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7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Extended testing of xenon ion thruster hollow cathodes

A hollow cathode wear-test of 508 hours was successfully completed at an emission current of 23.0 A and a xenon flow rate of 10 Pa-L/s. This test was the continuation of a hollow cathode contamination investigation. Discharge voltage was stable at 16.7 V. The cathode temperature averaged 1050 C with a 7 percent drop during the wear-test. Discharge ignition voltage was found to be approximately 20 V and was repeatable over four starts. Post-test analyses of the hollow cathode found a much improved internal cathode condition with respect to earlier wear-test cathodes. Negligible tungsten movement occurred and no formation of mono-barium tungstate was observed. These results correlated with an order-of-magnitude reduction in propellant feed-system leakage rate. Ba2CaWO6 and extensive calcium crystal formation occurred on the upstream end of the insert. Ba-Ca compound depositions were found on the Mo insert collar, on the Re electrical leads, and in the gap between the insert and cathode wall. This wear-test cathode was found to be in the best internal condition and had the most stable operating performance of any hollow cathode tested during this contamination investigation.

Sarver-Verhey, Timothy R.↗
NASA NTRS1992

Extended-testing of xenon ion thruster hollow cathodes

A hollow cathode wear-test of 508 hours was successfully completed at an emission current of 23.0 A and a xenon flow rate of 10 Pa-L/s. This test was the continuation of a hollow cathode contamination investigation. Discharge voltage was stable at 16.7 V. The cathode temperature averaged 1050 C with a 7 percent drop during the wear-test. Discharge ignition voltage was found to be approximately 20 V and was repeatable over four starts. Post-test analyses of the hollow cathode found a much improved internal cathode condition with respect to earlier wear-test cathodes. Negligible tungsten movement occurred and no formation of mono-barium tungsten was observed. These results correlated with an order-of-magnitude reduction in propellant feed-system leakage rate. Ba2CaWO6 and extensive calcium crystal formation occurred on the upstream end of the insert. Ba-Ca compound depositions were found on the Mo insert collar, on the Re electrical leads, and in the gap between the insert and cathode wall. This wear-test cathode was found to be in the best internal condition and had the most stable operating performance of any hollow cathode tested during this contamination investigation.

Sarver-Verhey, Timothy R.↗
DOE OSTI2020

Materials Data on BaCa by Materials Project

CaBa is Tetraauricupride structured and crystallizes in the orthorhombic Cmmm space group. The structure is three-dimensional. Ba is bonded to four equivalent Ba and eight equivalent Ca atoms to form a mixture of distorted face, edge, and corner-sharing BaBa4Ca8 cuboctahedra. All Ba–Ba bond lengths are 4.36 Å. There are four shorter (4.10 Å) and four longer (4.21 Å) Ba–Ca bond lengths. Ca is bonded in a distorted body-centered cubic geometry to eight equivalent Ba atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba3Ca by Materials Project

Ba3Ca is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ba is bonded to eight equivalent Ba and four equivalent Ca atoms to form BaBa8Ca4 cuboctahedra that share corners with four equivalent CaBa12 cuboctahedra, corners with fourteen equivalent BaBa8Ca4 cuboctahedra, edges with six equivalent CaBa12 cuboctahedra, edges with twelve equivalent BaBa8Ca4 cuboctahedra, faces with four equivalent CaBa12 cuboctahedra, and faces with sixteen equivalent BaBa8Ca4 cuboctahedra. There are a spread of Ba–Ba bond distances ranging from 4.31–4.37 Å. There are two shorter (4.32 Å) and two longer (4.34 Å) Ba–Ca bond lengths. Ca is bonded to twelve equivalent Ba atoms to form CaBa12 cuboctahedra that share corners with six equivalent CaBa12 cuboctahedra, corners with twelve equivalent BaBa8Ca4 cuboctahedra, edges with eighteen equivalent BaBa8Ca4 cuboctahedra, faces with eight equivalent CaBa12 cuboctahedra, and faces with twelve equivalent BaBa8Ca4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba3Ca by Materials Project

