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Pretreatments are thin, adherent, and protective layers deposited directly on cleaned metal surfaces to enhance the performance of the multi-coat finishing system on metal and alloy substrates. Regulatory and environmental considerations dictate that industries replace the extant toxic and hazardous chromate-based pretreatments used for aluminum alloys with more sustainable ones. Two new families of organic-inorganic hybrid (OIH) pretreatments for aluminum alloys have been developed using customized silane-type sol-gel precursors--Epoxy-silane and Bis-ureasil--as primary components. Two series of sol-gel compositions varying in concentrations of silane precursor, organic corrosion inhibitor, and nano-silica particles have been prepared and used to deposit OIH pretreatments on aluminum alloy substrates (AA-2024-T3). The corrosion resistance performance of these OIH pretreatments has been studied by electrochemical impedance spectroscopy (EIS), direct current (DC) polarization resistance, and neutral salt spray test and compared with the resistance performance conventional hexavalent chromium-based pretreatment, as a benchmark and industry standard for Al alloys. This research specifically investigates the effects of key components of sol-gel compositions on the corrosion performance of the OIH pretreatments on Al-2024-T3. Using the Box-Behnken Design of Experiment (DoE) methodology and Minitab software for analysis, the key factors affecting corrosion performance have been identified and sol-gel compositions optimized. This study revealed that for both families of OIH pretreatments, the film deposited in the sol-gel bath containing 25% by weight of precursor provided the best performance. Furthermore, incorporation of nano-silica particles to an optimum level of 5% by weight led to a remarkable improvement of the corrosion-resistance performance of the pretreatments for both families. This study has also very clearly shown that the use of the organic corrosion inhibitor mercaptobenzthiazole is effective in enhancing the corrosion-resistance performance of both families of pretreatments when used at the optimum level of 3% by weight. A comparison of the corrosion-resistance performance of the two families of OIH pretreatments with chromate conversion coating (control) showed that pretreatments based on epoxy-silane precursor when used at optimum compositions clearly outperform chromate conversion coatings used as a control in this study. Furthermore, OIH based on a bis-ureasil precursor, while showing a slightly lower performance than its epoxy-silane counterpart, is comparable or slightly superior to the commercial conversion coating when used at optimum compositions.
Intelligent Coatings for Corrosion Control covers the most current and comprehensive information on the emerging field of intelligent coatings. The book begins with a fundamental discussion of corrosion and corrosion protection through coatings, setting the stage for deeper discussion of the various types of smart coatings currently in use and in development, outlining their methods of synthesis and characterization, and their applications in a variety of corrosion settings. Further chapters provide insight into the ongoing research, current trends, and technical challenges in this rapidly progressing field. Reviews fundamentals of corrosion and coatings for corrosion control before delving into a discussion of intelligent coatings—useful for researchers and grad students new to the subject Covers the most current developments in intelligent coatings for corrosion control as presented by top researchers in the field Includes many examples of current and potential applications of smart coatings to a variety of corrosion problems
A book to cover developments in corrosion inhibitors is long overdue. This has been addressed by Dr Sastri in a book which presents fundamental aspects of corrosion inhibition, historical developments and the industrial applications of inhibitors. The book deals with the electrochemical principles and chemical aspects of corrosion inhibition, such as stability of metal complexes, the Hammett equation, hard and soft acid and base principle, quantum chemical aspects and Hansch' s model and also with the various surface analysis techniques, e.g. XPS, Auger, SIMS and Raman spectroscopy, that are used in industry for corrosion inhibition. The applications of corrosion inhibition are wide ranging. Examples given in this book include: oil and gas wells, petrochemical plants, steel reinforced cement, water cooling systems, and many more. The final chapters discuss economic and environmental considerations which are now of prime importance. The book is written for researchers in academia and industry, practicing corrosion engineers and students of materials science, engineering and applied chemistry.
In order to prevent corrosion on aluminium and aluminium alloys, many surface treatments have been developed, such as silane films, which are environmentally compliant coatings. During this work we investigate corrosive behaviour of aluminum alloys AA2024 in a NaCl 0.05mol L-1 coated with MEMO/Bis-EGMP/TiB, during the Part A and TEOS/ATMP/GPTMS during the Part B. The aluminium alloy substrates were pre-threated before the coating deposition. The silane coatings were applied using sol-gel system. After silane curing process, all the substrates were covered with a commercial epoxy coating in order to provide the topcoat protection before the samples immersion in the aggressive solution for corrosion tests (NaCl 3.5%). Electrochemical techniques were applied during Part A in order to evaluate the corrosion protection of silane coating. Microscope and optical analysis was carried on during this work to evaluate the film surface homogeneity and the presence or absence of defects. The samples prepared were tested under accelerated corrosion environment, which showed that the samples prepared on Part A of the present study did not have good protection performance. On the other hand, samples prepared during Part B showed excellent behaviour and the silane coating prepared from TEOS/ATMP/GPTMS system protected the aluminium surface from the aggressive corrosion medium. Adherence of silane system and also the topcoat applied is essential to obtain a long time protection. Therefore, pull-off tests were performed to confirm the efficacy of the coating adherence.
