• Title/Summary/Keyword: Cryo-adsorption

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Measurement of the Ar Recovery Time of a Cryopump and Analysis on the Ar Instability (크라이오펌프 알곤 회복시간 측정과 알곤 불안정성 분석)

  • In, Sang Ryul;Lee, Dong Ju
    • Journal of the Korean Vacuum Society
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    • v.22 no.5
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    • pp.225-230
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    • 2013
  • Cryopump removes gas molecules by condensation and adsorption. Therefore, cryo-surface temperature and corresponding vapor pressure influence directly the pumping performance. If the surface temperature of any part is neither low nor high, there occurs the desorption of gas molecules condensed or adsorbed, and the emitted molecules can be captured again, which leads to a time-consuming and fluctuating change of the pressure. Though every gas can show such a pressure instability at a specified temperature range, the instability generated in a sputter system using Ar as a working gas and operating with a cryopump is especially undesirable. In this paper the cause of the argon instability is analyzed and corrective is provided through the measurement of the Ar recovery time.

Adsorption Characteristics of Hydrogen in Regular Single-Walled Carbon Nanotube Arrays at Low Temperature (저온에서 규칙적인 단일벽 탄소나노튜브 배열의 수소 흡착 특성)

  • Yang Gon Seo
    • Clean Technology
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    • v.29 no.3
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    • pp.217-226
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    • 2023
  • The amount of hydrogen adsorbed in arrays of single walled carbon nanotubes (SWNTs) was studied as a function of nanotube diameter and distance between the nearest-neighbor nanotubes on square arrangements using a grand canonical Monte Carlo simulation. The influence of the geometry of a triangle array with the same diameters and distances was also studied. Hydrogen-carbon and hydrogen-hydrogen interactions were modeled with Lennard-Jones potentials for short range interactions and electrostatic interactions were added for hydrogen-hydrogen pairs to consider quantum contributions at low temperatures. At 194.5 K, Type I isotherms for large-diameter SWNTs and Type IV isotherms without hysteresis between adsorption and desorption processes for wider tube separations were observed. At 200 bars, the gravimetric hydrogen storage capacity of the SWNTs was reached or exceeded the US Department of Energy (DOE) target, but the volumetric capacity was about 70% of the DOE target. At 77 K, a two-step adsorption was observed, corresponding to a monolayer formation step followed by a condensation step. Hydrogen was adsorbed first to the inner surface of the nanotubes, then to the outer surface, intratubular space and the interstitial channels between the nanotube bundles. The simulation indicated that SWNTs of various diameters and distances in a wide range of configurations exceeded the DOE gravimetric and volumetric targets at under 1 bar.