US3445662A - Composite coated heat reflectors and infrared lamp heaters equipped therewith - Google Patents

Description

May 20, 1969 R. c. LANGLEY 3,445,662

COMPOSITE COATED HEAT REFLECTORS AND INFRARED LAMP HEATERS EQUIPPED THERE-WITH Filed Dec. 28, 1964 Sheet 01'2 INTERDIFFUSION ANTl-GLARE LAYER BARRIER LAYER 1 I n I IS IO \d' 13 METALLIC SUBSTRATE V ll PRECIOUS METAL, e.g. GOLD, LINING f PRECIOUS METAL, 12.9 GOLD, LINING METALLIC SUBSTRATE INTERDIFFUSION BARRIER LAYER INVENTOR. ROBERT C. LANGLEY BY f ATTOPAZ'Y COMPOSITE COATED HEAT REFLECTORS AND INFRARED LAMP HEATERS EQUIPPED THEREWITH y 20, 1969 R. c. LANGLEY 3,445,662

Filed Dec. 28, 1964 Sheet 2 or 2 I NVENTOR.

ROBERT c. LANGLEY BY Arm/(W5? United States Patent 3,445,662 COMPOSITE COATED HEAT REFLECTORS AND INFRARED LAMP HEATERS EQUIPPED THEREWITI-I Robert C. Langley, Millington, N.J., assignor to Engelhard Minerals & Chemicals Corporation, a corporation of Delaware Filed Dec. 28, 1964, Ser. No. 421,247 The portion of the term of the patent subsequent to Apr. 6, 1982, has been disclaimed Int. Cl. G21h 3/02 US. Cl. 25088 Claims ABSTRACT OF THE DISCLOSURE An infrared lamp heater is disclosed wherein an infrared source is mounted in front of a reflector comprising a metallic substrate having an infrared-reflective coating of a precious metal on its surface, and a refractory oxide diffusion barrier layer from 200 A. to 2000 A. thick between the reflective surface and the metallic substrate to prevent diffusion of the reflective coating into the substrate.

This invention relates to heat reflectors and more especially to composite coated heat reflectors characterized by freedom from interdiffusion of an infrared reflective thin precious metal coating or lining thereof and the metal of the reflector substrate or wall, and to infrared lamp heaters incorporating the composite coated heat reflectors.

Infrared lamp heaters have been utilized experimentally heretofore as a replacement for electrical resistance element heating units in domestic cooking ranges. The infrared lamp heaters have a concav-o-convex metallic "base with a thin coating of a precious metal such as gold on the concave surface for purpose of reflecting the heat to the locus or place where it will be utilized. A high intensity infrared source is mounted within the lamp envelope in front of the heat-reflecting coating, and a glass plate or sheet is secured in front of the infrared source in spaced relation thereto as part of the lamp envelope. While such lamp heaters are satisfactory in many respects for use in domestic cooking ranges, they suffer from the premature loss of the heat-reflective gold surface or coating. Thus the precious metal of the heatreflecting surface interdiffuses with the metal of the substrate or base in a short time at an elevated temperature, for instance of 500 C. and higher, to the extent of actual disappearance of the precious metal, and hence the heat reflective surface is lost.

In accordance with the present invention, infrared lamp heaters are provided which overcome and eliminate the problem of loss of the precious metal heat-reflective surface by interdiifusion of the precious metal and the metal of the reflector substrate. The infrared lamp heater of this invention comprises a metallic substrate having a concave inner surface, a thin adherent infrared-reflective lining or layer of a precious metal over the concave surface, a thin barrier layer of a refractory oxide intermediate the infrared-reflective lining and the metallic substrate inner surface, and an infrared source mounted in front of the infrared reflective lining.

The barrier layer serves to prevent interdiffusion of the precious metal of the lining and the metal of the substrate inner surface normally occurring at high temperature in the absence of the barrier layer, to the extent of actual disappearance of the precious metal.

