Tech Briefs Magazine - January 2024 - 19

kinetics often contradict each
other from study to study. Raumann
found a new rate equation
for the CVD process, putting the
smaller pieces from literature together
as a whole.1 But how?
He designed an experimental
single-fiber setup with very
well-known boundary conditions.
With the help of the COMSOL
Multiphysics® software and a parameter
study, he found the rate
equations. He then used the equations
to model the Wf/W production
with multiple fibers. For this, Raumann
applied COMSOL Multiphysics®
again, followed by a parameter optimization.
The resulting parameters were also
applied in reality with success.
Developing and Validating a
Multiphysics Model
The
goal of
the FZJ
research was
to reduce porosity
which depend on the reactor geometry,
heater temperature, gas flow rates, and
gas composition.
One important motivation for predicting
the CVD process is to avoid
the formation of pores in the tungsten
material. During the CVD process, gas
flows through the fiber substrate and
tungsten is deposited between fibers.
The area between the fibers is supposed
to be filled up with the solid W; however,
some gaseous domains can become
isolated from fresh reactants when the
path from the bulk of the gas phase is
closed, or obstructed, by the W deposits.
In other words, the pores do not have
access to the reactants needed to fill
them with tungsten, thus they remain
pores throughout the process.
In order to reduce or avoid material
strength-reducing pore formation,
the substrate geometry and the parameters
of the CVD process need to be
carefully adjusted.
Tech Briefs, January 2024
in Wf/W. For this, Leonard
Raumann, Material Engineer at FZJ,
needed to find the W deposition rate
equation as a first step. Existing literature
about CVD for tungsten is controversial
and incomplete, because the equations
and values for tungsten deposition
a)
The single-fiber setup to develop
the new models for the chemical vapor
deposition rate of tungsten is shown in
Figure 2, including a preheater and
a main heater. The researchers wanted
to see how fast the tungsten would
grow and how this rate of growth was
affected by the temperature and partial
pressure. They then adjusted the
tungsten hexafluoride (WF6) reaction
order between one and zero, depending
on the temperature and the WF6
b)
Figure 1. A diverter in a fusion reactor. (Image: COMSOL)
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Tech Briefs Magazine - January 2024

Table of Contents for the Digital Edition of Tech Briefs Magazine - January 2024

Tech Briefs Magazine - January 2024 - Intro
Tech Briefs Magazine - January 2024 - Sponsor
Tech Briefs Magazine - January 2024 - Cov1
Tech Briefs Magazine - January 2024 - Cov2
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Tech Briefs Magazine - January 2024 - Cov3
Tech Briefs Magazine - January 2024 - Cov4
Tech Briefs Magazine - January 2024 - PIT-Cov1
Tech Briefs Magazine - January 2024 - PIT-Cov2
Tech Briefs Magazine - January 2024 - PIT-1
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Tech Briefs Magazine - January 2024 - PIT-Cov4
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