Vacuum Thermionic Work Functions and Thermal Stability of TaB2, ZrC, Mo2C, MoSi2, TaSi2, and WSi2

Wilson, R. G.; McKee, W.E.

doi:10.1063/1.1709747

Cited by 18 publications

(7 citation statements)

References 4 publications

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“…Au was chosen as a default coating based on its widespread use in spacecraft [19] while Nb was chosen because of flight heritage as coating for the GP-B gyroscopes [14]. In addition, several carbides were selected because of their mechanical toughness [20] and workfunction ( [21], [22], [23], [24], [25]). Carbides are commonly used in applications such machine tool coatings and disk brakes where mechanical toughness is a concern, making them an attractive choice for meeting the proof mass protection requirement.…”

Section: Coating Requirements and Candidate Selectionmentioning

confidence: 99%

UV LED charge control of an electrically isolated proof mass in a Gravitational Reference Sensor configuration at 255 nm

Balakrishnan¹,

Sun²

2012

Preprint

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Precise control over the potential of an electrically isolated proof mass is necessary for the operation of devices such as a Gravitational Reference Sensor (GRS) and satellite missions such as LISA. We show that AlGaN UV LEDs operating at 255 nm are an effective substitute for Mercury vapor lamps used in previous missions because of their ability to withstand space qualification levels of vibration and thermal cycling. After 27 thermal and thermal vacuum cycles and 9 minutes of 14.07 g RMS vibration, there is less than 3% change in current draw, less than 15% change in optical power, and no change in spectral peak or FWHM (full width at half maximum). We also demonstrate UV LED stimulated photoemission from a wide variety of thin film carbide proof mass coating candidates (SiC, Mo 2 C, TaC, TiC, ZrC) that were applied using electron beam evaporation on an Aluminum 6061-T6 substrate. All tested carbide films have measured quantum efficiencies of 3.8-6.8×10 −7 and reflectivities of 0.11-0.15, which compare favorably with the properties of previously used gold films. We demonstrate the ability to control proof mass potential on an 89 mm diameter spherical proof mass over a 20 mm gap in a GRS-like configuration. Proof mass potential was measured via a non-contact DC probe, which would allow control without introducing dynamic forcing of the spacecraft. Finally we provide a look ahead to an upcoming technology demonstration mission of UV LEDs and future applications toward charge control of electrically isolated proof masses.

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Section: Coating Requirements and Candidate Selectionmentioning

confidence: 99%

UV LED charge control of an electrically isolated proof mass in a Gravitational Reference Sensor configuration at 255 nm

Balakrishnan¹,

Sun²

2012

Preprint

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“…ZrC is a metallic material, and the value of its work function (Φ WF = 3.7 eV) is smaller than that of ZrPd 3 (Φ WF = 4.7 eV, calculated by DFT). Given that ZrC and the intermetallic ZrPd 3 species are electronically contacted, this characteristic feature should promote the electron-donating ability of Pd–ZrC, together with negatively charged Pd active sites.…”

Section: Resultsmentioning

confidence: 83%

“…In this context, we have focused on ZrC NPs as a candidate of the support. They are metallic materials with a low-work function feature (Φ WF = 3.7 eV). , Although ZrC can be synthesized by calcining a Zr organic polymer (polyzirconosaal, PZSA), this approach did not result in noticeable particle aggregation . The robustness with respect to high temperatures allows intermetallic catalysts to grow on the surface of ZrC without decreasing its surface area.…”

Section: Introductionmentioning

confidence: 99%

Intermetallic ZrPd₃-Embedded Nanoporous ZrC as an Efficient and Stable Catalyst of the Suzuki Cross-Coupling Reaction

Park

et al. 2020

ACS Catal.

