Submicron Spheres Research Articles

Spherical submicron YAG:Ce particles with controllable particle outer diameters and crystallite sizes and their photoluminescence properties.

The purpose of this study was to demonstrate the preparation of spherical submicron YAG:Ce particles with controllable particle outer diameters and crystallite sizes and their photoluminescence (PL) properties, which were produced using a flame-assisted spray-pyrolysis method followed by the annealing process. The correlation of particle outer diameter, crystallite size, and PL performance of the prepared particles was also investigated. Experimental results showed that the increases in the particle outer diameters have an impact on the obtainment of higher PL performance. Large particle outer diameters permitted the crystallites to grow more, whereas this is in contrast to the condition for small particle outer diameter having limitations in crystallite growth. This study also found that too large outer diameter (>557 nm) was not effective since crystallites cannot grow anymore and it permits possible scattering problems. This study provides significant information for optimizing synthesis parameters for controlling particle outer diameters and crystallite sizes, which could be relevant to other functional properties, especially for lens, solar cell, and LED applications.

Effect of Solvothermal Reaction-Time on Microstructure and Microwave Absorption Properties of Cobalt Ferrite.

Cobalt ferrite is synthesized via a simple solvothermal method. Then, the effect of the degree of cobalt-ferrite growth on its morphology, structure, electromagnetic performance, and microwave absorption is studied as a function of the solvothermal reaction time. When the reaction time during synthesis is 8 h, the structure of cobalt ferrite is hollow spheres. In addition, when the reaction time is 12 h and 16 h, it becomes a submicron sphere with a diameter of 100–150 nm. With the increase of reaction time, cobalt ferrite underwent the process of cobalt ferrite formation, hollow structure formation, hollow structure disappearance, agglomeration separation and reagglomeration in 4–16 h. In general, CoFe2O4-8h shows better microwave absorption-the effective absorption bandwidth is 9.84 GHz (6–15.84 GHz) for a thickness of 1.72–3.72 mm. This represents a minimum return loss of −47.24 dB. A better understanding of both the synthesis parameters and the relationship between structure and electromagnetic properties can open new possibilities for applications and the development of microwave absorbing materials.

Sb-doped SnO2 (ATO) hollow submicron spheres for solar heat insulation coating

Antimony doped Tin Oxide (ATO) hollow submicron spheres were synthesized with a carbon ball template using the hydrothermal method, and compared to commercial nano-ATOs that differed in particle size. To study the thermal insulation performance and the mechanism of different ATOs, their morphology, crystalline structure and microstructure were examined using XRD, SEM and HRTEM. Meanwhile, the optical and thermal characteristics of the different ATOs, including absorption, reflectance, thermal conductivity, infrared emissivity (8–14 μm), and specific heat capacity, were also measured. Silicone acrylic emulsion coatings containing different dosages of ATO were then prepared, and their UV–Vis–NIR transmittance and solar heat shielding performances were tested. ATO hollow submicron spheres showed a thermal insulation performance comparable to that of nano-ATO, but their main respective thermal insulation mechanism was different. ATO hollow submicron spheres primarily relied on better particle dispersion, lower thermal conductivity, higher specific heat capacity and higher infrared emissivity. The 50 nm ATO absorbed the least solar heat but reflected the most light, while 100 nm ATO showed the opposite behavior. Both nano-ATOs had better transmittance in the visible light range but relatively low transmittance in the ultraviolet and infrared range. The results of this study indicate that ATO hollow submicron spheres are promising materials equivalent to nano-spheres that can be applied as a coating for energy conservation.

