A multi-technique study of the effect of aqueous aluminium speciation on hydrolytic gelation of aluminium (oxy)hydroxide (original) (raw)
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The systematic study of aluminium speciation in medium concentrated aqueous solutions
Journal of Inorganic Biochemistry, 2001
Industrial applications and environmental problems involving the aqueous chemistry of aluminium require an understanding of the speciation of this metal ion at a wide range of concentrations. The formation of polynuclear species is of special interest due to the complexity of the hydrolysis mechanisms and the diversity of the hydrolysis products. Kinetic aspects of speciation are also important considering the different stability ranges of polycationic species formed during the hydrolysis process. In the present paper we report results of systematic studies on the formation of aluminium polycations at room temperature. Automated potentiometric titrations have been used to study the hydrolysis of aluminium-ions in solutions (0.01-0.2 M) on a short time scale (2 min between titrant additions). 27 Al NMR spectroscopy and dynamic light scattering have been used for investigations on a longer time scale (24 h). The effects of alkali 2 2 22 strength (KOH, NH OH and KHCO ) and concentration (0.45-2.0 M), counterion identity (Cl , NO , SO ) and ionic strength have 4 3 3 4 been investigated. Optimum conditions for the generation of Al -mer are proposed on short and long time scales. On a short time scale, 13 aluminium chloride and nitrate should be used as starting materials, KOH and KHCO should be used for hydrolysis and experiments 3 conducted at low ionic strength. For solutions that have been left to age, there is a considerable hydrolysis window that can be used to generate significant quantities of the Al -mer that vary little with the alkali used. Al -mer species are not generated from alum as the 13 13 precursor. The presence of sulphate ions alters the pathway of aluminium polymerisation to form polymeric and solid materials. On the 27 basis of the potentiometric titration data, dynamic light scattering and Al NMR measurements evidence is provided for the detrimental role of sulphate-ions in the formation of Al -mer and an alternative mechanism of aluminium ion polycondensation is proposed, based on 13 the increased stability of monomeric and oligomeric species (dimer and trimer) in the presence of sulphate-ions.
IEEE Transactions on Instrumentation and Measurement, 2000
A cross-disciplinary experimental study related to both ultrasonic instrumentation and analytical chemistry is reported. The hydrolysis process was conducted by time-resolved titration in a fully automated manner. Acquired ultrasonic records were processed in order to estimate the propagation delay of the ultrasonic pulse in the evolving medium. The limited hardware resolution of two different ultrasonic instruments employed was improved by calculating the center of gravity of the recorded pulses. Application of signal averaging to the acquisition of raw records in the custom-built instrument eliminated spurious records almost completely. The estimated ultrasonic delays were corrected for temperature changes that were measured independently. This procedure transformed the ultrasonic titration curves into two almost straight lines that intersected at the equivalence point. The results obtained showed that it was possible to detect changes as small as 200 ppm by using the ultrasonic instrument in situ at significantly lower setting times compared to a conventional pH-meter.
Influences of pH value on the microstructure and phase transformation of aluminum hydroxide
Powder Technology, 2009
The effects of pH value on the composition, structure, morphology, and phase transformation of aluminum hydroxides prepared by chemical precipitation were studied. Aluminum hydroxide precipitated at the pH values of 5 and 6 is amorphous and transforms to α-Al 2 O 3 at 950°C via the amorphous aluminum hydroxide → amorphous Al 2 O 3 → α-Al 2 O 3 transformation path. Aluminum hydroxide precipitated at pH = 7 is boehmite and transforms to α-Al 2 O 3 at 950°C via the γ-AlOOH → γ-Al 2 O 3 → α-Al 2 O 3 path. Aluminum hydroxide precipitated at pH values in the 8 to 11 range is bayerite and transforms to α-Al 2 O 3 at 1000°C via the α-Al(OH) 3 → γ-Al 2 O 3 → ε-Al 2 O 3 + θ-Al 2 O 3 → α-Al 2 O 3 path. Moreover, the pH value affects not only the morphology of aluminum hydroxide particles which changes from ultrafine floccules through 50 nm blowballs then to 150 nm irregular agglomerates with increasing pH value but also the microstructures of final decomposition products of aluminum hydroxides.
