Synthesis of Alumina Through Hydrothermal Oxidation of Aluminum Powder Conjugated with
Surfactant-Directed Oriented Growth
Materials Research Innovations
, E-ISSN: 1433-075X
||C3 alcohols, Hydrothermal oxidation of aluminum, Structure and texture of alumina
Tikhov Sergey F.
Potapova Yulia V.
Sadykov Vladislav A.
Fenelonov Vladimir B.
Yudaev Ivan V.
Lapina Olga B.
Salanov Aleksey N.
Zaikovskii Vladimir I.
Litvak Galina S.
Boreskov Institute of Catalysis SB RAS
Russian Foundation for Basic Research
International Association for the Promotion of Co-operation with Scientists from the New Independent States of the Former Soviet Union
The synthesis of Al2O3 by aluminum metal oxidation finds an increasingly wide application
for preparation of catalysts and supports, sensor devices and filter elements despite high
energy expenses for the synthesis of aluminum metal (high-temperature electrolysis, spraying
during powder production, rolling during foil production, etc.) . This method yields
aluminum oxide with novel textural, mechanical and chemical properties that cannot be
obtained for samples prepared by precipitation.
For example, oxidation of powder aluminum with In and Ga additives made it possible to
prepare aluminum oxide with different ratios of η- and γ- modifications in the final product.
The aluminum conversion degree in this process was typically close to 100%. The slit-like
pore structure of the oxide consisted of pores 30 Å wide, whereas its surface area reached
320m2/g. Anodic oxidation of aluminum foil yielded Al2O3 consisting of cylindrical pores
with honeycomb structure having a narrow size distribution. Depending on the
electrochemical oxidation conditions, the mean pore size varied from 90 to 300 Å, with the
surface area varying from 28 to 73 m2/g. The aluminum conversion degree and the texture
of the prepared oxide were controlled by such parameters as temperature, electrolyte
composition, current, reaction time, etc.
Slow oxidation of a micron aluminum wire by oxygen at temperatures above the aluminum
melting point (up to 1400 °C) yielded aluminum oxide with the corundum structure formed
into a mechanically sound device with 80–90% porosity and submicron size pores.
Hydrothermal oxidation of aluminum powder placed in a special die providing access of
water vapor from an autoclave at 120–250 °C produced highly porous granulated composites
with varying Al2O3/Al ratios preserving the shape of the die. Partial oxidation of
aluminum with the formation of hydroxides accompanied by the growth of the solid phase
volume resulted in consolidation of the product into a durable monolith with developed
mesoporous structure. Aluminum oxide was formed after calcination due to thermal
decomposition of the hydroxide. The formed alumina was characterized by a highly ordered
microporous structure with slot-like pores and channels from 10 to 60 Å wide. The
specific surface area of the prepared oxide could be varied from 120 to 340 m2/g. Its phase
composition was analyzed in detail. During the experiments it was found that under the
hydrothermal conditions, substances dissolved at high pressures and temperatures could
transfer from the die to the autoclave and back. This phenomenon allowed for additional
modification of the aluminum oxide properties.
The presence of organic surfactants during the precipitation stage and under hydrothermal
conditions is known to have a significant effect on the properties of aluminum oxide.
Therefore, in this study, we modified the properties of the obtained hydroxide (and oxide after
thermal decomposition) using the simplest surfactants—C3 organic alcohols having different
numbers of the alcohol groups and, thus, boiling temperatures, densities, etc.