Types of Solid

Solids that are arranged in an orderly fashion are called crystalline. Most solids form large, well-formed crystals if they are prepared carefully enough—solidified from the liquid or gas phase very slowly, for example. (Even large biomolecules like hormones, proteins, and DNA can form crystals. For example, the hormone insulin was first crystallized by the American biochemist John J. Abel in 1925.) If not prepared carefully, many solids form a host of tiny crystals and would be described as polycrystalline. 

Compounds that are composed of ions form ionic crystals. In this case, the need for opposite charges—cations and anions—to neutralize each other dictates a certain arrangement of ions in a crystal. Ionic crystals are typically very hard but very brittle (that is, they break easily if subjected to sudden forces). They also tend to have relatively high melting points. Coulombic attraction between opposite charges is the strongest known force it takes a lot of energy, in the form of temperature, to break those attractions and turn an ionic solid into a liquid. 

Finally, certain elements are hard but ductile and malleable, conduct electricity, are shiny, and have variable but usually high melting points. These elements are metals, and their collective characteristics are explained by an idea called metallic bonding. In this type of bonding, the electrons of the individual metal atoms pool together to become electrons not of the individual atoms but of the whole solid. This explains the electrical and thermal conductivity of metals, and deeper analysis of this idea explains their other characteristics, too. This is beyond our scope, but understand that the interactions between atoms of metals is a different sort of crystalline bonding that does in fact account for the unique properties of metals. 

In this chapter, we will focus on crystalline solids, although many of the concepts are applicable to molecular, covalent network, and metallic solids as well. There are techniques for studying the structures of amorphous solids however, they will not be considered here. 

FIGURE 21.1 Amorphous or glassy materials, like the ones shown, have randomly arranged molecules. Crystalline materials, on the other hand, are solids that are built up of units that repeat in three dimensions. 

There are only two types of solid matter. There are amorphous substances and there are crystalline substances. There are, of course, mixtures of these and there are some substances that have some partial crystalline properties, but should be classed as amorphous, and there are liquid substances that can be classed as crystals. 

Amorphous solid substances have no fixed arrangement of their molecular bulks and are not in a definable state, either in energy content or structurally. One view is to consider an amorphous substance as an entanglement of molecules of many shapes and sizes. This is particularly true of phosphate and silicate glasses when considered as supercooled liquids. Their properties depend upon much history. They are not in a thermodynamically defined state. This means that they are not in equilibrium with their environment under existing conditions. Then there must be some other state of matter made of these same molecules (or ions) that has less energy than the amorphous system. These lower-energy systems are usually crystalline. 

The photochemical properties of molecules that are part of a solid or are embedded in a solid matrix depend greatly on the nature and organization (if any) of the solid lattice. In order of increasing organizational structure, solids can be classified for our purpose as glasses, polymers and crystals. 

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A very important but rather complex application of surface chemistry is to the separation of various types of solid particles from each other by what is known as flotation. The general method is of enormous importance to the mining industry it permits large-scale and economic processing of crushed ores whereby the desired mineral is separated from the gangue or non-mineral-containing material. Originally applied only to certain sulfide and oxide ores. 

Whereas the tight-binding approximation works well for certain types of solid, for other s. items it is often more useful to consider the valence electrons as free particles whose motion is modulated by the presence of the lattice. Our starting point here is the Schrodinger equation for a free particle in a one-dimensional, infinitely large box ... 

For solids, there is now a very wide range of inlet and ionization opportunities, so most types of solids can be examined, either neat or in solution. However, the inlet/ionization methods are often not simply interchangeable, even if they use the same mass analyzer. Thus a direct-insertion probe will normally be used with El or Cl (and desorption chemical ionization, DCl) methods of ionization. An LC is used with ES or APCI for solutions, and nebulizers can be used with plasma torches for other solutions. MALDI or laser ablation are used for direct analysis of solids. 

Goldberg and Boothroyd [Br Chem. Eng., 14, 1705-1708 (1969)] describe several types of solids-in-gas flowmeters and give an extensive bibhography. 

Types of Solids Geldart [Fowder TechnoL, 7, 285-292 (1973)] has characterized four groups of solids that exhibit different properties when fluidized with a gas. Figure 17-j shows the division oi the classes as a function of mean particle size, d,, Im, and densitv difference, (p, — P/ ), g/cm, where p, = particle density and p = fluid density... 

Rake-speed requirements depend on the type of solids entering the thickener. Peripheral speed ranges used are, for slow-setthng sohds, 3 to 8 m/min (10 to 25 rt/min) for fast-setthng solids, 8 to 12 iTi/min (25 to 40 ft/min) and for coarse sohds or crystalline materials, 12 to 30 iTi/min (40 to 100 ft/min). 

