US3450925A - Mercury bismuth halide photochemical arc lamp light sources - Google Patents

Description

June 17, 1969 p, JOHNSON 3,450,925

MERCURY BISMUTH HALIDE PHOTOCHEMICAL ARC LAMP LIGHT SOURCES Filed March 17, 1967 [n ve r7220 r-z- Pe feral Johnson is A tto r21 ey.

United States Patent 3,450,925 MERCURY BISMUTH HALIDE PHOTOCHEMICAL ARC LAMP LIGHT SOURCES Peter D. Johnson, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Mar. 17, 1967, Ser. No. 623,971 Int. Cl. H01j 17/20, 61/18; H011: 1/50 US. Cl. 313-429 11 Claims ABSTRACT OF THE DISCLOSURE A photochemical light source includes an evacuated arc chamber containing a pair of arc-electrodes and a filling of mercury sufiicient to yield under operating conditions a mercury pressure of approximately /2 to atmospheres, and a quantity of a bismuth halide suflicient to yield a partial pressure of approximately to 200 torr of yaporized halide. The bismuth halide is thermally dissociated in a mercury vapor arc. High intensity, efficient photochemically useful radiation within the wavelength bands of 2800 to 3200 AU. and 3200 to 4200 AU. is produced by the combined line spectra of the excited mercury and bismuth atoms at their respective radiating wavelengths. Means are provided to supply the arc-electrodes with a sufficiently high voltage to initiate a high power, high current electric arc within the lamp envelope.

The present invention relates to vapor arc lamps and, more particularly, to such lamps as are adapted to emit selective radiations within the wavelength bands of 2800 to 3200 AU. and 3200 to 4200 A.U., those wavelength bands which are most useful in the production of photochemical reactions in industrial and scientic uses.

Prior are photochemical wavelength emitting lamps have primarily been mercury lamps, preferably low or medium pressure mercury lamps. Since, however, a substantial portion of the medium pressure mercury arc spectrum occurs at wavelengths substantially in excess of 4200 A.U., the upper limit of the useful photochemical radiation wavelength, and even extends upward to 6000 A.U., the mercury arc source is a rather ineflicient photochemical light source, since it is required that a substantial portion of the radiation be wasted for photochemical purposes. In some instances, this radiation may be harmful, and in these instances it is necessary that an appropriate filter be utilized to remove the unwanted radiation. Even in the most favorable conditions in which the radiation is not harmful, that which does not fall within the photochemically useful area is lost and this, therefore, reduces the efficiency of the mercury lamp as a photochemical light source.

Accordingly it is an object of the present invention to provide an improved photochemically useful source.

Still another object of the present invention is to provide a vapor arc lamp having a concentration of radiation in the photochemically useful wavelength bands.

Yet another object of the present invention is to produce lamps which selectively emit with high intensity and efliciency in the wavelengths useful for photochemical purposes.

Briefly stated, in accord with one embodiment of the present invention, I provide a medium pressure metallic vapor arc lamp containing a vaporizable filling therein comprising suflicient mercury to provide, upon complete vaporization thereof, an atmosphere of from approximately /2 to 5 atmospheres, and a sufiicient quantity of a halide, preferably a chloride of bismuth, sufiicient, upon vaporization under operating conditions, to provide a partial pressure of bismuth halide of approximately 10 to 200 torr. In operation the application of a sufficiently Patented June 17, 1969 high voltage and the establishment of an arc therein causes an intermediate pressure mercury arc to be established which arc vaporizes and dissociates the bismuth halide, causing thermal excitation thereof to cause the bismuth to emit characteristic line spectra within the photochemically useful wavelength bands, which radiation, when added to the band spectra of the mercury radiation, produces a highly etficient concentrated source of photochemically useful wavelength radiation.

The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following detailed description taken in connection with the appended drawing in which the sole figure illustrates a photochemically useful wavelength-producing lamp con structed in accord with the invention in vertical crosssection, with parts broken away.

