Partic. vol. 42 pp. 190-198 (February 2019)
doi: 10.1016/j.partic.2018.03.002

Novel technique for measurement of coating layer thickness of fine and porous particles using focused ion beam

M. Goslinska^a,*, I. Selmer^b, C. Kleemann^c, U. Kulozik^c, I. Smirnova^b, S. Heinrich^a

monika.goslinska@tuhh.de

Abstract

A novel technique for the measurement of the coating layer thickness of fine particles was developed in this work based on cross-sectioning of micrometre-sized single coated particles using focused ion beam (FIB) milling. This technique was tested on two batches of aerogel particles coated with thin coatings in a spouted bed. The FIB milling procedure consisted of two steps. First, the desired part of the coated particle was removed using a high ion beam current. The resulting cross-sectioned area was then polished using a lower ion beam current to make the cross-section clearly visible. The FIB milling process was controlled with simultaneous scanning electron microscopy (SEM). Afterwards, the coating layer thickness was evaluated using the SEM images.
The coating layer was successfully applied on the porous aerogel microparticles in the spouted bed. The coating uniformity of the highly porous particles increased with increasing sprayed coating solution amount, with up to 91% of the particle pores being covered. The FIB-cross-sectioning technique using an ion beam of 2.50 nA for the first milling and 0.43 nA for polishing of the surface resulted in successful generation of cross-sections of representative particles with a visible particle core and coating layer. A coating layer thickness of approximately 700 nm was achieved on particles with sizes of below 45 μm.

Graphical abstract

Keywords

Coating layer thickness; Focused ion beam; Microparticle; Aerogel; Spouted bed; Dilute spouting