The challenge
The objective of this study is to characterize the outermost surface of a zirconium tube at three circumferential positions in order to verify the coating uniformity around the entire tube circumference.
The client wishes to verify the uniformity of the coatings over the entire tube. To do so, FILAB proposed a comparative study using XPS technology. The aim is to perform elemental, structural and quantitative analysis of the outermost surface (a few nanometers deep) of a sample taken from three different areas of the tube, in order to meet the client’s requirements.
Characterizing the outermost surface of a zirconium tube by XPS
Objective:
Determine whether the coating on the client’s zirconium tube is homogeneous throughout. To do so, the outermost surface of the tube is characterized by XPS analysis in three different areas.
Approach:
Study three areas of the tube to determine whether they are identical. XPS was used for this purpose. The XPS analysis showed that the zirconium tube was not homogeneous throughout. It consists first of a partially oxidized chromium layer, followed by a zirconium layer. At all three circumferential positions, the chromium detected at the surface is present both in oxidized form as Cr2O3 and in metallic form, while the zirconium is present only in oxidized form (ZrO2).
The depth analysis carried out over approximately 60 nm, combined with the analysis of the outermost surface, revealed heterogeneities between the different positions.
At all three positions, the oxygen content appears to stabilize at approximately 20% after 60 nm of abrasion.
Analysis and interpretation of the XPS results
Observations:
For each profile, a very rapid decrease in carbon content is observed over the first few nanometers. This change corresponds to the removal of the thin layer of atmospheric contamination present on most samples.
Beneath this layer, there is initially always a chromium layer followed by a zirconium layer. However, the thickness of these layers varies significantly depending on the position. In addition to the difference in chromium thickness, a difference in oxygen content can also be observed.
Conclusion of the comparative study of the three areas
Each sample displays a distinct chemical stratification comprising a thin layer of surface contamination, followed by chromium and zirconium layers. Variations in layer thickness and composition according to position reveal significant differences in the chemical structure of the samples.
At all three positions, the oxygen content appears to stabilize at approximately 20% after 60 nm of abrasion. The base metal was therefore not reached, meaning that the zirconium oxide layer in all three areas appears to be more than 30 nm thick.
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Frequently asked questions
How can coating heterogeneity around a zirconium tube be investigated?
The approach involves comparing several positions around the tube, with analysis of the outermost surface and depth profiles. FILAB studied three circumferential positions using XPS. This comparison made it possible to investigate differences in composition and chemical stratification between the areas examined. Discover XPS analysis.
Why combine a surface XPS measurement with a depth profile?
The initial analysis provides information about the first surface layers, while measurements taken after abrasion make it possible to track changes in composition beneath these layers. In this study, combining the two approaches highlighted heterogeneities between the tube positions, particularly in the relative thickness of the layers and in the oxygen profiles.
Which chemical forms of chromium and zirconium were identified?
At the locations studied, the chromium detected at the surface appeared in metallic form and as oxidized Cr₂O₃. Zirconium was detected in oxidized form as ZrO₂ within the scope of the analysis presented. XPS therefore provided information on the chemical states, complementing the identification of the elements and their evolution with depth.
How should a rapid decrease in carbon at the beginning of an XPS profile be interpreted?
In this case, the rapid decrease in carbon after the initial abrasion steps was interpreted as the removal of a thin layer of surface contamination. The analysis then revealed a chromium-rich layer, followed by a layer containing zirconium. This interpretation is based on the evolution of the profile and the stratification observed in the samples.
Did the profile studied by FILAB reach the metallic zirconium in the tube?
The article indicates that the base metal was not reached within the depth examined, which was approximately 60 nm. The zirconium remained associated with an oxidized form in the areas studied. This limitation must be retained in the interpretation: the profile describes the layers accessible to the protocol and does not represent an analysis of the entire thickness of the tube.