JPH0338321B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to fine metal powder, and more specifically,
This invention relates to acicular fine metal powder produced by electrolytic deposition using ultrafine pores in an anodic oxide film formed on the surface of Al or its alloy. Fine metal powders are mainly produced and used for powder metallurgy or pigments, but these metal powders have an average particle size of several microns to several hundred microns, the size of a so-called subsieve or sieve region,
These powders are manufactured by pulverization, atomization, electrolysis, and other physical and chemical methods. In contrast, in recent years so-called ultrafine powders with particle sizes in the angstrom range have been produced, and useful properties different from those of conventional metal powders have been discovered in these ultrafine powders, and their uses are expanding. I've been doing it. In other words, magnetic powders (Fe, Co, Ni, and their alloys) for high-density magnetic recording media, pigments for conductive and resistive paints (Ag, Ni, Cu, etc.),
Fillers for conductive rubber and resins, surface chemical reaction elements (Ag, Ni, etc. for catalysts, battery plates, low-temperature sintering media, etc.)
Pt, Pa, etc.) Particulate filters (Ni, etc.), Combustion aids for rocket fuel (Al, Ni) Dispersion strengthened alloys (Ni, etc.)
etc.), and the light-receiving paint (Au) for infrared radiation detectors. These ultrafine powders are manufactured by several chemical methods in addition to physical methods such as the so-called air evaporation method in which metals are evaporated in a low-pressure inert gas. Chemical methods include reducing metal compounds at high temperatures, chemically precipitating ultrafine metal salt particles and reducing them by heating, and atomizing an aqueous salt solution containing metal ions and freeze-drying it. A method of atomizing metal ions and thermally reducing them, a method of thermally decomposing salts containing metal ions using low-temperature gas plasma, etc. have been proposed, and some of these methods have been commercialized. However, the aerial evaporation method requires a large amount of energy to evaporate the metal, requires large vacuum equipment, and has low productivity.
It has the disadvantage of high cost. In addition, chemical methods are disadvantageous in that the preparation of the raw material compound is expensive, and a heating reduction step is unavoidable, which causes grain growth of the produced fine particles during heating, resulting in poor particle size stability. An object of the present invention is to provide a method for producing angstrom-sized ultrafine powder of a metal or alloy at a stable quality and at low cost, and in particular, a method for producing ultrafine powder with excellent magnetic properties. The present inventors have developed the present invention as a result of various studies based on the knowledge that fine pores with extremely uniform pore diameters and depths are densely present in an anodic oxide film formed on the surface of metal, especially Al or its alloy. Reached.
That is, the present invention relates to an acicular fine metal powder produced by electrolytically depositing metal or alloy fine particles into the fine pores and then selectively dissolving and removing the anodic oxide film. The method of the invention is carried out by a two-step electrolytic reaction in the aqueous phase and an oxide dissolution reaction. 1st step: Step of forming an anodized film on the surface of Al or Al alloy (primary electrolytic treatment) 2nd step: Step of electrolytically depositing metal or alloy fine particles into the micropores in the film (secondary electrolytic treatment) Processing) Third step: Step of selectively dissolving and removing the anodic oxide film (film dissolving treatment) Each of the above steps will be explained below. (1) Primary electrolytic treatment It is well known that when Al or its alloy is used as an anode and subjected to direct current or alternating current electrolysis in an acid bath, an oxide film with corrosion resistance, wear resistance, and decorative properties is formed on the surface. As the acid bath, various inorganic acids, organic acids, or mixed acids thereof are used. The anodic oxide film has a dual structure: a porous layer with densely packed micropores, and a thin, dense barrier layer that extends from the bottom of the micropores to the metal surface. The fine pores of the porous layer have a diameter on the order of angstroms and are arranged almost regularly in a direction perpendicular to the metal surface, and the tops of the pores are open. The pore size of the micropores varies depending on the type of electrolytic bath, bath temperature, etc., but under certain conditions, phosphoric acid has the largest diameter and sulfuric acid has the smallest diameter.
