Kinetics of decomposition of gibbsite and boehmite and the characterization of the porous products

Abstract

Langmuir 1987, 3, 681-686 681 is deposited upon the larger particles ( Figure 10). CBET values remain unchanged, which show that nitrogen adsorption takes place on the same kind of surface, as similar silanol groups are present in both amorphous silica and unattacked montmorillonite surfaces. A change is shown in N2 adsorption-desorption isotherms, and in the f-plot a peak in the higher pore size region appears. DRX patterns and IR spectra correspond almost exclusively to amorphous free silica.Finally, as the insolubilization of polymeric silica increases, a progressively thicker silica layer is formed on the unaltered or partially altered bentonite particles, thus reducing or impeding the posterior attack. An apparent "passivation" of the samples takes place and losses in the total amount of N2 adsorbed and in the cations abstracted are produced. The amount of adsorbed nitrogen diminishes, but the general appearance of the isotherm remains because silica is always present. In the f-plot a small shift of the peak toward the higher p / p o is produced. DRX and IR show a corresponding reverse in the characteristic peaks.

Analysis of Mechanically Induced Reactivity of Boehmite Using Kinetics of Boehmite to γ-Al2O3 Transformation

“…The nature of the curves indicates that a value between 1 and 2 seems appropriate for n. Although the Avrami-Erofeev models A1.5 and A2 also had good correlation coefficients (R 2 ), the activation energy derived from these was small compared with that deduced from the Kissinger method (227 kJ/mole) and earlier reported values. [9,10] To determine whether the reaction mechanism remains the same or changes as a result of MA, similar analysis was carried out for MA boehmite (240 minutes) also. The details are given in Figure 12 and Table IV.…”

“…[8][9][10][11] Eyraud and Goton [8] found that their low-pressure decomposition data between 713 K and 813 K (440°C and 540°C) could be described by the power law with f(a) = a 2/3 , where a is the extent of decomposition. The activation energy E a deduced from their analysis (around 18 kJ/mol) was much lower than those reported later.…”

“…The activation energy E a deduced from their analysis (around 18 kJ/mol) was much lower than those reported later. [9][10][11] Studies by Callister et al [9] showed that the atmospheric pressure decomposition of boehmite between 703 K and 773 K (430°C and 500°C) obeyed a linear rate law and proposed the interface model for the dehydroxylation mechanism. Stacey [10] studied the kinetics using constant rate thermal analysis methods and reported an activation energy of 272 kJ/mol for boehmite/c-Al 2 O 3 transition.…”

Applications of sample-controlled thermal analysis (SCTA) to kinetic analysis and synthesis of materials

“…This temperature control allows both minimizing the heat and mass transfer phenomena and performing a very precise control of the atmosphere surrounding the samples.These features have been exploited for developing materials with controlled porosity and structure for being used either as adsorbents or catalysts [5,9,21-23, [95][96][97][98][99][100].…”

Development of a universal constant rate thermal analysis system for being used with any thermoanalytical instrument

“…This is because the ability of SCTA for performing a direct or indirect control of both the partial pressure of the gases generated in the reaction and the heat evolution proportional to the reaction rate, minimizing the influence of heat and mass transfer phenomena on the forward reaction. This advantage has been also used for synthesising materials with controlled texture and structure (43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57). The scope of this work is to develop a new SCTA control system that does not require a control signal directly proportional to the rate of the process like in the SCTA controllers previously developed and, therefore, would be easily adapted to any thermoanalytical instruments.…”