INDUSTRIAL A N D ENGINEERING CHEMISTRY
January 15, 1931
106
Determination of Zirconium in Plain Carbon and Alloy Steels' Thos. R. Cunningham and R. J. Price U N I O N CARBIDE AND CARBON RESEAR-
LABORATORIES, INC.,LONGISLAND CITY, N. Y.
I R C O N I U M is separated from the elements enumerated below as ZrHPO,, which is converted to ZrP207 on ignition. A determination may be completed on steels free from tungsten, tin, tantalum, or columbium in not over 2 hours. The exact determination of very small percentages of zirconiun in the presence of varying amounts of one or more of the elements titanium, aluminum, tungsten, molybdenum, chromium, vanadium, uranium, cobalt, nickel, copper, tin, arsenic, manganese, tantalum, columbium, and silicon, all of which are found in one type or another of plain carbon or alloy steel, is a somewhat difficult analytical problem. The method herein described is designed to be applicable to any commercial steel. From 5 to 10 grams of the drillings are transferred to a 500-cc. covered beaker and dissolved in 40 to 60 cc. of hydrochloric acid (sp. gr. 1.19). When all action appears to have ceased from 8 to 15 cc. of Perhydrol (30 per cent hydrogen peroxide) are introduced to oxidize the iron, to break up any separated carbides, to oxidize tungsten, and to peroxidize the titanium. If the steel contains tungsten, a yellow precipitate of tungstic acid will be noticed a t this point, in which case the procedure must be modified as described below. Titanium is not precipitated as phosphate when in the sexivalent state. The solution is diluted with warm water to 350 cc., treated with 8 to 10 grams of diammonium phosphate dissolved in 50 cc. of water, and stirred vigorously for several minutes. Some ashless paper pulp is introduced, and after allowing the solution to stand for one-half hour at a temperature of approximately 70" C. it is filtered on an 11-om. paper. The precipitate and paper are washed 15 to 20 times with 2 per cent hydrochloric acid, ignited in porcelain a t a low temperature to burn off the paper, and transferred to a 30-cc. platinum crucible. Two cubic centimeters of sulfuric acid (1 to 1) and 5 cc. of hydrofluoric acid (48 per cent) are added and the solution is evaporated to strong fumes of sulfur trioxide. The sulfuric acid solution is transferred to a 150-cc. beaker, the crucible being rinsed with 5 cc. of hydrochloric acid (sp. gr. 1.19) and a little water, and added to the beaker. The solution is diluted with warm water to 75 cc., treated with 3 grams of diammonium phosphate dissolved in 25 cc. of water, stirred vigorously, and allowed to stand for onehalf hour a t a temperature of approximately 70" C. The solution is filtered on a 9-cm. paper containing some ashless paper pulp and the precipitate of Zr (HPO& and paper washed 15 to 20 times with 2 per cent hydrochloric acid. The precipitate is ignited in platinum first at a low temperature to burn off the paper, and finally a t 1000" C., cooled in a desiccator, and weighed. The weight of ZrPz07 is multiplied by 34.23 and divided by the weight of sample taken to give the percentage of zirconium in the sample. For extreme accuracy the precipitate of ZrPz07, which may be contaminated with small amounts of TizPz09, is fused with several grams of potassium pyrosulfate and the fusion dissolved in 40 cc. of 10 per cent sulfuric acid containing 5 cc. of 3 per cent hydrogen peroxide. The titanium is then determined by the hydrogen peroxide colorimetric method and the calculated weight of TiaPzOg deducted from the weight I Received
October 16, 1930.