Controllable synthesis of (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 submicron sphere by hydroxide co-precipitation method

The grain growth behavior during the ceramic sintering process is largely dependent on the size uniformity of precursory powders; therefore, a controllable synthesis of uniform precursory powders is a key to synthesize fine-grained dense ceramics. In this paper, we propose a simple and controllable hydroxide co-precipitation method to synthesize submicron spherical powders (Ba0.85Ca0.15)(Zr0·1Ti0.9)O3 (BCZT) with high uniformity. Molar ratio of (Ba + Ca)/(Zr + Ti), concentration of mineralizer and Zr(NO3)4·5H2O input proportion were found to be important factors in order to produce stoichiometric intermediates Ba0.85Ca0·15Zr0.1Ti0·9O2·92(C2O4)0.08 powders, which then release CO and CO2 at ~456 °C and ~608 °C, individually, and eventually become pure phase of BCZT powders at ~696 °C during the calcination process. The phase-pure ceramics sintered at 1440 °C for 6 h displayed high recoverable energy storage performance (0.54 J/cm3). The obtained uniformly distributed BCZT precursory powders could be used to prepare fine-grained BCZT ceramics for multipurpose applications.

Signature of Short-Range van der Waals Forces Observed in Poisson Spot Diffraction with Indium Atoms.

The phase of de Broglie matter waves is a sensitive probe for small forces. In particular, the attractive van der Waals force experienced by polarizable atoms in the close vicinity of neutral surfaces is of importance in nanoscale systems. It results in a phase shift that can be observed in matter-wave diffraction experiments. Here, we observe Poisson spot diffraction of indium atoms at submillimeter distances behind spherical submicron silicon dioxide particles to probe the dispersion forces between atoms and the particle surfaces. We compare the measured relative intensity of Poisson's spot to theoretical results derived from first principles in an earlier communication and find a clear signature of the atom-surface interaction.

Room-temperature NO2 sensor based on a hybrid nanomaterial of methylammonium tin iodide submicron spheres and tin dioxide nanowires

Perovskite halide materials are currently attracting considerable attention owing to their superior optical and electrical properties. This study proposes a reliable process for synthesizing hybrid nanomaterials made of methylammonium tin iodide (MASnI3) submicron spheres and tin dioxide (SnO2) nanowires. Post-fabricated hybrid nanomaterials were investigated for NO2 sensing properties at 25 °C in the dark. The effect of moisture on the NO2 sensitivity of this material was investigated. The durability of sensor components using this material was also investigated. In this paper, we also discuss the NO2 sensitivity mechanism of MASnI3/SnO2 hybrid nanomaterials in detail.

A Sub-Micron Spherical Atomic Force Microscopic Tip for Surface Measurements.

We report a novel methodology for fabricating a sub-micron spherical atomic force microscope (AFM) tip controllably-a silicon sub-micron sphere atop microcantilevers, which is desired for precise nanoscale tribology measurements, biological studies, and colloid science. Silicon sub-micron spheres are fabricated through swelling of single-crystal silicon with proper high-energy helium ion dosing, a traditionally undesired phenomenon known in helium ion microscopy. Silicon sub-micron spheres with diameters from 100 nm to 1 μm are demonstrated, and the placement of silicon sub-micron spheres can be as accurate as 10 nm or even below. This AFM tip demonstrates robust measurements during friction tests on graphene/silicon oxide substrates for more than 10 000 cycles. This AFM tip overcomes a critical challenge of reducing the size of spherical AFM tips from the micrometer scale to the sub-micron scale and is promising in cross-scale mechanics studies, nanotribology, colloid science, and biology.

Controllable phase/morphology tailoring of REF3 and NaREF4 (RE = La-Lu, Y), and insights into the up-conversion luminescence of GdF3:Yb3+/Tm3+ spheres

