Glass microballoons (GB) of about 1 mm in diameter were prepared by ultrasonic spray pyrolysis from sodium silicate solution. A silica-rich type of glass microballoons (SB) was prepared by acid treatment of GB. The structural changes of both microballoons with thermal treatment up to 973 K were examined. Both GB and SB showed properties similar to hydrated sodium silicate glass, to some extent. SB was more thermally stable than GB, but the spherical structures of both microballoons were collapsed by heating at 973 K; cristobalite was observed in samples heated at 973 K. The loosely and tightly incorporated water molecules evolved up to 573 K and near 850 K, respectively. The crystallization of cristobalite caused tightly incorporated water molecules to develop. The ultramicropores accessible only to H 2 O molecules in SB gradually decreased by heating and disappeared by heating at 773 K.

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The magnetic properties of alumite magnetic film and its application are investigated. The alumite magnetic film is known to perpendicular magnetic media. The preparation process of alumite magnetic film is controlled to get the maximum energy product. This film was formed on the side of rotary drums, and multipolariy magnetized, then assembled with MR sensor to new precision magnetic t"otat"y encoders. And the properties of magnetic anisotropy, magnetic output dependance on recording wavelength 1 related to magnetised depth were discussed.

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