In this figure a photochemically emissive light source constructed in accord with the present invention includes an exterior evacuable ultraviolet light transmissive envelope I mounted upon a screw-type contact-making base 2, and including therein an interior arc-containing inn-er envelope 3. Inner light transmissive envelope 3 is generally cylindrical in shape, hermetically sealed and terminated with pinched-off sections 4 and 5 at the upper and lower ends thereof, which pinched-01f sections both serve to hermetically seal the inner envelope as it is fabricated from a tubular member and to make appropriate seals with various lead-in electrodes passing therethrough.

Envelopes 1 and 3 may be of any ultraviolet light transmissive substance such as quartz, Lucalox (US. Patent 3,026,210) or high density yttria as disclosed and claimed in the copending application of R. C. Anderson, Ser. No. 582,755, filed Sept. 28, 1966, and assigned to the present assignee.

A pair of arc-electrodes =6 and 7, which may conveniently comprise coiled helical members of tungsten wire or thoriated tungsten wire, or tungsten wire with a sliver of thorium contained therein or coiled-coil helices, as is well known in the arc lamp technology, are centrally located within interior envelope 3, at opposed ends thereof, a suflicient distance apart so as to sustain a high current electric arc therebetween for the vaporization of the vaporizable constituent contained therein and the production of high intensity radiation of the appropriate wavelengths. Electrodes 6 and 7 are supported upon electrode lead members 8 and 9 respectively, which are sealed through pinched regions 4 and 5 respectively, in hermetic seal. A starting electrode 10 is located within one end of inner envelope 3 and is sealed through and hermetically sealed within pinched'region 5 of inner envelope 3. Starting electrode 10 is connected through a resistance 11 to a lead and support member 12 which is at the same potential with another lead and support member 13, both of which are connected to one contact member of connecting base 2. It will be appreciated, however, that other means than starting electrode 10 may be utilized to start the lamp.

Inner envelope 3 is suspended within outer envelope 1 by means of a simple set of saddle- clamp members 14 and 15 which are dependent from lead and support member 13 and which are securely mechanically fastened about the flattened portions of pinched regions 4 and 5 of inner envelope 3. Lower saddle-clamp 14 is connected between support members 12 and 13 and upper saddleclamp 15 is connected between support member 13 and a suspended support member 15 which is connected with a collar 16 which fits over a re-entrant nipple 17 within the upper portion of exterior bulb member 1 which serves to anchor the upper end of lead and support member 13.

One arc-electrode 6 is connected to support member 13 and the other arc-electrode 7 is connected to a separate lead member 18 which is connected to the contact member of screw-base 2 remaining after lead and support member 13 and 12 are connected to the first mentioned contact member thereof.

Enevelope 3 contains a filler substance 19 which exists in the form of a liquid globule, for example, with solid constituents contained therein during quiescent, nonoperating conditions. The liquid globule is composed of sufficient mercury so that upon the attainment of a stable operating condition, the mercury is totally volatilized and the vapor thereof produces a pressure within envelope 3 of approximately /2 to atmospheres. It is essential in the operation of the lamps in accord with the present invention at their higher operating temperatures and pressures of the order of 1 atmosphere or less, that no remaining mercury exist in the liquid state, since the operating temperature that is required to volatilize the remaining constituent is substantially higher than that which may be obtained with the presence of liquid mercury within the bulb. Thus for example, since the boiling point of mercury is approximately 355 C., if any liquid mercury remains in the inner envelope 3 during operation, that is the maximum equilibrium temperature which may exist within that envelope. Accordingly, the quantity of mercury is so established as to completely volatilize and establish the desired operating pressure.

