MODELING OF CHEMICAL VAPOR DEPOSITED ZIRCONIA FOR THERMAL BARRIER AND ENVIRONMENTAL BARRIER COATINGS Page: 4 of 8
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Experiment and refined model results are shown in Figures 2 and 3. Model boundary conditions are
set to match ORNL experimental conditions for YSZ with nozzle temperature of 200 C, a range of
substrate temperatures, oxygen flow of 100 sccm, solution flow of 0.87 ml/min, solution of
tetrahydrofuran (THF) with 0.040 g/ml precursor with Y/(Y+Zr) =0.165.
Model results show that, in the region between the inlet and substrate, fluid flow and temperature
profiles closely match those expected for ideal
stagnation point flow, i.e. temperature and axial
velocity are independent of radial position and 2.5
depend only on height above the substrate r 2
surface. Near the outlet, the flow approaches
fully developed, parabolic flow. Very slight .5
recirculation zones are formed in the annular . 1
region outside of the nozzle. Precursor 0.5
c0.
concentrations above the substrate are
independent of radial position and show near
90% depletion of the precursors at the surface -0.5
for temperatures above approximately 930 C. z ____
Under these conditions, the deposition rate is -
controlled by the rate of diffusion across a mass- -1.5
transport pseudo-boundary that is approximately 0.6 0.8 1 1.2 1.4
0.6 cm wide. 1OOO/T(K)The model-predicted deposition rate matches
experimental results reasonably well over the
full range of temperature and pressure. At
low temperature the surface reactions, (la)
and (lb), control the deposition rate. At
higher temperature the rate is controlled by
transport and solvent pyrolysis dilutes the
gas phase concentration of precursor. At
higher pressure gas phase reactions deplete
the precursor and produce a decreasing
deposition rate with increasing temperature.
Pyrolysis of the THE solvent has a
significant effect on the maximum
achievable deposition rate. This "solvent
effect" on CVD rate in direct liquid injection
has not been recognized previously. The
exact decomposition path likely involves
many gas-phase and surface reactions, and is
unknown. Our assumption represents a
limiting case for solvent pyrolysis. ItFigure 2. Experiment (solid symbol) and model (open
symbol) deposition rate at low pressure (7 torr).2.5
2
S1.5
c 0.5
0
-g 0
0
0.
w -0.5
z -1
-J
-1.50.6
0.8
1 1.2 1.4
1000/T(K)
Figure 3. Experiment (solid symbol) and model (open
symbol) deposition rate at high pressure (70 torr).Q
---m-0
D4
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Starr, T.L; Xu, W. & Qiu, S. MODELING OF CHEMICAL VAPOR DEPOSITED ZIRCONIA FOR THERMAL BARRIER AND ENVIRONMENTAL BARRIER COATINGS, article, April 22, 2003; United States. (https://digital.library.unt.edu/ark:/67531/metadc781206/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.