Determining Size Distribution of Oxides in Plain Carbon Steels by HaIogen- in-0rganic-Solvent Extraction and Coulter Counter Measurement D. A. Flinchbaugh Homer Research Laboratories, Bethlehem Steel Corporation, Bethlehem, Pa. 18016
Previously reported methods for using the Coulter Counter to measure the size distribution of oxides isolated from steel have employed acid extraction techniques. These methods are limited in scope because of the solubility of various oxide phases in acid. This paper describes a method for processing and counting oxides extracted from plain carbon steels by the halogen-in-organic-solvent technique. The as-filtered residue, including oxide inclusions, membrane filter, and carbon from decomposed carbides, is treated in a low-temperature oxygen plasma to destroy the carbon and filter without altering the inclusions. The purified residue is then dispersed in a conducting electrolyte and measured by Coulter Counter. Test data are presented to demonstrate the validity of the method. Also included are some typical size-distribution data such as can be applied to the study of the effect of oxide inclusions on the mechanical properties of steel.
RECENT METALLURGICAL RESEARCH on the influence of nonmetallic phases on the mechanical properties of steel has shown that the size distribution of oxide inclusions can affect these properties more significantly than do the composition or total amount of oxides in steel (1-7). The present paper describes a new method, based on inclusion extraction and residue analysis, by which the size distribution of oxides in nearly all grades of plain carbon steels can be measured more accurately than has been possible before, either with extraction methods or with quantitative metallographic methods. The essentials of the new method are: extracting the oxides using bromine in methanol or bromine in methyl acetate, dry-ashing the as-extracted residue on its membrane filter to destroy all noninclusion components, and measuring the size distribution by Coulter Counter. Although quantitative metallographic methods have, until recently at least, been the only available approach to size distribution measurements on metallurgical precipitates, this approach suffers from limitations associated with the following factors: Small sample size. The number of nonmetallics exposed on one polished section is small, especially in the case of oxides in low-oxygen steel; Nonspherical particle shape. Formidable statistical problems are encountered in measuring size distributions of nonspherical particles on a polished cross section ; The presence of extraneons phases. Metallographic etchants and dyes are generally incapable of reliably bringing out one particular phase while at the same t h e masking all other phases. This is a particularly ag(1) W. M. Wojcik, R. M. Raybeck, and E. J. Paliwoda, J. Metals, 19 (12), 36 (1967). (2) J. Plateau and J. Gurland, Compt. Rend., 256, 1109 (1963). (3) A. Buch and J. Chodorowski, Reo. Met., 65, 257 (April 1968). (4) W. E. Duckworth, Metullurgiu, 69 (412), 53 (1964). (5) J. J. Hauser and M. G. H. Wells, Fall Meeting, AIME, Detroit, Mich., October 1968. (6) G . P. Airey, T. A. Hughes, and R. F. Mehl, Trans. Met. SOC. AZME, 242,1853 (1968). (7) Y . Miyashita, Tetsu To Hagune, 52, 1049 (1966).
