Anal. Chem. 1982, 5 4 , 2073-2079
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Comparison of Four Surface Analytical Techniques for Analysis of Haynes Pdloy Susan W. Graham’ aind David M. Hercules’ Department of Chemistry, University of Plttsburgh, Pittsburgh, Pennsylvania 15260
Haynes alloy conslsts prlmarily of cobalt, chromlum, nickel, and tungsten. The prerient study Involves the use of multltechnlque surface anallysls Including X-ray photoelectron spectroscopy (XPS or E:SCA), Auger electron spectroscopy (AES), secondary Ion mass spectrometry (SIMS), and lowenergy Ion scattering spectrometry (ISS)to characterlze the surface of Haynes alloy both before and after chemlcal and physlcal treatments. The physlcal treatments Involve hand pollshlng and cleaning; the chemlcal treatments include treatment wlth HCI, HNO,, HCIO,, H,SO,, NaOH, Na,CO,, and “,OH. Physical treatments dld not cause slgnificant changes in the surface of Haynes alloy. Treatments with H,SO,, NaOH, and NaHCO, drastlcally atfected the Haynes alloy surface composltlon. These studlee have shown that Haynes alloy Is very Inert to most forme of chemlcal and physlcal attack and that the surface of Haynes alloy Is prlmarlly a layer of chrombm oxldes. The studles further relnforce the usefulness of multltechnlque giirface analysls for examinlng complex surf,aces.
Haynes alloy is a metallic biomaterial used primarily in ball and joint heart valves and their casings. ‘The major components of Haynes alloy are cobalt (48--56%), chromium (19-23%), nickel (9-11‘70), and tungsten (14-1670); minor components are iron (max 3%),magnanese (1-270), silicon (max l%),and carbon (0.15-0.54%). Because this alloy is a biocompatible material, information about the composition of its surface and changes in the surface with various treatments are of interest. Surfaces of metals frequently show chemical states which are different from the bulk. Therefore, understanding how various treatments affect Haynes alloy surfaces is important for understanding itt3 biocompatibility. In the present work thle surfaces of Haynes alloy samples were studied “as received” and ”hand polished”. Additionally, samples which were treated with mineral acids and bases at different concentrations For varying times were compared to the “as-received” samples and to one another. X-ray photoelectron spectroscopy (ESCA), Auger electron spectroscopy (AES), low-energy ion scattering spectroscopy (ISS), and secondary ion niass spectrometry (SIMS)have been used to investigate the surface properties of Haynes alloy. Comparison of data from the various surface techniques before and after treatment provides information about how the surface changes with treatment and demonstrates the complementary information available from the various surface techniques. EXPERIMENTAL SECTION Auger spectra were obtained with a PHI Model 545 scanning Auger microprobe. The base pressure of the vacuum system is approximately 1 x torr. The system uses a monenergetic beam of electrons (5 keV) to initiate the Auger process and uses Present address: American Cyanamid Co., 1937 W. Main St., Stamford, CT.
Table I. Relative Percentages of Metals Present in Haynes Alloy from ESCA and Auger Data Cr untreated (AES) (ESCA) untreated sputtered (AES) polished (AES) (ESCA) polished sputtered (AES) bulk percentagesa a
31.5 29.0 22.5 30.9 29.3
Co
38.3 39.5 54.3 38.6 39.3 22.7 54.7 19-23 49-56
Ni
W
10.2
20.0 11.0 20.5 8.2 15.3 10.8 19.7 10.2 21.1 8.6 14.1 8-11 14-16
Manufacturer’s specifications.
