## 3 Results  
The SEM micrographs of the TiH\({}_{2}\) and Al powders are shown in Figure 1a,b, respectively. It can be seen from Figure 1a that most TiH\({}_{2}\) particles have an irregular polygonal shape and a rugged surface. Al particles are mostly hollow and spherical and much smaller than TiH\({}_{2}\) particles. The particle size distribution analysis is presented in Figure 2, and the result shows that the TiH\({}_{2}\) particles have a wide size distribution with a D50 of 21.7 \(\upmu\)m, while the Al particles have a narrow size distribution with a D50 of 1.58 \(\upmu\)m. The results of the size distributions are in keeping with the SEM micrographs in Figure 1.  
For gel casting, it is quite essential to obtain stable slurries with good fluidity; hence, dispersants are added to stabilize solid particles and avoid aggregation or subsidence. There are mainly three mechanisms of dispersion, namely, steric hindrance, electrostatic repulsion, and their combination. In non-aqueous gel casting, steric hindrance dominates [27]. Therefore, polymer dispersants which have a strong steric effect are preferred. In this study, PVP was chosen as the dispersant, and the rheological properties of TiH\({}_{2}\)/Al slurries with a solid content of 46 vol % were measured by a rotary rheometer. During the preparation of TiH\({}_{2}\)/Al slurries, it was found that when the ratio of PVP to powder mass was less than 1 wt %, TiH\({}_{2}\) particles were easily sedimented due to their big size and  
Figure 1: SEM micrographs of (**a**) TiH\({}_{2}\) and (**b**) Al particles. Figure 2: Size distribution curves of TiH\({}_{2}\) and Al Powders. density of 3.8 g/cm\({}^{3}\), which would result in a non-uniform distribution of powders. Hence, a sufficient dose of PVP was needed. Three PVP addition ratios relative to the TiH\({}_{2}\)/Al powder mixture were chosen: 1, 2, and 3 wt %. The effects of the dispersant dosage on the rheological behavior of the TiH\({}_{2}\)/Al slurries are shown in Figure 3. It can be seen that all the TiH\({}_{2}\)/Al slurries exhibited a shear-thinning behavior over the measured shear rate range, which indicates that the TiH\({}_{2}\) and Al particles were in the flocculation state in the static slurries. When shear force was applied, the flocculation structure was dismantled and the apparent viscosities decreased. Once the flocculation structure in the slurries was completely dismantled, the viscosities did not decrease anymore. In addition, both the apparent viscosity and the shear stress of the slurries increased while the PVP content rose from 1 to 3 wt %. At the shear rate of 100 s\({}^{-1}\), the slurry prepared from the precursor solution containing 1 wt % PVP relative to the TiH\({}_{2}\)/Al powders exhibited a shear viscosity of 169.3 mPa-s, while the slurries with 2 wt % and 3 wt % PVP displayed viscosities as high as 382.6 mPa-s and 919.2 mPa-s, respectively. For the sake of adequate mold filling, TiH\({}_{2}\)/Al slurries with low viscosity were necessary, and 1 wt % was chosen as the optimum amount of PVP addition to the slurry. For the gel casting process, the solid loading of the slurry has great effects on the fluidity of the slurry and the density of the green and sintered parts. Low viscosity of the slurry is conducive to uniform filling of the mold, while high solid loading has the benefit of reducing the volume shrinkage and increasing the sintering density of the green body during drying and sintering, which is particularly important for the deformation control of products with a complex structure. However, low viscosity and high solid loading of the slurry often contradict each other. Therefore, a balance between the two must be considered when preparing a gel casting slurry. Figure 4 shows the respective rheological curves of the TiH\({}_{2}\)/Al slurries with solid loadings of 40, 42, 44, 46, and 48 vol %. As expected, the apparent viscosity and shear stress of the slurries displayed a remarkable increasing tendency with the rise of the solid loading content.