The thickness of the porous layer, that is, the depth of the pores, depends on the purity of Al,
Although it varies depending on the alloy composition, electrolytic conditions, etc., it is generally thicker for pure Al and thinner for alloys containing heavy metals. Also, depending on the electrolysis time, there is a maximum point in the thickness of the porous layer, and once formed, the film becomes thinner as it dissolves in the electrolytic bath. The components of the film are mainly amorphous anhydrous Al ₂ O ₃ in both the barrier layer and the porous layer, but depending on the electrolytic conditions, some crystalline Al ₂ O ₃ is formed, and the part in contact with the electrolytic bath is It has changed to trihydrate. The primary electrolytic treatment solution for forming an anodized film having micropores suitable for the purpose of the present invention includes inorganic acids such as sulfuric acid, chromic acid, phosphoric acid, etc., or fatty acids such as oxalic acid, sulfamic acid, tartaric acid, maleic acid, etc. Examples include organic acids such as group carboxylic acids and aromatic sulfonic acids, or mixed acids thereof, but sulfuric acid, chromic acid, phosphoric acid, and oxalic acid are preferable from the viewpoint of uniformly forming the necessary porous layer.In particular, sulfuric acid Electrolytic baths are most advantageously applied to the present invention because they form small pores and are economical because they are inexpensive and require little electrolysis power. By the way, currently many Al or its alloy products are anodized using a sulfuric acid electrolytic bath, but in this case the concentration of the bath is 10 to 30 wt% H ₂ SO ₄ .
The bath temperature is maintained at a predetermined temperature within the range of 15 to 25℃.
Electrolysis is carried out at a current density of 0.5 to 3 A/cm ² and an electrolytic voltage of 15 to 20 V. The heat generated as electrolysis progresses causes the bath temperature to rise, leading to the dissolution of the film once formed.Furthermore, the film formed at high bath temperatures is soft and has poor wear and corrosion resistance, so the bath must be forcibly cooled using a cooling means. The actual situation is that the amount of power required for this cooling exceeds the amount of electrolysis power. However, in the present invention, since the micropores in the coating are utilized, there is no need to make the coating hard and impart wear resistance, and therefore, the increase in bath temperature is regulated from another perspective. As a result of various studies in this regard, the present inventors have found that the bath temperature of the sulfuric acid electrolytic bath suitable for the present invention is in the range of 30 to 80°C. If the bath temperature exceeds this upper limit, the film once formed will dissolve too quickly, making it impossible to uniformly form a film of the required thickness. On the other hand, if the bath temperature is less than the above lower limit, the film formed will be hard, and the film will dissolve slowly after depositing metal particles in the micropores, and its removal will be insufficient, so the effect of the present invention will not be achieved. I can't perform to my full potential.
What should be noted further is that the magnetic properties (coercive force, saturation magnetization, residual magnetization) of the ferromagnetic metal fine powder obtained through the secondary electrolytic treatment are better when the primary electrolytic bath temperature is higher. As described above, since the present invention uses high bath temperature electrolysis, the bath cooling energy is less than that of conventional anodizing treatment, and because the present invention uses low voltage electrolysis, the amount of electrolytic power can be significantly reduced. (2) Secondary electrolytic treatment The secondary electrolytic treatment in which metal or alloy particles are electrolytically deposited into the fine pores of the porous layer is performed by using Al or Al alloy on which the anodic oxide film has been formed as an electrode, and using water-soluble Electrolysis is carried out by applying a direct current, alternating current, AC/DC superimposed current, etc. between an aqueous solution of a metal compound alone or a mixture thereof to form an aqueous electrolytic bath, and other suitable electrodes. Precipitated metals include Fe, Co, Ni, Pa, Pt, Ir, Mn, Cr,
Mo, W, V, Nb, Ta, Bi, Ti, Zr, Y,
Most of the metallic elements such as La, Ce, Sm, Zn, Cu, Ag, and Au are targeted. Water-soluble compounds of the above metals include sulfates,
Inorganic compounds such as nitrates, phosphates, pyrophosphates, cyanates, halides, metal salts,
One or two selected from the group consisting of organic compounds such as acetate, tartrate, sulfamate, etc.
Applicable to more than one species. The type of metal element in these metal salts and the level of their valence have selectivity in the electrolytic current, and low valence metal salts require the coexistence of an appropriate antioxidant.
For example, in the case of Ni and Co salts, AC electrolysis is suitable;
Furthermore, in the case of Fe, the metal does not precipitate in either alternating current or direct current electrolysis with ferric salts, and Fe can be precipitated only by alternating current electrolysis of ferrous salts. In this case, oxidation during electrolysis (Fe ⁺² → Fe ⁺³ ) produces Fe(OH) ₃ precipitates and reduces the Fe utilization rate, so it is recommended to add a small amount of an antioxidant such as hydroquinone to the electrolyte. is good. Generally, it is effective to add boric acid and glycerin to the electrolytic bath for secondary electrolytic treatment. The former addition has the effect of buffering the pH of the electrolytic bath and complexing the metal ions, while the latter addition has the effect of increasing the viscosity of the electrolytic bath and homogenizing the electrolytic deposition. Glycols and sugars can also be used as additives. The necessary addition amount varies depending on the metal salt to be electrolyzed, and the appropriate amount is determined by experiment. For example, in the case of Fe, Ni, and Co, boric acid is 25 to 40 g as H ₃ BO ₃ in the bath, and glycerin is 10 to 40 g in the bath. 30g/
Add to a concentration of . By electrolyzing a compound of two or more metals in a secondary electrolytic treatment, an alloy of these metals can be electrolytically deposited. In this case, it is necessary to select the type of salt, bath composition, etc. for effective electrolytic deposition.