Argon ions at a pressure of approximately 3 X torr for sputtering. An AEI ES200 electron spectrometer with a DSlOO data system was used to obtain ESCA spectra. The vacuum system routinely operates at pressures below torr. The AEI ES200 employs an aluminum anode (A1 Ka = 1486.6 eV) which was operated at 12 kV and 22 mA. Peak areas from the ESCA spectra were calculated with an HP2114-A computer and overlapping peaks were deconvoluted with a DuPont 310 curve resolver. SIMS and ISS spectra were recorded with a 3M combination instrument; the ion scattering spectrometer is Model 525 and the secondary ion mass spectrometer is Model 610. The base pressure of the 3M instrument before the addition of noble gas torr. The SIMS spectrometer uses was approximately 5 X 20Neat a pressure of approximately 4 X lo4 torr to produce the primary ion beam and uses a quadrupole mass analyzer (0-300 amu) to measure secondary ions. The ISS spectrometer also employs a monenergetic *ONe ion beam; the pressure is (1-2) X torr and a cylindrical mirror analyzer is used to measure the energy of the scattered ions. All Auger data were corrected by sensitivity factors (1) t o calculate relative percentages. Data presented are averages of at least three measurements;relative standard deviations are *7 %. All ESCA data have been corrected using published sensitivity factors (2) and are the average of at least four sets of data; relative standard deviations are 110%. Only the metals have been taken into account for the calculation of relative concentrations. Carbon contamination is approximately equal to the sum of the metal concentrations for “as-received” samples and is approximately equal to half of the sum of the metal concentrations for the hand-polished samples before sputtering. After sputtering the carbon concentration is less than 5% of the sum of the metal concentrations. Haynes alloy was investigated by using surface analysis techniques both “as-received” and after various treatments. The treatments included hand polishing and cleaning with trichloroethylene and treatment with hot or room-temperature mineral acids and bases. The acids and bases used in this study were HC1, “OB, HC104,H2S04,Na2C03,NaHC03, and NaOH. The acids were diluted 1:l by volume with distilled water or were 0.1 M; the bases were 0.1 M. The Haynes alloy samples were treated for either 1or 24 h in the hot (100 “C) or room temperature solutions. RESULTS AND DISCUSSION A. Quantitative Measurements by AES and ESCA. “As-received” Haynes alloy samples were studied by AES and ESCA, to characterize the surface before treatment. These data are shown in Table I. Before sputtering, the Cr and W percentages are high relative to the bulk composition while
0003-2700/82/0354-2073$01.25/00 1982 American Chemical Society
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ANALYTICAL CEMISTRY. VOL. 54. NO. 12. OCTOBER 1982
W BEaY ON
CO
Cr
C
N,
20
60
IO0
Sputtering Time ( m i n l
~ b m 2 ospnpomofunireatedpowmdHaynesabaysanrpls: . ~r pressure, 3.1 X loJ tar: beam voltage. 3 kV: lha zero Intensity Ina Is marked as " 0 on ttm y axis
I
C
Flpur 1. Elemmtal AES rrdamphs of an unheated POaJwrd sanrpls 01 Haynes alloy.
Co and Ni are lower than the bulk percentages as measured by both ESCA and AES spot analysis. After the samples have
been sputtered, the metal percentages as measured by AES are all within the manufacturer's specifications. The formation of a chromium passivating layer (3)on the surface of Haynes alloy explains the high Cr composition of the as-received samples. It should be noted that the changes reported in Table I are for surface percentages. As will be seen from AES depth profiles, the W signal intensity remains constant even though the surface percent decreases. The escape depth of W Auger electrons is a factor of 2 larger than that for the other metals in Haynes alloy and may be partially reaponsible for the large concentration of W measured by AES. Additionally. beeause of its large atomic size, W is more likely to surface segregate. Generally, readily oxidized components surface segregate on metals exposed to air. According to Seah ( 4 ) the surface free energy of an element in a binary alloy depends on melting temperature, mole fraction, and heat of mixing. However, the greatest contribution to the surface free energy is a factor depending on atomic size. Therefore, the larger the atomic size the greater the surface free energy and the more likely an element is to be surface segregated. The atomic size of W is about 1.5 times those of Co,Cr, or Ni. Thus, b e c a u s e of its large atomic size,W is likely to surface segregate according to Seah's model. Because the percentages of W measured after sputtering fall within the manufacturer's specifications, i t is quite likely that the high W percentages measured in Table I are due to the surface segregation rather than an escape depth effect. B. AES Micrographs. AES micrographs were taken before and after sputtering and are shown in Figure 1. Before sputtering the high-intensity region in the cobalt and oxygen micrographs track one another while the carbon micrograph shows high intensity regions nearly opposite to the cobalt maps. The chromium, nickel, and tungsten micrographs in-
F@m9. Spot analysis (a) b l u e and (b) alter spmaing: elecwn beam. 5 kV; base presswe. - 1 X 10-e tw: pressure 01 AI l a sputtering. 3 X 10.' ton; AI s+Miering h m . 3 kV.
