論文題目「Nanoparticle Synthesis of Metal-doped ZrN by Induction Thermal Plasma」
Induction thermal plasma has unique advantages such as ultra-high temperature
even up to 10,000 K, high cooling rate about 10^4–10^6 K/s, no contamination
since less of electrode, as well as long residence time. Due to its wide
range of operating parameters, induction thermal plasma can be considered
as an innovative and powerful tool for synthesis of functional nanoparticles
with high purity.
Zirconium nitride (ZrN) is widely used as diffusion barriers, hard coatings,
and corrosion-resistant layers on optical and mechanical components. Limited
oxygen resistance restricts further usage of ZrN, especially when temperature
surpasses 700℃. Doping reactive elements is considered as a useful mean
to inhibit oxidization because dopant ions diffuse outwardly and segregate
in grain boundaries. This phenomenon reduces inward diffusion rate of the
oxygen molecule effectively during high-temperature oxidation. Furthermore,
doped ZrN nanoparticle has large potential on the field of photocatalyst
due to the decrease of band gap energy.
Induction thermal plasma has been widely applied on the material doping.
Ishigaki et al., reported the synthesis and formation mechanism of cobalt
and iron-doped TiO2 nanopowder by induction thermal plasma. This research
is aim to synthesize metal-doped ZrN nanoparticles with high purity and
understand formation mechanism. Ta, Nb, and Al are selected as dopants
because these three metals were reported to enhance electronic and mechanical
properties of ZrN.
The experiment equipment mainly consists of plasma torch, reaction chamber,
power supply of 4MHz at plate power of 20 kW, and quenching tube. The raw
materials are supplied as powder along with carrier gas and injected into
plasma torch. Raw materials then evaporate instantly and nanoparticles
are produced through homogeneous nucleation and heterogeneous condensation
in the tail region of plasma flame. Final product is collected from inner
chamber wall and filter.
Argon is taken as sheath gas, carrier gas, and inner gas. The mixture of ammonia and argon is used as quenching gas. Each experiment was conducted with the quenching tube fixed at 150 mm downstream from the end of the torch. The raw material is composed of ZrN and dopant materials including Ta, Nb, and aluminium nitride. ZrN and dopant materials are mixed at given composition and then fed into plasma system at feed rate of 300 mg/min.
The phase composition of product and lattice constant was detected by
X-ray diffractometry (XRD, Rigaku Multiflex), operating with a Cu Kα source
(λ = 0.1541 nm). Lattice constant a is calculated by the following equation,
based on the Bragg’s law. Element distribution were measured by scanning
TEM-energy dispersive X-ray spectrometry (STEM-EDS, JEOL JEMARM 200F).
Element mole ratio and bond information were obtained by X-ray photoelectron
The XRD patterns of Ta, Nb, and Al-doped ZrN nanoparticles shows that the
products under all experiment conditions exhibit main peak from ZrN. The
peak of ZrO2 comes from passivation process and Zr2N is generated from
nitridation deficiency. This result can confirm high purity of final product.
Lattice constants of three different doping conditions are obtained from
Bragg’s law calculation. Lattice constant of ZrN decreases when Zr4+ ions
are replaced by elements with smaller ionic radius (Nb5+ and Al3+). Lattice
constant does not change with doping of Ta, which has the same ionic radius
as Zr4+ ions.
The XPS survey analysis of different metals-doped ZrN show that main peaks
come from Zr, N, O, and dopant elements. Other peaks belong to Au from
reference and carbon from conductivity type. The integrated intensity of
Zr and dopant peak from survey scan analysis can provide information about
mole ratio of Zr to dopant in final product. The mole ratio is similar
with that of raw material, indicating most dopant elements enter final
product. Narrow scan analysis of dopant elements indicate that metal-nitride
bonds exist in all samples, which come from Zr4+ replacement in ZrN lattice.
Metal-oxide bonds are from oxidation on particle surface.
