@article{dudek_tian_blivin_neal_zhao_li_2019, title={Perovskite oxides for redox oxidative cracking of n-hexane under a cyclic redox scheme}, volume={246}, ISSN={["1873-3883"]}, url={https://doi.org/10.1016/j.apcatb.2019.01.048}, DOI={10.1016/j.apcatb.2019.01.048}, abstractNote={Steam cracking of naphtha is a commercially proven technology for light olefin production and the primary source of ethylene in the Europe and Asia-Pacific markets. However, its significant energy consumption and high CO2 intensity (up to 2 tons CO2/ton C2H4), stemming from endothermic cracking reactions and complex product separations, make this state-of-the-art process increasingly undesirable from an environmental standpoint. We propose a redox oxidative cracking (ROC) approach as an alternative pathway for naphtha conversion. Enabled by perovskite oxide-based redox catalysts, the ROC process converts naphtha (represented by n-hexane) in an auto-thermal, cyclic redox mode. The addition of 20 wt.% Na2WO4 to SrMnO3 and CaMnO3 created highly selective redox catalysts capable of achieving enhanced olefin yields from n-hexane oxy-cracking. This was largely attributed to the redox catalysts’ high activity, selectivity, and stability towards selective hydrogen combustion (SHC) under a redox mode. Na2WO4/CaMnO3 demonstrated significantly higher olefin yield (55–58%) when compared to that from thermal cracking (34%) at 725 °C and 4500 h−1. COx yield as low as 1.7% was achieved along with complete combustion of H2 over 25 cycles. Similarly, Na2WO4/SrMnO3 achieved 41% olefin yield, 0.4% COx yield, and 73% H2 combustion at this condition. Oxygen-temperature-programmed desorption (O2-TPD) indicated that Na2WO4 hindered gaseous oxygen release from CaMnO3. Low-energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS) revealed an outermost perovskite surface layer covered by Na2WO4, which suppressed near-surface Mn and alkaline earth metal cations. The formation of non-selective surface oxygen species was also inhibited. XPS analysis further confirmed that promotion of SrMnO3 with Na2WO4 suppressed surface Sr species by 90%, with a similar effect also observed on CaMnO3. These findings point to the promoting effect of Na2WO4 and the potential of promoted SrMnO3 and CaMnO3 as selective redox catalysts for efficient production of light olefins from naphtha via the ROC process.}, journal={APPLIED CATALYSIS B-ENVIRONMENTAL}, publisher={Elsevier BV}, author={Dudek, Ryan B. and Tian, Xin and Blivin, Millicent and Neal, Luke M. and Zhao, Haibo and Li, Fanxing}, year={2019}, month={Jun}, pages={30–40} }
 @article{tian_dudek_gao_zhao_li_2019, title={Redox oxidative cracking of n-hexane with Fe-substituted barium hexaaluminates as redox catalysts}, volume={9}, ISSN={["2044-4761"]}, url={https://doi.org/10.1039/C8CY02530D}, DOI={10.1039/c8cy02530d}, abstractNote={Promoted hexaaluminate redox catalysts achieved excellent olefin yield while allowing autothermal redox oxidative cracking of naphtha with low COx formation.}, number={9}, journal={CATALYSIS SCIENCE & TECHNOLOGY}, publisher={Royal Society of Chemistry (RSC)}, author={Tian, Xin and Dudek, Ryan B. and Gao, Yunfei and Zhao, Haibo and Li, Fanxing}, year={2019}, month={May}, pages={2211–2220} }
 @article{liu_zhao_yong_xu_wang_xu_hui_qiu_2013, title={Improving mechanical and electrical properties of oriented polymer-free multi-walled carbon nanotube paper by spraying while winding}, volume={53}, ISSN={["1879-1069"]}, DOI={10.1016/j.compositesb.2013.05.043}, abstractNote={In this study, a new method is introduced for fabricating carbon nanotube (CNT) paper, in which the solvent is sprayed on the CNT sheet while it is wound on a rotating mandrel. As the solvent evaporated, the capillary force pulls CNT closer together, resulting in a CNT paper with a high degree of alignment and a high packing density. Three batches of multi-walled CNTs with different wall thicknesses, tube diameters and lengths are utilized for synthesizing highly oriented CNT papers. It is found that CNTs with smallest diameter of 8 nm form strongest CNT paper with a tensile strength of 563 MPa and a tensile modulus of 15 GPa, while that made with CNTs of 10 nm diameter shows the highest electrical conductivity of 5.5 × 104 S/m.}, journal={COMPOSITES PART B-ENGINEERING}, author={Liu, Wei and Zhao, Haibo and Yong, Zhenzhong and Xu, Geng and Wang, Xin and Xu, Fujun and Hui, David and Qiu, Yiping}, year={2013}, month={Oct}, pages={342–346} }
