Electronic, mechanical, and thermal properties of [Ca₂₄Al₂₈O₆₄]⁴⁺(4e⁻) electride ceramic

Abstract

The compound [Ca 24 Al 28 O 64 ] 4+ (4e-) named as C12A7:e-has outstanding properties because of a low work function and high electron conductivity due to a cage like crystal structure. For the application of the material as hollow cathodes in small satellite propulsion systems, its preparation as sinterable glass ceramics via the powder route is purposeful. However, the mechanical and thermal properties of the C12A7:e-glass ceramics have only been insufficiently measured so far. In this study, the measured Vickers hardness (HV0.5) is 6.7 ± 0.2 GPa. The ceramic has a fracture toughness of 1.6 MPa m 0.5 (calculated by Shetty model) and a 4-pt.bending strength of σ = 75 ± 12 MPa (σ 0 = 90 MPa). The coefficient of thermal expansion CTE is between 4.2 and 6.0 × 10 -6 K -1 (RT-1000 °C) and the thermal conductivity ranges between 2.3 W m -1 K -1 (20 °C) and 1.7 W m -1 K -1 (1000 °C). For calculating the thermal conductivity, the heat capacity and the thermal diffusivity are measured.

Improved Thermal and Mechanical Properties of [Ca24Al28O64]4+(4e−) Electride Ceramic by Adding Mo Metal

“…The preparation of the C12A7 oxide is described in Waetzig et al, 2019 [10] and Waetzig et al 2021 [17] and was done by mixing CaCO 3 (VWR Chemicals) and Al 2 O 3 (NABALOX, Nabaltec) with ratio of 12:7 in a tumbling mixer. A homogenous C12A7 glass was achieved by melting the mixture in a platinum crucible at a temperature above 1450 °C and additionally quenching on a brass block.…”

“…[15] Although the material has very good electronic properties, its low strength and toughness combined with a low thermal conductivity reduces its reliability and hinders its use in real applications due to the formation of cracks in the ceramic structure as a result of thermal shocks when used under thermal load. [16,17] In this study, the thermal properties were improved by mixing C12A7:e-with molybdenum metal particles and creating a ceramic-metal composite (CerMet) by sintering the mixtures. The hardness, toughness, thermal conductivity, and coefficient of thermal expansion of these composites in dependence on the Mo content are determined.…”

Fabrication and electron emission of [Ca24Al24.08Zr3.92O64]4+(4e−) electrides

“…5 Therefore, it is a potential material for catalytic reaction, thermoelectric conversion, and electron emission. [27][28][29][30][31][32][33][34][35][36] In recent years, related scholars have conducted research on [Ca 24 Al 24.08 Zr 3.92 O 64 ] 4+ (4e − ) in catalytic reactions and electron emission. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Some scholars found [Ca 24 Al 24.08 Zr 3.92 O 64 ] 4+ (4e − ) has an extremely low intrinsic work function (∼2.4 eV), and the value is lower than the noble metal Ru (∼4.7 eV).…”

“… 2–8 This cage structure with electronic storage enables [Ca 24 Al 24.08 Zr 3.92 O 64 ] 4+ (4e − ) to have good physical and chemical stability, low work function (∼2.4 eV), 16–28 and outstanding electron emission potential 5 . Therefore, it is a potential material for catalytic reaction, thermoelectric conversion, and electron emission 27–36 …”