Solvent and plasma gas influence on the synthesis of Y 2 O 3 nanoparticles by suspension plasma spraying
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Suspension plasma spraying was used to synthesize Y2O3 nanoparticles. The Y2O3 starting material was first dispersed in a solvent to form a suspension and then injected axially into the plume of an inductive radio frequency plasma. It was found that the as-sprayed Y2O3 particles had a size distribution from nano to micron scale and various morphological features, which varied with processing conditions as well as solvent and plasma gas type. In comparison with water, organic solvents led to a higher productivity and smaller particle size, whereas water introduced impurities such as Y2O2C2, which is isotypic to La2O2C2. Introduction of oxygen as an auxiliary plasma gas was an effective way to eliminate this impurity. In addition, complete combustion of the organic solvent and recombination of oxygen atoms above 4000 K also elevated the heat treatment degree of Y2O3. As a result, application of O2 with an organic solvent resulted in an even smaller mean particle size and narrower size distribution.
I. INTRODUCTION
Rare-earth oxides have unique properties that make them versatile functional materials in many applications, including phosphors,1 catalysts,2 and fuel cells.3 One of these applications is to dope rare-earth sesquioxides into BaTiO3-based multilayered ceramic capacitors (MLCC) for performance improvement.4 Recently, with the trends toward thinner dielectric layers and miniaturization of MLCC components, a nano-sized rare-earth oxide dopant has become a necessity. Nanoparticles are nanometerscale aggregates of atoms. Their size gives them physical and chemical properties different from those of conventional bulk materials, caused by size-dependent surface effects or quantum-mechanical and coulomb-charging effects. Hence, they present an attractive potential for technological applications.5 The synthesis methods of nanoparticles can be classified into two categories: chemical methods, such as solgel,6 hydrothermal,7 and hydrolysis processing8; and physical methods, including laser ablation,9 flame spraying,10 and plasma spraying.11 Inductively coupled radio frequency (rf) plasma spraying, as one of the physical processing methods, has been used in a variety of industries to synthesize metal, alloy, ceramic, and composite nanoparticles.12,13 It has advantages such as high temperature and high enthalpy density, flexibility in pressure a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0161 1306 J. Mater. Res., Vol. 22, No. 5, May 2007 http://journals.cambridge.org Downloaded: 24 Mar 2015
and atmosphere, and minimum contamination. However, there are still a few challenges to overcome. One of these challenges is that the poor flowability of the starting material restricts its smooth flow through the spray nozzle and reduces the momentum that the particles acquire for penetrating the plasma jet. To solve this problem, a novel process known as suspension plasma spraying (SPS) was introduced.14,15 The suspension, made by dispersing starting material in a liquid carrier,
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