~
Table 111.
~
~~~
0.80% KN03 0.80% KNOa
0.83% KN03 0.80% KNOI
lants did not interfere. Oxidizing agents caused high results and nitrite produced a purplish red color. The approximately 0.5% water and 1% residual solvent (alcohol, ether, ethyl acetate) found in small arms propellants did not interfere.
0.8070 KN03 0 , 8 0 7 , KNO3
0,83% KXOs
ACKNOWLEDGMENT
0.80% KNO3 0.80% KNOI 0.80% KXOI
0.79% KNO, 0.82% KNOI 0.79% KN03
The author is indebted to Samuel Sitelman of this laboratory for his suggestions.
88 5 mg.
90 0 mg.
Results for Nitrate in the Presence of Possible Interferences
Synthetic Sample (gram)
+ 0.03 T K T + 0.03 Z-nitrodiphenylamine 0 , 3 M9 + 0.03 dinitrotoluene + 0 , 0 3 camphor 0 . 3 319 + 0.03 diphenylphthalate + 0 . 0 3 lead stearate 0 . 3 M9 + 0 , 0 3 triacetin + 0.03 metallic tin 0 . 3 ?*I9 + 0 , 0 3 ethyl centralite + 0.03 lead stearate 0 . 3 119 + 0 . 0 3 IIF 0.3 119 + 0.01 nitroguanidine 0 . 3 M9 + 0,0800 KNOn + 0.0800 Ba(S03)l + 0 012 starch + 0 001 aurin 0 3 M9 + 0 0800 IIs03 + 0 0800 Ba(NO$)?+ 0 012 starch + 0 001 aurin
Present
Found
0 . 3 1!9
88 5 mg.
so3-
0.78% K r O s
so3-
87 4 mg. NOS-
LITERATURE CITED
(1) Bandelin, F. J., Pankratz, R. E.,
ANAL.CHEM.30,1435 (1958).
( 2 ) Enelish. F. L.. IND.ENG. CHEM., ANA:. ED. 19, 850 (1947). \
sulfate, calcium carbonate, barium carbonate, graphite, and tin dioxide. To test for possible interference from other constituents of propellants, synthetic samples were prepared and analyzed. Included was a synthetic E. C. (Explosive Company) type propellant containing starch. The results are shown in Table 111. The following substances also did not interfere: dinitrotoluene, trinitrotoluene, 2-nitrodiphenylamine, ethyl centralite, triacetin, camphor, diphenylphthalate, lead stearate, aurin, starch, and metallic tin. Potassium fluoride, 0.03 gram, did not interfere
(although the colorimetric reading be made to prevent POssible attack of the glass cell by the hydrofluoric acid). The maximum amount of nitroguanidine that could be handled in the method 0.01 gram. Amounts greater than this did not completely dissolve in the acetone and the undissolved portion later dissolved in the water and gave a purplish red color with the ferrous sulfate sohtion. Inorganic nitrates and nitroguanidine are usually not found in the same ~ r o ~ e l l a n t Oxalate, . perchlorate, and cations that might be found in propel-
,
(3) Military Specification MIGP-3984, November 1956. (4) Military Standard Propellants: Sampling, Inspection, and Testing, MILSTD-286, Methods 304.1, 310.3, 310.4, 310.5) June 1956. (5) Olive, T. R., Chem. E'%'* 53, g2 December 1946. (6) Pearson, J., Howard, A. J., Analyst 74, 183 (1949). (7) Semel, s., Laccetti, M. A.7 Roth, xf.3 ANAL.CHEM.31,1050 (1959). (8) Swann, M. H., Adams, M. L., Ibid., 28,1630 (1956). (9) U. S. Army Specification NO.50-12-14, January 1g42. RECEIVEDfor review May 29, 1961. Accepted December 4, 1961.
