Application of Colorimetry to Analysis of Corrosion-Resistant Steels Determination of Boron SIDNEY WEINBERG, KENNETH L. PROCTOR, A N D OSCAR MILNER Industrial Test Laboratory, United States N a v y Yard, Philadelphia, Pa.
EXPERIMENTAL
A rapid procedure for the determination of small amounts of boron, ranging from 0.001 to 0.005% i n corrosion-resistant steels is suggested. The bulk of the elements present are removed from boron b y adding sodium hydroxide. The use of quinalizarin as the color reagent is subject to few interferences-arsenic and germanium. However, the amount of these elements present must b e several hundredfold the quantity of boron to cause noticeabk interference under the proper conditions. The method is satisfactory for routine use in highly colored solutions where the boron cannot b e determined directly. A spectrophotometric study is included. Estimation may b e b y photometric measurement or b y visual comparison against permanent standards.
Several of the more promising methods were investigated. The accepted umpire procedure, consisting of voIatilization of the boron followed by titration, as outlined by Hague and Bright ( 7 ) , was tried. While consistent results could be obtained, the method had several disadvantages. The large weight of sample needed to obtain the required precision was not always available. The amounts of standard alkali solution used to titrate the blank runs were of greater magnitude than the alkali necessary for the maximum per cent of boron; this introduced a possibly serious error if blanks were not consistent. The apparatus necessary and the time consumed were not suitable for routine analysis. Attempts to determine the boron directly in corrosion-resistant steels by the method of Rudolph and Flickinger were unsuccessful. This procedure, however, gave excellent results when employed on low-alloy steels, I n the latter instance, the ferrous sulfate precipitated in the concentrated sulfuric acid solution and left an almost colorless solution. No precipitation was obtained under similar conditions in the chromium-nickel steels employed; moreover, the intensely green solution masked any change of color occurring after the addition of quinalizarin. The only alternative remaining for the direct color procedure would be to dilute the sample until the inherent color of the solution caused no interference. However, a t this concentration, the boron content of the solution could not be determined. The use of mercury cathode separation and determination with quinalizarin, as proposed by Kar, was investigated. Some modifications of his procedure were introduced. An additional separation by sodium hydroxide was included and the filtrate evaporated to small volume in the alkaline state. The results obtained were satisfactory, but a more simple procedure was subsequently adopted. The curcumin procedure suggested by Kar gave acceptable results. However, the method is open to the objection that many
T
H E determination of traces of boron in corrosion-resistant steel was included in a recent investigation conducted by this laboratory (14). As part of this project, available methods for the determination of boron of the magnitude of 0.001 to 0.005~oand their applications to highly alloyed steels were investigated. Tlie distillation of boron ad methyl borate and titration with alkali, as devised by Chapin ( S ) , has been modified and applied to ferrous alloys ( 7 ) . The distillation procedure has also been combined with estimation by turmeric paper ( I O ) . Preliminary separation of the boron has also been accomplished by the use of alkaline-earth carbonates, Kith final estimation by the use of turmeric paper or titration (9). Khile gravimetric and potentiometl,ic procedures are also known, they are of little value in determining boron in the range under consideration. Spectrographic evaluation has proved to be a satisfactory means of analysis (12). Horrever, the spectrographic method as employed in this laboratory is limitetl by requiring an accurate series of standards of similar type steel, relying on standardization by chemical means. In addition, sample specimens must be of uniform size, a condition which cannot be fulfilled