Low thermal expansion materials based on Al2TiO5 ceramics are of great importance because they can be mixed with other materials having positive thermal expansion coefficients to make composites which have a zero or negative thermal expansion coefficient. Zero level thermal expansion materials based on Al2TiO5-ZrTiO4 (ZAT) composites up to 1000ºC were synthesized by reaction sintering. The ZAT composites also had a much lower thermal expansion coefficient (0.2~1.3×10−6/K) than that of polycrystalline Al2TiO5 (1.5 × 10−6/K). These low thermal expansion coefficients are apparently due to a combination of microcracking caused by the large thermal expansion anisotropy of the crystal axes of the Al2TiO5 phase. The thermal properties of the ZAT composites were analyzed after various thermal treatment by scanning electron microscopy, X-ray diffraction, and a dilatometer.

Keywords: negative thermal expansion, Al2TiO5, ZrTiO4, anisotropy, grain-boundary microcracks