Electrical conductivity temperature variation

These measure the change in thermal conductivity of a gas due to variations in pressure—usually in the range 0.75 torr (100 N/m2) to 7.5 x 10"4 torr (0.1 N/m2). At low pressures the relation between pressure and thermal conductivity of a gas is linear and can be predicted from the kinetic theory of gases. A coiled wire filament is heated by a current and forms one arm of a Wheatstone bridge network (Fig. 6.21). Any increase in vacuum will reduce the conduction of heat away from the filament and thus the temperature of the filament will rise so altering its electrical resistance. Temperature variations in the filament are monitored by means of a thermocouple placed at the centre of the coil. A similar filament which is maintained at standard conditions is inserted in another arm of the bridge as a reference. This type of sensor is often termed a Pirani gauge. 

To a good approximation, thermal conductivity at room temperature is linearly related to electrical conductivity through the Wiedemann-Eran2 rule. This relationship is dependent on temperature, however, because the temperature variations of the thermal and the electrical conductivities are not the same. At temperatures above room temperature, thermal conductivity of pure copper decreases more slowly than does electrical conductivity. Eor many copper alloys the thermal conductivity increases, whereas electrical conductivity decreases with temperature above ambient. The relationship at room temperature between thermal and electrical conductivity for moderate to high conductivity alloys is illustrated in Eigure 5. 

Electrical Conductivity This is often a convenient and accurate measurement of salinity or chlorinity. Here, too, there is considerable variation with temperature, so that simultaneous observation of temperature is essential. Figure 2.16 shows the relationship between conductivity and chlorinity at various temperatures. 

The Contact between Solvent and Solute Particles Molecules and Molecular Ions in Solution. Incomplete Dissociation into Free Ions. Proton Transfers in Solution. Stokes s Law. The Variation of Electrical Conductivity with Temperature. Correlation between Mobility and Its Temperature Coefficient. Electrical Conductivity in Non-aqueous Solvents. Electrical Conduction by Proton Jumps. Mobility of Ions in D20. 

The room temperature electrical conductivity of single crystals of M03S7 (dmit)3 along the c axis is 25 S cm, which is very high for a neutral molecular crystal. The variation of the magnetic susceptility (/) with the temperature does not follow a Curie-Weis law with a continuous decrease of /T vs. Tupon cooling... 

Fig.4.4. Relative variation rate of the electric conductivity of the sensor D = (jda/dt)e as a function of the temperature of the pyrolysis filament, plotted in V - T axes (a) and Ig t - r axes (6). The temperatures in the vessel are 370 C (/) and 380 C (2), the pressure of hydrogen = 10 2 Torr.

Fig.4.8. Oscilloscope traces of variation of the electric conductivity of a ZnO sensor upon admission of isopropyl alcohol vapor to the vessel (the initial vapor pressure is 0.01 Torr) at the temperature of 390 C (/), 370 C (2), 350 C (5), 320 C (4), and upon admission of H2 at the temperature of 390 C (5).

Fig.4.9. Oscilloscope traces of temporal variation of the electric conductivity of a ZnO sensor for different initial pressures of the isopropyl alcohol vapor 5-2-t0-2 Torr (0, 3-6.10-2 (2), 1.65-10-1 0 and 3.25 10- Torr. The temperature of the ZnO film is 390 C.

The scheme of the element is shown in Fig. 4.16. In order to increase variation of electric conductivity semiconductor film was deposited in the center of the plate, whereas activator was deposited at the plate edges at above specified distances through a mask. All stages of preparation were conducted in high vacuum ( 10" Torr). Sensitivity of such sensors to adsorption of hydrogen atoms at room at lower temperatures was about 10 - 10 at/cm, which corresponds to surface coverage of only 10-8 10-7% ( )... 

Fig. 4.20. Variation of electric conductivity of ZnO film under bombardment with silver atoms (to the left from the dashed line) and after termination of the atomic beam (to the right from the dashed line). The film temperature is equal to 1 - 94 C 2 - 193°C Ta = 780 C...

The influence of other active components, such as 1, OH, H on a semiconductor sensor, with other conditions being the same, is comparable with the influence of atomic oxygen [50]. Contribution of N and OH is proportional to their relative contents (compared to that of atomic oxygen) in the atmosphere and may become essential at altitudes lower than 60 - 70 km. The use of selective detectors excludes the influence of atomic hydrogen. Studies of adsorption of water vapours on ZnO films [50] show that their influence is negligibly small at the film temperatures below 100°C. Variations of electric conductivity of the films under the influence of water vapours and of an atomic oxygen are comparable at the ratio of their concentrations [H20]/[0] = 10" . 

Fig. 4.27. Variation of electric conductivity of ZnO film under the influence of adsorption of CH3 radicals at room temperature for various pressures of acetone vapours 1,2 - 200 Torr 5-1 Torr 1, 2 - before and after immersion of the film in liquid acetone 4 - the film covered with a liquid layer.

