Phase transformations in periclase-spinel roofs of open-hearth furnaces with blowing through of the bath by compressed air

Abstract

The crystallochemical properties of the periclase and the spinels of the periclase-spinel bricks were radically changed during service in open-hearth furncces with blowing through of the bath with compressed air; new types of ferrite spinels and their solid solutions in periclase were formed. Periclase forms magnesiowustite and magnesioferrite with ferric oxides resulting in a lowering of the melting point from 2800 to 1600°C. This type of transformation of periclase is one of the main causes of wear of periclase-spinel roofs by fusion. Under the service conditions chrome spinel is transformed into magnesioferrite and magnetite, with a lowering of the melting point from 2100 to 1750°C. In the working zone the lattice parameters of the solid solutions in periclase (magnesiowustite) increased from 4.204 to 4.218 A, indicating a considerable amount of divalent iron and manganese cations in the periclase crystal lattice. In the periclase-spinel bricks we identified independent types of spinel, represented by inverted (magnetite), almost inverted (magnesioferrite), partially inverted (chrompicotite) and ordinary (magnesiospinel) structures. In the spinels the cations are variously distributed at tetrahedral and octohedral lattice sites. In the working zone ferrite spinels (up to 90%) — magnesioferrite and magnetite — predominated; they have an inverted structure and low melting points. The content of easily fusible ferrite spinels increased with increasing intensity of blowing of air through the bath. The formation of a large amount of ferrite spinels is one of the main causes of the fusion and rapid wear of periclase-spinel roofs of open-hearth furnaces.