readily in the case of certain materials such as deposited weld metals. Colorimetric estimation appeared worthy of trial, as there are several very sensitive reagents suitable for the determination of boron. The earlicst of these to be used was turmeric which, under proper conditions, has remained the most sensitive ( 2 ) . Comprehensive studies of the applications of quinalizarin to the determination of boron and the variable factors concerning its use have appeared ( I , 6 , 1 S , 1?). These procedures, however, were concerned with materials other than steel. Extension of the use of these reagents to the determination of boron in ferrous alloys has been suggested. Cunningham ( 4 ) determined the boron content of low alloy steels with curcumin by a colorimetric method after preliminary distillation. Kar (8) also employed this reagent, but utilized a preliminary alkali separation of the heavy metals. The use of curcumin, however, requires quantitative separation of the majority of elements present in ferrous alloys. Quinalizarin (1,2,5,&tetrahydroxyanthraquinone) is much less subject to interference, and Rudolph and Flickinger (16) have found chemical separations unnecessary in steels of low alloy content. Kar (8) had previously combined the mercury cathode separation with the colorimetric estimat ion of boron by quinalizarin. Chromotrop 2B (p-nitrobenzene-azochromotropic acid) has been satisfactorily substituted for quinalizarin in steel analysis (18). The conditions of its use and interferences are similar to those of the quinalizarin procedures. The reagent is somewhat less sensitive to boron, however, and therefore was not tested,
Table 1. Sample 1 (257,
Cr, 207, Ni)
2 (25% Cr, 20.70 Xi)
4 (19% Cr,
419
9% Ni)
Results of Quinalizarin-Boron Procedure Boron Present
Boron Added
Boron Found
7, 0.000 0.000 0.000 0.000 0.000
%
%
%
0.001 0.002 0.003 0.004
0.001
0.000 0.000
0,001 0.001 0.001 0.001 0.001
0.000 0,000 0,000 0.000 0.000
0.002 0.002
Deviation
-0.001
0.004 0.005
0.000 0.000
0.001 0.002 0.003 0.004 0.005
0.002
0.000 -0.001 0.000 0.000
0.001
0.001 0.002 0.002
0.005
0.002
0.003 0.004
0.005
0.002 0.004 0.005 0.005
0.004 0.005
-0.001
0.000 0.000 -0,001 0,000 0.000
420
INDUSTRIAL AND ENGINEERING CHEMISTRY Table
II. Results of Curcu,min-Boron Procedurea
Sample
Boron Present
% 1 (25% Cr, 20% Ni)
a
Vol. 17, No. 7
0.000 0.000 0.000 0.000
Boron Added
Boron Found
0.001 0.002 0.002 0.004
Deviation
%
%
0.001 0.002 0.001 0.004
0.000 0.000 -0.001 0.000
%
Procedure of Iiar used.
of the elements ordinarily present in steels interfere by giving similar colors, and separations must be made with care. I n the presence of columbium or tantalum, the recommended separations would not suffice (11). Moreover, colorimetnc comparison must be made within one hour (16), as the color is unstable. However, the results obtained by the method and given in Table I1 warranted its retention as a n alternate procedure. I n view of the above, quinalizarin was believed to be more suitable for routine determination of boron. Those elements which interfere are rarely encountered in significant amounts in steel. Standard solutions of quinalizarin-boron complex have remained unchanged for months after preparation (I). I n addition, the elapsed time for a determination is less than that required by the use of curcumin. The method finally adopted is simple and rapid. The sample is dissolved in dilute hydrochloric acid under a reflux condenser. Hydrogen peroxide is added to decompose carbides and the excess is decomposed by boiling. The insoluble material is filtered, fused with sodium carbonate, and combined with the main solution. The solution is adjusted to volume, made just alkaline to litmus with sodium hydroxide pellets, and filtered. A clear, aliquot portion of the filtrate is acidified with sulfuric acid and evaporated to sulfur trioxide fumes. (Acid evaporation without loss of boric acid is possible in the presence of alkali salts, 6.) The volume is adjusted with concentrated sulfuric acid and quinalizarin solution added. After full development of color, the solution is compared either visually or on the photoelectric colorimeter.
10. 4k0 0
' ,b ' *v ' 4-
51,
WAVELENGTH IN MlLLlMlCRi3NS Figure 1.
