2006
ANALYTICAL CHEMISTRY
(11) Bailey, C. R., Cassie, A. B. D., Proc. Roy. SOC. London A135, 375 (1932). (12) Bartunek, P. F., Baker, E. F., Phys. Rev.48, 518 (1935). (13) Bellamy, L. J., “Infrared Spectra of Complex Nolecules,” Wiley, Xew I’ork, 1954. (14) Dimbat, II., Porter, P. E., Stross, F. H., .%SAL. CHEY.28, 290 (1956). (15) Eggertsen, I?. T., Knight, H. S., Groennings, S., Ibid., 28, 303 (1956). (16) Fredericks, E. AI., Brooks, F. R., Ibid., 28, 297 (1958). (17) Hersberg, G., “Infrared and Raman Spectra of Polyatomic Molecules,” Van Kostrand, New York, 1945. (18) Hersberg, G., “Molecular Spectra and llolecular Strurtiire,” Van Xostrand, New York, 1950. (19) LeRoy, D. J., Can. J . Research B28,492 (1950).
(20) Morris, J. C., J . Chem. Phys. 1 1 , 230 (1943). (21) Osborne, J. S., Adamek, S., Hobbs, 11. E., .%SAL. CHEM.28, 211 (1956), (22) Pickett, L. W., J. Chem. Phys. 10, 660 (1942). (23) Price, D., Ibid., 9, 725 (1941). (24) Rasmussen, R. S., Tunnicliff, D. D., Brattain, R. R., Ibid., 11, 432 (1943). (25) Thompson, H. W., Harris, G. P., Tiatis. Faraday SOC.38, 37 (1942). (26) Titeica, R., Ann. phys. 1 , 533 (1934). (27) Wu, Ta-You, “Vibrational Spectra and Structure of Polyatomic Molecules,” J. W. Edwards, .kin -libor, hIich., 1946. RECEIVED for review June 6, 1956. Accepted August 8. 1956.
Determination of Oxygen in Titanium, Zirconium, Chromium, Vanadium, and Steels by Bromination-Carbon Reduction Method MAURICE CODELL
and
GEORGE NORWITZ
Pitman-Donn Laboratories, Frankford Arsenal, Philadelphia, f a .
Improvements ha\ e been made in the brominationcarbon reduction method for the determination of oxygen in titanium and titanium alloys. The factors contributing to the blank were investigated and the blank was reduced considerably by purification of the bromine. The method has been extended to the determination of oxygen in zirconium, chromium, vanadium, and steels.
R
C J X T L I - this laboratory developed a nex procedure for the deterinination of osygen in titanium and titanium alloys by means of a bromination-carbon reduction technique (7). The sample was inked with graphite and treated with bromine a t 825” C., helium being used as a carrier gas. The oxygen in the sample was converted to carbon monoxide, which was osidized to carbou dioxide Tvith hot copper oside and absorbed into a weighted bulb containing Ascarite. The titanium tetrabromide and bromine were frozen out by means of a dry ice and water trap, followed by two dry ice and alcohol traps. As a result of further investigations, improvements have bren made in the method as applied to titanium and titanium alloys, and the method has been esteuded to the determination of osygeii in zirconium! cli~~oniiiini, vmadirim, and steels. 1
SPECIAL REAGEKTS
Granular blister copper (Ledoux and Co., Teaneck, S . J.). Fluorolube, MG grade, and liquid grade S (Hooker Electrochemical Co., Niagara Falls, X. Y.). AGR graphite powder, prepared by scraping 0.75-inch graphite rods, grade AGR (National Carbon Co., Kiagara Falls, Y.I-.), with a clean razor blade. Discard the scrapings from the exterior surface of the rod. Store in a glass-stoppered bottle. Spectrographic raphite powder. National spectrographic graphite powder, krade SP-2, Xational Carbon Co., Siagsra Falls, N. Y . Purified Bromine,. Set up a purification train by assembling the following items in consecutive order: tank of oxygen, column of Ascarite and Anhydrone t o purify oxygen, inlet tube of bromine bottle, 1-liter bottle with a ground;glass mouth, outlet tube of bromine bottle, reaction tube packed with pieces of broken Vycor glass, a dry ice and water tmp (250-ml. capacity), first dry ice trap, and second dry ice trap. Add about 500 ml. of C.P. bromine and 200 ml. of sulfuric acid t o the 1-liter bottle. Heat to about 30” C. by means of a beaker of warm water. Bubble oxygen through the bromine a t a fairly fast rate and pass the mixture of oxy en and bromine through the reaction tube heated to 1000” Condense the bromine in the traps in the usual man-
6.