Four typical rare earth fluorides of hexagonal/orthorhombic REF3 and hexagonal/cubic NaREF4 (RE = La-Lu, Y, excluding radioactive Pm), have been hydrothermally synthesized from mixed solutions of the rare earth nitrate solutions and ammonium fluoride (NH4F), in the presence of EDTA-2Na. The phase and the morphology are closely related to the ionic radius of RE3+. Large RE3+ ions, La3+, Ce3+, Pr3+, Nd3+ and Sm3+, crystallize in hexagonal REF3 (nanocrystals), and middle RE3+ ions (RE = Eu-Dy) crystallize in orthorhombic REF3 (micron-sized spheres/polyhedral micro-crystallites). For small RE3+ ions, Ho3+, Er3+, Tm3+, Yb3+ and Y3+, they tend to being incorporated into the host lattice of cubic NaREF4 (submicron spheres). However, the smallest Lu3+ tends to crystallizing in orthorhombic LuF3. Varying the F-/RE3+ molar ratio (R) and the reaction temperature can efficiently induce the phase/morphology evolution of rare earth fluorides. Increasing R up to 10–30 yielded hexagonal NaREF4 (RE = Dy, Tb, Gd, Eu, Sm, micron prisms), although the original products were orthorhombic REF3 (RE = Dy, Tb, Gd, Eu) and hexagonal SmF3 at R = 5. However, increasing R is inefficient to the phase transition for large RE elements of La, Ce, Pr, Nd. Lowering the reaction temperature from 180 °C to 80 °C gave rise to the phase transition from orthorhombic LuF3 to cubic NaLuF4. GdF3:Yb3+,Tm3+ spheres exhibited intense blue emission at ~476 nm (1G4 → 3H6 transition of Tm3+), deep-red emission at ~646 nm (1G4→3F4 transition of Tm3+), and near-infrared emission at ~695 nm (3F2,3 → 3H6 transitions of Tm3+) under the 980 nm infrared excitation. The intense near-infrared emission under the infrared excitation suggested that they might hold great potential in bio imaging application.

Preparation and Characterization of Spherical Submicron CL-20 by Siphon Spray Refinement

In order to improve the safety of hexanitrohexaazaisowurtzitane (CL-20), submicron CL-20 particles were prepared by a siphon ultrasonic-assisted spray refining experimental device. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC), and the impact sensitivity of the samples was tested. The results show that the particle size of siphon-refined CL-20 is about 800 nm~1 μm, which is more smooth, mellow, and dense than that of CL-20 prepared by a traditional pressure-refined method. The peak diffraction angle of pressure- and siphon-refined CL-20 is basically the same as that of raw CL-20, and their crystal forms are ε type. The peak strength of pressure- and siphon-refined CL-20 decreased obviously. The apparent activation energy of pressure-refined CL-20 and siphon-refined CL-20 is 13.3 kJ/mol and 11.95 kJ/mol higher than that of raw CL-20, respectively. The thermal stability of CL-20 is improved. The activation enthalpy (ΔH#) is significantly higher than that of raw CL-20, and the characteristic drop is 70.4% and 82.7% higher than that of raw CL-20. The impact sensitivity of siphon-refined CL-20 is lower than that of pressure-refined CL-20, so the safety performance of an explosive is improved obviously.

Rapid Room-Temperature Synthesis of Mesoporous TiO2 Sub-Microspheres and Their Enhanced Light Harvesting in Dye-Sensitized Solar Cells.

Submicron sized mesoporous spheres of TiO2 have been a potential alternative to overcome the light scattering limitations of TiO2 nanoparticles in dye-sensitized solar cells (DSSCs). Currently available methods for the growth of mesoporous TiO2 sub-microspheres involve long and relatively high temperature multi-stage protocols. In this work, TiO2 mesoporous sub-microspheres composed of ~5 nm anatase nanocrystallites were successfully synthesized using a rapid one-pot room-temperature CTAB-based solvothermal synthesis. X-Ray Diffraction (XRD) showed that the grown structures have pure anatase phase. Transmission electron microscopy (TEM) revealed that by reducing the surfactant/precursor concentration ratio, the morphology could be tuned from monodispersed nanoparticles into sub-micron sized mesoporous beads with controllable sizes (50–200 nm) and with good monodispersity as well. The growth mechanism is explained in terms of the competition between homogeneous nucleation/growth events versus surface energy induced agglomeration in a non-micelle CTAB-based soft templating environment. Further, dye-sensitized solar cells (DSSCs) were fabricated using the synthesized samples and characterized for their current-voltage characteristics. Interestingly, the DSSC prepared with 200 nm TiO2 sub-microspheres, with reduced surface area, has shown close efficiency (5.65%) to that of DSSC based on monodispersed 20 nm nanoparticles (5.79%). The results show that light scattering caused by the agglomerated sub-micron spheres could compensate for the larger surface areas provided by monodispersed nanoparticles.

