Synthesis of SiCNYO nanopowders by spray pyrolysis

SiCNYO nanopowders have been elaborated by a spray pyrolysis method from an organometallic precursor which is synthesized by two different routes. Fourier-transform infrared spectroscopy and solid state nuclear magnetic resonance were used to identify the silylation and the amminolysis mechanism applied for the synthesis of each precursor. The SEM micrographs of the each “as-pyrolysed” product revealed spherical SiCNYO nanopowders with a bimodal size distribution. A drop-to-particle and a gas to particle exchanges seem to be the two mechanisms at the origin of grains size distribution. The nature and the reactivity of the carrier gas used in the aerosol indicate a significant influence on the powder morphology. It was found also that evaporation rate of the as-prepared precursor may lead to prevent the enlarging of particles.     

Hydroxyapatite coatings by pulsed ultrasonic spray pyrolysis

Hydroxyapatite coatings on 316L stainless steel substrates were prepared using ultrasonic spray deposition with substrate temperature kept at 300 °C. Two spray patterns, continuous and pulsed (intermittent), were used coupled with precisely control of substrate movement. It was determined that the ability to form continuous and relatively dense, well bonded coatings, was related primarily to the control of the flowrate of precursor solution and temperature and movement of the substrate. The microstructure and bonding strength of the coatings were evaluated in relationship with continuous and pulsed (intermittent) spray routes. Coatings prepared by continuous spray contained relatively large cracks while coatings by pulse spray exhibited finer cracks and higher bonding strength.     

Preparation of SOFC anode composites by spray pyrolysis

Lowering the SOFC working temperature would also be greatly attractive, but low temperature working SOFCs require high-performance anodes. The cermet SOFC anodes, which are composed of nickel and samarium doped ceria, were prepared by spray pyrolysis (SP), because SP produces spherical particles with small size distributions. SP-derived particles of NiO, SDC, and NiO/SDC composite had a round shape and comprised nanometer-sized primary grains. The cermet anodes were prepared by using SP-derived NiO/SDC composite particles or mixing SP-derived NiO and SDC particles. The anode prepared with the composite particles showed higher SOFC cell performance than that with the mixed ones. The composite particles had high surface areas and a capsule-type form. The outer shell would be composed of SDC and the inner core was NiO. The capsule-type composite particles would depress aggregation of Ni or NiO during reduction from NiO to Ni metals, and this depression would enhance SOFC anode performance.     

Formation of BaTiO3 nanoparticles from an aqueous precursor by flame-assisted spray pyrolysis

By manipulating process parameters, BaTiO₃ nanoparticles with tunable size were successfully prepared by flame-assisted spray pyrolysis (FASP) from an aqueous solution of barium acetate and titanium-tetra-isopropoxite. Particle size was controlled over a wide range (from about 23 to 71 nm) by varying the concentration of precursor and methane flow rate. Flame temperature was a key factor in producing particles with a narrow size distribution. The BaTiO₃ nanoparticles were cubic in crystal structure, dense, spherical and softly agglomerated. The particles contained OH, carboxyl and CO₂ bonding groups that could be completely removed by post-heat treatment. At room temperature, BaTiO₃ pellets had relatively high dielectric constants (2578.8–3611.8) with loss factors ranging from 2.6% to 7.1% at the frequency of 1 kHz. The results of this study indicate that BaTiO₃ nanoparticles can be fabricated using continuous and industrially applicable FASP.     

Cu-Sn binary metal particle generation by spray pyrolysis

Cu-Sn binary particles were generated via spray pyrolysis from metal salt precursors with ethylene glycol as the co-solvent and reducing agent. The morphology, crystallinity, and elemental distribution of particles were tunable by changing the reaction temperature, residence time, and quench gas flow rate. Hollow porous particles were fabricated with a higher Sn concentration on the particle surface when the furnace set point was 500°C, while solid particles with a lower surface Sn concentration were generated when the furnace set point was 1000°C. Particles with spherical morphologies were obtained at long residence time conditions (4.5 s). Cu-Sn binary particles with irregular structures (e.g., pores on the particle surface, fragmented spherical particles, and lamellar fragments) were formed at short residence time conditions (0.92 s). A possible spray pyrolysis mechanism was proposed that incorporates chemical reaction steps and structural progression. By this mechanism, the metal salts are believed to sequentially undergo hydrolysis to metal hydroxides, decomposition to metal oxides, reduction to metals, and finally diffusion of Sn into the Cu matrix to generate the Cu-Sn solid solution.

