High silicides

Higher chlorides, Si2Cle to Si6Cl,4 (highly branched - some cyclic) are formed from SiCU plus Si or a silicide or by amine catalysed disproportionations of Si2Cl,5, etc. Partial hydrolysis gives oxide chlorides, e.g. CUSiOSiCla. SiCU is used for preparation of silicones. 

Titanium Silicides. The titanium—silicon system includes Ti Si, Ti Si, TiSi, and TiSi (154). Physical properties are summarized in Table 18. Direct synthesis by heating the elements in vacuo or in a protective atmosphere is possible. In the latter case, it is convenient to use titanium hydride instead of titanium metal. Other preparative methods include high temperature electrolysis of molten salt baths containing titanium dioxide and alkalifluorosiUcate (155) reaction of TiCl, SiCl, and H2 at ca 1150°C, using appropriate reactant quantities for both TiSi and TiSi2 (156) and, for Ti Si, reaction between titanium dioxide and calcium siUcide at ca 1200°C, followed by dissolution of excess lime and calcium siUcate in acetic acid. 

Another problem in the construction of tlrese devices, is that materials which do not play a direct part in the operation of the microchip must be introduced to ensure electrical contact between the elecuonic components, and to reduce the possibility of chemical interactions between the device components. The introduction of such materials usually requires an annealing phase in the construction of die device at a temperature as high as 600 K. As a result it is also most probable, especially in the case of the aluminium-silicon interface, that thin films of oxide exist between the various deposited films. Such a layer will act as a banier to inter-diffusion between the layers, and the transport of atoms from one layer to the next will be less than would be indicated by the chemical potential driving force. At pinholes in the AI2O3 layer, aluminium metal can reduce SiOa at isolated spots, and form the pits into the silicon which were observed in early devices. The introduction of a tlrin layer of platinum silicide between the silicon and aluminium layers reduces the pit formation. However, aluminium has a strong affinity for platinum, and so a layer of clrromium is placed between the silicide and aluminium to reduce the invasive interaction of aluminium. 

Silicides are usually prepared by direct fusion of the elements hut coreduction of Si02 and a metal oxide with C or A1 is sometimes used. Heats of formation are similar to those of borides and carbides but mps arc substantially lower e.g. TiC 3140°, TiBj 2980°, TiSij 1540° and TaC 3800°, TaB2 3100°, TaSi2 1560°C. Few silicides melt as high as 2000-2500°, and above this temperature only SiC is solid (decomp 2700°C). 

The theoretical studies " have been focused on TiSi2. Some attempts, with use of high-symmetry crystal structures, have been made to understand some of the other titanium silicides. This paper deals vith Ti,5Si.3. Because of the crucial interplay between structure and bonding we have studied the proposed stable low-symmetry crystal structure. This will give a better picture of the electronic structure and the bonding properties in this system. An investigation of seven members in the Ti-Si system will be presented in a future publication. ... 

When the coating metal halide is formed in situ, the overall reaction represents the transfer of coating metal from a source where it is at high activity (e.g. the pure metal powder, = 1) to the surface of the substrate where is kept less than 1 by diffusion. The formation of carbides or intermetallic compounds such as aluminides or silicides as part of the coating reaction may provide an additional driving force for the process. 

Silicides are useful compounds characterized by their refractoriness and high electrical conductivity. There are many silicides, since silicon reacts with most metals and often more than one silicide is formed. For instance, there are five known tantalum silicides. 

Deposition temperature from the fluoride is 250-300°C at a pressure of < 2 Torr. Deposition temperature from the chloride is 650-950°C at low pressure. In Reactions (1) and (2)—and in other silicide deposition reactions as well— the silane gas is usually highly diluted with an inert gas such as argon. 

The nozzle of original design was fabricated from a niobium alloy coated with niobium silicide and could not operate above 1320°C. This was replaced by a thin shell of rhenium protected on the inside by a thin layer of iridium. The iridium was deposited first on a disposable mandrel, from iridium acetylacetonate (pentadionate) (see Ch. 6). The rhenium was then deposited over the iridium by hydrogen reduction of the chloride. The mandrel was then chemically removed. Iridium has a high melting point (2410°C) and provides good corrosion protection for the rhenium. The nozzle was tested at 2000°C and survived 400 cycles in a high oxidizer to fuel ratio with no measurable corrosion.O l... 

Triferric tetroxide gives rise to a highly violent detonation when it was heated with calcium silicide combined with aluminium and sodium nitrate. 

This has been used, for instance, to follow the formation of palladium silicide in a silicon wafer for thicknesses up to 6nm [Vanleerdam et al., 1990]. More recently, investigation of the tails in LEIS has been used as a tool for high resolution nondestructive in-depth composition analysis of ultrathin layers [Brongersma et al., 2003] and shallow interfaces [Janssen et al., 2004]. 

A mixture of potassium nitrate (or sodium nitrate) and calcium silicide (60 40) is a readily ignited primer which bums at a very high temperature. It is capable of... 

Excess red phosphorus will bum admixed with barium or calcium sulfates if primed at a high temperature with potassium nitrate-calcimn silicide mixture. 

It is known about the existence of lithium silicide, Li6Si2, which is close to intermetallic compounds, and also that silicon is capable to form with lithium different alloys. We have calculated the theoretical specific capacity of such possible compounds, as well as pure silicon (Table 2). It is possible to explain from the Table 2 the noticeable increase of capacity for graphite electrodes (11%) even at the small content of Si (3wt%). We can suppose that some of such compounds (LixSiy) with high capacity may form... 

The new type of Raney samples can be considered Al-oxy-hydrate and Al-hydroxide supported Al-Ni catalysts containing about 30 w/w% of Ni [9]. With the new process -described by Petro et al. [10] - high Ni distribution can be achieved and the pyrophoric character can be avoided. In sample RNi-212 the Al was substituted Si, forming Ni-silicide. The samples 222B and 222C were calcined for an hour at 120 and 320 °C, respectively, while samples 212 and 222A were dried at 50 °C, without further heating. 

Rotating Disk Atomization (RSR) -60 Standard deviation 1.4-1.6 Ni-superalloys, Al, Be, Ti, Mo, Cu alloys, Steels, Silicide 105-107 3-18 <0.9 Spherical, clean, smooth particles, Narrow size distribution, High EE Relatively low capacity throughput... 

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