Formation of selenium superstructures: Self-assembly of monodispersed sub-micron spheres and nanorods

Self-assembly of monodispersed nanospheres and nanorods into nano- and micro-scale superstructures are important from the viewpoint of developing small scale devices. Synthesizing monodispersed particles with minimal polydispersity index is challenging due to the complexity involved in the nanoparticle growth from the constituent atoms. Monodispersed a-Se spherical particles, with polydispersity index much smaller than 0.1, are synthesized through the reduction of selenious acid using hydrazine in ethylene glycol. The size of the particle readily changed from 190 to 350 nm by varying the molar ratio of selenious acid to hydrazine. The optical extinction spectra obtained from the colloidal solution show peaks corresponding to magnetic and electric dipole resonances as verified from the Mie theory, as well as from the theoretical investigation of the local electric field using the finite element method. Interestingly, very small agitation of the a-Se nanospheres resulted in the formation of t-Se nanorods via crystal growth mechanism. Under ambient conditions, the nanorods self-assemble to form sub-micron spheres, which in turn grow into micron-sized superstructures. The mechanisms involved in the formation of such self-assembled superstructures are discussed.

Role of ethanol on particle size and morphology during copper oxalate synthesis by Precipitation-Stripping

Copper oxalate particles were synthesized from a copper loaded oil phase using the precipitation-stripping (PS) technique with oxalic acid as the stripping and precipitating agent. The copper source was a spent ammoniacal printed circuit board etch solution and LIX 84I was the metal extractant. The role of ethanol in stripping solution on stripping rates, particle morphology and size was investigated. An increase in ethanol concentration enhanced both rate and extent of stripping. PS with aqueous oxalic acid resulted in cushion shaped particles with a wide size distribution which changed to flat discs with an increase in precipitation time. Changes in the polarity, dielectric strength, coupled with significant reduction in the interfacial tension between oil and aqueous phases due to the presence of ethanol in the stripping solution resulted in spherical submicron particles with a narrow size distribution. This investigation paves way for a process to synthesize submicron oxalate particles.

Emerging wet electrohydrodynamic approaches for versatile bioactive 3D interfaces

There is a compelling need for delicate nanomaterial design with various intricate functions and applications. Electrohydrodynamics applies electrostatic force to overcome the surface tension of a liquid jet, shrinking the jet through intrinsic jetting instability into submicron fibers or spheres, with versatility from a huge selection of materials, feasibility of extracellular matrix structure mimicry and multi-compartmentalization for tissue engineering and drug delivery. The process typically involves the collection and drying of fibers at a solid substrate, but the introduction of a liquid phase collection by replacing the solid collector with a coagulation bath can introduce a variety of new opportunities for both chemical and physical functionalizations in one single step. The so-called wet electrohydrodynamics is an emerging technique that enables a facile, homogeneous functionalization of the intrinsic large surface area of the submicron fibers/spheres. With a thorough literature sweep, we herein highlight the three main engineering features integrated through the single step wet electrospinning process in terms of creating functional biomaterials: (i) The fabrication of 3D macrostructures, (ii) in situ chemical functionalization, and (iii) tunable nano-topography. Through an emerging technique, wet electrohydrodynamics has demonstrated a great potential in interdisciplinary research for the development of functional 3D interfaces and materials with pertinent applications in all fields where secondary structured, functional surface is desired. Among these, engineered biomaterials bridging materials science with biology have already shown particular potential.

