Composition and stability of iron powders prepared by a borohydride process

Abstract

Iron powders have been produced by the reduction of ferrous ion with borohydride and stabilized by a chromating procedure. The saturation moments is 140 to 160 emu/g. The coercivity can be controlled between 375 and 1150 Oe. Remanence is 0.45 to 0.5 for unoriented powders. The powders are fibers up to 3 μm long and 1000 Å wide consisting of agglomerated spherical crystallites 300 to 450 Å in diameter. Chemical analyses show that typical powders contain about 82–85% Fe, 2–3% B, 3% Cr, 5–6% O, and 0.2% H. The moment indicates that only 70% is metallic iron. Measurements up to 100 KG show no superparamagnetic fraction. Fe(OH)2 and FeOOH were identified by electron diffraction in some but not all the preparations. Chromating may result in the removal of some non-magnetic by-products. Following the chromating treatment, water is removed with methanol. Solvent-wet powder containing less than 0.1% water can be stored at least 3 months without loss in moment. Cured films of dispersions in a typical epoxy-type binder lose moment in an accelerated atmosphere test containing SO2 and NO2 at a rate indicating a lifetime of 10 years in a worst-case indoor ambient.

A study of Fe-B and Fe-Co-B alloy particles produced by reduction with borohydride

“…Mossbauer spectra of the passivated samples showed less than 5% iron in oxides. In fact, elemental analysis of the alloys accounted for 96 to 100% of the mass, in contrast to the results of other authors who reported up to 40 at.% oxygen in their samples [3,5,6,7,16].…”

Nanoscaled Metal Borides and Phosphides: Recent Developments and Perspectives

“…Indeed, the intensive work conducted during the 1980s and 1990s on amorphous M–B nanoparticles relies on very similar procedures. Freitag et al followed by Dragieva et al showed by TEM that the as-obtained powders were made of spheres of 50–100 nm diameter . These studies were completed by nitrogen sorption experiments .…”

Morphological and Mechanical Properties of Poly (Vinyl Alcohol) Doped with Inorganic Fillers

“…After the removal of water, the polymer chains come closer to each other and chain entanglement reduces the mobility of metal ions, which are now linked to hydroxyl groups of polymer backbone [29]. The borohydride reduces the metal salts to the metallic state through a combined process of hydrolysis and reduction [30]. Conversion of salts to nanosized metallic form was realized by change in color, as mentioned under synthesis.…”