of the precipitate of ZrPz07. The weight of Ti2Pz09is obtained by multiplying the weight of titanium found by 3.16. The ignited and weighed residue may not correspond exactly to the composition of ZrP2O.l ( 1 ) but it is believed to be very close to it, since the results obtained by the above described procedure agree almost exactly with those obtained by the cupferron method. By the latter procedure the zirconium is weighed as zirconium dioxide. This method should not be applied to the determination of large amounts of zirconium because the precipitate of Zr(HPO& is somewhat gelatinous, which makes it rather difficult or almost impossible to wash out the excess of the precipitant completely. I n the case of chromium steels that do not dissolve completely in the hydrochloric acid-Perhydrol treatment, the ignited residue, instead of being treated with sulfuric acid and hydrofluoric acid to remove silica, is treated with 5 cc. of hydrofluoric acid (48 per cent), 3 cc. of nitric acid (sp. gr. 1-42), and 3 cc. of perchloric acid (60 per cent), and the solution evaporated to strong fumes of perchloric acid. The perchloric acid serves to break up chromium carbide and to oxidize the chromium to chromic acid which does no harm. In the case of tungsten steels, after aiding the Perhydrol, the solution should be boiled for about! 5 minutes before diluting with warm water to 350 cc. and treating with the diammonium phosphate solution. After allowing the solution to stand for one-half hour at a temperature of about 70" C., it is filtered on an 11-cm. paper and the paper and precipitate washed well with 2 per cent hydrochloric acid, ignited in porcelain a t a low temperature, and transferred to a 30- or 50-cc. platinum crucible. The residue is fused with about 10 grams of sodium carbonate and the melt is dissolved in hot water in a 250-cc. beaker. Some ashless paper pulp is added and the precipitate of sodium zirconate is filtered on a 9-cm. paper and washed thoroughly with 2 per cent ammonium nitrate solution to remove all sodium tungstate and sodium salts. The precipitate of sodium zirconate is ignited in the same platnium crucible previously used aiid fused with 1 to 2 grams of potassium pyrosulfate. The fusion is dissolved in 75 cc. of hot 5 per cent hydrochloric acid containing 5 cc. of 3 per cent hydrogen peroxide, and the zirconium precipitated with diammonium phosphate as previously described. The precipitate is allowed to stand one-half hour a t a temperature of about 70" C., filtered on a 9-cm. paper, washed well with hot 2 per cent hydrochloric acid, and ignited in a weighed platinum crucible. The precipitate is treated with a few drops of sulfuric acid (1 to 1) and several centimeters of pure hydrofluoric acid (48 per cent), and any silica is expelled by evaporating the solution to the complete expulsion of the sulfuric acid. The crucible is heated a t 1000" C., cooled in a desiccator, and weighed. The weight of ZrPz07 is multiplied by 34.23 and divided by the weight of sample taken to give the percentage of zirconium in the sample. Should the steel be known to contain tin, tantalum, or columbium, the phosphate precipitate is filtered, washed thoroughly with 2 per cent hydrochloric acid, ignited in porcelain, transferred to a platinum crucible, and in the case of tin, fused with sodium carbonate, or transferred to a
Vol. 3, No. 1
ANALYTICAL EDITION
106
nickel crucible if tantalum or columbium are present and fused with several grams of potassium hydroxide. The melt is dissolved in water and the determination completed as described for tungsten steels. Experimental Proof of Accuracy of Method
A number of experiments were carried out to obtain dependable dnta concerning the accuracy of the method. It is a well-known fact that unless hydrogen peroxide is added to peroxidize the titanium, it, will be carried down with the zirconium phosphate precipitate, and for this reason alone, when extreme accuracy is desired, the final zirconium phosphate precipitate should be tested for titanium. The procedure consisted in saltins a number of samples of plain carbon steels, a sample of Cr-W-V steel, and stainless steel of the 18 chromium-8 nickel variety known to be free of zirconiuni, with varying amounts of pure zirconium chloride. Five-, ten-, and twenty-gram samples, respectively, were used.
The accurately measured aliquot portions of the standard solution of pure zirconium chloride were added to the weighed samples of steel, which were then dissolved and otherwise treated as given in the description or the method. The results obtained are given in the table. EXPBRIMENT
2
Experiments to Test Accuracy of Method KIND
STEEL
Plain Plain c
STEEL
ZIRCoNIUM
TAKEN ADDED
Grams 20
Gram 0.00101 0.00101 0.0025 0 0025
FOUND
Gram 0 00095 0.00102
ERROR Gram -0 00006 $0 00001
20 5 0.0025 5 0,0025 10 0.0006 0 00058 -0'00002 6 18 Cr-8 Ni 6 0.00133 0.00132 -0.00001 (1 Bureau of Standards standard sample 50A of high-speed steel. Two 5-gram portions were taken and the precipitates combined after making the sodium carbonate fu4on t o separate the tungsten.
