The global market requirement of ultra-fine iron powder (UFIP), with a range size of 0.1–1 μm, is more than 20,000 tons per annum. However, no low-cost nontoxic synthesis route of UFIP is known. In this study, we used the low-cost, rapid, and scalable flame aerosol synthesis (FAS) method to synthesize iron oxide nanoparticles with different size and morphology. Combining with a postreduction heat treatment process, a feasible synthesis route of UFIP which meets the commercial production criteria has been developed. By optimizing the precursor concentration and postreduction heat treatment parameters, the final particle size of UFIP can be controlled. The evolution of the microstructure, phase formation, and magnetic properties during the postreduction heat treatment are systematically investigated, and a feasible reaction model has been established. This work provides an important starting point for the facile commercial synthesis of UFIP and can be readily expanded to other pure metals.

Efficient catalysts for the oxygen evolution reaction (OER) are widely applied in fuel cells and rechargeable lithium air batteries. It is desirable but challenging to achieve comparable activity to that of the noble-metal catalyst with non-precious metal catalyst. Highly active Co3O4 thin film electrodes have been successfully synthesized by a rapid one-step flame combustion synthesis method called Reactive Spray Deposition Technology. X-ray diffraction confirms the absence of any impurity phase with this synthesis process. The detailed morphology of the Co3O4 thin film is investigated with scanning electron microscopy and transmission electron microscopy. Cyclic voltammetry is used to investigate the redox activity of Co3+ to Co4+ which is crucial for the OER performance. The as-prepared Co3O4 catalyst demonstrates promising activity for OER, with an overpotential of 399 mV (at 10 mA cm-2) for OER.

A simple and scalable method is developed to prepare highly wrinkled graphene sheets – carbon nanospheres (WG-CN) composite for ultra high energy density supercapacitor application. Here, we introduce a novel simple paraffin wax candle flame technique for the simultaneous reduction of graphene oxide (GO) and deposition of carbon nanospheres on the graphene sheets. This is followed by introducing permanent wrinkles to the composite. The WG-CN composite exhibit the high specific capacitance values of 290 F g-1 and 253.7 F g-1 (138.5 F cm-3) for 6M KOH and EMIMBF4 ionic liquid electrolytes respectively. The ultra high energy density values of 108 Wh Kg-1 and 58.9 Wh L-1 has been obtained at the power density of 3955 W Kg-1 and 2157 W L-1 simultaneously. These attractive performances exhibited by the WG-CN composite supercapacitor electrode make them potential candidate for future energy storage devices. The key to success of this composite is the ability to make full utilization of the high intrinsic specific surface area of the nanocomposite.

SnO2 doped with Sb and Nb has been investigated for its use as catalyst support materials replacing carbon to enhance PEM fuel cells stability. Nanostructured powders of various doping levels were prepared by flame spray pyrolysis (FSP). The specific requirements of surface area >50 m2g-1 and electronic conductivity >0.01 Scm-1 were obtained, and pore sizes ranging mainly from 10 to 100 nm. Pt particles (9-20 wt.% in loading targeted) of ∼1 nm well dispersed in Sb-doped SnO2 was prepared by a one-step FSP procedure providing microstructures of high interest for further investigations as cathode in PEM fuel cells.

Lanthanum zirconate (La2Zr2O7) nano-crystalline films with cubic structure have been successfully prepared by a facile synthesis approach called reactive spray deposition technology (RSDT). La2Zr2O7 nanoparticles are produced by combusting a precursor solution of lanthanum acetylacetonate hydrate and zirconium acetylacetonate dissolved in an organic solvent mixture. The nanoparticles formed during the combustion process are directly deposited onto the substrate. The composition and microstructure of the as-deposited films are extensively characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The thermal diffusivities of the films are investigated by the means of laser flash method.