Organic and Inorganic Coatings for Corrosion Prevention - Research and Experiences is a collection of Papers from EUROCORR '96 and published for the European Federation of Corrosion by The Institute of Materials. In the session on Coatings the following topics were discussed: • Life-time prediction of organic coatings; • Environmentally friendly coatings; • Testing; and • Surface preparation techniques. This book contains a selection of the scientific work presented in the Conference with the aim of focusing on the research developments in the frame of corrosion protection coatings for industrial use. The book is in four sections describing, respectively, organic coatings, zinc coatings, other metallic coatings and ceramic coatings.
Finish Manufacturing Processes are those final stage processing techniques which are deployed to bring a product to readiness for marketing and putting in service. Over recent decades a number of finish manufacturing processes have been newly developed by researchers and technologists. Many of these developments have been reported and illustrated in existing literature in a piecemeal manner or in relation only to specific applications. For the first time, Comprehensive Materials Finishing, Three Volume Set integrates a wide body of this knowledge and understanding into a single, comprehensive work. Containing a mixture of review articles, case studies and research findings resulting from R & D activities in industrial and academic domains, this reference work focuses on how some finish manufacturing processes are advantageous for a broad range of technologies. These include applicability, energy and technological costs as well as practicability of implementation. The work covers a wide range of materials such as ferrous, non-ferrous and polymeric materials. There are three main distinct types of finishing processes: Surface Treatment by which the properties of the material are modified without generally changing the physical dimensions of the surface; Finish Machining Processes by which a small layer of material is removed from the surface by various machining processes to render improved surface characteristics; and Surface Coating Processes by which the surface properties are improved by adding fine layer(s) of materials with superior surface characteristics. Each of these primary finishing processes is presented in its own volume for ease of use, making Comprehensive Materials Finishing an essential reference source for researchers and professionals at all career stages in academia and industry. Provides an interdisciplinary focus, allowing readers to become familiar with the broad range of uses for materials finishing Brings together all known research in materials finishing in a single reference for the first time Includes case studies that illustrate theory and show how it is applied in practice
Water-based inorganic-organic hybrid sol-gel coatings were developed on aluminium. The coatings were based upon epoxy-silane, glycidoxypropyltrimethoxysilane (GPTMS) and methyltrimethoxysilane (MTMS) as inorganic silane precursors crosslinked with the organic polymer, hexamethylmethoxymelamine (HMMM). The aim of the present work was to modify the hybrid sol-gel coating to obtain hydrophobic properties which could be achieved by either lowering the surface energy or increasing the surface roughness of the coatings. Lowering of surface energy was achieved by incorporating various fluoro-alkylsilanes (FASs) with two different chain lengths, of 3 and 17 fluorine atoms. The subsequent water contact angles achieved were 100° and 110° respectively for FAS modification. As a result, a commercial fluoro emulsion (FE) which was a water based six carbon atom perfluoro polymer, was employed as co-precursor. A substantial improvement in hydrophobicity was achieved with FE modification resulting in contact angle of 118°. Further, the surface roughness of the fluorinated sol-gel coating was enhanced by incorporating various nano-particles with different size, surface area and surface chemistry, namely nano-Zinc Oxide (ZnO), hexadecyltrimethoxysilane (HDTMS) modified nano-silica, dichlorodimethylsilane (DDS) modified nano-silica and hexamethyldisilazane (HMDZ) modified nano-silica. Out of these HMDZ nano-silica modification resulted in maximum hydrophobicity with contact angle of 125° and sliding angle of 25° on aluminium surface. Furthermore an independent study was carried out on application of as developed composite coatings on chemically and mechanically roughened aluminium surfaces. It was found that contact angle increases up to 130° using techniques like chemical etching, plasma etching, sand blasting and grinding etc. The as developed nano-composite coatings when applied on other non-metallic substrate such as glass, cotton, cardboard, paper, concrete and wood, it showed excellent hydrophobicity with a contact angle of > 135°. Furthermore, all the substrates showed a sliding angle of about 15°.The as developed coatings were characterised for their chemical and morphological structures, using techniques including FTIR, XPS, SEM and AFM. The wetting properties were analysed using contact angle goniometry. The performance of the as developed coatings was evaluated by determining corrosion resistance, hardness, adhesion and scratch resistance properties. Finally, the role of nano-particles distribution was studied in detail. It was found that maximum hydrophobic properties were achieved at optimum concentration of nano-particles.