The filter 19 also includes a quantity of a bismuth halide, preferably bismuth trichloride, in such quantities as to provide sufficient bismuth halide as to provide a partial pressure of bismuth halide at the operating temperature of the lamp within the range of approximately to 200 torr and preferably at a pressure of approximately 25 to 50 torr. The amount of bismuth halide supplied within the lamp is not exceedingly stringent at the upper limit, since the amount of bismuth halide which is supplied is generally set by the operating temperature. It is desirable that an excess thereof be supplied so that, if the relatively small quantity of bismuth halide is depleted by deposition upon the walls or reaction with other constituents within the envelope, this depletion does not result in a removal of sufiicient bismuth halide from within the envelope so as to negate the contribution made by the bismuth radiation in accord with the present invention.

In addition to the foregoing constituents within inner envelope 3 of the device of FIGURE 1, a starting gas which may conveniently be neon or other suitable readily ionizable inert gas is provided at a convenient pressure of, for example, to torr. As set forth hereinbefore, the halides of bismuth, other than fluoride which is too reactive, may be utilized in the practice of the invention and include bismuth chloride, bismuth bromide, and bismuth iodide. The chloride (BiCl is, however, highly preferred in the operation of the present invention because of the relatively higher vapor pressure and lower tendency to react with other are tube components.

In operation of devices in accord with the present invention, an operating voltage which may range from as low as 40 volts for a low mercury pressure to 500 volts for a high mercury pressure, both at an arc length of approximately 5 cm., for example, is applied between the respective contacts of screw-base 2 causing the full voltage to be applied between arc-electrodes 6 and 7. A portion of this voltage is applied between starting electrode 10 and arc-electrode 7, due to the voltage-dropping characteristics of resistance 11. The voltage gradient between starting electrode 10 and arc-electrode 7 is sufficient to ionize the starting gas, preferably argon, and cause a glow discharge within the vicinity of arc-electrode 7. Since a quantity of mercury is invariably within the influence of such a glow discharge, the mercury is heated by the glow discharge, causing the evolution therefrom of a partial pressure of mercury. This partial pressure of mercury gradually builds up and is ionized by the glow discharge to a point at which an arc discharge sustained by ionized mercury is established between arc-electrodes 6 and 7.

Since the glow discharge set between starting electrode .10 and arc-electrode 7 in argon exhibits the relatively low power and low current characteristic of the glow discharge, it is insufficient to vaporize the bismuth iodide. The discharge established between arc-electrodes 6 and 7, on the other hand, is a high current, high temperature are discharge which is of an entirely diflerent characteristic from the glow discharge in that it has a plasma temperature of the order of several thousand degrees centigrade. This plasma temperature is sufiicient to cause the entire envelope 3 to be raised to a temperature sufiicient to volatilize a substantial portion of the bismuth halide present so as to cause a partial pressure of from 10 to 200 torr thereof to exist within envelope 1. Such temperatures conveniently are from 300 to 450 C. when the iodide of bismuth is utilized and from approximately 275 C. to 425 C. when the bromide of bismuth is used, and 250 C. to 400 C. when bismuth trichloride is utilized as the bismuth halide in accordance with the present invention.

Once the bismuth halide has been volatilized and fills the envelope with a partial pressure as described hereinbefore, the bismuth halide enters into the column of the arc between the arc-electrodes and is dissociated, causing the bismuth to exist in the atomic state and to be raised to excited states from which it may undergo radiative transitions and emit characteristic bismuth lines within the photochemically useful wavelength band. Some important lines of bismuth which are emitted within this band are to be found at 2898 A.U., 2938 A.U., 2989 A.U., 3024 A.U. and 3068 A.U.

