US2113984A - Quartz seal - Google Patents

Description

N. L HARRIS ET AL. 2,113,984

QUARTZ SEAL Filed Sept. 28, 1937 April 12, T938.

WWMW II II Inventor's: Nor-man L..Har-r-is, John W. Rgde,

Their" Attorney.

Patented Apr. 12, 1938 UNITED STATES QUARTZ SEAL Norman England,

L. Harris and John W.

assignors to General Electric Com- Ryde, Middlesex,

pany, a corporation of New York Application Claims.

' Our invention metically sealing electric conductors into or through quartz wherein the conductor, prefer- 5 ably in the form of a very thin strip, may be placed within a quartz tube which is then caused to collapse onto the strip by externally applied heat. When the metal of the conductor is tungsten or molybdenum, the thickness of the strip should not exceed 20 microns, a thickness of to microns being usually preferable. This process is particularly valuable in the manufacture of high-pressure metal-vapour lamps with quartz envelopes, such as those disclosed in United States application Serial No. 46,952, B01 et al., filed October 26, 1935, Patent No. 2,094,694.

It is known that if the metal is oxidizable, like tungsten or molybdenum, the space between the strip and the quartz tube must be evacuated, or otherwise rendered free from oxidizing gases, before the quartz isheated for the formation of even a thin film of oxide on the metal makes it impossible to obtain a satisfactory seal. The manufacture of the seal is thereby complicated. The object of this invention is to provide a modification of the said process in which, although an oxidizable refractory metal is used, the seal can be made without removing oxidizing gases.

According to the invention, this object is attained by coating the strip, before it is heated within the quartz tube, with a layer of a refractory non-oxidizable metal, which is preferably rhodium, the said layer belngmuch thinner than the strip. Refractory" means having a melting 35 point substantially higher than the softening temperature of quartz. Sinceit is essential that the strip should be very thin, the thickness of the coating must be suillcient to prevent oxidation, and yet not so great as to interfere with the process of sealing.

The drawing is a longitudinal sectional view, on an enlarged scale and taken at an angle to show the strip in perspective, of a high pressure lamp of the type disclosed in the above-mentioned Patent 2,094,694.

Referring to the drawing, the lamp comprises a tubular quartz envelope iii containing thermionic electrodes H--li each of which is sup ported by a lead-in .conductor comprising wires 50 i2 and it, of tungsten for example, welded to the ends of the strip II which is'sealed directly into the end portion of the envelope Ill. The strip ll,

- in accordance with our invention, consists preferably of molybdenum or tungsten having a coat- 55 ing of rhodium thereon.

The preferred method of forming the layer or coating is by the known process of distillation. For this purpose the uncoated clean strip may be placed in a vacuum adjacent to a tungsten helix o0 enclosing a bead of rhodium, and the tungsten relates to the sealing of metal tovitreous material and more particularly to her- I September 28, 1937, Serial No. 166,226 Great Britain June 30, 1936 heated by a current passed through it until the rhodium evaporates and is deposited on the strip. Since the strip has to be coated on all sides, the process may be repeated with different surfaces of the strip turned towards the helix, or it may be surrounded by several helices each containing a rhodium bead. Several strips may be coated at the same time.

Alternatively, the thin layer may be formed by the known process of cathodic sputtering or even by electro-piating.

The layer need not be more than 1 micron thick. Thus with a molybdenum strip 10 microns thick and a few millimeters wide, a layer of rhodium 0.75 micron thick has been found satisfactory.

In the sealing of the strip it to the quartz tube it, although complete removal of the air is not necessary, partial removal is desirable in order that the collapse of the tube onto the strip may be aided by the external pressure, a reduction of the pressure of the air within the tube by about one-quarter being sufllcient. Alternatively the pressure may not be reduced at all, and collapse aided by mechanically applied pressure, as in the known process of making a pressed seal.

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

1. In combination with an article of quartz, a conductive member sealed directly therein and consisting of an oxidizable refractory metal not substantially greater than twenty microns thick and having thereon a coating of rhodium of a thickness muchless than that of said conductive member.

2. In combination with an article of quartz, a conductive member sealed directly therein and consisting of an oxidizable refractory metal not substantially greater than twenty microns thick and having thereon a coating of rhodium of a thickness of less than one micron.

3. In combination with an article of quartz, a

conductive member sealed directly therein and consisting of a strip of molybdenum not substantially greater than twenty microns thick and having thereon a coating of rhodium of a thickness of less than one micron. 4. In combination with an article of quartz, a conductive-member sealed directly therein and consisting of an oxidizabie refractory metal having thereon a very thin coating of rhodium.

5. In combination with an article of quartz, a conductive member sealed directly therein and consisting of a strip of tungsten not substantially greater than twenty microns thick and having thereon a coating of rhodium of a thickness of less than one micron.

NORMAN L. HARRIS. JOHN W. RYDE.

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