US3132279A - Electrical discharge device - Google Patents

Description

May 5, 1964 G. LEWIN ELECTRICAL DISCHARGE DEVICE Filed Aug. 11, 1961 I I I INVENTOR. GERHARD LEWIN BY wz m gaaw 3,132,279 ELECTRICAL DISCHARGE DEVICE Gerhard Lewin, West Orange, N .J., assignor to Engelhard- Hanovia, Inc, Newark, N.J., a corporation of New Jersey Filed Aug. 11, 1961, Ser. No. 130,990 3 Claims. (Cl. 313-490) The present invention deals with an electrical device and more particularly with an electrical discharge device in combination with a particular electrode and lead-in conductor construction.

Dicharge devices such as electrical gaseous discharge lamps having a fused quartz or high temperature glass envelope containing a filling of a rare gas, e.g., xenon, or a rare gas and a vaporizable metal, e.g., mercury, are provided with at least a pair of spaced electrodes contained by the envelope and connected to a source of electrical current by means of lead-in conductors, e.g. tungsten conductors, hermetically sealed through the lamp envelope. The quartz-to-metal hermetic seal is a critical significance since the lamps operate at high temperatures and the difference in co-efficients of expansion of the metal and the quartz induces mechanical stresses which tend to crack the quartz and destroy the hermetic seal. When the hermetically sealed lead-in conductor is a thin wire of less than about 20 microns in diameter, it is possible to provide an adequate hermetic seal directly with the quartz of the envelope, but such thin wires are disadvantageous in that they cannot carry appreciable current loads. For the desirable heavier current loads required by discharge lamps having a filling of, e.g., xenon or xenon and mercury, the thin lead-in conductors are inadequate. Heavier tungsten lead-in conductors cannot be suitably hermetically sealed directly to the quartz of the envelope. Heavier tungsten lead-in conductors can be hermetically sealed through the wall of a fused quartz envelope, for example, when a leached seal or graded seal as known in the manufacture of high pressure are lamps is employed between the lead-in conductor and the fused quartz of the lamp envelope. or graded seal constitutes an expansion transition means having a co-efiicient of expansion between that of the tungsten lead-in and the quartz of the envelope, with the transition means being located adjacent the tungsten leadin and having a co-efiicient of expansion appropriating that of the tungsten. At least one layer of an aluminaborosilicate glass may be employed as an expansion transition glass. However, such lead-in conductors as known are disadvantageous in that they provide a steep temperature gradient from the inner end'of the seal to the outer end with the temperature difference between the two ends being excessive and creating thermal stresses in the seal.

In accordance with the present invention, the abovementioned disadvantage of the undesirable steep temperature gradient in the seal is substantially eliminated by a change of the electrical and thermal conduction of the 1ead-in conductor at the seal which operates to localize the high temperatures generated at the electrode and to restrict steep temperature gradients to the region within the envelope, whereby comparatively low temperature gradients are provided through the seal.

It is an object of the invention to provide an electrical discharge lamp having a lead-in conductor hermetically sealed through the lamp envelope and including means to reduce the temperature gradient through the lamp seal.

It is another object of the invention to provide an electrode and lead-in conductor construction for electrical discharge devices, whereby high temperature gradients are localized along selected portions of the conductor.

Other objects and advantages of the invention are be- In such case, the leached j 3 ,132,279 7 Patented May 5, 1964 ice coming apparent from the description hereinafter following and the drawings forming a part hereof in which: FIGURE 1 illustrates a partly cross-sectional and partly elevational view of a discharge lamp according to the invention, and

FIGURE 2 illustrates a partly cross-sectional and partly elevational fragmentary view of a modified form of discharge lamp;

Regarding the drawings,:FIGURE 1 illustrates an electrical discharge lamp 1 having an elongated envelope 2,

composed of fused quartz. The lamp envelopenis provided with an ionizable atmosphere of a rare gas or a rare gas and a vaporizable metal. The atmosphere may consist of, for example, .xenon or xenon and mercury. The ends of the quartz envelope 2 are provided with axial openings 3 and 4 whichv are capped with an assembly comprising a lead-in conductor, electrode and expansion transition seal means. The lead-in conductor comprises a first wire or a rod portion 5 and a second wire or rod portion 6 extending preferably axially of the first portion,

the first portion, as illustrated by FIGURE 1, being of.

larger diameter than the second portion. For example, the first portion has a cross-sectional area about 3 to 4 times that of the second portion. An electrode 7 is mounted on the end of the second portion of the conductor, with the electrode being of substantial mass and having a cross-sectional area substantiallygreater than the second conductor portion.