The pure line emission of the excited bismuth atoms manifests itself as a plurality of very narrow lines which are theoretically useful but which, as a practical matter, do not contain sufficient energy to independently provide practically useful radiation within the photochemically useful wavelength spectrum. At this point the advantages of the combination of the intermediate pressure mercury atmosphere within lamp envelope 3 and the low pressure atmosphere of bismuth radiating atomic specie becomes of importance. While the narrow bismuth lines are not photochemically useful in that they lack sufiicient energy, the presence of the mercury vapor results in the phenomenon known as line broadening due to collisions with the mercury atoms within envelope 3. Such collision induced line-broadening causes the lines radiated by the excited bismuth atoms to appear as substantially broadened lines. In computing the energy con tained within .a given spectral line the energy is found to be measured essentially by the integrated area contained under the curve representative of the line. Hence, provided that the amplitude of the line is not sufficiently decreased, the broader the line, the more energy contained therein. As an example of the line broadening in accord with the invention typical unbroadened lines of bismuth are approximately 0.05 A.U. wide. Collision broadening by interaction with 1 atmosphere pressure of mercury typically results in line widths of from 10 to 25 A.U. The broadened lines, as a result of collision with mercury atoms, do contain a sufiiciently high energy to substantially add to the mercury lines contained within the photochemically sensitive photochemically useful wavelength. Some lines of mercury which are contained within this range are, within the first photochemically useful range of 2800 to 3200 A.U., 2803 A.U., 2848 A.U., 2894 A.U., 2967 A.U., 3021 A.U., 3125 A.U. and 3132 A.U. Within the second photochemically useful wavelength band of 3200 to 4200 A.U., 3341 A.U., 3650 A.U., 3655 A.U., 3663 A.U., 3906 A.U., 3984 A.U., and 4045 A.U.

The combination of the aforementioned collisionbroadened bismuth lines and the mercury lines (which are also collision broadened to a certain extent) results in:

the unique high intensity, high efliciency photochemicallyuseful radiation of lamps constructed in accord with the present invention.

In view of the foregoing it may readily be seen that the improved photochemical metallic vapor arc lamp light sources of the present invention require a combination of features. Initially there must be a suflicient quantity of mercury within the vapor arc chamber which, upon vaporization thereof, yields a mercury pressure of from /2 to 5 atmospheres. This mercury pressure is necessary in order to establish means for supporting a high temperature, high current electric arc. There must be within the vapor arc chamber a sufficient quantity of bismuth halide (preferably the chloride) to establish and maintain, under the influence of the electric arc supported by the mercury vapor, a partial pressure of from to 200 torr of bismuth halide. Furthermore, the configuration of the arc chamber must be such that the arc is effective to maintain the coldest portion of the interior of the arc chamber wall at a temperature sufiiciently high to establish the desired vapor pressure of the bismuth halide.

As a consequence of the aforementioned conditions, the bismuth halide must dissociate and be excited in order that characteristic bismuth line spectra be emitted. Concurrently, the pressure of the mercury vapor within the chamber must be sufficient to cause collision line broadening of the bismuth emission to increase the energy thereof but insufiicient to cause depletion of the halide. Similarly, the pressure of the mercury contained therein must be suflicient to permit useful photochemical radiation from the mercury spectrum within the desired wavelength bands. From the foregoing it is readily apparent that if the bismuth halide alone is present, the collision induced line broadening cannot occur. Similarly, if the pressure of the mercury is insufiicient to allow for an arc discharge and permit only a glow discharge, the requisite temperature rise necessary to volatilize the bismuth halide would not be present, as is required in lamps of the present invention.

While line broadening is a useful feature of the present invention, the pressure of mercury within envelope 3 of the lamp of FIGURE 1 must not be so high that the pressure of mercury vapor present is conducive to excess chemical reaction with the bismuth halide and clean up of bismuth within the envelope. For this reason the maximum mercury pressure utilized in accord with the present invention is approximately 5 atmospheres, a pressure which allows for sutficient line broadening of the bismuth radiation to achieve the increase of energy output without permitting depletion of the bismuth halide.

