MAGNESIUM AND IRON OXIDES INFLUENCE ON SINTERING PROCESSES AND PHASE FORMATION OF ANORTHITE CERAMICS BASED ON NATURAL RAW MATERIALS

Abstract

Ceramic proppants based on silicates and aluminosilicates with various structures are used in the hydrocarbons mining with hydraulic fracturing method. The disadvantage of these known proppants is their high apparent density. Anorthite CaO∙Al2O3∙2SiO2 is a prospective material for proppants production. However, its wide application in this field is restricted due to insufficient knowledge of the MgO-CaO-Fe2O3(FeO)-Al2O3-SiO2 system. Consequently, the physical and chemical processes in the mixes of kaolin and chalk with magnesium oxide and iron(III) oxide additives during firing for anorthite ceramics were studied. It was found that adding of 5 – 10% magnesium oxide in batch for anorthite synthesis leads to obtain ceramics with near-zero water absorption at 1250 °C. Increasing the firing temperature to 1300 °C leads to overfiring of the ceramic and a decrease in its strength. Magnesium oxide reacts with the kaolin to form spinel and forsterite. The highest compressive strength (350 – 390 MPa) is achieved for ceramics with 5% MgO in the batch. The ceramics has fine-grained structure with the grain sizes less than 5 μm. Iron(III) oxide is a weak mineralizer for anorthite synthesis, and its mineralizing effect occurs during the formation of gehlenite-based solid solutions. The sintering process of anorthite ceramics is intensified at 1350 °C due to the melting of the anorthite – iron(III) oxide eutectic. This leads to decrease the water absorption of ceramics with 5 – 10% Fe2O3 in batch to about 2 – 3%. The compressive strength of this ceramics is about 230 – 250 MPa.