NEW DATA ON KINETICS OF TOPOCHEMICAL REACTIONS OF CARBONATES DISSOCIATION

Shamshurov V.M., Timoshenko T.I.

Belgorod State Academy of Building Materials, Kostukov Str. 46, Belgorod, 308012, Russia, rms13@rprog.belgorod.su

The searching of the new theoretical and experimental approaches to a research of a kinetics of topochemical responses of expansion of carbonates is actual, in view of uniqueness of properties of yields, obtained from them, of a burning, presence of huge stores and simplicity of development of quarries, wide use them all over the world as basic initial components in such multitonnage power-consuming industries, as building materials, cement, fire-bricks.

With the help of original high-temperature x-ray diffractometer with a horizontal disposition of a plane of a sample, have established essential difference of a kinetics of processes of a dissociation of dolomites from conventional - two stage.

Research subjected natural dolomites of various deposits essentially distinguished on morphology, chemical structure and presence in them of impurity. Shooting have carried out from a surface of the condensed stratum of a powder of a dolomite by a thickness of 0.5 mm (fig. a) and from a surface of test protected from interaction with an atmosphere of the furnace by a beryllium plate (fig. b). The plate from a beryllium, thickness of 0.2 mm, practically did not hinder with passage of x-ray rays, but ensured modelling of processes of topochemical responses of a dissociation of dolomites in rather massive samples.

Experimentally is established, that the process of expansion of dolomites in conditions of small volume of researched substance passes in one stage CaMg(CO₃)₂ - > CaO + MgO +2CO2, and completely is finished with temperatures on 150-200 degrees below. In similar conditions the dissociation of carbonates happens as with noticeably reduced (on 250-300^o) temperatures, as against earlier established. The outcomes of work are confirmed also by other methods of researches, in particular, differential - thermal analysis.

The carried out researches give a foundation to make the following conclusions:

- the mechanism of expansion of a dolomite taking place in rather small volumes researched substance is established which with a burning dissociates one stage - simultaneously on CaO and MgO since 500, and completely is finished to 750 ^oC;

- the established mechanism of expansion of a dolomite essentially differs from known - two stage, which happens only in rather massive samples;

- the applied principle of use for researches is minimum possible mass of substance, essentially corrects temperatures of expansion of carbonates. So, the expansion of a magnesite (MgCO₃) happens in an interval of temperatures 400 - 470 ^oC (literary datas 640-710 ^oC), and calcite (CaCO₃) with 530 - 590 ^oC (812-928 ^oC );

- will allow deeper to understand and to explain processes which are taking place with a burning of dolomite fire-resistant materials, and as processes of a dissociation of carbonates with their burning, as separate and in structure portland-cement and other technological mixtures;

- will predetermine a possibility to development theoretically justified and controlled, more low-temperature and ecologically of pure process engineering.