Microscopic level, solids

At the macroscopic level, a solid is a substance that has both a definite volume and a definite shape. At the microscopic level, solids may be one of two types amorphous or crystalline. Amorphous solids lack extensive ordering of the particles. There is a lack of regularity of the structure. There may be small regions of order separated by large areas of disordered particles. They resemble liquids more than solids in this characteristic. Amorphous solids have no distinct melting point. They simply become softer and softer as the temperature rises. Glass, rubber, and charcoal are examples of amorphous solids. 

Figure 19.2 shows, at a microscopic level, what is going on. Atoms diffuse from the grain boundary which must form at each neck (since the particles which meet there have different orientations), and deposit in the pore, tending to fill it up. The atoms move by grain boundary diffusion (helped a little by lattice diffusion, which tends to be slower). The reduction in surface area drives the process, and the rate of diffusion controls its rate. This immediately tells us the two most important things we need to know about solid state sintering ... 

Matter (anything that has mass and occupies space) can exist in one of three states solid, liquid, or gas. At the macroscopic level, a solid has both a definite shape and a definite volume. At the microscopic level, the particles that make up a solid are very close together and many times are restricted to a very regular framework called a crystal lattice. Molecular motion (vibrations) exists, but it is slight. 

Know the differences between a solid, a liquid, and a gas at both the macroscopic and microscopic levels. 

THE DOUBLE LAYER. On a microscopic level, boundaries between solids and liquids (also referred to as interfaces ) are complicated transition zones (see Fig. 2). The physical theories for interfacial behavior are different from those for regular solutions, and this is especially true for crystals in aqueous environments. 

The surface can be characterized either as external when it involves bulges or cavities with width greater than the depth, or as internal when it involves pores and cavities that have depth greater than the width (Gregg and Sing, 1967). All surfaces are not really smooth and they exhibit valleys and peaks at a microscopic level. These areas are sensitive to force fields. In these areas, the atoms of the solid can attract atoms or molecules from a fluid nearby. 

Most methods (electron probe microanalysis, micro-Auger, secondary ion mass spectrometry) cannot be considered as really accurate methods except when applied to quite simple systems. Their application relies on the use of CRMs but these are, with very few exceptions, not available. The reason for the lack of CRMs is the absence of any reliable methods of microanalysis. None of the limited range of primary methods is applicable for the analysis of a solid at a microscopical level. The world of microanalysis is badly in need of at least one method which is able to act as a reference for the other techniques and to link RMs or round-robin exercises to the SI units [22],... 

In this section, we shall focus on the use of CMs to study molecules at the interface between a solid and a fluid (gas or liquid). In particular, we reserve the term continuum models to approaches that consider both the solid and the fluid as structureless continuum bodies characterized by their dielectric response, and treat the molecule at some microscopic level. 

Our work has applied these techniques to the study of the binary insulating materials including the fluorites, alkali halides, alkaline earth oxides, and perovskites. Many of these are simple materials that are commonly used as models for all solid state defect equilibria. Our work has had the goal of determining at the microscopic level the defect equilibria and dynamics that are important in understanding solid state chemistry as well as developing new tools for the studies of solid materials. 

The successful development of the time-domain dielectric spectroscopy method (generally called time-domain spectroscopy, TDS) [79-86] and broadband dielectric spectroscopy (BDS) [3,87-90] have radically changed the attitude towards DS, making it an effective tool for investigation of solids and liquids on the macroscopic, mesoscopic, and, to some extent, microscopic levels. 

The nature of an interface (liquid/liquid, solid/liquid, air/liquid and so on) should reflect on the relevant interfacial phenomena, so that detailed understandings of chemical and structural characteristics of the interface at a microscopic level are of primary importance for further advances in various sciences. In practice, solid/liquid and air/liquid interfacial systems have been studied widely by various experimental techniques, and the knowledges about the characteristics of the interfaces have been accumulated. However, very little is known about the chemical and structural characteristics of a liquid/liquid interface at a microscopic level. So far, thermodynamic and electrochemical techniques have been applied to study liquid/liquid interfacial chemistry. Nonetheless, its dynamic aspects have rarely been explored. 

Porous solids having a regular pore structure have gathered much attention in the fields of chemistry and physics[l-7]. Those solids are expected to elucidate the interaction of gas with pores from the microscopic level. lUPAC classified pores into micropores, mesopores, and macropores using pore width w ( micropores w< 2nm, mesopores 2 nm < w< 50 nm, and macropores w> 50 nm)[8]. Physical adsorption occurs by the mechanism inherent to the pore width. Vapor is adsorbed on the mesopore wall by multilayer adsorption in the low pressure range and then vapor is condensed in the mesopore space below the saturated vapor pressure P . This is so called capillary condensation. Capillary condensation has been explained by the Kelvin equation given by eq. (1). 

Random versus Partially Ordered Solid Solutions.—One of the points that needed to be clarified in order to understand the nature of the interactions at the microscopic level within the disordered phase is whether the heterochiral molecules are randomly distributed in the crystals, in which case the contacts are of (RR), (SS), and RS) natures, or if they are ordered in homochiral stacks, where the contacts are mainly of (RR) and (S5) natures. ... 

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