Pyrolysis-based Techniques

Pyrolysis is the breaking of large, complex molecules into smaller fragments by the application of heat. If the heat energy applied to a molecule is greater than the energy of specific bonds in that molecule, these bonds will dissociate in a predictable, 

A good pyrolysis instrument must be able to heat a sample reproducibly to a preset temperature at a known rate for a specific amount of time. Inability to control any of these variables will result in a pyrogram that cannot be reproduced. 

Inorganic Thermogravimetric Analysis, T Edition, Elsevier, New York, NY, USA, 1953. 

Newkirk and E.L. Simons, Report No 63-RL-3498C, General Electric, 

Friedman, Office of Technical Services PB Report No,145, US Department of Commerce, Washington, DC, USA, 1959, p.l82. 

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Data obtained from a combination of pyrolysis-based techniques with compound specific GC-Combustion-Isotope Ratio-MS (GC-C-IRMS) have provided important insight into the formation of this material. 

Electron spin resonance spectroscopy [26-31] Mass spectrometry Pyrolysis-based techniques... 

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). 

In addition, the decomposition of the carboxyl groups was studied by measuring the carboxylate concentrations in the chars after pyrolysis. The technique to determine the carboxyl group content is outlined in detail elsewhere (11), and is based on the work of Schafer (17). There are three basic steps involved acid washing, exchange with barium acetate and determination of the extent of exchange. 

Elastomeric or rubber-like materials are typically difficult to use with transmission-based techniques however, dependent on the ingredients, they are ideal for ATR-based measurements. Most elastomers conform well with the IRE surface, providing good intimate contact. Elastomers with a high filler content, and in particular with dispersed carbon black, will cause problems because of the absorption characteristics of the carbon. In such cases, either ATR with a high refractive index IRE (such as germanium) or a photoacoustic measurement may be employed. In the event that such an approach is not available, then a destructive method such as pyrolysis can be used (see Section 5). 

As an alternative to wet ehemical routes of analysis, this monograph deals mainly with the direct deformulation of solid polymer/additive compounds. In Chapter 1 in-polymer spectroscopic analysis of additives by means of UV/VIS, FTIR, near-IR, Raman, fluorescence spectroseopy, high-resolution solid-state NMR, ESR, Mossbauer and dielectrie resonance spectroscopy is considered with a wide coverage of experimental data. Chapter 2 deals mainly with thermal extraction (as opposed to solvent extraction) of additives and volatiles from polymerie material by means of (hyphenated) thermal analysis, pyrolysis and thermal desorption techniques. Use and applieations of various laser-based techniques (ablation, spectroscopy, desorption/ionisation and pyrolysis) to polymer/additive analysis are described in Chapter 3 and are critically evaluated. Chapter 4 gives particular emphasis to the determination of additives on polymeric surfaces. The classical methods of... 

In direct insertion techniques, reproducibility is the main obstacle in developing a reliable analytical technique. One of the many variables to take into account is sample shape. A compact sample with minimal surface area is ideal [64]. Direct mass-spectrometric characterisation in the direct insertion probe is not very quantitative, and, even under optimised conditions, mass discrimination in the analysis of polydisperse polymers and specific oligomer discrimination may occur. For nonvolatile additives that do not evaporate up to 350 °C, direct quantitative analysis by thermal desorption is not possible (e.g. Hostanox 03, MW 794). Good quantitation is also prevented by contamination of the ion source by pyrolysis products of the polymeric matrix. For polymer-based calibration standards, the homogeneity of the samples is of great importance. Hyphenated techniques such as LC-ESI-ToFMS and LC-MALDI-ToFMS have been developed for polymer analyses in which the reliable quantitative features of LC are combined with the identification power and structure analysis of MS. 

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... 

In addition to GC/MS, high performance liquid chromatography (HPLC/MS) has been used to analyse natural resins in ancient samples, particularly for paint varnishes containing mastic and dammar resins [34]. A partial limitation of chromatographic techniques is that they do not permit the analysis of the polymeric fraction or insoluble fraction that may be present in the native resins or formed in the course of ageing. Techniques based on the direct introduction of the sample in the mass spectrometer such as direct temperature resolved mass spectrometry (DTMS), direct exposure mass spectrometry (DE-MS) and direct inlet mass spectrometry (DI-MS), and on analytical pyrolysis (Py-GC/MS), have been employed as complementary techniques to obtain preliminary information on the... 

Over the past few years, a large number of experimental approaches have been successfully used as routes to synthesize nanorods or nanowires based on titania, such as combining sol-gel processing with electrophoretic deposition,152 spin-on process,153 sol-gel template method,154-157 metalorganic chemical vapor deposition,158-159 anodic oxidative hydrolysis,160 sonochemical synthesis,161 inverse microemulsion method,162 molten salt-assisted and pyrolysis routes163 and hydrothermal synthesis.163-171 We will discuss more in detail the latter preparation, because the advantage of this technique is that nanorods can be obtained in relatively large amounts. 

Until recently, synthesis of nanostructured carbon materials was usually based on very harsh conditions such as electric arc discharge techniques [1], chemical vapor deposition [2], or catalytic pyrolysis of organic compounds [3]. In addition (excluding activated carbons), only little research has been done to synthesize and recognize the structure of carbon materials based on natural resources. This is somewhat hard to understand, as carbon structure synthesis has been practiced from the beginning of civilization on the base of biomass, with the petrochemical age only being a late deviation. A refined approach towards advanced carbon synthesis based on renewable resources would be significant, as the final products provide an important perspective for modern material systems and devices. 

While the carbon arc method yields products in amounts that are easily characterized, there is a number of caveats of which one must be aware. Since the carbon arc operates at extremely high temperatures (>2000 °C) and emits copious amounts of light, there is the very real possibility of pyrolysis and/or photolysis of both substrate and products. These problems may be minimized by carrying out control experiments in which pyrolysis and photolysis products are identified and excluded. Maximum yields in carbon arc reactions are obtained when carbon and substrate are cocondensed. However, this technique can result in pyrolysis of substrate, which can be avoided by alternately depositing substrate and carbon on the cold reactor walls. Often both methods are employed in order to identify pyrolysis products. Since the carbon arc results in removal of macroscopic pieces of graphite from the rods, it is impossible to measure product yields based on actual carbon evaporated. 

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