Process for reducing hexavalent chromium in oxidic solids, which comprises the steps: a) heating of the oxidic solid containing Cr(VI) to a temperature of from 600 to 1400 C. in an atmosphere containing less than 0.1% by volume of an oxidizing gas and b) cooling of the reaction product obtained after step a) to a temperature below 100 C. in an atmosphere containing less than 0.1% by volume of an oxidizing gas,
characterized in that no reducing agent is added to the oxidic solid or to the atmosphere in step a) and b) in the process.

Disclosed are a passivation layer (200), a preparation method therefor and an application thereof. The passivation layer (200) comprises a first passivation layer (210), the first passivation layer (210) being disposed adjacent to a secondary battery negative electrode plate (100) and having ionic conductivity and a thickness of 0.1-10 nm. The passivation layer (200) also comprises a second passivation layer (220), the second passivation layer (210) being disposed at a side surface of the first passivation layer (210) distant from the negative electrode plate (100) of the secondary battery, comprising a corrosion-resistant material and having a thickness of 0.1-5 nm. The passivation layer (200) has the effect of increasing safety performance and cycle performance of a secondary battery. The preparation method is simple and has high applicability. Furthermore, the obtained passivation layer (200) can be applied in multiple types of batteries and multiple fields.

A powder mixture of a magnetoplumbite-type hexagonal ferrite is a mixture of powders of two or more kinds of compounds represented by Formula (1), the two or more kinds of compounds represented by Formula (1) are two or more kinds of compounds having different values of x in Formula (1), and are a powder mixture satisfying a relationship of x.sub.max?x.sub.min?0.2, in a case where a maximum value of x is defined as x.sub.max and a minimum value of x is defined as x.sub.min, in two or more kinds of compounds having different values of x in Formula (1), and the application. In Formula (1), A represents at least one metal element selected from the group consisting of Sr, Ba, Ca, and Pb, and x satisfies 1.5?x?8.0.
AFe.sub.(12-x)Al.sub.xO.sub.19Formula (1)

A magnetoplumbite-type hexagonal ferrite powder containing a powder of a magnetoplumbite-type hexagonal ferrite represented by Formula (1) and a powder of a compound represented by Formula (2), in which a magnetic field strength H, which corresponds to 90% of a magnetization quantity obtained in a case where an external magnetic field of 50 kOe is applied, satisfies 19 kOeH28 kOe, a radio wave absorber, and a method of controlling resonance frequency of a magnetoplumbite-type hexagonal ferrite powder are provided. In Formula (1), A represents at least one metal element selected from the group consisting of Sr, Ba, Ca, and Pb, and x satisfies 1.5x8.0. In Formula (2), A.sup.a represents at least one metal element selected from the group consisting of Sr, Ba, Ca, and Pb.
AFe.sub.(12-x)Al.sub.xO.sub.19Formula (1)
A.sup.aAl.sub.2O.sub.4Formula (2)

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.

There is provided a radio wave absorber including a magnetic powder and a binder, in which a volume filling rate of the magnetic powder in the radio wave absorber is 35% by volume or less, and a volume filling rate of a carbon component in the radio wave absorber is 0% by volume or more and 2.0% by volume or less.

The powder of the magnetoplumbite-type hexagonal ferrite is an aggregate of particles of a compound represented by Formula (1), and, in a particle size distribution based on number measured by a laser diffraction scattering method, in a case where a mode value is defined as a mode diameter, a diameter at a cumulative percentage of 10% is defined as D10 and a diameter at a cumulative percentage of 90% is defined as D90, the mode diameter is equal to or greater than 5 m and less than 10 m and an expression of (D90D10)/mode diameter3.0 is satisfied. In Formula (1), A represents at least one metal element selected from the group consisting of Sr, Ba, Ca, and Pb, and x satisfies 1.5x8.0.
AFe.sub.(12-x)Al.sub.xO.sub.19Formula(1)

A lithium-supplementing material, a preparation method therefor, and application thereof are provided. The lithium-supplementing material is applied to a cathode plate and a cell. A chemical formula of the lithium-supplementing material is Li.sub.x-naA.sub.aM.sub.yO.sub.z, where A is selected from other metal elements except lithium (Li), M is selected from at least one transition metal element, and 1<x8, y>0, 0<z<6, 1n4, 0<a2.

There is provided a radio wave absorbing composition containing a magnetic powder and a binder. There is also provided a radio wave absorber containing a magnetic powder and a binder. The magnetic powder is a powder of a substitution-type hexagonal ferrite subjected to surface treatment with a surface treatment agent, and the binder is a polyamide.

A cathode lithium-supplementing material and preparation method and application thereof are provided. The cathode lithium-supplementing material includes the cathode lithium-supplementing material includes a lithium-containing core and a coating layer coated on a surface of the lithium-containing core, the material of the coating layer is selected from a semi-finished carbon layer containing hydroxyls. The provided coating layer, on the one hand, plays a role in isolating harmful components such as water and carbon dioxide in the air, thereby effectively ensuring the stability of the lithium-rich material contained in the cathode composite material layer; on the other hand, the coating layer is the semi-finished carbon layer containing hydroxyls, which has a partial conductivity function and can improve the conductivity of the cathode lithium-supplementing material; moreover, the semi-finished carbon layer containing hydroxyls has high toughness, which is conducive to completely coating the lithium-containing core, ensures the effect of isolating the cathode lithium supplementing material from water vapor during storage, thereby having stable performance and being beneficial for the widespread application.