dicate that there is no significant x-y segregation of these metals on the untrented surfaces. After sputtering, the cobalt and oxygen micrographs are nearly opposite rather than being similar as they were in the unsputtered samples. Carbon, chromium, nickel, and tungsten showed no x-y segregation after sputtering. C. AES Depth Profile. An AES depth profile of 'asreceived" Haynes alloy is shown in Figure 2. Because the major oxygen and chromium lines are close to each other, they are difficult to separate for depth profiling; thus they have been monitored as 0 + Cr in Figure 2. After initially recording a base line for each element (-10 min) the beam voltage was turned on, as indicated by "beam on". Initially C is reduced and the 0 + Cr peak incream. After carbon reaches a steady state, the 0 + Cr peak to peak height decreases and achieves a steady state. The Co concentration increases during the same time. The Ni and W peak heights are small relative to the others and do not change much during depth profiling; in fact, the peak heights increase slightly. The reason the W and Ni peaks are small is because AES is less sensitive for these elements. However, becaw the intensities of the other elements increase dramaticallyduring sputtering, this amounts to a decrease in relative concentrations of Ni and W, since carbon is not considered in calculated compositions. D. AES Spot Analysis. AES spectra obtained on single spots both before and after sputtering are shown in Figure 3. Before sputtering the 0 + Cr region contains primarily an 0 peak at 503 eV with small Cr peaks on either side. After sputtering the primary peaks in this region are the Cr peaks (higher binding energy a t 529 eV) with only a small contribution from the oxygen peak. After sputtering there is also an increase in the signal-to-noise ratio of the whole spectrum.
ANALYTICAL CHEMISTRY, VOL. 54,NO. 12, OCTOBER 1982 Cr
2075
Table 11. ISS Relative Intensities for Hnad-Polished Ilaynes Alloy peak height (rela tive )
time, min 2.9 9.0 20.2 31.4 45.8 63.1 75.1 82.4
co,
Cr
Nia
96 97 95 102 95 96
29 34 35 33 37 37 59 84
74 60
SIN'
Wb
10 11 18 25 28 26 25 24
100 100 100 100 100 100 100 100
Cobalt and nickel cannot be separated by ISS because Since W is the most intense peak in the ISS spectra the other peak intensities are calculated relative to the W intensity (100). Signaito-noise ratio measured for the Cr peak. a
of their close atomic masses.
0.2
0.4
EI/EO
0.6
0.8
-
Figure 4. *'Ne ISS spectra of Haynes alloy (a) "as received" and (b) hand polished: beam energy, 2.0 kV; base pressure, lo-' torr: "Ne
gas presure, - 4 x
torr.
