sign in sign up
<<
Home , Barium oxide

June 10, 1947. E. N. BOBROW 2,421,984 MATERIAL FOR GETTERING ELECTRON DISCHARGE DEVICES Filed April 25, 1944

a 47A/2/7 7774//47 a/ya aa/ZZ/Z/Y

azuza/YeazrowSnoentor

04a (7 Cattorney Patented are 10, 1947 2,421,984 UNITED STATES PATENT OFFICE 2,421,984 MATERIAL FoR GETTERINGELECTRON DISCHARGE DEVICES, Edwin N. Bobrow, East Orange, N.J., assignor to Radio Corporation of America, a corporation of Delaware Application April 25, 1944, Serial No. 532,650 4 Claims. (C. 252-181.) My invention relates to the introduction into 2 evacuated or gas filled containers, such as elec in a position where it may be heated at will to tron discharge devices, of chemically active met a temperature at which reduction of the als or clean-up agents, and more particularly to compound Occurs. the introduction of alkaline earth metals, es as a reducing agent has given high pecially barium, into such devices and to an im yields of barium metal from very stable com proved clean-up agent or for this purpose. pounds of barium With the acidic Barium is a desirable and useful clean-up of metals from the first sub-groups of Groups IV, agent or getter for electron discharge devices W, and VI of the Mendeleef periodic table, for and similar tubes. Frequently a reducing agent example , zirconate, molybdate, is mixed with a barium compound, and when tungstate, Vanadate, columbate, and tantallate. the mixture is heated a reaction occurs and Of these stable barium compounds the one which barium metal is liberated as a vapor. One Com has been found preferable is barium titanate hav pound which gives a high yield of barium in a ing a composition 1BaOi TiO2. The getter ma readily controlled well directed pure barium flash terial with which good results have been obtained is the barium berylliate, disclosed in U. S. Pat is a mixture of finely powdered or comminuted ent 2,173,258, Lederer, mixed with pow barium titanate 1BaOlTiO2 and finely powdered der as a reducing agent. In very humid weather or comminuted beryllium in the ratio of from such as frequently occurs in Summer when the 1 to 2 moles of beryllium to 1 mole of barium relative humidity may be greater than 60% this titanate, good results having been obtained in material is not as stable as desired for factory 2) many cases with a mixture having a ratio of use as shown by a tendency to puff up to several about 1% moles of beryllium to 1 mole of barium times normal size when exposed to Inoisture and titanate, and in other cases a ratio of 2 moles of then heated. InVestigation had indicated that beryllium to 1 mole of the barium titanate. In a high efficiency barium getter necessarily had the getter mixture containing One mole of barium poor resistance to moisture and that only rather 25 titanate less than 1 mole of beryllium does not unstable barium compounds would give high give a reduction complete enough for practical barium yields. purposes, and more than 2 moles of beryllium Tests on the comparatively few stable barium is apt to result in some vaporization of beryllium compounds of high barium and low gas content, at 1300° C. with some impairment of the getter including barium titanate, which contains ini 30 action. tially nearly 60% by weight of barium, made For getter requirements the highest ratio of with titanium, , and as re barium oxide to titanium oxide consistent with ducing agents showed either low or no yield of Stability is desirable. Tests have shown that barium, or the vapor of some other metal. These if a dried powder of barium titanate 1BaO-1TiO2 tests indicate that none of the compounds of is soaked in water, only about 0.1% of moisture barium which are stable and moisture resistant is retained; if the compound has the composi would give a high barium yield. y tion 2BaO1TiO2, up to about 10% of moisture may be retained. Although either of these com The principal purpose of this invention is to pounds may be used without encountering the provide an active high yield reaction barium 40 puffing observed with barium berylliate in a very getter which is very resistant to moisture and humid atmosphere, the greater stability of the will give a high yield of barium when heated to 1BaO. 1TiO2 barium titanate makes it the pref the temperatures of about 1300° C. at which get erable barium compound. flashed.ters of the barium berylliate type are usually Barium titanate for use in accordance with In accordance with my invention the chem 45 the invention may conveniently be prepared by ically active metal, such as barium, is introduced mixing 990 grams of anhydrous barium into the device in the form of a compound of ate BaCO3 preferably of a purity of 99.5% or the metal which is very stable and resistant to better with 400 grams of pure anhydrous titanium moisture, together with a reducing agent which oxide TiO2 and firing the mixture in air at 1250 by a reaction that does not evolve gas liberates 50 C. for from 4 to 6 hours. The fired mass is the active metal in pure form and free from broken up into powder of about 20 mesh, then water vapor. The stable barium compound, pref finely powdered by ball-milling for 6 to 7 hours erably barium titanate, is brought into contact and sifted through a 200 mesh sieve. The beryl with metallic beryllium which serves as a reduc lium metal powder may be prepared from beryl ing agent. The metallic beryllium may be a 55 lium chips, preferably of a purity of 99.5% or mass of the metal, for example a ribbon or strip, better, cleaned and degreased in , dried, but for Convenience both the barium titanate and then ball-milled for 20 hours or more to and the metallic beryllium may be finely pow comminute the beryllium chips into a fine pow dered and thoroughly mixed to form the in der of beryllium particles which will pass through () a 200 mesh screen. Good results have been ob proved getter material. This getter mixture may tained with a getter material prepared by mix be supported in conventional ways in the device ing about 226 grams of the barium titanate with 2,421,984 4. 