Fumed silica is a synthetic amorphous silicon dioxide produced by burning silicon tetrachloride in an oxygen-hydrogen¯ame. Surface areas range from 50 up to 400 m 2 /g. Using particle sizing techniques, fumed silica shows micro-sized particles leading to surface areas markedly lower than expected. Fumed silica appears as a¯uffy solid with bulk densities down to 0.03 g/cm 3 , being invariant over the wide range of surface areas. Attempts to relate the variation of the surface area directly to the performance of fumed silica in technical applications, such as its thickening ef®ciency in¯uids, mainly fail and remain ambiguous. The aim of this work was to investigate the particle sizes and structures of fumed silica aggregates and agglomerates, using different particle dispersion and sizing techniques.
Fumed silica is a synthetic amorphous silicon dioxide produced by burning silicon tetrachloride in an oxygen‐hydrogen flame. Surface areas range from 50–400 m2/g. Using particle sizing techniques, fumed silica shows micron sized particles leading to surface areas markedly lower than expected. Fumed silica appears as a fluffy solid with bulk densities down to 0.03 g/cm3, being invariant over the wide range of surface areas. Attempts to relate the variation of the surface area directly to the performance of fumed silica in technical applications, such as its thickening efficiency in fluids, mainly fail and remain ambiguous.
Electrical tribocharging is a fundamental physicochemical phenomenon and the basis of electrophotographic development. Despite extensive study, a complete understanding of the mechanism-commonly referred to as electron or ion transferremains unclear. Using a quantum chemical (QCh) approach, we studied the electron charge transfer (ECT) as one possible atomicscale mechanism of tribocharging. We also describe ECT for several systems based on two materials in contact (tribopairs). Methods of density function theory and time-dependent density function theory were applied to QCh modeling using a cluster approach. A series of energetic and charge characteristics at the atomic level were calculated: including the highest-and lowest-occupied molecular orbitals (respectively) and the Fermi levels of complex components in their individual (free) as well as contact states, before and after electron excitation, ECT-excited energy states, charge distribution in the complexes, and the dipole moments of the excited complexes with ECT. Correlations were evaluated between the transferred charges and dipole moments and between transferred charges and Fermi levels. Furthermore, we could show that the QCh analysis offers insight into the ranking of tribocharging agents based on their chemical nature.
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