Project on amorphus solids

What is Amorphous Solid?

An amorphous solid is that in which the constituent particles do not possess a regular three-dimensional arrangement.

Amorphous solids, lacking the three-dimensional long-range order of a <a href="https://byjus.com/chemistry/crystal-structure/" style="box-sizing: border-box; background-color: transparent; color: rgb(115, 173, 33); text-decoration-line: none; user-select: initial !important;">crystalline material</a>, possess a more random arrangement of molecules, exhibit short-range order over a few molecular dimensions, and have physical properties quite different from those of their corresponding crystalline states.

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.