Low-pressure Spray Pyrolysis Research Articles

Droplet evaporation on a substrate at the final stage of Low Pressure Spray Pyrolysis and the final morphology of nanoparticles

Abstract For lowered pressure conditions femtoliter droplets evaporation on metallic substrate is investigated by experimental and theoretical methods. Simulation results of the kinetics of droplet evaporation, which substantially used the pinning effect, are presented. It was shown that the evaporation time of a droplet with the height 5 μm is about 0.01 s. For evaporation on the substrate droplets of aqueous solution with nanoparticles inside it was predicted the formation of the core–shell structure of nanoparticles. Qualitative confirmation of this effect is obtained. For Low-Pressure Spray Pyrolysis of droplets of aqueous solution of salts, the core is a metal oxide and the shell is a deposited layer of the initial salt.

Droplet Generation and Nanoparticle Formation in Low-Pressure Spray Pyrolysis

In the present study, we found that pressure-dependent droplet-to-particle formation is important for the control of both droplet and particle characteristics during the production of particles with enhanced properties. Using experimental and simulation approaches, the present study investigated the droplet-to-particle formation of zinc oxide as a model material that was synthesized via low-pressure spray pyrolysis. The size distributions of both the droplets generated under low-pressure and the synthesized particles were measured and compared. The effects of operating conditions, i.e., operating pressure, carrier gas-, and liquid-flow rates, reactor temperature, and precursor concentration, on the characteristics of the generated droplets and synthesized zinc oxide particles were systematically investigated. We found that broad and bimodal droplet size distributions shifted to narrow and monodispersed distributions as chamber pressures were reduced. The low-pressure-synthesized zinc oxide nanoparticles were highly crystallized with unimodal distributions and sizes of approximately 8 nm. Droplet temperature decreased with decreasing chamber pressure, which confirmed both the evaporative cooling of droplets and the formation of smaller droplet sizes. The chamber temperature and droplet size simulation results were in accordance with the experimental results. In conclusion, we found that the chamber pressure is the primary determinant of monodispersity with respect to droplet size distribution and to the size and morphology of the synthesized particles.

Nanoparticle formation in spray pyrolysis under low-pressure conditions

The formation of zirconia particles prepared by low-pressure spray pyrolysis (LPSP) was studied experimentally and numerically. A numerical model was developed, and it is the first to quantitatively explain the phenomena occurring in the LPSP system. Under certain operational conditions, particle formation was based on a one-droplet to one-particle conversion, as found in the spray pyrolysis process under atmospheric pressure conditions. On the other hand, nanoparticles were generated at higher temperatures and under conditions of lower pressure. Zirconia nanoparticles were successfully produced under experimental conditions of 1600 °C, 30 Torr with 10 l/min nitrogen as a carrier gas. The mass and heat transport calculation indicated that the evaporation rate would increase rapidly with increasing temperature and decreasing pressure in the furnace. The model considered flow regimes, and accounted for the regime range from continuum to free-molecular, depending on the Knudsen number. A very high evaporation rate led to the assumption that droplets were ruptured instantaneously, resulting in the production of monomers. Nanoparticles were then formed by the nucleation of monomers to form clusters, and then by the coagulation between clusters and surface condensation of monomers onto clusters. To predict the size distribution of nanoparticles, a population balance analysis called the nodal method was used. The simulation results showed reasonable agreement with the experimental results.

Direct synthesis of highly crystalline transparent conducting oxide nanoparticles by low pressure spray pyrolysis

In this article, we firstly reported a general preparation method for the production of highly crystallized and single crystalline transparent conducting oxide (TCO) nanoparticles: tin-doped indium oxide (ITO), zinc-doped indium oxide (IZO), aluminum-doped zinc oxide (AZO), and gallium-doped zinc oxide (GZO). Low-pressure spray pyrolysis was applied by means of a modified-atomizer and preheated carrier gas. The effects of pyrolysis pressure, temperature and carrier gas temperature on the size and morphology of the synthesized TCO nanoparticles were systematically investigated. The synthesized TCO nanoparticles were 17 nm large with crystallite size of 8–11 nm. The resistivities of the formed pellets were measured and compared. These results showed that this method successfully produces various TCO nanoparticles using neither dispersing agents nor post-heating treatments, which allows rapid, continuous, single-step preparation.

Single crystal ZnO:Al nanoparticles directly synthesized using low-pressure spray pyrolysis

Aluminum-doped zinc oxide (AZO) nanoparticles powder were prepared using low-pressure spray pyrolysis (LPSP). AZO nanoparticles sized 16 and 20 nm with nearly spherical shapes and a crystal size of 11 and 15 nm were yielded using zinc acetate precursor at a low-pressure of 8.0 kPa with a pyrolysis temperature of 800 and 1000 °C. The thin films were deposited using a dip-coating method derived from the as-prepared AZO nanoparticles. The thin films that were heated for 1.5 h showed a transmittance higher than 97% in the wavelength range of 400–800 nm and a resistivity of 4.0 × 103 ohm cm with a film thickness of 250 nm. The high crystallinity and high transmittance of AZO nanoparticles that are directly synthesized using the LPSP process have potential for applications as transparent conducting material.

