Freeze Granulation: A novel technique for low-loss Mn-Zn ferrites

Vasiliki Tsakaloudi, George Kogias, Vassilios Zaspalis

Laboratory of Inorganic Materials, Chemical Process Engineering Research Institute,
Centre for Research and Technology-Hellas, 57001 Thermi-Thessaloniki, Greece

Freeze Granulation – A novel technique for low-loss Mn-Zn ferrites

In the present study the freeze granulation technique is applied in the manufacturing process of Mn-Zn power ferrites. The powders are prepared by the solid state reaction method and a comparison between the standard industrially used spray-drying method and the freeze granulation process with subsequent freeze drying has been carried out, in terms of granulate morphology, compaction behavior and pore size distribution, sintering behavior and magnetic performance. It apeared that the freeze granulation process enables the formation of homogeneous green compact microstructures and finally leads to sintered products of good magnetic quality. Consequently, Mn-Zn ferrites with low losses of 287 mW/cm3 (at measuring conditions f=100 kHz, B=200 mT and T=1000C) are manufactured. 

Spray-freezing and freeze drying

Spray-freezing and freeze drying – Freeze Granulation

PowderPro AB develop, manufacture, market and sell equipment and know-how for Freeze Granulationspray freezing and subsequent freeze drying (lyophilization or cryodesiccation). Freeze Granulation was developed in late 1980s at Swedish Ceramic Institute in Göteborg and it is also a development of Spray Freeze Drying (SFD) and Spray Freezing into Liquid (SFL).

Spray cooling or rather called spray freezing is the first step in the freeze granulation process where a suspension is atomized, sprayed with a nozzle, into a chamber with liquid nitrogen. The small droplets are then rapidly frozen with a minimum of ice crystal growth. The frozen material (granules) are then transferred to a freeze dryer where the ice is removed by sublimation, i e never go through a liquid state that ensure homogeneity preservation.

Below you can see an illustration of the Freeze Granulation process.

Please contact us for more information and a test-granulation of your powder system.

Illustration of Freeze Granulation

Illustration of Freeze Granulation

Granule drying

In the Freeze Granulation process, freeze drying/lyophilizing is used as the granule drying method for to sublimate the nano ice and there by avoid melting of the frozen granulate.

Please contact us for more information and a test-granulation of your powder system.

Freeze dryer Lyovac GT-2

Freeze drying

Spray Freeze Drying for Soft Granules by Freeze Granulation

Freeze drying is an important processing step in Freeze Granulation where we sublimate the solvent (ice if water) from our spray frozen (spray freezed) granules, resulting in a free-flowing and dust-free granulated material suitable for pressing of components.

Please contact us for more information and a test-granulation of your powder system.

 

Freeze dryer Lyovac GT-2

Spray-freezing and freeze drying

Spray-freezing and freeze drying – Freeze Granulation

PowderPro AB develop, manufacture, market and sell equipment and know-how for Freeze Granulationspray freezing and subsequent freeze drying (lyophilization or cryodesiccation). Freeze Granulation was developed in late 1980s at Swedish Ceramic Institute in Göteborg and it is also a development of Spray Freeze Drying (SFD) and Spray Freezing into Liquid (SFL).

Spray cooling or rather called spray freezing is the first step in the freeze granulation process where a suspension is atomized, sprayed with a nozzle, into a chamber with liquid nitrogen. The small droplets are then rapidly frozen with a minimum of ice crystal growth. The frozen material (granules) are then transferred to a freeze dryer where the ice is removed by sublimation, i e never go through a liquid state that ensure homogeneity preservation.

Below you can see an illustration of the Freeze Granulation process.

Please contact us for more information and a test-granulation of your powder system.

Freeze granulation illustration

Freeze Granulation illustration

Freeze Granulation of ceramic powders

Freeze Granulation offers the possibility to produce very soft, spherical granules which show an excellent flowability. The granules can be compressed to compacts of high homogeneity and they are completely redispersable. Freeze Granulation is a granulation technique which combines the advantages of spray drying and freeze drying. Hard granules are prevented by this technique excluding capillary forces during drying.

Please contact us if you would like to test-granulate your powders or chemicals.

Granule homogeneity

Migration and segregation of the constituents that is common in other granulating processes such as spray drying is avoided in Freeze Granulation. By instant freezing of small droplets critical ice crystal growth is avoided. The freeze drying where the liquid medium is sublimated ensures homogeneity preservation, limited oxidation and soft bonds within the granules. This provides the best possible condition for any subsequent processing such as easy pressing to homogenous compacts, easy re-dispersing in a liquid, sintering of catalytic particles, dosage processes etc.

Interested in test-granulation of your material?

If you would like to test-granulate your powders or chemicals using Freeze Granulation, please contact us for details. You send your material and binders to us, we make the test-granulation using freeze granulation and then send the granulated material (granulaes) back to you for your evaluation and testing.

Freeze granulation is considered to be a natural tool in most kind of material processing and development where optimal material performance is to be reached. PowderPro provides test granulations to reduced cost to evaluate the performance regarding your specific material system and application.

When purchasing of granulation equipment, PowderPro provides help in concepts for suspension formulation/preparation and how to operate the equipment to achieve high yield and high-quality granules.

 

LS-2 - Lab-scale Freeze Granulator