INSTRUMENTS E M P L O Y E D
A General Electric recording spectrophotometer with a nominal slit width of 10 millimicrons. A Klett-Summerson photoelectric colorimeter. Klett-Summerson glam filters. KleteSummerson 2-cm. glass absorption cells. SPECTROPHOTOMETRIC STUDY
A spectrophotometric investigation of the boron complexes of quinalizarin and curcumin was made for the purpose of estimating both with the photoelectric colorimeter. Their transmission curves are shown in Figures 1 and 2. Two-color systems exist in both solutions, as no suitable procedures for the removal of the excess of reagent in either instance have as yet been devised. A study of Figure 1 discloses that a solution of quinalizarin reagent has absorption peaks a t approximately 530 and 570 millimicrons, while the boron complex has one a t 600 millimicrons. Resolution is not possible, for a t the maximum absorption of either component the other absorbs strongly-for example, a t 600 millimicrons the absorption by the quinalizarin reagent is about two thirds that of the boron complex, Observation of the data obtained by making photoelectric colorimeter measurements in the regions of 530 and 600 millimicrons, respectively, disclosed that the latter is more suitable for the determination of the low percentages of boron under consideration. Accordingly, the remainder of the investigation was confined to measurements in this region. For the determination of larger quantities (over 0.010%), however, the lower wave length is preferable, since the measurement of the absorption by the excess quinalizarin is more sensitive than that of high concentrations of the complex (Table 111).
Transmission of Boron-Quinalizarin System 1, Quinalirarin reagent 2. Quinalirarin rrclgent 0.003% boron 3. Quinalirarin reegcnt: 0.008% boron 4. K.S. filter 54 5. K.S. Rk8r 60
Table 111. Boron Present, Mg. Blank 0.01 0.02
0.03
0.04 0.05 0.06 0.08 0.12 0.16 0.20
Comparison of Sensitivity of Glass Filters (K.S. No. 60)
Reading
Corrected Reading
120.5 152.0 176.0 190.0 201.5 211.5 216.0 224.0 234.5 237.5 238.5
32.5 56.6 70.5 81.0 91.0 95.5 103.5 114,O 117.0 118.0
...
(K.S. No. 54)
Reading
Corrertc(1 Reading
218.0 202.5 187.5 173.5 164.5 159.0 155.0 152.0 145.5 141.0 138.0
15: 5 30.5 44.5 53.5 69.0 63.0 66.0 72.5 77.0 80.0
I n an attempt to follow the behavior of the component colors of the system, several solutions containing varying quantities of quinalizarin reagent were prepared under conditions similar to those of actual determinations. The concentrations of quinalizarin were made to diminish as they ordinarily would if boron were present to combine with a portion of the free reagent. The solution of greatest quinalizarin content contained 0.50 mg. of the reagent in 100-ml. volume, which is the amount normakly added. After absorption values were determined, boric acid cryst a h were added in large excess to convert the quinalizarin a \ quantitatively as possible to the boron complex. Upon complete development of color, readings were again taken (Table IV). Adherence to Beer's law is observed in both cases. It would appear, therefore, that if the reaction proceeds stoichiometrically, a straight line should also result from the plotted readings of a series of boron-quinalizarin standards. That this is not the case is apparent from the parabolic curve actually obtained.
ANALYTICAL EDITION
July, 1945
Data from photoelectric colorimeter measurements not only establish the deviation from Beer's law, but also indicate that far more boron may be added before complete conversion of the quinalizarin to the colored complex is attained than the two atoms huggested by the equation of Berger and Truog ( 1 ) . I t was found experimentally that the ratio of boron to quinalizarin exceeded 5 to 1 before saturation occurred. In addition to depending upon the concentration of sulfuric acid (17), the reaction appears reversible, varying with the quantities of boron and quinalizarin. The results shown in Table I V are indications of the behavior of the individual colors of the system. They cannot, however, be combined and compared to values obtained by following the regular procedure, for the conditions are not comparable if the reversibility of the reaction is accepted. I n the first instance a large excess of boron is employed and in the latter case-under routine conditions-the quinalizarin is always present in excess. The curcumin-boron transmission curves, shown in Figure 2, ~
~~~
~~
Table IV. Photoelectrometric Readings of Individual Colors of Boron-Quinalizarin System aolution NO.
