Curie Point Method

For isothermal measurements, it is advisable to use a furnace of low thermal capacity unless suitable arrangements can be made to transport the sample into a preheated zone. The Curie point method [132] of temperature calibration is ideally suited for microbalance studies with a small furnace. A unijunction transistor relaxation oscillator, with a thermistor as the resistive part with completion of the circuit through the balance suspension, has been suggested for temperature measurements within the limited range 298—433 K [133]. 

Figure 11.4. Curie-point method of temperature calibration...

Figure 10.25 The Curie point method for temperature calibration. (Reproduced with kind permission of Springer Science and Business Media from M. Brown, Introduction to Thermal Analysis, Kluwer Academic Publishers, Dordrecht. 2001 Springer Science.)...

Figure 16.5 The TGA Curie point method records for each standard an apparent sharp weight change at a well-defined temperature, which corresponds to a known transformation in the standard s ferromagnetic properties at that temperature. The figure shows the relative temperature precision from three replicate calibration runs using alumel and nickel Curie point standards. (Courtesy of TA Instruments, New Castle, DE, www.tainst.com.)...

Curie point method The materials selected for temperature calibration are metals and alloys which are ferromagnetic at low temperature but which lose their ferromagnetism at well-defined Curie points. If the magnetic material is placed in the sample holder with a magnet placed below the sample, as shown in Figure 15.9c, the magnetic force on the sample will cause an apparent increase in mass. In a TG rim, the force will disappear fairly abruptly at the Curie point as shown in Figure 15.10. The mid-temperature... 

The Curie Point flash evaporation-pyrolysis gas chromatography-mass spectrometric method [32] described in section 2.2.1.2 for the analysis of aromatic hydrocarbons in soils has also been applied to the determination of heteroaromatic compounds (Table 2.2) such as methyledene, isomeric methylidenes, biphenyl and methylbenzofurans. 

De Leeuw et al. [35] have described a method based on Curie Point flash evaporation-pyrolysis GC-MS for the fast screening of anthropogenic aliphatic... 

A Curie Point flash evaporation-pyrolysis gas chromatography-mass spectro-metric method [35] has been applied to the determination of polystyrenes in soil via identification and determination of their unzipping pyrolysis products, such as styrene monomer, a-methylstyrene, 3-methylstyrene, 4-methylstyrene, a-3-dimethylstyrene, 3-ethylstyrene, a-4-dimethylstyrene, 3,5-dimethylstyrene, a-2- or 2,5- or 2,4-dimethylstyrene, as well as various phenyl ethers. 

Analytical pyrolysis is defined as the characterization of a material or a chemical process by the instrumental analysis of its pyrolysis products (Ericsson and Lattimer, 1989). The most important analytical pyrolysis methods widely applied to environmental samples are Curie-point (flash) pyrolysis combined with electron impact (El) ionization gas chromatography/mass spectrometry (Cp Py-GC/MS) and pyrolysis-field ionization mass spectrometry (Py-FIMS). In contrast to the fragmenting El ionization, soft ionization methods, such as field ionization (FI) and field desorption (FD) each in combination with MS, result in the formation of molecule ions either without, or with only very low, fragmentation (Lehmann and Schulten, 1976 Schulten, 1987 Schulten and Leinweber, 1996 Schulten et al., 1998). The molecule ions are potentially similar to the original sample, which makes these methods particularly suitable to the investigation of complex environmental samples of unknown composition. 

Most of the pyrolysis experiments in the field of natural polymer characterization involve the use of Curie-point instruments or resistance-heating apparatus. Both methods are described in the following sections. Laser pyrolyzers are not yet common in biopolymer analysis and will not be discussed here. 

Determination of volatiles at the trace level is also possible by pre-concentrating the headspace volatiles on a suitable adsorbent. The trapped compounds are subsequently recovered by thermal desorption in front of a cooled trap connected to the capillary column or by solvent elution followed by splitless or on-column injection. These methods, called dynamic headspace enrichment or purge-and-trap , have been applied to trace level analysis of volatiles, using conventional electrically heated systems [ 31, 32 ], a Curie-point Pyrolyser... 

The adoped value for the Curie point, T = 631 K, is from the study of Connelly et al. (9), using an ac calorimetric method to measure relative heat capacity vlaues, and Vollmer et al. (6) using a high temperature adiabatic calorimeter. 

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