Effect of FetO on viscosity and structure of Na2O3-B2O3-CaO-SiO2-Al2O3 slag

The effects of FetO on the characteristic melting temperature, viscosity, and structure of Na2O3-B2O3-CaO-SiO2-Al2O3 slag were investigated. Understanding the viscous behavior and structure of borate slag containing FetO can guide the design of mold powders for copper alloy casting. The melting temperature (Th) suddenly increased and exceeded 800 degrees C when the FetO content increased from 15 to 23 wt%. The viscosity changed significantly with increasing FetO content when the temperature was below 1050 degrees C. The slag structure exhibited a boron-iron anomaly. The viscosity of the Na2O3-B2O3-CaO-SiO2-Al2O3 slag gradually increased with increasing FetO content. When the content of FetO was low, sufficient oxygen in the slag promoted iron and boron to enter the network structure in the form of [FeO4] and [BO4], thereby reducing free oxygen and free [BO3]. As the FetO content exceeded a certain value, free oxygen decreased proportionally, and some iron ions existed in the form of [FeO6] with the network modifiers. Simultaneously, the amount of free [BO3] that is not bound to oxygen increased. Based on the optical basicity viscosity prediction model, the viscosity of borate slag with high iron content was predicted, and the M-O bond strength reflected by optical basicity was closer than the strength predicted for the network structure based on slag viscosity.