Iridium-sheathed wire for electron tubes

Abstract

Abstract A method of producing iridium coated tungsten or molybdenum wire, e.g. for use in grids of electron discharge tubes, comprises inserting into a tube of sintered iridium powder having a V.P.N. of from 220-310 a core of tungsten or molybdenum having a V.P.N. of 480/540 or 330/400 respectively and swaging the filled tube to rod and drawing the rod to wire. In a first example iridium powder having a surface area of 0.3 m.2/gm. is compacted about a 0.25 inch diameter polished mild steel former under hydrostatic pressure of 15 tons/inch2. The former is flange at one end and the powder is supported by a latex sheath. The compact 4 inches long and having 0.25 inch and 0.375 inch inside and outside diameters respectively is sintered in vacuum at 1500 DEG C. to give a density of 18 gms./cm.3. A sintered tungsten rod of a density of 15-16 gms./cm.3 is ground to produce a sliding fit and inserted into the compact, the assembly being subsequently swaged at 1500 DEG C. to 0.125 inch diameter rod, hot drawn at 750-650 DEG C. to 0.10 inch diameter wire, drawn at 600 DEG C. to 0.02 inch diameter and finally at 550-500 DEG C. to 0.01 inch diameter wire. The drawing rate initially is from 1-2 ft./min. to about 12 ft./min. at a diameter of 0.02 inch. The thickness of the iridium sheath is usually 0.001-0.002 inch but may be 0.0005 inch and the hardness of the iridium and tungsten 582 V.P.N. and 803 V.P.N. respectively. Plugs of iridium may be used to plug the tube if the heating is carried out under oxidizing conditions. In a second example a rod of swaged and drawn molybdenum containing 0.5% titanium and having a hardness of 375 V.P.N. is inserted in the tube, the ends plugged with iridium and the assembly hot-swaged and hot-drawn to a final diameter of 0.012 inch and a core diameter of 0.005 inch. The iridium and molybdenum hardness values were 698 V.P.N. and 386 V.P.N. respectively. The tensile strengths of the tube and core are preferably between 5000/12,000 p.s.i. and the density of the iridium, tungsten and molybdenum 16 to 20; 14 to 17 and 10.2 gms./cm.3 respectively. It is stated that no fusing bond exists between the metal core and the iridium sheath which can be easily peeled therefrom.

Inventors

• 👤 Price Edward George

Bibliographic Details