CC+
The change in the peak-to-peak height of the 0 + Cr region during depth profiling must be attributed both to a decrease in 0 on the surface and to an increase in Cr. The sputtering time required to reach a steady state is on the order of 10 min; the samples were sputtered for an additional 1.5 h to ensure that there would be no ]further changes. It is very significant that once the "as-received" samples were sputtered, the surface elemental composition is the same as the bulk. This indicates that Haynes alloy has a thin covering layer which is removed by short periods of sputtering. The thickness of the layer sputtered during depth profiling is approximately 15 A. This value was determined from a calibrated sputter rate of 1.5 A/min established by sputtering A1,03/A1 standards, having known oxide thickness, under conditions identical with those used for Figure 2. E. ISS Data. ISS is more surface sensitive than the other surface analysis techniques, sampling only the top one or two atomic layers of the surface. During the first several minutes of ion bombardment contamination (primarily C and 0) is removed. Because C and 0 have lower atomic masses than ,')Ne, they are not seen in the 20NeISS spectrum. The net effect of the contamination being sputtered is a decrease in the overall noise level. Once contamination has been removed, the relative peak heights of the metals are constant during an hour of ion bombardment. Figure 4 shows the ,ONe ISS spectra of as-received arid hand-polished samples after 30 minutes of ion bombardmlent. In both spectra the intensities of the Cr and W peaks are about equal while the intensity of the Co-Ni peak is approximately one-third the Cr intensity. After an hour of ion bombardment the relative peak intensities begin to change as shown in Table 11; Cr decreases while Co increases without much change in W. Changes in the ISS spectra can be partly attributed to secondary effects like preferential sputtering, knock on induced by the ion beam, and mixing of surface laylers by sputtering. During the first hour of ion bombardment Eiputtering occurs only in the oxide layer, because the sputteir rate used in this study for ISS is much slower than the sputker rate used for AES depth profiles. Unfortunately, the cobalt isotope at 59 amu is flanked by nickel isotopes a t 58 and 60 amu, so it i13 not possible to differentiate between thern with ISS becausie of limited mass resolution.
h O
-
Positive ion SIMS spectrum of untreated, hand polished Haynes alloy: beam energy, 2 kV; base pressure, lo-' torr; *'Ne gas pressure, - 4 x lo-* torr. Figure 5.
AES data have indicated that the Ni concentration does not change drastically from one sample to another, so changes in the intensity of the Co-Ni peak have been assigned to changes in Co concentration. F. SIMS Results. Figure 5 shows the positive SIMS spectrum of a hand-polished sample. The SIMS spectrum of the as-received sample shows the same peaks with similar relative intensities. However, the most intense peaks in the as-received SIMS spectrum are about half as intense as the same peaks in the spectrum of the hand-polished sample. Additionally, CH3 fragments are much more intense in the as-received spectrum. The Co peak intensity is approximately one-fourth of the Cr peak, and the Ni and W peaks are very weak relative to the Cr peak. The rapid quadrupole falloff in the mass region of W dramatically decreases the signalto-noise ratio in that region making it difficult to interpret the W spectrum. Other peaks in the spectrum have been assigned to metal oxide peaks. G. Oxidation States from ESCA. ESCA measurements were performed to determine the oxidation states of the metals on the surface of Haynes alloy. As would be expected, elements on the surface are present both as the metal and as the most stable oxide. Comparison of ESCA data for Haynes alloy with authentic standards for each element indicates the nature of the species present on the surface. Two Ni 2p3j2lines are observed, having maxima at 852.7 and 855.5 eV; these correspond to Ni metal and NiO, respectively. The Ni spectrum is very noisy which makes curve resolving difficult. High noise
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ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982
Table 111. ESCA Escape Depth
oxide N io c0304
Cr203
escape depth ( A ) ~ 10.3 11.8 15.8
( h ) and
hand polished
10.8 13.0 14.5
Oxide Layer Thicknesses ( d ) for Haynes Alloy Samplesa HC1 added
thickness ( d ) for different treatments HNO, HC10, Na,CO, added added added
10.7 13.3 14.2
10.9 11.3
16.3
",OH added
11.3 13.1 14.2
11.5 12.8 14.7
11.3 12.7 14.4
13.1 i 1.3
13.4 i 1.5
13.0 t 1.4
WO, av oxide thickness a
-
13.0 i 1.6 13.3 i 1.8 13.0 i 2.4 Escape depths ( h ) and oxide layer thickness ( d ) given in angstroms.