gravating problem when, for example, both oxides and sulfides are present and automatic counting equipment is being used. Although inclusion extraction and analysis methods for measuring the size distributions of nonmetallic phases in steel are still being developed, such methods offer at least three main inherent advantages of the quantitative metallographic approach-namely, sampling problems can be minimized by extracting the oxides from a very large volume of steel, residue extraction and purification techniques are capable of generating samples containing only oxides, and these residues can be analyzed by any of the standard methods available for characterizing powders. The most commonly used of these extraction-analysis methods to date is comprised of the following steps: extracting the oxides with a dilute mineral acid, filtering the solution, removing the oxides from the filter, and determining the size distribution by the Coulter Counter ( I , 7-9). Analytical results obtained by this method on killed steels are subject to some question because of the solubility of certain types of complex oxides in acid. More importantly, this method is totally unsuited to the measurement of oxides in rimmed steel because of the nearly complete acid solubility of (Fe,Mn)O, the major oxide phase found in rimmed steels. Current analytical research is directed toward measuring the size distributions of oxides extracted by the more quantitative halogen-in-organic-solvent techniques. The results of the first effort in this direction were recently published by Kammori and Taguchi (18, 11). They extracted oxides from rimmed steel with an ultrasonically agitated iodine-inmethanol technique, classified the residue particles by microsieving, and then quantitatively determined Al, Ca, Fe, Mn, and Si on each of the size fractions. Kammori and Taguchi’s method has limited practical usefulness because the iodine-inmethanol extraction technique, unlike bromine-in-methanol or bromine-in-methyl acetate, leaves oxide residues contaminated with manganese sulfide and iron carbide, and size distribution data must be estimated from the results of many lengthy quantitative elemental determinations on size fractions having rather wide limits. The fact that the as-extracted residue contains elemental carbon and possibly elemental sulfur would rule out using direct Coulter Counter measurement of size distribution data on oxides from the types of residues obtained with the halogen-in-organic-solvent method. However, in the method described in the present paper, use of the Coulter Counter for this purpose is made possible by incorporating a dry-ashing (8) R. M. Raybeck and L. C. Pasztor, paper presented at the Pitts-
burgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1967. (9) Y.Miyashita and K. Nishikawa, Tetsu To Hagane, 53,400 (1967). (10) 0. Kammori and I. Taguchi, 156th National Meeting, ACS, Atlantic City, N. J., September 1968. (11) 0. Kammori, I. Taguchi, Y. Ariura, and K. Takimoto, Nippon Kinzoku Gakkaishi, 32,773 (1968).
ANALYTICAL CHEMISTRY, VOL. 41, NO. 14, DECEMBER 1969
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Table I. Approximate Sample Weights Recommended for Various Oxide Size Distribution Determinations Typical oxygen Sample Type of content, weight, steel ppm Information required grams Al-killed 50 Overall size distribution 20 Al-killed 50 Accurate count of oxides 240 greater than 10 p equivalent spherical diameter Rimmed 500 Overall size distribution 4
'
step in the procedure. Dry ashing in this method is the use of a low-temperature oxygen plasma to destroy the carbon, sulfur, and membrane filter without altering the inclusions. Tne new method employs either the bromine-in-methanol or the bromine-in-methyl acetate technique for extracting oxides from plain carbon steels because both techniques provide residues free of carbides and sulfides. We carried out an experimental program to test and evaluate the effectiveness of combining three independent techniquesextraction, dry ashing, Coulter Counter measurement-into a reliable method for determining the size distribution of oxide inclusions in plain carbon steel grades. The following sections describe the experimental procedure for making the determinations, list data showing the validity of the method, and provide some typical results obtained on some commercial and experimental steels. EXPERIMENTAL
Sampling. Samples can be taken at any stage of steel processing, from ingot through finished rolled product, and can be cut in almost any configuration. Millings and drillings are not satisfactory because of surface oxidation and because inclusions are frequently lost during sample preparation. The weight of steel taken for extraction depends on the size and quantity of inclusions in the steel. Examples of typical sample weights are given in Table I. Extraction. The halogen-in-organic-solvent oxide extraction techniques used in our laboratory have already been published (12) and will not be repeated in detail here. Briefly, the extractions are carried out in an apparatus similar to that of Bohnstedt (13), as shown in Figure 1. The ultrasonic water bath is used only for the bromine-in-methyl acetate extraction. Rimmed steels are extracted by bromine-inmethyl acetate and fully killed steels are extracted by brominein methanol. Up to 20 grams of steel can be dissolved in 1.5 hours using 3 ml of bromine and 5 ml of solvent per gram of steel taken. The extraction solutions are filtered, residues washed, and then placed directly in sample boats for dry-ashing. Residues containing aluminum nitride are treated with warm dilute sodium hydroxide solution in the filter holder, and then placed in the dry-ashing boats. Dry-Ashing. The sample boats containing the residues and filters are placed in a Tracerlab LTA 600L Dry Asher and ashed for 0.5 hour at 325 watts forward power with an oxygen Row rate of 70 cc per minute. The boats are then removed from the asher and about 10 ml of acetone is added to the partially ashed residue. The boat is then placed in an ultrasonic water bath for about 15 seconds to stir and redistribute the sample. The acetone is evaporated and the (12) R. 6. Smerko and D. A. Flinchbaugh, J. Metals, 20 (7), 43 (1968). (13) U.Bohnstedt, 2.Anal. Chern., 199,109 (1964). 2018
