Silica a-quartz

In Table 3, the elastic constants obtained from the pair potential calculations are given for two low density forms of crystalline silica a-quartz and... 

The importance of the inflammatory reaction to the pulmonary response to particles, and the knowledge that epithelial cells are capable of synthesis and secretion of potent inflammatory mediators, have led to the investigation of cytokine expression by epithelial cells following dust exposure. In primary isolated and immortalized cell lines in an in vitro siliea exposure model (35), type II cells respond directly to silica (a-quartz) by increasing expression of MIP-2 and CINC mRNA. 

Fig. 5.7 Adsorption isotherms of n-p>entane vapour on A), quartz and pyrex glass and (B), wide-pored silica gel. O,, quartz pyrex glass A, A wide-pored silica gel. Solid symbols denote desorption. (Courtesy...

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). 

Premier and Schupp have made vapour-density measurements with sulphur enclosed in a quartz bulb heated electrically and connected with a manometer consisting of a spiral of silica tubing attached to a small mirror. The pressure was measured by the amount of unwinding of the spiral. The same method has been used by Bodenstein and Katavama in studving the equilibrium ... 

FIGURE 14.33 Three common forms of silica (Si02) (a) quartz (b) quartzite and (c) cristobalite. The black parts of the sample of cristobalite are obsidian, a volcanic rock that contains silica. Sand consists primarily of small pieces of impure quartz. 

Serizawa et al. (2002) studied experimentally, through visualization, the two-phase flow patterns in air-water two-phase flows in round tubes. The test section for air-water experiments consisted of a transparent silica or quartz capillary tube with circular cross-section positioned horizontally. The two-phase flow was realized through a mixer with different designs, as shown in Figs. 5.4 and 5.5. The air was injected into the mixer co-axially while water was introduced peripherally. 

More than 20 different forms of silica exist, because the bonds and lone pairs around the oxygen atoms can be arranged in various ways. Each arrangement creates a different stmctural form for the silica network. Quartz, the most common form of silica, is found in granite, sandstone, and beach sand. 

Abdelrazig, Sharp El-Jazairi (1988, 1989) prepared a series of mortars based on a powder blend of MgO and ADP with a quartz sand filler. They were hydrated by mixing with water. A mortar I (MgO ADP silica water = 17T 12-9 70-0 12-5), with a water/solid ratio of 1 8, formed a workable paste which set in 7 minutes with evolution of ammonia. The main hydration product, struvite, was formed in appreciable amounts within 5 minutes and continued to increase. Schertelite also appeared, but only in minor amounts, within the first 5 minutes and persisted only during the first hour of the reaction. Dittmarite appeared in minor amounts after 15 minutes, and persisted. 

Preparation of column. Pack the chromatographic tube in the following order a quartz-wool plug, 1.0 g of silica gel (deactivated with 1.5% water), then a 5-10-mm layer of sodium sulfate. Finally, insert a small amount of quartz-wool on top of the column packing. Before use, rinse the column with 5 mL of n-hexane and discard the eluate. 

A colorless gel formed which was isolated by vacuum evaporation of the volatiles. The resulting colorless glassy solid was pyrolyzed in vacuo at 900°C for 24 hours in a quartz tube and the evolved volatiles identified as NH3 and NH4CI. The remaining solid was briefly (2 hours) heated in air at 1200°C in order to remove minor carbon impurities and to improve crystallinity. This solid was then treated at room temperature with 40% aqueous HF to remove boric acid and silica formed in small quantities. The solid obtained at 900°C was identified as boron nitride however, the majority of the material was amorphous. After treatment at 1200°C, white crystalline boron-nitride was obtained in about 55% yield. 

Mixtures of silica gel and the liquid difluoride sealed in tubes at 334 mbar exploded above -196°C, presence of moisture rendering the mixture shock-sensitive at this temperature [1], Reaction of oxygen difluoride with silica, alumina, molecular sieve or similar surface-active solids is exothermic, and under appropriate conditions may be explosive [2], A quartz fibre can be ignited in the difluoride [3],... 

