Incipient doping

Organic solvent soluble polvelectrolvte polymers and Incipient Doping... 

One piece of evidence which supports the above mechanism is that in order to observe incipient doping, the conversion must be carried out in a very small, closed vessel i.e., in a large or open container, ASF5, PF5,12, etc. escape before they have an opportunity to interact with the "nascent PPV. 

We have also shown that poly(phenylenevinylene) polyelectrolyte precursor polymers can be processed into fibers by a novel ion exchange precipitation. Ion exchange of these polymers can also be achieved in a phase transfer process on cast films. Finally we have shown that a new concept of incipient doping of PPV-type polymers can be realized when the ion exchanged precursor polymers containing the anions PF6 , AsF6", or T, are heated in a closed vessel to the temperatures required for dimethyl suMde elimination. 

A. O. Patil, S. D. D. V. Rughooputh, and F. Wudl, Poly(p-phenylene vinylene) incipient doping in conducting polymers, Synth. Met. 29 E115 (1989). 

Fibers spun by this method may be isotropic or asymmetric, with dense or porous walls, depending on the dope composition. An isotropic porous membrane results from spinning solutions at the point of incipient gelation. The dope mixture comprises a polymer, a solvent, and a nonsolvent, which are spun into an evaporative column. Because of the rapid evaporation of the solvent component, the spinning dope solidifies almost immediately upon emergence from the spinneret in contact with the gas phase. The amount of time between the solution s exit from the spinneret and its entrance into the coagulation bath has been found to be a critical variable. Asymmetric fibers result from an inherently more compatible solvent/nonsolvent composition, ie, a composition containing lower nonsolvent concentrations. The nature of the exterior skin (dense or porous) of the fiber is also controlled by the dope composition. 

Fig. 8. (a) Cross section of cellulose acetate isotropic porous hoUow-fiber dry-jet wet spun at incipient gelation point of dope mixture (b) magnification at... 

It has been shown (, , 2.) that a membrane casting dope is a strongly structurlzed polymer solution, and that the morphology of the membrane surface layer can be correlated to the structure of the casting solution. The latter parameter affects the nature and details of the phase inversion process occuring in the upper part of the cast solution, in an incipient skin. Thus the solution structure is one of the factors responsible for the skin properties, and consequently for the performance of the ultimately formed asymmetric membrane. 

With the sol-gel preparation method (Navio et al., 1996, 1999), however, all doped catalysts yielded lower activities than the untreated Ti02. These authors showed that only those doped catalysts prepared through incipient wetness impregnation and low Fe% produced better results than the untreated Ti02. 

This phenomenon has also been observed for catalysts prepared using an aqueous route (182). Both the iron and cobalt promoters led to an increase in selectivity. The iron-promoted catalyst was characterized by an increase in activity, but the cobalt-promoted catalyst was characterized by a decrease in activity. The decrease in activity of the cobalt-doped catalyst was attributed to the formation of VOPO4 in the final catalyst. The VOPO4 is formed by the oxidation of V0HP04 1 H20 during the introduction of the promoters in the incipient wetness technique. A similar effect was reported for catalysts doped with indium and tetraethy-lorthosilicate (TEOS) (181). The improved performance was observed only with both promoters in the catalyst. It was proposed that the... 

Catapal B y-alumina doped with copper, zinc, or both copper and zinc were used for mechanistic studies. All three samples were prepared by incipient wetness impregnation, with Zn(N03)2 and Cu(N03)2 as precursors, followed by calcination in air at 500 C for 4 hours. 

From these results it may be concluded that only oxidizable metals influence the ignition temperature and that metals forming peroxides are usually effective. The metal itself when in a state of incipient oxidation is the effective part of the organo-metallic dopes that suppress detonation in an engine, and this metallic oxide is the seat of the action on the combustion process. The most effective metals, with the exception of iron and nickel, are molten and vaporizable at the ignition temperatures. 

Addition of foreign cations (doping) was achieved by the method of incipient wetness using an aqueous.solution of the nitrate salt of the cation. A drying step (2A hours at 110°C) and a calcination step (1 hour at 600°C) followed for each preparation. 

Gadolinium-doped ceria (CGO) substrates are prepared from nitrate salt precursors by either coprecipitation or glycine-nitrate combustion techniques. Pt, Rh, orNi is loaded onto the CGO using the incipient wetness technique. Typical weight loadings are 1 wt% or less for Pt and Rh and up to 10... 

A Pt-doped carbon xerogel containing 10 wt% Pt was prepared by an incipient wetness technique [88]. The mean particle size was around 2 nm. The activity of the catalyst for methanol electrooxidation was higher in alkaline than in acid solution. In addition, the Pt surface slowly developed more favorable sites during cycling in alkaline solution. Pt supported on carbon xerogel showed better performance in the methanol electrooxidation than another Pt catalyst supported on Vulcan XC-72R with the same metal content. The large mesoporous surface... 

Aneggi et al investigated various silver-doped ceria (1-10 wt%) catalysts prepared by incipient wetness impregnation. A CeSAg catalyst exhibited the lowest 50 of the different samples tested (Zr5Ag, A15Ag). This was attributed to a different distribution of Ag/AggO over the ceria and to the fact that ceria itself is an active catalyst for soot oxidation. 

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