Reactions and emissivity of cerium oxide with phosphate binder coating on basic refractory brick

High emissivity coatings which aim to help the cement industry reduce heat loss in its production process have been developed with different CeO₂ and AlH₆O₁₂P₃ ratios (1:3, 1:5, and 1:12 by volume). The coating slurries were shear thinning and after heat treatment in air at 1300°C, 1°C/min, dwell 3 hours, XRD revealed that CePO₄ forms more easily as the Ce/P ratio decreases. The composition with a 1:5 ratio of CeO₂:AlH₆O₁₂P₃ was gun sprayed on basic refractory bricks, then heat treated under the same conditions as the slurries. SEM, (S)TEM and EDX were used to study thickness, microstructure, and chemical composition of the coatings which revealed that the coating was composed of pores, CeO₂ grains, CePO₄ grains, and M-P-O glass. SEM images show that CePO₄ was nucleated from a reaction between CeO₂ and AlH₆O₁₂P₃. Consequently, CePO₄ grains (~2 µm diameter) were smaller than CeO₂ (~10 µm diameter). The emissivities of un-coated and coated basic refractory bricks were measured at 1100 and 1300°C over the wave number range of 700-12 000 cm⁻¹. At both temperatures, the emissivity of the coated bricks was higher than the uncoated bricks and the emissivity was measured to be higher at a higher temperature for both samples. The coated bricks gave the highest emissivity of 0.81 from 1050 to 11 000 cm⁻¹ which is about twice the un-coated bricks for the same conditions. This demonstrates that the developed high emissivity coating has potential to be used with basic refractory brick.