 @article{liu_zhao_inoue_wang_bradford_kim_qiu_zhu_2012, title={Poly(vinyl alcohol) reinforced with large-diameter carbon nanotubes via spray winding}, volume={43}, ISSN={["1878-5840"]}, DOI={10.1016/j.compositesa.2011.12.029}, abstractNote={For practical application of carbon nanotube (CNT)/polymer composites, it is critical to produce the composites at high speed and large scale. In this study, multi-walled carbon nanotubes (MWNTs) with large diameter (∼45 nm) and polyvinyl alcohol (PVA) were used to increase the processing speed of a recently developed spraying winding technique. The effect of the different winding speed and sprayed solution concentration to the performance of the composite films were investigated. The CNT/PVA composites exhibit tensile strength of up to 1 GPa, and modulus of up to 70 GPa, with a CNT weight fraction of 53%. In addition, an electrical conductivity of 747 S/cm was obtained for the CNT/PVA composites. The good mechanical and electrical properties are attributed to the uniform CNTs and PVA matrix integration and the high degree of tube alignment.}, number={4}, journal={COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING}, author={Liu, Wei and Zhao, Haibo and Inoue, Yoku and Wang, Xin and Bradford, Philip D. and Kim, Hyungsup and Qiu, Yiping and Zhu, Yuntian}, year={2012}, month={Apr}, pages={587–592} }
 @article{zhao_yuan_2011, title={Carbon nanotube yarn sensors for structural health monitoring of composites}, volume={7983}, ISSN={["0277-786X"]}, DOI={10.1117/12.880938}, abstractNote={With increasing application of composite materials, real time monitoring of composite structures becomes vital for maintenance purpose as well as prevention of catastrophic failure. It has been reported that carbon nanotubes (CNTs) have excellent piezoresistive properties, which may enable a new generation of sensors in nano or micro scales. We report here a novel prototype of carbon nanotube yarn sensors with excellent repeatability and stability for in-situ structural health monitoring. The CNT yarn is spun directly from CNT arrays, and its electrical resistance increases linearly with tensile strain, which makes it an ideal strain sensor. Importantly, it shows repeatable piezoresistive behavior under repetitive straining and unloading. Yarn sensors show stable resistances at temperatures ranging from -196° to 110°. Neat yarn sensors are also embedded into resin to monitor the loading conditions of the composites. With multiple yarn sensor elements aligned in the composite, the crack initiation and propagation could be monitored. Yarn sensors could be easily incorporated into composite structures with minimal invasiveness and weight penalty to enable the structure has self-sensing capabilities.}, journal={NONDESTRUCTIVE CHARACTERIZATION FOR COMPOSITE MATERIALS, AEROSPACE ENGINEERING, CIVIL INFRASTRUCTURE, AND HOMELAND SECURITY 2011}, author={Zhao, Haibo and Yuan, Fuh-Gwo}, year={2011} }
 @article{wang_bradford_liu_zhao_inoue_maria_li_yuan_zhu_2011, title={Mechanical and electrical property improvement in CNT/Nylon composites through drawing and stretching}, volume={71}, ISSN={["1879-1050"]}, DOI={10.1016/j.compscitech.2011.07.023}, abstractNote={The excellent mechanical properties of carbon nanotubes (CNTs) make them the ideal reinforcements for high performance composites. The misalignment and waviness of CNTs within composites are two major issues that limit the reinforcing efficiency. We report an effective method to increase the strength and stiffness of high volume fraction, aligned CNT composites by reducing CNT waviness using a drawing and stretching approach. Stretching the composites after fabrication improved the ultimate strength by 50%, 150%, and 190% corresponding to stretch ratios of 2%, 4% and 7%, respectively. Improvement of the electrical conductivities exhibited a similar trend. These results demonstrate the importance of straightening and aligning CNTs in improving the composite strength and electrical conductivity.}, number={14}, journal={COMPOSITES SCIENCE AND TECHNOLOGY}, author={Wang, Xin and Bradford, Philip D. and Liu, Wei and Zhao, Haibo and Inoue, Yoku and Maria, Jon-Paul and Li, Qingwen and Yuan, Fuh-Gwo and Zhu, Yuntian}, year={2011}, month={Sep}, pages={1677–1683} }
 @article{liu_zhang_xu_bradford_wang_zhao_zhang_jia_yuan_li_et al._2011, title={Producing superior composites by winding carbon nanotubes onto a mandrel under a poly(vinyl alcohol) spray}, volume={49}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2011.06.089}, abstractNote={A simple method for processing high-performance carbon nanotube (CNT)/poly(vinyl alcohol) (PVA) composites by coupling the spraying of a PVA solution with the continuous winding of CNT sheets from an array onto a rotating mandrel is reported. This method allows the CNT composites to have a high CNT volume fraction, while having a high degree of alignment, long CNTs, and good integration with the matrix, which are extremely difficult to realize simultaneously by other processes. As a result, the composites have a toughness, strength and electrical conductivity up to 100 J/g, 1.8 GPa and 780 S/cm, respectively. Such a one-step synthesis process is promising for industrial productions and also works for different types of polymers.}, number={14}, journal={CARBON}, author={Liu, Wei and Zhang, Xiaohua and Xu, Geng and Bradford, Philip D. and Wang, Xin and Zhao, Haibo and Zhang, Yingying and Jia, Quanxi and Yuan, Fuh-Gwo and Li, Qingwen and et al.}, year={2011}, month={Nov}, pages={4786–4791} }
