Effect of temperature on conductivity

Figure 1. Effect of temperature on conductivity of (C6H5)2CHLi/2TMED in various solvents (1 KHz)...

Naturally, the smaller the band gap, the more probable is the promotion of electrons. The effect of temperature on conductivity is related to the size of this gap. For an insulator such as diamond, the gap is large and the number of electrons promoted at room temperature is too small to be detected in terms of increased conductivity. 

Temperature changes have important effects on concrete resistivity. A higher temperature causes the resistivity to decrease and vice versa (for a constant relative humidity). This is caused by changes in the ion mobility in the pore solution and by changes in the ion-solid interaction in the cement paste. As a first approach an Arrhenius equation can be used to describe the effect of temperature on conductivity (inverse of resistivity) ... 

Conductance versus thickness for (111) AgBr films evaporated on mica. The effect of temperature on conductance is also indicated. 

Holroyd, R.A., Tames, S., and Kennedy, A., 1975b, Effect of temperature on conduction band energies of electrons in nonpolar liquids, J. 

How might the unique anatomy (Fig. 16.7) of the template-synthesized nanostructures affect the mechanism of electronic conduction in thin films prepared from these materials We have been exploring this question in collaboration with Professor H. D. Hochheimer in the Physics Department here at Colorado State University and Dr. P.-H. Hor of the Texas Center for Superconductivity (50,59-63J. These investigations (which are very much ongoing) entail measurements of both the temperature and pressure dependence of conductivity in thin films prepared from our template-synthesized nanostructures. Preliminary results of the effect of temperature on conductivity are briefly reviewed here. 

Thermal Properties. Before considering conventional thermal properties such as conductivity it is appropriate to consi r briefly the effect of temperature on the mechanical properties of plastics. It was stated earlier that the properties of plastics are markedly temperature dependent. This is as a result of their molecular structure. Consider first an amorphous plastic in which the molecular chains have a random configuration. Inside the material, even though it is not possible to view them, we loiow that the molecules are in a state of continual motion. As the material is heated up the molecules receive more energy and there is an increase in their relative movement. This makes the material more flexible. Conversely if the material is cooled down then molecular mobility decreases and the material becomes stiffer. 

Figure 4 Effect of temperature on the interfacial tension of an Alberta heavy oil in produced water containing LTS-18 surfactant. Data are from three separate replicate experiments conducted under the same conditions.

Parker et al. (1981) conducted tests with a 5 cm diameter cyclone at temperatures up to 700°C with 20 micron fly ash. They found that cyclone efficiencies decreased with temperature as expected. Patterson and Munz (1989) investigated the effect of temperature on cyclone efficiency up to 1700°C in a 10-cm-diameter cyclone, and also found that cyclone efficiency decreased with temperature. However, this effect was only seen at very small particle sizes (below about 12 microns) where cyclones become relatively inefficient. 

The total electrical resistance at room temperature includes the contribution from scattering of conduction electrons by the vacancies as well as by ion-core and impurity scattering. If the experiment is repeated at a number of high temperature anneals, then the effects of temperature on the vacancy contribution can be isolated, since the other two terms will be constant providing that... 

Experiments were conducted to assess the effect of temperature on the pressure of a fixed quantity of gas kept in a 2.0-L vessel. Assuming that the ideal gas law is valid, determine the slope and intercept of the line which arises from the following data ... 

Functionalizations were usually conducted at room temperatures. In certain experiments, the bottom part of the cell was maintained at elevated temperatures in order to examine the effect of temperature on the functionalization process. 

Cantwell, A. M. Effect of temperature on response of plants to ozone as conducted in a specially designed plant fumigation chamber. Rant Dis. Rep. 52 957-960. 1968. 

The effect of temperature on the extraction of methional from ethanol solution and its derivatization on a PFBOA-loaded fiber was examined for 35 and 50 °C (Figure 2). Increasing the extraction temperature caused an increase in the peak area of the derivatized methional. Based on this result, subsequent derivatizations were conducted at 50 °C. 

The equations describing the concentration and temperature within the catalyst particles and the reactor are usually non-linear coupled ordinary differential equations and have to be solved numerically. However, it is unusual for experimental data to be of sufficient precision and extent to justify the application of such sophisticated reactor models. Uncertainties in the knowledge of effective thermal conductivities and heat transfer between gas and solid make the calculation of temperature distribution in the catalyst bed susceptible to inaccuracies, particularly in view of the pronounced effect of temperature on reaction rate. A useful approach to the preliminary design of a non-isothermal fixed bed catalytic reactor is to assume that all the resistance to heat transfer is in a thin layer of gas near the tube wall. This is a fair approximation because radial temperature profiles in packed beds are parabolic with most of the resistance to heat transfer near the tube wall. With this assumption, a one-dimensional model, which becomes quite accurate for small diameter tubes, is satisfactory for the preliminary design of reactors. Provided the ratio of the catlayst particle radius to tube length is small, dispersion of mass in the longitudinal direction may also be neglected. Finally, if heat transfer between solid cmd gas phases is accounted for implicitly by the catalyst effectiveness factor, the mass and heat conservation equations for the reactor reduce to [eqn. (62)]... 

