CERAMICS INTERNATIONAL
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2022
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IF 5.532
Zhijian Wang,Lanlan Liu,Qifeng Du,RuiTao Tang,Jun Ai,Ying Chen
Ti-related oxide ceramics often exhibit excellent microwave dielectric properties and are widely applied in the microwave communication field. However, their microwave dielectric properties are often influenced by unstable defects, which are caused by the relatively low oxygen partial pressure at high sintering temperatures . In this work, Al 2 O 3 was introduced to improve the defect structures of the 0.85CeO 2 -0.15TiO 2 ceramics. According to the XPS pattern and AC conductivity analysis, Al 2 O 3 doping could stabilize the valence state of Ti but increase the oxygen vacancy concentration. Q × f first increased and then decreased as the Al 2 O 3 content increased. The highest Q × f value of 54361 GHz was obtained for the CTA0.015 sample sintered at 1275 °C, as well as the ε r of 29.41 and τ f of +7.8 ppm/°C. Finally, the CTA0.015 sample was used to prepare a microstrip antenna via the screen-printing process, which exhibited a good temperature-independent resonant frequency and indicated good application prospects.
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高影响因子
ACS Catalysis
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2022
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IF 13.7
Rui Ma,Junxian Gao,Jiajing Kou,David P. Dean,Christian J. Breckner,Kaijun Liang,Bo Zhou,Jeffrey T. Miller,Guojun Zou
Nickel has been considered a promising nonprecious metal for propane dehydrogenation (PDH) because of its appealing ability to activate alkane molecules; however, synthesis of selective and stable Ni sites remains a challenge. Herein, we describe an alumina-supported isolated Ni(II) site by settling Ni2+ cations into Al3+ vacancy on γ-Al2O3 as a selective and stable Ni-based catalyst for PDH. Based on the results from combined characterizations, including in situ X-ray adsorption spectroscopy (XAS), scanning transmission electron microscopy (STEM), and in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS), atomically dispersed Ni(II) sites with bonding to oxygen ions from the alumina support are demonstrated. PDH catalyst tests shows that the Ni(II) single-site catalyst delivers superior performance compared to a supported metallic Ni NP catalyst, possessing >93% propylene selectivity at considerable propane conversions (15–45%), which surpasses Ni nanoparticle (NP) catalysts. The correlation of selectivity to propylene on different Ni structures with the structural characterizations suggest that the coordinatively unsaturated tetrahedral Ni(II) sites facilitate the desorption of propylene, which inhibits the side reactions for coking. Moreover, the atomically dispersed Ni(II) sites remain in its local structure in the reaction-regeneration cycles, as evidenced by in situ XAS. This study on alumina-supported nickel catalysts affords insights into the nature of selective and stable nickel sites involved in the PDH reaction.
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APPLIED CATALYSIS B-ENVIRONMENTAL
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2022
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IF 24.319
Qiu Xu,Chungang Wang,Zongling Shang,Chao Zhang,Xinchao Wang,Qiang Liu,Lingling Dang,Yanchun Liu,Fengyu Zhao
The activation and ring opening reaction of lactone bond is of great significance in biomass utilization. Cu-based catalysts are widely used in the biomass hydrogenation processes, in which the effect of oxide promoters on Cu catalysts is one of the most attractive research topics. Herein, the transformation of lactones to diols over Cu/Al 2 O 3 and CuLa x /Al 2 O 3 catalysts was studied and the promoting role of LaO x has been discussed. The CuLa 0.25 /Al 2 O 3 catalyst showed outstanding catalytic performance with high 1,4-butanediol yield of > 90 %, and it also showed high efficiency for the hydrogenation of series of five- and six-membered lactones (γ-butyrolactone, γ-valerolactone, δ -hexalactone, etc) to diols. Based on the comprehensive analysis of the XRD, TEM, TPR, XPS, low temperature CO-DRIFT results, the crucial contribution of LaO x species in promoting the selectivity and stability of catalysts were investigated in detail. The presence of LaO x species not only results in the formation of Cu + -LaO x interfacial active sites, which facilitate the adsorption and activation of lactones, but also promotes the stability of catalyst.
