Microstructures and strengths of microporous MgO–Al₂O₃ ceramics from Al(OH)₃ and calcined magnesite

Abstract

Seven microporous MgO-Al 2 O 3 ceramics with an Al 2 O 3 content of 15-90 wt% were prepared using Al(OH) 3 and calcined magnesite as raw materials. A wet mixing process was employed during sample preparation to transform the calcined magnesite with a larger particle size to smaller Mg(OH) 2 particles. The in situ decomposition synthesis method and the Kirkendall effect were utilized to produce and control the pore structure of the microporous MgO-Al 2 O 3 ceramics. There were two kinds of pores in the microporous MgO-Al 2 O 3 ceramics. The first one resulted from the in situ decomposition of Al(OH) 3 and Mg(OH) 2 particles, which were small and equally distributed. Another one originated from the position of the Mg(OH) 2 particles due to the Kirkendall effect caused by MgO diffusion. They were similar in size to the Mg(OH) 2 pseudomorph particles. Simultaneously, the Al 2 O 3 content affected the packing behavior and the spinel formation, which changed the characteristics of the pores and necks among the particles. These mechanisms also affected the strengths of the microporous MgO-Al 2 O 3 ceramics. Thus, when the Al 2 O 3 content was 45-90 wt%, the microporous MgO-Al 2 O 3 ceramics had a high compressive strength (10.0-18.3 MPa) and apparent porosity (52.2%-58.4%).

Hierarchical porous MgAl2O4 ceramic in situ structured by hollow particles: Low‐shrinkage and high‐strength

“…In addition, thickening the cell wall by expanding particles also increases its strength. The comparison of porosity and compressive strength of MgAl 2 O 4 porous ceramics, which were prepared using various raw materials and methods, [21][22][23][24][25] is presented in Figure 5. The particle stabilization method has great advantages in the preparation of porous ceramics with high porosity, but its strength is usually low.…”

Preparation and enhanced mechanical properties of novel Al2O3‐C ceramic filter reinforced by microporous powder and SiC whiskers

“…% Al 2 O 3 , 8.60 wt. % MgO, bulk density: 2.53 g/cm 2 , apparent porosity: 33.6 %, prepared by in situ decomposition pore‐forming technique 23–27 ), Si powder (d 50 = 27 μm, 98.5 wt. % Si), nano‐Al 2 O 3 powder (d 50 = 30 nm, 99.99 wt.…”

“…22 Thus, we propose a new strategy to enhance the mechanical properties of Al 2 O 3 -C ceramic filters. By using the microporous raw material [23][24][25][26][27][28][29][30] to replace the dense one for the fabrication of novel Al 2 O 3 -C ceramic filters, the microporous raw material can increase the roughness of the filter skeleton surface because it contains a lot of micropore structures, as shown in Figure 1, which will have the potential for improving the adsorption capacity of the filter skeleton surface for non-metallic inclusions. On this basis, adding Si powder into the filter skeleton to form SiC whiskers in situ through the vapor-solid reaction mechanism [31][32] can also help to enhance the mechanical properties of the novel Al 2 O 3 -C ceramic filters.…”

Properties and microstructures of porous corundum‐spinel aggregates fabricated via the Kirkendall effect

“…The firing temperature and PSM affect the production amount of spinel in the aggregate, the morphology of spinels, and the solid dissolution of Al 2 O 3 into spinel, which in turn affects the LC of the samples because the formation of spinels is accompanied by volume expansion 13,34 and the solid dissolution of Al 2 O 3 into spinel can delay the sintering of spinel. 35 Additionally, the firing temperature affects the sintering process, including the sintering of the α-Al 2 O 3 micropowder and spinel, which changes the LC of the samples.…”