Hydrothermal growth-quartz

Hydrothermal euhedral quartz (blue-green/red CL colors), of Type II veins exhibit growth textures and are related to sulfide mineralization during early Salinic Orogeny. 

Figure 5.8. (a) Typical spiral pattern (phase contrast photomicrograph of (0001) face of Sic grown from the vapor phase), and spiral growth hillocks which appear as (b) polygonal and (c) conical pyramids due to narrow step separation. Part (b) is a differential interference photomicrograph, (1010), and part (c) is a reflection photomicrograph, (1011), of hydrothermally synthesized quartz. 

M. Hosaka and S. Taki, Hydrothermal growth of quartz crystals in NaCl solu tion,... 

Hydrothermal Growth. Hydrothermal growth is used in the form of solution transport for the growth of synthetic quartz. Cmshed natural quartz is placed into the lower part of a high pressure steel vessel, called a bomb, and thin seed plates are located in the upper region, as seen in Figure 5. The vessel is filled, for example, to 80% capacity with a 4% NaOH [1310-73-2] solution the NaOH acts as a mineralizer to increase the solubility of Si02. 

Fig. 5. A small silver-lined hydrothermal growth vessel, 35-cm long, as used for synthetic quartz.

Figure 1. Autoclave used for hydrothermal growth of quartz. (Courtesy of D. R. Kinloch.)...

Hydrothermal growth is used for the growth of materials such as silicates, which form glasses and are, therefore, difficult to crystallize by alternative methods. As for quartz, silicates grow hydrothermally in nature, which makes the synthesis of such materials as fayalite (Fe2Si04) of interest. Materials such as tourmaline and malachite are crystallized only hydrothermally. 

Fig. 11 (A) Schematic sketch of hydrothermal growth of quartz crystals. (B) The crystal basket after growth. (Courtesy of Hantek Inc., Taiwan.) (View this art in color at www. dekker. com.)...

Beyond the abundant natural sources of quartz and other silicas, techniques for synthetic production of these materials have provided a significantly wider range of applications [27,34], Large, high-quality crystals of quartz can be grown by the well-established technique of hydrothermal growth in an autoclave filled with a solution of... 

The main types of SiOj used in indu.siry are high-purity a-quanz, vimeous silica, silica gel. fumed silica and diaiomaceous eanh. The most important application of quartz is as a piezoelectric material (p. 58) it is used in crystal oscillators and filters for frequency control and modulation, and in electromechanical devices such as transducers and pickups tens of millions of such devices are made each year. There is insufficient natural quartz of adequate purity so it must be synthesized by hydrothermal growth of a s crystal using dilute aqueous NaOH and vitreous SiOy at 4(I0°C and... 

While we have discussed how to produce queirtz crystals by hydrothermal growth, we have not addressed the applications in which they are used. Two very important technical fields use quartz crystals. These are as frequency oscillators and as thin-film monitors. Both of these technologies take advantage of the fact that quartz can be act as a crystal oscillator Iqr applying a controlled voltage. 

In the radioactive tracer experiments H- or C-labeled D- or L-Alanine hydrochloride (Ala HCl) in DMF solutions were equilibrated with finely powdered d- or /-quartz Differences in rates of radioactive disintegrations of solutions before and after equilibration gave a measure of the amount of Ala HCl adsorbed on the quartz samples. In general, r/-quartz preferentially adsorbed D-Ala HCl and the /-quartz Z,-Ala HCl to the extents of 1-1.8%. These experiments used finely powdered samples of d- and /-quartz which had been prepared from known morphological handedness and optical rotation, but the authors failed to mention how the Brasilian twins (if any) were removed from quartz samples They did note that samples of quartz were prepared by hydrothermal growth and that crystals were checked... 

Crystals are grown by hydrothermal growth method, a- to -Quartz like transition takes place at 950°C in this material. Material properties and their temperature coefficients see Table 7.6. 

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. 

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