US3022437A

US3022437A - Electric lamps

Info

Publication number: US3022437A
Application number: US5525A
Authority: US
Inventors: Jr Dexter P Cooper
Original assignee: Polaroid Corp
Current assignee: Polaroid Corp
Priority date: 1960-01-29
Filing date: 1960-01-29
Publication date: 1962-02-20
Anticipated expiration: 1979-02-20
Also published as: GB898115A; NL260575A; DE1912565U; FR1280917A; BE599574A

Description

Feb. 20, 1962 D. P. COOPER, JR ELECTRIC LAMPS Filed Jan. 29, 1960 IN V EN TOR a A T'ORNEYS Uni ed S t s vPatat f "Q ice 3,022,437 ELECTRIC LAMPS Dexter P. Cooper, Jr., Lexington, Mass., assignor to Polaroid Corporation, Cambridge, Mass., a corporation of Delaware Filed Jan. 29, 1960, Ser. No. 5,525 3 Claims. (Cl. 313-218) This invention relates to electric lamps and more particularly to new and improved electric incandescent lamps adapted to be operated at relatively high temperatures and possessing relatively long, useful operating life at such high temperatures.

A principal object of the present invention is to provide in incandescent lamps of the character described at least one filament comprising tantalum carbide and at least one other metal carbide selected from the group consisting of the carbides of titanium, thorium, vanadium, niobium, molybdenum, tungsten and uranium, and a substantially oxygen-free atmosphere comprising, at operating temperatures, hydrogen and volatilized carbon.

Another object of the invention is to provide a filament comprising tantalum carbide and a small amount of at least one other metal carbide selected from the group consisting of the carbides of titanium, thorium,lvanadium, niobium, molybdenum, tungsten and uranium which will not sag appreciably at operating temperatures even after prolonged use and which will not readily break when' subjected to rough service such as shocks, bumps, vibrations and the like.

Still another object of the invention is to provide a filament of the above type for use in an atmosphere comprising, at operating temperatures, a halogen such as chlorine, hydrogen and volatilized carbon.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the products possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing which is a representation of a section through a typical vehicle headlamp of the sealed-beam type.

There is a demand for incandescent lamps adapted to be operated at relatively high filament temperatures and possessing relatively long, useful operating life as well as such properties as resistance to shock, vibration, sagging and the like. Such lamps would be desirable, for example, in vehicle headlighting, in floodlighting for photographic purposes, picture projection and the like. In vehicle headlamps, for instance, the filament in order to withstand shock, vibrations and so forth must possess some flexibility, that is, it should not be brittle so as to readily break or disintegrate. However, the flexibility must not be such that sudden shock would bring the filament into contact with another metallic part of the lamp and cause shorting. Moreover, the filament should not be such that it appreciably sags at operating temperatures since such sagging increases the chances of shorting and possibly of having an unsatisfactory positioning of the filament from the focus of the reflector.

This invention accordingly contemplates the use within a-lamp bulb or envelope of a refractory or hard metal carbide filament of the type heretofore described and an atmosphere the elements of which interact with each other and with the described carbide filament in such a manner that the filament does not deteriorate over an extended period of operation at high filament temperatures.

The invention thus yields a lamp adapted for long operating life, rough service and high efliciency.

The drawing illustrates a vehicle headlamp of the sealed-beam type which comprises a cup-shaped base member 10 having its inner surface 12 silvered or otherwise coated to provide a metallic reflector, preferably of paraboloidal shape. The base member has hermetically sealed thereto a transparent cover plate 14 of, for example, glass which may serve as a lens element for controlling the dispersion of light emitted from the lamp. Within the bulb there is mounted or suspended a multicarbide filament 16 on lead wires 18 which, in turn, are attached to subleads 20. The subleads may be connected to a source of electric power outside the bulb or envelope. The multi-carbide filament is located at the focus of the reflector. After assembly, the bulb is evacuated and filled with an atmosphere which, at operating temperatures,

preferably comprises hydrogen, a halogen such as chlorine about 12 inch in length may be mounted on 40-mil leads.

