a i d Hagan Chemicals and Contrors, Inc., Pittsburgh, Pa., is gratefully ackno\\ ledged. LITERATURE CITED
11) Critchfield. F. E.. Johnson. J. B.. ANAL.CI&. 28, 430 (19%). ’ 12) Zbid., p. 436. ( 3 ) Zbid., 29, 957 (1967). ( 4 ) Zbid., p. 1174. ( 5 ) Hershenson, H. lI., Hume, D. S., Ihid., 29, 16 ( 1 9 5 T ) . \
,
(6) Hopps, G. L., Getz, M. E., Berk, A. A., “Trace Concentrations of Octadecylamine and Some of its Degradation Products,” -4SlIE Paper S o . 58-A-264 (1958). (7) Jackson, J. E., ASAL. CHEK 25, 1‘764 (1953). 1 8 ) McIntire. F. E.. Clemets. L. M.. Sproull, Li., Ibid., ‘25, 1957 11953). ‘ ( 9 ) Milun, A. J., Zbid., 29, 1E02 (1957). (10) Pvlilun, A,, Moyer, F., Ibid., 28, 1204 (1956). (11) Milun, 1. J., Nelson, J. P., Ibid., 31, 1655 (1959). > - ,
(12) Munter, C. J. (to Hayan Chemicals and Controls), U. S. Patent 2,977,200
(March 28, 1961). (13) Pearce, 4 . S., Chem. a n d Znd. ( L o n d o n ) 1961, 825. (14) Sass, S., Kaufman, J. J., Cardenas, -4.A., Martin, J. J., ANAL.CHEM.30, 529 (1958). RECEIVEDfor review June 25, 1962. lccepted December 10, 1962. Division of Water and Waste Chemietry, 141st Meeting, ACS, Washington, D. C., March 1962.
Determination of Boron in Boron Nitride, Boronated Graphite Rods, Titanium Borides, and Zirconium Borides Using Tiron or EDTA as Masking Agent JOSEPH W. TERESHKO Development laboratory, National Carbon Co., Division of Union Carbide Corp., Fosforia, Ohio
b An investigation of various boron determinations results in a method which replaces the classical barium carbonate precipitation with a chelating agent. The elimination of metal interference in the Group IV borides due to titanium and zirconium i s ac., complished by chelating them with 4 3 dihydroxy-m-benzenedisulfonic acid disodium salt (Tiron). The elimination of metal interference in boron nitride and boronated graphite rods caused b y iron, aluminum, and manganese i s accomplished by chelation with (ethylenedinitri1o)tetraacetic acid disodium salt. The presence of silicon has no bearing on the results obtained b y this method. These chelating agents have been successfuily applied to the analysis of boron nitride, boronated graphite rods, titanium borides, and zirconium borides. This method should be useful as a fast and accurate procedure for routine analysis. have been devised to determine boron in refractory borides and other Loroii containing compounds. Some of these procedures employ separation of boron by volatilization as methyl borate, the extraction of boric acid using ether, or by weighing the boron as calcium borate ( 6 ) . There are many other procedures suggested in the literature but they are too numerous to mention. Herman Blunierithal ( I ) describes a n excellent method for determining boron in metal borides. The interfering metal ions which he encounters after a sodium carbonate fusion are separated with A polyhydric barium carbonate. alcohol, such as mannitol or glycerol, ARIOUS METHODS
produces a titratable acid, and sodium hydroxide is used as the titrant. The method described by Blumenthal gave satisfactory results, but we felt that a chelating agent could be used to inactivate metal interferences, thereby eliminating the precipitation step. The methods developed while investigating man! samples, are based on using a chelating agent to inactivate metal ions nhich mould interfere n i t h the sodium hydroxide titrant (6). After suitable chelating agents were found, a pol) hydric alcohol was sought n i t h 11hich these chelating agents could be used without unfavorable effects. An investigation of sorbitol (4) and invert sugar (?) failed to giIe the desired results. Mannitol appeared to have the qualities needed, and with this knowledge, simple and accurate methods were devised. EXPERIMENTAL
Standardization of Sodium Hydroxide for Boron Nitride and Boronated Graphite Rods. Dissolve 0.5
