this kind of silica submerge nozzle has hige strength , good corrosion resistance and thermal shock resistance , , it's competitive price reduced your production cost.chemical and physical properties as follows:Item indexCRS QRS SiO2 % 99 99 Apparent porosity % 19 18 Refractoriness 1750 1750 Bulk of density g/cm3 1.82 1.84 C.C.S. Mpa 39 39 Thermal shock times 30 30