Tingting Bao,Hui zhou,Yi Zhang,Chenxu Guo,Wenming Guo,Hang Qin,Pengzhao Gao,Hanning Xiao,Weixiong Liu
Ni/CeO 2 catalysts ( n CeO2 : n Ni = 0, 1, 4, 7, 10) supported on SiC porous ceramics for ethanol steam reforming (ESR) were investigated with respect to hydrogen production performance and growth of carbon deposition. The oxygen released from CeO 2 enables the oxidation of CH x species to serve as carbon precursors, thus providing Ni/CeO 2 catalysts with stronger resistance to carbon deposition compared with Ni catalysts. The Ni/CeO 2 catalysts prepared by inverse microemulsion and impregnation methods exhibit regular semicircular spherical shape on SiC porous ceramics. Under 500 °C for 25 h of ESR reaction, the ethanol conversion rate over Ni/CeO 2 catalysts ( n CeO2 : n Ni = 7) is sustained up to 100% and H 2 selectivity is essentially kept at 74%. The by-product selectivity declines stepwise with increasing content of CeO 2 , which is attributed to the adsorption and oxidation of CO and of CH x species as CH 4 precursor from CeO 2 . The scanning electron microscopy (SEM) and transform electron microscopy (TEM) results reveal that further loading of CeO 2 on the surface of Ni catalysts can alleviate both migration and sintering of Ni particles. Furthermore, carbon deposition on Ni/CeO 2 catalysts preferentially outgrow filamentous rather than amorphous carbon , with a tendency for the latter to be more deactivated.
Zihe Li,Jian Sun,Xu Zhang,Jingde Zhang,Guifang Han
Mullite-bonded SiC porous ceramics are of potential in hot gas infiltration while the insufficient mechanical performance limits its application. In-situ mullite whisker reinforcement is a potential solution but the formation temperature mismatch between mullite whisker and bonding layer is a challenge. In that case, mullite whiskers massively form ahead of the bonding layer excessively consuming alumina leading to poor bonding layers between SiC particles and thus, the mechanical performance. Herein, the mismatch was solved by using CaF 2 as a temperature-controlled reaction switch. As a result, both the bonding layer and whisker synchronously formed. The material showed significant reinforcement effects, and exhibited a flexural strength of 124.8 MPa and a fracture toughness of 1.53 MPa·m 1/2 with an open porosity of 36.6 vol%, realizing a breakthrough in the mechanical performance. Interestingly, an increase in oxygen vacancy concentration with the sintering temperature was first reported, which may benefit the whisker growth.
Yushi Qi,Jiangfan Xu,Yanhan Fei,Lanjun Du,Yan Ren,Wenbo Han,Gang Chen,Zhiming Du
This study investigated the preparation of SiC porous ceramics using an organic foam impregnation-high temperature sintering process. To address the poor wettability of SiC ceramics when used as the reinforcement phase, the surface of SiC porous ceramics was modified with Al 2 O 3 . SiC-Al 2 O 3 /2A50 co-continuous composites were then fabricated by infiltrating 2A50 aluminum alloy into the SiC-Al 2 O 3 porous ceramics under pressure. Microstructural observations, along with friction, wear performance, and thermal stability test, demonstrated that Al 2 O 3 surface modification significantly enhances the friction and wear performance as well as the thermal stability of the co-continuous composites. The prepared SiC-Al 2 O 3 /2A50 co-continuous composite exhibited excellent wear resistance, good thermal stability and stable bonding at heterogeneous interfaces. Compared to 38CrSi steel, the SiC-Al 2 O 3 /2A50 co-continuous composite not only offers the advantage of reduced weight but also shows a significantly lower wear rate of 9.3 × 10 −5 mm 3 /N·min under a 50 N load. These findings suggest that the SiC-Al 2 O 3 /2A50 co-continuous composite has the potential to replace 38CrSi steel as a wear-resistant material.
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