China
Africa
Explore chapters and articles related to this topic
Imperfections and Diffusion
Published in Yip-Wah Chung, Monica Kapoor, Introduction to Materials Science and Engineering, 2022
The ultimate imperfection in a solid is total disorder – an amorphous structure. Generally, an amorphous solid maintains some degree of short-range order, i.e., the nearest neighbor atomic arrangements are similar to those of a crystalline solid. Beyond the nearest neighbors, an amorphous solid does not possess the long-range order of its crystalline counterpart. A common amorphous solid is fused quartz (amorphous silicon dioxide). In amorphous silicon dioxide, each silicon atom maintains a local four-fold coordination similar to crystalline SiO2, with Si–O bond length of 0.21 nm.
Petroleum Geochemical Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
Atom, ion and molecule particles are randomly arranged in an amorphous solid. The particles lack symmetry and order. Glass, wood and plastics are amorphous solids. The particle disorder resembles the disorder of liquid and gas particles. Glass is actually not a solid. It is a super cooled liquid. A very old window glass can be observed to be thicker at the bottom than at the top, because of extremely slow downward flow of glass particles. A small quantity of glass material is found in association with igneous rock minerals.
The Rejection of Perfection
Published in Sharon Ann Holgate, Understanding Solid State Physics, 2021
The substrate is much colder than the vapour of the compound, so when atoms from the vapour arrive on the surface, they are “frozen” into the random positions in which they hit the substrate. Since the atoms are too cold to move into the positions needed to form a crystalline solid, an amorphous solid is produced instead. In fact, to produce amorphous semiconductors—such as amorphous selenium (which can be written as a-Se for short), amorphous germanium (a-Ge), and amorphous gallium arsenide (a-GaAs)—the substrate is often held at about room temperature. These semiconductors are covalently bonded solids, but although thermal evaporation can also be used to form the amorphous form of some metals, in this case the substrate needs to be held at around 4K to stop polycrystalline films from forming.
Glass transition, structural relaxation and stability of spray-dried amorphous food solids: A review
Published in Drying Technology, 2019
Runjing Li, Duanquan Lin, Yrjö H. Roos, Song Miao
Amorphous materials have been known for centuries, and scientific understanding of these systems has evolved for several decades.[1] The important role played by amorphous solids has been increasingly recognised within food and pharmaceutical industries during the past decades.[2345678910111213] An amorphous solid is characterized by the lack of long-range order symmetry operators (translational, orientational, and conformational order) found in crystalline solid.[14] The molecular pattern of an amorphous solid is often depicted as that of a frozen liquid with the viscosity of a solid having internal degrees of freedom and conformational diversities (disorder). Hancock and Zofrafi[15] stated that an amorphous solid has a liquid-like structure with a viscosity >1012 Pa · s. At the molecular level, it has properties similar to liquids; but at the macroscopic level, it has properties of solids.[14]
Use of powder bath sintering for the fabrication of hard ceramic tools
Published in Materials and Manufacturing Processes, 2022
Diwakar Makireddi, V D Ghuge, Alok Behera
The microstructure of the etched specimens was analyzed using Scanning Electron Microscopy (SEM). The non-uniform heat transfer in conventional sinter formed an amorphous grain structure with scattered porosity which was severely damaged after etching as shown in Fig. 15. Amorphous solids have higher energy states as the atoms and molecules are not organized in a definite lattice pattern. This causes defect concentration and dangling bonds with higher solubility.[26] Subsequently, the etching rates are higher in amorphous structures caused by the greater degree of fluorination and ligand-exchange reaction.[27]