Further error is introduced if reactions distinct from those for which data is available affect the chemistry of a natural fluid. Consider as an example the problem of predicting the silica content of a fluid flowing through a quartz sand aquifer. There is little benefit in modeling the reaction rate for quartz if the more reactive minerals (such as clays and zeolites) in the aquifer control the silica concentration. 

Fig. 26.3. Silica concentration (bold lines) in a fluid packet that cools from 300 °C as it flows along a quartz-lined fracture of 10 cm aperture, calculated assuming differing traversal times At. Fine lines show solubilities of the silica polymorphs quartz, cristobalite, and amorphous silica.

Fig. 26.5. Calculated silica concentration in a fluid packet flowing through a quartz sand aquifer. The fluid descends from the surface (T = 20 °C) to a depth of about 2 km (80 °C) and then returns to the surface (20 °C). Results are shown for time spans At (representing half of the time the fluid takes to migrate through the aquifer) of 0.1, 1, and ten years. In the latter calculation, the fluid remains near equilibrium with quartz.

Fig. 27.2. Concentration of dissolved silica and the quartz dissolution rate along a quartz sand aquifer being recharged at left by rainwater, for the scenario considered in Figure 27.1. Results were calculated assuming a range of flow velocities rapid flow corresponds to a Damkohler number Da less than one, whereas Da is greater than one for slow flow.

Crystalline silica, or quartz, is an abundant mineral found in sand, rock, and soil. Respirable silica dust (particles <5pm) is a known occupational hazard of the dusty trades (e.g., pottery or china manufacturing, work involving sandblasting or abrasive grinding, some construction trades). High level exposure to respirable silica can result in the chronic, progressive lung disease silicosis, characterized by inflammation and fibrosis. 

Pure silica zeolites or molecular sieves are metastable with regards to the thermodynamic stable polymorph at ambient conditions, a-quartz. However, they are... 

Wire mini-grid OTEs. A mini-grid" is constructed with an array (or mesh ) of microscopically thin wires criss-crossing the face of a sheet of glass, silica or quartz. The wires are themselves too thin to see, but as soon as product is formed, it diffuses away from the wire. Since diffusion is entropy-driven (i.e. random), electrogenerated material does not diffuse in straight lines, but moves in all directions at once. In practice, as soon as material is formed, it is seen between the wires, and hence can be detected by the light beam of a spectrometer. 

Figure 8.5 shows a schematic representation of a cell used for obtaining in situ spectroelectrochemical EPR spectra. This cell has to be constructed from silica or quartz since normal glass or plastic will itself have a paramagnetic signal. The counter electrode (CE) needs to be... 

In a solution containing oxygen, photolysis yields a mixture of 6,12-, 1,6-, and 3,6-diones. Nitration by nitrogen dioxide forms 6-nitro-, 1-nitro-, and 3-nitrobenzo[a]pyrene. When benzo [a] pyrene in methanol (1 g/L) was irradiated at 254 nm in a quartz flask for 1 h, the solution turned pale yellow. After 2 h, the solution turned yellow and back to clear after 4 h of irradiation. After 4 h, 99.67% of benzo[a]pyrene was converted to polar compounds. One of these compounds was identified as a methoxylated benzo[a]pyrene (Lu et al, 1977). A carbon dioxide yield of 26.5% was achieved when benzo [a] pyrene adsorbed on silica gel was irradiated with light (A, >290 nm) for 17 h (Freitag et al, 1985). 

Photooxidation of chlorobenzene in air containing nitric oxide in a Pyrex glass vessel and a quartz vessel gave 3-chloronitrobenzene, 2-chloro-6-nitrophenol, 2-chloro-4-nitrophenol, 4-chloro-2-nitro-phenol, 4-nitrophenol, 3-chloro-4-nitrophenol, 3-chloro-6-nitrophenol, and 3-chloro-2-nitrophenol (Kanno and Nojima, 1979). A carbon dioxide yield of 18.5% was achieved when chlorobenzene adsorbed on silica gel was irradiated with light (A. >290 nm) for 17 h. The sunlight irradiation of chlorobenzene (20 g) in a 100-mL borosilicate glass-stoppered Erlenmeyer flask for 28 d yielded 1,060 ppm monochlorobiphenyl (Uyeta et al., 1976). 

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