Silicone precursor

Silicone Fluids. Sihcone fluids are used in a wide variety of appHcations, including damping fluids, dielectric fluids, poHshes, cosmetic and personal care additives, textile finishes, hydraiflic fluids, paint additives, and heat-transfer oils. Polydimethylsiloxane oils are manufactured by the equihbrium polymerisation of cycHc or linear dimethyl silicone precursors. Trifunctional organosilane end groups, typically trimethylsilyl (M), are used, and the ratio of end group to chain units (D), ie, M/D, controls the ultimate average molecular weight and viscosity (112). Low viscosity fluids,... 

Until now, several methods have been reported for ALD of hafiiium silicate thin films. However, all these methods require the combination of a hafhium precursor with another silicon precursor and a single precursor for hafiiium silicate has been tried recently [3,4]. 

Tetravalent silicon is the only structural feature in all silicon sources in nature, e.g. the silicates and silica even elemental silicon exhibits tetravalency. Tetravalent silicon is considered to be an ana-logon to its group 14 homologue carbon and in fact there are a lot of similarities in the chemistry of both elements. Furthermore, silicon is tetravalent in all industrially used compounds, e.g. silanes, polymers, ceramics, and fumed silica. Also the reactions of subvalent and / or low coordinated silicon compounds normally lead back to tetravalent silicon species. It is therefore not surprising that more than 90% of the relevant literature deals with tetravalent silicon. The following examples illustrate why "ordinary" tetravalent silicon is still an attractive field for research activities Simple and small tetravalent silicon compounds - sometimes very difficult to synthesize - are used by theoreticians and preparative chemists as model compounds for a deeper insight into structural features and the study of the reactivity influenced by different substituents on the silicon center. As an example for industrial applications, the chemical vapor decomposition (CVD) of appropriate silicon precursors to produce thin ceramic coatings on various substrates may be mentioned. 

Figure 5.2. Gel permeation chromatogram (GPC) of the liquid silicon precursor for Si film formation for (a) cyclopentasilane (CPS) and (b) UV-irradiated CPS, both of which were diluted with toluene (1 vol.%) before GPC measurements. The UV-irradiation conditions were 405 nm, 100mW/cm2, and a 10-min irradiation for 1cm3 of CPS. The broad peak around Mw = 2600 corresponds to polysilanes of various molecular weights, as a result of the photo-induced polymerization of CPS. [Reproduced with permission from Ref. 10. Copyright 2006 Nature Publishing Group.]...

These and several other researchers extended the methodology with the aim to widen functionality, using dopant molecules and silicon precursors derivatized with organic moities giving place to a vast class of hybrid organic-inorganic organosilica nanocomposites capable to meet numerous, advanced requirements in fields as diverse as catalysis,... 

Control of the particle size while retaining precise control over the release rate is enabled by compartmentalization of the sol-gel solution into droplets of definite size. This can be achieved by emulsification of the sol-gel solution by mixing it with a solution composed of a surfactant and a non-polar solvent (Figure 2.13). When an active molecule is located in the aqueous droplet of a W/O emulsion, encapsulation occurs as the silicon precursors polymerize to build an oxide cage around the active species. By changing the solvent-surfactant combination, the particle size can be varied from 10 nm to 100 pm as the size of the particles is controlled by the size of the emulsion droplet, which acts as a nano-reactor for the sol-gel reaction (Figure 2.13). 

The properties and applications of five commercially important groups of silanes those containing Si-H (hydride functional silanes), Si-X (halosilanes), Si-C (organosilanes), Si-OSi (siloxanes), and Si-OR (silicon esters) are thoroughly discussed by Arkles.14 As the role of functional siloxanes grows, so does the importance of the hydrosilylation reactions in this field. A broad introduction to hydrosilylation processes as applied to the synthesis of silicone precursors and to the functionalization of siloxanes is provided in the earlier editions of COMC, and,... 

Silicones play a very important role in the coating industry because of the versatility of polymeric silicone precursors and the unique combination of properties silicones can offer. One can discuss silicone coatings within a couple of loosely defined categories ... 

To Ph2SiCl2 (3 g, 12 mmol) in a 50-mL round-bottomed flask equipped with a condenser were added NaBF4 (2.8 g, 26 mmol) and tetraglyme (5 g, 22 mmol). The mixture was refluxed for 0.5-0.75 h. Distillation under vacuum afforded the Ph2SiF2 in near-quantitative yield. Fluorodeehlorinations of other silicon precursors with NaBF4 and other alkali metal salts were similarly carried out. The products were distilled either at atmospheric pressure or under reduced pressure as needed. 

The silicon precursor and N, N-dimethyldodecylamine oxide exhibit different electronic properties under different pH conditions, thus the driving forces and the corresponding sample structure may be different in various pH values. We performed the synthesis process at pH<0, pH=2, pH=7, and pH>10, respectively. The silicon precursor did not condense when pH<0. Figure 2 illustrates the Figure 1. TEM image of calcined LZC... 