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The Suzuki cross-coupling reaction, which is generally catalyzed by Pd-based materials, is a practical approach to create C–C bonds. Although heterogeneous catalysts, including metal-loaded and intermetallic catalysts, afford simple reaction conditions and catalyst reusability, it is challenging to achieve high catalytic activity, durability, and Pd-atom economy together in a single catalyst. Herein, we report the successful preparation of Pd–ZrC, a Pd-based catalyst with the described desirable features. In it, a-few-nanometer-sized nanoparticles of intermetallic ZrPd3 are uniformly dispersed on the surface of nanoporous ZrC with a surface area of 340–450 m2 g–1. As a result of the presence of electron-rich Pd sites and the material’s strong electron-donating ability, Pd–ZrC achieved high catalytic performance in Suzuki cross-coupling reactions at room temperature. Because a low Pd content (1 wt %) is sufficient to produce highly catalytically active Pd–ZrC, this material represents a great improvement in terms of Pd-atom economy over previously reported catalysts. Moreover, no catalytic degradation was noted over up to the presented 15 reaction cycles as the active Pd sites were stabilized in the ZrPd3 lattice. These results indicate that Pd–ZrC has the advantages of both metal-loaded and intermetallic catalysts, providing an approach to enhance the degree of freedom for designing heterogeneous catalysts.

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“…Similarly, over a CeO2 catalyst, CO appears from 450 K and peaks at 600 K [60]. Contrary to what is generally observed in metal catalysts [58,59], the change in the concentration of H2 is not observed before 350 K. In metal catalysts, the electronegative hydrogen adatoms are stabilised by the electropositive metals as they move away from the surface [61] for associative desorption, but the presence of carbon in the Mo lattice in Mo2C decreases the overall electropositivity of the surface and increases the work function [62,63]; Therefore, a higher temperature is required to facilitate the hydrogen atoms' associative desorption from the surface. The formation of H2 on the surface (reaction 12) also has slow kinetics (10 -1 s -1 ).…”

Section: Temperature Programmed Reaction (Tpr) Modelmentioning

confidence: 93%

Decomposition of Formic Acid over Orthorhombic Molybdenum Carbide

Agrawal

Roldán²,

Kishore³

et al. 2021

Preprint

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The decomposition of formic acid is investigated on the β-Mo2C (100) catalyst surface using density functional theory. The dehydration and dehydrogenation mechanism for the decomposition is simulated, and the thermochemistry and kinetics are discussed. The potential energy landscape of the reaction shows a thermodynamically favourable cleavage of H-COOH to form CO; however, the kinetics show that the dehydrogenation mechanism is faster and CO2 is continuously formed. The effect of HCOOH adsorption on the surface is also analysed, in a temperature-programmed reaction, with the decomposition proceeding at under 350 K and desorption of CO2 observed.

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Vacuum Thermionic Work Functions and Thermal Stability of TaB2, ZrC, Mo2C, MoSi2, TaSi2, and WSi2

Abstract: Interfacial reactions and thermal stability of ultrahigh vacuum deposited multilayered Mo/Si structures J.

Cited by 18 publications

References 4 publications

UV LED charge control of an electrically isolated proof mass in a Gravitational Reference Sensor configuration at 255 nm

UV LED charge control of an electrically isolated proof mass in a Gravitational Reference Sensor configuration at 255 nm

Intermetallic ZrPd₃-Embedded Nanoporous ZrC as an Efficient and Stable Catalyst of the Suzuki Cross-Coupling Reaction

Decomposition of Formic Acid over Orthorhombic Molybdenum Carbide

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Vacuum Thermionic Work Functions and Thermal Stability of TaB2, ZrC, Mo2C, MoSi2, TaSi2, and WSi2

Abstract: Interfacial reactions and thermal stability of ultrahigh vacuum deposited multilayered Mo/Si structures J.

Cited by 18 publications

References 4 publications

UV LED charge control of an electrically isolated proof mass in a Gravitational Reference Sensor configuration at 255 nm

UV LED charge control of an electrically isolated proof mass in a Gravitational Reference Sensor configuration at 255 nm

Intermetallic ZrPd3-Embedded Nanoporous ZrC as an Efficient and Stable Catalyst of the Suzuki Cross-Coupling Reaction

Decomposition of Formic Acid over Orthorhombic Molybdenum Carbide

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Intermetallic ZrPd₃-Embedded Nanoporous ZrC as an Efficient and Stable Catalyst of the Suzuki Cross-Coupling Reaction