Electrostatic charge measurement

There was no significant damage to equipment in the fire tests, and it was demonstrated that a Jet Airmix mixer may safely handle the mixing of RP formulations on a routine basis. Since a high risk of fire is always associated with any method of transfer of RP, a pneumatic conveying system [dynamic air, two phase positive pressure transfer system was evaluated to load RP into the Jet Airmix mixer. Electrostatic charge measurements were minimal and indicated the system was satisfactory to load the blender. 

Two things are certain. First, most measurements are made with electrical contacts of questionable character, and second, it is not yet possible to isolate reliably bulk-dominated from contact-dominated effects. To elucidate the mechanism of electrically initiated detonation it will be necessary to devise and perform experiments for accurate contact characterization and for the separation of bulk- and contact-dominated phenomena. To point the way, it is convenient to consider two classes of electrical measurements those where the specimen is electroded (conductance, injection, capacitance measurements), and those where the sample is electrode-free (spark discharge and electrostatic charging measurements) [31]. The remainder of this section gives a brief discussion of these techniques. 

In practice, the occurrence of steric effects in adsorption of simple ions is probably not common. Evidence for this lies in the fact that adsorption equations using single value/concentration independent mass action constants are frequently found to fit experimental adsorption data quite well. Also, since typical surface sites occupy an area of the order of 50-100 based on surface electrostatic charge measurements... 

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). 

Gady found that, depending on the charge of the particle, van der Waals forces dominated over the forces associated with electrostatically charged patches when the particle-to-substrate separation was between 3 and 10 nm, depending on the particle charge. In addition, he found that the distance at which the snap-together occurred required that van der Waals forces dominate over electrostatic. In all his measurements, however, a component of the total attractive force, even at close separations, was observed to be electrostatic in nature. 

Thus, in the relatively simple case of oil in water emulsions, where a surface active agent such as a soap is used as the emulsifying agent, it is known that the soap adsorbed on the surface of the oil particles decreases the interfacial tension, thus stabilizing the emulsion. The adsorbed soap ions also give a net electrostatic charge to the dispersed oil droplets, serving to repel other oil droplets, with the net effect that flocculation is hindered (and stability is increased). It is even possible to measure the amount of adsorbed soap ions and to calculate the values of the surface potential. 

Wada, K, Sasaki, K and Masuhara, H. (2002) Electric charge measurement on a single microparticle using thermodynamic analysis of electrostatic forces. Appl. Phys. Lett., 81, 1768—1770. 

The dipole moment of a molecule can be obtained from a measurement of the variation with temperature of the dielectric constant of a pure liquid or gaseous substance. In an electric field, as between the electrostatically charged plates of a capacitor, polar molecules tend to orient themselves, each one pointing its positive end toward the negative plate and its negative end toward the positive plate. This orientation of the molecules partially neutralizes the applied field and thus increases the capacity of the capacitor, an effect described by saying that the substance has a dielectric constant greater than unity (80 for liquid water at 20°C). The dipole moments of some simple molecules can also be determined very accurately by microwave spectroscopy. 

In each of these plants, the characterization of the dust explosion potential was carried out by sampling transport ducts for explosive dust concentrations during an actual plant operation. The critical measurements taken were the quantification of explosive dust concentrations and level of electric energy generated from the electrostatic charge accumulations found in the duct. 

Graf (G8) measured the pressure buildup due to electrostatic charging of stationary drops. He found this pressure to be some 30-60% of the value given by Eq. (4), independent of polarity of charge or dielectric constant of the liquid. This factor, which he terms a charging factor, was a function of both geometry and liquid properties. It may also reflect polarization effects that are neglected in Eq. (4). 

Samples suitable for SEM measurements include most solids which are stable under vacuum (metals, ceramics, polymers, minerals). Samples must be less than 2 cm in diameter. Non-conducting samples are usually coated with a thin layer of carbon or gold in order to prevent electrostatic charging. 

Carter, P. A., Rowley, G., Fletcher, E. I, and Sylianopoulos, V. (1998), Measurement of electrostatic charge decay in pharmaceutical powdersand polymer materials used in dry powder inhaler devices, Drug Dev. Ind. Pharm., 24,1083-1088. 

USP 2421778 (1947), p 5 8t CA41, 5724 (1947) [El ectrostatic charges were detd by means of an electroscope for pure LA (Lead Azide), DLA (dextrinated LA), and PVA-LA (polyvinyl.alcbhoI LA), before and after tumbling. Before starting the experiment each sample was allowed to stand for 16 hours before its electrostatic charge, prior to tumbling, was measured. 

L. Schmitz, Chem Ing Tech 21, 386-89 (1949) CA44, 1259 (1950) (Measurement of electrostatic charge and ignition sensitivity of various primary and initiating explosives) 7) R.F. Wilkerson "Research and Development in the Field... 

Electroscope. An apparatus for detecting electrical charges consists in its simplest form of two strips of gold-leaf attached to an insulated conductor suspended from the stopper of a glass container (See Fig on p 300 of Ref 1), When desired to determine the potential of an electrostatic charge, a so-called measuring electroscope" is used. 

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