US3219753A

US3219753A - Gas-impervious electrical feedthrough for use between two zones of differing pressures

Info

Publication number: US3219753A
Application number: US280568A
Authority: US
Inventors: Vassos Nicholas
Original assignee: University of Illinois
Current assignee: University of Illinois; University of Illinois Foundation
Priority date: 1963-05-15
Filing date: 1963-05-15
Publication date: 1965-11-23
Anticipated expiration: 1982-11-23

Description

Nov. 23, 1965 N. vAssos 3,219,753

GAS-IMPERVIOUS ELECTRICAL FEEDTHROUGH FOR USE BETWEEN TWO ZONES 0F DIFFERING PRESSURES Filed May 15, 1965 5 Sheets-Sheet l METALLIC SEALING MEANS E fl /52722 7 5707/ 754 a 021 533 777%) MM %w@ 5 Sheets-Sheet 2 Nov. 23, 1 N. VASSOS GAS-IMPERVIOUS ELECTRICAL FEEDTHRCUGH FOR USE BETWEEN TWO ZONES OF DIFFERING PRESSURES Filed May 15, 1963 flzbXaiQ: a sag NOV. 23, 1965 VASSQS 3,219,753

GAS-IMPERVIOUS ELECTRICAL FEEDTHROUGH FOR USE BETWEEN TWO ZONES OF DIFFERING PRESSURES Filed May 15, 1963 3 Sheets-Sheet 3 f fl/ afg m. I U

United States Patent GAS-IMPERVIOUS ELECTRICAL FEEDTHROUGH FOR USE BETWEEN TWO ZONES OF DIFFERING PRESSURES Nicholas Vassos, Urbana, Ill., assignor to University of Illinois Foundation, a non-profit corporation of Illinois Filed May 15, 1963, Ser. No. 280,568 7 Claims. (Cl. 174152) The present invention relates generally to electrical feedthroughs which extend through a wall to electrically connect a pair of terminals on respective opposite sides of the wall, and more particularly to feedthroughs which electrically connect a first terminal in a zone of very low pressure (e.g., 1X10 torr or lower) and a second terminal in a zone of relatively high pressure (e.g., atmospheric pressure).

Such pressure differentials exist between the interior and exterior of a low pressure testing system vessel. In such a system the extremely low interior pressures are obtained after the entire system, including the electrical feedthroughs, are assembled in place. Typically, the interior of the vessel is initially partially evacuated by conventional roughing pumps; and, to assure attainment and maintenance of the desired low pressures, the entire vessel is subjected to a bake-out which causes gaseous molecules in the walls of the vessel to be emitted into either the atmosphere or the interior of the vessel from where these gaseous molecules may be removed by conventional pumping means (e.g., a diffusion pump).

It is important that electrical feedthroughs for use in such low pressure systems constitute a sealed assembly of the various components to prevent entry of gases from the high pressure zone to the low pressure zone between which the feedthrough extends. It is also important that the feedthrough be capable of withstanding the aforementioned bake-out without breaking the seal among the various components.

In accordance with the present invention, an electrical feedthrough is provided, for extension between a zone of very low pressure and a zone of relatively high pressure, which feedthrough includes a sealing arrangement among the components which prevents leakage of gas from the high pressure zone through the feedthrough components to the low pressure zone, and which will withstand the heat of the bake-out without interrupting the seal among the components.

Other features and advantages are inherent in the structure claimed and disclosed or will become apparent to those skilled in the art from the following detailed description in conjunction with the accompanying drawings wherein:

FIGURE 1 is a perspective view of an embodiment of a feedthrough constructed in accordance with the present invention;

FIGURE 2 is a vertical sectional view of the feedthrough of FIGURE 1;

FIGURE 3 is a vertical sectional view illustrating the components of the embodiment of FIGURES 1 and 2 prior to the assembly of the components;

FIGURE 4 is a perspective view illustrating an assembly including several feedthroughs of the type illustrated in FIGURE 1;

