CONCLUSION
I n aromatic sulfonation reaction mixtures the quantity of sulfonic acid can be found directly, following removal of sulfate with barium hydroxide and passage of the filtrate through a cation exchange column. The regenerated sulfonic acid is determined alkalimetrically. Sulfate and sulfuric acid may be calculated, folloming determination of total acid and total sulfate. I n an alternative procedure sulfonic acid, total acid, and total anion are determined. Because of the lon solubility of their barium salts, some aryl sulfonates are not satisfactorily determined. I n the analysis of polysulfonation reaction mixtures the possible presrnce of sulfonated sulfones must he considered. The precision of the sulfonic acid determination is n ithin 1%. LITERATURE CITED
(1) Biffen, F. AI., Snell, F. D., 1x0. EKG. CHEX,X s . 4 ~ ED. . 7, 234 (1935).
Table IV.
Total Acid and Total Anion in Prepared Sulfonation Mixtures
Sulfonate Added Sodium benzene sulfonate Sodium p-toluene sulfonates
Total Acid, Added 2.50 2.50 2.50 2.50
2.50 2.50
Meq. Found 2.50 2.51 2.51 2.51 2.50 2.51
Total Snion, Xeq. Added Found 5.33 5.35 5,44 5.49 5.55 5.55 5.52 5 57 552 5.53 5.52 5 56
a Aliquot portions of stock solution. Amount of sulfate would be difference between total anion and sulfonic acid.
Epton, S. R., l'rans. Faraday Soc. 44, 226 11948). Hart, R . , I ~ DEKG. . CHEW,B s . 4 ~ . ED. 11, 33 (1939). House, R., Darragh, J. L., .%SAL. CHEM.26, 1492 c1954). Jones, J. H., J . Assoc. O#c. A y r . Chemists 28. 398 11945). Kling, IT.,Puschel, F:, Jlelliand Teztilber. 15, 21 (1934). Marron, T. V., Schifferli, J., ISD. ENG. CHEM.,ANAL. ED. 18, 49 (1946). Shiraeff, D. -1., S m . Dyestuff Reptr. 36, 313 (1947).
(9) I b z d , 37, 411 (1948). (10) Stupel, H I Segesser, A. V., HelL. Chim. Acta 34, 1362 (1951) (11) Swisher, R. D. (to Monsanto Chemical Co.), Brit. Patent 679,826, 679,827 (Sept. 24, 1952). (12) Keiss, F. T., O'Donnell, A . E , Shreve, R. J., Peters, E. D , ANAL. CHEN 27, 198 (1955). (13) Kickbold, R , Z. anal. Chem. 132, 241 (1951).
RECEIVED for revien- May 10, 1 9 5 i . .ICwpted August 12, l95i.
Determination of Oxygen in Niobium W. R. HANSEN and M. W. MALLETT Battelle Memorial Institute, Columbus, Ohio Oxygen in niobium is determined by a diffusion-extraction method using conventional vacuum-fusion equipment. The mean deviation of analyses at the 0.019 weight oxygen level is less than 0.001 weight %. The sensitivity of the analysis could be increased by increasing the sample size.
by fusing the sample in an iron bath, and it seems likely that hydrogen in niobium could be determined by a hotextraction technique. A suitable technique for the determination of oxygen in niobium was developed.
W
Initial experiments were carried out by established vacuum-fusion practice. Specially prepared analytical specimens were dissolved in carbon-saturated metal baths. Analyses \\-ere made in iron and nickel baths a t operating temperatures of 1650" C. (3000' F.) to 1750" C. (3180" F.).
