Influence of calcined temperatures on the microstructure and electrochemical properties of LiFePO4/C nano-particles with a core-shell structure and It’s thermal stability study

Pengzhao Gao,Bing Yan,Ling Wang,Wei Liu,Weiwei Gong,Xiao-pan Liu 한양대학교 세라믹연구소 2015 Journal of Ceramic Processing Research Vol.16 No.1

Influence of calcined temperatures on the microstructure and electrochemical properties of LiFePO4/C nano-particles as well as it’s thermal stability were studied using HRTEM, XRD, electrochemical workstation and TGA. The results indicated that when calcined at 973 K, the LiFePO4/C nano-particles consisted of a well-crystalline LiFePO4 core with size of 58.6-80.1 nm and an amorphous carbon shell with thickness of 2 nm. With the increase of calcined temperature, the electrochemical properties of LiFePO4/C materials increased first and then decreased, it reached maximum when temperature equaled to 973 K. The initial discharge capacity of the sample was 142 mAh/g, the discharge capacity of it maintained 132 mAh/g with capacity retention of 93.0% after 40 cycles. The decomposition reaction of LiFePO4/C material calcined at 973 K occurred at 938.38- 1194.52 K under 10 K • min−1 in N2 atmosphere and corresponded to approximately 5.8% of the total weight. The decomposition mechanism of it consisted of three stages: the first stage was controlled by gas diffusion in carbon shell; the second stage was controlled by chemical reaction and gas diffusion; the third stage was controlled by chemical reaction

Growth behavior of flower-shaped nano-CdS clusters on biomorphic porous carbon (BPC) substrates using a hydrothermal method

Pengzhao Gao 한양대학교 세라믹연구소 2017 Journal of Ceramic Processing Research Vol.18 No.3

Flower-shaped nano-CdS clusters grown on biomorphic porous carbon (BPC) substrates have been successfully preparedusing a hydrothermal method. Influence of growth time, types of substrate and carbonized temperature on the growthbehavior of flower-shaped nano-CdS clusters were studied using XPS, XRD, TGA, and SEM. The results indicated thatwurtzite nano-CdS clusters were successfully integrated into the inner wall of BPC with various morphologies: couch grassshapedclusters can grow on the inner wall of BPC derived from pine, sunflower-shaped clusters can grow on that derived frombamboo and chrysanthemum-shaped clusters can grow on that derived basswood. The crystal size of nano-CdS clusters grownfor 24 h on BPC derived from pine was approximately 7 nm. The size and number of nano-clusters grown on BPC substratewere mainly affected by the growth time and the substrate carbonized temperature, respectively. Finally, the growthmechanism of nano-CdS clusters on BPC substrates was also discussed.

Preparation and oxidation properties of biomorphic porous carbon derived from native bamboo

Pengzhao Gao,Shiting Huang,Weiei Gong,Wenxiang Wang 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.6

A biomorphic porous carbon (BPC) was prepared by carbonized native bamboo under an Ar atmosphere through a controlled heating process. Microstructural properties of BPC were studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The pyrolytic behavior of bamboo and non-isothermal oxidation properties of BPC were studied by thermogravimetric analysis (TGA). Experimental results show that BPC has a porous interconnected honeycomb microstructure, with a multi-peak pore size distribution, and is a typical non-graphitizable carbon. With an increasing carbonization temperature, the (002) peak of the XRD spectrum becomes stronger, the interplanar spacing decreases, the structure of BPC slowly evolved towards that of ideal graphite, and also the density increases, and bulk porosity decreases. The non-isothermal oxidation properties of BPC exhibit a self-catalytic characteristic, which is discussed through a schematic model.

Model-free kinetics applied to an oxidation mechanism of a biomorphic carbon template derived from pine

Pengzhao Gao,Wenxiang Wang,Weiei Gong 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.4

A biomorphic carbon template (BCT) was developed by carbonizing pine under vacuum. Structural and oxidation properties of BCT were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). Experimental results show that BCT has a topologically uniform interconnected porous network microstructure, and is typical non-graphitizable carbon containing C =C bonds, C–O–C bonds and a C–H structure. The non-isothermal oxidation properties of BCT exhibit a partially self-accelerating characteristic; the oxidation process of BCT is firstly controlled by a chemical reaction, and then controlled by a chemical reaction and gas diffusion together, which is obtained from a Vyazovkin model-free method, and the corresponding activation energy (E a) is also calculated.

Influence of temperature on the carbonization context, oxidation properties and mechanism of a porous biomorphic carbon template

Pengzhao Gao,Pengfei Hu,Wenxiang Wang,Weiwei Gong 한양대학교 세라믹연구소 2010 Journal of Ceramic Processing Research Vol.11 No.3

A porous biomorphic carbon template (BCT) was prepared using a carbonized native aspen under an Ar atmosphere. Microstructural properties of the BCT were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Non-isothermal oxidation properties and the mechanism of the BCT formation were studied by thermogravimetric analysis (TGA). Experimental results show that microstructure of the BCT exhibits a honeycomb interconnected porous network and double-peaked distribution of pore diameters. The BCT phase belongs to amorphous carbon, with an increase of the carbonization temperature, the (002) peak of the XRD spectrum becomes stronger, the interplanar spacing decrease, and the structure of BCT slowly evolved towards that of ideal graphite. The non-isothermal oxidation process of BCT is controlled by a chemical reaction and gas diffusion together, and the two stages have different influences on the whole reaction rate with an increase of the conversion (a). The corresponding activation energy (E a) is also calculated.

