Technical information


Technical information

How to deal with the “troublemaker” of the slurry - air bubbles?

How to deal with the “troublemaker” of the slurry - air bubbles?

  • May 20,2020.

How to deal with the “troublemaker” of the slurry - air bubbles?

Many people may have the same problem when producing slurry, there are too many bubbles in the material. If these bubbles are not removed in time, it will often cause serious consequences-for example, bubbles in ceramic slurry will cause more pores in the blank body after molding. Bubbles in textile slurry will affect penetration and make sizing uneven. Bubbles in electronic slurry will affect the capacity and service life of the product. Bubbles in coating will cause surface defects in the application of the product, which will not only damage the appearance, but also affect the corrosion resistance and weather resistance of the coating film.

Ceramic slurry with bubbles

Therefore, in many similar production occasions, "deaeration" has become a very critical step in the process. As for how these bubbles come from and how they go, please see below for details.

Causes of slurry foaming and bubbling

The generation of air bubbles in liquids is a very complicated problem. The generally accepted view of the formation mechanism of bubbles in liquids is cavitation phenomenon, that is, due to its certain solubility, the gas usually exists in the liquid as bubble core. When the liquid flows through a region with a very low absolute pressure in a very short time, the bubble core will quickly evaporate or dissociate. If you want these bubbles to disappear naturally, usually will need to wait for four stages: the bubbles move to the liquid surface - Liquid film is formed at the interface - Film ruptures - Bubbles separate from the liquid surface or the bubbles burst.

Ways to deal with bubbles

At present, there are three main ways to eliminate the bubbles generated in the slurry producing process:

①Use defoaming agent: defoaming agent can be added in twice, before slurry preparation and at the end of slurry preparation.

②Slow stirring: put the slurry in the container and stir slowly.

③Vacuum method: slurry in a closed container to stir, while keeping the container in a vacuum state (use a vacuum pump).

The reason why defoaming agent can defoam is mainly because when defoaming agent diffuses in the foam, it will form a double film on the foam wall. During this diffusion process, the stabilizing surfactant is displaced, and reduce the local surface tension of the foam, destroy the self-healing effect of the foam, so that the foam burst.

But since the defoaming agent may react with the compound in the slurry or affect the performance of the slurry, the vacuum method is more common, especially in high viscosity slurry. This is because the bubbles in high viscosity slurry rise very slowly by their own buoyancy, so they must rely on external force to bring the bubbles to the liquid surface. Currently, the more effective vacuum defoaming method include vacuum stirring defoaming and vacuum film defoaming.

1、Vacuum stirring defoaming method

For the stirring of high-viscosity liquids, slow-type stirrers are often used, such as anchor type, screw type, and screw ribbon type. At present, some vacuum stirrers on the market use both the strong shear force and centrifugal force produced by rotation and orbit motion, forcing the expanding bubbles at the bottom of the material to float to the surface for defoaming, and pumping vacuum while stirring. Compared with the vacuum chamber method, this method can not only quickly perform defoaming, but also effectively remove bubbles at the bottom of the material.

Schematic diagram: Rotation and Orbit motion + Vacuum defoaming (Photo source: THINKY)

2、Vacuum film defoaming method

The separation device of the vacuum film defoaming method will be equipped with a stepless speed regulation orbit motion disk and a material self-rotation diversion head. Under high vacuum status, the material is pressed to the separation device for self rotation under external pressure and vacuum, and under the centrifugal force of the orbit motion disk, the film is uniformly rotated and extruded. In the case of a strong pressure difference, the bubbles rapidly expand, escape or burst.

The vacuum Deaerator

The vacuum Deaerator (Photo source: PUHLER)

When bubbles are removed, the application performance of the slurry will no longer limited by it. It is believed that with the electronics, medicine, coatings and other industries continue to be hot, the industry demand for slurry defoaming will increase more and more.

(From: 粉体圈)

© Copyright: 2020 PUHLER (Guangdong)Smart Nano Technology Co.,Ltd. All Rights Reserved.

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