SINTERING PROCESSES, PHASE AND STRUCTURE FORMATION AND PROPERTIES OF ELECTRICAL PORCELAIN WITH THE USE OF MARSHALLIT AND WOLLASTONITE ADDITIVES

Abstract

The effect of marshallite upon its complete replacement of quartz and wollastonite additions (2.0 wt.%) on the sintering and phase formation processes, as well as the structure and properties of insulation porcelain was studied. The object of study is insulation porcelain of typical component composition (kaolin, soft clay, feldspar, quartz sand). It has been established that the processes of melting and sintering at firing of the investigated porcelain compositions are not equilibrial. The formation of ternary eutectics fusions of the R2O-Al2O3-SiO2 systems at temperatures of 985 and 1050 °C in amounts of 45–60% does not occur. The formation of a fusion during firing of ceramics occurs due to partial binary eutectics “white feldspar-earth silicon” and “orthoclase feldspar-earth silicon” during the interaction of feldspar with silica-containing components (990–1060 °C). This is due to the fact that primary mullite is formed at temperatures of its stable state above 1200 °C. The actual processes of fusion formation during porcelain firing are not equilibrium. Recrystallization of mullite occurs due to the dissolution of primary mullite in the fusion, followed by crystallization of acicular mullite. Replacing of quartz sand with marshallite leads to a decrease in the temperatures of earth silicon with feldspar interaction and the formation of a primary fusion, which results in a decrease in the ceramics firing temperature by 70° from 1340 to 1270 °C. The addition of wollastonite – CaSiO3 (2 %wt.) intensifies the process of primary mullite dissolution and crystallization of acicular mullite. The length of the mullite needles increases from 2–3 μm up to 7–10 μm, the mullite needles form aggregates, which provides an increase in the bending strength of porcelain by 36% up to 80 MPa. For citation: Vereshchagin V.I., Kurbanbayev M.Ye., Yessimov B.O., Root L.O., Mogilevskaya N.V. Sintering processes, phase and structure formation and properties of electrical porcelain with the use of marshallit and wollastonite additives. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 5. P. 87-98. DOI: 10.6060/ivkkt.20246705.6960.