Determination of Sodium in Aluminum I. Chemical Analysis R. W. BRIDGES AND M. F. LEE, Aluminum Research Laboratories, New Kensington, Pa.
T
H E problem of determining sodium in aluminum is not a new one. As early as 1859, Sainte-Claire Deville (24) developed a leaching method for the determination of sodium. He converted the aluminum to nitrate, ignited a t low temperature, and leached the alkalies with water. This method has been used or modified by Diehl (8), Richards @S), Hunt, Langley, and Hall ( 1 4 , Moissan (18), Jean (15), Seligman and Willott (96), KohnAbrest (16), Belasio (S), Bhattacharyya (5), Pattison (22), Villavecchia (97), and Bertiaux (4). Handy ( I S ) dissolved aluminum in hydrochloric acid and nitric acid, ignited gently, and applied the J. Lawrence Smith method to the oxides formed. Allen ( 1 ) dissolved aluminum in hydrochloric acid, made an ammonium hydroxide separation, and determined alkalies in the filtrate. Nicolardot (19) proposed to disintegrate the aluminum with mercuric chloride, filter, and determine alkalies in the filtrate. When small amounts of sodium and large amounts of aluminum are present, these methods do not achieve quantitative recovery of the sodium. An electrolytic method has been proposed by Gaith (12) in which the aluminum is dissolved in hydrochloric acid, the excess acid neutralized with calcium carbonate, the copper group removed as sulfides, and the resulting solution electrolyzed with a mercury cathode and carbon anode. The amalgam is decomposed with sodium chloride and the sodium hydroxide formed is titrated. This method has been tried by several workers without success. Aluminum hydroxide is formed during the electrolysis, and doubtless occludes much sodium. The uranyl acetate method is considered the best gravimetric procedure. Difficulty in securing satisfactory magnesium acetate has led to unsatisfactory results with the magnesium uranyl acetate method of Caley and Sickman ( 7 ) . However, the zinc uranyl acetate method of Barber and Kolthoff (2) gives satisfactory results. Feldstein and Ward (10) used nickel uranyl acetate. Of the longer and more tedious methods, those of Fairlie and Brook (9), and of Schurman and Schob (25) are feasible. The limitation of these methods is that the sodium content of aluminum is for the most part 0.01 per cent or less, which makes a gravimetric determination very difficult. From a qualitative test used in the Aluminum Research Laboratories, a quantitative procedure called the fusion-leach method has been developed. This method takes advantage of the fact that when aluminum is held just above the melting point the sodium comes to the surface of the metal and forms sodium compounds which, after cooling, may be leached out with water. The alkalinity so produced is titrated and the fusion and leaching repeated until the sodium is removed. The method cannot be applied to aluminum containing other alkali or alkaline earth metals. Fortunately, these are absent as a rule or present in negligible amounts. Results obtained with the fusion-leach method have been checked satisfactorily with the uranyl acetate and nitrate crystallization methods. One good feature of the fusion-leach method is that besides being the shortest chemical method, it is applicable over the range of 0.001 to 0.05 per cent sodium, in which the sodium content of aluminum and aluminum alloys is usually found. The uranyl acetate method is not applicable for determination
of sodium below 0.01 per cent. Procedures for these three methods follow. FUSION-LEACH METHOD SPECIAL REAGENTS.One-hundredth N sulfuric acid; 0.01 N sodium hydroxide. PROCEDURE. Place approximately 50 g r a m of metal (if sodium is between 0.001 and 0.01 per cent) or 25 grams (if sodium is between 0.01 and 0.05 per cent) in an iron crucible fitted with a water-cooled lid. Place the crucible in a crucible furnace fitted with a transite cover cut so that only two-thirds of the crucible is directly exposed to the heat. Apply sufficient heat to melt the metal'and then just enough to hold it in a molten condition for 15 minutes. Cool the