Coprecipitation and Processing of Mullite Precursor Phases

Abstract

Ultrafine powders of aluminum‐rich mullite precursor phases were prepared by spraying mixed acid solutions of silicic acid and aluminum chloride into ammonium hydroxide at different pH values. The aluminum‐rich composition was chosen to avoid abnormal grain growth of the mullite grains caused by silica‐rich liquid phases. The influence of coprecipitation pH on particle size, zeta potential, and the mixing degree of aluminum and silicon in the precipitated powders and on the sintered microstructures have been described. In the basic pH region, the degree of mixing of both components increased as the pH of coprecipitation decreased. Under these conditions, direct slip casting of the coprecipitated slurries was possible, and fine and equiaxed microstructures could be obtained in the sintered bodies.

Preparation of low-cost mullite ceramics from natural bauxite and industrial waste fly ash

“…The mullitization temperature is as high as 1600 • C for the conventional fabrication method, i.e., the solid-state reaction of high-purity Al 2 O 3 and SiO 2 (quartz). But in recent years, some other techniques have been frequently reported in the literatures such as sol-gel, hydrolysis, ultrasonic spray pyrolysis, hydrothermal synthesis and co-precipitation [2][3][4][5][6][7]. The disadvantages of these processes include expensive starting materials, low yields and complicated processing procedures, which are not suitable for large-scale industrial production.…”

Кинетический Анализ Кристаллизации Муллита Из Соосажденных Аммиаком Прекурсоров В Процессе Термообработки

“…Среди способов синтеза муллита можно отметить золь-гель метод, соосаждение дисперсий и др. [4,5]. Эти методы дают возможность получить продукт с высокой однородностью и чистотой, который способен спекаться при пониженной температуре.…”

Formation and Densification Behavior of Mullite Aggregates from Beach Sand Sillimanite

“…Being an extremely rare natural material, commercial mullite products are usually synthesized from various alumina and silica precursors through techniques such as coprecipitation and sol–gel, hydrothermal, and chemical vapor deposition. Alumina precursors include γ‐alumina, 4 aluminum fluoride, 5 aluminum hydroxide, 6 and α‐alumina, 7 or aluminum salts, 8,9 whereas silica sources can be pure natural quartz, 2 cristobalite, 4 amorphous silica, 5 sodium metasilicate (NaSiO 3 ·5H 2 O), 8,9 colloidal, fumed, and precipitated silica, etc 1–3 . However, the mullite products produced from high‐purity reagents/precursors are expensive and not commercially viable for bulk refractory applications.…”