Co-reporter:Rong Ge;Yujian Liu;Jun Fang
Journal of Materials Science: Materials in Electronics 2017 Volume 28( Issue 8) pp:5898-5905
Publication Date(Web):31 December 2016
DOI:10.1007/s10854-016-6263-x
Gd2O3/Al2O3 ceramic composites with different weight percent of Gd2O3 were prepared by adopting a pressureless sintering approach. The effect of Gd2O3 addition on the phase composition, sintering property, microstructure, bending strength, thermal conductivity and shielding property of the composites was investigated. The results show that the properties of ceramic can be improved greatly by introducing a small amount of Gd2O3, owing to the promotion of reaction between MgO, SiO2 and Al2O3 to produce spinel and forsterite. Compared with ordinary Al2O3 ceramic, the bending strength and thermal conductivity coefficient of Gd2O3/Al2O3 composite with 5 wt% Gd2O3 have increased by 38.03 MPa and 8.95 W/(m K), respectively. When the amount of Gd2O3 surpasses 15 wt%, however, the performances of the composite would become worse for excessive new phases formed in the composite hindering its densification. In addition, screening ratio of the composites for Co-60 gamma rays radiation increases with the addition of Gd2O3. And the Gd2O3/Al2O3 composites also exhibit good mechanical stability when exposed to continuous gamma rays irradiation.
Co-reporter:Yan Zhang;Wenwen Dai;Yujian Liu;Binge Ma
RSC Advances (2011-Present) 2017 vol. 7(Issue 14) pp:8250-8257
Publication Date(Web):2017/01/23
DOI:10.1039/C6RA26841B
By using hydrochloric acid (HCl) as an acidity regulator, boron-doped ordered mesoporous carbon (B-OMCs) were synthesized via solvent evaporation induced self-assembly (EISA) method. And the self-assembly mechanism of the B-OMCs under HCl conditions was investigated. Not only low-molecular weight boron-modified phenolic resin (BPF), but also triblock copolymer F127 can be protonated by HCl, which results in enhancement of the interaction between precursor and template. Both double-layer hydrogen bonding and electrostatic Coulomb forces act as the driving force for self-assembly of B-OMCs under HCl conditions. In addition, the effect of HCl content on the mesostructure and character of the B-OMCs was studied. With the increase of HCl content, the pore size of B-OMCs decreases, while the surface area, pore order and boron content of B-OMCs increase initially, and then drop off gradually. When pH = 4, the obtained B-OMC has a well-ordered mesoporous structure, highest surface area (690 m2 g−1) and boron content (1.96 wt%). Besides, it possesses excellent electrochemical and capacitance performance (200 F g−1).
Co-reporter:Jing Song, Yan Zhang and Yujian Liu
RSC Advances 2015 vol. 5(Issue 27) pp:20734-20740
Publication Date(Web):11 Feb 2015
DOI:10.1039/C4RA13078B
Boron-doped ordered mesoporous carbons (B-OMCs) were prepared via solvent evaporation induced self-assembly (EISA) method by using triblock copolymer (Pluronic F127) as a soft template and boron modified phenolic resins as both boron and carbon precursors. The effect of molar ratio of formaldehyde to phenol (F/P) on the microstructure and character of B-OMCs was especially investigated. The results show that the specific surface area of B-OMCs increases along with the increase of F/P, while pore size and boron content of B-OMCs increase at first, then drop off. The material prepared with F/P = 1.5/1 possesses best-ordered mesostructure, higher specific surface area (667 m2 g−1), larger pore size (7.9 nm), and highest boron content (1.26 wt%). And it also exhibits superior electrochemical performances and high specific capacitance (180 F g−1).
Co-reporter:Le Chang, Yan Zhang, Yujian Liu, Jun Fang, Weilin Luan, Xiangmin Yang, Weidong Zhang
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 2015 Volumes 356–357() pp:88-93
Publication Date(Web):1 August 2015
DOI:10.1016/j.nimb.2015.04.062
Tungsten/epoxy composites were prepared by blending epoxy resin with different weight percent of tungsten powder. The effect of filler loading on shielding and mechanical properties of composites was investigated by using two different activities of Co-60 source. And radiation degradation mechanism was studied according to the changes of free radicals concentrations, mechanical properties and thermal properties of composites. The results show that with the increment of tungsten loading, shielding property of composites increases. However, with the increase of irradiation dose, thermal stability and mechanical properties of composites decrease firstly, then increase slightly, and decline sharply at the end due to competition reaction between chain scission and cross-linking originated from γ-rays radiation.
