Magnetic transformation

Type J thermocouples (Table 11.58) are one of the most common types of industrial thermocouples because of the relatively high Seebeck coefficient and low cost. They are recommended for use in the temperature range from 0 to 760°C (but never above 760°C due to an abrupt magnetic transformation that can cause decalibration even when returned to lower temperatures). Use is permitted in vacuum and in oxidizing, reducing, or inert atmospheres, with the exception of sulfurous atmospheres above 500°C. For extended use above 500°C, heavy-gauge wires are recommended. They are not recommended for subzero temperatures. These thermocouples are subject to poor conformance characteristics because of impurities in the iron. 

The last arrangement of voltage feedbaek is the isolated feedback. This is used when the input voltage is eonsidered lethal to the operator of the equipment (>42.5 VDC). The two aeeepted methods of eleetrieal isolation are optical (optoisolator) or magnetic (transformer). This seetion will talk about the more eommon method of isolation, when an optoisolator is used to isolate the lethal portions of the eireuit from the operator portion. The optoisolator s Ct (eurrent transfer ratio (or drifts with temperature, ean degrade slightly with age,... 

Nickel normally crystallises in the f.c.c. structure it undergoes a magnetic transformation at 357°C and is ferromagnetic below that temperature. In all the alloys shown in Table 4.21 the f.c.c. (austenitic) structure is substantially retained, and in consequence most of the alloys possess the combination of properties required of materials for widespread industrial acceptability, i.e. tensile strength, ductility, impact strength, hardness, hot and cold workability, machinability and fabrication. 

Polynomial expressions are conveniently used to represent a condensed phase which is stable in the whole temperature range of interest and which does not undergo any structural, electronic or magnetic transformations. The Gibbs energy of a compound is in the CALPHAD approach represented relative to the elements in their defined standard state at 298.15 K as a power series in terms of temperature in the form of [16] ... 

Z.S. Wronski, A.H. Monish, A.M. Stewart, Hydrogen induced magnetic transformation in Fe90Zrl0 glass, Phys. Lett. 101A(5,6) (1984) 294-296. 

Integration of experimental Cp data with temperature can be used to bypass the plethora of models described in the previous sections, as it provides both the critical ordering temperature and the ratio of sro to Iro. This route has been extensively used to describe magnetic transformations (Inden 1977a, Hillert and Jarl 1978, Nishizawa et al. 1979) and generalised through the develq)ment of a series of approximate... 

The energy of magnetic transformations can be deceptively large, often exceeding that released by ordinary phase transformations. The following effects have been... 

In the Tokamak fusion reactor depicted in Fig. 21.9, electric current to the poloidal coils on the primary magnetic transformer generates the axial current in the secondary plasma composed of deuterium and tritium ions. These ions are heated to ignition temperature and then the reaction becomes self-sustaining. The toroidal field coil suspends the plasma away from the metal conducting walls. Contact with the wall would both cool the plasma below ignition temperature and contaminate the plasma with heavy ions. The relevant reactions are given below. 

Studies on the thermal properties of lanthanum, cerium, neodymium, and gadolinium hexaborides in the cryogenic region from 5° to 350°K. 193) have shown the presence of two types of anomalies in the latter three substances. At temperatures near 10 °K. there appears a lambda-type anomaly in each which is rather characteristic of a magnetic transformation. At slightly higher temperatures this is followed by Schottky-... 

Soft magnets Transformer cores [(Zn, M)Fe203, with M = Mn, Co, Mg] magnetic tapes (rare-earth garnets)... 

The effect of Curie temperature on catalysis is paralleled in corrosion by change in oxidation rate above and below the magnetic transformation temperature. In oxidation, the effect appears to be related to change in work function at the Curie temperature. 

We also performed Mossbauer spectra measurements over various metal-promoted iron oxide catalysts [13]. We introduced selected transition/inner transition metal ions (M = Cr, Mn, Co, Ni, Cu, Zn and Ce) into the iron oxide spinel lattice that were screened for effectiveness for the WGSR. Fe Mossbauer spectra of pristine Fe203 sample exhibits a six-line Zeeman spec-tmm as a result of the complete stractural and magnetic transformation. 

Thermomagnetometry is directly related to thermogravimetry and involves heating the sample in a constant applied magnetic field. Magnetic transformations in the sample are manifested as apparent mass changes. Temperature modulated thermomagnetometry has been applied to study the nanophase crystallization characteristics of amorphous... 

Magnetic susceptibility, resistivity, thermopower from 2 to 300 K and specific heat (2-20 K) of SmNiSn were measured by Sakurai et al. (1995). The dependence x ( ) is not linear, the p T) function has a negative curvature, and the thermopower has a small negative value. A kink on the X ( )> P(T) and C(T) curves reveals an antiferromagnetic transition at 9.3 K. The second magnetic transformation is observed at 4.1 K. 

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