Core-shell particles containing crystalline iron oxide in the core and amorphous silicon dioxide in the shell and in which a) the shell contains from 5 to 40% by weight of silicon dioxide, b) the core contains b1) from 60 to 95% by weight of iron oxide and b2) from 0.5 to 5% by weight of at least one doping component selected from the group consisting of aluminum, calcium, copper, magnesium, silver, titanium, yttrium, zinc, tin and zirconium, c) where the % by weight indicated are based on the core-shell particles and the sum of a) and b) is at least 98% by weight of the core-shell particles, d) the core has lattice plane spacings of 0.20 nm, 0.25 nm and 0.29 nm, in each case+/0.02 nm, determined by means of HR-TEM.

Ferrite powder of the present invention is ferrite powder detectable with a metal detector, comprising: hard ferrite particles containing Sr of 7.8 mass % or more and 9.0 mass % or less and Fe of 61.0 mass % or more and 65.0 mass % or less, wherein an amount of Na to be measured by ion chromatography is 1 ppm or more and 200 ppm or less. It is preferable that a volume average particle diameter of the particles constituting the ferrite powder is 0.1 m or more and 100 m or less. It is preferable that residual magnetization by a VSM measurement when magnetic field of 10 K.Math.1000/4A/m is applied is 25 A.Math.m.sup.2/kg or more and 40 A.Math.m.sup.2/kg or less.

Ferrite powder of the present invention is ferrite powder detectable with a metal detector, comprising: hard ferrite particles containing Sr of 7.8 mass % or more and 9.0 mass % or less and Fe of 61.0 mass % or more and 65.0 mass % or less, wherein an amount of Na to be measured by ion chromatography is 1 ppm or more and 200 ppm or less. It is preferable that a volume average particle diameter of the particles constituting the ferrite powder is 0.1 m or more and 100 m or less. It is preferable that residual magnetization by a VSM measurement when magnetic field of 10 K.Math.1000/4A/m is applied is 25 A.Math.m.sup.2/kg or more and 40 A.Math.m.sup.2/kg or less.

A method for efficiently preparing ferrate based on nascent state interfacial activity. The method is as follows: (a) preparing nascent iron solution; (b) adding an oxidizing agent to the iron solution of step (a); (c) adding alkali solution or alkali particles to the mixed solution of step (b), mixing by stirring, and carrying out solid-liquid separation; (d) adding a stabilizing agent to the liquid separated out in step (c), and thus obtaining ferrate solution. The yield is 78-98%. The prepared ferrate solution is stable and can be stored for 3-15 days.

A process and reactor for arsenic fixation in which a first gas stream comprises oxygen and an iron-containing particulate material. The oxygen and particulate material may be fed to reactor through respective first and second inlets. A second gas stream containing one or more volatile arsenic compounds is fed through a third inlet and mixed with the first gas stream and the particulate material to produce a combined gas stream containing the volatile arsenic compounds and the particulate material. The arsenic compounds are reacted with iron in the particulate material as the combined gas stream flows through the reactor to produce solid iron arsenates which are then recovered. The portion of the reactor including the first, second and third inlets is vertically oriented, and the reactor may include a venturi arrangement having a throat at which the second inlet is located.

A method for modifying a fine particle dispersion liquid has excellent dispersibility and dispersion stability. In this method for modifying a fine particle dispersion liquid having improved fine particle dispersibility, impurities included in an agglomeration of fine particles contained in the fine particle dispersion liquid are released into the dispersion liquid by applying physical energy to the agglomeration and performing dispersion processing for dispersion into particles that are smaller than the agglomeration of fine particles. The impurities are removed from the dispersion liquid by means of a removal unit provided with a filtration membrane before reagglomeration is caused by the impurities.

A method for modifying a fine particle dispersion liquid with which dispersibility and dispersion stability can be improved includes performing filtration to remove impurities in a dispersion liquid using a dispersion liquid modifying device provided with a removal unit that uses a filtration membrane. The quantity of impurities is reduced from a first region until said quantity reaches a second pH-dependent region. In the second pH-dependent region, the dispersibility of the fine particles in the dispersion liquid is in a range in which the dispersibility depends more on a change in dispersion liquid pH than on a change in the quantity of impurities in the dispersion liquid. With the quantity of impurities reduced to the second pH-dependent region, the dispersibility of the fine particles is controlled by adjusting the pH of the fine particle dispersion liquid.

Methods to fabricate tightly packed arrays of nanoparticles are disclosed, without relying on organic ligands or a substrate. In some variations, a method of assembling particles into an array comprises dispersing particles in a liquid solution; introducing a triggerable pH-control substance capable of generating an acid or a base; and triggering the pH-control substance to generate an acid or a base within the liquid solution, thereby titrating the pH. During pH titration, the particle-surface charge magnitude is reduced, causing the particles to assemble into a particle array. Other variations provide a device for assembling particles into particle arrays, comprising a droplet-generating microfluidic region; a first-fluid inlet port; a second-fluid inlet port; a reaction microfluidic region, disposed in fluid communication with the droplet-generating microfluidic region; and a trigger source configured to trigger generation of an acid or a base from at least one pH-control substance contained within the reaction microfluidic region.

The present disclosure provides for compositions of magnetic nanoparticles and methods of making magnetic nano-particles with large magnetic diameters.

Methods, systems, and devices are disclosed for fabricating and implementing optically absorbing coatings. In one aspect, an optically selective coating includes a substrate formed of a solar energy absorbing material, and a nanostructure material formed over the substrate as a coating capable of absorbing solar energy in a selected spectrum and reflecting the solar energy in another selected spectrum. A concentrating solar power (CSP) system includes heat transfer fluids (HTFs); thermal energy storage system (TES); and solar receivers in communication with HTFs and including a light absorbing coating layer based on cobalt oxide nanoparticles.