Atmosphere electrical conductivity

Fig. 9. Atmospheric electrical conductivity profiles

FIGURE 2 Approximate atmospheric electrical conductivity profiles under various conditions. 

Process. Any standard precursor material can be used, but the preferred material is wet spun Courtaulds special acrylic fiber (SAF), oxidized by RK Carbon Fibers Co. to form 6K Panox B oxidized polyacrylonitrile (PAN) fiber (OPF). This OPF is treated ia a nitrogen atmosphere at 450—750°C, preferably 525—595°C, to give fibers having between 69—70% C, 19% N density less than 2.5 g/mL and a specific resistivity under 10 ° ohm-cm. If crimp is desired, the fibers are first knit iato a sock before heat treating and then de-knit. Controlled carbonization of precursor filaments results ia a linear Dow fiber (LDF), whereas controlled carbonization of knit precursor fibers results ia a curly carbonaceous fiber (EDF). At higher carbonizing temperatures of 1000—1400°C the fibers become electrically conductive (22). 

Early models used a value for that remained constant throughout the day. However, measurements show that the deposition velocity increases during the day as surface heating increases atmospheric turbulence and hence diffusion, and plant stomatal activity increases (50—52). More recent models take this variation of into account. In one approach, the first step is to estimate the upper limit for in terms of the transport processes alone. This value is then modified to account for surface interaction, because the earth s surface is not a perfect sink for all pollutants. This method has led to what is referred to as the resistance model (52,53) that represents as the analogue of an electrical conductance... 

Most polymers are very good electrical insulating materials because of their chemical composition, i.e., their electrical conductivity is exceptionally low. Because of this important property, many plastics are used to produce electrically nonconductive parts. However, the high surface resistance leads to an unwanted property the material is prone to electrostatic charge accumulation. To facilitate dissipation of the charge, antistatic agents are incorporated, which combine with atmospheric moisture on the plastic surface to form a conductive film. 

Since the pioneering work of Rohrer and Binning,77 scanning tunelling microscopy (STM) has been used to image atomic-scale features of electrically conductive surfaces under ultra-high-vacuum but also at atmospheric pressure and in aqueous electrochemical environments. The ability of STM to image chemisorption and surface reconstruction is well... 

Manheim (1970) presents a critical review of the confusing variety of data found in the literature, but according to Home et al. (1969), pressures up to several thousand atmospheres seem to have no significant effect on Dg. Values for Ds are sometimes not available or are difficult to estimate but can be obtained indirectly by means of electrical conductivity measurements (Klinkenberg, 1951). Table 8-7 provides a list of Ds values found in the literature for the most... 

Fig. 1.22. The kinetics of change in electric conductivity of polycrystalline oxide during adsorption of donor particles 1 - CO on Sn02, 0.11 vol.-% CO in atmosphere, T = 300 C 2 - H atoms on ZnO, = 510-2 Torr, Tp = 1400 C,...

Let us dwell on existing key models describing chemisorption induced response of electric conductivity in semiconductor adsorbent. Let us consider both the stationary values of electric conductivity attained during equilibrium in the adsorbate-adsorbent system and the kinetics of the change of electric conductivity when the content of ambient atmosphere changes. Let us consider the cases of adsorption of acceptor and donor particles separately. In all cases we will pay a special attention to the issue of dependence of the value and character of signal on the structure type of adsorbent, namely on characteristics of the dominant type of contacts in microcrystals. 

One of basic experimental facts is provided by existence of the power law between the value of equilibrium electric conductivity of adsorbent and pressure of oxygen in ambient atmosphere ... 

We should note that this effect of the hydrogen on electric conductivity is related neither to reduction of oxide nor to the volume dissolution of hydrogen in oxide. The first option was ruled out due to initial heating of adsorbent in hydrogen atmosphere up to establishing the stationary value of electric conductivity at the temperature exceeding the maximum temperature of experiment (Theati 400 420 C). The con-... 

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" . 

At room temperature, unsaturated vapours of the above specified polar and nonpolar liquids do not influence considerably the rate of adsorption and chemical activity of not only adsorbed oxygen layers, but also of acceptors of semiconductor electrons of another type, namely, of alkyl radicals [54]. This is seen from the electric conductivity of ZnO films with adsorbed alkyl radicals or oxygen being invariable in the atmosphere of the saturated vapours of the above specified solvents. In the case of oxygen, this can be also seen from the fact that the oxygen concentration features no decrease. 

In the present work, a somewhat different approach was chosen in order to produce conducting polymers the basic idea was to start with a cheap material, like PVC, and try to remove all the hydrogen and chlorine atoms from the polymer chain. The purely carbon material thus obtained was expected to exhibit the electrical conductivity of a semimetal, while being insensitive to the atmospheric oxygen. In this paper, we report for the first time how PVC can be completely dehydrochlorinated by simple exposure to a powerful laser beam that combines both the photochemical and the thermal effects. 

The atmosphere is a good insulator but it does have a conductivity which like the ion density is not affected by the radon daughter ions. It is of interest to note that the electrical conductivity is balanced with respect to positive and negative polarity within the accuracies indicated. 

Oxides play many roles in modem electronic technology from insulators which can be used as capacitors, such as the perovskite BaTiOs, to the superconductors, of which the prototype was also a perovskite, Lao.sSro CutT A, where the value of x is a function of the temperature cycle and oxygen pressure which were used in the preparation of the material. Clearly the chemical difference between these two materials is that the capacitor production does not require oxygen partial pressure control as is the case in the superconductor. Intermediate between these extremes of electrical conduction are many semiconducting materials which are used as magnetic ferrites or fuel cell electrodes. The electrical properties of the semiconductors depend on the presence of transition metal ions which can be in two valence states, and the conduction mechanism involves the transfer of electrons or positive holes from one ion to another of the same species. The production problem associated with this behaviour arises from the fact that the relative concentration of each valence state depends on both the temperature and the oxygen partial pressure of the atmosphere. 

---