THE APPLICATION OF X-RAY TECHNIQUES TO STUDIES OF CORROSION AND PROTECTION .2. EXPERIMENTAL X-RAY-DIFFRACTION MEASUREMENTS

The level of sophistication of X-ray diffraction (XRD) experiments is considered with respect to the sample environment and the control of e lectrode potential. In the simplest case, a sample may be scraped from a surface, followed by grinding and ex-situ powder diffraction using a classical scanning powder diffractometer. On the other hand, more ad vanced techniques are being developed which permit the surface to be e xamined in-situ i.e. in the presence of electrolyte and with the facil ity for potential control. Such techniques allow electrochemical metho ds to be coupled with XRD measurements. The use of XRD is illustrated by laboratory research and industrial case studies. Ex-situ powder dif fraction of debris from a marine, white-metal bearing surface allows t he identification of the phase composition of the bearing metal as wel l as that of pitting corrosion products (SnO2). Energy dispersive meas urements using synchrotron radiation reveal the presence of SnO follow ing a controlled potential during anodic oxidation of tin in NaOH. In- situ, potential modulation XRD is used to investigate the reversible f ormation of oxides (CuO, Cu2O) on copper in NaOH. Information on the p hase composition and preferred orientation of phosphated layers on aut omotive steel sheet may be obtained by scanning powder diffraction usi ng synchrotron radiation.