*
Figure 1. Extraction apparatus
whole process repeated. The boat is then returned to the dry asher for a third cycle. By this time the filter and all other non-oxide material in the residue have been destroyed, and the oxides are ready to be dispersed in electrolyte and counted. Figure 2 shows residues in various stages of processing by dry-ashing. Size-Distribution Measurement by the Coulter Counter. The size-distribution measurements are made with a Model B Coulter Counter using standard operating procedures. The dry-ashed residue is removed from the sample boat b y dispersing the residue in about 5 ml of particle-free 0.85% saline solution with the help of ultrasonic agitation. The oxide residue is then washed into a 200-ml round-bottom beaker with saline solution. Three milliliters of a 4% solution of Triton X-100 and 5 ml of glycerine is added to the sample. Glycerine increases the density of the electrolyte to maintain sample dispersion during analysis and is used only when large inclusions greater than 10-15 microns in diameter are to be measured. The sample is diluted to 200 ml with saline solution and placed in the ultrasonic bath for 1 minute. The beaker is then placed on the Coulter Counter aperture stand and the size-distribution measurements are taken. Inclusions larger than about 15 microns in diameter are measured with a 200-micron aperture tube. Smaller inclusions are measured using a tube with either 100- or 70micron aperture. EVALUATION OF METHOD
The present state of the art is incapable of providing reliable steel standard samples for adequately testing all types of inclusion analysis methods, including size-distribution measurements, by the extraction-analysis approach. Nevertheless, we were able to perform a reasonably comprehensive evaluation of our method by applying tests on each of the three main components of the method-extraction, dryashing, and size-distribution measurement-and then testing the combined procedures by carrying known weights of alpha alumina (otAlzQa) powders through the entire procedure and comparing sample weights recovered, as calculated from size-
ANALYTICAL CHEMISTRY, VOL. 41, NO. 14, DECEMBER 1969
Figure 2. Residues in various stages of processing by dry-ashing distribution data, with the weights of the powders initially taken. Finally, examples of data obtained by the method will be shown to illustrate the capability of the method and to indicate how the method can be applied to metallurgical studies. Extraction Procedures. Since there are numerous publications from many nations describing the development and evaluation of halogen-in-organic solvent inclusion extraction techniques (12), a fairly brief summation will suffice for this part of the evaluation. It is generally accepted that for plain carbon steel grades, oxygen values calculated from elemental determinations on extracted residues can be as accurate and precise as those obtained by direct vacuum fusion or neutron activation oxygen analysis of the steel. For example, the extracted oxygen data shown in Table I1 were obtained with the bromine-in-methanol and the bromine-in-methyl acetate procedures (12) developed and tested at the Homer Research Laboratories. The two sigma (20) precision values associated with the extracted oxygen data were calculated from the precision of the colorimetric methods used to determine Al, Cr, Fe, Mn, and Si, and were expressed in ppm oxygen. The 2u values reported with the vacuum fusion values were calculated from four determinations on samples adjacent to those taken for extraction. Finally, the 2u values associated with the neutron activation oxygen values were calculated from five replicate determinations on the very same sample that was later taken for extraction. The neutron activation oxygen determinations were performed by Kaman Nuclear, Colorado Springs, Colo. Dry-Ashing. We have already reported the successful application of dry-ashing techniques for purifying as-extracted residues prior to identification by either X-ray diffraction or optical microscopic techniques (12). By purifying we mean
Sample 1 2
3
Figure 3. Alumina powder before and after dry-ashing destroying elemental carbon and sulfur, if present, and the membrane filter without altering the oxides in any way. During the course of our early dry-ashing work, other laboratories reported that dry-ashing does not affect naturally OCcurring compounds of the type found in steel (14-16). Therefore, it appeared that dry-ashing might be the link needed to combine the quantitative halogen-in-organic-solvent oxide extraction techniques with the Coulter Counter size-distribution measuring technique. All that was needed were data to show that contaminants and filters are quantitatively destroyed and that oxides are not lost or agglomerated during dry-ashing, The data in Table 111 show that carbon and sulfur are effectively removed from synthetic mixtures representing asextracted residues from 240 grams of Al-killed sheet steel. This weight of steel represents the size of sample needed for accurate measurements of very large oxides and is about 12 to 60 times more residue than is usually processed when overall oxide size distributions are required. We assume that if these large quantities of material can be dry-ashed effectively, then smaller residues can be dry-ashed at least as effectively. (14) H. J. Gluskoter, Fuel, 44, 285 (1965). (15) H.J. Gluskoter, J. Sediment. Petrol., 37, 205 (1967). (16) P. A. Estep, J. J. Kovach, and Clarence Karr, Jr., ANAL. CHEM. 40, 358 (1968).