within a standard T-20 envelope of about 270 cu. capacity,

into which about 2 cc. of carbon tetrachloride vapor and 20' cc. of hydrogen, at atmospheric pressure and room temperature, have been introduced, along with sufiicient argon to bring the total pressure within the bulb to at least slightly less than one atmosphere. components may be cleaned and prepared in ways well known to the art. It is desirable to coat the inner surface of the envelope (preferably after the formation of the reflector if such is used) with a material that will protect the envelope material, for example, glass, from attack. This may be done by evaporating calcium fluoride, for example, upon the inner surface of the envelope before the lamp is completely assembled.

The filaments of the present invention comprise tantalum carbide and at least one other refractory metal carbide selected from the group consisting of the carbides of titanium, thorium, vanadium, niobium, molybdenum, tungsten and uranium. The multi-carbide filaments may comprise solid solutions or mixtures of two refractory carbides such as, for example, tantalum carbide-titanium carbide, tantalum carbide-thorium carbide, tantalum carbide-niobium carbide, tantalum carbide-tungsten carbide, etc. Although-refractory metals such as, for example, molybdenum, tungsten, thorium, uranium, etc. are believed to form more than one carbide, the preferred filaments will be considered as binary carbide systems. The carbide filaments of the present invention comprise tantalum carbide and less than about 10 percent by weight of at least one of the carbides of the refractory metals of groups IVa, Va and Vla of the periodic chart or systern. Carbide filaments containing tantalum carbide and amounts ranging from about 1 percent up to about 10 percent by weight of one or more of the previously mentioned refractory carbides have been found to have increased flexibility and strength at elevated temperatures while substantially retaining other desirable properties such as high melting points, thermal and electrical conductivities and the like.

Although any convenient method of forming the carbide filaments may be used, it may be convenient to convert a filament comprising an alloy of tantalum and at least one of the preferred refractory metals to the carbide structure after the bulb has been assembled. For example, the bulb may be constructed with all elements identical with those disclosed in the embodiment described above, except that the filament and leads may comprise an alloy of, for example, tantalum and tungsten; one specific tantalum-tungsten alloy comprising about 7 per- Patented Feb. 20,1962 W The bulb and cent of tungsten. The filament may then be converted to the carbide form by passing suificient current through the filament to yield a filament temperature of about 3100 C. In this way, the tantalum and tungsten, for example, comprising the filament and lead ends associated with the filament will be substantially converted to carbides.

The carbide filaments heretofore described may be of any suitable configuration, whether straight, coiled, crimped or otherwise shaped. It should also be noted that many materials may be used for leads. For example, the leads may be similar to the filament in composition or they may be made of carbon, tungsten, platinum, palladium, rhodium, or a suitable metal clad or coated with, for example, platinum, palladium or rhodium.

The envelope atmosphere may comprise a volatile hydrocarbon and hydrogen such as disclosed in US. Patent 2,596,469, or preferably the envelope atmosphere may comprise, at operating temperatures, a halogen, hydrogen and a volatilized carbon. The preferred envelope atmosphere may be provided by a number of materials or sources. For example, single compounds, such as ethylenediamine hydrochloride, methylamine hydrochloride and the like, are satisfactory. The necessary elements may also be provided by introducing into the envelope a combination of materials, such as ethylene or another hydrocarbon and a gaseous hydrogen halide, for example hydrogen chloride; or a combination of hydrogen, chlorine and any convenient hydrocarbon, for example methane, ethane, ethylene and the like; or a combination of hydrogen and any convenient halogenated hydrocarbon such as benzene hexachloride, the polyhalogen derivatives of methane, ethane, etc., e.g., carbon tetrachloride, tetrachloroethane and the like; or a combination of hydrogen and poly-halogenated organic compounds such as tetrachloroethylene and the like. It is obvious that the desired atmosphere thus may be obtained in any number of suitable ways. Other inert gases, such as xenon or krypton, may be used instead of argon.

