Organic acids effect on crystallization kinetics of cordierite obtained by diphasic gel

Resumo

α-Cordierite (Mg2Al4Si5O18) was obtained, by a sol-gel aqueous route, from aqueous solutions containing Si:Al:Mg in a molar ratio equal to 5:2.15:2.25 and citric (Lcit samples), or oxalic (Lox samples), or tartaric acid (Ltart samples), in such amount that the molar ratio organic acid/aluminum ion was equal to 1. The effect of each organic chelating upon the quantity of crystallized α-cordierite was investigated. The influence of a heating treatment time, to eliminate the organic material from the xerogels containing citric acid, on the quantity of α-cordierite formed was also investigated. Thermal gravimetric analysis was used to investigate the thermal decomposition process of each sample. Based on thermal gravimetric results we suggest that the thermal decomposition of the Lcit, Lox and Ltart xerogels takes place in three major steps and little difference was observed for each case. X-ray diffraction (XRD) measurements were carried out to determine the crystalline phases present after heat treatment of each sample at 1000 °C. X-ray diffraction results showed that the sequence for the quantity of crystallized α-cordierite from each sample is: Lcit > Lox > Ltart. XRD results also indicate that the quantity of crystallized α-cordierite from samples containing citric acid (Lcit) increased with the time of the heating treatment used to eliminate the organic material. © 2002 Elsevier Science B.V. All rights reserved.