The Synthesis Of Non-Stoichiometric Cordierite Via Glass Ceramic Route Using Calcined Talc And Kaolin
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Date
2011-06
Authors
Johar, Banjuraizah
Journal Title
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Publisher
Universiti Sains Malaysia
Abstract
Various non-stoichiometric cordierite compositions were synthesized via glass route. Densification and crystallization behavior of the glass were determined by dilatometry and differential thermal analysis, while phase transformation of glass to glass-ceramic by X-ray diffraction. CTE, dielectric properties, density and porosity percentages as well as the microstructure of glass-ceramic were carried out to correlate its variation with the compositions. 100 wt% α-cordierite phase with the density 2.54 g/cm3, porosity 0.4% has succesfully being obtained at lower heat treatment temperature of 900oC for 2 hours using non-stoichiometric cordierite compositions synthesized from mainly calcined talc and kaolin as initial raw materials. This demonstrates that this composition is suitable for LTCC application. The CTE (2 x 10-6 C-1), dielectric constant (5.5) and dielectric loss (1.6 x 10-2) obtained are also fulfilled the properties required for high frequency application. Partially amorphous phase in initial glass powder should be avoided since it will significantly affect the densification and crystallization behavior of the glass. α-cordierite synthesized from minerals as raw materials has a comparable properties with the one synthesized reagent grade oxide. Although it has slightly lower degree of crystallinity and high dielectric loss, however it has lower densification and crystallization temperature as compared to composition synthesized from the reagent grade oxides. The addition B2O3 and P2O5 are effective in reducing the softening temperature but not necessarily enhance the crystallization process. The addition of B2O3 and P2O5 is only effective for samples in the series xMgO.2Al2O3.5SiO2 with lower MgO mole. It is also a very important to melt the mixtures of compounds above its melting point before crystallize since glass plus glass-ceramic in the same system would not facilitate densification due to its relatively high kinetic barrier within the system.
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Non-stoichiometric cordierite compositions synthesized , from mainly calcined talc and kaolin