Development and characterization of porous moldable refractory structures of the alumina-mullite-quartz system

Preparation and Characterization of Mullite-Alumina Structures Formed "In Situ" from Calcined Alumina and Different Grades of Synthetic Amorphous Silica

“…4d). This behavior was also observed in other studies 8,9,15 and can be related to the mullite generation reaction. In comparison to the calcined alumina matrix (ρ = 3.8-4 g.cm -3 ), the density of mullite is lower (ρ = 3.2 g.cm -3 ), therefore, its formation can be followed by a volumetric expansion, depending on the compacting level of the structure.…”

“…Its formation is a complex set of high-temperature (800-1400°C) solid state reactions [22][23][24] between silica (SiO 2 ) and alumina (Al 2 O 3 ) [25][26][27][28][29] based on the mutual diffusion of Al 3+ , Si 4+ and O -2 ions amongst particles [30][31][32][33] . Various studies have pointed out the characteristics of the silica source (crystallinity 35 , particle size distribution 25 , presence of impurities 26,27 ) and processing conditions (heating rate 28 , temperature of the thermal treatment 29 ) affect directly the yield, kinetics and morphology of the products formed 2,[7][8][9][10] . For instance, reactions between coarse alumina and micronized quartz particles (45 µm average size) generate porous mullite at temperatures above 1300ºC 9,28,31 , whereas the combination of finer nanoparticles of alumina and amorphous silica produced by alcoxi-based precursors reduced the range to 800-1100ºC and promote greater densification [35][36][37] .…”

“…Various studies have pointed out the characteristics of the silica source (crystallinity 35 , particle size distribution 25 , presence of impurities 26,27 ) and processing conditions (heating rate 28 , temperature of the thermal treatment 29 ) affect directly the yield, kinetics and morphology of the products formed 2,[7][8][9][10] . For instance, reactions between coarse alumina and micronized quartz particles (45 µm average size) generate porous mullite at temperatures above 1300ºC 9,28,31 , whereas the combination of finer nanoparticles of alumina and amorphous silica produced by alcoxi-based precursors reduced the range to 800-1100ºC and promote greater densification [35][36][37] . Therefore, by changing the characteristics of the silica source, ceramics of different microstructures, porosity levels and thermomechanical properties can be designed.…”

“…Mullite (3Al 2 O 3 .2SiO 2 or Al 6 Si 2 O 13 ), one of the main raw materials for the ceramic industry [1][2][3][4] , is an input for the production of refractory materials 1,[5][6][7][8][9] , catalyst support 10,11 , electronic and optic devices [12][13][14] , thermal insulators 8,9,15 , hot gas filters (above 600°C) [16][17][18] and biological and biomedical scaffolds [19][20][21] . Its formation is a complex set of high-temperature (800-1400°C) solid state reactions [22][23][24] between silica (SiO 2 ) and alumina (Al 2 O 3 ) [25][26][27][28][29] based on the mutual diffusion of Al 3+ , Si 4+ and O -2 ions amongst particles [30][31][32][33] .…”

Evaluation of mechanical properties of porous alumina ceramics obtained using rice husk as a porogenic agent

“…The interest in the development and optimization of porous ceramics is due to the wide field of technology in which those materials are applied, for example, catalysts, furnace linings, furnace furniture, filters for the automotive industry, glass production and acoustic insulation [1]. Porous ceramics can be produced by mixing porogenic agents in the ceramic matrix, which, during sintering, burn out forming the pores [2].…”