Table 11. Comparison of Steel Oxygen Values-Extraction US. Direct Methods AI-killed steel Rimmed steel BromineVacuum Bromine-methyl Neutron methanol, ppm fusion, ppm Sample acetate, ppm activation, ppm 58 i: 4 5442 8 4 422 f 16 438 f 19 60 f 4 57 zt 12 5 443 i 12 433 f 31 49 + 4 60 + 12 6 442 j: 12 433 f 31
ANALYTICAL CHEMISTRY, VOL. 41, NO. 14, DECEMBER 1969
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Table 111. Composition of Dry-Ashed Synthetic Residues Representing 2460 Grams of Al-Kllled Sheet Steel“ Per gram steel Sample c , fig S, Pg 1 0.26 n.d.b 2 0.17 n.d. 3 0.12 n.d. 4 n.d.* 1.5 5 4.0 n.d. 6 n.d. 4.9 0.18 3.5 Average Total 3.7 a
Residue from I gram of a 50-ppm 0 2 steel weighs about 106 pg.
* Not determined.
Table IV. Effect of Dry-Ashing on Oxygen Recovery from Oxides Extracted from Rimming Steel Ail samples are fromIthe same piece of steel Average 2a Chemically determined ppm 0%in residue Not dry-ashed, 416, 409, 417, 422, 412 415 10 Dry-ashed, 419, 416, 414, 422, 410, 421, 416 18 397, 415, 430 Vacuum-fusion determined ppm 02 in Steel 380, 380, 370, 390 380 16 ~
~
Table V. Effect of Oxide Weight on Recovery of Four-Micron aA1203 by Weight-In, Weight-Out Method Recovery Sample Recovery z3 wt., mg Recovery, range average 2 114.0, 99.6, 98.6, 92.5-1 14.0 101.o 100.4, 92.5 8 112.4, 105.4,”107.3,a 105.4-114.5 110.3 114.5,lll.X
z
a
z,
Data used in Figure 5.
