Liquid Vacuum Research Articles

Detection of a single electron produced inside bulk superfluid helium

The HERON project is an effort to develop a detector for low-energy solar neutrinos in real time by observing their elastic scattering from electrons using superfluid helium as the target material. By applying appropriate electric fields, the recoil electron can be separated from the positive ion, drifted upward to the liquid–vacuum interface, transmitted through the surface with the aid of a vortex ring, and detected using a calorimeter. By studying the correlation of the 16eV photon signal produced by scintillation and the single-electron signal, we can locate a neutrino event in a large detector and distinguish it from the background events involving multiple Compton scattering.

Mesophase pitches for 3D-carbon fibre preform densification: rheology and processability ☆

Synthetic mesophase pitches, produced from naphthalene (ARA24, ARA24r), were examined in terms of fluidity and thermal stability in comparison with other mesophase, isotropic pitches, or mesophase pitch/softening molecules blends. Their interest for carbon/carbon (C/C) composites processing by liquid impregnation or vacuum transfer inside three-dimensional carbon preform is discussed. Viscosity versus reduced temperature plots is reported on the same graph to compare the studied pitches and to define a suitable C/C processing window. Methylnaphthalene-based pitch is a good candidate with viscosity and stability adapted to the processing temperature and high carbon yield.

Effects of environmental temperature and humidity on the flexural strength of alumina and measurement of environment-insensitive inherent strength

In the range of temperature, 10–55 °C, and relative humidity, 20–80%, it has been demonstrated that the flexural strength of alumina decreases significantly with increasing temperature and relative humidity. It has been also demonstrated that the environment-insensitive inherent strength may be obtained by testing under nitrogen gas atmosphere after coating specimens with liquid paraffin, vacuum grease or polyurethane.

Parallelism and differences of pervaporation and vacuum membrane distillation in the removal of VOCs from aqueous streams

In this work two gas–liquid separation processes, pervaporation (PV) and vacuum membrane distillation (VMD), have been compared in their application to the separation of chloroform–water mixtures. After selection of the adequate separation membrane the comparison of the PV and VMD should be based on the kinetics and selectivity towards the desired compound. The kinetic models and parameters previously reported by the authors (A.M. Urtiaga, E.D. Gorri, J.K. Beasley, I. Ortiz, J Membr Sci 156 (1999) 275–291 and A.M. Urtiaga, G. Ruiz, I. Ortiz, J Membr Sci 165 (2000) 99–110) for the separation of chloroform from aqueous solutions in the range of concentrations 200<C<2000 mg/l, temperature 5<T<44°C and flowrate 140<Re<1400 have been used to compare the mass transfer flux and selectivity in both separation processes. The use of hollow fiber membranes of polydimethylsiloxane in the PV system and microporous polypropylene in the VMD process resulted in the same rate of removal in both systems under the simulated conditions. Particularly, the PV system offered the uppermost selectivity, providing a high concentration of chloroform in the permeate.

Positive and negative ion emission from perfluorinated poly-ethers

Positive and negative ion ejection in the mass range below 200 Dalton is observed for perfluorinated poly-ether surfaces subjected to electron- and ion-beam irradiation. The exciting projectiles are Ar + ions of 300 and 4000 eV and electrons of 3000 eV. The main positive ions found are fragments of CF 3 + ions. Larger ions are found with lower probability. The main negative ion observed is F. The results show that the liquid–vacuum interface is formed by CF 3 groups from the polymer.