Copyright © 2017 American Association for Aerosol Research     

Formation of silver iodide particles from thermodynamically stable clusters using ultrasonic spray pyrolysis

Silver iodide particles in the submicronic size domain were synthesized in the process of ultrasonic spray pyrolysis (USP) using aqueous solutions of thermodynamically stable silver iodide clusters as precursor. After the process of USP, the AgI particles were collected in water. In order to study influence of aging time on the morphological and structural properties of the AgI particles, ultra-filtration was employed to isolate solid material from solution. The scanning electron microscopy showed change from spherical to hexagonal/triangular shape and increase of average particle size of the AgI particles as a function of aging time, which is characteristic for the Ostwald ripening growth mechanism. The X-ray diffraction measurements revealed the presence of wurtzite hexagonal and zinc blende cubic AgI modifications whose abundance is also dependent on the aging time.     

Preparation of BaZrO3 nanopowders by spray pyrolysis method

Barium zirconate based solid solutions of various compositions become ionic and/or electronic conductors and they are potential candidates for numerous types of applications in the field of electroceramics. This work investigated application of ultrasonic spray pyrolysis method based on thermal decomposition of barium and zirconium nitrate solution for preparation of fine barium zirconate powders. The aerosols of nitrate solutions of 0.1, 0.01 and 0.001 M were thermally treated at 800, 1000 and 1200 °C. The prepared powders were composed of the spherical particles which sizes, from 90 to 500 nm, were mainly depended on the concentration of nitrate solution and less depended on the pyrolysis temperature. The particles consisted of the crystallites of 25–60 nm in size. Their sizes strongly depended on the pyrolysis temperature and to the lesser extend on the solution concentration.     

Characteristics of samaria-doped ceria nanoparticles prepared by spray pyrolysis

Samaria-doped ceria (SDC) nanoparticles were prepared by spray pyrolysis. The means sizes of the samaria-doped ceria nanoparticles were controlled from 21 to 150 nm by changing the calcination temperatures between 700 and 1200 °C. The pellets formed from the SDC particles calcined at temperatures between 700 and 1000 °C had similar grain sizes between 0.75 and 0.82 μm. However, pellet formed from the SDC particles calcined at a temperature of 1200 °C had large grain size of 1.22 μm. The pellet formed from the SDC particles calcined at a temperature of 1000 °C had slightly smaller resistance of grain-boundary than those of the pellets formed from the SDC particles calcined at temperatures between 700 and 900 °C. However, the pellet formed from the SDC particles calcined at a temperature of 1200 °C had low resistance of grain-boundary. The pellet formed from the SDC particles calcined at a temperature of 1200 °C had conductivity of 44.65 × 10^?3 S cm^?1 at a measuring temperature of 700 °C that more twice than those of the pellets formed from the SDC calcined below 1000 °C.     

Additives content in ZnO films prepared by spray pyrolysis

ZnO films containing additives like bismuth, manganese, copper or cobalt have been deposited by spray pyrolysis of precursors dissolved in water. The additive content in the final material has been measured and it can be different from its value in the starting solution. These differences are discussed by looking at the chemistry of the starting solution.     

Highly-dispersible boron nitride nanoparticles by spray drying and pyrolysis

A spray drying and pyrolysis synthesis route was developed and it successfully prepared boron nitride (BN) nanoparticles with high dispersivity. During the experiment, the extremely rapid drying of the boric acid/urea solution during the spray-drying process resulted in the formation of homogeneous precursors, which was the key for the final pyrolysis synthesis of BN nanoparticles with high dispersibility and uniform diameters (~20 nm). Compared with boron nitride synthesized without using spray drying, the as-prepared BN nanoparticles possess higher specific surface area (145.01 m² g⁻¹) and larger pore volume (0.41 cm³ g⁻¹). Especially, we used the BN nanoparticles as lubricant and incorporated it into the liquid paraffin (LP). The experiment results show that the LP presents outstanding antifriction properties for a BN content of 1.5 wt%. These results suggest that the h-BN nanoparticles have significant potential applications in the field of tribology.     

