Reaction heat potential utilization in mullite and spinel based ceramics synthesis and sintering

Abstract

Present work studies the potential of the utilization of the heat released from exothermic reactions in ceramic synthesis and sintering. For example the initialization of the endothermic reaction of the mullite formation is studied with heat releasing co-reactions. Exothermically reactive raw material (aluminium powder) is examined for external energy saving ceramic synthesis. KEYWORDS: exothermic reactions, mullite synthesisPrzeanalizowano możliwości wykorzystania ciepła pochodzącego z reakcji egzotermicznej podczas syntezy i spiekania materiałów ceramicznych. Przykładowo zainicjowanie reakcji endotermicznej podczas formowania się mullitu analizowano wraz z ciepłem uwalnianym w reakcjach towarzyszących. Surowy materiał reaktywny egzotermicznie (proszek aluminiowy) poddano badaniom w celu obniżenia energii zewnętrznej niezbędnej podczas syntezy ceramiki. SŁOWA KLUCZOWE: reakcje egzotermiczne, synteza mullitu Porous ceramic materials for high-temperature applications are of great interest today (insulators, catalyst supports, filters etc.). Typically the synthesis of the technical ceramics, such as mullite and spinel based, requires high temperature and long sintering time. Traditional production routes consume a lot of energy and have long processing times, which increases the cost of products and consequently have high environmental burden. Therefore lower external energy requiring processing routes are sought for. Self-propagating High-temperature Synthesis (SHS) is offering one, energy efficient and rapid route for making advanced composites and intermetallic compounds and due to the low external energy consumption, SHS is feasible processing method even for environmental protection [1-2]. The SHS process is traditionally limited only to highly exothermic reactions where the released combustion energy is exploited. However, exothermic assisted synthesis of pure alumino-silicates and magnesium-aluminates based ceramics has very few publications. The utilization of the aluminium powder as the raw material for the mullite synthesis is presented in the studies of H. . In the present study of A. Esharghawi et al. [5] porous mullite-based bodies were produced by SHS starting from the kaolinitic clay, Al and Mg powder mixtures. Pure mullite has not been obtained but Si and Al in metallic phases, quartz, α-alumina and MgAl2O4 spinel were present in addition to the mullite phase. In the study of G. Xanthopoulou and G. Vekinis [6], MgO/MgAl2O4 refractories were produced by SHS resulting the spinel content up to 100%. The starting materials included Al and Mg powders mixed with various oxides and salts. Experimental procedureIn this study, the endotermic reaction of the synthesis combined with the in-situ exothermic reactions are examined and compared to the traditional sintering. Kaolin (Al2O3·2SiO2·2H2O), aluminium oxide hydroxide (AlO(OH)) and aluminium (Al) powders were selected as raw materials for the stoichiometric 3:2 mullite (3Al2O3·2SiO2) synthesis. Magnesium hydroxide (Mg(OH)2), aluminium oxide (Al2O3) and Al...