4"5
$;:Cr-W-Va !
Literature Cited (1) Lundell and Knowles, J . Am. Ckem SOC, 41, 1801 (1919)
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Rapid Colorimetric Method for Determination of Molybdenum in Plain Carbon and Alloy Steels' ^,
Thos. R. Cunningham and H. L. Hamner UNIONCARBIDE AND CARBON RESEARCH LA~OEATORIES, I N C . , LONGISLAND CITY, N. Y
N ACCURATE colorimetric method for the determination of 'molybdenum in the presence of nickel, chromium, tungsten, and other elements, is given. It is best adapted to steels containing a maximum of 1 per cent molybdenum. However, good results have been obtained when the molybdenum content was as high as 2.5 per cent. One-half gram or one gram of the sample (if the molybdenum is 0.10 pes cent or less) is transferred to a 150-cc. covered beaker and treated with 25 cc. of sulfuric acid (1to 4) at a temperature of approximately 60" C. When all action appears to have ceased, 3 cc. of Perhydrol (30 per cent hydrogen peroxide) are introduced and the liquid is boiled for several minutes. The solution.is then filtered on a 9-cm. paper to remove carbon and the residue washed with water and discarded. The filtrate and washings are collected in a 250-cc. beaker and boiled down to a small volume to decompose completely the excess of Perhydrol. The Perhydrol destroys the hydrocarbons and partially reduces the molybdenum to a lower state; part of the molybdenum is oxidized by the air. I n the case of plain carbon or alloy steels, or steels containing tungsten, the above filtering operation is omitted. One gram of tartaric or citric acid is added (to tungsten steels only) and the solution made slightly alkaline with 10 per cent sodium hydroxide and then acid with an excess of 10 cc. of sulfuric acid (1 to 1). The tartaric or citric acid serves to hold up the tungsten. If only a small amount of tungsten is present this treatment may be omitted. The cold solution is transferred to a 250-cc. separatory funnel provided with a glass stopper, diluted to a volume of 100 cc. with cold water, and treated with 10 cc. of 5 per cent potassium thiocyanate solution. The stoppered flask and contents are shaken vigorously for several minutes, then treated with from 5 to 10 cc. of stannous chloride solution and again shaken vigorously for several minutes. The stannous chloride reduces the iron from the ferric to the ferrous condition and the molybdenum from the sexivalent
A
1
Received October 16, 1930.
to the quinquevalent or quadrivalent state. The potassium thiocyanate reacts with the reduced molybdenum to form a complex potassium-molybdenum thiocyanate, which imparts an amber to reddish brown color to the solution, depending upon its intensity. The solution is cooled to approximately room temperature, 50 cc. of ether added, and the separatory funnel stoppered and shaken vigorously for 30 seconds and then allowed to stand until the liquid has separated into two distinct layers. The lower or acid layer, which will contain the greater part of any iron, chromium, nickel, or tungsten, is drawn off and discarded, and the upper or ethereal layer, which will contain practically all of the molybdenum, is then drawn off into a 50-cc. Camp comparison tube. The tube is stoppered with a soft cork to prevent evaporation of the ether and its contents are mixed thoroughly by manipulating the tube in the usual manner. After standing for several minutes it is ready for comparison with the standard. Preparation of Standard for Comparison
With a little practice it is not difficult to estimate approximately the percentage of molybdenum in the sample. Twenty-five cubic centimeters of 8 per cent ferric sulfate solution are transferred to a 250-cc. separatory funnel and the standard molybdenum solution added from a buret. The solution is diluted with cold water to approximately 100 cc. and the development of the molybdenum color and extraction are completed as previously described. It is advisable to allow the molybdenum solution to stand in the comparison tube for several minutes before comparing with the standard, as the intensity of the color sometimes changes a t first but remains stable thereafter for 7 days and even longer if kept in the dark when not in use. The percentage of molybdenum in the sample is then determined by comparing the intensity of the color of the ethereal solution of potassium-molybdenum thiocyanate with that of the standard. The darker of the two solutions, the sample and the standard, is diluted carefully with ether