ner. 24110~vthe bromine to melt and store it in a dry glass-stoppered bottle. Copper Sulfate-Asbestos Reagent. Ignite high purity asbe*tos in a muffle for 1hour a t 1000” C. to drive off organic material. Mix about 3 parts of asbestos with 1 part of C.P.anhydrous cupiic sulfate by shaking in a closed bottle. Heat the mixture in an oven a t 150’ C. for 2 hours. APPARATUS
The parts of the absorption tiain ale identified in Figure 1. Kallmann ( 1 7 ) has modified the adapter which connects the bromine bottle t o the reaction tube, so that samples can be inserted without disassembling the apparatus or turning off the heat. The adapter consists of a Vycor tube, 6 inches long and 1 inch in diameter, with a vertical tube in the center R-hich connects t o the bromine bottle. Large socket joints (35/25) are attached t o the ends of the adapter. One of the joints fits on a ball joint attached to the end of the reaction tube; the other is fitted with a ball stopper which is removed to introduce ne)\ samples or to remove completed ones. PROCEDURES
Titanium and Titanium Alloys. CASEI. SAMPLES COKTAIKLESS THAN0.5% OXYGEN. Prepare the train as shown iii Figure 1. Turn on all heaters exce t the one used to heat the reaction tube. Add to the bromine Eottle approximately 150 ml. of purified bromine and 50 ml. of sulfuric acid. K i t h the system disconnected before the reaction tube, pass helium through the bromine bottle for 15 minut,es. iYow turn the stopcocks so th:tt the helium bypasses the bottle containing the bromine. Prepare the sample in the form of chips about 0.02 inch thick. Clean with carbon tetrachloride and dry by heating a t 50” C. Weigh out 2 grams of the sample and 1.5 to 2 grams of spectrographic graphite powder or AGR graphite powder. Place about one half the graphite on the bottom of a plat,inum or a gold boat. Place the sample on the carbon and cover the sample with the remainder of the carbon. Push the sample to the center of the heater. Assemble the system but do not connect the absorption bulb. .4djust the flow of helium to a fast rate and allow the syst,em to flush for a few minutes. Decrease the flow of helium to 210 bubbles per minute. Turn on the heater for the reaction tube. While this heater is coming up to temperature, add about 150 nil. of water and several pieces of dry ice t o the beaker for the dry ice and water trap. Fill the beaker for the first dry ice trap two thirds full and the beaker for the second dry ice trap entirely full with pieces of dry ice about 0.5 cubic inch in volume. Use of dry ice alone, instead of dry ice and dcohol ( 7 ) , eliminates erratic results found with the latter. When the temperature of the heater for the reaction tube has reached 925” C., connect the absorption bulb, and allow thc helium t o pass through the system for 10 minutes. Close the stopcock of the absorption bulb and disconnect. Open the stop-
ING
V O L U M E 28, NO. 12, D E C E M B E R 1 9 5 6 cock momentarily to the atmosphere and mreigh. Reconnect the bulb and weigh again after 10 minutes. If constant weight has not been reached, repeat the process. Turn the stopcocks so that bromine flows through the system. Continue the flow of bromine for 30 minutes after the reaction is ended, as indicated by the complete disappearance of the cloud in the vertical portion of the reaction tube. Turn off the bromine and switch off the heater for the reaction tube but allow t h r helium to flow. Weigh the absorption bulb. Calculate per cent oxygen as follows: Per cent oxygen =
36.36 (Ti;
- BT\I
JI
2001 graphite owder. Place about one third of the graphite on the bottom o r a platinum boat and mix another third of the graphite intimately with the sample. Place the mixture on the graphite contained on the bottom of the boat, and cover with the remaining third of the graphite. Compress with a small spatula. Proceed as in the regular method. APPROXIMATELY 1 TO 3 5 CASE 111. SAMPLESCONTAISING OXYGES. Proceed as above, but use a 0.5-gram sample and aftei the run is finished transfer the graphite from the boat to a tared platinum crucible. Ignite in a blast burner, tilting the crucible to allow free access of air. Weigh the residue as titanium dioxide. Calculate per cent oxygen in the sample as follows:
where
Per cent oxygen =
36.36 (W
