*Article* **The Impact of Particle Size and Surface Treatment of Zirconia Suspension for Photocuring Additive Manufacturing**

**Mee-Jin Jun 1,†, Jin-Ho Kang 2,†, Kumaresan Sakthiabirami 2,3, Seyed Aliakbar Hosseini Toopghara <sup>4</sup> , Ye-Seul Kim <sup>2</sup> , Kwi-Dug Yun <sup>2</sup> and Sang-Won Park 2,3,4,\***


**Abstract:** To prepare a photocurable ceramic suspension for use in commercialized additive manufacturing equipment, the effects of the rheological properties of zirconia particles added to a binder, and the presence or absence of a silane coupling agent on the particles was evaluated. To this end, three experimental groups (ZSs, ZMs, ZLs) and three control groups (ZS, ZM, ZL) were designed depending on the size of the underlying zirconia particles. The test-group zirconia suspensions were prepared through silanization, which was not applied to the control-group suspensions. Depending on the particle size, viscosity differences between the test and control groups were 16,842, 18,623, and 12,303 mPa·s, respectively. Compared to the other groups, the viscosity of the ZLs group suspension decreased by 70.98–88.04%. This confirmed that the viscosity of the suspensions was affected by the particle size and the presence of silane coating. The dispersion stability of the zirconia suspensions was evaluated over 20 days. A sedimentation test confirmed that the sedimentation rate of the ZLs group was slower than those of the other groups. This study aimed to optimize the suspension manufacturing method to effectively be utilized in further commercializing zirconia three-dimensional (3D) printing and could also help to develop various medical applications.

**Keywords:** additive manufacture; dispersion stability; silane coupling agent; viscosity; zirconia suspension
