Static Electrification

In our preoccupation with thc dramatic developments in the numerous fields of modern physics with their beautiful instrumentation and exciting revelations, we tend to forget our profound ignorance of some of the longest known pheno­ mena of physics. Among these were, until the middle nineteen hundred and thir­ ties, ferromagnetism, friction, lightning stroke, the common electric spark, and static electrification. The first two have now been pretty weIl clarified and the und erst an ding of both of these phenomena have contributed greatly to our under­ standing of the structure of matter and surface physics. The lightning stroke and common spark are weH on their way to clarification. Strangely despite the ever expanding importance of static electrification in industry affecting as it does, a wide diversity of processes either as a useful tool or adversely and extending even to the realms of meteorology, this field has awakened little curiosity and stimulated little investigation in recent years except in so far as the immediate industrial problems it invoked required an immediate and often make-shift remedy. Trained in his early years as a chemist, and brought into contact with some aspects of colloidal chemistry involving electrokinetic potentials, cataphoresis, and spray electrification, thc author had his curiosity aroused by a number of these strange phenomena. Entering physics as a life career coincident with the development of the earl)' studies in atomic structure, in part through his teacher, R. A.

I. Static electrification by electrolytic process.- A. Basic principles in terms of galvanic action from metal surfaces.- B. Nature of systems leading to charge separation and their limitations.- 1. Flow charging systems.- 2. Limited contact charging.- C. Do adequate aqueous surface films exist for electrolytic charging ?.- D. Past evidence of electrolytic charging.- 1. Electrolytic flow electrification.- 2. Electrolytic flow charging in impacts of liquid jets on surfaces.- 3. Electrolytic contact charging.- E. Electrical endosmosis, streaming potentials, and cataphoresis (Verified aspects of electrolytic charging).- 1. Electrical endosmosis.- 2. The streaming potential.- 3. Cataphoresis.- F. The more accurate calculation of the double layer characteristics including ions of both signs.- G. The Workman-Reynolds freezing potential.- H. Summary and conclusions.- II. The contact potential difference or volta potential.- A. Introduction.- B. The metallic state energy bands, the Fermi law and basic principles.- C. Surface structure and the work function in relation to the Fermi level.- D. Influences modifying the work function.- E. The contact potential difference.- F. The measurement of contact potential and/or work function.- 1. Thermionic emission.- 2. Calorimetric measurement of work function.- 3. The photoelectric studies.- 4. Contact potential difference measurements.- G. Discussion and conclusion.- III. Static charging by spray electrification.- A. Introduction.- B. The Existence of an electrical double layer at gas-liquid interfaces.- 1. The studies of Coehn on double layers as related to dielectric constant.- 2. The electrical double layer in cataphoresis.- 3. Cataphoresis and the true nature of the double layer.- 4. The total potential difference at the water-air interface.- C. Relative potentials in double layers of water in relation to surface tension, for salt, acid and organic solutes.- D. The spray electrification phenomena.- 1. The studies of Lenard and his school.- 2. The studies of Chapman.- E. Spray electrification of water in relation to thunderstorm electrification.- F. Homogeneous or symmetrical charging of liquid droplets on dispersion.- 1. The spray and dust electrical analyses of Hansen and Kunkel using the Hopper and Laby technique.- 2. The measurements of Dodd on liquids.- 3. Significance of Dodd’s results.- G. Asymmetric charge distribution of droplets of micron size from bursting of small air bubbles in concentrated solutions.- H. Conclusions.- IV. Mechanisms of electrification on solid-solid contact.- A. Introduction.- B. Quantitative measuring techniques and the influence of electrical fields.- 1. Simple studies.- 2. The action of external fields on charging.- C. Initial investigation of controlled contact electrification of metal-inorganic insulator systems.- D. Electrification of dusts on dispersion and impact on surfaces.- 1. Experimental techniques.- 2. Observations.- E. The contact charging by rolling of inorganic insulator spheres on metal surfaces.- a) Design of apparatus.- b) Experimental results on fused quartz.- c) Effect of gas pressure.- d) The charging rate.- e) Borosilicate glass.- f) Interpretation of charging data.- g) Primary process of charge transfer.- h) Secondary processes governing redistribution of charge.- i) Surface conduction.- F. Extension of Peterson’s investigations by Wagner.- 1. Experimental techniques.- 2. Basic theory.- 3. Experimental observations.- a) Saturation charge.- b) Single crystal studies on quartz.- c) Aluminum oxide, synthetic single crystals, (white sapphire).- d) Single crystals of alkali halides.- e) Magnesium oxide single crystals (periclase).- f) Effect of surface finish.- g) High saturation charges.- h) Charging and work function.- i) Leakage currents.- j) Charging under ultra high vacuum with measured work function.- 4. Interpretation of results.- a) Surface and bulk conductivity.- b) Dependence of charging rate on surface exposed.- c) Maximum or saturation charge.- ?) Effect of surface roughness.- ?) Effect of electrostatic forces.- d) The true charge separation qs and back discharge.- e) Influence of rolling speed on qs.- f) The nature of charge exchange mechanisms.- 1. For quartz — 2. For Al2O3 — 3. For alkali halides — 4. MgO.- G. Contact charging of ice on ice.- H. Other possible charge transfer mechanisms.- 1. Asymmetric rubbing, true tribo electrification.- 2. The Henry model for contact charging of solids having a common ion.- 3. The charging of solids by rupture of surface dipoles.- 4. Luminosity in contact charging processes.- V. The generation of static charges by processes involving ionization of gases and miscellaneous other matters.- A. Introduction.- B. Various gaseous electronic mechanisms.- 1. Photoelectric and thermionic emission of carriers.- 2. IJnipolar corona discharges.- 3. The effect of plasmas from arcs and glows in static generation.- 4. Induction charging in auxiliary fields.- C. Static elimination.- 1. Introduction, grounding of all conductors.- 2. Reduction by increasing conductivity of insulators.- a) Volume conductivity.- b) Surface conductivity.- c) Agencies aiding surface os volume conductivity.- 3. The use of electrostatic dischargers.- a) By self-discharge.- b) By use of floating insulating systems.- c) Ions from electrostatic sources.- ?) By ions of both signs.- ?) By monitored ions of one sign.- d) The use of radioactive ionizing radiations.- e) The problems of elimination in dust and spray electrification.- f) Precipitation static in aircraft.- D. Thunderstorm electrification.- a) Capture or fission of drops.- b) Spray charging.- c) Ice-ice impact.- d) Separation through freezing potentials.- E. Protection against lightning stroke.- Author Index.