US2018143A - Method of making aluminum-barium alloys - Google Patents

Description

Patented a. 22, 1935 UNITED STATES PATENT OFFICE METHOD or MAKING ALUMINUM- BARIUM ALLOYS No Drawing.. Application August 6, 1932, Serial No. 62'1,80l

7 Claims. (Cl. 75-1) This invention has to do with alloys of barium and aluminum. We have discovered that alloys of barium with pure aluminum can be readily made by a simple melting procedure. A description of. the methodof alloying is as follows: The

aluminum is first melted in a graphite crucible and maintained at a temperature of from 1300 to 1350 F. Barium is added in small amounts pref-' erably not exceeding 5% of the weight of alumil0 num at any one time. The barium is carefully cleaned of oxides and wrapped in aluminum foil before adding to the molten metal. In order to prevent oxidation of the barium during handling,

the clean metal is coated with a pyroxylin lacquer before the aluminum foil is added. After each addition of barium to the molten aluminum the resultant light slag is skimmed off and additions are continued until the required barium content is :obtained. After the last addition a period of from three to five minutes is allowed for thorough mixing by the currents induced in the molten metal by the high frequency furnace after which the metal is poured into heated iron molds, the mold temperature being 500 to 800 F.

We have described above the preferredme hod of making the alloy but this is subject to co derable variation in practice. We prefer to employ a graphite crucible for the reason that the graphite tends to inhibit the oxidation of aluminum and to reduce any aluminum oxide that may be formed. We prefer to add barium in small amounts because if larger amounts are employed the barium sputters and some is wasted. The

skimming off of the slag is essential where barium is added in successive increments, for otherwise the subsequent additions would push some of the slag into the metal. We have employed heated iron molds in accordance with usual aluminum foundry practice, but other mold materials may be employed, if preferred.

The resultant alloy we believe consists of an eutectic (barium and aluminum) d istributed uni- .i'ormly through a ground mass of an alloy of barium and aluminum of much lower barium concentration. I

By the above process we have succeeded in obtaining uniform and very stable alloys of aluminum and barium in proportions up to 30 to 35% of barium by weight. These alloys are not greatly affected by exposure to atmospheric moisture, do not tend to deteriorate on long standing,.and when out or filed do not give of! the characteristic odor of most barium containing alloys. The alloy may be immersed in water without any visible 6. surface attack.

The properties of this barium alloy indicate that it may be very useful for the following pur-. poses:

1. Its low work function due to the presence of barium shows that it is useful as a cold cathode in a gas discharge tube. Experiments show that the use of this alloy reduces the operating voltage considerably below that necessary for nickel or copper electrodes. The rate of disintegration was found to be surprisingly .low. It is also useful 10 asa heated cathode as the melting points of the alloys (for example, 20% barium and aluminum at 2400".F.) are well above that of pure aluminum (1210 F.) and appreciable thermionic emission results due to the high barium content.

2. These alloys provide a convenient method of handling barium for-use as a getter in vacuum tube construction or for other purposes where presence of barium is desired.

3. It is a powerful deoxidizing and de-gasifying agent as an addition to molten metals such as nickel or iron or other alloys. The alloy has been successfully used in this way.

4. Experiments show that this material will, 25 when molten, adhere to other metals including aluminum. This suggests its use as a solder forarticles made of aluminum and other metals, but the compositions set forth herein have such high melting points that it would be necessary, as a 30 practical matter, to add other ingredients to lower the melting point to make ituseful for this purpose.

5. Inasmuch as electron emission varies more or less directly with the barium content) of this alloy series, electrodes can be made varying in cathode current per unit area so that a series of these alloys could be usedin indicating instruments tomeasure electrical quantities such as voltage and current. To make a voltage measur- 40 mg instrument, for example, known practices may be followed. The alloy may be niade in the form of a long wire placed within a partially evacuated tube equipped with a second electrode which is preferably shorter and so arranged as 45 to bebut slightly visible to the 'observer. The electrodes would be connected to the points be-. tween which the voltage is to be measured. The applied voltage produces a glowdischarge on the surface of the wire. Over the operating range of 50 the instrument there is a direct relation between the area of the wire that is visibly illuminated and the voltage applied across the electrodes. By

providing a suitably calibrated scale extending I along the wire, the length of the wire which is 65 illuminated may be measured in terms of the applied voltage. In the case of an ammeter the instrument should be connected across a suitable shunt resistance, or two terminals of a conventional voltage transformer. The range of such glow-type instruments can be varied by proper selection of one of the alloys of this series.

6. Thermal expansion values decrease from that of pure aluminum (0.315;: 10- in. per in. per degree centigradewithin the range of room temperature to 600 C.) to 0.281 x'l0- (room temperature to 600 C.) .for one of this alloy series containing 9% barium, 91% aluminum, and less with increasing barium content. This indicates valuable properties for use as a piston alloy for internal combustion engines.

These alloys as cast are ductile and may be rolled or drawn into wire by the usual processes.

We claim:

v 1. The method of making an alloy of aluminum and barium which consists in melting aluminum and. maintaining it at a temperature in the neighborhood of from 1300 to 1350 F., providing barium with a coating to prevent oxidation and immersing it in the melt, removing the resultant slag, adding another portion of barium in like manner, removing the slag, and repeating until the desired barium content has been obtained, holding the melt for a. few minutes to insure thorough alloying and pouring it into a suitable mold.

2. The method of making an alloy of aluminum and barium which consists in melting aluminum and maintaining it at a temperature in the neighborhood of from 1300 to 1350 F., providing barium with a coating to prevent oxidation and immersing it in the melt, removing the resultant slag, adding another portion of barium in like manner, removing the slag, and repeating until the desired barium content has been obtained,

holding the melt for a few minutes to insure thorough alloying and pouring it into a suitable mold, the amount of barium added at one time not exceeding of the weight of the melt.

3. The method of making an alloy of aluminum and barium which consists in melting aluminum and maintaining it at a temperature in the neighborhood of from 1300 to 1350 F., coating barium with a quickly drying lacquer such as pyroxylin lacquer, wrapping it in aluminum foil, and immerslng it in the melt, removing the resultant slag, adding another portion of barium prepared 5 in like manner, removing the sla and repeating the process until the desired barium content has been obtained, holding the melt for a few minutes to insure thorough alloying and pouring it into a suitable mold. 10

4. The method of making an alloy of aluminum and barium which consists in melting aluminum in a graphite crucible and maintaining it at a temperature in the neighborhood of from l300 to 1350 F., coating barium with a quickly drying lacquer such as pyroxylin lacquer, wrapping it in aluminum foil, and immersing it in the melt, removing-the resultant slag, adding another portion of barium prepared in like manner, removing the slag, and repeating the process until the desired barium content has been obtained, holding the melt for a few minutes to insure thorough alloying and pouring it into cast iron molds heated to a temperature in the neighborhood of from 500 to 800 F. f

5. The method of preparing alloy of aluminum and barium which consists in melting aluminum, and adding barium metal thereto by successive increments immersed beneath the surface of the melt and removing the resultant slag between additions.

6. The method of preparing alloy of aluminum and barium which consists in melting aluminum in a crucible of graphite, which tends to inhibit oxidation of aluminum and reduce any aluminum oxide that may be formed and introducing barium metal by immersion beneath the surface of the melt.

'7. The method of preparing alloy of aluminum and barium which consists in melting aluminu 40 in a crucible of graphite, which tends to inhi t oxidation of aluminum and reduce any aluminum oxide that may be formed, adding barium metal to the melt by successive increments, and removing the resultant slag between additions.

DONALD W. RANDOLPH. JOHN E. MCCARTY.