For Ni−Co, the deposition potentials are close, but for Fe−
In Ni, Fe-Ni-Co, etc., since the deposition potential of Fe is far apart, it is necessary to bring these two or more metals closer together by selecting the type of salt, complexing agent, etc. The conditions for electrolytic deposition are almost the same as those for alloy plating that has already been put into practical use. The electrolytic bath temperature in the secondary electrolytic treatment varies depending on the type, concentration, etc. of the metal compound, but under a constant electrolytic voltage, the higher the bath temperature, the greater the amount of metal deposited. For example, when alternating current electrolysis is carried out using a cobalt sulfate aqueous solution (PH = 4.3) as an electrolytic bath, the amount of metal deposited at a bath temperature of 50°C reaches approximately 150% of that at a bath temperature of 20°C. However, in general, when the bath temperature exceeds 75°C, the metal precipitation efficiency is saturated, and on the other hand, energy loss for maintaining the high bath temperature increases. Therefore, as an industrial operating condition, the bath temperature is 20 to 60℃.
Desirably maintained in the °C range. (3) Film dissolution treatment The operation of selectively dissolving only the anodic oxide film without dissolving as much as possible the fine metals or alloys in the micropores precipitated by the secondary electrolytic treatment is a process that dissolves the film and the deposited metal or Based on the use of differences in the chemical reactivity of alloys. As mentioned above, the composition of the anodic oxide film that forms micropores is mainly Al oxide and partially hydroxide, and the chemical activity of the film varies depending on the primary electrolytic treatment conditions. In the present invention, as described above, by increasing the bath temperature in the primary electrolytic treatment, the Al oxide becomes easily soluble in acids and alkalis. As a liquid with excellent film solubility, the concentration of acid is approximately 1.
~10% phosphoric acid aqueous solution with a liquid temperature of 50℃ or higher is applied. For alkaline, the concentration is about 0.5 to 10%, and the liquid temperature is 30
Caustic alkali above ℃ is applied. If the precipitated metal or alloy is a heavy metal type, caustic alkali is suitable. If the precipitated metal or alloy is a non-heavy metal type, such as Sn, Se, Zn, Bi, etc., a film dissolving solution containing an inhibitor suitable for the precipitated metal is suitable. It is effective to add a metal surface oxidation inhibitor (inhibitor) to the film solution, and in an alkaline solution, add a water-soluble silicate, such as Na ₂ SiO ₃ .
When 9H ₂ O is added, the resulting metals and alloys have excellent magnetic properties. In order to prevent oxidation of the fine particles of metal or alloy remaining in the solution after film dissolution treatment, they are separated from the solution as soon as possible, washed, and dried. Separation from the solution is best carried out by filtration or centrifugation, and as the washing solution, in addition to water, organic solvents such as alcohol and ether are more effective. Low temperature and reduced pressure drying is suitable for drying. The precipitated metal after the film dissolution treatment has a diameter d, for example, as shown in FIGS.
