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Growth Techniques
Published in Alan Owens, Semiconductor Radiation Detectors, 2019
Recrystallization, also known as fractional crystallization, is a procedure for purifying an impure compound in a solvent and is commonly used to produce silicon stock material for the semiconductor industry. The method of purification is based on the principle that the solubility of most solids increases with increased temperature. This means that as temperature increases, the amount of solute that can be dissolved in a solvent increases. In practice an impure compound is dissolved in a solvent (the impurities must also be soluble in the solvent), to produce a highly concentrated solution at a high temperature. If the solution is then cooled, the solubility of the impurities in the solution and the substance being purified, decreases. Solubility curves can be used to predict the outcome of a recrystallization procedure, but ideally the substance to be purified crystallizes before the impurities, excluding their molecules from the growing crystal lattice and leaving them behind in the solution. The slower the rate of cooling, the larger the crystals that form. The result is a purer crystal in a soup of impurities. A filtration process must then be used to separate the more pure crystals. The procedure can be repeated. The advantage of this technique is that it is a very simple and effective way of purifying a sample. Its main disadvantage is that it takes a long time.
Greening Undergraduate Organic Laboratory Experiments
Published in Vera M. Kolb, Green Organic Chemistry and Its Interdisciplinary Applications, 2017
One area of further greening of this experiment could be the recrystallization of the products. Solvents used for recrystallization were ethanol, ethanol–water, and toluene–ethanol. Although the yields of the crude products were high (81%–94%), the recovery of some of the products after recrystallization was low (10%–30%). Students could seek better solvents for recrystallization and try to eliminate toluene, which is not a green solvent. This would make even the simple steps of recrystallization, such as making choice of solvent, a meaningful green chemistry exercise.
Measurement Techniques for Refractive Index and Second-Order Optical Nonlinearities
Published in Hari Singh Nalwa, Seizo Miyata, Nonlinear Optics of Organic Molecules and Polymers, 2020
Toshiyuki Watanabe, Hari Singh Nalwa, Seizo Miyata
High purity of the material is an essential prerequisite for crystal growth. Therefore the first step in the crystal growth is the purification of an organic material in appropriate solvents. Impurities as low as possible at the scale of 10 ~ 100 parts per million are required. The high solubility of the material is important and purification needs repetition of the recrystallization process in an appropriate solvent. Although (he chromatographic techniques of high-performance liquid chromatography (HPLC) or gas chromatograpgy (GC) can be used for purification, they yield a very small quantity of purified product per cycle. In particular, zone refining, sublimation, and distillation methods have been frequently used for ultrapurification to obtain large quantities of materials. In a recrystallization process, the material is dissolved in a hot solvent, then gradually cooled down to crystallize. Of great importance is the appropriate selection of organic solvents used in the recrystallization process. Recrystallization is the most common technique of purifying organic materials. Organic solvents generally used in the purification process of organic NLO materials such as 2- cyclooctylamino-5-nitropyridine (COANP) from 4:1 isoctane/toluene mixture,111 4-(7V,N'-dimethylam- ino)-3-acetamidonitroben/ene (DAN) from tetrahydrofuran,112 2-(a-methylbenzylamino)-5-nitropyridine (MBA-NP) from toluene/isooctrane mixture,113 methyl-3-nitro-4-pyridine-l-oxide (POM) from acetone and water,114 m-nitroaniline (w-NA) from acetone,115 NPP from 2:1 chloroform/cyclohexane or toleune57 and chloronitrobcnzene (CNB) from acetone.116 Zone refining method has been found to be the most effective in producing ultrapure materials at a scale of parts per billion. Sublimation is used for thermally unstable solid materials that possess good volatility at temperatures below their decomposition points. Sublimation is generally performed at 10 " to 10 9 torr to avoid decomposition.
Evolution of recrystallization texture in nickel-iron alloys: experiments and simulations
Published in Philosophical Magazine, 2023
Gyan Shankar, Shuchi Sanandiya, Luis A. Barrales-Mora, Satyam Suwas
The process of recrystallization is sensitive to multiple parameters such as composition, annealing temperature, grain-boundary mobility, impurity drag effects, crystallographic texture, microstructure inhomogeneity, etc. All these parameters interact with each other in a nonlinear fashion [35–38]. All the past efforts in simulating recrystallization texture can be divided into two broad categories: statistical and spatially discrete models [39,40]. Under the statistical model, various statistical variants of the original JMAK approaches were suggested to predict recrystallization textures [41,42], e.g. Bunge–Köhler transformation model [43] and the Gottstein kinetic model variants [44]. In these models, growth of the newly formed nuclei is assumed to be isotropic, however, it ceases when the nuclei impinge with other new grains [45–47]. Statistical JMAK-type neglects important local features of the microstructures such as grain topology, different interfaces, and the local curvature of an interface. In the spatially discrete models, the influence of local grain boundary characteristics (mobility, energy), the local driving forces, and local textures are of particular interest [30,48]. These models can be practically used to predict microstructural parameters such as grain size and crystallographic texture [47,48]. The most popular spatially discrete models are cellular automata [49–52], Potts-type Monte Carlo multi-spin models [53], and vertex (front-tracking) models [54,55].
Synthesis and properties of supramolecular gels based on tetrathiafulvalene and cyanobiphenyl units
Published in Soft Materials, 2021
Lina Ma, Li Wang, Yongqi Bai, Yan Xia, Dongfeng Li, Bingzhu Yin, Ruibin Hou
Silicone is made of 100–200 mesh silica gel produced by Qingdao Ocean Chemical Plant. The chemical reagents were all analytically pure ordered by Belling, and the reaction solvents were all anhydrous. All the reactions were carried out under nitrogen. If not specified, the mixed solvent of dichloromethane and petroleum ether (60–90°C) was used for recrystallization.