Kelvin force microscopy measurements on films of noncrystalline silica and aluminum phosphate particles reveal complex electrostatic potential patterns that change irreversibly as the relative humidity changes within an electrically shielded and grounded environment. Potential adjacent to the particle surfaces is always negative and potential gradients in excess of +/-10 MV/m are found parallel to the film surface. These results verify the following hypothesis: the atmosphere is a source and sink of electrostatic charges in dielectrics, due to the partition of OH(-) and H(+) ions associated to water adsorption. Neither contact, tribochemical or electrochemical ion or electron injection are needed to change the charge state of the noncrystalline hydrophilic solids used in this work.
Charge distribution in insulators has received considerable attention but still poses great scientific challenges, largely due to a current lack of firm knowledge about the nature and speciation of charges. Recent studies using analytical microscopies have shown that insulators contain domains with excess fixed ions forming various kinds of potential distribution patterns, which are also imaged by potential mapping using scanning electric probe microscopy. Results from the authors' laboratory show that solid insulators are seldom electroneutral, as opposed to a widespread current assumption. Excess charges can derive from a host of charging mechanisms: excess local ion concentration, radiochemical and tribochemical reactions added to the partition of hydroxonium and hydronium ions derived from atmospheric water. The last factor has been largely overlooked in the literature, but recent experimental evidence suggests that it plays a decisive role in insulator charging. Progress along this line is expected to help solve problems related to unwanted electrostatic discharges, while creating new possibilities for energy storage and handling as well as new electrostatic devices.
Production of electricity by friction is well known but poorly understood and it is the source of electrostatic discharge causing serious accidents. Recent results are in agreement with one of the conflicting views on this problem, according to which triboelectricity in polymers is triggered by mechanochemical and wear or mass transfer phenomena. These results also challenge the widely accepted paradigm of one-way charge transfer that is the basis of the triboelectric series. Experimental results from powerful analytical techniques 10 65 mechanisms leading to solids contact electrification and/or triboelectric charging? The explanation of the production of electrostatic charge comes from a transfer of electrons, ions or both, which are presented in the literature? 16 Poor knowledge on charge accumulation and dissipation 70 mechanisms 17-19 is a root of large-scale personal and property losses, including serious industrial accidents and explosions that are described further in the next section. This is ultimately due to the lack of scientific understanding of the basic phenomena.On the other hand, fundamental electrostatic concepts are well 75 established for semiconductors and metals. 20 When two metals with different work functions are brought into contact, electrons migrate across the interface creating a potential difference between them.
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