Temperature coefficient permeability

There are two ferrite material properties which were not discussed in Section 9.3.1 but which are important in the inductor context they are the temperature and time stabilities of the permeability which, of course, determine the stability of the inductance. The temperature coefficient of permeability must be low, and this has been achieved for certain MnZn ferrite formulations as indicated in Fig. 9.18. A small residual temperature coefficient of inductance can be compensated by a suitable coefficient of opposite sign in the capacitance of the resonant combination. 

Permeability is an essential property of the materials that constitute the membrane and is independent of membrane thickness [23], Additionally, permeability can be described as the product of the diffusion coefficient and the solubility constant (see Equation 10.3) and is temperature dependent. Permeability can then be represented by the following Arrhenius-type expression (see Section 5.6.1)... 

It may be correspondingly noted that the in-situ fluorinated containers exposed to toluene at room temperature would still be far from steady state after 1000 hours of solvent exposure. The underestimation of the room temperature toluene permeability coefficient for the in-situ fluorinated containers was minimized in Table 1 by using the differential weight loss rate in Equation 1. 

Comparison of the dependence of dry oxygen permeability on temperature with some conventional barrier polymers (after Watanabe)(15) are presented In Figure 9 In normalized units of cc/mV24 hours for a one mil (25.4 micrometers) film thickness. The temperature coefficient of the grafted slloxane polymer appears to be comparable to that of BAREX 210 and ethylene vinyl alcohol. The EVAL shown (EVAL-E) Is 44% by weight ethylene. The silane Is considerably better than that of the polyvinylIdene chloride (Saran 468) sample shown In the figure. The data are plotted so that the temperature Increases to the right on the abscissa. 

Fig. 5.5. Negative temperature coefficient of initial permeability by adding a positive-anisotropy cation (schematic).

Rare earth oxides are used for manufacturing ceramic capacitors. Their presence extends the capacitor s lifetime and improves some properties such as the compensation temperature coefficient, dielectricity and magnetic permeability. Specifically, Ce, La, Pr and Nd help keep the dielectric constant of a capacitor virtually unchanged [9]. 

Table 5.4 summarizes some of the unusual physical properties exhibited by PDMS. - Atypically low values are exhibited for the characteristic pressure - ° (a corrected internal pressure, which is used in the study of liquids), the bulk viscosity t], and the temperature coefficient of >j. Also, entropies of dilution and excess volumes on mixing PDMS with solvents are much lower than can be accounted for by theory. - Finally, as has already been mentioned, PDMS has a surprisingly high permeability. 

Coil (communication) Pulse transformer lkHZ lMHz 0.5 80MHz MnZn NiZn MnZn NiZn Low loss Low temperature coefficient Inductance adjustment High permeability Low loss Low temperature coefficient... 

Table 22. The temperature coefficients of permeability constants in glasses in cal.lmoL... 

Table 23. Temperature coefficients of permeability in caLjmoL at loiv temperatures ...

When discussing the temperature coefficients of the permeabilities, we considered these temperature coefficients to be approximately those for the activated diffusion process within the silica. This viewpoint was justified because, as the data now to be given show, the solubility of hydrogen and hehum in silica varies only to a very minor extent with temperature, and the permeability constant (P), diffusion constant (D) and solubility k are related by... 

Even when all phase-boundary processes occur much more rapidly than any other processes, the temperature coefficients of the permeability constants are governed by the terms (iii) and (iv) above. But one notes the general correspondence between the differences AE in the temperature coefficients of permeability of metals to hydrogen and deuterium, and... 

Table 101. Temperature coefficients, E, of permeability constants (33,35a) in caLjmoL... 

The data of previous sections indicates that at low humidities one may use the linear Fick law as an approximation which breaks down as the humidity increases. The influence of temperature upon permeability constants is two-fold. There is first the effect upon the diffusion constant and secondly the effect upon the absorption coefficient, k. Sometimes in colloidal systems the coefficient k increases with temperature even when... 

Some data giving permeability constants and permeation rates at different temperatures are presented in Tables 113 and 114, for systems with high temperature coefficients, and ilegli ble coefficients respectively. For a number of resin, and rubber, membranes the curves of log P (P permeability constant) against l/T are linear, and from the slopes one may evaluate E in the equation P = Some of these values... 

For both membranes, the temperature eflTect was less pronounced when the partial pressure of ethylene was din shed. When the ethylene partial pressure was reduced to about 100 mm Hg, there was almost no change in the ethylene permeability with a 20 C temperature increase. However, the same was not true for ethane. At constant temperature, the permeability of ethane was almost constant over the same range of partial pressure. The permeabilities of ethane at 5,25 and 35 C were 3.7, 5.8 and 7.5 Barrer, respectively. This suggests that raising the temperature increases the difEusion coefBcients of the gases in the membranes. The mathematical model developed by Way and Noble (27) was used to determine the diffiision coefficients of uncomplexed ethylene (Da) and the Ag -ethylene complex (Dab)- The equiUbrium constants (Keq) for the reversible reaction between ethylene and Ag were also calculated (Tables V and VI). 

The effect of temperature on the permeability coefficients and permselectivity of air separation for all the polyphenylene oxides studied is the same. Qualitatively it agrees with the numerous similar dependencies reported in the literature, i.e. permeabilities of oxygen and nitrogen increase as the temperature rises, while the permselectivity decreases (Fig. 2). It is worth noting that even at 348K the permselectivity for the polyphenylene oxide copolymer is still above 4. At this temperature the permeability coefficients are twice those at 273K. 

BiaxiaHy orieated PPS film is transpareat and nearly colorless. It has low permeability to water vapor, carbon dioxide, and oxygen. PPS film has a low coefficient of hygroscopic expansion and a low dissipation factor, making it a candidate material for information storage devices and for thin-film capacitors. Chemical and thermal stability of PPS film derives from inherent resia properties. PPS films exposed to tolueae or chloroform for 8 weeks retaia 75% of theh original streagth. The UL temperature iadex rating of PPS film is 160°C for mechanical appHcatioas and 180°C for electrical appHcations. Table 9 summarizes the properties of PPS film. 

The temperature dependence of the permeability arises from the temperature dependencies of the diffusion coefficient and the solubility coefficient. Equations 13 and 14 express these dependencies where and are constants, is the activation energy for diffusion, and is the heat of solution... 

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