of atomic ratio of Al/Si in the xerogel, the amount of Al2O3 in the powder synthesized increases, which reduces bothε', the real part of complex permittivity, and tgδ(ε'/ε'), the dissipation factor, whereε' is the imaginary part of complex permittivity.

Kinetic Mechanism in the Process of Carbothermal Reduction of Ferrum Niobate

Ferrum niobate was synthesized by solid-phase sintering method in a vacuum carbon tube furnace at 1 300 ℃ for 180 min. The phase transformation of ferrum niobate carbothermal reduction process was studied by XRD. The reduction reactions of ferrum niobate in different temperature stages were determined by the TG-DSC curve. Meanwhile, according to the TG curve, the reaction kinetics parameters were calculated by A.W.Coats integration and the control steps in different temperature stages were ascertained. The results showed that the reduction of ferrum niobate starts at the temperature of 1 000 ℃, and the reduction process carries out in two steps according to sintering temperature.In a temperature range of 1 000-1 238 ℃(the first step), the main reduction products are Nb O2 and Fe; the kinetic equation of initial stage is [-ln(1-α)]4=kt, controlled by nucleation growth, and the apparent activation energy is 388 k J/mol; with the temperature increasing, the kinetic equation is α+(1-α)ln(1-α)=kt, which is the Valensi two-dimensional diffusion kinetic equation, and the apparent activation energy is 264.4 k J/mol. The main reaction in a range of 1 238-1 344 ℃(the second step) is the reduction of Nb O2 to Nb C, the kinetic equation is [(1-α)-1/3-1]2=kt, which is controlled by the three-dimensional diffusion, and the apparent activation energy is 482.7 k J/mol.

Synthesis of Al_2OC Compound by Carbothermal Reduction Process with Boron Oxide Additive

The synthesis method of Al2OC by adding B2O3 was studied to modulate the traditional synthesis process.The mixtures of active carbon,alumina and boron oxide with different carbon contents were heated at 1 700 ℃ for 2 h in flowing argon atmosphere to get the Al2OC product.The results indicate that the addition of B203 promotes the formation of Al2OC,which is dependent on the addition of B2 O3,and the Al2 OC content in the products increases with the increase of carbon.By systematically exploring the ratio of active carbon,alumina and boron oxide,the best formulation and the corresponding reaction mechanism were determined.

Synthesis of ZrN-Si_3N_4 Composite by Carbothermal Reduction and Nitridation of Zircon

Zircon （ ≤44 μm） and carbon black （≤30μm） were used as starting materials and mixed for 24 h using anhydrous ethanol as medium with the mass ratio of 100：40, dried fully at 60 ℃ and then dry mixed for 10 h. Specimens with size of Ф20 mm × 5 mm were pressed under 60 MPa, then dried fully at 120 ℃ , put into a furnace with 1. 0 L ·min^-1 nitrogen gas and fired at 1 400, 1 450, 1 480 and 1 500℃ for 6, 9 and 12 h, respectively. The phase composition and microstructure of the specimens were studied by XRD and SEM, and the carbothermal reduction and nitridation reaction process was thermodynamically analyzed. The results show that using zircon and carbon black as starting materials, ZrN - Si3N4 composite is synthesized by carbothermal reduction and nitridation reaction in nitrogen atmosphere. The composites with different compositions are obtained by controlling the firing temperature and partial pressure of CO gas. The proper firing temperature and holding time to synthesize ZrN - Si3N4 composite are 1 500 ℃ for 12 h.

Production of metallic nanopowders(Mg,Al)by solar carbothermal reduction of their oxides at low pressure

The carbothermal reduction of MgO and Al_(2)O_(3) in argon flow at low pressure allows to lower the onset temperature of metal vapor formation.Thermodynamic calculations indicate that metal formation begins at 1400 and 1700 K for a primary vacuum(1000 Pa),respectively,for Mg and Al.In the experimental section,concentrated solar energy was used for the process heating in order to favor energy savings.The products of the reaction between MgO or Al_(2)O_(3) and 2 varieties of carbon(graphite,carbon black)in flowing argon atmosphere at a total pressure of around 1000 to 1600 Pa were studied using X-ray diffraction,and microstructure observations revealed the formation of metallic nanopowders with some by-products.Metallic conversions close to 45 wt%and 52 wt%,respectively,for Mg and Al,were obtained.The low conversion yield of the carbothermal reduction of MgO can be attributed to a backward reaction reforming MgO powder and to a sintering process between oxide particles at high temperature.Aluminum production challenge is to avoid formation of undesired by-products:Al_(2)O,Al_(4)C_(3) and Al-oxycarbides.Advantages and weaknesses of the used process are described and some improvements are proposed to increase metallic yields.

Carbothermal Reduction Synthesis of Al_2O_3-SiC Powders from Coal Gangue

The Al2O3 -SiC composite powders were prepared in argon atmosphere rising coal gangue and carbonaceous materials （ carbon black, active carbon and antbravite） as starting materials by carbothermal reduction. Effects of excessive carbon addition, carbon types. temperature, soaking time. shaping pressure, types and amount of additives on phase composition and micro-structure of the Al2O3 - SiC composite powders were investigated. The re.suits indicate that： temperature, soaking time and chloride additi＇ve have significant influence on the synthesized Al2O3 -SiC composite powders. Based on the results, the optimized Al2O3 -SiC composite powders , Al2O3 58 mass% and SiC 42 mass%, with particle size d50 ≤5μm were prepared using coal gangue and carbon black as starting materials after 3 h firing at 1550 ℃. and proper additive addition could reduce the temperattlre by 50 ℃.