Quartz, formation

The formation of crystalline quartz from a gel at low temperatures has not been established experimentally. Direct crystallization of quartz from sea water has been observed (Mackenzie and Gees, 1971). In the opinion of Harder and Fleming (1970), quartz is formed only by adsorption of Si02 by hydroxides of Fe, Al, Mg etc. from undersaturated solutions, while amorphous silica arises in supersaturated solutions. The mechanism of crystallization of gels to quartz was studied in detail in our laboratory by Mitsyuk (1974). It was established that in amorphous silica the process of quartz formation goes on at an appreciable rate in hydrothermal conditions —T— 150-250°C and F = 0.5-4.0 kbar—and is characterized by the following features ... 

Rates of minerogenesis are less studied than rates of dissolution. In part this is due to xmcertainty of intermediate products of reactions, which in conditions of high oversaturation may precipitate together with the basic mineral. For instance, studies of quartz formation are obstructed by the precipitation of amorphous silicon. Because of this the study of dissolution and minerogenesis kinetics is based mostly on the study of dissolution processes assuming the principle of microscopic reversibility. 

All of the layered silicate hydrates listed in Tables 3 and 4 represent metastable phases during the process of quartz formation. The stability depends on the reaction conditions and the composition when the products are separated from the mother liquor. After isolation and drying they are stable and can be stored under ambient conditions for long periods of time without any structural changes. 

Table 7 Product Sequences During Hydrothermal Quartz Formation with Metal Silicate Hydrates as Intermediate Phases... 

In accordance with (DE-OS 34 00 130), increasing the synthesis pressure above the autogenous pressure by the use of an inert gas has nearly no effect on the synthesis of kenyaite. On the other hand, a strong acceleration of quartz formation and the appearance of different potassium silicate hydrates under enhanced pressure has been described [6,41,87]. 

The examples in the preceding section, of the flotation of lead and copper ores by xanthates, was one in which chemical forces predominated in the adsorption of the collector. Flotation processes have been applied to a number of other minerals that are either ionic in type, such as potassium chloride, or are insoluble oxides such as quartz and iron oxide, or ink pigments [needed to be removed in waste paper processing [92]]. In the case of quartz, surfactants such as alkyl amines are used, and the situation is complicated by micelle formation (see next section), which can also occur in the adsorbed layer [93, 94]. 

Hydrothermal crystallisation processes occur widely in nature and are responsible for the formation of many crystalline minerals. The most widely used commercial appHcation of hydrothermal crystallization is for the production of synthetic quartz (see Silica, synthetic quartz crystals). Piezoelectric quartz crystals weighing up to several pounds can be produced for use in electronic equipment. Hydrothermal crystallization takes place in near- or supercritical water solutions (see Supercritical fluids). Near and above the critical point of water, the viscosity (300-1400 mPa s(=cP) at 374°C) decreases significantly, allowing for relatively rapid diffusion and growth processes to occur. 

The addition of 2,2, 4,4, 6-pentanitro-6 -methyldiphenylamine [64653-47-0] to seawater precipitates potassium (38). Aromatic amines, especially aminotetrahydronaphthalenes and their A[-aryl derivatives, are efficient flotation agents for quartz. The use of DPA for image formation in films has been patented (39,40). Diarylamines are used as intermediates (41) for azo, sulfur, oxidative base, triaryhnethane, oxazine, nitro, and safranine dyes (see Dyes and DYE INTERLffiDIATES). 

A -Bridgehead compounds have been obtained from the photochemical cyclization of cfi-1-styrylimidazoles. For example, irradiation of the imidazole (532) in methanol in the presence of I2 resulted in cyclization at the 2-position of the imidazole ring with the formation of an imidazo[2,l-a]isoquinoline (533) (76JCS(Pl)75). Isomerization of the trans-to the c/i-styrylimidazole was followed by photodehydrocyclization, trans- 1-Styrylbenzimidazole (534) was isomerized under Pyrex-filtered light in the presence of one molar equivalent of I2. The resulting cis isomer on irradiation through quartz gave the benzimidazo[2,l-a]isoquinoline (535) in 53% yield. 

Film-forming chemical reactions and the chemical composition of the film formed on lithium in nonaqueous aprotic liquid electrolytes are reviewed by Dominey [7], SEI formation on carbon and graphite anodes in liquid electrolytes has been reviewed by Dahn et al. [8], In addition to the evolution of new systems, new techniques have recently been adapted to the study of the electrode surface and the chemical and physical properties of the SEI. The most important of these are X-ray photoelectron spectroscopy (XPS), SEM, X-ray diffraction (XRD), Raman spectroscopy, scanning tunneling microscopy (STM), energy-dispersive X-ray spectroscopy (EDS), FTIR, NMR, EPR, calorimetry, DSC, TGA, use of quartz-crystal microbalance (QCMB) and atomic force microscopy (AFM). 

DNA microarrays, or DNA chips consist of thousands of individual DNA sequences arrayed at a high density on a single matrix, usually glass slides or quartz wafers, but sometimes on nylon substrates. Probes with known identity are used to determine complementary binding, thus allowing the analysis of gene expression, DNA sequence variation or protein levels in a highly parallel format. 

Calcium Oxide (lime, Quicklime, Burnt Lime, Calx, Unslaked Lime, Fluxing Lime). CaO, mw 56.08, white or greyish-white lumps or powd, mp 2580°, bp 2850°, d 3.25-3.40g/cc. SI sol in w with formation of calcium hydroxide and evolution of large amts of heat sol in acids, and insol in ethanol. Coml prepn consists of heating calcium carbonate in kilns at 1000—1100° until all of the C02 is driven off. Lab prepn is by burning calcium carbonate or calcium oxalate at about 800° using a quartz crucible in an electric furnace... 

Quantum chemical calculations, 172 Quantum chemical method, calculations of the adsorption of water by, 172 Quantum mechanical calculations for the metal-solution interface (Kripsonsov), 174 and water adsorption, 76 Quartz crystal micro-balance, used for electronically conducting polymer formation, 578... 

Considering the formation of saturated five-membered heterocycles with two heteroatoms, it is worth to note the possibility to prepare 1,3-dioxolanes, dithiane, oxathianes 148 [93] and dioxolanones 149 [94] by condensation of the corresponding carbonyl compounds under microwave irradiation in acid medium (Scheme 52). The reaction, which is very useful for the protection of carbonyl compounds or for the preparation of useful synthetic intermediates, has also been carried out under batch conditions over Montmorillonite KIO clay in more than 150 g scale, using a 1 L quartz reactor [95]. 

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