Edwin Dipl Ing Erben

Development of new selective absorber coatings for high-temperature applications

Abstract Aiming at the development of new selective absorbers for high temperatures above 350–400°C and the application in solar farm and solar tower plants, work has been performed covering new materials and possible coating methods. New materials were developed and integrated into high temperature photothermal stacks. These new materials include compounds containing transition metals of the periodic system. The coating methods include chemical vapor deposition (CVD), topochemical reactions, techniques of catalysis and electroplating. The characterization of these selective absorber coatings has been confirmed by measuring thermal and optical data (α, ϵ), by X-ray examination, mechanical compatibility and by chemical analysis.

Selection of a black chrome bath for continuous tube-plating and the properties of the coatings deposited from it

Abstract The planning and design of a 50-kW experimental solar thermal power plant which was to have a selective coating on the absorber initiated an investigation into black chrome deposition in order to find the most suitable type of solution for a continuous plating process. Acetic acid-type and fluorosilic acid-type electrolytes were tested with a variety of additives and deposition parameters. The best results were achieved with an electrolyte containing fluorosilic acid as the catalyst. With this solution, coatings with optimum thermo-optical properties were formed in only 22 sec at current densities of 0.5 A cm−2 and a temperature of 15°C. These yielded values of 0.97 for total absorptance (AM2 spectrum) and 0.08 (100°C) for the thermal emittance on a basis of light Watts-type nickel. Other nickel undercoatings which were investigated produced less satisfactory results. Both the thermal stability of the plating up to temperatures of 400°C and the dependence of its IR emittance on temperature were investigated. The tubes coated in the way described have a uniform, matt-black appearance and the thermo-optical properties are constant along their whole length and round their whole circumference.

CVD black chrome coatings for high temperature photothermal energy conversion

Abstract Black chrome absorber coatings have been developed by CVD-technique involving deposition of chrome hexacarbonyl. The deposition of the black chrome absorber films by CVD proceeds through pyrolysis of chrome hexacarbonyl at atmospheric pressure in the presence of oxygen. The black chrome absorber coatings demonstrate a significant solar absorptance (as deposited α > 0.95 ) coupled with a high infrared reflectance (as deposited ϵ ) which is necessary for efficient conversion of solar energy into heat. Coatings deposited on steel substrates have remained intact and substantially after 1000 h of lifetime testing in air at 600°C. The characterization of these selective absorber coatings has been carried out by measuring the thermal optical properties (α, ϵ), by X-ray examination and by surface analysis using SEM and AES. The deposition at atmospheric pressure offering the potential of large-scale continuous flow-through manufacture. Substrates of such long pipes can be easily coated for solar farm plants.

Development Of High Temperature Solar Selective Absorbers Utilizing Rare Earth, Transitional, And Group Metals

Development of new selective absorbers for high temperatures above 350-400°C and the application in solar farm and solar tower plants. Extensive theoretical work has been per-formed in order to examine the existing potential concerning the available materials and the possible coating methods. Concerning the materials new chemicals will be developed and their integration into high temperature photothermal stacks studied. The new materials include the rare earth metals, transition metals and the elements of the 8th group of the periodic system. The coating methods are chemical vapor deposition (CVD), techniques of catalysis, electroplating, heterogeneous reactions between a gas and a solid phase and topochemic reactions. The characterization of these selective absorber coatings will be carried out by measuring the thermal optical data (∝ , ∈)by X-ray examination, determination of the mechanical compatibility and chemical analysis.