In one embodiment of the lamp heater of this invention, a high intensity infrared source, i.e. a source radiating infrared wavelengths principally in the range of 3,445,662 Patented May 20, 1969 about 0.753.0 microns, is mounted in front of the reflective lining. In this embodiment, which is for use for high heat application, for instance as a heating unit in 'a domestic cooking range, an infrared-transmissive thermally refractory face member, preferably a plate or sheet, for instance of a heat-resistant glass, is employed to complete the envelope of the lamp heater. However, in another embodiment of the lamp heater herein wherein an appreciably lower intensity infrared source, for instance a source radiating longer wavelengths in the infrared such as wavelengths from 5.0 to 15.0 microns, is employed, for instance a lamp heater for drying ink on a thermally unstable material such as paper, it is preferred no such face member be used due to the material of fabrication of the face member absorbing materially at these longer wavelengths.

The high intensity infrared lamp heater is especially well suited for use as a heating unit in a cooking range for the reason it is a virtually instantaneous source of high heat, as contrasted with the electrical resistance element heating units which require a relatively longer time and typically a period of minutes, to reach peak temperature.

The diffusion barrier is essentially a thin layer, preferably of thickness between about 200 and 2000 angstrom units. Such thinness of this barrier layer enables a materially better bonding of the outer precious metal lining to the reflector metallic substrate or base than when a layer of thickness much in excess of 2000 A. is used, despite inherent differences between the three layers in expansion and contraction with changes in temperature.

Refractory oxides suitable for the interdifiusion barrier layer are, for example, CcO A1 0 BeO, Cr O HfO MgO, MnO, ThO Y O SiO ZnO and ZrO These refractory oxides are characterized by exhibiting good resistance to thermal shock and to material diffusion thereof into the metal base or substrate and into the precious metal of the liner and, in addition, have desirably high melting points. CeO has been found to be especially well suited for forming the interdiffusion barrier. The term refractory oxide is used herein and in the appended claims in designating the material of the interdiffusion barrier layer in a broad sense, to mean an oxide of a metal, for instance a metal disclosed immediately above, or an oxide of a nonmetal, for instance silicon, and characterized by having good resistance to heat and heat shock, good stability to high temperatures which may be encountered up to as high as 1200" C., and showing good resistance to diffusion thereof into the precious metal of the liner and the metal of the base.

The precious metal of the infrared-reflective lining is preferably gold, due to its efficiency in reflecting wavelengths in the infrared region and its resistance to oxidation. However, palladium, platinum or rhodium or alloys of these metals can be utilized in place of the gold for the heat-reflective lining. The thin infrared-reflective lining is preferably of thickness between about 200 and 2000 Angstrom units.

The material of the interditfusion barrier layer is applied over the inner metallic surface of the reflector wall or substrate as a thin layer of a liquid composition comprising a thermally decomposable organo compound of the particular element, for instance an organo compound of the aluminum, cerium, silicon, beryllium, chromium, hafnium, magnesium, manganese, thorium, yttrium, zinc or zirconium, e.g. a soluble resinate of aluminum, cerium, silicon, beryllium or of one of the remaining elements, in solution in an organic solvent such as, for instance, the organic solvents hereinafter disclosed for applying the precious metal inner lining by spraying or brushing, preferably spraying due to more readily obtaining thinner and more uniform films. The applied solution is then fired in air at a temperature of about 3000 C.-800 C. to drive off the organic matter and deposit on the metallic surface a thin film or coating of A1 or CeO One or a plurality of such coatings may be applied as aforesaid depending upon the particular thickness desired, each coating when applied 'by spraying followed by firing as described supra having a typical thickness of about 200 A. described supra having a typical thickness of about 200 A.

Examples of suitable compositions for applying the thin barrier layer by brushing or spraying follow, parts and percentages being by weight unless otherwise specified.

