Formation of anorthite containing cordierite materials through reaction sintering kaolin, MgO and CaO precursors

Smail Lamara,Nouari Saheb,Menad Heraiz,Djaida Redaoui,Foudil Sahnoune

doi:10.2298/sos2002135l

Abstract

The effect of CaO on cordierite formation from kaolin-MgO-CaO powder mixtures, milled for 5 h and reaction sintered for 2 h in the temperature range 900-1400?C, was investigated. Phases formed in the developed materials were characterized by x-ray powder diffraction method (XRD) and Raman spectroscopy. Non-isothermal differential thermal analysis (DTA) and thermogravimetric (TG) experiments were performed from room temperature to 1400?C, at heating rates from 20 to 40?C/min. Activation energies were determined using Kissinger method. It was found that sintering the stoichiometric kaolin-magnesia mixture led to the nucleation and growth of monolithic cordierite; while cordierite along with anorthite were present in the other two samples where 4 or 8 wt% of CaO was added. The increase in CaO decreased cordierite formation temperature and increased the activation energy, which ranged from 445 to 619 kJ/mol for ?-cordierite and from 604 to 1335 kJ/mol for ?-cordierite.

Highlights

It is known that kaolin, a natural clay mineral composed primarily of Al2O3 and SiO2, experiences many reactions and transformations where the oxides and additives react to yield mullite [1] or cordierite [2, 3] based materials
Typical TG/DTG and differential thermal analysis (DTA) resulting curves for DTM08C sample, which was heated to 1300 °C at 20 °C/min, are presented in Figure 1 (a) and (b), respectively
The third 11 wt% mass loss (500–700 °C) is related to change of the dehydroxylated kaolinite to metakaolinite and matches the endothermic peaks at 560 and 568 °C seen in the DTG and DTA curves, respectively

Summary

Introduction

It is known that kaolin, a natural clay mineral composed primarily of Al2O3 and SiO2, experiences many reactions and transformations where the oxides and additives react to yield mullite [1] or cordierite [2, 3] based materials. As one of the main phases of the magnesiaalumina-silica system, cordierite has values of 2.53 g/cm3, 1470 °C, and 10 12 Ω cm for its density, melting temperature, and electrical resistivity, respectively It has very low thermal expansion (values of α betw×ee1n0 1 -6 2 × 10-6 C-1) and conductivity. It possesses satisfactory mechanical characteristics and is very stable in harsh environments [4, 5]. Because of these attributes, cordierite materials are widely used in several industries [4,5,6,7].

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