chemicals for use in the manufacture of bonded, coated, and loose abrasives and refractories, namely, inorganic, fused, or sintered non-metallic hard materials of oxidic or non-oxidic composition, fused or sintered inorganic oxides as additives for ceramics and building materials, fused inorganic oxides as aggregates for refractories, and fused inorganic oxides as slag-forming aggregates or refining slags for remelting processes