11' = weight of carbon dioside,, grams
B = blank, grams of carbon dioxide per hour T = time for run, hours
Jf
'-
B T ) f 40.05 P M
where P = weight of titanium dioxide, grams
= weight of sample, grams
Determine the blank by carrying 1.5 to 2 grams of graphite through the determination. Continue the flow of bromine for 2 hours and divide the gain in Ti-eight by 2 to obtain the hourly blank. To prepare for the next run disconnect the reaction tube and three traps. Cautiously pour the contents of the dry ice and water trap into a 4-liter beaker containing about 1 liter of tap xvater. Allow the dry ice traps to thaw out for a few minutes, then add witer and pour the contents into the 4-liter beaker. Add ammonium hydroxide (technical grade) or sodium thiosulfate (technical grade) to the contents of the beaker to destroy the bromine. Rinse all three traps thoroughly with hot water and dry by heating in an oven a t 200' C. Remove the boat from the reaction tube and wash the react,ion tube u-ith ordinary household cleanser using a brush. I t may be necessary,to soak the react'ion tube a few minutes in 1 to 3 hydrofluoric acid. Rinse the reaction tube ne11 with hot water and dry it by heating with a blast burner vhile holding it with an asbestos glove. Remove the carbon from the boat and clean the boat by rubbing with steel ~ o o and l cleanser on a small glass plate. Soak the boat for a few m i n u t e in an acid mixture made of equal parts of nitric and hydrofluoric acids stored in a plastic beaker. K a s h the boat Jvith water and dry it by heating in a Bunsen flame. Cool the heater used for heating the reaction tube to approximately room temperature by means of an air blast, or substitute another heater. Two or three successive runs on the same day may be made n-ithout cleaning the traps. CASE 11. &4MPLES COSTAISISG 0.5 TO L"PPR0XIMATELY 15;) OXYGEN. Crush the sample nith a steel mortar and pestle. Keigh oiit 1 gram of snmple and 2 grams of spectrographic
Zirconium. Oxygen in zirconium has been determined by vacuum fusion (35, 36), isotopic dilution (ZO),chlorination using chlorine or hydrogen chloride (22, 27) and by igniting in oxygen and observing the gain in n-eight (sa). Because of the similarity in the metallurgical and chemical properties of t'he zirconiumoxygen and titanium-oxygen Bystems (8, 252, the method can be readily applied to zirconium. Zirconium tetrabromide (m-hite) is produced in the bromination reaction (31). As with titanium, the end of the reaction is noted by the disappearance of the cloud in the vertical port'ion of the reaction tube. Zirconium tetrabromide and also chromium, vanadium, and iron bromides sublime on heating and do riot have definite melting or boiling points a t atmospheric pressure. This is in contrast to titanium tetrabromide, which has a definite melting and boiling point at atmospheric pressure. Commercial zirconium and zirconium alloys contain about 0.03 to 0.5% os>.gen. The determination of oxygen in zirconium is carried as for titanium Chromium. Oxygen has been determined in chromium 1))vacuum fusion (15, 35') and by digesting with hydrochloric acid and filtering off the chromic oxide after annealing in a vacuum a t 800" C. ( 4 , SO, 37). Oxygen is present in chromium as chromic oride inclusions (37'). In electrolytic chromium the osxgeii may be present. as hydrous chromic oxide inclusions (4,ST:.
U
Figure 1. Apparatus for determining oxygen in metals 1.
2. 3.
3:2.
hlercury ,. Ground-glass joint (29/42j 8. Copper-copper oxide tube, 96% silica, 1 inch in diameter and 16 inc1it.s long 9. Electric heater for copper-copper oxide tube, 500' C., 11 inches long 10. hscarite-copper sulfate tube, borosilicate glass, 1 inch in diameter and 11 inches long 11. Granular blister copper, or purified granular copper used in powde:. metallurgy I ? . Copper oxide, fine wire form 13. 4scarite-.4nhydrone purifiration tube, borosilicate glass. 1 inch in diameter and 8 inches long 11. Glass wool 1.5, Ascarite 16. Anhydrone 17. Ball joint (18/9) 18. Borosilicate glass tubing, 10 mm. 1 0 . Buck-back trau for bromine, caoacitv . . about 250 nil 20. Stopcock 21. Bromine bottle, 250-ml. gos washing bottle with 29/12 ground-glass joint
22. 23. 2-1, 25. 213.
2i. 28. 29. 30. 31. 32. 3.3. 34. 33. 313. 37.
38. 39. 10. 41. 42.
-13.