The results obtained in above experiments confirm the removal of chemisorbed particles in the process of immersion of the film with preliminary chemisorbed radicals in a liquid acetone. Note that at low pressures of acetone, the CHa-radicals absorbed on ZnO film could be removed only by heating the film to the temperature of 200 - 250°C. Moreover, if the film with adsorbed radicals is immersed in a nonpolar liquid (hexane, benzene, dioxane), or vapours of such a liquid are condensed on the surface of the film, then the effect of removal of chemisorbed radicals does not take place, as is seen from the absence of variation of electric conductivity of the ZnO film after it is immersed in liquid and methyl radicals are adsorbed anew onto its surface. We explain the null effect in this case by suggesting that the radicals adsorbed on the surface of the ZnO film in the first experiment remained intact after immersion in a nonpolar liquid and blocked all surface activity of the adsorbent (zinc oxide). 

Fig. 4.30. Variation rate of the electric conductivity of a ZnO film as a function of the intensity of the electron beam bombarding the film, for different times of preliminary exposure of the film to molecular hydrogen at room temperature (/) - ZnO surface free of hydrogen, (2) - the exposure time is 5 min, (i) - the exposure time is 30 min, (4) - the exposure time is 120 min.

High electrical conductivity is also attained in oxides with very narrow, partially filled conduction bands the best known example is Ru02. This material has a conductivity of about 2-3 104S/cm at the room temperature, and metal-like variations with the temperature. Some authors consider Ru02 and similar oxides as true metallic conductors, but others describe them rather as n-type semiconductors. 

In the system Mo,Fe3 x04, there is a regular variation with x, from Fe304 to MoFe204, in the lattice parameter (ao), the magnetization (Ms), the Curie temperature (Tc) and the electrical conductivity (a, AH ) apparently substitution of Fe by Mo leads to a mixed iron valence on both sites for 0 < x < 1. It is worth noting that AH varies smoothly with x from a AH < kT for x = 0 in the temperature interval 300 < T < 600 K to 0.027 eV for x = 1.0, where the narrow minority-spin band is maximally perturbed and filled by the introduction of substitutional Mo ... 

The only new chemistry concerns electrochemical oxidation of the tetrathiafulvene derivative 41 to the radical cation perchlorate 42 (Equation 1) <2005MCL575>. The salt 42 was formed electrochemically as a dense thin film on the electrode surface and shown to be a conducting cation-radical salt that behaves like an organic metal. The electrical conductivity shows an interesting variation with temperature which may be related to a phase transition at 102K <2005MCL575>. 

Experimentally, as illustrated in Figure 6.34, the electrical conductivity of CU2O is found to be proportional to Pq, which is in reasonable agreement with the prediction of Eq. (6.54). The variation of another oxide semiconductor, CdO, with temperature is also shown in Figure 6.34 for comparison. 

Fig. 7.1 Variation of electrical conductivity of xSrxV03 as a function of reciprocal temperature (Dougier and Hagenmuller 1975).

As is to be expected the equilibrium between the two above-mentioned forms of liquid sulphur affects other properties in addition to the colour and the viscosity. Thus, the electrical conductivity 5 and the surface tension6 of molten sulphur exhibit abnormal variation with alteration in temperature also the solubility curves for A-sulphur and p-sulphur in high-boiling solvents such as triphenylmethane are quite distinct, the solubility of the former increasing and that of the latter decreasing with rise of temperature the respective coefficients of expansion are also quite independent.7 The reactivities of the two forms towards rubber arc practically equal.8... 

Mulder and Walstra (1974) presented data for liquid fat, which is synonymous with butter or the core fat of globules. Variations exist, but the causes are usually unknown (Mulder and Walstra 1974). The authors state that the thermal conductivity is about 4 X 10 4 call cm"1/51/°9C 1 at room temperature and the specific heat of the liquid fat is about 0.5 cal/g V C"1. The latter is temperature dependent. The electrical conductivity is less than 10 12 S/cm (mho/CM) and the diele-tric constant is about 3.1. 

Temperature control is important in conductivity measurements, since the conductivity of milk increases by about 0.0001 ohm 1cm 1 per degree Celsius rise in temperature (Gerber 1927 Muller 1931 Pinkerton and Peters 1958). Increased dissociation of the electrolytes and decreasing viscosity of the medium with increasing temperature are undoubtedly responsible for this effect. An investigation (Sudheendra-nath and Rao 1970) of the viscosity and electrical conductivity of skim milk from cows and buffaloes failed to reveal a simple relationship. The authors attributed the lack of linear correlations to variations in casein structure and its hydration. 

A large number of partially oxidized divalent cation salts of the bis(oxalato)platinates have been reported (see Table 2).63 Only the series Mx[Pt(C204)]-6H20 (MOP where M = Fe, Co, Ni, Zn, Mg and 0.80 < x < 0.85) has been extensively studied.68 83 For most of these salts detailed studies have been made of their crystal structures and optical reflectivity at room temperature, and the variation of superlattice reflections, diffuse X-ray scattering, thermopower and DC electrical conductivity with temperature. 

Figure 6 Variation of electrical conductivity with inverse temperature for a series of bis(oxalato)platinate salts...

Most nonequilibrium systems are characterized by variation of velocity, temperature, composition, or electrical potential with position and the consequent transport of momentum, energy, mass, or electric charge. Naturally, transport of two or more of these may occur simultaneously. Attention is focused here, however, on situations where only one transport process occurs and a transport coefficient can be calculated from its measured rate. For example, thermal conductivity can be calculated if the rate of energy transport and the temperature variation in the system are measured. 

For the variation of the electrical conductivity with temperature an Arrhenius type equation is used ... 

---