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CERAMICS INTERNATIONAL
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2022
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IF 5.532
Qiaoyu Meng,Keqiang Zhang,Shuo Yang,Rujie He,Zhaoliang Qu
Thermal shock resistance is critical to ensure the service safety of ceramic hot-end components. The thermal shock performance of stereolithographic additive-manufactured ceramics has not yet been studied. In this study, a series of thermal shock experiments with various temperature differences was conducted on stereolithographic additive-manufactured Al 2 O 3 ceramics. The surface cracks were analysed based on photographs captured before and after the thermal shock experiments. Three-point bending tests with in situ X-ray digital radiography were conducted to determine the thermal shock resistance. Crack initiation, propagation, and coalescence were observed under flexural loads. The critical temperature difference of the stereolithographic additive-manufactured Al 2 O 3 ceramics was determined to be 267.22 °C. The crack length increased and residual strength decreased with increasing temperature differences. The layered structure of the stereolithographic additive-manufactured ceramics slowed crack propagation . We expect that this study will serve as a reference for the performance of stereolithographic additive-manufactured Al 2 O 3 ceramics in extreme environments.
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高影响因子
International Journal of Applied Ceramic Technology
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2022
·Vol. 19
·期 6
·3255-3266
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IF 2.328
Jiakun Wu,Haikuo Wang,Zhicai Zhang,Zhiqiang Hou,Dazhuan Wu,Xiaoping Ouyang
Al 2 O 3 -cBN-hBN self-lubricating ceramics were synthesized by using a high-pressure sintering method. The mapping relationships between sintering thermodynamic conditions, component content, and mechanical properties were established using the response surface method. The main factors influencing the mechanical properties are clarified. The formation mechanism of the excellent mechanical properties is explained. It is found that the undesired phase transformation from cBN to soft hBN can be effectively inhibited by using a low-temperature and high-pressure sintering process. Sintering temperatures improve the relative densities and elastic modulus of self-lubricating ceramic but have little effect on the hardness and fracture toughness. cBN content is the main factor affecting the mechanical properties of the composites. The microcracks developed during the high-pressure sintering process contribute to the fracture toughness of the composites.
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CERAMICS INTERNATIONAL
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2022
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IF 5.532
Zijun Peng,Lei Yuan,Xudong Luo,Jingkun Yu,Chen Tian,Zhenli Liu
MgO–Al 2 O 3 –SiO 2 composite ceramics were prepared by spark plasma sintering (SPS). In addition, phase composition, microstructure, mechanical properties , and thermal shock properties have been systematically characterized. Introduction of Al 2 O 3 and SiO 2 significantly increased mechanical properties and thermal shock resistance of these composite ceramics. MgO–Al 2 O 3 –SiO 2 composite ceramics prepared by spark plasma sintering (SPS) exhibited fine grain size. Reduced grain size may result in extraordinary properties. Experimental results showed that MgO–Al 2 O 3 –SiO 2 composite ceramics had the highest flexural strength and hardness among all studied ceramics of 269.6 ± 9.22 MPa and 12.51 ± 0.29 GPa, respectively. Moreover, MgO–Al 2 O 3 –SiO 2 composites can reach 16 thermal cycle times. This shows that it is feasible to prepare high-performance MgO composite ceramics by SPS. Furthermore, introduction of Al 2 O 3 and SiO 2 is effective method to improve mechanical properties and thermal shock resistance of MgO composite ceramics.