Application of Carrier Distillation to the Spectrographic Determination of Tramp Elements in Cast Irons and Low Alloy Steels JANUS Y. ELLENBURG' McWane Cast Iron Pipe
Co., Birminghum, Ala.
b A method for the quantitative determination of aluminum, arsenic, chromium, copper, lead, manganese, molybdenum, nickel, titanium, tin, vanadium, and zirconium in cast irons and low alloy steels is described. Carrier distillation provides suppression of the iron spectrum, increases sensitivity for the analysis elements and smooth arcing of the sample. Volatilizution characteristics of the elements were investigated b y moving-plate studies. Representative sampling is possible in the present method because the entire sample may be used. Also, the analysis is performed on samples in a corroded state and/or much too small to be done by other methods. Dissolution of the sample eliminates previous metallurgical history. The relative standard deviation for the determination is 2.9. 230
0
ANALYTICAL CHEMISTRY
T
of tramp elements in cast irons and low alloy steels greatly influences the physical properties of the alloys. These residual elements previously have been determined spectrographically b y high voltage spark (2, S), a.c. arc (4, la), or intermittent d.c. arc (11) techniques. These methods must have the following conditions fulfilled for accurate and reproducible results: homogeneity of sample; mass and dimensions of the sample large enough so as not to influence the analytical results; and previous metallurgical history and thermal treatment of the sample match the spectrographic standards, or no bias between sample and standard. Numerous investigators have shown that it is difficult to satisfy the above requirements. Cast irons and steels which appeared homogeneous under an optical microscope often conHE PRESENCE
tained inhomogeneous spots of magnesium, manganese, nickel, silicon, and titanium (1'7). Other evidence of segregation was found by Kajima, Yasuda, and Sanada (8). The heating of samples of small mass (below 10 to 30 grams) b y a condensed spark had produced systematic errors in the analysis of t h e residual elements in steels (9). There was observed bias in the spark excitation of annealed and forged samples (6). There are two possible ways to overcome the problems of small mass, representative sampling, and previous metallurgical history. I n one approach, t h e past history of the sample was destroyed by dissolution of the cast iron and stee1
1 Present addrese, Engineering Materials Laboratory, The Hayes Corp., Birmingham, Ala.
(6, 7 , 10). Solutioning techniques presented the problem of the removal of undissolved graphite and its possible adsorption of the ions in the solution. I n the other approach, the conversion of the entire sample to a ponder eliminated the graphite problem. Weisberger, Pristera, and Reese (16) converted the sample t o iron oxide and used a n a.c. arc technique. Although this was a n approximation to a universal method, the accuracy and precision were not too satisfactory. The relative standard deviation ranged from 4.0 for titanium to 20.3 for cobalt with an average of 10.7. The advantages slioim for carrier distillation of U308(15) might be applicable to improving the reproducibility of a powder technique. If the iron oxide were direct current arced, residual elements could be swept out of the oxide M ith a carrier. Germanium dioxide proved to be a satisfactory carrier as the iron spectrum was suppressed, the sensitivity of the tramp elements was increased, and the burning of the arc was stable ANALYTICAL TECHNIQUES
Reagents a n d Apparatus. Graphite Electrodes. Preformed 0.242 inch diameter center post electrodes, S a t i o n a l Special Spectroscopic Grade A G K S P (National Catalog S o . 1,3939) n ere used. Graphite Stock and Powder. Kational Special Spectroscopic Grade AGKSP 0.242 inch diameter by 1.50 inches long graphite electrode was used. A section a t one end of the rod was reduced t o 3 mm. in diameter by 7 mm. in length to form a counter electrode. Graphite powder, Sational Grade S P 2 , was used as a diluent. Germanium Dionide. Johnson Matthey, &- Co., Inc. Specpure germanium dioxide was obtained from Jarrell-Ash Co., Newtonville, Mass. Kitric Acid. Reagent grade nitric acid mas redistilled in a quartz still. It was stored in polyethylene or quartz bottles and diluted 1: 1 b y volume with redistilled water immediately before use. Crucibles. Fused silica crucibles nere used for all chemical manipulations. Standard Samples. National Bureau of Standards chemical iron and steel standards, 4i, 6f, 7g, IOe, and 129b, in chip form were used. Drillings were made from NBS 1100 series spectrographic standards to supplement the chemical standard?. Preparation of Samples a n d Standards. Fifty t o one hundred milligrams of sample was treated in a crucible n i t h 5 ml. of 1:1 b y volume nitric acid. The cruciblc n-as heated gently to ensure complete solution of the sample. Additional nitric acid n as added as required. T h e solution was evaporated to dryness. T h e nitrates n e r e decomposed t o the oxides b y heating t h e sample at 300' C. for 15 minutes. T o ensure homogeneity, t h e oxide mixture mas ground in a n agate
mortar for 10 minutes. T h e previously listed standard samples were treated in a n identical manner. Spectrographic samples were prepared b y mixing accurately weighed amounts of the desired constituents in the ratio of 4 parts oxide sample, 3 parts germanium dioxide, and 10 parts pure graphite powder. Procedure. Seventeen milligrams of the spectrographic mixture was placed i n a center post electrode. T h e electrode was then tapped gently to settle t h e powder. T h e sample electrode, used as the anode, was placed in water-cooled electrode chips and direct current arced according to the conditions of Table I. T h e film was calibrated a n d developed according to recommended practice (1). Background corrections \!-ere made for all spectra (14).
