WO2005108860A1

WO2005108860A1 - Ceramic reflector

Info

Publication number: WO2005108860A1
Application number: PCT/NL2004/000587
Authority: WO
Inventors: Paulus Marinus Hermanus Van Den Bergh
Original assignee: Euromedley B.V.
Priority date: 2004-05-10
Filing date: 2004-08-20
Publication date: 2005-11-17
Also published as: NL1026156C2

Abstract

The invention relates to a ceramic reflector, comprising a carrier body of which at least one surface is at least partly provided with at least one light-reflecting ceramic cover layer. The invention further relates to a method for manufacturing a ceramic reflector, comprising - applying a suspension of a light-reflecting ceramic material to a carrier body; and then - sintering the applied suspension.

Description

Title: Ceramic reflector

The present invention relates to a ceramic reflector, in particular to a ceramic reflector for use in a lamp fitting. Reflectors for lamp fittings are usually made of a metal such as aluminum. For a good action of such reflectors, it is desired that they have a good thermal resistance and that the side(s) of the fitting facing the lamp has/have a good light reflection of the desired wavelengths. In general, aluminum lamp fittings can only be used safely for lamps with a low to medium high power, namely with a power of maximally approximately 600 W. It is an object of the present invention to provide a new reflector, in particular a reflector suitable for use in lamp fittings for horticulture. It has now been found that this object is achieved by a reflector made of a ceramic material. The invention thus relates to a ceramic reflector, comprising a carrier body of which at least one surface is at least partly provided with a light-reflecting ceramic cover layer. A reflector according to the invention has good thermal properties compared with conventional metal fittings. In particular in (greenhouse) horticulture, this offers advantages since lamps with a higher power can be used and fewer lamps are sufficient for a same lighting. A reflector according to the invention has very good reflecting properties. In particular, the invention provides a ceramic reflector with a total light reflection (more in particular a total reflection of electromagnetic radiation in the visible range, such as white light) of more than 85%, preferably of at least 90%. The light reflection may, for instance, be measured with a commercially available reflectometer in which the reflection of light with a wavelength of 400-700 nm is determined. A conventional aluminum reflector generally has a reflection of less than 85%. Compared with metal reflectors, a reflector according to the invention usually has a more diffuse reflection. As a result, a simpler geometry is sufficient than with metal reflectors, which shows specular reflection to a large extent. Incidentally, it is possible to increase the extent of specular reflection if desired, for instance by applying an appropriate coating, for instance a vanadium pentoxide coating, over the light -reflecting cover layer or over a glazing with which the light -reflecting cover layer may be coated. Due to the good material properties (such as material strength), thermal properties and the light -reflecting properties, the reflector itself can serve as a fitting for a lamp, without a separate casing being necessary. The invention thus provides inter alia a lamp fitting which at least substantially consists of ceramic material. In this context, "at least substantially" is understood to mean at least a fitting of which, if desired, only the socket(s) for the lamp(s) and the channels (such as wires) for the electricity supply to the lamp consist of non-ceramic material. A reflector according to the invention is very simply cleanable. A reflector according to the invention is very robust, and is usually less prone to reflection losses with the passage of time than metal reflectors, whose reflection considerably decreases in practice due to gloss losses. A reflector according to the invention can be used in various applications and particularly offers an advantage in a use in demanding environments such as a humid/vapor-containing environment, a warm environment, environments with greatly varying temperatures, a corroding environment and/or an environment rich in dust and/or other dirt. Terms such as "at least substantially free from", "about", "approx" and the like are understood to include at least a deviation of maximally 5%, in particular of maximally 2%. When terms such as "at least substantially", "mainly" and the like are used herein to indicate the (relative) amount of a component of a substance, material or physical phenomenon and the like, then these are at least understood to mean that this component makes up more than half, preferably 90-100%, in particular 95-100%, more in particular 98-100% of ^* the substance, the material or physical phenomenon and the like. An at least substantially diffuse reflection is thus at least understood to mean that 50-100%, preferably 90-100%, in particular 95-100%, more in particular 98-100% of the reflection (i.e. the phenomenon) is diffuse (i.e. the component). Weight percentages are based on the total weight unless stated otherwise. Partly in view of above-mentioned advantages, a reflector according to the invention is inter alia very suitable