button and transfer to a 250-cc. beaker. Wash the crucible and cover into the beaker containing the button. Add enough water to cover the button and allow to stand for 15 minutes. Remove the button, rinse, add two drops of methyl red, and titrate with 0.01 N sulfuric acid, using approximately 0.5 cc. in excess. Boil for 5 minutes and titrate back with 0.01 N sodium hydroxide, and repeat the fusion and leaching until the net titration falls to 0.5 cc. or less. The number of leaching3 necessary will depend on the sodium content. net titration in terms of 0.01 N sulfuric acid X 0.023 Per cent sodium = weight of sample URAKYLACETATEMETHOD SPECIALREAGENTS SOLUTION A
SOLUTION
Uranyl acetate Acetic acid Water t o make
10 6 65
B Uvama
Grams
Zinc acetate Acetic acid Water t o make
80 3 65
Mix solution A with solution B and allow to stand for a t least 24 hours. Filter before using. PROCEDURE. Dissolve 1 gram of sample in a minimum amount of 1 to 1 hydrochloric acid, filter, and evaporate to a volume of 5 cc. Add 100 cc. of zinc uranyl acetate solution, stir for 45 minutes with a mechanical stirrer, and allow to stand overnight. Filter through a Gooch or sintered-glass crucible. Wash first with reagent, then twice with ethyl alcohol and six times with acetone. Dry for 30 minutes a t 105" C. and weigh as sodium zinc uranyl acetate. A blank must be carried through in parallel with the determination. Sodium = sodium zinc uranyl acetate X 0.01495 NOTE. Instead of weighing the sodium zinc uranyl acetate precipitate, its sodium content may be calculated from a volumetric determination of the uranium by the following procedure: Dissolve the washed precipitate with hot water, add 15 cc. of 1 t o 1 sulfuric acid, and weak potassium permanganate until pink. Add a few zinc ahot, warm gently for 15 minutes, cool, filter through a cotton plug into a beaker containing 100 cc. of cold water, and titrate with potassium permanganate of suitable strength (0.07 N and 0.02 N have been used). A blank must be carried through with the determinations.
A comparative study of the gravimetric method and the volumetric method has been made and the results obtained are given in the following table:
264
July 15, 1932
265
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
SODIUM WEIQHEDAS NaZn(U0z)aAco .6H20
%
SODIUM DETD.VOLUMETRICALLY BY TITRATION OF URANIUM
%
0.44 0.45
0.44 0.45
0.30 0.15 0.15 0.074 0.074 0.037 0.037 0.015
0.30 0.14 0.14 0.074 0.074 0.037 0.036 0.014
0.008
0.008
0.0016
0.0017
0.29
0.29
Blenkinsop (6) has proposed a method in which the uranium is determined by reduction with titanium chloride. McCance and Shipp (17) have introduced a colorimetric method in which the uranium is determined with potassium ferrocyanide. NITRATECRYSTALLIZATION METHOD SPECIALRESGENTS. Mercuric chloride, saturated sohtion. Special nitric acid. Eight parts of 70 per cent nitric acid to 7 parts of water. PROCEDURE. Weigh on a rough balance an 8-inch (20.32em.) quartz dish, add 250 cc. of water, 10 cc. of mercuric chloride solution, 30 grams of fine aluminum drillings, and warm gently until reaction starts. Add 10 cc. of concentrated nitric acid and heat until vigorous reaction starts. Place the dish in a cooling pan and slowly add 390 cc. of concentrated nitric acid. If the mass becomes viscous, add another 100 cc. of water. When apparent action has ceased, heat on a hot plate until the solution of the sample is complete. If the weight of the liquid falls below 600 grams before solution is complete, add special nitric acid. Finally evaporate the solution to 600 grams, cool, with continual stirring, in a water bath, and, when dish and contents are cold, allow to stand for 1 hour or more. Filter the crystals formed through a 5-inch (12.7-cm.) Biichner porcelain funnel, using suction to dry the crystals. Press well with a flattened rod, and, when dry, wash with 50 cc". of concentrated nitric acid. Allow the wash acid to stand on the crystals for a few minutes before suction is again applied. Receive the filtrate in a 4.5-inch (11.43-cm.) quartz dish. Evaporate the solution until a hot saturated solution is obtained, crystallize, and allow to stand as before. Filter through a quartz funnel,
