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Xiao‑Bo Mei,Bao‑Chuan Liu,Wei Jiang,Quan Xu,Qi‑Dong Zhang,Yu‑Bai Ma,Fang‑Qiu Zu 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.9
The influence of cooling rates on the mechanical properties of a Zr-based bulk metallic glass prepared with high rheologicalrate forming (HRRF) was investigated and compared with traditional suction cast methods. Amorphous samples of Zr57Cu-20Ni8Al10Ag5 were prepared in copper molds with different sizes in order to obtain different cooling rates for both HRRFand traditional cast methods. These specimens were subjected to compression experiments, including microhardness testing,X-ray diffraction testing and differential scanning calorimetry analysis. The results indicate that the plasticity of the samplesformed by HRRF are higher than that of the as-cast ones at the same cooling rates, while the microhardness manifests theopposite principle. As the cooling rate increases further, the difference in plasticity further increases between two methods,indicating that the plasticity of metallic glasses is more sensitive to cooling rates during the HRRF process. At the core ofthis phenomenon is the fact that HRRF methods can introduce more free volume into glasses than traditional cast methodswith an elevated cooling rate are able to.
Xiao-Bao Zuo,Jia-Lin Wang,Wei Sun,Hua Li,Guang-Ji Yin 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.19 No.1
This paper uses modelling and experiment to perform a quantitative analysis for the gypsum and ettringite formations in cement pastes subjected to sulfate attack. Firstly, based on Fick’s law and chemical reaction kinetics, a diffusion model of sulfate ions in cement pastes is proposed, and then the model of the gypsum and ettringite formations is established to analyze its contents in cement pastes with corrosion time. Secondly, the corrosion experiment of the specimens with cement pastes immersed into 2.5%, 5.0% and 10.0% Na2SO4 solutions are carried out, and by using XRD-Rietveld method, the phases of powder samples from the specimens are quantitatively analyzed to obtain the contents of gypsum and ettringite in different surface depth, solution concentration and corrosion time. Finally, the contents of gypsum and ettringite calculated by the models are compared with the results from the XRD experiments, and then the effects of surface depth, corrosion time and solution concentration on the gypsum and ettringite formations in cement pastes are discussed.
Numerical investigation on tortuosity of transport paths in cement-based materials
Xiao-Bao Zuo,Wei Sun,Zhi-Yong Liu,Yu-Juan Tang 사단법인 한국계산역학회 2014 Computers and Concrete, An International Journal Vol.13 No.3
Based on the compositions and structures of cement-based materials, the geometrical models of the tortuosity of transport paths in hardened cement pastes, mortar and concrete, which are associated withthe capillary porosity, cement hydration degree, mixture particle shape, aggregate volume fraction andwater-cement ratio, are established by using a geometric approach. Numerical simulations are carried out to investigate the effects of material parameters such as water-cement ratio, volume fraction of the mixtures, shape and size of aggregates and cement hydration degree, on the tortuosity of transport paths in hardened cement pastes, mortar and concrete. Results indicate that the transport tortuosity in cement-based materials decreases with the increasing of water-cement ratio, and increases with the cement hydration degree, the volume fraction of cement and aggregate, the shape factor and diameter of aggregates, and the material parameters related to cement pastes, such as the water-cement ratio, cement hydration degree and cement volume fraction, are the primary factors that influence the transport tortuosity of cement-based materials.
Xiao-Xiao,Zuo-Xi Li,Bao-yi Yu,Guang-hua Cui 대한화학회 2015 Bulletin of the Korean Chemical Society Vol.36 No.7
Two new copper(II) complexes with the formulas [Cu(btb)(pydc)(H2O)]n (1) and [Cu(btb)0.5(nph)(H2O)]n (2) have been synthesized under hydrothermal conditions by employing a rigid bis(triazole) ligand (btb = 4,4′-bis(1,2,4-triazolyl-1-yl)-biphenyl) and two carboxylic acids mixed ligands (H2pydc = pyridine-2,5-dicarboxylic acid and H2nph = 3-nitrophthalic acid). The copper atoms present different environments, with a tetragonal pyramidal geometry in 1 and octahedral configuration in 2. Complex 1 displays a dinuclear cluster, which is further packed into a 2D supramolecular layer by classical OH · · · O hydrogen bonds. Complex 2 possesses a trinodal 3,4,4-connected 3D framework with a rare sqc69 topology. In addition, thermal stability and luminescence property were investigated.