 @article{deng_lu_zhao_zhu_kim_chou_2011, title={The properties of dry-spun carbon nanotube fibers and their interfacial shear strength in an epoxy composite}, volume={49}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2010.12.061}, abstractNote={Continuous fibers composed of carbon nanotubes have been adopted as reinforcements for polymeric composites. This paper presents several fundamental studies relevant to the mechanical behavior of CNT fibers, including fiber tensile behavior; in situ SEM observation of fiber deformation mechanisms; and fiber modulus, ultimate strength and fracture strain measurements. A modified Weibull strength distribution model that takes into account the flaw density variation with fiber diameter has been adopted for the statistical strength analysis. The interfacial shear strength between the carbon nanotube fiber and the epoxy matrix has been measured using fragmentation tests of single-fiber composites.}, number={5}, journal={CARBON}, author={Deng, Fei and Lu, Weibang and Zhao, Haibo and Zhu, Yuntian and Kim, Byung-Sun and Chou, Tsu-Wei}, year={2011}, month={Apr}, pages={1752–1757} }
 @article{bradford_wang_zhao_zhu_2011, title={Tuning the compressive mechanical properties of carbon nanotube foam}, volume={49}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2011.03.012}, abstractNote={A post-growth chemical vapor deposition (CVD) treatment was used to tune the compressive mechanical properties of carbon nanotube (CNT) arrays. Millimeter tall CNT arrays with low compressive resilience were changed to a foam-like material with high compressive strength and almost complete recovery upon unloading. The foam was tuned to provide a range of compressive properties for various applications. The treated arrays demonstrated compressive strength up to 35× greater than the as-grown CNT array. Unlike polymeric foams, the CNT foam did not decompose after exposure to high temperatures. Investigation of the foam structure revealed that the CVD treatment increased CNT diameter through radial growth, while increasing the CNT surface roughness. The morphological changes help to explain the increase in CNT array compressive strength and the transition from permanent array deformation to foam-like recovery after compressive loading.}, number={8}, journal={CARBON}, author={Bradford, Philip D. and Wang, Xin and Zhao, Haibo and Zhu, Y. T.}, year={2011}, month={Jul}, pages={2834–2841} }
 @article{bradford_wang_zhao_maria_jia_zhu_2010, title={A novel approach to fabricate high volume fraction nanocomposites with long aligned carbon nanotubes}, volume={70}, ISSN={["1879-1050"]}, DOI={10.1016/j.compscitech.2010.07.020}, abstractNote={Conventional micro-fiber-reinforced composites provide insight into critical structural features needed for obtaining maximum composite strength and stiffness: the reinforcements should be long, well aligned in a unidirectional orientation, and should have a high reinforcement volume fraction. It has long been a challenge for researchers to process CNT composites with such structural features. Here we report a method to quickly produce macroscopic CNT composites with a high volume fraction of millimeter long, well aligned CNTs. Specifically, we use the novel method, shear pressing, to process tall, vertically aligned CNT arrays into dense aligned CNT preforms, which are subsequently processed into composites. Alignment was confirmed through SEM analysis while a CNT volume fraction in the composites was calculated to be 27%, based on thermogravimetric analysis data. Tensile testing of the preforms and composites showed promising mechanical properties with tensile strengths reaching 400 MPa.}, number={13}, journal={COMPOSITES SCIENCE AND TECHNOLOGY}, author={Bradford, Philip D. and Wang, Xin and Zhao, Haibo and Maria, Jon-Paul and Jia, Quanxi and Zhu, Y. T.}, year={2010}, month={Nov}, pages={1980–1985} }
 @article{zhao_bradford_wang_liu_luo_jia_zhu_yuan_2010, title={An intermetallic Fe-Zr catalyst used for growing long carbon nanotube arrays}, volume={64}, ISSN={["1873-4979"]}, DOI={10.1016/j.matlet.2010.05.045}, abstractNote={Metallic nanoparticles containing single and binary components have been known for their catalytic properties to grow carbon nanotube (CNT) arrays. In this paper, an intermetallic catalyst consisting of iron and zirconium was used to grow millimeter long, well aligned arrays. The Fe–Zr catalysts enabled the growth of 1.7 mm-long carbon nanotube arrays in 45 min. A comparison with pure iron catalyst indicated that adding Zr to iron can stabilize the Fe catalyst at the CNT growth temperature and moderate its reactivity. SEM images showed the different growth behaviors for Fe–Zr and Fe catalysts. The long, uniform CNT arrays grown here have potential applications in many advanced composites.}, number={18}, journal={MATERIALS LETTERS}, author={Zhao, Haibo and Bradford, Philip D. and Wang, Xin and Liu, Wei and Luo, Tzy Jiun Mark and Jia, Quanxi and Zhu, Yuntian and Yuan, Fuh-Gwo}, year={2010}, month={Sep}, pages={1947–1950} }