Very fine particles tend to form agglomerates or even aggregates. The interparticle adhesive forces are then unusually high in relation to gravity. This complicates the homogenization process in the mixer. Disagglomerating nanofine particles is difficult and requires the use of high-speed tools. amixon® installs high-speed cutting rotors, HighShearBlades or rotor stators in the mixer. Hardened materials, armor plating and coatings prevent wear. They also prevent contamination of the nanopowders with the material of the dispersing tools.
Particle technology
Unlike in mechanical engineering, it is not individual workpieces - with the unit of measurement millimeter = 10-3 m - that are the object of consideration, but heterogeneous particle systems.
Let us assume that we have calcinated 100 kg of a ceramic color body in a kiln. We would then grind this mass in a pan grinder or air jet mill. After the crushing process, we may assume that each particle of this 100 kg batch looks slightly different from all other particles. In this respect, the definition of characteristic features of the particle collective can only be done with the help of statistical methods. The typical length measure to describe a particle is the micrometer: 1 µm = 10-6 m = 1E-6 m. Particle diameters typical for bulk materials can be, for example, 0.1 µm or several 200 µm. However, the particles of a bulk material can also be much smaller. They are then called nanoparticles. Their particle diameter is one thousandth of a micrometer. The unit of measurement then used is the nanometer: 1 nm = 1/1000 micrometer = 10-9 m = 1E-9 m.
Characteristic features of bulk materials can be: Particle diameter, particle size distribution, particle shape, sphericity of particles, packing density, bulk density, adhesion and cohesion behavior, sintering behavior, time consolidation, flow behavior, flow locations and yield points, moisture content, mixing ability, segregation tendency, particle hardness, agglomeration tendency, sinking behavior and dispersibility in gaseous or liquid media, affinity to liquid or gaseous media, solubility, absorption tendency, porosity, specific surface area, air holding capacity, electrostatic charge, dust tendency and much more.
If a bulk material is ground or sprayed very finely, then the solid surface area increases exponentially.
If bulk materials are converted to the nano-fine state, their chemical activity is increased. In addition, chemical and physical properties can change significantly. Ceramic materials created from nanoparticles, for example, can be similarly ductile to metallic materials. Their extremely increased specific surface area makes them interesting as catalysts in chemistry. They are powerful light absorbers and can be used as UV protection in sunscreens and in emulsion paints. Nanotechnology is also used in medical technology and in the production of semiconductors. Nanoparticles are also formed naturally when goods burn. For example, they are deliberately generated to produce carbon black as a black pigment (pyrolysis). Structure agglomeration of nanoparticles. Handling very fine particles can trigger hazards. amixon® mixers offer a high level of safety. They are permanently gas-tight and their mixing tools rotate at relatively low rotational frequencies. Further details on the subject of Atex and type examination.
With each particle division, the surface area of the powder increases. The surface area grows exponentially. The bulk material changes its flow properties. It becomes increasingly sticky. It resembles a highly viscous paste (ceramic materials). In the nanoparticulate state, however, a powder can also exhibit increased "air holding capacity" and fluidize (industrial soot from pyrolysis). Both phenomena complicate the handling of nanoparticulate bulk materials.
amixon® twin-shaft mixer with two cutting rotors.
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