US2959705A

US2959705A - Shielded tube and method of making the same

Info

Publication number: US2959705A
Application number: US310318A
Authority: US
Inventors: Harry A Downing; Albert J Laliberte
Original assignee: American Optical Corp
Current assignee: American Optical Corp
Priority date: 1952-09-18
Filing date: 1952-09-18
Publication date: 1960-11-08
Anticipated expiration: 1977-11-08

Description

Nov. 8, 1960 H. A. DOWNING EI'AL 2,959,705

SHIELDED TUBE AND METHOD OF MAKING THE SAME Filed Sept. 18, 1952 ALBERT d LALIBERTE.

ATTO

SHIELDED TUBE AND METHOD OF MAKING THE SAlVlE Harry A. Downing, Auburn, and Albert J. Laliberte, West Brookfield, Mass., assignors to American Optical Company, Scuthbridge, Mass., a voluntary association of Massachusetts Filed Sept. 18, 1952, Ser. No. 310,318

9 Claims. (Cl. 313-313) This invention relates to electrically conductive shields for electron discharge tubes or the like and has particular reference to novel means and method of forming such shields and to the improved tube resulting therefrom.

One of the principal objects of the invention is to provide an improved shielded article such as an electron discharge tube and novel means and method of making the same wherein the shield not only functions as a ground for the tube but also functions as protective means which renders the resultant composite tube structure highly resistant to humidity, corrosion and abrasion, and which is chemically stable, and resistant to extreme temperature changes.

Another object is to provide an electrically conductive shield of the above character having a controlled resistance.

Another object is to provide a relatively smooth electrically conductive shield of the above character firmly adherent to the glass envelope of the tube and having a hardness which will withstand abrasion by a finger nail or blunt metallic instrument.

Another object is to provide an electrically conductive shield which will withstand the above-rnentioned abrasion test after being subjected to extremely high humidity for long periods of time.

Another object is to provide an electron discharge tube having an electrically conductive shield thereon which renders the resulting structure resistant to high and low temperature changes throughout relatively long intervals.

Another object is to provide an electron discharge tube with an electrically conductive shield so controlled as to greatly increase the resistance of the resultant tube to injury by impact or crushing.

Another object is to provide a shielded electron discharge tube of the above character having greater durability and more general adaptability.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings and it will be apparent that many changes may be made in the details of construction, arrangement of parts, and steps of the method shown and described without departing from the spirit of the invention as expressed in the accompanying claims. We, therefore, do not wish to be limited to the exact details of construction, arrangement of parts and steps of the method shown and described as the preferred forms only are given by Way of illustration.

Ground shields for electron discharge tubes or other similar articles are not new in the art. Many different attempts have been made, in the past, to provide tubes of this character with electrically conductive shields to reduce the capacity between certain tube elements, to shield the tubes from other circuit elements and to provide external shield grounding means for such tubes.

It has been found, however, that such prior art shields, while efiicient as electrically conductive means, were not acceptable for use under different temperature and at- A States Patent mospheric conditions or were not chemically stable or abrasion resistant. Another factor which, as far as is 'known, has not been considered is that of increasing the resistance of the inherent tube to impact or crushing as well as providing the tube with an electrically conductive coating.

The present invention, therefore, is directed to providing an electron discharge tube or similar article with an electrically conducting coating possessing characteristics for overcoming all of the prior art difiiculties in a simple, efficient and inexpensive manner while providing the tube with means for increasing its resistance to impact and crushing.

Referring to the drawings:

Fig. 1 is a side elevation of a tube embodying the invention; and

Fig. 2 is an enlarged sectional view taekn as on line 2-2 of Fig. 1 and looking in the direction indicated by the arrows.

Referring to the drawings, the tube 4 embodying the invention comprises a glass envelope 5 in which is encased its operative components A. A plurality of leads 9, operatively associated with the respective components A, are extended outwardly through the base 11 of the tube. The glass envelope has an outer roughened surface 6 formed thereon and further has a coating 7 of an electrical conductive metal formed on said surface. The coating 7 and the roughened surface 6 are in mechanically bonded relation with each other. An outer coating 8 of a metal particularly resistant to abrasion, and which renders the resultant composite structure further resistant to varying atmospheric and temperature changes, resistant to high humidity and having a controlled electrical conductivity is formed on the inner coating 7. The outer coating 8 and inner coating 7 form a composite shield which in addition to the above characteristics is so controlled as to greatly increase the resistance of the tube to injury by impact or crushing.

