X-ray Diffraction Instrument

It is generally known that the stainless steels have a two-layer oxide film composed of an inner compact layer rich in Cr and a porous outer layer with large magnetite and small spinel crystallites. X-ray diffraction (XRD) is a commonly used method to study the oxide film structure. However, a regular XRD test for an oxide film formed at HT HP water is not valid as the oxide film structure changes and the film contaminates during the cooling phase.

Cormet has designed and built a testing cell for HT HP XRD tests for the University of Wisconsin – Madison. The core of the instrument is a specimen holder that can be rotated accurately around its vertical axis. The testing cell has two sapphire windows positioned almost opposite in the round testing cell walls. The operator feeds the X-ray beam through one window on the specimen. The diffraction beam exits the testing cell through the other window. The diffraction beam is typically monitored using a sensor that rotates around the specimen. In this case, it is the specimen that rotates, whereas the monitoring sensor remains stable.

The oxide layer composition can be modified as the specimen can be electrochemically polarized. The testing cell has a Pd/H2 RHE reference electrode and a platinum counter electrode. The XRD specimen also acts as a working electrode.

The testing cell is a stainless steel autoclave (AISI 316 / EN 1.4404) designed for 360°C temperature and 200 bar pressure.