(70dc) Measuring Slurry Quality and Stability of Pyrogenic Silica Suspensions Using Photon Correlation Techniques

Photon correlation techniques provide a multitude of possibilities to evaluate particle interactions, stability and thus quality of colloidal slurries. With new PCS instruments, that minimize multiple scattering, even concentrated suspensions can be examined. Nevertheless, each characterization task has to cope with different concentration and interaction effects that are specific for the material system under consideration. Thus, the usual algorithms to analyse photon correlation data, second cumulants or inversion methods, may give ambiguous results for the purpose of slurry characterization. Therefore, in the presented work the authors have tried to identify schemes that enable the analysis of different characterization tasks in pyrogenic silica suspensions with concentrations up to 15 wt.-%. First we investigated correlation functions measured in concentrated slurries with regard to quality assurance purposes. A method based on a principal component analysis was established that allows for the detection of smallest deviations from slurry specification. A second issue is the gelation of silica suspensions, when the electrostatic repulsion between the particles is screened. Photon correlation offers an excellent tool to observe the onset of gelation and estimate the gelation time.