Acicular bodies with a diameter of ≒100 to 500 Å and a length l of 0.2 to 3 um are closely assembled in the length direction. d and l of each of these needle-like bodies can be controlled by the electrolytic treatment conditions described above. Furthermore, the needle-shaped bodies can be easily separated by a weak pressing force, and can also be separated in the radial direction if necessary. For such crushing and crushing, an impact type crusher or a jet flow crusher that causes particles to impact each other is suitable. EXAMPLES Hereinafter, the present invention will be explained based on Examples and Examples, but the present invention is not limited thereto. Example 1 (1) Base material; [A]...Aluminum foil (99.9% Al, thickness 0.1 mm
Width 50mm x length 100mm) [B]…Industrial pure aluminum plate (JIS A1100−
H24, thickness 1.0 mm x width 50 mm x length 100 mm) (2) Preliminary surface treatment: Substrate was immersed in 5% NaOH aqueous solution at 40°C for 2 minutes, then desmatted in 30% HNO ₃ solution for 1 minute. Washed with water and dried. (3) Primary electrolytic treatment; (1) Electrolytic bath: (a): 15% H ₂ SO ₄ , bath temperature kept constant at 20°C or 50°C (b): 25% H ₃ PO ₄ , bath temperature 20°C (2) Electrolysis: Using a pure Al plate as the counter-negative electrode, direct current electrolysis was performed at a specified current density for a certain period of time. (4) Secondary electrolytic treatment; (1) Electrolytic bath: Bath in an aqueous solution containing 2.5% H ₃ BO ₃ and 2.0% glycerin...FeSO ₄ 7H ₂ O 5.0% Bath... CoSO ₄ 7H ₂ O5. 0% was dissolved and the pH was adjusted to 3.5 using H ₂ SO ₄ to prepare an electrolytic bath. The bath temperature was kept constant at 30°C. (2) Electrolysis: AC electrolysis was performed for a certain period of time at a predetermined current density as the counter electrode of the carbon plate. (5) Film dissolution treatment, etc.: After completing the above secondary electrolysis, the base material, which has a dark brown color due to the deposited metal, is immersed in a 2% NaOH aqueous solution at 40°C for 3 minutes to dissolve the film, and then settle in the solution. The precipitated metal fine particles were suctioned off using Toyo Paper 5C. After washing the fine particles with distilled water and then with ethyl alcohol, they were placed in a vacuum desiccator using magnesium perchlorate as a desiccant and dried at room temperature for 24 hours. (6) Results; Table 1 shows the yield of fine metal powder according to the conditions of primary electrolytic treatment and secondary electrolytic treatment, and the magnetic properties of the fine metal powder. Comparison of results for primary electrolytic bath temperatures of 20°C and 50°C in the table (Execution Nos. 1, 2, 5, 6 and Experiments
Comparison of Nos. 3, 4 and 7, 8), the higher bath temperature significantly reduces the power consumption of primary electrolysis, the amount of metal deposited in secondary electrolysis is larger, and the magnetic properties of the resulting metal fine powder also improve. Recognized as excellent.
Both sulfuric acid and phosphoric acid can be used effectively as the primary electrolytic treatment solution, but in the case of phosphoric acid, a film will not be formed at a bath temperature of 30°C or higher, and the current density will decrease.
If the temperature exceeds 1A/αm ² , burning will occur, so the conditions in Table 1 are the limit. Example 2 (1) Base material; aluminum foil (99.99% Al

[Table] Thickness 0.1 mm x Width 125 mm x Length 250 mm) (2) Preliminary surface treatment: Immerse for 3 minutes in a 3% aqueous solution of Alclin #100 (commercially available Al degreasing agent manufactured by Okuno Seishin Kogyo Co., Ltd.) at 60°C. After etching, it was washed and dried. (3) Primary electrolytic treatment; (1) Electrolytic bath: 15% H ₂ SO ₄ , bath temperature kept constant at 45°C. (2) Electrolysis: 3A/dm ² × using pure Al plate as counter negative electrode
Direct current electrolysis was performed for 3.3 minutes or 5 A/dm ² × 2 minutes. (4) Secondary electrolytic treatment; (1) Electrolytic bath: H ₃ BO ₃ 2.5% and glycerin 2.0%, and some hydroquinone 0.4% as an antioxidant
Bath in an aqueous solution containing FeSO ₄ 7H ₂ O4.0% + NiSO ₄ .
7H ₂ O1.0% bath...〃 〃 2.0%＋〃
・Dissolve 7H ₂ O3.0% and PH with each H ₂ SO ₄ and NH ₄ OH
= 3.7 and used as an electrolytic bath. Bath temperature is 30℃
was held constant. (2) Electrolysis: 14V x 7.5 with carbon plate as counter electrode
Separate current electrolysis was carried out. (5) Film dissolution treatment, etc.; Dissolution solution S1...2% NaOH aqueous solution 〃 S2...S1 + 0.2% Na ₂ SiO ₃ 9H ₂ O aqueous solution dissolution conditions 40℃ x 3 minutes Filter, wash, and dry the precipitated metal fine particles Same as example 1. (6) Results: FeSO ₄ in the secondary electrolytic bath was oxidized during electrolysis.
Produces precipitation of Fe(OH) ₃ . Implementation No. 11-12 in the table,
As is clear from the comparison of Nos. 13 and 14, the addition of hydroquinone has a negative effect on the magnetic properties of the obtained fine powder metal or alloy.