Quinaliiarin, Mg./lOO MI. Volume
Reading
Solution
Reading
NO.^
Combined Readingsb
Same solutions as in first column with large excesses of boric acid crystals added. b Appropriate readings of two solutions added together t o obtain equivalent of 0.50 mg. of quinalizarin originally present. TheoreticalJy, readings should be same as those obtained under actual working conditions if reaction proceeded quantitatively.
421
indicate that resolution of the two component colors is a simple task. Absorption maxima occur a t 420 and 535 millimicrons, respectively. The boron complex was successfully determined using a No. 55 filter, the spectral transmission of which is also shown in Figure 2. Absorption by curcumin reagent within this range is negligible. The results obtained, as shown in Table 11, indicate acceptable precision. In both the quinalizarin-boron and curcumin-boron systems visual comparison to standards gave satisfactory results. REAGENTS
All reagents used are of C.P. grade. Dilute hydrochloric acid. Mix 100 ml. of hydrochloric acid (sp. gr. 1.19) with 150 ml. of water. Hydrogen peroxide (3y0) ; sulfurous acid (saturated, approximately 6%); sodium hydroxide (pellets); sulfuric acid (sp. gr. 1.84). Quinalizarin reagent solution. Dissolve 10 mg. of quinalizarin in 100 ml. of sulfuric acid (sp. gr. 1.84). Dilute hydrochloric acid wash solution (1%). Mix 1 ml. of hydrochloric acid (sp. gr. 1.19) with 100 ml. of water. PRECAUTIONS
Use only glassware known to be free of boron or of low boron content. (Corning alkali-resistant glassware was found satisfactory.) Since the concentration of sulfuric acid used will affect the boron color, it is necessary t o ensure uniform concentration or t o compensate for variations. Uniform concentrations of acid may be obtained by assaying the sulfuric acid and adjusting to 97.5% sulfuric acid by weight, employing fuming sulfuric acid ( 1 ) . As an alternate procedure several standards may be determined simultaneously with the unknowns, making any necessary corrections t o compensate for the variance of the sulfuric acid concentration. The highly colored quinalizarin reagent must be accurately dispensed; otherwise a noticeable error is introduced. A blank must be run along with every series of determinations. The decomposition of the hydrogen peroxide must be complete, for oxidizing substances destroy the quinalizarin reagent. ANALYTICAL PROCEDURE
I I. REAGENT
BLANK 2 REAGENT+O.OOI% EORON 3 . R E A G E N T + 0 . 0 0 2 % BORON 4. REAGENT 0.003%BORON 5. K.S,FILTER NO. 55
+
I
WAVELENGTH Figure 2.
IN
I
I
MILLIMICRONS
Transmission of Boron-Curcumin System 1-cm. cell
I
Introduce 1 gram of finely divided drillings into a 250-ml. Erlenmeyer flask and place on a hot plate. Connect the flask to a reflux condenser and add 12.5 ml. of dilute hydrochloric acid. Heat to just below the boiling point. When solution 1s complete, add 10 ml. of hydrogen peroxide through the condenser tube and boil to decompose the carbides. A clear or almost clear, solution should result. Rinse the reflux tube k i t h 15 ml. of water and boil the solution vigorously for 15 to 30 minutes to decompose the hydrogen peroxide present, Wash'the condenser tube free of ,condensed vapors with 75 ml. of water. Remove the flask and add 3 or 4 drops of sulfurous acid, with swirling. Filter t,hrough a 9-cm. close paper, catching the filtrate and washings in a 200-ml. graduated flask or lass stoppered graduated cylinder. Transfer the insoluble resifue io the paper and wash about five times with dilute hydrochloric acid wash solution (lye). Place the paper in a platinum crucible and ignite a t low red heat until free of organic matter. Add a small quantity of sodium carbonate (approximately 0.25 gram) to the crucible, cover, and heat until fusion is complete. Leach the soluble material with several milliliters of the dilute hydrochloric acid wash solution