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Materials Science in Additive Manufacturing Photocatalytic PA6/TiO powder for LPBF
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A B

Figure 1. (A) Reaction kettle system. (B) Schematic diagram of DPPC method for the preparation of PA6/TiO composite powders.
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was carried out according to the standard ASTM D7481-18. A B
A metal measuring cylinder was placed under the funnel to
receive powder quantitatively. The volume of the measuring
cylinder was 100 mL. Thermal experiments were performed
by Diamond differential scanning calorimetry (DSC,
PerkinElmer Instruments, USA) to analyze the melting/
crystallization properties of composite powders. The DSC
testing was carried out under a nitrogen atmosphere at a
heating and cooling rate of 10°C/min. The variation of the Figure 2. Morphological characteristics of PA6 powders precipitated
crystalline structure was tested on an X’pert3 powder X-ray by (A) rapid cooling at 120°C/h and (B) natural cooling at 20°C/h. The
diffractometer (PANalytical B.V., Netherlands) using Cu dissolved concentration of PA6 is 50 g/L.
Kα radiation at a scan speed of 3°/min.
It is obvious that the temperature recovery of PA6
3. Results and discussion solution occurred in the cooling process, and the dynamic
3.1. Control of precipitation cooling process temperature fluctuation occurred in the temperature
holding process. This is mainly due to the crystallization
First, the precipitation process of PA6 was studied. The exotherm generated during the precipitation of PA6, which
precipitation cooling process had an important effect on increases the temperature of the system. Therefore, the
the morphology and particle size distribution of powders. crystallization precipitation temperature of PA6 can be
Figure 2 shows the morphology difference between determined according to the transition of the temperature
powder precipitated by rapid cooling at 120°C/h and curve. Figure 3 shows that the starting temperature of
natural slow cooling at 20°C/h. The powders precipitated crystallization precipitation was 124°C. The cooling rate
by rapid cooling were mainly solid particles, but many before precipitation was 24.4°C/h, while the cooling rate
of them were featured by incompletely grown sheets. By after precipitation significantly decreased to 16.8°C/h. The
contrast, the slow-cooling particles stuck with each other. exothermic enthalpy during crystallization precipitation
The porous structure of the particle surface is beneficial increased the temperature of the whole system by 1.8°C,
to the improvement of light absorption efficiency [23,24] . indicating the large exothermic heat from crystallization.
The cooling of the reaction kettle directly determines the Meanwhile, the final steady-state temperature was 0.2°C
particle morphology, size, and surface quality. In the whole higher than the equilibrium temperature of 125°C due to
cooling process, the control of the precipitation stage plays the existence of crystallization exothermic enthalpy.
a key role in the powder properties. Therefore, the whole The typical morphology and particle size distribution
cooling process was monitored, and the precipitation of powders precipitated at 125°C were studied. It is shown
temperature holding method was adopted to analyze the in Figure 4A that the morphology of the powder was
variation of powder properties.
nearly spherical. Most of the particles were solid structures
Figure 3 shows the cooling curve when the reaction without obvious pores, indicating the high solid density
kettle was kept at 125°C immediately after precipitation. of powders. The analysis of particle size distribution

Volume 1 Issue 3 (2022) 3 https://doi.org/10.18063/msam.v1i3.14