Research On Alumina-based Porous Ceramics For High Temperature Insulation

High-temperature insulation materials for ships play a crucial role in their ability to sail and comfort.Based on the requirements of high-temperature insulation materials with low cost,simple preparation process,and simultaneous enhancement of thermal performance and mechanical properties,this paper takes Shandong Alcoa Corporation?-Al2O3,Suzhou Clay,and Guangdong Yingde Quartz as main raw materials.PS?polystyrene?balls were pore-forming agents.A novel route was proposed to fabricate alumina-based porous ceramics for high temperature insulation by slip casting.Relationships between the composition,preparation process,microstructure and performance of the alumina based porous ceramics were researched by using modern testing techniques such as XRD,SEM,EPMA and so on.Effects and mechanisms of formula composition,temperature,the amount of pore-forming agent,Y₂O₃ and Sm₂O₃ on the microstructure and performance of the porous ceramics were investigated.To make the PS balls distributed evenly in the slurry and firing in-situ hole,four kinds of clays were selected as the modifier for rheology of grouting slurry.PS balls could be stably distributed evenly in the grout body by means of the thixotropy of the clay.The formulation of alumina-based porous ceramic slurry was designed,besides the influence of various clays on the rheology of grout was studied.The alumina-based porous ceramic with uniform pore size and uniform distribution was prepared successfully.The results show that the ceramic slurry containing Suzhou clay has the highest thixotropic,the value is 2.20,and its thixotropic ring area is240.20 Pa·s^-1,and the sintered sample had the most uniform pore distribution,the open porosity was 62.68%,and the compressive strength was 6.5 MPa.The greater the thixotropy of the slurry,the greater the increase in viscosity at the same time,The PS balls are subjected to greater friction because of the higher viscosity of slurry.The gravity of the PS ball,the friction and buoyancy of the slurry against the PS ball,these three forces are balanced.Slurry will prevent the PS ball from floating up,thereby achieving the in-situ fixation of the PS ball.For improving the thixotropy of the slurry and determining the formula composition and firing temperature,the effects of the addition of CMC,gum arabic,and tap water on the thixotropy of the slurry were studied,and the effects of formulation composition and sintering temperature on the composition,structure,and properties of the material were investigated.The results showed that the optimal amount of CMC was 0.6 wt%,the optimum amount of gum arabic was 0.7 wt%,and the best amount of tap water was 37.5%.When the content of?-Al₂O₃ is high and the content of quartz is low,it is beneficial to the synthesis of mullite.The samples composed mainly of corundum and mullite have good thermal shock resistance,and the samples containing quartz and quartzite are poor in thermal shock resistance.The reasons for the poor thermal shock resistance of the sample are that there are some cracks produced due to the volume effect caused by the crystalline transformation of quartz and cristobalite.The composition of the alumina-based porous ceramics for high temperature insulation is that,70%?-Al₂O₃,20%Suzhou Clay,10%quartz.The sintering temperature should be 1500? or above.In order to obtain low porosity,high porosity,alumina-based porous ceramics,sintering aids?MgO,TiO₂,Y₂O₃,Sm₂O₃?were added to the formulation.The effects of two rare earth oxides on the porosity,phase composition,microstructure,and thermal shock resistance of the material were investigated.Studies have shown that the optimal addition amount of Sm₂O₃ and Y₂O₃ is 1.5 wt%,and the optimal sintering temperature is at 1550?.When both rare earth oxides are added at the same time,the sample performance is better,the open porosity is as low as 20.03%,the closed porosity is as high as 52.80%,and thermal shock resistance is not cracked for 30times.The addition of Y2O3 mainly promotes the formation of high-temperature liquid phase,and the liquid-phase filling the pores to form independent closed micro-voids.At the same time,the atmosphere pores are mutually independent,so the closed porosity of the sample is increased.The effects of the addition of PS balls and the addition of sintering aids on thermal insulation properties of alumina-based porous ceramics for high temperature insulation were investigated.The study found that the closed pores have a significant effect on the thermal conductivity of the ball.When the PS ball addition amount is1.25 g/?100g body powder?,the sample has the best comprehensive performance,thermal shock 28 times without cracking,the compressive strength is as high as 26.28MPa,and the thermal conductivity is as low as 0.31 W/?m·K?.The addition of sintering aids results in a high closed porosity of the sample,leading to heat conduction through the gas to conduct heat through itself,which reduces the thermal conductivity of the sample.Y₂O₃ and Sm₂O₃ are uniformly distributed in the sample,which can cause lattice mismatch,increase the scattering effect of phonons,and then reduce the thermal conductivity.