Range of liquid ring vacuum pumps

Range of liquid ring vacuum pumps

Effect of contact with air on the photoluminescence spectrum of porous silicon

A study has been made of the transformation of photoluminescence (PL) spectra of porous silicon (PS) induced by its ageing, including the early stages of contact with air. The sample was prepared under conditions that minimized this contact, and spectral measurements were carried out in a high vacuum or in liquid nitrogen. The PS PL spectra obtained under continuous measurement in high vacuum are always dominated by one emission band of PS nanoelements, which shifts toward shorter wavelengths with ageing by 150 nm. At 80 K, the band intensity is considerably higher than at 300 K, and this difference grows with ageing. Exposure of a sample to air for a few tens of seconds is long enough to strongly transform its time-resolved PL spectra, which is evidence of a change in the sample surface. The effect of immersion of PS samples in liquid nitrogen on PL spectra is associated not only with their cooling, but also with the field of adsorbed nitrogen molecules, whose influence becomes weaker with increasing thickness of the oxidized near-surface layer. The variation of the spectral properties and kinetics of the long-wavelength PS PL band with temperature, medium (liquid nitrogen or vacuum), and exposure time suggest that these factors affect carrier migration between silicon nanoelements.

The absolute magnetization of 3He at zero pressure

We have measured the absolute magnetization of liquid 3He at saturated vapor pressure over the temperature range 0.3–500 mK. The technique compares the magnetization of the liquid to that of vacuum by passing the liquid–vacuum interface through a SQUID coil. We find that, contrary to expectations, the electronic diamagnetism of the normal liquid is approximately 6% less than the calculated atomic value. This appears to be the first measurement of the diamagnetic susceptibility of any noble gas in a condensed state.

Surface Bose–Einstein condensate: clusters and free surface of 4He

The role of surface fluctuations on the local Bose–Einstein condensate (BEC) in a self-bounded system like 4He is investigated at T=0 K. We find that when the wave function (wf ) properly includes these fluctuations the local BEC only reaches about 50% and not 100% as found with a standard wf. Further, out of the surface the condensate decreases and correspondingly there is an enhanced population of small momentum states. We find this behaviour both for the liquid–vacuum interface and for clusters larger than about 200 particles. Our results are based on a novel shadow wave function which describes the self-binding of 4He only via interparticle correlations.

Direct current and pulsed operation of contaminated liquid metal ion sources

Gallium liquid metal ion sources (LMISs) have been exposed to common gas and liquid phase laboratory and vacuum system contaminants. Minor changes in the direct current and pulsed operation of the LMISs were observed after contaminant exposure. Time-of-flight mass analysis of the ion emission revealed that contaminant species are primarily field evaporated with the gallium substrate. Low vapor pressure contaminants have been observed to constitute a significant portion of the total emitted ion current.

Compact simplified design of optical cell for single-molecule spectroscopy

A simplified modification of an optical assembly for single-molecule spectroscopy with the sample located at the joint focus of a parabolic mirror and a focusing lens is described. The optical cell fits a small helium cryostat with a 33 mm diam neck and can be used for experiments with thin films of frozen solutions as well as with other types of thin films. Described is the procedure of preadjustment of the position of a fixed focusing lens for work in different environments with the known index of refraction, such as superfluid liquid helium, helium gas, or vacuum; no adjustment of the lens during the experiment is required. A similar design of an optical cell could be used in a high-pressure cryostat with solid helium where the position of the lens cannot be adjusted. A signal-to-noise ratio of 15:1 was achieved for single-molecule spectra of terrylene in the Shpol’skii matrix n-decane.

半導体化ＢａＴｉＯ３‐Ｉｎ複合粒子接触界面のＩ‐Ｖ特性

The authors fabricated semiconductive BaTiO3-In complex particles in the previous work. The aggregate of them could be a new FTC material, which can be used in arbitrary shapes, being different from the conventional rigid FTC materials. The interface between semiconductive BaTiO3 particles and indium particles plays an important role. In this work I-V characteristics of the interface are investigated in detail.The conclusions obtained in this research are as follows.(1) The existence of an indium thin plate at an interface between two semiconductive BaTiO3 particles drastically reduces electric resistance. This effect is ascribed to a good plasticity and a low value of the work function of the indium thin plate.(2) In-Ga eutectic liquid alloy and vacuum deposited indium film electrodes for a semiconductive BaTiO3 disc satisfy Ohm's law and does not form Schottky barrier.(3) Vacuum deposited gold film electrode forms a high electric resistance barrier at the interface. This high resistance may be caused by Schottky barrier.