Room-Temperature No <sub>2</sub> Sensor Based on a Hybrid Nanomaterial of Methylammonium Tin Iodide Submicron Spheres and Tin Dioxide Nanowires

Perovskite halide materials are currently attracting considerable attention owing to their superior optical and electrical properties. This study proposes a reliable process for synthesizing hybrid nanomaterials made of methylammonium tin iodide (MASnI3) submicron spheres and tin dioxide (SnO2) nanowires. Post-fabricated hybrid nanomaterials were investigated for NO2 sensing properties at 25°C in the dark. The effect of moisture on the NO2 sensitivity of this material was investigated. The durability of sensor components using this material was also investigated. In this paper, we also discuss the NO2 sensitivity mechanism of MASnI3/SnO2 hybrid nanomaterials in detail.

Well-ordered layered LiNi0.8Co0.1Mn0.1O2 submicron sphere with fast electrochemical kinetics for cathodic lithium storage

Abstract Nickel-rich layered oxides have drawn sustainable attentions for lithium ion batteries owing to their higher theoretical capacities and lower cost. However, nickel-rich layered oxides also have exposed several defects for commercial application, such as uncontrollable ordered layered structure, which leads to higher energy barrier for Li+ diffusion. In addition, suffering from structural mutability, the bulk nickel-rich cathode materials likely trigger overall volumetric variation and intergranular cracks, thus obstructing the lithium ion diffusion path and shortening the service life of the whole device. Herein, we report well-ordered layered LiNi0.8Co0.1Mn0.1O2 submicron spheroidal particles via an optimized co-precipitation and investigated as LIBs cathodes for high-performance lithium storage. The as-fabricated LiNi0.8Co0.1Mn0.1O2 delivers high initial capacity of 228 mAh g–1, remarkable energy density of 866 Wh kg–1, rapid Li ion diffusion coefficient (10–9 cm2 s–1) and low voltage decay. The remarkable electrochemical performance should be ascribed to the well-ordered layered structure and uniform submicron spheroidal particles, which enhance the structural stability and ameliorate strain relaxation via reducing the parcel size and shortening Li-ion diffusion distance. This work anticipatorily provides an inspiration to better design particle morphology for structural stability and rate capability in electrochemistry energy storage devices.

Fabrication and Characterization of Submicron Scale Spherical RDX, HMX, and CL-20 without Soft Agglomeration

In this study, a novel spray drying-assisted self-assembly (SDAS) technology was proposed to prepare submicron elemental explosives with good morphology, uniform dispersion, and low sensitivity and spherical submicron RDX, HMX, and CL-20 particles without soft agglomeration were fabricated via such a method. Structural characterizations and thermal stability of the composites were systematically studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimeter (DSC). Moreover, safety performance was analyzed by qualitative testing of impact sensitivity and friction sensitivity. The XRD analysis demonstrated that HMX and CL-20 refined by SDAS maintained the crystal structure of β-HMX and ε-CL-20 before and after refinement, whereas the HMX crystal structure after spray recrystallization refinement was transformed from β-HMX to α-HMX. The DSC results indicated that the thermal decomposition peak temperature of the three particles refined by the SDAS technology had a minimum advancement, and the thermal stability of the particles was relatively superior. More importantly, the H50 of the RDX, HMX, and CL-20 refined by this novel method was increased to 48.3 cm, 44.6 cm, and 31.1 cm, and the probability of friction explosion was decreased to 62%, 62%, and 80%, respectively, thus significantly improving the safety performance as compared with the sample refined by spray recrystallization.

Influence of working temperature on the structure and gas-sensing properties of γ-FeOOH submicron spheres

Iron oxyhydroxide (FeOOH) is an interesting material with major applications in water treatment. However, the gas-sensing properties of this nano-/micromaterial are not understood. Herein, we introduce a facile process for synthesizing submicron-sized γ-FeOOH spheres. The formation process of the γ-FeOOH phase after treatment is proposed, and the gas-sensing properties of the as-synthesized materials are investigated using NH3, H2S, NO2, and SO2. The influence of working temperature (from 25 °C to 300 °C) on material structure and gas-sensing performance is also studied and the gas-sensing process is explained and discussed.

