Fused silica, synthetic

Table 8. Dielectric Properties of Synthetic Fused Silica ...

Use of 10 pm LiChrosorb RP18 column and binary eluent of methanol and aqueous 0.1 M phosphate buffer (pH 4.0) according to suitable gradient elution program in less than 20-min run time with satisfactory precision sensitivity of spectrophotometric detection optimized, achieving for all additives considered detection limits ranging from 0.1 to 3.0 mg/1, below maximum permitted levels Simultaneous separation (20 min) of 14 synthetic colors using uncoated fused silica capillary column operated at 25 kV and elution with 18% acetonitrile and 82% 0.05 M sodium deoxycholate in borate-phosphate buffer (pH 7.8), recovery of all colors better than 82%... 

The synthesis of phtalocyanine dyes was followed by CE and the purity and composition of the end product was investigated by the same method. The chemical structure of the newly synthetized zinc phtalocyanine tetrasulphonic acid is shown in Fig. 3.163. An uncoated fused silica capillary (65cm X 75 /.an i.d.) was employed for the separation of dye components. Running buffers were 10 mM ammonium acetate (pH adjusted to 9.4 with ammonia) and 10 mM potassium dihydrogenphosphate (KH2P04) (pH = 9.0). Samples were injected hydrodynamically (50 mm for 10 s). Separation was realized in the constant current mode at 30 pA, which required about 28 kV separation voltage. Analytes... 

The synthesis of a new near-infrared cyanine dye was monitored by CE and fluorescence detection. The chemicals structure of the dye and its synthetic precursor are depicted in Fig. 3.165. The analysis of the dye was realized in fused-silica capillaries of 75 and 100 /an i.d. The total and effective lengths of capillaries were 75 and 60 cm, respectively. The separation voltage was 30 kV and separations were carried out at ambient temperature. The running buffer was 2.5 mM Na2B407 (pH = 9.2). A near-infrared laser-induced fluorescence detector was applied. Electropherograms illustrating the separation of the dye are shown in Fig. 3.166. 

The configuration of the probe is as shown in Figure 11.24. The sensor element itself, a small (approximately) rectangular-shaped (2x2x1 mm) piece of the synthetic crystal alexandrite, is held in a ceramic enclosure at the end of two fused silica fibers. The first fiber, that with a 0.4-mm core diameter, is used to transmit light from the excitation source to the sensor element. The second fiber, with a 1.0-mm core diameter, is used to receive the fluorescence response emitted from the sensor element. 

For qualitative analyses, the GC system was equipped with a J W Scientific HP-5 or a Supelco Simplicity 1 fused-silica capillary column. Injector and detector temperatures were set at 220 °C and 240 °C respectively the oven temperature was programmed from 60 to 230 °C at 40 °C min V Helium was employed as carrier gas (1 mL min ). Compound identification was based on a comparison of mass spectra with those of synthetic racemic and enantiomeric-enriched samples. The retention times for tetralin, 1-tetralol and 1-tetralone were 5.6 min, 6.5 min and 6.6 min respectively. 

MMVF are synthetic fibers with glasslike structures. The term usually refers to silicate-based glass fibers, because these compositions form the largest volume of fibers produced. However, in addition to fiberglass and fused silica (Si02), there are other amorphous fibers used in commerce alumina (AI2O3) and silica combinations, rock and slag wool, as well as fibers with nonsilicate compositions such as carbon. Many of these amorphous fibers have proprietary names. 

Transparent Vitreous Silica. Clear, transparent, bubble-free vitreous silica maybe obtained by melting natural quartz minerals, ie, fused quartz, by flame or plasma vapor deposition (synthetic fused silicas), and by sol—gel processing. 

Synthetic fused silicas with low OH levels have also been made experimentally using a C02 laser instead of the plasma torch (62,63). The glass rate of this process, however, is at least 10 times slower than the plasma approach. 

Peroxy entities may indeed represent an ubiquitous type of defects in oxides and silicates, both natural and synthetic. The reason is that traces of dissolved "water" are everywhere. In optical waveguide fibers made of low-OH fused silica a dramatic increase of Si-OH and attendant loss of transmittance have been reported upon exposure to H2 probably by way of the reaction Si/°° Si + H2 2 Si-OH (15,35). ... 

Historically, fused quartz referred to transparent products produced from quartz crystal rock, and fused silica referred to opaque products produced from sand. With the advent of new manufacturing techniques, transparent products can now be produced from sand, so the old distinction is no longer applicable. Currently, the term fused quartz is used whenever the raw product is either quartz rock or sand. The term fused silica is used whenever the raw product is synthetically derived (from SiCl4). Generically, the term quartz glass or, better yet, vitreous silica can be used to cover the whole range of materials. 

The silica surfaces used were fused silica microscope slides (1 X 2 X 1/16 inches, A. H. Thomas and Co.) and the alumina surfaces were 3/4 inch diameter, 1/8 inch thick, synthetic, a-alumina discs (synthetic sapphire, Linde Division, Union Carbide Corp.). The specimens were cleaned by heating in a mixture of equal parts of sulfuric and nitric acid, given a preliminary rinse in hot tap water and then soaked in three suc-... 

The reactor was fed with 1.6 Nl/min of 1000, 2000 and 4000 ppm of methane in air. The mixtures were obtained by mixing N-50 synthetic air and 2.5 % (vol.) CH4 in N-50 synthetic air (Air Products). 40 ppm of SO2 (from a cylinder of 370 ppmV SO2 in N-50 synthetic air. Air Products) were added when the effect of sulphur on the catalysts activity was studied. Flow rates were controlled by calibrated mass flow controllers (Brooks 5850 TR). Exhaust gas was analysed by gas chromatography (Hewlett Packard HP 5890 Series II). Methane in the inlet and outlet streams was analysed using a 30 m fused silica capillary column with apolar stationary phase SE-30, and a FID detector. CO and CO2 were analysed using a HayeSep N 80/100 and a molecular sieve 45/60 columns connected in series, and a TCD detector. Neither CO, nor partial oxidation were detected in any experiment, the carbon mass balance fitting in all the cases within 2%. Methane conversions were calculated both from outlet methane and CO2 concentrations, being both values very close in all the cases. Methane (2000 ppmV) and SO2 (40 ppmV) concentrations have been selected because they are representative of industrial emissions, such as coke oven emissions. 

A) Synthetic fused silica. (B) Natural fused silica. (C) Titanium doped natural fused silica. (D) Cerium doped natural fused silica. (E) FVrex glass. (F) Nonex glass. 

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