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Vacuum and Gas Kinetics
Published in Eiichi Kondoh, Micro- and Nanofabrication for Beginners, 2021
Diffusion pumps can make quite high vacuum, have a very simple construction, are therefore very affordable and do not require frequent maintenance actions if operated properly. One major concern is oil contamination. Liquid nitrogen oil traps are generally used, but they are not always enough to satisfy the cleanliness requirements in industries involved in the development of recent semiconductors. Another issue is probably rather longer boot-up/shut-down time required for heating and cooling the oil reservoir.
Polyphenyl Ether Lubricants
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
Sibtain Hamid, Stephen A. Burian
The vapor pressure of the 5P4E fluid, which is commercially sold as a vacuum pump fluid, is shown in Table 9.10. The PPEs have a very low vapor pressure, which is the major requirement for the working fluid in a diffusion pump. The PPEs have found their way into this application because of a combination of a number of properties, such as superior thermal stability, exceptionally low vapor pressure, and a tendency to wet surfaces less readily and “creep” to a lesser extent than is common with other fluids. The fluid is employed for the cleanest high vacuum and ultrahigh vacuum applications, where its excellent high vacuum performance and low tendency to migrate into the pump system are crucial. Since the fluid is chemically stable, noncorrosive, safe, nontoxic, and has excellent lubricating properties, it is also used to lubricate mechanisms in the overall vacuum system [7]. Since diffusion pumps work by boiling their fluid with an electric heating element, there are conditions under which the fluid will experience high surface temperatures.
Mass Spectrometry
Published in Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus, Environmental Chemical Analysis, 2018
Somenath Mitra, Pradyot Patnaik, Barbara B. Kebbekus
The most important part of the vacuum system is the pump. Usually, a mechanical pump is used as a roughing pump or forepump, to reduce the pressure to a few millimeters. Then the high vacuum pumps reduce the pressure still further to the range of 10−5 to 10−8 Torr required in the analyzer. Until recently, diffusion pumps were most commonly used for achieving high vacuum. The turbomolecular pump which requires less maintenance and which provides much cleaner backgrounds than the diffusion pumps has become much more popular, in spite of the higher cost. The diffusion pump contains a high boiling liquid, a highly purified oil or mercury, which is heated to provide a stream of heavy vapor molecules. The vaporized pump liquid is condensed at the top of the pump, and carries molecules of gas from the space being pumped, down into the pump. Despite chilled traps between the pump and the analyzer, some of the oil vapor can reach the analyzer and contribute to the background spectrum. Mercury gives a somewhat cleaner spectrum than an oil pump does, with only a single mass peak, but mercury is heavy, toxic, and expensive.
State of the Art in Cyclotrons for Radionuclide Production in Biomedicine
Published in Nuclear Science and Engineering, 2023
Mario Marengo, Gianfranco Cicoria, Angelo Infantino, Sara Vichi, Federico Zagni, Domiziano Mostacci
The PETtrace is an isochronous cyclotron, with a vertical acceleration plane that makes maintenance operations very simple. It can accelerate H− ions up to 16.5 MeV and optionally D− ions up to 8.4 MeV (Ref. 15). It has six target ports, all on the same side. The extraction system, based on two carousels with graphite stripping foils, allows two targets to be irradiated simultaneously according to combinations of target slots. The ion source is an internal, Penning type with two different chimneys for the H− ions, and optionally, for the D− contained in the same assembly. The maximum beam current for single-beam irradiation has been gradually increased from 75 µA in the initial versions up to 100 µA, introducing improvements in the ion source itself and in its positioning.16 The vacuum system includes a single diffusion pump, plus a rotary pump. As for all cyclotrons with an internal ion source, during the irradiation phase there is a certain pressure of the hydrogen gas. The residual molecules of the gas involve the neutralization, and therefore the loss of control, of a part of the H− ions of the beam. The transmission of the beam is typically on the order of 60%.
Chemical, thermophysical, rheological, and microscopic characterisation of rubber modified asphalt binder exposed to UV radiation
Published in Road Materials and Pavement Design, 2020
Mehdi Zadshir, Desiree Ploger, Xiaokong Yu, Cesare Sangiorgi, Huiming Yin
A Philips FEI (XL20) SEM was used to study the microscopic morphologies of the asphalt binders. Image formation in an electron microscope requires a high vacuum environment. Thus, the drying of samples was a prerequisite for viewing and obtaining good images in normal high vacuum SEM system. A rotary and a diffusion pump were used to vacuum-seal the samples at a maximum vacuum level of 1 × 10−4 torr. The metallisation process was performed using the aluminium coating. Coating of samples is required to make the samples conductive to avoid charging of electrons as well as to reduce thermal damage and improve the secondary electron signal required for topographic examination in the SEM. Therefore, a thin layer of aluminium (with a thickness of about 8 ± 3 Å) was coated on all samples. It should be noted that the increase in temperature during the coating phase is negligible with respect to the heating generated by the electron band during SEM scanning.
Two-stage thermocatalytic upgrading of fuel oil to olefins and fuels over a nanoporous hierarchical acidic catalyst
Published in Petroleum Science and Technology, 2019
Mohammad Ghashghaee, Samira Shirvani, Mehdi Ghambarian, Ali Eidi
The thermo-catalytic upgrading process was implemented at atmospheric conditions. In the first (pretreatment) step, the applied FO was thermally cracked in the liquid phase; about 50 g of FO was heated from room temperature to 440 °C with the heating rate of 7 °C/min and remained at this temperature for a certain time. Prior to the thermal pretreatment, all sealed connections and the reactor chamber were purged by pure nitrogen. At certain intervals, the gaseous products were collected and analyzed by a gas chromatograph (GC) equipped with FID and TCD. Then, the reactor was cooled down to room temperature and the obtained liquid products (CO) were introduced as an upgraded feedstock into the subsequent vapor-phase reactions in a microactivity test (MAT) unit, shown in Figure 1. About 1.5 g of pelletized (0.3-1 mm) GNM-2 was loaded at the center of a plug flow reactor located in a tubular furnace. The catalyst was activated in air with the flow rate of 70 mL/min at 600 °C followed by reducing the bed temperature to 550 °C in nitrogen with the same flow rate. At this temperature, CO was injected using a diffusion pump (0.5 mL/min) and the liquid and gaseous products were analyzed. The same catalytic procedure was also adopted with FO as a heavy feedstock.