Submicron-sized Spherical Particles Research Articles

Solution Precursor Plasma Spraying of TiO2 Coatings Using a Catalyst-Free Precursor.

The microstructural characteristics and phase composition of solution precursor plasma-sprayed (SPPS) titania-based coatings using a catalyst-free precursor are reported in this work. An ethanol-based solution containing titanium isopropoxide was used to deposit TiO2 coatings. The thermal behavior of the solution precursor changed as its phase transformation temperature increased when the molar concentration was increased from 0.3 M to 0.6 M. Scanning electron micrographs showed that the surface of the coatings was composed of nano- and submicron-sized spherical particles (<1 μm) with sintered and melted particles. The cross-sections showed a porous structure using lower concentrations and dense coating formation with micropores using higher concentrations, with thicknesses of about 5 µm-8 µm. Moreover, the coatings when the number of spray passes was increased were 16 µm-20 µm thick, giving an average layer thickness of 0.6 µm deposited per spray pass in all cases. Phase analysis revealed the presence of both the anatase and rutile phases of TiO2 in coatings sprayed with various concentrations at various stand-off distances. More detailed discussion is presented with respect to the effects of the solution concentration, stand-off distance, and number of spray passes on the coating's phase composition and microstructure.

Aerosol synthesis of TiO2:Er3+/Yb3+ submicron-sized spherical particles and upconversion optimization for application as anti-counterfeiting materials.

Er3+/Yb3+-doped TiO2 up-conversion (UC) phosphors were prepared by spray pyrolysis, and the UC luminescence properties were optimized by changing the calcination temperature and the concentration of Er3+ and Yb3+ dopants. TiO2:Er3+/Yb3+ showed green and red emissions due to the 2H11/2/4S3/2 → 4I15/2 transition and the 4F9/2 → 4I15/2 transition of Er3+ ions, respectively. The R/G ratio between red (R) and green (G) emissions does not change significantly with Er concentration but increases linearly with increasing Yb3+ concentration. The dependence of UC luminescence intensity on 980 nm IR pumping power showed that both the red and green UC luminescence of TiO2:Er3+/Yb3+ occurred through a typical two-photon process. In terms of achieving the highest red UC emission intensity, the optimal Er3+ and Yb3+ contents are 0.3% and 7.0%, respectively. The UC intensity of TiO2:Er3+/Yb3+ particles increases until they are calcined at temperatures up to 600 °C and then decreases rapidly above 800 °C. This is because when the calcination temperature is 800 °C and higher, not only does the phase transition of TiO2:Er3+/Yb3+ occur from anatase to rutile, but also the Yb2Ti2O7 impurity phase is formed. According to SEM and TEM/EDX analysis, the prepared TiO2:Er3+/Yb3+ UC powders have an average particle size of 680 nm, a spherical shape with a dense structure, and Er and Yb are uniformly dispersed throughout the particles without local separation. A mark prepared using TiO2:Er3+/Yb3+ powder was found to have a UC emission high enough to be visually observed when irradiated with a portable 980 nm IR lamp.

Softwood Lignin Self-Assembly for Nanomaterial Design.

Lignin is a natural, renewable biopolymer synthesized by plants. It is a macromolecule consisting of aromatic structures with high density of functional groups making it an ideal precursor for the design of sustainable biomaterials for applications such as drug delivery. The rational design of these materials requires an in-depth understanding of the underlying lignin self-assembly in solution. Colloidal transformations from nanosized lignin assemblies to submicron-sized spherical particles upon solvent exchange were studied using small-angle X-ray scattering, dynamic light scattering, and electron microscopy. The surface fractal structure and stability of these particles was found to be strongly solvent and pH dependent, with aggregation to a gel-like material at low pH. The results may have important implications for the design of nanostructured lignin-based functional materials for consideration in various fields such as food science and biomedicine.

