=D I S C H A R G E
4
’ 0PRESSURE REGULATOR -X P N C H CLAMP
Figure 6. Test apparatus for measurement of ammonia
$2 FLOWMETER i i
01
02 03
05
IO
2
3
5
IO
PPY A Y Y O N I A
Figure 7.
TC THERMOCOUPLE
Concentration of ammonia
vs. nuclei reading
saturated anmonia gas lenving the bottle mas determined. Further detection \vas accomplished b y dilution with N,. The flow was adjusted to match the requirement of the condensation nuclei detector (100 cc. uer second). After dilution., theammonia gas ~ ’ a spassed through the HC1 bubbler. The concentration oc ammonia in the gas entering the HCI bottle ~vaqcomputed from the vapor pressure and the flowmeter data and plotted against the nuclei reading (Figure 7 ) . The HCI concentration i:, given in terms of the molar concentration of the liquid. When the HC1 molar concentration was changed from to s%, great increase in sensitivity was noted. The cause for this is unknown; howvei., a t 8ycmolar,
the stoichiometric ratio was exceeded and a n excess of HC1 n-as present in the converter. Additional work is now under m y to study this further. OTHER GASES DETECTED
‘I‘ahle I indicates some type3 of gases whirh have been detected and the conversion mechanisms used. The semitivities indicated are those n hich nere readily obtained nithout evtensive tests and do not indicate ultimate performance. LITERATURE CITED
(1) Dm Gupta, s.E.,C;hosh, 8 , K,, R ~hfod. ~ . phys. 18, 225-90 (1946). (2) Dunham, S. R., General Electric Co.,
Schenectady, S . T.,private correspondence, 1960. (3) Dunham, S. B., S a t c u e 188, 51-2 (Oct. 1. 1960). (4j Gerhard, G. It., Johnstone, H. F., I n d . Eng. Chern. 47, 972-6 (1955). ( 5 ) Nolan, P. J., Pollack, L. IT., Proc. Roy. Irish Acad.,SlA, 9-31 (1946). (6) Rich, T. -4.,‘Continuous Recorder for Condensation. Nuclei,” 4th International Srmuosium on .\tniosDheric Condensation huclei, Heidelburg; Germany, May 1961. (7) Skala, G. F., General Electric Co., Schenectady, K. Y., private correspondence, 1959. RECEIVEDfor review April 23, 1962. Accepted September 7 , 1962. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 6, 1962.
General X-Ray Spectrographic Solution Method for Analysis of iron-, Chromium-, and/or Manganese-Bearing MateriaIs BETTY J. MITCHELL and HUGH J. O’HEAR Technology Department, Union Carbide Metals Co., Division o f Union Carbide Corp., Niagara Falls, N. Y.
b A simple and accurate x-ray spectrographic method i s described for the determination of iron, chromium, and manganese in samples which can be put into solution. For 1 gram of sample per 100 ml. of solution, these elements plus other heavy elements present may be determined in the range from 0.1 to 99.9% of the original sample. The method has been applied to the analysis of manganese and chromium alloys, slags and ores, Alnico, steels, and refractories for combinations of iron, chromium, manganese, nickel, copper, and cobalt. Fluorescent intensity changes due to variations in the volume, temperature, acid, and acid concentration of the solution sample are corrected b y ratioing against the intensity of an added control element. Manganese, nickel, and copper are discussed as controls for samples in perchloric, nitric, and sulfuric acid solution. The method may be classified as a uni1620
ANALYTICAL CHEMISTRY
versal spectrographic method in the respect that only a single calibration system per element i s required for all materials and acid matrices.
X
fluorescence methods have been applied successfully to the analysis of a variety of materials for elements in widely varying concentrations. Specialized sample preparation and interelement effect correction are necessary for accurate analysis. Because of their physical properties. many ferroalloys, carbides, and steels are not amenable to accurate x-ray analysis in powder or chip forms; complex ore samples require sets of similar standards. Solution methods (4, 6) have been developed for the analysis of several types of steels, but require careful control of the acid matrix. Since chemical methods for the determination of iron, chromium, and manganese are among the most rapid in use, an x-ray spectrographic method should be simple and -RAY
accurate to compare favorably. This paper describes such an x-ray method. It may be used to make significant analytical savings for the analysis of large numbers of similar samples or samples requiring multiple determinations. The general technique or variations thereof may be eltended to include heavy elements in any sample which can be put into solution form. INSTRUMENTATION
An x-ray Industrial Quantometer (Applied Research Laboratories’ XIQ) (6) was programmed for the simultaneous measurement of iron, chromium, manganese, nickel, and copper. The K a line of each element is measured using LiF crystaIs and Multitron detectors, operating at 1400 and 1800 volts, for concentrations ranging from 0.1 to 10 and 0.01 to 0.1 mg. per ml., respectively. I n the X I Q the sample is excited by the end-window x-ray tube located above it, and the sample or sample
3ol
,
20
-__dp_L--pi-.l 30
PER CENT
40
50
Fe,Mn.Cr.N>
01
Cu
Figure 1. Effect of acid matrix and sample volume on fluorescent intensities
is fused with sodium bisulfate: dissolved, a n d transferred t o t h e main solution. Some samples contain elements t h a t form insoluble sulfates which should b e removed by filtering. M e t h o d B. T h e sample is fused with sodium peroxide in a zirconium or nickel crucible. T h e melt is dissolved and t h e solution is acidified with nitric acid. M e t h o d B1. If the s w i p l e contains manganese, it is prepared as in B a n d hydrogen peroxide is added. M e t h o d B2. If the solution contains prrcipitated S O 2 , it is filt'ered off and volatilized. and an). residue is dissolved or f u d and added t o thc main solution. M e t h o d C. l'hc sample is leached fCJr 2 hours in 1072 sulfuric acid. VARIABILITY IN FLUORESCENT INTENSITIES DUE TO ACID MATRIX
holder distance from the x-ray tube is held constant by spring loading. -4 simple solution holder was devised by covering a 20-ml. plastic storage box (Cargille Laboratories) n i t h 1/4-mil Mylar film and placing it in a n aluminum holder for positioning. The plastic holders are easily washed and niay be handled when loaded with comparative ease, since the level of the solution sample is about inch below the l f y l a r cover.