gram of high purity boric acid in 150 nil. of distilled water. Make t h e solution acid to methyl purple with 1 t o 1 hydrochloric acid. Cover and boil t h e solution for 15 minutes to remove carbon dioxide. During this 15-minute boiling period, the solution must be kept acid by adding 1 to 1 hydrochloric acid dropwise. Cool t h e solution t o room temperature a n d neutralize t o pH 7 . Adjust to a b o u t pH 4 n i t h mannitol (6 t o 8 grams) and titrate to p H 8.2. R u n a blank on t h e reagents used. Standardization of Sodium Hydroxide for Titanium and Zirconium Borides. Same as for boron nitride
a n d boronated graphit e rods, except
after adjustment to p H 4 with mannitol, t h e boron is tit’rated to p1-I 7. Procedure for Analyzing Boron Nitride and Boronated Graphite Rods. Keigh 0.2 gram (=k0.0001 gram) of
sample into a 30-mi. platinuin crucible, add 1 gram of sodium cnrbonate, and mix until t h e sample and carbonate are homogeneous. (lover t h e niixt’ure with a n additional gram of sodium carbonate, and begin the fusion over a Fisher burner at, a loiv temperature. Gradually increase t h e temperature t o a bright rcd heat’. Care must be taken that t,here is no mechanical loss of sample due to excessive gassing. When tlie fusion is complete, remove from tlie heat and rotate the crucible allon-iiig the melt to solidify on the sides of the crucible. Place the crucible and lid in a 600-ml. beaker containing 200 ml. of hot distilled water and cover the ljenker with a watch glass. Heat the contents to accelerate tlie leaching. TVhen the melt has completely disintegrated, remore and rinse platinum ware with distilled water. Make the solution acid t o methyl purple or methyl red with 1 t,o 1 hydrochloric acid. Cover and boil the solution for 15 minutes t o remove carbon dioxide. During this 15-minute boiling period, the solution must be kept acid by adding 1 t o 1 hydrochloric acid dropvise. Cool the solution to room temperature and add 2 nil. of a 0 . l J I aqueous solution of EDTA. Seutrnlize the solution to approximately pH i with 20% carbon dioxide-free sodium hydroxide, and adjust to exactly p H 7 Iyith 0 . 2 5 carbon dioxide-free sodium hydroxide or 0.2.V hydrochloric acid. Adjust, to approximately pH 4 with mannitol (6 to 8 grams). Titrate t o a p H of 8.2 nit11 standard sodium hydroside. Repeat the mannitol addit’ion and sodium hydroxide titration until a p H of 8.2 VOL. 35, NO. 2, FEBRUARY 1963
157
is maintained after the addition of mannitol (Table I). The end point is quite easily read at p H 8.2, but in a m r m solution the end point may not be as sharp because the stability of the complex acid falls off rapidly as the temperature increases.
Procedure for Analyzing Titanium and Zirconium Borides. T h e procedure for preparing t h e sodium carbonate fusion of titanium a n d zirconium borides is the same as for BS. After the fusion is complete place the crucible and cover in a 600-ml. beaker containing 60 ml. of 7 S hydrochloric acid. Cover the beaker with a n-atch glass and dissolve the melt. If necessary, heat gently, but do not boil. Remove and rinse the platinum ware with water. Adjust the volume of solution to 200 ml. Boil the solution for 15 minutes to remove carbon dioxide. Cool the solution t o room temperature and add the calculated amount of 2% aqueous solution of Tiron to complex completely titanium and zirconium, plus 1 ml. in excess. Add 2 ml. of 0.1W FeCI3 and 2 ml. of 0.1N tartaric acid. Adjust the solution to approximately p H 7 with 207, sodium hydroxide, and then exactly pH 7 with 0.2.Y sodium hydroxide or 0 . 2 S hydrochloric acid. Adjust to approximately pH 4 with mannitol (6 to 8 grams) and titrate to p H 7 . (Table 11). CISCUSSION
Many of the available methods suggest that carbon dioxide be expelled under reflux to avoid loss of boron ( 5 ) . All of the samples analyzed were made
Table I. Reproducibility of Boron in Boron Nitride and Boronated Graphite Rods
Boron 9: Present Found
Sample
Compound
2
B?;
43.3
43.2 43.3
4
Boronated graphite rods Boronated graphite rods
19.7
19.8 19.9
5
Table II.
