Preparation And Properties Of Unfired SiC-Si₃N₄ Refractories

This study based on the problems of high temperature, high cost and high energy consumption to fire Si C-Si3N4 refractory which widely used in high temperature industrial in current. The study used Si C、Si3N4 and metal Si powder as non oxide raw materials, and using phenolic resin as binder to study the prepatation technology and properties of the unfired Si C-Si3N4 refractory. The study mainly discussed the modification of phenolic resin binder by adding the content of B4 C powder and Al powder, in order to improve the moderate and high temperature strength of unfired Si C-Si3N4 refractory and have obtained some reaearch results.Using 30 mesh Si C particles as carse aggregate, 120 mesh Si C particles as moderate aggregate, 325 mesh Si C、Si3N4 and metal Si powder as fine powder and using 12wt%PF as binder can make unfired Si C-Si3N4 refractory of excellent comprehensive properties after machine pressure molding with 10 MPa and drying. Then, to sudy the modification of unfired Si C-Si3N4 refractory which using 12wt%PF as binder and adding B4 C powder or Al powder. We finally found that the unfired Si C-Si3N4 refractory which using 12wt%PF as binder with adding 2wt% B4 C powder or 2wt% Al powder has the best comprehensive performance. The unfired Si C-Si3N4 refractory which adding 2wt% B4 C powder to modificate 12wt%PF have room temperature flexural strength of 37.0MPa and room temperature compressive strength of 95.2MPa and respectively in situ high temperature compressive strength of 26.4MPa and 32.9MPa in 800℃ and 1400℃ while the unfired Si C-Si3N4 refractory with adding 2wt% Al powder have room terpreature flexural strength of 36.7MPa and room temperature compressive strength of 89.7MPa and in situ high temperature compressive strength of 46.1MPa and 154.7MPa in 800℃ and 1400℃, respectively. The erosion wear rate of unfired Si C-Si3N4 refractory which adding 2wt% B4 C powder or 2wt% Al powder to modificate 12wt%PF have decreased which was 16.97 mm3g-1 and 15.68 mm3g-1, respectively.The unfired Si C-Si3N4 refractory material has excellent resistance erosion performance of cryolite and blast furnace slag. After analizing we found the mechanism was that the unfired Si C-Si3N4 refractory oxided and generated Si O2 protective layer and the products of cryolite or blast furnace slag reacted with Si O2 have high melting point and viscosity which prevent the further oxidation of Si C-Si3N4 refractory and can improve the density of material to prevent erosion deepening.Furthermore, the unfired Si C-Si3N4 refractory formed protective layer by adding B4 C powder or Al powder and their oxidation products improve the cryolite resistance and high slag erosion performance of the unfired Si C-Si3N4 refractory materials.The results of this paper show that the modification of phenolic resin by adding B4 C powder or Al powder can effectively increase the mechanical properties of unfired Si C-Si3N4 refractory in the range of 800~1200℃ and it is significant to develop a new generation of high-performance non oxide refractory materials.