In carrying out the invention, the leads 9 as well as a controlled portion of the ground lead 10 and base 11 of the tube are provided with an acid protective coating such as paraffin or other stop off lacquer. The tube is then immersed in an etching solution from five to thirty seconds to produce a desired roughened outer surface thereon. An etching solution which has proven satisfactory is as follows:

10 grams BaSO --Bariurn sulfate 4 grams (NH SO --Arnmoniurn. sulfate 4 grams NH HF Ammonium bifluoride 16 grams C H (OH) Glycerol 2 grams H C O Oxalic acid 4 grams H 0Water If desired, instead of roughening the surface by etching, the said surface may be sand-blasted or otherwise treated to produce the desired roughening. It has been.

found, by actual tests, that the toughening of the surface by acid treatment does not weaken the envelope of the tube to crushing.

- When roughened by acid etching, the tubes are rinsed in distilled water and completely freed from residual acid. A continuance of the process may be carried on either with the tube in a wet or dry state. The tube, however, is preferably dried for purposes of examining the roughened surface. Following the roughening process, the tubes are treated with a sensitizing or fluxing solution. This is preferably accomplished by scrubbing or rubbing the roughened surface of the tube with solution saturated absorbent cotton or other suitable means. A sensitizing or fluxing solution which has been found to produce de-' sirable results is formed by dissolving stannous chloride (SnCl in an equal amount by weight of hydrochloric 3 acid (Hcl) and diluting to five percent with distilled water (H O).

Following the rinsing of the tubes with distilled water, they are provided with an electrically conductive coating of silver which is preferably deposited by a dual spraying method.

This coating may be applied by making a solution of ammoniacal silver nitrate which is a mixture of chemically pure silver nitrate and chemically pure ammonium hydroxide (28-29% NH OH). A second solution is made of dextrose or formaldehyde dissolved in distilled water, with the amount of dextrose or formaldehyde in the solution being controlled according to the percentage of silver in the ammoniacal mixture in order to bring about the proper chemical reaction during the dual spraying mentioned above. The solutions are used with a spray gun having dual spray nozzles, each of which is coupled with separate containers in which the respective solutions are placed. The two spray nozzles are so related as to form an intermingling mist of said two solutions whereupon a chemical reaction takes place in such manner that a substantially uniform coating of silver is deposited on the glass tube surface. This produces a substantially uniform coating of silver in suflicient thickness to produce desired electrical conductivity and which is firmly adherent to the roughened surface of the tube. This coating, although electrically conductive, is susceptible to chemical reaction or weathering and is insufiiciently resistant to scratching. It merely functions as a forerunner for an electrolytically deposited outer surface of nickel, rhodium, chromium or other similar non-corrosive, hard and abrasion resistant metal which is to be subsequently deposited on the outer surface thereof.

The silver coating is such that the outer subsequent electrolytically deposited metal will be smooth and of relatively uniform thickness and will firmly adhere and bond therewith.

The composite coating, due to the outer electrolytically deposited layer, is not only resistant to scratching or abrasion but also renders the resultant composite tube structure more chemically stable and resistant to weathering, atmospheric and temperature changes as well as resistant to exposure to humidity.

Although the silver coating has been described above as being applied by a dual spray method, a suitable silver coating might be deposited in the following manner:

A silver solution is formed comprising:

13.52 oz. of water (H O) 0.71 oz. of silver nitrate (AgNO 0.35 oz. of potassium hydroxide (KOH).

To this solution, 50 ccs. of ammonium hydroxide, (NH OH specific gravity 0.90) is added. To the above mixture is further added 0.07 oz. of silver nitrate dissolved in 1.01 oz. of water. The above solution is designated solution A.

A reducing solution is formed as follows:

33.81 oz. water 3.17 oz. sugar 0.14 oz. nitric acid (specific gravity 1.42).

This solution is designated B.

The glass envelopes of the tubes which have been acid-etched and sensitized, as described by the firstrnentioned silvering process, are then suspended in distilled water in a suitable container. Equal amounts by volume of solutions A and B are then mixed and immediately poured into the water having the glass envelopes of the tube suspended therein whereupon the chemical reduction of thesilver salt by the reducing agent results in the deposition of the silver on the outer surface of the tube.

