Pore characteristics and phase compositions of porous corundum-mullite ceramics prepared from kaolinite gangue and Al(OH)₃ with different amount of CaCO₃ addition

Abstract

Porous corundum-mullite ceramics were prepared from Al(OH) 3 and kaolinite gangue with different CaCO 3 amount through an in-situ decomposition pore-forming technique. The effect of the amount of CaCO 3 added (ACA) on the phase compositions and pore characteristics was investigated through X-ray diffractometer (XRD), scanning electron microscopy (SEM), and mercury porosimetry measurements, etc. It's interesting that the granular mullite crystals are in the Al(OH) 3 pseudomorphs but the needle-like mullite crystals are in the gangue pseudomorphs, and found that the ACA slightly affects the apparent porosity (AP), but strongly affects the formation of liquid phase, and then affects the secondary mullitization, microstructure, pore size distribution and crystal morphology. With an increase in ACA from 0 to 2.36 wt %, the increasing liquid phase make the rate of secondary mullitization increase markedly; when the ACA is 2.36 wt %, the secondary mullitization reaches the maximum; with a further increase of ACA to 3.54 wt %, the secondary mullitization decreases due to the formation of anorthite. With an increase in ACA from 0 to 3.54 wt %, the APs are in the range of 40.742.3%, whereas, the average pore size increases from 0.326 to 2.750¯m, and the crystal sizes of mullite in both pseudomorphs increase evidently.

Effect of sintering atmosphere on microstructures and properties of synthesized microporous MgO refractory raw material

“…Thus, Yan et al put forward the lightweight design of using microporous aggregates to replace dense aggregates for fabricating working layer refractories, which can effectively reduce the thermal conductivity of refractories on the basis of ensuring high-temperature service performance. [17][18][19][20][21][22][23][24] For example, lightweight periclase-spinel castable prepared by Yan et al had a lower bulk density of 10.8% and a lower thermal conductivity of 18.8% (1000 • C) compared with conventional castables. 25 This proved that the lightweight design was an effective strategy to reduce the energy loss due to working lining refractories.…”

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

“…Compared with the previous methods, in situ decomposition synthesis is more suitable for preparing porous ceramics with smaller pore sizes having a uniform pore distribution. [38][39][40][41] Moreover, the raw materials are readily available, and the preparation process is simpler. For example, in a previous study, 42 we prepared porous spinel ceramics with an apparent porosity of 62% and an average pore size of 4.94 μm using magnesite and Al(OH) 3 as raw materials.…”

“…However, the obtained pore size of the ceramics was too large to be useful as a raw material of lightweight refractories for working linings. Compared with the previous methods, in situ decomposition synthesis is more suitable for preparing porous ceramics with smaller pore sizes having a uniform pore distribution 38–41 . Moreover, the raw materials are readily available, and the preparation process is simpler.…”

Microstructures and properties of microporous mullite‐corundum aggregates for lightweight refractories

“…Compared with the above methods, the in situ decomposition synthesis, which utilizes the decomposition of raw materials to form pores, can not only produce microporous ceramics with suitable pore characteristic and high strength, but also has the advantages of low cost, simple, and environment-friendly preparation process, and thus it is conducive to large-scale industrial production. [21][22][23][24][25][26] For example, in the previous work, the porous mullite ceramics with apparent porosities of 39.8%-45% and compressive strengths of 52-53.5 MPa were obtained by the in situ decomposition synthesis method using Al(OH) 3 and kaolinite gangue as raw materials as well as MgCO 3 and CaCO 3 as additives. As we know, closed and smallersize pores are conducive to improving heat insulation effect and slag resistance.…”