in one or more uses chosen from photography lighting, projector lighting (for instance for projecting light images, comparable with a slide screen), studio/film set lighting, ship lighting, horticultural lighting, interior lighting, exterior 1 ighting, street lighting, security lighting, construction lighting, laser applications, infrared applications, transport lighting, airplane lighting, car lighting, bicycle lighting, runway lighting, industrial lighting, kitchen lighting, healthcare lighting (for instance operating room lighting or lighting for a dental practice), oven lighting, specific location lighting (such as parking lots, gas stations), stadium lighting, sports center lighting, lighting of water, theater lighting, art/object lighting, handheld lighting (such as a portable lamp, a flashlight and the like), hallway lighting, LEDs (light -emitting diodes), fume hood lighting, and the like. In addition to the general advantage of a good light reflection (and accordingly a favorable efficiency), the nature of the reflection can offer specific advantages for specific uses. It has, for instance, been found that the use of a reflector according to the invention with a high diffuse reflection, in particular with at least substantially diffuse reflection, in water lighting, such as underwater lighting and/or lighting of a water surface, for instance a swimming pool, an aquarium or a waterway, produces less glitters to the water surface than use of an at least substantially specular reflector. There are also indications that growth and/or the wellbeing of living creatures, in particular plants, coral, anemones and the like, can favorably be influenced by exposure to diffuse light which can be produced with the aid of a reflector according to the invention. A high diffuse reflection, realizable with a reflector according to the invention, is also particularly advantageous in uses such as handheld lighting because a more even light distribution is obtained and thus a better visibility can be created than with a metal reflector. With uses with an aesthetical aspect, such as with art/object lighting, it has been found that the lighted object gets a higher visual appreciation with light reflected by means of a highly diffusely reflecting reflector according to the invention than with a specularly reflecting reflector. A reflector according to the invention can further be provided on a surface, such as a wall, ceiling, facade or another object, in particular a reflection with a large extent of diffuse reflection to bring about diffuse even indirect reflection. This is particularly advantageous for use in a building, a swimming pool or with infrastructural constructions such as bridges, for instance to mark a bridge pillar. The carrier body is usually a ceramic material. An advantage of this is the high heat resistance compared with metals. Thus, it has been found that a reflector according to the invention with a ceramic carrier body has a very good heat resistance which allows use in, for instance, fittings where the reflector is exposed to temperatures of more than 300°C or even 400°C or more, whereas conventional aluminum fittings are not well resistant to temperatures of more than 300°C. Preferably, a white ceramic material is used as a carrier body. Preferably, the material has a relatively low thermal expansion coefficient. Very suitable is, for instance, a ceramic material with a thermal expansion coefficient of less than about 6xl0 ⁶ K ¹, most preferably from about 3.5xl0-⁶ K ¹ to about 5.5 xlO"⁶ K ¹. Very suitable is porcelain, in particular hard porcelain. (Hard) porcelain has been found to have a positive influence on the light reflection. In addition, the porcelain has a relatively low thermal expansion coefficient, which has been found to be favorable in view of uses where large temperature changes occur, such as with uses in fittings for high-power lamps such as growth lamps. This is further advantageous in uses in which temperature shocks to the material may occur, for instance by exposure to water. Possibilities are spray water in horticultural greenhouses and outdoor uses in general. Hard porcelain is also particularly suitable due to the extremely good forming properties. The terms porcelain and hard porcelain are generally known terms in the field. In particular, the (hard) porcelain is a ceramic material mainly built up from aluminum oxide and silicon oxide. In a suitable manner, the (hard) porcelain can be based on a mixture of kaolin, potassium feldspar and quartz. Very suitable is a (hard) porcelain based on about 50+5 wt.% kaolin, about 25±5 wt.% potassium feldspar and about 25+5 wt.% quartz. Such materials are natural minerals and may inter alia differ widely in mineralogical and chemical structure. The quality of the materials is in part determined by the purity, in particular with regard to the extent of absence θf coloring elements such as Fe₂O3, Mnθ2, Cr2θ3, Tiθ2 (in combination with, for instance, Fe₂O3). A skilled person will be able to choose suitable formulations on the basis of the materials and process conditions used (such as firing curve ovens). As hard porcelain, preferably a porcelain is chosen which has been fired at a top temperature of about 1380-1420°C. The density of a very suitable (hard) porcelain is about 2.4-2.7 g/cm³. Particularly suitable is a hard porcelain with a hardness (Mohs) of 7-9. Hard porcelain is generally at least substantially free from open pores. In particular, the open porosity is so low that the saturation moisture absorption (at approx 25°C) is less than 0.1 wt.