GB2036799A - Manufacturing Reflector having Silver or Gold Reflecting Surface - Google Patents

Abstract

The reflector is formed by providing a substrate of a material which does not alloy to a significant extent with the metal to form the reflecting surface and which, substrate is capable of being wetted by the metal, the substrate having a surface as smooth as conveniently can be provided without mechanical polishing but not smooth enough for the reflecting surface, and which conforms to the shape required for the desired reflecting surface; providing the metal on the surface, for example, by electrolytic deposition, and brazing the metal to the surface in a suitable atmosphere, such as hydrogen; the thickness of the deposited metal layer being such that the provided reflecting surface has a reflectivity of at least 80% in at least the infra red region of the spectrum, for example, the layer thickness being 5 micrometres. The substrate may be Ni and/or Co for Ag, and W or Mo for Au. The substrate may be a layer on a preform e.g. of steel.

Description

SPECIFICATION Manufacturing Reflectors This invention relates to manufacturing reflectors.

It is an object of the present invention to provide reflecting surfaces without mechanical polishing.

According to the present invention a method of manufacturing a reflector with a reflecting surface of silver or gold comprises providing a substrate of a material which does not alloy to a significant extent with the metal to form the reflecting surface, and which substrate is capable of being wetted by the metal, the substrate having a surface as smooth as conveniently can be provided, by known manufacturing techniques, and conforms to the shape required for the desired reflecting surface, the method also including providing a layer of the metal on said surface of the substrate, heating, and then cooling, the metal in a suitable atmosphere so that the metal melts, and then is brazed to the substrate, the thickness of the metal layer provided on the substrate being such that the reflecting surface so provided has a reflectivity of at least 80% in at least the infra red region of the spectrum.

In order to obtain a reflectivity of at least 80% it is essential both that the thickness of the metal layer provided on the substrate is sufficient that the layer, when brazed to the substrate, does not have a reflecting surface at least partially conforming to the contours of the inherently insufficiently smooth underlying surface of the substrate, which underlying surface is insufficiently smooth for a reflecting surface when conveniently provided by known manufacturing techniques; nor that the provided metal layer has a thickness so great that the layer when brazed has a non-uniform thickness. Usually the thickness of the metal layer required to be provided on the substrate is substantially 5 micrometres.

When the metal providing the reflecting surface is silver, the substrate may be of nickel, or cobalt, or an alloy of nickel and cobalt.

When the metal providing the reflecting surface is gold, the substrate may be of molybdenum or tungsten.

The metal providing the reflecting surface may be deposited electrolytically on the substrate.

According to another aspect the present invention comprises a reflector when manufactured by any one of the methods referred to above.

The present invention will now be described with reference to the following Examples.

Example 1 A support of mild steel, which has been outgassed, and which retains adequate strength at 10500C, is provided, a surface of the support conforming to the required reflecting surface and being free from deep scratches. Such a support can be formed in any convenient way.

A substrate layer, at least 5 micrometres thick, of nickel is electro-deposited upon the surface of the support. The exposed nickel surface is as smooth as conveniently may be provided. The nickel layer has a dull matt surface, and is suitable to provide a substrate for a reflecting surface of silver. The exposed nickel surface conforms to the required reflecting surface.

A layer, substantially 5 micrometres thick, of silver is electro-deposited upon the surface of the substrate in a known process step, the electrolyte comprising a silver cyanide solution without bright additives. The silver layer is then melted at a temperature of approximately 1 0250C, and in an atmosphere of hydrogen, the silver wetting the underlying nickel layer. Whilst still in this reducing atmosphere the reflector is cooled rapidly, and the metal is brazed to the nickel substrate. The hydrogen does not react with the silver, even whilst the silver is molten. Substantially only 0.1% of the melt comprises nickel from the substrate. The brazed silver layer has a substantially uniform thickness, and has a reflecting surface which does not follow the contours on the inherently insufficiently smooth underlying nickel surface.Consequently the reflecting surface has a reflectivity of at least 80%, and preferably of 90%, for incident radiation of wavelengths greater than 0.4 micrometre.

Further, the silver layer adheres well to the nickel substrate.

