In parabolic dish solar collectors, walk-off of the spot of concentrated sunlight can be a hazard if a malfunction causes the concentrator to stop following the sun. A test program, therefore, was carried out to evaluate the behavior of various ceramics, metals, and polymers under solar irradiation of about 7000 kW/m2 (peak) for 15 min. The only materials that did not slump or shatter were two grades of medium-grained extruded graphite. High-purity slip-cast silica might be satisfactory at somewhat lower flux. Oxidation of the graphite appeared acceptable during tests simulating walk-off, acquisition (2000 cycles on/off sun), and spillage (continuous exposure of a receiver aperture lip).

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