Naslov
Influence of grinding of amorphous, sol-gel derived, premullite powder on structure and microstructure of sintered mullite

Autori
Kurajica ; Stanislav, Tkalčec ; Emilija, Mandić ; Vilko

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Mullite 2011 Abstract Book / Schneider ; Hartmut - Aviles, 2011

Skup
5th International Workshop on Mullite & Mullite-type Materials

Mjesto i datum
Avilés, Španjolska, 08.05.2011. - 11.05.2011

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Nije recenziran

Ključne riječi
mullite; precursor; grinding; microstructure

Sažetak
The process of grinding of amorphous pre-mullite powder has been investigated. The powder has been obtained by sol-gel process followed by drying, calcination and wet milling in planetary ball mill for various periods. The pre-mullite powder particle size distribution shifts to finer sizes as the grinding time increases. This shift is more pronounced for shorter grinding times. The shape of the size distribution curve of the feed sample presents several modal diameters. The curves of the samples ground for shorter periods are bimodal while curves of samples grinded for longer intervals become monomodal reflecting narrow distributions. Specific surface area dependence on grinding time show complex behavior due to the agglomeration in the course of calcination. The decrease of specific surface area at the prolonged grinding intervals has been noted. The agglomeration is confirmed by SEM of powder samples. In the course of grinding in alcohol media slight re-esterification of the sample surface occurs. Carbon, an alcohol degradation product, remains in the sample until spinel crystallization temperature is reached. Cubic and monoclinic zirconia mill wear debris has been observed in the samples ground for 256 and 512 min. The crystallization behavior of mechanically treated diphasic gel is similar to that of type III mullite precursors. The ground gel converts to mullite via the spinel phase, some amount of -alumina also crystallizes. The mullite is alumina-rich in composition ; changes in mullite composition and the amount of -alumina in sample, with the duration of grinding, have been noted. A sample ground for 128 min has the greatest amount of alumina in mullite and the smallest amount of -alumina. The great enhancement of mullite sintering behavior by milling operation, i.e. the increase of sintered density with the duration of grinding has been established. For the samples ground for 512 min, the final relative bulk density of the sample sintered at 1600 °C for 4 h was 3.10 g cm-3. The duration of grinding influences the microstructure to a great extent. The SEM micrographs of sintered samples revealed that the feed sample and samples ground for shorter intervals are extremely porous while sample grinded for 512 min showed far less porosity. Equiaxial mullite grains points out to dominancy of solid state sintering.

Izvorni jezik
Engleski

Znanstvena područja
Kemijsko inženjerstvo

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