Melting and degradation of nylon-11 particles during HVOF combustion spraying

Numerical predictions and experimental observations have been correlated to improve the qualitative understanding of the degree of thermal degradation occurring during the HVOF spray deposition of nylon‐11. Particle residence time (∼ 1 ms) in the HVOF jet was insufficient for significant decomposition of the nylon‐11, but was sufficient for noticeable discoloration (yellowing) of the particles of a powder with a mean particle size of 30 μm. Experimental observation showed this to be the case even though numerical predictions indicated that the temperature of a 30 μm diameter particle should be considerably higher than the upper degradation limit of nylon‐11. Initial thermal oxidation of nylon‐11 promotes the formation of carbon–carbon double bonds that strongly absorb in the visible spectrum even at concentrations of parts per million causing discoloration of the nylon. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007