Macrostructures with hierarchical porosity produced from alumina–aluminum hydroxide–chitosan wet-spun fibers

Development of densification-resistant castable porous structures from in situ mullite

“…The literature describes many combinations of ceramic phases (Al 2 O 3 , SiO 2 , ZrO 2 , MgAl 2 O 4 , SiC, amongst others) with organic particles (starch, casein, chitosan, alginate, polymer latexes, saw-dust) and foams (stabilized with surfactants and nanoparticles) [2,[4][5][6]. Particles of inorganic hydroxylated or carbonated compounds can also be used as pore generators [7][8][9] and offer important technological advantages: i) they can be easily added to many matrixes through standard equipment and additives; ii) during the forming step, the structure attained is less sensitive to variations in the environmental and application conditions; iii) they do not release toxic volatiles during the first heatup.…”

“…The Al 2 O 3 -Al(OH) 3 system is the most explored example of this technique [2,4,5,8,9] and its mechanism of pore formation involves a two-step process, described as follows [2,5,8,9]. 1) Al(OH) 3 particles are consolidated with the Al 2 O 3 (D-Al 2 O 3 , from calcined alumina, for instance) ones by means of pressing or use of a binding agent.…”

Characterization of aluminum hydroxide (Al(OH)3) for use as a porogenic agent in castable ceramics

“…The presence of highly reactive transition alumina particles also induces the grain growth of the ␣-Al 2 O 3 ones during the sintering. 18 The latter effect is the main limitation of porous Al 2 O 3 -Al(OH) 3 structures regarding their use as a thermal barrier for applications in which temperature ranges are above 1000 • C for long periods, despite their high refractoriness.…”

“…[19][20][21][22] To produce such structures, Al(OH) 3 particles (in contents of up to 90 wt%) must be inserted into a dense calcined or tabular alumina matrix (comprised by ␣-Al 2 O 3 ) and consolidated by pressing 19 or using binding agents. 18,21,22 After the Al(OH) 3 decomposition, high-porosity structures are attained due to the loss of water and the large volume of micro-and meso-pores formed on their surface. 19 Moreover, these phase transformations are strongly affected by the seeding effect of the surrounding ␣-Al 2 O 3 particles.…”

“…For instance, transition aluminas attained from the flash calcination (heating rates higher than 100 • C s −1 ) of gibbsite can produce low crystallinity and defect-rich phases (such as -Al 2 O 3 ), [14][15][16] whereas, when the material is gradually decomposed in the same temperature interval, crystalline phases (-Al 2 O 3 and -Al 2 O 3 ) are attained. 6,7,10 (2) Porous structures based on the Al 2 O 3 -Al(OH) 3 system have found applications in hot gas filtration, 3 scaffolds for growing biological tissues and microorganisms, 17 biomaterial for bone replacement 18 and thermal insulation. [19][20][21][22] To produce such structures, Al(OH) 3 particles (in contents of up to 90 wt%) must be inserted into a dense calcined or tabular alumina matrix (comprised by ␣-Al 2 O 3 ) and consolidated by pressing 19 or using binding agents.…”