Apparatus and method for removing minute particles from a substrate

Apparatus for removing small particles from a substrate comprising:

• (a) A source of pure fluid carbon dioxide under pressure and having an enthalpy of below about 135 BTU per pound based on an enthalpy of zero at 150 psia for a saturated liquid, so that a solid fraction will form upon expansion of the fluid carbon dioxide to the ambient pressure of said substrate;
• (b) a first expansion means for expanding a portion of the fluid carbon dioxide obtained from the source into a first mixture containing gaseous carbon dioxide and fine droplets of liquid carbon dioxide;
• (c) a coalescing means operatively connected to the first expansion means for converting said first mixture into a second mixture containing gaseous carbon dioxide and larger liquid droplets of carbon dioxide;
• (d) a second expansion means operatively connected to the coalescing means for converting said second mixture into a third mixture containing discrete, minute solid particles of carbon dioxide not normally resolvable by the human eye and gaseous carbon dioxide;
• and
• (e) means connected to said second expansion means for directing said third mixture toward the substrate.