Example 2 A support is not provided. A substrate of molybdenum, at least 5 micrometres thick, is fabricated in any convenient way. In particular, one surface of the substrate conforms to the required reflecting surface; and is made as smooth as conveniently can be provided by known manufacturing techniques. Then a layer substantially 5 micrometres thick, of gold is electro-deposited upon the surface of the substrate, in a known process step, the electrolyte comprising gold cyanide solution without bright additives. The gold layer is melted at a temperature of approximately 1 000C, in an atmosphere of hydrogen, the gold wetting the underlying molybdenum layer. Whilst still in this reducing atmosphere the reflector is cooled rapidly, and the metal is brazed to the molybdenum substrate.The hydrogen does not react with the gold, even whilst the gold is molten. The brazed gold layer has a substantially uniform thickness, and has a reflecting surface which does not follow the contours of the inherently insufficiently smooth underlying molybdenum surface. Consequently the reflecting surface has a reflectivity of at least 80% for incident radiation, of wavelengths greater than 0.6 micrometre. Further, the gold layer adheres well to the molybdenum substrate.

For any reflector manufactured in accordance with the present invention, a support, if provided, may be of any convenient material, and be such that the substrate adheres well thereto.

When the reflecting surface is of silver, the substrate may be of cobalt, or an alloy of nickel and cobalt.

When the reflecting surface is of gold, the substrate may be of tungsten.

It is essential that the substrate is of a material which does not alloy significantly with the metal of the reflecting surface, and is wetted by the metal of the reflecting surface. Further, it is essential that the substrate surface upon which the metal is deposited is as smooth as conveniently can be provided by known manufacturing techniques.

Instead of depositing the metal layer providing the reflecting surface in an electrolytic deposition process step, the metal layer may be provided in any convenient, and known manner, for example, either in a chemical deposition process step, or by supplying a layer of foil of the metal on the substrate.

The metal may be brazed to the substrate in an atmosphere of any suitable gas, which does not react with the molten metal, usually a reducing atmosphere for the metal being provided by the gas.

Any reflector according to the present invention is advantageous in that mechanical polishing if obviated in its manufacture. During mechanical polishing, inevitably, and inadvertently, particles of polish are left in the reflecting surface, reducing the reflectivity of the surface. For this, and other reasons, a reflector manufactured by a method including a mechanical polishing step is not as advantageous as reflectors manufactured according to the present invention, for example, for use as reflectors with lasers.

Claims (9)

Claims

1. A method of manufacturing a reflector with a reflecting surface of silver or gold comprising providing a substrate of a material which does not alloy to a significant extent with the metal to form the reflecting surface, and which substrate is capable of being wetted by the metal, the substrate having a surface as smooth as conveniently can be provided, and conforms to the shape required for the desired reflecting surface, the method also including providing a ' layer of the metal on said surface of the substrate, heating, and then cooling, the metal in a suitable atmosphere so that the metal melts, and then is brazed to the substrate, the thickness of the metal layer provided on the substrate being such that the reflecting surface so provided has a reflectivity of at least 80% in at least the infra red region of the spectrum.

2. A method as claimed in claim 1 in which the thickness of the metal layer provided on the substrate is substantially 5 micrometres.

3. A method as claimed in claim 1 or claim 2 in which, when the metal providing the reflecting surface is silver, the substrate is of nickel, or cobalt, or an alloy of nickel and cobalt.

4. A method as claimed in claim 1, or claim 2, or claim 3 in which the metal provided for the reflecting surface is silver, and the reflecting surface so provided has a reflectivity of at least 90% in at least the infra red region of the spectrum.

5. A method as claimed in claim 1 or claim 2 in which, when the metal providing the reflecting surface is gold, the substrate is of molybdenum or tungsten.

6. A method as claimed in any one of the preceding claims in which the metal providing the reflecting surface is deposited electrolytically on the substrate.

7. A method as claimed in any one of the preceding claims in which the atmosphere in which the metal is heated, and then cooled, is of hydrogen.

8. A reflector when manufactured by a method as claimed in any one of the preceding claims.

9. A method of manufacturing a reflector substantially as described herein with referece to Example 1, or Example 2.