Fabrication And Controlled Permeability Of Porous Ceramics With Directional Aligned Pore Structure

Freeze-casting is an emerging green environmental protection technology for preparing porous ceramics by replicating crystal morphology of solvent.The obtained porous ceramics have controllable pore structure,and can be widely used in bioengineering,filtration,catalyst carriers and so on.However,the pore structure（pore morphology,pore size,porosity,etc.）should be adjusted to meet actual needs for different application environments.In this paper,porous hydroxyapatite was prepared for the dentin barrier with low permeability.The pore structure was controlled and the permeability was decreased by changing the solid content of slurry,the freezing temperature or the TBA concentration in the TBA/water binary mixed solution.Secondly,porous alumina ceramics with high permeability values were prepared for the porous filtration.Pore porosity and filtration efficiency of the porous alumina were improved by adjusting the pore structure.Through systematic studies,the pore-forming mechanism of porous ceramics was clarified when the TBA concentration was between 70vol.%and 85vol.%and the variation of pore structure around 90 vol.%TBA.The relationship between the pore structure of the porous material and the permeability value was revealed.The following results were obtained:（1）In tert-butanol/water binary mixed solution,the ceramic slurry with 92 vol.%TBA concentration was fabricated by directionally freeze-casting to obtain needle-liked porous hydroxyapatite,and the lowest permeability value was 2.6±1.77μL·cm^-2·min^-1,which was satisfied with the dentin barrier for low permeability values.This material achieved structural and functional bionics for dentin barrier;（2）The main factors affecting the permeability value of the dentin barrier included pore size and open porosity.The main factor by changing the permeability value is the open porosity when adjusting the solid content of slurry;Changing the freezing temperature and the TBA concentration had a great influence on the pore size of the material.At this time,the pore size mainly affected the permeability value;（3）When the TBA concentration increased from 70vol.%to 85vol.%,the pore morphology of porous alumina changed from snowflake to dendritic to needle-liked.The dendritic porous alumina obtained by 75 vol.%TBA can also improve the filtration efficiency and ensure high permeation flux.When the filtration solution was PH=7.2,the filtration efficiency of the six-layer sample was the highest,up to 94.2%.（4）The porous alumina by using spherical nano-alumina particles had thin pore walls and more than 70%high open porosity.The high open porosity and large pore size can improve the permeability of the material.