The first conductor portion 5 is coated with a layer 8 of a glass having a co-efiicient of expansion approximately that of the metal of which the portion 5 is composed, e.g. tungsten. At least one layer 8, 9 and 10 of a transition glass material is fused to the opening 3 and 4 of the envelope 2, thereby hermetically sealing the envelope at both ends. While electrodes 7 are illustrated as identical electrodes for lamps employing alternating current, the electrodes may also be dimensioned with one being of greater mass than the other for direct current operated lamps. Regarding the electrode and lead-in conductor assembly illustrated by FIGURE 1, the first portion 5 of the conductor may have a length of about one-half inch and a diameter of about .12 inch and the second portion 6 may have a length of about one inch and a diameter of about .06 inch. This yields the mini-' mum heat flow for a current of 50 amp. The electrode 7 is dimensioned to have sufficient mass to maintain a 7 low evaporization rate of the electrode metal.

ence between the two ends of portion 6. Consequently,

the temperature along portion 5 is uniformly low and almost equal to the temperature of the outside end of portion 5. Therefore, the lamp can be effectively water cooled without creating thermal stresses at the seal.

The cross section of the portion 5 is about 4 times larger than that of portion 6. This increases the thermal conduction more than 4 fold and reduces the Joule heat generated in this portion resulting in a negligible temperature drop through the portion 5 within the seal area of glass layer 8.

FIGURE 2 illustrates a modification of the invention and comprises an elongated fused quartz envelope and seal construction identical to that described with respect to FIGURE 1. However, the lead-in conductor comprises a heat conduction varying means of dilferent form.

3 In FIGURE 2, the lead-in conductor comprises a first conductor portion 11 and a second portion 12 extending preferably axially outwardly of the first portion 11. An electrode 13 is mounted at the end of the second portion. The second portion 12, as illustrated, has a cross-sectional area equal to that of portion 11, but the first portion is composed of a metal of higher heat and electrical conductivity than the portion 12. For example, the first portion is composed of tungsten and the second portion is composed of tantalum. With this construction, the

steep temperature gradients occur along the portion of lower heat conductivity and within the envelope 2 with the result that a smaller temperature drop occurs through the portion 11 passing through seal'component 8.

Various modifications of the invention are contemplated within the scope of the appended claims.

What is claimed is:

1. An electrical discharge device comprising a light transmissive envelope containing an ionizable atmosphere, a conductor extending through the envelope wall into the envelope, said conductor comprising a first portion sealed through the envelope wall and a second portion extending into the envelope from the first portion with an electrode element on the inward end of the second portion, the cross-sectional area of the first and second portions being substantially equal, and said first portion being made of material having higher heat and electrical conductivity than the second portion whereby the second portion has a steeper temperature gradient than the first portion.

2. An electrical discharge device according to claim 1 in which the first portion of the conductor is made of tungsten and the second portion is made of tantalum.

3. An electrical discharge device according to claim 1 including expansion transition material between the said first portion and the envelope wall.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. AN ELECTRICAL DISCHARGE DEVICE COMPRISING A LIGHT TRANSMISSIVE ENVELOPE CONTAINING AN IONIZABLE ATMOSPHERE, A CONDUCTOR EXTENDING THROUGH THE ENVELOPE WALL INTO THE ENVELOPE, SAID CONDUCTOR COMPRISING A FIRST PORTION SEALED THROUGH THE ENVELOPE WALL AND A SECOND PORTION EXTENDING INTO THE ENVELOPE FROM THE FIRST PORTION WITH AN ELECTRODE ELEMENT ON THE INWARD END OF THE SECOND PORTION, THE CROSS-SECTIONAL AREA OF THE FIRST AND SECOND PORTIONS BEING SUBSTANTIALLY EQUAL, AND SAID FIRST PORTION BEING MADE OF MATERIAL HAVING HIGHER HEAT AND ELECTRICAL CONDUCTIVITY THAN THE SECOND PORTION WHEREBY THE SECOND PORTION HAS A STEEPER TEMPERATURE GRADIENT THAN THE FIRST PORTION.

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