% based on the weight of the reflector. As a starting material for the light -reflecting cover layer, usually, a light-reflecting ceramic material is used. The suitable materials include calcium pyrophosphates, barium sulfates, magnesium oxides, titanium dioxides and aluminosilicates (oxides which, in addition to oxygen, mainly contain silicon and aluminum). These can be used alone or in any combination. The light-reflecting material preferably has a relatively low expansion coefficient, in particular of less than about 6xl0"⁶ K^_1, more in particular of less than about 5xl0 ⁶ K ^x. Preferably, the reflecting cover layer has a thermal expansion coefficient which is approximately equal to or lower than the expansion coefficient of the body on which the cover layer has been applied. Very good results have been obtained with a reflector where the ratio of the thermal expansion coefficient of the carrier body to the thermal expansion coefficient of the light -reflecting ceramic cover layer is at least about 1, most preferably at least about 1.1. The ratio of the thermal expansion coefficient of the carrier body to the thermal expansion coefficient of the light-reflecting ceramic cover layer is preferably maximally 1.5, more preferably maximally 1.4, most preferably maximally about 1.25. Such a reflector has been found to be extremely well resistant to temperature shocks. Most preferably, the expansion coefficient of the light -reflecting cover layer is 0 to about lxlO ⁶ K ¹ lower than the expansion coefficient of the carrier body. Very good results have been achieved with a reflector with a light -reflecting cover layer whose expansion coefficient is about O.δxlO ⁶ K ¹ to about lxlO"⁶ K'¹ lower than the expansion coefficient of the carrier body. In this respect, very good results have been obtained with a reflecting cover layer of an aluminosilicate, in particular in the case that the body comprises a (hard) porcelain material. It has been found that a reflection of white light of 93% and more is achievable with this. Preferably, the light-reflecting cover layer (and if desired the carrier body) comprises an aluminosilicate with a molecular ratio of AI2O3 to Siθ2 of about 3:2. Preferred weight percentages for these oxides are shown in Table 2b (see Example 1). Examples of particularly suitable aluminosilicates for use in the reflecting cover layer are mullite and zirconium mullite. Mullite is an inorganic oxide with the overall formula 3Al2θ3.Siθ2. Zirconium -mullite is an inorganic oxide based on oxides of zirconium, aluminum and silicon. Herein, Zrθ2 is usually present in a content of about 34-38 wt.%, AI2O3 in a content of about 43.8-47.8 wt.% and Si0₂ in a content of about 16.5-18.5 wt.%. Most preferably, the light-reflecting cover layer consists at least substantially of sintered mullite. This has been found to have a very good reflection for light. It has further been found that a cover layer of mullite is very suitable for manufacturing a reflector which is well resistant to temperature changes. Another reflecting ceramic material is alumina. However, alumina has been found to be less suitable for use in ceramic reflectors for high-power lamps than an aluminosilicate. This is because it has been found that the durability of the reflecting cover layer is relatively low and already begins to show cracks after relatively short heating by lighting, compared with an aluminosilicate cover layer. There is a possibility to use formulations in which, in addition to mullite or another ceramic light -reflecting material, one or more substances have been added which reduce the transparency of the cover layer and/or contribute to the reflection of light. In this manner, for instance, the reflected intensity can be set. The reflection of light may, for instance, be improved with an additive chosen from the group of zirconium, tin oxide and cerium oxide, in particular in a cover layer based on an aluminosilicate. The thickness of the cover layer can simply be determined experimentally, depending on the desired reflection properties, commercial considerations and the like. Inter alia because of commercial considerations (the material for the cover layer is usually relatively expensive), the average thickness of the reflecting cover layer is preferably less than about 1.5 mm, most preferably less than 0.7 mm. With a view to a high reflection, the layer thickness is preferably at least about 100 μ . Very good results have been obtained with an average layer thickness in the range of 100-500 μm. If desired, over the light-reflecting cover layer, a glazing has been applied. A glazing contributes to the smoothness of the surface and simplifies the cleaning of a reflector. Such a layer* is particularly desired in an embodiment in which the assembly of carrier body and light -reflecting cover layer is open-porous, more in particular in the case that the open porosity is such that the saturation moisture absorption (at approx 25°C) is less than 0.1 wt.