Non-isothermal thermogravimetric analysis was used for determination of the kinetics of aluminium hydroxide dehydration in an air atmosphere and for processing of the experimental results by the method due to Chatterjee.
Authors:D. Zamboulis, P. Misaelides, D. Bakoyannakis, A. Godelitsas, N. Barbayannis, G. Stalides, and I. Anousis
The adsorption of perrhenate ions onto aluminium hydroxide gels was investigated. These gels were prepared by the sol-gel method in non aqueous solutions using a tertiary amine as template. They were amorphous and presented high specific surface areas. The amount of perrhenate ions adsorbed from aqueous solutions depended on the specific surface area of the gels. Removal of perrhenate ions up to 84% could be achieved without reaching saturation.
Factors that influence the sorption of Cr(VI) and Cr(III) on aluminium hydroxide were investigated. The sorption of chromates decreases as the pH of the suspension increases. The mechanism of CrO
sorption was interpreted in terms of reactions between chromates and –OH and/or H2O groups at the hydroxide/liquid interface. It has been shown that chromates are more tightly sorbed on aluminium hydroxide compared to other anions, e.g. chlorides. On the other hand, specifically absorbed anions, such as molybdates, compete strongly with chromates for the sorption sites. The sorption of chromium(III) increases with the pH of the suspension. Also, the sorption of chromium(III) is suppressed in the presence of citrate ions. The best conditions for the fixation of Cr(VI) and Cr(III) by aluminium hydroxide are presented.
Authors:A. M. George, N. C. Mishra, M. S. Nagar, and N. C. Jayadevan
Thermal decomposition of the amorphous coprecipitate of yttrium and aluminium hydroxides forming yttrium aluminium garnet has been investigated employing thermal analyses, X-ray diffraction and IR spectroscopy. On heating, the coprecipitate progressively loses water forming a stable but highly disordered hydroxy garnet which crystallizes at ∼1180 K and decomposes to YAG at ∼1290 K. Nucleation of the crystalline phase appears to begin at ∼800 K.
EPR spectra of paramagnetic centers originating from X-ray-irradiation of aluminium hydroxide at room temperature have been measured. The EPR spectrum represents a superposition of EPR spectra of ionic centers O–, holes of type and trapped electrons. Radiation chemical yield of paramagnetic centers observed at room temperature (293 K) is G(spins.)=4.4±0.6) spins per 100 eV absorbed energy. The decay of paramagnetic centers in irradiated Al(OH)3 was oberved at 293 K. The rate constant of the paramagnetic centers decay in irradiated Al(OH)3 is K2=(0.0980±0.0019) kg·mol–1·min–1 and their half-life is 9.43±0.18 days.
The present work is an attempt to use the waste water stream, containing considerable amounts of aluminium chloride, for the
manufacture of mineral–carbon sorbents. The use of the wastewater has given a possibility of obtaining a suitable mineral
matrix of aluminium hydroxide for the sorbents. Atactic poly(propylene) (APP) have been used as the necessary carbon raw material.
The modification of aluminium hydroxide was attained by preliminary mixing with the organic component, followed by carbonisation.
Optimum conditions for obtaining Al(OH)3 have been determined and the effect of the amount of carbon matter on the properties of the materials obtained has been evaluated.
The studies have enabled to trace the changes in the structure and properties of the sorbents obtained.
Authors:Barbara Pacewska, Olga Kluk-Płoskońska, and D. Szychowski
to obtain aluminium hydroxide that could give aluminium oxides of increased
thermal stability was made. Aluminium hydroxide was precipitated during a
hydrolysis of aluminium chloride in ammonia medium. The influence of preparative
conditions, such as a dosing rate of aluminium precursor, pH, duration of
the precipitate refluxing and temperature of calcination, on the properties
of obtained hydroxides and oxides was investigated. The materials were studied
with the following methods: thermal analysis, IR spectroscopy, low-temperature
nitrogen adsorption and adsorption–desorption of benzene vapours.
Precipitated boehmites had high values of SBET
determined from nitrogen adsorption (220–300 m2g–1),
good sorption capacity for benzene vapours, developed mesoporous structure
and hydrophilic character. It has been proved that a high pH value during
the precipitation of aluminium hydroxide favoured better crystallisation of
boehmite structure, higher temperature of its dehydroxylation into γ-Al2O3,
and delayed transformation of γ phase into α-Al2O3.
Aluminium oxides derived from the hydroxides precipitated at a high pH were
the most stable at high temperatures, and were characterised with the best
Authors:Barbara Pacewska, Olga Kluk-Płoskońska, and Dariusz Szychowski
The paper concerns aluminium hydroxides precipitated during hydrolysis of aluminium acetate in ammonia medium, as well as
aluminium oxides obtained through their calcination at 550, 900 or 1200�C for 2 h. The following techniques were used for
analysing of obtained materials: thermal analysis, IR spectroscopy, X-ray diffraction, low-temperature nitrogen adsorption,
adsorption-desorption of benzene vapours and scanning electron microscopy.
Freshly precipitated boehmite/pseudoboehmite had high value of SBET, very good sorption capacity for benzene vapours, developed mesoporous structure and hydrophilic character. After prolonged
refluxing at elevated temperature its crystallinity increased which was accompanied by a decrease of specific surface determined
from nitrogen adsorption, decrease of sorption capacity for benzene vapours and weakening of the hydrophilic character. Calcination
of all hydroxides at the temperature up to 1200�C resulted in the formation of α-Al2O3 via transition forms of γ-, δ-and θ-Al2O3. The samples of aluminium oxides obtained after calcination at 550 and 900�C were characterised with high values of specific
surface area and displayed quite high heat resistance, probably due to a specific morphology of starting hydroxides. The process
of ageing at elevated temperature developed thermal stability of aluminium oxides.
Authors:Barbara Pacewska, Olga Kluk-Płoskońska, and D. Szychowski
Aluminium hydroxide was precipitated
during a hydrolysis of aluminium perchlorate in ammonia medium. The materials
were studied with the following methods: thermal analysis, IR spectroscopy,
X-ray diffraction, low-temperature nitrogen adsorption and adsorption–desorption
of benzene vapours.
Freshly precipitated boehmite had a high value
of SBET=211 m2 g–1
determined from nitrogen adsorption, good sorption capacity for benzene vapours,
developed mesoporous structure and hydrophobic character. After prolonged
refluxing at elevated temperature its crystallinity increased which was accompanied
by an increase of specific surface determined from nitrogen adsorption up
to 262m2g–1 ,
decrease of sorption capacity for benzene vapours and stronger hydrophobic
character. The calcinations of all boehmites at temperature up to 1200C
resulted in formation of -Al2O3
via transition form of γ-, δ- and θ-Al2O3.
The samples of aluminium oxides obtained after calcination at 550 and 900C
were characterised with high values of specific surface area of 205–220
and 138–153 m2 g–1
, respectively. The SBET values calculated for the oxide samples derived from
aged hydroxides and calcined at 1200C are higher than for the analogous
sample prepared without the ageing step. It was concluded that the process
of ageing at elevated temperature developed thermal stability of aluminium