Comparison of Physical and Mechanical Properties of Cordierite Based Ceramics Produced from Natural Raw Materials and Synthetic Powders

Abstract

Mechanical and physical properties of cordierite materials produced from natural raw materials and synthetic powders were investigated. Kaolinite, sinter magnesite, talc and pyrophyllite as natural raw materials and Al 2O3, MgO and SiO 2 as synthetic powders were used to obtain the synthetic cordierite. 6 different mixtures were prepared for the selected three target compositions in the Al 2O3-MgO-SiO 2 quaternary diagram. Each mixture was milled in a planetary ball mill followed by pressing in an unaxial press and sintering in an electrical furnace at 1350 o C for 1, 3 and 5 hours. Sintered cordierite bodies were characterized using X-ray diffraction(XRD), Archimedes method and three point bending strength tests. It was shown that the cordierite ceramics produced from natural raw materials had denser structure, finer porosity, lower water absorption and better bending strength than those produced from synthetic powders. In this study, natural raw materials such as kaolinite (Balokesir region, Turkey), pyhrofillite (Malatya region, Turkey), talc (Kars region, Turkey), silica (Aydon region, Turkey), sinter magnesite (Kutahya region, Turkey) and synthetic powders such as alumina (Alcoa), magnesia (Merck) were used to constitute the α-cordierite composition. Six different powder batches with an average particle size of 1 µm were prepared for three target cordierite compositions given in Table 1. The mixtures were designated for natural raw materials as D1, D2, D3 and for synthetic powders as S1, S2, S3 depending on the target compositions. 2% PVA was added to the mixtures as a pressing aid. The mixed and milled mixtures were unaxially pressed at 200 MPa to form cylindrical discs having a diameter of 12 mm, followed by heating in air from room temperature up to 1000 o C at a rate of 5 o C/min. The specimens were sintered at 1350 o C for 1, 3 and 5 hours. The chemical compositions of starting materials are given in Table 1. Two mixtures were prepared from raw