Recently, the VLS growth method has been extended beyond the gas-phase reaction to synthesis of Si nanowires in Si-containing solvent (Holmes et al, 2000). In this case 2.5-nm Au nanocrystals were dispersed in supercritical hexane with a silicon precursor (e.g., diphenylsilane) under a pressure of 200-270 bar at 500°C, at which temperature the diphenylsilane decomposes to Si atoms. The Au nanocrystals serve as seeds for the Si nanowire growth, because they form an alloy with Si, which is in equilibrium with pure Si. It is suggested that the Si atoms would dissolve in the Au crystals until the saturation point is reached then they are expelled from the particle to form a nanowire with a diameter similar to the catalyst particle. This method has an advantage over the laser-ablated Si nanowire in that the nanowire diameter can be well controlled by the Au particle size, whereas liquid metal droplets produced by the laser ablation process tend to exhibit a much broader size distribution. With this approach, highly crystalline Si nanowires with diameters ranging from 4 nm to 5 nm have been produced by Holmes et al. (2000). The crystal orientation of these Si nanowires can be controlled by the reaction pressure. 

As can be seen in Figure 1, the silicon precursor is fed to the reaction cell at the side where the y-alumina layer is situated. The oxygen is fed to the other side of the membrane. The membrane is clamped gas-tight in the cell by polymer O-rings. Before each experiment the apparatus was checked for possible leaks by pressure testing. The cell was heated to the reaction temperature at a rate of 2°C/min. 

Process Reaction and its application to the preparation of silicone precursors (6-9), plus a corresponding industrial preparative method for tetraal-kyllead compounds (10), spurred further investigations into the use of direct reactions between solid metals and liquid alkyl halides to synthesize alkylmetal derivatives, generating an extensive literature on this subject (3.4.11). 

A number of reactions and precursors have been used to deposit SiOi from the gas phase. The most common silicon precursors are silane and chlorosilanes, which readily react with a variety of oxidizers above 400°C " . There are two reactions that take place between silane and oxygen gas ... 

Experimentally, there are two growth regimes as shown in Fig. 10.2 for each silicon precursor. 

In the case of in-situ doping during epitaxy, a small amount of dopant gas is introduced into the reactor at the same time as the silicon precursor. The... 

The actual incorporation of dopants in silicon is determined by a factor of segregation Keg. It is given by the concentration of dopants in silicon divided by the ratio of partial pressure of dopant gas (Pgopant) and silicon precursor... 

An ionic 2-chloro-l,3,2-diazaphospholene (72) was prepared from a silicon precursor (73). Since the saturated analogue 74 was covalent, the phosphenium ion 72 is probably stabilised by having an aromatic 6n electron structure. The phosphadiazonium compound 75 with a sterically hindered phenol or aniline gave the phosphenium ions 76 this constitutes a new preparative route to phosphenium ions. A series of phosphenium ions (77), stabilised by two intramolecular dative P-N bonds, has been prepared, and the X-ray crystal structure of one (77, X = H, Y = PFg) determined. ... 

Hunt LP (1990) Silicon precursors their manufacture and properties. In O Mara WC, Herring RB, Hunt LP (eds) Handbook of semiconductor silicon technology. Noyes, Park Ridge, NJ, ppl-33... 

A large number of silicon precursors are commercially available, or can be prepared by well-established routes such as hydrosililation with HSi(OR )3, or HSiCls.P l... 

In summary, we synthesized various types of silica by using a non-ionic surfactant as template in the presence of different platinum salts in the synthetic gel. The salts were found to induce substantial structural and porosity changes in the materials obtained. In fact, they promote the hydrolysis and condensation of the silicon precursor the degree of cross-linking... 

The most common technique used to grow epitaxial SiC is CVD. The standard gas chemistry used is hydrogen-propane-silane, or TG-CsHs-SiEG, respectively. In this chemistry, C3H8 is the carbon growth precursor while SiTC is the silicon precursor. 

The CVD growth of silicate glasses follows that of Si02. with SiH4 and TEOS being the most commonly employed silicon precursors. A summary of common CVD precursor systems for silicate glasses is given in Table 5-6. 

H. Ichikawa, K. Okamura, and T. Seguchi, Oxygen-fiee Ceramic Fibers From Organo-silicon Precursors and E-beam Curing, Proc. Second International Conference on High-temperature Ceramic Matrix Composites, Santa Barbara, CA, USA, 65-74 (1995). 

Fig. 10 Processing pathway for obtaining nanocomposite material. (1) Colloidal dispersion of y-Fe203 nanoparticles in hexane. (2) Initial sol with silicon precursor, water, solvents, and iron oxide NPs at ambient conditions, (i) Expanded sol under supercritical conditions with gel composite particles. (4) Dry composite particles. V volume, P pressure, T temperature...

However, both the tin and the silicon precursors are generally synthesized from the corresponding lithium compounds and therefore these methods have limited apphcabihty. 

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