Interaction of vacuum-arc-generated macroparticles with a liquid surface

The concept of trapping vacuum-arc-generated macroparticles by a liquid is introduced. Experiments have been performed using a pulsed vacuum arc plasma source operating with a carbon cathode. Vacuum pump oil was used as the trapping liquid in vacuum. It was experimentally shown that trapping did not work as anticipated: a substantial number of particles experienced elastic reflection from the liquid surface. With simplified energy and momentum balances it is shown that the liquid behaves increasingly like a solid when the approaching particle is fast. A significant portion of its kinetic energy is transformed into deformation energy which can reappear as kinetic energy of the reflected particle. Particle reflection is likely to be additionally supported by a Leidenfrost-type effect: a thin oil vapor layer of relatively high pressure can be formed between the liquid surface and the macroparticle caused by the macroparticle’s high temperature.

New techniques for solvent recovery and elimination of wastewater emissions during vacuum process operations

AbstractThe pharmaceutical and chemical process industries are concerned with controlling volatile organic compound (VOC) emissions for several reasons: to meet environmental regulations, for increased worker safety, and to minimize product losses. Various methods can be used including flaring and carbon adsorption. These techniques are end‐of‐the‐pipe solutions and are not integral with the process operation itself.An improved technique for the recovery of solvents during reaction, distillation, evaporation, drying, filtration, mixing, and other vacuum operations is the APO‐VAC vacuum/gas compressor system. The skid‐mounted, engineered package is based upon a single stage liquid ring vacuum pump. The system allows for the recovery and reuse of clean solvent with minimum air emissions and zero liquid emissions. VOC and biological oxygen demand (BOD) regulations are met by this technology.The paper reviews the technical details of the system and presents test results and on‐site operational data. Specific case histories involving methylene chloride recovery and acid/toxic gas neutralizations are also included.In the chemical processing industry (CPI) the generation of vacuum is a necessity. Many chemical processes take place more easily, more quickly and more efficiently under vacuum than under atmospheric pressure, thus allowing better product quality at lower production cost. If it is a “wet” process involving the use of solvents then solvent recovery becomes an important consideration because of cost savings associated with its recovery as well as environmental benefits.These objectives have stimulated the development of the APOVAC system concept which is based on the principle of closed loops or circuits. Since its development, the APOVAC system has enhanced today's chemical process technology through solvent recovery and recycling, elimination of wastewater effluent, and reduction of gas emissions thus contributing to a technically efficient and environmentally acceptable operation.

Applications for small photoelectron emission microscopes

Several applications of simple photoelectron emission microscopes for the observation of real time in situ surface processes are reviewed, including field emission, chemical vapor deposition, tribochemistry and liquids in ultra-high vacuum, and pulsed supersonic molecular beam film growth.

The mean electrostatic potential difference between liquid water and vacuum by MD simulation

A negative mean electrostatic potential relative to that of a vacuum exists in liquid water represented by the extended single point charge (SPC/E) model and can be computed by molecular dynamics simulations. The mean potential difference between the liquid phase and vacuum can also be estimated analytically from the charge distribution in the SPC/E water molecule with respect to its mass and force centers. Other models of water molecules are also discussed.

