Inductively heated pyrolyzer

Pulse-mode pyrolyzers include resistively-heated electrical filaments or ribbons and radio frequency induction-heated wires [841,842,846,848,849]. The filament or ribbon-type pyrolyzers are simple to construct. Figure 8.45, and typically consist of an inert wire or ribbon (Pt or Pt-Rh alloy) connected to a high-current power supply. Samples soluble in a volatile solvent are applied to the fileutent as a thin film. Insoluble materials are placed in a crucible or quartz tube, heated by a basket-lilce shaped or helical wound filiunent. The coated filament is contained within a low dead volume chamber through which the carrier gas flows, sweeping the pyrolysis products onto the column. The surface temperatui of the filament is raised rapidly from ambient temperature to He equilibrium pyrolysis temperature. This... 

Curie-point pyrolyzer (high frequency inductive heating of a ferromagnetic carrier). 

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. 

Radio-frequency induction heated wires (Curie-point pyrolyzers)... 

There are several construction principles for pyrolyzers, such as with resistively heated filaments, inductively heated, furnace type, and radiatively heated. Detailed descriptions for instrument construction can be found in literature [1] or obtained from instrument manufacturers. The pyrolysis unit usually consists of a controller and the pyrolyzer itself. The controller provides the appropriate energy needed for heating. A simplified scheme of a pyrolyzer based on the design of a flash heated filament system (made by CDS Inc.) is shown in Figure 3.1.1. 

A factor that must be considered with furnace pyrolyzers as well as with the other types of pyrolyzers is the achieving of short TRT values. A slow sample introduction in the hot zone of the furnace will end in a long TRT. A poor contact between the sample and the hot source may also lead to long TRT, most of the heat being transferred by radiation and convection and not by conduction. However, fairly short TRTs in furnace pyrolyzers were reported in literature [14, 15]. Also, in furnace pyrolyzers it is more common to see differences in the temperature between the furnace and the sample. 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. This may be the explanation why there were reported variations in the pyrolysis products in microfurnace systems as compared to the results obtained in inductively or filament heated pyrolyzers [16,17]. 

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. 

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... 

Not unlike the case of superplastic ceramics, ductility and strength relations are influenced by strain rate. The conditions of the experiment must be above the DBT to observe plastic flow, which is different for various ceramics. An illustration of the effect of strain rate and temperature on the strain (ductility) at some stress level can be seen in monolithic Si-C-N. Silicon-nitride-based ceramics are quite promising candidates for mechanical applications at elevated temperatures. Specimens were prepared by hot isostatic pressure (henceforth HIP) of pyrolyzed powder compact at 1500 °C and 950 MPa, without any sintering additives. These compression tests were conducted at temperatures from 1400 to 1700 °C in a nitrogen atmosphere with a servo-hydraulic-type testing machine at constant crosshead speed in an induction heating furnace. In Fig. 2.5, stress-strain curves... 

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. 

Apparatus. Pyrolysis experiments were conducted in a quartz tube heated by an induction furnace. A continuous flow of argon was used to sweep out gaseous pyrolysis products. The materials to be pyrolyzed were contained in alundum boats, which could be readily admitted and removed from the quartz pyrolysis tube. 

Commonly used RF frequencies in Curie point pyrolyzers are 400 to 1000 kHz, and the power outputs range from 100 to 1500 watts. The rate of temperature rise depends on the conductor mass and specific heat, as well as on the power consumption of the ferromagnetic conductor. This power consumption per unit surface is related to the amount of heat generated by the conductor and implicitly to the temperature. More detailed descriptions of the parameters implicated in the heating of a ferromagnetic conductor located inside a high frequency induction coil are found in literature [5, 10]. 

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. 

Bunton et al. (1954, 1958c) analyzed methanol and other organic compounds by pyrolyzing them to carbon monoxide in a tube heated by an induction furnace (c. 1200 C.), and Cohn and Drysdale (1955) have analyzed very small quantities of barium phosphate (10-20 jitmoles, 6 mg.) by heating it with carbon (5 mg.) in a molybdenum foil held... 

---