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Influence of dicalcium phosphate dihydrate coating
on the in vitro degradation of
Mg-Zn alloy
Shao-Xiang ZHANG, Jia-Nan LI, Yang SONG, Chang-Li ZHAO, Xiao-Nong ZHANG,
Front. Mater. Sci.. 2010, 4 (2): 116-119.
https://doi.org/10.1007/s11706-010-0026-z
To reduce the degradation rate and further to improve the biocompatibility of magnesium alloy, dicalcium phosphate dihydrate (CaHPO4·2H2O, DCPD) has been fabricated on a kind of magnesium-zinc alloy by way of electrodeposition method. The experimental results of XRD, SEM and EDS showed that the electrodeposited coating on the Mg-Zn alloy mainly contains the flake-like DCPD, along with some octacalcium phosphate (Ca8(HPO4)2(PO4)4·4H2O, OCP). After the in vitro degradation of the coated alloy in modified-simulated body fluid (m-SBF), it was proved that the coating could reduce the degradation rate effectively, and the samples were covered by calcium phosphate salts with a higher Ca/P ratio. Therefore, it indicates that compared with the bare alloy, the DCPD coating rendered a more biocompatible surface, and is a promising coating candidate for biomedical magnesium materials.
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Corrosion and bone response of magnesium implants
after surface modification by heat-self-assembled monolayer
Jia-Cheng GAO, Li-Ying QIAO, Ren-Long XIN,
Front. Mater. Sci.. 2010, 4 (2): 120-125.
https://doi.org/10.1007/s11706-010-0029-9
The corrosion degradation behavior and in vivo test of 4N-Mg after surface modification by heat-self-assembled monolayer (HSAM) were studied in this paper. Comprehensive techniques were used to analyze the corrosion process, corrosion rate and corrosion mecha-nism. The Mg samples with and without modifications were embedded in the thigh bones of white rabbits, and TC4 was used as the control. The concentration of Mg2+ ion in blood were analyzed after 2, 6, and 12 weeks of implantation. Then the specimens were analyzed by scanning electron microscope (SEM), and tissue slices were observed by optical microscope. The results show that the modified Mg had better corrosion resistance. The in vivo study confirmed that the magnesium concentration in blood was in the normal scale, and the Mg have good bone inducement and showed excellent capabilty of contact with bone. After implantations for a few weeks, the new bone obviously mineralizes on the interface between the modified Mg and bone. The untreated magnesium corroded faster than the HSAM treated magnesium in vivo. All the results indicated that Mg showed better biocompatibility and the capacity of inducing new bone due to HSAM had an effect on controlling the corrsion rate of Mg.
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Fabrication and corrosion behavior of HA/Mg-Zn
biocomposites
De-Bao LIU, Ming-Fang CHEN, Xin-Yu YE,
Front. Mater. Sci.. 2010, 4 (2): 139-144.
https://doi.org/10.1007/s11706-010-0034-z
The thermal-treated hydroxyapatite (HA) particles, Mg and Zn powders were used to prepare the HA/Mg-Zn composites with different HA contents by means of powder metallurgy technology. The microstructures, formation phases, and corrosion behaviors in simulated body fluid (SBF) were studied in comparison with pure magnesium and HA/Mg composites fabricated by the same preparation technology. As a result, no evident reaction happened between HA particles and Mg matrix during sintering process, and Zn atoms diffused into Mg matrix to form a single phase Mg-Zn alloy matrix. The addition of HA particles changed the corrosion mechanism of Mg matrix. During the corrosion process, HA particles would adsorb and Ca 2+ ions efficiently and induce the deposition of Ca-P compounds on the surface of composites. HA could improve the corrosion resistance of magnesium matrix composites in SBF and restrain the increase of pH of SBF. Furthermore, the addition of Zn was favorable to improve the corrosion resistance of HA/Mg composites due to the densification of composites and the formation of Mg-Zn alloy matrix.
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A mesoporous silica modified conjugated polymer
film: Preparation and detection nitroaromatics in aqueous phase
Feng LIU, Li-Juan ZHANG, Jian-Hua XIAO, Jun HU, Hong-Lai LIU,
Front. Mater. Sci.. 2010, 4 (2): 158-163.
https://doi.org/10.1007/s11706-010-0018-z
The linear conjugated polymer of polyfluorene/poly(p-phenylenevinylenes) (PFO/PPV) was synthesized and selected as the matrix film. The incorporation of a small fraction of inorganic mesoporous silicas into the polymer matrix resulted in a significant increase in overall detection efficiency of nitroaromatics. The structure of the obtained mixed films was characterized by 1H-NMR, IR, and XRD. The optical and fluorescence properties of the mixed films were demonstrated by ultraviolet and visible spectroscopy (UV-Vis) and photoluminescence (PL) spectra in ethanol/water solution. Compared with the pure conjugated polymer film, the mixed films had high fluorescence quenching sensitivity toward nitroaromatic compounds, especially 2,4,6-trinitrophenol (TNP), in the aqueous phase. The fluorescent emission quenching is quantitative and can be analyzed on the basis of the Stern-Volmer model relation with the quenching process. The results revealed that such mixed matrix films of conjugated polymer/mesoporous silicas can be a promising strategy of designing chemosensory materials for detecting nitroaromatic compounds.
