Bubuk ultrahaluss refer to powders with extremely small particle sizes. Their size ranges from a few nanometers to several tens of micrometers. Although there is no strict definition, the term is widely used across industries. It is often categorized according to application and preparation method. A common classification is as follows:
Fine powder: particle size between 10 and 45 μm.
Micron powder: particle size between 1 and 10 μm.
Submicron powder: particle size between 0.1 and 1 μm.
Nanopowder: particle size between 0.001 and 0.1 μm, that is, 1 to 100 nm.
As particle size decreases, the properties of ultrafine powders change greatly. When the particle scale reaches the submicron or nanometer level, the surface atomic arrangement and crystal structure change significantly. These changes lead to surface effects, size effects, quantum effects, and quantum tunneling effects. Ultrafine powders therefore show unique physical, chemical, and interfacial properties in special applications.
However, ultrafine powders also face challenges. Their large surface area and high surface energy make them unstable. They tend to agglomerate to reduce surface energy. This agglomeration can cause particle coarsening and reduce performance. It also makes further grinding more difficult.
Mechanical Impact Ultrafine Mills
Principle and Types
The mechanical impact ultrafine mill uses high-speed moving impact elements to apply strong forces on the material. The grinding process occurs through particle–particle collisions and impacts between particles and grinding parts.
The main working mechanism involves energy generated by multiple impacts. This energy is much higher than the actual energy needed for crushing. Higher impact speed and shorter contact time increase the energy applied per unit time. This makes the material easier to grind.
In the gap between the stator and rotor, the material experiences shearing forces. It then rebounds into the chamber and collides with other fast-moving particles. This keeps the grinding process going.
A strong high-speed turbulent field forms between the stator lining and rotor impact elements. The pressure variations in this field create alternating stresses that crush the material. Therefore, the grinding effect depends on rotor speed, stator–rotor gap, and material properties.
Technical Advantages of Jet Mills
Basic Principle of Jet Milling
Jet mills use high-speed gas streams or superheated steam to create a strong turbulent field. Grinding occurs through particle–particle collisions, airflow-induced impact and shear, and friction with the chamber wall.
Jet mills are used widely in industries. They come in many types, such as flat, circulating-tube, opposed jet, and impact jet mills. The grinding mainly happens near the nozzles. The collision frequency between particles is much higher than that between particles and walls. Therefore, interparticle collisions dominate the grinding process.
Flat-Type Pabrik Jet
High-pressure gas enters the air distribution chamber, which connects to the grinding chamber. When gas passes through the nozzles, it reaches speeds of hundreds or even thousands of meters per second. The gas inlet and jet tubes intersect at a specific angle, forming a rotating vortex. This promotes particle collisions, friction, and shear. Centrifugal force enables accurate particle classification.
Opposed Jet and Fluidized Bed Designs
The opposed jet mill, also called a counter jet mill, uses two opposing gas streams. The particles collide head-on from the start. This design reduces wall abrasion and contamination. It is suitable for hard materials and ultrafine powder production. However, its structure is complex and energy consumption is high.
The fluidized bed opposed jet mill combines the opposed jet principle with fluidized bed expansion flow. It forms an efficient gas-solid grinding system. The EPIC Powder MOQ series fluidized bed jet mill is a representative model. The working process is as follows. The material enters the feed hopper through a valve. It is then conveyed into the grinding chamber by a screw feeder or gravity. High-pressure air is injected through opposing nozzles. The particles become fluidized and collide at high energy to achieve ultrafine grinding.
Kesimpulan
Ultrafine powders, defined by their specific size ranges, show strong surface and size effects. They have great potential in modern industries. However, their instability and agglomeration create challenges.
Mechanical impact mills and jet mills, including flat, opposed jet, and fluidized bed types, help solve these problems. They use high-speed impacts, particle collisions, and strong turbulence to achieve efficient and precise grinding and classification.
Future powder technology will focus on stable dispersion, low-energy ultrafine grinding, and environmental protection. These advances will further enhance the unique properties of ultrafine powders and support the progress of advanced materials and high-tech industries.
