The development of magnetic particles with high coercivity has been required for higher density recording. In the history of magnetic particles, there have been several remarkable inventions produced almost every ten years, i.e., acicular 7-Fe203, Cr02, Co-adsorbed 7-Fe203, and metal particles, etc. Respective features and prospects are outlined. The size of 7-Fe203 is decreasing now to lower both audio and video noise. The appearance of Cr02 and the succeeding Co-adsorbed 7-Fe203 particles has brought about the growth of high performance audio and video recording. Metal particles were put to practical use for audio cassettes in 1979, and the Introduction of metal video tapes to the market is expected soon.

No abstract

An improved method for the determination of the orientation distribution function of a powder consisting of preferentially oriented plate-like and needle-like particles was reported. Using this method, the coarse and fine powders of benzamide and α-2-pyrazinecarboxamide were investigated. It was found that the domains (a domain is defined as a collection of particles having the same preferred orientation plane or axis) of preferentially oriented particles exhibit two distinct changes when undergoing grinding of the powder. One change involves a decrease and the other an increase in volume, indicating that the particles in the domain showing the former change transform into those in the domain showing the latter change following grinding. The increase in volume of the domain can be well explained in relation to the existence of molecular layers connected to each other by weak van der Waals force in the crystal.

In order to investigate the effect of cyclic stress change on creep crack propagation, deformation tests on smooth specimens and crack propagation tests on notched specimens of 0.16% carbon steel were carried out at 673 K (400•Ž) under a time-dependent fatigue condition. The crack propagation rate in time-dependent fatigue was much faster than that in static creep. It was owing to the acceleration of creep strain rate in the vicinity of crack tip because the dynamic recovery took place in the compression period. In these tests, the effect of the transition from small scale creep to large scale creep was small. The crack propagation rate had fairly good correlation with the experimentally evaluated creep J-integral range, ƒ¢Jc, which was equivalent

No abstract