FIGURE 5 is a vertical sectional view illustrating in detail the attachment of a feedthrough to the assembly shown in FIGURE 4;

FIGURE 6 is a perspective view, partially broken away, and partially in section, illustrating another embodiment of a feedthrough constructed in accordance with the present invention;

FIGURE 7 is a vertical sectional view of the feedthrough of FIGURE 6;

FIGURE 8 is a vertical sectional view illustrating the components of the feedthrough of FIGURES 6 and 7 prior to assembly of the components;

FIGURE 9 is a vertical sectional view illustrating the attachment of the feedthrough of FIGURE 6 to an assembly constituting a portion of a system with which the feedthrough is intended to be used;

FIGURE 10 is a vertical sectional view illustrating components of a further embodiment of a feedthrough, in accordance with the present invention, prior to the assembly of the components;

FIGURE 11 is a fragmentary vertical sectional view illustrating a step in assembling a component of the embodiment of FIGURE 10 in a tubular arrangement;

FIGURE 12 is a fragmentary vertical sectional view, similar to FIGURE 11, with the component in an assembled condition with respect to the tubular arrangement;

FIGURE 13 is a fragmentary vertical sectional view illustrating the components shown in FIGURE 10 in an assembled condition;

FIGURE 14 is a vertical sectional view illustrating components of still another embodiment of a feedthrough, in accordance with the present invention, with the components in an unassembled condition;

FIGURE 15 is a vertical sectional view of the embodiment of FIGURE 14 with the components in an assembled condition;

FIGURE 16 is a fragmentary perspective view illustrating another embodiment of an assembly for feedthroughs of the type illustrated in FIGURE 1; and

FIGURE 17 is a vertical sectional View of the assembly of FIGURE 16.

Referring initially to FIGURES 1 through 3, there is illustrated an embodiment, indicated generally at 20, of an electrical feedthrough constructed in accordance with the present invention. Embodiment 20 includes a first member in the form of a wire or rod 21 composed of molybdenum, a metal having good electricity-conducting characteristics; a mounting cup or member, indicated generally at 22, also composed of molybdenum; and a glass sealing means 27 constituting a seal and insulator between cup 22 and rod 21 and maintaining them in the relative positions illustrated in FIGURES 1 and 2.

Rod 21 and cup 22 are initially supported, in an unassembled condition, on a graphite jig 30 in the relative positions illustrated in FIGURE 3. A tubular glass slug 29, having an opening 31 for receiving rod 21, is positioned atop a rearward face 24 of cup 22. Rod 21 extends through an opening 26 in a dimple 25 extending in a forward direction axially of rod 21. Also extending forwardly from cup 24, in the same direction as dimple 25, is a peripheral cup flange 23.

T o obtain a tenacious bond between glass seal 27 and the surfaces of rod 21 and cup 22, the latter two are, before assembly of the components, subjected to an oxidizing treatment, or are coated with chrome which in turn is subjected to an oxidizing treatment. As a result, the molybdenum wire 21 and cup 22 are coated with a tenacious oxide which is readily bondable to the glass of seal 27. One typical oxidizing treatment comprises heating the molybdenum wire and cup with a torch in air. Another treatment comprises coating the molybdenum rod and cup with chromium and heating them in a wet hydrogen atmosphere. This produces a very tenacious chrome oxide on the surface of the molybdenum rod and cup.

After the unassembled components have been arranged in the configuration illustrated in FIGURE 3, the arrangement is heated to melt glass slug 29 which flows downwardly into the recess formed by dimple 25 and through opening 26 in dimple 25 into the recess 32 in graphite jig 30. The arrangement is then cooled and removed from the jig as a completed feedthrough of assembled components illustrated in FIGURES l and 2. In the assembled condition, rod 21 and cup 22 are bonded together, in a sealed gas-tight arrangement, by the glass means 27 having a portion 28 extending through opening 26 in cup dimple 25.