Preparation of submicron-sized spherical particles of gold using laser-induced melting in liquids and low-toxic stabilizing reagent

Laser-induced melting in liquids (LIML) was applied to prepare spherical submicron-sized particles of gold (AuSMPs) from gold nanoparticles (AuNPs) stabilized using NaCl. Because undesirable byproducts, which might be generated when organic reagents such as citrate are used as the stabilizing reagent, are not generated from NaCl by laser irradiation, AuSMPs fabricated from AuNPs stabilized by NaCl will be low toxic. The AuSMPs were obtained by laser irradiation of the source AuNPs in NaCl solutions stabilized by NaCl at the proper concentration. Similar to the preparation of AuSMPs from AuNPs stabilized by citrate, the agglomeration of the source AuNPs, which is necessary to obtain AuSMPs, was controlled both by the NaCl concentration and by laser irradiation. However, the formation process and the laser-fluence dependence of the particle size of AuSMPs differed for various NaCl solutions and citrate solutions.

炭酸保護金ナノ粒子へのレーザー照射による金サブミクロン粒子の作製

Laser irradiation for colloidal gold nanoparticles stabilized by Na2CO3 was carried out to prepare submicron-sized spherical particles of gold. The source gold nanoparticles stabilized by Na2CO3 (CO32-) were prepared using laser ablation in an aqueous solutions containing Na2CO3 and then non-focused laser irradiation for the source nanoparticles was carried out to induce the agglomeration and fusion of the nanoparticles. Similarly to the case using the source nanoparticles stabilized by citrate, submicron particles were obtained. It was found that the formation process and size of the submicron particles strongly depend on the stabilizing reagents.

Porous In2O3 powders prepared by ultrasonic-spray pyrolysis as a NO2-sensing material: Utilization of polymethylmethacrylate microspheres synthesized by ultrasonic-assisted emulsion polymerization as a template

NO2-sensing properties of porous In2O3 (pr-In2O3) powders prepared by ultrasonic-spray pyrolysis employing polymethylmethacrylate (PMMA) microspheres as a template has been investigated in this study. The PMMA microspheres were synthesized in water by ultrasonic-assisted emulsion polymerization employing methyl methacrylate monomer, sodium lauryl sulfate as a surfactant and ammonium persulfate as an initiator. The PMMA microspheres synthesized was quite uniform and the particle size was ca. 60.2nm (measured by dynamic light scattering). The microstructure of pr-In2O3 powders prepared was largely dependent on the kind of In2O3 sources. The pr-In2O3 which was prepared from In(NO3)3 as an In2O3 source (pr-In2O3(N)) consisted of submicron-sized spherical particles with well-developed spherical mesopores (several tens of nanometers in pore diameter) and each oxide wall among pores was constructed with meso-sized In2O3 particles connected continuously. On the other hand, the pr-In2O3 which was prepared from InCl3 as an In2O3 source (pr-In2O3(Cl)) was composed of a large number of dispersed meso-sized particles and a few submicron-sized dense spherical particles. In contrast, the morphology of conventional In2O3 powder (c-In2O3) prepared by ultrasonic-spray pyrolysis of PMMA-free In(NO3)3 aqueous solution as a reference was relatively dense and roughly spherical with a diameter of ca. 100–700nm. The responses to 1.0 and 10ppm NO2 of pr-In2O3 sensors in air were much larger than those of a c-In2O3(N) sensor in the temperature range of less than 250°C and 300°C, respectively. In addition, the response and recovery speeds of both the pr-In2O3 sensors were much faster than those of the c-In2O3(N) sensor, because of the well-developed porous structure of the pr-In2O3 sensors.

