JPS58217602A - Treatment of metal powder for preventing oxidation thereof - Google Patents

Abstract

PURPOSE:To easily prevent the oxidation of esp. ferromagnetic metal powder coated with an inorganic macromolecular film, by immersing the metal powder coated with the inorganic macromolecular film in inactive liquid substance held at a temp. lower than that of the metal powder in the atmosphere of inert gas. CONSTITUTION:Metal powder (esp. ferromagnetic iron powder composed of Fe only or the like) coated with an inorganic macromolecular film based on oxides of Si and/or Al is treated by immersing it in liquid substance inactive to said metal powder. As said liquid substance, one or more of substances, e.g. hydrocarbon solvents such as toluene, having a stable property to the property and oxidation of the metal powder and being liquid at an ordinary temp. may be used. By charging and immersing the metal powder coated with the inorganic macromolecular film held at a high temp. in said liquid substance hold at a temp. lower than said high temp. in the atmosphere of inert gas, the oxidation of the metal powder is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION More specifically, the present invention relates to an improved antioxidant treatment method in which ferromagnetic metal powder coated with an inorganic polymer is immersed in an inert organic solvent.

Metal powders are generally extremely susceptible to oxidation in the air, and there is even a risk of ignition due to rapid oxidation. In ferromagnetic metal powders such as nonferromagnetic powder and ferromagnetic alloy iron powder used as recording elements and magnet materials for magnetic recording media such as magnetic tapes and magnetic disks, oxidation causes various problems such as a decrease in saturation magnetization (σ8). This causes rapid deterioration of magnetic properties. One way to prevent metal powder from oxidizing is to immerse the metal powder in an organic solvent such as toluene, xylene, or methyl ethyl ketone to avoid contact with air and store it, but in the case of ferromagnetic metal powder, immersion storage is Among them, a decrease in saturation magnetization (σS) was observed over time, and in order to avoid direct contact between metal powder and air when turning it into paint for manufacturing magnetic tapes, magnetic disks, etc., the work was carried out under air-blocking conditions. must be considered. As a method of forming an oxidation-resistant film on the surface of the metal powder in order to prevent such changes in oxidation over time, the metal powder is immersed in an organic solvent and the solvent is gradually volatilized in dry air to form an oxide film. An air-drying method for forming an oxide film, and a method for forming an oxide film by blowing an oxygen-containing gas into an organic solvent in which metal powder is immersed have been proposed (see Japanese Patent Publication No. 56-28961).

However, these methods do not work well for ferromagnetic metal powders.
The oxidation prevention treatment is performed only when the saturation magnetization (σB) is at a low value, and it cannot be said to be a sufficient method for preventing changes in magnetic properties over time due to oxidation.

The present invention aims to provide an improved method for the anti-oxidation treatment of metal powders, especially ferromagnetic metal powders coated with inorganic polymers.

As a result of intensive research to achieve the above object, the present inventors found that when metal powder coated with an inorganic polymer film is immersed and stored in an organic solvent, changes over time in the physical properties of the metal powder are different from those of the inorganic polymer. The present invention was completed based on the discovery that this is caused by oxidation of the metal powder by oxidizing substances that remain in the gaps between the coating and the small pores in the inorganic polymer coating.

In the present invention, when a metal powder coated with an inorganic polymer film is immersed in a liquid substance that is inert to the metal powder, the metal powder is heated at a temperature lower than that of the metal powder. This is an oxidation prevention treatment method for metal powder, which is characterized by immersing metal powder in a liquid substance in an inert gas atmosphere.

In the present invention, the gold μ powder is a single powder of iron, cobalt, nickel, chromium, zinc, soot, aluminum, etc. or an alloy powder of two or more of them; in particular, ferromagnetic iron powder made of iron alone or iron-based powder. 1 of cobalt, nickel, chromium, zinc, tin, aluminum, etc. as the metal, if desired.
A ferromagnetic alloy powder containing one or more species is important. Also included are metal powders on which an oxidation-resistant film is formed by the above-mentioned air-drying method or the like. Inorganic polymer coatings are mainly composed of inorganic or organic water-soluble silicon and/or aluminum compounds, with or without the addition of alkali metals or alkaline earth metal salts such as phosphoric acid or boric acid. This is an inorganic polymer coating mainly composed of silicon and/or aluminum oxides, which is formed on the surface of the metal powder by coating it on the metal powder and then subjecting it to a heat dehydration treatment. In addition, a liquid substance that is inert to the metal powder refers to a liquid substance that does not alter the quality of the metal powder, does not react with the metal powder to form a compound, or does not form a compound on the surface layer of the metal powder even if it reacts. A solution of a single substance or a mixture of two or more substances, which has properties such as not changing the essential properties of the metal powder and properties that are stable against oxidation and is liquid at room temperature, or a solid substance into the liquid. It is a mixed solution in which substances are dissolved. Many liquid substances with these characteristics are organic compounds, and... l
ld:) Hydrocarbon organic solvents such as toluene, xylene, anisole, and decalin, organic acid esters that are liquid at room temperature, higher alcohols, and organometallic compounds such as alkyl titanates alone or in mixed solutions with organic solvents. Can be mentioned. In particular, a solution with a boiling point of 180°C or higher and difficult to absorb moisture in the air, such as decalin, inoctyphthalate, olive oil, linseed oil, etc., or a mixed solution of these alone or two or more with an organic solvent such as toluene. is preferably used.

