Silicium oxide

Avvakumov E.G., Chizhevskaya S.V., Stoyanov E.S., et al. Influence of components nature of mechanically activated mixture of zirconium and silicium oxides on soUd-state synthesis of zircon. Zhurn. Prikl. Khimii 1999 72 1420-24. 

Taking silica (bulk composition silicium oxide, Si02), from which capillary material in capillary electrophoresis (CE) is manufactured, as an example, one can readily understand this when taking into account that on the silica surface, there are silicium hydroxide groups that are subject to an acid-base equilibrium according to... 

Non-rcactive mineral compounds, suth as kaoline in powder form in proportion 2.5% [4]. Carbonates. should not be advised as they can react with ammonium salts to form unstable ammonium carbonate.. Also silicates arc not advised as they can produce silicium oxide which is dangerous in underground work as a cause of silicosis. 

Silicium Oxide Si02 Si quartz, silicate minerals... 

Fired ceramic spheroids have been described for use as a well proppant [1051], Each spheroid has a core made from raw materials comprising mineral particulates, silicium carbide, and a binder. The mixture includes a mineral with chemically bound water or sulfur, which blows the mixture during firing. Therefore the core has a number of closed air cells. Each spheroid has an outer shell surrounding the core, comprising a metal oxide selected from aluminum oxide and magnesium oxide. The fired ceramic spheroids have a fired density less than 2.2 g/cm. ... 

Membranes with extremely small pores ( < 2.5 nm diameter) can be made by pyrolysis of polymeric precursors or by modification methods listed above. Molecular sieve carbon or silica membranes with pore diameters of 1 nm have been made by controlled pyrolysis of certain thermoset polymers (e.g. Koresh, Jacob and Soffer 1983) or silicone rubbers (Lee and Khang 1986), respectively. There is, however, very little information in the published literature. Molecular sieve dimensions can also be obtained by modifying the pore system of an already formed membrane structure. It has been claimed that zeolitic membranes can be prepared by reaction of alumina membranes with silica and alkali followed by hydrothermal treatment (Suzuki 1987). Very small pores are also obtained by hydrolysis of organometallic silicium compounds in alumina membranes followed by heat treatment (Uhlhom, Keizer and Burggraaf 1989). Finally, oxides or metals can be precipitated or adsorbed from solutions or by gas phase deposition within the pores of an already formed membrane to modify the chemical nature of the membrane or to decrease the effective pore size. In the last case a high concentration of the precipitated material in the pore system is necessary. The above-mentioned methods have been reported very recently (1987-1989) and the results are not yet substantiated very well. 

In all these studies which were carried out over the five-year period, 1904-1909, the effects of catalysts on these fixations of nitrogen were investigated. For the barium compounds, iron oxide acted as a catalyst. For the titanium nitrides, various other metal oxides as well as a number of inorganic salts proved to be effective. For the silicium nitrides and aluminum nitrides, again metal oxides and salts had beneficial effects but in other proportions and to another extent than found for the titanium nitrides. Often, two or more catalysts were added to the reaction mixtures with beneficial effects, but no systematic quantitative comparisons were carried out at this time. Table I lists some of these experiments. 

An oxide layer is produced on the surface of the silicium wafer (Si02). This layer of silicium dioxide is an isolating layer on the surface, it is usually grown in an atmosphere containing oxygen, water vapor or other oxidants (02, 03, H202). 

Turpin (Poudres dites double effet). These expls patented in 1881 1883 contained K chlorate about 80 coaltar about 20 with some charcoal and may be considered as precursors of "Pyrodialytes . It was allowed to replace half of chlorate by K or Pb nitrate or to replace 10% of chlorate by K permanganate. Some of die formulations contd silicium or kieselguhr if. tar were too fluid (pp 777—78) Turpin s Explosives patented in 1887 contd as main ingredients chloro-, bromo-, or iodo-nitrates of coal tar without inorganic oxidizers. They could be initiated by a MF detonator or by a cartridge of Dynamite (p 778)... 

Anodic oxidation of ring-substituted aryl(trimethylsilylmethyl)-sulfides results in a cleavage of the carbon-silicium bond [211]. Oxidation of hexaalkyldisilanes in MeCN results in a cleavage of the Si-Si bond in a two-electron reaction [135]. 

Arsen bildet ahnlich wie Silicium kovalente Oxide, die aus As-O-Einfachbindungen bestehen. 

Finally, deactivation of the catalyst by poisoning elements should be mentioned. Precious metal based catalysts are poisoned by sulfur oxides which mainly originate from the combustion of sulfur-containing fuel constituents, by phosphorus and zinc which mainly originate from some additives in the engine lubricating oil, and by silicium which was sometimes present in some engine seals (Table 21). Also, traces of lead, present in the fuel because of contamination of the fuel supply chain, made an important contribution to the deactivation of the catalyst in the past. 

In Figure 2 it is shown that the reaction continues unabated in the absence of the solid catalyst, whereas the recovered catalyst has lost the major part of its activity. The leaching of the titanium was further investigated by ICP-OES analysis. The silicium/titanium ratio of the Ti-MCM-41 as-synthesised is 230, while after the reaction this ratio was increased till 4720. We found that the native catalyst was hydrolytically stable under aqueous conditions, whereas in the presence of hydrogen peroxide rapid leaching was observed. Apparently the titanium hydroperoxide is more sensitive to hydrolysis than the native catalyst. The homogeneous titanium species is apparently an oxidation catalyst. A recent paper on Ti-MCM-41 also reports Ti-leaching in the liquid phase . 

The working time of HT-probes decreases quickly over glass meltings with increasing temperature [55]. Vapors of the oxides, above all of sodium, potassium, silicium, lead, an-timon and arsen condense on the probe material in the temperature gradient from the inside to the outside of the tank wall. The condensed substances penetrate into the ceramic material over grain boundaries and lead to tube bursts. Thereby the stabilized zirconium dioxid is more sensitive than alumina. Componenu which contain Si02 must not be used in HT-probes [56]. 

Also known as silicium occurs in three allotropic forms Amorphous silicon, formed when silicon ehlorid is passed over heated K or Na, is a dark brown powder, heavier than water. When heated in air, it bums with a bright flame to tiie dioxid. It dissolves in potash and in hydrofluoric acid, but is not attacked by other acids. Graphitoid silicon is obtained by fusing potassium fluosilicate with aluminium. It forms hexagonal plates, of sp. gr. 2.49, which do not burn when heated to whiteness in 0, but may be oxidized at that temperature, by a mixture of iiotassium chlorate and nitrate. It dissolves slowly in alkaline solutions, but not in acids. Crystallized silicon, corresponding to the diamond, forms crystalline needles, which are only attacked by a mixture of nitric and hydrofluoric acids. 

With metallic oxides, hydrofluoric acid gives rise to water and metallic fluorides HF - - MO = HO -F MF. The afiinity of fluorine for silicon is such, that hydrofluoric acid decomposes all silicious compounds and this explains its corrosive action on glass and porcelain. Berzelius has employed this acid as a means of analysing silicious minerals. As the fluoride of silicium is gaseous, any such mineral, if digested with hydrofluoric acid, soon loses all its silica, and is dissolved, so that the other ingredients may be determined. 

Synonyms Silicic anhydride Silicium dioxide Silicon dioxide Classification Inorganic oxide... 

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