70
ITH the ever-increasing reaiization of the gross effects which interstitials such as oxygen, hydrogen, nitrogen, and carbon can have on the physical properties of metals, considerable effort has been directed toward quantitative determination of these elements. For the most part, adequate methods have been developed fo: the determination of nitrogen and carbon. Probably the most versatile method for determining oxygen and hydrogen in ferrous and nonferrous metals is the vacuum-fusion method, which was originally developed for steels. The physical and thermodj namic properties of the various metals differ so widely that no single vacuum-fusion technique can be applied to all. When niobium and niobium alloys were considered for use in nuclear and other applications a means of determining oxygen and hydrogen n as needed. A brief study showed that hydrogen could be determined readily '
1868
ANALYTICAL CHEMISTRY
EXPERIMENTAL
The results were low and erratic. Varying the temperature of the bath had no effect on the consistency of results. These initial analyses were made with arc melted reference materials which subsequent analyses indicated were not homogeneous. 9 limited number of analyses were made using a platinum bath and an operating temperature of 1900" C. (3460" F.). Although satisfactory material was used, again the results \\ere loiv and erratic. rlng and Wert (1) demonstrated that oxygen could be extracted from niobiumniresheatedat2000"C. (3630°F.) in a vacuum of 10-5 mm. of mercury. This technique was investigated to
determine if it could be used for quantitative analysis. APPARATUS
The vacuum-extraction apparatus ( 2 ) is sensitive to a change of 0.005 nil. a t gas volumes less than 0.5 ml. and a change of 0.01 ml. in the range 0.5 to 2.5 ml. For a 0.3-gram sample, used for most of the determinations, 0.01 ml. of carbon monoxide is equivalent to 0.0023 weight % oxygen. PROCEDURE
Preparation of Samples. T K Oseries of reference samples n-ere prepared : one by arc melting and t h e other by a manometric technique. High-purity niobium and known amounts of U.S.P.-grade niobium pentoxide were melted together under a helium atmosphere in a tungsten electrode arc furnace. To distribute the oxygen as uniformly as possible. the arcmelted buttons were turned over and remelted twice. Other reference samples n ere prepared by cutting 1.5-inch-long samples from a length of ','*-inch diameter highpurity niobium rod. These pieces nere dry abraded with silicon carbide paper and suspended in a quartz tube by means of a platinum-platinum plus 10% rhodium thermocouple spot-welded to one end. They were heated in the gas
addition apparatus for 1 hour a t 1100' C. 12010" F.), cooled to room tempcratu)e, and removed from the system. This twatment removed hydrogen and honiogenizcd the oxygen content of the nioliiuni. Approximately 1 gram of the treated rod was cut off for analysis to establish the base oxygen level. The remaining length was again placed in the manometric apparatus and heated to 1100" C. (2010" F,). A measured quantity of oxygen, produced by the thermal decomposition of potassium permanganate, was added and reacted with the sample. After the sample had been held a t temperature for approximately 5 hours, it was cooled in vacuum and subsequently analyzed. Arc-melted materials were sanipled by sawing pie-shaped pieces from the button ingots. Rods treated by the manometric technique were sawed into crosssectional segments. Although there n-as no visual evidence of undissolved oxide on the surfaces of the rods after the additions, only the cut surfaces were abraded to prevent inadvertent loss of added oxygen. Analysis. Weighed samples were loaded in t h e furnace arm of t h e vacuum-extraction apparatus and the system was evacuated and degassed a t 2400' C. (4530' F.) for approximately 2 hours. T h e temperature was then lowered t o 2000' C. (3630" F.) and a blank collected for 5 minutes. If the blank rate was equivalent to or less than about 0.025 cc. per 30 minutes. the temperature \vas lowered t o 1200" C. (2190" F.) and a 30-minute blank started. Kithin 5 minutes the temperature was raised to 2000' C. (3630" F.), thus following the heating schedule t o be used for the sample. After the blank had been analyzed, the sample n a s dropped into the graphite crucible a t 1200" C. (2190" F.) and the temperature was raised to 2000" C. (3630F.). Usually 30 minutes was required to extract the gases completely. The evolved gases were analyzed by the fractional-freezing technique. RESULTS AND DISCUSSION
The results obtained by the diffusionextraction method for the arc melted reference materials are listed in Table I. I n all cases, the analytical values were lon-er than the estimated total oxygen content. The deviation of the analytical values from the intended oxygen content was greater than the 10% usually expected for analyses on homogeneous materials. The low oxygen contents may have resulted from spattering during arc melting. Table I1 lists the results obtained for the reference materials prepared by manometric additions. The analyses are in very good agreement with the estimated total oxygen contents of the samples. All values agree within +10 relative %. The reproducibility of the diffusionextraction method is shown by Table 111. The mean deviation of the results
Table I.