Tin oxide thin films deposited by ultrasonic spray pyrolysis

This study investigated microstructure of SnO₂ thin films deposited by ultrasonic spray pyrolysis technique using 0.2 M of SnCl₄·5H₂O in absolute ethanol as a precursor. The deposition temperature (350–450 °C) and time (20–90 min) were varied. The influence of film-deposition conditions on grain size and orientation were discussed. The deposited SnO₂ films were textured polycrystalline films. The preferred orientation of SnO₂ films were quantitatively evaluated by texture coefficient (TC). The mean grain size and film thickness determined by SEM could be controlled over a range of 50–325 nm and 80–2690 nm, respectively.     

Characteristics of Ag-doped BaTiO3 nanopowders prepared by spray pyrolysis

Pure and Ag-doped BaTiO₃ nanopowders were prepared by spray pyrolysis. Precursor powders, prepared from a spray solution with citric acid and ethylenediaminetetraacetic acid (EDTA) as chelating agents, had large, hollow particles irrespective of Ag doping. Both pure and Ag-doped powders had partially aggregated particles after post-treatment at 900 °C that could be easily milled to nanoparticles. The mean sizes of the pure and Ag-doped BaTiO₃ particles were 75 and 91 nm, respectively. The Ag-doped particles were mainly of cubic BaTiO₃ crystal structure, with small Ag phases observed. High-density BaTiO₃ pellets were formed by sintering the powders at the low temperature of 1000 °C. The silver was uniformly distributed in a tetragonal BaTiO₃ phase without phase separation in the doped pellet. The dielectric constants of the pellets formed from the pure and Ag-doped BaTiO₃ powders were 1826 and 2400, respectively.     

喷雾热解法合成高性能球形钴蓝的研究

研究了喷雾热解法合成高性能球形钻蓝。试验对比了两种不同喷雾热解前驱体溶液对钻蓝形貌及反射性能的影响，一种是硝酸盐溶液体系；另一种是聚合物溶液体系，聚合物溶液是由硝酸铝溶液加入氨水水解合成的。由X射线荧光光谱分析可知，喷雾热解合成的钻蓝较商品钻蓝的纯度高。喷雾热解产物再经1000℃煅烧2h，由硝酸盐溶液体系合成的钻蓝的形貌是不规则的，而由聚合物体系合成出的是实心球形的钻蓝，且比不规则外形的及商品的钻蓝有较高的反射性能。     

Nanoparticle synthesis at high production rates by flame spray pyrolysis

Scaling-up of nanoparticle synthesis by the versatile flame spray pyrolysis process at production rates up to is investigated. Product silica powder is collected continuously in a baghouse filter unit which is cleaned periodically by air-pressure shocks. The effect of powder production rate, dispersion gas flow rate and precursor (hexamethyldisiloxane, HMDSO) concentration on product particle size, morphology and carbon content is investigated. Droplet size distributions of the cold spray are measured by laser diffraction, while N₂ adsorption (BET), transmission electron microscopy and thermogravimetric analysis coupled with a mass spectrometer are employed to characterize the product powder. The product primary particle size was precisely controlled from 10 to and compared to a well-established vapor-fed flame aerosol reactor.     

Photoluminescence of spray pyrolysis deposited ZnO nanorods

Photoluminescence of highly structured ZnO layers comprising well-shaped hexagonal rods is presented. The ZnO rods (length 500-1,000 nm, diameter 100-300 nm) were grown in air onto a preheated soda-lime glass (SGL) or ITO/SGL substrate by low-cost chemical spray pyrolysis method using zinc chloride precursor solutions and growth temperatures in the range of 450-550°C. We report the effect of the variation in deposition parameters (substrate type, growth temperature, spray rate, solvent type) on the photoluminescence properties of the spray-deposited ZnO nanorods. A dominant near band edge (NBE) emission is observed at 300 K and at 10 K. High-resolution photoluminescence measurements at 10 K reveal fine structure of the NBE band with the dominant peaks related to the bound exciton transitions. It is found that all studied technological parameters affect the excitonic photoluminescence in ZnO nanorods.PACS: 78.55.Et, 81.15.Rs, 61.46.Km.     

