Moisture alternating currents

Lynntech, Inc. s (Lynntech s), electrokinetic remediation of contaminated soil technology is an in situ soil decontamination method that uses an electric current to transport soil contaminants. According to Lynntech, this technology uses both direct current (DC) and alternating current (AC) electrokinetic techniques (dielectrophoresis) to decontaminate soil containing heavy metals and organic contaminants. A non homogeneous electric field is applied between electrodes positioned in the soil. The field induces electrokinetic processes that cause the controlled, horizontal, and/or vertical removal of contaminants from soils of variable hydraulic permeabilities and moisture contents. 

At moisture contents above 24 or 25%, readings are less reliable than readings below 24 or 25% for two reasons. First, the rate of change of resistance with moisture content decreases markedly, so the sensitivity is reduced. Second, the moisture content reading decreases substantially with time because of polarization effects. The latter effect can be minimized by the use of alternating current (AC) rather than the direct current (DC) instruments traditionally used for resistance meters. 

Electrical moisture meters provide a quick and reasonably accurate nondestructive alternative. The direct-current resistance of the timber is measured or either the alternating-current capacitance or power loss can be measured. Direct-current resistance moisture meters are more common a pair of needles, a fixed distance apart, is driven into the wood across or along the grain (depending on the manufacturer s instructions) and the electrical resistance measured. The procedure is reasonably accurate between the fibre saturation point (defined later) at 30% and about 6% moisture content (at which point the resistance becomes too great to measure with reasonable accuracy). In this moisture content range, the relationship between electrical resistance and moisture content is represented by a log-log plot. 

The corrosiveness of a soil depends on a number of factors including resistivity, pH, aeration, moisture, and chemical contents. It is highly location-dependent and is influenced further by the presence of alternating current as well is galvanic couples with other buried metals. 

Environmental concern with reference to PVC and the fact that burning (possibly as a distinction from controlled incineration) may generate obnoxious acid fumes has created pressure on the pharmaceutical industry to move away from PVC. The alternative materials which have been considered include PET (polyester) and PP (polypropylene). Both require higher softening temperatures than PVC and good heat control, which can be more readily achieved with modem equipment with an effective preheat system. However, this only applies to certain selected and special material grades. Although these materials can be coated with PVdC to improve the moisture barrier, there are pressures to ban PVdC as it also contains a chloride component. Suffice it to say that the replacement of PVdC and its associated barrier/heat seal features may not be easy to achieve. Current opinion is that PVC will not be replaced. 

The oxidation of alcohols to carbonyl compounds is one of the most fundamental and important processes in the fine chemical industry. The classical methodology is based on the stoichiometric use of heavy metals, notably Cr and Mn (1,2). Alternatively metal-free oxidation, such as the Swern and Pfitzner-Moffat protocols, is based on e.g., dimethylsulfoxide as oxidant in the presence of an activating reagent such as N,N -dicyclohexylcarbodiimide, an acid anhydride or acid halide (3). Although the latter methods avoid the use of heavy metals, they usually involve moisture-sensitive oxidants and environmentally undesirable reaction media, such as chlorinated solvents. The desired oxidation of alcohols only requires the formal transfer of two hydrogen atoms, and therefore the atom economy of these methods is extremely disadvantageous. The current state of the art in alcohol oxidations... 

In polluted conditions where moisture and solid pollutants collect and in the condition of electrical stress which obtain in HV applications, small leakage currents flow across the surface of the outer insulator. The currents cause a rise in temperature which in turn causes dry bands to form on the surface of the insulator. Small sparks then cross the dry band the temperature of the sparks is 2000-3000 C, and the surface of the insulator can reach 450-600 C. Such temperatures can easily cause degradation of polymers with the development of carbonaceous tracking which extends in dendritic fashion. Alternatively, erosion can occur, causing cratering and final breakdown of the insulator. The worst damage is caused by currents of less than 20 mA. See Fig. 26.4. 

The LFAC laminates are compatible with current brown oxides and reduced copper oxide treatments.The oxide treatment should be kept thin, not exceeding 0.4 mg/cm. Alternative oxide treatments, such as peroxysulfuric oxide, are strongly preferred for some HF laminates.The cores for ML-PWBs that will be subject to LFA should be post-oxide baked to remove moisture— generally 120°C for at least 30 minutes for signal layers and 60 minutes for power/groimd layers. 

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