Silica, crystalline-quartz

A characteristic of the early neutron reflectivity studies of nonionic surfactant adsorption was some variability in the pattern of adsorption. This was investigated in more detail and more systematically by McDermott et al. [55], who compared the adsorption of Ci2E6 onto a range of different substrates, amorphous silica, crystalline quartz, and the oxide layer on a silicon single crystal. The adsorbed surfactant was found to form a bilayer with an overall thickness 49 4 A, with a structure similar to that determined in the previous studies (see Fig. 4). 

Granular silica (crystalline quartz) and transparent silica plates (1 X 3 inches) were used for the sorption studies. The granular silica was supplied by the Ottawa Silica Co. and the Fisher Scientific Co. The silica was sized by dry-sieving with U. S. Standard sieves. In most cases, as narrow a range as possible was chosen, and the mean diameters, except where size was a variable, ranged from 275 to 387 microns. The transparent silica plates were fused silica with a smooth amorphous surface. 

Silica, crystalline, quartz 3241 Silicon zirconium oxide (SiZr04) 4169... 

SILICA, CRYSTALLINE QUARTZ, RESPIRABLE DUST (SiOj, 60.09)... 

Silica, crystalline (quartz, fused amorphous silica, crislobolile, tridymite, tripoli [CAS 14464-46-1]) Inhalation of dusts causes silicosis, a progressive, fibrotic scarring of the lung. Individuals with silicosis are much more susceptible to tuberculosis. Some forms of crystalline silica are carcinogenic (lARC 2A). 0.1 mg/m (respirable dust quartz, fused silica. tripoll) 0.05 mg/m (respirable dust cristo-bollte, tridymite) 25 mg/m (cristobolite, tridymite) 50 mg/m (quartz, tripoll) Coloriess, odorless solid with a negligible vapor pressure. A component of many mineral dusts. 

CAS 14808-60-7 EINECS/ELINCS 238-878-4 Synonyms Agate Amethyst Chalcedony Crystalline silica Flint Free crystalline silica Onyx Pure quartz Quartz glass Rose quartz Sand Sea sand Silica Silica, crystalline quartz Silica flour Silica glass Silica, quartz Silicic anhydride Silicon dioxide Classification Inorg. silicon compd. 

Synonyms Agate Chalcedony Rose quartz Silica, crystalline quartz Silicic anhydride Silicon dioxide... 

Silica, crystalline. See Cristobalite Silica, crystalline fused. See Silica, fused Silica, crystalline quartz. See Novaculite ... 

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. 

Silica, Crystalline (Respirable) Cristobalite Quartz Tridymite Tripoli... 

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. 

Stober (173) found also a close relation of the adsorption sites for ammonia and the number of surface silanol groups. Fused silica and crystalline quartz behaved in a similar manner. About the same concentration of adsorption sites was found in the SOj adsorption. 

In principle, there is no difference in the surface groups on quartz and on amorphous silica. The most important question discussed in the literature is whether the structure of crystalline quartz is represented in its surface, too. Many investigators (282-287) reported that there is a disturbed layer of amorphous character present on the quartz surface. It is more readily dissolved by water or by hydrofluoric acid. Holt and King (288) claimed that only a monomolecular layer of silicic acid was adsorbed on quartz surfaces. 

The 2003 ACGIH threshold limit valuetime-weighted average (TLV-TWA) for crystalline quartz silica is O.Img/m for the respirable fraction of dust. 

At room temperatures, crystalline quartz is thermod3mamically more stable than silica glass. From ancient times, humans have converted quartz to silica... 

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