INDUSTRIAL A S D ENGIiYEERING CHEIMISTRY
524
Vol. 17, N o . 5
Rapid Determination of Molybdenum in Steel’ By 0.L. Maag and C. H. McCollam T H E TIMKENROLLERBEARING Co., C A N T O NOHIO ,
I
N COKTROL work in a steel mill it is essential that
laboratory determinations be made quickly and accurately. For determining the molybdenum content in the charges of the electric furnaces, this laboratory has been using for six months, with satisfactory results, a method which is a combination of the color method of the U. S. Steel Corporation’ and that of King3 The molybdenum content of the charges at this plant ranges from 0.02 to 0.15 per cent, and the time required for making a determination varies from 20 to 25 minutes. This time may be apportioned approximately as follows : Sampling Weighing Solution with acid Fuming
Minutes 2 1
2 6
Dissolving salts Cooling Ether extraction Matching colors
Minutes 3 2 3 1
Procedure Weigh a 0.5-gram sample of steel and place in a 250-cc. beaker. Add 10 cc. of nitric-sulfuric acid mixture. Heat gently unt’il the sample is in solution, bhen evaporate carefully and rapidly on a hot plate to copious fumes. Do not use a cover glass. Some trouble due to spattering, may be experienced at first; however, a little practice in regulating the temperature of the hot plate xi11 readily overcome this difficulty. To obtain concordant results all nitrates must be driven off, which necessitates steady fuming. Cool the contents of the beaker; add exactly 30 cc. of hydrochloric-sulfuric acid mixture and boil until the salts dissolve. The amount of hydrochloric acid used in this operation is very important; too much will cause a fading of the coior even before the ether extraction can be made, while not enough of this reagent may present difficulties in the solution of the salts. Cool the solution to room temperature; add from a buret, 5 cc. of potassium sulfocyanate solution. Stir well and add 10 cc. of stannous chloride solution from a buret and again stir thoroughly. It is very important that all of the iron be reduced before the extraction is made; therefore, after the addition of the stannous chloride care should be taken that none of the unreduced solution is left on the sides of the beaker. EXTRACTIOX WITH ETHER-Transfer the acid solution to a separatory funnel of suitable > b e ; add 10 cc. of ether and shake well. Return the acid solution to the original beaker and draw off the ether solution into a clean, dry, 50-cc. graduated cylinder. Shake out the acid mixture with successive 10-cc. portions of ether until all color is remored. The volume of ether used for the sample should be approximately the same as is required to give a corresponding color with the standard. Transfer the combined ether Lolutions to a graduated matching tube. COLORCoiwARISOx-For this operation a KennicottCampbell Hurly co-orimeter is used in this laboratory. Illumination is supplied by a Wratten Safelight No. 2, made especially for dark-room purposes. This fixture carries a 50-watt bulb, which gives sufficient light and does not materially affect the atmospheric temperature and thus cause a Received November 10, 1924. 2 “Methods of the Chemists of the United States Steel Corporation for the Sampling a n d Analysis of Alloy Steels,” 1921, 2nd ed., p. 72. 8 THISJOURNAL, 16, 350 (1923). 1
rapid deterioration of the standard due to evaporation of the ether. I t is essential that the light be so placed that the illumination is equal on both mirrors. Place the matching tube containing the unknown in the colorimeter, and adjust the leveling device until the depth of color in the tube containing the standard equals that of the unknown. Take the reading in cubic centimeters of the standard solution in the graduated matching tube. From this value the molybdenum content of the unknown steel can be calculated. STAXDARD SoLuTIoh--\veigh two 0.5-gram samples of standard steel. Run through in the usual manner and make the ether extract up to exactly 50 cc. in the standard matching tube. Place in the co!orimeter and compare. If the color tints match, one sample may be diluted to exactly 100 cc. as a standard for low percentage molybdenum, or the two may be united to make a standard for steels w.th a higher molybdenum content. Transfer to the leveling tube of the colorimeter. The top of the leveling tube should be covered when not in use, in order to increase the time that a standard can be uaed. Since the deterioration of a standard is generally due to evaporation of the ether rather than breaking down of the salt, its life is largely dependent on the room temperature. In this laboratory the standard is renewed every 2 hours, two samples of standard steel being kept fuming slightly on the cooler portion of the hot plate, to be used whenever the standard in use is suspected. Calculation of Results
If a steel containing 0.23 per cent molybdenum is used as a standard, a 1-gram sample will contain 0.0023 gram of molybdenum; on dilution to 100 cc. each cubic centimeter will contain 0.000023 gram of molybdenum. If 14 cc. of the standard are used to match the color of the unknown steel, the unknown must contain 14 X 0.000023, or 0.000322 gram. Since the weight of unknown used is 0.5 gram, it will contain twice this amount per gram, or 0.064 per cent: Cc. standard (14) X grams/cc. (0.000023) - Per cent hlo (0.0ti4) Grams sample (0.5)
Solutions HzO “01 His01 Hz0 HzSOI HCI KCNS Hi0 SnClr HCI H20
Xirrtc-sulfuric acid mixture
750 cc. Sp. gr. 1.42 350 cc. Sp. gr. 1.84 225 cc. Hydrochloric-sulfuric acid mixfure 1450cc. s p . gr. 1.84 450 cc. SD 1.19 100 cc. .. ZK. Potassium sulforvanale solution ~50 grams 1000 cc. Slannous chloride solution 250 grams s p . gr. 1.19 200 cc. so0 cc.
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Dissolve the stannous chloride in the hydrochloric acid, boil until clear, and add the water. Add a few pieces of metallic tin to prevent oxidation. International Industrial Exposition in Bolivia-This exposition will be opened in La Paz on August 6 , next, in connection with the celebration of the Bolivian Centennial of Independence. An invitation is extended to the manufacturers of the United States to participate in the exposition.
