US3063778A

US3063778A - Method for introducing iodine into a lamp envelope

Info

Publication number: US3063778A
Application number: US102480A
Authority: US
Inventors: Emery G Audesse
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1961-04-12
Filing date: 1961-04-12
Publication date: 1962-11-13
Anticipated expiration: 1979-11-13
Also published as: GB945020A

Description

Nov. 13, 1962 E. G. AUDESSE METHOD FOR INTRODUCING IODINE INTO A LAMP ENVELOPE Filed April 12, 1961 iim il l INVHVTOR.

MERY G. AUDESSE A TORNE United States Patent C) 3,063,778 METHOD FOR INTRQDUCING IODINE INTO A LAMP ENVELOPE Emery G. Audesse, Salem, Mass assignor to Sylvania Electric Products Inc, a corporation of Delaware Filed Apr. 12, 1961, Ser. No. 102,480 5 Claims. (Cl. 316-25) This invention relates to lamps having tungsten filaments enclosed in envelopes, the latter usually being of fused quartz or other suitable glass. Such devices are generally called iodine or iodine-quartz lamps. More particularly this invention concerns an improved method for introducing controlled quantities of iodine into such lamps during the manufacturing process.

Incandescent lamps having quantities of iodine in the envelope are known to the art. Such lamps operate on a tungsten-iodine cycle which is a regenerative, continuing process in which tungsten iodide is produced when the iodine combines chemically with particles of tungsten evaporating from an incandescing tungsten filament. Subsequent thermal decomposition of this compound replaces the tungsten particles on the filament. In conventional filament lamps not containing controlled quan tities of iodine, these particles are deposited on the envelope, thus gradually causing a loss of light output due to blackening, Rupturing of the filament may occur when a sufiicient quantity of tungsten particles evaporates and the lamp must be replaced. However, the iodine-tungsten cycle eliminates lamp blackening and reduces lamp outage by its getter action.

The iodine, together with the heat of the lamp, prevents the tungsten from accumulating on the lamp envelope and darkening it. As the vaporized tungsten iodide circulates back into the area of the incandescent filament, the intense heat of the filament frees the tungsten from the tungsten iodide by thermal decomposition and this tungsten is deposited back on the filament, leaving the iodine free to begin a new cycle. Theoretically, if the evaporating tungsten particles could be returned to the filament in a perfectly even coating, the lamp might never burn out. But since there is no way to control exactly where the tungsten particles return to the filament, one spot will eventually wear out, thus rendering the iodine-quartz lamp inoperative. This condition, however, occurs after operation in the order of hundreds of hours and possibly even thousands of hours before lamp failure. Furthermore, during the life of an iodine lamp the maintenance of light output is substantially constant.

The iodine present in the lamp envelope must be in controlled quantities and, in particular, must be in an adequate quantity to elfect a regenerative getter action, but inadequate to absorb appreciable quantities of light. Previous methods of adding the iodine to the lamp envelope to effect such regenerative getter action have been tedious and time consuming and, furthermore, have tended to introduce undesirable impurities into the lamp which shorten its life. Such methods have made use of a time-consuming operation of installing traps in the exhaust tubing of the lamp; for example, a glass container with a supporting tungsten spring was slipped into the exhaust tubing to support the iodine crystals. These traps were previously necessary to position the iodine securely during an exhaust and fill step, but the disadvantages of their use were the expense of fabrication together with the possibility of vaporizing impurities from the trap into the lamp.

According to my process, materials not directly contribtuing to the addition of iodine into the exhausted lamp are eliminated. My process comprises placing iodine crystals of a random quantity intermediate the ends of an exhaust tube that is appended to the side of the "ice 2 lamp envelope and the bore of which is in communication with the interior of the envelope.

The iodine crystals are then melted by gently warming the exhaust tube over a gas flame, thus causing themelted iodine to wet the inside wall of the exhaust tubing. Upon cooling, the solidified iodine will adhere tenaciously to the internal surface of the tube and will not be displaced even during the operations of exhausting and filling the envelope. After such operations, the envelope is sealed from the atmosphere by fusing the glass of the exhaust tube at a point below the adhering iodine. 'Ihe sealed lamp is then placed in a constant temperature bath for a sufficient time to vaporize controlled quantities of iodine from the exhaust tube to the envelope. After adequate quantities of iodine are vaporized, the lamp is removed from the constant temperature bath, washed and chilled to reduce internal gas pressures. The exhaust tube is then sealed from the envelope at a point closely adjacent to the lamp envelope to produce the finished lamp.

