Thermospray method for production of aluminum porous boiling surfaces

Method for making an aluminum porous boiling surface having an open cell structure top coating on a metal substrate comprising

• (a) melting an essentially pure aluminum oxide free wire by means of a thermospray gun;
• (b) entraining said molten aluminum in an inert gas stream to shield from the surrounding atmosphere, and thereby minimize oxide formation, atomize, and transport, such atomized aluminum particles;
• (c) positioning said thermospray gun so that the nozzle to substrate distance is in the range of about 2 to 4 inches;
• (d) impinging said inert gas stream containing the aluminum particles on said metal substrate to form bond coating having less than 15 percent porosity and having a thickness of not greater than 4 mils;
• (e) than increasing the nozzle to substrate distance to a distance in the range of from 4 to 10 inches;
• and
• (f) impinging said inert gas stream containing the aluminum particles on said bond coating to form an open cell structure essentially oxide free top coating, having porosity of greater than 18% and having a thickness of at least four times the thickness of the bond coating, thereby producing a porous boiling surface having sufficient open cell porosity required for effective performance as a boiling surface while exhibiting good adhesion and mechanical strength.