Quartz, synthesis

MACKENZIE (F.T.) and GEES (R.), 1971. Quartz Synthesis at earth-surface conditions. Science, 173, 533-5. 

I would like to describe hydrothermal quartz synthesis and commercialization as an example of synergistic interaction between synthesis and processing physical chemistry leading to better materials and more cost-effective devices. My discussions here and in the subsequent section on hydrothermal KTP will be at somewhat greater length because the role of chemists in hydrothermal synthesis and processing is perhaps not very well known and because of my familiarity with the subjects due to personal involvement. 

The dependence of solubility on pressure requires an understanding of the equation of state of hydrothermal solutions saturated with quartz. Systematic P-V-T studies have been conducted.(77) Fig. 4(77) summaries some of this data. As can be seen, behavior is qualitatively like that for pure H2O but with pressures substantially reduced. Pressure in hydrothermal quartz synthesis is established by the initial fraction of the vessel volume (% fill) filled with (OH) solution at the beginning of the growth run. 

Where R is the growth rate, t the thickness of the diffusion layer and D the diffusion constant. The understanding gleaned from studies such as those of Fig. 6 was used to improve the Q of synthetic quartz from initial Q s of 30,000 to present Q s in excess of 2 x 106. Thus systematic studies of the defect chemistry of quartz lead to procedures for defect control so as to provide device quality material equal and in some cases superior to natural quartz. Fig. 7 shows an early commercial quartz synthesis run in the AT T factory facility in North Andover, Massachusetts. 

Mackenzie F. T. and Gees R. (1971) Quartz synthesis at Earth-surface conditions. Science 173, 533-535. 

Although the CFCs and HCFCs are not as stable as the PFCs, they still can be rather stable compounds (3,11)- Dichlorodifluoromethane, CCI2F2, is stable at 500°C in quartz CCl F and CHCIF2 begin to decompose at 450 and 290°C, respectively (7). The pyrolysis of CHCIF2 at 650—700°C in metal tubes is the basis of a commercial synthesis of tetrafluoroethylene ... 

Other Industrial Applications. High pressures are used industrially for many other specialized appHcations. Apart from mechanical uses in which hydrauhc pressure is used to supply power or to generate Hquid jets for mining minerals or cutting metal sheets and fabrics, most of these other operations are batch processes. Eor example, metallurgical appHcations include isostatic compaction, hot isostatic compaction (HIP), and the hydrostatic extmsion of metals. Other appHcations such as the hydrothermal synthesis of quartz (see Silica, synthetic quartz crystals), or the synthesis of industrial diamonds involve changing the phase of a substance under pressure. In the case of the synthesis of diamonds, conditions of 6 GPa (870,000 psi) and 1500°C are used (see Carbon, diamond, synthetic). 

The Ru metal area was determined by volumetric H2 chemisorption in the quartz U-tube of an Autosorb 1-C set-up (Quantachrome) following the procedure described in ref. [16]. Prior to chemisorption, the catalysts were activated by passing 80 Nml/min high-purity synthesis gas (Pnj / Phj -1/3) from a connected feed system through the U-tube and heating to 673 K for alkali-promoted catalysts or to 773 K for alkali-free catalysts with a heating rate of 1 K/min. The BET area was measured by static N2 physisorption in the same set-up. 

We have extended the seed-mediated technique for the synthesis of bimetallic nanoparticles, having core-shell type structure appending photoreduction of metal ions. It has been proved that the deposition of a less noble metal (M) as shell on a preformed nobler nanoparticle core (M ) seems to be very effective by UV activation. Using this seed-mediated method we were able to synthesize Aucore Agsheii particles. First for the preparation of gold seeds (S), TX-lOO (10 M) and HAuC (5.0 x 10 %) were taken in a quartz cuvette so that the final concentration of Au(III) ion remained 5.0 x 10 M. Then the... 

Milestone [23] have produced a range of MW reactor systems for organic synthesis, including a quartz or ceramic MW reactor (MRS) for high pressure (up to 4 MPa) and temperature reactions, designed for large volume batch synthesis and a multiple batch reactor MPR/HPR for up to 12 vessels, with volumes 2-270 mL for operation at 3.5-10 MPa. 

Tolstoi, V. P. Molotkina, E. V. 1994. The synthesis of copper-peroxide nanolayers on silicon and fused-quartz surfaces by the ionic deposition technique.. Russ J. Inorg Chem. 39 372-374. 

Tolstoi, V. R Tolstobrov, E. V. 2002. Synthesis of highly oriented a-Pb02 layers on the surfaces of single-crystal sihcon and quartz by successive ionic layer deposition. Russ. J.Appl. Chem. 75 1529-1531. 

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