US2179381A - Insulated member - Google Patents

Description

Nov. 7 1939. PALMATEER 7 2,179,381

INSULATED MEMBER Original Filed March 18, 1935 INVENTOR ATTORNEY Patented Nov. .1, 1939 Original application ,March 18, 1935, Serial No.- 11,696. Divided and this application July. 22,

1936, Serial No. 92,050

- Claims. (01. 154-25) This invention relates to insulator members and more particularly to composite insulators,- prepared preferably in accordance with the method described in application Serial No. 11,696,

5 filed March 18, 1935 of which this is a division.

An object of the invention relates to an im-- proved insulator body particularly adapted asan insulator for radio tubes, lamps and other electrical devices. Another object relates to an insulated member for radio tubes, lampsand the like consisting of a base of one kind of insulator material and a coating of ceramic insulating material.

Another object is to provide an improved form of spacer member for spacing or supporting the electrodes of a radio tube, lamp or similar device. A feature of the invention relates to a mica body having a coating of a ceramic insulation.

A further feature relates to a mica or similar insulator body having thereon a coating of a specially salt.

A still further feature relates to improved form of mica spacer for radio tubes and the like which is provided with a protective coating serving to protect the mica against chipping orsplitting and providing a refractory insulator sheath therefor. Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims. While the invention will be described herein as embodied in the form of an electrode spacer for radio tubes, it will -be understood that this is done merely for explanatory purposes and not by way of limitation.

' While the invention is not limited to the coating of any-particular insulator body, it is peculiarly advantageous in the .coating of men. or similar insulators such as are at present widely 40 used in radio tubes and similar devices. As is well-known the mica insulators or spacer members used in radio tubes are usually in the form of sheets ordiscs which may be provided with one or more perforations to receive a metal insert or other part of theradio tube mount. Unless certain precautions are taken, these mica members may tend to chip or flake. In accordance with the present invention, the mica members are provided with a coating of a specially preprepared and dried hydrolyzed metallic I pared insulator material preferably, although not necessarily, constituted of a dried hydrolyzed me- ,tallic salt having the desired refractory and electrical insulation properties. In applying this insulator coat I have found it highly desirable to employ for the coating solution one which is free from carbon or carbonaceous material. Thus as illustrated in the drawing the'spacer member consistsv of a disc I of mica, having a series of perforations 2 to receive for example, the socalled electrode side-rods of any form of radio tube mount. This mica spacer is provided preferably over its entire surface with a coating or sheath of a ceramic insulating material 3 which is prepared and applied as described in detail herein. This ceramic insulator is preferably constituted of a material such for example as a dried hydrolyzed salt of aluminum, or any other metal whose dried hydrolyzed salt has the desired refractory properties and electrical insulating properties. Merely as illustrative, the present specification will describe the application of a coating consisting of dried hydrolyzed aluminum nitrate.

The coating solution for producing the protective refractory or insulating layer consists for the most part of a material having the apparent composition of a hydrolyzed metallic nitrate but which is so prepared that when subjected to drying treatment it retains its stickiness and tackiness. In achieving this result it has. been found that there are certain limits to the proportionsof constituents necessary in the preparation so that when heated the material neither crystallizes nor gels but does retain its tackiness or stickiness. Thus the preferred procedure is to add to an acid a metal in respective molar proportions in excess of those necessary to produce a normal or neutral salt of the metal and acid. As one typical example metallic aluminum pref-. erably, although not necessarily, in comminuted form may be treated with nitric acid in the proper amount so that there results a viscous solution having the apparent composition of a hydrolyzed nitrate of aluminumi- Upon continued evaporation of this liquid, it becomes correspondingly more viscous and finally assumes a clear non-crystalized solid state. This clear solid upon further drying over a water bath be-' comes brittle and cracks so that it may be readily comminuted or reduced to powdered state, this powder being readily solublein water or in an alcohol to produce a viscous liquid. This water or alcohol solution may then be used for any purpose for which a liquid binder is ordinarily used, for example to hold the particles of insulating material on a support or article to be coated, while the latter is being subjected to heat treatment; or it may be used directly as a coating solution, without the addition of the particles of insulating material. The powderif ignited to terial were used as a binder or as a coating solution in coating operations, the coating would not be mechanically strong but would tend to powder oif, particularly where the coated article is a filamentary wire or ribbon. On the other hand, if the acid is used in insufficient amount, the material when dried will have an increased tendency to gel. Preferably therefore and in accordance with the invention, the acid and metal are mixed in such a proportion that the resultant dried product when added to water in sufficient amounts is capable of producing a pH in the range between 3.9 and 5.1.

