Mechanical and thermal properties of boehmite bonded alumina bodies

Abstract

Abstract The paper describes the fabrication and the properties of boehmite bonded alumina shapes. The term boehmite bonding refers to the utilization of steam cured reactive alumina as an intermediate binder in alumina shapes. Bodies were prepared by mixing tabular alumina. After drying the shapes were treated in an autoclave at around 200°C and saturated steam pressure. During steam treatment the reactive alumina is converted to boehmite, γ-Al 2 O 3 · H 2 O. Cold crushing strength figures up to 1200 kp/cm 2 have been obtained. Relations between mechanical properties and porosity have been examined. The paper gives details on reaction kinetics of the formation of boehmite as well as the dehydration of boehmite at around 500°C. Boehmite dehydrates to γ-alumina at 500–520°C. Due to the high reactivity of the so formed γ-alumina, ceramic bonds are formed at low temperatures. Therefore the conversion from boehmite to γ-alumina is followed by only a slight decrease of the strength. The dehydration process has been followed by means of surface area and pore size distribution measurements and X-ray diffraction and DTA-TGA investigations. The boehmite bodies have been subjected to normal refractory testing procedure i/e hot modulus of rupture, Youngs modulus, creep, refractoriness under load, resistance to slag attack and spalling. The testing shows that the boehmite bonded ceramics have refractory properties comparable with those of normal fired chemically bonded bricks. The boehmite bonding method have also been tested on aluminosilicate, i/e cyanite, with good results. Possible applications of the method are discussed in the paper.