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Title: Chemical stability of barium calcium aluminate dispenser-cathode impregnants

Abstract

A thermodynamic model has been formulated to describe the effects of temperature and composition on the chemistry of barium and barium oxide (Ba/BaO) generation from dispenser cathode impregnants. Our approach is to make use of the BaO-CaO-Al/sub 2/O/sub 3/ phase diagram and BaO vapor pressures of impregnant phases to calculate the BaO vapor pressure of the impregnant. This BaO vapor pressure is used to calculate the Ba vapor pressure resulting from reactions between BaO vapor and the tungsten cathode. The Ba/BaO vapor pressures are used to calculate Ba/BaO generation and evaporation rates from a wide range of impregnant compositions. Ba/BaO evaporation rates from dispenser cathodes, reported in the literature over a range of Ba and calcium (Ca) concentrations, are consistent with the rates predicted from this study. Two trends are evident. First, increasing the Ba concentration in the impregnant generally forms high vapor pressure Ba-rich phases leading to high Ba/BaO evaporation rates. Second, increasing Ca concentration in the impregnant lowers in the Ba/BaO vapor pressures by forming more stable barium-calcium-aluminate solid solutions. Ca has little effect on Ba/BaO vapor pressure once its solubility limit is reached and a separate CaO phase is formed. This model illustrates the possibility of extendingmore » cathode life by selecting impregnants composed of fairly stable solid-solution phases for use in cathodes that must be operated at high temperature for high current density.« less

Authors:
;
Publication Date:
Research Org.:
Aerospace Corp., El Segundo, CA (USA). Chemistry and Physics Lab.
OSTI Identifier:
5081549
Report Number(s):
ATR-82-8424-1
ON: DE82906406
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 42 ENGINEERING; ALUMINATES; STABILITY; ALUMINIUM OXIDES; PHASE DIAGRAMS; BARIUM; EVAPORATION; VAPOR PRESSURE; BARIUM OXIDES; CALCIUM OXIDES; CATHODES; ELECTRON EMISSION; IMPREGNATION; ELECTRON TUBES; BARIUM COMPOUNDS; CALCIUM COMPOUNDS; CALCULATION METHODS; EXPERIMENTAL DATA; TEMPERATURE EFFECTS; ALKALINE EARTH METAL COMPOUNDS; ALKALINE EARTH METALS; ALUMINIUM COMPOUNDS; CHALCOGENIDES; DATA; DIAGRAMS; ELECTRODES; ELEMENTS; EMISSION; INFORMATION; METALS; NUMERICAL DATA; OXIDES; OXYGEN COMPOUNDS; PHASE TRANSFORMATIONS; PHYSICAL PROPERTIES; THERMODYNAMIC PROPERTIES; 400201* - Chemical & Physicochemical Properties; 420800 - Engineering- Electronic Circuits & Devices- (-1989)

Citation Formats

Lipeles, R A, and Kan, H K.A. Chemical stability of barium calcium aluminate dispenser-cathode impregnants. United States: N. p., 1982. Web.
Lipeles, R A, & Kan, H K.A. Chemical stability of barium calcium aluminate dispenser-cathode impregnants. United States.
Lipeles, R A, and Kan, H K.A. 1982. "Chemical stability of barium calcium aluminate dispenser-cathode impregnants". United States.
@article{osti_5081549,
title = {Chemical stability of barium calcium aluminate dispenser-cathode impregnants},
author = {Lipeles, R A and Kan, H K.A.},
abstractNote = {A thermodynamic model has been formulated to describe the effects of temperature and composition on the chemistry of barium and barium oxide (Ba/BaO) generation from dispenser cathode impregnants. Our approach is to make use of the BaO-CaO-Al/sub 2/O/sub 3/ phase diagram and BaO vapor pressures of impregnant phases to calculate the BaO vapor pressure of the impregnant. This BaO vapor pressure is used to calculate the Ba vapor pressure resulting from reactions between BaO vapor and the tungsten cathode. The Ba/BaO vapor pressures are used to calculate Ba/BaO generation and evaporation rates from a wide range of impregnant compositions. Ba/BaO evaporation rates from dispenser cathodes, reported in the literature over a range of Ba and calcium (Ca) concentrations, are consistent with the rates predicted from this study. Two trends are evident. First, increasing the Ba concentration in the impregnant generally forms high vapor pressure Ba-rich phases leading to high Ba/BaO evaporation rates. Second, increasing Ca concentration in the impregnant lowers in the Ba/BaO vapor pressures by forming more stable barium-calcium-aluminate solid solutions. Ca has little effect on Ba/BaO vapor pressure once its solubility limit is reached and a separate CaO phase is formed. This model illustrates the possibility of extending cathode life by selecting impregnants composed of fairly stable solid-solution phases for use in cathodes that must be operated at high temperature for high current density.},
doi = {},
url = {https://www.osti.gov/biblio/5081549}, journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Aug 01 00:00:00 EDT 1982},
month = {Sun Aug 01 00:00:00 EDT 1982}
}

Technical Report:
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