Nano-sized manganese oxide particles prepared by low-pressure spray pyrolysis using FEAG process

Nano-sized manganese oxide particles were prepared by low-pressure spray pyrolysis using the new type of liquid aerosol generator called as FEAG process. The particles prepared from polymeric precursors spray solution with organic additives had large size, hollow and fractured morphologies due to the gas evolution from the decomposition of the organic additives. The precursor particles with micron size, hollow and thin wall structures turned to nano-sized manganese oxide particles after post-treatment at temperatures of 700 and 800 °C. The optimum concentrations of citric acid (CA) and ethylene glycol (EG) to prepare the nano-sized manganese oxide particles by spray pyrolysis using the FEAG process were 0.3 M each. The manganese oxide particles prepared from the polymeric precursors spray solutions with high concentrations of CA and EG had spherical shape and porous morphologies.

The Characteristics of Nano-sized Cobalt Oxide Particles Prepared by Low Pressure Spray Pyrolysis

Nano-sized cobalt oxide powders were prepared by low pressure spray pyrolysis process. The precursor powders obtained by low pressure spray pyrolysis process from the spray solution with ethylene glycol had several microns size and hollow structure. The precursor powders obtained from the spray solution with optimum concentration of ethylene glycol formed the nano-sized cobalt oxide powders with regular morphology after post-treatment without milling process. On the other hand, the cobalt oxide powders obtained from the spray solution without ethylene glycol had submicron size and spherical shape before and after posttreatment. The mean size of the cobalt oxide powders formed from the spray solution with concentration of ethylene glycol of 0.7M was 180 nm after post-treatment at temperature of <TEX>$800^{\circ}C$</TEX>. The mean size of the powders could be controlled from several tens nanometer to micron sizes by changing the post-treatment temperatures in the preparation of cobalt oxide powders by low pressure spray pyrolysis process.

Characterization of dip-coated ITO films derived from nanoparticles synthesized by␣low-pressure spray pyrolysis

In2O3:Sn (Indium Tin Oxide; ITO) films were prepared from a sol solution with highly crystalline ITO nanoparticles (less than 20 nm in size with 10 at.% Sn) which had been prepared by low-pressure spray pyrolysis (LPSP) in a single step. The ITO sol solution was prepared by dispersing LPSP-prepared ITO nanoparticles into ultra pure water. The nanoparticle ITO film was deposited on a glass substrate using a dip-coating method and then annealed in air at various temperatures. The optical transmittances of the ITO films were measured by UV–Vis spectrometry, and the films were found to have a high transparency to visible light (in the case of a film thickness of 250 nm annealed at 400°C, the transparency was in excess of 95% over the range λ=450–800 nm, with a maximum value near 100% at wavelengths above λ=700 nm). The optical transmittances of the films were influenced by the size of the ITO particle used, the film thickness and the annealing temperature. The ITO films showed a minimum resistivity of 9.5×10−2 Ω cm, and their resistivity was affected by both the ITO particle size and the annealing temperature used.

One-step synthesis of titanium oxide nanoparticles by spray pyrolysis of organic precursors

Titanium oxide (titania) nanoparticles (with a nominal size of about 10 nm) were synthesized directly from three organic precursors: titanium tetraisopropoxide (TTIP), and water-soluble titanium sources TC-300 ® and TC-400 ®, by using a low-pressure spray pyrolysis (LPSP) method. Effects of temperature, solvent, concentration and precursor type have been investigated systematically. We found that a higher temperature and a higher concentration were beneficial for the formation of nanoparticles. Addition of ethanol as a co-solvent improved breakup of droplets, and subsequently formation of nanoparticles. Water-soluble titanium sources showed great potentials for preparation of titania nanoparticles. The nominal size of nanoparticles calculated from electron microscopical images agreed well with that estimated from corresponding X-ray diffraction patterns, implying that nanoparticles were single crystals. The possible mechanism of particle formation in the LPSP process is also provided.

Direct Synthesis of Barium Titanate Nanoparticles Via a Low Pressure Spray Pyrolysis Method

The one-step synthesis of barium titanate (BaTiO3) nanoparticles was studied by employing a low-pressure spray pyrolysis (LPSP) method. The effects of temperature, pressure, and the addition of urea to the precursor were investigated experimentally. The results were compared with the experimental data of the conventional (atmospheric) spray pyrolysis method. It was shown that the BaTiO3 nanoparticles could be synthesized by the low-pressure method, while only spherical hollow particles with smooth surfaces could be produced by the conventional spray method. The addition of urea greatly improved the crystal growth and particle breakup due to extra heat supplied during the combustion reaction coupled with the evolution of gases. The dispersity of nanoparticles increased with the quantity of urea and with a decrease in pressure. The possible mechanism of the formation of BaTiO3 nanoparticles in the LPSP process was also proposed.

