Grazing incidence X-Ray diffraction (GIXRD)

We have characterized corrosion products using the GIXRD to confirm the crystalline phases present in the corrosion products. Rietveld analysis was used for evaluating the phase fraction using GIXRD pattern. The penetration depth of the X-ray is limited inside the iron sample. Therefore, X-ray can reveal the corrosion film. However, the entire iron sample could not be analysed using GIXRD. GIXRD data were collected using a PANalytical Empyrean diffractometer using Cu Kα radiation. The incident beam had a parabolic mirror with 2.3° Soller slits, and was fixed at 2° to the specimen surface. The diffracted beam had 2.3° Soller slits, a 0.18° parallel plate collimator, and a point detector with a 0.05 mm receiving slit. Diffraction data were taken over the range 10°–100° 2θ in steps of 0.02°. The diffraction data were collected in this fixed-incident beam geometry in order to enhance the contribution from surface layers. Phase identification was carried out using the software package EVA14 with the ICDD PDF2 database. Crystal structures for the phases were taken from the ICDD PDF 4 + database. Fluorescence, which is considered as an unwanted phenomena in diffraction, depends on the type of X-ray radiation source used (Copper (Cu) Kα radiation in our case) and the type of analysed material (iron sample in our case). Iron causes the development of high fluorescence with Cu Kα radiation which leads to the poor signal to noise ratio in diffraction pattern. Therefore, we have chosen neutron diffraction, used at the Australia’s Nuclear Science and Technology Organisation (ANSTO), Sydney, to analyse iron samples thoroughly because neutrons penetrate deeper inside the iron sample and provide better signal to noise ratio²².