A Low current density black chrome electrolyte for photothermal conversion of solar energy

During the course of operation of black chrome electrolyte, current densities of the order of 2000-6000 A/m2 are required. This is associated with the difficulties of the higher heating effect of the electrolyte and current transmission problems for full size collectors. This prompted the authors to develop suitable additives for operation at low current density. The plating solution produces black deposits at a current density of 400 A/m2 with optical properties alpha=0.94 and e=0.07 by the use of sodium selenate and acetic acid as additives. The influences of variables such as plating time, current density and temperature on optical properties (alpha, e) are studied. Polarization characteristics of the solution are compared with the conventional tetrachromate solution. The use of sodium selenate and acetic acid helps to attain the deposition of black chrome at low current densitie