TY - JOUR
T1 - Kinetics of thermal dehydroxylation and carbonation of magnesium hydroxide
AU - Butt, Darryl P.
AU - Lackner, Klaus S.
AU - Wendt, Christopher H.
AU - Conzone, Samuel D.
AU - Kung, Harriet
AU - Lu, Yung Cheng
AU - Bremser, Julie K.
PY - 1996/7
Y1 - 1996/7
N2 - The kinetics of simultaneous dehydroxylation and carbonation of precipitated Mg(OH)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)2 underwent rapid dehydroxylation and subsequent phase transformation, whereas thermodynamics favored the formation of carbonate. During carbonation, MgCO3 precipitated on the surface of disrupted Mg(OH)2 crystals acting as a kinetic barrier to both the outward diffusion of H2O and the inward diffusion of CO2.
AB - The kinetics of simultaneous dehydroxylation and carbonation of precipitated Mg(OH)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)2 underwent rapid dehydroxylation and subsequent phase transformation, whereas thermodynamics favored the formation of carbonate. During carbonation, MgCO3 precipitated on the surface of disrupted Mg(OH)2 crystals acting as a kinetic barrier to both the outward diffusion of H2O and the inward diffusion of CO2.
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U2 - 10.1111/j.1151-2916.1996.tb08010.x
DO - 10.1111/j.1151-2916.1996.tb08010.x
M3 - Article
AN - SCOPUS:0030189477
VL - 79
SP - 1892
EP - 1898
JO - Journal of the American Ceramic Society
JF - Journal of the American Ceramic Society
SN - 0002-7820
IS - 7
ER -