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

An UHV dynamic expansion system to study gassing and outgassing of metals under friction in vacuum has been developed. The vacuum chamber of the system has two main parts separated by a wall with a central orifice of nominal conductance of 5.27 l s⁻¹ for N₂ at 300 K. The main part of the system is equipped with a quadrupole mass-spectrometer, ion gauge and the gas line supply. The chamber closer to the pumping systems is also equipped with an ion gauge. The pumping of the system is performed by: (I) a turbomolecular and (II) a cryogenic pump, which can operate either independently or in parallel. 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 indent allows the friction experiments. The sample holder lets to apply a load to 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°C is provided by electron bombardment. The temperature of the sample as well as the electrical resistance between the indent and the sample surface can be measured. The results show that pressure increase caused by the deformation of the sealing bellow of the friction cell, i.e. without friction, is 1.7×10⁻¹¹ 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 pressure is characterised by an oscillating current supported on a continuous current, which is not possible to explain at present time.