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Nano ´03 October 21st -23rd, 2003 Faculty of Mechanical Engineering VUT, Brno, Czech Republic. Discrete. Mechanical Forces. Host. +. Continuous. Guest. Powder Flowability Improvement using Nanoparticle Surface Modification. A leš Slíva a* , Jiří Zegzulka and Jaromír Polák

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Powder flowability improvement using nanoparticle surface modification

Nano ´03October 21st -23rd, 2003Faculty of Mechanical Engineering VUT, Brno, Czech Republic








Powder Flowability Improvement using Nanoparticle Surface Modification

Aleš Slíva a*, Jiří Zegzulka and Jaromír Polák

aVŠB-Technical University of Ostrava, Faculty of Mechanical Engineering, Institute of Transportation, Laboratory of Bulk Materials

17. Listopadu 15, CZ 708 33 OSTRAVA-PORUBA

[email protected]; phone 420 59732 5110; fax +420 596 916 490


Essential property in a transport process of a particulate material is flowability in vessels, bunkers, and silos. The flowability as a property influences the creation of falls, such an arching, piping, ratholing in a storage transport system. Elimination of the phenomena, for example by using air pumps and vibrators for existing storage system, is mechanically very ineffective and time consuming. However, coating a small amount of additive, and thereby decreasing the angle of internal friction, is one way of improvement flow properties of storage particulate materials. Although flow property improvement of a particulate material is achieved, issues such as the applicability for food industry and quantifying how much coating batch is necessary for optimal storage of transport conditions still remain.

Dry Particle Coating

Dry Particle coating is accomplished by any process that allows for mechanically fixing fine particles (guests) onto the surface of relatively larger particles (hosts).

Operating parameters and properties for MAIC

Flowability investigated on Jenike Powder Tester

Jenike Shear Measurement (JSM) was developed to attain behavior of particulate solids. Although, a lot of usably results and resolutions of a storage conditions have been achieved, there are still problem with repeatability of measurement to ensure its accuracy. Moreover, a lot of research centers and laboratories even utilize results received by JSM and thus interpretation of errors accepted by JSM analyses help us to understand of particle solids behavior.

Angle of Repose (AOR)

The angle of repose (AOR) is a commonly used index for flowability hence, it is used to evaluate the coating effectiveness in terms of improving flow properties.

Angle of Repose measurement on Hosokawa Micron Powder Characteristics Tester (HMPCT)

The Powder Characteristics Tester, Model PT-N, is a single instrument which provides seven mechanical measurements and three supporting measurements of dry bulk powders. It complies with Standard Test Method ASTM D6393-99 “Bulk Solids Characterization by CARR Indices”. It has been developed to improve handling, efficiency, and accuracy in testing the bulk properties of dry powders. 

The primary functions of the PT-N device are to provide measurements in a single convenient unit, to provide an additional basis of data for quality control of powdered products, and to provide numerical evaluations of flowability and floodability of powders.

Flowability parametric values received by Jenike Powder Tester Measurement

  • Advantages of Dry Particle Coating

  • new particles may have completely different functionality and/or much improved properties

  • much reduced use of high-priced or rare materials

  • the process is environmentally benign

  • The improved properties may be:

  • Flowability, Dispersibility, Wettability, Coloring, Flavor/Taste, Hydrophilic/Hydrophobic Properties, Electrostatic/Electric/Magnetic/Optical Characteristics, Particle Size Distribution, Particle Shape/sphericity,

  • Solid Phase Reactivity

Angle of Repose of uncoatedcornstarch measured by HMPCT

Angle of Repose of MAICoated cornstarch by 1% fumed silica measured by HMPCT

Flowability of coated and uncoated samples measured on FT3 Flowmeter

Magnetically Assisted Impaction Coating


Results of HMPCT showing Flowability Improvement

The FT3 Powder Rheometer provides a totally innovative approach to powder testing by measuring the energies needed to establish specific flow conditions. The technique offers several benefits that are new and which in combination, make it possible to classify powder in terms of their flowability performance and their processability.

Use magnetic barium ferrite particles to “fluidize” or agitate host and guest powders, thus including “soft” coating by powder impaction.

Energy consumed during agitator traverse revealing incline to consolidation

Energy consumed during agitator traverse by its various speed;measurement repeatability

Governing equations

Each magnetic particle is treated as a small magnetic dipole for the sake of simplicity. When this particle is subjected to an external oscillating magnetic field, the amount of actual magnetization will change and there will be a hysteresis effect. However, for the sake of simplicity it is assumed that these particle has a constant magnetic dipole moment, Then the torque Text , existing on a magnetic particle due to the external field is given by

Angle of Repose (AOR) measurement using Rotating Drum

While the angle of repose by motion Qm is clearly a fundamental property of particulate materials and evidently reflect a critical phenomenon, things are not so clear when it comes to the angle of repose by quiet Qr after the system has relax. Even for large-sized piles, the angle of repose is generally affected by the fact the flowing sheet has to come to a stop at the bottom of the drum.

where m is magnetic dipole moment of the particle, and Bexternalis the magnetic flux density of the external field.

The Bexternalis given by

where m0 is the permeability, N is the number of turns per meter in the coil, given by I=I sin(wt) , and is the unit vector in the direction of solenoid axis. This dipole-dipole induced flux density, is given by

The parameters characterize of the powder flowability

  • Conclusions

  • Tendency to essential improvement of flowability of coated materials due to their aeration and predisposition to sudden flow change

  • Hydrophilic silica coated materials are characterized by sudden move (avalanching) and tendency to creation falls (funnel, arch, rat-holing, piping, etc.)

where the vector r is the position where the field is computed with respect to the coordinate system and m is the magnetic dipole moment. Due to this field, in addition to generating a net torque, there is also a net magnetic force F , acting on a magnetic particle in consequence of the combined magnetc flux, B is

and the net torque, T on a particle is

where B is the total magnetic flux density, which includes the external field. A simple equation for the rotational motion of a particle is

Profile of the free surface of a pile in a slowly rotating drum (W=60 RPM )