Table II.
Table I. Spectrographic Conditions for Tramp Elements in Iron Oxide
Spectrograph: 3-meter Eagle niount Slit: 25 microns by 15 mm. Portion of the image photographed: Center one third Analytical gap: 3 mm. Excitation: d.c. arc Current: 10 amperes on the short circuit Voltage: 220 volts d.c. Pre-arc: 9 secondsa Arc: 39 secondsb Film: Spectrum analypis S o . 1 Pre-fog of film: Approximately 0.03 density unit or 93% transniission 4 For all elements except zirconium. Zirconium required 1-50 seconds. * For all elements except aluminum and zirconium. ,4luminnm required 30 and zirconium 36 seconds.
Analytical Line Pairs for Tramp Elements
Analytical Line Internal Standard Line Concentration Itange, 70 0 01 -0 04 Fe I 3937.332 A1 I 3944.032 0 01 -0 15 Fe I 2840.932 As I 2349.840 0 01 -0 15 Fe I1 2732,448 Cr I1 2677,159 0.08 -0 70 Fe I1 2733,448 Cr TI 2860.934 0.15 -0 50 Fe I 2564.548 Cu I 2824 369 0.02 -0 20 Fe I 2i92.402 RIn I1 2933.063 0 30 -1 00 Fe I 2792.402 Rln I 3070 266 0 02 -0 30 Fe I1 2732 448 %IoI1 2816 154 0 005-0 03 Fe I 3143 245 310 I 3170 347 0 03 -0 TO Fe I 3143 245 SII 2992 595 0 01 -0 05 F e I 3143 245 NI I 3050 819 0 30 -1 00 S i I 3105 469 Fe I 2820 809 0 002-0 02 Fe I 2820 809 Pb I 2833.069 Sn I 3175 019 Fe I 2820 809 0 004-0 045 0 004-0 25 F e I 3143 245 Ti I 3199 915 0 007-0 035 Fe I1 2732 448 V I 1 3093 108 0 02 -0 10 Fe I 3143 245 1-1 3185 396 0 02 -0 30 Fe I1 3281.300 Z r I I 3958 Corrected for titanium interference by subtracting 0.90 times net relative intensity of Ti 13198.915 from net relative intensity of Zr I1 3958.218 hrfore cnlcnlntion~.
The amount of iron volatilized was reproducible enough to be used as the internal standard. Analytical line pairs are given in Table 11. DISCUSSION
Gallium oxide (15), germanium dioxide, and cupric oxide were chosen a s possible carrier compounds. While gallium oxide and cupric oxide stabilized the arc, they were not effective in sweeping out the residual elements (Table 111). Germanium dioxide n-as acting a s a carrier b y enhancing selective volatilization of the tramp elements. There was not total suppression of the iron as in the case of uranium (16). The partial volatilization of iron was advantageous as it provided a n internal standard for the method. If the mechanism of the carrier compound added to a n iron oxide sample were simple buffering, then the d.c. arc residues should have contained approximately the same amount of iron oxide under identical arcing conditions.
