THE CONSTRUCTION OF ISOTHERMAL QUATERNARY PHASE-DIAGRAMS OF THE NA-M-O-S TYPE FOR HOT CORROSION APPLICATIONS

This paper presents a computer program for the calculation of the isothermal phase diagrams of quaternary systems involving sodium, a pure metal, oxygen and sulfur, which are useful for examining the experimental results concerning the hot corrosion of metallic materials. The procedures adopted to calculate the location of the points where four condensed phases are simultaneously present (quadruple points) and to draw the regions of stability of each phase containing the metal are presented by means of examples concerning a practical system. The nature of these quaternary phase diagrams is examined with reference to the various types of quadruple points and to their interconnections with lines of equilibrium involving the participation of three different phases. Examples of phase diagrams of some quaternary systems calculated by means of the present program are given.