3 may be applied to obtaining a high yield of other about 14 grams of the beryllium powder, thus alkaline earth metals and of alkali metals from obtaining a getter mixture of the approximate stable compounds such as titanate which composition 1.6 moles beryllium to 1 mole of is stable and produces an effective getter reac barium titanate, and in which the beryllium is tion with beryllium. Titanium, , and sim about 6% by Weight of the mixture, the balance ilar reducing agents are effective and useful in being barium titanate. To this mixture a nitro thermionic cathodes coated with oxides of the cellulose binder may be added to facilitate the alkaline earth metals. The properties of beryl placing of the getter material in the getter holder. lium are such that it may be used to advantage The getter material of the invention may be O in the same Way as these other reducing agents. used in the conventional way, and may be heated The invention may be used as illustrated in the to the flashing temperature of about 1300° C. accompanying drawing, in which Fig. 1 is a view either electrically or by induction heating, as of the getter holder or trough containing the get shown in U. S. Patent 2,173,258, Lederer, relating ter, and Fig. 2 shows the preferred way of using to barium berylliate . the getter in a conventional metal radio tube, In some cases the getter material made in ac s, such as shown in U. S. Patent 2,208,692, Wams cordance with this invention does not adhere as ley, July 23, 1940. Well to the getter trough or container as SOme Fig. 1 shows the getter f, preferably a finely other getters containing barium compounds. If powdered mixture, contained in a getter holder this lack of adherence is objectionable, the in or trough 2 of a metal such as which corporation in the barium compound of a small 20 may be electrically heated and which will retain amount, preferably about 2%, of its shape at 1300° C. or more. The holder and will improve the adherence of the getter mate the getter mixture in it are electrically heated at rial wtihout deleteriously affecting the evolution will to a temperature of about 1300 C., where of the barium and its action as a getter. upon a reaction occurs which liberates barium in Beryllium metal has desirable properties as a 25 the form of vapor and leaves in the trough stable reducing agent for stable moisture resistant bari and gas-free reaction products. um or other alkaline earth compounds. The Fig. 2 shows the getter holder containing the strong affinity of beryllium for does not getter mounted on a pair of 3 of the metal appear until high temperatures are reached, radio tube 4. The getter holder and getter may hence it is stable at room temperature. It is 30 be electrically heated at will by passing current less volatile than barium and the other alkali through the getter holder by connecting the leads and alkaline earth metals, and has little or no 3 to a source of voltage. In accordance with tendency to volatilize before the stable barium conventional practice, the getter holder is pref compound is reduced. erably so mounted that the flash of barium is di Reducing agents, such as tantalum, titanium, 35 rected away from the electrode assembly of the zirconium, , and aluminum, which have been used to liberate barium from its compounds, tube. w are elements which are beyond the second group 1.claim: A getter material consisting of barium ti in the periodic table and which form oxides much tanate mixed with powdered beryllium in a ra more acidic than barium oxide. Apparently the 40 tio of from about 1 to about 2 moles of beryllium, acidic oxides of these reducing agents combine strongly with the basic barium oxide to form to 2.1 moleA getter of barium material titanate. consisting of a mixture very stable barium compounds which are difficult of finely powdered barium titanate and finely to reduce and which retain a considerable part powdered beryllium in which the beryllium con of the barium, so that the yield of barium is not 45 stitutes about 6% by weight of the total mix as high as would be expected. The effectiveness of beryllium as a reducing ture.3. A clean-up agent capable of evolving barium agent for stable barium compounds appears to be due to the being more basic whendered heatedbarium and titanate consisting and ofpowdered a mixture beryllium of pow than the oxides of other reducing agents beyond 50 containing from 5% to 10% beryllium by Weight the Second group in the periodic table, Such as titanium, zirconium, and tantalum. Apparently of 4.the A mixture. getter material consisting of barium ti beryllium oxide is sufficiently basic to combine tanate having the composition 1BaO1TiO2 mixed readily with the acidic oxide TiO2 in the barium compound 1BaO-1TiO2, thus making more bari 55 with beryllium in a ratio of from about 1 to um available than would be obtained if the OX about 2 moles of beryllium to one mole of barium ide formed from the reducing agent did not com titanate. EDWIN. N. BOBROW. bine readily with the acidic oxide of the barium compound. It is believed that the acidic oxide of REFERENCES CTED titanium does not hold back barium oxide to any 60 appreciable extent because the beryllium oxide The following references are of record in the acting as a relative to the titanium file of this patent: oxide holds the titanium oxide as berylluim titan ates and titanites. Whatever the reaction may be, UNITED STATES PATENTS I have found that when the mixture of beryllium 65 Number Name Date and barium titanate is heated to a reaction ten 1835,117 Marden ------Dec. 8, 1931 perature, usually about 1300° C., a reaction does 1,873,730 . Wiegand ------Aug. 23, 1932 occur which liberates a larger percentage of the 2,208,692 Wamsley ------July 23, 1940 barium than has heretofore been obtainable from 2,254,727 Beggs ------Sept. 2, 1941 these stable compounds of barium and which 70 1,172,568 Schroter ------Feb. 22, 1916 produces a very stable gas free reaction product consisting essentially of an oxygen compound of FOREIGN PATENTS beryllium and titanium. Number Country Date The principles involved in the use of beryl 300,265 Great Britain ------Nov. 11, 1927 lium for reduction of stable barium compounds 75