Influence Of Polycarbosilane On Structure And Properties Of Low Carbon Al₂O₃-C Refractories

Carbon composite refractories have been widely used as the linings of converters,electric arc furnaces,steel ladles and RH vacuum degassers due to the excellent corrosion resistance and thermal shock resistance.Owing to the high carbon content,traditional carbon composite refractories have a series of drawbacks,such as carbon pick up in the molten metal,graphite resources waste,etc.However,decreasing the content of flake graphite in the traditional carbon composite refractories can deteriorate the thermal shock resistance and corrosion resistance,which lead to the decrease in thermal conductivity and increase in thermal expansion of the refractories.The carbon source of carbon composite refractories include component carbon and bonding carbon.And bonding carbon has a significant effect on the properties and structure of refractories,especially the low carbon refractories.In this study,Polycarbosilane?PCS?was used as an additive to modify bonding phase.The influence of the PCS type,PCS amount and heat-treatment temperature on the microstructure and mechanical properties of bonding carbon and low carbon Al₂O₃-C refractories were studied.Also the pyrolysis of PCS under reducing atmosphere and the growth mechanism of Si-containing fibers were discussed.The main results are as follows:?1?The PCS solidifies to form insoluble and infusible three-dimensional network structure.During heat-treatment,PCS reacts with the resin,which can change the morphology and structure of the resin-bound carbon.The isotropic dense glassy carbon structure transforms into a porous network structure,which could increase the toughness of the simple.When the heat treatment temperature is higher than 1400?,a large amount of Si-containing fibers are generated inside the bonded carbon.?2?Solid polycarbosilane?SPCS?has lower reactivity than Liquid hyperbranched polycarbosilane.With the increase of SPCS content,the material strength drops first and then increases.When the content of SPCS is 0.6 wt%and the heat-treatment temperature is950°C,the sample presents higher CMOR,HMOR and CMORst.After heat-treatment at1550°C,CMOR,HMOR and CMORst are the highest,but the retaining rate of strength decreases.?3?Liquid hyperbranched polycarbosilane?LPCS?have better flowability and more active reactive base ends than SPCS.LPSC reacts violently with the phenolic resin,and the bonded carbon structure changes into a more porous structure.With the increase of heat-treatment temperature,LPCS finishes the organic-inorganic conversion,and the pyrolysis products transform from an amorphous SiCx Oy three-dimensional network to a Si-containing fibers.Under this experimental conditions,the low-carbon Al₂O₃-C refractories present the better comprehensive performance after heat-treatment at 1550°C.?4?The reaction of PCS with phenolic resin makes the bonded carbon structure change from a dense glassy carbon structure to a porous structure,resulting in the increase in the porosity and decrease in the oxidation resistance of the materials.The SiCxOy produced by the pyrolysis of PCS can work as antioxidants,however,this effect is not obvious due to the low content of PCS.