levels are encountered in the Ni 2p31zregion because Ni is not present in very high concentration, and there are several Auger peaks (particularly from Co) near the Ni peak which increase the background. The ESCA spectrum of the Co 2p312region is a convolution of the metal and Co304with maxima at 778.0 and 781.0 eV, respectively, along with a broad satellite a t higher binding energy. The Cr 2p312envelope is made up of the peak from Crz03with a maximum at 576.4 eV and a peak from the metal at 574.0 eV. The W 4f envelope contains two sets of doublets, one set from the W 4f7l2and 4fEl2peaks of W 0 3 a t 35.3 and 37.4 eV and one set from the metal at 31.1 and 33.5 eV. H. Layer Thickness Calculations from ESCA Data. Using ESCA data, it is possible to calculate an approximate thickness of the oxide layer on the surface of Haynes alloy. By use of Penn's (5) method for determining mean free paths, photoelectron escape depths for the surface species on Haynes alloy have been calculated as shown in the left-hand column of Table 111. With these calculated mean free paths and the equation of Storp et al. (6) peak area oxide = (1 - exp-d/x)/exp-d/x peak area metal (where X is the mean free path of the oxide and d is the oxide layer thickness) an oxide layer thickness was calculated from the ESCA spectrum of each element (Ni, Co, Cr, W). An average value of 13.0 f 1.6 A was determined for hand-polished samples as can be seen in Table 111. AES sputtering data indicated an oxide layer of about 15 A for the handpolished samples which is in very good agreement with the oxide layer thickness calculated from the ESCA data. Also, included in Table I11 are oxide thicknesses for samples treated in HC1, "OB, Na2CO3, and ",OH solutions. As will be shown in the following section, these treatments had no affect on the surface composition of Haynes alloy. It is interesting to note that the oxide layer thicknesses are the same as for the hand-polished samples, within experimental error. Table IV shows oxide layer thicknesses calculated from ESCA data for Haynes alloy samples treated with solutions of HZSO4,NaHC03, and NaOH, a t several times and temperatures. It will be shown subsequently that these treatments have a significant effect on surface composition, and generally, their oxide thicknesses differ from those obtained for the hand-polished samples. I. Chemical Treatments. Part of the present study was to determine the effect of chemical treatment on Haynes alloy and to see if the surface analytical techniques could detect such changes effectively and uniformly. To accomplish this, we treated samples with solutions of the following mineral acids and bases: HC1, HN03, HC104, HzSO4, Na2CO3,NH4OH, NaHC03, and NaOH. For each acid or base, samples were treated for 1 or 24 h and for each time samples were treated at room temperature and at 100 "C. The surface composition for each treatment of each sample was determined by ESCA, AES, ISS, and SIMS with a minimum of three replicates each. This experiment generated a massive amount
Calculated according to Penn (5).
Table IV. Oxide Layer Thicknesses for Treated Haynes Alloy Surfacesa ele-
ment measd Ni Co Cr
W
av Ni Co Cr W av
1 h at room
temp
24 h at room temp
1 h hot
24 h h o t
H,SO, Treatment 12.9 11.6 12.8 15.9 13.1 14.1 20.4 19.8 15.4 13.9 22.2 13.0 i 1.4 18.0 i 4.2 15.0 I3.6
15.1 17.6 25.4 24.9 20.8 i 5.2
NaHCO, Treatment 11.3 12.1 15.2 15.9 13.8 13.3 12.9 13.8 14.0 13.9 14.2 13.1 i 1.4 13.7 i 1.3 13.5 I1.6
12.5 17.3 12.3 13.8 14.0 i 2.3
11.1
11.0
NaOH Treatment 5.8 5.2 5.3 Co 13.3 13.8 Cr 13.4 11.9 10.6 W 14.2 12.8 8.8 av 12.3 i 2.7 11.0 t 3.5 8.2 i 2.7 a Oxide layer thicknesses ( d ) given in angstroms. Ni
8.1
of data (384 values) and thus some form of data reduction was necessary to determine which were the significant treatments. To accomplish this, we established control charts and present them here. The original data used to calculate the control charts can be obtained from another source (7). A control chart consists of a central line and a pair of limit lines spaced above and below the central line. The central line is the total average value and the limit lines are some function of the total variance, uw. For calculation of uwthe individual readings are divided into samples, k , each with an equal number of measurements, n. Then an average, Ti, is calculated from each sample group and (xij is determined where xii is the individual reading in a group k . The total variance, ow, is given by
C&(xij- fi)' uw =
i J
k ( n - 1)
(1)
The control limits are defined as old
fz -
6
(2)
where n is the same as above, uwis the total variance calculated above, and z is a factor dependent on the confidence level. For a 95% confidence level which has been used in this study z = 1.96. Data points which fall within the limit lines are not significantly different than the average value, while points outside the limit lines are considered to deviate signficantly from the average.
