Vacuum Science and Technology (VST), e-chapter 10 Material selection lubrication cleaning working discipline
The selection of materials for application in vacuum must always be preconditioned by their suitability to give a ‘proper’ vacuum. Outgassing, vapour pressure, leak tightness and corrosion resistance, thermal degradation and permeation are important characteristics to be taken in account. Depending on the specific employment of the material, other more general material properties may also play an important role. For metals there is the question of enough mechanical strength (Pressure Equipment Directive PED). In practice, many incidents of collapsing vacuum systems upon first evacuation are known. In the selection of elastomer seals, elasticity and dimensional stability are particularly important features. Under pressure, in particular at elevated temperatures, permanent deformation may occur, which also may result in leakage. In certain circumstances the wear resistance and the flexibility should be taken into account.
The choice of materials can also be determined by a large number of physical circumstances. Magnetic properties, heat conductivity, thermal expansion, electric conduction in metals, electrical and thermal insulation in case of glass, ceramics and synthetics, light transmittance through viewports, light absorption in optical experiments and optical emission properties mat play a role. Depending on the process circumstances chemical material properties must also be considered carefully. Finally, factors such as cost, machinability and deliverability play an important role in addition to vulnerability, reliability and security. Selection criteria for the choice of metals and alloys, glasses, creamics and synthetic materials are reviewed in detail.
For the lubrication of moving parts under vacuum conditions both wet and dry lubricants are available. Motion mechanisms for application in vacuum are initially designed as being intended for use under atmospheric conditions. However, in the choice of a lubricant one must take into account the influence of a vacuum environment.
The section about cleaning procedures is completely revised, adapted to the changed views in this area and more focused on complete vacuum systems.