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Easy method enhancing the sensitivity of a helium mass-spectrometer leak detector
No full textCommercial He mass spectrometer leak detectors usually do not provide sufficient sensitivity to perform accurate measurements of the permeation rate of He through glass. Ultrasensitive dedicated systems have adeguate sensitivity but involve high costs and complex procedures. However, both cryogenics and photomultiplier technology routinely demand this goal. Here, we propose a novel method to increase the sensitivity of commercial devices to easily measure accurate permeation rate. We modified a commercial leak detector by reducing the pumping speed at the inlet of the rotary pump, thus increasing its sensitivity by one order of magnitude. The modified detector was used to measure the leak rate of the permeation of He through the glass walls of a photomultiplier. Further improvements made to decrease the minimum detectable signal were limited by the high ultimate pressure in the spectrometer tube
REFERENCE LEAKAGE DEVICE FOR LEAK CALIBRATION
No full textReference leakage device (1) for use in leakage detection of gas, comprises a membrane (5) adapted to be interposed between two environments having respective pressures pu and pa, where (I). The membrane has an orifice (6) adapted to determine a controlled gas flow depending on the pressure pu. The orifice has a preset diameter D and length L such that (II). The diameter D and the length L are further dimensioned in such a manner that the equivalent diameter De of the orifice is De≦100 nm, where De is defined by the relation De=D.a1/2 wherein a is the transmission probability of the orifice, function of the L/D ratio. The orifice is adapted to operate in molecular flow regime in an entire range of pυ values comprising the value of atmospheric pressure
FOCUSED ION BEAM (FIB) FABRICATION OF ORIFICES FOR LEAK DETECTION APPLICATION
No full textNowadays helium permeation leaks are the most diffused leaks in the lowest flow range, but its flow rate is temperature dependent. On the contrary, orifice leaks has a low coefficient temperature, but they have a size (about 1 μm) that limits their applicability in the lowest flow range. The Focused Ion Beam is used in widespread fields, both technological and scientific, from nano-technology to semiconductor and material science applications. In the last years a class of Dual Beam workstations, combining a FIB column with a Scanning Electron Microscope (SEM), appeared on the market making easier to treat materials at nano-scale with precise metrology. By means of FIB it is now possible to produce orifices with a diameter on the nanoscale that allow to have flow rates, with 1 atm of pressure differential, comparable to the ranges obtained with permeation leaks. In this work we present a method to produce orifices having a diameter at nanometer scale. The orifices can be used for any gas, including mixtures, and can change continuously the flow rate simply varying the inlet pressure. The paper will present several orifices produced on different materials like silicon nitride, silicon, and metal foils. All membranes have been installed on a copper gasket mountable on NW16 Conflat® flange and tested as calibrated leaks
Oil-in-water nanoemulsions loaded with lycopene extracts encapsulated by spray drying: Formulation, characterization and optimization
No full textLycopene is very susceptible to degradation once released from the protective chromoplast environment. In this study, oil-in-water (O/W) nanoemulsions coupled with spray drying technology were applied for the encapsulation and stabilization of lycopene extracted from tomato waste. Tomato extract was obtained by ultrasound-assisted extraction. Nanoemulsions were prepared by a high-speed rotor stator using isopropyl myristate as the oil phase and Pluronic F-127 as the emulsifier for the aqueous external phase. The effect of emulsification process parameters was investigated. Spray drying of the produced emulsions was attempted to obtain a stabilized dry powder after the addition of a coating agent. The effect of different coating agents (maltodextrin, inulin, gum arabic, pectin, whey and polyvinylpyrrolidone), drying temperature (120–170 °C), and feed flow rate (3–9 ml·min−1) on the obtained particles was evaluated. Results revealed that the emulsion formulation of 20/80 (O/W) with 1.5% (mass fraction) of Pluronic F-127 as stabilizer in the aqueous phase resulted in a stable nanoemulsion with droplet sizes in the range of 259–276 nm with a unimodal and sharp size distribution. The extract in the nanoemulsion was well protected at room temperature with a degradation rate of lycopene of about 50% during a month of storage time. The most stable emulsions were then processed by spray drying to obtain a dry powder. Spray drying was particularly successful when using maltodextrin as a coating agent, obtaining dried spherical particles with mean diameters of 4.87±0.17 μm with a smooth surface. The possibility of dissolving the spray dried powder in order to repristinate. The original emulsion was also successfully verified
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