Effect of Al(Oh)3 particle size on microstructures and strengths of porous MgAl2O4 ceramics

Abstract

Porous MgAl 2 O 4 ceramics were prepared via in-situ decomposition pore-forming (ISDP) technique using Al(OH) 3 and magnesite as raw materials. The influence of Al(OH) 3 particle size (0-44 µm, 44-88 µm, 88-100 µm, 100-150 µm) on the microstructures and strengths of porous spinel ceramics were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The bimodal distributions were observed among all the pore size distributions of the porous spinel ceramics. The small pores existed inside the particles and the big pores existed between the particles. When the Al(OH) 3 particle size decreased from 100-150 µm to 0-44 µm, the peak of large pores shifted towards left while intensity of the peak of small pores decreased. Simultaneously, the neck-bonds formed between particles grew significantly, which resulted in the increase of compressive strength from 1.4 to 10.8 MPa. The optimized product is the sample with the Al(OH) 3 particle size of 0-44 µm, which has a high apparent porosity (55.2%), a high compressive strength (10.8 MPa) and a relatively homogeneous pore size distribution.

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

“…The microporous MgO–Al 2 O 3 ceramics with compressive strengths of 10.0–28.5 MPa and apparent porosities of 28.4%–57.9% as well as median pore sizes of 5.29–7.56 μm were prepared using Al(OH) 3 and calcined magnesite as raw materials via a wet mixing route. Compared with our earlier work, 37,38,42,43 the compressive strengths of the microporous MgO–Al 2 O 3 ceramics in the present study were substantially improved. For example, comparing the sample A71.8 of the present work and the sample made from magnesite and Al(OH) 3 as raw materials, 42 the compressive strength rose from 3.90 42 to 13.21 MPa in this study, but only four percentage points apparent porosity were sacrificed, although the same conditions of sintering temperature and no sintering additives were applied.…”

“…To reduce the sintering temperature, the effects of the Al(OH) 3 particle size and TiO 2 addition on the microstructures and strengths of porous MgO-Al 2 O 3 ceramics at 1600 • C were investigated, respectively. Zhi et al 43 found that the median pore size of porous ceramics decreased from 7.9 to 3.4 μm, whereas the strength increased from 1.4 to 10.8 MPa by reducing the Al(OH) 3 particle size from the range of 100-150 to 0-44 μm. This result was attributed to an increased coordination number 44 between the magnesite and Al(OH) 3 particles, which promotes the formation and growth of sintering necks among particles, which then improves the strength.…”

“…To reduce the sintering temperature, the effects of the Al(OH) 3 particle size and TiO 2 addition on the microstructures and strengths of porous MgO–Al 2 O 3 ceramics at 1600°C were investigated, respectively. Zhi et al 43 . found that the median pore size of porous ceramics decreased from 7.9 to 3.4 μm, whereas the strength increased from 1.4 to 10.8 MPa by reducing the Al(OH) 3 particle size from the range of 100–150 to 0–44 μm.…”

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.…”

“…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 17–24 . For example, lightweight periclase–spinel castable prepared by Yan et al.…”