Noncrystalline or amorphous solids

We shall be discussing other types of inclusion compounds formed by layered graphite and Ta 2 as well as other varieties of hosts in Chapter 8, which deals with intercalation chemistry. 

At the glass transition temperature, the glass melts or an undercooled liquid freezes (Zallen, 1983 Elliott et al, 1986). 

One of the early models to describe the amorphous state was by Zachariasen (1932), who proposed the continuous random network model for covalent inorganic glasses. We are now able to distinguish three types of continuous random models  

Continuous random network (applicable to covalent glasses) 

Random close packing (applicable to metallic glasses) 

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Solid structures are categorized as either noncrystalline (also called amorphous) or crystalline. The difference between the two is how the atoms are arranged. Noncrystalline, or amorphous, solids are made up of small particles that are about 100 A in size. The atoms composing these particles are... 

Noncrystalline or amorphous (i.e without form) ceramics are supercooled liquids. Liquids flow under their own mass, but they can become very viscous at low temperatures. Very viscous liquids (for example, honey in the winter time) have solid-like behavior although they maintain a disordered structure characteristic of a liquid, i.e they do not undergo a transformation to a crystalline structure Thus, noncrystalline ceramics, i.e glasses, may behave, in many respects, like solids but structurally they are liquids. 

Some cotton cellulose is noncrystalline or amorphous in the sense of lacking definite crystalline form. One reason is that cotton cellulose has a broad molecular weight distribution, making high-crystalline perfection impossible. The small crystallites constitute deviations from ideal crystals that are infinite arrays. The remaining amorphous character of most polymers is often thought to arise from the fringed micelle model of the solid structure. In... 

Fundamental Atoms in crystalline solids are positioned in orderly and repeated patterns that are in Concepts contrast to the random and disordered atomic distribution found in noncrystalline or amorphous materials. 

The extruder temperature profile for a single-screw extruder is set such that the functions of the process convert the polymer from a solid to a fluid. These two words are in quotation marks because for noncrystalline glassy (or amorphous)... 

To describe the thermodynamics and kinetics of clusters with due regard for the multiplicity of the structure states (SS) of these nuclei, it is necessary to introduce the SS sets. The mutual transformations of clusters by atom attach ment or detachment, or by atom rearrangements are possible. It means that the SS set may be ordered to form a space. Then, it is possible to consider the nucleation of noncrystalline nuclei (clusters) as a diffusion process in an extended space of cluster structure states (CSS), which is, in fact, the join of hierarchy of ultrametric subspaces. The kinetic criterion of glass transition can be formulated as a condition of the overwhelming transformation of a liquid into a noncrystalline amorphous solid. 

The word solid will be applied only to crystalline solids, since it is always possible to distinguish between a crystalline solid and noncrystalline phases such as liquid and amorphous solids. Structurally, the constituent particles—atoms, molecules, or ions— of a crystalline solid are arranged in an orderly, repetitive pattern in three dimensions. If we observe this pattern in some small region of the crystal, we can predict accurately the positions of particles in any region of the crystal however far they may be removed from the region of observation. The crystal has long-range order. 

The concept of applies only to noncrystalline solids, which are mostly either glasses or rubbers. Noncrystalline materials are also known as amorphous materials. Amorphous materials are materials that do not have their atoms or molecules arranged on a lattice that repeats periodically in space. For amorphous solids, whether glasses, organic polymers, or even metals, is the critical temperature that... 

Throughout the remainder of this chapter we wiU focus on how the properties of solids relate to their structures and bonding. Solids can be either crystalline or amorphous (noncrystalline). In a crystalline solid the atoms, ions, or molecules are ordered in well-defined arrangements. These solids usually have flat surfaces or faces that make definite angles with one another. The orderly stacks of particles that produce these faces also cause the solids to have highly regular shapes (Figure 11.29 T). Quartz and diamond are crystalline solids. 

A glass is undoubtedly a solid that belongs to the disordered state of matter. The most common definition for these materials is noncrystalline solids (i.e., amorphous" solids or glasses). There is no generally accepted convention that distinguishes one of these names from the other. 

Literature references to experimental work on the crystallization or precipitation of products of organic reaction are rare, even though this is a common reaction type. The difference between crystallization and precipitation is not well defined and is interpreted differently by different investigators. The interpretation that is used here is that crystallization generates a crystalline product, whereas precipitates form rapidly and can be crystalline or amorphous. The differences are often blurred, however, because many organics actually appear first as amorphous noncrystalline solids which later turn truly crystalline. In these cases nucleation is difficult to separate from precipitation of an amorphous solid. Mersmann and Kind (1988) present an excellent discussion on precipitation as it is affected by micromixing. Additional discussion of mixing effects in crystallization may be found in Chapter 17. 

Metals normally form crystalline solids, but some ceramic materials are crystalline, whereas others—the inorganic glasses—are amorphous. Polymers may be completely noncrystalline or semicrystalline consisting of varying degrees of crystallinity. More about the structure and properties of amorphous ceramics and polymers is contained in Chapters 12 and 14. 

Solids may be either crystalline or noncrystalline. The crystalline state is characterized by a perfectly ordered lattice, and the noncrystalline (amorphous)... 

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