Hydrolysis of aluminium metal and sol–gel processing of nano alumina
Materials Letters, 2004
Aluminium metal has been hydrolysed at 100 jC to synthesize boehmite. Gelatinous and dry boehmite were used to prepare stable sol. In the case of gelatinous boehmite, sol was prepared by peptizing and in the case of dry boehmite an ultrasonic bath was used to prepare the sol. Gelation was carried out by heating on a hot plate, which resulted in sol -gel processed powder. For sol -gel processed boehmite the u ! a transformation occurred at 1078 jC and for the as prepared boehmite the same occurred at 1206 jC. Sol -gel processed powder could be transformed to a alumina completely, when calcined at 1000 jC for 1 h. D
ESI-MS study of speciation in hydrolyzed aluminum chloride solutions
Journal of the Brazilian Chemical Society, 2012
Soluções de AlCl 3 foram analisadas em concentrações de 0,03 a 5,0 mmol dm -3 e pH de 3,5 a 6,0 por espectrometria de massas com ionização por electrospray e analizador quadrupolar (ESI-Q-MS). Esses dados espectrais foram comparados com os obtidos por ressonância magnética nuclear (NMR) de 27 Al e potenciometria. Espécies resultantes da hidrólise do cátion alumínio em solução apresentaram-se principalmente como complexos carregados positivamente (+1) com moléculas de água coordenadas (n = 1-3) ao metal. As análises revelaram que complexos poliméricos de carga +2 e +3 (em concentrações mais elevadas de Al e pH > 4) contêm íons cloretos coordenados. O aspecto geral dos espectros de massas é dependente de parâmetros instrumentais tais como taxa de fluxo de solvente, temperatura na fonte de ionização e voltagens do cone e capilar. Assim, o ajuste fino do instrumento com relação a estes parâmetros foi realizado. Uma tensão de cone de amostra não superior a 50 V levou à melhor correspondência entre dados de potenciometria, ressonância magnética nuclear de 27 Al e espectrometria de massas.
Colloids and Surfaces a Physicochemical and Engineering Aspects, 2003
The action of pre-hydrolysed coagulants such as basic aluminium chloride (BAC) and sulphate (BAS) in water treatment is of considerable practical and fundamental interest. Variables such as working solution concentration, dosage, pH and ionic strength are known to be important. We have investigated the influence of these variables on the ζ-potential and degree of hydration of hydrolysis products of basic aluminium sulphate samples with different basicities. The products were characterised by a timed ferron complexation procedure, giving information on the degree of polymerisation of the BAS samples. Electrokinetic measurements showed that the ζ-potentials of hydrolysis product particles were consistently higher (more positive) for the higher basicity samples. The ζ-potential decreased with increasing concentration of the working solution and with increased dosage.
Stabilization of aluminum hydroxide gel by specifically adsorbed carbonate
Journal of Pharmaceutical Sciences, 1983
Ion-free aluminum hydroxide gel, prepared by the hydrolysis of aluminum tri-sec-butoxide, was observed by IR, X-ray analysis, and pH-stat titration to undergo rapid structural changes leading to the formation of pseudoboehmite and bayerite. The rate of development of order was directly related to the water-aluminum molar ratio. The AI-0 bands a t 625 and 470 cm-1 were the most sensitive indicators of the development of order in the gel structure. Direct evidence for the stabilizing effect of specifically adsorbed carbonate was obtained when carbon dioxide was introduced during the hydrolysis of aluminum tri-sec-butoxide. The resulting aluminum hydroxycarbonate gel possessed excellent antacid properties, retained its amorphous nature upon aging, and contained no cations other than aluminum. Hydrolysis of aluminum trisec-butoxide in the presence of stoichiometric amounts of sodium bicarbonate resulted in the immediate formation of crystalline sodium aluminum hydroxycarbonate (dawsonite).