Glassy materials, definition

The consolidated titanate waste pellets are similar in appearance to their glass counterparts, i.e., both are dense, black and apparently homogeneous. Microscopic analyses, however, reveal important differences between these two waste forms. While little definitive work has been done with glassy waste forms, it is apparent that several readily soluble oxide particulates of various nuclides are simply encapsulated in the glass matrix. The titanate waste form has undergone extensive analyses which includes optical microscopy, x-ray, scanning electron microscopy, microprobe, and transmission electron microscopy (l ) The samples of titanate examined were prepared by pressure sintering and consisted of material from a fully loaded titanate column. Zeolite and silicon additions were also present in the samples. 

Specifically for mineral science, XAS became definitively established in the middle 1980s, after a period of parasitical development during which the technical and theoretical principles of the method were adapted and finalized to all types of Earth materials the crystalline ones, mostly, as well as those in the glassy state (cf Brown et al. 1978 Galas et al. 1980, 1984 Waychunas et al. 1983, 1986 Davoli et al. 1987, 1988 Brown and Parks 1989 Bassett and Brown 1990 see Brown et al. 1988, 1995 for reviews). 

Compared to crystalline materials, the production and handling of amorphous substances are subject to serious complexities. Whereas the formation of crystalline materials can be described in terms of the phase rule, and solid-solid transformations (polymorphism) are well characterised in terms of pressure and temperature, this is not the case for glassy preparations that, in terms of phase behaviour, are classified as unstable . Their apparent stability derives from their very slow relaxations towards equilibrium states. Furthermore, where crystal structures are described by atomic or ionic coordinates in space, that which is not possible for amorphous materials, by definition, lack long-range order. Structurally, therefore, positions and orientations of molecules in a glass can only be described in terms of atomic or molecular distribution functions, which change over time the rates of such changes are defined by time correlation functions (relaxation times). 

Membrane technologists are well aware that the most permeable glassy polymers are those which possess a very high free volume, where the term free volume refers to the intermolecular voids within a material [1], Scientists who work with molecular sieves, such as zeolites, commonly use the term microporous material to describe those materials which contain pores or channels less than 2nm in width, a definition that arises in the context of gas adsorption studies [2],... 

A noncrystalline polymeric material that has no definite order or crystallinity. A polymer in which the macromo-lecular chain has a random conformation in solid (glassy or rubbery) state. On the one hand, an amorphous polymer may show a short range order, while on the other, a crystalline polymer may be quenched to the amorphous state (viz., polyethylene terephthalate (PET)). The maximum value of a periodically varying function, e.g., used to describe the energy transmitted from the ultrasonic welding horn to the weld joint. 

The term ceramics refers to a broad range of materials including not only polycrystalline materials, but also powdered materials, thin films and single crystals, and glassy inorganic materials. In this section, we will use a slightly narrower definition of ceramics as polycrystalline sintered materials. 

---