US1885234A - Ceramics - Google Patents

Description

Patented Nov. 1, 1932 UNHTED STATES Fries & CO. INC., OF'EAST ORANGE,

NEW JERSEY, A CORPORATION OF NEW JERSEY CERAMICS No Drawing. Application filed March 2,

This invention relates to ceramics and more particularly to a method of eliminating corrosive efl'ects inceramic materials.

An object of the invention is the provision of a method which will secure the elimination of such corrosive effects.

A further object of the invention is to provide a method in the production of ceramic material which will provide a product free from chemical reaction.

A further object of the invention is to provide a method of purifying the material utilized in the fabrication of ceramic products.

Further objects of the invention will appear more fully hereinafter.

The invention consists substantially in the method of procedure and the product obtained thereby, all as will be more fully hereinafter set forth and finally claimed in the appended claims.

In ceram c materials where a metal in a completely fabricated structure is employed in contact with the ceramic material, such for example as a porcelain-like tube with one or more orifices through which a metal extends, it has been found that when the completed structure is subjected to heat a chemi cal reaction between the tube and the metal occurs resulting in the corrosion of the metal having various deleterious effects on the completed structure or the operation thereof. For example, in the radio vacuum tube industry, and particularly in the so-called alternating current tubes where a heater element is employed as the cathode of the radio tube, it is customary to employ a ceramic tubing as the heater element, which tubing is provided with one or more (usually two) hair-like orifices extending therethrough and through which the hairpin or other shaped incandescing filament passes. Corrosionthus occurring in the hair-like incandescing filament (usually but not always formed of tungsten or other rare earth metal) has the bad effect of imparting a short life for the filament in use and hence a short life for the radio vacuum tube of which it forms a part. We have discovered that this cause for short life of the filament, viz: corrosion thereof caused by chemical reaction between the cc- 1929. Serial No. 844,091.

ramic tubing and the filament can be elimi- I been due to the presence of alkali in the respective materials. In accordance with our invention, therefore, we eliminate the alkali from the materials forming the ceramic product, as well as from the metal structure or the CROWLEY, OF JERSEY CITY,

associated elements forming part of the com- I 'pleted article of manufacture.

For the purpose of disclosing our invention to enable those skilled in the art to utilize the same and readily appreciate the commercial,

scientific, and practical advantages thereof, we will adhere to the illustration hereinabove given, to wit: a radio vacuum tube, but We wish it to be understood that our invention in its broad scope is not to be limited or confined to any particular application or utilization as the advantages thereof, now made apparent, can be readily appreciated and utilized in any art where deleterious or undesirable corrosive effects between a ceramic product and an associated metal are sought to be obviated.

In constructing a heater element of a radio vacuum tube operating on alternating current in accordance with our invention We choose materials which are as free as possible from alkali. By this .we do not mean that it is necessary to obtain one hundred per-' cent purity, though it is desirable. Small traces of alkali may be present without an undesirable deleterious effect but ordinary precautions in the selection of material, as Well as in the treatment forming part of our invention, will permit the substantial attainment of our present invention.

. In producing the ceramic tubing we take the selected powdered material and add thereto a non-alkali binder, such as beryllium oxide or any such similar material which may be selected in accordance with the diagonal law of the periodic table which forms the subject matter of the copending application Serial No. 332,555 filedJanuary 14, 1929.

1 upon the particular material bein Binders other than beryllium oxide may be emplo ed, notably those that burn out in the final ring. However, beryllium oxide may be employed as a binder and, if employed, does not burn out in the final firing but fluxes, thereby addin strength and rigidity to the ultimate pro uct. The powdered ceramic material and the binder .are each subjected to a heat, preferably by baking. them 11 a furnace, at a temperature below their fusion point and for a period which is dependent baked and the degree of purity desired. This effects a burning out of all the impurities sublimable at the temperature at which the ma- 'terials are being subjected, and causes a coagulation of all other impurities, which may be readily siftedout of the powdered .materials being treated. The. binder and the ceramic material, both in the powdered form, are then mixed and extruded under pressure I into the desired formv determined by the die of the extrusion press. The material is then subjected to machining, where desired and necessary. 1

These various steps are described in more detail in the copending application above identified, the foregoing description being deemed to be suflicient for the purposes of the present case.

The roduct thus obtained is finally fired, i. e. su jected to heat, for example baked in a furnace, in a strongly reducing atmosphere, i. e. more gas (CO) than air. In other words, it is desirable to eliminate the presence of all free oxygen. By this means the occluded gas in the materials being subjected to the heat treatment will consist largely, if not entirely, of the gas in which the alkali was reduced, viz: carbon monoxide (CO), to the exclusion of free oxygen. By reason of this heat treatment, for example in the case of the radio vocuum tube, when the tube is in use excess heating releases from the heater element carbon monoxide and no oxygen and therefore the metal of the filament (for example tungsten where that metal is used) is not oxidized. In fact, due to the affinity of carbon monoxide and any free oxygen which may be present in the tube irrespective of its source, the carbon monoxide will combine with such free oxygen and "form carbon dioxide, an inert gas, with the result that the heater element produced in accordance with our invention in itself acts in use as a getter.