Each mixture tested contained 16 Gelman alpha-6 Metricel membrane filters, 145 rng carbon, 73 mg sulfur, and 26 mg CYA~Z&.The very low carbon values show that the filters are completely destroyed along with the free carbon and sulfur to levels well within the experimental errors of the extraction techniques. Finally, carbon determinations were made on two dry-ashed residues from 250 g of commercial AI-killed sheet steel. The results expressed as micrograms of carbon per gram of steel were 0.49 and 0.51. Sulfur was not determined on similar residues because the small amount of adsorbed bromine on the oxides interfered with the method used for making the sulfur determinations. ?el results of an experiment to determine whether oxides are mechanically lost during dry-ashing are shown in Table IV. Oxides from 14 samples taken from the same piece of rimmed steel were extracted using bromine in methyl acetate. The average and 2u values calculated from four vacuum fusion oxygen determinations in this material were 380 i 16 ppm. Mine of the 14 residues were dry-ashed, and then the oxides were washed from the sample boats onto other filters. These samples, along with the remaining five residues, were analyzed far Al, Cr, Fe, Mn, and Si and the results converted to ppm oxygen. Comparison of the average oxygen values and the statistical deviations about these values shows that no oxides were lost during dry-ashing. 2020
Finally, to show that inclusions are not agglomerated or sintered during dry-ashing, a sample of crAlz03 powder was photomicrographed before and after a one-hour dry-ashing treatment. The photographs shown in Figure 3 show that the particles were not altered during dry-ashing. Additional evidence that dry-ashing does not alter the size distribution of extracted inclusions is given in the Section “Tests on Synthetic Residues” which appears later in this article. From these experiments it is concluded that dry-ashing is a completely effective method for preparing extracted oxides for size-distribution analysis. Coulter Counter Measurement. Both the operating principles (17, IS) of the Coulter Counter and the results of experiments to empirically test the ability of the instrument to measure the size distribution of a large variety of powdered samples (19) are well documented in the literature and therefore need not be reviewed here. The Coulter Counter was calibrated by the half-count method (20) using two of the monosized standards available from Coulter Electronics. The 200-micron-aperture tube was calibrated with a 27.0-micron Lycopodium standard and the 100- and 70-micron aperture tubes with a 3.49-micron Latex standard. Long-term stability was verified by calibrating the Coulter Counter with the Lycopodium standard two or three times each working day for three weeks. The drift in the calibration constant was negligible; computer calculations showed that if the instrument had been calibrated on day 1 with a 27.0-micron standard and then that same standard measured on day 15, the equivalent spherical diameter would have been read as 26.98 microns. This negligible error still further decreases as the diameter of the particles decreases. The technique for testing the ability of the Coulter Counter to determine the size distribution of actual inclusion residues and the optimum quantity of oxides to be extracted from steel for analysis was as follows: the size distributions of carefully weighed samples of aAlsO3 powder were determined and the original sample weights were calculated from the size distribution data. Two experiments were performed: one with an oxide size range representing the major proportion of oxide inclusions generally found in sheet steels, and another with larger particles which, though occurring less frequently in sheet product, are of practical interest. The first experiment was with a sample of aAl2Q3 powder having an average equivalent spherical diameter of 4 microns. The measurements were made with a 100-micron-aperture tube, taking 500-pl aliquots from an initial sample volume of 200 ml. The data in Table V show that samples of smaller oxides can be reliably counted at least over the range 2 to 8 mg of sample dispersed in 200 ml of solution. These sample weights are approximately equivalent to the oxides extracted from 20 grams of 50 ppm oxygen AI-killed steel or 5 grams of 500 ppm oxygen rimming steel. The second experiment was conducted with powder