| Περίληψη: | Science is nowadays directed towards application; however, the path from basic to applied research has been proven sometimes difficult. This is the case of the titanium dioxide nanotube layers (TNTs), discovered more than a decade ago; immediately after being reported, it has been predicted that they would give miraculous characteristics to materials in electronic, biomedical and photovoltaic applications. The synthesis of the titanium dioxide nanotube layers through the electrochemical anodization was considered a very convenient method, due to its simplicity and low cost. Although this method is simple to apply, the dependency on a great number of manufacturing parameters require deep understanding and control on the whole fabrication process. Until the moment, a great difficulty has been encountered in applying this method on titanium for large scale applications (e.g. in mechanical systems and implantology). Different research groups focused on synthesizing these self-organized nanostructures on pure titanium plates, provided at high cost, from well known suppliers. However, the thin, well polished, high quality titanium plates are not appropriate for application to an industrial level. Mechanical structures in aeronautics and naval industries involve thick titanium plates with various internal and external characteristics. Further on, in biomedical applications, titanium implants present complex geometries and porosity. These technical aspects represented a strong impediment in processing the titanium surface and synthesizing the titanium dioxide nanotube layers on various titanium grades with complex geometry, such as for example a titanium dental screw type implant. In practice, a great difference exists between processing a plate surface and an implant surface. Suitable anodizing conditions result in titanium dioxide nanotube layers on pure titanium plates, while the same conditions can only enable the formation of pores on a titanium implant surface. A great need exists for a deeper understanding of the formation of highly organized microstructures on titanium surfaces through the electrochemical anodizing method.
The present manuscript describes a set of experiments applied for the surface processing of different titanium plates and implants, through the electrochemical anodizing method and the manufacturing of TNTs based multilayered nanocomposites. The final target of this investigation is the application of the titanium dioxide nanotubes in three main directions: mechanical systems, implantology and solar cells.
The first part of this study consists in a bibliographic investigation. An introduction in the self-organization of materials at nano-level is presented in Chapter 1. Self-organization of materials is a complex scientific area, widely used nowadays in materials’ surface processing. Titanium surface may be processed through self-organizing phenomena during an electrochemical anodization, which leads to titanium dioxide nanotubes formation. The second chapter (Chapter 2) describes several already reported case studies involving carbon and titanium dioxide nanotubes. Considering that composite materials are gaining ground in all kind of application, nanostructured phases such as nanotubes are of particular interest in composites manufacturing. Combining two nanostructured phases is an almost impossible target, except when it comes about multilayered composites. In multilayered composites, two nanostructured phases may come in direct contact. Interactions at nano-level result in improved structural, mechanical and electrical properties of the composite. Such an example is that one of titanium dioxide nanotubes as a substrate for CNTs in a multilayered architecture. A main issue when studying multilayered hybrid nanocomposites is the interphase effect. Thus, Chapter 3 is about a semi-empirical model, namely the Viscoelastic Hybrid Interphase Model, applied for the prediction of the mechanical properties of a composite, based on an interphase concept. Modeling the interphase properties is an extremely useful tool in advanced composites design and application. Finally, Chapter 4 mentions a number of application areas of multilayered hybrid nanocomposites.
Chapter 5 mentions all technical aspects related to TNTs based multilayered hybrid nanocomposites manufacturing and methods used in their investigation. The experimental and theoretical investigations are presented in Chapters 6-8. Chapter 6 describes a number of anodization protocols involving several electrochemical parameters used for processing the titanium surface. Chapter 7 presents two case studies: (i) an investigation of the nanomechanical properties of TNTs based multilayered hybrid nanocomposites and (ii) an investigation of the mechanical properties of TNTs reinforced adhesive single lap joints. Chapter 8 is about the application of the TNTs in implantology, with emphasis on the ‘material-human cell’ interphase effect on implant integration in the host body; this chapter also includes an application of the Viscoelastic Hybrid Interphase Model, already presented in Chapter 3, to predict the properties of the interphase between living and nonliving materials when in contact, as well as an accurate prediction of human cells adhesion quality to various substrates, including TNTs and CNTs, through the model. Chapter 9 is an investigation of the reflectivity of TNTs based multilayered hybrid nanocomposites with possible application in solar cells. Finally, the global conclusions of the entire work and future scientific avenues on this subject are presented in Chapter 9.
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