Accordingly, an object of my invention is to prepareincandescent lamps having controlled quantities of iodine in the envelope by an eificient and inexpensive process.

Another object of my invention is to introduce iodine into lamp envelopes in a manner so as to avoid con-- tamination and further, to produce batches of lamps containing uniform quantities of iodine.

An advantage of my invention is that lamps containing uniform quantities of iodine may be produced without the introduction of undesirable contaminating material, even though closely controlled quantities of iodine are enclosed in each envelope.

A feautre of this invention is wetting the inner surface of an exhaust tube with a random quantity of melted iodine and then allowing the iodine to solidify, thereby permitting the entrance and exit of gases through the exhaust tube during lamp fabrication methods, without dislodging the iodine.

Other objects, features and advantages will become apparent to those skilled in the art upon reading the following specification when taken in conjunction with the accompanying drawings.

The various figures of the drawings are the schematic views in the nature of a flow. sheet depicting the various treatment steps in my method of inserting controlled quantities of iodine in the lamp envelope. For

simplicity, the tungsten filament is shown only in FIGS." 1 and 10, although it is to be understood that the filament is present in lamps shown in each and every treating step of FIGS. 2-9 respectively,

FIGURE 1 is an elevational view of a quartz-iodine lamp before evacuation and before insertion of the iodine.

FIGURE 2 is a schematic elevational view of a quartziodine lamp and shows in particular the insertion of a quantity of iodine crystals into the exhaust tube with a FIGURE 3 is a schematic elevational view of the spatula. t, z

quartz-iodine lamp showing in particular the heating of the iodine crystal to wet the walls of the tube.

FIGURE 4 of the drawing is a schematic elevational view of the quartz-iodine lamp being exhausted of atbath, which is shown in cross section.

FIGURE 7 is a schematic elevational View of the quartz-iodine lamp positioned in a washing tank, which is shown in cross section.

FIGURE 8 is a schematic elevational view of the quartz-iodine lamp positioned in a tank of liquid nitrogen, which is shown in cross section.

FIGURE 9 is a schematic elevational view illustrating the tipping operation for the removal of the exhaust tube and sealing of the lamp.

FIGURE 10 is an elevational view of a completely fabricated quartz-iodine lamp.

In each of the figures of the drawing similar numerical designations are indicative of similar elements of structures.

Referring to FIGURE 1 of the drawing, the lamp illustrated therein comprises a high silica content glass envelope 1, preferably of fused crystalline quartz or possibly of fused vycor. The diameter of the envelope may be, for example, to /2 inch, although other diameters are possible. Each end of the envelope is flattened into a press or seal portion 2 and hermetically sealed and embedded therein are lead-in conductors which comprise outer sections 3 of molybdenum wire, inner sections of tungsten wire and intermediate thin foil sections 4 of molybdenum. Each of the inner and outer sections, 3 and 5 respectively, is attached to the molybdenum foil section 4 by spot welding, soldering or merely puncturing, although other means for establishing electrical contact may be used. A coiled coil filament 6 of tungsten wire extends axially of the envelope 1 and is connected at its ends to the inner end portion 5 of the lead-in conductors. Appended to the central portion of the glass envelope 1 is an exhaust tube 10, the bore of which is in communication with the interior of the envelope 1.

In the first step of the operation, the assembly of the envelope 1 and exhaust tube It) is grasped by the exhaust tube 10 and horizontally oriented. Care must be exercised in the handling of the envelope 1 so that per piration and oils present on the hands are not transferred to the envelope, since such substances would tend to adhere to the surface of the lamp and cause devitrification of the envelope upon illumination of the lamp. Devitrification may be avoided by handling only the exhaust tube 10 or by carefully manipulating the envelope 1 with gloved hands, although other preventative methods such as described in the co'pending application of Leo Duval, Serial No. 38,601, filed June 17, 1960 are also applicable.

'The iodine crystals are inserted in the horizontally oriented exhaust tube 10, as shown in FIGURE 2, by inserting a spatula 11 which has randomly selected quantitles, for example .4 gm. of iodine crystals on the end thereof. For convenience, the handle 12 of the spatula 11 has a greater diameter than the internal bore of the exhaust tube 10 and uniform positioning of the iodine crystals in the exhaust tube 10 is insured by placing the spatula handle 12 directly against the end of the exhaust tube 10.

