Abstract
Basic magnesium carbonate, usually 4MgCO3·Mg(OH)2·4H2O, can be crystalized from the aqueous solution by various methods. There are some preceding states of this usual basic salt. In this study, these substances were separated from each other and divided into three types I, II and III in accordance with the characteristics of their X-ray diffraction patterns.
These three types of substances have the composition of 4MgCO3·Mg (OH)2·5H2O and orthorhombic structure. The values of lattice constant a0(and b0) in these types are not very different, but c0 can be calculated as 21.18 Å in type I, 41.10 Å in type II and 62.02 Å in type III, respectively.
Also, these densities are 2.05-2.14 (25°C) and refractive indexes 1.49-1.52 (20°C). The solubilities (25-75°C) are in order of type I<type II<type III. This order is just opposite to that (III→II→I) of the transformation among these types.
In the thermal decomposition process, type I shows three endothermic changes, type II two endothermic changes, and type III two endothermic changes and one exothermic change. Furthermore, the thermal decomposition of type III is resemble to that of the usual basic salt.