Nanoparticle with mole ratio of Zr : Al=90 :10 is selected as representative
to exhibit the particle morphology and element distribution of Zr and dopant.
All particle exhibits spherical structure and average particle diameter
is 10.8 nm with the standard deviation of 3.28. Element mapping image by
STEM-EDS shows taht the mole ratio shows small value in all selected points.
Results suggest that Zr is well overlapped by Al, indicating that elements
distribute evenly in the whole particle.
Homogeneous nucleation temperatures of metals can be calculated based on
nucleation theory considering non-dimensional surface tension. When nucleation
rate is above unity, nucleation can become stable. The saturation ratio
at this time has dominant influence on determining nucleation temperature.
Compound melting point is normally considered as nucleation temperature
because compounds usually nucleate near their melting point.
The nucleation temperature of ZrN is the highest with the doping of Nb
and Al, suggesting that ZrN nucleates firstly during synthesis of Nb and
Al-doped ZrN. However, nucleation temperature of Ta and TaN is higher than
that of ZrN. The equilibrium diagram shows that Ta amount is sufficiently
small to decrease nucleation temperature of TaN, which is lower than that
of ZrN. The existence of Ta vapor is observed after ZrN nucleation, indicating
Ta is likely to be doped into ZrN.
Formation mechanism is clarified based on above-mentioned discussion. Raw
material is evaporated in thermal plasma region. ZrN nucleates firstly
at 3253 K and dopant element and Zr-N vapor then condense near ZrN nucleate
from upstream to downstream of synthesis process. Passivation is finally
operated to form oxidation protect layer on particle surface.
Metal-doped ZrN nanoparticles were successfully synthesized by induction
thermal plasma. The product exhibits even element distribution, enough
doping amount, and high purity. Formation mechanism was clarified based
on nucleation temperature and thermal equilibrium calculation. ZrN firstly
nucleates and dopant elements enter zirconium nitride during the condensation
process to form final product.
Student Presentation Award Kaiwen Zhang, Yuta Tanoue, Manabu Tanaka, and Takayuki Watanabe: Nanoparticle
Synthesis of Tantalum Oxynatiride by Induction Thermal Plasma, The 5th
International Union of Materials Research Societies International Conference
of Young Researchers on Advanced Materials, C-O4-002, p.116 (2022.8.4 Kyushu
Kaiwen Zhang, Manabu Tanaka, and Takayuki Watanabe: Nanoparticle Synthesis
of Heteroatoms-Doped ZrN by Induction Thermal Plasma, 32nd Materials Reserch
Society of Japan, E-O6-005 (2022.12.6 Yokohama, Industry & Trade Center
Yirong Wang, Kaiwen Zhang, Kohei Yamashita, Manabu Tanaka, and Takayuki
Watanabe: Synthesis of Ternary Ti1-xNbxN Nanoparticles by Induction Thermal
Plasma, 32nd Materials Reserch Society of Japan, E-O5-018 (2022.12.5 Yokohama,
Industry & Trade Center Building).
Kaiwen Zhang, Manabu Tanaka, and Takayuki Watanabe: Nanoparticle Synthesis
of Heteroatoms-Doped ZrN by Induction Thermal Plasma, 2022 International
Industry-University-Research-Application Cooperation Conference (2022.12.10
Yirong Wang, Kohei Yamashita, Kaiwen Zhang, Manabu Tanaka, and Takayuki
Watanabe: Nanoparticle Synthesis of Ternary Titanium Niobium Nitrides by
Induction Thermal Plasmas, Proceedings of 25th International Symposium
on Plasma Chemistry, POS-7-121 (2023.5.22 Miyako Messe, Kyoto).
Kaiwen Zhang, Kohei Yamashita, Manabu Tanaka, and Takayuki Watanabe: Formation
Mechanism of Metal-Doped ZrN by Induction Thermal Plasma, Proceedings of
25th International Symposium on Plasma Chemistry, POS-7-223 (2023.5.23
Miyako Messe, Kyoto).