Getter films with a reactive component K. Chuntonov a, * , A. Ivanov b , D. Permikin b a Free Space Materials Ltd., 32 Alon St., Karmey Yosef 99797, Israel b Ural State University, Lenin avenue, 51, 620083 Ekaterinburg, Russia article info Article history: Received 28 April 2010 Received in revised form 12 November 2010 Accepted 12 November 2010 Keywords: Lithium or barium alloys Solid solutions Sorption capacity Getter materials abstract Abstract: Numerical solutions for the sorption problem for the films of the solid solutions of the reactive metal under a constant pressure P of the sorbed gas have been found. These solutions depend on the value of the kinetic coefficient H, which is proportional to gas pressure P . According to the found dependence the relative sorption capacity S of the getter film is the larger the smaller is pressure P , and this relation between the values S and P is due to the concentration changes taking place in the getter material during the diffusion of the reactive component to the film surface. The practical importance of the dependence of S on P is obvious: it serves the basis for a new method of increasing the efficiency of the getter materials and increasing the life span of vacuum devices by controlling the value P . Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Highly reactive metals like barium, calcium, strontium or lithium demonstrate perfect sorption properties [1e4] excelling transition metals in sorption capacity at room temperature by orders of magnitude. This is certainly a strong incentive for the development of new getters based on the mentioned metals because sorption capacity is a critical parameter in many getter applications. Alloys are a more convenient initial product for the creation of highly efficient gas sorbents than elemental metals as the reactivity of the alloys can be controlled and the optimal for the sorption process microstructure can be obtained in this case by rather simple means, which directly follow from the character of phase equilibriums in the corresponding metallic systems. However, gas sorption by the alloys with a chemically active component takes place not in the same way as in the case of the well studied tran- sition metals. Therefore experimental studies as well as a theoret- ical analysis of mass transfer processes in the systems of reactive alloy/active gas type are necessary for the general understanding of the sorption phenomena and for the correct employment of the new gas sorbents. In our previous paper [5] we described the behavior of the reactive getter film sealed inside a small chamber with the initial pressure of sorbed gases 1 atm. It came out that for a typical case of the MEMS cavity a getter film with an average concentration of a reactive component is able not only to capture all the initial gases fulfilling in this way the job of a vacuum pump but also to maintain high vacuum in the cavity further for many years. In the present paper we will continue our analysis by researching another variant of the sorption problem when constant negative pressure of an active gas is maintained above the getter, which as often as not occurs in practice. Building up a mathematical model for this kind of processes will facilitate the faster assimilation of the getter materials with a chemically reactive component. 2. Problem statement Let us consider sorption of a certain gas X by a smooth surface of a continuous solid body AMe, where A is a reactive metal of IA or IIA group of the Periodic table and Me is the second metal, which is stable to the gas X. This solid body can be dense films or foils of solid solutions of metal A in metal B or films of intermetallic phases AMe with a noticeable homogeneity field, which can be considered as solid solutions of A in AMe. Solid solutions of Ca in Co, solid solutions of Li or Mg in Ag, etc. can serve as examples of the first ones and such intermediate phases as Ba 2 Pb, Au 9 Ca 10 , Li 2 Zn 3 , etc. [6] can serve as examples of the second ones. Solid solutions of a reactive metal in a more or less stable metallic matrix are singled out into a separate class of getter materials, which react with gases by forming chemical compounds AX growing on AMe surface. The mentioned growth takes place due to the diffusion of the active component A from AMe into the AX layer. So, let a getter film AMe with the thickness L be on the wall of the vacuum chamber (Fig. 1) containing a gas X under a pressure P  1 bar. A layer of a compound AX grows on the surface AMe due * Corresponding author. Tel.: þ972 777571006. E-mail address: konstantin@chuntonov.com (K. Chuntonov). Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum 0042-207X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2010.11.011 Vacuum 85 (2011) 755e760