Endothermal peaks calcium hydroxide

Flame retardant polyurethanes are mostly manufactured with compounds of phosphorus, such as ammonium phosphate or polyphosphate. Aluminum hydroxide alone or in combination with melamine is an alternate approach. In intu-mescent applications, graphite is frequently used. Calcium carbonate is useful as a flame retarding additive, in combination with other flame retarding materials, because of its large endothermic peak found in DTA curves. 

It is important to acquire information on the hydration processes that occur when cement is subjected to low temperatures. Even at temperatures below zero cement hydrates slowly, as water does not freeze due to the presence of soluble materials in the pores. The products that form at low temperatures are calcium aluminate hydrates at earlier periods and after several months, the products of hydration of tricalcium silicate. A weak endothermal peak at about 330°C could be due to the presence of silica gel and this is preceded by the appearance of calcium hydroxide and C-S-H gel.t l... 

The carbonation effect on synthesized tobermorite has been examined by XRD / DTA.I ] An endothermal effect at about 180°C indicated the dehydration of tobermorite and an exothermal effect at about 800°C was caused by the formation of wollastonite. The carbonated samples exhibited a broad endothermal effect in the range of 450-600°C and a sharp peak at about 600-650°C. The former indicated the presence of vaterite and the latter, calcite. The carbonation decreased the peak due to wollastonite. Thermal methods can also be used to estimate the amount of carbonation that has occurred at different depths in concrete. These techniques estimate the amount of calcium carbonate formed and also the amount of calcium hydroxide remaining in an uncarbonated form. 

Problem. A finely ground sample of hardened concrete is to be investigated by DTA analysis. The pmpose of the analysis is, among others, to determine the degree of carbonation of the concrete sample (see example 1.4). The content of calcium hydroxide Ca(OH)2 in the sample shows as an endothermic peak starting around 500°C. This peak occurs because heat is consumed for the dehydration of Ca(OH)2 by the reaction... 

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