Spectrographic Analysis of High Purity Nickel RICHARD L. RUPP, GEORGE 1. KLECAK, and GEORGE H. MORRISON General Telephone & Electronics laboratories, Inc., Bayside, N. Y.
b A rapid direct spectrographicmethod is described for the determination of impurities in high purity nickel in the concentrotion range of 0.1 to 100 p.p.m. By performing spectrographic excitation in atmospheres of argon and nitrogen, it has been possible, under proper conditions, to increase the sensitivity for many elements several orders of magnitude over previous methods.
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N CONNECTION with a research program on purification and fabrication processes used in the preparation of nickel components of electron tubes, a rapid direct spectrographic method for the determination of trace impurities has been developed which is applicable to many elements in the concentration range of 0.1 to 100 p.p.m. High purity nickel is used as a base for the alkaline earth emitters in electron tubes. The use of materials of higher purity is essential to understand better the phenomenon of thermionic emission and the interaction of materials in the tube. Although chemical methods are generally employed for the determination of trace impurities in nickel, they require large samples, are time-consuming, and are subject to contamination by reagents. A direct spectrographic method which is capable of analyzing simultaneously for many impurities in samples of limited size is preferred; however, previous methods could be employed only down to a concentration OS 40 p.p.m. (8, 4). These procedures were based on a total burn method in air, whereby the sample was completely burned in a spectrographic arc to ensure total volatilization of impurities into the arc stream. The simultaneous volatilization and excitation of the matrix material over the entire period of arcing contributed heavily to the background on the photographic emulsion, so that the spectral lines of the impurity elements were heavily masked. By performing the arcing under less rigorous conditions achieved through the use of argon or nitrogen atmospheres, it is possible to increase spectrographic sensitivity several orders of magnitude. EXPERIMENTAL
Apparatus. SPECTROGRAPH. JarrellAsh 3.4-meter plane grating spectro-
Figure 1.
Spectrographic arc chomber
graph. Grating contains 15,000 lines per inch blazed for 3000 A. in t h e first order. A three-lens system is used with a step sector (ratio 1 to 2). ARC SOURCE. Jarrell-Ash Custom Varisource. ARC Box. Jarrell-Ash type fitted with a demountable glass box for inert atmosphere work (Figure 1). The box consists of a borosilicate glass cylinder, 7.8 em. long and 11.5 em. in outside diameter, and with a wall thickness of 0.6 em., similar to that previously described (5). One side of the box is fitted with a side tube in line with the optical center of the spectrograph and containing a quartz window. The ends of the glass chamber are fitted with tight-fittig aluminum disks which are machined to fit and center the electrodes. An outlet port was drilled into the upper disk and an inlet port was drilled into the lower disk. SPECTROGRAPHIC PLATES.Eastman Kodak 103-0. Plates were tank developed for 3 minutes a t 20OC. in D-19 developer. Plates were fixed in acid hardening fixer for 10 minutes at 20°C. and washed for 10 minutes in clear cold running water. DENSITOMETER.Jarrell-Ash console microphotometer. Slit setting was 10 microns a t 0.7-mm. height. ELECTRODES. Anode, United Carbon carbon electrode No. C423; cathode, United Carbon graphite electrode No. 5770. FLOWMETER. Scientific Glass 5-2540 rotameter containing 5/32inch diameter stainless steel ball. Flow rate range, 100 to 1200 cc. per minute. Spectrographic Standards. Mond carbonyl nickel powder Lot 9/14
(particle size 6 to 9 microns) served a s t h e matrix to which known amounts of impurities were added. A series of standards was prepared by successive powder dilutions of a master mix containing the oxides of 11 elements: Al, Go, Cr, Cu, Fe, Mg, Mn, Pb, Sn, Ti, Zn, and elemental Si powder. Each of these impurities was a t a concentration of 0.57% in the master mix. Attempts to add the impurities in the elemental form resulted in anomalous results in the low concentration range. The anomalies were found to he due to unfavorable particle size distribution of the impurity elements. Glass vials were used in all blending operations rather than plastic vials to avoid the creation of electrostatic charges, which tended to separate powdered oxide impurities from the matrix. Procedure. Nickel powder, sheet, or turnings are placed in t h e carbon electrode crater and lightly compacted so t h a t three fourths of the cup is filled. The electrodes are then nlaced in t h e demountable glass arc box and flushed for 3 minutes with argon or prepurified nitrogen gas at a flow rate of 600 cc. per minute. Samples and standards a& arced in both argon and nitrogen. It is suggest.ed that standards be run on all plates to correct for lateral shifting of working curves. Conditions for the analysis are:
GENERAL Amperage d.e. 14 Analytical gap, mm. 3 First 2 mm. from Arc region used anode Exposure, see. 10 Slit width, microns 15 Source to slit distance, 75.0 om.
_. Spectral re- 2300-3600 2300-4600 gion, A. Atmosphere Argon, 3 min. Prepurified Flush nitrogen, 3 mi”. Flowing arFlawing Run prepurified gon, 600 nitrogen, cc./min. 600 cc.1 min.
PHOTOMETRY. Line pairs listed in Table I are read on the densitometer. The intensity ratios are computed in the conventional manner using emulsion calibration curves obtained by a sixVOL. 32, NO. 8, JULY 1960
-
931
L
10c
C. r -B L-A-. N K. -.
1 ; :
01
I00
IO
Figure 2.
step sector (1). The analytical ranges for all the elements are given in Table I. RESULTS AND DISCUSSION
Studies of the effects of various atmospheres on the arcing process have shown that argon is particularly ef-
Table I.
Line Pairs and Analytical Ranges
Kave Length,
Internal Standard, Range, P.P.11.a Element A. A. 1 0-100 A1 3092.71 2881 25 3 0-100 CO 3405 12 2881 25 2 0- 20 4254 35 4244b Cr 0 4- 10 CU 3273 96 2881 25 Fe 3020 64 2881 25 30 -100 0 3- 30 1 1 ~ 2779 83 2881 25 0 3- 30 2576 10 2881 25 11; 0 3- 30 I’h 2883 07 2881 25 20 -100 Si 2881 58 2881 25 1 0- 30 3175 0 2 2881 25 Sn 10 -100 3349 41 2881 25 Ti 0 2- 10 Zn 3345 0 2 2881 25 a Limits of sensitivities for i l l , Cr, Cu, Fe, and Si could not be determined tiecause of these residual impurities i n matrix material used in preparation of standards. b Unlisted nickel line. Table II. Residual Impurities in Nickel Powder Used in Preparation of Standards
Impurity
Residual Estimated, P.P.11.
A1 co
1 6 < 3
Cr cu
Fe
Mg Mn Pb Si Sn
2 0
0.1
26 0 30
