We have prepared different alumina powders (fine/submicron-sized) from waste sources at different calcination temperatures (C.T.). From zeta potential-pH graph, we saw that IEP values decreased from 7.3 to 5.1with the increasing of C.T. from 500---1200 C.
Since there is no information about the particles size after different calcination temps and tthe source contamination can be another issue. Please check them and correlate with each other since bigger particle size can deteriorate the properties and produce coagulation as agglomerated particles can precipitatee faster than smallers.
Dear Mr. Ali Özer , 1. The particle size of alumina increases with the increasing of C.T. and vice versa is obtained for sp. surface area. 2. In the wd-xrf analysis, our samples are 99.6% pure with minute Na20, SiO2, Cl, Fe203 etc. impurities. 3. We have got different single-phase alumina(gamma-theta-alpha) at different CT. Could you please interpret the reason now?
The increased powder size may be the reason of decrease in IEP. The decrease in sp surface area was obtained as you mentioned. Different alumina phases may also differ for IEP due to attraction of acidic or basic specis as Cl or OH. The phase packing factor for specific planes can also be the reason of IEP change as higher atomic packing density will react with OH if they are in alpha alumina crystal and in contrary if they are beta phase in hexagonal crystal, they can react with more Cl containing aqueous solution to provide lower IEP. These should also be approved by XRD as high in haxagonal or alpha cubic phase or vice versa to decrease IEP to increase the reaction ability of acidic species. As XRD, XEM may also be employed to see the alumina powders grown hexagonal or cubic. The increase in calcination temp should be longer to see if the phases are stabilized to cubic or hexagonal since we expect a cubic phase at longer times and wait for IEP at higher pHs.
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