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Abstract: The wetting and penetration of two non-stoichiometric cordierite liquids (labelled G1=25wt.% Al2O3, 63wt.% SiO2 and 12wt.% MgO, and G2=20wt.% Al2O3, 64wt.% SiO2 and 16wt.% MgO) on sintered cordierite and mullite substrates were investigated. Their chemical compositions (G1 and G2) correspond to those glasses present in materials sintered from a commercial powder of non-stoichiometric cordierite powder at 1450 or 1400°C, respectively. Sessile drop assemblies for wetting and penetration tests, consisting of cordierite or mullite disks as substrates and pellets of pressed powder glasses positioned above them, were employed. Commercially available cordierite and mullite powders were used to prepare the substrates by uniaxial pressing and sintering at 1450 and 1700°C, 2h, respectively. The glass pellets were prepared by uniaxial pressing of G1 and G2 glass powders. The assemblies were heating at 25°C/min up to 1450 or 1400°C depending on each glass, soaking at these temperatures for 10, 120 or 360min and cooling at 25 and 5°C/min down to 1100°C and room temperature, respectively. The contact angles between each glass and both cordierite and mullite substrates according to the temperature, were determined by heating microscopy technique from optical images. Their penetration behavior of both glasses into cordierite or mullite substrates were also studied analyzing by SEM the microstructures of the specimens transversally cut, polished, and chemically etched. [Copyright &y& Elsevier]

Abstract: The indentation crack profiles under mechanical and thermal stresses of cordierite materials obtained from a commercial powder were studied. Disks were prepared by slip casting and sintering, and they were indented (Vickers; 44.1N; 15s) at the center of one of their surfaces to be subjected to flexion in the mechanical test or to a sudden temperature change in the thermal shock test. Indented specimens were fractured in biaxial flexure (BF) or thermal shock (TS) tests. Some indented disks were thermally treated following two different schedules that involve exposures at high temperatures without (T 1) and with a sudden cooling (T 2). These specimens were fractured in biaxial flexure to observe the fracture surfaces. In all specimens (BF, TS, T 1 and T 2), the evolution of the indentation crack profiles was fractographically analyzed by SEM. In order to study the crack shape and the profile evolution, both the length and the depth of the indentation cracks were measured. [Copyright &y& Elsevier]

The crystallisation of a cordierite non-stoichiometric glass (25wt.% Al2O3, 63wt.% SiO2 and 12wt.% MgO) located in the cordierite crystallisation field in the Al2O3·SiO2·MgO system was studied. Glass fragments were obtained by quenching the melt in cold water. Two granulometric fractions, fine (51.8wt.% < 37μm) and coarse (D50 = 239μm), were prepared by crushing, dry milling and/or sieving. A great tendency to devitrify and a high glass transition temperature (Tg = 830°C) were determined. Temperatures between 940 and 1300°C and times up to 24h were selected in order to crystallise the glass. The crystallisation was followed by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Three exothermic peaks between 970 and 1180°C assigned to μ- and α-cordierite crystallisations with different overlapping degrees depending on both the glass particle size and the heating rate were registered by DTA. No difference was established with respect to the crystallisation mechanism of stoichiometric cordierite glass. However, it was possible to differ the temperature of crystallisation of α-cordierite from both surface and bulk mechanisms. Three non-isothermal methods were used to estimate the activation energy to μ-cordierite crystallisation from both glass granulometric fractions. [Copyright &y& Elsevier]

The sintering behavior of cordierite based materials obtained from powders with different granulometric characteristics (single fractions and binary granulometric mixtures) has been studied. Commercially available cordierite powder was used to prepare these materials by attrition milling, uniaxial pressing and sintering at 1450 °C. The employed cordierite powders were classified as coarse, medium and fine single granulometric fractions. Binary mixtures of them with 30, 50 and 70 wt.% of the smaller component were prepared. Densification degree and kinetics of sintering were studied through density measurements and microstructural analysis (SEM). Phases were determined by XRD and FTIR techniques and examining the isothermal section at the Al2O3–SiO2–MgO system at sintering temperature. The contact angle of the glassy phase present at this temperature was measured using the heating microscopy technique. The characteristics of the starting powders and the particle packing were correlated to the developed microstructures and a sintering mechanism was proposed. [Copyright &y& Elsevier]