Sulphate-reducing bacteria are known to play an important role in anaerobic corrosion processes. They are often found associated with metal surfaces and their activities can be of particular economic significance in many industrial areas. The aim of this thesis was to investigate anaerobic corrosion of metals by the sulphate-reducing bacteria in the presence of mixed microbial consortia in various heterogeneous marine environments. A laboratory model system was designed, based on part of an offshore oil storage system. An extensive bacteriological analysis and comprehensive study of the consequent physicochemical parameters involved in the microbial corrosion process was carried out. Particular attention was paid to the activity of the sulphate-reducing bacteria on metal surfaces. A method was developed to measure both acid-volatile and non-acid-volatile sulphur formation, produced by the activity of the sulphate-reducing bacteria on mild steel coupons. The importance of this method is firmly stressed. Previous results involving rates of sulphate reduction estimated without considering non-acid-volatile sulphur product formation, must be interpreted with caution. A study of non-biological methods of analysing corrosion and their various limitations was carried out to assess their usefulness in determining the effect of microbial corrosion in various environments. It must be stated that no single technique can be used to study anaerobic microbial corrosion. Therefore, it is recommended that a series of tests should be utilised. These should include microbiological, chemical and metallurgical methods.

Corrosion behaviour of Al, Zn, Cu and steel samples under the conditions of constant temperature and humidity were performed in the media containing the following microorganisms. Bacillus mycoides, Aspergillus fumigatus Aspergillus niger, Cladosporium herbarum, Penicillium frequentans. The influence of metal surface morphology on the vitality of microorganisms was investigated, as well as the proceeding of microbial corrosion was under the study. The real surface area of Cu electrode was determined by means of electrochemical techniques, while the method for comparison of surface areas of other metals was proposed and this method was based on atomic force microscope measurements. It was determined that the metal nature and morphology influenced the vitality of microorganisms. The results of electrochemical impedanse spectroscopy enabledus to evaluate the corrosion behaviour of metals. The results were found to indicate the corrosion inhibition for Al, steel and Cu, however, the effect depended on the metal surface morphology and exposure time.

Η προστασία των μετάλλων με δραστικές ενώσεις που έχουν τη δυαντότητα σχηματισμού επιφανειακών ενώσεων εντάξεως είναι ένας κλάδος της Χημείας και της Επιστήμης των Υλικών μεγάλης επιστημονικής, αρχαιολογικής και τεχνολογικής σημασίας. Οι αντιδιαβρωτικές ιδιότητες του βενζοτριαζολίου και μικρού αριθμού υποκατεστημένων βενζοτριαζολίων για ορισμένα μέταλλα, ειδικά του χαλκού και των κραμάτων του, έχουν προσελκύσει το ενδιαφέρον για τη χημεία ένταξης του βενζοτριαζολίου και της συζυγούς του βάσεως, του βενζοτριαζολάτο ανιόντος. Έχουμε ξεκινήσει ένα ανόργανο μοντέλο προσέγγισης της παρεμπόδισης της διάβρωσης του Zn με βενζοτριαζόλια. Στην παρούσα εργασία έχουμε μελετήσει λεπτομερώς τη χημεία ένταξης του 1-μεθυλοβενζοτριαζολίου (Mebta) με Zn(II). Παρασκευάσθηκαν τα νέα σύμπλοκα [ZnCl2(Mebta)2](1), [ZnBr2 (Mebta)2](2), [ZnI2(Mebta)2](3), τετ-[Zn(ΝΟ3)2(Mebta)2](4), οκτ-[Zn(ΝΟ3)2(Mebta)2] (5), [Zn(Mebta)4](ClO4)2(6), [Zn(Mebta)4](PF6)2(7) και [Zn3(Ο2CPh)6(Mebta)2](8). Οι μοριακές και κρυσταλλικές δομές των συμπλόκων έχουν προσδιορισθεί με κρυσταλλογραφία ακτίνων-Χ μονοκρυστάλλου. Η γεωμετρία ένταξης του ZnΙΙ στα 1-4, 6 και 7 είναι τετραεδρική, ενώ στο σύμπλοκο 5 το μεταλλοϊόν έχει παραμορφωμένη οκταεδρική στερεοχημεία. Τα μεταλλικά κέντρα στο 8 υιοθετούν τετραεδρικές και οκταεδρικές γεωμετρίες. Το Mebta συμπεριφέρεται στα σύμπλοκα ως μονοδοντικός υποκαταστάτης με το άτομο δότης να είναι το άζωτο της θέσης 3 του αζολικού δακτυλίου. Τα σύμπλοκα χαρακτηρίσθηκαν με φασματοσκοπία IR. Τα δεδομένα συσχετίζονται με τον τρόπο ένταξης των υποκαταστατών και τις γνωστές δομές. Επίσης αναλύεται η τεχνολογική σημασία των αποτελεσμάτων μας. Φαίνεται ότι τα Ν-υποκατεστημένα βενζοτριαζόλια με ομάδες που δεν περιέχουν άτομα δότες δεν μπορεί να οδηγήσουν σε αποτελεσματικούς παρεμποδιστές της διάβρωσης εξ’αιτίας της αδυνμίας αυτών των μορίων να σχηματίζουν πολυμερικά είδη. / Protection of metals with reactive compounds capable of forming surface-phase coordination compounds is an area of chemistry and materials science which is of considerable scientific, archaeological and technological importance. The anticorrosion properties of benzotriazole and few substituted benzotriazoles towards certain metals, particularly copper and its alloys, have focused interest on the coordination chemistry of the parent molecule and its conjugate base, the benzotriazolate anion An inorganic model approach to the corrosion inhibition of Zn by benzotriazoles has been initiated. The coordination chemistry of 1-methylbenzotriazole (Mebta) with Zn(II) has been studied in detail. The new complexes [ZnCl2(Mebta)2](1), [ZnBr2 (Mebta)2](2), [ZnI2(Mebta)2](3), tet-[Zn(ΝΟ3)2(Mebta)2](4), οkt-[Zn(ΝΟ3)2(Mebta)2](5), [Zn(Mebta)4](ClO4)2(6), [Zn(Mebta)4](PF6)2(7) and [Zn3(Ο2CPh)6(Mebta)2](8) have been prepared. Their molecular and crystal structures have been determined by single crystal, X-ray crystallography. The coordination geometry of ZnII in 1-4, 6 and 7 is tetrahedral, while complex 5 has a distorted octahedral stereochemistry. The metal sites in 8 adopt both tetrahedral and octahedral geometries. Mebta behaves as a monodentate ligand in the complexes; the donor atom is nitrogen of the position 3 of the azole ring. The complexes were characterized by IR spectroscopy; the data are discussed in terms of the coordination modes of the ligands and known structures. The technological relevance of our results is also discussed. It seems that benzotriazole N-substitution with groups containing no donor atoms cannot lead to effective corrosion inhibitors due to the inability of these molecules to form polymeric species.