I Due to the fact that the silver coating, as formed by either of the above methods, is firmly adherent with the roughened surface of the tube and that the outer finally deposited metal firmly bonds with the silver, the said resultant shield will be held in proper anchored relation with the tube. In order to more positively retain the anchored relation of the shield with the tube, the tube is initially formed to a controlled contour shape which is such as to have substantially

parallel sides

12 and 13 terminating adjacent the lower portions thereof in converging or inwardly curving

portions

14 and 15 extending throughout the perimeter of the tube and which, in turn, terminates in an outwardly flared lower base portion 16. This controlling of the initial shape of the tube envelope and the fact that the outer and inner metallic coatings inherently conform to the outer contour shape of the tube further adds to the anchoring action thereof with the tube. The thickness of the outer shield is further controlled so as to render the resultant tube more resistant to fracture or crushing while providing the desired electrical conductivity. It has been found that for a coating ranging frorn one to three thousandths of an inch in thickness that the resistance of the resultant tube to fracture and crushing, as compared with the inherent glass envelope of the tube, has been approximately doubled, depending upon the actual thickness of the nickel coating. However, it has been found that the metal shield on the tube has a resistance to fracture and crushing of approximately ten to one as compared with the inherent glass envelope of the tube. The coating is so formed as to overlie and have electrical contact with the upper tube encircling portion 17 of the ground lead 10 and will function as means for permanently retaining the ground lead in desired position on the tube. The electrolytic process may be any of the commonly known types and is preferably carried out by standard procedures.

A solution of the type giving a hard and desirable deposit is as follows:

Material Formula Solution,

ozjgal.

Nickel snlite hept hydrate NiSOLT ZO 32. 0 Ni kel chloride hexihydrate NiClLG bO 4. 0 S"diumfor'n te NaHGOz 5. 0 Crbalt s 11f te he tahydrste COSO4.7TIQO (I. 6 Am nanium sulfite (NHthSOi 0.10 Forrn 'ldehyde TTCWO 0. 33 BOIIC Acid H3130: 4. 0

having a pH factor of approximately 3.7, cathode current density 7 to amps. per square foot, temperature to F. with suitable agitation. The above is a formula set forth in Louis Weisberg and William B. Stoddard, Jr., Patent No. 2,026,718, issued January 7, 1936. The above patent also gives additional formulae which might be employed.

Another plating solution which has produced desirable results is as follows:

Brightener No. 1-RL, Brightener No. 3, and Non Pitter No. 22 are made and sold by The Udylite Corporation, 1651 East Grand Building, Detroit 11, Michigan.

A brightener which might be used may be selected from the following group:

Benzyl naphthalene sodium sulfonate as set forth in Lutz and Westbrook Patent No. 1,818,229;

Complex lead citrate as set forth in Pinner Patent No.

1,837,835; Sulfuric acid reaction products of oleoresins and natural resins as set forth in Pine Patents Nos. 2,029,386 and 2,029,387;

Reaction products of alkali metal cyanides and certain.

aldehydes and ketones as set forth in Hull Patent No.

Zinc or cadmium plus naphthalene-sulfonic acids as set forth in Waite Patent No. 2,112,818;

Selenium plus sulfonates as set forth in Harshaw and Long Patent No. 2,125,229;

Cd or Zn plus sulphonamides or suphonimides as set forth in Brown Patent No. 2,191,813;

Halogenated aldehydes as set forth in Brown Patent No.

Sodium formate as set forth in forth in Baker Patent No.

Aminopolyaryl methane plus naphthalene sulfonate as set forth in Lind, Harshaw, and Long Patent No. 2,198,267;

Aminopolyaryl methane plus single ring aryl sulfonamides and sulfimides as set forth in Lind, Harshaw, and Long Patent No. 2,198,268;

Azo compound plus naphthalene sulfonates, single ring aryl sulfonamides, or single ring aryl sulfimides as set forth in Lind, Harshaw, and Long Patent No. 2,290,- 342;

Aromatic amino compounds plus an organic compound characterized by a ductilizing tendency as set forth in Lind, Harshaw, and Long Patent No. 2,238,861;

Safranine compounds plus ortho benzoic sulfimide (saccharin) and its salts as set forth in Lind, Harshaw, and

Long Patent No. 2,326,999;

Mercaptopyrimidines as set forth in Ter Horst Patent Starchates as set forth in Gaver Patent No. 2,406,072;

Sulfonated arylaldehydes as set forth in Stocker and Freed Patent No. 2,409,119; and

Thiourea as set forth in Stocker and Freed Patent No.

Optimum brightness and brightener stability depend upon proper interrelationship between solution formulation, temperature, pH and current density and all of these factors must therefore be carefully considered. The use of a brightener is of minor importance as it deals primarily with the resultant appearance of the outer coating and has no effect as to its main functional characteristics.

A non-pitter which may be employed is hydrogen peroxide, formaldehyde or any other suitable surface-active agent and the amount thereof is controlled according to the base formula as commonly known.