~~
Table
111. Signal/Noise" Ratios for Various Carrier Compounds
Line CuO Ga203 GeOz 1.28 2.59 2349.84 1.35 2 06 2.90 C r I I 2860.93 2.17 126 2.51 RloII2816.15 1.58 1.14 2.01 X i 1 3105.47 1 . 2 9 2.85 3.25 M n I 3070.27 1.97 1.13 1.91 S n I 3175.02 0.96 a Signal/noise ratio is defined as: Relative intensity line Relative intensity background Relative intensity background -4s I
Representative mixes were made for each carrier compound with NBS 1163 standard oxide Ten samples of each buffered mix n-ere arced b y the standard technique. The residues from the burned electrodes n-ere carefully removed and weighed. They were ashed a t 450' C. for 12 hours to eliminate the graphite. The residual osides were dissolved in concentrated hydrochloric VOL. 34, NO. 2, FEBRUARY 1962
231
__ FE U _ _ Cr 2 __ V E
I
11
-
2 7 3 2 45
2677 16
3093
--
I
I1
30 0
L t i
::
_/-
F
~ 3D 2 a i 29
2 , L 3958 2 4
I
-
GE I 3319 OE
8
j
1 \-< .
15
35
45
60
75
90 ARCING
15
O
30 ARC,NG
60
45 T8ME
IN S E C O N D S
75
Figure 2. carrier
90
105 TIME
120 IN
135
150
165
180
195
210
225
SECONDS
Distillation o f zirconium with germanium dioxide
Figure 1. Volatilization curves for carrier distillation of some tramp elements in iron oxide
acid. The iron was extracted into diethyl ether, re-extracted into dilute hydrochloric acid, and determined colorimetrically as the thiocyanate complex. There was approximately twice as much iron oxide residue in the germanium dioxide system (Table IV), therefore the germanium was enhancing selective volatilization of the tramp elements.
Table IV.
Average of Analyses of D.C. Arc Residue
Sample CuO buffer GanOs buffer GeO? buffer
Table V.
Residue Residue from after Fez03 Initial Carbon ReBurn Burn maining (mg.) (w.1 (mg.) 10.5 3.7 1.38 9.3 3.1 1.27 9.1 4.1 2.89
Relative Standard Deviation" for Tramp Elements in Cast Iron and Low Alloy Steel
Sample Cast iron, NBS 7g
Low alloy steel, NBS 1164
0
Element Arsenic Chromium Copper Manganese Molybdenum Nickel Titanium Vanadium Arsenic Chromium Copper Manganese XIolybdenum Lead Nickel
Defined aa:
Where: v-is relative standard deviation X is average concentration in per cent d is difference of determination from mean n is number of determinations b N o data.
232
T o apply carrier distillation to the present analysis, it was necessary to study the volatilization characteristics of the tramp elements in relation to the proposed internal standard lines. Probable internal standard lines were selected on the basis of freedom from interference and excitation potentials from Moore's tables (IS). The final selection of analytical lines was made from tlLe moving plate studies and reproducibility studies. Figure 1 shows a typical volntilization graph. The course of the arcing cycle was characterized by the usual distinct periods of, first, a n initial erratic phase (6 to 10 seconds), second, a quiet steady burn (ca. 190 seconds) during which most of the germanium was distilled (Figure 2), and third, a return to an unsteady state. Distillation of the tramp elements was drawn out over a long period of time. Most of the elements showed a con-
ANALYTICAL CHEMISTRY
Without GeOz Carrier 33.40 11.04 19.90 3.60 8.87 11.09 7.68
...
...
6.46 15.40 11.23 6.43
...
8.30
With GeOp Carrier
...
b
3.06 5.43 4.28 1.29 1.26 2.01 2.86 6.22 2.59 2.48 2.57 1.68 2.88 3.36
KO. of Detns.
