The mineralogy and elemental composition of corrosion deposits provides insight into corrosion mechanisms and local conditions. XRD is used to identify and determine the relative abundances of minerals including various iron oxides (e.g. goethite, magnetite), iron sulfides (e.g., mackinawite, greigite, pyrite), scales (e.g., calcite), and other crystalline materials. Energy dispersive x-ray spectroscopy (EDS) is often performed in addition to XRD to give the overall elemental composition (percent C, O, S, Fe, etc.) of the deposit sample.
X-RAY DIFFRACTION (XRD) AND ENERGY DISPERSIVE X-RAY SPECTROSCOPY (EDS) ADVANTAGES:
IDENTIFICATION
XRD is the primary method to identify unknown crystalline materials in corrosion and other system deposits. Comparison of XRD results for deposits provides a valuable line of evidence in identifying corrosion mechanisms including microbiologically influenced corrosion.
BROAD APPLICABILITY
XRD can identify a broad spectrum of minerals including iron oxides (magnetite, goethite, hematite, siderite, etc.), iron sulfides (mackinawite, pyrite, greigite, etc.), metal salts and scales (calcite, silica, sodium chloride, calcium chloride, etc.) and is applicable to nearly any construction material (iron, low alloy steel, stainless steel, copper, etc.).
RELATIVE ABUNDANCES
XRD results will provide the relative abundances of the crystalline minerals. In addition, XRD provides the relative abundance of the total amorphous material present in the sample.
ELEMENTAL COMPOSITION
While XRD identifies crystalline minerals, EDS provides the overall elemental composition including amorphous (non-crystalline) as well as crystalline materials. The elemental composition along with other lines of evidence provides insight into potential processes contributing to corrosion.
HOW TO USE XRD AND EDS
As part of a multiples lines of evidence approach, use XRD and EDS to provide insight into corrosion processes and mechanisms in a system.
Use XRD and EDS to help answer…
- What minerals are present in corrosion deposits?
- Are these minerals different than observed in areas without corrosion?
- Are iron oxides present? Are iron sulfides present?
- In the XRD results, what are relative abundances of mackinawite (Fe9S8) and greigite (Fe3S4)?
- Do EDS results show high percentages of Fe and S?
- Do XRD and EDS results correspond to CENSUS® qPCR or QuantArray®-MIC results for sulfate reducing bacteria?
