US2673387A - Electron emission coating mixtures - Google Patents

Description

Patented Mar. 30, 1954 UNITED STATES ATENT OFFICE 2,673,387 ELECTRON EMISSION CGATING MIXTURES Gordon M. Forker, Lyndhurst, Ohio, assignor to General Electric Company, a corporation of New York No Drawing. Application May 18, 1951, Serial No. 227,115

2 Claims. (01. 29-2514) 2 My invention relates to electric discharge deadvantages of employing Cellosolve acetate as vices and more particul rly to electron emissive the solvent are found in the improved character, catho es therefor. More particularly my invenas well as the heavier Weight of the filling of tion relates to compos tions of electron emissive the electron emissive mixture in the cathode coil. coating mixtures useful for activating such In a given size coil, the weight of the emissive cathodes. material is increased from an average of about My invention is particularly useful in connecmg. to about 5 mg. for Cellosolve acetate ticn with the application of electron emissive mixes as compared With amyl acetate mixes.

fl to "0116i Wire t o e p fii u fly However, even aside from the increased Weight, colei-coil cathodes as employed in the conven- 1U is noticeable that the Cellosolve acetate mix tional fluorescent lamps. Such cathodes are penetrates into, and more completely fills, the

composed of a refractory wire, such as tungsten, primary coil of the cathode. The material withwhich is helically wound into a primary coil in the primary coil fullv effective andis retained which is, in turn, helically wound. into a secondfor a long useful life, whereas any material left ary 001 to constitute the coiled coil. It has been hanging on the outside of the coil becomes disthe DraCtiCe to st u 8 as y pp lodged end. falls oil during operation of the lamp with an electron emission mixture comprising 2. containing the cathode. The improved characsuspension of electron emissive material usually ter of th 1-111 r coating i evidenced by the comprising alel'ne earth carbonates including fact that the primary coil contains a higher probarium, calcium ani strontium carbonates which portion of solid slugs of the emission material may e u s y a double p e and a lower proportion of annular segments. bonates and which are carried in suspension in Th e r ult may be due, in part, t the f ct a cellulosic ester or ether binder such as a solu that since the Cellosolve acetate requires more ton of nitro-cellulose in a solvent like amyl aceti t va or t it gives the mixture time to tate- In subsequent m ufac u n steps, after sin: deeper into the primary coil before it freezes the cathode has b n s in the lamp bulb 0 or sets. However, it is also fact that other solen e ope, t s a i activated y heating to vents, even some having slower evaporation rates break down the alkaline earth carbonates to the t c t t Such as djacetone 1 corresponding oXides, the bi d being bu cohol and acetonyl acetone, are not satisfactory.

out. I have obtained good results by employing In accordance with the present inventio I mixtures comprising a suspension of about have discovered that materially improved results 13e 2 o grams of am i a th carb nate in are obtaine When he ConventiOnal solvent of about 115 to 145 ml. of a binder of nitrocellulose amyl ace-tote is replaced by Cellosolve acet dissolved in Cellosolve acetate and having a (ethy S monoethyl Ethel acetate)- viscosity of about 30-100 centipoises. I prefer One O t a a a e of emp oy Ce to employ triple carbonates of barium, strontium solve acetate as the solvent in place of amy and calcium. The composition of the triple acetate is that it makes a more stable mixture carbonate may be aried idely but good re because of its slower evaporation rate (21 comit h b e obtained with proportions of par d t 6 on an ar itrary s ale where bu approximately 33.6 mole per cent barium, 31

acetate is s t t The amyl acetate mole per cent strontium and 30.4 mole per cent tures require frequent dilution as the solvent i i evaporates. The necessity of dilution is evi- A specific l by way of illu trati n, f

danced by a bridging of the emission mixture a mixture with which good results have been across the secondary coils of the coiled-coiled obtainedis t follgwjng:

cathodes. However, each dilution is likely to Th3 binder i prepared by mixing 2.1 kg. of go too with the result that the 0011 than is nitrocellulose with 147 kg. of Cellosolve ace- 9 filled with a 9 weight of w emission tate and rolling the mixture until the solution is mlxture- Another dlsadvamage of mlxtures complete. The solution is then filtered, checked ploying amyl acetate is that they tend to form for a solid content of 3.5-1.5 per cent and a viscrusts on the coating equipment, such as that osity of 3e Seconds t 25 C in a #7 d p t disclosed in Patent 2.54 t W- P- Za l cup, and adjusted if necessary. A mixture is which is as ned 13 e assignee Of the present then made of 17.04 liters of the aforesaid binder invention. with 30 kg. of triple carbonates of the alkaline Even more important, and wholly unexpected, 5: earth metals. This mixture may be ball-milled for approximately 20 hours. The mixture is then stored until ready for application to cathodes in any suitable manner such as that disclosed in the aforesaid Patent 2,545,909.

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

1. A coating composition for coiled-coil cathodes and consisting essentially of a suspension, in proportions corresponding to the stated amounts, of about 130 to 260 grams of finely divided alkaline earth carbonates in about 115 to 145 ml. of a binder of nitrocellulose dissolved in ethylene glycol monoethyl ether acetate and having a viscosity in the range of about 30 to 100 centipoises.

2. The method of introducing activating alkaline earth materials on cathodes in electric discharge devices which comprises suspending powdered alkaline earth metal carbonate in a binder of nitrocellulose dissolved in ethylene glycol monoethyl ether acetate in proportions corresponding to about 130-260 grams of carbonate in about 115-145 ml. of a binder of nitrocellulose dissolved in ethylene glycol monoethyl ether acetate and having a viscosity in the range of about 30-100 centipoises, coating a coiledcoil cathode with said suspension, sealing the cathode in said device, and activating the oathode by heating to break down the alkaline earth carbonate to the corresponding oxide and to burn out the binder.

GORDON M. FORKER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,791,301 Davidson Feb. 3, 1931 1,842,161 Fredenbaugh Jan. 19, 1932 2,083,372 Guthmann June 8, 1937 2,223,977 Wamsley Dec. 3, 1940 OTHER REFERENCES Handbook of Material Trade Names, Zimmerman and Lavine 1946 pg. 95, Industrial Research Service, Dover, N. H.

Claims (1)

1. A COATING COMPOSITION FOR COILED-COIL CATHODES AND CONSISTING ESSENTIALLY OF A SUSPENSION, IN PROPORTIONS CORRESPONDING OF A SUSPENSION, AMOUNTS, OF ABOUT 130 TO 260 GRAMS OF FINELY DIVIDED ALKALINE EARTH CARBONATES IN ABOUT 115 TO 145 ML. OF A BINDER OF NITROCELLULOSE DISSOLVED IN ETHYLENE GLYCOL MONOETHYL ETHER ACETATE AND HAVING A VISOCITY IN THE RANGE OF ABOUT 30 TO 100 CENTIPOISES.