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SURFACE & COATINGS TECHNOLOGY
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2022
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IF 4.865
Jingjing Ma,Chaoyang Cai,Jiawei Xie,Wenming Guo,Hang Qin,Jingxiong Liu,Wen Xie,Pengzhao Gao,Hanning Xiao
The low coefficient of thermal expansion (CTE) coating was designed for SiC oxidation-resistant applications by using Al 2 O 3 and LiAlSiO 4 as positive and negative expansion materials. The CTE value, relative density and flexural strength of LiAlSiO 4 -Al 2 O 3 coating were characterized. The effect of LiAlSiO 4 -Al 2 O 3 coating on the oxidation resistance and flexural strength of SiC substrate was systematically studied by cyclic oxidation tests at 1400 °C. Results showed that LiAlSiO 4 -Al 2 O 3 coating with 20 wt% LiAlSiO 4 exhibited optimal properties, featuring the excellent relative density of 93.14 %, appropriate CTE of 5.815 × 10 −6 /°C, and high flexural strength of 56.35 MPa. The weight gain of the SiC with LiAlSiO 4 -Al 2 O 3 coating was 0.49 % after 100 h of oxidation, much lower than 2.25 % of bare SiC substrate, indicating that LiAlSiO 4 -Al 2 O 3 coating effectively hindered the diffusion of oxygen and improved the oxidation resistance of SiC substrate. Moreover, the dense coating blunted defects on the SiC substrate surface, which maintained the high strength of the coated SiC after long periods of oxidation.
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JOURNAL OF ANALYTICAL AND APPLIED PYROLYSIS
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2022
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IF 6.437
Koïta Djakaria,Ziyue Tang,Jingai Shao,Xu Chen,Haoyu Xiao,Joseph Smith,Haiping Yang,Hanping Chen
Furfural is one of the top valuable building block chemicals, the selective production of furfural from biomass has attracted increasing concerns in recent years. In this work, a novel method for the selective production of furfural through cellulose catalytic pyrolysis with WO 3 /γ-Al 2 O 3 was reported, and the synergistic effect between γ-Al 2 O 3 and WO 3 was explored. Compared with cellulose pyrolysis alone, the addition of γ-Al 2 O 3 improved the selectivity of furans and greatly inhibited the formation of sugars; while, WO 3 addition promoted the formation of levoglucosenone . When (20–40%) WO 3 /γ-Al 2 O 3 were added, the amount of sugars was further reduced, and the yields of furans (furfural and 2-methylfuran, in particular) were further increased at the same time. Under the optimum conditions (temperature = 600 °C, residence time = 15 s, and catalyst to cellulose mass ratio of 4), 30%WO 3 /γ-Al 2 O 3 showed the best performance, and the selectivity and yield of furfural were improved by nearly 100% and 300%, respectively, as compared with cellulose pyrolysis alone. In addition, compared with γ-Al 2 O 3 , the addition of 30%WO 3 /γ-Al 2 O 3 further increased the yield of furfural and 2-methylfuran to about 50% and 200%, respectively. The high selectivity and yields of furans with WO 3 /γ-Al 2 O 3 addition might be due to that WO 3 crystals in the composite promote the formation of levoglucosenone, which is further converted to additional furans through the Lewis acid sites of γ-Al 2 O 3 . The study may provide some meaningful advices for improving the production of furfural from green catalytic pyrolysis of cellulose.
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高影响因子
FUEL
·
2021
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IF 6.609
Zhong Ma,Guofu Liu,Yonggang Lu,Hui Zhang
Iron-based oxygen carriers often underwent severe phase segregation in the process of chemical looping, resulting in the reduction of the cyclic performance of oxygen carriers. The phase segregation characteristics of Fe 2 O 3 /Al 2 O 3 calcined at different temperature (900 °C, 1100 °C, 1300 °C) were investigated in this study. The obtained samples were recorded as 900-FeAl, 1100-FeAl and 1300-FeAl, respectively. XPS results showed that the surface oxygen vacancies of Fe 2 O 3 /Al 2 O 3 increased with the increase of calcination temperature. In the redox cycles, the deactivation rate of the three samples were 5.57% (900-FeAl), 6.99% (1100-FeAl) and 31.69% (1300-FeAl), respectively. After 20 cycles, the 1300-FeAl presented serious surface sintering and the largest enrichment degree of surface Fe (137.05%). It can be inferred that the severe enrichment of surface Fe leads to the serious sintering, which aggravates the deactivation of the 1300-FeAl in cyclic reactions. The low calcination temperature (900 °C, 1100 °C) makes the Fe 2 O 3 /Al 2 O 3 exhibit rich pore structure, which generates space barrier for the outward migration of Fe cation and inhibits the phase segregation of Fe 2 O 3 /Al 2 O 3 . The results of this study are of great significance to understand the phase segregation of iron-based oxygen carriers, and provide guiding value for the synthesis of high-performance iron-based oxygen carriers.
