as boron nitride were detected. In sample 1 the nitrogen is present mostly as Tic&, rather than as TiN, whereas in sample 2 the opposite was found. In the last sample, the DTA-EGA patterns show that two nitrides were present. The second nitride is probably also a zirconium nitride, oxynitride, or carbonitride. No x-ray diffraction patterns were obtai1,able for any of the nitrides. In nearly all the samples shown here, this was probably due to the preponderance of oxides and carbides in the extracted residue.
LITERATURE CITED
( 1 ) Bandi, W. R., Karp, H. S., Straub, W. A., Melnick, L. M., Talunta 11, 1327-37 (1964). ( 2 ) Bandi, W. R., Straub, W. A., Karp,
H. S., Melnick, L. M., Am. SOC.Test-
ine Mater.. Svec. Tech. Pub. 393. 22-38 (1366). ( 3 ) Bandi, W. R., Straub, W. A., Karp, H. S., Melnick, L. M., National Meeting, AIME, Philadelphia, Oct. 19, I
.
1O A A
(4jBeeghly, H. F., ANAL. CHEM.2 1 , 1513 (1949). ( 5 ) Ibid., 24, 1095-1100 (1952). ( 6 ) Ibid., p. 1713-21. ( 7 ) Frame, J. W., Schunk, F. B. S.,
AIME Special IMD Rept. Ser. No. 6, 57 (1958). (8) Garn, P. D., Talantu 11, 1417-32 (1964). ( 9 ) Holthaus, C., Holtmann, W., Archiv. Eisenhuttenw. 17, 247-60 (1944). (10) Kempf, H., Abresch, K., Ibid., pp. 261-70. ( 1 1 ) Marot, J., Ind. Chim. BeEge. 22,116174 (1957). (12) Shapiro, C. L., Trans. Am. SOC. Metals 27, 666-95 (1939). (13) Straub, W. A., Bandi, UT. R., Melnick, L. M., Karp, H. S., Eastern
Analytical Symposium, New York, Nov. 11, 1964. RECEIVED for review March 31, 1966. Accepted June 13, 1966.
Determination of Metallic Impurities in Molybdenum by a Combined Ion Exchange-X-Ray Spectrographic Method ERNEST F. SPAN0 and THOMAS E. GREEN U. S. Deparfmenf o f fhe Inferior, Bureau of Mines, College Park Metallurgy Research Cenfer, College Park, Md.
b Trace quantities of cobalt, copper, iron, lead, magnesium, manganese, nickel, and zinc are separated by ion exchange, from molybdenum samples weighing up to 10 grams. The separated trace metals, other than magnesium, are collected on ion exchange resin loaded paper disks and determined by x-ray spectrography. Magnesium is separated from molybdenum by the ion exchange technique and determined by atomic absorption. All the above trace metals are determined at the part per million level with a precision within =t10% of the amount present. The method also provides a semi-quantitative estimate of the aluminum and calcium concentration. Attempts to include chromium and titanium in the method were unsuccessful.
A
ANALYTICAL METHOD for determining trace metal impurities in molybdenum was required in support of the Bureau of Mines program for producing and evaluating high purity metals. Spectrophotometric methods for determining some trace metals in molybdenum have been developed. However, these methods generally require a separate sample for each metal to be determined. Although optical spectrographic methods are capable of determining a number of metallic impurities in a single sample, they do not provide the required sensitivity and precision. An x-ray spectrographic method in which the elements to be determined are collected on an ion exchange resin loaded paper disk (1) makes it possible to I,
determine a large number of elements in a single sample with good precision. The sensitivity of this method is increased by preconcentrating the impurities from a large sample before collecting them on the ion exchange paper disks. This ion exchange paper x-ray spectrographic method w&s previously developed to determine trace metal impurities which had been separated from high purity tungsten by ion exchange (4,6)or solvent extraction ( 2 ) . Development of an ion exchange column technique for separating trace metals from molybdenum made it possible to use the above method to determine trace metals in molybdenum. This report describes the evaluation of an analytical method based on the ionexchange column separation, and ion exchange paper-x-ray spectrographic determination of trace elements in molybdenum. The trace metals investigated were aluminum, calcium, chromium, cobalt, copper, iron, lead, magnesium, manganese, nickel, titanium, and zinc. EXPERIMENTAL
All chemicals used were of reagent grade. All water used throughout the procedure was prepared by single stage distillation, followed by passage through a mixed bed laboratory demineralizer. Stock solutions of trace metals were prepared by dissolving each metal or oxide in then diluting to a conHC1 or "03 centration of 100 pg. per ml. Titanium was dissolved in HzSOI and complexed with HzOz. Aliquots of each stock solution were taken to prepare working Reagents.