Crystallization kinetics and magnetic properties of spinel transition metal ferrite nanoparticles

Yukun Sun,Dongyun Li,Pengzhao Gao,Zhouli Lu,Hongliang Ge 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.5

Spinel transition metal ferrite TMFe2O4 (TM = Co2+, Ni2+, Cu2+, and Zn2+) nanoparticles were prepared via a template-assistedsol-gel method followed by a calcining process, using metal nitrate precursors as raw materials. The prepared specimens werecharacterized using X-ray diffraction (XRD) and a vibrating sample magnetometer (VSM). Their structures, magneticproperties, crystallization kinetics, and the influence of crystal size (D) on the magnetic properties were investigated. It wasfound that the crystal sizes of TMFe2O4 were positively proportional to the calcined temperature and time, and thecrystallization growth activation energy (Ea) increased with the increase of metal ionic radius. The optimum calcinationparameters were obtained to form a crystal closest to the standard crystal. Additionally, the saturation magnetization ofinverse spinel structure specimens was enhanced monotonously and their coercivity showed a potential decrease trend, whilethere was an opposite change trend for normal spinel structure specimens.

Effect of SiO2 content on the microstructure and consolidation mechanism of recrystallized silicon carbide

Wenming Guo,Hanning Xiao,Haibo Lei,Pengzhao Gao,Wen Xie,Qing Li 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.6

In this paper, the influence of SiO2 on the microstructure and consolidation mechanism of recrystallized silicon carbide (RSiC)was studied by comparing the relationship of the weight losses and microstructural evolution with the SiO2 contents at different firing temperatures. The results showed that the presence of SiO2 resulted in a basic weight loss proportional to the SiO2 content and an additional weight loss independent of the SiO2 content. The consolidation mechanism of SiC was not altered by the introduction of SiO2, involving surface diffusion at low temperatures and an evaporation-condensation process at the high temperature, while the residual ambient atmosphere primarily including SiO(g), Si2C(g) and Si(g) inhibited the recrystallization of SiC by altering the mass transport from SiC2(g), Si2C(g) and Si(g) for pure SiC to that combined with the gaseous transport of SiO(g), Si2C(g), Si(g) and SiC(g), and the surface diffusion of C(s) at the high temperature.

Mechanical properties and cushioning mechanism of shear thickening fluid

Peng Zhao,Qian Chen,Xue Gao,Zhaoyong Wu 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.11

Shear thickening fluid (STF) is one type of dispersed system with rapidly changing rheological properties under an impulse load. The apparent viscosity of such a suspension system changes dramatically under high-speed impact, and the system can even change from suspension to quasi-solid. Once the load is removed, the STF will quickly return to its original state. In this paper, a mechanical model based on a particle-jammed model and added mass was proposed by calculating the acceleration response of the impact bar, and the local hardening phenomenon of STF in the low-speed impact test was interpreted. Then with the low-speed impact test, the rheological properties of STF in the cushioning process were recorded by a high-speed camera. Meanwhile, a comparison was made with the cushioning efficiency of AV-200, a closed-cell foam material, by using the force-displacement curve. Finally, based on the constitutive relation of STF and by using the fluid-solid coupling method in the FEM, the lowspeed impact test of STF was analyzed to obtain more comprehensive dynamic characteristics. The acceleration response obtained in the test was consistent with the theoretical results, which further verified the rationality and effectiveness of the theoretical model. Compared with AV-200, STF has a cushioning efficiency of 50 %-60 %, and its cushioning performance was superior to AV-200. Starting with the rheological cloud map of STF and the acceleration response of the impact bar by the numerical model, a comparison was made with the results of low-speed impact test, and a good agreement is observed.

A Review of Computational Phantoms for Quality Assurance in Radiology and Radiotherapy in the Deep-Learning Era

Peng Zhao,Gao Ning,Wu Bingzhi,Chen Zhi,Xu X. George 대한방사선방어학회 2022 방사선방어학회지 Vol.47 No.3

The exciting advancement related to the “modeling of digital human” in terms of a computa- tional phantom for radiation dose calculations has to do with the latest hype related to deep learning. The advent of deep learning or artificial intelligence (AI) technology involving convo- lutional neural networks has brought an unprecedented level of innovation to the field of organ segmentation. In addition, graphics processing units (GPUs) are utilized as boosters for both real-time Monte Carlo simulations and AI-based image segmentation applications. These ad- vancements provide the feasibility of creating three-dimensional (3D) geometric details of the human anatomy from tomographic imaging and performing Monte Carlo radiation transport simulations using increasingly fast and inexpensive computers. This review first introduces the history of three types of computational human phantoms: stylized medical internal radiation dosimetry (MIRD) phantoms, voxelized tomographic phantoms, and boundary representation (BREP) deformable phantoms. Then, the development of a person-specific phantom is demon- strated by introducing AI-based organ autosegmentation technology. Next, a new development in GPU-based Monte Carlo radiation dose calculations is introduced. Examples of applying computational phantoms and a new Monte Carlo code named ARCHER (Accelerated Radia- tion-transport Computations in Heterogeneous EnviRonments) to problems in radiation pro- tection, imaging, and radiotherapy are presented from research projects performed by students at the Rensselaer Polytechnic Institute (RPI) and University of Science and Technology of China (USTC). Finally, this review discusses challenges and future research opportunities. We found that, owing to the latest computer hardware and AI technology, computational human body models are moving closer to real human anatomy structures for accurate radiation dose calcula- tions.