l'rc~iously reported work (4. 5 ) indicated that the acid concent,ration should bc controllcd closely for arcurate x-ray analysis of solution samples. X-ray sensitivity wrics from arid to acid and wit,h acid ronccnt'ratioii (3, 71, dilutc H S 0 3 being prefc>rahlv l m a u s e of thtl 1011- ai)sorl)tion roefficicmts of
METHOD OF PREPARING SOLUTION SAMPLES
I3,cwiusc. of the widely I arying composition of the materials analyzed. onc single method of preparation was not adequate. I n general, it n a s determined that acid dissolution, sodium peroxide fusion, or dissolution plus fusion was satisfactorj for lorn- and high-carbon iron-rhrornium or ironmanganese alloys, -Unico, steels, manganese, and chromium slags and ores. Table I summarize.. the chemical procedures for satisfactory preparation of these materials, and the final acid matrix of the sample -111 samples of the tvpes listed may not be amenable to exactly the same preparation. Changes may usually be made as rrquired without changing the accuracy of the procedure. .Although 1-gram samples were prepared in 100-ml. volumes and all calibrations discussed here Lvere drawn on that basis (100% concentration equivalent to 1 gram), smaller weights may be taken and perccntages calculated accordingly. M e t h o d A. T h e sample is dissolved in acids and fumed with perchloric acid. Volatilization of a n y chromiuiii present b y hydrochloric acid is prevented by the addition of nitric acid. M e t h o d A l . If t h e sample contains manganese, several drops of hydrogen peroxide are added subsequent t o t h e fuming t o dissolve t h e precipitated M n 0 2 . M e t h o d A2. If t h e sample yields a r e d u e after treatment, the residue
0'
10
20 30 Per Cent Chromium
40
Figure 2. Effect of manganese control element for acid-soluble chromium
I
'
20
I
25
I 30
35
Per Cent Iron
Figure 3. Effect of manganese control on variations in sample volume
oxygen, hydrogen, and nitrogen. Uccause different acids and flux(,'s arc rcquired for dissolving a variety of materials and care is required to keep their concentration constant from sample t o sample (such as controlling HClO4 fuming time closely), a different approach was necessary to avoid the necessity for separate standards in each acid matrix. Figure 1 shows t,he s c \ w e effect of variations in acid matrix and sample level on fluorescent intensit'irs. h small change-for example, a lyO change in HC104 coneenbration or a O.&ml. change in sample volumccould cause an error of greater tlian 1% in the analysis. The error ivith a 1% change in HzS04 wo~ild htx nhout 2% iron. manganese, chromium, nickcl, or copper. The scatter of the intensities of chromium in chromium ore solutioiis containing chroniiuni and iron in various conccntrations of sulfuric acid is iilustrated in Figure 2 9. A reduction in thc scat,ter is shown in B , in which chromium intensities are ratioed to background intensities measured a t 1.53 A., according to the technique of -Indcrmann and Kemp ( 2 ) . The atidit'ion of a control element 60 the solution sample which would be affected by the acid !miations in the saniv elements being analyzed \vas studicd. Figurci 2 C, is a neat exan~pleof the effectiveness of the control element. A constant \-olunie of a rnangancse solution was added to the chrcme ore solutions; the intensities of manganese, iron, and chromium were measured simultaneously, and the intcnsity ratios of iron and chromium to manganese calculated. The scatter which cxistcd under A and B was eliminated. Copper, manganese, and nickel were evaluated as control elements. The ratio of the fluorescent intensity of the element being analyzed to the control element held const'ant in spite of differ ences in the acid and its concentration and as an additional benefit, held con stant with some change in samp temperature and sample depth in the x-ray holder. Although the standard VOL. 34, NO. 12, NOVEMBER 1962
1621
Table I.