Environmentally friendly sol-gel nanocomposite coatings have been processed and characterized for corrosion protection of aerospace alloy AA2024-T3. The hybrid nanocomposite coatings were processed in solution using acid-catalyzed hydrolysis and condensation of precursors Glycidoxypropyl trimethoxysilane (GPTMS) and Tetramethoxysilane (TMOS) forming self assembled nanoscale composite followed by curing using a one step and a two step process. Nanometer scale montmorillonite clay, Cloisite 15A was dispersed in the precursor solution prior to film coating. The structure and composition of the hybrid coatings was determined using Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction Spectrometry (XRD). Hydrolysis and condensation kinetics were tracked using FTIR and a semi-quantitative equation was developed. Viscosity studies performed to understand the rheology of the hybrid nanocomposite, shows two distinct regimes for hydrolysis and curing. XRD results indicate a physical structure that is mostly amorphous with selective crystalline regions due to siloxane bridge formations. The Cloisite 15A clay was exfoliated, as determined by the disappearance of clay peak. Atomic Force Microscopy (AFM) was used to study the surface morphology, showing increase in surface roughness with the addition of clay. Corrosion performance was determined using DC Polarization and Electrochemical Impedance Spectroscopy (EIS). The DCP results were used to determine the optimal composition of the hybrid nanocomposite and optimal time of reaction for the first layer. The corrosion current and hence the corrosion rate for the two-step system was around three orders of magnitude lower than the one-step system, with the corrosion potential being correspondingly higher. EIS results show that the two-step system has a corrosion resistance two orders of magnitude higher than the mono-layer. The impedance was in the order of E+6 Ohms, which remained consistent over 8 weeks of testing, with a low water uptake of around 20%. Modification of the coating with diamine curing agent and clay provided significantly better results with higher resistance (E+6 Ohms) and water uptake values as low as 3-5% over 6 weeks.
Materials are at the center of all technological advances; it is evident in considering the spectacular progress that has been made in fields as diverse as engineering, medicine, biology, etc. Materials science and technology must develop researches allowing the generation of new methods of protection to reduce fundamentally the losses of human life as well as the economic ones. The former are impossible of quantifying, while the latter are highly significant; thus, only those derived from corrosive processes in their different forms reach, in technologically developed countries, about 4% of the Gross National Product (GNP), while those derived from fire action range from 0.5 to 1.0% of the mentioned GNP. The book, in the different chapters, displays original systems of superficial protection and of low environmental impact to minimize the losses by corrosion and the fire action.
This work was directed at the synthesis and structure-property behavior of hybrid organic-inorganic network materials prepared by a sol gel reaction. Specific focus concerned the development of optically abrasion resistant coatings that could be utilized for both polymeric and metallic substrates. In the case of the latter, the purpose of the coating was to not only to supply abrasion resistance but, if possible, provide corrosion resistance as well. Considerable success was achieved in that several hybrid coatings were synthesized by reacting one or more metal alkoxides with functionalized organic moieties such as triethoxysilanated diethylene triamine (DETA) and related diamines or di or triol species. These functionalized organics, in conjunction with the alkoxide, were spin or dip coated on appropriate substrates and thermally cured. In some cases a primer molecule was also utilized to promote higher adhesion with the substrate the principal example being amino propyltrimethoxysilane. It has been demonstrated that the coatings display very good abrasion resistance for polymeric substrates, aluminum and copper but do not perform as well on steel or a phosphate coated steel. The final portion of the work concerned the development of porous inorganics made by the calcination of hybrid organic-inorganic network materials but where these networks were prepared by the use of functionalized polytetramethylene oxide oligomers of varied molecular weight that had been reacted with tetraethylorthosilicate (TEOS). It was demonstrated that calcination of these materials could lead to porous silicate powders possessing a specific surfaces near 1000 meters2/gram. Furthermore, pore size characteristics of these powders were analyzed. It was concluded that such hybrid materials could serve as the base for developing highly porous powder materials for chromatography, catalyst.