Pyrolysis, laser

In both cases, GC fingerprint libraries must be built before quantitative analysis can be routinely carried out. In analysis of QTLC by laser pyrolysis scanning (LPS), the TLC plates are placed in a chamber after development, and were irradiated with an IR laser to produce a high temperature at the location of the spot. The analyte is swept by a carrier gas to a GC, and detected with FID or ECD. The technique combines the separation power of TLC and the detection modes of GC [846]. 

Our data can be used to estimate the effective temperatures reached in each site through comparative rate thermometry, a technique developed for similar use in shock tube chemistry (32). Using the sonochemical kinetic data in combination with the activation parameters recently determined by high temperature gas phase laser pyrolysis (33), the effective temperature of each site can then be calculated (8),(34) the gas phase reaction zone effective temperature is 5200 650°K, and the liquid phase effective temperature is 1900°K. Using a simple thermal conduction model, the liquid reaction zone is estimated to be 200 nm thick and to have a lifetime of less than 2 usee, as shown in Figure 3. 

In a review by Gonsalves el al. (2000), techniques for the fabrication of nano-structured materials are outlined. Synthesis from corresponding organo-metal precursors of nano-structured metals (Fe, Co, Ni) and alloys (Fe-Co, Pt-Pd, and special steels) are discussed and various methods considered such as thermal decomposition, ultrasonic irradiation, chemical vapour deposition, laser pyrolysis and reduction. 

The various methods of preparation employed to prepare nanoscale clusters include evaporation in inert-gas atmosphere, laser pyrolysis, sputtering techniques, mechanical grinding, plasma techniques and chemical methods (Hadjipanyas Siegel, 1994). In Table 3.5, we list typical materials prepared by inert-gas evaporation, sputtering and chemical methods. Nanoparticles of oxide materials can be prepared by the oxidation of fine metal particles, by spray techniques, by precipitation methods (involving the adjustment of reaction conditions, pH etc) or by the sol-gel method. Nanomaterials based on carbon nanotubes (see Chapter 1) have been prepared. For example, nanorods of metal carbides can be made by the reaction of volatile oxides or halides with the nanotubes (Dai et al., 1995). 

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. 

Figure 19.6 XRD results for iron carbide catalyst synthesized by laser pyrolysis at various times of the Fischer-Tropsch Synthesis (1-Fe304, 2-x-Fe5C2, 3-e -Fe2 2C).

Figure 27.1 (a) C02 Laser Pyrolysis System, (b) Detail of the gas nozzle, R = gas mixture of reactant gases Ig = coaxial flow of inert gas, usually argon. 

The catalytic activity for Fischer-Tropsch synthesis of the Fe-carbides (Fe2C and Fe7C3) produced by laser pyrolysis has been evaluated and compared to that of a precipitated iron oxide catalyst. Details of the results of these studies are the subject of chapter 19 of this book.35... 

Figure 19.2 Synthesis gas conversion as a function of time for the iron carbide catalyst synthesized by laser pyrolysis (weight = 12.0 g, Sg = 70 m2 g ). O, CO , H2 O, CO +...

It was found that an iron carbide catalyst produced by laser pyrolysis and a commercially available ultrafine iron oxide catalyst are not as active for FTS as a precipitated iron catalyst. Operating under industrial conditions, it was found that the unpromoted precipitated catalyst had a hydrocarbon productivity 93% of that reported by Kolbel while the novel catalysts were far below Kolbel s benchmark. It was found, however, that at similar CO conversion, the iron carbide catalyst had a higher hydrocarbon production rate and had a better selectivity for C5+ hydrocarbons. 

Exposure to synthesis conditions caused all three catalysts to oxidize to Fe304. It is interesting that even though each catalyst ultimately transformed to Fe304, they each had different activity and selectivity. This implies that the active phase is on the surface of the. catalyst and not in the bulk. The catalyst prepared by laser pyrolysis appeared by XRD to be a... 