Co-reporter:Yan Zhang, Shihong Shen, Yujian Liu
Polymer Degradation and Stability 2013 Volume 98(Issue 2) pp:514-518
Publication Date(Web):February 2013
DOI:10.1016/j.polymdegradstab.2012.12.006
A new titanium modified phenolic resin (Ti–PF) was prepared by using tetraisopropyl titanate, phenol and formaldehyde with mild and friend reaction condition. The structure of the modified resin was demonstrated by means of FT-IR spectra. The titanium modified resin is soluble only in a few solvents such as DMF, DMAc, DMSO, but exhibits poor solubility in most universal solvents. The thermal degradation behavior of the Ti–PF was studied by thermal gravimetric (TG) method. Compared with the unmodified resin (PF), the temperature at the maximum decomposing rate of the Ti–PF increases by 43 °C and its charring yield enhances by 11 percent. The carbonized products of PF (C–PF) and Ti–PF (C–Ti–PF) were further investigated by X-ray diffraction and Roman spectroscopy, respectively. The analysis indicates that the incorporation of titanium into carbon lattice results in an increase of crystallite height and decrease of interlayer spacing. Titanium modified PF becomes much more ordered with a d002 of 0.3572 nm as compared to that of 3.7811 nm for C–PF. And the crystal size of C–Ti–PF increases to 4.37 nm, 2.13 nm larger than that of C–PF. In addition, the ID/IG value of C–Ti–PF decreases from 2.85 (C–PF) to 2.62. The results prove that the incorporation of titanium exhibited obvious effects on improving thermal stability of the phenolic resin and on promoting its graphite crystallite.
Co-reporter:Yan Zhang, Junjun Lv, Yujian Liu
Polymer Degradation and Stability 2012 Volume 97(Issue 4) pp:626-631
Publication Date(Web):April 2012
DOI:10.1016/j.polymdegradstab.2012.01.005
A novel bismaleimide monomer 2,2′-Bis[4-(4-maleimidophenoxy)phenyl]-hexafluoropropane(BAPOFP-BMI) was prepared by using maleic anhydride and 2,2′-bis(4-(4-amino- phenoxy)phenyl)hexafluoropropane, with toluene and N,N′-Dimethylformamide as the solvents. The monomer was characterized by means of FT-IR spectra, 1H NMR, MS and element analysis. The result of HPLC shows that the purity of BAPOFP-BMI is 97.4%, melting point of BAPOFP-BMI is 153.2 °C and curing exothermic peak is 290 °C, which means that BAPOFP-BMI has a relatively wider processing window. Moreover, BAPOFP-BMI has better solublility in a variety of organic solvents. Further experiments indicate that BAPOFP-BMI has better dielectric properties and thermal performance compared with o-diallyl-bisphenol-A-modified N,N′-(4,4′-diphenylmethane) bismaleimide (MDA-BMI/DABPA), too.
Co-reporter:Zhang Yan;Liu Yujian;He Qi ;Han Zhewen
Journal of Applied Polymer Science 2008 Volume 108( Issue 5) pp:3009-3015
Publication Date(Web):
DOI:10.1002/app.27776
Abstract
The research indicates that in comparison with other solvents, such as ethanol, propanol, butyl alcohol and acetone, which are usually selected as the solvent in phenolic solution, methanol can increase curing rate and enhance crosslinking density of phenolic resins. Therefore, the chain conformations of resole dissolved in different solvents are investigated by using viscosity method. It shows that the chain conformation of resoles changes from loose coil to compact ball, as the strength of hydrogen bond between resole and solvent drops along with the decrease of polarity of solvents. The transition of the chain conformation causes the decrease of reaction probability and reaction rate between functional groups of resoles. The number of unreacted molecules increases, and the crosslinking density of cured resins decreases. The differential scanning calorimetric analysis shows that compared with the resins in methanol, ethanol, propanol, and butyl alcohol, exothermic peak of resole in acetone is obviously wider, and its peak exothermic temperature is lower. Both optical microscope pictures and atomic force microscope pictures demonstrate that the crosslinking density of resins in methanol is higher than those in other solvents. The research concludes that the type of solvent has a great influence on the curing rate and curing degree of resoles. © 2008 Wiley Periodicals, Inc. JAppl Polym Sci, 2008
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