Nitrogen dioxide contributes to acid rain, it is a precursor to photochemical smog and low-level ozone, and prolonged exposure can damage both eyes and lungs. Oxy-fuel firing technology for glass melters dramatically reduces nitrogen dioxide and particulate emissions providing a cleaner environment, but imposes a high stress on superstructure refractories. Where silica in melter design is inappropriate, fused cast alternatives have been utilised. However, these products have a number of drawbacks including cost, density, thermal conductivity, block design, poor thermal shock resistance and high potential for knot and stone. Consequently, there is a defined requirement for a product that fills the gap between silica and fusion cast: spinel offers the intermediate solution, the case for which is reviewed in this article.