% based on the weight of the reflector. The glazing may be based on the usual materials for glazing ceramic, in particular for glazing porcelain. Very suitable are glazings based on an aluminosilicate . With regard to the thermal expansion coefficient of preferably used glazings, the same considerations apply as for the light -reflecting cover layer (see above). The glazing may be transparent or opaque. In the case of an opaque glazing, the glazing may have been applied on a light -reflecting cover layer or serve as a light-reflecting cover layer itself and optionally be applied directly to the carrier body, without intermediate light -reflecting layer. An opaque glazing preferably comprises one or more opacifying agents, preferably chosen from the group consisting of tin oxide, cerium oxide or zirconium oxide. An advantage of an opaque glazing, in addition to the above-mentioned advantages of glazings in general, is that it can contribute to the reflection or can even completely serve as light -reflecting cover layer. The thickness of the glazing can be chosen within a wide range. Good results have inter alia been achieved with an average glazing thickness of 400 μm or less (in combination with a separate light -reflecting cover layer) or with an average layer thickness as stated for the light -reflecting cover layer (when the glaze has been applied directly on the carrier body and no separate light-reflecting cover layer is present). For practical reasons, the glazing is preferably at least 100 μm, if present. To increase the specular reflection, on the glazing, a (top) layer may have been applied which improves the specular properties. Very suitable for this is a layer based on vanadium pentoxide. Such a layer has been found to contribute to very good specular properties of the reflector. Very suitable is a specular reflection-improving layer with a thickness of about 10-100 μm. The surface of a reflector according to the invention may be uniform, i.e. consist of one type of material. It is also possible to provide a multiform surface, that is, a surface built up from different types of materials next to one another and/or over one another. Thus, the surface of a reflector according to the invention may be built up from different types of material, which may have been applied next to one another and/or over one another, with optionally different light -reflecting properties. In this manner, the specular/diffuse reflection ratio, the total extent of reflection and/or the reflection pattern can be set. The surface may, for instance, be formed by different types of materials chosen from transparent glaze, opaque glaze, light-reflecting material (such as mullite), specularly reflecting material (such as vanadium oxide) and the like. The invention further relates to a method for manufacturing a ceramic reflector, such as a reflector described hereinabove, comprising applying a suspension of a light -reflecting material to a carrier body; and then - sintering the applied suspension, thereby forming a light -reflecting cover layer. Most preferably, the carrier body (with optionally one or more layers already applied to it) is, at least at some moment, exposed to a sintering temperature of approx 1400°C, more in particular to a sintering temperature of approx 1380-1420°C. This is particularly advantageous for obtaining hard porcelain. Fig. 1 shows seven preferred processes (processes A-G). The carrier body, such as a (hard) porcelain body (or a precursor material thereof which is converted into (hard) porcelain during the method) can be obtained in any manner. The material may, for instance, be fired in a usual manner. Good results have been achieved with a carrier body obtained by a biscuit firing at about 1000-1420°C (top temperature). The carrier body may be sintered before, during or after the application of the cover layer, most preferably at a temperature of about 1380-1420°C (top temperature), which temperature is particularly suitably for obtaining a hard porcelain carrier body. The suspension can be obtained by mixing the ingredients in a usual manner. Usually, a water-based suspension is used. As light-reflecting material, such as the mullite or another aluminosilicate, usually a starting material is chosen which mainly consists of microp articles (i.e. particles with a diameter of less than 1000 μm). Preferably, the material consists at least substantially of relatively small microp articles, in particular at least substantially of particles with a diameter of less than 50 μm. It has been found that shrinkage behavior during sintering and reflection properties of the sintered light -reflecting cover layer can inter alia be set by the choice of particle size distribution of the light -reflecting starting material. The light-reflecting material preferably has (at least before sintering) a particle size distribution where at least 90% of the particles, preferably at least 95% of the particles have a diameter of less than about 50 μm. Preferably, at least 50% of the particles have a diameter of less than about 25 μm. Preferably, at least 25% of the particles have a diameter of less than about 1 μm. Very good results have been achieved with a light -reflecting material, in particular mullite, of which at least 95% of the particles have a diameter of maximally 40 μm, 15 to 75% of the particles have a diameter of maximally 25 μm and 1 to 50% of the particles have a diameter of less than

