EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Lithium aluminum silicate (LAS) system is frequently used in many fields of applications due to its low or even negative coefficient of thermal expansion, good thermal shock resistance, high thermal stability, and high chemical durability. However, materials with negative CTE often have low fracture strength because the expansion anisotropy causes microcracking. In order to improve its rigidity, mechanical behaviour and obtaining a CTE close to zero, second phases such as SiC are added to LAS matrix.

Complex shaped parts or large dimension components with low CTE are highly demanded. Nonetheless, the fabrication of big and complex ceramic parts is difficult, require cost effective procedures and time-consuming. In this way, slip casting is considered as a traditional method of manufacturing ceramics into complex shapes. Inter-particle interactions in highly loaded ceramic slurries play a critical role in the forming of ceramic bodies. These interactions at a fixed solids loading depend on the particle size, and/or use of additives that provide steric hindrance. The knowledge of the rheological behaviour turns out to be of great importance in the ceramic industry.

In this work, the dispersion characteristics of LAS-nSiC suspensions has been investigated in terms of their rheological properties. Tetramethyl ammonium hydroxide (TMAH) has been used as dispersant. In order to obtain the minimum viscosity of the suspension, 0.06 wt.% of TMAH is recommended. LAS-nSiC slurries with 55 wt.% of solids have been slip-casted and sintered at different thermal treatments in controlled atmosphere. FESEM, mechanical and CTE properties of the sintered samples have been characterized. LAS-nSiC composite sintered at 1430ºC for 6h shows full density and free-cracked microstructure with a coefficient of thermal expansion close to zero.