Material Low-carbon iron-chromium alloy Low-carbon iron-manganese alloy Alnico Steels High-carbon iron-manganese alloy High-carbon iron-chromium alloy Treated chrome ore Total metals Acid-soluble metals Refractories (high Cr, Fe) Nickel-cobalt alloy Chrome slag Total metals Acid-soluble metals Manganese slag Manganese ore
procedure is to pipet a 20-ml. volume into the plastic holders, the level of the solution surface is not critical. Figure 3 shows that the variation in iron concentration, with manganese control, is small with changes as large as 5 ml. in total volume. I n Figure 4, the ironmanganese and chromium-manganese ratios for solutions containing iron and chromium in a 1 to 1 ratio plot linearly in H2SO4, Hh'Ol, or HClO, matrices, and for a variety of materials. CONTROL ELEMENT CHOICE
Since the programming of the XIQ is limited, it was possible to use only a few elements as controls. If iron and chromium were being determined, manganese, nickel, or copper could be added; if manganese and iron were being determined, chromium, nickel, or copper could be added, etc. Although these added elements are internal standards, they mere not chosen according to the normal considerations for internal standardization ( I ) , but because they were not present as im-
Table II.
Summary of Conditions for Solution Sample Analysis
Method for typical preparation A A1 A A or A1
B1 B
Acid matrix HClOa HClOi HClOi HClOd HYOo HSOB
Elements detd. Cr. Fe Mn, Fe Co, Fe, Ni, Cu Cr, Fe, Xi, hfn PvIn. Fe Cr, 'Fe
Control element Preferred Alternate cu Mn or Xi Xi cu Mn Zn cu Ni cu Mn Ni or Cu
B or B1 C B or A2 A or -42
Cr, Fe, 11n Cr, Fe Cr, Fe Xi, Co, Cr, Fe
cu cu Mn cu
Si i Mn or S Ni or Cu
B or B2
Cr, Fe Cr, Fe Ah, Fe Mn, Fe
Mn cu cu cu
Yi or Cu Mn or Si Ni Ni
c
B l or B2 A2, B1, or B2
purities in the sample and were programmed on the XIQ. T o avoid confusing them with internal standards which are intended to eliminate interelement effects, the name "control element" was chosen. The elements determined in the various materials and the results using various controls are listed in Tables I and 11. Copper is generally preferred as the control for solutions prepared by Method A, AI, or C, but may be used for all materials. In steels or Alnico, its presence requires an alternate element. Zinc and tantalum were given a preliminary study in solutions of steels and were found effective. For preparations involving a fusion step, the crucible material should be considered. Nickel crucibles with manganese control or zirconium crucibles with nickel control may be used for iron-chromium materials. If the nickel crucible loss is fairly constant from sample to $ample, copper may be added as the control and a separate calibration curve plotted for ironchromium or iron-manganese solutionq.
Zirconium crucibles with nickel control are satisfactory for iron-manganese combinations if the zirconium contamination is constant. The control element is added in all cases in the ratio of 5 ml. of a 50 mg. per ml. solution to 50 ml. of a 10 mg. per ml. solution of the sample or standard. The ratio 5 to 50 ml. permits the analysis of duplicate samples from a 100-ml. sample volume and is equivalent to the addition of 0.5 gram of the control to 1.0 gram of the sample. This proportion is satisfactory for element concentrations from 0.001 to 1.0 gram per 100 ml. PREPARATION
OF STANDARD SAMPLES
With the initiation of this program of solution sample analysis, many types of chemically analyzed materials were ac-
Matrix Effects
Eloment combination Description Absorption of Fe by Cr Fe Cr
Magnitude of effect Approx. 0.06% Fe for each 1% Cr at 50% Fe level with Mn control. Approx. 0.02% Fe for each 1%Cr at 5Oy0Fe level with nickel or copper control Enhancement of Cr by Fc Approx. 0.0570 Cr for each lyOFe at 50y0 Cr level with Ni or Cu control. Approx. 0.0270 Cr for each 1% Fe at 50% Cr level with Mn control Enhancement of Fe and Cr T o effect on ratio of Fe or Cr to Mn control. Increases ratio of Fe or Cr to Cu control by Ni contamination Line interference of Fe KOC Approx. 0.08% Fe for each 1% Mn at Sop0 Fe level with S i or Cu control by Mn KP Enhancement of Mn by Fe Approx. 0.0870 Mn for each 1% Fe at 5OyG Mn level with Cu or Ni control Enhancement of Fe and &In Increases ratio of Fe and Mn to Cu control by Ni contamination Line interference of ;\In KOC Increases ratio of Mn to control by Zr K p (3)
+
Fe
+ Mn
~~~
~
1622
ANALYTICAL CHEMISTRY
Figure 4. Effect of manganese control element for iron and chromium in widely varying matrices
1.3 1.4
1
Cu K
Cu K5
1.5
N K
NI K B
t u Ka
16
CO K
Co K 8 Ni K a
17 Fe K
F e KB
4
co Km
l a
Mn K
1.9
2 0 21
''
''
-
Cr K
Mn
