In situ and ex situ studies on thermal decomposition process of hydromagnesite Mg5(CO3)4(OH)2•4H2O

We investigated crystal structure and the local structure changes during the thermal decomposition of hydromagnesite by using in situ high-temperature XRD and ex situ high-temperature X-ray total scattering measurements. Hydromagnesite displayed anisotropic thermal expansion up to 220 degrees C. The a and c lattice parameters exhibited an increase trend with temperature, whereas the b lattice parameter and ss angle did not show a regular trend with temperature. The relative expansion between 25 and 220 degrees C followed the c/c0 > a/a0 >> b/b0. At 260 degrees C, the a, b, and c lattice parameters significantly decreased. Above 280 degrees C, hydromagnesite underwent a structural collapse with dehydration and dehydroxylation reactions, but was never accompanied by nucleation and growth of crystal phases up to 425 degrees C. During the thermal decomposition from hydromagnesite to periclase, the Mg atoms maintained the octahedral coordination environments in the structure.

Automated summary

During the thermal decomposition of hydromagnesite, significant changes were observed in the crystal structure, with lattice parameters showing different trends with increasing temperature. Structural collapse and chemical reactions occurred above 280 degrees C without nucleation and growth of crystal phases up to 425 degrees C.