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We fabricated iron oxide particles from iron(III) nitrate in a liquid flame spray synthesis. Unlike in most liquid flame spray studies, we implemented a secondary oxygen flow. The effect of the gas flow setup and two additives to the precursor solution, oxalic acid and citric acid, on the resulting particles was studied, with the focus on crystallographic phase composition. The synthesis yielded either pure maghemite or maghemite/hematite mixed phase powders. For solutions without additives, the maghemite fraction was almost linearly dependent on the equivalence ratio. The specific surface area was highest for the smallest equivalence ratios, then decreased, and increased again for the highest values. Some variation was observed between samples with equal equivalence ratios but the total oxygen flow divided differently between the two oxygen channels, a higher atomization flow promoting larger hematite fraction and higher specific surface area. Both additives reduced the amount of hematite in the powder samples, citric acid being the more efficient one. Citric acid slightly raised the specific surface area, whereas oxalic acid dropped it in half. publishedVersion

Superomniphobic, i.e. liquid-repellent, surfaces have been an interesting area of research during recent years due to their various potential applications. However, producing such surfaces, especially on hard and resilient substrates like stainless steel, still remains challenging. We present a stepwise fabrication process of a multilayered nanocoating on a stainless steel substrate, consisting of a nanoparticle layer, a nanofilm, and a layer of silane molecules. Liquid flame spray was used to deposit a TiO2 nanoparticle layer as the bottom layer for producing a suitable surface structure. The interstitial Al2O3 nanofilm, fabricated by atomic layer deposition (ALD), stabilized the nanoparticle layer, and the topmost fluorosilane layer lowered the surface energy of the coating for enhanced omniphobicity. The coating was characterized with field emission scanning electron microscopy, focused ion beam scanning electron microscopy, x-ray photoelectron spectroscopy, contact angle (CA) and sliding angle (SA) measurements, and microscratch testing. The widely recognized requirements for superrepellency, i.e. CA > 150° and SA < 10°, were achieved for deioinized water, diiodomethane, and ethylene glycol. The mechanical stability of the coating could be varied by tuning the thickness of the ALD layer at the expense of repellency. To our knowledge, this is the thinnest superomniphobic coating reported so far, with the average thickness of about 70 nm.

Silica and titania aerosol nanoparticles are coated with silver through a physical coating process. The silver is evaporated in a tubular furnace flow system and condensed on the ceramic carrier particles with diameters of approximately 100 nm. The temperature gradient in the furnace system is optimized in order to avoid homogeneous nucleation of the silver. The generated ceramic–silver composite nanoparticles are characterized with aerosol measurements and analytical transmission electron microscopy. Two completely different particle morphologies are clearly observed, silver-decoration and composite doublet, with amorphous silica and crystalline rutile titania as the carrier particles, respectively. The former morphology consists of multiple silver nanodots with diameters of 1–10 nm, while in the latter morphology the silver had formed a larger structure with a size comparable to that of the carrier particle. Different shapes are observed in these larger silver structures, such as triangular, rodlike, an...

In this study we have used liquid flame spray (LFS) process to synthetize γ-Fe2O3 nanoparticles of two different average sizes. Different sized nanoparticles were generated with two different liquid precursor feed rates in the spray process, higher feed rate resulting in larger nanoparticles with higher saturation magnetization. The nanoparticles were used in bidisperse magnetorheological fluids to substitute 5% of the micron sized carbonyl iron particles. To our knowledge this is the first time particles synthetized by the LFS method have been used in magnetorheological fluids. The bidisperse fluids showed significantly improved sedimentation stability compared to a monodisperse suspension with the same solid concentration. The tradeoff was an increased viscosity without magnetic field. The effect of the nanoparticles on the rheological properties under external magnetic field was modest. Finally, the dynamic oscillatory testing was used to evaluate the structural changes in the fluids under magnetic field. The addition of nanoparticles decreased the elastic portion of the deformation and increased the viscous portion.

Nanotechnology has become a very important branch of research and industry especially during this millenium, and it keeps growing constantly. Simultaneously, demand for large volumes of quality nanomaterial is increasing. Flame spray pyrolysis (FSP) is one of the most promising fabrication methods for inexpensive and simple large-scale production. However, the details of the synthesis process still remain reasonably poorly understood. Liquid flame spray (LFS), a certain type FSP method, was chosen as the focal point of this dissertation. Because both the knowledge on the synthesis process and utilization of LFS in applications are essential for capitalizing on its the strengths in the long term, half of this dissertation was dedicated to improving the understanding of the process, and the other half for exploring its potential in two distinct applications. In the first part, factors determining the crystallographic phase composition of iron oxide particles in LFS synthesis was studied. The synthesis yielded maghemite (γ-Fe2O3) and hematite (α-Fe2O3), and the equivalence ratio was found as the best measure for predicting their ratio. However, the correlation between the phase ratio and the equivalence ratio was observed to differ between different experimental setups. Modifying the precursor solution through mixed solvents or additives also had a clear effect on the phase composition, which indicates that the solution chemistry likely has unknown effects on the process. The first of the two applications was bidisperse magnetorheological (MR) fluids, where LFS-made nanoparticles were added to a more traditional MR fluid to counteract sedimentation. The addition reduced the sedimentation rate considerably without impairing its performance. The second application was a liquid-repellent nanocoating consisting of a nanoparticle layer produced with LFS, an ALD mid layer, and a topmost silane layer. The ultrathin final coating repelled several test liquids effectively, but possessed lower stability than initially hoped.