690310 Refractory ceramic goods, Containing by weight more than 50 percent of graphite or other forms of carbon or of a miture of these products
690320 Refractory ceramic goods, Containing by weight more than 50 percent of alumina (Al2O3) or of a miture or compound of alumina and of silica (SiO2)
690390 Other refractory ceramic goods , Containing by weight more than 50 percent of alumina (Al2O3) or of a miture or compound of alumina and of silica (SiO2)
