Crushed crystal method

Hierarchical mesoporous TS-1 MFI T etxabutyl titanate TEOS TPAOH Steam-assisted crystallization method (SAC) Dried under stirring at 80 °C, then crushed into powder and placed in autoclave for crystallization Zhou, 2010 (17)... 

Overlayer (also Two Layer and Seed Layer) Method this method (several variants have been developed by different research groups) is a combination of the crushed crystal and fast evaporation methods. Fast solvent evaporation is used to form the first layer of small matrix-only crystals, followed by deposition of a solution of matrix plus analyte on top of the crystal layer. The difference between the fast evaporation and the overlayer methods is in the second layer solution, where the addition of matrix to the latter is believed to provide improved results particularly for mixtures. The method has several convenient features that make it a popular approach. It inherits all the advantages of the fast evaporation method and avoids some of its limitations, while providing enhanced sensitivity and better spot-to-spot reproducibility. 

Meihylamine hydrochloride method. Place 100 g. of 24 per cent, methyl-amine solution (6) in a tared 500 ml. flask and add concentrated hydrochloric acid (about 78 ml.) until the solution is acid to methyl red. Add water to bring the total weight to 250 g., then introduce lSO g. of urea, and boil the solution gently under reflux for two and three-quarter hours, and then vigorously for 15 minutes. Cool the solution to room temperature, dissolve 55 g. of 95 per cent, sodium nitrite in it, and cool to 0°. Prepare a mixture of 300 g. of crushed ice and 50 g. of concentrated sulphuric acid in a 1500 ml. beaker surrounded by a bath of ice and salt, and add the cold methylurea - nitrite solution slowly and with mechanical stirring and at such a rate (about 1 hour) that the temperature does not rise above 0°. It is recommended that the stem of the funnel containii the methylurea - nitrite solution dip below the surface of the acid solution. The nitrosomethylurea rises to the surface as a crystalline foamy precipitate. Filter at once at the pump, and drain well. Stir the crystals into a paste with about 50 ml. of cold water, suck as dry as possible, and dry in a vacuum desiccator to constant weight. The yield is 55 g. (5). 

Crystallization of CaCOj is highly dependent on nucleation condition. The precipitation of CaCOj in the absence or the presence of the G4.5 PAMAM dendrimer was carried out by a carbonate diffusion method similar to the method described by Addadi et al. [35]. A solution of the dendrimer with calcium chloride in 200 ml of distilled water was adjusted to pH 8.5 with aqueous NHj, and then placed in a closed desiccator containing crushed ammonium carbonate (Fig. 5). Carbon dioxide was introduced to the solution via vapor diffusion. The critical point of the appearance in the turbidity of the solution was observed at around 5 min. These solutions were kept at 30 °C under N2 for one day. The crys-... 

Two preferred methods for preparing clean surfaces consist of generating the surfaces under high vacuum at the beginning. Using remote control manipulators to crush a sample under vacuum exposes fresh surface to an environment in which adsorption equilibrium is very slow. This technique produces a heterogeneous array of crystal faces, however. Far more suitable for the specific and localized examination that diffraction methods offer is crystal cleavage... 

In this chapter the sequence of observations followed in the microscopic method of identification is outlined. The immersion method for the identification of small separate crystals forms the main subject of this chapter, though some remarks on methods for large aggregates will be found at the end. When the immersion method is to be used aggregates may be crushed or ground carefully. 

Crushing has been recommended as a primary method because it is safe and will lead to the determination of the principal refractive indices of any crystalline substance, provided a sufficient number of randomly oriented fragments is observed it is a beginner s method. But the more experienced worker may often dispense with it, when the crystals being examined have a well-defined polyhedral shape. If the relation between crystal shape and optical properties is properly understood, it is possible to determine the principal indices by a limited number of observations on crystals selected because they lie in such positions that they necessarily show their principal indices. 

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