Microstructural characteristics, properties, synthesis and applications of mullite: a review

Abstract

Mullite, an intermediate phase of the binary alumina-silica system, is one of the most important phases of ceramic products containing alumina and silica in the initial composition. Its stoichiometry ranges from 3Al 2 O 3 .2SiO 2 (3:2) to 2Al 2 O 3 .SiO 2 (2:1) and its crystalline structure is orthorhombic, characterized by the presence of octahedral chains of AlO 6 interconnected by tetrahedral chains of aluminum-oxygen and/or silicon-oxygen (AlO 4 /SiO 4 ). Properties such as high chemical and thermal stability, low thermal expansion and conductivity, and good mechanical strength enable a wide range of applications. Due to the relevance of this material, it is important for the scientific community to understand its microstructural characteristics, properties, methods of synthesis, and various applications. Therefore, this article aimed to make a comprehensive review on the mullite to gather and present to the reader a series of relevant information that makes it possible to deepen the knowledge about mullite.

Sintering and characterization of in situ formed porous cordierite ceramics with nano boehmite additions

“…Only van Der Waals forces exist between molecules when the water in boehmite is removed, and the original bent whiskers transform into needle‐like morphology, forming the γ‐Al 2 O 3 phase 41 . However, alumina particles with a greater specific area favored the dissolution of Al 3+ ions in the siliceous glass phase, contributing to the nucleation and growth of mullite needles 42 …”

“…41 However, alumina particles with a greater specific area favored the dissolution of Al 3+ ions in the siliceous glass phase, contributing to the nucleation and growth of mullite needles. 42 In addition, the results showed that increasing the nano boehmite additions increased the crystallinity of the in situ formed phases, as shown in Figure 7D,H with 10 µm magnification for microstructure of samples A15 and C33, respectively. This is because of the rapid reaction of active alumina with other oxides at low temperatures, followed by grain growth when sintered at high temperatures.…”

Highly Stable and Robust Mullite Whisker/Silica Aerogels with Exceptional High-Temperature Resistance

“…26,27 Additionally, mullite whisker exhibits a high melting point, excellent oxidation resistance at elevated temperatures, and a low thermal expansion coefficient. 28,29 It has been extensively employed in refractory insulation materials for an extended period of time. 30,31 Yi et al prepared aluminum silicate fiber/mullite whisker/silica aerogel by vacuum impregnation in silica sol.…”

“…Mullite, as one of the stable aluminum–silicon compounds, represents an ideal phase in ceramics due to its exceptional high-temperature resistance, creep resistance, thermal shock resistance, mechanical properties, chemical stability, and dielectric properties. , Additionally, mullite whisker exhibits a high melting point, excellent oxidation resistance at elevated temperatures, and a low thermal expansion coefficient. , It has been extensively employed in refractory insulation materials for an extended period of time. , Yi et al prepared aluminum silicate fiber/mullite whisker/silica aerogel by vacuum impregnation in silica sol . The incorporation of the mullite whisker enhances the compressive strength by a factor of 9.32 compared to the composite without whiskers.…”