Silanes processes

Feasibility of the Silane Process for Producing Semiconductor Grade Silicon,]e.. Propulsion Laboratory Contract 954334, June 1979. 

Vitreous silica produced by this route contains small amounts of impurities such as Fe, Cr, A1 and Ca. To achieve metal ion impurities < 10 % the synthetic hydrolysed silane process is used. Organic silica compounds or SiCl4 are hydrolysed in a flame to produce fine molten droplets of SiOj which is deposited on a cold base. 

Increasing the hydrophobic nature of the resin should decrease the water sorption and the resulting undermining of the mechanical properties [195,215,216]. The solubility of these systems is extremely small ( < 0.01 mg/cm2 in a 1 mm thick sample) [204], but some of the water sorption and solubility problems could be attributed to variations in the silanation process [217, 218] and to the different solubilities of the quartz and barium-silica glass [219-220],... 

For the purpose of this illustrative model, a particularly simple reaction mechanism is used. However, while not the complete mechanism used in practice, it captures the essential features of a silane process. Moreover it illustrates some of the competitive physical processes that characterize many CVD processes. The gas-phase reaction mechanism consists of a single, irreversible, decomposition reaction... 

The silanization process has also been employed to permit tailoring, for various applications, surfaces such as kaolin clays, Wollastonite, talc, and sodium aluminum silicate with amino, epoxy, mercapto, methacryloxy and vinyl groups. 

Figure 9. Contact angle vs. the number of prime cycles for an SVG track silane process at 1 atm.

Chemical modification (<chemical bonding). An electroactive species is immobilized on the electrode surface by chemical reaction. Normally the fact that the electrode is covered by hydroxyl groups owing to the oxygen in the atmosphere is used. For example, the silanization process is... 

Figure 7, Schematic of a bilayer poly silane process for the production of high-resolution images using O 2-RIE techniques for image transfer.

Typically, this reaction is carried out at atmospheric pressure in a cold-wall CVD system. The growth rate by the silane process is rather high, usually 8-17 A/s. 

In an ideal surface structure, one out of every two silicon atoms has a silanol group which can be silanized by either mono-, di- or trichlorosilane. If the surface of the silica matrix is completely silanized by the bonded organic phase, the organic phase can prevent the corrosion of the silica gel by acid or basic solutions. If the silanol groups are not completely silanized by the first reaction, a second silanization process, known as end-capping, is required. The carbon content did not significantly increase in this endcapping process. 

The synthesis of the new MSSA is depicted in Scheme 1.2. The first step was the activation of the silica gel surface with HCI, then an excess of dimethylchlorosilane (DMCS) was used to accomplish the silanization process. Conversion of Si-Cl to Si-OH occurred when water was added to the solid product after 10 min of stirring at room temperature. After completion of all reactions, samples were dried in a nitrogen stream at 120°C for 24 h. Finally, the silanol groups were allowed to react with chlorosulfonic acid to yield the desired MSSA, without any side products as HCI gas evolved from the reaction vessel immediately. 

The rubber chemist has recognized and reacted to the growing trend to employ silica as reinforcing filler for rubber with development of multiple silane ester coupling agents and alkyl silane process aids for improved processability and performance. 

FIGURE 1.18. Flow diagram of the silanization process (courtesy J. B. Brzoska). 

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