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Single Phase Dense LaB(6) for Electron Emission Cathodes

IP.com Disclosure Number: IPCOM000091926D
Original Publication Date: 1968-Jul-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Cuomo, JJ: AUTHOR

Abstract

Dense, single-phase lanthanum hexaboride LaB(6) provides a low work function, highly stable electron emissive cathode with a high output power capability and a tendency not to poison. When powdered LaB(6) arc-melted in a water-cooled hearth, the resultant crystalline structure exhibits a second phase of lanthanum tetraboride LaB(4) of near 5% concentration. The presence of such concentration of the second phase tends to degrade the density and the mechanical properties of the resultant crystalline structure. The effectiveness of the material in its application as an electron emission cathode is thus impaired.

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Single Phase Dense LaB(6) for Electron Emission Cathodes

Dense, single-phase lanthanum hexaboride LaB(6) provides a low work function, highly stable electron emissive cathode with a high output power capability and a tendency not to poison. When powdered LaB(6) arc-melted in a water-cooled hearth, the resultant crystalline structure exhibits a second phase of lanthanum tetraboride LaB(4) of near 5% concentration. The presence of such concentration of the second phase tends to degrade the density and the mechanical properties of the resultant crystalline structure. The effectiveness of the material in its application as an electron emission cathode is thus impaired.

The mechanism for the second phase formation is that ascribed oxygen on the powder surface reacts with boron to produce B(2)O(3). 2LaB(6) + 30(2) 2LaB(4) + 2B(2)O(3). The loss of boron as B(2)O(3) necessarily results in the formation of second phase LaB(4) in the formed crystalline structure. Compensation for the loss reaction is obtained by adding boron to the powdered LaB(6) starting material in proportion to its expected loss and thoroughly mixing so that LaB(4) + 2B approaches LaB(6).

The measured density of the crystalline LaB(6) thus produced exhibits a measured density of 4.669 as compared with a theoretical density of 4.71.

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