Thermal Plasma Synthesis of Nano Composite Particles

[SeRDaRr]

1. Introduction
Plasma Display Panel (PDP) is considered as the most promising
candidate for large area display among various Flat Panel Displays
(FPD’s) due to its manufacturing process appropriate for a large
displaying area, high speed addressing ability and good display
quality [1]. The large plasma display panel is divided into tiny cells
by barrier ribs, and the electric discharge gas filled in the cell is
one of important factors determining the display quality and life time
of the PDP. By
the nature of plasma, heavy ions in the cell continuously bombard
surrounding walls during operation, resulting in the emission of
undesired species from the wall, in turns contaminating the plasma
gas, and consequently degrading the display quality. To extend the
PDP’s life time
with good display quality, it is necessary to continuously eliminate
contaminants emitted from protective layer, barrier rib and
fluorescent substances[2,3]. Installation of getter materials, such as
Zr-V-Fe alloy powder, in the PDP cell is a potential solution to
overcome such problems.
In fact, Zr-V-Fe getter materials are currently utilized in various
applications[4,5] and commercially available (for an example, ST707
from SAES Getters, Inc.). However the particle size of the commercial
getters is in the range of micrometers, limiting their applicability
to the
PDP cell. Hence it is imperative to produce the Zr-V-Fe getter
material with the particle size in the range of nanometers. Nano
particles can be produced by various methods, such as sol-gel[6],
spray pyrolysis[7], infrared heating[8] freeze-drying[9], laser
ablation [10], wire explosion[11], and thermal plasma[12]. While most
methods, requiring pre- and post-treatment, are time consuming and
expensive, thermal plasma is simple and fast, thus cost effective
technique to produce nano particles, specially for materials with
extremely high evaporation
temperature such as Zr. In this work, nano composite particles were
prepared from a bulk ZrVFe alloy ingot by transferred DC thermal
plasma. Effects of plasma gas flow rate on the characteristics of the
produced nano composite particles, such as particle size distribution,
mean particle size, surface area, particle composition and
crystallinity, were investigated.

Conclusions
A transferred DC plasma was utilized to synthesize spherical nano
composite particles from a ZrVFe ingot. Although the size of the
produced
particles was, in overall, in the range between 30 nm and 200 nm, the
small particles near 50 nm became more abundant as the plasma gas flow
rate increased due to the shorter residence time of the particles in
the plasma flame region and to the higher quenching rate.
Consequently, the average particle diameter monotonically decreased
from 91 nm to 55 nm, and the surface area increased from 200 m 2/g to
255 m 2/g as the plasma gas flow rate increased from 20 L/min to 40 L/
min. Furthermore the particle size distribution became narrower
implying that the particle size became more uniform, and the
crystallinity also improved. The results imply that the particle
properties can be controlled by the plasma gas flow rate.