Controlling the phase of iron oxide nanoparticles fabricated from iron(III) nitrate by liquid flame spray

Abstract

Iron oxide nanoparticles were synthesized in a liquid flame spray process from iron(III) nitrate. The choice of chemicals and all other process parameters affects the crystallographic phase composition and the quality of the material. Adjustment of the solvent composition and the gas flow rates was used to control the phase composition of the produced particles. All samples consisted of pure maghemite (γ-Fe 2 O 3 ) or a mixture of maghemite and hematite (α-Fe 2 O 3 ). When using pure alcohols as solvents, the maghemite/hematite phase ratio could be adjusted by changing the equivalence ratio that describes the oxidation conditions in the flame zone. A large residual particle mode formed in the size range of ~20-700 nm along with a dominant very fine particle mode (2-8 nm). Both phases seemed to contain large particles. A partial substitution of methanol with carboxylic acids turned the hematite phase into maghemite completely, even though some of particles were possibly not fully crystallized.Residual particles were still present, but their size and number could be decreased by raising the heat of combustion of the precursor solution. 30 vol-% substitution of methanol with 2-ethylhexanoic acid was adequate to mostly erase the large particles. K E Y W O R D Siron/iron compounds, liquid flame spray, nanoparticles, synthesis

Crystallographic phase formation of iron oxide particles produced from iron nitrate by liquid flame spray with a dual oxygen flow

“…The results for CitA and OxA cannot be directly compared to the results for carboxylic acid addition in the previous study 15 , because the experimental setup was different, and the precursor concentration a little bit higher. What makes the two situations somewhat comparable, though, is that the chosen parameters with pure methanol as the solvent produced very similar phase compositions in both cases (42.3 % vs 44.6 % of hematite).…”

“…With this setup, a φ range of 0.10-0.33 was achieved, and therefore we continued down from where we left off in the previous study (0.32-1.76). Figure 2 shows the calculated weight fraction of maghemite (the rest was hematite) as a function of φ, alongside the results from the previous study 15 , obtained with another burner design. The Rietveld plots and refinement parameters are presented in Figures S1-S4 and Table S1.…”

“…For CitA and OxA samples, the additive was dissolved in the precursor solution after the dissolution of iron nitrate in methanol. The samples were collected as a powder with an electrostatic precipitator described by Sorvali et al 15 .…”

“…The phase compositions were calculated from the XRD data with Rietveld refinement by BRASS 2 program 24 . The crystal structure models used for iron oxide were obtained from American Mineralogist Crystal Structure Database (AMCSD) with the codes 0020585 for maghemite (space group Fd-3m) and 0000143 for hematite (space group R-3c), as in the previous study 15 .…”

“…This study aims to build on the previous paper by Sorvali et al 15 that focused on factors affecting the phase of iron oxide nanoparticles produced in an LFS synthesis from iron(III) nitrate. The two main factors studied in the previous study were: (1) the equivalence ratio (φ), controlled through adjusting O 2 and H 2 gas flows, when using pure alcohols as solvents, and (2) substituting part of the alcohol with a carboxylic acid in the precursor solution.…”