Foam is a mass of bubbles created when certain types of gas are dispersed into a liquid. Strong films of liquid than surround the bubbles, forming large volumes of non-productive foam.

The cause of foam is a complicated study in physical chemistry, but we already know that its existence presents serious problems in both the operation of industrial processes and the quality of finished products. When it is not held under control, foam can reduce the capacity of equipment and increase the duration and costs of processes.

Antifoam blends contain oils combined with small amounts of silica. They break down foam thanks to two of silicone's properties: incompatibility with aqueous systems and ease of spreading. Antifoam compounds are available either as powder or as an emulsion of the pure product.

Powder

Antifoam powder covers a group of products based on modified polydimethylsiloxane. The products vary in their basic properties, but as a group they introduce excellent antifoaming in a wide range of applications and conditions.

The antifoams are chemically inert and do not react with the medium that is defoamed. They are odourless, tasteless, non-volatile, non-toxic and they do not corrode materials. The only disadvantage of the powdery product is that it cannot be used in watery solutions.

Emulsions

Antifoam Emulsions are aqueous emulsions of polydimethylsiloxane fluids. They have the same properties as the powder form, the only difference is that they can also be applied in watery solutions.

http://www.lenntech.com/products/chemicals/water-treatment-chemicals.htm#Antifoams