Application of X-ray diffraction for studies on microbially induced metal corrosion

Corresponding author: Professor Beata Cwalina – Ph.D., D.Sc., Eng., e-mail: beata.cwalina@polsl.pl Introduction Metals and their alloys often undergo corrosion. in some cases it is related to activity of microorganisms forming biofilm on the metal surface. Such a situation is also typical for drinking water supply system. Cells and the organic matter they produce collect in a places, where water continuously acts on pipe walls. Such conditions promote the growth and proliferation of microbes [1 – 3]. Microbes present in water mains are adapted to low content of nutrients in drinking water (less than 2 mg of organic matter per 1 l of water) and are very hard to manage [4]. The presence of bacteria in water supply networks brings a number of problems, e.g. increased consumption of disinfectants, which means higher water treatment costs [5, 6]. The biofilm may also serve as a reservoir of pathogenic microbes [7], including coliforms. Search for their potential source has lead to the conclusion they must have been present in biofilms formed on pipe walls of drinkable water supply system. when released from the biofilm, they entered the water and were detected as suspended (planctonic) bacteria [7]. The bacteria also contribute to the corrosion of piping [8, 9]. This results in decrease of their strength, as well as generation of favourable conditions for growths of other microorganisms on the surface of the corroded porous surfaces [3, 6]. Pipe corrosion among others leads to releasing iron compounds into water, which causes its turbidity and deterioration of organoleptic properties [10, 11]. Bacteria may have direct effect on the quality of supplied water by changing its colour related to the content of compounds containing iron and/or other metals (their presence may be a result of bacterial metabolic activity, e.g. Galionella genus) as well as unpleasant odour and taste (e.g. due to the presence of hydrogen sulphide produced by sulphate reducing bacteria; RBS) [3, 10, 12]. Biofilm generation in water supply network may also lead to hydraulic losses due to the increase of pipe wall roughness and deposition on them insoluble compounds of iron and other metals [5, 12, 13]. Microbiologically induced/influenced corrosion (MIC) occurs also in tanks and pipelines used for transportation of waste water, oil, gas and diesel oils. The same problem applies also to components of water construction, waste water treatment plants, many components of power plans, cooling systems and fire sprinkler systems [14 18]. X-ray Diffraction (XRD) is a research technique applied both in structural and applied radiography. applied X-ray analysis includes both qualitative and quantitative phase analysis, measurements of lattice parameters, determination of dimensions of crystallites and mosaic blocks, determination of macroand microstrains, deformations of crystal lattice, as well as texture testing [19]. in the MiC studies, XRD is employed for determination of individual crystalline phases forming part of corrosion products formed on metal surfaces. The aim of this paper is to present the current state of knowledge on XRD in terms of the use of this technique to study the corrosion induced by microorganisms. X-ray Diffraction (XRD) XRD jest a research technique enabling analysis of structure and defects of crystalline substance, as well as analysis of varieties of amorphous substance and forming various materials, including geological and construction materials, industrial wastes (ashes, dust), useful materials and substances (metal alloys, pharmaceuticals). The majority of naturally occurring substances has crystalline structure (the atoms are arranged in space in a regular and orderly manner). Crystalline substances occurs as monocrystals or polycrystals, i.e. technical materials such as metals and ceramics [20]. Depending on the type of tested material, various techniques of X-ray diffraction are used. it uses principle of interference reflection from set of lattice plane of defined interplanar spacings (Fig. 1) using X-ray diffraction on crystal lattice. The technique takes into account observations of laue, Braggs and wulf. They noticed that X-ray reflection from crystal planes occurs only some, specific angles of incidence.