UPPER AND LOWER SOLUTION METHOD FOR FRACTIONAL EVOLUTION EQUATIONS WITH ORDER 1 < α < 2
Xiao-Bao Shu,Fei Xu 대한수학회 2014 대한수학회지 Vol.51 No.6
In this work, we investigate the existence of the extremal solutions for a class of fractional partial differential equations with or- der 1 < α < 2 by upper and lower solution method. Using the theory of Hausdorff measure of noncompactness, a series of results about the solutions to such differential equations is obtained.
Stability of Zirconium Metal Organic Frameworks with 9,10- Dicarboxylic Acid Anthracene as Ligand
Xiao, Sheng-Bao,Chen, Sai-Sai,Liu, Jin,Li, Zhen,Zhang, Feng-Jun,Wang, Xian-Biao,Oh, Won-Chun The Korean Ceramic Society 2016 한국세라믹학회지 Vol.53 No.2
With high specific surface area and pore structural diversity, MOFs show important applications in gas storage, catalysis, sensing, separation, and biomedicine. However, the stability of the structure of MOFs has restricted their application and development. In this study, zirconium metal organic frameworks with 9,10-dicarboxylic acid anthracene as ligand, named UIO-66 ($H_2DCA$), were synthesized and their properties and structures were characterized by XRD, SEM, and $N_2$ adsorption. We focus on the stability of the structure of UIO-66 ($H_2DCA$) under different conditions (acid, alkali, and water). The structural changes or ruins of UIO-66 ($H_2DCA$) were traced by means of XRD, TG, and FT-IR under different conditions. The results show that the UIO-66 ($H_2DCA$) materials are stable at 583 K, and that this structural stability is greatly influenced by different types of acid and alkali compounds. Importantly, we found that the structures maintain their stability in environments of nitric acid, triethylamine, and boiling water.
Modeling of diffusion-reaction behavior of sulfate ion in concrete under sulfate environments
Xiao-Bao Zuo,Wei Sun,Hua Li,Yu-Kui Zhao 사단법인 한국계산역학회 2012 Computers and Concrete, An International Journal Vol.10 No.1
This paper estimates theoretically the diffusion-reaction behaviour of sulfate ion in concrete caused by environmental sulfate attack. Based on Fick’s second law and chemical reaction kinetics, a nonlinear and nonsteady diffusion-reaction equation of sulfate ion in concrete, in which the variable diffusion coefficient and the chemical reactions depleting sulfate ion concentration in concrete are considered, is proposed. The finite difference method is utilized to solve the diffusion-reaction equation of sulfate ion in concrete, and then it is used to simulate the diffusion-reaction process and the concentration distribution of sulfate ion in concrete. Afterwards, the experiments for measuring the sulfate ion concentration in concrete are carried out by using EDTA method to verify the proposal model, and results show that the proposed model is basically in agreement with the experimental results. Finally, Numerical example has been completed to investigate the diffusion-reaction behavior of sulfate ion in the concrete plate specimen immersed into sulfate solution.
Modeling of ion diffusion coefficient in saturated concrete
Xiao-Bao Zuo,Wei Sun,Cheng Yu,Xu-Rong Wan 사단법인 한국계산역학회 2010 Computers and Concrete, An International Journal Vol.7 No.5
This paper utilizes the modified Davis model and the mode coupling theory, as parts of the electrolyte solution theory, to investigate the diffusivity of the ion in concrete. Firstly, a computational model of the ion diffusion coefficient, which is associated with ion species, pore solution concentration, concrete mix parameters including water-cement ratio and cement volume fraction, and microstructure parameters such as the porosity and tortuosity, is proposed in the saturated concrete. Secondly, the experiments, on which the chloride diffusion coefficient is measured by the rapid chloride penetration test,have been carried out to investigate the validity of the proposed model. The results indicate that the chloride diffusion coefficient obtained by the proposed model is in agreement with the experimental result. Finally, numerical simulation has been completed to investigate the effects of the porosity, tortuosity, water-cement ratio, cement volume fraction and ion concentration in the pore solution on the ion diffusion coefficients. The results show that the ion diffusion coefficient in concrete increases with the porosity, water-cement ratio and cement volume fraction, while we see a decrease with the increasing of tortuosity. Meanwhile, the ion concentration produces more obvious effects on the diffusivity itself, but has almost no effects on the other ions.