Characterization of microstructural and thermal properties of the steatite powders applied as fillers in the ceramic coatings

Abstract

Steatite is a magnesium silicate multi-componential composite that can be synthesized from natural raw materials, and eventually produced via standard ceramic processing methods and readily machined or sintered into a variety of forms. Due to its excellent electrical properties, high mechanical resistance, low dielectric loss and high temperature resistance, steatite is widely utilized as a material for thermal insulation and heath protection. The raw materials used in steatite powder synthesis are: talc mixture for calcination, clay minerals as bonding agent, and feldspar or BaCO3 as melting agents. The synthesis is usually conducted at approximately 1400°C, and its product is a crystalline phase of magnesium metasilicate (MgSiO3 ) obtained from talc, while melting agent forms a vitreous phase which melts and surrounds the crystalline phase. Steatite ceramics’ fillers were fabricated via combined method of high-energy ball milling, cold pressing and sintering. The powder blends containing same amounts of components in all 4 mixtures were dry-pulverized for 30 min a laboratory mill, with ceramic vial and ceramic balls. After milling, the powders were compacted to cylindrical tablets with a diameter of 25 mm by uniaxial compression at 4 tons/cm2 . The green compacts were sintered at 1000-1400°C (10°C/min) for 2 h in an air atmosphere. The effect of dry grinding on phase, microstructural and thermal properties of the sintered tablets were carried out by using X-ray diffraction technique (XRD), thermogravimetry/differential thermal analyzer (TG/DTA) and scanning electron microscope (SEM). The effects of grinding on the change of the particle diameter, crystallinity and the phase transformations, and reactivity of the powders were studied. The powders that were pulverized for 30 min showed properties which positively influenced on the decrease of sintering temperature and the increase of the sintering rate of steatite fillers.