of antimony tetroxide is to be found in the larger treatises on inorganic chemistry. From the literature, it was expected that considerable difficulty would be encountered in dissolving antimony tetroxide in hydrochloric acid and it was surprising, therefore, to find no particular trouble from this source. Again, it was to be expected that in dissolving the roasted product, when some unchanged sulphide was present, some reduction of the pentavalent antimony and corresponding oxidation of the hydrogen sulphide to free sulphur would occur. The accompanying table gives a summary of the results obtained in the analysis of the roasted stibnite. * The values obtained when sulphide was present were a little high for trivalent antimony and a little low for sulphur. [SUBJECT TO REVISION] DISCUSSION OF THIS PAPER IS INVITED. It should preferably be presented in person at the New York meeting, February, 1916, when an abstract of the paper will be read. If this is impossible, then discussion in writing may be sent to the Editor, American Institute of Mining Engineers, 29 West 39th Street, New York, N. Y., for presentation by the Secretary or other representative of its author. Unless special arrangement is made, the discussion of this paper will close Apr. 1, 1916. Any discussion offered thereafter should preferably be in the form of a new paper. A Development of Practical Substitutes for Platinum and its Alloys, with Special Reference to Alloys of Tungsten and Molybdenum* BY FRANK ALFRED FAHRENWALD, CLEVELAND, OHIO (New York Meeting, February, 1916) I. INTRODUCTORY METALLURGICAL research has discovered many an alloy possessing properties not combined in any single metal, and progress still consists chiefly in the investigation and utilization of alloys. In the case of iron, the demands of automobiles, high-speed machines and high-duty engines have led to the production of special iron alloys which will meet any reasonable specifications in that field. In like manner, the bronzes, brasses and other alloys of copper have been brought to remarkable perfection, and for nearly every industrial purpose some alloy has been found more suitable than the pure metal. Less complete success has attended the attempt to find substitutes for gold, platinum, and the other precious metals. Indeed, it is not likely that a material can be produced which will possess all the properties of any one of them; yet it is reasonable to hope that, for any given use, the properties required may be found in some less expensive material. Thus, in incandescent electric lamps, the wire passing through the thick glass neck of the bulb was, until recently, almost universally made of platinum, for the single reason that no other known material, suitable as a conductor, had the same coefficient of expansion as glass. But a comparatively recent investigation of the iron-nickel series1 has shown that alloys of those metals may be produced, the coefficient of expansion of which can be accurately controlled between that of iron or nickel and zero. Thus, in that particular industry, a substitute for platinum has been found. According to statistical reports, not only considerable quantities of gold and iridium, but also more than one-third of the annual supply of platinum, are used (and, in the nature of the case, irrevocably lost) by dentists. Platinum is thus employed in several forms. As a thin foil, it serves various purposes for which its high melting point, pliability, chemical resistance, and other properties-including the ease with which Condensed from a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the University of Michigan. 1 C. E. Guillaume: Non-expansive Alloys, The Metallographist, vol. vi, p. 162, 1903. Grenet and Charpy: Dilation of Steels at High Temperatures, vol. vi, p. 238, 1903. it may be soldered-are invaluable. But it is most extensively used in the alloy with iridium, which is more resistant chemically than pure platinum, solders as readily, and possesses, besides, the quality of stiffness, and is not seriously softened by annealing at ordinary soldering temperatures. These advantages dictate its use, in spite of its high cost. The discovery of a substitute in dentistry for platinum and platinumiridium, especially if it possessed useful properties which they lack, would be eagerly welcomed, and would find wide application in other arts also. The solution of this problem has been undertaken by the Research Foundation of the National Dental Association, for which the work described in this paper was done by the writer.† The substitute desired must satisfy the following conditions: 1. Its melting point must be high, at least well above 1,200°C. 2. It must not be affected by those chemical compounds formed in its application, nor should it oxidize at a soldering temperature. 3. It must possess sufficient strength to resist stresses tending to change its form while in place, and at the same time be sufficiently pliable to be worked to the desired shape. 4. Its coefficient of expansion must be low, in order that desired dimensions may be easily produced in the finished product. (This factor is important, since the range through which this material is manipulated is often more than 1,000°C.) 5. It should unite readily with gold, silver and similar metals, and their solders. 6. Its cost of production should be low, as compared with that of platinum. After the entire list of metals had been considered with respect to these conditions, it was evident that any search for the desired material must be among the alloys, since experience has shown that the physical properties of a metal may be radically changed by the addition of varying amounts of another element, or of several elements, as in the case of steels, brasses and bronzes. Considerations based upon the periodic law of atomic weights, and the table constructed in accordance therewith by Mendeléeff and Lothar Meyer, led to the conclusion that the field for profitable research was narrowed to the elements chrome, manganese, iron, cobalt, nickel, copper, silver, palladium, gold, molybdenum and tungsten, and their alloys (ruthenium, iridium and osmium, likewise theoretically indicated, being ignored because of their costliness and scarcity).2 †This work was done in the Department of Mining and Metallurgy, Case School of Applied Science, and the Department of Chemical Engineering, University of Michigan. 2 [NOTE. The original thesis contains an interesting discussion of the theoretical considerations above mentioned. It assumes the probability that the physical properties (such as the melting points) as well as the chemical (such as base-forming or acid-forming) properties of the elements bear certain relations to their arrangement according to the periodic law. This discussion has been omitted here to save space.] When two or more metals are brought together in the liquid state, they mix exactly like two ordinary liquids. When the temperature is lowered the solidified mass may contain any one of the four following constituents: Pure components; solid solutions; compounds; and eutectics or some combination of these. A comparison of the properties of different alloys containing these constituents has shown that they impart their characteristic properties to the alloy of which they form a part; in fact, the relation between the constitution of an alloy and its mechanical properties is so clearly defined that the possibilities of industrial application may be predicted for a given alloy, if its constituents are definitely known. Conversely, if a certain application is desired, as in the problem under consideration, a definite limit may be placed upon the number and amount of constituents permissible. Fortunately, the number of constituents is limited to four, as given above. Pure metals impart their own characteristics; solid solutions are, in general, the ductile constituents (if formed of ductile metals or of a preponderance of one ductile metal); compounds and (usually) eutectics are hard and brittle, while the latter, even when present in very small amounts, tend to solidify between the grains of the alloy, thus destroying its ductility. The problem was to determine what combination, if any, of the elements named, in whatever form, would meet the assumed set of specifications. Accordingly, each of the 11 elements was combined, in varying proportions, with each of the other 10, giving 55 binary series to be considered with regard to their suitability as practical substitutes for platinum and platinum-iridium alloys. II. WORK ON ALLOYS MADE BY FUSION Behavior under the hammer, or when drawn through draw plates, and under the influence of acids and alkalies, was sufficient to indicate whether any particular specimen should be discarded at once or made the subject of further investigation. It was not considered necessary to measure the various melting temperatures encountered, as only a complete fusion, free from all contaminants, was desired. The purity of all components was the highest obtainable, while the purity of the resulting alloys was checked by microscopical and, if necessary, by chemical analysis. 1. Apparatus The Gran-Annular electric furnace3 was used in this set of experiments, and served as no other type of furnace would have done under Zay Jeffries: Notes on the Gran-Annular Electric Furnace, Metallurgical and Chemical Engineering, vol. xii, p. 154, 1914; also, C. H. Fulton: Trans., vol. xliv, p. 769 (1912). |