Tungsten/Bromine Cycle Lamp

The invention relates to a tungsten/bromine cycle lamp having a transparent lamp vessel in which a tungsten filament is arranged and in which a metal selected from the group consisting of Ti, Zr, Nb, Ta, V and Hf is present as a getter and a gas mixture containing inert gas, hydrogen and bromine.

Such lamps are disclosed in Netherlands patent application No. 7,206,616. In these lamps the metal getter the object of which is to remove oxygen from the gas filling, is provided as a wire piece, foil or bead. In practice the getter is usually secured to a part of the filament or to the lamp vessel. This requires an extra operation in the manufacture of the lamp and the handling of a very small component, since only a small quantity of getter (approximately 100 .mu.gr) is used.

In addition the known lamps must be provided with a measured quantity of bromine and hydrogen. Although the Application states that the getter can be provided in the lamp as a metal bromide, the quantities of metal bromide and separately added hydrogen should nevertheless be matched to each other.

It is the object of the invention to provide a metal getter and a reactive gas with which the manufacture of such lamps is simplified.

Accordingly the invention relates to a tungsten/bromine cycle lamp of the kind mentioned in the preamble and is characterized in that the lamp contains a compound of the formula Me NH.sub.x Br.sub.y C.sub.z or decomposition products thereof, in which formula z has the value 0 or 5, in which, if z = 0, Me is vanadium, niobium or tantalum, x = 1,2 or 3 and y = x + 1 or Me is titanium, zirconium or hafnium, x = 1 or 2 and y = x + 1, and in which, if z = 5, Me is tantalum and x = y = 5.

The compounds MeNH.sub.x Br.sub.x+1 decompose in an operating lamp into metal, nitrogen, bromine and hydrogenbromide, the compound Ta Br.sub.5 C.sub.5 H.sub.5 N into tantalum, hydrogenbromide, carbon and nitrogen. The compounds are, however, readily stable in air at room temperature. The preparation of the compound TaNH.sub.3 Br.sub.4 is described in Izv. Akad.Nauk SSSR, Neorg. Mater. 3 (12) 2259 (1967). The other compounds of the formula MeNH.sub.x Br.sub.x+1 can be obtained in an analogous manner. The compound Ta Br.sub.5 C.sub.5 H.sub.5 N is described in Adv. Chem. Ser. 37 243 (1963).

The compounds are preferably introduced into the lamp as a dispersion in an organic solvent. The compound Ta Br.sub.5 C.sub.5 H.sub.5 N is soluble in polar solvents, for example pyridine. The remaining substances give suspensions. Suspending agents which may be used are, for example, hydrocarbons, such as benzene, and toluene. From a point of view of lamp manufacture, Ta Br.sub.5 C.sub.5 H.sub.5 N is therefore to be preferred.

For lamps having a very high filament temperature, the compounds MeNH.sub.x Br.sub.x+1 may be preferred because in addition to hydrogenbromide they also supply free bromine, which may be desired in the said lamps.

The quantity of a compound which is introduced into a lamp is generally so large that the partial pressure of HBr in the lamp after decomposition of the compound is 2-20 Torr, measured at room temperature. As a rule, a partial pressure of HBr of 3-10 Torr is used.

The advantage of the lamps according to the invention is that both the quantity of getter and the quantity of HBr and of HBr and Br.sub.2, respectively, in the lamp are accurately adjustable. The advantage of the manufacture of these lamps is that getter metal and reactive gas can be introduced into the lamp in one operation and furthermore that no mechanical operations are necessary to fix the getter in the lamp. Of course, mixtures of two or more of the said compounds may also be used.

The invention also relates to a method of manufacturing a tungsten/bromine cycle lamp having a transparent lamp vessel and a tungsten filament in which a compound containing bromine and Ti, Zr, Nb, Ta, V or Hf is introduced into the lamp vessel, the lamp vessel is filled with an inert gas and then sealed, characterized in that a dispersion of a compound of the forumla Me H.sub.x Br.sub.y C.sub.z is introduced into the lamp and the solvent is then evaporated and expelled.

As an inert gas in the lamps is used a gas (mixture) which is useful for this purpose, for example nitrogen, argon, krypton.

The lamps may be used as motorcar lamps, projection lamps, photolamps, and the like.

An embodiment of the invention will be described in greater detail with reference to the Figures and the Examples.

The Figure shows a 12V/55W H1 motorcar lamp.

In the Figure a quartz glass lamp vessel 1 is sealed at either end by means of pinch seals (2 and 3) in which molybdenum foils (4 and 5) are incorporated. Connected to these are current conductors (6 and 7) and the supports (8 and 9) of the filament 10. At the end of the manufacturing process the lamp vessel is sealed at 11. The lamp vessel has a capacity of 0.27 cm.sup.3, inside length 10 mm, width 6 mm.

1. Lamps are shown in FIG. 1 but with an exhaust tube at 11 were manufactured in the usual manner. A solution of Ta Br.sub.5 C.sub.5 H.sub.5 N in pyridine was introduced into the lamp in a quantity (5.7 .mu.g) which after decomposition gives a partial pressure of HBr of 3 Torr at room temperature. The solvent was evaporated by evacuating the lamp vessel to a residual pressure of 10.sup.-3 Torr. Although it is usual to fill such lamps with inert gas to a pressure of 3.5 atm., only 1.5 atm. krypton was introduced into the lamps so as to be able to evaluate the operation of the gas filling and the getter in a shorter time. In order to test the gettering function, 1 Torr oxygen was also introduced into the lamp, after which the exhaust tube was sealed. The lamps were operated at 13.2 Volts, a filament temperature of 3200.degree. K. being reached. After 200 hours in operation the lamps were still completely bright and no phenomena could be observed which indicated the presence of oxygen.

2. In an analogous manner lamps were manufactured with 7.8 .mu.g of TaNH.sub.3 Br.sub.4 which after decomposition of that material and a partial pressure of HBr of 3 Torr at room temperature. The results of operating tests were similar to those described in Example 1.