Hexagonal Ferrite Powder Manufacturing via pH-Controlled Hydrothermal Synthesis
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Solution Overview
Problem
In the field of magnetic recording, there is a need for hexagonal ferrite powder with fine particle size and uniform distribution to minimize noise and increase fill rate, as existing methods like continuous hydrothermal synthesis do not allow independent control of precursor preparation conditions, leading to variations in particle size and coarseness.
Innovation Solution
A method involving continuous hydrothermal synthesis where the precursor preparation step is conducted by continuously feeding starting materials, including an iron salt, alkaline earth metal salt, and base, with controlled pH variation within ±2 of the initial pH, allowing for the production of hexagonal ferrite with a sharp particle size distribution and reduced size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous hydrothermal synthesis is used to manufacture hexagonal ferrite, then productivity is improved, but particle size uniformity deteriorates
Solution Approach 1:
The continuous hydrothermal synthesis process is segmented into two independent stages: (1) precursor preparation stage with controlled pH variation, and (2) hydrothermal conversion stage. This segmentation allows independent optimization of each stage - the first stage controls nucleation and particle size uniformity through pH management, while the second stage completes the transformation to hexagonal ferrite, thereby achieving both high productivity and sharp particle size distribution.
Solution Approach 2:
The invention controls the pH parameter during precursor preparation to vary within ±2 units, which fundamentally changes the reaction conditions to promote uniform nucleation. This parameter control, combined with the continuous hydrothermal process, enables the system to maintain high productivity while achieving coefficient of variation in particle size of 25% or less.
2Quantity of substance
If particle size is reduced to increase fill rate, then recording density is improved, but thermal fluctuation effects worsen
Solution Approach 1:
The invention replaces conventional batch synthesis with a continuous hydrothermal synthesis process that uses controlled chemical reactions in a continuous flow system. This substitution enables precise control over particle formation dynamics, producing ultrafine particles with narrow size distribution that maintain thermal stability while achieving high fill rates in magnetic recording media.
3Object-affected harmful factors
If particle size is reduced to decrease noise, then signal quality is improved, but particle size control difficulty increases
Solution Approach 1:
The invention implements feedback control by monitoring and controlling pH variation during precursor preparation. By maintaining pH variation within ±2 units, the process automatically adjusts reaction conditions to ensure uniform particle nucleation and growth, producing particles with coefficient of variation ≤25% without requiring complex external control systems.
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 approach results in hexagonal ferrite powder with an average particle size of ≤35 nm and a coefficient of variation in particle size of ≤25%, enhancing magnetic recording medium performance by reducing noise and improving recording density.
Implementation Method 1
a method for obtaining hexagonal ferrite by placing a precursor of hexagonal ferrite in the presence of highly reactive water that has been heated and pressurized to convert the precursor to hexagonal ferrite
Implementation Method 2
preparing a hexagonal ferrite precursor-containing water-based solution by stirring and mixing a reaction solution which comprises an iron salt, an alkaline earth metal salt, and a base
Data Source
AI summary
An aspect of the present invention relates to a method of manufacturing hexagonal ferrite powder, which comprises preparing a hexagonal ferrite precursor-containing water-based solution by stirring and mixing a reaction solution which comprises an iron salt, an alkaline earth metal salt, and a base in a reaction tank, and removing the hexagonal ferrite precursor-containing water-based solution that has been prepared from the reaction tank and continuously feeding the hexagonal ferrite precursor-containing water-based solution into a reaction flow passage while conducting heating and pressurizing to converting the hexagonal ferrite precursor to hexagonal ferrite, wherein the preparation of the hexagonal ferrite precursor-containing water-based solution comprises a continual feed period during which feeding of the iron salt, the alkaline earth metal salt, and the base into a reaction tank which comprises a prereaction solution in which an iron salt and a base are not both present is continuously or intermittently continued, during the continual feed period, at least a base is fed over a feed passage separate from feeding of the iron salt and the alkaline earth metal salt, and an amount of at least one from among the iron salt, the alkaline earth metal salt, and the base that is fed per unit time during the continual feed period is controlled and/or acid is added to the reaction solution in the reaction tank so that a pH of the reaction solution within the reaction tank during the continual feed period falls within a range relative to a pHbefore, a pH of the prereaction solution, ofpHbefore−2≦pH≦pHbefore+2.