To assure the desired type of seal between the

components

21, 22, and 27, and to assure that the seal is maintained during the subsequent bake-out to which the feedthrough is subjected (as a part of the aforementioned system), it is important that seal 27 be composed of a glass having thermal expansion characteristics substantially identical to those of cup 22 and rod 21. The latter two components are composed of molybdenum, and glass compositions having the same thermal expansion characteristics as molybdenum, are alumino silicate glasses identified as Codes 1720 and 1723 by Corning Glass Works, Corning, New York. These glasses are described in a bulletin prepared by the Industrial Bulb Sales Department of Corning Glass Works, Corning, New York, issued February 15, 1961, and entitled, Product Information, Calcium Alumino Silicate Glass, Glass Codes 1720 and 1723.

Because the glass of seal 27 has the same thermal expansion and contraction characteristics as the molybdenum from which rod 21 and cup 22 are composed, the glass seal 27 and the molybdenum rod and

cup

21, 22, respectively, will remain in tight, sealing engagement, during all heat-ups and cool-downs to which the feedthrough is subjected, whether the heat-ups and cooldowns occur during the assembly of the components of the feedthrough or during the subsequent bake-outs to which the feedthrough may be subjected.

Another important property for the components of feedthrough 20 is an imperviousness to gas, so as to prevent gas leakage through the individual components of the feedthrough when the latter extends between zones of vastly different pressures. With respect to cup 22, cross-rolling the molybdenum sheet material from which cup 22 is fabricated increases the density of the molybdenum cup in all directions, and the problem of gasleakage between grains in the microstructure of the molybdenum cup material is essentially eliminated.

Because molybdenum rod 21 is subjected to deformation in a longitudinal direction, during the drawing of the rod, gas leakage radially through the rod and outwardly through the side surfaces thereof is not a problem. However, the microcrystalline grains in the microstructure of rod 21 are elongated in the direction of drawing, and leakage through the tip or free end of rod 21 may be a problem. To offset this problem, the tip of rod 21 which is exposed to the relatively high pressure zone is coated by fusing thereto a brazement 39 (e.g., composed of copper-gold brazing alloy), as illustrated in FIGURE 2. This prevents the leakage of gas from a relatively high pressure zone through the tip of rod 21.

Seal 27 has good gas-impervious properties when composed of a glass of the type described above (Corning Codes 1720 and 1723).

Referring to FIGURES 4 and 5, there is illustrated an assembly 40 including a plurality of feedthroughs 20. Assembly 40 includes a ring 34, composed of a material such as stainless steel, and a flange or plate 35 mounted and attached to the top of ring 34, as by brazing. Plate 35 is preferably composed of copper, for reasons to be subsequently described, and includes a plurality of openings 36 each defined by an upstanding rim 37. Rim 37 is dimensioned to be slidably received within flange 23 of cup 22, in the manner illustrated in FIGURE and rim 37 thus functions to maintain cup 22 in a centered position, preparatory to attaching feedthrough to assembly 40 by brazing cup flange 23 to assembly plate 35, e.g., at 38. Brazing 33 may be composed of copper-gold.

It is desirable that plate be composed of copper because the latter is relatively resilient, and, during brazing of cup flange 23 to assembly plate 35, expansion and contraction of the two can be accommodated by the relatively resilient plate rim 37 which will yield and then spring back in accordance with said expansion and contraction. This also helps to assure a tight seal among the components of assembly 40.

Referring now to FIGURES 6 and 7, there is illustrated another embodiment, indicated generally at 50, of a feedthrough constructed in accordance with the present invention. Feedthrough includes a rod or wire 51, composed of molybdenum, a mounting tube 52 composed of an alloy such as Kova-r (registered trademark of Westinghouse Electric Corporation), having thermal expansion and contraction characteristics substantially identical to those of molybdenum rod 51; and glass means 54- constituting a seal holding tube 52 and rod 51 together in a gas-impervious, sealed, electricity-conducting feedthrough.