This study reports the development of a one-step method for the production of antimicrobial protective coatings for aluminum surfaces with titania nanoparticles. An aerosol flame synthesis system was used to produce monodisperse, ultra-fine TiO2 nanoparticles, which were directly deposited by thermophoresis onto plates of aluminum alloy by means of a rotating disc. Fuel-lean reactor conditions were used to synthesize pure anatase nanoparticles of 3.5 nm in diameter. Substrates were mounted onto the rotating disc that repetitively passes through the flame. Convection due to the rotational motion cooled the substrates, on which particles were deposited as films by thermophoresis. Such a system allowed to obtain submicron coatings of different thickness, by varying the total time of deposition. The antimicrobial activity of TiO2 coatings was tested against the Gram positive bacterium Staphylococcus aureus. To determine the inhibition of biofilms formation, microbes were plated on TiO2 coatings and a semi-quantitative colorimetric assay was performed using crystal violet. The tests showed that the TiO2 coating obtained with tdes=10 s inhibits up to 70-80% Staphylococcus aureus biofilm formation, and the inhibition of biofilms formation was confirmed by means of Scanning Electron Microscopy observation. Also, the antimicrobial properties of the coatings was enhanced by irradiating the samples in the UV region. The results of the present work are promising for using titania films as protective coatings for applications where an antimicrobial activity is required.

Yttria (Y2O3) films were deposited on stainless steel substrates from ethylenediaminetetraacetic·yttrium·hydrogen (EDTA·Y·H) complexes by flame spraying. The gas mixtures of acetylene-oxygen (C2H2-O2) or hydrogen-oxygen (H2-O2) were used for the combustion flame and the effects of the combustion gas species on Y2O3 films were investigated. Experiments revealed that the particles propelled in the H2-O2 flame had lower temperature and higher velocity compared with the particles in the C2H2-O2 flame. The existence of Y2O3 crystalline phases and complete decomposition of the EDTA·Y·H were confirmed. The porosity of the film was 25% when the H2-O2 flame was used and 32% when the C2H2-O2 flame was used. In addition, the Y2O3 films showed excellent adherability in tape tests. The H2-O2 flame is thus considered suitable for fabricating dense Y2O3 films.

Carbon nanomaterials are viewed as promising building blocks of future nanotechnology because of their superior electrical, thermal, and mechanical properties. Carbon nanomaterials can be synthesized by a variety of methods, in which flames offer a potential route in large quantities at a significantly lower cost. Our group has worked on growth of carbon nanomaterials involving carbon nanotubes (CNTs), carbon nanofibers (CNFs) and graphenes in flames for more than 15 years, and almost 100 journal papers have been published. In this paper, we review the advances in synthesis of carbon nanomaterials from flames in detail together with discussion on the major challenges and opportunities for practical applications.

Flame spray pyrolysis (FSP) was applied to produce nanopowders of Ti1-xMxO2 and Sn1-xMxO2, where x = 0.05 and M = Nb/Sb, for use as catalyst support materials in PEM fuel cells/ electrolysers. FSP powders in the SnO2-IrO2 system were produced for the same applications. Homogenous particle size distribution (5-20 nm) was demonstrated by TEM, supported by BET and XRD analysis. Whereas two polymorphs were indicated for the Ti-based oxides, the Sb/Nb-doped SnO2 powders were single phase. FSP powders of Mn3O4 intended for supercapacitors were produced and the influence of the precursor/solvent mixtures on the physical and electrochemical properties evaluated.

Nanostructured coatings have been prepared on a flexible, moving paperboard using deposition of ca. 10-50-nm-sized titanium dioxide and silicon dioxide nanoparticles generated by a liquid flame spray process, directly above the paperboard, to achieve improved functional properties for the material. With moderately high production rate (∼ g/min), the method is applicable for thin aerosol coating of large area surfaces. LFS-made nanocoating can be synthesized e.g. on paper, board or polymer film in roll-to-roll process. The degree of particle agglomeration is governed by both physicochemical properties of the particle material and residence time in aerosol phase prior to deposition. By adjusting the speed of the substrate, even heat sensitive materials can be coated. In this study, nanoparticles were deposited directly on a moving paperboard with line speeds 50-300 m/min. Functional properties of the nanocoating can be varied by changing nanoparticle material; e.g. TiO2 and SiO2 are used for changing the surface wetting properties. If the liquid precursors are dissolved in one solution, synthesis of multi component nanoparticle coatings is possible in a one phase process. Here, we present analysis of the properties of LFS-fabricated nanocoatings on paperboard. The thermophoretic flux of nanoparticles is estimated to be very high from the hot flame onto the cold substrate. A highly hydrophobic coating was obtained by a mass loading in the order of 50–100 mg/m2 of titanium dioxide on the paperboard.

