Induction Heating Curie-Point Pyrolysis

Curie-point pyrolysis employs high-frequency (HF) inductive heating of a ferromagnetic wire (d 1 mm). A diagram of a Curie-point pyrolyzer designed for Py-GC is shown in Fig. 4.7.2. 

Several Curie-point pyrolyzers are obtainable from Fischer (Germany), Scientific Glass Engineering (Australia), Horizon Instruments (England) and Japan Analytical Industries. In addition, laboratory-constructed models have been described in the literature (Saiz-Jimenez and De Leeuw 1984, 1986, Boon et al. 1987, Genuit et al. 1987, Pouwels and Boon 1987, Saiz-Jimenez et al. 1987). 

Clean wires should be used in pyrolysis experiments. A preferred cleaning method is to wash the wires with solvent and heat them overnight at 600 to 700 °C, or preheat the wires with the system immediately prior to performing the 

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TABLE 4.2.1. The isoprene/dipentene ratio as a function of temperature for the pyrolysis of Kraton 1107 in an inductively heated (Curie point) or a resistively heated filament pyrolyzer. 

One of the methods of studying the composition of macromolecular sedimentary organic matter in more detail is the molecular analysis of pyrolysis products. For this purpose, the pyrolysis products are transferred to a gas chromatographic column and analyzed as described for extractable organic matter in Sect. 4.5.5, with or without the combination with a mass spectrometer. Both flash pyrolysis (Curie-point pyrolysis samples are heated on a magnetic wire by electrical induction almost instantaneously, e.g., to 610°C) or off-line pyrolysis at various heating rates have been applied to geological samples (see Larter and Horsfield 1993 for an overview of various pyrolysis techniques). 

Curie point pyrolysis involves coating of the sample on a ferromagnetic conductor (wire or capillary tube). The conductor is inductively heated to a specific temperature when exposed to a radiofrequency field. The composition of the conductor determines the Curie temperature (300- 10(X)°C). The major advantage of the Curie point PGC is the ability to heat samples reproducibly to accurately defined temperatures in milliseconds. The major disadvantage is the inability to vary temperature since a different rod is needed for each point. 

Curie-point pyrolysis which involves rapid inductive heating (10 -10 K/s),... 

An important capability of Curie point pyrolysers should be that the sample does not suffer any modifications before the pyrolysis step itself. As previously indicated, the housing of the pyrolyser must be heated (commonly with electrical resistances) to avoid condensation or other modifications of the pyrolysate. However, because a waiting time is inherent between the moment of sample introduction in the pyrolyser and the start of the pyrolysis itself, the sample may be heated by radiation from the sample housing. Several Curie point pyrolysers [8b] have the capability to drop the ferromagnetic foil containing the sample from a cool zone into the induction area, which is pre-heated to avoid condensation. The pyrolysis takes place immediately after the sample is transferred into this induction area such that no uncontrolled preliminary sample decomposition takes place. 

Another problem with the furnace pyrolysers can be the difference in the temperature between the furnace and the sample. Again, due to the poor contact between the sample and the hot source, the sample may reach a lower actual temperature than the temperature of the furnace wall. It is interesting that in microfurnace systems there were reported variations in the pyrolysis products as compared to the results obtained in inductively or filament heated pyrolysers [7,18]. As an example, a study done on Kraton 1107 [7] decomposition found linearity between the oven temperature and the ratio of two decomposition monomers (styrene and dipentene) only in a narrow temperature range, namely from 450° C to 625° C. Kraton 1107 was found to decompose in filament or Curie point pyrolysers such that linearity can be noticed between temperature and styrene/dipentene ratio from 500° C to 850° C. The reproducibility of pyrolysis in a furnace was also found lower than for other pyrolysers [7]. 

Fig. 3.3B shows an induction-heating pyrolyser with a filament made of a ferromagnetic material. This arrangement provides for rapid heating of the filament with the sample to a temperature corresponding to the Curie point of the filament material, which is in fact the pyrolysis temperature. Fig. 3.3C shows various types of filaments on which samples are placed and pyrolysed. 

In a Curie-point pyrolyzer, an oscillating current is induced into the pyrolysis filament by means of a high-frequency coil. It is essential that this induction coil be powerful enough to permit heating the wire to its specific Curie-point temperature quickly. In such systems, the filament temperature is said to be self-limiting, since the final or pyrolysis temperature is selected by the composition of the wire itself, and not by some selection made in the electronics of the instrument. Properly powered, a Curie-point system can heat a filament to pyrolysis temperature in milliseconds. Providing that wires of the same alloy composition are used each time, the final temperature is well characterized and reproducible. 

Because the Curie-point filament is heated inductively, no connections are made to the wire. This facilitates autosampling and permits loading the wires into glass tubes for sampling and insertion into the coil zone. Unlike the isothermal furnace, which is on continuously, the Curie-point wire is heated only briefly and is cold the rest of the time. This necessitates heating the pyrolysis chamber separately to prevent immediate condensation of the fragments made during pyrolysis. Therefore, Curie-... 

Pyrolyzers have been adapted to provide automatic, imattended control of Py-GC. An early system used precoated pyrolysis wires held in quartz tubes on a turntable. These were sequentially loaded, accurately positioned in the induction coil, pyrolyzed, analyzed by capillary GC, and ejected. An alternative has used an automatic solids injector for samples enclosed in iron foil, and a furnace system has enabled sampling of the Martian surface. Autosampling systems based upon conventional pyrolyzers are now commercially available for resistively heated filaments, microfurnaces, and Curie-point pyrolyzers. One such system... 

The Curie-point pyrolyzer uses the Curie points of ferromagnetic sample holders to achieve precisely controlled temperatures when the holder containing the sample is subjected to high-frequency induction heating. Foils of various ferromagnetic materials enable the analyst to select pyrolysis temperatures from 150 to 1000°C. 

Resistively heated devices (filaments, coils, and ribbons), inductively heated devices (Curie-point), microfumaces, laser, direct pyrolysis (DPMS), in-colunm, PTV... 

The Curie-point flash pyrolyser was originated by Szymanski et al. [522], initially developed by Simon et al. [523] and later improved [511]. A Curie-point system (Fig. 2.24) can heat a ferromagnetic metal wire inductively with radio frequencies to the pyrolysis temperature in milliseconds. The final temperature is well characterised and reproducible. The alloy of the ferromagnetic material used achieves control of the pyrolysis temperature in a Curie-point instrument. Curie-point reference values are alumel 154.2°C, nickel 355.3°C, Perkalloy 596°C, iron 780° C, Hisat-50 1000°C. A set of six certified and traceable Curie temperature materials is available (ICTAC/TAI). 

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