29.5
29.5 29.5 29.6
acid to methyl purple and boiled in a covered beaker for 15 minutes t o ensure complete expulsion of carbon dioxide. There was no noticeable loss of boron in any of the samples, and i t was concluded that expulsion of carbon dioxide under reflux was not necessary. KO experiments were conducted to determine if hafnium is chelated by Tiron, but there is no reason why it should not be, together with zirconium. These metals form a chelate with Tiron on a 1 to 1 molar ratio. Other chelating agents tried for titanium and zirconium included (9): tartaric acid, citric acid, 8-quinolinol, and EDTA. These reagents either did not chelate the metal ions in question or interfered with the titration of the organic borate. Titanium and zirconium are chelated with a calculated amount of Tiron and an excess is added. Ferric chloride is added to eliminate interference due to the excess Tiron, and tartaric acid is used to keep the excess iron in solution. The tartaric acid does not interfere when a pH 7 end point is used. Addition of Known Amounts of Metals to Boron Nitride. T h e elimination of interference due to iron, aluminum, and manganese in boron nitride and boronated graphite rods is accomplished by chelating them with EDTA. EDTA also forms a chelate with the metals on a 1 to 1 molar ratio ( 3 ) . These metals precipitate when leached from a sodium carbonate fusion, but no adverse effects n-ere noticed with iron or aluminum, because these precipitates are soluble when the sample solution is acidified (approximately p H 2 to 3). The manganese precipitate which occurs from a water leach is insoluble in the above p H range; therefore, an acid leach is used to keep this metal in solution. T o prove that EDTA would work satisfactorily, synthetic samples containing iron, aluminum, and manganese were prepared using high purity boron nitride powder and the ovides of these metals. These samples were analyzed for the knonn boron content by the method described. As shown in Table 111, no noticeable interference was observed as a result of these metals. Silicon does not appear to have any bearing on the results obtained by this method. Synthetic samples containing high purity boron nitride and up to 30
Reproducibility of Boron in Titanium and Zirconium Diborides
Boron recovered, % Sample 3 Sample 2 Zr. 75 3% Ti, 58 8 5 B, 17 3y0 B, 25 2c70 25 3 17 1 25 2 17 2 25 2 17 4 25 1 17 2 ~
Sample 1 Ti, 67.0% B, 29 5% 29.3 29.4 29.3 29.6
158
ANALYTICAL CHEMISTRY
Sample 4 Zr, 77 8% B, 18 1% 18 1
18 3 18 2 18 I
Table 111. Reproducibility of Synthetic Samples of Boron Nitride
43.67, boron present Sample No. 1
2 3
1
2 3
Metal added Fes(SO& MnSOa AI203
SOn SiOn SiOs
Boron found, Gram 0.010 0.010 0.005 0.0218 0.0410 0.873
a7
/O
43.5 43.5 43.5 43.7 43.6 43.7
weight per cent silicon dioxide were analyzed with and without EDTA additions. The results obtained from these analyses mere the same as that of the known boron content. rill indications show that silicon does not interfere when the p H is adjusted to seven before the organic borate is formed with mannitol. EDTA has no bearing on silicon interference because it does not chelate with thiq metal (Table 111). In using EDTA, a maximum error of & O . l % nil1 occur if all of the chelating agent is used to inactivate metal ions when 2 nil. of a 0.1X solution is used for a 0.2 gram sample. I n determining the blank required by EDTA, a study was made using 1, 2, and 3 grams of sodium carbonate m-ith 2 ml. of a 0.1M solution of E D T -1 and mannitol. The amount of sodium hydroxide required for the three varied bv 0.05 ml. which proved insignificant. TThen 10 ml. of EDTA were used, the blank varied considerably with different amounts of sodium carbonate. Therefore, if more than 2 ml. of EDTA are required, a study should be made of EDTA us. sodium carbonate. ACKNOWLEDGMENT
The author acknowledges the technical assistance and encouragement of Jacob Weinard and Vernon Rolland, and the assistance of the National Carbon Development Laboratory in carrying out this investigation is appreciated. LITERATURE CITED
(1) Blumenthal, H., ANAL. CHEM. 23,
992 (1951).
(2) Cheng, K. L., Ibid., 33, 783 (1961). (3) Flaschka, H., ilbdine, I
