Pyrolysis methods

The most important nanomaterial synthesis methods include nanolithography techniques, template-directed syntheses, vapor-phase methods, vapor-liquid-solid (VLS) methods, solution-liquid-solid (SLS) approaches, sol-gel processes, micelle, vapor deposition, solvothermal methods, and pyrolysis methods [1, 2]. For many of these procedures, the control of size and shape, the flexibility in the materials that can be synthesized, and the potential for scaling up, are the main limitations. In general, the understanding of the growth mechanism of any as-... 

After the first unsuccessful attempts to record a matrix IR spectrum of the methyl radical, reliable data were obtained by the use of the vacuum pyrolysis method. IR spectra of the radicals CH3 and CD3 frozen in neon matrices were measured among the products of dissociation of CH3I, (CH3)2Hg and CD3I (Snelson, 1970a). The spectra contained three absorptions at 3162 (1 3), 1396 V2) and 617 cm (I l) belonging to the radical CH3 and three bands 2381, 1026 and 463 cm assigned to the radical CD3. Normal coordinate analysis of these intermediates was performed and a valence force field calculated. In accordance with the calculations, methyl radical is a planar species having symmetry >31,. 

Pyrolysis method involves thermal decomposition of suitable precursors to produce free radicals. Pyrolysis sources based on continuous molecular beam nozzles are well developed (for example, methyl6 8 and benzyl9). Recently, Chen and co-workers have pioneered a flash pyrolysis/supersonic jet technique to produce free radical beams (Fig. I).10 In this radical... 

The use of HMDS as a derivatization reagent in the analysis of triterpenoid resins has been less explored. The TMS derivatives of triterpenoids bearing hydroxyl groups [a-amyrine, p-amyrine and hop-22(29)-en-3p-ol] have been identified in the triterpenic fraction of Burseraceae resins, thus demonstrating that HMDS combined with Py-GC/MS is effective in the derivatization of triterpenoid compounds [59]. However, the range of structures that can be fully derivatized and detected must be extended and, in order to get comprehensive results comparable with those coming from the well assessed off-line GC/MS procedures, general improvements in the on-line trimethylsilylation-pyrolysis method are needed. 

Tegelaar E, deLeeuw J, Largeau C, Derenne S, Schulten H, Muller R, Boon J, Nip M, Sprenkels J (1989) Scope and limitations of several pyrolysis methods in the structural elucidation of a macromolecular plant constituent in the leaf cuticle of Agave americana L. J Anal Appl Pyrolysis 15 29-54... 

Shpilrain, E., Shterenberg, V., and Zaichenko, V., Comparative analysis of different natural gas pyrolysis methods, Int.. Hydrogen Energ., 24, 613,1999. 

Films at NASA GRC were deposited using homemade spray or aerosol-assisted chemical vapor deposition (AACVD) reactors to exploit the lower deposition temperature enabled by the simpler decomposition chemistry for the SSPs.6 9 AACVD is a simple and inexpensive process that offers the advantage of a uniform, large-area deposition, just like metal organic CVD (MOCVD), while also offering the low-temperature solution reservoir typical of spray pyrolysis methods. 

Hsu CS and Hwang BH. Microstructure and properties of the La06Sr04Co02Fe08O3 cathodes prepared by electrostatic-assisted ultrasonic spray pyrolysis method. J. Electrochem. Soc. 2006 153 A1478-A1483. 

The present procedure uses sodium methoxide in methanol for generation of the tosylhydrazone salt. This procedure gives the highest reported yield and, unlike other procedures, also gives pure diazo compounds free from solvents. This vacuum pyrolysis method appears applicable to the formation of relatively volatile aryldiazomethanes from aromatic aldehydes. Table I gives yields of diazo compounds produced by this vacuum pyrolysis method. The yields have not been optimized. The relatively volatile diazo esters, ethyl a-... 

The major limitation of the vacuum pyrolysis method appears to be thermal decomposition of less volatile diazo compounds during the pyrolysis. The vacuum pyrolysis method was unsuccessful for the preparation of 1-naphthyl diazomethane and 3,5-dichlorophenyldiazomethane. However, such diazo compounds could be prepared from the corresponding tosylhydrazone salts by pyrolysi s in ethylene glycol and extraction of the aryldiazomethane into... 