After placing the iodine crystals within the exhaust tube 10, the spatula 11 is withdrawn and the exhaust tube 1 heated directly beneath the crystals 14, in a gas flame 15, as shown in FIGURE 3. Such heating should be quite rapid and of relatively short duration so as to raise the crystals to their melting point, thereby causing them to wet the walls of the exhaust tube 10. Generally, temperatures above about 114 C. can be used, but care must be exercised to avoid overheating the iodine since temperaturesin excess of 183 C. would cause the iodine to boil off or possibly oxidize, which would of course be detrimental to lamp fabrication methods. Subsequent cooling of the melted iodine will cause the melted iodine to adhere tenaciously to the walls of the exhaust tube 10. As illustrated in each of FIGURES 2 and 3, the exhaust tube 10 is horizontally oriented while the iodine is inserted and during the iodine melting process because if the exhaust tube 19 was vertically oriented, the iodine crystals would tend to fall into the envelope 1, thereby increasing the possibility that improper quantities of iodine might be added.

As shown in FIGURE 4, the exhaust tube 10 is inserted in a schematically illustrated exhausting and filling chamber. In this step, atmospheric and other gases present in the lamp envelope are withdrawn from the lamp through exhaust tube 16 and fill gases are forced into the lamp through exhaust tube 10. In both the exhausting and filling steps the gases will pass over the melted iodine crystals which tenaciously adhere to the exhaust tube walls and are not dislodged even by such gaseous movement. Apart from the iodine in the lamp which will be described later, suitable filling gases include argon, krypton, xenon and mixtures thereof, at substantial pressures, for example argon at a pressure of several hundred mils. mercury, preferably about 600 mils. Such gaseous fillng not only retards vaporization of the tungsten filament, but apparently causes a more uniform deposition of tungsten back upon the filament. Of course, in addition to the iodine and the gases mentioned above, other fill gase may be added at other gas pressures when desired, if such additional gases are not detrimental to the efficient operation of the lamp and do not adversely affect the regenerative cycle of the tungsten and iodine.

After exhausting the lamp and filling the envelope 1 with appropriate gases, the exhaust tube It) is tipped and sealed below the adhering iodide 14 as shown in FIGURE 5 In this manner, the entire assembly of the lamp envelope 1 together with the exhaust tube 10 is sealed from the atmosphere while all of the fill gases and the iodine are present therein. Methods available for tipping the exhaust tube 10 are those conventionally used in the art and may be, for example, the type illustrated in the drawing wherein a flame 17 contacts the exhaust tube 10 and melts the glass. It generally is important to make the seal a considerable distance below the adhering iodine 14 (generally about one inch) since extremes in temperature due to the proximity of melting glass might cause vaporization of the iodine and the possible addition of undesirable quantities of iodine to the lamp envelope. After such sealing operations, the lamp is grasped by the exhaust tube 10 and transferred to the next step of the operation and the residual exhaust tube of the first sealing stage removed from the exhausting equipment 16 and discarded.

Since the iodine 14- now adheres to the walls of the exhaust tube 10, steps must be made to transfer an appropriate quantity to the lamp envelope 1. Such transfer is acomplished as shown in FIGURE 6 of the drawing wherein the lamp is suspended on support rods 20 with the exhaust tube down and immersed in a constant temperature bath 19 containing a suitable heat conducting liquid, for example Dowtherm. Conveniently, the heat conducting liquid may be heated by connecting electrical resistance elements 23 to an appropriate power source, although other suitable heating means may also be used. The bath 19 is maintained at a constant temperature by connecting a thermostat 20 and a thermocouple 21 to the resistance elements 23. Although heating times may vary depending upon the amount of iodine to be vaporized into the envelope 1 and heating temperatures may also be varied, depending upon such requirements, it has been found that heating times of 15 to 30 minutes and preferably 20 to 30 minutes when the bath temperature is between and 115 C. and preferably between and C. vaporizes at the lower limit sufiicient iodine to assure the regenerative getter process, but a the upper limit does not exceed that quantity which would result in any appreciable absorption of light by the iodine vapor in an illuminated lamp. For successful operation of the lamp, it has been found that the envelope should contain iodine in quantities of at least 0.1 micrornole per cubic centimeter to 1.0 micromole per cubic centimeter of bulb volume.

