Thermal decomposition of nanoparticulate Ca(OH)₂-anomalous effects

The degree of crystallinity and particle size of Ca(OH)₂inclusions in a hydrated cement matrix influence their rate of dissolution in aggressive media such as distilled water. Durability of cement-based systems (e.g. resistance to leaching and carbonation) is generally dependent on the dissolution characteristics of the products – a process leading to increased permeability and porosity. Relevant features of nano-scale Ca(OH)₂particles are explored using thermal analysis. Different forms of Ca(OH)₂with varying degrees of crystallinity and surface area were prepared using Ca(OH)₂and CaCO₃as starting materials. They were decomposed and the hydrated CaO formed at different conditions. The nitrogen surface area values of Ca(OH)₂ranged from 3.7 to 31.1m²/g. The presence of two separate and distinct thermal decomposition events (in derivative form of thermogravimetric analysis results) was observed, depending on the degree of crystallinity. Endotherms occurred at temperatures of about 426°C and 454°C. Binary mixtures of Ca(OH)₂with substantially different degrees of crystallinity exhibited a well-defined thermal decomposition doublet. The height of each endotherm peak was dependent on the mass proportions of each mixture component. Factors, including thermodynamic considerations, affecting the character of the decomposition behaviour of Ca(OH)₂are discussed.