1 μm. The particle sizes stated herein are based on values which are available, such as determined on a Coulter particle size counter. Besides the reflecting material (usually in powder form, for mixing), one or more additives may be added to the suspension. For instance, a reflection-improving additive may be added as already mentioned hereinabove. Preferably, the suspension also contains one or more sintering auxiliaries. Amount and nature of these materials are determined by the application method and in particular at which temperature the suspension^" is sintered to the carrier. Very suitable sintering auxiliaries are zeolites, sodium aluminum silicates, potassium silicates, alkaline -earth aluminum silicates, aluminum boron silicates, magnesium silicates and (complex) synthetic glass frits, such as complex compounds of alkalis, alkaline -earth metals, lead, strontium, magnesium, and the like. The term complex is understood to mean a compound comprising various metal ions. One or more of the sintering auxiliaries and/or reflection-improving additives may also be used to influence the expansion coefficient. Thus, a non-stress adhesion can be effected between the light-reflecting cover layer and the carrier. Other properties of the suspension and/or the final light-reflecting cover layer may also be set with additives, in particular additives for modifying a property chosen from the group consisting of viscosity, rheology, suction behavior to the body, flow behavior, spray behavior and liquation behavior. Such additives are known per se for use in ceramics. A skilled person will be able to choose suitable substances. Very suitable is, for instance, a polyglycol or a carboxymethyl cellulose. These have been found to also contribute to a good adhesion and smudge resistance after drying of the suspension. The application can be effected in a known manner, for instance by immersion or spraying. The application takes place preferably after the biscuit firing of the carrier (such as the (hard) porcelain). The suspension is applied in an amount corresponding with the desired final layer thickness of the sintered reflecting cover layer. The suspension is then sintered at a suitable temperature. In principle, the conditions can be chosen within a wide range. A skilled person will be able to choose suitable conditions depending on the desired porosity and the choice of the light-reflecting cover layer. Very suitable is a temperature in the range of approximately 1000-1420°C, in particular for sintering a suspension with an aluminosilicate as reflecting material. A skilled person is able to set the porosity, for instance on the basis of the sintering temperature and/or by using one or more sintering auxiliaries. For obtaining a low -porous (or non-open-porous) light-reflecting cover layer, a relatively high sintering temperature may be chosen and/or use may be made of one or more sintering auxiliaries. For obtaining a very highly porous light-reflecting cover layer, generally, a relatively low sintering temperature will be chosen. A porous carrier body, as a semimanufacture, is preferably used for the manufacture of a reflector with a glazing. It has been found that the glazing adheres very well to a porous carrier body (optionally provided with a separate light-reflecting cover layer). For obtaining a reflector with a low porosity (of the carrier body), after applying the glazing, sintering preferably takes place at a high temperature (such as for instance 1380-1420°C for obtaining hard porcelain). An example of a suitable process is shown in Fig. ID. A skilled person will be able to choose suitable conditions for applying the glazing, depending on the materials used, the desired properties and what is described in the present specification. It has further been found that the sintering temperature influences the reflection properties. In particular for cover layers based on an aluminosilicate, very good reflection properties have been obtained with a light-reflecting cover layer formed by sintering at a temperature in the range of about 1200-1350°C, such as at about 1300°C. After sintering of the reflecting cover layer, if desired, a glazing may be applied which may then be gloss-fired. Suitable techniques for this are known per se. Very suitable is gloss-firing at about 1200-1350°C. Such a treatment is particularly suitable for an aluminosilicate. Over the glazing, a layer for improving specular properties may be applied, for instance a layer with vanadium pentoxide, after which a temperature treatment, for instance at about 1200-1350°C, may take place. It has been found that, by means of the invention, ceramic reflectors can be manufactured with very high reflections and good thermal properties, which have not or at least less simply been realized with other reflectors for lamp fittings. It has further been found that a ceramic reflector has good mechanical properties. So, the invention further relates to a reflector obtainable by means of a method according to the invention. The invention further relates to a lamp fitting comprising a reflector according to the invention. At least during use, a fitting according to the invention also comprises a lamp, such as a growth lamp for making plants grow, for instance- in (greenhouse) horticulture. Very good results have been achieved with a lamp with a power of more than 600 W. The invention further relates to use of a reflector or fitting according to the invention in street lighting. By means of the invention, street lighting can be provided with a high intensity. This is inter alia interesting with a view to street safety. The invention further relates to the use of a reflector according to the invention as a thermal insulator. Here, a reflector according to the invention with high reflection of infrared radiation, preferably of more than 85%, most preferably of at least 90% is particularly suitable (for instance measured with infrared with a wavelength of 800-1000 nm). The purpose of the thermal insulation may be to better retain heat, for instance for an oven of which one or more inner walls are wholly or partly provided with a reflector according to the invention. In addition, the thermal insulation may serve to cool a space or goods, for instance with a cool box of which one or more outer walls are wholly or partly provided with a reflector according to the invention. Further, a reflector according to the invention may serve as insulating construction material, for instance as (sun-protective) thermal insulation of a building. For this purpose, one or more outer walls of a building and/or the roof may be wholly or partly provided with a reflector according to the invention. Thus, the invention also relates to an oven, a cool box and a building, respectively, provided with a reflector according to the invention. Further, a reflector according to the invention is suitable as reflector in a photodiode, in particular in a photovoltaic cell, more in particular in a solar cell. Preferably, the reflector has at least substantially diffusely reflecting properties in this. A reflector according to the invention is particularly advantageous for use in a solar cell with one or more diodes with at least two light-sensitive sides (the so-called bifacial cells). A suitable diode is known by the brand name Sliver®. A suitable design of such a cell is for instance known from Weber et al. http://solar.anu.edu.au/pages/publications2004/2CV_l_36.pdf. The contents of this publication are incorporated herein by reference. An example of such a solar cell is diagrammatically shown in Fig. 2. One or more diodes 1 are embedded in a transparent material 2, for instance divided into multiple layers 2a (overlying layer), 2b (encapsulating layer) and 2c (underlying layer). The surface b of the transparent material which faces away from the light source during use is provided with the reflector 3. During use, light enters via surface a, where a part of the light reaches the side of the diode facing the light source and a part of the light reaches the reflector. The reflector reflects the light. Of this light, one part reaches the side of the diode facing away from the light source and another part is reflected from the surface a. With such a setup, a very good efficiency can be achieved.