The synthesis of pure titania and carbon-titania nano-powders in a premixed atmospheric fuel-rich flame was studied. The variation of the flame C/O ratio allows to produce both pure titania and carbon-TiO2 nanoparticles. Raman Spectroscopy, X-ray Diffraction, Atomic Force Microscopy, Electrical Low Pressure Impactor and Scanning Electron Microscopy were used to characterize the synthesized nano-powders, in terms of crystallinity, phase content, size and morphology. Produced nano-powders with a dimension of 25-40 nm are composed by both rutile and anatase phases, with rutile being the predominant one. Reactive Oxygen Species analysis performed on the synthesized nano-powders showed that the inclusion of carbon in the nano-powders results in a reduced adverse health effect, in terms of ROS production.

Crystalline TiO2 nanoparticles were produced by scalable flame spray pyrolysis of organometallic solutions. A protocol is presented for the optimized functionalization of these particles with fluorescein isothiocyanate (FITC), an important biomedical dye via a lysine linker. The pH, stoichiometry and time for lysine reaction were determined for highest dye loading and minimized degree of polylysine formation. Acidic reaction conditions, low lysine concentration and short reaction times were found to meet this aim. The resulting particles were used for imaging single neurons, showing high fluorescence emission and ability for the particles to diffuse into small neuron structures such as dendrites.

The fast dissolution of certain calcium-containing compounds makes them attractive carriers for trace minerals in nutritional applications, e.g., iron and zinc to alleviate mineral deficiencies in affected people. Here, CaO-based nanostructured mixed oxides containing nutritionally relevant amounts of Fe, Zn, Cu, and Mn were produced by one-step flame spray pyrolysis. The compounds were characterized by nitrogen adsorption, x-ray diffraction, (scanning) transmission electron microscopy, and thermogravimetric analysis. Dissolution in dilute acid (i.d.a.) was measured as an indicator of their in vivo bioavailability. High contents of calcium resulted in matrix encapsulation of iron and zinc preventing formation of poorly soluble oxides. For 3.6 ≤ Ca:Fe ≤ 10.8, Ca2Fe2O5 coexisted with CaO. For Ca/Zn compounds, no mixed oxides were obtained, indicating that the Ca/Zn composition can be tuned without affecting their solubility i.d.a. Aging under ambient conditions up to 225 days transformed CaO to CaCO3 without affecting iron solubility i.d.a. Furthermore, Cu and Mn could be readily incorporated in the nanostructured CaO matrix. All such compounds dissolved rapidly and completely i.d.a., suggesting good in vivo bioavailability.

A sectional method for determining particle size distributions has been implemented within the particle tracking module included with CHEMKIN-PRO. The module is available for use with many types of reactor models, ranging from 0-D batch reactors to laminar flame simulations. Coupled with the Burner-stabilized Stagnation Flame (BSSF) Model, the sectional model offers a high-fidelity, robust, and efficient computational framework for simulating flame synthesis of particles in a laminar, premixed stagnation flame environment. The CHEMKIN-PRO coupling allows inclusion of detailed gas-phase chemistry that determines key particle-formation precursors, along with physical processes such as nucleation and coagulation of particles. These capabilities are demonstrated for two flame-particle systems of practical importance, viz. nanocrystalline titania synthesis and soot formation. The results are compared with experimental data obtained at the University of Southern California (USC) flame facility. Computed particle size distributions show good agreement with experimental data. Simulations have led to exploration of the parameter space for particle production and particle-size influences.

The purpose of this work is the development and control of a high temperature reactor for the production of engineered nanoparticles, taking advantage from our previous studies on combustion-generated fine carbonaceous particles. The reactor consists of a laminar premixed flame, homogenously doped with monodisperse droplets of metal precursors dissolved or dispersed in volatile solvents. The droplets are generated by a vibrating orifice aerosol generator, and injected directly into the burner. Fuel-lean and stoichiometric flames allow producing pure metal oxide particles of nanometric sizes.

Particles are collected by thermophoresis inserting a cold substrate in the flame by means of a pneumatic actuator. Morphological and dimensional analysis are performed on the collected particles by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). SEM and AFM allow inferring both qualitative and quantitative information on many physical properties including size, morphology, surface texture and roughness.

Experimental results have been obtained from a premixed stoichiometric flame of ethylene and air, doped with 75 microns droplets of magnesium nitrate hexahydrate dissolved in ethanol. Roughly monodisperse magnesium oxide particles, having a desired size ranging from 50 nm down to 7 nm, have been produced by altering the precursor concentration in the solution and the residence time of the synthesis process.