solutions containing 2.0 or 5.0 pg. per ml. of the trace metals. Short range hydrogen ion test paper (pH 1.0 to 2.5) was used for pH measurements. The ion exchange columns used to separate the trace metals from molybdenum contained 100- to 200-mesh Dowex 50W X 12 resin in the hydrogen form. (Trade names are used for information only, and endorsement by the Bureau of Mines is not implied.) The resin was pretreated by stirring approximately 200 grams of the resin in 750 ml. of water, allowing the coarser particles to settle, and decanting the broken and fine particles which were discarded. The washing and decanting procedure was repeated several times. Glass chromatographic tubes, 1.5 cm. in diameter, were filled to a bed height of 10 cm. with the washed resin. These tubes had sintered glass plates to support the resin and valves of Teflon to control the flow rate. A layer of acid-washed glass wool was placed on top of the resin bed and a 3-inch layer of acid-washed 50-mesh ground glass was placed on top of the glass wool. The prepared columns were washed with 150 ml. of 6 N HC1 a t a flow rate of 0.5 ml. per minute, then washed free of acid with water. The ion exchange resin loaded paper disks used to collect the separated metals for x-ray spectrographic determination were Reeve Angel SA-2 paper containing Amberlite IR-120 resin in the sodium form, purchased as precut 3.5-cm. diameter disks. These disks were cleaned by the following treatment. Five to ten disks were soaked in water for a few minutes and placed in the filtering apparatus (1). Two 40-ml. portions of 6N HCl were filtered five times through the disks VOL 38, NO. 10, SEPTEMBER 1966
1341
Table 1.
Determination of Cobalt, Copper, Iron, Lead, Manganese, Nickel, and Zinc in Molybdenum and Molybdenum Trioxide
Trace metal added, Sample M o metal,
pg. 0.0
5.00
Cobalt, pg. Iron, pg. Lead, pg. Manganese, pg. Nickel, pg. Zinc, pg. Copper, ag. Total Found Total Found Total Found Total Found -Total Found Total Found Total Found
...
grams 10.0
10.5
25.0
25.5
50.0
50.5
0.2 0.5 0.5 0.6 9.7 10.3 25.4 25.5 24.8 25.8 50.4 51.5
38.5 53.5
78.5
51.8
75.0 100.0
MoOa,
0.0
7.50
grams
25.0 50.0
51.4 75.5 76.2 100.5 100. 101. 101. ... 100. 1.6 1.2 26.4 25.5 26.5 51.4 49.5
1342
ANALYTICAL
CHEMISTRY
99.6 100. 101. 101. 112.
5 3 . 2 125. 54.8 54.8 53.6 7 8 . 8 150. 78.0 80.8
125. 129.
25.0
151. 148.
50.0
103.5 106. 128.5 123. 128. 126.
...
130.
155.
150.
180.
175.
and .the excess acid was removed by passing several portions of water through the disks. The resin in the disks was then reconverted to the sodium form by passing two 40-ml. portions of saturated NaCl solution through the disks five times. The disks were then rinsed with distilled water to remove excess NaCl and dried. Apparatus. X-ray spectrographic instrumentation consisted of a Philips Electronics 60-kv., 50-ma., full-wave rectified power supply with an FA-60 tungsten target x-ray tube, an inverted three-position sample chamber, a 0.005- by 4-inch, or 0.02- by 4-inch parallel plate collimator, a P E T (pentaerythritol) or LiF crystal, and a scintillation counter or gas flow proportional counter, both with pulse amplitude discrimination. A Philips Electronics vacuum x-ray spectrograph with a Machlett OEG-60 chromium target x-ray tube and a PET crystal were used for aluminum determinations. The filtering appartus used to collect the trace metals on ion exchange resin loaded disks and the holder for inserting the disks in the x-ray spectrograph are described in a previous publication (1). A Perkin-Elmer Model 303 atomic absorption spectrophotometer was used to determine magnesium in column eluates. Procedure. A reagent blank is carried through the entire procedure with each set of samples to provide a correction for impurities introduced by reagents. The following procedure is for 5-gram samples; for 10-gram samples, double the quantities of the reagents used to dissolve the sample. Transfer the weighed sample to a 100-ml. beaker and add 15 drops of concentrated HaPO4and 5 ml. of water.
...
29.2 ... 28.5 28.0 28.3 3 7 . 9 110. 38.9
175. 200.
...
177. 201.
84.5
134.5 135.
10.0
