Nonthermal Microwave Plasma Synthesis of Crystalline Titanium Oxide & Titanium Nitride Nanoparticles
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NONTHERMAL MICROWAVE PLASMA SYNTHESIS OF CRYSTALLINE TITANIUM OXIDE & TITANIUM NITRIDE NANOPARTICLES Prabhjot Mehta, A. K. Singh* and A. I. Kingon Dept. Mat. Sci. & Eng., North Carolina State University, Raleigh, NC, 27695-7919 *On study leave from Phy. Dept. BHU, VARANASI-221005, INDIA
ABSTRACT We report the nonthermal synthesis of ultrafine crystalline nanoparticles of titanium oxide and titanium nitride. The nanoparticles are formed by gas phase reactions between precursor gases dissociated in the microwave plasma. For the production of titanium nitride, titanium tetraisopropoxide (TTIP) and ammonia or nitrogen precursor gases are used. For titanium oxide production TTIP and oxygen are used as precursor gases. In both cases ultrahigh purity argon serves as a carrier gas and diluent.Transmission electron microscopy (TEM) revealed that the titanium nitride powders so formed were either cubic (TiN) or tetragonal (Ti2N) depending on the operational conditions, particularly the relative nitrogen gas flow rates. Ammonia gas was found to be a much more reactive nitrogen source than molecular nitrogen gas. For the titanium oxide growth an excess of oxygen was utilized to achieve TiO2. Powders collected from the gas phase corresponded to the rutile (tetragonal) phase. However, powders collected from the cavity walls corresponded to the high temperature and pressure (orthorhombic) 13-TiO2. There was also evidence of a polytypically modulated phase of TiO2, with the observed c-periodicity double the parent c-periodicity of the rutile phase. Using a low oxygen flow rate during powder formation led to the formation of orthorhombic Ti305 "powders". The powders were easily sinterable by in situ electron beam annealing in the electron microscope, with an estimated temperature of around 550 0 C. This is much lower than the temperatures normally required to sinter these materials.
1. INTRODUCTION Titanium nitride (TiN) is an important material for advanced refractory applications. TiN powders are often used as reinforcements in metal, ceramic and polymer matrix composites [1]. Gas phase production of titanium nitride powder has been reported previously [2,3]. In these previous reports, high temperature processing is necessary, and the resulting powder sizes are in the micron range. Titanium oxide is being used in many applications due to its high dielectric constant, high refractive index and high chemical stability. It is used as filters in visible and near infrared wavelength, insulating coatings, photoanodes, memory cells, capacitors of high dielectric constant, antireflecting coatings and wave guides, etc. In fine particle state these can be used as pigments, magnetic compounds for recording sound and images, thickening and reinforcing agents, fuel pellet powders for nuclear plants, in catalysis, in automobile parts and in peizoelectric materials [1-7]. There are several papers describing the synthesis of titanium oxide chemically, thermally, or by laser [4,5]. This paper describes the synthesis of ultrafine crystalline pow
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