Doped flame

Modem thermionic ionization detectors evolved out of earlier studies of alkali-metal-doped flame ionization detectors [253]. Adding an alkali metal salt to a flame enhanced the response of the detector to compounds containing certain elements, such as N, P, S, B, as well as some metals (e.g. Sb, As, Sn, Pb). In its early versions, however, the detector response was unreliable and critically dependent on experimental parameters. Recent studies involving the continuous introduction of alkali metal salt solutions or aerosols into the flame demonstrated more reliable performance but have not been taken up [268,269]. 

To test the reaction mechanism pure ammonia-oxygen-diluent flames were studied under a wide range of stoichiometries and dilutions. Peterson and Laurendeau(23) had previously studied NH3 doped flames which elucidate much of the NHi oxidation chemistry. The present experiments probe the same reactions and also reactions between nitrogeneous species. Flame speeds were first considered in order to establish a subset of literature reaction rates which would describe this major flame feature. Comparison of the other flame features confirm that the flame speed is a good test bed for the reaction mechanism. 

Padley and Sugden noted that, in sodium-doped flames burning at low temperatures where there is expected to be a great excess of hydrogen atoms near the reaction zone, there was an intense emission from the Na D lines at the reaction zone, but that the main body of the flame only developed the characteristic golden yellow some distance downstream. They ascribed this to the chemiluminescent excitation of sodium by the recombination process... 

Hybrid Phosphorus- and Phosphorus/Nitrogen-Doped Flame Retardant Silica Coatings... 

These reactions are involved in the catalytic recombination cycles of H atoms with the formation of Hz. It is these reactions that are responsible for the rise in the inhibition effectiveness with increasing of ( ). Under the catalytic recombination responsible for scavenging of radicals in OPC-doped flames, all the authors meant reactions involving phosphorus oxides and acids (PO, PO2, HOPO, and HOPO2). It was assumed that organophosphorus combustion intermediates play a negligible role in the inhibition processes. However, in these specific flames reactions of OPCs with active species are of importance. 

Its conductivity increases slightly with exposure to light. It can be doped with silver, copper, gold, tin, or other elements. In air, tellurium burns with a greenish-blue flames, forming the dioxide. Molten tellurium corrodes iron, copper, and stainless steel. 

Alloy Rayons. It is possible to produce a wide variety of different effects by adding materials to the viscose dope. The resulting fibers become mixtures or aUoys of ceUulose and the other material. The two most important types of aUoy arise when superabsorbent or flame retardant fibers are made. 

Incorporation of Flame Retardants in Fiber. Flame retardants suitable for cotton are also suitable for rayon. A much better product is obtained by incorporating flame retardants in the viscose dope before fiber formation. The principal classes of flame retardants used in viscose dope are tabulated aimuaHy (111). 

Inside" processes—such as modified chemical vapor deposition (MCVD) and plasma chemical vapor deposition (PCVD)—deposit doped silica on the interior surface of a fused silica tube. In MCVD, the oxidation of the halide reactants is initiated by a flame that heats the outside of the tube (Figure 4.8). In PCVD, the reaction is initiated by a microwave plasma. More than a hundred different layers with different refractive indexes (a function of glass composition) may be deposited by either process before the tube is collapsed to form a glass rod. 

Mole fraction profiles of C3H3 in a series of fuel-rich propene flames (C/O = 0.5) doped with ethanol, measured by EI-MBMS (left) and VUV-PI-MBMS (right). The inset shows the effect of ethanol addition on the peak mole fraction, normalized to the value in the undoped flame r, mole fraction, h. height. 

Rahinov, I., Goldman, A., and Cheskis, S., Absorption spectroscopy diagnostics of amidogen in ammonia-doped methane/air flames. Combust. Flame, 145, 105, 2006. 

Active heterogeneous catalysts have been obtained. Examples include titania-, vanadia-, silica-, and ceria-based catalysts. A survey of catalytic materials prepared in flames can be found in [20]. Recent advances include nanocrystalline Ti02 [24], one-step synthesis of noble metal Ti02 [25], Ru-doped cobalt-zirconia [26], vanadia-titania [27], Rh-Al203 for chemoselective hydrogenations [28], and alumina-supported noble metal particles via high-throughput experimentation [29]. 

Mention has already been made of the application of alkoxycyclophos-phazenes, [NP(OR)2] , as flame retardants in rayon. Although the methoxy-derivatives, with their high phosphorus content, were expected to be most efficient in this respect, their water solubility proved a major shortcoming. However, the n-propoxy series, [NP(OPr )2] ( mainly 3—6), were found to impart excellent flame resistance and were well retained by rayon. The cyclophosphazene alkoxides were obtained by the addition of sodium-n-propoxide to the chloride homologues, (NPCl2)n, and were added to the viscose dope before the rayon was spun. The flame resistance imparted by various amino- and thioalkoxy-derivatives was also tested, but found to be inferior to the results obtained with alkoxy-deriva-tives. Several patent applications have resulted from work on this topic. ... 

Used industrially as a fumigant, doping agent for semiconductors, and intermediate for preparation of some flame retardants. 

Polycrystalline oxide materials, both undoped and doped, have been extensively examined for use as photoanodes. Ti02 electrodes have been prepared by thermal oxidation of a Ti plate in an electric furnace in air at 300-800°C (15-60 min) and in a flame at 1300°C (20 min) [27-30]. XRD analysis of thermally oxidized samples indicates the formation of metallic sub-oxide interstitial compounds, i.e. TiOo+x (x < 0.33) or Ti20i y (0 < y < 0.33) and Ti30 together with rutile Ti02 [27]. The characteristic reflection of metallic titanium decreases in intensity after prolonged oxidation (60 min) at 800° C indicating the presence of a fairly thick oxide layer (10-15 pm). Oxidation at 900°C leads to poor adhesion of the oxide film... 

A photoanode comprised of flame oxidized carbon doped n-Ti02 films have been reported to perform water splitting with high photoconversion efficiencies [65]. While chemically modified n-Ti02 can be prepared by the controlled combustion of Ti metal in a natural gas flame the authors, in investigating this technique [66], have found reproducibility to be a challenge. Various authors [67,68,69] have discussed in considerable depth issues surrounding the stated photoconversion efficiencies of [65]. 

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