Synthesis of Alkali Aluminosilicates — Materials for Alkali Contaminated Environments at High Temperatures

Alkali corrosion has become a problem in industrial furnaces especially because of the increasing use of secondary fuels. In the corroded lining material alkali aluminosilicates such as kalsilite, leucite or nepheline could be identified. According to ternary phase diagrams these substances have very high melting points which would make them suitable for high temperature applications in alkali corrosive environments. This study presents systematic synthesis experiments to produce alkali aluminosilicates by thermal (800°C, 1000°C, 1200°C) and hydrothermal (200°C) treatment starting from the nominal compositions of KAlSi ₂ O ₆ , KAlSiO ₄ , and NaAlSiO ₄ ., KOH NaOH, quartz powder, and Al(OH) ₃ were used as raw materials. The phase composition was analyzed by using X‐ray diffraction (XRD). The alkali corrosion was tested using alkali salts as corrosive substances. The synthesis experiments resulted in multiphase reaction products. The hydrothermal method yielded only for the initial composition according to the stoichiometry of KAlSiO ₄ crystalline phases of the same composition. The thermal method produced for all sets of synthesizing parameters mixtures of stoichiometric and nonstoichiometric alkali aluminosilicates. In the corrosion test, material of the nominal composition of KAlSiO ₄ showed the best results. The material was corrosion resistant independently from the initially applied synthesizing parameters.