Negative Thermal Expansion Occurs in a Bauxite-Based Aluminum Borate Ceramic Whisker with a Nanofiber Microstructure

摘要

Whisker-like microstructured ceramic was synthesized using bauxite [Al(OH)(3)] raw material and boric acid (H3BO3). Stoichiometric (Al18B4O33) and non-stoichiometric compositions were prepared through a ceramic route or a solid reaction method, respectively. The suggested compositional design resulted in two crystalline phases: aluminum borate (Al20B4O36) and alpha-corundum (Al2O3). An increase in the B2O3/Al2O3 ratio led to the formation of the aluminum borate phase rather than the alpha-corundum phase; however, in general, an increase in the ratio corresponds to an increase in the alpha-corundum phase. The studied microstructure was characterized as interlocking wire-like and fiber-like crystals that form whisker-like textures. The densities of the sintered samples were between 3.2340 and 2.7474 g/cc, and in general, density decreased as the aluminum borate phase increased. The coefficient of thermal expansion ranged from - 3.73 to 3.79 x 10(-7)/degrees C (20 degrees C to 500 degrees C), which demonstrates the outstanding physical properties of the ceramic. (C) The Minerals, Metals & Materials Society and ASM International 2018