tailieunhanh - Ebook The coming of materials science: Part 2

(BQ) Part 2 book "The coming of materials science" has contents: Functional materials, the polymer revolution, craft turned into science, materials in extreme states, materials chemistry and biomimetics, computer simulation, the management of data, the institutions and literature of materials science, epilogue. | Chapter 7 Functional Materials . INTRODUCTION A major distinction has progressively emerged in materials science and engineering, between structural materials and functional materials. Structural materials are selected for their load-bearing capacity, functional materials for the nature of their response to electrical, magnetic, optical or chemical stimuli; sometimes a functional material is even chosen for aesthetic reasons. It is much harder to define a functional material accurately than it is to distinguish a structural material. For present purposes, I have decided to include functional ceramics in this chapter. Those ceramics developed for their resistance to mechanical stress or simply their beauty are discussed in Chapter 9. In what follows, I make no attempt to present a comprehensive account of the huge field of functional materials, but instead aim to pick a few historically important aspects and focus on these. . ELECTRICAL MATERIALS Semiconductors Silicon is today the most studied of all materials, with probably a larger accumulated number of scientific papers devoted to its properties than for any other substance. It is the archetype of a semiconductor and everybody knows about its transcendent importance in modern technology. Things looked very different, as little as 70 years ago. The term ‘semiconductor’ appears to have been used first by Alexander Volta, after whom the volt is named. in a paper to the Royal Society of London in 1782. According to a fine historical overview of early work on semiconductors (Busch 1993), Volta examined the rate at which a charged electrometer would discharge when its contact knob was touched by different substances connected to earth. In this way, Volta was able to distinguish between metals, insulators and (in the middle) semiconductors. In 1840, Humphry Davy was the first to establish clearly that metals become poorer conductors as the temperature is raised, and he was soon followed by Michael .