Example I I Parts Cerium resinate dissolved in a mixture of oil of rosemary, nitrobenzene and toluene (5% CeO 36.0 Rosin dissolved in oil of spike (50% rosin) 27.0 Oil of lavender 9.0 Oil of camphor 9.0 Oil of petitgrain 9.0

Example II Aluminum resinate dissolved in a mixture of oil of rosemary, nitrobenzene and toluene (5 A1 0 33.3 Rosin dissolved in oil of spike (50% rosin) 33.3

The soluble resinates of the metal of the interdifiusion barrier are prepared by reacting a soluble salt of the metal with rosin. Aluminum acetate can be reacted with rosin by heating a mixture of the two materials at temperature of about 150 C. The soluble resinate of silicon is prepared by heating at 120 C-l30 C. a mixture including silicon tetrachloride and pine rosin as disclosed in US. Patent 2,842,457, column 7, lines 1l7. The solution resinate of cerium is prepared by reacting cerous hydroxide with the sodium salt of rosin at a temperature of about 75 C. Exemplary of suitable solvents for preparing the solutions for applicaiton are a mixture of essential oils; oil of turpentine; and a mixture of oil of rosemary, nitrobenzene and toluene.

The infrared-reflective outer lining or coating is provided by applying over the surface of the refractory oxide of the interdilfusion barrier, for instance by brushing or spraying, a thin coating of a liquid composition comprising a soluble thermally-decomposable organo compound of the precious metal, for instance a soluble resinate of the gold, platinum, palladium or rhodium, and an organic solvent for the precious metal compound. Suitable solvents for preparing such compositions are a mixture of essential oils; oil of turpentine; and a mixture of oil of rosemary, nitrobenzene and chloroform. A flux for the precious metal is also preferably present in such composition, for instance chromium oxide, bismuth oxide, lead oxide and mixtures thereof. Application is by spraying or brushing. The article with applied solution is then fired in .air at a temperature within the range of about 150 C.900 C. to decompose the particular precious metal. One or a plurality of coatings of the precious metal can be applied in the manner described depending on the particular thickness desired. Each application yields a precious metal coating of typically about 1000 A. in thickness. A preferred temperature for firing the gold Example IV Percent Gold resinate dissolved in a mixture of oil of rosemary, nitrobenzene .and ethyl acetate (24% Au) 40 Rosin dissolved in oil of spike (3 0% rosin) 10 Oil of rosemary 30 chloroform 20 Example V Palladium resinate dissolved in a mixture of oil of rosemary, nitrobenzene and chloroform (9% Pd) 50 Rosin dissolved in oil of spike (30% rosin) 11 Oil of lavender 13 Oil of camphor 13 Oil of petitgrain 13 Example VI Platinum resinate dissolved in a mixture of oil of rosemary, nitrobenzene and toluene (12% Pt) 50 Rosin dissolved in terpineol (40% rosin) 10 Oil of lavender 20 Terpineol 20 Example VII Rhodium resinate dissolved in a mixture of nitrobenzene, chloroform and oil of spike (5% Rh) 50 Rosin dissolved in oil of spike (30% rosin) 15 Chloroform 30 Terpineol 5 Example VIII Gold tertiary dodecyl mercaptide dissolved in a mixture of heptane and chloroform (28% Au) 20 Oil of peppermint 20 Terpineol 2 Toluene 29 Chloroform 29 The high-intensity infrared lamp heater herein prefer ably has a thin continuous, selective filter, anti-glare layer over the inner surface of its infrared transmissive, thermally refractory face member, which absorbs the waves in the visible range but transmits the infrared waves. The selective filter layer enables the lamp heater to be utilized without causing undue strain on a humans eyesight due to glare. The selective filter, anti-glare layer is preferably of thickness in the range between about 500 A. and about 2000 A. Such layer is composed of an intimate fused mixture of gold and a lesser amount of silver and a glass, the glass being obtained by the fusing together of SiO;, CaO and ZnO as glass-making ingredients formed in situ during firing, and cooling of the fusion melt.