having an average equivalent spherical diameter of 16 microns representing the larger oxide inclusions such as are counted in residues extracted from large volumes of steel. The distribution data were taken by counting the particles in 50O-pl aliquots from a 200-ml sample drawn though a 200-micron(17) R. H.Berg in “’Symposium on Particle Size Measurement,” A‘STM Spec. Tech. Publ. 234, Philadelphia, Pa., 1959, p 245. (18) T. Allen in “Particle Size Analysis,” The Society for Analytical Chemistry, London, England, 1967, p 110. (19) “Bibliography,” Coulter Electronics Industrial Division, Hialeah, ga.; 1968. (20) E. Palik, Anachem Conference, Detroit, Mich., October 1967. ’
ANALYTICAL CHEMISTRY, VOL. 41, NO. 14, DECEMBER 1969
I
I
I
I
IO
20
30
40
Equivalent Spherical Diameter, A Figure 4. Increasing sample size reduces ability of counter to register smaller oxides in presence of large oxides
+
Counts from 0.0100-g sample = 100 % 0.0300-g sample 0.0600-g sample ia 0.1000-g sample
0 A
aperture tube. The data in Table VI show that sample recoveries were excellent for 10- and 30-mg samples but that recoveries fell sharply when 60- and 100-mg samples of the same powder were tested. An attempt was made to determine whether the loss of counting efficiency at higher sample weights was a function of particle size. The average number of counts taken at each size level on the 10-mg samples (averaging 95.7% recovery by weight) was used to calculate the expected count at each particle size level for each of the sample weights taken. From these numbers and from the actual Couiter Counter data, the per cent of expected count that was observed was plotted against particle size for the 30-, 60-, and 100-mgsample weights. The results are shown in Figure 4. The curves show that on a percentage basis the loss of counting efficiency observed at the 60- and 100-mg sample size levels was much greater at the smaller particle sizes. The causes for this loss
Size, fi 64 51 40 32 25 20 16 13 10 8 6
5 4 3 2.5
Actual sample (S) 0 0
1 2 5 26 110 343 990 1,850 2,280 2,150 2,750 5,500 10,000
OP counting efficiency are not known. They were not investigated since it is not necessary to analyze extracted residues containing more than 30 mg of large inclusions. In summary, the results of these two experiments show that the Coulter Counter is capable of measuring the size distribution of extracted oxides as presented to the Counter. Contribution of Background Counts. Once the validity of the method as a whole was demonstrated, it remained only to find out whether background counts, that is, instrumental noise and counts from extraneous particulate matter, were sufficient to significantly alter the shape of the sizedistribution curve. Accordingly, we ran through all three steps of the procedure without steel samples. In Table VII, the numbers of background counts from four of these blank runs are compared with numbers of counts from an actual sample. With the exception of one data point-at the 25micron level-less than 10% of the total counts at every size level is due to background. Therefore, we conclude that background counts do not significantly influence the shape of the size-distribution curves over the range 2.5 to 60 microns equivalent spherical diameter. Tests on Synthetic Residues. A test of the practicability of combining the extraction, dry-ashing, and size-distribution measurements into one analytical method was made by measuring the size distribution of carefully weighed samples of the alumina powders after mixing them with bromine and methanol, filtering, and dry-ashing the powder and filters.
Table VI. Effect of Oxide Weight OD Recovery of 16-Micron aAIZ03by Weight-In, Weight-Out Method Recovery Sample Recovery %, Wt., mg Recovery, range average 10 94.8, 109.2, 94.9, 87.3-109.2 95.7 93.8, 100.5 97.0, 95.3, 88.7, 87.3 30 100.1, 92.6, 97.5 92.6-100.1 96.7 60" 64.1, 70.9, 7 1 . 7 64.1-71.7 68.9 1005 57.3, 52.2, 86.7, 52.2-86.8 68.7 86.8, 82.1, 54.6, 61.1 a
Not acceptable for inclusion size-distribution studies.
Table VII. Per Cent of Total Count Due to Background Counts obtained from: Blank runs ( B ) No. 1 No. 2 No. 3 No. 4 0 0 0
0 0 0 1
6 6 21 42 75 152 297 594
0
0
0 0 0 3
0 0 0 0 1
5 14 26 42 71 130 241 425 702 1,389
z,
z
2 4 10
16 36 87 169 296 493
0 0
0 0 0
4 5 14 28 38 76 139 269 500 1,068
Average of blanks
(a 0 0 0 0
0.8 2.5 5.5 12.5 21.5 36.5 70.5 136 254 449 886
Per cent due to background @IS x 100)
...