Although the initial silver coating has been described as preferably being deposited by a particular chemical reduction, it might be applied by other known methods or techniques if properly controlled so as to obtain a coating having the relatively smooth, uniform texture as obtained by the chemically reacted mists process described herein.

The inner conductive coating 7 has been referred to as being silver. However, other coatings of conducting materials such as a chemical deposition of copper may be utilized. This could be accomplished by reducing copper from a fluohorate solution as set forth in Narcus Patent No. 2,454,610. To accomplish this, the roughened surface of the glass is cleansed by a suitable proprietory cleaner such as soap. The surface is then sensitized through the use of a solution embodying approximately 50 ccs. of titanous chloride, 50 ccs. hydrochloric acid, and 1000 ccs. distilled water. After the surface has been so activated, and after thoroughly rinsing the article in clean water, the article is then subjected to a so-termed seeding solution. This is accomplished through the use of a dilute solution of chloroplatinic acid made up of 1 gram of chloroplatinic acid per gallon of distilled 6 water with five to ten minutes immersion. The article is then transferred directly to a solution made up by mixing equal weights of a copper solution and a reducing Although only silver and copper have thus far been disclosed as being suitable for the base electrically conductive coating 7, other metals such as platinum, gold or the like might be employed and applied by conventionally known methods if properly controlled to obtain the desired result.

Instead of using metal, the inner conductive coating may be formed of graphite applied by known methods but controlled in accordance with the end result desired. It has been found that due to the rough texture of the outer surface of the glass envelope, the graphite might be applied directly to the surface by rubbing it into said surface to a uniformly smooth texture. Another method has been to apply a lacquer or other tacky substance to the surface and then dip the tube into powdered graphite. Here again, the graphite is rubbed to a uniformly smooth texture. The use of an undercoating of this nature makes it possible to electrolytically deposit the outer coating 8 on the envelope of the tube.

However, the silver coating, as first described, has thus far proven most desirable.

In all instances, the outer protective coating is applied by an electrolytic process.

Subsequent to the forming of the final surface on the tube, the paraffin or other stop off lacquer is removed. This parafiin or stop off coating may, however, be allowed to remain on the tube as protective means until it is ready for actual use. This paraffin or other stop off lacquer is used in all of the above-described coating techniques and not only protects the leads 9 from the acid but also restricts the coatings at the lower end of the tube in such manner as to prevent their forming a short across said leads.

From the foregoing description, it will be seen that a novel shielded tube as well as simple, eificient and economical means and method of making the same have been provided.

Having described our invention, we claim:

1. An electron discharge device comprising an envelope in which is encased the operative components of said device and having a base through which leads to said operative components extend, said envelope constituting a thin frangible glass wall covered by a thin coating embodying an outer layer of a hard, abrasion and corrosion resistant metal bonded to the surface of said glass wall by means of an inner film of softer and less inert but more highly electro-conducting material, said inner film being mechanically interlocked with said surface of the glass wall and grounded to one of the leads in the base to electrically shield the operative components of said device, and said outer layer serving to protect said shielding film and to increase the resistance of the envelope to fracture and crushing, the metal of said outer layer being chemically stable and generally inert so as'to impart to the device a resistance to temperature change and humidity.

2. An electron discharge device comprising an envelope in which is encased the operative components of said device and having a base through which leads to said operative components extend, said envelope constituting a thin frangible glass wall covered by a thin coating embodying an electrolytically deposited outer layer of a hard, abrasion and corrosion resistant metal bonded to the surface of said glass wall by means of an inner film of softer and less inert but highly electro-conducting material, the surface of said glass wall being roughened and the film being interlocked with the irregularities of said surface, said film being grounded to one of the leads in the base to electrically shield the operative components of said device, and said outer layer serving to protect said shielding film and to increase the resistance of the envelope to fracture and crushing, the metal of said outer layer being chemically stable and generally inert such as to impart to the device a resistance to temperature change and humidity.

3. An electron discharge device comprising an envelope in Which is encased the operative components of said device and having a base through which leads to said operative components extend, said envelope constituting a thin frangible glass wall covered by a thin coating embodying an outer layer of a hard, abrasion and corrosion resistant metal from the group consisting of nickel, chromium and rhodium which is bonded to the surface of said glass wall by means of an inner film of silver which issofter and less inert but more highly electroconducting than the metal of said outer layer, said film being mechanically interlocked with said surface of the glass wall and grounded to one of the leads in the base to electrically shield the operative components of said device, and said outer layer of metal serving to protect said shielding film of silver and to increase the resistance of the envelope to fracture and crushing, the metal of said outer layer being sufficiently chemically stable and generally inert as to impart to the device a resistance to temperature change and humidity.

