Effects of alumina on the stability of ferrite–calcium sinter with dicalcium silicate

Laboratorial production of agglomerate with basicity CaO/SiO2 = 1.3-1.5 is accompanied by its spontaneous friability, what leads to forming of visible cracks in agglomerate. When studying the influence of these sintering parameters on agglomerate strength, it is necessary to take into account content of not assimilated calcium oxides in sinter. Strength binding of agglomerate is formed on the base of calcium ferrites. Investigations were conducted on aluminium oxide of PA grade, Fe2O3, CaCO3 of PA grade, aqueous silicic acid of P grade. Stability of sinters for above-mentioned systems was determined visually and using high-frequency method. In the first case the hightemperature Tamman furnace is used, where briquetted samples are put in a platinum cup and they are heated up to the temperature 1300 °C. Then, after 5 minutes holding for homogenization, the samples are cooled slowly together with the furnace to the temperature 500 °C. To determine the temperature of β→γ transition of dicalcium silicate, dielectric permeability is measured; it reacts on structural changes which cause variation of density. The boundary of sinters stability is situated along the line which is close to galenite. The part of aluminium oxide interacts with dicalcium ferrite and forms solid solutions together with complete Fe replacement by Al in dicalcium ferrite. Stable sinters are characterized by monotonous variation of dielectric losses and capacity in the conditions of complete dicalcium silicate binding by aluminium oxide. It was established that monocalcium ferrite does not form new compounds with aluminium oxide, which completely interacts with dicalcium silicate. The stable samples of the system CaFe2O4–Ca2SiO4–Al2O3 are characterized by increase of alumosilicate amount and decrease of dicalcium silicate amount. When Ca2SiO4 content decreases from 45 % to 28 %, the temperature reduces from 390–405 °C до 265–275 °C. Agglomerate containing 7 % of alumina practically does not contain free calcium oxide, what removes the cause of stresses appearing in the sinter. As a result of stabilization of ferrite-calcium sinter via replacement of silicon module by aluminium one, compression strength value increases up to 235 daN for a briquette.