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Mechanism of shear strength deterioration of loess during freeze-thaw cycling
Xu, Jian,Wang, Zhangquan,Ren, Jianwei,Yuan, Jun Techno-Press 2018 Geomechanics & engineering Vol.14 No.4
Strength of loess that experienced cyclic freeze and thaw is of great significance for evaluating stability of slopes and foundations in loess regions. This paper takes the frequently encountered loess in the Northwestern China as the study object and carried out three kinds of laboratory tests including freeze-thaw test, direct shear test and SEM test to investigate the strength behaviors of loess after cyclic freeze and thaw, and the correlation with meso-level changes in soil structure. Results show that for loess specimens at four dry densities, the cohesion decreases with freeze-thaw cycles until a residual value is reached and thus an exponential equation is proposed. Besides, little change in the angle of internal friction was observed as freeze-thaw proceeds. This may depend on the varying of soil structure, based on which a clue can be found from the surface morphology and mesoscopic scanning of loess specimens. Clearly we observed significant changes in surface morphology of loess and it tends to aggravate at higher water contents or more cycles of freeze and thaw. Moreover, freeze-thaw cycling leads to obvious changes in the meso-structure of loess including lowering the particle aggregates and increasing both the proportion of fine particles and porosity area ratio. A damage variable dependent on the ratio of porosity area is introduced based on the continuum damage mechanics and its correlation with cohesion is discussed.
Xu, Jian,Cao, Lei,Feng, Yongyi,Huang, Yanlin,Wang, Yaorong,Qin, Lin,Seo, Hyo Jin Elsevier 2017 Journal of luminescence Vol.183 No.-
<P><B>Abstract</B></P> <P>In<SUB>2</SUB>Si<SUB>2</SUB>O<SUB>7</SUB> is a known indium-based scintillator with fast ultraviolet photoluminescence. Unfortunately the emission only can be detected below 200K. the poor thermal stability limits its application at room temperature. In this work, the luminescence improvement of In<SUB>2</SUB>Si<SUB>2</SUB>O<SUB>7</SUB> was realized by F<SUP>−</SUP>-ions doping in the lattices. The ceramic phosphors were via typical solid-state reaction method. The pure crystalline phase with thortveirite-type structure was confirmed by X-ray diffraction (XRD) Rietveld refinements. The photoluminescence (PL) emission and excitation spectra together with the luminescence thermal stability were tested. The fluorescence decay curves CIE emission Stokes shifts were measured. The ceramic samples could present blue luminescence with maximum wavelength at about 340nm under the excitation of UV light or high energy X-ray irradiation. The pure sample only presents luminescence below 200K, however, the F-doping can be greatly enhance the luminescence thermal stability. The F-doped In<SUB>2</SUB>Si<SUB>2</SUB>O<SUB>7</SUB> could present emission signals with fast decay lifetime of 850ns at room temperature. The luminescence transitions from the In<SUP>3+</SUP>-O<SUP>2−</SUP> charge transfer (CT) were discussed on the structure properties.</P>
Xu, Jian,Qin, Chuanxiang,Huang, Yanlin,Wang, Yaorong,Qin, Lin,Seo, Hyo Jin Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.396 No.-
<P><B>Abstract</B></P> <P>Pure and V<SUP>5+</SUP>-doped Bi<SUB>6</SUB>Mo<SUB>2</SUB>O<SUB>15</SUB> (3Bi<SUB>2</SUB>O<SUB>3</SUB>·2MoO<SUB>3</SUB>) photocatalysts were synthesized through electrospinning, followed by low-temperature heat treatment. The samples developed into nanoparticles with an average size of approximately 50nm. The crystalline phases were verified via X-ray powder diffraction measurements (XRD). The surface properties of the photocatalysts were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses. The UV–vis spectra showed that V doping in Bi<SUB>6</SUB>Mo<SUB>2</SUB>O<SUB>15</SUB> shifted the optical absorption from the UV region to the visible-light wavelength region. The energy of the band gap of Bi<SUB>6</SUB>Mo<SUB>2</SUB>O<SUB>15</SUB> was reduced by V doping in the lattices. The photocatalytic activities of the pure and V-doped Bi<SUB>6</SUB>Mo<SUB>2</SUB>O<SUB>15</SUB> were tested through photodegradation of rhodamine B (RhB) dye solutions under visible light irradiation. Results showed that 20 mol% V-doped Bi<SUB>6</SUB>Mo<SUB>2</SUB>O<SUB>15</SUB> achieved efficient photocatalytic ability. RhB could be degraded by V-doped Bi<SUB>6</SUB>Mo<SUB>2</SUB>O<SUB>15</SUB> in 2h. The photocatalytic activities and mechanisms were discussed according to the characteristics of the crystal structure and the results of EIS and XPS measurements.</P> <P><B>Highlights</B></P> <P> <UL> <LI> V<SUP>5+</SUP>-doped Bi<SUB>6</SUB>Mo<SUB>2</SUB>O<SUB>15</SUB> was synthesized by the electrospinning preparation. </LI> <LI> The band gap energy of Bi6Mo12O15 was greatly reduced by V-doping in the lattices. </LI> <LI> V-doped Bi<SUB>6</SUB>Mo<SUB>2</SUB>O<SUB>15</SUB> shows high activity in RhB degradation under visible light. </LI> <LI> Crystal structure of Bi<SUB>6</SUB>Mo<SUB>2</SUB>O<SUB>15</SUB> is favorable for high photocatalytic capacity. </LI> </UL> </P>