Analysis of physical-chemical processes occurring on the boundary between the melt and non-stick coating

Abstract

This research presents the results of thermodynamic analysis of interaction between iron-carbon melts and graphite-containing non-stick coating during manufacture of iron castings in the temperature interval from 500 to 1400 °С. SCh20 cast iron and aqueous-base non-stick coating with use of natural hidden crystalline graphite were taken as the objects in this research. The processes on the boundary between the melt and non-stick coating, its reduction by the melt components (carbon, silicon) and interaction with dissolved oxygen were considered during evaluation of interaction between the system phase components. The conducted thermodynamic calculations displayed that reactions of interaction between coating carbon and oxygen are passing mainly to carbon (II) which forms reducing atmosphere in the mould cavity and provides decrease of burning-on. Forming of mixed Fe 3 O 4 during reaction of coating carbon with Fe (III) oxide is confirmed. The forming CO interacts only with Fe 2 O 3 . It should be noted that presence of pyrite in coating composition through the chain of reducing and oxidizing processes lead to forming of oxysulfates and oxysulfides, which support forming of burning-on on the surface of castings. It is concluded that thermodynamic analysis of chemical reactions of interaction between coating phases and melt components as well as mould atmosphere can help to predict operating efficiency of carbon-containing coating during its development.