Sintering effects related to filtration properties of porous continuously gradient ceramic structures

Abstract

A single-step processing method has been previously established to prepare porous alumina microstructures by a controlled sedimentation technique whereby fine powder from an aqueous suspension consolidates over a casting slab. Metastable surface chemical control of the suspension properties was able to produce a highly porous flat disc structure with a continuously increasing mean pore size from top to bottom. Formation of this gradient structure was facilitated by using a relatively broad particle size distribution. Top layer pore sizes less than 50 nm have been achieved. Without modification, these structures are suitable for use as ultrafiltration media.The present work presents a comparison of properties and performance data for samples made with the above mentioned functionally gradient characteristics, to samples made with a more uniform microstructure. The effects of sintering time and temperature were analysed in view of overall porosity, pore size distribution and the extent of densification from the green state. These results are presented along with permeation measurements from a filtration test module. Crown Copyright

Applying Taguchi method for optimization of the synthesis condition of nano-porous alumina membrane by slip casting method

“…It was seen that porosity became smaller with increase in sintering temperature which was in agreement with findings by others [5,8,15,16]. A lower sintering temperature or sintering time led to higher final porosity and lower interparticle contact surface.…”

“…This can be achieved by using powder with broad particle size distribution and dispersant, causing segregation based on particles diameter. This produces a functionally gradient or continuously enlarging mean pore diameter profile from bottom to top over the cross section of the structure [5,6].…”

Effect of sintering temperature in preparation of granular ceramic filter

“…As shown in the table, the thickness, actual weight, porosity, and median pore size decreased with increasing sintering temperature ranging from 1350 1C to 1450 1C; however, they increased from above 1500 1C. Several previous studies have pointed out that the porosity of porous ceramic materials determined by specimen thickness decreases with increasing sintering temperature due to the densification of the porous structure through shrinkage and fusion [18][19][20][21]. However, the calcium carbonate is vaporized at sintering temperatures higher than 1450 1C, and this phenomena leads to expansion of the ceramic filter [22].…”

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“…Samples made with APA-0.2 have been shown to have some amount of sealed or closed pores in their structure [11]. It is known that mercury porosimetry has its limits in profiling extremely fine pores.…”