A dust core includes large particles having an average particle size of 8-15 μm, medium particles having an average particle size of 1-5 μm, and small particles having an average particle size of 300-900 nm when a cross section thereof is observed. An area ratio occupied by the large particles is 50% to 90%, an area ratio occupied by the medium particles is 0% to 30%, and an area ratio occupied by the small particles is 5% to 30%, when a total area ratio occupied by the large particles, the medium particles and the small particles is 100% in the cross section. Vickers hardness (Hv) of the large particles, the medium particles and the small particles is 150-600 respectively. The small particles are alloy powder containing Fe and at least Si or N. The dust core may be included in an inductor element.

A dust core includes large particles having an average particle size of 8-15 μm, medium particles having an average particle size of 1-5 μm, and small particles having an average particle size of 300-900 nm when a cross section thereof is observed. An area ratio occupied by the large particles is 50% to 90%, an area ratio occupied by the medium particles is 0% to 30%, and an area ratio occupied by the small particles is 5% to 30%, when a total area ratio occupied by the large particles, the medium particles and the small particles is 100% in the cross section. Vickers hardness (Hv) of the large particles, the medium particles and the small particles is 150-600 respectively. The small particles are alloy powder containing Fe and at least Si or N. The dust core may be included in an inductor element.

A soft magnetic composite comprising an iron or iron alloy ferromagnetic material coated with an oxide material. An interface between the ferromagnetic material and the layer of oxide contains antiphase domain boundaries. Two processes for producing a soft magnetic composite are also provided. One process includes depositing an oxide layer onto an iron or iron alloy ferromagnetic material by molecular beam epitaxy at a partial oxygen pressure of from 1×10.sup.−5 Torr to 1×10.sup.−7 Torr to form a coated composite. The other process includes milling an iron or iron alloy ferromagnetic material powder and an oxide powder by high-energy milling to form a mixture; compacting the mixture and curing in an inert gas atmosphere at a temperature from 500° C. to 1200° C. to form a soft magnetic composite.

A soft magnetic composite comprising an iron or iron alloy ferromagnetic material coated with an oxide material. An interface between the ferromagnetic material and the layer of oxide contains antiphase domain boundaries. Two processes for producing a soft magnetic composite are also provided. One process includes depositing an oxide layer onto an iron or iron alloy ferromagnetic material by molecular beam epitaxy at a partial oxygen pressure of from 1×10.sup.−5 Torr to 1×10.sup.−7 Torr to form a coated composite. The other process includes milling an iron or iron alloy ferromagnetic material powder and an oxide powder by high-energy milling to form a mixture; compacting the mixture and curing in an inert gas atmosphere at a temperature from 500° C. to 1200° C. to form a soft magnetic composite.

A soft magnetic composite comprising an iron or iron alloy ferromagnetic material coated with an oxide material. An interface between the ferromagnetic material and the layer of oxide contains antiphase domain boundaries. Two processes for producing a soft magnetic composite are also provided. One process includes depositing an oxide layer onto an iron or iron alloy ferromagnetic material by molecular beam epitaxy at a partial oxygen pressure of from 1×10.sup.−5 Torr to 1×10.sup.−7 Torr to form a coated composite. The other process includes milling an iron or iron alloy ferromagnetic material powder and an oxide powder by high-energy milling to form a mixture; compacting the mixture and curing in an inert gas atmosphere at a temperature from 500° C. to 1200° C. to form a soft magnetic composite.

Alloy nanoparticles, and a method for forming the alloy nanoparticles, an alloy nanocatalyst comprising the alloy nanoparticles are provided. The alloy nanoparticles are formed by a method comprising mixing a first metal complex including a first metal and a second metal complex including a second metal to form a multimetal compound and heat-treating the multimetal compound to form an alloy compound. The first metal and the second metal comprise transition metal, the first metal complex comprises a pyridine-based ligand, and a carbon shell containing N is formed on the surface of the alloy compound by the heat treatment.

Alloy nanoparticles, and a method for forming the alloy nanoparticles, an alloy nanocatalyst comprising the alloy nanoparticles are provided. The alloy nanoparticles are formed by a method comprising mixing a first metal complex including a first metal and a second metal complex including a second metal to form a multimetal compound and heat-treating the multimetal compound to form an alloy compound. The first metal and the second metal comprise transition metal, the first metal complex comprises a pyridine-based ligand, and a carbon shell containing N is formed on the surface of the alloy compound by the heat treatment.

Aspects of this disclosure include a method for repairing a component having narrow passage, a three-dimensional printer, and composition for three-dimensional printing. One embodiment of the method may comprise mixing a filler material for three-dimensional printing with a carrier fluid, and applying a controlled electromagnetic field to bias the filler material towards a repair location in a narrow passage of a component. The method may further comprise coating a ferromagnetic material with the filler material to form a microcapsule, wherein the ferromagnetic material is adapted to interact with the controlled electromagnetic field to attract the microcapsule to the repair location. 3D printing techniques may be used to coat the ferromagnetic core with the filler material.

Aspects of this disclosure include a method for repairing a component having narrow passage, a three-dimensional printer, and composition for three-dimensional printing. One embodiment of the method may comprise mixing a filler material for three-dimensional printing with a carrier fluid, and applying a controlled electromagnetic field to bias the filler material towards a repair location in a narrow passage of a component. The method may further comprise coating a ferromagnetic material with the filler material to form a microcapsule, wherein the ferromagnetic material is adapted to interact with the controlled electromagnetic field to attract the microcapsule to the repair location. 3D printing techniques may be used to coat the ferromagnetic core with the filler material.

A method for producing fine copper particles includes producing fine copper particles having a coating film containing cuprous oxide on a surface by heating copper or a copper compound in a reducing flame formed by a burner. The fine copper particles are produced by adjusting a mixing ratio between a combustible gas and a combustion supporting gas which form the reducing flame such that a volume ratio of CO/CO.sub.2 is in a range of 1.5 to 2.4.