Conductivity as a function of time

Morrison (31), using sintered zinc oxide, applied a different technique to study the conductivity effects in the range between room temperature and 500°C. He studied the variation in conductance as a function of time with the temperature held constant. Figure 3 shows one such conductivity-time experiment. The sample used was a slab of zinc oxide cut from a pill which had been compressed and sintered in air for eighteen hours at 1000°C. The sample was immersed in oil (the oil does not penetrate into the pores of the sample) at the start of the run. The sample container was immersed in boiling water, the temperature reaching 100 C in the order of one-half of a minute. The conductance was recorded as a function of time while the sample was held at 100°C. The results are shown in Fig. 3. The inverse of the Hall voltage is also plotted as a function of time. An interpretation of the Hall measurement is discussed in Section III. 

The decrease in conductivity as a function of time is what one would expect from the theory given in this section, the decrease being attributable to the adsorption of oxygen following the temperature change from 20°C to 100°C. The initial increase is not expected on the basis of this simple theory. 

FIGURE 10.3 Conductivity as a function of time for doped Bi203, measured at 500°C. 

Figure 6.9. Evolution of nickel oxide s electrical conductivity as a function of time and for different oxygen injections curve a P =8 Pa, curve b P = 10.6 Pa...

The creaming profiles are presented as the deviation in specific conductivity as a function of time. Creaming rates were quantitatively determined by calculating the slope of the first linear part of the creaming profiles. 

Figure 9. Ionic conductivity as a function of time during isothermal cures of a 1.18 stoichiometry ECN-PN formulation catalyzed with 0.50 phr TPP.

The interpretation of the results is expressed from the curve of electrical conductivity as a function of time [13]. Two parallel lines are drawn and they intersect at a point that corresponds to the induction time or OSI. It is believed that below the point of intersection practically no secondary oxidation compoimds are formed, but above this point there is a rapid increase in the oxidation rate with the formation of various volatile compounds. 

Dielectric analysis (DEA) or dielectric thermal analysis (DETA) is another important thermoanalytical technique that is rapidly evolving. This technique measures two fundamental electrical characteristics of a material—capacitance and conductance—as a function of time. 

An analogy between a-c and d-c measurements (51) can be seen in a comparison of a-c conductivity as a function of frequency with d-c conductivity as a function of time. The charging current is given as a function of time in... 

When the process of spontaneous gel emulsion formation, depicted in Figure 11.13, was followed by conductivity as a function of time, a monotonic decrease in conductivity of about four orders of magnitude in a short period of time (less than one minute) was observed when the O/W microemulsion (Figure 11.13a) was... 

Figure 4.8 Fraction of amorphous polyethylene as a function of time for crystallizations conducted at indicated temperatures (a) linear time scale and (b) logarithmic scale. Arrows in (b) indicate shifting curves measured at 126 and 130 to 128°C as described in Example 4.4. [Reprinted with permission from R. H. Doremus, B. W. Roberts, and D. Turnbull (Eds.) Growth and Perfection of Crystals, Wiley, New York, 1958.]...

Figure 50. CUSUM test, stability and convergence of the estimates of ground thermal conductivity as a function of starting time and amount of data included, obtained in the reference...

Figure 3. Temporal and Spatial Evolution of Reaction Rates in the Liquid Phase Reaction Zone. Rates were calculated as a function of time and distance from the bubble surface assuming only conductive heat transport from a sphere with radius 150ym at 5200K, embedded in an infinite matrix at 300K.

When heat is liberated or absorbed in the calorimeter vessel, a thermal flux is established in the heat conductor and heat flows until the thermal equilibrium of the calorimetric system is restored. The heat capacity of the surrounding medium (heat sink) is supposed to be infinitely large and its temperature is not modified by the amount of heat flowing in or out. The quantity of heat flowing along the heat conductor is evaluated, as a function of time, from the intensity of a physical modification produced in the conductor by the heat flux. Usually, the temperature difference 0 between the ends of the conductor is measured. Since heat is transferred by conduction along the heat conductor, calorimeters of this type are often also named conduction calorimeters (20a). 

One approach to the study of solubility is to evaluate the time dependence of the solubilization process, such as is conducted in the dissolution testing of dosage forms [70], In this work, the amount of drug substance that becomes dissolved per unit time under standard conditions is followed. Within the accepted model for pharmaceutical dissolution, the rate-limiting step is the transport of solute away from the interfacial layer at the dissolving solid into the bulk solution. To measure the intrinsic dissolution rate of a drug, the compound is normally compressed into a special die to a condition of zero porosity. The system is immersed into the solvent reservoir, and the concentration monitored as a function of time. Use of this procedure yields a dissolution rate parameter that is intrinsic to the compound under study and that is considered an important parameter in the preformulation process. A critical evaluation of the intrinsic dissolution methodology and interpretation is available [71]. 

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