## 3 Results
### Sample Characterization  
In order to gain insights into the debinding process and the effect of the debinding atmosphere, thermogravimetric analyses of the LithaNit 720 materials were carried out. Figure 8 depicts the mass changes of samples in air (blue dotted line) and in nitrogen (red solid line). The decomposition of the organic binder was completed at approximately 350 \({}^{\circ}\)C-400 \({}^{\circ}\)C in the air, whereas binder decomposition was shifted to 400 \({}^{\circ}\)C-450 \({}^{\circ}\)C in the nitrogen atmosphere, illustrating a difference in weight loss behavior due to oxidation processes. Total mass losses were 35.3% and 34.8%, respectively. Figure 8: TGA curves for LithaNit 720 green bodies during debinding as a function of atmosphere (blue dashed line: air; red solid line: nitrogen). Figure 7: Viscosity of the photocurable silicon nitride-based suspension as a function of the shear rate for Week 0 and Week 8. The density of the sintered ceramics was determined according to the Archimedean principle by immersing in water with a measured density of 3.24 g cm\({}^{-3}\), corresponding to a relative density of 99.8 (\(\pm\) 0.2)% (taking into account the theoretical density reported for silicon nitride-based ceramics). These excellent densification values are comparable to conventionally produced silicon nitride-based ceramics. Surface roughness was determined for a variety of surface orientations, as shown in Figure 9a. Measurements were performed in five different directions for three different orientated samples (namely X, Y and 45\({}^{\circ}\)) and the \(R_{a}\) values were summarized in Figure 9b. Due to the minor effect of the orientation on the building platform, the average values were noted for three different orientated samples. The average roughness \(R_{a}\) was 0.50 (\(\pm\) 0.03) mm along the layer boundaries (4) and 0.70 (\(\pm\) 0.04) mm perpendicular to the individual layers in the printing direction (5). The surface roughness value is a combination of the layer thickness, the angle of sample, and also the accuracy of the additive manufacturing process. Surfaces of (1) 45\({}^{\circ}\), (2) top and (3) 60\({}^{\circ}\) show an average roughness \(R_{a}\) of 1.97 (\(\pm\) 0.11) mm, 0.76 (\(\pm\) 0.04) mm and 2.36 (\(\pm\) 0.12) mm, respectively. This can be explained by the staircase effect, which is caused by the layer-by-layer part building and also the surface angles of ceramic parts such as 45\({}^{\circ}\) (3) and 60\({}^{\circ}\) (1), resulting in a surface roughness greater than the roughness along other sample orientations [41]. However, the \(R_{a}\) values observed in this study are lower than values typically observed in nonlithographic AM methods [42], and are even lower than surface roughness values reported for alumina ceramics generated by LCM [30]. Due to the elimination of edge failures by multiaxial stress, the biaxial flexural strength has advantages over uniaxial bending strength. Figure 10 shows the compressive load (N) of the tested biaxial discs, which was 1011 (\(\pm\) 171) N. The biaxial strength was calculated as 764 (\(\pm\) 137) MPa. This value can be converted into a three-point bending strength of about 950 MPa, which is the same value as for conventionally manufactured iso-pressed silicon nitride-based ceramics 945 MPa [43]. Although the printing direction was the nominally weakest orientation, the mechanical properties are very similar to conventionally iso-pressed silicon nitride-based ceramics. In addition to strength, the hardness of the biaxial discs was also measured. The resulting value of HV\({}_{10}\) 1500 is comparable to values reported for conventionally produced silicon nitride-based ceramics. Figure 9: (a) Directions of roughness measurement; (b) summary of surface roughness of measured samples. After determining the biaxial flexural strength and hardness of the sintered silicon nitride-based ceramic discs, fracture surfaces of the disc samples were investigated via SEM.