Synchrotron X-ray diffraction studies of products of the steel pipe corrosion measured in the native aqueous suspension

Paweł Piszora 1Jacek Nawrocki 1Jolanta Darul 1Waldemar Nowicki 1Alexander Evans 2

1. Adam Mickiewicz University, Faculty of Chemistry, Grunwaldzka 6, Poznań 60-780, Poland
2. European Synchrotron Radiation Facility (ESRF), Grenoble 38043, France

Abstract

Corrosion scales play an important role in modifying water quality in drinking water distribution systems. The corrosion scales from steel pipes were analyzed for their structure and composition. The tubercle deposits were collected from pipelines in the distribution systems of a large agglomeration. Scales were studied both before and after drying, and goethite, magnetite and lepidocrocite were identified as the primary constituents of the dried samples. High concentrations of layer double hydroxide (LDH) phases were detected in the samples loaded in diffractometer as a aqueous suspension in native water. Therefore the sample preparation play a key role in X-ray measurements of so labile system.

X-ray powder diffraction data were collected with the high-resolution X-ray powder diffractometer on beamline ID31 at ESRF, selecting X-rays from the white undulator source with wavelengths of 0.41274(6) Å. Small quantities of rust-in-water suspension were ground with a pestle in an agate mortar, and as a paste, introduced into 0.5 mm diameter glass capillaries, mounted on the axis of the diffractometer and spun during measurements. Data were collected for half an hour and normalized against monitor counts and detector efficiencies, and rebinned into steps of 2θ= 0.001°. Samples were introduced in a glass capillary for avoiding degradation of the LDH, which is sensitive to the air, but also for minimising the effect of preferential orientation.

Our synchrotron X-ray radiation studies and refinements with Rieveld method enabled to point out important differences between the corrosion products found in several different water distribution systems. The most intrinsic phases of all rust samples were LDH phases. Three of them were identified as iron(II,III) hydroxysalts commonly named green rust, which belong to the family of divalent-trivalent ions minerals, characterised by a crystal structure that consist of the stacking of brucite-like layers carrying a positive charge and layers constituted of anions and water molecules. The structure and composition of green rust depend upon the specific anions they incorporate. Products of biologically induced redox processes are proved as a result of metabolic activity of bacteria and subsequent chemical reactions involving metabolic byproducts. The organisms secrete metabolic products that react with ions or compounds on the pipe surface resulting in the subsequent deposition of mineral particles. Presented results are a part of wider studies needed to establish the role of the transitional corrosion products in the mechanism of a biotic release of iron from corroded pipes.

Acknowledgments
We acknowledge the European Synchrotron Radiation Facility for provision of synchrotron radiation facilities and we would like to thank Dr Michela Brunelli for assistance in using beamline ID31.

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Presentation: Oral at 11th European Powder Diffraction Conference, Microsymposium 15, by Paweł Piszora
See On-line Journal of 11th European Powder Diffraction Conference

Submitted: 2008-05-06 11:11
Revised:   2009-06-07 00:48
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