I. Wuled Lenggoro

Preparation of nanoparticles via spray route

Nanometer-sized particles (1–100 nm) are of considerable interest for a wide variety of applications, ranging from electronics via ceramics to catalysts, due to their unique or improved properties that are primarily determined by size, composition and structure. In this study, we report a simple, rapid and generalizable aerosol decomposition (spray pyrolysis) process for the continuous synthesis of nanoparticles with adjustable sizes, narrow size distribution, high crystallinity and good stoichiometry. The production of spherical-shaped porous particles with nanoscale ordering porosity and the zinc oxide quantum dots in silica nanoparticles matrix by means of a spray drying method using a colloidal mixture as the precursor and by the combined sol–gel and spray drying method were also reported. ? 2003 Elsevier Science Ltd. All rights reserved.

YAG:Ce phosphor particles prepared by ultrasonic spray pyrolysis

Abstract Spray pyrolysis was applied to the preparation of fine YAG:Ce phosphor particles. The characteristics of particles such as crystallinity, morphology, and photoluminescence were investigated. Phase-pure YAG:Ce particles with high crystallinity were obtained after annealing at lower temperatures than those of conventional preparation processes. The mean size of the particles increased from 0.46 to 1.2 μm when the overall solution concentrations were changed from 0.03 to 1 mol/L. The YAG:Ce particles annealed at 1300°C were nonaggregated and spherical. The particles absorbed excitation energy in the range 403–510 nm, and the maximum excitation wavelength was near 470 nm. The YAG:Ce particles showed broad emission peaks in the range 480–650 nm and had maximum intensity at 528 nm. The photoluminescence intensity of the particles increased monotonically with increasing annealing temperature and showed the maximum value at 1 at% Ce.

An experimental and modeling investigation of particle production by spray pyrolysis using a laminar flow aerosol reactor

The influence of operating parameters on the morphology of particles prepared by spray pyrolysis was investigated using a temperature-graded laminar flow aerosol reactor. Experimentally, zirconia particles were prepared by spray pyrolysis using an aqueous solution of zirconyl hydroxide chloride. Hollow particles were formed if the reactor temperature was high, the temperature gradient was too large, the flow rate of carrier gas was high, and the initial solute concentration was low. A numerical simulation of the pyrolysis process was developed using a combination of two previous models. The simulation results compared well with the experimental results. (c) 2000 Materials Research Society.

PREPARATION OF ZnS NANOPARTICLES BY ELECTROSPRAY PYROLYSIS

Zinc sulfide particles 20–40 nm in diameter were prepared by electrically driven spray pyrolysis. Solutions of ethyl alcohol with zinc nitrate (Zn(NO3)2) and thiourea (SC(NH2)2) at concentrations from 0.0025 to 0.2 mol l-1 and electrical conductivities between 10-4 and 10-1 S m-1 were electrosprayed from steady cone-jets at flow rates from 0.05 to 0.25 ml h-1, with positive and negative polarity. The initially highly charged drops formed were neutralized by bipolar ions from a radioactive source to increase the overall transmission efficiency through a reactor furnace. This process was made particularly effective by the innovation of placing the ion source directly within the electrospray chamber. The diameters of the final ZnS particles were measured on-line by a differential mobility analyzer and a condensation nucleus counter. In spite of ambiguities in the flow rate of liquid through the cone–jet (associated to solvent evaporation from the meniscus), these diameters agree approximately with values expected from available scaling laws. Transmission electron micrographs also confirmed these results. Electrospray pyrolysis is hence able to generate non-agglomerated and spherical ZnS nanoparticles with geometrical standard deviation σg of about 1.3.

