Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Reexamination Certificate
2002-05-29
2004-12-07
Mai, Ngoclan T. (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
Reexamination Certificate
active
06827757
ABSTRACT:
BACKGROUND
1. Field of the Invention
This invention relates to a magnetite-iron based composite powder, a magnetite-iron based composite powder mixture and a method for producing the magnetite-iron based composite powder mixture. The invention also relates to a method for remedying polluted soil, water or gases with the aid of the reducing activity of the magnetite-iron based composite powder and to an electromagnetic wave absorber and other magnetic material using the magnetism of the magnetite-iron based composite powder.
2. Description of the Related Art
Iron powders are used as materials for powder metallurgy for fabricating mechanical parts and magnetic parts such as magnetic powder cores and electromagnetic wave absorbers. In addition, iron powder is used as a powder in catalysts, food additives, antioxidants and carriers for copier toner and for remedying soil and other media. Conventional techniques and problems thereof will be illustrated below specifically regarding methods for remedying soil and other media using a fine iron powder as a reducing agent and electromagnetic wave absorbers using the magnetic properties of the iron powder.
Remediation of Soil and Other Media Using Iron Powder
Methods for remedying soil or groundwater polluted by an organic halogen compound can roughly be classified as (1) a method in which polluted soil or groundwater is decomposed in situ (an in situ decomposition method), (2) a method for treating gases in the polluted soil or polluted groundwater after pumping from the ground (treatment after in situ extraction), and (3) a method for treating the polluted soil after excavation (excavation treatment).
Methods using an iron powder as a reducing agent for decontamination of harmful organic halogen compounds by dehalogenation have been proposed. For example, PCT Japanese Translation Patent Publication No. 5-501520 and Japanese Unexamined Patent Application Publications No. 10-263522 each propose a method for remedying soil and soil moisture by forming a dispersed iron powder layer in the soil followed by bringing groundwater into contact with the layer to thereby decompose organic halogen compounds. Japanese Unexamined Patent Application Publication No. 11-235577 also proposes a method for remedying soil by adding iron powder to and mixing with the soil (excavated or not) to thereby decompose organic chlorine compounds.
The iron powder used in the former method (PCT Japanese Translation Patent Publication No. 5-501520 and Japanese Unexamined Patent Application Publications No. 10-263522) is, for example, scrap iron produced in the cutting process of iron. It is hard to control the composition and structure of the iron powder to be suitable as a reducing agent for organic halogen compounds. As a result, the iron powder exhibits insufficient effects. In addition, the former two publications mention that iron oxides are formed on the surfaces of iron particles by reaction with oxygen in the soil to thereby deteriorate reduction power of the iron powder. As a countermeasure to this problem, the publications also propose deoxygenation of soil in the vicinity of the iron powder by allowing a reducing substance to disperse in the soil. This means that the iron powder used in this method does not have sufficient durability in its reduction power.
The latter method (Japanese Unexamined Patent Application Publication No. 11-235577) proposes an iron powder containing equal to or more than 0.1% by weight of carbon and having a specific surface area of equal to or more than 500 cm
2
/g. This iron powder comprises sponge like particles having a pearlite texture as a structure with a particle size distribution that allows equal to or more than 50% by weight of the total powder to pass through a 150 &mgr;m sieve. However, even this configuration may not effectively dehalogenate such organic halogen compounds.
Japanese Unexamined Patent Application Publication No. 12-80401 proposes an iron powder containing 0.020 to 0.5% by weight of phosphorus, sulfur or boron as iron powder that can effectively remove phosphor compounds in drainage. The iron powder contains specific trace elements and the objective effect thereof is to accelerate decontamination of phosphor in the drainage by increasing the dissolving speed of the iron into the drainage. Specifically, according to the mechanism of the aforementioned iron powder, a compound which hardly dissolves and has a low solubility product constant, such as iron phosphate, is formed between the dissolved iron and phosphor in the drainage to remove phosphor from the drainage by precipitation. This technology is fundamentally different from the technology for reductive decomposition of harmful substances on the surface of iron according to this invention.
Japanese Unexamined Patent Application Publication No. 2000-5740 proposes an iron powder containing 0.1 to 10% by weight of copper as an iron powder that can efficiently remove organic chlorine compounds from soil and/or groundwater. However, copper itself is a harmful metal with a danger of causing secondary pollution.
In addition, all of the aforementioned iron powders mainly contain iron having a valency of zero (Fe
0
) and thereby exhibit insufficient decomposition power for organic halogen compounds.
An iron powder having an average primary particle size of less than 1 &mgr;m has not been readily available, and those having a large average primary particle size of about 80 &mgr;m have been used for the above application. However, such iron powders having a large particle size cannot sufficiently be dispersed into the soil or groundwater, have a small specific surface area and thereby cannot sufficiently decompose the organic halogen compounds with efficiency. Even if such fine iron powder particles can be obtained, their reduction power may be rapidly consumed.
Application of Iron Powder to Magnetic Materials
A carbonyl ion powder obtained by reduction of carbonyl iron, and an acicular iron powder obtained by reduction of goethite iron (acicular iron oxide) are widely used as magnetic materials for use in electronic equipment and communication equipment. However, a demand has been made on magnetic materials that can exhibit their functions in the high frequency regions as a result of recent advances in electronic and communication equipment.
The carbonyl iron powder comprises relatively large particles with a particle size of about several micrometers and its permeability decreases with increasing frequency. The carbonyl iron powder cannot, therefore, be used in a noise filter or an electromagnetic wave absorber in the high frequency regions with a frequency on the order of gigahertz (Ghz).
The acicular iron powder comprises relatively small particles with a particle size of about 0.1 &mgr;m, but such constitutive small particles easily aggregate to thereby form an aggregate having a relatively large particle size. Accordingly, the acicular iron powder is also limited in its application as in the carbonyl iron powder.
In addition, the material carbonyl iron and goethite iron cannot stably be manufactured in a high volume and are expensive, thereby causing increased manufacturing costs.
As such an electromagnetic wave absorber for use in the high frequency regions on the order of gigahertz, a sheet prepared by molding a mixture of a flat powder and a resin is used (e.g., Yasuo Hashimoto: “Ceramics” vol. 35, No. 10 (2000), p. 857-862). The flat powder used herein is prepared by processing a Fe—Si alloy powder, sendust powder or stainless steel powder into a flat powder. However, such flat powders require expensive material powder and expensive treatments for pressing the material powders, thereby causing increased manufacturing costs of the product electromagnetic wave absorber.
Japanese Unexamined Patent Application Publication No. 1-136910 proposes a method of manufacturing a reduced iron including fewer impurities and oxide films by reducing an iron oxide obtained from a pickling device for hoop steel. However, fine particles of the resulting pure iron with a
Nakamaru Hiroki
Nakamura Yukiko
Ozaki Yukiko
Saito Shingo
Takajo Sawae
JFE Steel Corporation
Mai Ngoclan T.
Piper Rudnick LLP
Takajo Sawae
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