Microstructure and Mechanical Properties of Mullite Prepared by the Sol‐Gel Method

Abstract

Mullite (3Al2O3-2SiO2) of stoichiometric composition was prepared by mixing boehmite sol and silica dispersion and gelling at a pH of 3. Complete mullitization takes place at or above 1300°C. Ultrafine mullite powder prepared by calcining gel at 1400°C and attrition milling could be sintered to >98% (theoretical density) at 1650°C for 1.5 h. Thejexural strength of the sintered body at room temperature was 405 MPa and 350 MPa at 1300°C. Only traces of a secondary phuse were observed along the grain boundaiy. ULLlTE (3A120,-2Si02) is one of the tensivel y studied crystalline phases in the AI2On-SiO2 binary system. Because of the growing interest in using mullite as a high-temperature structural material due to its high creep resistance,' low thermal expansion, and good thermal and chemical stability, different processes of preparationx-'] of high-purity mullite have been tried recently. Except for the mullite prepared by the process given in Ref. 10, others showed low mechanical strength. The main difficulty in the preparation of mullite is to get a homogeneous mixing of Al2O3 and Si02. In the present process the sol-gel technique was employed to get a homogeneous mixing of A120n and S O z . The mullite powder prepared was sintered to >98% of its theoretical density at a tem-CONTRIBUTING EDITOR-E. R. F u L w

Influence of Agglomeration and Contamination in the Course of Amorphous Powder Grinding on Structure and Microstructure of Sintered Mullite

“…14 as well as Ismail et al 17 Both works consider that these phases do not influence the structure evolution of the powders during heat treatment, or its influence is negligible, the same is noted in this study.…”

Development of densification-resistant castable porous structures from in situ mullite

“…Rare in natural occurrences, synthetic mullite can be prepared by three main routes [20,23]: fusion in electric furnaces [19][20][21]26], calcination of chemically prepared precursors [20,27,28] and in situ reaction that generates sinter-mullite [24,[29][30][31][32]. Each process has several variations and produces mullite structures and particles of different characteristics ( Table 1).…”

Preparation and Characterization of Mullite-Alumina Structures Formed "In Situ" from Calcined Alumina and Different Grades of Synthetic Amorphous Silica

“…RFS is the ratio between the experimental results of FS and the theoretical value obtained for a 100% dense sample (for mullite [2][3][4]16,30,34,51 , FS Theoretical = 180 MPa). Such an approach is useful for investigating the mechanical behavior of porous (RD ≤ 50 %) and semi-porous structures (95% ≤ RD > 50 %).…”