US 2673945 A
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March 30, 1954 E. E. KADUK 2,673,945
METHOD OF TREATING ELECTRIC INLEAD CONDUCTORS Filed Dec. 30, 1952 Inventor": Edward E. KaduK,
His Attorney Patented Mar. 30, 1954 METHOD-OF TREATING ELECTRIC INLEAD I CONDUCTORS Edward E. Kaduk, Ma 'signor to General El ration of New York yfield Heights, Ohio, as-
ectric Company, a corpo- Application December 30, 1952, Serial No. 328,643
5 Claims. 1
The present invention relates generally to electric devices having current leading-in conductors having molybdenum portions extending outwardly from a sealed vitreous envelope and more particularly the invention relates to methods for cleaning the exposed molybdenum parts of such conductors sealed directly into the wall of quartz envelopes of electric lamps.
In the manufacture of gaseous electric discharge lamps having quartz envelopes and molybdenum leading-in wires having a flattened section sealed directly to the quartz envelope Without the interposition of a sealing glass between the quartz and the molybdenum wire, the molybdenum wire is heated to about the softening temperature of quartz during fabrication of the seal. Also, the step of exhausting the quartz envelope after the seals between the leading-in wires and the quartz envelope have been made and before the envelope is sealed off from the exhaust system is carried out at elevated temperatures.
During the above steps in the manufacture of such lamps a coating of molybdenum oxide forms on the inlead. Oxide formation is light during fabrication of the seals between the inlead wire and the seal because of inert gas, such as nitrogen, is used to surround the inlead during this step in the manufacture of the lamp. However, during exhaust of the quartz envelope with the inleads sealed therein oxidation is much heavier at the parts of the molybdenum extending outwardly from the ends of the envelope because those parts of the inleads are at elevated temperatures and exposed to air during this step in the manufacture of the lamp.
An oxide coating on this portion of the inlead is highly undesirable because it creeps along the inlead and into the hermetic fused joint between the inlead and the quartz to make the seal gas pervious and terminate the useful life of the lamp.
The principal object of the present invention is to minimize during manufacture of the lamps the formation of molybdenum oxide on the external parts of molybdenum inleads of electric lamps having quartz envelopes and to expeditiously remove the small amount of molybdenum oxide which does form on such parts. Further objects and advantages of the invention will appear from the following detailed description.
The invention attains its objects by first coating the external parts of the molybdenum inleads with magnesium oxide prior to the ex hausting step in the manufacture of the lamp;
to minimize the formation of molybdenum oxide and after the lamp is sealed off from the exhaust system the entire lamp is immersed in a non-alkali containing mixture of glacial acetic acid and hydrogen peroxide to remove from the exposed parts of the inleads the small amount of molybdenum oxide formed in spite of the protective coating of magnesim oxide.
Heretofore the said external parts of the inleads have been coated with boron oxide prior to the high temperature exhaust of the envelope to reduce the formation of molybdenum oxides during exhaust. This was effective for preventing the formation of excessive molybdenum oxide but it also formed a scale of oxides which was exceedingly difficult to remove.
The use of magnesium oxide in accordance with the present invention is equally as effective for protecting the inlead wires from excessive oxidation and has the highly desirable characteristic of being readily removable by an acetic acid, hydrogen peroxide mixture as I have demonstrated.
The best mode contemplated by me of carrying out the invention is described below in con junction with the accompanying drawings in which:
Fig. l is a perspective view of a high pressure mercury vapor electric discharge lamp showing the end portions of the inleads extending outwardly from each end of the tubular quartz envelope of the lamp.
Fig. 2 is a side elevational view of an apparatus useful for cleaning from a number of such lamps magnesium oxide coating from the said end portions of the inleads extending outwardly from the lamp envelope.
Referring to Fig. l of the drawing the lamp l illustrated has a tubular envelope 2 consisting entirely of quartz and provided at each of its ends with pinch seals 3 and 4. A single molybdenum inlead 5 extends through seal 4 and is connected to and supports the main discharge supporting electrode 6. Two molybdenum inleads l and 8 extend through the other of said seals. The inlead 8 is connected to and supports the main electrode 9 and the inner end ill of the inlead 1 constitutes an auxiliary electrode for facilitating the starting of the main discharge between the electrodes 6 and 9.
The tubular portion of the envelope 2 of the completed lamp I is filled with a discharge conducting starting gas, such as argon, at a few millimeters pressure and contains a measured amount of mercury, indicated at ll, sufficient to produce a high pressure, superheated, luminosity producing mercury vapor atmosphere dur-' ing operation of the lamp I. The electrodes 6 and 9 include a coil of fine tungsten wire supporting a pencil of material of higher electron emissivity, such as thorium.
