Preparation And Properties Of Diatomite-based Porous Ceramics

Porous ceramics are a new type of inorganic materials with pores as the main phase.It has the advantages of high porosity,large specific surface area,high temperature resistance,corrosion resistance,good heat insulation,uniform distribution of pore sizeand long service life.Therefore,porous ceramics are widely used in the fields of environmental protection,chemical engineering,metallurgy,energy sources and bioengineering as materials for filtration,separation,sound absorption,heat insulation,carriers and sensitive components.The many advantages and applications of porous ceramics have attracted the attention of material science researchists.They actively explored and hoped to study the preparation methods of porous ceramics with green environmental protection and low cost.Diatomaceous earth is a siliceous sedimentary rock formed by the deposition of ancient diatom biological residues on the bottom of the water.It is a very important non-metallic mineral.China's proven reserves of diatomite rank second in the world.At present,there are more than 70 diatomaceous earth mines have been found in 14 provinces,municipalities and autonomous regions in China.The identified resource reserves are about484 million tons and the prospective reserves are 2 billion tons.The chemical composition of diatomaceous earth is mainly amorphous SiO₂,and contains a small amount of Al₂O₃,Fe₂O₃,P₂O₅,CaO,MgO and organic matter,Diatomaceous earth has a wide range of sources and low price.In this paper,diatomaceous earth was used as the main raw material,two different types of porous ceramics were prepared by organic foam impregnation method and pore-forming agent method.The effects of each process step on the performance of porous ceramics were studied.The main technological steps were as follows:pretreatment of organic foam,solubility of PVA solution,solid content of slurry,addition amount of dispersant,ratio of ceramic raw material,sintering temperature,and the like.Firstly,the organic foam was pretreated with different concentrations of NaOH solution for different time.It was found that the effect of hanging pulp was proportional to the NaOH solution and the treatment time,but when the treatment time was above 4h,the effect of the hanging slurry was not obvious;when the concentration of NaOH solution was not obvious;When it is more than 20wt%and the treatment time is above 6h,the organic foam will reduce its resilience due to serious hydrolysis,and eventually it will not return to its original state when impregnating the slurry,which will affect the impregnation effect.When the concentration of NaOH solution is 25wt%and the pretreatment time is 4h,the organic foam has the highest amount of pulp and the best effect.Secondly,the organic foam and ceramic powder were subjected to TG-DSC analysis to determine the sintering system.By using different concentrations of PVA solution as solvent to prepare ceramic slurry,the experimental results show that the porosity of porous ceramics prepared by using PVA solution with a concentration of 4wt%as solvent is larger,and the distribution of porosity is more uniform,more than 70%.The pore size is concentrated in the range of 100-199.99?m.By formulating ceramic slurry with different solid content,it is found that with the decrease of solid content,the porosity of porous ceramics increases,the quality decreases,and the larger the solid content,the more pores of small size.Using carboxymethyl cellulose?CMC?as dispersant,the effect of different dispersant additions on the properties of the slurry was studied.It was found that as the amount of dispersant added increased,the dispersibility and stability of the slurry were better.When the addition amount is 0.4 wt%,the effect is the best.Sintering samples at different temperatures were used to study the effect of sintering temperature on porous ceramics.Taking diatomaceous earth and calcium carbonate as main raw materials,starch as pore-forming agent and PVA as binder,calcium silicate porous ceramics were prepared by reaction sintering.The effects of powder ratio and sintering temperature on sample volume shrinkage,compressive strength and phase composition were investigated.At the same time,the effect of pore-forming agent content on porosity and strength was studied.The results show that the shrinkage rate increases with the increase of sintering temperature,and the pore former content is proportional to the porosity and inversely proportional to the compressive strength.When the content of calcium carbonate is 20wt%and the content of pore-forming agent is 15wt%,a porous ceramic having a porosity of 48.79%and a compressive strength of 12.2 MPa is prepared by sintering at 1250?.