[Table] It has the effect of preventing the above-mentioned oxidation without causing any adverse effects, giving flexibility in the elapsed time after bath preparation, and not reducing the amount of precipitated metal. As a film dissolving solution, it is recognized that S2, which uses NaSiO ₃ as an inhibitor in combination, is superior to S1, which contains only NaOH, and its magnetic properties do not deteriorate much even when the dissolution time becomes longer. The magnetic properties of the fine powder obtained differ depending on the Ni/Fe ratio of the secondary electrolytic bath, and this ratio is 1/4 (Ni20%-
Fe80%) has a high coercive force but low saturation magnetization and residual magnetization, and this ratio is 3/2 (Ni60% - Fe40
%), the opposite is true. Example 3 (1) Base material; aluminum plate (99.8% Al plate-H24,
(Thickness: 5 mm x Width: 1000 mm x Length: 2000 mm) (2) Preliminary surface treatment: Etching by immersing in 5% NaOH aqueous solution at 50℃ for 30 seconds, washing with water, and then soaking in 10% HNO ₃ aqueous solution at room temperature for 2 to 3 minutes. It was soaked and desmatted, then washed with water. (3) Primary electrolytic treatment; width 500mm x length 1500mm x depth
A 15% H ₂ SO ₄ aqueous solution was prepared in a 1500 mm electrolytic bath. Industrial pure aluminum plate (JISA1100−H24)
as the counter negative electrode at 50℃ for 3 minutes, DC 5A/dm ²
Immediately after primary electrolytic treatment was performed under the following conditions, it was washed with water. (4) Secondary electrolytic treatment: The dimensions of the electrolytic cell are the same as in the primary electrolytic treatment. (1) Electrolytic bath: FeSO _{4.7H 2} O4.3%, NiSO ₄ .
6H ₂ O 0.7%, H ₃ BO ₄ 2.5%, glycerin 2%,
(NH ₄ ) ₂ SO ₄ 1% aqueous solution with H ₂ SO ₄
The pH was adjusted to 4.5±0.2 with NH ₄ OH to prepare an electrolytic bath. (2) Electrolysis: Using lead as a counter electrode, constant voltage commercial alternating current electrolysis at 14V was performed for 10 minutes, followed by washing with water immediately after. (5) Film dissolution treatment, etc. After completing the secondary electrolysis and washing with water, the base material, which has a black color due to the deposited metal, is suspended in an empty tank from both sides.
A 5% NaOH aqueous solution containing 1% Na ₂ SiO ₃ 9H ₂ O is sprayed strongly from a nozzle for 1 minute at 50°C to dissolve the anodic oxide film formed by the primary electrolytic treatment and at the same time remove the precipitated metal from the NaOH. It was suspended in an aqueous solution. This suspension (black color) was separated from the solid precipitated metal fine particles and the NaOH aqueous solution using a centrifuge, and immediately washed and dried at a warm temperature. The separated NaOH aqueous solution can be used repeatedly. (6) Results: The average yield was 1.3 g/m ² . The magnetic properties are
The particles have a saturation magnetization of 94 emo/g, a residual magnetization of 70 emo/g, and a coercive force of 12,000 Oe, and are sufficiently durable for use as magnetic fine particles. The fine powder metal produced according to the present invention was examined under an electron microscope (transmission electron microscope manufactured by Hitachi, Ltd., H-
70OH) is shown in the photographs in Figures 1 and 2. This was illustrated in the case of Example No. 11 in Table 2, but the appearance was almost similar in other cases as well. Figure 1 shows the appearance immediately after the film dissolution treatment, showing an aggregate of fine needle-shaped precipitated metals. FIG. 2 shows the final appearance of the metal fine powder obtained by the method of the present invention, with the precipitated metal of FIG. 1 disintegrated by gentle mechanical means. As shown in the figure, the metal fine powder has a needle shape with a diameter of 100 to 500 Å and a length of 0.2 to 3 μm. The metal fine powder according to the present invention produced as described above has excellent magnetic properties, and has a magnetic material such as γ, which has been conventionally used as magnetic powder for magnetic recording tapes.
-It can be used with Fe ₃ O ₄ , CrO ₂ , Co-modified iron oxide, etc. without color loss, and can also be applied to the various ultrafine powder applications mentioned above.

[Brief explanation of drawings]

The drawing shows Fe-20 manufactured by the method of the present invention.
%Ni fine powder. Figure 1 shows an aggregate of precipitated metal particles immediately after film dissolution treatment (35,000x magnification), and Figure 2 shows an aggregate of acicular metal particles obtained by dismantling the aggregate in Figure 1. Appearance (35000x).

Claims (1)

[Claims] 1 Al or Al alloy with an anodic oxide film on its surface is electrolyzed in an aqueous phase containing one or more metal ions to precipitate metal into the micropores in the anodic oxide film, and then the anode A method for producing acicular fine metal powder, which is characterized in that it is produced by selectively dissolving and removing an oxide film.