The invention will now be illustrated in more detail in and by a number of examples.

Example 1; preferred formulations

Table 1: Carrier body (hard) porcelain

Table 2: suspension for reflecting cover layer

Table 2a: ceramic materials and sintering auxiliaries

A suspension is usually obtained by mixing 100 parts by weight of dry inorganic matter (light -reflecting material plus any sintering auxiliaries) with 20.-60 parts by weight of water and 20-60 parts by weight of additives.

In the examples described hereinafter, 42.8 parts by weight of water and 36.7 parts by weight of poly gly cols were added.

Table 2b composition of cover layer after sintering

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Table 3: transparent glazing

Example 2: preparation of an aluminosilicate reflector

A number of ceramic carrier bodies in the form of a test plate (80 x 80 mm) were, in a usual manner, manufactured from a porcelain standard type 1 (ST 1) and from a porcelain standard type 2 (ST 2), with a composition as shown in Table 1. Example 2a: open-porous carrier

A part of the carrier bodies was biscuit-fired at approx 1000°C, which resulted in an open-porous carrier. After biscuit firing, the suspension (as shown in Table 2) was applied. The applied amount was about 10.5 g/dm². A part of the carrier bodies was sintered at 1000°C, subsequently glazed and then fired at 1400°C; another part was sintered at 1400°C and not provided with a glazing; again another part was sintered at 1400°C, glazed and then gloss-fired at 1200 or 1350°C. Fig. 1 shows suitable processes in block diagram. The reflectors had a reflection for white light of 93% or more. They had no visible cracks in the cover layer after prolonged exposure to varying temperatures between room temperature and a temperature of 400°C or more. Of a reflector whose cover layer had been sintered at 1300°C, without glazing, a reflection of up to 97% was measured.

Example 2b: non-porous carrier The other carrier bodies were biscuit-fired at approx 1400°C, thereby forming a carrier which was free from open pores (saturation moisture absorption <0.1%). The suspension was applied as described under Example 2a. After this, sintering took place at 1100°C, 1300°C or 1400°C. A part of the reflecting layers was then provided with a glazing which was gloss-fired at 1200 - 1350°C. The reflectors had a reflection for white light of 93% or more. They had no visible cracks in the cover layer after prolonged exposure to varying temperatures between room temperature and a temperature of 400° C OF more.

