Method for improving corrosion resistance of high abundance rare earth permanent magnet

Abstract

A method for improving corrosion resistance of a high abundance rare earth permanent magnet by high temperature oxidation is provided. By the oxidation at 7001000 C., a rare earth oxide film grows in-situ on the surface, which can greatly improve the corrosion resistance of the high abundance rare earth permanent magnet. The method makes full use of phase formation rule and diffusion kinetic behavior of high abundance rare earth elements La/Ce/Y, which is different from other rare earth elements Nd/Pr/Dy/Tb. The method grows the rare earth oxide film in situ with strong adhesion to the matrix, which can not only greatly improve the corrosion resistance of the magnet, but also improve the magnetic and mechanical properties. The method has advantages of green environmental protection, long service life and simple process, and can be popularized and applied in large quantities.

Claims

1. A method for improving corrosion resistance of a rare earth permanent magnet, consisting of: in situ growing a rare earth oxide film on a surface of the rare earth permanent magnet by an oxidation reaction; wherein a temperature of the oxidation reaction is controlled to be in a range from 700 Celsius degrees ( C.) to 1000 C.; and components of the rare earth permanent magnet, measured in atomic percentages, are (RE.sub.aRE.sub.1-a).sub.x(Fe.sub.bM.sub.1-b).sub.100-x-y-zM.sub.yB.sub.z, RE is one selected from the group consisting of lanthanum (La), cerium (Ce) and yttrium (Y), RE is one or more of other lanthanide elements except for La, Ce, and Y, Fe is an iron element, M is one or more selected from the group consisting of cobalt (Co) and nickel (Ni), M is one or more selected from the group consisting of niobium (Nb), zirconium (Zr), tantalum (Ta), vanadium (V), aluminum (Al), copper (Cu), gallium (Ga), titanium (Ti), chromium (Cr), molybdenum (Mo), manganese (Mn), silver (Ag), gold (Au), lead (Pb) and silicon (Si), B is a boron element; and a, b, x, y and z satisfy the following conditions: 0.25a<1, 0.8b<1, 12x18, 0y2, and 5.5z6.5.

2. The method according to claim 1, wherein the oxidation reaction to the rare earth permanent magnet is performed in a heat treatment furnace; and a reaction time of the oxidation reaction is controlled to be in a range from 0.2 hours (h) to 5 h and an oxygen partial pressure during the oxidation reaction is less than 10.sup.4 Pascals (Pa).

3. The method according to claim 1, wherein a thickness of the rare earth oxide film is in a range from 10 nanometers (nm) to 100 micrometers (m).

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) The disclosure is further explained in conjunction with specific embodiments, but the disclosure is not limited to the following embodiments:

Embodiment 1

(2) Components of a high abundance rare earth permanent magnet measured in atomic percentages are: [(Pr.sub.0.2Nd.sub.0.8).sub.0.5Ce.sub.0.5].sub.13.9(Fe.sub.0.98Co.sub.0.02).sub.78.6(Cu.sub.0.2Co.sub.0.2Al.sub.0.3Ga.sub.0.1Zr.sub.0.2).sub.1.5B.sub.6.

(3) By performing a high temperature oxidation reaction to the high abundance rare earth permanent magnet in a heat treatment furnace, the temperature is controlled at 900 C., the reaction time is controlled at 4 h and the oxygen partial pressure is 10 Pa.

(4) The thickness of a rare earth oxide film grown on the surface of the high abundance rare earth permanent magnet in situ is 7 m (about 7 m). Results of AMT-4 permanent magnetic measurement instrument show that the remanence and coercivity of the high abundance rare earth permanent magnet after the high temperature oxidation reaction (also referred to as surface oxidation treatment) are respective 12.4 kilo Gauss (kG) and 9.0 kilo Oersted (kOe). Results of AMETEK electrochemical workstation show that the corrosion current of the high abundance rare earth permanent magnet after the surface oxidation treatment is 7 microampere per square centimeter (A/cm.sup.2) in 3.5% sodium chloride (NaCl) solution.