Particle surface characteristics Type of solid (in terms of internal liquid content) gel, flocculated, hard particle Strength of particle (resistance to deformation under pressure) compressibility over time expressed cake... 

Types of Solids-Mixing Machines There are several types of solids-mixing machines. In some machines the container moves. In others a device rotates within a stationaiy container. In some cases, a combination of rotating container and rotating internal device is used. 

Uniformity of Mixture The proper type of mixer shoiJd be chosen to assure the desired degree of batch homogeneity. This cannot be compromised for other conveniences. Information is given under Types of Solids-Mixing Machines about the special abilities of various lands of machines to blend different types of materials. 

Types of Solid Wastes The term solid wastes is aU-inchisive and encompasses all sources, types of classifications, compositions, and properties. As a basis for subsequent discussions, it will be helpful to define the various types of solid wastes that are generated. It is important to note that the definitions of solid-waste terms and the classifications vary greatly in prac tice and in literature. Consequently, the use of published data requires considerable care, judgment, and common sense. The following definitions are intended to serve as a guide. 

Contamination of the seal by foreign objeets leads to seal failures. The running gap between the primary and mating gas seal rings is typieally around 3 mierons. Injeetion of any type of solids or liquids into this very... 

Ardcle No. Technique P- ii o 8 eu 0 3 In Depth prohed (typical) Width probed (typical) Trace capability (typical) Types of solid sample (typical) S 1 T3 H 1 > 8 ... 

Ion Scattering Spectroscopy (ISS) is one of the most powerful and practical methods of surface analysis available. However, it is undemtilized due to a lack of understanding about its application and capabilities. This stems from its history, the limited number of high-performance instmments manufactured, and the small number of experienced surface scientists who have actually used ISS in extensive applications. Ironically, it is one of the easiest and most convenient sur ce analytical instruments to use and it provides usehil information for almost any type of solid material. 

As already remarked in Sect. 4.5.1 (Introduction), LA was primarily designed as a technique for direct sampling in the bulk analysis of solid samples. The main advantages of LA are the possibility of ablating all types of solid material (metals, isolators, glasses, crystals, minerals ceramics, etc.), no special requirements on the... 

If the relatively high standard deviation is not acceptable, each type of solid can be correlated separately. This is a standard approach in the literature but we shall not repeat it here. 

Much of what has been said about the four structural types of solids in Sections 9.3 and 9.4 is summarized in Table 9.5. 

Of tile four general types of solids, which one(s)... 

The elements carbon and silicon form oxides with similar empirical formulas CO2 and SiOi. The former sublimes at —78.5°C and the latter melts at about 1700°C and boils at about 2200°C. From this large difference, propose the types of solids involved. Draw an electron dot or orbital representation of the bonding in C02 that is consistent with your answer. 

Solids. It is with solids that real difficulties over homogeneity arise. Even materials that superficially have every appearance of being homogeneous in fact may have localised concentrations of impurities and vary in composition. The procedure adopted to obtain as representative a sample as possible will depend greatly upon the type of solid. This process is of great importance since, if it is not satisfactorily done, the labour and time spent in making a careful analysis... 

R.S. Brown et al, AdvanChemEng 7, 1—69 (1968) CA 72, 11368 (1970) The topics reviewed include types of solid proplnts, sohd-proplnt rocket motors, ignition, steady-state combustion, and combustion instability and termination... 

Characteristically, the mechanisms formulated for azide decompositions involve [693,717] exciton formation and/or the participation of mobile electrons, positive holes and interstitial ions. Information concerning the energy requirements for the production, mobility and other relevant properties of these lattice imperfections can often be obtained from spectral data and electrical measurements. The interpretation of decomposition kinetics has often been profitably considered with reference to rates of photolysis. Accordingly, proposed reaction mechanisms have included consideration of trapping, transportation and interactions between possible energetic participants, and the steps involved can be characterized in greater detail than has been found possible in the decompositions of most other types of solids. 

Other factors have been identified as rate controlling in other types of solid—solid interaction, and some of these are described in subsequent sections. These include, for example, the decomposition of a solid catalyzed by a (different) solid and rate processes in which one reactant is volatilized, e.g. reaction of carbon (-> C02) with a solid oxidizing agent. 

This account of the kinetics of reactions between (inorganic) solids commences with a consideration of the reactant mixture (Sect. 1), since composition, particle sizes, method of mixing and other pretreatments exert important influences on rate characteristics. Some comments on experimental methods are included here. Section 2 is concerned with reaction mechanisms formulated to account for observed behaviour, including references to rate processes which involve diffusion across a barrier layer. This section also includes a consideration of the application of mechanistic criteria to the classification of the kinetic characteristics of solid-solid reactions. Section 3 surveys rate processes identified as the decomposition of a solid catalyzed by a solid. Section 4 reviews other types of solid + solid reactions, which may be conveniently subdivided further into the classes... 

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