Synthesis of WO3 thin films by surfactant mediated spray pyrolysis

WO₃ thin films were prepared by surfactant mediated spray pyrolysis deposition on fluorine-doped tin oxide (FTO) conductive glass using hexadecylthymethylammonium bromide (HTAB) as structure-directing agent. The crystalline structure, topography, electrical conductivity and optical properties were investigated as function of cationic surfactant concentration. High transparency and conductivity were obtained for the sample which contained the lowest amount of surfactant (50 ppm) in the spraying solution. Significant changes in the morphology were observed with increasing HTAB addition level; samples lost their homogeneity and porosity, while the layer roughness increased. The surfactant by-products resulted after annealing were investigated based on FTIR analysis and a decomposition scheme was proposed. The modified surface composition and morphology influenced the hydrophilic character of the samples.     

Realization of Eu-doped p-SnO2 thin film by spray pyrolysis deposition

We report the fabrication of p-SnO₂ thin films by spray pyrolysis deposition using europium (Eu) as an acceptor. Structural and chemical investigations verified that Eu³⁺ ions were successfully incorporated into the SnO₂ crystal by substituting the Sn⁴⁺ sites in the lattice. Even though the undoped SnO₂ thin film showed n-type properties with a charge carrier concentration of −2.343 × 10¹⁸ cm⁻³, SnO₂ showed p-type properties as the Eu was incorporated. In addition, the charge carrier concentration of the Eu-doped SnO₂ increased to 9.121 × 10¹⁹ cm⁻³ as the molar content of the Eu source was increased to 0.2 mM. The optical transmittance was not degraded by the Eu doping and was maintained between 70 and 80% in the visible wavelength spectral range, while the optical band gap of the Eu-doped SnO₂ increased due to the Burstein-Moss effect. The thin film field-effect transistor fabricated by using the Eu-doped SnO₂ showed the typical gate-modulated drain current characteristic of a p-channel transistor with depletion mode. These results demonstrated the effectiveness of Eu as a dopant for p-SnO₂.     

Firing characteristics of size-controlled silver-glass composite powders prepared by spray pyrolysis

Size-controlled spherical silver-glass composite powders were directly prepared by using spray pyrolysis. The mean sizes of the composite powders changed from 0.34 to 0.78 μm when the concentration of the spray solution was changed from 0.05 to 2 M. The firing characteristics of composite powders formed from the spray solutions with a glass content equal to 3 wt.% of the silver component were affected by the mean sizes of the powders. Silver-conducting films formed from large-sized composite powders had a denser structure than those formed from small-sized composite powders. Further, silver-conducting films formed from composite powders with a mean size of 0.78 μm had specific resistances of 3 and 2 μΩ cm at firing temperatures of 450 and 500 °C. However, silver-conducting films formed from composite powders with a mean size of 0.34 μm had specific resistances of 8.2 and 6.9 μΩ cm at firing temperatures of 450 and 500 °C.     

Doped ceria powders prepared by spray pyrolysis for gas sensing applications

In the present study, ceria powder with and without gadolinium (Gd) or zirconium (Zr) dopants were synthesized by a spray pyrolysis (SP) process. The resulting powders (undoped CeO₂, Gd-doped ceria and Zr-doped ceria) were first mixed with organic binders, screen printed on alumina substrates, and then heat treated at 1200 °C for 2 h in air. Experimental results showed that the as-pyrolyzed powders were nanocrystalline and spherical in shape with uneven surfaces. After heat treatment, the powder coatings showed a 3-D network structure with interconnected pores exhibiting a high surface area. The electrical conductivity of CeO₂ was increased by the dope of Zr. The increasing rate of conductivity of ZDC (Zr-doped ceria) with decreasing oxygen pressure was also higher than that of undoped CeO₂. The CeO₂ and ZDC exhibited an n-type semiconductance in all the oxygen pressure regions, showing promise as candidates for sensor applications. The GDC (Gd-doped ceria) revealed a p-type and an n-type semiconductance in high- and low-oxygen pressure regions, respectively. The sensor applications of GDC are thus limited. Meanwhile, the ZDC exhibited a shorter response time due to its smaller grain size, showing a better oxygen sensing behavior.