Overall Aspects of Non-Traditional Glasses: Synthesis, Properties and Applications

This chapter revisits the concepts of the vitreous state and the main theories concerning the glass structure and the criteria for glass formation.

First, the conditions for the formation of a vitreous solid from cooling down from a melt are presented, together with the meaning of transformation temperature of glass. Also it is referred the influence of the thermal history of a glass on its properties.

Next, a survey of the existing literature on the structure of glasses is made.

Several structural theories are presented: Zachariasen, Lebedev, Huggins and Porai- Koshits which are here considered to be the most important theories for glass structure.

Also, it is relevant the presentation of diverse theories which postulate the criteria which have to be followed by an oxide to be considered as a glass-forming oxide.

In this way criteria based on crystal chemistry concepts (Goldschmidt, Zachariasen), criteria based on the correlation between the ability to form glass and the bond strength (Dietzel, Sun, Rawson) and between the glass-forming ability and the type of bonding (Smekal, Stanworth) are discussed.

Finally, the main experimental techniques commonly used to the study of glasses structure are briefly presented.

Such techniques include X-ray diffraction, Small angle X-ray scattering, Fourier transform Infrared spectroscopy, Infrared reflection spectroscopy, Raman spectroscopy, Nuclear magnetic resonance and Electron microscopy (scanning and transmission, coupled with electron probe microanalysis). And for the study of chemical composition of glass and surface glass layers: Auger electron spectroscopy, secondary ion mass spectrometry and Rutherford back spectrometry.

The search for a biomaterial capable of promoting a biological and mechanically effective link between it and the living tissues around was the major motivation for the advancement of bioactive glasses. The physicochemical characteristics of such materials allow the occurrence of a series of complex biological reactions at the interface with the biological tissue. Fundamental concepts such as biocompatibility, bioactivity and degradation on a physiological environment and their inter-relations are discussed. While being mechanically fragile, bioactive glasses have the huge advantage of being able to strongly connect the hard and soft tissues thanks to the ability to form a Hap film to its surface when immersed in a biological environment. To overcome the inherent glass fragility, new approaches based on tailored bioglasses (coatings and glass-ceramics) were developed.

Bioactive glasses inspired by the 45S5 composition have been widely investigated since 60 years but recently a new line of research in biomaterials with an emphasis on regeneration instead of replacement tissues has been proposed, providing new opportunities for the application of bioactive glasses in engineering tissues.

The inherent glass brittleness can be overcome by tailoring glass coatings and glassceramics.

During the last century, new materials have been developed and improved envisaging specific properties in diverse applications, from the conventional ones to those in which high tech is imperative. Glass-ceramics are among those materials since they can exhibit attractive properties for usage in cookware or architectural components, for example, but also remarkable performances in advanced applications such as electronic devices, medical prosthesis, tissue engineering, etc.

Glass-ceramic materials are polycrystalline solids consisting of tiny crystals homogeneously dispersed in a residual glass phase, where the number of precipitated crystals, their growth rate and final size can be manipulated by suitable heat treatments. It is this controlled crystallization, generally induced by nucleating additives that yields an array of materials with interesting, sometimes unusual, combination of properties.

In this chapter a simple approach of the concept of glass-ceramic is made, based on practical aspects of its development. The methodologies for the production of a glass-ceramic and the typical heat-treatment cycles through which a parent glass is converted into a crystallized structure are presented.

The final microstructure and thus the properties of a glass-ceramic depend on the time-temperature schedule imposed to the base glass but are also affected by its composition and the additives that catalyze crystallization. The most common nucleating agents are presented and the ways through which they act as precipitation catalyzers are discussed.

Finally a very brief reference is made to a few experimental techniques, considered as essential tools for glass-ceramics study at the different development stages.

In 1975, a new class of glass materials based on ZrF4 was accidentally discovered in the University of Rennes. This new family of synthetic halide glasses exhibited an exceptional wide transmission window ranging from ~ 0.2 m in the UV until ~ 7.6 m in the IR, making them a first choice for military and intelligence optical fibers, during several decades. Heavy metal fluoride glasses structure and properties are revised and discussed in this chapter.

The first reports on chalcogen and/or chalcogenide glasses date from the beginning of the XX century. However, it was only in the 1950s that started the systematic study of chalcogenide glasses. Presently the research on this type of glasses is very active due to their great potential for practical use. The unique photoconductive properties, infrared transparency, ionic conduction, phase-change phenomenon and electrical and thermal transport properties of chalcogenide glasses make them highly attractive for a wide range of applications, from photoreceptors to high-density optical memories, infrared optical components, ionic sensors or thermoelectric devices.

This chapter intends to give a brief overview on the uniqueness properties of chalcogenide glasses. It starts with a picture of their structure and electronic structure, followed by their glass formation characteristics, a description of their physical properties and finalizing with a non-exhaustive presentation of their applications.

Photonic crystals (PCs) as it is often called photonic band gap materials (PBGs), are artificial composite materials, micro/nanostructured on an optical length scale (e.g. few hundreds of nm). The resulting periodicity in the dielectric constant is responsible for inhibiting light from propagating through the material as a result of Bragg diffraction. The forbidden frequency range is called a stop band. In PCs the electromagnetic waves within the band gap are completely reflected by the crystal, while spontaneous emission (within the band gap) are totally concealed.

This chapter introduces the physical concepts behind PC structures, along with bottomup fabrication methods, properties, and applications.

This chapter provides an overview of the employ of glass in solar energy devices, beginning with a introduction to the actual needs of energy followed by a review of some particular domains where glass is used in solar energy at present, or is emergent as an alternative for the future. Some physical parameters describing the optical and thermal characteristic of glass are introduced.