8 12
12 12 12 12 12
12 8
8
8 8 8 8
e
sistent pattern nhereby 50 to 60% of the total energy was emitted in 45 second3 S i n e seconds pre-arc and a 39-second arc for a 48-second burn seemed a reasonable compromise of distillation pattern Being more refractory than most of the other tramp elements, zirconium required a somewhat different procedure Figure 2 shows the early erratic distillation of zirconium The zirconium did not distill smoothly until a t least 135 seconds had elapsed. Consistent volatilization was obtained bet.rT een I50 and 190 seconds of arcing. Precise results mere obtained only b y careful standardization of each phase of the procedure This ensured that a reproducible fraction of each impurity was volatilized. Zirconium presented a n additional problem because of the interference of titanium I 3958.21 with zirconium I1 3958.22. Zirconium was determined in NBS sample 1162 without titanium correction. The zirconium concentration mas 20.670 greater than the stated value. Moving plate studies indicatetl that titanium I 3199.92 was distilled similarly to titanium I 3958.21. Independent measurements showed that an accurate estimate of the relative intensity of the interfering titanium line was made by multiplying the observer1 net relative intensity of titanium 1 3199.92 by a n empirically determined intensity ratio. The net relative intensity of titanium I 3199.92 times 0.90 was subtracted from the net relative intensity of the zirconium line. Then the corrected net relative intensity of zirconium I1 3958.22 was used to calculate the per cent zirconium. K h e n this correction was applied to the XBS sample 1162, zirconium was determined as 0.061%, a deviation of 3.2% from the actual value of 0.063. The relative standard deviation for XBS sample 7g without germanium dioxide (Table V) was in the same range as the procedure of Weisberger et al. (16) for iron oxide with a n ax. arc. The advantages of the carrier distillation were demonstrated by the enhancement of signal/noise ratios of some of the analytical lines (Table VI) and the improved relative standard
Table VI. Enhancement of Signal/ Noise Ratios by Carrier Distillation
- S/N Ratio
Line C‘ri
T 2821
26’3
Cr I1 ‘2677 150
Pb I Mn I &Io I XI I
28-33 06‘3
3070 266 3170 347
29‘32 505
Without GeOz 0 340 0 585 1 068 1 290
I 102 0.193
iVith GeOn 0 580 1.282 1 572 1 862 2 446 0 402
additional advantage of being adaptable to very small samples as well as t o corroded samples. Partly corroded water pipe circa Louis XIV as well as ancient British cannon have been analyzed by this procedure. The present technique was designed primarily for the elements and concentration ranges of current interest. However, the method could be expanded easily to other elements and concentration ranges for which NBS samples already exist. LITERATURE CITED
deviations (Table V). Relative standard deviations were determined on one s:imple per day over a period of several months to include a n y day-to-day variations in the analysis. During this investigation, covering 7 months, over 1500 analyses mere completed. All results fell within the limits of the relative standard deviations. Millings, drillings, and small chips were analyzed easily without resorting to pelletizing. The method had the
(1) Am. Soc. Testing Materials, Philadelphia, Pa., “Methods for Emission
Spectrochemical Analyeis,” pp. 1-35, 1957. A.,VarsBnyi, F., Acta Tech. Acad. Sci. Hung. 13,409 (1955). (3j Berta, R., Palisca, .4., Spectrochim. Acta 5 , 87 (1952). (4) Canody, L. J., Harris, T., Jr., Woodruff, J. E., J . Opt. Sac. Am. 43, 145 (1953). (5) Carlsson, C. G., Jernkontorets Ann. 129, 193 (1945). (6) Grikit, I. A., Izvest. Akad. S a d S.S.S.R., Ser. Fiz. 19, 171 (1955). (7) Iijima, H., Bunk6 K e n k y d 6 , 16 (195.7).
