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 crystalline material, 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.
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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.
Difference between Crystalline and Amorphous Solid
|Properties||Crystalline solid||Amorphous solid|
|Structure||The constituent particles, atoms, ions or molecules are arranged in regular and definite three dimensional patterns. For example, sodium chloride, diamond, sugar etc.||The constituent particles are arranged in irregular three dimensional patterns.|
|Cutting with a knife||Gives clean, sharp cleavage.||Unclean cleavage.|
|Compressibility||Rigid and incompressible||Usually rigid and can not be compressed to any appreciable extent.|
|Melting point||They have a sharp and definite melting point.||Melting point is not definite. Melt over a range of temperatures.|
|Heat of fusion||Definite||Not definite.|
|Physical properties||These are anisotropic in that their physical properties are not identical in all directions.||These are isotropic, that is their physical properties are identical in all directions.|
Amorphous solids find many applications because of their unique properties. For example, inorganic glasses find applications in construction, houseware, laboratories, Rubber another amorphous solid is used in making tyres, tubes, shoe soles etc. Plastics are used extensively in household and industry.
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.
Frequently Asked Questions – FAQs
What is an amorphous solid example?
Amorphous solids comprise materials that are both natural and manmade. Glass is the most often cited example of amorphous solids. Amorphous solids are however common to all solid subsets. Further sources are thin-film lubricants, metallic lenses, polymers, and gels.
How are amorphous solids formed?
If an amorphous solid is maintained for long periods of time at a temperature just below its melting point, the component molecules, atoms, or ions may gradually rearrange themselves into a more highly ordered crystalline form. Crystals have sharp melting points which are well defined; amorphous solids do not.
What does amorphous solid mean?
An amorphous solid has no definite form, either geometric or crystalline. An amorphous solid is any non-crystalline solid that does not organize the atoms and molecules in a definite lattice pattern. There are glass, plastic, and gel solids.
Is Sugar an amorphous solid?
Sugar is a pure material relatively sweet. It forms normal, crystalline structures, as with many solids that precipitate from solution. Sugar can, of course, be in an amorphous state too. You will also be left with a transparent amorphous ‘glass’ by melting sugar and cooling it easily.
Why is glass an amorphous solid?
The material (often containing silica) is easily cooled from its liquid state when a glass is made but does not solidify if its temperature drops below its melting point. The material is further cooled, below the glass-transition temperature, to become an amorphous solid.
Why crystalline solids are anisotropic?
By fact, crystalline solids are anisotropic, that is, some of their physical properties, such as electrical resistance or refractive index, give varying values when measured in the same crystals in different lines. It is because of different particle configurations in different directions.
Why is amorphous isotropic?
By comparison, amorphous solids are isotropic by nature. This is because they have no long term order and organization in all directions is sporadic. Therefore, the worth of every physical property in either direction will be the same.
How do you identify amorphous solids?
Amorphous solids have two defining properties. They create particles of odd, often twisted surfaces when cleaved or broken; and they have poorly described patterns when exposed to x-rays, because their components are not organized in a typical sequence. A transparent, amorphous material is called wine.