Corrosion Behavior of Sliding Materials in NH3-H2O Solutions at High Temperature

To investigate the shaft seal for NH3-H2O binary vapor turbines, first of all, immersion tests of several sliding materials were carried out in a static NH3-H2O mixture (NH3 concentration: 30wt%) for 100h under the condition of maximum temperature at 450°C. The test materials were selected from the sliding materials commonly used as mechanical seal rings, such as SiC ceramics, Al2O3 ceramics, hard metals and carbon materials. (1) SiC specimens prepared with B (boron) and C (carbon) as sintering additives under the pressureless sintering process were confirmed to be most preferable. On the other hand, pressureless sintered SiC with Al2O3 additive and reaction bonded SiC indicated worse anti-corrosive resistivity. The Al2O3 additive in the pressureless sintered SiC and the excess metallic Si in the reaction bonded SiC were the most corrosive parts in the structure of SiC ceramics. (2) Al2O3 were recognized as anti-corrosive materials. (3) Hard metals were corroded easily. (4) The resin was corroded selectively in resin impregnated carbon material. Non-impregnated carbon material was hardly corroded. (5) These materials, with better anti-corrosive properties, can be used for the mechanical seal of NH3-H2O binary vapor turbines, although the increase in the surface roughness and the reduction of the bending strength were observed slightly.