As an example of one proportion of constituents that has been found to produce a product with the desired characteristics may be mentioned, one part by weight of metallic aluminum with 4.55 parts by weight of nitric acid, which is approximately one and one-half times the amount of aluminum necessary to produce a normal solution of A1(NO3)3. Approximately expressed, the preferred proportion is one molar quantity of metallic aluminum with two molar quantities of nitric acid, or 1.95 grams of metallic aluminum to ten cubic centimeters of nitric acid (sp. g. 1.4 and containing 65% nitric acid). Upon completion of the chemical reaction between the aluminum and the nitric acid, there is produced a liquid which upon evaporation forms the brittle solid material described above. It will be understood of course that the invention is not limited to the specific proportions of aluminum and nitric acid just mentioned. For example desirable results may be attained by employing as low as one and one-half molar quantity of aluminum to one molar quantity of nitric acid, and as high as one molar quantity of aluminum to three molar quantities of nitric acid. That is, the aluminum content may be varied from as low as one and one-half to three times the amount of aluminum necessary to produce the normal aluminum nitrate salt. While the exact constitution of the resultant material is not directly ascertainable it shows upon analysis to have a similar composition to hydrolized aluminum nitrate, however the chemical and physical properties indicate that it is probably aluminum hydroxide, peptized by the nitrate ion present.

The brittle material obtained in the manner described is readily soluble in water or in an alcohol to produce a viscous liquid. When dissolved in water the material possesses greater stability than when dissolved in an alocohol, and

furthermore the instability of the alcohol solution increases with the degree of dilution thereof.

When an alcohol solution of suiiicient concentration to prevent gelling is used, this solution may be subsequently diluted with an alcohol saturated with aluminum nitrate, without any substantial danger of the solution gelling when heated. In the case of water solutions, it is posvsible to carry the concentration of the solution to as low as one gram of aluminum to 2.5 grams of nitric acid. While the viscous liquid resulting from the aluminum and nitric acid may be maintained' at approximately 100 C. for a considerable period of time, long-continued heating at this temperature may induce a slight decomposition of the brittle material and it may be necessary to digest the remaining undecomposed material with water for some time before dissolv- While the alcohol or water solution of the powder previously prepared as above-described, may be used as a binder, it will be understood that this solution may also be used without any additional materials to provide an insulator coat- .ing. This results from the fact that when the solution is sprayed, brushed, dipped or otherwise applied to the mica and the coating is raised to a suitable temperature, or to a temperature suiiicient to drive off water and the oxides of nitrogen and other gases produced by the heat, there results a uniform coating consisting substantially entirely of dried hydrolyzed aluminum nitrate which possesses high electrical insulating properties.

When the alcohol solution is to be used as a binder it may have incorporated therein a comminuted material or materials preferably in finely powdered form. For this purpose an oxide or mixture of oxides of aluminum, beryllium, titanium, zirconium may be employed; or asilicate or silicates of magnesium, aluminum, beryllium, titanium, zirconium, may be employed. Preferably the major part of the said insulation material comprises one or more of the abovementioned oxides and a smaller quantity of one or more of the silicates mentioned. Thus for example when the solution is formed by the action of aluminum and nitric acid in the proportions specified, the added insulating material may consist of aluminum oxide and magnesium silicate, care being taken that the proper amount of insulating material is added so as to provide the {desired consistency to the coating liquid. This consistency will of course be determined by the particular method of coating employed viz. spraying, dipping, cupping, brushing, etc., and also by the size of the area to be coated.

After the coating has been properly applied, the coated article is heated to a suitable temperature for a sufllcient time to drive oil the water content and any gases that are produced. In any event the article ispreferably heated to such a temperature that the heating of the binder results in a residue of protective insulating material and the temperature is preferably such that the bonding agent such as silicon dioxide bonds the particles of the aluminum oxide together without requiring actual fusion of the aluminum oxide itself. It will be understood of course that the above procedure may be cyclically repeated so as to increase the thickness of the insulating coating,

In coating the mica'body, a suitable quantity of the dry powder resulting from the action of nitric acid and aluminum, is dissolved in a suitable quantity of alcohol such as a methyl alcohol and the mixture stirred'until the-solution is complete, as indicated by its completely clear character. This solution may be subsequently diluted to the desired concentration by adding methyl alcohol, the concentration of the solution depending to a large degree upon the size of the mica part to be coated, and the thickness of the coating desired. The mica parts having been previously freed from oil, grease and dirt by any well-known process are then placed in a suitable foraminous container e. g., an aluminum mesh cage or any similar cage which is not attacked by the alcohol or nitric acid. The cagecontaining the parts is then completely immersed inthe above-described solution which is preferably contained in an earthen-ware container or any similar container which is resistant to nitric acid and alcohol.

