E. A. Peretti University of Notre Dame Notre Dame, Indiana
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Three Dimensional Models in Phase Rule Studies
In a recent paper R. H. Petruccil described the construction, from plaster of paris, of excellent phase models of one-component and polycomponent systems. For the past 30 years the author has been using space models to illustrate phase relationships involving metals, oxides, and sulfides. The material of construction chosen, however, was copper or iron wire. The copper wires were soldered together to form the desired model, and the iron wires were joined with a spot welder. Because the iron wire produces a stiffer model which can withstand handling better, most of our models have been made of this material. The earlier models were made of 22-gauge wire and were mounted on a wooden base (see figures), but we then changed to larger diameters (16-and 19-gauge) which give the model sufficient rigidity and strength so that it needs no other support and can take severe student use; however, it cannot, as one of our students discovered, be sat upon. The iron wire we found quite suitable was black annealed, which is sold in l/n-lb and 1-lb spools by nlalin and Company of Cleveland, Ohio. The models are all schematic, hut can just as well be made to scale if one so desires. The boundary conditions are constructed first, giving a shell which is filled
Figure 1. W i r e T-X model of ternory ryrtem. Two of the bounding binory ryrtemr are eutectifemus ond exhibit only minute rnutuol solid solubility. The third binory ryrtem is o peritectic type with large terminal solid rolubilifin~.
in to give a complete view of the model a t a glance; this is the big advantage of wire models over those made of opaque materials. I n the ternary concentrationtemperature models (Fig. 1) the surfaces are formed by a series of wires which represent traces of isothermal planes through the model. This is the simplest means of construction, because the elements of many of such surfaces are straight lines. The intersections of surfaces form part of the preliminary skeleton and can be made of larger wire than the surface traces. Visulization of the various phase regions has been enhanced by painting the wires in each phase area a different color of bright enamel. Examination of a wire model by a student permits him to draw quickly an isotherm or an isopleth of the system. Figure 2 shows a pressure-temperature-concentration model of a eutectiferous binary system. The wires are traces of isotherms for the regions below the triple point, hut are isobaric traces for regions above the triple point. The space models not only have proved useful for beginning students of phase equilibria, but have been helpful to students in planning and interpreting phase diagram studies of new systems. Most of our models were constructed by the author, but several were made by some of our senior students.
Figure 2. W i r e P-T-X model. This dercriber o binory eutectiferous rystem with negligible solid solubility.
Volume 43, Number 5, Moy 1966
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