Small-Angle X-ray Scattering Study of the Thermal Decomposition of Magnesium Hydroxide

The submicroscopic porous structure developed in the isothermal decomposition of Mg(OH)₂ was studied in situ by means of small-angle X-ray scattering (SAXS). The scattering intensity in the 100% decomposed system has a good fit with an exponential correlation function, g(r) = exp(- r/a ) (where a is the correlation distance), according to the Debye, Anderson, and Brumberger (DAB) model which holds for a random distribution of pore shape and size in the solid. The DAB correlation distance is about 3.2 nm for systems decomposing at 583 and 623 K. According to the available pore volume fraction, such a correlation distance would imply a porous structure built up by pores of 7-nm mean size randomly distributed in a solid skeleton of 6-nm mean particle size.