Purity, crystallization

Large high purity crystals ate cut into windows and refracting components for use in x-ray monochromators (14), and in the vacuum uv, uv, visible, and it ranges. 

For a product of special purity, crystallization from benzene is advisable. For most purposes, however, the nitrobenzoic acid may be used without crystallization, since its melting point is found to be within 20 of the correct value of 238°. 

Traps and recombination centers which depend on purity, crystal defects and preparation, can exert an influence, and electrode contacts, carrier injections, and other factors can interfere with measurements. Yet there is no doubt that the photoconductive gain (quantum yield) G can be reproduced by different methods. As in the case of dark conductivity, the photoconductivity properties are related to the electronic and structural behavior of pure and doped organic compounds, also those in the polycrystalline state. 

The primary use of lithium fluoride is in the ceramic industry. It reduces the firing temperature and improves the resistance to abrasion, acid attack and thermal shocks. It is essential component of the fluorine cell electrolyte. An addition of small amount (1-1.5%) to KHF2 HF electrolyte improves the wettability of the carbon anodes and lowers the tendency of the cell to polarize. Another important use of LiF is in flux compositions containing chlorides, borates and other fluorides. Lithium fluoride windows made from high purity crystals are used for X-ray monochromators, UV, visible or IR regions [18]. 

The influence of impurities can be ruled out in tow ways by preparation of high-purity crystals or by elimination of the influence of the charge carriers introduced by the impurities. 

In this country within the last few years an important improvement in process increases the yield of high purity crystals at the expense of those of low purity. Many salt wells contain measurable quantities of barium salts, which are decidedly poisonous and have caused much loss through the use for stock of low purity salt containing salts of barium. The improvement in process is purification by. precipitation of impurities. The brine as it comes from the wells receives a calculated quantity of salt cake (acid sodium sulphate), which, being a byproduct of nitric acid manufacture, is very cheap. The sulphuric-acid radical combines with the barium salts to form the insoluble barium sulphate, which is removed by a settling process and the practically barium-free brine concentrated as usual. Crystallization by concentration has been treated thus fully because it is a somewhat rare case. 

Grade Technical (90-92%), 99% pure, high-purity crystals. 

Grade Technical, powder, pure sticks, ingots, slabs, high-purity crystals (<10 ppm impurities). 

Available forms (1) Chromium metal as lumps, granules, or powder (2) high- or low-carbon ferro-chromium (3) single crystals, high-purity crystals, or powder run 99.97% pure. 

To explore these factors we have chosen a-AEOs (sapphire) as a model substrate for our IN studies. High purity crystals are readily available. The a-AEOs (0001) face has an hexagonal lattice whose constant is within a few percent of that of the basal face of ice. The (0001) face can be annealed into a smooth form and characterized by atomic force microscopy (AFM). The face can be chemically treated to make it hydrophilic. Finally a-AEO3 can be produced in forms rich in defects. 

Many industrial crystallization processes, by necessity, push crystal growth rates into a regime where defect formation becomes unavoidable and the routes for impurity incorporation are numerous. Since dislocations, inclusions, and other crystal lattice imperfections enhance the uptake of impurities during crystallization, achieving high purity crystals requires elimination of impurity incorporation and carry-over by both thermodynamic and non-thermodynamic mechanisms. Very generally, the impurity content in crystals can be considered as the sum of all of these contributions... 

With this method, high-purity crystals of a-hexathiophene, pentacene and of many other substances can be grown. The method produces the best single crystals in terms of structural perfection and purity, and can be carried out rapidly (over night). More details can be found in Kloc [10] and Laudise [9]. 

The yield and kinetics of phenol hydroxylation are strongly dependent on the purity, crystal size, and the concentration of TS-1, and on the temperature. High selectivity is directly correlated to framework titanium, whereas extra-framework titanium species initiate the decomposition of hydrogen peroxide and subsequent hydroxylation paths, which are far less selective. 

The weak interchain coupling orders the modulated structure three-dimen-sionally at the Peierls transition temperature, Tp. The force due to an applied electric field, within regions where the CDW is coherent, is counterbalanced by the pinning force of impurities or other defects. For high-purity crystals the application of small electric fields may depin the CDW from the lattice, and the modulated structure slides as a whole. 

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