US2241565A - Grid electrode - Google Patents

Description

y 13, 1941- v E. a. WIDELL I 2,241,565

GRID ELECTRODE Filed May 31, 1940' GRID 0F A/f-Mn ALLOY 1% 70.5% CARBON INVENTOR. EM/L GIDEO/V W/DELL 1 A TTORN E Y.

Patented May 13, 1941 UNITED STAT v GRID anac'raon'a Emii Gideon Widell, moomne'lain. 1., assignor to Radio Corporation Delaware of America, a corporation of Application my 31, 1949, Serial No.'338,0 11 s'ciaiins. (crest-21.5)

My invention relates to'electron discharge devices of the type having a thermionic cathode coated with alkaline earth metals, particularly to grids for such. devices and to the composition of the.- grids. a

Wire grids for radio tubes have been made of various metals and alloys but 'no material has heretoiorebeen produced that possesses all of the'qualities ne'cessary-forfgood wire grid structures. Molybdenum wire has been used because it is strong when hot, but it has high electron emissionin a tube with an oxide coated oathode, and various nickel alloys have beengused because of 16w emission from the gridbut they are soft and sag when heated. This emission most grids 5% manganese is'preferred. The manganese readily alloys; with nickel and the carbon in small quantities appears to enter into solid solutionxwith the alloy. and to hides with the metals of the alloy.

In manufacture it is preferred to melt the form carnickel or nickel and cobalt in a magnesia lined from the grid, probably caused by alkaline earth,. I

such as barium, driven from the oxide coated cathode and deposited on the grid, becomes objectionably high when the grid becomes hot during operation.

' The object of my invention is a grid material a that has low emission, that is strong yet work able, and is stiff even when hot. I

The characteristic features of my invention are defined in the appended claims and one embodiment thereof is described in the'following specification and shown diagrammatically in the accompanying drawing which shows my improved grid in a conventional electron discharge device.

comprises,- as shown in the drawing, an 'envelope I hermetically enclosing anode 2 and cathode 3. The cathode may be of the indirectly heated type comprising a nickel cylinder Iexteriorly coated with electron emissive materials :such as barium-strontium oxides.- Grid electrode 4 positioned between the anode and closely spaced to the cathode and exposed directly to heat from the cathode. and to any accrucible and to add small particles of manganese up to, about 10% of the-melt. The amount of carbon added depends upon the oxygen content of the melt since the carbon readily combines with the oxygen and passes oil as carbon monoxide gas. To the completely deoxidized melt sumcient. carbon is then added to carry the nickel through the drawing and annealing process to leave in the finished wire between .1%

and .5% carbon. I have found that about .2%

- carbon is suflicient to deoxidize the average melt cathode regulatesthe electron flow between the o cathode and anode and usually comprises wires melt.

tivemetals, such as barium, which may be evap-' orated from the cathode. Grids of the usual metals emit undersirable numbers of electrons I when operated at high temperatures with coatings of barium on the wire.

My improved grid wire comprises nickel or nickel and cobalt alloyed with a few percent of manganese and containing a small amount of carbon. This wire is sufficiently ductile to wind easily onto th side rods, yet has suflicient stiffness and-strength to hold its shape during and after severe exhaust heating. My improved gna further has'low electron emission even when operated at high temperatures adjacent an oxide coated cathode. Good results have been obtained with grid wire composed of, by weight, .5% ,to 10.0% mangansealloyed in nickel and containing between .1% and .5% carbon. For

. a .30 One conventional electron discharge device and that .then .1% to .5% additional carbon makes the ingots workable'and easily rolled to wire of uniform thickness .and texture as small as .001 inch. This wire, when prepared with commercial nickel and without cobalt, comprises,

by chemical analysis, approximately- Percent Manganese 0.5 to 10.0 carbon 0.1 to 0.5 Nickel Remainder with traces'of the metals usually found in commercial-grades of nickel.

To more accurately control the total amount of carbon added to the melt it may be convenient to first prepare a master .alloy by alloying carbon with nickel in the proportions of about 3% carbon and 97% nickel by melting the nickel in a graphite crucible and pouring into molds. Small pieces oi this "master alloy may then be broken off and dropped into the I have found that carbon in the nickel ingot I in excess of .5% makes the nickel too hard and brittle to conveniently work. Where special shapedgrids and grids of extra strength and rigidity are required, cobalt may .be substituted for part of the nickel up to as much as 50% of the.

alloy. Wherethe wire composition is approximately- Per cent Y Manganese 0.5 to 10.0 Carbon 0.1 to 0.5 Cobalt 5.0 to 50 Nickel Remainder grids with large unsupported turns of wire may be made and used in tubes with the standard barium-strontium oxide-coated cathode and 0perated at high temperatures without grid emission 0* sagging. Typical wire prepared, according to my. invention, with commercial nickel usually contains, by chemical analysis, traces of sill-' stiff enough to be handled the wire will not sag when con, magnesium, copper, and iron in addition to the manganese, carbon, cobalt and nickel. My new wrought nickel alloy wire may be easily reeled on the mandrel of a grid winding machine and peaned into notches in the side rod or welded to the side rod. The wire of the finished grid is without damage and heated to white heat during exhaust or operation. Grids made with my improved nickel alloy, whenoperated at high temperatures in'tubes with oxide coated cathodes, have an electron emission of about one-fifth of that of molybdenum and will hold their shape at high operating temperatures, which is important in assemblies of closely spaced electrodes. Apparently manganese carbide, MmC, or nickel carbide, NisC, possesses structures in which the carbon atoms are present as isolated units in the lattice. Nickel carbide appears to be less stable than Cementite, FeaC, while cobalt carbide, 003C,

rnay exist but cannot be isolated.

My improved grid has low electron emission, is

' strong and will not sag when hot.

n I claim- 1. An electron discharge devicev comprising an oxide coated cathode, a cooperating anode,and a cooperating grid electrode of an alloy of manganese and nickel which is predominantly nickel and containing within the alloy body 0.1% to .5% carbon, the grid electrode being interposed between said cathode and said anode. v

2. Anelectron discharge device comprising an oxide coated cathode, a cooperating anode, and

a grid electrode interposed between said cathode and said anode and made of an alloy predominantly or nickel and .5% to 10.% manganese, and containing0.1% to .5% carbon.

' 3. A grid electrode for an electron discharge device comprising a wire of an alloy consisting predominantly of nickel with .5% to l0. manganese and containing .l% to .5% carbon.

4. A grid electrode for an electron discharge device comprising a wire of an alloy consisting of, by weight, approximately .5% to 10.0% manganese, 1% to .5% carbon, 5.% to 50.% cobalt, and the remainder nickel, the carbon being included in the body of the alloy.

'5. An electron discharge device comprising an oxide coated cathode, a grid electrode spaced from and heated by said cathode, said grid electrode comprising a relatively long fine wire, said wire being made of an alloy of about .5% to 10.0% manganese',-5.0% to. 50.0% cobalt and the remainder nickel containing 0.1% to .5% carbon.

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