The selective filter, anti-glare layer is provided on the thermally refractory face member of the lamp, which face member is preferably of a heat-resistant glass, for instance a glass containing, by weight, 96% SiO and 4'% B 0 but which can be entirely of silica, by applying over the surface of the refractory face or sheet intended to be the underside or inner surface in the assembled lamp heater a thin coating of a liquid composition comprising a soluble thermally decomposable compound of gold and of silver, for instance gold resinate and silver resinate prepared by procedure similar to that previously disclosed herein for preparing the metal resinates of the interdiffusion barrier layer, an organic solvent for the organo compounds of gold and silver, and compatible compounds of silicon, calcium and zinc, for instance silicon resinate, calcium resinate and zinc resinate also prepared in accordance with the method previously disclosed herein for preparation of the other metal resinates. Such composition is fired on the face member at a temperature in the range of about 500 C.800 C. to decompose the organo compounds of gold and silver and convert the organo compounds of silicon, calcium and zinc to their corresponding oxides, SiO CaO and ZnO, and the firing is continued at the higher end of the firing temperature range whereby the SiO CaO and ZnO fuse together. The fired layer is then cooled on the refractory face member to obtain thereon the thin selective filter, anti-glare layer mentioned supra. An especially suitable composition for application to the refractory face member for the lamp for forming the anti-glare layer is set forth in Example IX which follows.

Example IX Percent Gold resinate dissolved in a mixture of oil of rosemary, nitrobenzene and ethyl acetate (24% Au) 17.5 Silver resinate dissolved in a mixture of oil of spike Oil of peppermint 10.0

The above solution after firing to obtain a film about 500 A. thick on a substrate which transmits visible and short wavelength infrared energy, substantially reduces visible transmission while having little effect on infrared transmission. The following table gives percent transmission of the uncoated substrate compared with the same substrate after coating.

Visible transmission Infrared transmission Wavelength (microns) 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 1. 2.0

Uncoated. 91 91 92 91 91 90 90 90 Coated 15 32 73 84 87 87 81 Reference is now made to the accompanying drawings wherein:

FIGURE 1 is a diagrammatic elevational sectional view of an infrared lamp heater of this invention;

FIGURE 2 is a diagrammatic elevational sectional view of a parabolic heat reflector of the invention;

FIGURE 3 is an end view partially broken away looking in the direction of the infrared transmissive refractory face member of the lamp heater of FIGURE 1; and

FIGURE 4 is a perspective view of the infrared lamp heater herein.

Referring to FIGURES 1, 3 and 4 of the drawings, high intensity infrared lamp heater 10 has metallic substrate or wall 11 of parabolic shape in longitudinal section and a paraboloid in its entirey of a high melting metal, for instance stainless steel. As shown in FIGURE 1, continuous, non-porous, adherent interdiflusion barrier layer 12 of thickness of about 1000 A. of the refractory oxide, for instance cerium oxide, is over substrate 11. Continuous, adherent, non-porous or substantially nonporous infrared reflective lining or layer 13 of a precious metal, for instance gold, is over the barrier layer 12. High intensity infrared source 14, for instance a tungsten filament sealed in a quartz envelope containing iodine therein, emits when heated high intensity infrared waves, the infrared waves being reflected by precious metal film 13 upwardly through anti-glare layer 15 and glass face plate 16 hereafter mentioned to the particular locus desired. Infrared source 14 is mounted in spaced relationship to reflective lining 13 and face plate 16. The filament of infrared source 14 is heated to a temperature of typically about 2500 C.3000 C. for obtaining the emission of the wavelengths in the range of about 0.75-3.0 microns; and to a filament temperature of about 500 C. to obtain a peak at a wavelength of about 5.0 microns, to a filament temperature of about 250 C. to obtain a peak at a wavelength of about 10 microns, and to a filament temperature of about C. to obtain a peak at a wavelength of about 15 microns. Conductor lead wires 14a and 14b extending through small diameter orifices or passageways 22 and 23 respectively, connect infrared source 14 to a source of electrical current. Face plate 16 of an infrared transmissive, high heat resistant silica glass known as Vycor and containing, by weight, 96% SiO and 4% B 0 is positioned normal to the principal axis of lamp heater 10 and sealed at its lateral edge portion to metallic substrate 11 with the aid of gasketing with a high temperature polymer such as, for instance, Teflon. Continuous adherent substantially non-porous infrared-transmitting, visible wavelength-absorbing layer 15 covers the underside of face plate 16 and functions to prevent glare and attendant undue eye strain to humans. Lamp heater has a diameter at its face plate 16 of about 6 /2, and a depth along its principal axis of about 5".