The .

feedthrough components

51, 52, 54 are initially assembled by arranging them in the configuration shown in FIGURE 8. An opening 40 in a graphite jig 56 supports rod 51, and a jig upper surface 41 supports a flange 53 of tube 52, to mount the rod and the tube in upright coaxial positions. A glass slug 57 is supported atop an inwardly crimped terminal portion 43 on tube 52, and slug 57 has an opening 53 for receiving rod 51. The entire arrangement is subjected to heat, thereby melting the glass and causing it to flow; so that upon cooling and solidification of the glass the components are arranged in the configuration shown in FIGURES 6 and 7.

In this configuration all of glass seal 54 encloses and insulates an intermediate portion 65 of rod 51, and substantially all of seal 54 is enclosed within tube 52. In very high voltage systems, it is desirable to remove a portion 66 of tube 52 adjacent the uninsulated part 67 of rod 51 which projects upwardly (as viewed in FIGURE 7) from the glass seal 54. This can be accomplished by using an etchant to remove a portion 66 of the tube down to, e.g., the dash-dot line 64 in FIGURE 7. Removal of a substanti-al portion 66 of tube 52 eliminates the danger of a short circuit between uninsulated rod portion 67 and tube 52. A substantial portion 68 of glass seal 54 is not enclosed by tube 52 in the embodiment wherein a portion 66 of tube 52 is removed by etching.

Referring now to FIGURE 9, there is illustrated the assembly of feedthrough embodiment 50 to a plate typically composed of stainless steel and having an opening 61 defined by a raised portion or shoulder 62 upon which rests a flange 53 projecting radially outwardly at an end of tube 52. Tube 52 and shoulder 62 are connected together by welding or brazing, at 63. The composition of tube 52, when the latter is composed of Kovar alloy, is as follows:

Element: Weight percent Nickel 29. Cobalt 17. Iron Remainder. Manganese 0.50 maximum. Silicon 0.20 maximum. Carbon 0.06 maximum. Aluminum 0.10 maximum. Magnesium 0.10 maximum. Zirconium 0.10 maximum. Titanium 0.10 maximum.

The total of aluminum, magnesium, zirconium and titanium should not exceed 0.20 weight percent.

To prevent gas leakage through the end of rod 51 exposed to higher pressure Zone, the tip of rod 51 should 'be coated with brazing such as the brazing 39 at the tip of rod 21 in FIGURE 2. Also, to prevent gas leakage through tube 52, it is important that the tube be composed of a material other than molybdenum, which in tubular form does not have satisfactory gas 1eakage-pre venting properties.

Inasmuch as feedthrough 50 is assembled to a stainless steel plate 60 (FIGURE 9) it would be desirable to utilize a tube 52 composed of stainless steel, because this would facilitate the thermal attachment of tube 52 to plate 60. However, a stainless steel tube presents problems in situations where gas leakage from the higher pressure zone through the feedthrough is undesirable. This is because the thermal expansion properties of stainless steel are not substantially identical to those of molybdenum rod 51 and glass seal 54 (composed of glass of the type described previously with respect to the composition of glass seal 27 in embodiment 20 illustrated in FIGURES 1 and 2). Thus, during heat-ups and cool-downs, such as those occurring during assembly and bake-outs of the feedthr-ough, minute leakage openings could form between the glass seal 54 and the tube 52, if the latter were composed of stainless steel.

However, in some situations where leakages of this nature are not a problem (e.g., in space vehicles wherein the feedthrough extended between a terminal on the interior of a space vehicle and a terminal in space) stainless steel could be used for tube 55. In outer space there is no disadvantage to have a minute leak-through of gases from the interior of the space vehicle into outer space because the vacuum in space would not be effected. An advantage of a stainless steel tube is that it may readily be brazed to a stainless steel plate 60 utilizing, e.g., a copper-gold brazing alloy. This is much simpler than the hell-arc welding procedure required to assemble a Kovar tube to a stainless steel flange.

An advantage of embodiment 50 is that a substantial portion of tube 52 adjacent flange 53 is not filled with glass seal 54. Therefore, in situations where the tube is welded or brazed to plate 60, the glass seal is so far removed from the area where the welding or brazing is being performed, that the Welding and/or brazing has no undesirable thermal effect on the glass seal.