C02 laser pyrolysis of reactant gases has been used to produce a wide variety of dispersed, single crystal nanoparticles (average size 2 to 20 nm). This chapter discusses the production of nitrides (oxynitrides) and carbides (oxycarbides) of Group 6B elements (Mo and W) and Fe by this technique. The emphasis is on the characterization of the atomic order in the particle and the chemical state of the particle surface. The catalytic properties of these particles for coal liquefaction and heteroatom removal from model compounds is also addressed briefly. 

In contrast with the Fe system, only one crystallographic phase has so far been produced by laser pyrolysis from Group 6 (Mo and W) carbonyls or chlorides. A variety of experimental conditions have been found to lead to fee Mo2NtQy, Mo2CAOv and W2Nj.Oy phase. However, an amorphous phase is obtained in the case of WCA (Table 27.1).6 BET surface areas measured for the Mo nitride and carbide systems are in the range of 50-80 m2 g-1. 

Laser pyrolysis has been shown to produce a wide variety of crystalline transition metal nitride and carbide nanoparticles with diameters as small as 2 nm. The nanopowders are in many cases monophasic and single crystalline. By varying the reaction conditions it is possible to control the particle diameter, and in some cases, the crystalline phase produced. Improvements in the synthesis are needed to control surface oxidation. 

D. Price, F. Gao, GJ. Milnes, B. Ehng, C.I. Lindsay, and T.P. McGrail, Laser pyrolysis/time-of-fhght mass spectrometry studies pertinent to the behavior of flame-retarded polymers in real fire situations. Polym. Degrad. Stab., 64, 403 110 (1999). 

J.R. Ebdon, D. Price, B.J. Hunt, P. Joseph, F. Gao, G.J. Milnes, and K.L. Cunhffe, Flame retardance in some polystyrenes and poly(methyl methacrylate)s with covalently bound phosphorus-containing groups Initial screening experiments and some laser pyrolysis mechanistic studies. Polym. Degrad. Stab., 69, 267-277 (2000). 

Lum, R. M. Antimony oxide-PVC synergism Laser pyrolysis studies of the interaction mechanism, Journal of Polymer Science Polymer Chemistry Edition, 1977, 15(2), 489-497. 

The use of phosphorus-based flame retardants in combination with other, better established, flame retardants is most effective in situations in which the combination proves synergistic. However, as yet our understanding of such synergistic effects is far from complete and more fundamental work is required in this area Work in which the gaseous and solid products of combustion, with and without the presence of flame retardants, are carefully analyzed. Such analyses can now be undertaken more readily than in the past, owing to the relatively recent development of techniques such as gas-phase FT-infrared spectroscopy and laser-pyrolysis time-of-flight mass spectrometry for the identification of volatiles, and solid-state NMR spectroscopy and x-ray photoelectron spectroscopy for the analysis of chars. 

Composites of 5 m/m% clay content were prepared in EVA copolymer matrix in a Brabender plastograph. In model studies, laser pyrolysis (LP) has been applied, using a C02 laser, for modeling the effect of fire, as described recently [37,38], The method was established by the basic work carried out by Price et al. [39], The effect of MMT of Fe-enriched surface layer (MMT-Fe) on the amount and composition of the evolved gas, compared to pristine EVA, can be seen in Figure 13.6. 

Bodzay, B., Marosfoi, B. B., Igricz, T., Bocz, K., and Marosi, G. 2009. Polymer degradation studies using Laser pyrolysis-FTIR microanalysis. Journal of Analytical and Applied Pyrolysis 85 313-320. 

Marosfoi, B. B., Marosi, G., Szabo, A., Vajna, B., and Szep, A. 2007. Laser pyrolysis microspectros-copy for modelling fire-induced degradation of ethylene-vinyl acetate systems. Polymer Degradation and Stability 92 2231-2238. 

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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