Preparation of functional nanostructured particles by spray drying

Abstract When particle dimensions are reduced to the order of several nanometers, their physical and chemical properties deviate significantly from the bulk properties of such materials. Because of this, there is abundant potential for their use in future technologies including electronic and optoelectronic, mechanical, chemical, cosmetic, medical, drug, and food technologies. However, due to their extremely small sizes, the particles suffer from many problems related to their surface and thermal stability, shape preservation, handling, assembly in devices, etc. It is therefore an important challenge to solve these problems by developing slightly larger particles (e. g. on the submicrometer scale) in which the properties generated by the nanoscale material are preserved. One approach to this is to trap nanoparticles in a micrometer-sized inert matrix. This approach allows the nanoscale properties to be retained, since nanoparticles are separated from each other in the inert matrix. The inert matrix also serves as a coating medium that inhibits any chemical changes to the surface of the nanoparticles. Their larger size allows easy handling or assembly in devices. A promising method for designing and fabricating these composite structures is a spray method, in which spherical particles can be produced. In this paper, we review the nanostructural processing (synthesis) of submicrometersized particles by a spray method, which provides a restricted reaction environment (such as pores or cages) in the matrix for their synthesis and handling. The characterization and potential applications of these composites are also discussed.

Synthesis of LaPO4:Ce, Tb phosphor particles by spray pyrolysis

Spray pyrolysis method was applied to prepare submicron LaPO4:Ce,Tb phosphor particles. The product characteristics such as photoluminescence, crystallinity, and particle morphology were investigated under various preparation conditions and compared with those of commercial ones. The prepared powders showed 543-nm green emission characteristics. The maximum photoluminescence intensity was obtained at 1550°C.

Preparation of nonaggregated Y2O3 : Eu phosphor particles by spray pyrolysis method

Ministry of Education, Culture and Science of Japan, Hiroshima Industrial Technology Organization, KOSEF (Korea Science and Engineering Foundation)

Functional Nanostructured Silica Powders Derived from Colloidal Suspensions by Sol Spraying

The preparation of silica powders derived from sols with a variety of primary particle sizes from 4 to 100 nm and the influences of preparation conditions such as drying temperature and initial concentration of precursor on the final powders morphology were investigated for the first time. The prepared silica powders have spherical morphology, and the final diameter (between 0.1 and 2 um) was controlled by changing the concentration of starting colloidal suspension. The preparation of silica based luminescent powders was investigated by adding europium ion as the dopant. The Eu-doped silica powders showed a visible-luminescence with wavelength of 613 nm, a red emission, under excitation of 394 nm light source. The effects of Eu-doping concentration, operation temperature and primary particle size of silica sols on the luminescence were also investigated.

Preparation of ZnS and CdS fine particles with different particle sizes by a spray-pyrolysis method

In the preparation of ZnS and CdS fine particles by an ultrasonic spray-pyrolysis method, the particle size was changed from submicrometre to micrometre size by changing the concentration of the metal nitrates in the starting aqueous solution containing Zn(NO3)2 or Cd(NO3)2 and SC(NH2)2. The effects of temperature profile in the reactor furnace on the properties of prepared particles were also investigated by varying the temperature profiles: constant and increasing temperature distributions. The volume mean diameter of the prepared particles was found to be approximately proportional to the one-third power of the concentration of the metal nitrates in the solution. The crystalline phase and fluorescence properties of ZnS and CdS particles did not depend on the particle size.

Nanoparticles of a doped oxide phosphor prepared by direct-spray pyrolysis

A gas-phase synthesis route based on spray pyrolysis with a residence/heating time of less than 0.1 s was designed to directly prepare Eu-doped Y 2 O 3 phosphor nanoparticles. The average size of the phosphor particles decreased from the submicron size to around 10 nm when the concentration of the starting solution was increased. By increasing the operating temperature, from 1500 to 1700 °C, the submicron-particles were converted into a nano-particle phosphor, and their photoluminescence intensities at 611 nm (254-nm excitation) were greatly improved. This synthesis procedure has considerable potential for preparing a variety of doped luminescent nanoparticles without the need for post-treatment processing.