and add to the filtrate. Adjust the volume to 200 ml. and mix thoroughly. Introduce a sufficient number of sodium hydroxide pellets (usually 20 to 25, depending on size) to make the solution barely alkaline to litmus paper. (Precipitation of the hydroxides should not be used as an indication of alkalinity, since i t occurs on the acid side.) Add two pellets of sodium hydroxide in excess and stir well. Allow the precipitate to set,tle for several minutes and decant through a dry filter paper. Discard the first 10 to 20 ml. of the filtrate and then collect 100 ml., transferring to a 250-ml. Erlenmeyer flask made of Corning No. 728 boron-free glass. Evaporate to 40 ml. and then add several drops of sulfurous acid and 20 ml. of concentrated sulfuric acid. Continue the evaporation until fumes fill the flask and fume gently for 5 minutes to remove moisture. Remove the flask from the heat and cover with a watch glass. When the solution has cooled to room temperature, adjust the volume to 50 ml. with concentrated sulfuric acid, add 2.5 ml. of quinalizarin reagent, and mix well. Transfer the solu-
422
INDUSTRIAL AND ENGINEERING CHEMISTRY
tion to a ground-glass stoppered bottle of soft glass (boron-free glassware is preferable, if available). After one hour, the solution may be compared visually to a series of sealed standards which can remain stable indefinitely. The photoelectric colorimeter may be employed as an alternate means of estimation. The instrument is adjusted to zero with concentrated sulfuric acid in the cell and readin s are taken on all solutions, including a blank determination steel which is run simultaneously. A No. 60 filter is used. The blank reading obtained is subtracted from the sample reading. The per cent of boron is then determined by referring to a curve previously drawn from a series of standards of increasing boron content. The standards are prepared from samples of boron-free steel, to which increments of standard boric acid solution equivalent to 0.001% boron are added. (Steel samples must be used in preparing the standards, as there is a proportionate retention of boron in the hydroxide precipitate.) A blank is carried along and deducted in the usual way.
on toron-free
ACKNOWLEDGMENT
The authors desire to thank H. A. Sloviter and R. T. Cook for the preparation of the spectrophotometric transmission curves. LITERATURE CITED
(1) Berger, K. C., and Truog, E., IND.ENQ.CHEM.,ANAL.ED.,11, 540-6 (1939). (2) Bertrand, G.,and Agulhon, H., Compt. rend., 157, 1433 (1913).
Vol. 17, No. 7
(3) Chapin, W.H., J . A m . C h a . SOC.,30, 1G91 (1908). (4) Cunningham, T. R., Union Carbide and Carbon Research
Laboratories, Niagara Falls, N. Y., private communication, 1943.
( 5 ) Fejgl, F., “Spot Tests”, p. 224,New York, Nordeman Publish-
ing Co., 1939. (6) Feigl, F.,and Krumholz, P., Mikrochen. Pregl Festschr., p. 77, (1929). (7) Hague, J. L., and Bright, H. A., J . Research Nail. Bur. Standards, 21, 125-31 (1938). (8) Kar, H. A., Metals and Alloys, 9, 175-7 (1938). (9) Lindgren, J. M., J . A m . Chem. SOC.,37, 1137 (1915). (10) Low, W.H., Ibid.,28,807 (1906). (11) Lundell, G.E.F., and Hoffman, J. I., “Outlines of Methods of Chemical Analysis”, p. 82, New York, John Wiley & Sone, 1938. (12) Masi, O., Spectrochim. Acta, 1, 462-70 (1940). (13) Maunsell, P.W.,New Zealand J . Sci. Tech., 22B, 100-11 (1941). (14) Milner, O.,Proctor, K. L., and Weinberg, S., IND.ENQ.CHEM., ANAL.ED., 17,142-5 (1945). (15) Naftel, J. A . , Ibid., 11, 407-9 (1939). (16) Rudolph, G.A.,and Flickinger, L. C . , Steel, 112,114-15 (April 5. 1943). (17) Smith, T.: Analyst, 60, 735 (1935). (18) Woodward, T. S., Carnegie-Illinois Steel Corp., Youngstown Ohio, private communication, 1943. TEEopinions expressed are those of the authors and are not to be construed as reEecting the official views of the Navy Department, through whose permission this article is published.
