Calcium aluminates

About: Calcium aluminates is a research topic. Over the lifetime, 490 publications have been published within this topic receiving 9200 citations.

A Time-Resolved Neutron and X-Ray Powder Diffraction Investigation of Reactions between Ca12Al14O33, CaCl2, CaBr2 and Water.

Abstract: Etude de l'effet des additifs CaCl 2 et CaBr 2 sur la reaction entre Ca 12 Al 14 O 33 et l'eau. L'hydrolyse est plus rapide en presence de CaCl 2 et CaBr 2 que dans l'eau pure

Some studies on the hydraulic activity of calcium aluminates

Abstract: Calcium aluminates such as CA,CA2 and C12A7 (C=CaO, A=Al2O3) are the important hydraulic phases of high alumina cements having wide refractory applications. In the present study, some hydraulic properties of synthetically prepared CA, CA2 and C12A7 have been studied. The compressive strength results show that development of strength is dependent on curing temperature, time and nature of aggregate. The degrees of hydration values are correlated with the strength development to CA and C12A7.

High temperature processes of phase formation in the system «cement «Gorkal-70» — microsilica»

Abstract: The use of microsilica in the refractory concrete on calcium aluminates cement contributes to the formation of an effective structure and physico-mechanical properties of concrete in linings of thermal units. The features of high-temperature processes in the system "calcium aluminates cement – microsilica", and the formation of the crystalline and amorphous phases are determined by the ratio of components, their mineralogical and chemical composition. The article presents the results of studies of the physical and chemical processes occurring during the thermal heating of model mixtures of hydrated compositions "cement« Gorkal-70 " – mcrosilica." Using the differential thermal analysis and X-ray diffraction, we have studied the effect of low quality microsilica on the mechanism of phase formation and established the mineralizing effect of impurities on the formation of the crystalline and amorphous phases. The article shows the possibility of directional control of the synthesis of anorthite and gehlenite by varying the proportion of the components of the system "cement« Gorkal-70 "- microsilica," which affects the formation of a given structure and properties of refractory concrete.

Si3N4–TiN Composites Produced by Hot-Pressing Silicon Nitride and Titanium Powders

Abstract: Si3N4–TiN ceramic composites have been produced by hot-pressing mixtures of silicon nitride and metallic titanium powders at temperatures from 1600 to 1800°C in a nitrogen atmosphere. We have examined the influence of the concentration and morphology of metallic Ti particles in the starting mixture and synthesis conditions on the microstructure, phase composition, and mechanical strength of the Si3N4–TiN ceramic composites. The results demonstrate that the sintering process ensures complete titanium nitridation, leading to the formation of a nonstoichiometric titanium nitride with the composition TiN0.9. The Si3N4–TiN composites prepared from the mixtures containing 5–30 wt % Ti have densities in the range 3.02–3.41 g/cm3, water absorption from 0.01 to 0.14%, open porosity from 0.03 to 0.44%, and bending strength from 250 to 584 MPa. The Si3N4–TiN ceramics prepared using calcium aluminates as sintering aids consist of dense intergrowths of silicon nitride crystallites, which ensures increased strength of the materials. Moreover, the samples containing 25–30 wt % TiN offer high electrical conductivity.

Interaction between magnesia-spinel refractory grains and cement clinker at high temperature

Abstract: Interaction between cement clinker and refractory grains plays a key role in determining lifetime of refractory bricks. In the current study, magnesia-spinel refractory grains were corroded in cement slag at various temperatures. During the corrosion test, the cement clinker melted at above 1300 °C, and molten slag interacted strongly with the refractory particles. Appearance of calcium aluminates around the spinel indicates the spinel have chemically reacted with molten slag. However, there is no variation of the compositions of slag around the periclase, which suggests no reaction has occurred between the periclase and cement slag. In addition, the reaction products are concentrated in local regions around reacting particles, and the aluminum content in bulk slag does not increase as the concentration of refractory particles increases. Therefore, diffusion of reaction products is much slower than the chemical reaction, and diffusion rate determines overall rate of corrosion.