Vacuum Stage Research Articles

Fundamental studies of the sampling process in an inductively coupled plasma-mass spectrometer Part IV.-Replacement of the inductively coupled plasma with a helium microwave-induced plasma

A fundamental investigation was performed to assess the feasibility of replacing the argon source in an inductively coupled plasma mass spectrometer (ICP-MS) with a helium plasma source. For this study an argon ICP-MS interface was modified to sample a helium plasma. However, despite efforts to increase pumping efficiency in the mass spectrometer first stage, the conventional ICP-MS interface could not be reconfigured for optimal skimming of the first-stage free-jet expansion as gas dynamic theory advocates. Moreover, coulombic forces produced by ion-beam space charge after the skimmer cone were found to influence ion movement more strongly than gas-kinetic forces. These conclusions were based on kinetic energies measured across the mass range for ions as they exited the first vacuum stage of the interface. Because of the importance of these coulombic forces on ion movement, gas-kinetic factors need not be a primary consideration in skimming a helium free-jet expansion.

Two‐stage vacuum pumps for high working pressures and high water vapor tolerances

Two stage rotary vane pumps have to be lubricated in the high vacuum stage with a small amount of degassed oil to reach good ultimate pressure. In industrial applications occurs the demand for long time high working pressure besides the good ultimate pressure of the two stage pump. Under this condition more lubrication may increase the pump performance. Means for the adaptation of the lubrication to the working conditions of the pump will be described. To avoid harmful contamination of the rotor bearings out of the process they have to be lubricated separately. The problems of the realization of the separate lubrication in a two stage rotary vane pump are described and a possible solution is given. The high water vapor tolerance of a two stage rotary vane pump is managed by the use of gas ballast. A graduated system will be described, that enables the user to adapt the water vapor tolerance to the working conditions.

Low-load metal seals to replace elastomer O-rings: the Helicoflex-delta (Δ) seals

The sealing principle of the new Helicoflex delta type is based upon a new concept which putts the metal seals at the same compression load level as standard elastomer O-rings. They are designed in such a way that they can be installed as replacements for existing elastomer O-rings, which means the possibility of using the same flange and bolting configurations. The sealing level which can be reached is at ultra-high vacuum stage, i.e. 10 −10 atm cm 3 s −1, for temperatures ranging from cryogenic to high (no bake-out limitation). Specific test programs have been completed by CEA (the french Commissariat à l'Energie Atomique), especially regarding seal performance vs temperature, pressure, and cryogenic conditions. Complete test results are available for seals up to 300 mm diameter having performed at 10 −10 atm cm 3 s −1 under temperature cycles of 350° amplitude. The most significant high-tech applications are: linear particle accelerators; fusion reactors (JET, TORE SUPRA, etc.); Space industry (ARIANE Projects); and the gaseous diffusion enrichment process (EURODIF).

Chemistry of Isolated Transition Metal Clusters

Clusters containing two to several hundred atoms are generated by pulsed laser vaporization of a metal target located in a flow tube reactor. A continuous flow of inert carrier gas entrains and cools the vaporized plume of metal, resulting in rapid cluster growth. Reactant gases are injected into the flow downstream of the target, at a point where cluster growth has finished. After reagent mixing and chemical reactions occur, the products exit the tube into a vacuum, and are formed into a molecular beam by collimators located in successive stages of differential pumping. In the highest vacuum stage the reaction products are identified by pulsed laser ionization and time-of-flight mass spectrometry. Studies to be discussed include measurements of absolute reaction rate constants, hydrogen uptake experiments, laser-induced desorption of adsorbates from clusters, and cluster-catalyzed chemical reactions. Such work provides us with information about the dependence of reactivity on cluster size, the geometrical configuration of cluster binding sites, the thermodynamics of adsorbate bonding, and the mechanisms of chemical reactions of cluster surfaces. These studies are bringing us closer to a detailed understanding of the interactions of metal surfaces with atoms and simple molecules.

Boltzmann and Vlasov kinetic equations in anisotropic cosmological models

The structure of the Boltzmann and Vlasov Kinetic equations is considered for spatially uniform cosmological models taking into account the Einstein equations. A successive approximation technique is proposed for solving Boltzmann's equation at the intensely anisotropic vacuum stage of expansion for the type I Bianci cosmological model. It is shown that during the hadron stage the collisional gas can be found in a highly nonequilibrium state.

A 252Cf fission fragment-induced desorption mass spectrometer: Design, operation and performance

This time-of-flight mass spectrometer utilizes the 252Cf fission fragment-induced ionization of organic solids and electrostatic desorption. It is designed for the high sensitivity needed in the quantitative analysis of pharmaceuticals and can be combined with a high-performance liquid chromatograph. The solute emerges into a rough vacuum stage sampling up to twelve fractions in a vacuum-drying process. Samples with low vapor pressure are introduced periodically into the ion source by means of an interfacing disk and analysed successively. The sensitivity of ion detection employing conversion electrons and microchannel plates is investigated. The performance of the mass spectrometer is discussed in terms of mass resolution, efficiency and reproducibility.

Combined liquid chromatography time‐of‐flight mass spectrometry: An application of 252Cf fission fragment induced desorption mass spectrometry

AbstractA 252Cf fission fragment induced desorption mass spectrometer has been coupled on‐line to a high‐performance liquid chromatograph. The polar effluent (MeOHH2O) is introduced directly into a rough vacuum stage, where a thin sample of non‐volatile compounds is collected in a vacuum‐drying process (<1 cm3 min−1). The interface which spans the difference in operating pressure between the collection site and the ion source consists basically of a sample changing disk. Twelve discrete samples are collected consecutively and analysed, typically one per minute. The system has been tested for the quantitative analysis of some antitumor drugs in serum using homologous compounds as internal standards.

