MATERIALS Research for Advanced Inertial Instrumentation. Task 3. Rare Earth Magnetic Material Technology as Related to Gyro Torquers and Motors.
Technical rept no. 1, 30 Sep 77-30 Jun 78,
CHARLES STARK DRAPER LAB INC CAMBRIDGE MA
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For inertial applications aligned SmCo5 magnets with high flux stability, close-to-zero reversible temperature coefficient of magnetization, and a thermal expansion similar to that of beryllium are required. High flux stability is being attempted by producing high Hcu high resistance to demagnetization and high Hk high second quadrant loop squareness magnets through the attainment of fine grain size, low oxygen content and high density in the material. Low reversible temperature coefficient will be achieved by suitable samarium replacement with a heavier rare earth element while the thermal expansion coefficient will be tailored to that of beryllium by controlling the alignment of the crystals in the magnet. In line with these requirements a magnet sintering facility capable of ultra-high vacuum operation has been fabricated for oxygen-free processing of these magnets. Techniques for producing powder with low oxygen contamination from the environment have also been developed for this purpose. The total amount of oxygen incorporated into the powder is found to be considerably less than what is obtained with conventional procedures. This has resulted in remarkably high values of Hci and Hk in sintered SmCo5 magnets produced so far. AN unprecedented value of 29 kOe has been measured for Hk in a few of the magnets as compared to 5 to 10 kOe found tin most commercial magnets. The energy product values of these magnets have been limited to about 13 mGOe because of poor alignment. Pressure sintering hot isostatic pressing techniques have also been used for densification of powder compacts.
- Electricity and Magnetism