Four Classes of Materials

And so, as you can see from the Contents list, the chapters are arranged in groups, with a group of chapters to describe each of the four classes of materials. In each group we first introduce the major families of materials that go to make up each materials class. We then outline the main microstructural features of the class, and show how to process or treat them to get the structures (really, in the end, the properties) that we want. Each group of chapters is illustrated by Case Studies designed to help you... 

Nonstaining antioxidants This ciass of antioxidants is subdivided into four groups phosphites, hindered phenols, hindered bisphenols, and hydroquinones. Hindered bisphenols such as 4,4 -thiobis(6-r-butyl-m-cresol) are the most persistent of the four classes of material. Because of then-lower molecular weight, hindered phenols tend to be volatile. Phosphites tend to be used as synthetic rubber stabilizers, and hydroquinones such as 2,5-di-re t-amylhydroquinone are used in adhesives ... 

Figure 2.6 Mechanical resistances (elastic, plastic and brittle) of the four classes of materials (F Young s modulus, Yyield stress, toughness, according to Ashby and Jones, 1991).

These four classes of source materials have given rise to at least 13 coalified products that appear to be optically distinguishable. These 13 products may represent as many as nine separate sequences in which plant substances are altered to coal substances and in which the coal substances are further metamorphosed from one maceral to another. 

There is a high incidence (eight out of twenty-four) of SHG-active materials among this class of materials. A success rate of 33% with regard to... 

The Federal safety standards included in 49 C.F.R. 193 (1990) define four classes of impounding systems ranging from dikes constructed within 24 inches of the component served to remote impounding spaces (see 49 CFR 193.2153). The structural requirements specify performance reliability and integrity as a result of imposed loading caused by a full liquid head of spilled material, erosive spill action, thermal gradients, fire exposure, and catastrophic rupture of storage or transport vessels into or near the system (see 49 C.F.R. 193.2155). 

Surfactant-based synthesis of mesoporous metal oxides and metal sulfides emerged about four years after the initial report of MCM-41 [21-36]. High surface area and thermally robust mesoporous metal oxides and sulfides represent a new class of materials with diverse opportunities for the development of improved fuel and solar cells, batteries, membranes, chemical delivery vehicles, heavy metal sponges, sensors, magnetic devices and new catalysts. All of these applications could benefit from tailorable Bronsted and Lewis acidity and basicity, flexible oxidation states, and tunable electronic, optical and magnetic properties. 

We turn now to a very important class of materials that have the formula /IBC3, with the C frequently oxygen. Strontium titanate is a familiar example and one we shall use for illustrative purposes. Titanium is in the D4 column of the Solid State Table, having four electrons beyond its argonlike core. Strontium has two electrons outside its kryptonlike core, so we may think of the six valence electrons as having been transferred to the three oxygen atoms to form a simple ionic system. As we shall see, however, the titanium d states form the lowest conduction band and are important in the bonding properties as well. 

The chemical elements provide examples of three of the four classes of crystalline solids described in this section. Only ionic solids are excluded, because a single element cannot have the two types of atoms of different electronegativities needed to form an ionic material. We have already discussed some of the structures formed by metallic elements, which are sufficiently electropositive that their atoms readily give up electrons to form the electron sea of metallic bonding. The nonmetallic elements are more complex in their structures, reflecting a competition between intermolecular and intramolecular bonding and producing molecular or covalent solids with varied properties. 

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