Characterization and Structural Aspects of Synthetic Silica

In sharp contrast with carbon black, there is no standard classification for commercially available silica but elementary particle size and the morphology of the reinforcing object (that we call the cluster in the case of silica, keeping the term aggregate for carbon black) are recognized as two important parameters for reinforcement performance. However, surface character-isdcs play a larger role in the case of silica than for carbon black, thanks to the rich surface chemistry of silica particles. 

Depending on the manufacturer and the manufacturing process, i.e., essentially by pyrogenation or by precipitation, different characteristics are measured, not always with standard methods. Primary characteristics include (see Table 4.9 for typical ranges)  

Specific surface area using the well known BET method for nitrogen adsorption (ASTM D3037/4820). 

Average cluster size (or morphology) DBP absorption is used (ASTM D2414) TEM can be used for a more precise (but also more tedious) measure of cluster and elementary particle sizes. 

Porosity ideally through mercury absorption, to be preferred to more common oil absorption techniques. pH silica are normally slightly acidic (5.5-7.0). 

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