Comparative Embodiment 1

(5) The difference from the embodiment 1 is that the oxygen partial pressure during the high temperature oxidation of the high abundance rare earth permanent magnet is 10.sup.5 Pa. Results of the AMT-4 permanent magnetic measurement instrument show that the remanence and coercivity of the high abundance rare earth permanent magnet after the surface oxidation treatment are respective 12.3 kG and 8.5 kOe, which are lower than that of the embodiment 1. Results of the AMETEK electrochemical workstation show that the corrosion current of the high abundance rare earth permanent magnet after the surface oxidation treatment is 50 A/cm.sup.2 in 3.5% NaCl solution, which is larger than that of the embodiment 1.

Comparative Embodiment 2

(6) The difference from the embodiment 1 is that the reaction time of the high temperature oxidation of the high abundance rare earth permanent magnet is 10 h. Results of the AMT-4 permanent magnetic measurement instrument show that the remanence and coercivity of the high abundance rare earth permanent magnet after the surface oxidation treatment are respective 12.2 kG and 7.9 kOe, which are lower than that of the embodiment 1. Results of the AMETEK electrochemical workstation show that the corrosion current of the high abundance rare earth permanent magnet after the surface oxidation treatment is 41 A/cm.sup.2 in 3.5% NaCl solution, which is larger than that of the embodiment 1.

Comparative Embodiment 3

(7) The difference from embodiment 1 is that the high abundance rare earth permanent magnet is not treated with the high temperature oxidation. Results of the AMT-4 permanent magnetic measurement instrument show that the remanence and coercivity of the high abundance rare earth permanent magnet are respective 12.3 kG and 8.6 kOe, which are lower than that of the embodiment 1. Results of the AMETEK electrochemical workstation show that the corrosion current of the high abundance rare earth permanent magnet is 82 A/cm.sup.2 in 3.5% NaCl solution, which is more than one order of magnitude larger than that of the embodiment 1.

Comparative Embodiment 4

(8) The difference from embodiment 1 is that the element contents of Cu and Co are improved. The components of the high abundance rare earth permanent magnet measured in atomic percentage are:

(9) [(Pr.sub.0.2Nd.sub.0.8).sub.0.5Ce.sub.0.5].sub.13.9(Fe.sub.0.98Co.sub.0.02).sub.77.1(Cu.sub.0.4Co.sub.0.3Al.sub.0.15Ga.sub.0.05Zr.sub.0.1).sub.3B.sub.6. The high abundance rare earth permanent magnet is not treated with the high temperature oxidation. Results of the AMT-4 permanent magnetic measurement instrument show that the remanence and coercivity of the high abundance rare earth permanent magnet are respective 11.8 KG and 5.7 kOe, which are lower than that of the embodiment 1. Results of the AMETEK electrochemical workstation show that the corrosion current of the high abundance rare earth permanent magnet is 73 A/cm.sup.2 in 3.5% NaCl solution, which is more than one order of magnitude larger than that of the embodiment 1.

Comparative Embodiment 5

(10) The difference with the embodiment 1 is that the high abundance rare earth permanent magnet is treated with surface coating to obtain a dark silver nickel coating without a high temperature oxidation treatment, and the thickness of the dark silver nickel coating is 7 m (about 7 m). Results of the AMT-4 permanent magnetic measurement instrument show that the remanence and coercivity of the high abundance rare earth permanent magnet are respective 12.1 kG and 8.1 kOe, which are lower than that of the embodiment 1. Results of the AMETEK electrochemical workstation show that the corrosion current of the high abundance rare earth permanent magnet is 18 A/cm.sup.2 in 3.5% NaCl solution, which is larger than that of the embodiment 1.

Embodiment 2

(11) Components of a high abundance rare earth permanent magnet measured in atomic percentages, are: [(Pr.sub.0.2Nd.sub.0.8).sub.0.55(La.sub.0.15Ce.sub.0.85).sub.0.45].sub.15Fe.sub.77.8(Ga.sub.0.6Cu.sub.0.2Al.sub.0.25Nb.sub.0.32).sub.1B.sub.5.83.

