| Recently,lightweight refractories have become a research hotspot.The thermal insulation materials are made of alumina and silica at home and abroad,magnesia materials are rarely used to prepare thermal insulation materials due to their large thermal conductivity,so the preparation of a new type of magnesia porous material is of great significance.This article first used carboxylate potassium oleate(PO)as a foaming agent to prepare magnesia porous aggregates by the foaming method,and then used porous aggregates as raw materials to introduce pore-forming agents to prepare magnesia porous materials,this process is called"secondary pore-making method",finally,the walnut shell powder was treated with silica sol,alumina sol,composite sol and oleic acid to prepare a new type of pore-forming agent,and again to prepare magnesia porous materials.The research results show that:when PO is used as a foaming agent to prepare magnesia porous aggregate,with the increase addition of PO,the bulk density and the cylinder compressive strength of the aggregate decreases.When PO is added 8g,the bulk density of the porous aggregate is 1.65 g·cm-3,the apparent porosity is 32%,the cylinder compressive strength is 21MPa,and the pore size is about 20?80?m.The magnesia material is prepared by the casting method using magnesia porous aggregate as the raw material,compared with the sample prepared by sintered magnesia,the bulk density of the sample is reduced by 16.4%,the apparent porosity is increased by 69.5%,the thermal conductivity is reduced by39.1%(1050?)and the compressive strength is equivalent.The sample prepared by adding floating beads has the largest bulk density;the sample prepared by adding polystyrene balls has the largest porosity and a larger internal pore size;there are through pores around the aggregate of the sample with potato starch;the sample prepared by adding carbon black have through-net pores inside;there are many closed pores inside the sample with walnut shell powder and the distribution is even.With the increase in the addition of walnut shell powder,the apparent porosity of the sample after sintering increases,the compressive strength decreases,the number of through pores increases,and the pore wall becomes thinner.The pore walls and pore ribs of the samples prepared by alumina sol-treated walnut shell powder contain magnesia-alumina spinels with an octahedral structure;the magnesia-alumina spinel and forsterite are interlaced on the inner pore wall of the sample prepared with the walnut shell powder treated with silica and alumina sol;the sample prepared by oleic acid-treated walnut shell powder has the lowest thermal conductivity,which is0.428W/(m·k),the closed porosity of the sample prepared by the silica sol-treated walnut shell powder is 10.6%,the compressive strength is 22MPa,and the thermal conductivity is 0.466 W/(m·k),forsterite is formed around the pores;a pore-shell structure is formed.Walnut shell powder treated with silica sol is a new type of pore-forming agent,when the addition amount is the same,with the increase of the sintering temperature,the bulk density of the sample increases,and the compressive strength increases,and the pores inside the sample change from round to oval;when the sintering temperature is constant,with the increase in the addition of new walnut shell powder added,the apparent porosity of the sample increases,the closed porosity decreases,the number of internal pores increases,the thermal conductivity and the compressive strength decreases;when the new style of walnut shell powder is added20%,and the sintering temperature is 1300?,the bulk density of the sample is1.03g·cm-3,the closed porosity rate is 13.3%,the cpmpressive strength is 7MPa,and the thermal conductivity is 0.382 W/(m·k). |
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