Illustrated in this talk will be the use of premixed and diffusion flames as reaction environments for carbon nanotube synthesis. We have tested both systems using catalysts as aerosols and supported upon substrates. Highlights will be shown demonstrating success and further challenges. For illustration, this abstract illustrates two key parameter spaces, namely gas composition and catalyst size and composition in premixed and diffusion flames, respectively.

Iron deficiency affects approximately 2 billion people worldwide, especially young women and children. Food fortification with iron is a sustainable approach to alleviate iron deficiency but remains a challenge. Water-soluble compounds with high bioavailability (e.g. the “gold standard” FeSO4) usually cause unacceptable sensory changes in foods, while compounds that are less reactive in food matrices are often less bioavailable. Solubility (and therefore bioavailability) can be improved by increasing the specific surface area (SSA) of the compound, i.e. decreasing its particle size to the nm range. Here, iron oxide-based nanostructured compounds with Mg or Ca are made using scalable flame aerosol technology. Addition of either element increased iron solubility to a level comparable to iron phosphate. Furthermore, these additions lightened the powder color and sensory changes in fruit yoghurt were less prominent than for FeSO4.

Y2O3:Eu3+ nanophosphor was synthesized by flame spray pyrolysis (FSP) from urea added nitrate based liquid precursor. In this study, urea serves as fuel and subsequently provides additional heat in the flame zone during the synthesis of phosphor particles. The end product shows cubic phase Y2O3:Eu3+ nanophosphor successfully prepared by FSP without heat treatment. The influence of synthesis conditions such as different mol of urea and nitrate source materials in aqueous solution, and doping concentration on luminescent properties, were investigated. The characteristics of nanophosphor such as crystallinity and morphology under various experiments of conditions were carried out by x-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM). The particle size of product was found to be in the range of 20–30 nm from transmission electron microscopy (TEM). In photoluminescence (PL) properties, Y2O3:Eu3+ nanophosphor emitted red light with a peak wavelength of 609 nm when excited with 398 nm wavelength photons.

A novel ceramic synthesis technique, flame spray pyrolysis (FSP) was investigated for the production of nanophosphor particles. Among the various types of synthesis technique for phosphors, FSP is a powerful method which is capable of producing particles with good crystallinity and high luminescence efficiency. Red light emitting Eu3+ doped Y2O3 nanophosphor was prepared by FSP from nitrate based liquid precursors with high flame temperature. Flame temperature is an important factor to obtain phosphor particles with dense and spherical shape. Different molar percentage of urea was added into the precursor, addition of urea increases the temperature in the flame zone and promotes the formation of nano-size and spherical shaped particles. The importance of urea in the precursor to obtain well dispersed Y2O3:Eu3+ nanophosphor has been studied. The characteristics of nanophosphor such as crystallinity, morphology and photoluminescence in the presence of different moles of urea in nitrate based aqueous solution were investigated. On varying the overall concentration of the precursor, both the optical properties and crystallinity were investigated. XRD spectra showed as-prepared phosphors were obtained directly as cubic phase Y2O3:Eu3+ nanophosphor with high crystallinity and without any post-heat treatments. Luminescence intensity of nanophosphor increased with the amount of urea till 2 M percentages, further increase in urea concentration was found to reduce the PL intensity. We have developed a continuous single-step fabrication method for nanocrystalline Y2O3:Eu3+ nanophosphor without any post-heat treatments procedure.

Dry aerosol synthesis applying the flame spray pyrolysis was used to manufacture and directly (in situ) deposit tin dioxide nanoparticles on sensor substrates. For the first time this technique was used to synthesize a combination of two porous layers for gas-sensor fabrication. Two different sensing layers were deposited on ceramic substrates, i.e., pure tin dioxide and palladium-doped tin dioxide. The top layer was a palladium-doped alumina as a filter. The fabricated sensors were tested with methane, CO, and ethanol. In the case of CH4, the pure tin dioxide sensor with the Pd/Al2O3 filter showed higher sensor signals and improved selectivity with respect to water vapor compared to single tin dioxide films. At temperatures up to 250 °C the Pd doping of the tin dioxide strongly increased the sensitivity to all gases. At higher temperatures the sensor signal significantly decreased for the Pd/SnO2 sensor with a Pd/Al2O3 filter, indicating high catalytic activity.