One typical photochemically useful light emitting vapor arc lamp constructed in accord with the present invention was constructed similar to a 400 watt mercury vapor arc lamp envelope. The envelope utilized comprised a mm. outside diameter, 18 mm. inside diameter. The inner envelope contained 5 cm. separated thoriated tungsten coiled coil helical electrodes. It contained approximately 50 mgms. of mercury and approximately 50 mgms. of bismuth trichloride, with a starting gas atmosphere of 18 torr of argon. During operation, the are discharge operated at a current of 3.2 amperes at 60 volts arc drop. The output of the mercury spectrum within the photochemically useful wavelength band was supplemented by strong broadened bismuth emission lines of approximately 2898 A.U., 2938 A.U., 2989 A.U., 3024 A.U., and 3068 A.U. This resulted in a doubling of total output within the first photochemically useful wavelength of from 2800 A.U. to 3200 A.U. as compared with a mercury lamp conventionally utilized to produce such radiation, utilizing the same power input.

While the invention has been set forth hereinbefore with respect to specific embodiments and particular examples thereof, it should be readily appreciated that many modifications and changes will readily occur to those skilled in the art. Accordingly, by the appended claims, I intend to cover all such modifications and changes as fall within the true spirit and scope of the present invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A vapor arc photochemically useful light source comprising:

(a) an ultra-violet light transmissive evacuable envelope (b) a pair of arc-electrodes disposed within said envelope and defining therebetween an arc path,

(0) a filler within said envelope comprising 1) a quantity of mercury suflicient upon volatilization thereof to establish within said errvelope a pressure of mercury vapor sufficient to sustain an arc discharge between said electrode and raise the inner Wall of said envelope to operating temperature (2) a quantity of a halide of bismuth (other than the fluoride) sufiicient at lamp operating temperature to produce a partial pressure of bismuth halide sufficient to dissociate in said are and radiate photochemically useful radiation characteristic of the bismuth atom (3) a quantity of a starting gas sutficient to ionize upon application of operating voltages to said lamp and vaporize said mercury,

(4) said quantity of mercury being sufiicient to cause collision line-broadening of the emission of said bismuth atom, but insufiicient to cause depletion of bismuth halide.

2. The lamp of claim 1 wherein said quantity of mercury is sufficient to establish within said envelope a pressure of mercury vapor of 0.5 to 5 atmospheres.

3. The lamp of claim 1 wherein said quantity of bismuth halide is sufficient to establish and maintain under operating conditions of temperature and pressure a partial pressure of bismuth halide vapor of approximately 10 to 200 torr.

4. The lamp of claim 1 wherein said bismuth halide is bismuth trichloride.

5. The lamp of claim 3 wherein said bismuth halide is bismuth trichloride.

6. The lamp of claim 3 wherein the radiation of said lamp is strongly emissive with the band of 2800 A.U. to 3200 A.U.

7. The lamp of claim 3 wherein lamp operating temperature is such that the minimum temperature of the interior of the lamp bulb wall is approximately 250 450 C.

8. The lamp'of claim 7 wherein the bismuth halide is bismuth trichloride and the minimum temperature is approximately 250 C. to 400 C.

9. The lamp of claim 7 wherein the bismuth halide is bismuth triiodide and the minimum temperature is approximately 300 to 450 C.

10. The lamp of claim 7 wherein the bismuth halide is bismuth tribromide and the minimum temperature is approximately 275 to 425 C.

11. The lamp of claim 2 wherein the quantity 'of bismuth halide is sufficient to establish and maintain under operating conditions a partial pressure of bismuth halide of approximately 25 to 50 torr.

References Cited UNITED STATES PATENTS 2,765,416 10/1956 Beese et a1. 313-13 3,234,421 2/1966 Reiling 313-25 3,351,798 11/1967 Bauer 313-229 X 3,379,916 4/1968 Delrieu et a1 313229 X JAMES W. LAWRENCE, Primary Examiner. R. F. HOSSFELD, Assistant Examiner.

U.S. Cl. X.R. 313184, 185, 225, 227

Notice of Adverse Decisions in Interferences In Interference No. 97,505 involving Patent No. 3,450,925, P. D. Johnson, MERCURY BISMUTH HALIDE PHOTOCHEMICAL ARC LAMP LIGHT SOURCES, final judgment adverse to the patentee was rendered Mar. 28, 1973, as to claim 1.

[Ofioial Gazette September 4, 1.973.]

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