Tham khảo tài liệu 'tribology - lubricants and lubrication part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 272 Tribology - Lubricants and Lubrication With increasing utilisation of hydrogen it will be necessary to optimize components which are in contact with this medium. If these components contain tribosystems directly exposed to hydrogen they are critical in respect of excess wear because of vanishing protective oxide layers in the presence of a chemically reducing environment. Furthermore liquid lubricants are often not applicable because of purity requirements or very low temperatures in the case of liquid hydrogen. Thus for numerous components in hydrogen technology solid lubrication is the only possible method for reducing friction and wear. Although the tribological behaviour of typical solid lubricants such as graphite DLC and MoS2 has been characterized comprehensively Landsdown 1999 Donnet Erdemir 2004 Gradt et al. 2001 information about their suitability for hydrogen environment is very limited. Therefore based on available literature and own measurements an overview of solid lubricants and other materials for tribosystems in hydrogen environment is given in the following. 2. Tribosystems in hydrogen environment Prominent examples for extremely stressed components in hydrogen environment are turbopumps for cryogenic propellants in rocket engines. They comprise numerous tribosystems such as shaft seals or self-lubricated bearings which have to work in hydrogen environment at low temperatures and high pressures. In the tribo-components of a turbopump various solid lubricants such gold silver silver-copper alloy PTFE graphite and MoS2 or wear resistant coatings as WC Cr Cr2O3 and TiN are applied Nosaka 2011 . The LH2-turbopump of the LE-7 engine for the Japanese H-2 rocket has a flow rate of 510 l s a shaft power of 19 700 kW and a rotational speed of 42 000 rpm. All steel bearings made from AISI 440C with lubrication by PTFE transfer from the retainer to the raceways showed sufficient performance. These bearings were operated at 50 000 rpm without severe wear