After vaporizing the desired amount of iodine from the exhaust tube It} to the lamp envelope 1, the assembly is washed by immersing it in a cold water bath 22 as shown in FTGURE 7. To prevent residual and unvaporized iodine 14 from falling from the exhaust tube 1e into lamp envelope 1, the lamp is suspended between a pair of support rods 28 with the exhaust tube beneath the envelope 1. After a few minutes in the wash bath 22, the oil from constant temperature bath 19 is Washed oit and the lamp is ready for a chilling operation as shown in FIG- URE 8.

The chilling-operation is accomplished by immersing the assembly of the envelope and the exhaust tube It in bath 24, which contains a large quantity of liquid nitrogen. The chilling reduces internal gas pressures of the lamp for the final tipping operation. After an immersion of short duration, generally about one minute, the lamp 1 together with the exhaust tube 10 is withdrawn from the liquid nitrogen and transferred to a final sealing operation. In this sealing operation of passing the exhaust tube 10 between a pair of flames 26 (shown in FIGURE 9) the exhaust tube 16 is removed from the envelope 1 while the glass is still cold from the liquid nitrogen. This final tipping seals the envelope 1 from the exhaust tube 10 at a point closely adjacent to the lamp envelope. Residual or excess iodine present in the exhaust tube 10 is removed together with the exhaust tube in this step.

The finished lamp is shown in FIGURE 10. As shown, the lamp envelope 1 has been scaled from the atmosphere and separated from the exhaust tube and this separation has produced a pointed tipped end 27. All of the ele= ments of the lamp described with reference to FIGURE 1 are present, except the exhaust tube. The required quantity of iodine has been added.

It is apparent that changes and modifications may be made within the spirit of the instant invention. It is my intent, however, to be limited only by the scope of the appended claims.

As my invention I claimi L The process for adding controlled quantities of iodine to a glass envelope having a tungsten filament supported therein and having an exhaust tube appended to the side thereof, the bore of which is in communication with the interior of said envelope, the steps which comprise: inserting a small quantity of iodine in the bore of said exhaust tube intermediate the ends thereof; melting said iodine crystals by heating said exhaust tube, thereby causing the melted iodine to wet the Walls of said tube; cooling said exhaust tube, thereby solidifying the melted iodine; exhausting gases from said envelope and said tube and then adding a fill gas there to; sealing said exhaust tube at a point below the adhering iodine; heating said envelope and said exhaust tube for a period of time adequate to vaporize sufficient iodine from said exhaust tube into said envelope to effect a regenerative getter action with the tungsten of the filament, but inadequate to absorb appreciable quantities of light; chilling said envelope to reduce internal gas pressures and sealing said exhaust tube from said envelope at a point near said envelope.

2. The process for adding controlled quantities of iodine to a glass envelope having a tungsten filament supported therein and having a glass exhaust tube appended to the side thereof, the bore of said tube being in communication with the interior of said envelope, the steps which comprise: melting a small quantity of iodine crystals while said crystals are positioned within and intermediate the ends of said tube; cooling said melted crystals whereby said crystals solidify and adhere to the walls of said tube; exhausing said envelope and said exhaust tube of gasses held therein and then filling said envelope and said exhaust tube with a fill gas; sealing the end of said exhaust tube below the position of the adhering iodine; heating said adhering iodine for a sufficient time to vaporized said iodine from said exhaust tube into said enveloped in quantities adequate to effect the regenerative getter action with said tungsten filament, but inadequate to absorb appreciable quantities of light during subsequent operation of said lamp and sealing said envelope from said exhaust tube at a point near said envelope.

3. The process for adding controlled quantities 'of iodine to a glass envelope having a tungsten filament supported therein and having a glass exhaust tube appended to the side thereof, the bore of said tube being in communication with the interior of said envelope, the steps which comprise: inserting a small quantity of iodine crystals in said exhaust tube intermediate the ends thereof; heating said iodine crystals to a temperature slightly above the melting point, thereby causing the melted iodine to wet the walls of said tube; cooling the melted iodine thereby causing the iodine to adhere to the walls of said exhaust tube, exhausting gases present in said envelope and said exhaust tube through said exhaust tube and adding a fill gas to said envelope through said exhaust tube; sealing said exhaust tube from the atmosphere at a point below said adhering iodine; immersing said envelope and tube in a heated constant temperature bath for a sufi'icient time to vaporize said adhering iodine into said envelope from said exhaust tube in quantities adequate to effect a regenerative getter action with said tungsten filament, but inadequate to absorb appreciable quantities of light during subsequent operation of the lamp and sealing said envelope from said exhaust tube at a point near said envelope.

