Investigation of endothermal doublets occurring in the thermal decomposition of Ca(OH)2

The presence of at least two different forms of Ca(OH)2 is confirmed by the results of a thermoanalytical study on the decomposition and re-hydration characteristics of Ca(OH)2. The study comprised a series of differential scanning calorimetry (DSC) experiments (at temperatures up to 700\ub0C) performed in an atmosphere of a continuous flow of nitrogen pre-conditioned to various relative humidities ranging from 12 to 100%. The emergence of two separate and distinct decomposition endotherms occurred. The endothermic peak temperatures were dependent on the relative humidity and temperature history of the Ca(OH)2 samples. Exposure of CaO to higher temperatures and different humidities would appear to promote the formation of both crystalline and microcrystalline products. Under these conditions, higher temperatures give rise to formation of very crystalline products and after some time, vapor phase exposure promotes the formation of microcrystalline products. Factors affecting the formation of the different forms of Ca(OH)2 are described.La pr\ue9sence d?au moins deux (2) diff\ue9rentes formes de Ca(OH)2 est confirm\ue9e par les r\ue9sultats d?une \ue9tude thermoanalytique portant sur les caract\ue9ristiques de d\ue9composition et de r\ue9hydratation de Ca(OH)2. L?\ue9tude comportait une s\ue9rie d?exp\ue9riences d?analyse calorim\ue9trique \ue0 compensation de puissance (\ue0 des temp\ue9ratures allant jusqu?\ue0 700 \ub0C), r\ue9alis\ue9es dans une atmosph\ue8re form\ue9e d?un flot continu d?azote pr\ue9conditionn\ue9 \ue0 diverses valeurs d?humidit\ue9 relative allant de 12 % \ue0 100 %. Deux (2) endothermes de d\ue9composition s\ue9par\ue9s et distincts ont \ue9merg\ue9. Les temp\ue9ratures des pics endothermiques \ue9taient tributaires des ant\ue9c\ue9dents d?humidit\ue9 relative et de temp\ue9rature des \ue9chantillons de Ca(OH)2. Il semblerait que l?exposition de CaO \ue0 des temp\ue9ratures plus \ue9lev\ue9es et \ue0 diff\ue9rentes valeurs d?humidit\ue9 favoriserait la formation de produits tant cristallins que microcristallins. Dans ces conditions, les temp\ue9ratures sup\ue9rieures entra\ueenent la formation de produits tr\ue8s cristallins, et apr\ue8s un certain temps, l?exposition \ue0 la phase vapeur favorise la formation de produits microcristallins. On d\ue9crit les facteurs qui influent sur la formation des diff\ue9rentes formes de Ca(OH)2.Peer reviewed: YesNRC publication: Ye