Combustion Synthesis Of Boron Carbide-containing Composite Powders And Its Effect On Properties Of Low-carbon Magnesia-carbon Refractories

Mg O-C refractories have been usually used as lining materials,especially slag line for RH vacuum refining furnaces,basic oxygen furnaces,steel ladles and other equipment in the metallurgical industry due to their excellent thermal shock resistance and slag resistance.The conventional Mg O-C refractories contain 7-20wt%of graphite.However,the refractories suffered several drawbacks due to the increase of graphite content,including more porous after the oxidation of graphite,higher energy loss and high carbon pick-up in molten steel.Therefore,it is necessary to develop a new kind of Mg O-C refractories with low carbon content and maintain their similar performances with that of conventional Mg O-C refractories,to develop a low-carbon Mg O-C refractories and maintain their comparable performances with that of conventional Mg O-C refractories has become the development direction.Domestic and foreign studies have shown that the use of high specific surface area of nano-carbon such as CNTs,CB,GONs partly replacing flake graphite can improve the performance of Mg O-C refractories while reducing the carbon content.However,the addition of nano carbon to the refractory matrix is easy to agglomerate and is easily oxidized during use,which affects their performance.In order to improve the dispersity and oxidation resistance of nano cabon and make full use of the excellent oxidation resistance of B₄C,this subject is aimed to prepare a composite powders containing B₄C and nano carbon with smaller particle size by a green and fast combustion synthesis method in one step.And studied the effects of composite powders on the properties of refractories.The main contents of this paper are as follows:(1)The effects of carbon sources with different morphologies on the synthesis of B₄C powders by combustion synthesis with magnesium powder as reductant were studied.The results show that CB and ACF are more conducive to the synthesis of boron carbide powders in CB,ACF,CNTs,EG and FG,while the residual carbon in the products is less.(2)Using ACF as carbon source and fiber template,and magnesium powder as reductant,the optimum technological parameters of combustion synthesis and their effects on the morphology of products were studied.The results show that the optimum length of ACF is 150-200 um,and the optimum molding pressure is 2MPa.At this time,some fiber-like B₄C can be obtained,but the surface roughness and structure of the fibers are loose.And most of the products are still B₄C particles with smaller particle size.Therefore,the effect of template method on the preparation of B₄C fibers is not satisfactory.(3)Using CB as a carbon source,Mg and Al were used as reductant respectively,B₄C/Mg O/C and B₄C/Al₂O₃/C composite powders were prepared by a combustion synthesis method.The results show that the magnesium thermal product has impurity phase Mg₃(BO₃)₂in addition to B₄C,Mg O and C.The aluminum thermal product only has B₄C,Al₂O₃and C.(4)The microscopic morphology of B₄C/Al₂O₃/C composite powders is a large particle agglomerated by many small particles and regularized B₄C particles are embedded in the Al₂O₃,and the nano CB particles are evenly distributed in the product.At the same time,B₄C/Al₂O₃/C composite powders synthesized by combustion have better oxidation resistance than that mechanically mixed B₄C/Al₂O₃/C composite powders.(5)The effect of B₄C/Al₂O₃/C composite powders synthesized by combustion on the properties of low carbon magnesia-carbon refractories was studied.The results show that the low carbon Mg O-C refractories with synthesized powders have little effect on bulk density,the apparent porosity decreased by 14.1%and 8.4%,the thickness of decarbonized layer decreased by 22.4%and 10.2%,the erosion depth decreased by27.9%and 12.0%,and the strength retention rate increased by 17.2%and 15.8%,respectively.