B.V. Derjaguin

On two methods of calculation of the force of sticking of an elastic sphere to a rigid plane

Abstract Two methods for calculating the force of the adhesion of an elastic sphere with a rigid plane are considered, under conditions where the surface profile of the deformed sphere under the effect of a normal load and surface forces is very similar to that described by Hertz theory. The first method is based on the calculation of the first derivative of the total energy of the adhesive interaction; the second method is based on summing up the interactions outside the zone of direct contact of the deformable sphere with the right plane. The origin of discrepancy in the results obtained by the two aforesaid methods, are indicated. The maximum adhesion force proves to be equal to the force of interaction of the undeformed sphere with the substrate for the two approaches and within the approximation employed independent of the method of calculation.

On the relationship between the electrostatic and the molecular component of the adhesion of elastic particles to a solid surface

where F~ is the molecular component of the sticking force, Fc is the component dependent on the previous electrification of bodies that are brought in contact with one another, Fc is the attractive force which is conditioned by the double electric layer appearing in the zone of a contact on the formation of the latter and determined by the density of its charges. Let us limit ourselves to examining the case where there is no previous electrification and, hence, F~ = 0. In calculating the molecular component of the sticking force in the case of an elastic contact, the following circumstances will have to be taken into account. When a plastic contact is broken, a variation in the energy of interaction of two bodies may be connected only with a variation in the distance between them. However, in the case of breaking the elastic contact, a change in the spacing of interacting bodies occurs simultaneously with a change in the form between separate areas of the surfaces of those bodies, as well as in the size of the interaction zone. Therefore, in the case when an elastic contact is broken the interaction should be characterized by a generalized force which can be determined as a derivative of the interaction energy with respect to deformation (1-3). For the sake of simplicity, let us consider the case of contact between an elastic ball and an absolutely hard surface. The complete energy of the molecular interaction of the ball with a plane is equal to a sum (4) :

On the role of electrostatic forces in the adhesion of polymer particles to solid surfaces

Abstract Simultaneous measurements have been made of the adhesive force and double electric charge of particles after their removal from a metal surface. For the systems investigated, the adhesive force and charge on the particles increase with particle diameter according to a power law, with an exponent close to 2. Such dependence can be explained on the basis of the electrostatic nature of the adhesive forces. A double electric layer exists at the interface between the particles and the metal surface. A calculation was made of the surface density of charge for the polyvinyl chloride particle-steel system.

Influence of contact electrification on the collision of elastic particles with a rigid surface

The influence of the contact formation of an electrical double layer (EDL) on the collision of uncharged, perfectly elastic particles with a dry rigid surface is theoretically investigated. The kinetics of the formation of an EDL in the elastic collision of a particle, the work of the nonequilibrium separation of the plates of the EDL when it rebounds, and the magnitude of a charge gained by the particle on its collision are calculated. It is shown that the nonequilibrium forces associated with the EDL can considerably reduce the rebound velocity of particles, in the case of their elastic collision, and even cause their sticking to the surface, when impinging against it at a velocity lower than the critical one. The dependence of the critical collision velocity on the geometrical, mechanical, and electrosurface parameters of particles and the substrate is established. Some known experimental data are well described by the expression for the rebound impingement velocity ratio, obtained from consideration of the energy balance.

Influence of adhesion on the sliding and rolling friction

Abstract Yet in 1934, one of the authors had developed the molecular friction theory explaining the external friction by dissipation of energy on the molecular unevenness of the bodies in friction. This theory distinctly determines the role of adhesion in the processes of the external sliding friction. the adhesion forces are used in this theory only for explaining deviation from the Amontons law expressing the proportionality of the friction force to the normal load. The rolling friction process (in the absence of deformations) represents a process of formation and breakage of adhesion bonds. Using the electron theory as the basis, the mechanism of influence of the electrostatic component of adhesion on the rolling friction is considered, the electrostatic component being attributable to the formation of a double electric layer when solids are in friction, and when its plates are separated as the contact is broken.

The role of the pressing-on in the adhesion of elastic particles

Abstract One has carried out an analysis of the influence of the preliminary pressing-on on components of the adhesion force of different natures for the case of the contact of elastic particles with a rigid substrate. Two pressing-on variants are considered; as, - those realized under the effect of a dynamic and a static load. It has been shown that an increase in the adhesion of elastic particles to the surface resulting from the preliminary pressing-on is attributable to an increase in the adhesion force component due to a double electric layer in contact.

On the initiation of DD reactions in the zirconium-deuterium system

Abstract The possibility of initiating DD reactions on vibro-milling of zirconium together with heavy water and deuterated polypropylene has been investigated. Weak emission of neutrons has been detected both during the vibro-milling process and some time after its completion.

Emission of High-Speed Electrons and Other Phenomena Accompanying the Process of Breaking Adhesion Bonds

Abstract The process of breaking adhesion bonds is accompanied by the drawing apart of the plates of a flat condenser as formed by the double electric layer. An increase in the spacing between differently charged surfaces in the process of breaking the adhesion contact results in the falling off of a capacity, and in increasing the potential difference up to the breakdown voltage. If the breakdown occurs under conditions of a vacuum, then during the experiment a flux of free electrons is registered, whose energy amounts to a value of the order of 10 4 to 10 5 eV. Under ordinary conditions, owing to the ionization of the molecules of a surrounding gas by high-speed electrons, the gas-discharge processes arise accompanied by glowing, electromagnetic radiation, and acoustic emission, which are characteristic of those processes.

Electrical phenomena accompanying the formation of new surfaces, and their role in adhesion and cohesion

Abstract Upon tearing off polymer films from metals and glasses phenomena are observed which testify to the apparition of high differences of potentials between the interfaces formed. In particular, if the film is stripped under vacuum, electron emission is observed with electron velocities of the order of kilovolts. These phenomena are due to division upon stripping of the double electric layer, formed upon close contact between the polymer and the substrate, and to retardation of its discharge. The same retardation of the discharge of the double layer may explain quantitatively both the high value of the work spent on tearing off the film, the dependence of the latter on the speed of stripping and on the pressure of surrounding gas. Similar phenomena were found to take place during the destruction of many crystalline (but not amorphous) solids and are explained by the formation and division of an alternating-sign double layer of mosaic structure.

Excitation of nuclear reaction under mechanical effect (impact) on deuterated solids

Abstract Using the analysis data on the characteristics of radiation accompanying failure of solids as the basis, a supposition is made of the feasibility of dd-reactions taking place during fracture of deuterated dielectrics. The experiments carried out prove the feasibility of generation of neutrons at the moment of fracture of D 2 O LD crystals, indicating the excitation of nuclear reaction.