Electrical adhesion

Ikazaki, F. and M. Kamamura, Electric Adhesion Force of a Single Particle and of a Powder at Room Temperature and Above Ambient Temperature and its Application to a Fluidized Bed, Particle Sci. Tech., 2, 3, 1984, pp. 271-283. Inculet, I. I., N. H. Malak, and J. A. Young, Corona Charging of Immobilized Spherical Particles, in Electrostatics 1983, Ed. S. Singh, Conf. Ser., 66, Inst. Phys, 1983. pp. 98-105. 

In 1877, Edison patented a device based on the observation that a smooth metal electrode held at a high electrical potential adhered very strongly to a semiconducting surface. This electrical adhesion was directly related to the applied voltage, disappearing when the potential was removed. Unfortunately, the adhesion also failed when dust or scratches appeared on the semiconductor surface. As a result of these problems, there has as yet been no commercial exploitation of this invention. 

The cause of this electrical adhesion has not been explained completely but appears to be related to the electrical conductivity of the powder. Only for particles with resistivities between 10 and 10, ohm-metre is the adhesion apparent. Below this, the particles discharge on contact with the electrode, acquiring a charge of opposite sign and jumping off the electrode, the so-called pith-ball effect. For larger resistivities, locahzed electric breakdown occurs and no adhesion develops. 

Perhaps the most novel application of this electrical adhesion of sohds is the control of flowing particles. For example, the phenomenon has been used to stop the flow of powder out of a silo by applying a strong field across electrodes at the open base. Alternatively, the flow was metered by pulsing the electric field in a controlled fashion. 

Fig. 1. Results for electrical adhesion of a ceramic disc to a metal plate...

There are essentially three different situations that need to be considered under this title adhesion of pressure-sensitive tapes to metal surfaces, adhesion of vacuum-evaporated thin films of metal on polymer surfaces and the adhesion of ultra-small particles. The first two of these will be considered here, bnt the third one is dealt with quite separately under the heading Electrical Adhesion. 

The existence of an electrical double layer at the interface between a metal and a polymer adhering to it has been satisfactorily demonstrated. Undoubtedly, the electrostatic forces developed from this interaction could contribute to the total adhesive bond strength. However, the theories that have been advanced are less than rigorous and have been subject to severe criticism. Nevertheless, there are some phenomena that cannot be explained without recourse to this explanation in some form (see Electrical adhesion). 

Electrical adhesion K KENDALL Adhesion in a strong electrical field applications... 

Calculation of electrical adhesion force In order to calculate the electrical adhesion force, the charge distribution at the interface must be determined. This requires the solution of Poisson s equation in one dimension as... 

Inserting Eq. 2-12 into Eq. 2-11, one obtains the electrical adhesion force per unit area, pressure, as... 

The same considerations explain why the small water jet of Mr. Fuchs was continuous, in the absence of electricity, when it left by an oiled opening adhesion and friction being much decreased, the jet took its natural state, a state in which divisions arrived at the top before their complete ffansformation with the opening not oiled, on the contrary, the vibrations resulting from adhesion made the transformation faster, so that it was completed at a less distance from the opening finally, under the influence of electricity, adhesion being destroyed, the jet again took its natural state. 

The adhesion between two solid particles has been treated. In addition to van der Waals forces, there can be an important electrostatic contribution due to charging of the particles on separation [76]. The adhesion of hematite particles to stainless steel in aqueous media increased with increasing ionic strength, contrary to intuition for like-charged surfaces, but explainable in terms of electrical double-layer theory [77,78]. Hematite particles appear to form physical bonds with glass surfaces and chemical bonds when adhering to gelatin [79]. 

Chemistry produces many materials, other than drugs, that have to be optimized in their properties and preparation. Chemoinformatics methods will be used more and more for the elucidation and modeling of the relationships between chemical structure, or chemical composition, and many physical and chemical properties, be they nonlinear optical properties, adhesive power, conversion of light into electrical energy, detergent properties, hair-coloring suitabHty, or whatever. 

It is a very lightweight rubber and has very good weathering and electrical properties, excellent adhesion, and excellent ozone resistance. 

Silicone rubbers have excellent ozone and weathering resistance, good electrical properties, and good adhesion to metal. 

Adberabibty of the film may be enhanced by its treatment with flame, electric discharge, boron trifluoride gas, activated gas plasma, dichromate sulfuric acid, and a solution of alkab metal ia Hquid ammonia (84—87). A coating of polyurethane, an alkyl polymethacrylate, or a chlotinated adhesive can be apphed to PVF surfaces to enhance adhesion (80,88,89). 

The principal chemical markets for acetylene at present are its uses in the preparation of vinyl chloride, vinyl acetate, and 1,4-butanediol. Polymers from these monomers reach the consumer in the form of surface coatings (paints, films, sheets, or textiles), containers, pipe, electrical wire insulation, adhesives, and many other products which total biUions of kg. The acetylene routes to these monomers were once dominant but have been largely displaced by newer processes based on olefinic starting materials. 

Polymers. Ion implantation of polymers has resulted in substantial increases of electrical conductivity (140), surface hardness (141), and surface texturing (142). A four to five order of magnitude increase in the conductivity of polymers after implantation with 2 MeV Ar ions at dose levels ranging from 10 -10 ions/cm has been observed (140). The hardness of polycarbonate was increased to that of steel (141) when using 1 MeV Ar at dose levels between 10 -10 ions/cm. Conductivity, oxidation, and chemical resistance were also improved. Improvements in the adhesion of metallizations to Kapton and Teflon after implantation with argon has been noted (142). 

Flame spray metallising is widely used for the protection of metal against corrosion, especially for in situ protection of stmctural members. The principal metal used for spraying of plastics is sine. Aluminum and copper are also used. If the distance from the part is too great, the zinc solidifies before it touches the part and adhesion is extremely poor. If the molten zinc oxidizes, conductivity and adhesion are poor. If the distance is too short, the zinc is too hot and the plastic warps or degrades. These coatings are not as dense as electrically deposited coatings because of numerous pores, oxide inclusions, and discontinuities where particles have incompletely coalesced. 

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