The foraminous container having the coated parts therein, is then removed from the solution and allowed to drain thoroughly. When completely drained the mica parts are then loaded into a suitable container such as a glass bulb which is mounted for rotation or tumbling, and

into which hot air may be forced at for example a pressure of three pounds per square inch. The bulb and its contents are rotatedor tumbled for approximately thirty minutes and until the coated micas no longer cling together or to the walls of the bulb.

The coated micas are then removed from the bulb and heated for several hours in a suitable oven preferably, although not necessarily, an electric oven open to the air. The duration of this heating is largely determined by the thickness of the coating, and may last until substantially all the volatile material has been removed. It will be understood of course that instead of relying upon the residue to provide the insulator coating, insulating powdered materials may be added to the binder solution as described above in connection with the coating of filamentary members. It will be understood of course that mica parts have been chosen merely as an illustrative, and that the above method may be employed for the coating of any similar material or articles.

While the above-described methods specify that the binder or coating solution is prepared preferably by the action of nitric acid on aluminum powder, it is understood that the binder may be prepared by employing beryllium, magnesium titanium, zirconium and similar metals. Furthermore, while metallic aluminum has been described, it will be understood that any combination of aluminum with any one ormore of metals such as beryllium, magnesium, titanium or the like, may be employed.

Various changes and modifications may be made herein without departing from the spirit and scope of the invention. Thus if it is desired to produce a binder or coating solution which upon being ignited produces a residue of a refractory metallic oxide, a normal salt of the metal e. g., aluminum nitrate, beryllium nitrate, etc., may be hydrolized by suitable means for example by heating with water, to a composition suitable -for use as a binder, that is one having appreciable tackiness or stickiness. The powdered material resulting from the continued heating of this hydrolized normal salt may then be used in the-same manner as the powder described above resulting from the action of nitric acidon the various metals set forth.

A product possessing the desired binder or coating qualities may also be made by treating an aqueous solution of a metallic nitrate such as aluminum nitrate, that is, the normal or neutral metallic salt e. g., Al(NO3)3 with a quantity of the powdered metal e. g., aluminum equal to approximately twice the weight of the metal in the quantity of metallic nitrate used. Upon digesting this mixture, a viscous aqueous solutionis obtained which possesses substantially identical properties with the product described above obtained by dissolving powdered aluminum in nitric acid. While the proportions of material given herein show that the final product should contain a ratio of aluminum to nitrogen of approximately one atomic weight of aluminum to one atomic weight of nitrogen, products which depart somewhat from this ratio may be used as binders and coating material although the desiredviscosity of the solution is obtained when the ratios are approximatelythose as specified.

While it is preferred in accordance with the invention to employ a nitrate of aluminum, beryllium, magnesium, titanium, zirconium or similar metals to produce a binder or coating liquid having a pH range such as set forth above, it will be understood that any inorganic salt or inorganic compound of these metals may be employed so long as the salt or compoundis capable of aluminum nitrate. For example, one of these metals such as aluminum may be mixed with aluminum chloride or aluminum sulphate in the proportions above set forth and the mixture subjected to the treatment described to producea substance in which the respective molarproportions are in excess of those necessary to produce a normal or neutral salt of the acid and metal which may then be dissolved in water or alcohol to produce a binder or coating liquid having the desired pH range. By the expression a main body of refractory insulator material"-as employed in the claims is meant a material having the properties of such materials as mica and ceramics such as are customarily used in an evacuated radio tube-and which can be heated to a. relatively high temperature during the processing of the tube without contamination'of the cathode of the tube and without releasing undesirable products which would interfere with the operation of the tube.

What I claim is:

l. A composite insulator member for radio tubes comprising a sheet of refractory electric insulating material, and a separate coating of a refractory material thereon comprising a dried hydrolyzed metallic salt of high electric insulating qualities to improve the surface insulation characteristics of the member.

2. An insulator spacer member for spacing the electrodes of electric discharge tubes and the like comprising abody of refractory electric inthe like comprising a sheet of mica having an enclosing sheath of q a dried hydrolyzed aluminum salt.

.5. An insulator member for radio tubes and the like comprising a sheet of mica having an enclosing sheath of a dried hydrolyzed zirconium salt.

6. An insulator member for radio tubes and the like comprising a sheet of mica having an enclosing sheath of a'dried hydrolyzed beryllium salt.

'7. An insulator spacer member for spacing the electrodes of radio tubes and the like comprising 10 coating of a dried hydrolized metal nitrate.

9. An insulator member for radio tubes and the like revising a main body of refractory insulator material and a thin separate surface coating of a dried hydrolized metal nitrate containing a refractory metal oxide. 7

10. An insulator member for radio tubes and the like comprising a mica sheet having an enclosing sheath of ceramic material.

RUSSELL E. PALMATEER.

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