Enhancing the green mechanical strength of colloidal silica-bonded alumina castables using a silane coupling agent

Abstract The use of colloidal silica as a binder for refractory castables has attracted great interest in recent years. Nevertheless, the resultant low green mechanical strength of colloidal silica-bonded castables has hindered their application in relevant areas. A silane coupling agent, 3-methacryloxypropyltrimethoxysilane (CH 2 =C(CH 3 )COOC 3 H 6 Si(OCH 3 ) 3 ), normally called KH-570, has been added to colloidal silica-bonded alumina castables to enhance their green mechanical strength. The results show that KH-570 has a positive effect on the green mechanical strength improvement of colloidal silica-bonded alumina castables. The reaction between hydration products of KH-570 and the solid particles of colloidal silica (confirmed by Fourier transform infrared spectroscopy (FTIR)) could promote the formation of an organic-inorganic interpenetrating network structure, which is the main reason for the green mechanical strength improvement. Meanwhile, the water consumption by KH-570 hydration and the hydration products of methanol accelerate the gelling process of colloidal silica. This also has some positive influences on the early strength enhancement.