In an effort to corroborate theoretical and experimental techniques used for cold spray particle velocity analysis, two theoretical and one experimental methods were used to analyze the operation of a nozzle accelerating aluminum particles in nitrogen gas. Two-dimensional (2D) axi-symmetric computations of the flow through the nozzle were performed using the Reynolds averaged Navier-Stokes code in a computational fluid dynamics platform. 1D, isentropic, gas-dynamic equations were solved for the same nozzle geometry and initial conditions. Finally, the velocities of particles exiting a nozzle of the same geometry and operated at the same initial conditions were measured by a dual-slit velocimeter. Exit plume particle velocities as determined by the three methods compared reasonably well, and differences could be attributed to frictional and particle distribution effects.
Supersonic particle deposition (also known as cold spray) is a surface coating process whereby metal particles are accelerated to supersonic speeds while entrained in nozzle gas flow and are subsequently deposited by impact onto a surface. Particle velocity is critical for optimal deposition efficiency and coating quality, and several parameters, including gas conditions, particle characteristics and nozzle geometry affect particle velocity. This study investigates the relationship between particle velocity and coating quality and investigates how nozzle design influences particle velocity. Performance is described through modelling and verified by direct velocity measurements.
As part of the research and development effort, a device fabrication line was established whose mission was to reproducibly fabricate large area (10 cm2) CuxS/CdS solar cells of greater than 8% average conversion efficiency. This goal was accomplished mainly by the careful monitoring and control of the CdS deposition process. Material properties which influence cell performance, such as back contact reflection, CdS resistivity, and deposition rate, were monitored and controlled via temperature control. Photoluminescence of the CdS and resistivity of CuxS layers formed on the CdS were used to electronically characterize the films prepared and served as tools in observing changes in the deposition process and cell performance. The reproducibility of the process was confirmed by a 2-month qualifying run in which an average conversion efficiency of greater than 8% was achieved and maintained.
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