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高影响因子
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
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2021
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IF 5.816
Junji Chen,Mengqin Yao,Qizhuang Zou,Peng Chen,Fei Liu,Tianxiang Zhao
An effective strategy synthesis of Rh/meso-Al 2 O 3 catalysts was demonstrated by mechanochemistry for hydrolytic dehydrogenation of ammonia borane (AB). These catalysts are characterized systematically by N 2 adsorption-desorption isotherms, X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results show that the turnover frequency (TOF) and activation energy ( E a ) are 246.8 mol H2 ·mol Rh −1 ·min −1 and 47.9 kJ mol −1 for hydrolytic dehydrogenation of at 298 K catalyzed by Rh/Al 2 O 3 -CTAB-400, obviously higher than those previously reported catalysts. Furthermore, catalyst Rh/Al 2 O 3 -CTAB-400 can be recycled by simple centrifugal separation and the catalytic activity is still well maintained after five cycles. In addition, a plausible mechanism for hydrolytic dehydrogenation of AB has also been proposed. This mechanochemical synthesis method exhibits great application prospects for the preparation of heterogeneous catalysts .
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JOURNAL OF NON-CRYSTALLINE SOLIDS
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2021
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IF 3.531
Leibo Deng,Zhe Fu,Zhang Mingxing,Hao Li,Bin Yao,Jianli He,Hua Chen,Yonghong Ma
TiO 2 –ZrO 2 -codoped MgO–B 2 O 3 –Al 2 O 3 –SiO 2 glass-ceramics were prepared using the traditional melting method. The effects of replacing TiO 2 with ZrO 2 on the glass stability (GS), crystallization behavior, structures, and properties of the obtained samples were studied. Results showed that the addition of ZrO 2 increased the GS, which decreased the crystallization ability of the samples. When the heat treatment temperature was increased from 900 °C to 1000 °C, the mullite and quartz phases first precipitated in the glass matrix, and then converted into cordierite. Because of the low solubility of TiO 2 and ZrO 2 in this glass system, the rutile and zircon phases will precipitate from the parent glasses. Owing to changes in the composition and structure of the samples, the density and Vickers hardness increased, while the coefficient of thermal expansion of the samples first decreased and then increased when TiO 2 was replaced with ZrO 2 .
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JOURNAL OF ALLOYS AND COMPOUNDS
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2021
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IF 5.316
Jiaji Yang,Xiongzhang Liu,Wei Gong,Tao Wang,Xian Wang,Rongzhou Gong
Developing high-temperature microwave absorption (MA) materials remains a challenge in the field of radar stealth. Here, we propose a design concept of meta-structure for temperature-insensitive and broadband MA. The three-phase TiB 2 /Al 2 O 3 /MgAl 2 O 4 composites are prepared to realize the temperature-insensitive MA properties, which is ascribed to the interaction of different components in terms of the electrical conductivity , dipolar polarization and interfacial polarization as temperature increases. On this basis, we design and fabricate a three-layer meta-structure composed of the SiO 2 ceramics as environmental adaptation layer, the patch-type and flat composites as MA layers. Compared with flat composites, the meta-structure can optimize its effective permittivity, thereby realizing enhanced MA properties at elevated temperatures. This meta-structure can realize a reflection loss (RL) less than −5 dB at 8.2–18.0 GHz in the temperature range of 25 °C to 1100 °C. The experiment matches well with the simulation. The temperature-insensitive and enhanced MA properties are attributed to the consequence of the combination of traditional absorbing materials and metamaterial structures.
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