Preparation and investigation of the formation mechanism of submicron-sized spherical particles of gold using laser ablation and laser irradiation in liquids

Results of very recent studies have shown that laser irradiation (LI) of colloidal nanoparticles (NPs) using a non-focused laser beam at moderate fluence transforms the NPs to submicron-sized spherical particles (SMPs). For this study, we applied this technique to prepare gold SMPs from source gold NPs prepared by laser ablation of a gold plate in an aqueous solution. Results show that SMPs were obtained from NPs in pure water, but a considerably large amount of the source NPs were sedimented without LI. On the other hand, SMPs were not obtained from NPs stabilized by 1 mM citrate. These findings indicate that the agglomeration of the source NPs prior to the laser-induced melting is important to obtain SMPs, although the sedimentation of the source NPs caused by considerable agglomeration should be reduced to obtain SMPs efficiently. A proper condition of the agglomeration tendency of the source NPs to prepare SMPs reducing the sedimentation of the source NPs was obtainable by simply adjusting the citrate solution concentration. Moreover, investigation of the temporal dynamics of the formation process of SMPs suggested that the agglomeration of the source NPs not only is controlled by citrate but also is induced by LI. LI brings about the decomposition and removal of citrate molecules on the surface of the source NPs, and cause the agglomeration of the source NPs dynamically; then it brings about the fusion of the agglomerated NPs.

Phase constituents and microstructure of laser synthesized TiB 2–TiC reinforced composite coating on steel

The synthesis of hard composite coating reinforced with TiB2–TiC on steel using laser surface engineering has been investigated. Phase evolution was analyzed by correlating the experimental results with thermodynamic calculation performed by ThermalcalcTM software. The composite coating consists of α-Fe, γ-(Fe,Ni), TiB2, TiC and Fe3(B,C). Microstructure characterization reveals micro-sized blocky particles and submicron-sized spherical particles. Compared with the steel substrate, an improvement of microhardness value (3–4 times) was observed for the composite coating.

Phase evolution in Ce-doped yttrium–aluminum-based particles derived from aerosol

The common nitrates precursor solution leading to the Y 3Al 5O 12:Ce 3+ (YAG:Ce) composition with 2 at.% of cerium, is ultrasonically atomised and introduced into the tubular flow reactor at 320 °C. Having in mind that extremely high heating rates and short residence time are associated with spray pyrolysis, the low temperature regime is used for aerosol decomposition for the production of segregation-free precursor powder that is additionally heated at 900 and 1000 °C (2–6 h) for the purpose to determine the phase evolution. Formation of uniform and submicron-sized spherical particles with nano-clustered inner structure is proved by different analysing techniques (X-ray powder diffraction, scanning electron microscopy and energy dispersive spectroscopy). The effect of processing parameters and post-annealing treatment is discussed from the viewpoint of the targeted garnet phase formation.

Enzymatic polymerizations using surfactant microstructures and the preparation of polymer-ferrite composites

Horseradish peroxidase has been used as a biocatalyst to synthesize a polymeric material from alkyl-substituted phenols. The synthesis is carried out in a surfactant-based microemulsion environment, with the monomer partitioned at the oil/water interface. The spherical nature of the microemulsion nanodroplets may be acting as a template for the polymer synthesis. The resultant polymer particles are spherical and typically in the submicron size range. The characteristics of the morphology development are described. The templating effect of the surfactant environment becomes more evident when the polymer particles are fully dissolved in a suitable solvent and refolded in the presence of surfactant. Interestingly, submicron-sized spherical particles are obtained only in the presence of surfactant, and particles of arbitrary morphology are seen in the absence of surfactant. Aspects of morphology development leading to the preparation of polymeriron oxide composites are described.

The contribution of atmospheric aerosols to the Martian opposition effect

Mie scattering calculations have been made for atmospheric aerosols having various indices of refraction to determine their possible contribution to a Martian opposition effect, such as that reported by O'Leary in 1967. Neither substances with a real index between 1.20 and 1.50, such as ice, water, or solid CO2, nor highly absorbing materials, such as limonite, can produce the observed effect. Submicron-sized spherical particles with refractive indices of 1.55 to 2.00 do, on the other hand, exhibit a marked increase in reflectivity at small phase angles and might be responsible for the enhanced brightness at the shorter wavelengths.