receiving the filtrate in a 3.25-inch (8.25-cm.) quartz dish. Wash with 10 cc. of concentrated nitric acid, add 2 cc. .of concentrated sulfuric acid, evaporate to dryness and bake until no more fumes are evolved, cool, add 10 cc. of ammonium hydroxide, and allow to stand overnight. Warm, filter into a platinum dish, return the paper to the dish, add 5 cc. of concentrated hydrochloric acid, macerate the paper, warm, and precipitate with ammonium hydroxide. Filter, and wash with hot, slightly ammoniacal 2 per cent ammonium chloride solution. Combine the filtrates and evaporate to approximately 25 cc., add 10 drops of concentrated sulfuric acid, pass in hydrogen sulfide gas, filter, and evaporate the filtrate to dryness. Ignite to drive OB ammonium salts, add a few cubic centimeters of water and 2 cc. of saturated ammonium carbonate solution, filter, evaporate to dryness, and ignite for 30 minutes at 500" C., cool, and weigh. Add a few drops of water, 2 drops of ammonium hydroxide, warm, filter, ignite the paper at 500" C., cool, and weigh. The loss in weight is sodium sulfate. The filtrate should be examined for magnesium. Return the crystals from the first and second crystallizations to the 8-inch (20.32-cm.) quartz dish, add 150 cc. of concentrated nitric acid and 50 cc. of water, evaporate to 580 grams, cool, and recrystallize. Repeat the procedure outlined above. Deduct a determined reagent blank. Sodium
=
sodium sulfate X 0.3238
Some results obtained by the foregoing methods are as follows : SAMPLE
1 2
3 4 5 6
FUBION-LEACH NITRATE URANYL METHOD CRYSTALLIZATION ACETATE
%
%
0.040 0.016
0.040 0.015 0.010
0.009 0.008
0,009
0.040 0.017
%
0.038 0.016
ACKNOWLEDGMENT The authors wish to acknowledge the contributions made by W. I. Sivitz, formerly of Aluminum Research Laboratories, and P. M. Budge, chief chemist of the Fairfield Works Laboratory, toward the development of the fusion-leach method.
I I. Spectrographic Analysis A. W. PETREY, Aluminum Research Laboratories, New Kensington, Pa. RE determination of sodium in aluminum may be made by means of the spectrograph, and the results agree with chemical analysis within satisfactory tolerances. Chief among the advantages of the spectrographic determination, as contrasted with chemical determinations, is the rapidity with which a series of results can be reported. Eight to ten specimens may be examined within 2.5 hours, or an average of not more than 20 minutes per sample. The presence of other alkalies or alkaline earths does not interfere with the determination and, at the same time, the presence or absence of such impurities is established. Methods using both the direct current arc and the condensed spark have been investigated. Solution of the metal in acida with subsequent arc excitation of the dry salt, as used by Nitchie (20) in the analysis of zinc, was not entirely successful because of the relatively low solubility of aluminum and the strong continuous spectrum of the graphite electrodes in the regionbof the sensitive sodium lines. The sodium con-
tent of the solvents is also to be considered. Sparking the metal did not seem sensitive enough to warrant an attempt a t development, as the smallest amounts could not be detected and the intensity gradient was not well marked for the higher amounts. The method which seems most applicable for determining sodium in aluminum is arc excitation of the metal itself between electrodes of graphite. Papish and O'Leary (91) determine chromium in fused alumina by the arc. Fesefeldt (11) uses a similar method for determining beryllium in aluminum oxide. Metallic aluminurn cannot be used very successfully as electrodes with the arc because of its relatively low melting point and the formation of a heavy crust of oxide on the tips which is nonconducting and nonvolatile. However, the metal burns readily in the graphite arc and, when used in this way, the continuous spectrum of the graphite is practically eliminated. Since solutions have not been found successful for this