Referring now to FIGURE 10, there is illustrated a setup for assembling a fourth embodiment 70 of a feed through constructed in accordance with the present invention. The setup includes a graphite jig 73 which mounts a molybdenum wire or rod 71 in an upright position. At the top of rod 71 is a molybdenum head 79. A glass mounting plate 74, having a composition similar to that of the glass slugs 29 and 57 in

embodiments

20 and 50 respectively, rests atop jig 73 and includes an opening 75 through which rod 71 extends.

The entire setup illustrated in FIGURE is subjected to heat, whereupon the glass plate 74 softens allowing molybdenum head 79 to penetrate or press downwardly into the softened glass 74. This effects a seal between head 79 and glass 74. The resulting configuration is illustrated as 70 in FIGURE 13.

After the

components

71, 79 and 74 are assembled in the manner shown in FIGURE 13, the glass plate 74 is mounted so that the outer edges thereof rest atop a molybdenum tube 76 outwardly from the bottom of which extends a flange 77 (e.g., of stainless steel) attached to tube 76 by brazing as at 78. The setup illustrated in FIG- ure 11 is then subjected to heat which causes glass 74 to soften and to sink downwardly relative to tube 76, in effect causing the upper portions of tube 76 to penetrate or press into glass 74 and effect a connection between glass 74 and tube 76. Because glass 74 and molybdenum tube 76 have similar thermal expansion characteristics, subsequent heat-ups and/ or cool-downs will not affect the leakproof seal between plate 74 and tube 76.

Referring to FIGURE 14, there is illustrated a setup for producing still another embodiment of a feedthrough constructed in accordance with the present invention. In the setup of FIGURE 14, a molybdenum rod or wire 81 is supported in an upright position (e.g., by a jig not shown .but similar to that illustrated in the setup of FIGURE 10) and rod 81 terminates at an upper molybdenum head 89 connected to rod 81. Head 89 rests atop a glass slug 82 typically of the same glass composition as slugs 29 and 57 and including an opening 83 through which rod 81 extends. Glass slug 82 is supported atop a sapphire mounting plate 84 including an opening 85 through which rod 81 extends.

When the components are arranged in the setup illustrated in FIGURE 14, the entire setup is subjected to heat which causes the glass slug 82 to soften, and the weight of molybdenum head 89 causes the latter to press downwardly into glass slug 82, to effect a seal between head 89 and the glass slug. At the same time, the softened glass slug flows substantially into the configuration illustrated in FIGURE 15, and, in addition, forms a tight, leak-proof bond with sapphire plate 84. The resulting embodiment is illustrated generally at 80 in FIGURE 15 and includes a molybdenum wire or rod 81 terminating at a molybdenum head 89, sapphire plate 84, and a glass seal 86 binding the

components

81, 89 and 84 together into a leak-proof, gas-impervious feedthrough.

In embodiment 80 there is a minimum amount of glass as a component of the feedthrough, compared, for example, to the embodiment 70 illustrated in FIGURE 11. Accordingly, the possibility of a gas leakage through glass- 86 is further minimized. Sapphire plate 84 is not susceptible to gas leakage, and the sapphire plate and glass seal 86 effect an extremely good mutual bond.

Referring to FIGURES 16 and 17, there is illustrated an assembly normally mounting a pluraiity of feedthroughs such as 20. Assembly 140 includes a plate 141, composed of molybdenum, and having a depending rim 142 and a plurality of openings 143 each peripherally surrounded by a recessed plate portion 144. Flange 23 on cup 22 of feedthrough 20 has a downwardly depending terminal end portion which is received within and rests upon recessed plate portion 144; and feedthrough rod 21 extends through opening 143. Flange 23 is secured to plate 141 at 145, e.g., by brazing.

Because cup 22 and plate 141 are both composed of molybdenum, and thus have the same thermal expansion characteristics, there is no danger of a leak developing between the two during the expansion and contraction thereof caused by bakeout or other heating to which the assembly is subjected.