... 0 0
16.0 9.6 5.0 3.7 2.2 2.0 3.1
6.3 9.3 8.2 8.9
ANALYTICAL CHEMISTRY, VOL. 41, NO. 14, DECEMBER 1969 e 2021
I
I
I
I
I
I
I l l 1 1
I
I
I I l I l (
Equivalent Spherical Diameter, JJ
Figure 6. Size distribution of oxides extracted from commercialrimmed and AI-killed steels Equivalent
A
Diametel; y
Spherical
0
Rimmed Al-killed
Figure 5. Size distribution of alumina powder before and after processing through entire procedure 0 Before 0
After
The weight per cent recoveries shown in Table VI11 are as good as those obtained directly on equivalent weights of alumina powder, Tables V and VIII. Additional proof that the extraction, dry-ashing, and Coulter Counter procedures do not alter the size distribution of the inclusions is provided by plots (Figure 5 ) of the alumina powder before and after it is taken through the entire procedure. It is therefore concluded that the data obtainable by this method are well within the accuracy needed for studying the correlations between oxide size distributions and mechanical properties of steel. INTERPRETATION AND PRESENTATION OF DATA Most of the generally accepted practices for treating and extrapolating particle size-distribution data incorporate an assumption that the size distribution of the samples obeys one of the common statistical functions such as log-normal or Rosin-Rammler. Because of the inadequate quantity of size-distribution data available on any one grade of steel, we did not carry out the curve-fitting tests required to find out whether or not our inclusion size data obeyed these functions. Furthermore, it seems unlikely that a complete oxide inclusion population could be described with a simple sizedistribution curve when that population consists of at least two and as many as seven different oxide phases which originate from primary deoxidation, secondary deoxidation,
Table VIII. Recovery of Weighed Samples of 4- and 16Micron otAP203 Powder Processed by Method Combining Extraction, Dry-Ashing, and Size-Distribution Measurement Average diameter, Sample Recovery P wt., mg Recovery, average
z,
z
a
16
30
4 4
8 2
Data used in Figure 5.
2022
e
90.5, 99.2, 109.4, 93.9 104.8,a 102.5,a 116.7, 108.0
98.2 103.6 112.4
1
I
t
I
I I IIII
IO
I
I
I I
llellll
100
Equivalent Spherica I Diameter,
Figure 7. Size distribution of oxides extracted from experimental Al-killed steels e Sample A Sample B 6 Sample C A
or possibly from exogenous sources. Therefore, instead of using mathematical models, we prefer to report experimental results in the form of number of particles in a gram of steel us. equivalent spherical diameter of the inclusions. Data presented in this form can be directly applied in studies aimed at correlating mechanical properties of steel with the frequency of occurrence of oxide inclusions of a given size. Examples of Typical Data. The type of data obtainable by the new method is illustrated in Figures 6 and 7. The data are plotted on logarithmic coordinates in the form of number of inclusions per gram of steel us. equivalent spherical diameter of the oxide. Size distributions of oxides extracted from a commercial rimmed and a commercial Alkilled sheet steel are shown in Figure 6. The large differences in the quantities of inclusions between the two samples
ANALYTICAL CHEMISTRY, VOL. 41,NO. 14, DECEMBER 1969
reflect the more than tenfold difference in oxygen content of the steels, Figure 7 shows three distributions obtained on samples from experimental Al-killed steels. The shape of the curves for samples A and B as contrasted with that of the curve for sample C reflects the ability of the method to measure the mode of inclusion populations, provided it is assumed that the distribution is unimodal and that at least some of the particles smaller than the unimodal diameter can be measured by the Coulter Counter. Thus, in curves for samples A and B, the modes are 7 and 10 microns, respectively. On the other hand, the modal diameter of sample C could not be determined because the values of the data points on this frequency-distribution curve were still increasing at the smallest particle size measured. However, smaller particles could have been measured if the oxides greater than about 40
microns, which interfere with the counting of small particles, had been “sieved out” of a second as-extracted residue. ACKNOWLEDGMENT
The author thanks a number of colleagues at the Homer Research Laboratories, in particular T. B. Winkler, W. F. Horscroft, and E. H. Kottcamp for helpful discussions, R. D. Thwaite for petrographic examinations of extracted residues, B. S. Mikofsky for assistance in manuscript preparation, and Jane H. and R. W. Goerlich for technical assistance.
RECEIVED for review February 28, 1969. Accepted September 24, 1969. An abbreviated form of this paper was presented at the Pittsburgh conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, March 5 , 1969.
