X-Ray Fluorescence (XRF)

The components in a material determine its essential properties. For Nitinol, the specific ratio of elements also brings various characteristics. XRF is chosen to assess the composite elements and corresponding contents of Nitinol sample, for its fast and quantitative elemental analysis.

1. Principle

The wavelength of X-ray fluorescence is a characteristic for different elements.^[1] The intensity of the fluorescence is linearly related to the amount of elements that emit X-ray photos.^[2] Based on this, the spectrum of XRF can be quantitatively analyzed through direct comparison method, in which the elements amount can be obtained by comparing the integral area of the element peak with the standard curve.^[2]

2. Data and analysis

The experimental data presented here is found from literatures due to the limited experimental equipment.

Fig.1 is a XRF result of two types of samples, which are Ni-Ti-coated samples sprayed by HVOF using Ni-rich Ni50.8Ti (at. %) powder and bulk SMA samples with known composition Ni50.8Ti (at. %).^[3]

Fig.1 Ni and Ti X-ray transitions from the Nitinol coating versus the bulk Ni-rich Ni50.8Ti (at. %) sample.^[3]

The positions of peaks infer that there are two main elements, Ni and Ti in the sample. For the overlapping of the peaks of two samples, it is clearly presented that the chemical composition of the Nitinol coating sprayed using HVOF technique is almost identical with that of the bulk sample of known Ni50.8Ti (at. %) composition.

Fig.2 Standard X-ray fluorescence spectrometry curves of (A) Nickel and (B) Titanium.^[4]

In addition, without the bulk sample, the element concentration still can be acquired from the standard X-ray fluorescence spectrometry curves. Fig.2(A) and (B) illustrate the established standard XRF spectrometry curves of Nickel and Titanium, respectively.^[4]The relationships between intensity and XRF concentration are fitted to a regression line with a function shown in the figures. To get the concentration directly, the area of peak (i.e., the intensity of element) in Fig.1 need to be calculated first. Then use Fig.2 to find the corresponding XRF concentration in accordance with the calculated value of intensity. In this way, the concentration can be obtained.

For the components and corresponding concentration of Ni and Ti are identified, it is appropriate for teeth orthopaedic filament and other novel biomedical applications based on the biophilic metal element Ti and shape memory effect.

3. References

[1] Germanos Karydas. (2014). Introduction to Quantitative XRF analysis. Retrieved from,

http://indico.ictp.it/event/a13226/session/1/contribution/7/material/slides/0.pdf, accessed on 6/1/2021.

[2] Koleske, Joseph V., Paint and Coating Testing Manual - Fifteenth Edition of the Gardner-Sward Handbook: (MNL 17-2nd) - 76.3.6.5 Fundamental Parameter Methods, ASTM International, 2012, p 178-180.

[3] De Crescenzo C, Karatza D, Musmarra D, Chianese, and Baxevanis T., Ni-Ti Shape Memory Alloy Coatings for Structural Applications: Optimization of HVOF Spraying Parameters, Advances in Materials Science and Engineering 2018, 2018, 78, p 67-83.

[4] Bertin, E. P., Principles and Practice of X-ray Spectrometric Analysis, Kluwer Academic, Plenum Publishers, 2017, p 235-237.

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