Effects of Additives on Several Properties of Aluminum Titanate Ceramic

In order to improve the mechanical properties of an aluminum titanate ceramic which has a low thermal expansion coefficient, effects of seven additives were investigated. Some additives dissolved in aluminum titanate (Fig.3), and expelled Al2O2 as fine particles of corundum or reacted with Al2O2 or TiO2 to form fine particles of certain compounds (Table 5). These particles were distributed among grain boundaries of the aluminum titanate and inhibited growth of the grains. The additives were effective to produce a fine grained dense ceramic (Fig.5, 6). Among the additives, ones which did not form large aggregates of highly oriented aluminum titanate particles, i. e., MgO added for oxide mixture (Al2O2+TiO2) and MgO or ZrO2 for alumingm titanate powder, increased the mechanical strength of the aluminum tita nate ceramic markedly (Table 4). SiO2, which formed liquid phases at comparatively high temperature, promoted the densification of the aluminum titanate body, but did not promote the growth of the aluminum titanate grains. The liquid solidified as glassy phase among the aluminum titanate grains, resulting in the decrease in the formation of cracks between the grain boundaries, and the addition of SiO2 also increased the mechanical strength of the ceramic appreciably (Table 4). Despite of their comparatively high mechanical strength (300∼530 kgf/cm2), the aluminum titanate ceramics still kept their low thermal expansion coefficient (1-2×10-6/°C in the temperature range of RT to 1000°C), and did not show any tendency of the deterioration of their excellent properties after the repeated heat treatment (Fig.9, Table 6). Further, the ceramics showed little or no sign of the decomposition to corundum and rutile after heating at temperatures below 1250°C (Fig.10).