The hetero-aggregation of carbon black and colloidal silica in a spray flame is a promising approach to improve dispersibility and stability of carbon black. The mixing quality, i.e. homogeneity of local concentrations within the hetero-aggregate, is important for both properties, yet challenging to quantify. For this purpose, multiple TEM-EDX (Transmission Electron Microscopy with Energy Dispersive X-Ray Spectroscopy) scans are conducted on two distinct process conditions, leading to hetero-aggregates two different mixing qualities. By sampling cutouts of the images at randomized locations and applying principles adapted from classical mixing theory, hetero-aggregates are characterized with respect to mixing quality, irrespective of composition and primary particle size, Furthermore, correlation coefficient functions give insight to the length scale of primary particle clusters in the hetero-aggregates. In addition, on the basis of the \textit{intra-aggregate} mixing state and the distribution of hetero-aggregate composition, a suitable description of the \textit{inter-aggregate} mixing state is achieved. The developed methods present a generally valid, precise characterization of the mixing quality of hetero-aggregates.

This data includes the original TEM-EDX data as well as the segmented images.

The zipped folders include the original TEM-EDX data in the .bcf format as well as the segmented images of isolated C and Si signals in .png format. The images can be matched with each others according to their filename.