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The oxidation behavior of fayalite (Fe2SiO4) in water vapor at 1000°C was investigated. The phase constitution and microstructure of the solid products were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS). The gas product was continuously measured online by a gas analyzer. The results showed that fayalite was completely decomposed into magnetite (58.8 wt%), hematite (21.6 wt%) and silica (19.6 wt%) at 1000 °C for 40 min under water vapor condition. Compared with the result obtained in dry air, water vapor could promote fayalite to transform into magnetite by decreasing oxygen fugacity. In addition, the iron oxide product was further enriched via alkaline cleaning in 1 mol/L NaOH. As for the gas product, the hydrogen production capacity reached 24.41 mL/g when exposed to 50 vol% water-50 vol% Ar at 1000°C for 40 min.

In the present work, a novel process for effective extraction of valuable metals (V, Cr, Ti, Mn, Fe, Al, and Mg) from the vanadium slag is proposed. The leaching parameters for valuable metals extraction from the vanadium slag by acidic sodium chlorate solution were studied to obtain conditions for vanadium to be leached without using a pyro metallurgical step since the roasting process requires high energy consumption. The optimal H2SO4 concentration, weight ratio of NaClO3 to sample, leaching time, leaching temperature, agitation speed and ratio of liquid volume to solid mass were 6 M, 0.2, 6 h, 95℃, 200 rpm and 10, respectively. Under these optimal conditions, the extraction ratio of vanadium and valuable metals (V, Cr, Ti, Mn, Fe, Al, and Mg) were 85.8% and 91.2%, respectively. Compared with salt roasting, this process could simultaneously extract valuable metals from vanadium slag. More importantly, the experimental temperature was low underwater bath conditions.

The effect of rare earth metals addition on the Al2O3 inclusions in spring steel used in fastener of high speed railway was investigated by metallographic examination, SEM-EDS and composition analysis. To deform those harmful inclusions to improve material performance，the evolution process of Al2O3 inclusions was investigated through the surface and line scanning. Ce metal modifying Al2O3 is a stepwise reduction process based on a formation of ring shape Ce-riched band around the Al2O3 inclusions during reaction process. Through experiment and thermodynamic calculation, an evolvement rule about Al2O3 inclusions change after Ce addition is obtained, i.e. Al2O3→Ce2O3-Al2O3→Ce2O2S. Changing the inclusions from Al2O3 to rare earth inclusions could improve the resistance to pitting corrosion based on potentiodynamic anodic polarization test.

High quality ferrovanadium nitride was prepared successfully by carbothermal reduction nitridation process by using V2O5 and Fe as the raw materials. The effects of reaction temperature and C/O molar ratio (content of O is defined as the oxygen in V2O5) on the quality of ferrovanadium nitride were investigated in detail. It was demonstrated that C/O molar ratio had a great influence on the residue carbon, as well as the nitrogen content in the final products. It was found that the nitrogen content of the final product achieved 11.52% when the C/O molar ratio was 90% of the stoichiometric value. However, the nitrogen contents of the final products decreased with the further increase of C/O molar ratio. For the temperature higher than 1773 K, Fe became liquid phase and surrounded the solid V(C, N, O) particles tightly. The formation of liquid Fe was beneficial for the further removal of oxygen atoms left in the V(C, N, O) lattice, since it provided a liquid tunnel for carbon diffusion which greatly enhanced the reaction kinetics. From the results of X-ray diffraction (XRD) and thermodynamic calculations, phase evolution sequence of V2O5 can be obtained as: V2O5→VO2→V2O3→V(C, N, O). Moreover, the kinetic process from V2O3 to VN was studied and the results shown that the reaction rate can be described by Jander diffusion model with the extracted activation energy of 188.173 kJ/mol.