Relatively high pressures within the bulb will lengthen lamp life; it is desirable to maintain the pressure during operation at or near the highest level that the envelope can safely withstand. If the pressure generated by the reacting gases is great enough, the need for an inert gas is reduced.

Other halogens may be used in place of chlorine without departing from the invention; members of the class of halogens having an atomic weight of less than 100, e.g., bromine and fluorine, are especially effective. If fluorine is used, however, precautions must be taken to avoid decomposition of the bulb envelope and attack upon other lamp elements. If elemental halogens are used in preparing the lamp atmosphere, precautions should be taken to avoid inhalation or contact with the skin and eyes.

In general, any combination of materials may be used that will provide, at operating temperatures, an atmosphere of volatilized carbon and hydrogen and also, preferably, a suitable halogen, particularly chlorine, in the area surrounding the filament. The atmosphere should be substantially free of water or oxygen; specifically, the oxygen content should be less than the order of fifty parts per million. The amount of carbon in the atmosphere should be sufficient to prevent the carbide filament 4 from decomposing into free metal and carbon. Hydrogen and halogen may be used in varying proportions; it is critical only that enough hydrogen be present to prevent halogen from attacking the bulb components, and that the total amount of hydrogen and halogen be sufiicient to combine with the carbon atoms escaping from the region surrounding the filament to reduce to a minimum deposit of uncombined carbon upon the inner wall of the bulb or upon other exposed surfaces. Thus the atmosphere, at operating temperatures, preferably comprises an excess by volume of hydrogen and halogen over vaporized carbon and an excess by volume of hydrogen over halogen. For example, the employment of benzene hexachloride produces an atmosphere comprising an atomic ratio of approximately one carbon atom to one chlorine atom to six hydrogen atoms. If the preferred atmosphere is provided by a mixture of materials, such as a hydrocarbon and gaseous hydrogen chloride, a desirable atomic ratio is one carbon to three chlorine to five hydrogen. It is to be understood that these ratios may be varied widely, within the limits previously specified, without departing from the invention.

While the drawing particularly illustrates the applicability of the present invention to vehicle lamps, it is understood that the invention may be advantageously employed generally with incandescent lamps, for example photoflood lamps and related structures adapted to project carefully controlled or substantially collirnated light beams.

Moreover, While the drawing describes a specific lamp configuration or structure, it is understood that the 1ncandescent lamp may take any desired shape and have any desired size. It may, for example, have an envelope which is either transparent or translucent in whole or in part and, where a portion only of the envelope is light transmitting, the remainder may comprise a parabolic or other suitable reflector with the lamp filament positioned at the focus thereof.

Since certain changes may be made in the above products without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In an incandescent lamp, an atmosphere comprising, at operating temperatures, hydrogen and carbon, and a filament positioned within said atmosphere comprising tantalum carbide and from about 1 to about 10% by Weight of at least one metal carbide selected from the group consisting of the carbides of titanium, thorium,

vanadium, niobium, molybdenum, tungsten and uranium.

2. A lamp according to claim 1 wherein the atmosphere also includes at least one halogen.

3. A lamp according to claim 1 wherein the atmosphere also includes an inert gas of low heat conductivity.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. IN AN INCANDESCENT LAMP, AN ATMOSPHERE COMPRISING, AT OPERATING TEMPERATURES, HYDROGEN AND CARBON, AND A FILAMENT POSITIONED WITHIN SAID ATMOSPHERE COMPRISING TANTALUM CARBIDE AND FROM ABOUT 1 TO ABOUT 10% BY WEIGHT OF AT LEAST ONE METAL CARBIDE SELECTED FROM THE GROUP CONSISTING OF THE CARBIDES OF TITANIUM, THORIUM, VANADIUM, NIOBIUM, MOLYBDENUM, TUNGSTEN AND URANIUM.