Abstract: Very small iron-containing particles that are in the shape of facetted nodules. Such particles can be non-magnetic particles such as delta ferric oxide hydrate particles or magnetic particles such as magnetic iron oxide particles or metallic particles. Magnetic layers containing such magnetic particles combine excellent remanent magnetization with increased output signal level. The facetted nodular particles are prepared in a process in which (a) an aqueous solution of ferrous salt is added to an aqueous solution of alkaline hydroxide while avoiding substantial local excesses of the ferrous salt, and subjecting the ferrous salt solution to reducing conditions before or during its addition to the alkaline hydroxide solution and (b) the ferrous hydroxide particles are oxidized to delta ferric oxide hydrate particles in the presence of an iron complexing agent, for example, pyrogallol, that is capable of selectively forming ferric iron complexes that are soluble in the reaction medium.

Abstract: Magnetic recording elements having at least one magnetic recording layer containing acicular magnetic particles that have magnetocrystalline anisotropy, shape anisotropy which provides a preferred axis of magnetization and a coercivities of at least 450 Oersteds. These particles are dispersed in a binder and form a distribution that imparts an isotropic magnetic response to the magnetic recording layer.A Process for preparing the above magnetic recording elements is also disclosed. According to this process, the aforementioned magnetic particles are dispersed in a liquid medium. The dispersion is formed into a magnetic recording layer while establishing a distribution of particles that has spherically symmetrical magnetic properties (symmetry that is three-dimensional). The layer is then solidified while maintaining this distribution.A magnetic recording method is also disclosed.

Abstract: This disclosure relates to a process for preparing acicular magnetic iron oxide particles by (a) adding an aqueous solution of a ferrous salt to an aqueous solution of a stoichiometric excess of alkaline hydroxide while substantially avoiding local excesses of the ferrous salt, to form an aqueous dispersion of ferrous hydroxide particles, (b) oxidizing these particles to form non-magnetic alpha ferric oxide hydrate particles, and (c) converting the non-magnetic particles to magnetic iron oxide particles by dehydration and reduction or dehydration, reduction and oxidation. The ferrous salt solution is subjected to reducing conditions prior to and/or during the addition to the alkaline hydroxide solution to reduce contaminating ferric ions that are normally present to ferrous ions.

Abstract: A process for preparing acicular gamma ferric oxide (maghemite) crystals exhibiting excellent magnetic recording properties is disclosed. These acicular gamma ferric oxide crystals are new materials and can be used in magnetic media such as magnetic tapes to obtain a low level of white noise without sacrificing other electroacoustic properties. The crystals are basic in character, contain alkali metal ions and have an acicularity ratio of at least 15, often 15 to 40. These crystals are prepared under very carefully controlled reaction conditions, as more fully described in the following specification. In general, however, the process involves (1) reacting ferrous salt with a stoichiometric excess of an alkali hydroxide under non-oxidizing conditions and at a temperature below about 60.degree. C.

Abstract: Cobalt doped, acicular, gamma ferric oxide which exhibits reduced print-through without substantial loss in signal output or recording sensitivity is disclosed. This cobalt doped, acicular, gamma ferric oxide is prepared in the presence of a water soluble, acyclic dicarboxylic acid or its precursor which alters or modifies the usual distribution of the cobalt doping ions in the crystal lattice. The dicarboxylic acid directs the distribution of the cobalt doping ions into the crystal lattice in such a way that the crystals obtained by the process disclosed exhibit an increase of at least 5% in the ratios between the intensities of each of the triplet lines 110, 210 and 211 with respect to the 111 line, as shown upon examination by X-ray diffraction analysis. Typical dicarboxylic acids disclosed are oxalic acid, malonic acid, succinic acid, glutaric acid and maleic acid.