Synthesis of non-aggregated titania nanoparticles in atmospheric pressure diffusion flames (original) (raw)

ARTICLE IN PRESS G Model Diffusion flame synthesis of hollow, anatase TiO 2 nanoparticles

Well defined, dense, hollow spheres of anatase titania (TiO 2 ) nanoparticles were produced from TiCl 4 (as precursor) by diffusion flame technique. Flow rates of gases (LPG/air/N 2 compositions) were found to affect particle size. Titania nanoparticles were observed to decrease from 19 to 8 nm when the air flow rates were increased from 20 to 25 lpm. However, the particle size was found to increase from 15 to 21 nm when the nitrogen flow rate was increased from 0.8 to 2.0 lpm. LPG has been used as fuel. The increase in particle size of anatase TiO 2 was due to higher flame height and temperature. The anatase (TiO 2 ) phase was predominant compare to rutile phase in the ratio of 74:26 using air as an oxidant. In the gas phase reaction, the nanoparticles formation occurs due to spontaneous increase of number density of nuclei. The coagulation or aggregation of particles leads to the formation of larger particles due to higher chances of collisions among the particles and sintering at high flame temperature.

Characterization and sinterability of nanophase titania particles processed in flame reactors

Nanostructured Materials, 1996

Flame aerosol reactors are a routefor large scale processing of nanostructured materials. However, fundamentals about processing-structure-property relationships have not been extensively researched. This work utilized three dtflerent burners to obtain a wide range of flame processing conditions (different time-temperature histories) to study the formation of nanophase titaniaparticles. At low precursor reaction temperatures of about 400 "C, amorphous titania wasobtained. At intermediate temperaturesof900-1430"C,mixturesof anataseandrutile phase titania were obtained. At high temperatures of 1500-157O"C, spherical particles of 100% anatase titania were obtained. A qualitative explanation of the dtfferentphaseformation has been provided. Transmission Electron Microscopy was used to study particle morphology, size and agglomeration. Sizes of the titania particles produced by the designed burners variedfrom 10 to 100 nm, depending on processing conditions. In situ light scattering measurements were made to examine the evolution of the particle sizes. Post-sintering experiments were carried out to illustrate superior sinterability of the nanophase titania powders.

Carbon-coated titania nanostructured particles: Continuous, one-step flame-synthesis

Journal of Materials Research, 2003

Concurrent synthesis of titania-carbon nanoparticles (up to 52 wt.% in C) was studied in a diffusion flame aerosol reactor by combustion of titanium tetraisopropoxide and acetylene. These graphitically layered carbon-coated titania particles were characterized by high-resolution transmission electron microscopy (HRTEM), with elemental mapping of C and Ti, x-ray diffraction (XRD), and nitrogen adsorption [Brunauer-Emmett-Teller (BET)]. The specific surface area of the powder was controlled by the acetylene flow rate from 29 to 62 m2/g as the rutile content decreased from 68 to 17 wt.%. Light blue titania suboxides formed at low acetylene flow rates. The average XRD crystal size of TiO2 decreased steadily with increasing carbon content of the composite powders, while the average BET primary particle size calculated from nitrogen adsorption decreased first and then approached a constant value. The latter is attributed to the formation of individual carbon particles next to carbon-coate...

The role of gas mixing in flame synthesis of titania powders

Powder Technology, 1996

The formation of dtanla powders by oxidation of TiCI4 was studied in a laminar diffusion flame reactor. The effects of flame configuration ( fuel and oxidant flow rate and position) as well as precursorTiCh loading on the specific surface area and phase composition of the Inoduct titania powder were investigated. Specifically. the specific surface increased from 15 to 120 m~/g and the futile fraction was reduced from 15 to 0.1 wt.% by exchanging the position of the fuel and oxidant streams in the burner. Increasing the flame temperature increased due futile fraction and the avenge primary panicle size. Increasing the precursor TiCG concentration reduced the specific surface area, especially = low TiCh. loadings and flame temperalures. However, it had no effect on the phase composition .,,f the titania particles.

Characteristics of Titania Nanoparticles Synthesized Through Low Temperature Aerosol Process

2005

As one of the important process alternatives for the synthesis of nano materials with lower costs, flexibility and versatility, vapor phase synthesis of titania nano particles continue to attract attention. A low temperature aerosol process for the synthesis of titania nano particles is demonstrated by elucidating the influence of temperature, molar ratio of H 2 O/TiCl 4 and concentration of precursors on particle size and phase composition. This paper highlights the advantages of employing amorphous phase titania powder as solid precursor for its transformation to the rutile phase at temperatures less than 973K through vapor phase hydrolysis of TiCl 4. A mechanistic hypothesis is proposed to explain the catalytic role of water vapor in the enhancement of amorphous to anatase phase transformation at high (15 to 27) molar ratio of H 2 O/TiCl 4 .

Flame-Nozzle Synthesis of Nanoparticles with Closely Controlled Size, Morphology and Crystallinity

Chemie Ingenieur Technik, 2002

A process for close control of primary particle size, morphology and crystallinity of flame-made nanoparticles is presented. According to this, freshly made titania aerosol nanoparticles are rapidly quenched in a critical flow nozzle, essentially freezing particle growth at desired levels. The nanoparticles are produced in a methane/oxygen diffusion flame reactor by oxidation of titanium-tetra-isopropoxide (TTIP). Precise control of the average primary particle size, reduced agglomeration and phase composition is achieved by positioning of the quenching nozzle above the burner and controlling gas and precursor flow rates. D

Role of Gasāˆ’Aerosol Mixing during in Situ Coating of Flame-Made Titania Particles

Industrial & Engineering Chemistry Research, 2009

Rutile TiO 2 particles of 40 nm average diameter were made by flame spray pyrolysis (FSP) and in situ coated with ultrathin (2-4 nm) SiO 2 layers. The spray flame was enclosed by a quartz glass tube while hexamethyldisiloxane (HMDSO) vapor-laden N 2 was injected in swirling crossflow to and downstream of the flame through a metal torus pipe ring. The as-prepared powders were characterized by transmission electron microscopy (TEM), X-ray diffraction, and nitrogen adsorption. The effect of mixing between HMDSO-laden N 2 jets and freshly made titania aerosol on product coating quality was investigated by varying systematically the number and gas flowrate through these jets experimentally and by computational fluid dynamics. The coating quality of titanium dioxide was evaluated further by photocatalysis of isopropanol to acetone under UV light using suspensions of the above particles.

Characteristics of Tio 2 Nanoparticles Synthesized Through Low Temperature Aerosol Process

As one of the important process alternatives for the synthesis of nano materials with lower costs, flexibility and versatility, vapor phase synthesis of titania nano particles continue to attract attention. A low temperature aerosol process for the synthesis of titania nano particles is demonstrated by elucidating the influence of temperature, molar ratio of H 2 O/TiCl 4 and concentration of precursors on particle size and phase composition. This paper highlights the advantages of employing amorphous phase titania powder as solid precursor for its transformation to the rutile phase at temperatures less than 973K through vapor phase hydrolysis of TiCl 4 . A mechanistic hypothesis is proposed to explain the catalytic role of water vapor in the enhancement of amorphous to anatase phase transformation at high (15 to 27) molar ratio of H 2 O/TiCl 4 .