Friday, January 1, 2010

Napra Spins Molten Materials into Highly Uniform Spherical Metal and Magnetic Nano-Structured Powders for Use in Catalysts, Magnets, Batteries and More


Napra Co ., Ltd. (Tokyo, JP) inventor Shigenobu Sekine has created the means to quickly manufacture nano-structured powders with an extremely small, highly uniform spherical shape and high sphericity.  The process can be used to create nano-metals and nano-alloys composed of any single metals or alloys using a self-assembling procedure.   

The metal powders are produced by an apparatus in which molten metal, alloys or composites are dropped onto a fast-rotating dish shaped disk in an atmosphere containing one or more inert gases and a small amount of oxidizing gas, and the molten metal is dispersed to be tiny droplets for a predetermined time using centrifugal force, within a cooling-reaction gas, and cooled rapidly to form spherical particles. The products are characterized as nanoparticles being 1) substantially crystalline; 2) substantially amorphous; or 3) of controlled porosity. 

The nano-structured powder particles may be used as the starting materials of magnets, catalysts, electrodes, batteries, heat insulators, refractory materials, and sintered metals. For instance, the powders of the rare earth-iron-boron (R--Fe--B) alloy with the nanocomposite structure may be used a starting material for producing a sintered magnet or bonded magnet having excellent magnetic characteristics. The resulting novel nanostructure consists of micro-sized ferromagnetic phase and novel nano-sized nonmagnetic phase providing for the overall novel nanocomposite

The apparatuses, systems and self assembling processes of Sekine’s invention provides for the production of very small, spherical particles having a nano-composite structure which is a particularly important feature for producing high utility, strong,  permanent magnetic powders. Conventional apparatuses and methods "cannot produce a nanocomposite magnetic material at all, and certainly not in the form tiny spherical powders by a self-assembly technique," according to Sekine, in U.S. Patent Application 20090304834 

U.S. Patent Application 20090304834,  FIG. 1 shows a preferred embodiment of the system for making metal powders with a nano-composite structure from molten metals, including the centrifugal granulation apparatus (also described in U.S. Patent 7,547,346, June 16, 2009)



The spinning disk rotates at high speed ranging from 50,000 to 100,000 rpm. Such speeds may be attained  by using an electric motor employing an electromagnetic "bearings" spindle, as commercially available. The diameter of the spinning disk and the rotational speed of the disk both contribute to the centrifugal effect on the dispersed droplets. A measure of this effect is the product of the disk diameter and the rotational speed of the disk. Thus, a 30 mm diameter disk rotating at 50,000 rpm results in 1,500,000 rpm-mm. A 30 mm diameter disk rotating at 100,000 rpm results in 3,000,000 rpm-mm. A 40 mm diameter disk rotating at 50,000 rpm results in 2,000,000 rpm-mm.

Various kinds of the powders of metals, metal oxides, metal nitrides, metal silicides, and their mixed compounds have been used as the crude starting materials to produce such materials as magnets, catalysts, electrodes, batteries, heat insulators, refractory substances, and sintered metals.

However such powders commonly suffer from poor uniformity of composition, shape, granularity and for spherical powders, poor sphericity (degree of roundness). A mechanical pulverization apparatus is capable of producing particles that have fine structure and are composed of more than two types of components. While of possibly uniform composition, such particles are of poor uniformity in size and shape, and of course are not of spherical shape. Moreover, it is difficult to obtain a nanocomposite structure using mechanical pulverization for the production of fine powders.

In contrast to pulverization manufacturing methods, Sekine's fast spinning molten metal system is able to produce extremely small powders with a highly uniform spherical shape, having high sphericity, and composed of metal including single metals and alloys, including nano-composite structures, using a self-assembling procedure.   

U.S. Patent Application 20090304834, FIGS. 2A and 2B show scanning electron microscope (SEM) images of the powder particles (cross section size of about 20 .mu.m diameter) respectively produced according to Napra's system for producing crystalline (nanocomposite) spherical particles (2A)  and conventionally produced metal spherical particles (2B).


The nanocomposite structures provide for a permanent magnet with excellent magnetic properties employing nano-sized, non-magnetic material, which is a rare earth oxide, ROx, R2O3, RO, RO2, such as neodymium oxide or praseodymium oxide, (or MOx where M is a minor metal) that is incorporated at the inside of ferromagnetic grains, such as R--Fe--B, and/or at their grain boundaries.

Usually, Nd is preferably employed as R, and rare earth elements such as Pr is favorably employed. Nd2O3, RO and RO2 are preferably used in the Napra system. The resulting novel nanostructure consists of micro-sized ferromagnetic phase and novel nano-sized nonmagnetic phase providing for the overall novel nanocomposite structure. The aggregate of nano-sized metal components are separated within the particles by layers or discrete nano-sized bodies of metal oxides, metal nitrides, metal silicides, or separated by evacuated spaces, e.g. pores.

Napra's machine is able produce powder of extremely small, highly uniform spherical shape and high sphericity, composed of substantially amorphous or crystalline (e.g., nanocomposites) composition with controlled porosity.


Amorphous spherical nanoparticles  may be composed of almost any metal or metal alloy. Such metals  include: Fe, Ni, Sn, Ti, Cu and Ag with combinations of Ni--Al, Sn--Ag--Cu, B--Fe--Nd (and its variations) and Al--Ni--Co--Fe. More generally, the metals also include the following and includes combinations of them: Ag, Cu, Ni, Al, Ti, V, Nb, Cr, Mo, Mn, Fe, B, Ru, Co, Pd, Pt, Au, Zn, Cd, Ga, In, Ti, Ge, Sn, Pb, Sb, Bi, Ce, Pr and Nd.
 
The high degree of sphericity and high uniformity of spherical shape (high proportion having the same spherical shape) are further shown in the scanning electron microscope (SEM) images of FIG. 6 (176.times. magnification) and FIG. 7 (704.times. magnification).


FIGS. 2A and 2B (Napra’s U.S. Patent  7,547,346) show another scanning electron microscope (SEM) images of the powder particles (cross section size of about 20 .mu.m diameter) respectively produced  (crystalline (nanocomposite) spherical particles) and (conventional metal spherical particles). 





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