| Refractories for RH Degassers and Ways of Improving Their Lining Life
CHEN Zhaoyou
This paper attempts to clarify the systematic works of the refractories for the RH degassers and the ways of improving their lining life. It includes: (1) types of RH degassers; (2) the operating conditions of refining and the severely damaged areas in RH degassers; (3) the reasons why side wall and bottom of lower vessel, throat and snorkels become the severe wear areas are analyzed, such as erosion and abrasion caused by the high circulation rate of treated molten steel, thermal and structural spalling by the violent temperature change, high corrosion by the Fe-oxides containing siliceous slag and CaF2-riched desulfurization powders attack, degradation of texture by the vaporisation of refractory components in vacuum and in oxygen blowing; besides the above mentioned factors, what other reasons to make the snorkels become the most quick wear elements are also explained; (4) the studies of resistance to refining slags attack and slag penetration and its prevention; the evaluation of various refractory materials to withstand the attack of slags is based on the experimental results of rotating cylinder method, rotary drum test and induction furnace test, and the phase diagrams analyses; the measures to reduce the slag penetration are discussed, for example the deep of slag penetration can be decreased by reducing the size of brick pores; (5) suitable refractory materials selection and recent developments for the different severe wear areas in RH, and lining maintenance; (6) refractories for RH to refine silicon steel; (7) the ways of improving RH lining life.
Key words: Refractories for RH, Refine slag resistance, Magnesia-chrome brick, Structural spalling, Silicon steel
Effect of TiO2 on Synthesis of Al4SiC4/Al4O4C Composite
DENG Chengji, KUANG Jianlei, ZHU Hongxi, Bai Chen
Al4SiC4/Al4O4C composites were synthesized based on m(sintered clay)∶m(active carbon)∶m(aluminum powder)=39∶27.6∶33.4, adding TiO2 powder (anatase type, 0, 3%, 6%, 9%, respectively), adding <10% phenolic resin as binder, mixing well, pressing, drying, firing in a corundum tubular furnace in flowing argon at 1 300, 1 400, 1 500, 1 600 and 1 700 ℃ for 2 h, respectively. Effect of TiO2 addition on phase composition and microstructure of Al4SiC4/Al4O4C composites was investigated by TGA, chemical analysis, XRD and SEM. The results show that: (1) Ti in the specimens loses a little in the process of firing, all residual TiO2 transforms into TiC when the firing temperature is below 1 300 ℃, and the formed TiC exists stably at 1 300－1 700 ℃; (2) the TiO2 addition has little effect on phase composition of composites; however, when more than 3% of TiO2 is added, the formation temperature of Al4SiC4 and Al4O4C increases from 1 500 ℃ to 1 600 ℃; (3) with the concentration of Ti4+ increasing, Ti4+ may react easily with Al4SiC4 and Al4O4C forming the finite substitution solid solution resulting in lattice defect, which leads to the decomposition of Al4SiC4 at 1 700 ℃, the formation of more Al4O4C short fiber, and the formation of flake Al2O3 layer on surface of the specimen.
Key words: Al4SiC4/Al4O4C composites, Titanium oxide, Solid solution, Microstructure
Influences of Technological Parameters on Carbothermal Reduction and Nitridation of Titanium Dioxide
YU Renhong, ZHANG Xiaohui, JIANG Mingxue
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 important 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.
Key words: Titanium dioxide, Titanium nitride, Carbothermal reduction and nitridation, Technological parameters
Current Status and Application of Ceramic Foam Filter for Aluminum Melt
JI Shujun, GUO Xueyi, DONG Jianxiong, SU Peng
The importance of purification for aluminum and aluminum alloy casting was outlined. By comparing ceramic foam filters (CFF) in China and overseas, the existing problems and challenges of China’s CFF for aluminum were given. Measures to improve the performance of CFF were put forward based on material, preparation process, utility evaluation, etc.
Key words: Aluminum melt, Inclusion, Purification, Ceramic foam filter
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