Mechanical Activation of the Decomposition and Sintering of Kyanite

Abstract

The influence of attrition milling on the thermal decomposition of kyanite (Al2O3·SiO2) to mullite (3Al2O3·2SiO2) and SiO2, and its subsequent sintering, was studied. A commercial kyanite was attrition‐milled for times up to 12 h. Dilatometry confirmed that as‐received unmilled kyanite decomposes between 1300° and 1435°C. The decomposition reaction is slow initially and accelerates during the later stages until about one‐half of the decomposition occurs in the last 35°C. For the attrition‐milled kyanite, the onset decomposition temperature decreases, the transformation temperature interval is reduced, and both the decomposition reaction and subsequent sintering are accelerated. A dense microstructure of fine equiaxed mullite grains in the 1 μm size range, evenly dispersed in a glassy matrix, is obtained by sintering the attrition‐milled kyanites. These results are explained in terms of the energy accumulated during attrition milling, a reduction of the milled kyanite particle size, and the presence of a liquid phase during sintering.

Thermal Shock Resistance of a Kyanite-Based (Aluminosilicate) Ceramic

“…Note that their morphology changes to a tabular one with rounded edges at elevated temperatures. This is consistent with microstructural descriptions from other studies [9]. The SEM images also revealed that sintered compacts produced from larger particle sizes result in larger pore sizes than those produced from smaller particle sizes, Table 4.…”

Near‐net‐size preparation of porous mullite matrix ceramics with in situ formed 3D mullite whisker network

“…In comparison, the main crystalline phases of the specimens with MoO 3 pretreated at 1150°C are α‐Al 2 O 3 , cristobalite (SiO 2 ), mullite, and traces of kyanite. Among these phases, cristobalite (SiO 2 ) and mullite are from the decomposition of kyanite (Kyanite (Al 2 O 3 ⊕SiO 2 ) decomposes into mullite (3Al 2 O 3 ⊕2SiO 2 ) and SiO 2 ) 17 . It was reported that the decomposition of kyanite and transformation to mullite took place between 1200 and 1400°C 18,19 .…”

Dehydration-Rehydration Characteristics of Gibbsitic Bauxite under Equilibrium Condition

“…2 When bauxite is heat treated at an elevated temperature, dehydration reaction takes place with gradual expulsion of water molecules through the intermediate formation of several metastable transition phases like chi (), eta (), gamma (), delta (), iota () theta (), kappa (), beta (), etc with progressive variation in crystallographic nature, specific surface area and grain morphology until the most stable form of alumina, corundum (-Al 2 O 3 ), is obtained. [3][4][5] Similarly, the dehydration-rehydration characteristics of cordierite-alumina composite precursor derived through semi-colloidal route have been reported to be very much dependent on dehydration temperature, relative humidity of the environment and alumina content of the composite precursor. 6 The present investigation deals with the careful study of dehydration-rehydration behaviour of gibbsitic bauxite rock of Indian origin with respect to variation of heat treatment temperature and relative humidity of the environment.…”