Die Flüssigkeitsring-Vakuumpumpe als verfahrenstechnische Maschine

Flussigkeitsring-Vakuumpumpen werden in der verfahrenstechnischen Industrie sehr vielfaltig eingesetzt. Hierbei stehen zunachst die Forderung von Gasen und Dampfen sowie die damit verbundene Herstellung einer Druckdifferenz im Vordergrund des Interesses. Selbstverstandlich findet in Flussigkeitsring-Vakuumpumpen aber auch ein Warme- und Stoffaustausch zwischen den zu fordernden Gasen und Dampfen auf der einen und der Betriebsflussigkeit auf der anderen Seite statt. Dieser Warme- und Stoffaustausch kann gezielt fur verfahrenstechnische Grundoperationen eingesetzt werden. So konnen in diesem Pumpentyp neben den Hauptaufgaben Fordern und Verdichten auch gezielt Warmeaustausch, Kondensation/Verdampfung, Absorption/Desorption sowie chemische Reaktionen durchgefuhrt werden. Liquid ring vacuum pumps have many and diversified applications in the process industry. Primarily they are used to transfer gases and vapours from a lower to a higher pressure level. Due to the specific principles of operation, a heat and mass transfer between the gas or vapour and the sealing liquid takes place also. This can be utilised to perform unit operations. Beside transportation and compression of gases the pump can perform the following operations: exchange of heat, condensation/evaporation, absorption/desorption as well as chemical reactions. Because of these features is the liquid ring vacuum pump a „process engine” and an interesting alternative to other process apparatus. Following the definition of H. Brauer (1985) is the objective function of a process engine achieved by a moving element, whereas the objective function of a process apparatus is achieved without any moving element. For nearly all possible combinations of sealant, gases and vapours reliable empirical principles to determine the suction volume and the power requirements of liquid ring vacuum pumps are at hand. Besides has the use of liquid ring vacuum pumps to perform unit operations a long successful tradition. However, the field of applicability can be enlarged if the feasibility of the engine for individual unit Operations can be predicted with the help of physical models. Due to the eccentrically arranged rotor a sickle shaped space is formed between rotor hub and liquid ring where suction, compression and discharge of an gas/vapour mixture can be realised if the suction and discharge slots are arranged in a suitable manner. As the seal liquid is in direct contact with the gases and vapours all reactions inside the pump develop in the direction of a thermodynamical equilibrium between the two phases. An important consequence of this feature is the limit of operation of liquid ring vacuum pumps: the suction pressure has to be above the vapour pressure of the seal liquid. Another consequence is the possibility to utilise this type of pumps for unit operations. The turbulent surface of the liquid ring which is formed by a dense hale of droplets is ideal for heat and mass transfer processes. Following an attempt of C. Pfleiderer, the azimuthale distribution of the static pressure and the contour of the liquid ring can be determined under considerably simplifying assumptions. One of these simplifications is that the condensation and evaporation in the pump is neglected. The further simplifications deal with the significant idealisation of the geometry. Taking back the simplifying assumptions step-by-step and including the thermodynamical circumstances it is possible to calculate the azimuthale distribution of the static pressure and the real contour of the liquid ring for the condensation and the evaporation. These attempts can be carried on to taking several components in the vapour-portion of the gas/vapour mixture into account and form the basis of the calculation of the absorption and desorption. In this case the assumption that the thermodynamical equilibrium is attained instantly is no longer valid.

Liquid ring vacuum pump needs no cooling water

Liquid ring vacuum pump needs no cooling water

Molecular dynamics simulation of the free surface of liquid formamide

Molecular dynamics simulations of liquid formamide (HCONH2) were carried out using the GROMOS software. The formamide molecule is represented by all of its atoms with all internal degrees of freedom. In contrast to other simulations dealing with bulk properties, this study focuses on the interface liquid–vacuum for the first time. We show that the molecular plane is tilted out of the surface, exposing the HCO group to the vacuum. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 1123–1131, 1997

Measurement of Arsenic Emission from Doped Czochralski Silicon Crystal Growing Operation

AbstractThe level of arsenic from the effluent of a crystal grower was measured at different phases of the silicon crystal growth operation which includes arsenic doping, crystal body growth, burn‐in, and post burn‐in periods. Measurement of arsenic levels were made in the discharge water used as the sealing liquid for the liquid ring vacuum pump used for process effluent discharge. Gas phase measurements were also performed for both particulate arsenic as As2O3 as well as for compounds of arsenic in vapor phase as AsH3. Results of these analyses provided important information for developing strategy for emission treatment and control, reducing arsenic exposure to personnel and evaluating the feasibility for recycling argon used in the crystal growing process.