Pong H. Fong

Bio: Pong H. Fong is an academic researcher from The Chinese University of Hong Kong. The author has contributed to research in topics: Explained sum of squares & Brucite. The author has an hindex of 3, co-authored 5 publications receiving 109 citations.

Thermal analysis of magnesium hydroxide

Abstract: Natural brucite and two precipitated Mg(OH)2 samples were analysed in a simultaneous TG-DTG-DSC analyser. The initial dehydroxylation temperature of natural brucite is lower than those of the precipitated samples, but the maximum and final temperatures of the former are higher than those of the latter. The maximum temperatures of individual samples obtained from DTG and DSC curves are almost the same. Heats of reaction derived from peak areas for the three samples are not exactly the same, as they are influenced by the specific surface area of the individual sample. Activation energies deduced by Freeman and Carroll's method are very different from one another. This is attributed to the difference in pressure when the sample is crimped. A linear relationship is observed between the deduced activation energy and the specific height of the DSC peak.

Improvement of Differential Correction Method for Evaluation of Kinetic Parameters from TG Curves

Abstract: A new differential correction method for evaluating kinetic parameters from thermogravimetric data, based on the minimization of the sum of squares difference between the observed and calculated temperatures, is proposed. The new method was tested by the experimental data of acid catalyzed iodination of acetone.

Kinetics of Cellulose Pyrolysis in Nitrogen and Steam

Abstract: Kinetics of cellulose pyrolysis in nitrogen and steam at five different heating rates are presented. A single rate equation for each pyrolysis medium is discussed which provides a good engineering fit to the weight loss curves. The presence of steam in the pyrolysis medium was found to have no measurable affect on cellulose pyrolysis kinetics. The activation energy, pre-exponential factor and reaction order for nitrogen and 1 steam pyrolysis of cellulose are: 36.6 kcal/mol, 6.06 × 109sec-1, 0.46 and 34.2 kcal/mol, 1.67 / 109 sec-1, 0.51 respectively. Apparent differences in the data derived using steam rather than nitrogen as a pyrolysis medium are shown to be artifacts of heat transfer phenomenon within the TGA instrumentation used to measure rate of weight loss. Heat transfer effects observed here may explain the large discrepancies in previously reported studies of cellulose pyrolysis kinetics. Kinetic data given for steam pyrolysis are believed to be more accurate due to the more accurate mea...

Calcination of precipitated Mg(OH)2 to active MgO in the production of refractory and chemical grade MgO

Abstract: The processes that occur during the calcination of seawater or brine precipitated Mg(OH)2 to active MgO are reviewed. Details of the commercial calcination of Mg(OH)2, and of the crystallography, mechanism and kinetics of the thermal decomposition of Mg(OH)2 to MgO are given. The effects of calcination conditions, and of chemical and physical properties of the Mg(OH)2 on the properties of the active MgO product are discussed together with the influence of typical impurities in commercial products.

Kinetics of thermal dehydroxylation and carbonation of magnesium hydroxide

Abstract: The kinetics of simultaneous dehydroxylation and carbonation of precipitated Mg(OH){sub 2} were studied using isothermal and nonisothermal thermogravimetric analyses. specimens were analyzed using X-ray diffraction, transmission electron microscopy, and through measurements of the volume of carbon dioxide evolved in a subsequent reaction with hydrochloric acid. From 275 to 475 C, the kinetics of isothermal dehydroxylation in helium were best fit to a contracting-sphere model, yielding an activation energy of 146 kJ/mol, which was greater than values reported in the literature for isothermal dehydroxylation under vacuum (53--126 kJ/mol). The carbonation kinetics were complicated by the fact that dehydroxylation occurred simultaneously. The overall kinetics also could be fit to a contracting-sphere model, yielding a net activation energy of 304 kJ/mol. The most rapid carbonation kinetics occurred near 375 C. At this temperature, Mg(OH){sub 2} underwent rapid dehydroxylation and subsequent phase transformation, whereas thermodynamics favored the formation of carbonate. During carbonation, MgCO{sub 3} precipitated on the surface of disrupted Mg(OH){sub 2} crystals acting as a kinetic barrier to both the outward diffusion of H{sub 2}O and the inward diffusion of CO{sub 2}.

Improved Iterative Version of the Coats-Redfern Method to Evaluate Non-Isothermal Kinetic Parameters

Abstract: An improved version of the Coats-Redfern method of evaluating non-isothermal kinetic parameters is presented. The Coats-Redfern approximation of the temperature integral is replaced by a third-degree rational approximation, which is much more accurate. The kinetic parameters are evaluated iteratively by linear regression and, besides the correlation coefficient, the F test is suggested as a supplementary statistical criterion for selecting the most probable mechanism function. For applications, both non-isothermal data obtained by theoretical simulation and experimental data taken from the literature for the non-isothermal dehydration of Mg(OH)2 have been processed.