Preprints
https://doi.org/10.5194/ar-2023-14
https://doi.org/10.5194/ar-2023-14
03 Nov 2023
 | 03 Nov 2023
Status: this preprint was under review for the journal AR but the revision was not accepted.

On Formation of Carbonaceous Impurities in Flame Spray Synthesis of Maghemite Nanoparticles

Ricardo Tischendorf, Kristina Duschik, Sophie Dupont, Fabian Fröde, Heinz Pitsch, Reinhold Kneer, Mirko Schaper, and Hans-Joachim Schmid

Abstract. Particles generated by spray flame synthesis (SFS) can exhibit impurities, with surface adsorbates and soot being the best-known examples. Unfortunately, the extent to which the formation of these impurities can be characterized, and how their formation can be avoided is not fully understood yet. In order to contribute to the understanding of the formation of carbonaceous impurities, we investigated their formation using a standardized burner type (SpraySyn burner) while synthesizing maghemite by the gas-to-particle conversion. Two approaches were followed to characterize the formation of soot and surface adsorbates in this paper. Firstly, fabricated powders were analyzed by complementary powder analysis. In this term, the detection of soot was negative, but powders contained carboxylates and carbonates, which were bound to particle surfaces. The methodological procedure used allowed a reliable quantification of those adsorbates, and it was possible to normalize their relative mass fractions (up to ~16 %) to the powders' respective specific surface areas. The normalization approach yielded a surface loading values of 0.84–0.85 mg m-2. The methodical procedure and the data provided can be used in the future to denote/compare SFS materials in sensitivity studies. Secondly, particles were thermophoretically extracted from the process in situ and subsequently characterized by transmission electron microscopy (TS-TEM). Interestingly, particles extracted at 5 cm height above the burner (HAB) (representing the center of the visible flame) showed amorphous core-shell structures and amorphous aggregates, indicating a coexistence of soot alongside maghemite particles. Via reducing the sampling time of the TS system to 1.5 ms samples were taken either from flame pulses (a state of high flame activity) or from flame flickering (lower flame activity). A comparison of these samples showed that heterogeneous particle structures formed predominantly in flame pulses. As samples extracted at 15 cm HAB neither showed amorphous coating nor amorphous aggregates, it was indicated that soot fractions oxidize between 5 and 15 cm HAB.

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Ricardo Tischendorf, Kristina Duschik, Sophie Dupont, Fabian Fröde, Heinz Pitsch, Reinhold Kneer, Mirko Schaper, and Hans-Joachim Schmid

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on ar-2023-14', Anonymous Referee #1, 05 Dec 2023
    • AC3: 'Reply on RC1', Ricardo Tischendorf, 03 Feb 2024
  • RC2: 'Comment on ar-2023-14', Anonymous Referee #2, 27 Dec 2023
    • AC2: 'Reply on RC2', Ricardo Tischendorf, 03 Feb 2024
  • AC1: 'Comment on ar-2023-14', Ricardo Tischendorf, 05 Jan 2024

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on ar-2023-14', Anonymous Referee #1, 05 Dec 2023
    • AC3: 'Reply on RC1', Ricardo Tischendorf, 03 Feb 2024
  • RC2: 'Comment on ar-2023-14', Anonymous Referee #2, 27 Dec 2023
    • AC2: 'Reply on RC2', Ricardo Tischendorf, 03 Feb 2024
  • AC1: 'Comment on ar-2023-14', Ricardo Tischendorf, 05 Jan 2024
Ricardo Tischendorf, Kristina Duschik, Sophie Dupont, Fabian Fröde, Heinz Pitsch, Reinhold Kneer, Mirko Schaper, and Hans-Joachim Schmid
Ricardo Tischendorf, Kristina Duschik, Sophie Dupont, Fabian Fröde, Heinz Pitsch, Reinhold Kneer, Mirko Schaper, and Hans-Joachim Schmid

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Short summary
Although spray flame synthesis (SFS) is a promising approach to prepare nano materials with tailored properties, the impurity formation is not fully understood in SFS. To contribute to this topic, maghemite nanoparticles were prepared by SFS, and two complementary experimental approaches were used to investigate the evolution of soot and carbonaceous surface adsorbates. The methodological procedure and the data provided can be used to denote/compare SFS-materials more reliably in the future.
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