The inleads '5, I and 8 have flattened portions I2, I3 and I4, respectively, which are hermetically united with the quartz at the pinch seals 3 and 4. The end portions I5, I6 and I1 of the inleads 5, I and 8 respectively extend outwardly from the pinch seals 3 and 4 for connection with a suitable source of electric power.
Lamps having the above structure and enclosed in a sealed glass envelope having a base provided J with electrical contacts are commercially available in a 100 watt size and are known in the trade as EH-d lamps. V
In making the lamps the seals 3 and 4 are first made by heating the quartz at the ends of quartz tube to soften these ends and then pressing the softened quartz tube portions together onto the flattened portions I2, I3 and I4 of the inleads 5, I and 8 to form the flat, gas tight, pinch seals 3 and 4. During this operation the inleads 5, I and 8 are surrounded by an inert atmosphere, such as nitrogen and only a slight formation of molybdenum oxide takes place.
In accordance with the present invention, after the pinch seals 3 and 4 have been made and before the envelope 2 is connected to the vacuum system for exhaust through its quartz tubulation I9, shown as sealed off in Fig. l, a coating of magnesium oxide is applied to the exposed ends I5,
I6 and I! of each of the inleads 5, I and 8. This Y is accomplished by dipping the inlead ends 5, I and 8 into a suspension of about 100 grams magnesium oxide in about 500 cc. of a binder comprising preferably, nitrocellulose in butyl acetate.
A satisfactory binder solution is one containing 54 04-06% solids, as dynamite grade nitrocellulose, in a solvent of 60 parts butyl acetate to parts naphtha, by volume. Of course, any suitable method of applying the coating, such as painting, may be used.
The envelope 2 with the ends of the inleads so coated is then heated in air to a temperature slightly below the softening temperature of quartz and exhausted of air through the tubulation I9 while being maintained at an temperature. The envelope 2 is then allowed to cool. The other usual steps in the manufacture of such lamps, such as filling the envelope with the starting gas and introducing the mercury, are then carried out and the exhaust tubulation I9 is sealed off as shown.
Of course, the binder is driven off during the high temperature exhaust to leave a protective coating of magnesium oxide on the inlead ends.
During the high temperature exhaust in air a heavier formation of molybdenum oxide takes place on the end portions I5, I5 and I! of the inleads in spite of the protective coating of magnesium oxide. Removal of this molybdenum oxide is necessary to avoid termination of the useful life of the lamp I by the oxide creeping inward along the inleads 5, I and 8 into the hermetic fused joints between the quartz and the flattened portions I2, I3 and I4 of the inleads and making these joints pervious to gas.
In accordance with the present invention the molybdenum oxide and also the magnesium oxide is removed from the end portions I5, I6 and I! of the inleads by immersing the entire lamp I in a elevated mixture of glacial acetic acid (CH3COOH) and 30% hydrogen peroxide (H202).
The apparatus shown in Fig. 2 is suitable for treating a number of batches of the lamps I by immersing the lamps in the cleaning mixture and comprises a Pyrex beaker of about 800 cc. capacity supported by 'a ring stand 2I and an electric heater 22 having current leads 23 also supported by the ring stand 2| underneath the beaker 20.
In cleaning a number of the lamps I a mixture of 250 cc. ofglacial acetic acid and 150 cc. of 30% hydrogen peroxide is preheated in the beaker 20 by the heater 22 to a temperature of approximately to C., inclusive. A batch of lamps I, preferably about 50, is then placed in the beaker. The mixture completely covers the lamps I.
Due to the cooling effect of the lamps the temperature'of the mixture may drop below 80 C. in which event the heater is suitably energized to heat the'mixture and raise and maintain its temperature to within the range of approximately 80 to 90 C., inclusive.
With the first batch, the reaction proceeds slowly until a yellow color, due to the formation of peroxy-hexamolybdic acid, appears in the mixture. After this color becomes apparent the oxides are removed from the exposed inlead ends I5, I6 and II of the lamps I of the first batch in about 5 to 7 minutes.
Of course, with subsequent batches of lamps cleaned by immersion in the same mixture the reaction proceeds at the rate established after the yellow coloration appears in the solution when treating the first batch. Thus, the total immersion time for subsequent batches of lamps is approximately 5 to '7 minutes. The original mixture may be used to clean 'four batches of lamps, each batch containing 50 lamps.
The oxide coating is not completely removed from all the inlead ends I5, I6 and I! of the lamps I at exactly the same time so that visual observation as well as elapsed time of immersion should be used to determine'the time each batch is retained in the mixture.
The temperature range of 80 to 90 C. is preferred for the mixture because-at lowertemperatures the cleaning of the inlead'ends I5, I6 and [1 takes place at an appreciably slower rate and at temperatures higher than 90 C. the action is too rapid and results in too much of an attack on the metal'of the inlead ends.