As previously described molybdenum rod 21 and cup 22 are chrome plated and the chrome is oxidized. Molybdenum plate 141 is subjected to the same treatment. The resulting coating of chrome oxide on plate 141, on cup 22 and on rod 21 prevents the molybdenum, of which these three elements are composed, from oxidizing at the high temperatures of bakeout.

In brazing various components together, a brazing alloy which may be used advantageously in securing molybdenum to copper, molybdenum to molybdenum, stainless steel to stainless steel, and copper to stainless steel, contains 65% copper and 35% gold with a 1010 C. liquidus. To secure Kovar to stainless steel, a brazing alloy of copper-gold-nickel, having 1030 C. liquidus, is advantageous.

A stainless steel which may be used for ring 34 and for tube 52 is AISI type No. 304 containing, in weight percent, 0.08 maximum carbon, 18.0-20.0 chromium, 8.00 to 11.00 nickel, 2.00 maximum manganese, and the balance iron, a non-magnetic, austenitic, readily weldable alloy.

In summary, the invention relates to a feedthrough for extension between two zones of respectively differing pressures. The feedthrough, composed of materials which render it completely non-magnetic, includes an elongated, drawn, metallic, electricity-conducting first member having opposite ends each for positioning in a respective one of the two pressure zones. Also included are a mounting member, having an opening through which the drawn member extends, and glass means constituting a gas-leakpreventing seal between and in contact with the two members. At least the draw member and the glass means,

and preferably also the mounting member, have the same thermal expansion characteristics. Fused at that end of the drawn member which is to be located in the zone of higher pressure is metallic sealing means for preventing gas leakage through the end and between the elongated grains in the miscrostructure of the drawn member.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

1. A gas-impervious, electrical feedthrough-for extension between two zones of respectively difiering pressures, said feedthrough comprising:

a drawn, elongated molybdenum first member for conducting electricity between said two zones;

said first member having a pair of opposite ends at least one of which is a free end for positioning in a respective one of said two pressure zones;

said first member having elongated microcrystalline grains in its microstructure;

a gas-impervious, metallic mounting member having an opening through which said first member extends;

glass sealing means at said opening, between and in contact with said first member and said mounting member, for preventing a gas leak through said opening and for providing electrical insulation between the first member and the mounting member;

a tenacious oxide on at least those portions of said first member and said mounting member which are in contact with said glass sealing means;

said first member, said mounting member and said glass sealing means having the same thermal expansion characteristics;

and metallic sealing means fused at said free end of said first member for preventing gas leakage longitudinally through the first member and through said free end;

said feedthrough being composed entirely of non-magnetic material.

2. A feedthrough as recited in claim 1 wherein:

said mounting member is composed of cross-rolled molybdenum sheet;

said glass sealing means is composed of alumino silicate glass;

and said metallic sealing means is composed of coppergold alloy.

3. A feedthrough as recited in claim 1 wherein:

said mounting member has flange extending in a direction axially of said first member;

said flange being concentric with said opening and spaced therefrom in a radial direction relative to the opening.

4. In combination with the feedthrough of claim 3:

a plate having an opening therein;

said plate including a rim concentrically surrounding said plate opening at the opening;

said rim extending integrally from said plate;

said rim being slidably received within said flange on said mounting member of the feedthrough;

said first member of the feedthrough extending through said plate opening;

and means securing said flange to said plate.

5. A combination as recited in claim 4 wherein:

said mounting member of the feedthrough is composed of cross-rolled molybdenum sheet;

said plate is composed of copper;

said glass sealing means of the feedthrough is composed of alumino silicate glass;

and said securing means is a brazement of copper-gold alloy.

6. In combination with the feedthrough of claim 3:

a plate having an opening therein;

said plate including a recessed plate portion concentric with and surrounding aid opening at the periphery of the opening;

said flange on the mounting member of the feedthrough having a terminal end portion received in and supported by said recessed plate portion;

means securing said flange to said plate;

said first member of the feedthrough extending through said plate opening;

said mounting member being composed of cross-rolled molybdenum sheet and said plate being composed of molybdenum.

