SiC colloidal inks for the novel robocasting forming method were prepared using a two-step method, namely creating well-dispersed suspensions followed by inducing gelation via changing the pH values towards isoelectric points (IEPs). The effect of the adsorption behaviour of Polyethylene imine (PEI) on the rheological properties was systematically investigated for the both steps. Coincidentally, as SiC particles were saturated adsorbed with PEI, their respective rheological properties exhibited the optimum. For the first step, the strongest electrostatic repulsion was exhibited between SiC particles, and the corresponding suspension displayed the optimum dispersibility with a low shear viscosity ( η 0 ) of 27.86 Pa. For the second step, the colloidal gel presented the strongest elastic properties with an equilibrium storage modulus ( G ′) of 13,381.87 Pa and shear yield stress ( τ y ) of 355.89 Pa. The colloidal gel ink with solid loading as high as 51 vol.% behaved in a yield-pseudoplastic manner and was successfully utilized to fabricate 3-D periodic lattice structures.
Hierarchical porous silicon carbide (SiC) structures with total porosity in a wide range of 37.82 %− 94.34 % were achieved by combining robocasting and alkali-induced starch gelatinization technique. (i) 50 µm-2 mm sized pores, with porosities of 22.33 %− 82.13 %, were created by robocasting. (ii) 1–140 µm pores, with porosities of 20.20 %− 68.21 %, were induced by the starch template. Additionally, we firstly introduced an alkali-induced starch gelatinization technique to the gel inks for robocasting, which promoted its elastic properties (storage modulus and shear yield stress) and prolonged its preservation time to 3–7 days. The gelatinized starch granules were also used as binder, which facilitated high-velocity (3–20 mm/s) extrusion of the inks through fine (150–800 µm) nozzles. The porous SiC structures with two scales of porosity are promising for wide applications such as porous burners, liquid and gas filters, catalyst supports and so on.
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