CaLaCo Ferrite Magnet Sintering for High Coercivity
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Solution Overview
Problem
CaLaCo ferrite magnets fail to meet the requirements of high coercivity (HcJ) and high rectangularity (Hk/HcJ) necessary for thin, high-performance applications due to poor magnetic properties and uneven grain boundary phase dispersion.
Innovation Solution
A method involving the addition of 1.8% or less by mass of SiO2 and 2% or less by mass of CaCO3 as sintering aids, with a temperature-elevating speed of 1-4°C/minute from 1100°C to the sintering temperature and a temperature-lowering speed of 6°C/minute or more from the sintering temperature to 1100°C, resulting in a structure with fine, evenly dispersed grain boundary phases, improving HcJ while maintaining high residual magnetic flux density (Br) and Hk/HcJ.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If CaLaCo ferrite is used to improve residual magnetic flux density, then Br is improved, but HcJ and Hk/HcJ remain insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling the sintering temperature elevation speed (1-5°C/minute) and lowering speed (5-20°C/minute) to optimize the magnetic properties. This controlled rate change during sintering modifies the microstructure and phase distribution, achieving simultaneous improvement in Br, HcJ, and Hk/HcJ ratios that cannot be obtained by conventional fixed-temperature sintering methods
Solution Approach 2:
The patent creates a composite microstructure by controlling the formation of multiple phases during sintering. The specific heating and cooling rates produce a composite of ferrite phases with optimized grain boundary characteristics, combining the high Br of CaLaCo ferrite with the improved coercivity and rectangularity needed for high-performance applications
2Reliability
If sintering temperature is increased to improve magnetic properties, then Br and HcJ are improved, but grain boundary phase dispersion becomes uneven
Solution Approach 1:
The patent applies periodic action through controlled heating and cooling cycles during sintering. The temperature is elevated at 1-5°C/minute to a target temperature, held, then lowered at 5-20°C/minute. This periodic temperature variation promotes uniform phase transformation and grain boundary phase dispersion, preventing the uneven distribution that occurs with conventional single-stage sintering
Solution Approach 2:
The patent changes the thermal parameters dynamically during sintering by using different heating and cooling rates. The heating rate (1-5°C/minute) is slower than conventional methods to allow uniform phase formation, while the cooling rate (5-20°C/minute) controls the final microstructure. This parameter optimization achieves both improved magnetic properties and uniform grain boundary phase dispersion
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 method enhances the magnetic properties of CaLaCo ferrite magnets, allowing them to be made thinner with improved HcJ and Hk/HcJ, suitable for high-performance applications such as motors and electric generators.
Implementation Method 1
addition of 1.8% or less by mass of SiO2 and 2% or less by mass of CaCO3 as sintering aids
Implementation Method 2
the sintered ferrite magnet comprises main phases of ferrite having a hexagonal M-type magnetoplumbite structure, first grain boundary phases existing between two main phases, and second grain boundary phases existing among three or more main phases
Implementation Method 3
temperature-elevating speed of 1-4°C/minute from 1100°C to the sintering temperature and a temperature-lowering speed of 6°C/minute or more from the sintering temperature to 1100°C
Implementation Method 4
resulting in a structure with fine, evenly dispersed grain boundary phases
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A sintered ferrite magnet comprising main phases of ferrite having a hexagonal M-type magnetoplumbite structure, first grain boundary phases existing between two main phases, and second grain boundary phases existing among three or more main phases, the second grain boundary phases being dispersed in its arbitrary cross section, and the second grain boundary phases having an average area of less than 0.2 µm2, are produced by calcining, pulverizing, molding and sintering raw material powders having the general formula of Ca1-x-yLaxAyFe2n-zCoz, wherein 1-x-y, x, y and z and n representing a molar ratio are in desired ranges; 1.8% or less by mass of SiO2 and 2% or less by mass (as CaO) of CaCO3 being added to a calcined body after calcining and before molding; and the sintering step being conducted with a temperature-elevating speed of 1-4°C/minute in a range from 1100°C to a sintering temperature, and a temperature-lowering speed of 6°C/minute or more in a range from the sintering temperature to 1100°C.