Purified bromine Siilfnrir acid B e a k e r ~ t o ~ p r o t e bromine ct Reaction tube ( 7 ) Electric heater for reaction tube, 925' C., 10 inches Ions Copper sulfate mired with ignited asbestos B o a t about 3.5 inches long Ground-glass joint (24/40j Dry ice and water t r a u ( 7 ) Dry ice and water . ' D e v a r flasks, 500-nil. capacity. 3.5 inches a i d e and 0 inrhes higl Borosilicate glass tubing, 18 mm. First dry ice t r a p ( 7 ) D r y ice Second dry ice t r a p ( 7 ) Sulfuric acid bubble counter ( 7 ) Copper oxide-Anhydrone tube, 96% silica, 1 inch in diameter and 1 i: inches long Heater for copper oxide, 400' C., 7 inches long 96% Silica tube, 0.75 inch in diameter and 2 inches long, to separafp copper oxide from Anhydrone Small absorption bulb, or U-tube with stopcocks Small suck-back trap for sulfuric acid Small sulfuric acid bubble counter
ANALYTICAL CHEMISTRY
2008 On heating electrolytic chromium the hydrogen is given off as elemental hydrogen and not as water vapor (4,37). The bromination-carbon reduction method was found to be applicable to chromium. A reaction temperature of 925" C. must be used to obtain complete reaction of the oxides. Also, the sample should be powdered and mixed well with the graphite. Yo decomposition of the chromic oxide or reaction betneen the graphite and oxygen in the chromium Tl-ould be expected to take place hen the temperature of the reaction tube is raised to 925" C. (9,37). The latter point was checked by obtaining constant weight of the absorption bulb vhile the reaction tube was at room temperature, then heating the reaction tube to 925' C. and holding it a t this temperature for 1 hour. It is not possible to check for completion of the bromination reaction by examination for a cloud of chromic bromide in the vertical portion of the reaction tube, because most of the chromic bromide condenses toward the end of the horizontal part of the reaction tube. Therefore, an adequate time interval should be alloTved for completion of the reaction; 2 hours were required for the samples used by the authors. Chromic bromide rather than chromous bromide is formed in the reaction (31). Chromic bromide, once heated to redness, 17-as found to be an extremely insoluble substance. The only effective solvent xvas a hydrochloric acid solution containing some chromous chloride. Such a solution has been used previously for dissolving anhydrous chromic chloride (31). The effect of the chromous chloride is probably catalytic (31). The solution for cleaning the reaction tube is best prepared by adding sodium or potassium dichromate to dilute hydrochloric acid il to 3) and then adding several grams of granulated zinc. The reduction of the chromium to the divalent state is not quantitative but sufficient chromous ion mill be formed. The oxygen content of commercial chromium is approximately 0.1 to 0.5%. The procedure for the determination of oxygen in chromium is the same as for titanium, Case 11. Allow the reaction to proceed for 2 hours after turning on the bromine. Vanadium. Oxygen in vanadium has been determined by vacuum fusion (35), and by difference (29). The vanadiumoxygen system bears some resemblance to the titanium-oxygen system and the zirconium-oxygen system, but the solubility of oxygen in vanadium is not as great as in the other two metals (11, 29). As with chromium a temperature of 925" C. and intimate mixing of the graphite m-ith the crushed sample is recommended. S o decomposition of the vanadium oxide or ieaction between the graphite and the oxygen in the vanadium nould be expected to take place Then the temperature of the ieaction tube is raised to 925' C. i l l , 24), This point n a s checked in the same way as for the oxygen determination in chromium. S o evidence of the formation of vanadium oxybromide (VOBr3) (31) was noted, probably because there is an excess of carbon in close contact 171th the sample The bromide formed in the bromination is vanadium tribromide (black) (31). Gold boats used for vanadium samples were severely attacked; therefore, platinum boats are recommended. To test for completeness of the bromination reaction it is convenient t o form a "windom" by playing a flame on about I square inch of the vertical portion of the reaction tube, as has been suggested by Kallmann ( 1 7 ) . The presence or absence of a cloud can then be readily observed. Kallmann ( 1 7 ) found that, in analyzing vanadium alloys containing large amounts of aluminum, sometimes about 1 mg. of oxide, identified spectrographically as aluminum oxide (not yellow vanadic oxide), was left on igniting the graphite residue. I t is, therefore, necessary to calculate this aluminum oxide to oxygen and add this figure to the amount of oxygen found on weighing the absorption bulb. Occasionally, a small amount of silicon dioxide is found with the aluminum oxide. Since the factor for converting aluminum oxide t o oxygen is 0.471 and the factor for converting silicon dioxide to oxvgen is 0.533, no significant error is made for the small residue encountered if it is assumed that the
residue is all aluminum oxide. I n analyzing titanium samples containing several per cent of aluminum, the presence of unreacted aluminum oxide was never observed. Commercial vanadium and vanadium alloys contain about 0.1 t.0 2% oxygen. The samples available to the authors contained less than 0.'75% oxygen. There are a great number of experimental vanadium alloys being produced and it is not certain that the method would be applicable to all of them. The determination is the same as given for titanium, Case 11. Use a 1-gram sample of vanadium when the oxygen content is less than 0.5ycand a 0.5-gram sample \
