On the reactivity of organic solvents on the particle surface of metal pigment
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On the reactivity of organic solvents on the particle surface of metal pigment Kazushi Ohshima Central Research Institute, Mitsui Toatsu Chemicals Inc., 1190 Kasama-Cho, Sakae-Ku, Yokohama 247, Japan (Received 21 March 1997; accepted 13 May 1997)
For very fine, acicular particles of a –Fe prepared for audio/video magnetic recording media, the relationship between their chemical property and surface flatness of the tape material made from the particles was investigated experimentally. It was found that adsorption capacity of acidic resin on the particle surface can be a very good index to predict the flatness of the magnetic tape. Because this index depends strongly on the acidic and basic properties of the particle surface, the tape performance can be well controlled by chemically designing the particle surface of a –Fe. I. INTRODUCTION As is well known, the recording performance of the magnetic media depends strongly on the magnetic and mechanical properties of the media. The magnetic property of the media affects frequency dependence of the output level: For examples, large residual magnetization reveals the high maximum output level at low frequencies, whereas coercivity is one of the factors that affects the output performance at high frequencies. Magnetic inhomogeneity can be one of the noise sources. Therefore, the physical property of the magnetic particles useful for the media has been investigated experimentally and theoretically with relation to morphology and packing characteristics of the particles. In the case of the very fine acicular particles of a –Fe prepared industrially, we show that (a) the magnetization reversal of the particles is closely related with morphology whose typical TEM (Transmission Electron Microscope) image is given in Photo 1 and packing behavior and (b) the unavoidably created intraparticle pores and local aggregates among the particles can induce noise sources.1 On the other hand, it is also a well-known fact that flatness of the recording media affects dominantly the saturation output level at high frequencies. Recent highclass grade of the media has the flatness of 10 nm order (or less) as is indicated by the TEM image of the cross section and by the SEM (Scanning Electron Microscope) image of the surface top shown in Photo 2. Therefore, to investigate what is a most important factor to determine the media flatness can provide a key technology to develop the high-density magnetic recording media. At the present time, high-end magnetic material for the high-density recording media is metal pigment that is made from very fine acicular particles of a – Fe. Because (1) the particles of a –Fe are industrially prepared via dehydration, calcination, and hydrogen reduction of almost the same dimensional particles of goethite whose surface is modified chemically by Si- and/or Al-hydroxides to avoid “sintering” among the particles via the calcination/reduction process, and (2) these metal particles are usually well stabilized in a dried sta
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