Montmorillonite (M) saturated with H+,Li+,Na+,K+,Rb+,Cs+,NH4+,Mg2+,Ca2+,Sr2+,Ba2+,Mn2+,Co2+,Cu2+,Al3+ and Fe3+ were dry-ground with urea (U) in mass ratios U/M between 0.1 and 2.0 in an agate mortar and diffracted by X-ray. Extensive swellings occurred with H-, Li-, Na-, di-and trivalent
cation-clays, suggesting the formation of urea-montmorillonite intercalation complexes. Mechanochemically treated samples
were heated at different temperatures up to 375°C. The rise in temperature was accompanied by a decrease in the basal spacing.
There was a correlation between the results of the thermo-XRD-analysis and the fine structures of the urea-montmorillonite
complexes described in the literature. Five stages in the basal spacing vs. temperature curves were identified. In the first stage (at 150°C) the decrease was due to dehydration. In the second stage
(175°C) this dehydration was accompanied by some thermal intercalation of excess urea. The other stages (at 225, 325 and 375°C)
were associated with the degradation of urea and the condensation of the degraded species to polymeric products. At 375°C
Li-, Na-, K-NH4-, Mh-, Co- and Cu-montmorillonite collapsed, indicating that urea was evolved. The other urea-clay complexes did not collapse
due to intercalated polymers formed by the degradation products of urea.