Thermal decomposition of gibbsite under low pressures II. Formation of microporous alumina

Rouquérol, J.; Rouquérol, F.; Ganteaume, Max

doi:10.1016/0021-9517(79)90026-5

Cited by 64 publications

(14 citation statements)

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“…also presented some evidence for the formation of ink-bottle type pores by "intraparticle hydrothermal reaction" at the early stage of the dehydration and explained: "The development of water starts at the active spot in the gibbsite particle; water inside the particle cannot escape quickly enough and builds up a relatively high pressure, converting gibbsite into boehmite and water; on proceeding the reaction the water forces its way out; thus creating some ink-bottle type pores releasing the internal pressure, and inside the particle the conversion into boehmite has left some holes" . Brindley and Choe (1961) reported that when the dehydration ofgibbsite was about 75% complete (AIzO3 9 0.75 H20), the reaction rate was reduced to almost zero in all the temperatures employed (250"--297~ Rouquerol et aL (1975Rouquerol et aL ( , 1979 and Paulik et al (1983) reported that the thermal dehydration into such a transition alumina consists of two partial processes: The first process is a relatively rapid one, whose apparent order is zero toward the amount of unreacted gibbsite (Rouquerol et al, 1975(Rouquerol et al, , 1979 and is affected by the water pressure of environment Pokol et al, 1984). The second process is a slow dehydration which requires progressively higher temperatures.…”

Section: Mechanism For the Formation Of Boehmite By The Thermal Dehydmentioning

confidence: 99%

“…The second process is a slow dehydration which requires progressively higher temperatures. Rouquerol et al (1975Rouquerol et al ( , 1979 attributed the first process to the formation of 0-alumina (Tertian and Papre, 1958) and the second one to the dehydration of the p-alumina.…”

Section: Mechanism For the Formation Of Boehmite By The Thermal Dehydmentioning

confidence: 99%

“…The water content of p-alumina is known to be relatively high and to be dependent on the reaction conditions (Tertian and Papre, 1958;Rouquerol et al, 1975Rouquerol et al, , 1979. This phase can be transformed into x-alumina by developing its crystal structure by the aid of the water pressure (Rouquerol et al, 1975(Rouquerol et al, , 1978.…”

Section: The Formation and Nature Of X*-aluminamentioning

confidence: 99%

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Alcohothermal Treatments of Gibbsite: Mechanisms for the Formation of Boehmite

Inoue

1989

Clays and clay miner.

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Abstract--Gibbsite samples of various particle sizes (0.2-80 #m) were heated at 250~ in a series of straight-chain primary alcohols under the autogenous vapor pressure of the alcohol (alcohothermal treatment of gibbsite). The treatment in ethanol yielded pure boehmite, the morphology of which was similar to that of the boehmite obtained by hydrothermal treatment of gibbsite. In middle-range alcohols, the boehmite yields were low (50% if 80 t~m gibbsite was used), and the products were contaminated by a poorly crystallized phase, having a x-alumina-like structure. The products preserved the morphology of the originating gibbsite, this feature being similar to the thermal dehydration of gibbsite. Complete conversion to boehmite was also attained in mineral oil (a hydrocarbon mixture, which was used as a limit of higher alcohol. The morphology of the boehmite formed in this medium was identical to that of the product prepared by thermal dehydration of gibbsite in a sealed bomb without a medium. If fine particle-size gibbsite was used, the yield of boehmite decreased and the yield of the poorly crystallized phase increased in all the media.The reaction mechanisms may be discussed in terms of the reported mechanisms for the thermal and hydrothermal formations of boehmite from gibbsite. Thus, in lower alcohols boehmite formed by a dissolution-recrystallization mechanism, whereas in middle-range or higher alcohols it formed by intraparticle hydrothermal reaction mechanism proposed by de Boer and coworkers for the thermal dehydration of gibbsite. The difference in behavior in middle-range and higher alcohols can be explained in terms of the solubility of water in the medium: In the middle-range alcohols, water molecules formed by partial dehydration of gibbsite were removed from the gibbsite particles into the medium so that dehydration proceeded in a manner similiar to that of thermal dehydration, whereas in the higher alcohols, the low solubility of water in the medium allowed the water molecules to remain on the surface of the particles, thereby promoting the complete hydrothermal formation of boehmite.

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Section: Mechanism For the Formation Of Boehmite By The Thermal Dehydmentioning

confidence: 99%

Section: Mechanism For the Formation Of Boehmite By The Thermal Dehydmentioning

confidence: 99%

Section: The Formation and Nature Of X*-aluminamentioning

confidence: 99%

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Alcohothermal Treatments of Gibbsite: Mechanisms for the Formation of Boehmite

Inoue

1989

Clays and clay miner.

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“…For many years a great number of investigations on the thermal decomposition of aluminium hydroxides have been published, and a sample of relevant and recent papers about this topic is presented in references [11,[23][24][25][26][27][28]. Despite the different experimental methods employed, the dehydration processes nowadays accepted can be described as represented in Fig.…”

Section: Dehydration Process In the Systemmentioning

confidence: 99%

Thermodynamic evaluation of the Al2O3–H2O binary system at pressures up to 30MPa

Serena¹,

Raso²,

Rodríguez³

et al. 2009

Ceramics International

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“…[14][15][16] SCTA has been applied for the preparation of different kinds of materials. It has been shown that CRTA method has advantages for the synthesis of ceramics [17][18][19][20][21] and glasses, 22 and materials with controlled texture and structure, [23][24][25][26][27][28] including the preparation of different kinds of catalysts. 14,29,30 It has also been used for the thermal analysis of a wide range of reactions, such as dehydrations and dehydroxylations, [31][32][33][34] denitrations, 35 and decarbonations.…”

Section: Introductionmentioning

confidence: 99%

A Promising approach to the kinetics of crystallization processes: The sample controlled thermal analysis

et al. 2016

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Constant Rate Thermal Analysis (CRTA) method implies controlling the temperature in such a way that the reaction rate is maintained constant all over the process. This method allows determining simultaneously both the kinetic parameters and the kinetic model from a single experiment as the shape of the CRTA α‐T curves strongly depends on the kinetic model. CRTA method has been developed in the market only for thermogravimetric and thermodilatometric systems and, therefore, its use has been limited until now to the kinetic study of processes involving changes in mass or size of the samples, respectively. To overcome this obstacle, a method has been developed in this work for using the DSC signal for controlling the process rate in such a way that CRTA would be applied to the kinetic analysis of either phase transformations or crystallizations. The advantages of CRTA for performing the kinetics of crystallization processes have been here successfully demonstrated for the first time after selecting the crystallization of zirconia gel as test reaction.

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Thermal decomposition of gibbsite under low pressures II. Formation of microporous alumina

Cited by 64 publications

References 4 publications

Alcohothermal Treatments of Gibbsite: Mechanisms for the Formation of Boehmite

Alcohothermal Treatments of Gibbsite: Mechanisms for the Formation of Boehmite

Thermodynamic evaluation of the Al2O3–H2O binary system at pressures up to 30MPa

A Promising approach to the kinetics of crystallization processes: The sample controlled thermal analysis

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