Considerable amount of work has been done on the preparation and characterisation of solar selective films of sulphides and oxides of nickel, coated on commercially available substrates. These materials have shown promising characteristics as an efficient photothermal converter indicating values of solar selectivity (..cap alpha..s/epsilon..mu..) between 5.0 and 13.7. All the studies are made on black nickel films obtained on GI substrates by using electrolytic deposition techniques. For the economy of the overall solar collector system it is not only important to consider the solar selective properties of the surfaces but one has also to take into account the factors like the production cost, large area fabrication criterian, mechanical, thermal and chemical deteriorations of the system during the progress of its usage. In the present investigation, black nickel films were prepared in the laboratory by using spray pyrolysis techniques which is now very widely in use and is relatively a less expensive process. In the past, though these black nickel films were studied by several workers, this technique, namely, the spray pyrolysis has not been exploited. Films were prepared on GI substrates by spraying 0.1 M% solution of AR grade nickel chloride and thiourea mixed in different volum ratioes. Goodmore » adherent and thermally stable films in the thickness range 5-10 ..mu.. have been obtained which showed selective values in the range 11-12.5. In this paper some results on the studies on x-ray diffraction, SEM, EMA (Electron microprobe analysis), and photothermal properties of black nickel are presented and discussed.« less
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