NdFeB Magnetic Powder Manufacturing via Reduction-Diffusion
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Solution Overview
Problem
The existing methods for preparing NdFeB-based magnetic powder are inefficient due to the need for high-temperature melting, multi-step pulverization, and the use of expensive micro iron powder, which limits particle size and increases production costs, while also resulting in irregular particle shapes and decreased coercive force due to crystal grain growth during sintering.
Innovation Solution
A reduction-diffusion method is employed to prepare magnetic powder by heat-treating a molded article containing iron powder, neodymium oxide, and boron under high pressure and temperature, followed by pulverization and coating with organic fluoride, which suppresses crystal grain growth and enhances coercive characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional strip/mold casting or melt spinning methods are used to prepare NdFeB-based magnetic powder, then the magnet can be produced through established processes, but the pulverization process takes a long time and requires multi-step treatment including coarse pulverization and hydrogen crushing/jet milling
Solution Approach 1:
The invention changes the fundamental processing parameters by eliminating the high-temperature melting step (1500-2000°C) and replacing multi-step pulverization with a single-step jet milling process. The direct preparation of fine powder from raw materials through controlled reaction and jet milling dramatically reduces processing time while maintaining product quality.
2Manufacturing precision
If high-temperature melting (1500-2000°C) and multi-step pulverization are used to prepare microparticles, then the magnetic powder can be obtained, but the particle shape becomes irregular and particle size miniaturization is limited
Solution Approach 1:
The invention replaces the conventional mechanical pulverization system (coarse pulverization followed by hydrogen crushing/jet milling) with a controlled chemical reaction system followed by single-step jet milling. This substitution allows for better particle shape control and size miniaturization by avoiding the mechanical degradation that causes irregular shapes in conventional methods.
3Reliability
If sintering is performed at 1000-1250°C to achieve densification and net density, then the sintered magnet can be produced, but crystal grain growth occurs which decreases coercive force
Solution Approach 1:
The invention performs preliminary action by preparing ultrafine powder with controlled particle size and shape before sintering. This pre-prepared fine powder structure allows for lower sintering temperatures (reducing crystal grain growth) while still achieving the required densification and net density, thereby preserving coercive force.
4Manufacturing precision
If reduction-diffusion method using micro iron powder (carbonyl iron powder) is used to prepare NdFeB fine particles, then fine magnetic particles can be obtained, but the particle size is limited by the iron powder size and production cost increases due to expensive micro iron powder
Solution Approach 1:
The invention inverts the conventional reduction-diffusion approach by not using pre-formed micro iron powder as the starting material. Instead, it prepares fine magnetic powder directly from raw materials (Nd, Fe, B) through controlled reaction and jet milling, eliminating the need for expensive micro iron powder while achieving the desired fine particle size.
5Reliability
If existing methods are used to prepare magnetic powder, then the powder can be produced, but a surface coating process is required after pulverization to prevent oxidation and improve properties
Solution Approach 1:
The invention performs preliminary protection by preparing the powder in a controlled atmosphere (inert gas or vacuum) from the beginning of the process through jet milling. This preliminary action prevents oxidation before it can occur, eliminating or simplifying the need for subsequent surface coating processes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method produces ultrafine, regularly shaped magnetic particles with reduced manufacturing costs and improved coercive force by controlling particle size and preventing crystal grain growth during sintering, resulting in high-density, high-performance magnetic powder.
Implementation Method 1
heat-treating a molded article prepared by pressure-molding a mixture containing iron powder, neodymium oxide, boron and calcium
Implementation Method 2
heat-treating the molded article to a temperature of 800 °C to 1,100 °C under an inert gas atmosphere
Implementation Method 3
coating an organic fluoride on a surface of the magnetic powder
Implementation Method 4
sintering magnetic powder to obtain a sintered magnet, this sintering proceeds in a temperature range of 1,000 °C to 1,250 °C to carry out densification
Data Source
Figure 1~2
Figure 3
Figure 4a
AI summary
A method of preparing magnetic powder according to an embodiment of the present disclosure includes the steps of: preparing iron powder by a reduction reaction of iron oxide; preparing magnetic powder by heat-treating a molded article prepared by pressure-molding a mixture containing the iron powder, neodymium oxide, boron and calcium at a pressure of 22 MPa or more; and coating an organic fluoride on a surface of the magnetic powder.