Organic precursor

The proposed mechanism by which chlorinated dioxins and furans form has shifted from one of incomplete destmction of the waste to one of low temperature, downstream formation on fly ash particles (33). Two mechanisms are proposed, a de novo synthesis, in which PCDD and PCDF are formed from organic carbon sources and Cl in the presence of metal catalysts, and a more direct synthesis from chlorinated organic precursors, again involving heterogeneous catalysis. Bench-scale tests suggest that the optimum temperature for PCDD and PCDF formation in the presence of fly ash is roughly 300°C. 

Caprolactam [105-60-2] (2-oxohexamethyleiiiiriiQe, liexaliydro-2J -a2epin-2-one) is one of the most widely used chemical intermediates. However, almost all of the aimual production of 3.0 x 10 t is consumed as the monomer for nylon-6 fibers and plastics (see Fibers survey Polyamides, plastics). Cyclohexanone, which is the most common organic precursor of caprolactam, is made from benzene by either phenol hydrogenation or cyclohexane oxidation (see Cyclohexanoland cyclohexanone). Reaction with ammonia-derived hydroxjlamine forms cyclohexanone oxime, which undergoes molecular rearrangement to the seven-membered ring S-caprolactam. 

Solution Deposition of Thin Films. Chemical methods of preparation may also be used for the fabrication of ceramic thin films (qv). MetaHo-organic precursors, notably metal alkoxides (see Alkoxides, metal) and metal carboxylates, are most frequently used for film preparation by sol-gel or metallo-organic decomposition (MOD) solution deposition processes (see Sol-GEL technology). These methods involve dissolution of the precursors in a mutual solvent control of solution characteristics such as viscosity and concentration, film deposition by spin-casting or dip-coating, and heat treatment to remove volatile organic species and induce crystaHhation of the as-deposited amorphous film into the desired stmcture. 

There are many applications for diamonds and related materials, e.g., diamondlike carbon films, and there are potential applications for Fullerenes and carbon nanotubes that have not yet been realised. However, the great majority of engineering carbons, including most of those described in this book, have graphitic microstructures or disordered graphitic microstructures. Also, most engineering carbon materials are derived firom organic precursors by heat-treatment in inert atmospheres (carbonisation). A selection of technically-... 

Essentially, carbonization entails the heating of organic precursors in the absence of air. In so doing, a solid carbon residue along with gaseous and volatile hydrocarbons is created. Bituminous coals are used to make metallurgical-grade coke while wood and other similar substances make charcoal. The condensed volatile material can be further refined to yield chermcals, pitches, or other useful commodities. 

Hydrogen-Containing Carbons from Pyrolyzcd Organic Precursors... 

Hydrogen-Containing Carbons from Pyrolyzed Organic Precursors 358... 

Sol-gel primers use inorganic or metal-organic precursors (generally aluminum, silicon or titanium alkoxides) whose chemistry is closely related to the silane coupling agents discussed previously. These precursors are dissolved in alcohol, then hydrolyzed by the addition of water ... 

Even acetophenone reacts with the magnesium compound 17 (R1 = R2 = H) to yield the w-diastereomer 18 with 90 % de 22 24. The structure of the metal-organic precursor and, as well, of the major product was determined by an X-ray crystal structure analysis23. 

Thermal activation which typically takes place at high temperatures, i.e., >900°C, although the temperature can also be lowered considerably if metallo-organic precursors are used (MOCVD). 

Most metals can be deposited by MOCVD and in some cases the process is an important industrial operation. The metals most readily deposited by MOCVD are the non-transition metals. The following is a summary of the metallo-organic precursors and deposition condition presently used in development or production. 

Hoffman, D. M., et al., Plasma-Enhanced CVD of Silicon Nitride Films from a Metallo-Organic Precursor, J. Mater. Res., 9(12) 3019-3021 (1994)... 

Deposition at low temperature (200 00°C) is possible by plasma-CVD from the reaction of ammonia and a metallo-organic precursor tetrakis(dimethylamido)silicon, Si(NMe2)4. The films are essentially featureless. 

The reactive crystallization has some peculiar characteristics like insoluble product, initiation of reaction by change in pH and conductivity. In this case the solution becomes saturated and eventually supersaturated with respect to reactant nucleation [30], The ultrasound assisted decomposition precursors includes dissolving metal organic precursors in organic solvents/water with the assistance of surfactants leads to monodisperse and reduced metal/metal oxide nanoparticles. 

For some elements, there are a variety of possible precursors, sulfur for instance (Figure 11). Use of metal-organic precursors, used in MOMBE or MOVPE, are possible if they are soluble in water, or a nonaqueous solvent is used. Mixed aqueous-organic solvents could improve solubility. Overall, there would be an increased probability of carbon contamination, however. One of the benefits of using inorganic salts in aqueous solutions is that the number of constituents is limited, and thus the... 

---