Infrared-Radiation-Enhanced Nanofiber Membrane for Sky Radiative Cooling of the Human Body.

Extreme heat events are mainly responsible for weather-related human mortality due to climate change. However, there is a lack of outdoor thermal management for protecting people from extreme heat events. We present a novel infrared-radiation-enhanced nanofiber membrane (NFM) that has good infrared resonance absorption and selectively radiates thermal radiation of the human body through the atmosphere and into the cold outer space. The NFM comprises polyamide 6 (PA6) nanofibers and randomly distributed SiO2 submicron spheres and has sufficient air permeability and thermal-moisture comfortability because of its interconnect nanopores and micropores. We measure the sky radiative cooling performance under a clear sky, and PA6/SiO2 NFM produces temperatures that are about 0.4-1.7 °C lower than those of commercial textiles when covering dry and wet hands and temperatures 1.0-2.5 °C lower than the ambient temperature when thermal conduction and convection are isolated in a closed device. Our processed PA6/SiO2 NFM combines sky radiative cooling with thermal management of the human body very well, which will promote the development of radiative cooling textiles.

Extension of complex refractive index model and analysis of scattering properties of charged submicron spheres

In the optical measurement of submicron particle properties, extra scattering generated by excess surface charges is no longer negligible as that in micron particles. When the surface charge density exceeds a certain threshold, the scattering behavior of the particles will be jointly dominated by the particles themselves and the surface charges. In this paper, the complex refractive index model is extended to be appropriate for both electrically neutral particles and electrically charged particles, and the mechanism is explained how surface charges affects elastic scattering. Taking the Mie theory of charged submicron spherical droplets of water with salt as an example, the influence of the surface charges on the complex refractive index and the scattering properties is discussed. Further, a threshold of the surface charge density is confirmed, above which extra scattering cannot be ignored. By calculating a angular distribution of the scattered light intensity, it is found that electrically charges have a magnifying effect on forward and backscattering of the particles d < 0.5 µm. This effect is helpful to extend the lower limit of measurement of visible light scattering and is of great significance to understanding the interaction between charged particles and electromagnetic or optical waves.

Simultaneous catalytic oxidation of CO and Hg0 over Au/TiO2 catalysts: Structure and mechanism study

Au/TiO2 catalysts with different morphologies were prepared by the modulation of chlorine via a hydrothermal method, which were used for the simultaneous catalytic removal of CO and Hg0. Results showed that the Au/TiO2 catalyst with a structure of submicron sphere and ascorbic acid modification (denoted as AuV/2 M T) showed 38.2% (41.1%, without H2O) CO conversion at 50 °C and nearly 100% CO conversion at 275-350℃ (225-350℃, without H2O). This catalyst also exhibited stable catalytic efficiency of approximately 88% (95.7%, without H2O) for Hg0 removal at 300℃. The high catalytic activity of the AuV/2 M T was ascribed to a series of superior properties, including a high specific surface area, a large amount of adsorbed oxygen species and a large brookite/rutile TiO2 ratio. Moreover, the AuV/2 M T also exhibited excellent stability. The AuV/2 M T continued to exhibit nearly 90.5% CO conversion efficiency and 84.5% Hg0 conversion efficiency after continuous testing with 6 vol.% H2O for 120 h. Therefore, this catalyst is expected to be used in coal-fired power plants. The mechanism of CO removal over AuV/2 M T was in-depth investigated. The presence of chlorine promoted the catalytic oxidation of Hg0 while the presence of CO has no great effect on desorption of Hg0. Moreover, catalytic oxidation of CO over AuV/2 M T catalyst was found to follow L-H mechanisms. The formate was the intermediate species for CO catalytic oxidation, and it transformed to CO2 quickly by consuming the oxygen species (O2−, O− and −OH) adsorbed onto the catalyst surface. The oxygen species consumed on the surface of catalyst was supplied by oxygen, and it was the key factor in determining the reaction rate.