4. An electron discharge device comprising an envelope in which is encased the operative components of said device and having a base through which leads to said operative components extend, said envelope constituting a thin frangible glass wall covered by a thin coating embodying an outer layer of nickel which is a hard, abrasion and corrosion resistant metal, said layer being bonded to the surface of said glass wall by means of an inner film of silver which is softer and less inert but more highly electro-cond'ucting than the nickel, said film being mechanically interlocked with said surface of the glass wall and grounded to one of the leads in the base to electrically shield the operative components of said device, and said outer nickel layer serving to protect said shielding film of silver and to increase the resistance of the envelope to fracture and crushing.

5. An electron discharge device comprising an envelope in which is encased the operative components of said device and having a base through which leads to said operative components extend, said envelope constituting a thin frangible glass wall covered by a thin coating embodying an outer layer of a hard, abrasion and corrosion resistant metal and an inner film of softer and less inert but more highly electro-conducting material from the group consisting of gold, silver, copper and graphite, said inner film being mechanically interlocked with said surface of the glass wall and grounded to one of the leads in the base to electrically shield the operative components of said device, and said outer layer being electrolytically deposited on said film and serving to protect the film and to increase the resistance of the envelope to fracture and crushing, the metal of said outer layer being chemically stable and generally inert so as to impart to the device a resistance to temperature change and humidity.

6. An electron discharge device comprising an envelope in which is encased the operative components of said device and having a base through which leads to said operative components extend, said envelope constituting a thin frangible glass wall having an acid etched surface covered by a thin coating embodying an outer layer 'of a hard, abrasion and corrosion resistant metal and an inner film of a softer and less inert but highly electroconducting material from the group consisting of silver, gold, copper, and graphite, said inner film being mechanically interlocked with said acid etched surface of the glass wall and grounded to one of the leadsin the base to electrically shield the operative components of said device, and said outer layer serving to protect said shielding film and to increase the resistance of the envelope to fracture and crushing, the metal of said outer layer being chemically stable and generally inert so as to impart to the device a resistance to temperature change and humidity.

7. An electron discharge device as claimed in claim 6 wherein said outer layer comprises an electrolytic deposit of a metal from the group consisting of nickel, rhodium and chromium.

8. An electron discharge device comprising an envelope in which is encased the operative components of said device and having a base through which leads to said operative compbnents extend, said envelope constituting a thin frangible glass wall having a roughened outer surface, a thin film of highly electro-conducting material interlocked with the irregularities of said roughened surface and presenting a substantially smooth surface, and a uniformly thin layer of metal from the group consisting of nickel, chromium and rhodium electrolytically deposited on said film surface, the film of highly electro-conducting material being grounded to one of the leads in the base to electrically shield the operative components of the device, and said outer layer of metal being hard, abrasion and corrosion resistant and otherwise generally inert and chemically stable in comparison to the inner film of highly electro-conducting material to impart to the device a resistance to temperature change and humidity.

9. An electron discharge device comprising an envelope in which is encased the operative components of said device and having a base through which leads to said operative components extend, said envelope constituting a thin frangible glass wall having a roughened outer surface on which is chemically deposited a thin film of highly electro-eon'ducting material from the group consisting of copper, gold, silver and graphite, said film being interlocked with the irregularities of said roughened surface and presenting a substantially smooth surface to which is strongly bonded a uniformly thin electrolytically deposited layer of metal from the group consisting of nickel, chromium and rhodium, the film of highly electro-coriducting material being grounded to one of the leads in the base to electrically shield the operative components of the device, and said outer layer of metal being hard, abrasion and corrosion resistant and otherwise generally inert and chemically stable in comparison to the inner film of highly electro-conducting material to impart to the device a resistance to temperature change and humidity.

References Cited in the file of this patent UNITED STATES PATENTS 928,224 Shoemaker et al. July 13, 1909 1,128,817 Pickard Feb. 16, 1915 1,731,797 Strongson Oct. 15, 1929 1,802,371 Bullivant et a1 Apr. 28, 1931 2,214,646 Walker Sept. 10, 1940 2,421,079 Narcus May 27, 1947 2,424,583 Rahm July 29, 1947 2,464,270 Spencer Mar. 15, 1949 FOREIGN PATENTS 473,385 Great Britain Oct. 12, 1937 OTHER REFERENCES Metal Finishing, September 1944, pages 534 to 538.