Читать книгу Amorphous Nanomaterials - Lin Guo - Страница 18

The research on amorphous materials is still centered on the comparison with crystals. There are three most used names of disorder materials. Amorphous is the earliest and most widely used expression approach. Glass is another name of disorder material, especially in the metallic glass field. Non-crystal is used in the field of biomineralization.

Amorphous, the most common English expression of disordered materials, originated from Greek, where a is a prefix, indicating no; morphous comes from morph, referring to morphology. The original meaning of this word is material without morphology. It can be seen that before the establishment of modern crystallography, people have known the morphological differences between amorphous materials and crystalline materials to distinguish them.

In 1840, Justus von Liebig, the German organic chemist and father of mineral nutrition, described in his classic book Organic Chemistry in its Application to Agriculture and Physiology that when sulfur is heated to 160 °C, and then quickly pouring into cold water, sulfur does not crystallize but turns soft and transparent. In this chapter, he wrote “such solid bodies are called amorphous”. This may be the earliest report that compared morphologies between amorphous and crystalline materials. Liebig then published in the famous medical journal Provincial Medical and Surgical Journal in 1840, pointed out that in the extraction of quinine (the main component of antimalarial drugs), quinine obtained from quinoline tincture mainly exists in the form of amorphous [11]. It does not affect its medical value but can greatly enhance the natural quinoline. In 1862, G. Gore pointed out in On the Properties of Electro-Deposited Antimony that when antimony was electrodeposited, different deposition conditions would lead to two kinds of antimony monomers with different structures, i.e. crystalline antimony and amorphous antimony [12]. He also reported that amorphous antimony showed different physical and chemical properties.

Before the twentieth century, the research on amorphous materials was still in the enlightenment stage. The amorphous materials were mainly found in the preparation of traditional crystal materials. The morphology and properties of this “novel” material were fully compared with traditional crystal materials. Because X-ray has not been discovered and modern crystallography has not been developed, the essential characteristics of the disordered structure have not been discovered. However, these studies are very important for the development of amorphous and crystal. For example, in the study of amorphous sulfur, Liebig argued that the softness of amorphous sulfur proved a remarkable fact that the smallest particles that make up a solid are movable to some extent and not perfectly connected. Modern X-ray crystallography verified that the structure of amorphous sulfur should be a spiral chain structure changed from the S₈ ring of crystal sulfur, endowed it with the same elasticity as rubber. There is no doubt that, the recognition at that time has a great significance in the research of solid science.

The amorphous state of phosphorus is the same as that of sulfur. Similar to the octahedral ring structural unit of sulfur crystal, the structural unit of phosphorus crystal is a regular tetrahedral structure composed of phosphorus atoms (P₄). When the crystal of white phosphorus is melted at a high temperature, P₄ tetrahedron transforms into a chain-connected structure. Then, the amorphous red phosphorus could be obtained by quenching, maintaining its chain-like structure. Recently, amorphous phosphorus has showed great applications in lithium-ion batteries and sodium-ion batteries because of their superhigh theoretical capacity. Similarly, in some polymer materials, when the asymmetry of the atoms connected changes irregularly, the polymer will form a random stereomer, which will behave as an amorphous state. Because of the complexity of the molecular structure of ultralong chains, the atomic arrangement modes of amorphous nonmetallic elements such as amorphous sulfur, red phosphorus, and amorphous polymers are not clear yet. However, they all have glass transition temperatures similar to those of glass, so they belong to the category of amorphous.