In the vacuum tube art it will be readily seen with these elements the use of the alkali getters, such as potassium, etc., at present employed with their incident deleterious effects on the metallic filament while at the same time enabling the obtaining of the getter action of such vaporizable metals, for which purpose, without knowledge of the deleterious eflects of alkali, such materials ceramic which comprises extrudin were originall proposed and have been used in this and "a lied arts. However, we have found that in forming the ceramic material if a small (percentage of magnesium oxide in powdere form is used (ten per cent or less) on final firin part of the occluded gas in the ceramic tu e comprises magnesium oxide with the result that both a getter and a keeper action are obtained in the tube.

Many modifications and changes in details will readily occur to those skilled in the art without departing from the spirit and scope of our invention as defined in the claims but having now set forth the objects nature of our invention and having described a method and a product obtained in accordance therewith, 0th embodyin tion, what we claim as new an useful desire to secure by United States Letters Patent is:

1. The method of producing a non-corrosive ceramic which comprises extrudin under pressure a pulverized materlal an binder baking the same at a temperature sufliciently high to burn out the binder.

4. The method of producing a non-corrosiveceramic which comprises extruding under pressure a pulverized material and powdered eryllium oxide and bakin the same at a temperature. sufliciently high to flux the beryllium oxide. v

5. The method of producin a non-corrosive ceramic which comprises su jecting a powdered material to heat below its fusion temperature to purify the same and extruding the purified material under pressure and bak ing the same.

6. The method of producing a non-corrosive ceramic WhlCll comprises subjecting a pow- .dered material and a binder to heat below our invenand ion

their fusion temperatures to purify them,

temperature sufliciently high to burn out the binder without fusing the powdered material.

8. The method of producing a non-corrosive ceramic which comprises subjecting a powdered material free from alkali to heat below their fusion temperatures to purify the same, mixing the material with an alkali free binder similarly purified, extruding the material under pressure, and finally baking the extruded product.

9. The method of producing a non-corrosive ceramic which comprises subjecting a powdered material free from alkali to heat below their fusion temperatures to purify the same, mixing the material with an alkali free binder similarly purified, extruding the material under pressure, and finally baking the extruded product at a temperature sufficiently high to burn out the binder.

10. The step in the process of producing a ceramic product which comprises purifying the ceramic in powdered form by heating it below its fusion temperature, and firing the product in a stron ly reducing atmosphere of gas to cause any ee oxygen to be replaced by the reducing gas.

11. The step in the process of producing a ceramic product which comprises initially purifying the ceramic in powdered form by heating it below its fusion temperature, firing the product in a gaseous reducing atmosphere free from free oxygen to cause the free oxygen in the ceramic to be replaced by the reducing gas.

12. The step in the process of producing an alkali-freed ceramic product which includes the step of firing the product in a gaseous reducing atmosphere free from free oxygen to cause any free oxygen in the ceramic to be replaced by the reducing gas.

- 13. The step in the process of producing a ceramic product which comprises firing the product in an atmosphere of carbon monoxide to cause any free oxygen in the ceramic to be replaced by carbon monoxide.

14. The step in the process of roducing an alkali-freed ceramic product w ch comprises firing the product in an atmosphere of carbon monoxide to cause any free oxygen in the ceramic to be replaced by carbon monoxide.

15. A ceramic formed of a compressed and baked powder with its occluded gases consisting substantially entirely of carbon monoxide.

16. A ceramic formed of a compressed and baked powder containing in part a powdered form of a metal having getter properties.

17. In the art of manufacturing a metal filamentand a ceramic adjunct thereto capable of being used at high temperatures without corrosion of the filament, the method which comprises powdering a metal oxide, heating the powdered oxide to a temperature below its fusion point to separate out materials having an alkali reaction at high temperatures, siftingout the alkali freed powder and mixing it with a non-alkali binder, extruding the mixture under pressure to tubular form, and threading said filament through said tubular member.

18. The method according to claim 17 in which the extruded tubular member is baked before threading of the filament to flux the binder. p

19. The method according to claim 17 in which the powdered oxide is mixed with a non-alkaline binder of beryllium oxide.

20. The method according to claim 17 in which the extruded tubular member is baked before threading of the filament to flux the binder below the fluxing temperature of the powdered metal oxide.

21. The method according to claim 17 in which the extruded tubular member is baked before threading of the filament in a reducing gaseous atmosphere to cause the said gas to replace the free occluded gas in said member.

22. The method of manufacturing a heater element for radio tubes which comprises selecting a powdered metal containing substantially no impurities which have an alkali reaction at high temperatures, mixing with said powdered metal a small percentage of a metal having getter properties, extruding said mixture to tubular form, baking the extruded member and threading through said extruded member a metalfilament.

23. The method of manufacturing a heater element for radio tubes which comprises selecting a powdered metal containing substantially no impurities which have an alkali reaction at high temperatures, mixing with said powdered metal a small ercentage of a powdered oxide of a metal having getter properties, extruding said mixture to tubular form, baking the extruded member and threading through said extruded member a metal filament.

24. The method according to claim 23 in which the metal having getter properties consists of powdered magnesium oxide.

In testimony whereof we have hereunto set our hands this 21st day of February A. D.,

HENRY L. CROWLEY. ROBERT M. CROWLEY.