A variation of the method utilizes a laser as the heat source.52,53 This nonequilibrium technique involves fast growth and rapid heating/cooling rates (100 000 K s-1) in the reaction zone. Ochoa et al. (chapter 27), provide a synopsis of the laser pyrolysis method and describe an Fe3C product used for catalysis. 

La0 2Sro8Feo55Tio 4503 8 (LSFTO) powder, synthesized by using the spray pyrolysis method, was obtained from Praxair Specialty Ceramics (Woodinville, WA). The powder was preheated at 1250°C for 10 h in air with a 3°C/min ramp rate. The preheated powder was ground with ethanol in a mortar for more than 30 min. After drying to remove the ethanol, the powder was pressed into a cylindrical shape at 5000 psi with a 1 in. diam die. Dense ceramic disks were obtained by sintering in air at 1300°C for 20 h and 1400°C for 10 h. The sintered disks had a density of 90.3% of the theoretical den-... 

Analytical pyrolysis is defined as the characterization of a material or a chemical process by the instrumental analysis of its pyrolysis products (Ericsson and Lattimer, 1989). The most important analytical pyrolysis methods widely applied to environmental samples are Curie-point (flash) pyrolysis combined with electron impact (El) ionization gas chromatography/mass spectrometry (Cp Py-GC/MS) and pyrolysis-field ionization mass spectrometry (Py-FIMS). In contrast to the fragmenting El ionization, soft ionization methods, such as field ionization (FI) and field desorption (FD) each in combination with MS, result in the formation of molecule ions either without, or with only very low, fragmentation (Lehmann and Schulten, 1976 Schulten, 1987 Schulten and Leinweber, 1996 Schulten et al., 1998). The molecule ions are potentially similar to the original sample, which makes these methods particularly suitable to the investigation of complex environmental samples of unknown composition. 

Boon, J. J. Tracing the origin of chemical fossils in microbial mats Biogeochemical investigations of Solar Lake cyanobacterial mats using analytical pyrolysis methods, in Microbial mats Stromatolites (eds. Cohen, Y., et al.) p. 318, New York, Alan R. Liss Inc. 

A metallurgist should be consulted regarding both the freezing and the pyrolysis methods, as the reinforcing may pass through phase-change temperatures that may change the properties of the metal. 

The 50% yield of H2FeRu3(CO)13 from Eq. (33) constitutes a significant improvement over previous pyrolysis methods (101, 161). These particular reactions can be scaled up, to produce several grams of the clusters in a single reaction, and consequently these mixed-metal clusters are readily available for reactivity studies. Clusters that contain three differ-... 

N. R. Ayyangar, S. Biswas, and A. Tambe, Separation of opium alkaloids by TLC combined with flame ionization detection using the peak pyrolysis method, J. Chromatogr., 547 538 (1991). 

The attempted synthesis of [njcyclophenacenes has also been reported. Kuwata-ni and coworkers reported the synthesis of a pentabenzo[20]annulene, as a possible precursor to [10]cyclophenacene (Scheme 2.3) [16]. Light-induced electrocycli-zation of the precursor was unsuccessful because of isomerization of the (Z)-olefin into the (E)-olefin, which undergoes an undesirable transannular reaction [17]. St. Martin and Scott tried to synthesize [12]cyclophenacene, but attempts at the macrocyclic oligomerization of substituted naphthalene and phenanthrene building blocks by flash vacuum pyrolysis method were unsuccessful [18]. 

As has been seen, competitive analytical systems correlating thermal and chemical behaviour are TG-MS, TG-FTIR, TG-GC, TG-GC-MS, etc. This list of techniques may easily be extended with various pyrolysis methods. 

Several excellent reviews1-4 give an account of most of the works on pyrolysis of organic halides described in the chemical literature. For details of experimental pyrolysis methods used for kinetic determinations, the above-mentioned reviews and the original papers may conveniently be consulted. 

An IR laser pyrolysis method was developed for the determination of Arrhenius parameters for unimolecular elimination of chloroalkanes97. This technique was reported to be a clean, efficient method for the measurement of high-temperature homogeneous gas-phase reaction rates. A pulse of C02 laser radiation was used to excite multiphoton SiF4... 

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