The reaction of lanthanum bromide oxide (LaOBr) with water vapour was investigated by thermogravimetric analysis in the temperature range 323-358 K and in the relative humidity range 80-98%. The influences of temperature, water partial vapour pressure and relative humidity on the reaction were studied. A Fourier transform infrared spectrometer and an X-ray diffractometer were used to determine the reaction intermediates and products. Microscopic observations of the samples were made with a scanning electron microscope as the reaction proceeded. Lanthanum bromide hydroxide monohydrate [LaBr(OH)2 · H2O] was identified as a final product. The reaction is an auto-catalytic one. A model of the reaction mechanism is proposed, consisting of several steps: (a) adsorption of water vapour and the formation of a water film, (b) formation of La(OH)+2 and Br- ions in the water film and (c) nucleation and crystal growth of LaBr(OH)2 · H2O. The proposed model explains the various features of reaction very well.
ASJC Scopus subject areas