Synergic Extraction of Cobalt(I I) with Thenoyltr ifI uoroacetone Tetraphenylarsonium Chloride from Acetate Medium M. S. Rahamanl and H. L. Finston The City University of New York, Brooklyn College, Brooklyn, N . Y. Cobalt has been synergically extracted into benzene with thenoyltrifluoroacetone (TTA) in combination with tetraphenylarsonium chloride [(C6H&AsCI] from acetate medium. The composition of the synergic product at p H 3-8 has been determined. The plot of log D against log hydrogen ion concentration shows an inverse second power dependence on hydrogen ion concentration. The plot of log D vs. log TTA concentration gives a slope of 2. A similar plot of log D vs. log (OAc) gives a slope of 1 and the plot of log D against log [(CsH&AsCI] shows a first power dependence of distribution ratio on [(C6HJ4AsCl]. The synergic complex has been isolated from the organic phase and the absorption spectra of the dark brown compound has been compared with the yellow complex of cobalt formed with TTA only, similarly isolated from organic phase. The synergic complex is not polymeric whereas the complex formed with TTA only is polymeric. The ratio of cobalt, I T A , acetate, and tetraphenylarsonium thus i t is proposed that cobalt chloride is 1:2:1:1; forms a five coordinated anion complex with TTA and acetate. This anion forms an ion association complex with tetraphenylarsonium cation.
PREVIOUS INVESTIGATIONS in this laboratory have shown that thenoyltrifluoroacetone (TT’A) in combination with tetraphenylarsonium cation [(CsH&As+] can produce synergism in the extraction of metal ions from acetate medium. The extent of synergism is almost of the same magnitude as in the systems TTA-organophosphorous esters (1-4) and TTA-tri-n-octyl Present address, Department of Chemistry, University of Michigan, Ann Arbor, Mich. (1) C. A. Blake, C. F. Baes, K. B. Brown, C. F. Coleman, and J. C . White, Proc. 2nd hit. ConJ Peaceful Use A t . Energy, Geneva 1958, p 1550. (2) H. Irving and D. N. Edgington, J. Inorg. Nucl. Chem., 15, 158
(1960). (3) H. Irving and D. N. Edgington, ibid., 20,314, 321 (1961). (4) T. V. Healy, ibid., 19, 314, 328 (1961).
amine (5). The composition of the synergic products in this system, however, are not of the same type. In the extraction of gallium (6) with ITA-tetraphenylarsonium chloride, it had been found that gallium combines with acetate ion in addition to TTA and chloride to form an anionic complex, which forms an ion association complex with tetraphenylarsonium cation which is synergically extracted. This paper describes the application of TTA-tetraphenylarsonium chloride system to the synergic extraction of cobalt from acetate medium. The synergic product is presumably a five coordinated anion which is ion associated with tetraphenylarsonium cation. EXPERIMENTAL
Cobalt-60, 10 mCi in chloride form in 5N hydrochloric acid, was supplied by Oak Ridge National Laboratory. The original solution was diluted to give 80,000 counts per minute per milliliter and was used as stock solution. Thenoyltrifluoroacetone, Fisher Scientific, was used without further purification. Tetraphenylarsonium chloride was supplied by Eastman Chemical Co., New York. All other chemicals were of reagent grade. Benzene was used as solvent. Buffer solutions from pH 1.72 to 6.0 were prepared with monochloroacetic acid and sodium acetate. The effect of pH was determined using buffer solutions of high acetate concentration and cobalt-60 tracer. pH measurements were made with a Leeds and Northrup pH meter Model BC 0407. Radioactivity measurements were made with a RIDL Model 10-8 Well type NaI (Tl) scintillation probe (la/*X 2l/2 inch crystal) coupled with a Model 30-19 amplifier and Model 49-26 Timer Scaler. A Beckman DB Spectrophotometer was used for spectral measurements. ( 5 ) K. Batzar, D. E. Goldberg, and L. Newman, J. Znorg. Nucl. Chem., 29, 1511 (1967). ( 6 ) M. S. Rahaman and H. L. Finston, ANAL.CHEM.,40, 1709
(1968). ANALYTICAL CHEMISTRY, VOL. 41, NO. 14, DECEMBER 1969
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