0 314
0:0k
0.287
0.043
0.264 0 228 0 292
5
Analysis" of Arc Melted Reference Samples
0 070 0 098 0 124
0 395 By diffusion extraction. Table 11.
Sample Wt.,
Cram 0,259 0.341 0 343 0.228 0.220 0.180 0.463 0.398 0.364
0.032 0,042 0.064 0 086 0 096 0 123
0: 048 0.077 0 102 0 128 0 155
-0:006
-0.013 -0 016 -0 032 -0 032
Determination of Oxygen in Manometric Samples w t . C,r -
Added as 0 2 0: 095
Estd. total
o:i2o
0.095
0 120
0 : 200
0.200
0 : 229 0 229
0 : 300
o.3i9 0,319
0.300
a t the 0.019 weight % oxygen level is less than 0.001 weight %. Because the sensitivity of the apparatus is equivalent t o only =k0.002 weight yo for the sample weights used, the deviation is better than might be expected. The sensitivity of the analysis could be increased by increasing the sample size. However, to maintain the same gas extraction time, the sample thickness should remain the same, because the extraction process seems to be diffusion controlled. The results of the present investigation show the diffusion-extraction method to be applicable to the determination of oxygen in niobium. I t is probable that methods using the iron or nickel baths would have proved equally satisfactory if tested with samples prepared by the manometric method. Further investigation of the platinum bath might have shown it t o be satisfactory. Although the mechanism of the extraction is not fully understood, it appears that the oxygen diffuses to the sample surface \There it is desorbed as carbon monoxide. The source of the carbon is probably vapor from the graphite crucible because the vapor pressure of graphite is about 3.4 X low6 mm. of mercury ( 3 ) a t the extraction temperature, 2000" C. If any of the oxygen is desorbed as 02,it must immediately react with its surroundings to produce carbon monoxide. KO O2 or carbon dioxide n-as observed in the extracted gas. CONCLUSIONS
4 difiusion-extraction method developed for the determination of oxygen in niobium yields reproducible and ac-
Deviation
Exptl. 0.025 0 124
+0:004 $0.010
0.130 0 029 0 236 0.227 0 019
+0:007
-0.002 -0:013 +0.011
0.306 0.330
Table 111. Determination of Reproducibility of Method
Sample wt., Gram 0 432 0 480 0 382 0 476 0 349 0 428 0 382
Mean
Oxygen,
Wt. yo 0 018 0 019 0 0 0 0 0 0
Deviation
018
020 018 020 018 019
-0.001 0.000 -0 001 $0 001 -0 001 +o 001 -0 aoi 0 001
curate results. The meaqleviation of analyses of O.5-gram samples containing 0.019 weight yo oxygen was =tO.001 weight 97,. This precision could be increased to +0.0001 weight 97, by use of 5-gram samples. The analysis can be carried out in conventional vacuum-fusion equipment. Vnsatisfactory results obtained in a few attempts to use the platinum-bath technique do not preclude the applicability of this and other molten bath methods. ACKNOWLEDGMENT
The authors wish to thank W. 11. Albrecht v h o prepared the manometric reference materials, and R. G. Evans and R. C. Davis who performed the analyses. LITERATURE CITED
(1) Ang, C-Y., Wert, C., J . Metals 5 , AZME Trans. 197, 1032-6 (1953). (2) Mallett, M. W., Griffith, C. B., Trans. Am. SOC.Metals 46, 375-88 (1954).
(3) Simpson, 0.C., Thorn, R. J., Winslow, G. H., U.S. Atomic Energy Comm.,
Declassified Rept. AECD-2680 (May 6 , 1949). RECEIVED for review June 10, 1957. Accepted August 21, 1957. VOL. 29, NO. 12, DECEMBER 1957
1869
