Silicas and Silicates for Defoamers Will Burst Your Bubble
Effective Foam Controlling Performance Materials
Evonik Silicas for Defoamers – have been specially developed to facilitate the coalescing of foam bubbles. The silicas give full effect independent of the kind of foam, whether macro foam or micro foam.
Evonik Silicas for Defoamers
Evonik Silicas for Defoamers are easily made hydrophobic by the dry-roast or in-situ method of hydrophobization.
Benefits of Evonik Silica for Defoamers:
Easy to process
Uniform particle size
Effective in use
There are two basic method of making hydrophilic silica hydrophobic the In-situ and the Dry Roast Method:
1. In-Situ Method
The hydrophilic silica is reacted with hydroxy terminated silicone oil in a diluent vehicle like glycol. An organic amine or ammoniumcarbonate are used as catalyst. The condensation reaction takes place between silica and silicone oil at fairly low temperature (limited to the flash point of the diluent (100-120°C)). Once hydrophobic, the silicon dioxide is further suspended in the defoamer oil. Surfactants and wetting agents are added.
2. Dry Roast Method
The hydrophilic silica is reacted with the silicone oil (PDMS) (e.g. 100 cps) in a fluidized bed reactor to promote good contact between silica and silicone oil. Reaction takes place at about 250 °C. Water is released during the condensation reaction as by-product. The hydrophobic level is measured by the Methanol Wet Out method. Once hydrophobic the silicon dioxide is suspended in a diluent vehicle like mineral or silicone oil. Surfactants and wetting agents are added.