7. A gas impervious, electrical feedthrough for extension between two zones of respectively differing pressures, said feedthrough comprising:

a gas-impervious mounting member having an opening through which said first member extends;

glass sealing means at said opening, between and in contact with said first member and said mounting member, for preventing a gas leak through said opena tenacious oxide on at least those portions of said first member which are in contact with said glass sealing means;

said feedthrough being composed entirely of non-magnetic material.

References Cited by the Examiner UNITED STATES PATENTS 1,857,203 5/1932 Van Liempt 174-50.61 2,174,375 9/1939 Beggs 174-152 X 2,292,863 8/1942 Beggs 174152 X 2,450,780 10/1948 Bucklen 174152 X 2,458,748 1/1949 Stupakotf 174-152 2,479,872 8/1949 Seiden 17450.56 2,508,551 5/1950 Sykes 174152 X 2,807,074 9/1957 Schroeder 29497 X 2,933,635 4/1960 Lang et a1 313-331 2,944,102 7/1960 Tidd l74-l52 FOREIGN PATENTS 166,321 12/1955 Australia.

624,489 6/ 1949 Great Britain.

699,492 11/ 1953 Great Britain.

818,202 8/1959 Great Britain.

OTHER REFERENCES Hampel, Rare Metals Handbook, published by Reinhold Publishing Corp., New York, 1954, page 284.

Harwood, The Metal Molybdenum, published by the American Society for Metals, Cleveland, Ohio, 1958 pp. 117-118.

JOHN F. BURNS, Primary Examiner.

JOHN P. WILDMAN, E. JAMES SAX, Examiners.

Claims

1. A GAS-IMPERVIOUS, ELECTRICAL FEEDTHROUGH FOR EXTENSION BETWEEN TWO ZONES OF RESPECTIVELY DIFFERIG PRESSURES, SAID FEEDTHROUGH COMPRISING: A DRAWN, ELONGATED MOLYDBENUM FIRST MEMBER FOR CONDUCTING ELECTRICITY BETWEEN SADI TWO ZONES; SAID FIRST MEMBER HAVING A PAIR OF OPPOSITE ENDS AT LEAST ONE OF WHICH IS A FREE END FOR POSITIONING IN A RESPECTIVE ONE OF SAID TWO PRESSURE ZONES; SAID FIRST MEMBER HAVING ELONGATED MICROCRYSTALLINE GRAINS IN ITS MICROSTRUCTURE; A GAS-IMPERVIOUS, METALLIC MOUNTING MEMBER HAVING AN OPENING THROUGH WHICH SAID FIRST MEMBER EXTENDS; GLASS SEALING MEANS AT SAD OPENING, BETWEEN AND IN CONTACT WITH SAIF FIRST MEMBER AND SAID MOUNTING MEMBER, FOR PREVENTING A GAS LEAK THROUGH SAID OPENING AND FOR PROVIDING ELECTRICAL INSULATION BETWEEN THE FIRST MEMBERT AND THE MOUNTING MEMBER; A TENACIOUS OXIDE ON AT LEAST THOSE PORTIONS OF SAID FIRST MEMBER AND SAID MOUNTING MEMBER WHICH ARE IN CONTACT WITH AD GLASS SEALING MEANS; SAID FIRST MEMBER, SAID MOUNT MEMBER AND SAID GLASS SEALING MEANS HAVING THE SAME THERMAL EXPANSION CHARACTERISTICS; AND METALLIC SEALING MEANS FUSED AT SAID FREE END OF SAID FIRST MEMBER FOR PREVENTING GAS LEAKAGE LONGITUDINALLY THROUGH THE FIRST MEMBER AND THROUGH SAID FREE END; SAID FEEDTHROUGH BEING COMPOSED ENTIRELY ON NON-MAGNETIC MATERIAL.