Kinetics of thermal dehydroxylation and carbonation of magnesium hydroxide

Darryl P. Butt, Klaus S. Lackner, Christopher H. Wendt, Samuel D. Conzone, Harriet Kung, Yung Cheng Lu, Julie K. Bremser

Research output: Contribution to journalArticle

79 Scopus citations

Abstract

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.

Original languageEnglish (US)
Pages (from-to)1892-1898
Number of pages7
JournalJournal of the American Ceramic Society
Volume79
Issue number7
DOIs
StatePublished - Jul 1996
Externally publishedYes

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry

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