Claims

1. A ceramic reflector, comprising a carrier body of which at least one surface is at least partly provided with at least one light-reflecting ceramic cover layer.

2. A ceramic reflector according to claim 1, wherein the carrier body is made of porcelain, preferably of hard porcelain.

3. A ceramic reflector according to any one of the preceding claims, whose reflecting layer has a total light reflection of more than 85%, preferably of at least 90%.

4. A ceramic reflector according to any one of the preceding claims,0 wherein the light-reflecting cover layer comprises a calcium pyrophosphate, a barium sulfate, a magnesium oxide, a titanium dioxide, an aluminosilicate or a combination of one or more of these compounds. 5. A ceramic reflector according to any one of the preceding claims, wherein the light-reflecting cover layer comprises sintered mullite.

5

6. A ceramic reflector according to any one of the preceding claims, provided with a glazing, which has been applied to the light -reflecting cover layer on the side facing away from the carrier body.

7. A ceramic reflector according to any one of the preceding claims, wherein the carrier body, the light-reflecting cover layer and, if desired, the o glazing each comprise an aluminosilicate.

8. A ceramic reflector according to any one of the preceding claims, wherein the reflecting cover layer comprises an aluminosilicate whose molecular ratio of AI2O3 to Siθ2 in the aluminum silicate is about 3:2.

9. A ceramic reflector according to any one of the preceding claims, 5 wherein the ratio of the thermal expansion coefficient of the carrier body to the thermal expansion coefficient of the light-reflecting ceramic cover layer and/or the ratio of the thermal expansion coefficient of the carrier body to the thermal expansion coefficient of the glazing is at least about 1, preferably 1-1.5, most preferably 1.1- 1.4.

10. A method for manufacturing a ceramic reflector, if desired a reflector according to any one of the preceding claims, comprising - applying a suspension of a light -reflecting ceramic material to a carrier - body; and then - sintering the applied suspension, thereby forming a light -reflecting cover layer.

11. A method according to claim 10, wherein the sintering takes place at a temperature in the range of 1000 to 1420°C, preferably at a temperature of 1200-1350°C.

12. A method according to any one of claims 10 or 11, wherein the suspension comprises an additive, preferably an additive for modifying a suspension property chosen from the group consisting of viscosity, rheology, suction behavior to the body, flow behavior, spray behavior and liquation behavior.

13. A method according to any one of the preceding claims, wherein the suspension is applied by immersion and/or spraying.

14. A method according to any one of claims 10-13, wherein the suspension comprises at least one sintering agent, preferably at least one sintering agent chosen from the group consisting of zeolites, magnesium silicates, sodium aluminum silicates, potassium aluminum silicates, alkaline -earth aluminum silicates, aluminum boron silicates and (complex) synthetic glass frits.

15. A method according to any one of claims 10-14, wherein at least

90% of the particles of the light-reflecting material (at least before sintering) have a size of less than 50 μm.

16. A reflector obtainable by means of a method according to any one of claims- 10 to 15.

17. A lamp fitting comprising a reflector according to any one of claims 1-10 or 16.

18. A lamp fitting according to claim 17, provided with a lamp, preferably a growth lamp.

19. A lamp fitting according to claim 18, which at least substantially, consists of ceramic material.

20. A streetlamp, comprising a reflector or a lamp fitting according to any one of claims 1-10, 16 or 17-19.

21. A solar cell, comprising a reflector according to any one of claims 1-10 or 16.

22. An oven or cool box, of which at least one surface is at least partly provided with a layer of a reflector according to any one of claims 1-10 or 16.

23. Use of a reflector according to claims 1-10 or 16 or a lamp fitting according to any one of the claims 17-19 in a use chosen from photography lighting, projector lighting (for instance for projecting light images, comparable with a slide screen), studio/film set lighting, ship lighting, horticultural lighting, interior lighting, exterior lighting, street lighting, security lighting, construction lighting, laser applications, infrared applications, transport lighting, airplane lighting, car lighting, bicycle lighting, runway lighting, industrial lighting, kitchen lighting, healthcare lighting (for instance operating room lighting or lighting for a dental practice), oven lighting, specific location lighting (such as parking lots, gas stations), stadium lighting, sports center lighting, lighting of water, theater lighting, art/object lighting, handheld lighting (such as a portable lamp, a flashlight and the like), hallway lighting, LEDs (light-emitting diodes) and fume hood lighting.