In the present work, the rate of dissolution of Al2O3 rod in CaO-SiO2-Al2O3 and CaO-SiO2-Al2O3-Ce2O3 slags were carried out in the temperature range of 1793 K (1520ºC) - 1853 K (1580ºC) under static conditions. The cross section of the rod and the boundary layers were identified and analyzed by SEM-EDS. The dissolution of Al2O3 was favored with the increasing CaO/Al2O3 ratio, elevating temperatures as well as the addition of Ce2O3. An intermediate product 3CaO5Al2O3Ce2O3 was detected. The mechanism of dissolution of Al2O3 in the Ce2O3 containing slag were also proposed as three steps involved: 1) the formation of calcium aluminates CaO•Al2O3 at the interface 2) the formation of 3CaO5Al2O3Ce2O3 as the reaction progresses; and 3) the dissolution of 3CaO5Al2O3Ce2O3 into the slag.

In order to optimize the current reduction process of chromite, a good knowledge of reduction mechanism involved is required. The basic component in chromite ore is FeCr2O4 with gangue component like MgO and Al2O3. In lack of clear and consistent explanation about the effect of addition on the reduction of FeCr2O4, investigation of synthetic FeCr2O4 with different kind and amount of additions was carried out at 1673K under isothermal mode. Kinetic mechanism was also studied by linear fitting of different kinetic equations. Combined with rate-controlling step, it could be concluded as follows. CaO could enhance the reduction because Ca2+ would replace Fe2+, thus facilitated the ion diffusion in solid phase. Al2O3 had a positive influence as well, since Al3+ could form a solid solution phase with Cr3+ and made Cr3+ reduced more easily. MgO would hinder the reduction due to formation of a more stable phase MgCr2O4. SiO2 would also hamper the Cr metallization because there was a liquid phase formed when Cr3+ was reduced to divalent, which would impede the nucleation of reduction product.

A new method, combining KTH model with geometrical model (General solution model by Chou) to estimate viscosity of some ternary silicate slags, was proposed in this work. According to modified KTH model, viscous Gibbs free energy for mixing of ternary slags was estimated by employing general solution model. It was found that viscous Gibbs energy for mixing of ternary system could be calculated using solely viscous Gibbs energy for mixing of sub-binary systems. The viscosities of five ternary slags CaO-MnO-SiO2, CaO-FeO-SiO2, FeO-MnO-SiO2, CaO-MgO-SiO2 and FeO-MgO-SiO2 were estimated in the present work. A good agreement with available experimental data, with mean deviation less than 20%, was achieved. The modified KTH model has advantages with less model parameters and improved estimation ability by comparison to original KTH model.

A simple and efficient method for preparation of SiAlON ceramics including β-SiAlON, O'-SiAlON and AlN polytypoid (15R and 12H) using reduction-nitridation of coal gangue and reducing agents at 1800K for 6h was described. The phase transformation of SiAlON at various atmospheres was discussed from thermodynamic and experimental analysis. Thermodynamic calculation revealed that different SiAlON phases could be synthesized at 1800K with the suitable atmosphere parameter Y (Y = lg(PO2 /ρθ)--3 2 lg(PN2 / ρθ)). Low Y value was beneficial to synthesis of β-SiAlON. The experimental result showed that β-SiAlON ceramics with the content of 90% was fabricated at strong reductive atmosphere in flowing nitrogen. O'-SiAlON with the content of 85% can be synthesized in flowing nitrogen atmosphere. In view of AlN polytypoid, the suitable condition to produce 15R was flowing nitrogen and 12H was formed at a weak reductive atmosphere. The mechanical properties of SiAlON ceramics synthesized under optimum conditions, i.e., modules of rupture (MOR) at room temperature, have been reported.

In order to optimize the current reduction process of chromite, a good knowledge of reduction mechanism involved is required. The basic component in chromite ore is FeCr2O4, thus, kinetic investigation of synthetic FeCr2O4 with different amount of carbon were carried out in the temperature range of 1473K to 1673K under both isothermal and non-isothermal mode. The iron can be easily reduced compared with chromium. And higher reduction degree of chromite can be achieved by increasing temperature and carbon content. With the supporting of X-ray Diffraction and Scanning Electron Microscope methods, the formation of metallic products followed the sequence: Fe-C alloy, (Fe,Cr)7C3and Fe-Cr-C alloy. Kinetics analysis showed that the first stage was controlled by nucleation with an apparent activation energy of 120kJ/mol, while the chromium reduction was controlled by crystallochemical transformation with an apparent activation energy of 288kJ/mol.

