CHAPTER XXIV ANALYSIS OF FERROUS AND NON-FERROUS ALLOYS PROCEDURES FOR TUNGSTEN STEEL, BRASS AND SOLDER 387. General Remarks. The use of metallic mixtures, commonly known as alloys, has now become so widespread that the chemist is perhaps more often called upon to analyze this class of products than any other class. The great difficulty in alloy analysis is to obtain satisfactory and quantitative separations, as practically all the precipitations involve more or less coprecipitation of other substances. This necessarily requires purification of the precipitates, and this purification is usually very troublesome and not always satisfactory. A procedure designed for a particular combination of elements may fail entirely if the combination is varied by the introduction of other elements, even in small amounts. An intelligent quantitative analysis presupposes an approximate knowledge of all the substances present. If this is not known, a qualitative analysis must be performed. 388. Classification. - Alloys are divided into two classes. Ferrous Under ferrous alloys are included the alloy steels, and products like ferro-manganese, ferro-phosphorus, ferro-silicon, etc., which differ from the alloy steels in that their content of the alloying metal is much greater. The alloy steels are those which contain, in addition to the usual five elements of carbon, manganese, silicon, sulphur and phosphorus, one or more of the following elements: chromium, vanadium, titanium, molybdenum, tungsten and nickel. 389. The specifications adopted by the Society of Automotive Engineers for alloy steels are as follows these specifications giving the analyst a fair idea of what to expect: 1 S. A. E. Handbook. New York, 1922. Section D, Material Standards and Recommended Practices, pp. D5-D6. Alloy 2 Brasses 390. Under non-ferrous alloys are included the following: Composition Cu Zn Sn Pb (Fe) 391. It is too far beyond the scope of this book to consider in any extended manner the general subject of the analysis of ferrous and non-ferrous alloys, so that for information in this regard the reader must consult special works, such as Blair, Griffin, and Moore, as cited in § 13, also the works of Ibbotson 2 This classification of alloys is taken from W. Campbell, A List of Alloys, loc. cit., § 3. The reader should refer to this publication for the percentage composition of the various alloys. 3 Chiefly comprises the bearing metals, Britannia metals, and pewters. Chiefly comprises the bearing metals, solders, and type metals 7 and Aitchison,5 Price and Meade," and Wölbling. It will suffice for our purposes to take up one example under the ferrous alloys, and two under the non-ferrous. For the former we will select the analysis of a tungsten steel, and for the latter the analysis of a brass and of a solder, the latter being representative of a lead base alloy. 392. Exercise No. 37. Analysis of a Tungsten Steel (W, Cr, Mn, Si, S, P, C). Silicon. In a 600 c.c. beaker, dissolve 2 grams of sample in 50 c.c. of 12 molar hydrochloric acid, and when dissolved add 5-10 c.c. 16 molar nitric acid a little at a time and digest until the residue (WO) is bright canary yellow. Evaporate to dryness but do not bake. Redissolve in 20 c.c. of 12 molar hydrochloric acid, add a few drops of 16 molar nitric acid and boil for a few minutes until the iron appears to be all in solution, then add 100 c.c. of hot water and heat for a few minutes. Filter through filter paper and wash thoroughly with 2 molar hydrochloric acid; save the filter paper and its contents. Evaporate the filtrate to dryness and bake at 105°-110° to render the silica insoluble. Take up in 15 c.c. 12 molar hydrochloric acid, dilute with 100 c.c. of boiling water and filter through a fresh filter paper, washing with 2 molar hydrochloric acid as before; save this filtrate for the determination of phosphorus. Any tungstic acid which adheres to the beaker in the first filtration is dissolved in a few c.c. of 3 molar ammonium hydroxide and evaporated to dryness in a platinum crucible. Into this crucible are introduced the two filter papers containing the tungstic acid and silica and the whole is then ignited at a dull-red heat and weighed. Introduce 3-4 drops of 9 molar sulphuric acid and 10-15 c.c. of hydrofluoric acid and evaporate in an airbath (§ 40) until the sulphuric acid has been driven off, and then ignite at a dull-red heat and weigh again. The difference gives the weight of SiO2, from which the weight of silicon is calculated. 8 F. Ibbotson and L. Aitchison, Analysis of Non-ferrous Alloys. Longmans, Green & Co., London, 1915, 230 pp. 6 W. B. Price and R. K. Meade, Technical Analysis of Brass and Non-ferrous Alloys. J. Wiley & Sons, New York, 1911, 267 pp. 7 H. Wölbling, Die Bestimmungsmethoden des Arsens, Antimons und Zinns, und ihre Trennung von anderen Elementen. F. Enke, Stuttgart, 1914, 377 pp. 8 The tungstic oxide which results from the dehydration of the tungstic acid is slowly volatilized at a bright red heat. 393. Tungsten. The residue of WO3 + Fe2O3 in the crucible is fused with 6 times its weight of sodium carbonate, the melt leached with hot water and the insoluble ferric oxide filtered off on a filter paper and well washed with hot water; the fusion converts the tungstic oxide into the soluble sodium tungstate but does not affect the ferric oxide. The crucible is also well washed with hot water. Since the residue on the filter paper may still contain a little tungstic oxide, the paper and the residue are returned to the crucible, ignited and fused again with a small amount of sodium carbonate. The melt is leached as before, the residue of Fe2O3 collected on a filter paper, well washed, and ignited and weighed in the same crucible which has itself been well rewashed in the meantime. The difference between this weight and the weight after volatilization of the silica gives the weight of WO3, from which the weight of tungsten is calculated. 394. Chromium. - Dissolve 1 gram of sample in 10 c.c. of 6 molar sulphuric acid and 25 c.c. of water, in a 300 c.c. Erlenmeyer flask and dilute to 150-200 c.c. with boiling water. Run into the hot solution from a burette a solution of 1 molar sodium bicarbonate until a slight permanent precipitate is obtained and then 4 c.c. more. Boil the solution for one minute and filter through a fluted filter paper, washing just enough to clean the precipitating flask; save the filtrate for the determination of manganese. Transfer the precipitate to a platinum crucible, ignite the paper 10 and then fuse for 20 minutes at not more than a dull red heat with 6 to 8 times its weight of a fusion mixture consisting of 25 grams of sodium carbonate, 25 grams of potassium carbonate, 20 grams of fused borax, and 10 grams of sodium peroxide. The fusion should be kept at a dull red heat just enough to keep it completely liquid, but any higher temperature should be avoided. At the end of the 20 minutes the fusion is spread over the inside of the crucible, allowed to cool, put into a small beaker, covered with water and put on the steam-plate or water-bath to dissolve. When solution is complete, filter from An iron crucible will not answer as the action of the flux on the iron seems to bring about some kind of union between the iron and the chromium to make an insoluble compound, thereby removing chromium from the analysis. 10 Care should be taken in igniting the precipitate from the sodium bicarbonate treatment as it contains metallic chromium. |