Zinc iron phosphate glass for enameling applications

The zinc iron phosphate system is investigated for use as an enamel for the automotive industry. The thermal properties and chemical durability of the glass-forming region are measured. Compositions are selected based on their oxygen to phosphorus (O/P) ratio at values of 3.5, 3.25, and 3.0. Substitutions of SnO, CuO, Li2O, Na2O, K2O for ZnO and B2O3 for Fe2O3 are used to alter the properties of the base glasses to achieve a particular range of Tg, CTE and durability. The 3.25 and 3.0 O/P glasses are found have too low a durability to be used as an enamel. Within the 3.5 O/P glasses, high iron content produces too high a Tg to be useable. Of the lower iron glasses, the alkali modifiers are able to reduce Tg sufficiently without sacrificing CTE or durability. Li2O increases the tendency of the glass to crystallize so that it does not re-melt and flow. A combination of Na2O and K2O provides the correct range of thermal properties and durability and SEM images show a consistent wetting of the substrate glass. The final glass composition chosen was 5Na2O · 5Na2O · 20.2ZnO · 21.8 Fe2O3 · 48 P2O5. The wetting experiments determined an optimum enameling treatment of 650°C for 5 min --Abstract, page iii