Curie Point temperature

Fig. 4.7.3. Temperature-time profiles and Curie-point temperatures (Tc) for pure Ni, Fe, and Co wires. (Tromp 1987)...

Since there is no contact between pan and furnace, the thermal lag is higher than in DSC. The standards recommended by ICTA and distributed by NBS are ferromagnetic standards exhibiting loss of ferromagnetism at their curie point temperature within a magnetic field Nickel (354°C), Permanorm 3 (266°C),... 

Figure 5.4.10 (A) displays the low-voltage (14 eV) El mass spectrum (pyrolyser-mass spectrometer equipped with expansion chamber) for amylose analyzed from a sodium phosphate buffer matrix using a Curie-point temperature of 510° C. The spectra for the same sample (amylose pyrolysate) and the Ar I and Kr I PI spectra are shown in Figures 5.4.10 (B) and 5.4.10 (C).

Thermal analysis systems require calibration prior to routine use. In TGA, calibration for mass is carried out by calibrating the microbalance using a set of standard weights, as for any balance system. Temperature calibration is effected by measuring the Curie point temperatures of a suite of International Confederation for Thermal Analysis and Calorimetry (ICTAC) Certified Reference Materials, which have well-defined Curie points. ... 

Fig. 3 Curie-point pyrolysis gas chromatogram of the non-extractable residue of a Teltow Canal sediment (Curie-point temperature 510° C).

Norem et al. (14, 15) used the third method, as previously discussed, to calibrate the temperature of their type of furnace and/or sample container, A ferromagnetic material was placed in the sample container and suspended within a magnetic field. At the material s Curie point temperature, its equivalent magnetic mass diminishes to zero and the thermobalance indicates an apparent mass-loss. For calibration over the temperature range from ambient temperature to lOOOC, it is obvious that a number of ferromagnetic materials must be used. The criteria which were considered characteristic of an ideal standard were the following (15) ... 

Curie point temperatures can also be determined by DTA and DSC techniques. As illustrated in Figure 7.66, the specific heat of nickel, increases gradually up to the Curie point at 357°C, making a sudden change at this point. The sample size used was 75 mg. 

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. 

The Py-GC/MS analysis was performed with 20- J,g samples, a Curie-point temperature of 610°C, and a pyrolysis time of 4 sec. The resulting pyrolyzate was then swept onto a capillary GC column (50 m long x 0.32 nun I.D., with a l- jm film of methyl silicones) heated from 30 to 300°C at 4°C/min for a total analysis time of about 1 h. 

Curie-point pyrolysis involves placing the sample wire into a radio frequency field that induces eddy currents in the ferromagnetic material and causes a temperature rise. When the wire reaches the Curie-point temperature, it becomes paramagnetic and stops inducting power. The temperature at which the wire stabilizes (the Curie point) is a function of the type of metal. For example, the Curie points of cobalt, iron, and nickel are 1128, 770, and 358°C, respectively. Wires made from alloys of these metals produce intermediate temperatures. For example, the commonly used nickel-iron wire has a Curie point of 510°C. Differences between filament and Curie-point pyrolyzers depend on the pyrolysates examined and may be obscured by other instrumental differences, including the design of the transmission system to the detector. 

The weight calibration of thermobalances is done using standard weights. The temperature calibration is more difficult. The method using the Curie point temperature, as... 

The] Magnetometer apparatus Magnetization property and Curie point temperature doped p-SiC samples (2000 A depth) with 5 at.% (12.8 mass%) Fe maintained at 350°C in order to avoid amorphization and annealed at 700°C... 

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... 

The primary shutdown system is backed up by an ultimate shutdown system (USS). These control rods use magnetic latches, which can be actuated by either the reactor protection system (RPS) or automatically when the latch temperature exceeds the magnetic curie point temperature of the latch. 

Jackson and Walker [7] studied the applicability of pyrolysis combined with capillary column GC to the examination of phenyl polymers (e.g., styrene-isoprene copolymer) and phenyl ethers e.g., bis[w-(w-phenoxy phenoxy)phenyl]ether. In the procedure the polymer sample is dissolved in benzene. The pyrolysis Curie point temperature wire is dipped 6 mm into the polymer solution. The polymer-coated wires are then placed in a vacuum oven at 75-80 °C for 30 minutes to remove the solvent. Figure 6.2 shows a characteristic pyrogram of the copolymer (isoprene-styrene) resulting from a 10-second pyrolysis at 601 °C. When the polyisoprene is pyrolysed, C2, C3, C4, isoprene, and CjoHig dimers are produced. When PS is pyrolysed, styrene and aromatic hydrocarbons are the products. Figure 6.2 shows that the copolymer product distribution and relative area basis resemble the two individual polymer product distributions. 

Curie Point Temperature of a material below which there is a spontaneous magnetization in the absence of an externally applied magnetic field and above which the material is paramagnetic (i.e., extent of magnetization proportional to strength of the field). 

A very rigorous procedure (Fairburn, 1988), developed over the years, is implemented for each run. This methodology and the above described system have been proven very reliable and successful in providing the best possible qualitative and quantitative information on the product distribution derived from pyrolysis of various materials under carefully controlled temperatures and reaction times. Wires have been utilized in the experimental work having Curie Point temperatures from 300 to 1000°C and experiments performed with various feedstocks with carefully controlled reaction times between 50 and 2000 milliseconds. 

Tan et al. (1991) extended the temperature range studied by Fairburn et al. (1990) to 1000 °C. They showed the importance of the Temperature Rise Time (TRT) on the n-hexadecane conversion at these high temperatures (Figure 9), reporting conversions of 8% and 10%, corresponding to TRTs of 100 and 125 ms, at 900°C and 1000°C, respectively. Based on these results, they defined the Effective Residence Time (ERT) in the microreactor as the time period at which the exact Curie Point Temperature would yield the same conversion as the actual reaction for the Total reaction Time (TT). According to this definition... 

---