Ba3Ca is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Ba sites. In the first Ba site, Ba is bonded to eight Ba and four equivalent Ca atoms to form BaBa8Ca4 cuboctahedra that share corners with twelve equivalent BaBa8Ca4 cuboctahedra, edges with eight equivalent CaBa12 cuboctahedra, edges with sixteen BaBa8Ca4 cuboctahedra, faces with four equivalent CaBa12 cuboctahedra, and faces with fourteen BaBa8Ca4 cuboctahedra. There are four shorter (4.32 Å) and four longer (4.41 Å) Ba–Ba bond lengths. All Ba–Ca bond lengths are 4.41 Å. In the second Ba site, Ba is bonded to eight equivalent Ba and four equivalent Ca atoms to form BaBa8Ca4 cuboctahedra that share corners with four equivalent BaBa8Ca4 cuboctahedra, corners with eight equivalent CaBa12 cuboctahedra, edges with twenty-four BaBa8Ca4 cuboctahedra, faces with six equivalent CaBa12 cuboctahedra, and faces with twelve BaBa8Ca4 cuboctahedra. All Ba–Ca bond lengths are 4.32 Å. Ca is bonded to twelve Ba atoms to form CaBa12 cuboctahedra that share corners with four equivalent CaBa12 cuboctahedra, corners with eight equivalent BaBa8Ca4 cuboctahedra, edges with eight equivalent CaBa12 cuboctahedra, edges with sixteen equivalent BaBa8Ca4 cuboctahedra, faces with four equivalent CaBa12 cuboctahedra, and faces with fourteen BaBa8Ca4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BaCa3 by Materials Project

BaCa3 is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ba is bonded to twelve Ca atoms to form BaCa12 cuboctahedra that share corners with six equivalent BaCa12 cuboctahedra, corners with twelve CaBa4Ca8 cuboctahedra, edges with eighteen CaBa4Ca8 cuboctahedra, faces with eight equivalent BaCa12 cuboctahedra, and faces with twelve CaBa4Ca8 cuboctahedra. There are six shorter (4.04 Å) and six longer (4.08 Å) Ba–Ca bond lengths. There are three inequivalent Ca sites. In the first Ca site, Ca is bonded to four equivalent Ba and eight Ca atoms to form CaBa4Ca8 cuboctahedra that share corners with four equivalent BaCa12 cuboctahedra, corners with fourteen equivalent CaBa4Ca8 cuboctahedra, edges with six equivalent BaCa12 cuboctahedra, edges with twelve CaBa4Ca8 cuboctahedra, faces with four equivalent BaCa12 cuboctahedra, and faces with sixteen CaBa4Ca8 cuboctahedra. There are a spread of Ca–Ca bond distances ranging from 3.98–4.11 Å. In the second Ca site, Ca is bonded to four equivalent Ba and eight Ca atoms to form CaBa4Ca8 cuboctahedra that share corners with four equivalent BaCa12 cuboctahedra, corners with fourteen CaBa4Ca8 cuboctahedra, edges with six equivalent BaCa12 cuboctahedra, edges with twelve CaBa4Ca8 cuboctahedra, faces with four equivalent BaCa12 cuboctahedra, and faces with sixteen CaBa4Ca8 cuboctahedra. There are a spread of Ca–Ca bond distances ranging from 3.98–4.11 Å. In the third Ca site, Ca is bonded to four equivalent Ba and eight Ca atoms to form CaBa4Ca8 cuboctahedra that share corners with four equivalent BaCa12 cuboctahedra, corners with fourteen CaBa4Ca8 cuboctahedra, edges with six equivalent BaCa12 cuboctahedra, edges with twelve CaBa4Ca8 cuboctahedra, faces with four equivalent BaCa12 cuboctahedra, and faces with sixteen CaBa4Ca8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba3Ca by Materials Project

Ba3Ca is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ba is bonded to eight equivalent Ba and four equivalent Ca atoms to form BaBa8Ca4 cuboctahedra that share corners with twelve equivalent BaBa8Ca4 cuboctahedra, edges with eight equivalent CaBa12 cuboctahedra, edges with sixteen equivalent BaBa8Ca4 cuboctahedra, faces with four equivalent CaBa12 cuboctahedra, and faces with fourteen equivalent BaBa8Ca4 cuboctahedra. All Ba–Ba bond lengths are 4.38 Å. All Ba–Ca bond lengths are 4.38 Å. Ca is bonded to twelve equivalent Ba atoms to form CaBa12 cuboctahedra that share corners with twelve equivalent CaBa12 cuboctahedra, edges with twenty-four equivalent BaBa8Ca4 cuboctahedra, faces with six equivalent CaBa12 cuboctahedra, and faces with twelve equivalent BaBa8Ca4 cuboctahedra.

36 MATERIALS SCIENCE↗