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Synthesis and characterization of a thermo-sensitive
poly( N -methyl acryloylglycine methyl
ester) used as a drug release carrier
Kui-Lin DENG, Hai-Bin ZHONG, Yi-Suo JIAO, Ting FAN, Xiao QIAO, Peng-Fei ZHANG, Xiao-Bo REN,
Front. Mater. Sci.. 2010, 4 (2): 164-170.
https://doi.org/10.1007/s11706-010-0032-1
In this article, poly(N-methyl acryloylglycine methyl ester) (PNMAME) was prepared as a novel thermo-sensitive material with a lower critical solution temperature (LCST) at around 49.5°C. The chemical structures of the monomer NMAME and PNMAME were characterized by 1H NMR and IR measurements. The LCST was investigated systematically as a function of PNMAME concentration, inorganic salt solution and pH value. The results indicatedthat LCST of PNMAME was obviously dependent on PNMAME concentration and pH. The LCST was increased with a decrease in pH value and PNMAME concentration. To obtain a thermo-sensitive hydrogel with the phase transition temperature close to human body temperature, the copolymerization was conducted between NMAME and N-acryloylglycine ethyl ester (NAGEE). The release behavior of caffeine was evaluated at different temperatures and contents of cross-linkers (N, N-methylenebis(acrylamide) (NMBA)). The increase of cross-linker content led to a decrease in the release rate of caffeine due to higher crossing density in the hydrogel network. In addition, a faster release of caffeine from the hydrogel with 3% NMBA at 37°C was found in contrast to that at 18°C.
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Investigation on the stability of Li 5 La 3 Ta 2 O 12 lithium ionic conductors in humid environment
Wei-Guo WANG, Xian-Ping WANG, Yun-Xia GAO, Jun-Feng YANG, Qian-Feng FANG,
Front. Mater. Sci.. 2010, 4 (2): 189-192.
https://doi.org/10.1007/s11706-010-0017-0
In this paper, the stability in humid air of Li5La3Ta2O12 lithium ionic conductors synthesized by conventional solid-state reaction was investigated by internal friction, conductivity, weight variation, X-ray diffraction, and thermogravimetric analysis methods. It was found that when the Li5La3Ta2O12 samples were aged in open air at room temperature, the internal friction peaks associated with the short-distance diffusion of lithium vacancies gradually shift toward higher temperature and increase in height, while the weight of the sample increases and impurity phases of LiOH·H2O appear. These results reveal that the Li5La3Ta2O12 compounds are unstable against moisture in open air at room temperature. It was suggested that the protons from the moisture substitute the lithium ions in Li5La3Ta2O12 samples to form Li2O and new protonic derivatives, Li5−xLa3Ta2O12−x(OH)x (0<x<2.15), and the resultant Li2O may react further with water to form LiOH·H2O.
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Studies on softening kinetics of niobium microalloyed
steel using stress relaxation technique
Cheng-Liang MIAO, Cheng-Jia SHANG, Guo-Dong ZHANG, Guo-Hui ZHU, Hatem ZUROB, Sundaresa SUBRAMANIAN,
Front. Mater. Sci.. 2010, 4 (2): 197-201.
https://doi.org/10.1007/s11706-010-0023-2
Stress relaxation was studied in a series of low carbon, high Mn microalloyed steels containing 0.012 wt.%, 0.06 wt.% and 0.1 wt.% Nb. The stress-relaxation curves were modeled using a physically-based model that takes into account the time evolution of precipitation, recovery and recrystallization as well as their interactions. The results confirm that the high Mn, high Nb design can offer distinct advantage over the low Mn design for the application of near-net shape processing.
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Theoretical prediction of welding distortion
in large and complex structures
De-An DENG,
Front. Mater. Sci.. 2010, 4 (2): 202-209.
https://doi.org/10.1007/s11706-010-0019-y
Welding technology is widely used to assemble large thin plate structures such as ships, automobiles, and passenger trains because of its high productivity. However, it is impossible to avoid welding-induced distortion during the assembly process. Welding distortion not only reduces the fabrication accuracy of a weldment, but also decreases the productivity due to correction work. If welding distortion can be predicted using a practical method beforehand, the prediction will be useful for taking appropriate measures to control the dimensional accuracy to an acceptable limit. In this study, a two-step computational approach, which is a combination of a thermo-elastic-plastic finite element method (FEM) and an elastic finite element with consideration for large deformation, is developed to estimate welding distortion for large and complex welded structures. Welding distortions in several representative large complex structures, which are often used in shipbuilding, are simulated using the proposed method. By comparing the predictions and the measurements, the effectiveness of the two-step computational approach is verified.
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Numerical study of resin transfer molding (RTM)
curing process
Fei SHI, Xiang-Huai DONG,
Front. Mater. Sci.. 2010, 4 (2): 217-224.
https://doi.org/10.1007/s11706-010-0028-x
It is a very important phase in resin transfer molding (RTM) process that resin is cured. The result of the curing process determines the quality of a part, including mechanical properties, lifecycle of the part under high temperature and chemical properties. Therefore, it is very meaningful to discuss the curing process. In our work, the code is prepared based on unstructured mesh using divergence theorem. A case is used to verify properness of the code and the results are in good agreement with the published experiment data. In the paper, some factors of materials and numerical calculation, e.g., time step, reaction heat, the whole heat conductivity of fiber and resin and fiber initial temperature, which affect result of simulation, are emphatically investigated and carefully revealed. The conclusion shows that time step, the reaction heat and heat conductivity have an important effect on the curing process, while fiber initial temperature has very little impact. These are helpful to understand and adopt the curing process in order to produce good products.
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