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Magnetorheological suspension (MRS) dispersing spherical several gm of iron particles in the low vapor pressure of dimethylpolysiloxane has been prepared. Yield stress has been proportional to square of magnetic field intensity and increases as containing larger volume fraction of iron particles and using solvent that is more viscous. The plastic viscosity increased linearly as a function of volume fraction of iron particles. The burst pressure of MRF seal is related on the dispersed iron particle size. The burst pressure is related on the magnetization curve in the MRS dispersing less than several gm of iron particles. On the other hand, the surface tension of solvent influences on the burst pressure in the MRS dispersing more than several gm of iron particles. Also the burst pressure is affected on the seal gap. In the large gap, the burst pressure in stationary condition adds the pressure by the yield stress of MRS. However, in the small gap the burst pressure of rotating condition is almost the same as that of stationary condition because the arranged iron particles cannot be reconstructed in a small gap. The larger viscosity of solvent and volume of iron in MRS increases the burst pressure.

Interests in magnesium alloys increase as eco-material for its lightweight, and many investigations have been carried out on the development of manufacturing processes and alloy development. In 2001, Mg97Zn1Y2 (at%) alloy with a tensile yield strength of 610 MPa and an elongation of more than 5 % has been developed by rapidly solidified powder metallurgy (RS P/M) processing. The developed alloy was characterized by a novel phase with long period stacking ordered (LPSO) structure. Recently, we have investigated new compositions for LPSO RS P/M Mg-Zn-Y-X alloys in order to improve the corrosion resistance of the RS P/M Mg97Zn1Y2 alloy with maintaining the superior mechanical properties. Consequently, we have developed a RS P/M Mg96.7Zn0.85Y2Al0.45 alloy with high strength and high corrosion resistance. The RS P/M Mg96.7Zn0.85Y2Al0.45 alloy contained the LPSO phase and exhibited a tensile strength of 525 MPa, an elongation of 9 % and a fatigue strength of 325 MPa, which were similar to those of the RS P/M Mg97Zn1Y2 alloy. However, the corrosion resistance of the RS P/M Mg96.7Zn0.85Y2Al0.45 alloy was 1.5 times that of the RS P/M Mg97Zn1Y2 alloy. The specific tensile yield strength, the specific fatigue strength and the corrosion resistance of the RS P/M Mg96.7Zn0.85Y2Al0.45 alloy were about 1.7 times, 1.8 times, and twice those of extra-super-duralumin (7075-T6 or 7075-T73), respectively.

I II order to clarifY the illfluence oJ MgO ill pellets and sinters , the allthors measured the physical characteristics such as the I)ermeability resistallce and melting behaviours oJ the samples with different cOlltent oJ MgO in the sqfiening and melting process in blastjimlflce. 111 addition, some investigatiolls were carried out on the milleralogical and chemical behaviours if MgO ill the samples bifore and after reductioll by means qf X-ray micro-analYsis and optical microscolJ,Y. The results obtained were as Jollows " A ccording to the time-pressure drop curves measured at 1 100° to I 300°C with the al)paratus simulated to the softening alld meltillg zone, the f)ressure drop illcreases steeplY to the maximum value, as the wllstite and slag cOlltailled in pellets and sinters melt by heating and flo w into the voids in the packed bed if the samples. Whell the MgO content increased Jrom 0.7 to 1.3% , the maximum I)ressllre drol) decreased Jrom 2 000 to 700 mm Aq/ 10 cm at the redllction degree oJ about 50 %. From the reslilts oJ X-ray microanalysis and ol)tical microscoPJ', MgO proved to be concentrated to the magnetite and Ca-.ferrite in the samples bifore reduction , ond, during redllction, to make a solid solution with wllstite called magnesio-wustite having higher melting point.

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