In the present invention, a metal powder coated with an inorganic polymer film maintained at a high temperature is immersed in an inert liquid substance in an inert gas atmosphere into a nuclear metal powder maintained at a lower temperature than that temperature. , the metal powder is subjected to oxidation prevention treatment.

Normally, when metal powder is coated with an inorganic polymer film, a gap is created between the metal powder and the film due to the difference in shrinkage rate, and the diameter of the film is estimated to be several tens of angstroms or less. There are small pores caused by dehydration reaction,
Because gas containing oxidizing substances remains in these gaps and small pores, it is difficult to simply immerse the metal powder in the liquid material due to the pressure of the remaining gas. It is hardly expected that the metal powder will leak, and the oxidation prevention treatment will be incomplete. In the method of the present invention, the metal powder coated with an inorganic polymer film is inertly immersed in a liquid substance, which is maintained at a lower temperature than the metal powder. When cooled, the pressure of the retained gas in the interstitial space and/or in the pores decreases according to Boyleschard's law, which becomes the driving force for suctioning and introducing the liquid substance into the interstitial space and/or in the pores. As a result, the liquid substance is adsorbed on the inner walls of the gaps and/or the inner walls of the small holes, and further wets the outer surface of the metal powder, thereby completing the oxidation prevention treatment.

The temperature difference between the metal powder and the liquid substance that causes the liquid substance to be sucked into the gap and/or the small pores is changed depending on the conditions for forming the inorganic polymer film, the type of liquid substance used, etc. However, the temperature is preferably 80°C or higher. Specifically, when metal powder is heated in an inert gas stream or when metal powder that has completed a high-temperature reduction reaction is cooled with inert gas, the temperature is kept at a temperature higher than the liquid material temperature without sufficient cooling. After that, the object is achieved by immersing it in a liquid substance and rapidly cooling it.

The present invention provides a method for preventing the oxidation of metal powder, especially ferromagnetic metal powder coated with an inorganic polymer film, using an extremely simple operation. This is a method for producing a magnetic coating material with excellent dispersibility when it is converted into a coating material for the production of magnetic recording media such as disks, and its industrial significance is of great importance.

Hereinafter, the present invention will be explained in more detail with reference to Examples. However, the present invention is not limited to the following examples.

Example 1 was obtained by reducing 20 g of acicular a-Fe coated with silicon oxide at a concentration of 2.8% f in a hydrogen stream, and immersing the obtained acicular magnetic iron powder 102 in 100 mf of toluene. After putting it in a heating furnace and volatilizing the toluene at 80°C in a nitrogen stream and then raising the temperature to 130°C, it was poured into a mixed solvent of toluene and olive oil with a volume ratio of 95:5 kept at room temperature (21°C), Cooled to room temperature. After filtering the mixed organic solvent, it was washed with toluene, left for one week in an atmosphere of 60% R and H at 30°C, and an oxidation resistance test was performed.
The measured values of e+m+u/f) are shown in Table 1. The average length of the acicular magnetic iron powder used was 0.2 μm. Note that the saturation magnetization (σBe+m+u/
When measuring f), the amount of nine organic solvents adsorbed was corrected by elemental analysis.

Comparative Example 1 When the sample of the magnetic iron powder used in the example immersed in toluene was filtered as it was, it ignited.

Table 1 shows the measured values when the materials were air-dried using dry air at room temperature.

Chapter 1 Table Patent applicant: Nippon Soda Co., Ltd. Agent Haruyuki Ito Yoshimi Yokoyama

Claims (1)

[Claims] 1. When a metal powder coated with an inorganic polymer film is immersed in a liquid substance that is inert to the metal powder, the metal powder is maintained at a temperature lower than the temperature of the metal powder. A method for preventing oxidation of metal powder, the method comprising immersing the powder in the liquid substance in an inert gas atmosphere. The two metal powders are ferromagnetic iron powder made of iron alone, or cobalt, nickel, chromium, zinc, iron as a base metal,
Claim 1 is a ferromagnetic alloy powder containing one or more selected from the group of tin and aluminum.
Treatment method described in section. 3. Claim 1, wherein the inorganic polymer coating is a coating mainly composed of silicon and/or aluminum oxides.
Treatment method described in section. 4. Claims in which the liquid substance inert to the metal powder is a hydrogenated organic solvent, an organic acid ester that is liquid at room temperature, a higher alcohol, and an organometallic compound, either alone or in a mixture of two or more. The treatment method described in paragraph 1. 5. The treatment method according to claim 1, wherein the temperature difference between the metal powder and the liquid substance is 80° C. or more.