Defect formation by order coalescence in vermicular grains during alumina phase transformation

Wang, Ling; Hu, Jianfeng; Cheng, Yao; Fu, Zhengyi; Shen, Zhijian; Xiong, Yan

doi:10.1016/j.scriptamat.2015.05.020

Cited by 12 publications

(3 citation statements)

References 21 publications

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“…The calcined grains appears as agglomerate of α -alumina crystallites which are bigger when temperature of calcination is higher. The α -alumina crystallites have porous vermicular or wormy structure, as also found by other researchers (Cardarelli 2008; Yang et al 2009; Wang et al 2015). In the UC1150-2 sample (Figure 11(a, b)), due to large particle size and low calcination temperature, in some areas (denoted as A) α -alumina crystallites were not formed, but in the UC1300-2 sample (Figure 11(c, d)), although the gibbsite particle size was large, due to the higher calcination temperature α -alumina crystallites were fully formed in all areas of the sample, which corresponds to their XRD patterns (Figure 10(a, c)).…”

Section: Resultssupporting

confidence: 83%

The relation between particle size and transformation temperature of gibbsite to αLPHA-alumina

Ahmadabadi

Nemati

Arzani

et al. 2020

Mineral Processing and Extractive Metallurgy

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The transformation of gibbsite to α-alumina occurs in the range 1100 to 1300°C. The higher the calcination temperature, the larger the crystallites and this leads to abnormal grain growth. The main goal of this research was to reduce the transformation temperature of gibbsite to αalumina by reducing the gibbsite particles size. The sodium content of the gibbsite used in the study was reduced to less than 0.1% by washing it in HCl solution. It was then ground in a fast mill at ambient conditions for different times then calcined at different temperatures. The microstructure, particles size and thermal behaviour of the samples were examined with SEM, XRD, XRF, PSA and STA, respectively. In a sample ground for 180 min, the transformation temperature decreased from about 1300°C to 1150°C. The reduction in the calcination temperature led to a reduction in α-alumina crystallite size from about 77.16 nm to 64.37 nm.

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Section: Resultssupporting

confidence: 83%

The relation between particle size and transformation temperature of gibbsite to αLPHA-alumina

Ahmadabadi

Nemati

Arzani

et al. 2020

Mineral Processing and Extractive Metallurgy

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“…Annealing of the sample HA-CS in air at 1250 °C for 3 h resulted in the formation of a vermicular structure in HA-CS-A (Figure 8c,d). This type of microstructure was reported to form in alumina ceramics during γ-modification transition into α-Al2O3 on sintering [71][72][73]. The appearance of vermicular grains led to the increase of open porosity up to 60% due to the development of the grains' surface (Table 2).…”

Section: Resultsmentioning

confidence: 72%

Water-Assisted Cold Sintering of Alumina Ceramics in SPS Conditions

et al. 2023

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A developing energy-saving approach of cold sintering in a pure aqueous medium was applied to the preparation of α-Al2O3 ceramics and performed on spark plasma sintering equipment. The initial γ-Al(OH)3 and γ-AlOOH powders and the cold-sintered ceramics were studied by X-ray diffraction analysis, infrared spectroscopy, thermal analysis, and scanning electron microscopy to reveal the chemical and structural transformations they experienced during the cold sintering. At 450 °C and 70 MPa, initially γ-AlOOH transformed into a fragile α-Al2O3 material. Porous α-Al2O3 ceramics with about 60% porosity were obtained after cold sintering of γ-Al(OH)3 in the same conditions combined with subsequent annealing at 1250 °C for 3 h. The role of water molecules in the studied processes was considered as the enhancement of structural mobility in the cold-sintered material due to its reversible hydroxylation similar to earlier investigated supercritical water actions on the precursors during α-Al2O3 formation. Further improvement of the cold sintering setup and regimens would open prospects in α-Al2O3 ceramics manufacturing by an ecologically benign route.

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“…7,8,10,[13][14][15][51][52][53][54] However, in such macroporous structures, they seem to be more stable than in sol-gel 54 or inkjet printed 13 structures, and are not altered with increasing sintering time, discussed in detail elsewhere. 35 Classical sintering theory 55 predicts that such highly curved interfaces should be smoothed or reduced and such an open filter-like network with large domains is not expected. Moreover, instead of expected neck growth and porosity reduction, as observed in classic bulk-particle solid-state sintering, the sintering of the shells results in the enlargement of the connection points (Figure 5A) and grain growth.…”

Section: Macroporous Ceramics Structural Evolutionmentioning

confidence: 99%

Unraveling the role of shell thickness and pore size on the mechanical properties of ceramic‐based macroporous structures

et al. 2022

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Macroporous structures are of interest for several technological applications such as catalysis, sensors, filters, membranes, batteries, energy conversion devices, structural colors, and reflective thermal barrier coatings. Ceramic‐based inverse opal macroporous structures are especially interesting for high‐temperature applications. However, the interrelation between the structural parameters, mechanical properties, and thermal stability of such structures is not yet clarified. In this work, we analyzed the mechanical properties as well as the thermal stability of aluminum oxide inverse opal three‐dimensional macroporous structures with different macropore sizes and shell thicknesses produced by atomic layer deposition. Our results show that the structures’ thermal stability increased with increasing shell thickness and macropore size, however, their higher stability was not linked to their mechanical properties. To be able to explain this unexpected behavior, finite element modeling simulations were performed, showing that bending stresses became more pronounced with increasing shell thickness, potentially creating additional critical sites for crack initiation and consequent structural failure.

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Defect formation by order coalescence in vermicular grains during alumina phase transformation

Cited by 12 publications

References 21 publications

The relation between particle size and transformation temperature of gibbsite to αLPHA-alumina

The relation between particle size and transformation temperature of gibbsite to αLPHA-alumina

Water-Assisted Cold Sintering of Alumina Ceramics in SPS Conditions

Unraveling the role of shell thickness and pore size on the mechanical properties of ceramic‐based macroporous structures

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