Wet Air Atmosphere Research Articles

非酸化物セラミックスの高温水蒸気酸化

Nonoxide ceramics of hot-pressed AlN, hot-pressed Si3N4, sintered Si3N4, hot-pressed sialon and hot-pressed B4C were oxidized in wet nitrogen and/or wet air atmosphere at 1.5 to 20kPa of water vapor pressure and in dry air at 900-1400°C. All specimens were oxidized by both dry air and water vapor at high temperatures. AlN formed α-Al2O3 film on the surface above 1150°C. The oxidation rate of AlN increased with increasing water vapor pressure. The oxidation rate of AlN in wet nitrogen was much greater than that in wet air. Si3N4 and sialon formed oxide films consisting of SiO2, Y2Si2O7 and YAlO3. The oxidation kinetics obeyed the usual parabolic law. The oxidation rate in wet nitrogen, however, was unaffected by water vapor pressure and increased with increasing Y2O3 content. The apparent activation energy for the oxidation of Si3N4 based ceramics was about 800kJ/mol. On the other hand, since the oxidation of B4C by water vapor and dry air above 900°C resulted in weight loss, the formation of BO or HBO2 seemed to be the main reaction. The oxidation rate of B4C by water vapor above 900°C could be expressed by the surface chemical reaction controlled kinetics with the apparent activation energy of 200kJ/mol.

High temperature oxidation of hot-pressed aluminium nitride by water vapour

Hot pressed AIN without additives was oxidized et 1100 to 1400°C in dry air, wet air and wet nitrogen gas atmospheres with 1.5 to 20 kPa of water vapour pressure. AIN was oxidized by both air and water vapour, and formed α-Al2O3 film on the surface above 1150°C. The oxidation kinetics in air were parabolic end were promoted by water vapour. On the other hand, the oxidation kinetics in wet nitrogen were linear below 1250°C and parabolic above 1350°C. The oxidation rate in wet nitrogen was much greater than that in wet air. The rate of oxidation increased with increasing temperature until 1350°C, and then decreased. The parabolic rate constant decreased with increasing temperature and increased linearly with increasing water vapour pressure. The linear rate constant at 1150 to 1250° C increased with increasing the temperature with the apparent activation energy of 250 kJ mol−1. The relation between the linear rate constant and water vapour pressure was of the Langmuir type.

Corrosive wear as a failure mode in lubricated gear contacts

Corrosive wear due to oxygen and/or moisture in the air is shown to be a major form of gear failure. Using a Micro-Ryder Gear Tester, it is shown that with diester-based lubricants, damage is worse in air than in a dry inert atmosphere at low loads; at higher loads, damage is more severe in the inert atmosphere. For a highly-refined mineral oil, better performance is shown in an inert atmosphere than in either a room-air or wet-air atmosphere. Based on microscopic examination of damaged gears and surface finish measurements, it is concluded that tooth damage in air is due to corrosive wear while in inert atmosphere, scuffing occurs. Both corrosive wear and scuffing can be controlled by additive treatment. A mechanism is discussed which suggests that continued oxide formation from corrosive wear serves to prevent scuffing under high loads.