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Materials Science in Additive Manufacturing Ceramic vat photopolymerization

limitation with SL is the requirement of the build platform, resin. S and E remain constant for a fixed recipe of resin/
c
d
which has to be mechanically removed, necessitating surface slurry.
finishing. Figure 1A shows the SL working principle. The This cure depth is measured and calibrated to derive a
fundamental mechanism of photopolymerization is that the log-linear relationship between the cure depth of the resin
resin surface is exposed to UV light to trigger polymerization and the exposure power. The laser spot size determines the
via single-photon absorption by the photoinitiator.
feature size. Further, there must be good adhesion between
The mechanism of the linear photo-polymerization the lateral lines and the vertical layers of the model to
process involved in linear laser SL is shown in Figure 2B. obtain a contiguous full-density part.
A single-photon is absorbed by the photoinitiator
(Figure 2A) to form free radicals triggering the cross- In SL, where foreign materials such as ceramic particles
linking of the monomers. Because of the Gaussian nature are incorporated inside the resin, the polymerization
of the incident light beam, the number of photons hitting process is influenced significantly by the particle size, and
the resin surface will be maximum at the center of the laser the relationship between the cure depth and the particle
spot and will decay away from it. This leads to the parabolic size is described as: 11
cross-section in the resin during each laser scan. The depth d 1 I
of the parabola, i.e., cure depth (C ) of the resin is related to C ln 0 (II)
d
d
the exposure energy and is given by Beer–Lambert law as: Q I cure
E where  = ceramic solid loading, d = ceramic powder
C S ln (I) size, Q = suspension constant, I = exposure intensity, and
d
d
E c I = the critical exposure intensity for the suspension.
0
cure
where E is the exposure energy, E is the critical exposure Thus, greater ceramic particles result in larger cure depth as
c
2
energy and S is the transmission depth coefficient of the the scattering effect is reduced. Smaller-diameter ceramic
d
particles, which show strong scattering, would lead to
A B lower cure depth. However, small particles are desired
for increasing the solid loading printing and lowering the
sintering temperature, which is good for the final ceramic
products. In terms of the effect of particle shape, the semi-
liquid nature of the ceramic slurry is generally favorable in
favor of flowability, and there is no specific requirement for
particle sphericity and regularity.
2.2. Planar photopolymerization based on DLP
Figure 1. Schematic setup of linear scanning stereolithography technique DLP photopolymerization technique is based on a similar
(A) and image projection digital light processing (DLP) technique (B) 2
(schematics reused under the terms of the Creative Commons CC-BY principle as laser SL, but it uses a conventional UV light
license) source rather than a laser, and the patterns are transferred

A B

Figure 2. Single-photon absorption mechanism (A) and polymerization mechanism in linear stereolithography and digital light processing (B)

Volume 4 Issue 3 (2025) 3 doi: 10.36922/MSAM025200031