A study of the hydration of calcium orthoplumbate. VI.

Observation of the hydration process

Abstract

The following facts were observed regarding the process and products of the hydration of calcium orthoplumbate at various temperatures in an atmosphere of nitrogen-water vapor : i) In the hydration process, the mole ratio of CaO/PbO₂ in calcium orthoplumbate decreased linearly, while that of H₂O/CaO decreased step-by-step with the increase in temperature. ii) The powder which appeared in the hydration process changed in the color parallel with the liberation process of calcium oxide from the anhydrous compound. iii) The composition and nature of completely-hydrated products at various temperature were examined by X-ray diffraction analysis, thermo balance analysis and infrared absorption spectrum. The results of all the methods showed good agreement.
In this paper, the hydration products at various temperature were examined by X-ray diffraction analysis and electron microscopy, and the information thus obtained was used for analyzing the soluble behavior of the calcium oxide from anhydrous compound and dehydration behavior of calcium orthoplumbate hydrates.
The results of present experiment supported the conclusion of the previous paper, and results of electron microscopy and X-ray diffraction analysis agree well with the thermogravimetric analysis and other analysis.
The comparison of the electron micrograph in the present experiment with the thermogravimetric analysis suggests that the dehydrtion of crystalline waterin the hydrate mixture was retarded by the presence of the calcium hydroxide liberated. That is, the behavior of the binding of calcium hydroxide to hydrate is believed as follows : the crystals of calcium hydroxide produced by the hydration link together to form a three-dimensional network and that hydrated calcium orthoplumbate fills up the space existing in the calcium hydroxide network. The three-dimensional network of calcium hydroxide may be a linkage consisting of crystals of a spherical form, as suggested by the results of Sato, because the values of the reaction order in this study agree with those of Sato.