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Determination of Nickel, Manganese, Cobalt, and Iron in High-Temperature Alloys, Using Anion-Exchange Separations John L

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Determination of Nickel, Manganese, Cobalt, and Iron in High-Temperature Alloys, Using Anion-Exchange Separations John L Journal of Research of the National Bureau of Standards Vol. 53, No. 6, December 1954 Resea rch Paper 2552 Determination of Nickel, Manganese, Cobalt, and Iron in High-Temperature Alloys, Using Anion-Exchange Separations John L. Hague, Edwin E. Maczkowske, and Harry A. Bright A procedure is given for the determination of nickel, manganese, cobalt, and iron in a high-temperature alloy. Niobium, tantalum, tungsten, and silicon are rendered insoluble b~' hydrochloric acid dehydration after solution of the alloy in aqua regia. Molybdenum and copper a re precipitated with hydrogen sulfide, and the solution is filtered. The filtrate is evaporated several t imes wiLh hydrochloric acid and hydrogen peroxide to obtain a chlo­ ride solu t ion of these elements in the proper valence. The resulting solution is transferred to an anion-exchange column containing Dowex-l. The nickel and manganese, with chro­ mium and some other elements. are collected in t he first fract ion by elut ion with 9 N hydro­ ch loric acid. Cobalt is collected in a second fraction by elution wit h 4 N hydrochloric acid , and iron in a third by elution with 1 N hydrochloric acid. The cobalt is determined by electrolysis from a weakly ammoniacal chloride solution co ntaining hydroxylamine hydro­ chloride, and the other elements arc deLermined by con ven tional methods. 1. Introduction to compete with the chloride ions for a posi tion on the resin column, much as the competition that exists The increased use in recent years of high-tempera­ between chl oride and bisulfate ions [9]. Though ture alloys and alloys of controlled temperature­ suggested mechanisms are at present speculative, expansion characteristics has made the problem of practical and efficien t quan ti tative separations can determining cobalt, iron, nickel, and manganese in be made with quantities and volumes commonly appreciable quantities and in combination a pressing used in analytical work. one. Some of the difficulties encountered in this The procedure Oll tlin ed below was designed partic­ field of analysis have been summarized by Chirnside, ularly wi th the analys is of an S- 816 type of aUo),2 Cluley, and Proffitt l3] J in dealing with a ternary in mind. After solu tion of the alloy in aqua regia, all oy of iron, nickel, and cobal t. :rvrany of the all oys the niobium , tantalu m, tungsten , and silicon arc manuJactured today ma~T contain , in addition, rendered insolu ble by hydrochloric-acid dehyclra tion. appreciable percentages of chromium, molybdenum, The solution is treated with hydrogen sulfide to pre­ titanium, tungsten, niobium, and other elements. cipitate molybdenum and copper, and fi ltcred. The The problem of obtaining anaJyses of suffi cient fil trate is evaporated several times wi th hydrocliloric accuracy for the establisbment of standards of com­ acid and hydrogen peroxid e to obtain a chloride position is not an easy one; even the uSllall y simple solution of the elements in the proper valence. The determination of nickel may become qu i te complex resul ting solu tion is transferred to an anion-exchange in these mixtures [7]. A new f\, pproach to the prob­ column, and the nickel and manganese, with chro­ lem seems needed in order to put such methods on a mium and some other clements, arc collected in the basis of accuracy comparable to other less difficult first fraction by elu tion with 9 N lwdrochl orie-aeid combinations. solu tion. Cobalt is coll ected in a second fraction by The present paper describes the application of elu tion wi th 4 N hydrochloric acid, and iron in a anion-exchange separations to the analysis of high­ third by elu tion with 1 N hydrochloric acid. 1f an­ temperature alloys. Kraus and Moore [8, 12] have ganese and nickel arc determined in aliquots of the 11 0wn that nickel, manganese, co balt, and iron, as first fraction by the persulfate-arseni te titra tion and well as certain other elements, can be separated dimethylglyoxime gravimetric methods, respectively. by selective elu tion from an anion-exchange resin Cobalt is determin ed in the second fraction b\T elec­ with hydrochloric acid solutions. These separations trolysis from a weakly ammoniacal chloride solution depend on the fact that a number of metallic ele­ containing hydroxylamine hychochloride, and ilyn ments [10] can exist in aqueous solutions either as is determined in the third fraction by reduction WI th cations or as