PHC320H1 Lecture Notes - Lecture 33: Contact Angle, Colloidal Silica, Fred Lawrence Whipple Observatory
24 Mar 2015
School
Course
Professor
Document Summary
In order for all powder to flow, we need driving force > resistant force otherwise powder will not flow. Mechanical forces, sometimes powder itself can"t flow well, we have to add a bit more external forces so those force are energy to push powder to flow. Adhesive forces: forces that exists between 2 unlike surfaces. Frictional forces: when surface roughness increases, friction too big so can"t skate on stones. Mechanical interlocking: lego is perfect interlocking but for particles we may not get perfect interlocking but can be stuck together since the shape. Cohesive and adhesive forces are both molecular forces since they present on different surfaces so defined differently, van der wall forces are broad, and short range and we talk about particle particle interactions. If we want to make particles we should aim for spherical, oblong or cube. Rule of thumb is make particles >250 microns for better flowability if we can"t then make close to.