ANALYTICAL CHEMISTRY, VOL. 54,NO. 12, OCTOBER 1982
Data on the “as-received” samples were used to establish the average value and limit lines for the control charts used to study the effect of chemical treatmenh. Thus, it is assumed that if any treatment changes the composition from the ”as-received” sample!i, it has had a significant effect on the surface composition. For any point on the control chart, the average value and the values of the limit will depend on t’he element of interest and on the surface technique from which the data were derived. Therefore, the control charts presented here are normalized so that data fOr all elements and from all techniques can be plotted on the same graph. For example, AES data for the unsputtered alloy indicate f = 31.5% and 10.3% for Cr and Ni, respectivsly, with limits of &3.6% and &1.3%, respectively. Thus, when plotted, the “average value” line will correspond to 31.5% and 10.3% for Cr and Ni, respectively, and the “limit” will carrespond to a range of 35.1-27.9% for Cr and 11.6-9.0% for Wi. The figure captions will give both % and the limit values For each element and each technique. Average values for AES and ESCA are given as percentages of the surface composiition, while data €or SIMS and ISS are reported as relative intensities. This situation arises because of the lack of well-defined relative element sensitivity factors for ISS and SIMS. All AES data in Figure 7 have been corrected by using Auger sensitivity factors (I) and are thle average of a t least three sets of data. Relative standard deviations are 510%. Only the metals have been taken into account for the calculation of relative concentrations for AES and ESCA. All ESCA data have been corrected by using Wagner’s sensitivity factors (2) and are the average of four sets of data with a standard deviation 511%. ISS peak heights are averages of at least three values with standard deviation 515%. Since W is the most intense peak in the ISS spectra, its intensity is assumed to be 100 and the other peak intensities are calculated relative to the W intensity. Cobalt and nickel cannot be separated by ISS because of the Co peak is flanked by the two isotope peaks of Ni. One SIMS peak at m/z 15 designated CH3 is indicative of the carbon contamination on the sample surface. Since Cr is the most intense peak in the SIMS spectra, its1 intensity is assumed to be 100 and the other peak intensities are calculated relative to the Cr intensity. Peak heights are averages of at least three values with relative standard deviation 114%. A t the extreme left of each control chart, and separated from the rest of the points, are the data for the hand-polished samples. These are presented for comparison with the data for treatment with acids and bases. Also, this serves as an intensity comparison with the “as-received” samples, which were used to establish the average values and limits for the control charts. Figure 6 is the control chart for carbon contamination on Haynes alloy derived from SIMS data. Note that carbon contamination is affected significantly by only three chemical treatments: HzS04, NaHC03, and NaOH. There is no significant effect of time or temperature of treatment. Carbon contamination increases in each case after treatment. It i s interesting to note that the carbon contamination is decreased by polishing and that the result is statistically significant. This reinforces the qualitative judgement made from the SIMS data in part F of this paper. Figure 7 shows the control chart for elemental analysis of Haynes alloy samples that have been treated with acids and bases but have not been sputtered. Data in Figure 7 are from all techniques (ESCA, AES,ISS, and SIMS) for all cases in which is was possible to measure each element. (See caption of Figure 7 for details.) The only significant treatments were HzS04, NaHC03, and TVaOH, the same treatments which
x
2077
X
X
X
X
x VALUE
*
-
Figure 6. Control chart for carbon contamination on Haynes alloy samples from SIMS data: A, 1 h treatment; B, 24 h treatment; 1, room temperature, 2 hot; average value 27, limit f3.9.
