An UHV system to study gassing and outgassing of metals under friction

An UHV dynamic expansion system to study gassing and outgassing of metals u nder friction in vacuum has been developed. The vacuum chamber of the syste m has two main parts separated by a wall with a central orifice of nominal conductance of 5.271 s(-1) for N-2 at 300 K. The main part of the system is equipped with a quadrupole mass-spectrometer, ion gauge and the gas line s upply. The chamber closer to the pumping systems is also equipped with an i on gauge. The pumping of the system is performed by: (I) a turbomolecular a nd (II) a cryogenic pump, which can operate either independently or in para llel. The ultimate pressure of chambers 1 and 2 are respectively 5.2.10(-11 ) mbar and 1.10(-9) mbar. The friction cell allocated in chamber 2 consists of a sample holder and a linear motion feedthrough with a steel ball inden t allows the friction experiments. The sample holder lets to apply a load t o the sample surface with a normal force in the range of 0,02 N to 0,85 N. Heating of the sample up to 500 degrees C is provided by electron bombardme nt. The temperature of the sample as well as the electrical resistance betw een the indent and the sample surface can be measured. The results show tha t pressure increase caused by the deformation of the sealing bellow of the friction cell, i.e. without friction, is 1.7x10(-11) mbar (0.6% of the base pressure). The outgassing of the sample caused by friction depends on the normal force as well as on the sweep frequency. The behavior of the total p ressure is characterised by an oscillating current supported on a continuou s current, which is not possible to explain at present time. (C) 1998 Elsev ier Science Ltd. All rights reserved.