With reference to FIGURE 2, a composite coated infrared reflector unit 18 is shown. Reflector unit 18 has concavo-convex metallic substrate 19, and continuous, non-porous, adherent interdiffusion barrier layer 20 of thickness of about 1000 A. of the refractory oxide, for instance cerium oxide, over the concave inner surface of substrate 19. Continuous adherent non-porous or substantially non-porous infrared-reflective layer 21 of a precious metal, for instance gold, is over barrier layer 20. Reflector unit 18, in addition to being highly suitable for use in the high intensity, infrared lamp heater of this invention, can be also utilized as a heat reflector in applications where less intense heat is required, e.g., in drying printing ink on paper. In such applications, a lower intensity heat source, i.e., a source radiating at longer wavelengths in the infrared such as from 5.0 to 15.0 microns is used. Precious metals are very eflicient reflectors of energy of these longer wavelengths. In .a lower intensity heater it is preferred no face plate be used, since all known face-plate materials absorb appreciably at the longer infrared wavelengths.

What is claimed is:

1. An infrared lamp heater comprising a metallic substrate having a concave inner surface, a thin adherent infrared-reflective lining of a precious metal over the substrate concave inner surface, a barrier layer of a refractory oxide having a thickness between about 200 A. and 200A. intermediate the infrared-reflective lining and the metallic substrate inner surface, the barrier layer preventing interdiffusion of the precious metal of the reflective lining and the metal of the substrate, and an infrared source mounted in front of the infrared-reflective lining.

2. The lamp heater of claim 1 wherein the infraredreflective lining is of gold.

3. A high intensity infrared lamp heater comprising an envelope including a metallic substrate having a concave inner surface, a thin adherent infrared-reflective lining of a precious metal over the substrate concave inner surface, a barrier layer of a refractory oxide having a thickness between about 200 A. and 2000 A. intermediate the infrared-reflective lining .and the metallic substrate inner surface, the barrier layer preventing interdiifusion of the precious metal of the reflective lining and the metal of the substrate, and an infrared-transmissive thermally refractory face member: and a high-intensity infrared source mounted within the envelope in front of the infrared reflective lining.

4. The lamp heater of claim 3 wherein the infraredreflective lining is of gold.

5. The lamp heater of claim 3 wherein the barrier layer is of cerium oxide.

6. The lamp heater of claim 3 wherein the infraredtransmissive, refractory face member is of a heat-resistant glass.

7. The lamp heater of claim 6 wherein the infraredtransmissive face member has a thin, continuous, selective filter, anti-glare layer over its inner surface, the anti-glare layer being infrared-transmissive and visible wavelength absorptive.

8. A heat reflector comprising a metallic substrate having a concave inner surface, a thin adherent infraredreflective lining of a precious metal over the concave surface of the substrate, and a barrier layer of a refractory oxide having a thickness between about 200 A. and 2000 A. intermediate the precious metal lining and the metallic substrate concave surface, the barrier layer 8 preventing interdiffusion of the precious metal of the lining and the metal of the substrate.

9. The reflector of claim 8 wherein the infrared-reflective lining is of gold.

10. The reflector of claim 8 wherein the barrier layer is of cerium oxide.

References Cited UNITED STATES PATENTS 2,501,563 3/1950 Colbert et a1. 117-71 10 3,176,678 4/1965 Langley 1l771 3,188,513 6/ 1965 Hansler 117-33.3 X 3,284,225 11/1966 Smock et a1.

ALFRED L. LEAVITT, Primary Examiner.

15 c. K. WEIFFENBACH, Assistant Examiner.

US. Cl. X.R.

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