The composition and place of origin of the phases in portland cement clinker

When considering the phase composition of clinker should take into account the conditions of its formation. When firing the raw material batch contained therein impurities and ash fuels are unevenly distributed, resulting in variable composition produced clinker phases. They are characterized by the formation of solid solutions that can be placed in their crystal lattices involved impurity atoms under the conditions of their compensation charges. The components are solid solutions of alkalis, magnesium oxides, chromium, titanium, phosphorus and others. In the firing process, the stabilization of alite monoclinic. The greatest ability to involve the impurity atoms in the lattice has aluminates and calcium alyumoferrity; belite (6%) and alitame (about 4.8%).

Recognized called clinker phases by name of source of minerals - phase alite, belite phase. Alyth - phase tricalcium silicate C3S. One of the most important in the chemistry of cement lime and silica compounds is tricalcium silicate C3S. It is stable in the temperature range from 1523 to 2343 K at which melts with decomposition (incongruently) for the melt and the CaO; it can be formed by first crystallizing from a three- or four-component melt containing aluminum and iron. In this case, you can not get a clean crystal C3S, for their solid solution containing a small amount of calcium aluminate and ferrite. SM Rojaka and O. K. Aleshin observed C3S formation at 1273-1473 K in the area of ​​solid phase reactions in a layer of about 1.mu.m thickness around grains of CaO and less than 1% by weight of the material. This layer serves as a seed for the bulk of alite, crystallizing in the liquid phase at 1723 K. A method of producing from lime and C3S silica in the calcium chloride melt; After cooling, the melt is treated with alcohol and water vapor at 873 K. C3S may be formed by solid-phase reaction between silicic acid and lime at temperatures of 1723 - 1873 K; at 2073 K - reaction proceeds at a higher rate. However, this reaction requires a multiple firing micronized intermediate. Only under these conditions it is possible to obtain C3S, containing no free lime.

Belit - phase of dicalcium silicate (C2S) exists in four versions. In the study, by etching some reagents polished thin sections of Portland cement clinker in the reflected light much like a bright and a dark prismatic intermediate substance. Both of these components differ in reflectivity. Light intermediate substance having the highest reflectivity, calcium alyumoferritami presented with a high refractive index, as well as highly enriched iron glass. Dark prismatic intermediate substance with a lower reflectance is tricalcium aluminate clinker and glass, which is due to the rapid cooling has not had time to crystallize. Intermediate substance clearly emerges during etching polished section surface for 1 second at 20 ° C with a special solution of sulfuric acid in ethanol. With other reagents it is possible to distinguish phases iron, including iron-enriched glass, tricalcium aluminate, and others.

calcium Alyumoferrity. Crystals of calcium alyumoferritov characterized by a prismatic or rounded shape, they are yellowish-brown to dark brown or even black. Previously believed that the chemical composition of clinker alyumoferritpoy phase, named for the explorer brownmillerite, C4AF.

Tricalcium aluminate - dark interm appearing in the presence of alkali in a prismatic form, and if not - a rectangular. Despite the presence of etchant determination of the content of tricalcium aluminate clinker due to the difficulties. OM Astreeva and LY Lopatnikova developed a quantitative method for determining the immersion C3A in the clinker via staining. Particularly finely divided powder to stain a special clinker alcoholic solution of an organic dye "acid bright blue." As a result of intensively painted only C3A crystals, which allows to determine their content.

Tricalcium aluminate unstable. It forms Ci2A7 under firing cement clinker in the composition at a content of raw mix mineralizer - calcium fluoride or silicofluoride sodium, calcium or magnesium, as well as in the presence of calcium sulphate mineralizatora-. The crystal structure of C3A still not precisely defined. It is believed that the C3A Al + 3 ions in the centers of the sides of the unit cube in the correct order are surrounded by six oxygen ions. Other ions Al3 + in the centers of the faces cover the flat ring of four ions of oxygen. In the structure, there are two types of Ca2 +: one located in the corners of the cube, properly coordinated to six oxygen atoms, while others are grouped in small cube inside the structure correctly coordinated nine oxygen atoms. For the structure generally characterized by the presence of impurities in the crystal lattices of the voids having a size of about 1.7a. In industrial MgO clinker contains 2.5% by weight C3A dissolves to 9% Na2O; observed as the dissolution of minor amounts of Si02. For C3A characterized by the absence of polymorphism.

Pyatikaltsievy trehalyuminat. This compound is a Portland cement clinker as a separate phase does not crystallize. It dissolves in the glassy phase or part of the calcium alyumoferritov. The existence of metastable phase, which is present in the clinker obtained at extremely rapid firing.

The glassy phase. In sharp instantaneous cooling (freezing) the liquid phase of the clinker is theoretically possible content windows can reach about 25%; almost same vitreous phase in the clinker much less because in the real world it is cooled at an average speed. The glassy phase formed as a result of nonequilibrium conditions during melt crystallization clinker cooling.