Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-03-10
2001-01-09
Diamond, Alan (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192150, C204S192120, C204S192260, C204S192290, C204S298020, C204S298070, C204S298080, C204S298130, C204S298190, C204S298240, C204S298260, C136S256000, C136S259000, C136S243000, C136S244000
Reexamination Certificate
active
06171458
ABSTRACT:
The present invention relates to a method and device for manufacturing spectral selectively absorbing layers for solar collectors having a high absorbing ability and low thermal emittance on a movable receiving material by sputtering of metal in a coating zone having a sputtering atmosphere comprising at least one gas supporting the sputtering, preferably argon, (Ar), and a reactive gas, preferably oxygen (O
2
), whereby the metal constitutes the cathode and the receiving material constitutes the anode, between which a potential difference is obtained and thereby, a plasma, whereby metallisation of the receiving material is obtained by sputtering.
BACKGROUND OF THE INVENTION
Solar collectors having a high energy efficiency absorb the solar radiation falling in thereon, transform it to heat energy, and deliver the thermal energy to a heat exchanging medium with least possible losses.
The most critical part of a solar collector having high energy efficiency is its absorbing surface, which has to be spectral selective, i.e. have the ability of absorbing radiation in the wave length range of 0.3 to 2.5 micrometer where the substantial part of the solar radiation energy is present. It shall further posses a low thermal emittance in the wave length range of 4.0 to 50 micrometer.
A number of methods are known to obtain reflecting surfaces on e.g. A solar collector, viz., anodization with a subsequent metal pigmentation and sputtering or atomizing.
Sputtering is obtained by means of having the cathode bombed by ions in a plasma gas formed by a potential difference between the cathode and the receiving material, whereby the cathode material is being atomized and the material forms a coating upon the receiving material. The process takes place in a vacuum chamber.
Solar energy absorbing means are known from SE-C-7713121-7, which means comprises a sheet formed element of aluminum sheet and a surface layer applied upon this by means of anodizing, surface layer has a high spectral selectivity and which consists of an aluminum oxide layer having been tightened afterwards and having a maximum thickness of 1.5 micrometer. The surface layer comprises small pores comprising metal, which layer is completely included into the oxide layer and are isolated from each other. The manufacture of the absorbing surface takes place using anodization and introduction of metal into the pores in an electrolytic way. This method is carried out in two different process steps and two different metals are used. The methods are labour intense and requires a lot of man power. After the electrolytic treatment a number of environmentally dangerous residual products are produced which have to be safely stored and destructively treated.
Further, from U.S. Pat. No. 4,964,963 there is known a method using two process steps, whereby a solar energy reflector is primarily coated with a stainless steel in an oxidizing atmosphere by atomizing whereupon a second metal layer having a high reflecting ability is atomized above the steel.
From U.S. Pat. No. 4,990,234 and the international application WO 87/06626 there is known different methods for coating glass surfaces with another material, by means of the atomizing technology.
DE-3,022,714-C2 describes a method for the preparation of a selectively absorbing layer for a solar collector using an argon-nitrogen sputtering atmosphere, where nickel is transferred to nickel nitride by means of cathode atomizing. The process provides a surface having high absorption values and a relatively low thermal emittance, but it is not suited for industrial manufacturing as the treatment time (30 min for a treatment surface of 1.6 m
2
) during the atomizing is far too long.
THE OBJECT OF THE INVENTION AND ITS MOST IMPORTANT FEATURES
The object of the present invention is to obtain a spectral selective absorbing, surface on solar collector elements, which surface has a very high solar absorbing ability, in the range of 96 to 97% and having a low thermal emittance, in the order of 10%, and which can be produced with high capacity in industrial scale. These objectives have been solved by the fact that the reactive gas in an amount of 1 to 50 cm
3
/min, kW, preferably 10 cm
3
min, kW and the distribution hereof in the coating zone, provides that the metal layer deposed onto the receiving material partly oxidizes during the deposition, whereby a layer is obtained that comprises a grain mixture of metallic material and metal oxide, whereby 40 to 80%, preferably about 50%, of metallic material is embedded into the metal oxide closest to the receiving material, which metallic material is successively decreased to about zero at the surface of the layer by increasing the addition of oxygen at the end of the coating zone, that the metal is selected from the group consisting of nickel, chromium cobalt, molybdenum, or the similar, or a mixture thereof, preferably a nickel-chromium-alloy where the ratio of chromium is 4 to 30%, preferably about 20%, and that the grain size is <0.005 micrometer, preferably 0.001 micrometer.
By using the method of the invention the man power demand is reduced with about 60%. No environmentally dangerous residual products is produced at the sputtering. The manufacturing time, the manufacturing costs, and material and energy consumption can be reduced.
REFERENCES:
patent: 4441974 (1984-04-01), Nishikawa et al.
patent: 4661229 (1987-04-01), Hemming et al.
patent: 4885070 (1989-12-01), Campbell et al.
patent: 5108571 (1992-04-01), Ludwig et al.
patent: 5135581 (1992-08-01), Tran et al.
patent: 5993622 (1999-11-01), Szczyrbowski et al.
patent: 3022714 (1982-03-01), None
patent: 2079323 (1982-01-01), None
patent: 57-13172 (1982-01-01), None
patent: 07110401 (1995-04-01), None
patent: WO 87/06626 (1987-11-01), None
patent: WO 92/14860 (1992-09-01), None
International Search Report dated Jan. 16, 1998.
English abstract for JP 59-69658(A), Apr. 1984.
Diamond Alan
Klarquist Sparkman Campbell & Leigh & Whinston, LLP
Sunstrip AB
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