Non-ferromagnetic Particles Research Articles

Characteristics of Paramagnetic and Diamagnetic Anisotropy which Induce Magnetic Alignment of Micron-Sized Non-Ferromagnetic Particles

The effect of temperature is discussed on the magnetic-alignment process of micron-sized particles dispersed in a fluid medium, based on the experimental data compiled on various non-ferromagnetic materials having different concentrations of paramagnetic impurity ion. The field-intensity required to achieve alignment decreased with temperature following the relation calculated from the Langevin theory, when the diamagnetic particles were free of paramagnetic ions. The rotational Brownian motion was considered to randomize the direction of the micro-crystals in the theory. The above-mentioned temperature dependence was expected to occur for most of the diamagnetic oxides, since the oxides were expected to posses a finite amount of diamagnetic anisotropy according to a model proposed recently to explain the origin of anisotropy. The decease of temperature caused additional reduction on the field-intensity to achieve alignment, when finite amount of paramagnetic ion was contained in the particle. This was because the paramagnetic anisotropy increased which the reduction of temperature. The doping of paramagnetic ion on non-ferromagnetic materials in the course of processing a material expected to reduce the field intensity to achieve magnetic alignment at room temperature. The above findings, concerned with the reduction of field intensity to achieve magnetic alignment, may increase the possibility of practical applications of the phenomena of magnetic alignment.

Clustering of metal atoms in organic media: V. Production of tailored selectivity in nickel catalysts: Comparisons with Raney nickel

Nickel atoms dispersed in weakly complexing solvents (“solvated nickel atoms”) at low temperatures form small metal particles on warmup. These particles can be almost totally amorphous or in the form of small crystallites, depending on the solvent employed. The particles can be tailored to have high catalytic activity or selectivity in hydrogenation and isomerization reactions and to have unusual magnetic properties. Ferromagnetic or nonferromagnetic particles can be prepared, and these particles are effectively stabilized toward sintering by strongly bound organic fragments of the starting solvent. Catalytic activities of the black powders obtained from various solvents have been studied in some detail and indicate: (1) Ni-pentane is an extremely active hydrogenation catalyst for benzene, 1-butene, 1-heptene, and butadiene, more active than Raney Ni; (2) Ni-toluene is also quite active like Ni-pentane, but is selective for hydrogenation of 1,3-butadiene to 1- and 2-butenes before conversion to butane; and (3) Ni-THF is fairly unreactive as a hydrogenation or olefin isomerization catalyst.

ChemInform Abstract: THE FORMATION OF MANGANESE AND COBALT FERRITES BY THE AIR OXIDATION OF AQUEOUS SUSPENSIONS AND THEIR PROPERTIES

AbstractDurch geeignete Wahl von Temp. (50‐80°C) und Konzentration überschüssiger NaOH lassen sich wäßrige Suspensionen von Fe(OH)2 und entweder Mn(OH)2 oder Co(OH)2 durch Luftoxidation vollständig in die Spinell‐ ferrite MxFe3‐xO4 (M: Mn oder Co) überführen.

The Formation of Manganese and Cobalt Ferrites by the Air Oxidation of Aqueous Suspensions and Their Properties

Abstract Manganese and cobalt ferrites were prepared by the air oxidation of aqueous suspension of Fe(OH)2 and either Mn(OH)2 or Co(OH)2 at 50–80 °C. In alkaline suspensions, all the metal ions are transformed into spinel ferrites, MxFe3−xO4 (M=Mn or Co), by a suitable combination of the oxidation temperature and the concentration of the excess NaOH. Both manganese and cobalt ferrites consist of ferromagnetic particles (ferrite(A)) when x is smaller than 1.3, nonferromagnetic particles (ferrite(B)) when x is larger than 2, and mixtures of the two in the intervening range. The contents of Mn or Co, both in a solid solution of hydroxides, Mx⁄3Fe1−x⁄3(OH)2, and in ferrite, increase with the progress of the formation of the ferrite(A) caused by oxidation. The formation of the ferrite(B) begins when x in the solid solution reaches 2. Each particle in the ferrite(A) is less homogeneous in comparison with that in the ferrite prepared by a solid-state reaction, although with the same composition. The difference in the homogeneity causes the essential difference in magnetic properties.