(12) By performing a high temperature oxidation reaction to the high abundance rare earth permanent magnet in a heat treatment furnace, the temperature is controlled at 850 C., the reaction time is controlled at 5 h and the oxygen partial pressure is 0.5 Pa. The thickness of a rare earth oxide film grown on the surface of the high abundance rare earth permanent magnet in situ is 3 m (about 3 m). Results of the AMT-4 permanent magnetic measurement instrument show that the remanence and coercivity of the high abundance rare earth permanent magnet after the surface oxidation treatment are respective 12.4 kG and 7.2 kOe. Results of AMETEK electrochemical workstation show that the corrosion current of the high abundance rare earth permanent magnet after the surface oxidation treatment is 12 A/cm.sup.2 in 3.5% NaCl solution. Comparative embodiment 6:

(13) The difference from embodiment 2 is that the high abundance rare earth permanent magnet is not treated with the high temperature oxidation. Results of the AMT-4 permanent magnetic measurement instrument show that the remanence and coercivity of the high abundance rare earth permanent magnet are respective 12.4 kG and 5.6 kOe, which are lower than that of the embodiment 2. Results of the AMETEK electrochemical workstation show that the corrosion current of the high abundance rare earth permanent magnet is 135 A/cm.sup.2 in 3.5% NaCl solution, which is more than one order of magnitude larger than that of the embodiment 2.

Embodiment 3

(14) Components of a high abundance rare earth permanent magnet measured in atomic percentages, are: [Nd.sub.0.75(Y.sub.0.1Ce.sub.0.9).sub.0.25].sub.15.5(Fe.sub.0.92Co.sub.0.08)(Cu.sub.0.2Ga.sub.0.1Al.sub.0.35Si.sub.0.2Nb.sub.0.15).sub.1.5B.sub.6.1.

(15) By performing a high temperature oxidation reaction to the high abundance rare earth permanent magnet in a heat treatment furnace, the temperature is controlled at 700 C., the reaction time is controlled at 5 h and the oxygen partial pressure is 0.5 Pa. The thickness of a rare earth oxide film grown on the surface of the high abundance rare earth permanent magnet in situ is 800 nm. Results of the AMT-4 permanent magnetic measurement instrument show that the remanence and coercivity of the high abundance rare earth permanent magnet after the surface oxidation treatment are respective 12.6 kG and 12.2 kOe. Results of the AMETEK electrochemical workstation show that the corrosion current of the high abundance rare earth permanent magnet after the surface oxidation treatment is 20 A/cm.sup.2 in 3.5% NaCl solution.

Comparative Embodiment 7

(16) The difference from embodiment 3 is that the high abundance rare earth permanent magnet is not treated with the high temperature oxidation. Results of the AMT-4 permanent magnetic measurement instrument show that the remanence and coercivity of the high abundance rare earth permanent magnet are respective 12.3 kG and 10.1 kOe, which are lower than that of the embodiment 3. Results of the AMETEK electrochemical workstation show that the corrosion current of the high abundance rare earth permanent magnet is 250 A/cm.sup.2 in 3.5% NaCl solution, which is more than one order of magnitude larger than that of the embodiment 3.

Embodiment 4

(17) Components of the high abundance rare earth permanent magnet measured in atomic percentages, are: [(Pr.sub.0.2Nd.sub.0.8).sub.0.55(La.sub.0.15Ce.sub.0.85).sub.0.45].sub.15Fe.sub.77.8(Ga.sub.0.6Cu.sub.0.2Al.sub.0.25Nb.sub.0.32).sub.1B.sub.5.83.

(18) By performing a high temperature oxidation reaction to the high abundance rare earth permanent magnet in a heat treatment furnace, the temperature is controlled at 900 C., the reaction time is controlled at 3 h and the oxygen partial pressure is 0.01 Pa. The thickness of a rare earth oxide film grown on the surface of the high abundance rare earth permanent magnet in situ is 1 m. Results of AMT-4 permanent magnetic measurement instrument show that the remanence and coercivity of the high abundance rare earth permanent magnet after the surface oxidation treatment are respective 11.5 kG and 7.1 kOe. Results of AMETEK electrochemical workstation show that the corrosion current of the high abundance rare earth permanent magnet after the surface oxidation treatment is 35 A/cm.sup.2 in 3.5% NaCl solution.

Comparative Embodiment 8

(19) The difference from embodiment 4 is that the high abundance rare earth permanent magnet is not treated with the high temperature oxidation. Results of the AMT-4 permanent magnetic measurement instrument show that the remanence and coercivity of the high abundance rare earth permanent magnet are respective 11.2 kG and 6.1 kOe, which are lower than that of the embodiment 4. Results of the AMETEK electrochemical workstation show that the corrosion current of the high abundance rare earth permanent magnet is 580 A/cm.sup.2 in 3.5% NaCl solution, which is more than one order of magnitude larger than that of the embodiment 4.