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Microgravity Experiments to Evaluate Electrostatic Forces in Controlling Cohesion and Adhesion of Granular MaterialsThe bulk behavior of dispersed, fluidized, or undispersed stationary granular systems cannot be fully understood in terms of adhesive/cohesive properties without understanding the role of electrostatic forces acting at the level of the grains themselves. When grains adhere to a surface, or come in contact with one another in a stationary bulk mass, it is difficult to measure the forces acting on the grains, and the forces themselves that induced the cohesion and adhesion are changed. Even if a single grain were to be scrutinized in the laboratory, it might be difficult, perhaps impossible, to define the distribution and character of surface charging and the three-dimensional relationship that charges (electrons, holes) have to one another. The hypothesis that we propose to test in microgravity (for dielectric materials) is that adhesion and cohesion of granular matter are mediated primarily by dipole forces that do not require the presence of a net charge; in fact, nominally electrically neutral materials should express adhesive and cohesive behavior when the neutrality results from a balance of positive and negative charge carriers. Moreover, the use of net charge alone as a measure of the electrical nature of grain-to-grain relationships within a granular mass may be misleading. We believe that the dipole forces arise from the presence of randomly-distributed positive and negative fixed charge carriers on grains that give rise to a resultant dipole moment. These dipole forces have long-range attraction. Random charges are created whenever there is triboelectrical activity of a granular mass, that is, whenever the grains experience contact/separation sequences or friction.
Document ID
20010004341
Acquisition Source
Glenn Research Center
Document Type
Conference Paper
Authors
Marshall, J.
(Search for Extraterrestrial Intelligence Inst. Moffett Field, CA United States)
Weislogel, M.
(NASA Glenn Research Center Cleveland, OH United States)
Jacobson, T.
(NASA Glenn Research Center Cleveland, OH United States)
Date Acquired
August 20, 2013
Publication Date
March 1, 1999
Publication Information
Publication: Proceedings of the Fourth Microgravity Fluid Physics and Transport Phenomena Conference
Subject Category
Fluid Mechanics And Thermodynamics
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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