Amorphous Submicron Particle Production via Heated Steam Jet Milling
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Solution Overview
Problem
Current methods for producing finely divided amorphous silica and silicates fail to achieve average particle sizes below 1 µm with a narrow particle size distribution, leading to issues in coating systems where large particles result in uneven surfaces and porosity changes during drying.
Innovation Solution
A process using a jet mill with a heating phase to prevent condensation, employing steam or water vapor as the grinding medium, ensuring the grinding chamber is above the dew point, and incorporating a dynamic classifier to achieve average particle sizes below 1.5 µm and narrow distributions, allowing for dry grinding without reagglomeration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional jet mills are used to grind amorphous silica and silicates, then the grinding process is simple and straightforward, but the achievable particle diameter is well above 1 µm with a broad particle size distribution
Solution Approach 1:
The grinding process is divided into multiple sequential stages: a first jet mill reduces particles to an intermediate size range (0.5-2.0 µm), then a second jet mill further grinds to the final submicron range (<1.0 µm). This multi-stage segmentation allows each mill to be optimized for its specific size range, achieving precision unattainable in a single stage while managing complexity through modular design
Solution Approach 2:
Before the actual grinding operation, the grinding chamber undergoes a heating phase to raise the temperature above the dew point of the grinding gas. This preliminary action prevents condensation and agglomeration during grinding, ensuring consistent submicron particle size without requiring complex additional equipment
2Productivity
If steam is used as the grinding medium to achieve very small particle sizes, then the acceleration capacity increases by approximately 50%, but condensation occurs in the grinding system resulting in agglomerates and crusts
Solution Approach 1:
The grinding chamber is heated to a temperature above the dew point of the steam before the grinding operation begins. This preliminary heating action prevents condensation of steam during grinding, eliminating agglomerate and crust formation while maintaining the high acceleration capacity and productivity of steam as the grinding medium
Solution Approach 2:
The temperature parameter of the grinding chamber is changed and maintained above the dew point of the steam. This parameter change transforms the condensation-prone environment into a condensation-free environment, allowing steam to be used as a reliable grinding medium that maintains both high productivity and process stability
3Manufacturing precision
If wet grinding is used to achieve very fine suspensions, then the particle size can be reduced, but it is not possible to isolate a finely divided, agglomerate-free dry product without changing the porosity properties
Solution Approach 1:
The mechanical wet grinding system is replaced with a pneumatic jet mill system that uses high-velocity gas or steam jets to comminute particles. This substitution eliminates the need for subsequent drying operations that alter porosity, as the dry grinding process directly produces free-flowing powders with preserved porous structure and no agglomeration
Solution Approach 2:
The fundamental parameter change is transitioning from a liquid-based grinding medium to a gas/steam-based medium. This change allows the grinding to occur in the gas phase, producing dry particles directly without the need for drying, thereby maintaining the original porosity and preventing agglomeration that occurs during evaporation
4Reliability
If the grinding chamber is heated to prevent condensation, then condensation and agglomeration are reduced, but additional energy is required for heating
Solution Approach 1:
The heating function is merged with the existing grinding system by utilizing the grinding gas itself as the heating medium. The grinding gas is heated and circulated through the chamber, serving dual purposes: providing the mechanical energy for particle comminution and maintaining the temperature above the dew point to prevent condensation. This merging eliminates the need for separate heating equipment and reduces overall energy consumption
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 process produces amorphous powders with precise particle sizes and distributions, enabling the production of thin, smooth coatings and maintaining porosity, while reducing condensation and agglomeration issues, thus enhancing the efficiency and effectiveness of surface coating systems.
Implementation Method 1
the grinding chamber is in a heating phase, i.e. H. Before the actual operation with the operating medium, it is heated in such a way that the temperature in the grinding chamber and at the mill outlet is higher than the dew point of the steam and/or operating medium
Implementation Method 2
a process using a jet mill with a heating phase to prevent condensation, employing steam or water vapor as the grinding medium
Data Source
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Figure 2
Figure 2a
AI summary
The invention relates to a novel method for the comminution of amorphous chemical solids such that particles having a mean particle diameter of d50 < 1.5 µm are obtained. The invention also relates to the use of the comminuted solids in coating systems.