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Chemical Thermodynamics and Thermochemistry
Published in Armen S. Casparian, Gergely Sirokman, Ann O. Omollo, Rapid Review of Chemistry for the Life Sciences and Engineering, 2021
Armen S. Casparian, Gergely Sirokman, Ann O. Omollo
The third law of thermodynamics provides a basis for determining the absolute entropy of a substance or system. There are different ways of stating it. According to Max Planck, one way to state is that a perfect crystal has zero entropy at a temperature of absolute zero. A perfect crystal is one in which all of the atoms are aligned flawlessly with no defects of any kind in the crystalline structure. All of the atoms are motionless and have zero kinetic energy. This formulation is largely a statistical interpretation and involves the study of statistical mechanics, which is beyond the scope of this book. Nevertheless, it is a postulate, like the other two laws of thermodynamics, and its validity rests on experiment. However, since there are no means available to measure absolute entropies directly, it remains largely a theoretical principle.
Structural Description of Materials
Published in Snehanshu Pal, Bankim Chandra Ray, Molecular Dynamics Simulation of Nanostructured Materials, 2020
Snehanshu Pal, Bankim Chandra Ray
The defect can be defined as an “imperfection, shortcoming or a lack.” When we talk about defects in solids, it signifies explicitly the manifestation of various kinds of imperfections that could be found in different scales of engineering. The notion of defect or imperfection is used to recount the deviation from ideality of a perfect crystal. A perfect crystal is the one that has got a periodic arrangement of its constituents. Defects are also crucial because diffusion of elements is possible. Defects can be desirable or undesirable, depending on the specific applications. The three major factors that define the properties of materials are as follows: BondingDefectsStructure
Crystal Imperfections and Deformation
Published in Zainul Huda, Metallurgy for Physicists and Engineers, 2020
Perfect and Real Crystals. Theoretically, crystals are defined as three-dimensional perfectly ordered arrangements of atoms or ions. However, there are defects or imperfections in real crystals. Crystal imperfections refer to the missing of atoms/ions or misalignment of unit cell in an otherwise perfect crystal. Based on the inter-atomic bonding forces that exist in a metal, one can predict the elastic modulus of the metal. But, the actual elastic strength of most materials (real crystals) is far below their predicted strength values (Hertzberg, 1996). This discrepancy in the theoretical and actual strengths is due to crystal imperfections (see subsection 3.3.3). Crystal defects also influence electrical properties of solids. However, there are some beneficial effects of crystal imperfection. For example, many metal forming operations involving plastic deformation are due to crystal imperfections. Another example is an alloy (having point crystal defects); which may have higher strength as compared to pure metal.
Surface grown copper nanowires for improved cooling efficiency
Published in Cogent Engineering, 2018
Anagi M. Balachandra, A.G.N.D. Darsanasiri, Iman Harsini, Parviz Soroushian, Martin G. Bakker
It has been noted that, as in crystallization, nanowire growth via different routes (from vapor, liquid or solid) involves the two fundamental steps of nucleation and growth (Xia et al., 2003). As the concentration of the building blocks (atoms, ions or molecules) increases to a sufficiently high level, they aggregate into small clusters through homogeneous nucleation. With a continuous supply of such building blocks, these nuclei can serve as seeds for further growth to form larger structures. It is generally accepted that the formation of a perfect crystal structure requires a reversible pathway between the building blocks on the solid surface and those in the fluid phase. These conditions allow the building blocks to easily assume their correct positions while developing the long-range-ordered, crystalline lattice. The mechanisms involved in the formation of Cu(OH)2 nanowires require further investigation. However, nanowires appear to be produced from a highly non-equilibrium reaction system, in which different growth rates of the crystal faces determine the ultimate morphology of nanomaterials (Wen, Zhang, & Yang, 2002). The growth of Cu(OH)2 nanowires along the [100] direction can be understood on the basis of the assembly of oblate > Cu(OH)2Cu< chains in the plane (001), oriented along [100]. According to the Bravais-Friedel-Donnay-Harker law, the growth rate of orthorhombic Cu(OH)2 crystals is normally proportional to 1/dhkl. Hence, the growth of Cu(OH)2 along [100] is much faster than those along other directions, leading to the formation of nanowires and similar (e.g., ribbon-like) nanostructures.
Classification of thermoluminescence features of the natural halite with machine learning
Published in Radiation Effects and Defects in Solids, 2022
Dilek Toktamis, Mehmet Bilal Er, Esme Isik
In crystalline solids, there is a perfect order in the three-dimensional arrangement of the atoms, ions or molecules. Although a perfect crystal does not include any kind of defects, impurities or dislocations, there is no perfect crystal in the world. They include at least one of them. These defects and impurities in the solid crystals behave as a trap to store the ambient radiation until a kind of stimulation energy is applied. In thermoluminescence, the stimulation is done by heating the material to see the luminescence light.