Abstract
The high velocity oxy-fuel [HVOF] combustion spray technique has previously been shown to be an excellent solution for depositing crystalline matrix nano-reinforced polymer coatings. Dense polymer coatings can be produced by controlling both the particle dwell time in the HVOF jet and through substrate thermal management. Use of an amorphous matrix material, polycarbonate, will enable the role of matrix crystallinity on the structure and properties of thermally sprayed polymer matrix nanocomposite coatings to be separated from effects resulting from the reinforcing phase. An amorphous, commercial polycarbonate powder with a broad particle size distribution and irregular particle morphology has been successfully deposited by HVOF spraying using hydrogen as fuel gas. Polycarbonate matrix coatings up to 18 mils thick with zero to 10 vol. % loadings of nano-sized hydrophobic and hydrophilic silica, and carbon-black have been sprayed onto Al substrates. Results from optical microscopy. X-ray diffraction, scratch, density, microhardness and dilute-solution viscometry measurements will be presented. These indicate that incorporation of the nanosized filers improved the scratch resistance and microhardness of the coatings by 50 % and 23 %, respectively, relative to sprayed pure polymer. Some degradation of the polymer matrix was also detected, with molecular weight being reduced from 17,000 in the feedstock to ~5,000 in the sprayed deposits. The influence of variations in process parameters such as fuel:oxygen ratio, total gas flow, spray distance, nozzle length, total travel distance, and spray distance/nozzle length ratio on coating structure will also be addressed. The threshold loading of silica in the polycarbonate matrix for which dense coatings can be obtained has also been determined.
