Explain amorphous solids
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Explanation:
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Answer:
The definition of amorphous should be one that is readily understandable, accessible and provable for infringement purposes. Amorphous solid resemble liquids in that they do not have an ordered structure, an orderly arrangement of atoms or ions in a three-dimensional structure. These solids do not have a sharp melting point and the solid to liquid transformation occurs over a range of temperatures. The physical properties exhibited by amorphous solids are generally isotropic as the properties do not depend on the direction of measurement and show the same magnitude in different directions.
Properties of Amorphous Solids
Amorphous solid are sometimes described as supercooled liquid because their molecules are arranged in a random manner somewhat as in liquid state.
1. Lack of long-range order
Amorphous Solid does not have a long-range order of arrangement of their constituent particles. However, they may possess small regions of orderly arrangement. These crystalline parts of an otherwise amorphous solid are known as crystallites.
2. No sharp melting point
An amorphous solid does not have a sharp melting point but melts over a range of temperatures. For example, glass on heating first softens and then melts over a temperature range. Glass, therefore, can be moulded or blown into various shapes. Amorphous solid does not possess the characteristic heat of fusion.
3. Conversion into crystalline form
Amorphous solid, when heated and then cooled slowly by annealing, becomes crystalline at some temperature. That is why glass objects of ancient time look milky because of some crystallization having taken place.
Examples of Amorphous Solids
Examples of amorphous solids are glasses, ceramics, gels, polymers, rapidly quenched melts and thin-film systems deposited on a substrate at low temperatures. The investigation of amorphous materials is a very active area of research. Despite enormous progress in recent years our understanding of amorphous materials still remains far from complete. The reason is the absence of the simplifications associated with periodicity.
Nonetheless, from a comparison of the properties of materials in crystalline and an amorphous state the essential features of the electronic structure and thereby also macroscopic properties are determined by short-range order. Thus these properties are similar for solids in the amorphous and crystalline state.
Some examples of amorphous solids are glass, rubber, pitch, many plastic etc. Quartz is an example of a crystalline solid which has regular order of the arrangement of SiO4 tetrahedra. If quartz is melted and the melt is cooled rapidly enough to avoid crystallization an amorphous solid called glass is obtained.
Amorphous Solids are Isotropic
Amorphous solids are isotropic. That is, they exhibit uniform properties in all directions. The thermal and electrical conductivities, coefficient of thermal expansion and refractive index of an amorphous solid have the same value in whatever direction the properties are measured.
Any given crystalline solid can be made amorphous by the very rapid cooling of its melt or by freezing its vapour. This does not allow the particles to arrange themselves in a crystalline pattern.. When quartz the crystalline form of SiO2 is melted and then rapidly cooled, an amorphous solid known as quartz glass or silica glass results. This material has the same composition SiO2 but lacks the molecular level orderliness of quartz. Amorphous form of metal alloys are obtained when thin films of melted metal are rapidly cooled. The resulting metallic glasses are strong, flexible and much more resistant to corrosion than the crystalline alloys of the same composition.