Alumina calcium refractory cement

Alumina calcium refractory cement

The raw materials used to produce refractory cement or calcium alumina refractory cement are mostly bauxite and limestone. The use of high-iron bauxites, refractory cements, and low-iron bauxites produce low-iron cements. For high purity refractory cement, limestone with low percentages of impurities with alumina from the waste process is used.

Currently, the alumina cement that is marketed is classified into five groups according to its chemical composition. The table below shows the chemical composition of the main refractory cements of several countries.a

1. Group A includes high-calcium calcium alumina refractory cement such as fondue and uminaire cements
   Group B with lower iron than group A and both groups A and B are according to the second type (2) calcium aluminate refractory cement mentioned in the table above.
   Group C Low iron calcium alumina refractory cement (medium purity), according to the first type of cement (1).
   Group D Calcium refractory alumina cement is high purity alumina grade 70%, for example, alumina cement above Denka and Secar-71 Lafarge.
   Group E High-purity calcium alumina refractory cement with about 80% alumina, such as Denka super alumina cement, Alcoa CA-25, and Lafarge Secar-80.

   In these cements, in order to obtain high reactivity with water, strength and installation ability are very fine in terms of granulation. Depending on the specific surface area, the fineness of these products or blades is usually between 2500 and 5000 cm2 / gr. In alumina-rich cements, this number may reach 7000 to 10,000 cm2 / gr.

   Types of phases in calcium aluminate refractory cement and their general properties

   The differences between the constituents of alumina cement and Portland cement are expressed in the three-phase diagram Al2O3 -SiO2 -CaO. Refractory cements are mainly composed of Al2O3, SiO2 and CaO in terms of chemical composition and their degree of refractory varies according to the amount of alumina and impurities in the cement. The mineralogical composition of cements is shown in the Al2O3.SiO2.CaO ternary fuzzy diagram.

Ordinary Portland cement is located in area 1 of the three-phase diagram and is considered a component of calcium silicate (SiO2.CaO). Figure 2 shows this diagram of refractory cement with the composition of calcium alumina (Al2O3.CaO).

Portland cement is relatively high in the CaO region and phases C2S and C3S are the main phases. On the other hand, calcium alumina refractory cement is located in an area with a lower CaO content, a factor that makes this cement to be used as refractory cement. CA is the main phase of calcium alumina refractory cement and also includes phases C12A7, C A 2 and / or C2AS or C4AF, C6A4FS or a glass phase.

The following figure shows a two-phase diagram of Al2O3.CaO. In this diagram, five phases of calcium alumina are identified as C12A7, C3A, CA2, CA, CA6.