Refractory Materials and Products Based on Natural Wollastonite for Making Ceramic Accessories to be Used in Aluminium Industry

Abstract

A new technology has been developed for making refractory products based on the naturally occurring wollastonite (calcium metasilicate) intended for the aluminum industry. The application of natural wollastonite requires no hydrothermal treatment in an autoclave, which considerably simplifies the manufacturing process and reduces its cost. A qualitative comparative analysis of natural wollastonite from different mineral deposits was made to choose an optimal modification with consideration for its availability. The articles were made by using steel-mold pressing, slip casting and vacuum forming methods. For the development of technology for manufacturing large-sized complex-shaped products the slip casting method was used and the slip basic composition was determined comprising 80% of wollastonite as a basic solid phase and 20% of plasticizers. The improvement in the thermal resistance of wollastonite-based ceramics is assured by applying special techniques, namely by addition of course-grained fillers. Thus, addition of about 15% of a course-grained fraction into the fine wollastonite-based slip improves the thermal resistance of ceramics and affords 2-3 times increase in their service life. The efficient way to increase the wollastonite-based ceramics thermal resistance is addition of inorganic fibers. With the use of an inorganic fiber, the materials have been produced with an apparent density ranging from 0.5 to 1.5 g/cm3 and an ultimate compressive strength of 0.5 to 10 MPa. The study has been made into ceramics structure comprising inorganic fibers. The developed materials are chemically inert to aluminum melt. They show no sticking, no mechanical erosion and they are thermal-resistant. With the above methods, the following products are being made on the basis of the naturally occurring wollastonite: spouts, lining plates, heat nozzles, stopper-rod devices, pipes and other articles that have been operating successfully in the aluminum industry of Russia.