Microstructure and Mechanical Properties of Porous Alumina Ceramics Fabricated by the Decomposition of Aluminum Hydroxide

Abstract

The mechanical properties of Al 2 O 3 -based porous ceramics fabricated from pure Al 2 O 3 powder and the mixtures with Al(OH) 3 were investigated. The fracture strength of the porous Al 2 O 3 specimens sintered from the mixture was substantially higher than that of the pure Al 2 O 3 sintered specimens because of strong grain bonding that resulted from the fine Al 2 O 3 grains produced by the decomposition of Al(OH) 3 . However, the elastic modulus of the porous Al 2 O 3 specimens did not increase with the incorporation of Al(OH) 3 , so that the strain to failure of the porous Al 2 O 3 ceramics increased considerably, especially in the specimens with high porosity, because of the unique pore structures related to the large original Al(OH) 3 particles. Fracture toughness also increased with the addition of Al(OH) 3 in the specimens with higher porosity. However, fracture toughness did not improve in the specimens with lower porosity because of the fracture-mode transition from intergranular, at higher porosity, to transgranular, at lower porosity.

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

“…The most common methods for the production of such materials involve the addition of porogenic agents to a ceramic matrix. 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.…”

Preparation and characterization of porous MgO–Al2O3 refractory aggregates using an in-situ decomposition pore-forming technique

“…Unfortunately, these porous ceramics were not suitable for preparing porous refractory aggregates because of the processing complexity, high cost of raw materials used, low strength with large pore size. In contrast, in-situ decomposition pore-forming technique is an alternative approach to producing porous ceramics for lightweight refractory aggregates where micro-sized pores could be generated in the product by in-situ decompositions of raw materials in heating-up process [11][12][13][14][15][16][17][18][19]. Up till now several porous ceramics, such as mullite and cordierite have been produced by using this technique.…”

Possible improvements of alumina–magnesia castable by lightweight microporous aggregates

“…Among which, there have been quite a few reported methods for the preparation of lightweight aggregate, such as decomposition of organic matter [2][3][4][5][6], pore-forming in situ technique [7][8][9][10] and decomposition of hydrated/ carbonated inorganic compounds [11][12][13]. Lyckfeldt and Ferreira [2] prepared porous alumina with starch as both binder and pore former; Li et al [7] used kaolinite as poreforming agents to prepare porous corundum-mullite ceramics; Salomãoa et al [11] fabricated porous alumina-spinel ceramics by decomposing an aluminum-magnesium hydro-carbonate.…”