The present study is aimed to distinguish the different influences of CaO and MgO, as well as Al2O3 and SiO2 on viscosity of CaO-MgO-Al2O3-SiO2 melts. It is found that for melt without Al2O3, viscosity increases monotonously as CaO is gradually replaced by MgO. The addition of Al2O3 leads to a complex variation of viscosity. In different composition ranges, viscosity may exhibit different variation tendencies as changing the relative contents of CaO and MgO while keeping contents of other components constant. It is also found that when replacing SiO2 by equivalent mole of Al2O3, (i) in CaOAl 2O3-SiO2 system, viscosity increases when Al2O3 content is small relative to CaO content (there are enough Ca2+ ions to charge compensate Al3+ ions), but decreases when CaO content is inadequate for charge compensation; (ii) in MgO-Al2O3-SiO2 system, viscosity always decreases as substituting Al2O3 for SiO2. The reason for this difference for two systems may be resulted from the weak charge compensation ability of Mg2+ ion for Al3+ ion relative to Ca2+ ion. All the viscosity variations can be interpreted well by our new proposed viscosity model.

Extensive experiments have been carried out on the reduction of lead-rich slag in graphite crucible at temperature range of 1073 to 1473K. The reduction kinetics was also compared between industrial sinters and synthetic slags. The extent of reduction was measured by the volume of CO-CO2 gas produced at a given temperature and time. It was found that, at a given temperature, the reaction rate between the slag and carbon was initially fast and then slow as the extent of the reaction increases. Only limited reaction between slag and carbon occurred at temperatures below 1173K. At temperatures above 1173K, the reaction rate increased significantly with increasing temperature. The reduction reaction was found to be mainly liquid-solid reaction, which was chemically controlled at initial stage and diffusion controlled at later stage. The apparent activation energy was calculated to be 83.8 kJ/mol at chemically controlled stage and 224.9 kJ/mol at diffusion controlled stage for reduction of industrial sinter. For the synthetic slag, the reaction activation energy was 102.9 kJ/mol at chemically controlled stage and 259.4 kJ/mol at diffusion controlled stage. The difference of the activation energy between industrial sinter and synthetic slag can be explained by the difference in their CaO/SiO2 ratios.

The structurally based viscosity model proposed in our previous study is extended to include more components, e.g. SiO2, Al2O3, FeO, MnO, MgO, CaO, Na2O and K2O. A simple method is proposed to calculate the numbers of different types of oxygen ions classified by the different cations they bonded with, which is used to characterize the influence of composition on viscosity. When dealing with the aluminosilicate melts containing several basic oxides, the priority order is established for different cations for charge compensating Al3+ ions, according to the coulombic force between cation and oxygen anion. It is indicated that basic oxides have two paradox influences on viscosity: basic oxide with a higher basicity decreases viscosity more greatly by forming weaker non-bridging oxygen bond; while it increases viscosity more greatly by forming stronger bridging oxygen bond in tetrahedron after charge compensating Al3+ ion. The present model can extrapolate its application range to the system without SiO2. Furthermore, it could also give a satisfy interpretation to the abnormal phenomenon that viscosity increases when adding K2O to CaO-Al2O3-SiO2 melt within a certain composition range.

In view of successful application of mass triangle model in thermophysical properties, in the current work, the mass triangle model was extended to evaluate sulfide capacities of ternary systems with limited homogeneous region. Four ternary systems of Al2O3-FeO-SiO2, FeO-CaO-SiO2, CaO-CaCl2-CaF2 and CaO-CaF2-SiO2 were chosen to calculate iso-sulfide capacity based on the limited boundary data. The good agreement between reference data and calculated data indicated that this model is feasible and will play an indispensable role in the future. Compared with optical basicity model, the results obtained by mass triangle model are still competitive when containing Cl- and F- in the molten slag due to lacking the optical basicity values.