Synthesis, morphology, and formation mechanism of mullite particles produced by ultrasonic spray pyrolysis

Abstract

Submicrometer spherical particles of mullite powder were synthesized by ultrasonic spray pyrolysis of emulsion and solutions, using tetra-ethyl-orthosilicate (TEOS) or silicic-acid and Al(NO3)3 · 9H2O as initial compounds. Crystallization of mullite phase was determined by differential thermal (DT), thermogravimetric (TG), infrared (IR), and x-ray analyses. The synthesis of mullite from TEOS emulsion occurs by crystallization of γ–Al2O3 (or Al, Si-spinel) from the amorphous phase and its subsequent reaction with amorphous SiO2, as well as by crystallization of pseudotetragonal mullite below 1000 °C and its subsequent phase transformation into orthorhombic mullite. In the powders produced from silicic acid solutions, synthesis of mullite occurs only by crystallization of γ–Al2O3 between 900 and 1000 °C and its further reaction with amorphous SiO2 between 1100 and 1200 °C. Particle formation mechanism depended directly on the initial emulsion or solution preparation, i.e., on the phase separation in the emulsion and on the silicic-acid crosslinking conditions.

Crystallisation of amorphous spray-dried precursors in the Al2O3–SiO2 system

“…7 Spinel was the first crystalline phase from high temperature (≥ 900 • C) decomposition of an aerosol of Al nitrate and fumed silica 8 or from ultrasonic spray pyrolysis at 900 • C of aqueous solutions of Al nitrate and silicic acid. 9 In the present work we have studied the crystallisation of amorphous spray-dried powders in the whole range of compositions in the Al 2 O 3 -SiO 2 system. Spray-drying aqueous solutions being a less usual and less known process for mullite synthesis, 10,11 the kinetics of crystallisation have been determined for comparison with usual processes.…”

Cool, Dry, Nano-scale DIC Patterning of Delicate, Heterogeneous, Non-planar Specimens by Micro-mist Nebulization

“…The choice of the ultrasonic nebulizer comes from the fact that it can provide a narrower micro-droplet distribution in the mist when compared to, e.g., compressed air spray nozzles [37]. Due to the tighter control on the mist droplet size, the ultrasonic nebulizers have gained popularity in some applications as a replacement of compressed gas nozzles, notably in aerosol-based drug delivery devices [38,39] and spray pyrolysis based thin-film [40][41][42] and powder/NP synthesis [37,43,44]. Furthermore, due the compact nature of the ultrasonic nebulizers, which consists of a piezo transducer connected to a simple driving circuitry, compared to a nozzle attached to a compressor or pump, the ultrasonic nebulizers have gained popularity in portable commercial applications, such as aerosolbased drug delivery devices, household humidifiers, etc.…”

Aerosol route in Processing of Nanostructured Functional Materials

“…Moreover, a Pyrosol technique for thin film synthesis through aerosols is developed, too. Based on these techniques, the synthesis of fine, spherical, submicronic powders either in crystal or amorphous state based on oxides, metals and non-oxides have been processed as follows: ZnO 38,41,54,55) , ZnO-Pt(IV) 56) , ZnO-Ru(III) 57) ,, BaTiO3 42) , ZnO-Cr2O3 spinel 34) , Al2O3 based materials 58,59) , Ni, NiO 60) , SiC 61) , Q-TiO2 62) , nanocomposites Ag:(Bi,Pb)-2223) 15,63,64) , phosphors, Gd2O3: Eu 10,65,66,67) , Y2O3:Eu, (GdY)2O3:Eu 20,68,69) , Y3Al5O12: Ce 10,[70][71][72][73][74] , LiFePO4 75) . Those materials are applicable for electronics, optoelectronics, engineering ceramics, catalysts, biomaterials etc.…”