4. The process for adding controlled quantities of iodine to a glass envelope having a tungsten filament supported therein and having a glass exhaust tube appended to the side thereof, the bore of said tube being in communication with the interior of said envelope, the steps which comprise: melting a small quantity of iodine crystals while said crystals are positioned in said tube intermediate the ends thereof; cooling said melted crystals, thereby causing said iodine to solidify and adhere to the walls of said tube; exhausting gases present in said envelope and said exhaust tube through said exhaust tube and then adding a fill gas to said envelope through said exhaust tube; sealing said exhaust tube from the atmosphere at a point below said adhering iodine; vaporizing said adhering iodine crystals from said exhaust tube into said envelope in quantities adequate to effect a regenerative getter action with said tungsten filament, but inadequate to absorb appreciable quantities of light during subsequent operation and sealing said envelope from said exhaust tube at a point near said envelope.

5. The process for adding controlled quantities of iodine to a glass envelope having a tungsten filament supported therein and having a glass exhaust tube appended to the side thereof, the bore of said tube being in communication with the interior of said envelope, the steps which comprise: melting a small quantity of iodine crystals while said crystals are positioned in said tube intermediate the ends thereof; cooling said melted crystals thereby solidifying said crystals and causing them to adhere to the walls of said tube, exhausting said envelope and said exhaust tube of gasses held therein and then filling said envelope and said exhaust tube with a fill gas; sealing the end of said exhaust tube at a point below the position of the adhering iodine; heating said adhering iodine for a sufficient time to vaporize said iodine from said exhaust tube to said envelope and in sutficient quantities to effect a regenerative getter action with said tungsten filament, but inadequate quantities to absorb appreciable quantities of light, chilling said envelope and said exhaust tube, thereby reducing internal gas pressures and sealing said envelope from said exhaust tube at a point near said envelope.

References Cited in the file of this patent UNITED STATES PATENTS 395,9'62 Edison Ian. 8, 1889

Claims

1. THE PROCESS FOR ADDING CONTROLLED QUAMTIES OF IODINE TO A GLASS ENVELOPE HAVING A TUNGSTEN FILAMENT SUPPORTED THEREIN AND HAVING AN EXHAUSTED TUBE APPENDED TO THE SIDE THEREOF, THE BORE OF WHICH IS IN COMMUNICATION WITH THE INTERIOR OF SAID ENVELOPE THE STEPS WHICH COMPRISES: INSERTING A SMALL QUANTITY OF IODINE IN THE BORE OF SAID EXHUST TUBE INTERNEDIATE THE ENDS THEREOF; MELTING SAID IODINE CRYSTALS BY HEATING SAID EXHUSTED TUBE, THEREBY CAUSING THE MELTED IODINE TO WET THE WALLS OF SAID TUBE; COOLING SAID EXHUSTE TUBE, THEREBY SOLIDIFYING THE MELTED IODINE; EXHAUSTING GASES FROM SAID ENVELOPE AND SAID TUBE AND THEN ADDING A FILL GAS FROM SAID ENVELOPE AND SAID EXHAUST TUBE AT A POINT BELOW THE ADHERING IODINE; HEATING SAID ENVELOPE AND SAID EXHAUST TUBE FOR A PERIOD OF TIME ADEQUATE TO VAPORIZE SUFFICIENT IODINE FROM SAID EXHAUST TUBE INTO SAID ENVELOPE TO EFFECT A REGENATIVE GETTER ACTION WITH THE TUNGSTEN OF THE FILAMENT, BUT INADEQUATE TO ABSORB APPRECIABLE QUANTITIES OF LIGHT; CHILLING SAID ENVELOPE TO REDUCE INTERNAL GAS PRESSURE AND SEALING SAID EXHAUST TUBE FROM SAID ENVELOPE AT A POINT NEAR SAID ENVELOPE.