Bruno Ferrario

A nonevaporable low temperature activatable getter material

Nonevaporable getters have been widely used for many years in sealed vacuum or controlled atmosphere devices. They are also finding applications in other fields, where specific characteristics are required and tailor‐made getters are requested, in some cases sacrificing speed in favor of lower activation temperatures, or lower operating temperature, while still maintaining an adequate sorption capacity. With these objectives, a decade long research project was undertaken which involved investigation of Zr–V–Fe alloys. The physico‐chemical properties and the gettering characteristics (speed and capacity) of this family of alloys for some main gases usually present in vacuum devices (H2, CO, N2) have therefore been studied in a range of activation temperatures of less than about 700°C. The equilibrium pressure of H2 on these materials has also been studied as a function of concentration and temperature in a range of pressures less than ∠10 Pa. The results obtained, showing the efficiency of this type of all...

Equilibrium pressures of H2 and D2 for different getter materials and the effect of CO impurities

The 84% Zr–16% Al nonevaporable getter alloy has been used for a long time in vacuum technology and, more recently, has been adopted in advanced applications such as fusion technology and particle accelerators. A new getter material consisting of a Zr–V–Fe ternary alloy having interesting characteristics for these applications has also been proposed. Particularly in fusion technology hydrogen and its isotopes must be sorbed in relatively large amounts. Therefore, the equilibrium pressures of H2 and D2 have been investigated for the above mentioned alloys as well as for the more traditional getter material, titanium. A temperature range from 500 to 800 °C at pressures less than about 100 Pa has been covered. Moreover, as the hydrogen isotopes will contain various gaseous impurities, of which carbon monoxide is usually the most important, the effects of this gas on the H2 and D2 equilibrium pressures have also been investigated.

Hydrogen isotope sorption and recovery by a nonevaporable getter combined with a chemical compressor material

Due to the spreading use of hydrogen isotopes in many advanced fields of physics such as nuclear fusion, there is an increasing interest in devices able to sorb, store, and release these gases safely and controllably. In some cases there is also the requirement to purify the gas during the same adsorption–desorption process. A way to obtain this is to use a nonevaporable getter, which is able to sorb H2 isotopes reversibly and permanently sorb active gases, combined with a chemical compressor material (usually U). The present investigation refers particularly to a combination of getter materials with chemical compressors based on La–Ni–Al and Zr–Fe–V alloys. The nonevaporable getter sorbs H2 isotopes in the temperature range of 20–400 °C, at low pressures, and in a second stage, on heating, releases these gases at higher pressures allowing sorption by the chemical compressor at room temperature. Subsequent heating (200–400 °C) of the compressor provides a hydrogen isotope source at a substantially constan...

Gettering in cryogenic applications

Metallic cryogenic Dewars and pipes, used for storage and transportation of cold fluids such as liquid N2 or He, usually have a vacuum jacket as a thermal insulator. In this case, vacuum has to be maintained in a range of 10−1 Pa or lower. Nonevaporable getters are often used for this purpose. They are particularly useful for sorbing H2 which is released by the warmer walls or by the multilayer insulation; H2 is neither cryocondensed by the cold surfaces nor sorbed by the molecular sieves which may be used to physisorb other gaseous species. The working temperature of the getters may range from room temperature down to the cryogenic fluid temperature. The getter material here considered, and which appears to be adequate for these applications, is the Zr–V–Fe nonevaporable getter alloy. Its sorption characteristics (particularly for H2) are studied both at room temperature and in a cryogenic fluid environment. The behavior of a gettered Dewar jacket is finally studied and discussed.

A mathematical model for a tubular reactor performing ethylene oxidation to ethylene oxide by a catalyst deposited on metallic strips

Abstract Catalysts supported on metallic strips may be used advantageously in catalytic processes requiring a severe thermal control, i.e. the catalytic oxidation of ethylene to ethylene oxide. Following the characteristics of such catalysts, reported in two patents, a mathematical model allowing the calculation of the longitudinal temperature of reacting gas and/or the radial temperature of the catalytic module is presented for a tubular plug flow reactor. The pressure drop is also calculated and compared with that of the same reactor filled with traditional spherical pellets. It has been proved that the advantage of catalytic modules, employing metallic strips, are the following: (i) flattening of the longitudinal and radial temperature profiles; (ii) reduction of the pressure drop; (iii) high productivity of ethylene oxide.

Optimized Nonevaporable Getter Cartridges

A matrix method is described for calculating the pumping speed of a cyclindrical gettering surface with pleated strips. The effect of cartridge geometry and sticking probability of the incident gases were calculated using a theoretical model for the gases carbon monoxide, nitrogen, and hydrogen. The results of the computations show that the pumping speed can be increased by decreasing the angle between the strips to an optimum value that depends on the ratio of the thickness of the strip to its width and on the incident gas. A comparison of calculated and experimental values for H2 on Zr–Al agreed to within approximately 20%.

Behavior of sorb–ac wafer pumps in plasma machines

Vacuum pumps used in machines studying plasma physics are exposed to peculiar operating conditions. Especially the auxiliary pumps, such as cryopumps and getter pumps which are used in close proximity to the discharge or in injectors, can be exposed to very severe conditions. These pumps must exhibit very high pumping speeds and capacities, particularly for hydrogen, and must operate over a wide range of pressures. They must also be safe and reliable in use. Finally, their characteristics should not be influenced by energetic particle bombardment, radiation incidence, sputtered material on the sorbing surface, and by the presence of radioactive substances. The behavior of getter pumps based on the use of nonevaporable getter material and on a modular structure, known as sorb–ac wafer pumps, is reviewed and discussed here. The operating conditions and the behavior under radiation, particle bombardment, vacuum breakage accidents, etc. of these pumps meet most of the requirements in nuclear fusion machines a...

Mathematical modelling of gas purification with getter-based purifiers

Abstract The getter-based purification of a helium stream doped with nitrogen has been studied in a bench scale purifier. The absorption of nitrogen by a Zr-V-Fe alloy is the fundamental mechanism of this purification process. The data collected from performing several experiments under different conditions were simulated by a mathematical model.