Foil pyrolysis

A chemical degradation reaction initiated by thermal energy alone. 

The characterization of materials or of a chemical process by instrumental analysis of the pyrolysate. 

The graph of temperature against time for an individual pyrolysis experiment. 

The time required by a pyrolyser to reach the pre-set pyrolysis temperature from the start time. 

A pyrolysis which is carried out with a short TRT to achieve a constant final temperature. 

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In foil pyrolysis, the sample is applied to a thin platinum foil (Figure 2.35). The thermal mass of this device is extremely low. After application of a heating current, any desired temperature up to about 1400 C can be achieved within milliseconds. The extremely high heating rate results in high reproducibility. The temperature of the Pt foil can be controlled by its resistance. However, the temperature can be measured and controlled more precisely and rapidly from the radiation emitted by the Pt foil. An exact cahbration of the pyrolysis temperature can be carried out and the course of the pyrolysis is recorded by this feedback alone. Besides endothermic pyrolysis, exothermic processes can also be detected and recorded. 

A potential disadvantage of Curie point pyrolysis is the longer TRT compared with the direct resistively heated foil pyrolysis. The temperature rise time of up to 200 ms to reach the Curie point is significantly slower and depends on the... 

The Curie point of the alloy is determined by the iron-to-nickel ratio an Fe Ni ratio of 50 50 was used to give a Curie point of 530°C. This pyrolysis temperature was chosen because it has been shown22 to give a balance between fragmentation from polysaccharides and protein fractions. Foils with Curie points of 300°C to 1000°C are commercially available (Figure 15.2). How-... 

Storage of uranium foil in closed containers in presence of air and water may produce a pyrophoric surface [1], Uranium must be machined in a fume hood because, apart from the radioactivity hazard, the swarf is easily ignited. The massive metal ignites at 600-700°C in air [2]. The finely divided reactive form of uranium produced by pyrolysis of the hydride is pyrophoric [3], while that produced as a slurry by reduction of uranium tetrachloride in dimethoxyethane by potassium-sodium alloy is not [4],... 

Strong graphite fibres may be prepared by pyrolysis (at 1500°C or above) of oriented organic polymer fibres. Other graphite forms such as foams, foils, etc. can also be prepared. 

A distinct advantage of plastic pyrolysis into fuels as a means of recycling is its ability to handle mixed and unwashed plastics. Post-consumer plastics are often commingled and contaminated with extraneous materials such as soil, dirt, aluminium foils, paper labels and food remnants. While soil, dirt and glue can be removed from post-consumer plastics by washing, this is a fairly expensive operation and it leads to secondary waste streams... 

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. 

It has become the most popular method of heroin use in recent years due to searches for alternatives to IV injections and the drug s increased availability. The most common method of smoking heroin involves heating the drug on a piece of aluminum foil and inhaling the vapor. An often reported obser-vation is that the aluminum foil contains black residues of decomposed heroin after smoking. In pyrolysis studies, Huzier (1987) and Cook and Jeffcoat (1990) reported that heroin undergoes extensive decomposition at temperatures that are presumably required for volatilization. 

Fig. 40. Pyrolysis unit. A, Foil heating cup B, wires to variable voltage emf C, ground joint connection to top of chromatographic column. Reproduced from Nelson and Kirk (N3) with permission.

The mechanism of carbon formation on polycrystalline Cu foils was studied for the pyrolysis of benzene in the presence of hydrogen. The study was carried out on a microbalance tubular flow reactor at temperatures rapging form 800 to 1050°C. The rate of surface carbon deposition was constant after an initial period during which no appreciable deposition was observed. 

The pyrolysis filament may be shaped for convenience of sampling and may be a flat strip, foil, wire, grooved strip, or coil. In the case of the coil, a small sample tube or boat is inserted into the filament so that the sample is not heated directly by the filament, but is in effect inside a very small, rapidly heating furnace. The pyrolysis filament must be connected to a controller capable of supplying enough current to heat the filament rapidly, with some control or limit since the materials used for filaments are not self-limiting. The temperature of the filament may be monitored using the resistance of the material itself or some external measure, such as optical pyrometry or a thermocouple. ... 

The techniques of pyrolysis-mass spectrometry and gas chromatography both rely upon a good physical contact between the sample to be analyzed and the supporting material. Over the years, various shapes of materials have been developed to hold samples prior to pyrolysis. Many of these methods have been described elsewhere. - In aU aspects of sample preparation, cleanliness is of vital importance. The aim in preparing a sample is to obtain a thin coating of material over the inside surfaces of a foil (which is formed into a V), around the surface of a wire, crimped in a ribbon or placed onto a filament, with between 5 and about 25 pg dry weight. The method for doing this depends on the type of sample. 

In the preparation of the glass tubes, quartz tubes, and foils prior to sample loading, it is important that none are touched by hand. The method described by Sanglier et al. has proven to work well for foils used inside glass tubes. In this method, pyrolysis foils and tubes are washed in acetone, then dried overnight at 27°C. A single foil is inserted, with flamed forceps, into each pyrolysis tube so as to protrude about 6 nun from the mouth. The tubes may then be stored at 80°C in a clean, dry oven or vacuum dessicator until needed. For each strain, small amounts of biomass (25 Tg) are scraped from three different areas of the inoculated plate and smeared onto the protrading foil. The assembled foils are placed in an 80°C oven for 15 minutes to dry the biomass. 

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... 

In Curie-point pyrolysis the material is placed on an iron-nickel alloy foil which is heated to the Curie point of the foil (this is 530°C for 50 50 Fe-Ni foils). For a given type of foil, the Curie-point temperature is constant, therefore this type of pyrolysis is very reproducible. The foil holding the sample is rapidly heated to its Curie point by passing a radio-frequency current for 3 s (in the case of the Horizon 200-X instrument used at Aberystwyth) through a coil surrounding the foil. The foil takes around 0.5 s to reach this point at this temperature the material on the foil is thermally... 

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