affected carbon contamination in Figure 6. Note that the hand-polished samples (on the extreme left of Figure 7) group tightly around the average value. It should also be noted that the same elements (Co) are consistently high when the limit is exceeded independent of the treatment, while others (Cr, W) are consistently low. Figures 8 shows the control chart for treated samples of Haynes alloy that have been sputtered and measured by AES. Again, the only significant deviations are for treatment by H2S04,NaHC03, and NaOH. It is interesting that the control charts in Figures 6-8 all show significant deviations in surface composition introduced by the same three treatments. Because of this, data for the three treatments will be discussed individually below. However, the control chart data are significant for comparison of the four surface techniques used. First, by taking the composition data collectively for all elements, each technique is able to see a significant change when such occurs. Second, for the treatments where no significant changes occur, the data for all techniques fall within the limit lines, indicating that the precision of each is approximately the same. Careful examination of Figure 7 shows that AES data tend to group somewhat closer to the average value than the others, but there is no single technique that is a constant outlier. Thus, performing on red samples under real conditions of treatment, the four techniques show consistent behavior and show the same qualitative and quantitative capabilities. To the best of our knowledge, this represents the first study where all four surface techniques have been compared on real samples with regard to both qualitative and quantitative capabilities. It is encouraging to see that they are complementary and that they present a self-consistent picture. J. HzS04Treatment. Treatment with HzS04,particularly hot HzS04,tends to decrease Cr and W concentrations, increase Co concentration, and have little effect on Ni before sputtering (see Figure 7) as well as increasing the surface contamination (see Figure 6). AES depth profiling of samples treated in hot N2S04indicates that the oxide layer on the HzS04 treated sample is much thicker than on the “asreceivedn samples (-20-40 A thick). ESCA oxide layer thickness calculations (Table IV) show a similar increase in the oxide layer thickness with H2S04treatment. Additionally, the ESCA binding energy for the nickel oxide peak shifts to slightly higher binding energy with H2S04treatment (5)which indicates possible formation of NiS04. Even after Sputtering the surface of samples treated with hot HzSO4 have lower Cr and W concentrations, higher Co concentration, and similar Ni conentration to the “as-received” samples (see Figure 8). Conversely, samples treated with room temperature H,S04 are very similar to “as-received” samples after sputtering.
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ANALYTICAL CHEMISTRY, VOL. 54,NO. 12,OCTOBER 1982 0
'0
@
e 0
e
e
0
HN03
HCIO,
rn
A
I! HCI
P
rn
0
e '
O
0
NO2CO3
"4
NH40H
NO HCO 3
0
No OH
Flgure 7. Control chart for unsputtered Haynes alloy samples (treatments: A, 1 h; E, 24 h; 1, room temperature; 2,hot): Chromium data (U) AES data, average value 31.5,limit f3.6; (0) ESCA data, average value 29.0,limit f2.8; (E) ISS data, average value 98,limit f3.5; ( 0 ) SIMS data, average value 100,limit -; cobalt data (0)AES data, average value 38.3,limit f3.4; (0) ESCA Data, average value 39.5,limit f3.7; ( 0 )ISS data, average value 33.7,limit f4.9; (0)SIMS data, average value 22, limit f3.6; nickel data (A)AES data, average value 10.3,limit f1.3; (A)ESCA data, average value 11.0,limit f1.2; (A)ISS data, average value -, limit -; (A)SIMS data, average value 11, limit f4.4;tungsten data (e) AES data, average value 20.0,llmit f2.3; (0)ESCA data, average value 20.5,limit f2.5;(6)ISS data, average value 100,llmlt -; ( 0 ) SIMS data, average value