( 2 ) Bardocz,
((8) 8 ) Kaiima. Yasuda. Y.. Kalima, J.. J., Yasuda, Y., Sanada. Sanada, Japan Anal& Japdn Analyst 2, 108’( 108 (1953). 1953). \-,
K.. K.,
(9) Koritskii, V. G., Izvest. Akad. N a u k S.S.S.R., Ser. Fiz. 12, 429 (1948). (10) Lament, A., Congr. groupe. -atlance. mBhodes anal. spectrog. prod. mkt. 18, 77 (1955). (11) Mathien, V., Spectrochim. Acta 4, 185 (1950). (12) Mitsuhashi, T., Shiraishi, Y., Nakashima, T.. Tetsu to Haoane 39, 1277 (1953). (13) Moore, C. E., “Ultraviolet Multiplet Table,” Natl. Bur. of Standards ( U . S. ’I Circ. 488, Section I (1950), Section 11 (1952). (14) Nachtrieb, N. €I,, “Principles and Practices of Spectrochemical Analysis,” pp. 135-9, McGraw-Hill, New York, 1950. (15) Scribner, B. F., hfullin, 13. R., J . Research Natl. Bur. Standards 37, 379 (1946). (16) Weisberger, S , Pristera, F., Reese, E. F., A p p l . Spectroscopy 9, 19, (1955). (17) Yoshinaga, H., Minami, S., Fujita, S., Technol. Repts. Osaka Univ. 5 , 251 (1955). RECEIVED for review July 5, 1961. Accepted December 4, 1061. Division of Analytical Chemistry, 140th Meeting, ACS, Chicago, Ill., September 1961. I
,
Effect of Rate of Nitrogen Adsorption and Desorption on the Automated Determination of Pore Size Distributions E. V. BALLOU’ Gulf Research & Development Co., Pittsburgh, Pa,
P When pore size distributions of commercial petroleum processing catalysts, or other porous materials, are determined with an automatically programmed apparatus, it i s essential to set the rate of nitrogen adsorption or desorption to a value which yields meaningful daia for subsequent calculations. Several catalysts of different pore structures were studied, and adsorption and desorption data were taken at rates varying from apparent equilibration to markedly nonequilibrium conditions. The test results have aided in optimizing the use of an automatic apparatus to provide service from pore size data as a process research tool, Valid data on small pore catalysts-i.e., median pore radius less than 40 A.-can be obtained when 1.5% of the pore volume i s filled or emptied per minute, while valid data on large pore catalysts-i.e., median pore radius greater than 100 A.must b e obtained at rates of filling or emptying of less than 0.770of the pore volume per minute. Data for catalysts with pore size distributions between 40and 100-A, radius may be obtained at
a rate such that between 0.7 and 1.5% of the pore volume i s filled or emptied per minute, The sum of the equilibration times at all data points should range from 40 to 70% of the total time of the experiment.
s a n industrial catalyst research tool, nitrogen adsorption and desorption experiments yield data which characterize the pore structure of many experimental materials. An automatic apparatus for this purpose has been described ( 1 ) . A mechanically timed cycle n-as then suggested, for data matching that from manual equilibration for the catalysts used. However, the suggested timing cycle was limited in two respects; its application was only confirmed for small pore catalysts, and the maximum rate a t which adequate data could be obtained was not indicated. A more detailed study on both these points was needed to service process research programs properly with automatic equipment. Consideration was, therefore, given to the factors which could be varied
to obtain nitrogen adsorption data in minimum time on materials of both large and small pore diameters. The total time spent on a n experimental run was a function of the following interrelated factors: the number of data points; the gas dose size; the sample size; the orer-all rate of vapor addition or removal; and the relative amount of time spent in equilibrating a t data points, compared to the amount of time spent in gas flow into or out of the sample and vapor system volume. For the purposes of these experiments, 10 points were considered adequate to define an isothermal adsorption or desorption curve. In practice, this number varies viith the complexity of the curre and the degree of definition desired. The gas dose size was limited n-ith the apparatus used to bet1veen 1.0 and 2.5 cc., a t standard temperature and pressure, per dose. It was not experimentally convenient to reduce or increase this amount, and still retain the 1 Present address, Lockheed Missiles and Space Co., Sunnyvale, Calif.
VOL. 34, NO. 2, FEBRUARY 1962
233
