Silicon hexafluoride

SYNS AMIV IONIUM FLUOROSILICATE (DOT) AMMONIUM FLUOSILICATE AAIMONIUM HEXA-FLUOROSILICATE AMMONIUM SILICOFLUORIDE AMMONIUM SILICON FLUORIDE DL MMONIUM FLUOSILICATE DIAMMONTUM HEXAFLUOROSILIC-ATE(2-) DIAi LMONIUM SILICON HEXAFLUORIDE FLUOSILICATE de AMMONIUM (FRENCH)... 

In the presence of fluoride ions, we find formation of soluble silicon hexafluoride, SiFi", which is dominant in the acidic region. Figure 2.3 illustrates the stabihty... 

The mechanism of electrochemical etching to produce porous silicon has been studied by a number of researchers [11-13]. Although it is certain that several different reactions are occurring simultaneously, anodic etching of crystalline silicon ultimately leads to oxidation and dissolution of the surface to silicon hexafluoride (Scheme 16.1). Under these conditions, Si-Si bonds are electrochemically activated and react with fluoride ions to form soluble, molecular perfluoro species solvation of these silicon fluorides by the etching medium yields a physically irregular, high area porous silicon matrix. Visual indicators for the anodization are the appearance... 

Silicon atom belongs to group IV of the periodic table and its orbitals consist of Is 2s 2p 3s 3p similar to carbon. The outer electrons form covalent tetrahedral sp and octahedral sp d hybrid orbital with other atoms such as silane and potassium silicone hexafluoride respectively, but no stable sp or sp hybrid orbitals are found. Since the electronegativity of Si atom is smaller than that of carbon, the bond between Si and... 

An oxide layer on a silicon wafer Is most commonly removed with HP or NH4P-HP (BOB) solutions. The reaction results In formation of silicon hexafluoride which is water soluble (10). The buffered HP Is used when a constant oxide etch rate Is required. Complication due... 

Chemically stabilised Y zeolites (CSV) were pr jared ty reacting a slurry of NH4Y (Si/Al = 2.5) at 70°C and buffered at pH = 6.5 with an aqueous solution of (NH4)2SiP6 (9). Heteroatom Y zeolites were prepared in a similar way but using fluorides of gallium and zinc in place of silicon hexafluoride (12). A semi-batch reactor was used and in all cases products were washed free of fluoride. 

DIAMMONIUM SILICON HEXAFLUORIDE (1309-32-6) Aqueous solution is acidic. Contact with acid or acid fumes forms toxic fluorine. Keep away from strong oxidizers. 

The silicon hexafluoride ion, SiFg, is octahedral. What orbitals of the silicon atom are occupied by unshared electron pairs By bonding electron pairs What is the electric charge on the silicon atom and each fluorine atom, as calculated from electronegativity values ... 

Fluoride ions reacting with a silicon tetrafluoride molecule to form the silicon hexafluoride ion ... 

C3BH4BB2CU4F14Ng03Si 0.84 H2O, Aqua-(2,6-bis(N-(2-(4 imidazolyl)-ethyl)iminomethyl)-4-methylphenol) (/i-2-hydroxo)dicopper(II) dimer tetrafluoroborate silicon hexafluoride hydrate, 46B, 1196 C38H48C0N2O4 0.5 CyHB, (3,5-Di-tert-butylcatecholato)(3,5-di-tert-butylsemiquinone)(bipyridyl)cobalt(III) toluene solvate, 46B, 1160 C3bH5i,Cu2N,o025P2/ (Uridine 5 -monophosphate)-2,2 -dipyridylamine-copper(II) pentahydrate, 44B, 1013... 

There are two procedures used to prepare dealuminated zeolites. One procedure involves a rapid hydrothermal dealumination at a relatively high temperature of 500°C (10,11). The resulting material contains a network of larger zeolitic mesopores within the crystal and connecting directly to the zeolitic pore system. Another procedure uses silicon hexafluoride at a relatively low temperature, <100°C (12). The result is a slow dealumination with the formation of much less mesopore structure. The two procedures result in zeolites that differ in the distribution of active framework aluminum sites as well as in the presence or absence of mesoporosity. The liquid phase dealumination results in a zeolite with the active aluminum sites preferentially removed from the outside of the zeolite particle or crystal. Further, during the dealumination process, additional silicon is deposited on the zeolite surface (13). The exact opposite happens during hydrothermal dealumination. While the framework is more or less uniformly dealuminated, the aluminum atoms removed from the framework do not remain within the pore system, but are observed to migrate to the outside of the zeolite particle (14). Consequently, unless the alumina is removed, the outside of the zeolite particle is alumina rich. 

In both cases post dealumination chemical treatments are necessary. In the case of the use of silicon hexafluoride dealumination, it is necessary to remove every trace of fluoride in order to preserve stability (15). In the case of hydrothermal dealumination, additional sodium is removed, and nonframework alumina may or may not be removed as desired. 

