Aluminum Reduction and Nitridation of Bauxite

The application of bauxite with low Al2O3 content has been studied in this paper and β-SiAlON has been obtained from two kinds of bauxites （Al2O3 content 68.08 mass% and 46.30 mass% respectively） by aluminum reduction and nitridation method. The sequence of reactions has been studied using thermal analysis （TG-DTA）, X-ray diffraction （XRD） analysis and scanning electron microscopy （SEM） with EDS. Compared with carbon thermal reduction and nitridation of aluminosilicates employed presently, the reaction in the system of bauxite-Al-N2 occurs at lower temperature. β-SiAlON appears as one of the main products from 1573K and exists stably in the range of the present experimental temperature. The microstructure of β-SiAlON obtained at 1773 K is short column with 5-10μm observed by SEM.

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.

Influences of Technological Parameters on Carbothermal Reduction and Nitridation of Titanium Dioxide

The particle size of starting materials, the homogeneity of the carbon/oxide mixtures, and the carbon content are important parameters for a rapid reaction. The influences of technological parameters（carbon particle size, oxide particle size, mixing method, carbon content） on the reaction rate of carbothermal reduction and nitridation of titanium dioxide （TiO2 ） were investigated by a continuous thermo-gravimetric analyzer for large size specimen. The carbon particle size is the most impor tant parameter for a rapid reaction, but carbon particle may have no influence on the morphology of titanium nitride （TiN） powder. Oxide particles are the precursors of TiN powder, but the TiO2 particles size has very little influence on the reaction rate. The carbon content not only influences the reaction rate to some degree, but also influences the purity of TiN powder. The mixing method of the specimen has very little influence on the reaction rate. These results are suitable for other nitrides and carbides prepared by carbothermal reduction method.

Preparation of Sialon Powder from Coal Gasification Slag

X-ray fluorescence spectrometry（XRF）,X-ray powder diffractometry（XRD） and scanning electron microscopy（SEM） were used to characterize the chemical composition,phase constituent and microstructure of the coal gasification slag.Sialon powders were synthesized by carbothermal reduction and nitridation using the coal gasification slag as raw materials.The experimental results showed that glass and amorphous carbon were the main phases,quartz and calcite as minor crystalline phases were also presented in porous coal gasification slag.Main constituents of coal gasification slag were SiO2,Al2O3,CaO and residual carbon.Sialon powder with Ca-α-Sialon as main crystalline phase can be synthesized when coal gasification slag powders were reduced and nitrided at 1500 ℃ for 9 h using nitrogen flow of 500 ml/min.The coal gasification slag is a valuable and economic starting material for preparing Sialon powders.

Effect of Zircon Addition on Properties of Low Carbon AL_2O_3-C Refractories

Using tabular alumina as aggregate,tabular alumina fines,reactive alumina ultra-fines,aluminum powders,silicon powders,carbon black,flake graphite,B4 C and zircon fines as matrix,low carbon Al2O3-C refractories were prepared.Influences of zircon powders additions （0,3%,5% and 7%,in mass,the same hereinafter） on properties,phase composition and microstructure were investigated.The results show that the ZrO2-nitride can be in-situ formed through carbothermal reduction and nitridation in Al2O3-C refractories.With the increase of zircon powder,the oxidation resistance of the Al2O3-C refractories improves obviously,the oxidized layer thickness decreases from 7.94 mm without zircon to 2.71 mm with 5% zircon.HMOR at 1 400 ℃ of the Al2O3-C refractories reaches the maximum 14.9 MPa when zircon addition is 5%.With the increase of zircon powder,the apparent porosity and bulk density change a little,CMOR and CCS increase.

UNITECR 2011

Hosted by The Technical Association of Refractories, Japan, 12th Unified International Technical Conference on Refractories （UNTECR） will be held in Kyoto, Japan from Oct. 31 to Nov. 2, 2011.

Non-isothermal kinetics of synthesizing vanadium nitride by one-step method

Vanadium nitride was synthesized by one-step method using V2O5 and carbon black as raw materials in nitrogen atmosphere. The phases of different reaction products prepared in different reaction temperatures were analyzed by X-ray diffraction(XRD), and the dynamic behavior of the process of synthesizing vanadium nitride(VN) by one-step method was studied with non-isothermal thermogravimetry. The mechanism function and kinetic parameters of reaction process were calculated by thermal gravimetric analyses(TGA), and the reaction rate equation was established. The XRD results show that for the samples tested with minimal VN after holding for 4 h at 1273 K, the main phase of products is VN at 1476 K, while some vanadium nitrides transform into vanadium carbides again over 1573 K. It is found that N2 is beneficial to stimulate reduction and proceed carbonization reaction,and the reduction and nitridation reaction can occur simultaneously. The activation energy of preparing VN by one-step method is 104.005 kJ·mol-1, and the frequency factor is 470.52 at 1280–1358 K, and 150.052 kJ·mol-1 and 2.35 9 104 at 1358–1426 K, respectively.

Incorporation of europium (Ⅱ) nanostructures into the channels of mesoporous silicon oxy-nitride for enhanced photoluminescence

Divalent europium（Ⅱ）-doped mesoporous silicon oxy-nitride materials, as a novel type of nanoscopic photoluminescent material, are studied in which the optically active luminescent centers are isolated within the pores. Colorless and transparent blue emitting luminous Eu2＋-doped mesoporous silicon oxy-nitride materials were prepared from mesoporous silica via impregnation, nanocasting and nitrogen-assisted carbothermal reduction and nitridation method. The morphology and porosity of the silica remain unchanged during the synthesis process as revealed by SEM images and by nitrogen sorption studies. Photoluminescence studies reveal a strong blue emission band for Eu2＋ centered at 425 nm with a quantum efficiency of 47%. The luminescent intensity is greatly influenced by the amount of co-dopant, AI3＋ ions.