Synthesis and polymerization of novel formamidinium salts: A new pathway to polyamides derived from aromatic diamines

AbstractA new polycondensation pathway has been developed for the preparation of polyamides at high temperatures. p‐Phenylenediamine was converted to N,N‐p‐phenylene bis(N′,N′‐dimethylformamidine) (I), which formed 1–1 and 2–1 salts with terephthalic and adipic acids, respectively: magnified imageDicarboxylate salts were polymerizable by heating in bulk or suspension. Low‐molecular‐weight poly(p‐phenyleneterephthalamide) was obtained from N,N‐p‐phenylene bis(N',N'‐dimethylformamidinium) terephthalate above 225°C. The low degree of polymerization was due to terephthalic acid sublimation as well as to the well‐known intractability of poly(p‐phenyleneterephthalamide). High‐viscosity poly(p‐phenyleneadipamide) was obtained from N,N‐p‐phenylene bis(N′,N′‐dimethylformamidinum hydrogen adipate) above 200°C. Both salts liberated dimethylformamide (DMF) during polymerization. The adipate salt also released 1 mole of adipic acid during the high‐temperature vacuum stage of polymerization. A polycondensation mechanism was proposed for each salt, based on thermal gravimetric analysis (TGA‐MS) and infrared (IR) analyses.The hydrolysis of N,N‐p‐phenylene bis(N',N'‐dimethylformamidine), N,N‐p‐phenylene bis(N',N'‐dimethylformamidinium chloride), and the two dicarboxylate salts of (I) was monitored by nuclear magnetic resonance (NMR) at room temperature. The dihydrochloride salt was most resistant to hydrolysis (kH 6.9 × 10−9 sec−1; relative rate 1.0) followed by (I) 7.1, terephthalate salt, 14.9, and adipate salt, 27.2. Both dicarboxylate salts possessed sufficient hydrolytic stability for use as polycondensation monomers

A Scanning Electron Microscope Investigation of Statically Loaded Foundation Materials

Selected rock samples were tested to failure in bending, tension, and compression within the vacuum stage of a scanning electron microscope. The loads were applied very slowly so that crack initiation and growth could be observed visually and be recorded by both photography and video tape. The cracked surfaces of the failed specimens were further evaluated by more standard methods; two evaluation techniques were used to determine the failure mechanisms for each test mode and each rock type. Primary and secondary failure mechanisms were determined for selected rocks in each of the three failure modes.

Mechanism of austenite grain growth in structural steels

1. The use of high-temperature metallography and a vacuum stage makes it possible to reveal different mechanisms of austenite grain growth in carbon and alloy structural steels. 2. It was found that austenite grain growth occurs at 850–1250° by three different mechanisms: I) resorption of grains; II) formation of new boundaries and grains; III) boundary migration. The first and second mechanisms are accompanied by decomposition of old boundaries and the third is characterized by movement of the boundaries. 3. Resorption of grains predominates at temperatures 50–100° above Ac3, and the formation of new more even boundaries at temperatures 250–300° above Ac3. Boundary migration occurs at all temperatures but affects grain growth only above 1100°. 4. The resorption of grains evidently depends on rebuilding of dislocation arrays, and the formation of new grain boundaries on rebuilding of dislocation arrays and movement of atoms. The process of boundary migration may be determined by the movement of dislocation groups and collective diffusional movements of atoms.

452. High vacuum system with cryogenic pumping at forevacuum and high vacuum stages: B G Lazarev et al, Probl Atomic Sci Technol, Coll, Kharkov 1971, 109–111 ( in Russian).

452. High vacuum system with cryogenic pumping at forevacuum and high vacuum stages: B G Lazarev et al, Probl Atomic Sci Technol, Coll, Kharkov 1971, 109–111 ( in Russian).

The Design of Rotary Pumps and Systems to Provide Clean Vacua

The oil sealed rotary pump is the most common component used in vacuum systems but such pumps when charged with mineral oil can be a major source of organic backstreaming. Work in our laboratory has been concerned with studying (i) the mechanisms by which volatile organic material is formed within and released from working pumps and (ii) backstreaming under conditions where gaseous diffusion, gas flow and pipeline conductance can determine its flow rate into the vessel. Arising from these studies has been the possibility of showing that backstreaming can be reduced to negligible levels by the use of adsorption traps to eliminate oil molecules from the vacuum atmosphere. Unfortunately, such traps may impair the ultimate vacuum achieved by also trapping water vapor. This can be overcome by using a trapped oil sealed pump to back a dry vacuum stage. The dry stage can be of the blower type (out-of-contact). Higher compression ratios are possible with in-contact vane pumps which depend on use of materials with a low coefficient of friction and a pump is herewith described. In the conclusion, some of the characteristics of an alternative lubricating fluid (fluorocarbon) are described.

Dynamic sealing of continuous electric vacuum furnaces

1. Continuous vacuum heat treatment of metal strip can be recommended in apparatus in which only the technological process occurs in vacuum, while unwinding and rewinding occur in the atmosphere. 2. It was shown that it is possible to use equations of the conducting capacity of slotted channels with laminar and transition flow conditions for qpproximate calculations of the gas flow in different vacuum stages.

Flight Mechanics of Ascending Satellite Vehicles

The types of satel l ite orbits and types of ascending trajectories to achieve these orbits are discussed. Both analog and digital computor techniques for trajectory c o m p u tations are briefly described. A solution of the o p t i m u m vacuum stage thrust axis pitch program is presented for a satellite using cont inuous thrust all the way from ground to orbit. The procedure is explained for opt imizing the trajectory to min imize propellant consumpt ion for a vehicle using a power-off coast up to the orbit.