After the oxide coating has been removed from the inleads of one batch of lamps, the mixture is poured into another suitable vessel such as a 800 cc. Pyrex beaker and the-clean lamps in the beaker 25] are washed with cold tap water. Hot water should be avoided because its use occasionally causes a brown film to appear on the inlea'd ends I5, I6 and II. The step of rinsing the lamps with cold water should be done prompt- 1y on the removal of the mixture to avoid discoloration of the inlead ends. Such a discoloration can be prevented also by placing -a small amount of ammonium hydroxide in the beaker while running the tap Water thereinto.
After the lamps are washed thoroughly in the manner described above they are air dried or oven dried at a. low temperature and are then ready for mounting inthe usual glass envelope provided for such lamps in the commercial lamps of the EH-4 type.
The same mixture may be poured back into the beaker 20 orretained in-the same beaker in which-itwas placed when -rmsing-the lamps in the beaker 20 and used for cleaning subsequent batches of lamps as mentioned above.
The use of the glacial acetic acid, hydrogen peroxide solution in the method described above has a high degree of safety and is therefore eminently satisfactory for use in factory production of the lamps I. The reaction between the mixture and the molybdenum and magnesium oxide proceeds in an orderly manner when the lamps are immersed and does not increase in violence or temperature while the chemical action is taking place. On the contrary, the mixture must be heated for short intervals during the cleaning period in order to maintain a temperature within the range of so to 90 C. inclusive. A 30% hydrogen perioxide is preferred however for safety purposes initially. As the reaction proceeds water also is formed from the peroxide during the cleaning process thus providing an added safety factor. During the heat ing cycle the opening in the vessel containing the mixture may be covered to prevent excessive evaporation of water.
Another safety factor characteristic of the mixture is that it does not react violently with mer cury. This is an important feature in view of the droplet of mercury l I contained in each of the immersed lamps I one or more of which may be accidentally broken during the cleaning process.
The stability of the glacial acetic acid, hydrogen peroxide mixture is due to the presence of an acid with the peroxide solution. The mixture of about 1.66 parts glacial acetic acid and 1.0 part 30% hydrogen peroxide by volume utilized as a cleaning solution in the present method boils at approximately 107 C. without copious evolution of oxygen and is therefore a safe solution for use as contemplated by the present invention.
What I claim as new and desire to secure by Letters Patent of the United States is:
1. In the manufacture of electric lamps having quartz envelopes provided with electrical conductors extending through and sealed directly to the wall of the envelope, wherein the portions of conductors exposed outside of said envelope consist of molybdenum and wherein during exhaust the envelope with the conductors so sealed therein is heated in air to a temperature such that formation of molybdenum oxide occurs on the molybdenum portions of the conductors exposed outside the envelope, the method of protecting the said exposed portions of the conductors from excessive oxidation during exhaust of the envelope and of removing the molybdenum oxide formed on said conductor portions during the exhaust, which method comprises first applying a coating of magnesium oxide to the said conductor portions prior to heating and evacuating said envelope and therea ter, when the manufacture of said lamp has been otherwise completed, removing the molybdenum oxide and the magnesium oxide from said exposed conductor portions by immersing at least the said exposed conductor portions of the lamp in a mixture of glacial acetic acid and hydrogen peroxide.
2. The method of treating electric inlead conductors sealed directly into the wall of a quartz envelope of an electric lamp and having portions consisting of molybdenum exposed outside said envelope which comprises the steps of coating the said exposed molybdenum portions of said conductor prior to exhausting said envelope at elevated temperatures with magnesium oxide to minimize the formation of molybdenum oxide on said conductor portions during the said exhaust of the envelope and, after completion of said exhaust and the other steps in the manufacture of the lamp, removing the magnesium oxide and the molybdenum oxide from said exposed conductor portions by immersing the entire lamp in a mixture of glacial acetic acid and hydrogen peroxide having a temperature of about to 0., inclusive.
3. The method of treating electric inlead conductors as defined in claim 2 characterized by the fact that a 30% hydrogen peroxide is used in the mixture.
4. The method of treating electric inlead condoctors as defined in claim 2 characterized by he fact that the mixture consists of 1.66 parts glacial acetic acid and 1.0 part 30% hydrogen peroxide.
5. The method of treating electric inlead conductors as defined in claim 2 characterized by the fact that the mixture consists of 1.66 parts glacial acetic acid and 1.0 part 30% hydrogen peroxide and the fact that the lamp is retained in the mixture for a period of 5 to 7 minutes and is thereafter removed from the mixture and rinsed with cold water.
EDWARD E. KADUK.
No references cited.