Tetraethyl deposition

Bromine is used in the manufacture of many important organic compounds including 1,2-dibromoethane (ethylene dibromide), added to petrol to prevent lead deposition which occurs by decomposition of the anti-knock —lead tetraethyl bromomethane (methyl bromide), a fumigating agent, and several compounds used to reduce flammability of polyester plastics and epoxide resins. Silver(I) bromide is used extensively in the photographic industry... 

A widely used glass is phosphosilicate (PSG), which is used extensively in semiconductor devices as a passivation and planarization coating for silicon wafers. It is deposited by CVD by the reaction of tetraethyl orthosilicate (TEOS) (C2H50)4Si, and trimethylphosphate PO(OCH3)3, in a molecular ratio corresponding to a concentration of 5 to 7% P. Deposition temperature is usually 700°C and pressure is 1 atm. 

The public loved leaded fuel for its pep, not its efficiency. Interest in fuel conservation faded when new oil deposits were discovered. Reassured about lead s dangers, Americans reveled in unprecedented personal mobility and used tetraethyl lead to expand their reliance on automobiles. Surprisingly, Midgley did not think his discovery would increase passenger car ownership. Nevertheless, tetraethyl lead and the engine improvements it permitted helped form America s car-dependent society. Fuel-efficient cars and public transportation were no longer top priorities. 

Organic Lead. Following a single exposure to vapors of tetraalkyl lead compounds (approximately 1 mg/m3 breathed through a mouthpiece, 10-40 breaths of approximately 1 L volume) in four male subjects, 37% and 51% of inhaled tetraethyl and tetramethyl lead, respectively, were initially found in the respiratory tract, but a considerable percentage of these volatile compounds was lost through exhalation (Heard et al. 1979). Approximately 60-80% of the deposited tetraalkyl lead was absorbed by the lungs. 

Inhaled tetraethyl and tetramethyl lead vapors behave as gases in the respiratory tract and, as a result, their pattern and extent of deposition and absorption differ from that of inhaled inorganic lead particles (EPA 1994a Overton et al. 1987 Overton and Miller 1988). These differences result in a higher fractional absorption of inhaled tetraethyl and tetramethyl lead (Heard et al. 1979). 

We need to deposit a silica film on 200 jum wires by reacting tetraethyl siloxane. In the reactor configuration proposed the silane in N2 at a partial pressure of 10 tOIT flows over the wires at... 

The PbTi03 films were grown epitaxially on SrTiOs (001) substrates as described previously [2], Cation precursors were either titanium isopropoxide (tip) or titanium tertbutoxide (ttb), and tetraethyl lead (tel). The oxidant was O2, with N2 carrier gas. Films were typically deposited at 750°C at a total pressure of 10 Torr (P02 = 2.5 Torr). Under appropriate growth conditions, the PbTi03 films replicated the high crystalline quality of the substrates (0.01° typical mosaic). Films thinner than 40 nm remained lattice matched with the SrTiC>3, while the epitaxial strain was mostly relaxed in thicker films. 

S. Yan, H. Maeda, K. Kusakabe, S. Morooka and Y. Akiyama, Hydrogen-Permselective Si02 Membrane Formed in the Pores of Alumina Support Tube by Chemical Vapor Deposition with Tetraethyl Orthosilicate , Ind. Eng. Chem. Res., 33 2096-101 (1994). 

Sacrificial anode — is a piece of metal used as an anode in electrochemical processes where it is intended to be dissolved during the process. In -+ corrosion protection it is a piece of a non-noble metal or metal alloy (e.g., magnesium, aluminum, zinc) attached to the metal to be protected. Because of their relative -+ electrode potentials the latter is established as the -+ cathode und thus immune to corrosion. In -+ electroplating the metal used as anode may serve as a source for replenishing the electrolyte which is consumed by cathodic deposition. The sodium-lead alloy anode used in the electrochemical production of tetraethyl lead may also be considered as a sacrificial anode. 

Lastly, if the SiOj deposition is highly conformal, the regions between closely spaced metal lines may be filled without the production of gaps. If the film thickness is equal to half the space width, the space will fill completely and the comers of the film will join at the top of the space, thereby leaving a nearly planar film. Examples of CVD SiOj processes capable of the required high degree of conformality are ECR deposition and tetraethyl orthosilicate (TEOS) plasma CVD-enhanced. While this approach yields local planarization above closely spaced lines, the wide spaces between metal lines are not filled, and thus a sharp step is experienced at the edge of such spaces. Therefore, this approach is often coupled with SOG or resist etch-back processes or CMP.< >... 

Most of the bromine produced is converted into ethylene dibromide, C2H4Bro, which is an important constituent of ethyl gas, together with tetraethyl lead, (CoH-)4pb. Tetraethyl lead has valuable anti-knock properties, but its continued use would cause damage to a motor through the deposition of metallic lead, unless some way were found to eliminate this deposit. The ethylene dibromide that is added to the gasoline provides bromine on combustion, which combines with the lead, permitting its elimination as lead bromide, PSBro. 

In addition to the tetraethyl or tetramethyl lead, both types of antiknock fluids also contained 1,2-dichloroethane and 1,2-dibromoethane (ca. 35% by weight) to react with the lead released on combustion to form lead bromide and lead chloride. These lead halides are volatile at the cylinder combustion temperatures of 800-900°C, and leave the combustion chamber with the exhaust, which prevented the buildup of lead deposits. This was also the final step in the chain of events occurring with the alkylated lead antiknock compounds, which contributed to the widespread dispersal of lead compounds to the air and soil wherever gasoline powered vehicles operated. For this reason, and the toxic exposures during refueling, the alkylated lead addition rate was reduced to not more than 0.5 g of contained lead per U.S. gallon by 1980, even for leaded gasolines [29], and was phased out in the U.S. and Canada by 1985. 

The first example refers to the creation of functional groups on the fillef s surface during controlled synthesis of the filler. Silica-gel, prepared from tetraethyl orthosilicate under acidic conditions, has OH groups on its surface. A similar synthesis under basic conditions deposits alkoxy groups (OCH2CH3) due to an incomplete hydrolysis of the substrate. This simple example shows the numerous... 

A somewhat similar theory10 postulates the formation of colloidal lead by the decomposition of lead tetraethyl, which deposits on sharp points, edges, and projections in the cylinder which would otherwise aid reaction to an extent that a detonation wave would result. The theory fails to explain the action of organic amines, of di- and tetravalent. selenium, of the colloidal metal sols, and fails to account for the immediate recurrence of knocking when the antiknock dope is discontinued in the gasoline feed. However, tubes coated with lead oxide have been found to reduce the oxidation of hexane more than lead tetraethyl vapors.1158 On the basis of this finding the hypothesis was advanced that oxidation occurs to some extent prior to compression and at the first contact of the gaseous mixture with the hot walls, aud that in the presence of the lead... 

Silanation of zeolites through chemical vapour deposition of tetraethyl orthosilicate has been proved to be a very convenient and useful laboratory technique to modily zeolite characteristics in order to make it highly selective for para-dialkyl benzenes specially with... 

Several methods have been reported to deactivate the catalytic activity of the external surfaces of zeolites. Bhat et al. have modified the catalytic behaviour of ZSM-5 by chemical vapour deposition (CVD) of tetraethyl orthosilicate (TEOS).18 The CVD technique does not affect the channel size or acidity of the zeolite but deactivates the external surfaces by coating them with an inert layer of silica. As a result, the shape selectivity of the zeolite is greatly enhanced. 

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