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English Views: 0 Author: Site Editor Publish Time: 2020-08-19 Origin: Site
Contaminants And Wiping Theory-Particle adhesion mechanisms
l Cleanroom contaminants
l Sources of contamination
l Particle adhesion mechanisms
l Contaminant removal methods
l Considerations for contaminant removal
l Choosing the right tools and methods
l Myesde Cleanroom Wipes
Particle adhesion mechanisms
There are four mechanisms that hold particles to a surface：
l Gravity
adhesion force from gravity depends only on the mass of the particle
for particles less than 100 microns in size, gravity is not the strongest force holding the particles to a surface
l Electrostatic forces
electrostatic forces can both attract and hold a particle to a surface
electrostatic forces decrease with increased humidity
electrostatic forces may be minimized through use of static elimination devices
electrostatic forces are not the most dominant forces holding a particle to a surface
l van der Waals (atomic) forces
caused by attraction of unevenly grouped electrons in the atoms of the particle and the surface also called “intermolecular” forces
these forces come into play when the particle is very near the surface
van der Waals forces are independent of humidity and static
one of the two most dominant forces holding small particles to a surface
l Hydroscopic, or capillary forces
also called capillary forces
caused by thin liquid layer between a particle and a surface
adhesion increases with contact area of particle with surface - large, flat particles, and long thin fibers adhere more strongly
capillary force increases with humidity or the presence of other liquid vapor on the surface
l Conclusion
Particles are held to surfaces by a variety of forces
These forces vary according to many factors including particle size and shape, surface texture, and humidity
Small particles are more tightly held than large particles
Removal of small particles requires force greater than that holding the particles
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