Dec 16 2002
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Photographic film materials may have intricate surface chemistry and thus prone to a broad range of manufacturing issues. Identifying the cause, mostly small surface defects or using insufficient surface chemical characteristics, usually necessitates sensitive molecular-specific analytical tools with high spatial resolution.
Contemporary surface analysis methods such as Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS), and Dynamic Secondary Ion Mass Spectrometry (DSIMS) are specifically suitable to deliver such types of information. The case study discussed in this article shows how CERAM has been involved in assisting manufacturers to troubleshoot current processes and enhance research and development efforts.
Case Study—Discoloration of Steel Sheets Used to Produce Photo Film Canisters
The Problem
The objective of this examination was to find the cause behind the presence of brown spots and a more yellow appearance of the steel surface in the case of the faulty product. Both printed and non-printed sheets were supplied. The steel surface should have been electro-coated with about 10 nm of chromium. Preliminary SEM-EDX analyses carried out by the customer specified a chromium deficiency on the defective samples and the brown spots to be iron oxide, signifying that the chromium overlayer was not thick enough to stop corrosion.
However, surface analysis was ordered to understand the steel surfaces further, with the specific questions of whether the iron oxide was the sole species present in the stains, what was the nature of the yellow coloration, and ways to find a probable cause for a lower level of chromium on the defective sheets.
Analytical Techniques
Both XPS and ToF-SIMS were used for these analyses.
Results
Table 1. Surface chemical compositions (figures are in atomic %) from XPS.
| Sample |
Fe |
Cr |
O |
C |
F |
| Reference sample |
- |
8.3 |
41.5 |
46.1 |
4.0 |
| Problem sample (yellow area) |
4.5 |
3.6 |
38.1 |
50.0 |
3.8 |
| Problem sample (brown stain) |
10.1 |
trace |
44.1 |
45.8 |
- |
Table 2. Chromium and iron (2p) oxidation states (figures are in % of total chromium concentration).
| Sample |
Cr
(metal) |
Cr
(oxides) |
Fe
(metal) |
FeO |
Fe2O3 |
Fe3O4 |
| Reference sample |
25% |
75% |
- |
- |
- |
- |
| Problem sample |
0% |
100% |
0% |
40% |
37% |
23% |
Analysis of Data
The XPS data explicitly revealed that iron was not detected in the reference sample, signifying a chromium (and carbonaceous) overlayer having a thickness of more than 5 nm. On the other hand, iron oxides were observed in both yellow colored and stain areas, signifying that in the former case, the coloration was because of oxidation of the entire surface of the steel sheet.
Furthermore, the high-resolution chromium spectra revealed that primarily oxidized chromium was detected on the defective sample, while a metallic state was also found for the reference sample, signifying a well-organized protective chromium layer on that sample.
Summary
ToF-SIMS results were consistent with the XPS data where high levels of iron and low levels of chromium were seen on the defective sample. Furthermore, a bisphenol-A containing species was found on the surface of only the defective sample. It was suspected that this species was associated with, or in fact the cause of, weak chromium deposition.