Influence of Genesis on Mechanochemical Activation and Reactivity of Boehmite Prepared by Thermal and Hydrothermal Transformation of Gibbsite

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Vol. 55; no. 5; pp. 3407 - 3420
• Main Authors: Greifzu, Georg, Alex, Thomas C., Kailath, Ansu J., Senna, Mamoru, Stelter, Michael, Kumar, Rakesh
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.10.2024; Springer Nature B.V
• Subjects: Aluminum oxide; Amorphization; Bayer process; Boehmite; Bonding strength; Characterization and Evaluation of Materials; Chemistry and Materials Science; Correlation coefficients; Gibbsite; Interlayers; Leaching; Materials Science; Metallic Materials; Nanotechnology; Original Research Article; Particle size; Planetary mills; Pore size; Size distribution; Specific surface; Strain; Structural Materials; Surface area; Surfaces and Interfaces; Thermal transformations; Thin Films; Transformation temperature; Transitional aluminas
• ISSN: 1073-5615; 1543-1916
• DOI: 10.1007/s11663-024-03180-5

The focus of this paper is on the mechanical activation and reactivity of boehmite ( γ -AlOOH) synthesized by thermal transformation (B-TH) and hydrothermal transformation (B-HT) of the same gibbsite (Al 2 O 3 ·3H 2 O) precursor. The central idea is to emphasize the role of sample genesis. The samples used had similar size distribution and largely differed in their BET surface area, 264 and 2.98 m 2 /g for B-TH and B-HT, respectively. Mechanical activation was carried out for different durations, up to 240 minutes, using a planetary mill. On milling, the span of change in physicochemical properties, namely geometric specific surface area, BET specific surface area, degree of amorphization, microcrystalline dimension, and macro strain (in 〈020〉/stacking direction of AlO 4 (OH) 2 octahedra layers) was more for B-TH vis-à-vis B-HT. The anomalous decrease in the BET surface area reported in the literature for B-TH is not observed in B-HT. The nature of alteration in pore size distributions with milling time is used to present a plausible explanation for the contrasting change in BET surface area. The samples also showed the opposite sign for macro strain; a negative sign for B-TH which was characterized by a relatively weaker interlayer bonding. The reactivity of the samples was evaluated in terms of leachability in alkali and the lowering of boehmite to γ -Al 2 O 3 transformation temperature. In general, higher reactivity was observed for B-TH vis-à-vis B-HT. The reactivity was correlated with physicochemical changes. Despite wide differences in reactivity, the change in reactivity could be expressed in terms of simple multivariate equations with high correlation coefficients.