Atmosphere potential, electrical

The precautions generally applicable to the preparation, exposure, cleaning and assessment of metal test specimens in tests in other environments will also apply in the case of field tests in the soil, but there will be additional precautions because of the nature of this environment. Whereas in the case of aqueous, particularly sea-water, and atmospheric environments the physical and chemical characteristics will be reasonably constant over distances covering individual test sites, this will not necessarily be the case in soils, which will almost inevitably be of a less homogeneous nature. The principal factors responsible for the corrosive nature of soils are the presence of bacteria, the chemistry (pH and salt content), the redox potential, electrical resistance, stray currents and the formation of concentration cells. Several of these factors are interrelated. 

Ionospheric potential Electric potential with respect to earth of the highly conducting regions of the upper atmosphere, assumed to be equipotential (which is not always true). 

Instrumented corrosion sensors. Electrochemical sensors are based on the principle of electrochemical current and/or potential measurements and facilitate the measurement of atmospheric corrosion damage in real time in a highly sensitive manner. There are special requirements for the construction of atmospheric corrosion sensors. For the measurement of corrosion currents and potentials, electrically isolated sensor elements are required. Fundamentally, the metallic sensor elements must be extremely closely spaced under the thin-film electrolyte conditions, in which ionic current flow is restricted. Electrochemical techniques utilized to measure atmospheric corrosion processes include zero resistance ammetry (ZRA), electrochemical noise (EN),... 

The high potential and small radius of curvature at the end of the capillary tube create a strong electric field that causes the emerging liquid to leave the end of the capillary as a mist of fine droplets mixed with vapor. This process is nebulization and occurs at atmospheric pressure. Nebulization can be assisted by use of a gas flow concentric with and past the end of the capillary tube. 

Response to Electric and Acoustic Fields. If the stabilization of a suspension is primarily due to electrostatic repulsion, measurement of the zeta potential, can detect whether there is adequate electrostatic repulsion to overcome polarizabiUty attraction. A common guideline is that the dispersion should be stable if > 30 mV. In electrophoresis the appHed electric field is held constant and particle velocity is monitored using a microscope and video camera. In the electrosonic ampHtude technique the electric field is pulsed, and the sudden motion of the charged particles relative to their counterion atmospheres generates an acoustic pulse which can be related to the charge on the particles and the concentration of ions in solution (18). 

BS 5345. General Recommendations—Code of Practice for Selection, Installation and Maintenance of Electrical Apparatus for Use in Potentially Explosive Atmospheres. BSI, U.K. 

HS(Gj22 Electrical apparatus for use in potentially explosive atmospheres... 

AMD 2 Electrical apparatus for potentially explosive atmospheres - General requirements (AMD 10552J dated August 1999. Partially superseded BS EN 50014 1993 which remains cuiTcnt... 

AMD 1 Electrical apparatus for potentially explosive atmospheres- Intrinsic safety i (AMD 10040J dated June 1998. Read with BS EN 50014 1993... 

The study clearly shows that the observed electrical signals are electrochemical in origin, and the first-order description of the process is consistent with that expected from atmospheric pressure behaviors. Nevertheless, the complications introduced by the shock compression do not permit definitive conclusions on values of electrochemical potentials without considerable additional work. 

Contact with steel, though less harmful, may accelerate attack on aluminium, but in some natural waters and other special cases aluminium can be protected at the expense of ferrous materials. Stainless steels may increase attack on aluminium, notably in sea-water or marine atmospheres, but the high electrical resistance of the two surface oxide films minimises bimetallic effects in less aggressive environments. Titanium appears to behave in a similar manner to steel. Aluminium-zinc alloys are used as sacrificial anodes for steel structures, usually with trace additions of tin, indium or mercury to enhance dissolution characteristics and render the operating potential more electronegative. 

Consider the apparatus shown in Figure 14-3. A glass tube is fitted with electrodes so that a potential difference of 10,000 volts can be applied across a space filled with a desired gas at various pressures. Suppose neon, for example, is placed in the tube. With the voltage applied, the gas will begin to conduct electricity when its pressure is reduced to about 0.01 atmosphere. The tube then glows with the familiar color of a neon sign. If a different gas is used, the color is different, but otherwise, the behavior is about the same. If the pressure is reduced still further to about 10 atmosphere, the glow from the gas... 

---