what is Elingham Diagram ? and how it is use in iron and steel industries ?

what is Ellingham diagram?
It is graphical representation of DelG° ( y axis) and temperature in X axis. what it tells about? Basically, it tells about relative stability of oxides. That means, if you have SiO2 and CaO2 at same temperature how can you say which one is stable? This information we can get from this diagram. Obviously our next question is how it link with iron and steel making? we know that naturally iron occurs in oxide form – the main ores of iron are hematite and magnenite. Before going to further details let’s define iron making and steel making. Iron making is defined as removal oxygen from ore and steel making is defined as selective oxidation of impurities to remove those impurities. Our next question is how to remove oxygen from ore? Yes, here the application of Ellingham diagram comes into picture. let’s understand from simple examples. We know that large negative free energy compound is most stable compare to other compounds. From the diagram one can understand that CaO is most stable oxide compare to other oxides. That means let’s say you have SiO2 if you Ca to the system Ca will remove oxygen from SiO2 and form CaO. The reverse does not work. Because it increases the free energy. Similarly in iron making, we are using carbon as reducing element to remove oxygen from iron ore. Carbon positioned below the Fe line above some temperature ( just see the diagram). That carbon is used based on Ellingham diagram. let’s come to steel making. In this process you have to remove impurities without loss of iron. That means you need to avoid Fe oxidation. how to do that? So here it comes the application of Ellingham diagram.