Mesoporosity is a characteristic of hydrothermally dealuminated zeolites identified in the early 1980 s. Since then a considerable amount of TEM (19, 20) and adsorption (21) evidence has accumulated concerning the size and surface area of the mesopores as well as the potential activity and selectivity benefits associated with mesoporosity. It appears that mesoporosity is formed during the initial period of rapid dealumination. Although the use of slow, low temperature dealumination procedures do produce some mesoporosity, the amount is much less than is produced by high temperature rapid hydrothermal dealumination techniques. This is illustrated in Figure 2 where the mesoporosity development of two sieves, one hydrothermally dealuminated to 2.454 nm unit cell is compared to the same zeolite dealuminated using silicon hexafluoride to 2.452 nm. Both USY faujasites were subsequently treated hydrothermally to further reduce the unit cell size. There is a significant difference in the amount of mesoporosity developed after both the initial and subsequent hydrothermal treatments. 

Tungsten disilicide (WSi2) is refractory and stable with low resistivity. As with other silicides, a common deposition system uses silane as the silicon source with tungsten hexafluoride as follows ... 

See Xenon hexafluoride Silicon dioxide Xenon hexafluoride Caesium nitrate... 

See Silicon Metal hexafluorides See other METAL HALIDES, OXIDANTS... 

Dining the reduction of iridium hexafluoride, osmium hexafluoride or rhenium hexafluoride with silicon to the pentafluorides, the hexafluorides must not be condensed directly onto undiluted silicon powder, or explosions may result [1]. The same is true for molybdenum hexafluoride and uranium hexafluoride [2],... 

Silicon dibromide sulfide, 0281 Silicon tetralluoride, 4352 Sulfinyl bromide, 0274 Sulfinyl chloride, 4096 Sulfinyl fluoride, 4318 Sulfonyl chloride, 4099 Sulfur dibromide, 0280 Sulfur dichloride, 4113 Sulfur hexafluoride, 4374 Sulfur tetralluoride, 4350 Tellurium tetrachloride, 4175... 

SELENIUM TETRACHLORIDE SELENIUM HEXAFLUORIDE SELENIUM OXYCHLORIDE SELENIUM DIOXIDE SILICON... 

Liquid perchloryl fluoride is a typical nonpolar solvent. Most inorganic and organic salts are insoluble in it. Conversely, most covalent, essentially nonpolar substances, boiling within about 50°G of perchloryl fluoride, are completely miscible, e.g., chlorine, boron trifluoride, sulfur hexafluoride, silicon tetrafluoride, phosgene, nitrous oxide, chlorine trifluoride, chlorofluorocarbons, silicon tetrachloride, sulfuryl chloride, dinitrogen tetroxide, and thionyl chloride 106). 

Silicon study group. Vitrectomy with silicone oil or sulfur hexafluoride gas in eyes with severe proliferative vitreoretinopathy Results of a randomized clinical trial. Silicone study report 1, Arch. Ophthalmol. 110 (1992) 770-779. 

In a typical experiment the metal vacuum line and connections to the hexafluoride and HF storage tubes are pumped to at least KT4 torr over several hours. A 30-mL Kel-F reaction tube9 fitted with a metal valve closure is charged with silicon powder and a Teflon-covered stirring bar. The reaction tube is attached to the vacuum system and evacuated. 

Caution. Metal hexafluorides should not be condensed directly onto dry silicon powder. Explosions can occur. 

CVD processing can be used to provide selective deposition on certain areas of a surface. Selective tungsten CVD is used to fill vias or holes selectively through silicon oxide layers in silicon-device technology. In this case, the silicon from the substrate catalyzes the reduction of tungsten hexafluoride, whereas the silicon oxide does not. Selective CVD deposition can also be accomplished using lasers or focused electron beams for local heating. 

The combustion of fluorine in moist hydrogen sulphide or the interaction of fluorine and dry hydrogen sulphide in a glass vessel (the last-named supplying the necessary oxygen) also gives rise to a mixture of sulphuryl fluoride with thionyl fluoride, sulphur hexafluoride and silicon fluoride.3... 

Silicon, higher chlorides of, 42 Silicon tetrabromide, 38, 40 Silicon tetrachloride, 44 Silicopropane, octachloro, 44 Silicotungstic acid, 129 analysis, 131 ether complex, 131 Silver, metallic, 4 Silver chloride, reduction of, 3 Silver cyanamide, 98 Silver residues, purification of, 2 Sodium amalgam, 10 Sodium amide, 74 Sodium azide, purification of, 79 Sodium azidodithiocarbonate, 82 Sodium butoxide, 88 Sodium hypochlorite (solution), 90 Sodium iodate, 168 Sodium metaperiodate, 170 Sodium paraperiodate, chlorine method, 169 persulfate method, 170 Strontium amalgam, 11 Sulfur hexafluoride, 121 Sulfuryl chloride, 114... 

---