Novel light and strong hierarchical porous mullite-bonded SiC structures with total porosity ranging from 68 % to 95 % were fabricated by combining material extrusion (MEX) and in-situ reaction bonding technique. These structures comprise three porosity families and wide porosity hierarchization over four orders of magnitude in length scales. The pore parameters were precisely controlled by the nozzle path and starch (as a poreforming agent) content. The sintering temperature effect on phase composition, porosity, sintering shrinkage, and mechanical properties was systematically investigated. As the SiC powders were sintered at 1550 °C, they were compactly bonded by mullite and cristobalite necks. The single filaments demonstrated a flexural strength of 74 MPa at a porosity of 35 %. The hierarchical porous mullite-bonded SiC lattice structure with a total porosity of 69 % was near-net-shape sintered and exhibited a compressive strength as high as 41 MPa. Such structures are highly promising for wide applications such as electromagnetic shielding, burners, membrane supports, porous burners, filters, thermal insulation , catalyst supports, etc.
Jili Wei,Yihua Ren,Yiyang Zhang,Baolu Shi,Shuiqing Li
This work examines the effect of temperature-time history on the flame synthesis of titania nanoparticles using a specially designed swirl-stabilized tubular burner with two kinds of precursor feeding modes, the tangential inlet and the central jet inlet. When the Damköhler number is less than unity, a rapidly mixed type tubular flame is well-formed, which is chosen to be the condition for flame synthesis. The ex situ characterization of the synthesized TiO 2 nanoparticles shows that the particle samples from the tangential inlet feeding mode are mainly anatase (up to 84.3%) with a mean primary particle size of 13.0 ± 3.2 nm, whereas those from the central jet inlet feeding mode are large polydisperse rutile (up to 74%) nanoparticles with a mean size of 16.9 ± 8.8 nm. The significant differences in particle size and crystal phase are attributed to the varied temperature-time histories of two feeding modes, as the residence time of nanoparticles in high-temperature zone of the central jet inlet mode is much longer with larger variation than that of the tangential inlet feeding mode. Finally, the well-dispersed Pd/TiO 2 nanocatalysts are generated by elaborately feeding palladium acetate through the central jet inlet and titanium tetraisopropoxide through the tangential inlets, respectively, to better match the temperature-time histories with the decomposition properties of two different precursors. The study demonstrates the potential of this swirl-stabilized burner for producing tailored single- and multi-component nanomaterials for a variety of applications.
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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