Figure 3.5. Effect of temperature on the tensile strength of copper (A) effect of annealing on strength and ductility (B) hardened high-conductivity copper (29. ...

Experiments were conducted at Cornell in an attempt to learn more about the effects of temperature on oil toxicity. Small carrot and parsnip plants were placed at four temperature levels 40 to 50 , 50 to 60 , 60 to 70 , and 70 to 80 F. After 2 weeks at these temperatures, one sixth of the plants in each group were sprayed at the rate of 80 gallons per acre with a Stoddard solvent (Varsol No. 2) which contained an additional 4% diethylbenzene. One week after the first treatment a second lot of plants was sprayed in the same manner. Ten replications of carrots and five replications of parsnips were used. Harvests were made 2 weel after the treatments. 

The above studies dealt with temperature conditions during the growing period as well as at the time of spraying. Hence, it was not possible to distinguish between the effect of temperature on the structure and composition of the plant and the influence of temperature on the action of the oil. The following experiments were conducted to study the latter aspect of temperature effect. 

In summary, most of the CP biodegradation and bioremediation studies have been conducted using mesophilic microorganisms. The effects of temperature on CP bioremediation have not been systematically studied, even though environmental temperatures are generally well below those suitable for mesophilic organisms. Therefore, future studies should more carefully consider the temperature constraints of bioremediation. 

Further advancements in the theory of fixed bed reactor design have been made(56,57) but it is unusual for experimental data to be of sufficient precision and extent to justify the application of sophisticated methods of calculation. Uncertainties in the knowledge of effective thermal conductivities and heat transfer between gas and solid make the calculation of temperature distribution in the bed susceptible to inaccuracies, particularly in view of the pronounced effect of temperature on the reaction rate. 

The effect of temperature on kerogen conversion is not pronounced although some increase can be noted in the neighborhood of 1300°F. The test at 1200°F was conducted with a shale space velocity that was considerably higher than that used in the tests at 1300° and 1400°F. 

Fig. 30.—The Effect of Temperature on the Molecular Conductivity of Solutions of Hypophosphorous Acid.

When wet coal is exposed to higher temperatures (0 to 200°C, 32 to 392°F), an increase in electrical resistivity (with a concurrent decrease of dielectric constant) is observed. This is due to moisture loss. After moisture removal, a temperature increase results in lower resistivity (and higher dielectric constant). The dependency of conductive properties on temperature is mainly exponential, as in any semiconductor. At lower temperatures, the effect of temperature on electrical properties is reversible. The onset of irreversible effects is rank dependent and starts at 200 to 400°C (392 to 752°F) for bituminous coal and at 500 to 700°C (932 to 1292°F) for anthracite. 

The thermal conductivity is a property of any given material, and its value must be determined experimentally. For solids, the effect of temperature on thermal conductivity is relatively small at normal temperatures. Because the conductivity varies approximately linearly with temperature, adequate design accuracy can be obtained by employing an average value of thermal conductivity based on the arithmetic-average temperature of the given material. Values of thermal conductivities for common materials at various temperatures are listed in the Appendix. 

Several studies have focused on the mode of formation and properties of polypyrrole polymers. Studies of the effects of temperature on polypyrrole conductivity have shown that the polymer formed by electropolymerization of pyrrole and camphor sulfonate as dopant at low temperature has higher conductivity and is stronger than that formed at higher temperatures. X-ray scattering shows that interlayer distance increases with increasing temperature <2002IAS155>. 

As we can see from relations such as Equation 8.2 (J = gjAcj = ACjlrj), the conductances or the resistances of the various parts of the pathway determine the drop in concentration across each component when the flux density is constant. Here we will apply this condition to a consideration of water vapor concentration and mole fraction in a leaf, and we will also consider water vapor partial pressures. In addition we will discuss the important effect of temperature on the water vapor content of air (also considered in Chapter 2, Section 2.4C). 

Another important factor that is often not taken into consideration is the process temperature during polishing. Recent researches [12,13] have elucidated the effect of temperature on the coefficient of friction during both copper and ILD CMP by conducting polishing experiments at different pad and slurry temperatures. Sorooshian et al. [12] have attributed the changes in coefficient of friction to the changes in pad properties, which result in an increase in shear force. Conversely, removal rate, surface chemical analysis. 

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