complex chI oro-anions, the relative stannous chloride and titration with dichromate. amounts depending on the element and on the The method requires several days to carry to com­ concentration of chloride ions in the solu tion. The pletion as about 3 hI' are required for each of th e exact mechanism of the combination (or a.dsorp­ ion-exchange fractionations. The method is not tion) of thesc complexes with the resin has not been intended to replace rapid rou tine procedures, where established, bu t it may be related to the existence of they can be developed for a particular type [3] of these complex anions in solu tion as strong acids. material, but provides an independen t checking pro­ For example, iron is probably combined in the form cedure of general application. ) - , of a complex anion, such as (H 2FeC16 that is free 2 This alloy contains approximately 40 percent or cobalt, 20 percen t or nickel , 20 percent of chromium, aud 4 percent each of niobium, tun ~s t e n, and molyb. 1 Figures in brackets indicate the literature rererence at the cud or this paper. denum, the remainder being largely iroll, man ganese, carbon , and sili con. 353 2 . Apparatus a n d Resins delivered by gravity flow ft'om bottles, placed on the top stand, through a system of stopcoch:s and capil­ The apparatus required for an ion-exchange sep­ lary tubing, to the columns. Bccause most of the aration is simple, consisting of a glass column to hold usable resins are fine-mesh materials that tend Lo the resin. The column used in this investigation, slow the flow of liquid, it is advantageous to have a illustrated in figure 1, is 1 in. in internal diameter several-foot head of liquid to control the flow rate. and 12 in. long. As most of these separations require The resin selected for these columns was 200- to several hours, it is convenient to so arrange the 400-mesh Dowex- 1, with 8- or ] O-percen t cross­ columns that a number can be operated with mini­ linkage. 3 The finest and the coarsest materials are mum attention. Such an assembly is illustrated in removed by settling the resin in diluted hydrochloric figure 2. The solutions n ecessar ~- for elution are acid (1 + 19).4 After several cvcles of successivelv decanting the fine and main pOl·tions from the coars'e fraction, the column is fill ed with a slurry of the main portion of the resin to a settled height of 20 to 23 em (equivalent to approximately 75 g of resin) . A plug of glass wool in the bottom of the column serves to retain the resin, and a disk of plastic cloth is placed FIGUR]" 1. I on-exchange col umn. o on top to minimize the disturbance of the resin when solu tions are added. 3 . Procedures 3 .1. Preparation of the Solution of the Sample for TIl Ion -Exchange Separation Transfer an accurately weighed 1 g sample to a 600-ml beaker. Cover the beaker and add 20 ml of 1 aqua regia (3 parts of hydrochloric acid and 1 part of nitric acid). Set the beaker on the sid e of a steam bath until the reaction ceases, and then warm it gently until the sample is in solution,' except for small amounts of carbides and silica. Wash the cover glass and wall of the beaker with E a little diluted hydrochloric acid (1 + 19) and evap­ porate to dryness on a steam bath. Treat the dry residue with 10 ml of dilu ted hydroehloric acid (1 + 1), wi warm and mix well with a glass rod, and again evaporate to dryness . Repeat the addition of di­ luted hydrochloric acid and the evaporation to dry­ ness four times to insure the removal of nitric acid. 6 Finally, add 15 m l of dilu ted hydrochloric acid (1 + 1) and warm the solution on the steam bath until the cake is dissolved. Dilute to 300 ml with hot water, and pass a brisk stream of hydrogen sulfid e through the solution for 30 min.7 Let stand for 30 min and filter through a close-textured ll-cm paper containing a little paper pulp. Transfer the precipitate to the paper 8 and wash with a diluted hydrochloric acid (3 + 97) solution saturated with hydrogen sulfide until the volume of the fi ltrate and washings is at least 450 m!. Transfer the filtrate and washings to a steam bath and evaporate to dryness. 3 The fin e·mesh res ins were obtained from The Dow Chemical Co., T cchnical Scn ' ice and Development, ~r[idl a nd , ~1ich . , This denotes 1 volume of concentrated hydrochloric acid, sp gr 1.18, diluted with J9 volumes of water. If no dilution is specified, the conce ntrated reagent is meant. 'Some alloys dissolve slowly, but will dissoh'e more readily if the chlorine generated b y tho acid mixture is not driven ofT by heat. 6 M anganese a ppears to fOfm a complex chlOl'o manganitc anion of unknown composition in strong hydrochloric acid solutions in the presence of oxidizing agents.
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