Plasma Torch Production of Ti-Al Nanoparticles
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Plasma Torch Production of Ti-Al Nanoparticles Jonathan Phillips1, Lili Cheng1, Claudia Luhrs2, Hugo Zea2, Matthew Courtney2, and Caleb Hanson2 1 Los Alamos National Lab, Los Alamos, NM, 87545 2 Mechanical Engineering Department, University Of New Mexico, Albuquerque, NM, 87131 ABSTRACT Using the Aerosol-through-Plasma (A-T-P) technique high surface area (from 100 to 203 m /g) bi-cationic (Ti-Al) oxide particles of a range of stoichiometries were produced that showed remarkable resistance to sintering. Specifically, we found that homogeneous nanoparticles with surface areas greater than 150 m2/g were produced at all stoichiometries. In particular, for particles with a Ti:Al ratio of 1:3 a surface area of just over 200 m2/gm was measured using the BET method. The most significant characteristic of these particles was that their sinter resistance was far superior to that of TiAl particles produced using any other method. For example, A-T-P generated particles retained >70% of their surface area even after sintering at 1000 C for five hours. In contrast, particles made using all other methods lost virtually all of their surface area after an 800 C treatment. 2
INTRODUCTION Ti-Al ceramic compounds have attracted interest, due to their high surface area and good thermal stability, for applications in automotive catalytic converters, components exposed to high temperature in electric and electronic devices, shield material in nuclear reactors, and tools for a melting furnace (1). The textural, structural, and surface properties of these compounds are strongly influenced by the method of synthesis; techniques like precipitation, impregnation, and grafting have been used to prepare materials with tailor made surface areas, acid/ basic properties and defined porosity structures (2-5). Of particular interest to our team is the potential use of TiAl as a catalyst support material for automotive three-way catalysts. High temperatures affect all the components of the catalytic converter, the support sinters and can suffer a phase change, reducing the total surface area. The active metal particles sinter, resulting in a decrease in the fraction of the metal available for catalytic reactions (6-9). This low sintering resistance can be countered to some extent by the addition of elements as Ti, Ce and Zr as structural promoters, which also stabilize the very extensive alumina support against sintering (9-13). An enhanced oxygen storage capability is also a key feature in modern catalytic converters in order to boost the oxidation of CO, NOx and hydrocarbons (7, 11-14). Ti-Al oxides are among a handful of materials capable of ‘buffering’ the oxygen concentration in automotive exhaust. Experience indicates that mixed oxides, such as Al-Ce, AlCe-Zr, Ce-Zr, and Ti-Al are potentially the best oxygen ‘buffers’. That is, each is at least moderately stable at elevated temperature and each includes one ion capable of changing oxidation state at around 650 C. Hence, each can act as an oxygen ‘buffer’ during episodic spikes awa
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