THE OPTICAL CONSTANTS OF SULPHIDES

For the first time the optical constants of different sulphides were measuredusing interference layer microscopy to enable them to be utilized for quantitativemetallography. In addition to the measurement of the refractive index and absorp-tion coefficient it was also possible to give the conditions that enable the maximumpossible light-dark contrast as well as a good colour contrast to be achieved in thepolished specimen. The layer materials that almost completely extinguish thereflectivity of the different phases are reported together with the exact colouraccording to DIN 6164. A method of presentation was found for all phases, notonly the sulphides, that enabled the refractive index at which the amplitudecondition was fulfilled to be exactly determined. There is a mathematical relation-ship that can be simply derived for all phases between the reflectivity at theinterference minimum of a phase and the refractive index of the layer providingnon-absorbent layer materials are used.The sulphides represent a very complicated phase group for the metallographer as the amplitude condition can be over- or under- fulfilled by coating with the layer materials under discussion e.g. ZnS or ZnSe. One of the aims of this work was to provide the necessary data.