Colorimetric Determination of Copper in Aluminum Alloys ROBERT F. PATRIDGE Willyr-Overland Motors, Inc., Toledo, O h i o
A rapid, colorimetric method for the determination of copper in aluminum alloys containing up to 8.00% copper is described. In routine determinations the method i s accurate to within *0.03% copper, and can be applied to all commercial aluminum alloys, including those of high silicon content. The results agree closely with analyses obtained electrolytically and the colorimetric procedure offers the further advantage of rapidity.
Ii%
T H E chemical analysis of most aluminum alloys, the determination of copper is usually of prime significance, for this element is one of the major alloying constituents from the standpoint of both quantity and frequency of occurrence. Several well-established procedures for the determination of copper are in existence; perhaps the two most reliable and frequently used are electrolytic deposition upon a platinum cathode (18)and iodometric titration (6). Electrolysis demands the absence of those metals which would plate with or inhibit the deposition of copper (2) ; the iodometric type of analysis requires great care in manipulation. Both methods consume a considerable amount of time. These inherent faults of length and inconvenience became especially serious when it was found necessary, in this laboratory, to determine copper contents of aluminum alloys in a very limited time. The necessity for a faster and more convenient method was apparent. Aside from spectrographic analysis, the field of colorimetry seemed to offer the greatest promise, and the existence of several possible reagents and procedures was recognized (19). Of these reagents, potassium ethyl xanthate (2) and the blue ammonia complex (17) have been employed for copper in aluminum alloys. The xanthate method is worthless for large quantities of copper, and the less sensitive ammonia complex, to be of any value, requires a spectrophotometer. A study of Corm’s (7) exhaustive survey of compounds for colorimetric copper led to the choice of Callan and Henderson’s (6) reagent, sodium diethyldithiocarbamate. No literature was found pertaining to the use of this
chromogenic agent for the determination of copper in aluminum alloys, but the initial success in this laboratory wa.s sufficient to stimulate further research, which culminated in the procedure presented in this paper. The two main advantages over existing methods are its simplicity and rapidity. I Jingle determination may be completed in 15 minutes. The essence of the proposed method is that it allows colorimetric determination of copper in the presence of aluminum and other alloying elements. Since sodium diethyldithiocarbamate forms colored precipitates or solutions with other metals besides copper (8), these might seriously interfere. The eleven elements likely to be present in alloying quantities (3) are manganese, iron, zinc, nickel, silicon, magnesium, lead, chromium, tin, bismuth, and titanium. Table I shows the maximum percentages of these eleven elements ordinarily found in commercial alloys (1). It followed that experimental evidence of noninterference from aluminum and its alloying elements had to be obtained. Silicon need not be taken into consideration, since it is eliminated through dehydration and precipitation. Obtaining the evidence required (1) preparation of a standard reference curve for copper in the presence of aluminum only, (2) determination of the separate effect of each alloying metal on the curve, and (3) determination of the collective effect of all alloying metals on the curve. REAGENTS
All chemicals are of reagent grade. Acid Mixture 1 (Alcoa). To 475 ml. of water add 125 ml. of concentrated sulfuric acid, 200 ml. of concentrated nitric acid, and 200 ml. of concentrated hydrochloric acid ( 4 ) . Standard Aluminum Solution. Dissolve 0.800 gram of aluminum metal in acid mixture 1, reduce to sulfuric fumes, and dilute to. 1 liter with distilled water; 1 ml. contains 0.80 mg. of aluminum. Standard ,Copper Solution. Dissolve 1.OWgram of electrolytic copper in 10 ml. of concentrated nitric acid, add 5 ml. of concentrated sulfuric acid, reduce to fumes, and dilute to 1liter; 1.0
