I would like technical information (with references that provide
specific details on processes) on how dry or wet milling can be
performed using high energy ultrasound. Does ultrasonic milling
require that the substance being milled be placed in a liquid media,
such as water?  Does the substance being milled have to be pre-treated
in some way (ie, mechanically milled first to get the particles below
a certain size?)
I am especially interested in whether cacao bean nibs can be
ultrasonically milled, recognizing that traditional mechanical milling
results in the production of a goopy mess (the "chocolate mass"). 
What quantity of nibs can be ultrasoncially milled at one time---and
how long would it take to get the nibs particle size down to the range
of 20 microns (using a desktop ultrasonic device such as the Sonicator
3000 by Misonix)?