Nickel and nickel oxide nanoparticles prepared from nickel nitrate hexahydrate by a low pressure spray pyrolysis

Nickel nanoparticles prepared from Ni(NO 3) 2·6H 2O by using a low pressure spray pyrolysis (LPSP) are reported in this paper. Effects of pressure, carrier gas flow rate, concentration of precursor and type of reducing agents on the size, morphology and crystallinity of nickel nanoparticles were investigated. It is found that pressure and carrier gas flow rate play crucial roles in the reduction of NiO to nickel in the LPSP process. A relatively higher solution concentration is suitable for the generation of nanoparticles. Cosolvents such as, formic acid and ethanol, as well as H 2, were treated as the reductives in the synthesis of nickel (nanoparticles) in this work. Weak NiO peaks, together with strong nickel peaks, in powder XRD patterns, indicated that nickel nanoparticles are easier to be oxidized compared with the submicron-sized one investigated by conventional spray pyrolysis due to their higher surface potential. Another possible reason may come from the incomplete reduction in very short residence time because of the decrease of H 2 amount in some cases. A possible mechanism of nickel nanoparticles formation has been suggested based on the demonstration of our previous research as well.

Nickel and nickel oxide nanoparticles prepared from nickel nitrate hexahydrate by a low pressure spray pyrolysis

Nickel nanoparticles prepared from Ni(NO 3 ) 2 ·6H 2 O by using a low pressure spray pyrolysis (LPSP) are reported in this paper. Effects of pressure, carrier gas flow rate, concentration of precursor and type of reducing agents on the size, morphology and crystallinity of nickel nanoparticles were investigated. It is found that pressure and carrier gas flow rate play crucial roles in the reduction of NiO to nickel in the LPSP process. A relatively higher solution concentration is suitable for the generation of nanoparticles. Cosolvents such as, formic acid and ethanol, as well as H 2 , were treated as the reductives in the synthesis of nickel (nanoparticles) in this work. Weak NiO peaks, together with strong nickel peaks, in powder XRD patterns, indicated that nickel nanoparticles are easier to be oxidized compared with the submicron-sized one investigated by conventional spray pyrolysis due to their higher surface potential. Another possible reason may come from the incomplete reduction in very short residence time because of the decrease of H 2 amount in some cases. A possible mechanism of nickel nanoparticles formation has been suggested based on the demonstration of our previous research as well.

Direct Preparation of Nonagglomerated Indium Tin Oxide Nanoparticles using Various Spray Pyrolysis Methods

Indium tin oxide particles were prepared using three different spray synthetic techniques: conventional, salt-assisted, and low pressure. Optimum conditions for the preparation of small size, nonagglomerated particles were investigated for these three methods. The use of the conventional spray pyrolysis method resulted in only larger particles (submicrometer order). Salt-assisted spray pyrolysis (SASP) and low-pressure spray pyrolysis (LPSP) produced highly crystalline, dense, homogeneous, and nearly nonagglomerated nanoparticles that were less than 25 nm in size. The size of the particles was in the range 12–24 nm for the SASP method and 8–14 nm for the LPSP method. In addition, the LPSP method led to the production of single nanometer-size multicomponent particles in a single step with less heating time without the need for any post heat treatment and additives.

Control of size and morphology in NiO particles prepared by a low-pressure spray pyrolysis

Nickel oxides (NiO) nano- and submicron particles were synthesized by a low-pressure spray pyrolysis system. Conversion of micrometer droplets into particles in the gas phase using NiO synthesis as a model was studied. Different types of precursors (aqueous Ni(NO 3) 2·6H 2O, NiCl 2, and Ni(HCO 2) 2·2H 2O) and temperatures from 400 to 900 °C have great influences on controlling the size and morphology of final particles. The results show that operation of a low-pressure system leads to substantial changes in size and morphology of particles, and that the NiO particles having size around 20 nm can be generated under a limited of conditions.

Preparation of Functional Fine Particles by Low Pressure Spray Pyrolysis

Preparation of Functional Fine Particles by Low Pressure Spray Pyrolysis

Preparation of high surface area nanophase particles by low pressure spray pyrolysis

Abstract The influence of reactor pressure on the size and morphology of particles prepared by spray pyrolysis was investigated. Manganese, nickel and copper oxides particles were prepared from acetate and nitrate solutions at atmospheric pressure and 60 torr by ultrasonic spray pyrolysis. Particles with high surface area (17–58 m 2 /g) and good crystallinity were obtained even at high temperature (800 °C) at 60 torr. The original round shapes of agglomerates were fragmented into nanometer size crystalline particles ( 2 /g) and large crystallite sizes (> 40 nm) due to the intraparticle sintering. The pressure effect became much more pronounced as the reactor temperature increased.