Novel technique for measurement of coating layer thickness of fine and porous particles using focused ion beam--颗粒学报PARTICUOLOGY

Goslinska, M., Selmer, I., Kleemann, C., Kulozik, U., Smirnova, I., & Heinrich, S. (2019). Novel technique for measurement of coating layer thickness of fine and porous particles using focused ion beam. Particuology, 42, 190-198. https://doi.org/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

a Hamburg University of Technology, Institute of Solids Process Engineering and Particle Technology, Denickestr. 15, 21073 Hamburg, Germany
b Hamburg University of Technology, Institute of Thermal Separation Processes, Eißendorfer Str. 38, 21073 Hamburg, Germany
c Technical University of Munich, Chair of Food and Bioprocess Engineering, Weihenstephaner Berg 1, 85354 Freising, Germany

10.1016/j.partic.2018.03.002

Volume 42, February 2019, Pages 190-198

Received 16 November 2017, Revised 26 February 2018, Accepted 4 March 2018, Available online 27 June 2018, Version of Record 21 January 2019.

E-mail: monika.goslinska@tuhh.de

Highlights

• Light and highly porous aerogel microspheres were coated in dilute spouting regime.

• The coated microparticles were cross-sectioned using focused ion beam.

• Film thickness of cross-sectioned coated microparticles was precisely measured.

• Successful and uniform coating with layer thickness of around 1 μm was achieved.

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

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