R-T-B Sintered Magnet Corrosion Resistance via Ga-Modified Oxide Layer
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Solution Overview
Problem
R-T-B-based sintered magnets face corrosion issues due to the high reactivity of rare earth elements, especially under high temperature and humidity environments, leading to a decrease in mass and magnetic properties.
Innovation Solution
The development of an R-T-B-based sintered magnet with a magnet body containing Nd or Pr, Fe, Co, B, and Ga, and an oxidized layer composed of oxide phases with specific atomic ratios, which covers the grain boundary phase to enhance corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy rare earth elements (Dy or Tb) are substituted into the R2T14B phase to improve magnetic anisotropy, then coercivity at high temperature is improved, but material cost increases and supply stability deteriorates
Solution Approach 1:
The invention changes the compositional parameters by adding Ga to the R-T-B-based sintered magnet. This compositional modification enables achieving high coercivity at high temperature without relying on heavy rare earth elements, thus resolving the contradiction between improved reliability and supply stability.
Solution Approach 2:
The invention replaces expensive heavy rare earth elements with cheaper light rare earth elements combined with Ga addition. This substitution strategy achieves the same functional effect (high coercivity) while using more abundant and cost-effective materials.
2Reliability
If rare earth element R is used in the sintered magnet, then magnetic properties are achieved, but corrosion resistance deteriorates due to high reactivity of R
Solution Approach 1:
The invention introduces Ga as an intermediary element that modifies the grain boundary phase composition. This intermediary element facilitates the formation of a protective oxidized layer that mediates between the reactive rare earth elements and the corrosive environment, preventing direct corrosion while preserving magnetic properties.
Solution Approach 2:
The invention creates a composite structure consisting of the R-T-B main phase and a Ga-containing oxidized layer. This composite material combines the magnetic properties of the rare earth element with the protective characteristics of the oxidized layer, achieving both magnetic performance and corrosion resistance.
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
The solution significantly improves the corrosion resistance of the sintered magnet by forming a stable oxide phase that prevents penetration of corrosive substances, maintaining magnetic properties and mass integrity.
Implementation Method 1
the oxidized layer includes a plurality of oxide phases containing R, T, Ga, and O
Data Source
AI summary
An R-T-B-based sintered magnet 2 contains a rare earth element R, a transition metal element T, B, Ga, and O, the sintered magnet 2 includes a magnet body 4 and an oxidized layer 6 covering the magnet body 4, the magnet body 4 includes main phase grains 8 containing a crystal of R2T14B and a grain boundary phase 1 positioned between the main phase grains 8 and containing R, the oxidized layer 6 includes a plurality of oxide phases 3A containing R, T, Ga, and O, the oxide phase 3A satisfies the following Formulas (1) and (2) regarding the content (unit: atom %) of each element, and the oxide phase 3A in the oxidized layer 6 covers the grain boundary phase 1 in the magnet body 4. 0.3≤[R]/[T]≤0.5 (1)0.2≤[O]/([R]+[T]+[Ga]+[O])≤0.7 (2)