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Room temperature ferromagnetic behavior in the nanocrystals of Fe doped ZnO synthesized by soft chemical route

Abstract

In the present study, nanocrystalline undoped and Fe (5 wt.%) doped ZnO powder has been synthesized by soft chemical route. The structural, nano/microstructural, vibrational and magnetic properties of these samples have been studied as a function of calcination temperature (400 °C to 1100 °C). X-ray diffraction analysis of Fe doped ZnO powder has shown the major nanocrystalline wurtzite (ZnO) phase and the minor cubic spinel-like secondary nanocrystalline phase at 700 °C. At calcination temperature of 700 °C, the magnetization and coercivity have been enhanced in Fe doped ZnO. As the calcination temperature increased to 1100 °C, the major phase of ZnO and minor cubic spinel-like secondary phase turned into bulk in doped ZnO. Interestingly, the reduced magnetization and zero coercivity have been observed in this case. These changes are attributed to the conversion of secondary nanocrystalline ferromagnetic spinel phase to its bulk paramagnetic phase. The degree of inversion i.e. the occupancy of both sites with different symmetry by ferric ions is proposed to be solely responsible for the unusual behavior.

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Synthesis of new mesostructured cellular foams (MCFs) with NaY zeolite and their application to sorption of thorium ions

Abstract

The paper presents the new way of preparation of MCF foams with NaY zeolite. Significant changes in the amount of micro and mesopores in relation to the amount of NaY zeolite and 1,3,5-trimethylbenzene (TMB) added during the synthesis was observed. It suggests the possibility of controlling the micro/mesopores ratio by applying the proposed method. Environmental aspects of using new MCF/NaY foams is related to the adsorption of thorium ions (Th+4). The term of “MCF/NaY materials” refers to the general name of the material without referring to the content and state of zeolite. The obtained materials were highly effective in relation to Th+4. The adsorption capacity was greater when the number of micropores was lower. The dependence of adsorption capacity of Th+4 ions on aluminum atoms content was also confirmed.

Open access
Synthesis of single-crystalline Pb(Zr0.52Ti0.48)O3 nanocrystals by hydrothermal method

Abstract

PbZr0.52Ti0.48O3 nanocrystals were synthesized by a hydrothermal method. The effect of NaOH concentration, reaction temperature and time on nucleation and growth of PbZr0.52Ti0.48O3 nanocrystals was investigated. As the 0.05 mol/L PbZr0.52Ti0.48O3 precursors were heated at 200 °C for 21 h with NaOH concentration of 0.5 mol/L, the tetragonal PbZr0.52Ti0.48O3 nanocrystals were formed, and the grain size was more than 20 nm. With increasing the NaOH concentration from 0.5 to 1.5 mol/L, the grain size of PbZr0.52Ti0.48O3 nanocrystals decreased. When the precursors were heated at different temperatures (140 °C to 200 °C) for 21 h with 1.0 mol/L NaOH, single-phase PbZr0.52Ti0.48O3 nanocrystals were obtained at 160 °C to 200 °C. With increasing the reaction temperature from 160 °C to 200 °C, the grains size of PbZr0.52Ti0.48O3 nanocrystals increased from 5 nm to 9 nm. When the precursors were heated at 160 °C in different reaction times from 6 h to 21 h, the evolution from amorphous to crystalline PbZr0.52Ti0.48O3 nanocrystals in correlation with the reaction time was observed. Single crystalline PbZr0.52Ti0.48O3 nanocrystals with narrow size distribution (from 5 nm to 9 nm) were synthesized by controlling the NaOH concentration, reaction temperature and time. The obtained results can find potential application in preparing PbZr0.52Ti0.48O3 thin films on flexible substrates.

Open access
Analysis of crack propagation in a “pull-out” test

Abstract

The article describes a computer analysis of the pull-out test used to calculate the force needed to pull out a rock fragment and determine the shape of this broken fragment. The analyzed material is sandstone and porphyry. The analysis included the first approach to using own subroutine in the Simulia Abaqus system, that is, which task is undertaken to accurately determine the crack path of the Finite Element Method model. The work also contains a description of laboratory tests and analytical considerations.

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Effect of randomly distributed polypropylene fiber reinforcement on the shear behavior of sandy soil

Abstract

The inclusions of geosynthetic materials (fibers, geomembranes and geotextiles) is a new improvement technique that ensures uniformity in the soil during construction. The use of tension resisting discreet inclusions like polypropylene fibers has attracted a significant amount of attention these past years in the improvement of soil performance in a cost-efficient manner. A series of direct shear box tests were conducted on unreinforced and reinforced Chlef sand with different contents of fibers (0, 0.25, 0.5 and0.75%) in order to study the mechanical behavior of sand reinforced with polypropylene fibers. Samples were prepared at three different relative densities 30%, 50% and 80% representing loose, medium dense and dense states,respectively, and performed at normal stresses of 50, 100 and 200 kPa. The experimental results show that the mechanical characteristics are improved with the addition of polypropylene fibers. The inclusion of randomly distributed fibers has a significant effect on the shear strength and dilation of sandy soil. The increase in strength is a function of fiber content, where it has been shown that the mechanical characteristics improve with the increase in fiber content up to 0.75%, this improvement is more significant at a higher normal stress and relative density.

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Effect of settlement of foundations on the failure risk of the bottom of cylindrical steel vertical tanks for liquids

Abstract

Different types of foundations are used in steel, above-ground cylindrical storage tanks for liquids. If a sand-gravel foundation is used under the entire bottom of the tank or only in the central part of the tank, settlement can be expected, and it increases after many years of operation. The paper presents the typical kinds and types of soil settlements under the bottoms of the tanks, in which different types of foundations were used. Numerical analyses of the effect of the soil settlement on the state of deformations and stresses in steel sheets of the bottom under one of the real tanks, in which different types of foundations and different cases of settlement were assumed. The results of numerical analyses indicated the possibility of evaluating the state of the soil settlement and bottom sheet deformations on the basis of simple measurements of deformations of the lower part of the tank cylinder. These measurements can be very useful in assessing the possible risk of failure of the tank bottom during each period of its operation, as measurements of settlement of the bottom of a filled tank are not feasible in practice. It has been proposed that in each steel tank, the deformation of the cylinder’s sheets should be measured even before the beginning of exploitation, and that in subsequent periodical measurements, the influence of the soil settlement under the tank on the state of the cylinder deformation and bottom’s strain should be assessed more accurately.

Open access
Effective Friction Angle Of Deltaic Soils In The Vistula Marshlands

Abstract

This article presents the results of laboratory tests on soft, normally consolidated soils from the Vistula Marshlands. Samples of high-plasticity organic soils (muds) taken from 3.2–4.0 m and 9.5–10.0 m depth, as well as peat deposit at 14.0 m, are analysed. Presented case study confirms the applicability of the Norwegian Institute of Technology (NTH) method based on Cone Penetration Tests (CPTU) and allows for a conservative estimation of effective friction angle for muds. The plastification angle equal to 14.5° for organic silt, applied in the modified NTH method, fits well the triaxial test (TX) results. Moreover, the dilative-contractive behaviour according to the CPTU soil classification based on the Robertson’s proposal from 2016 corresponds well with volumetric changes observed in the consolidated drained triaxial compression tests. The internal friction angles of the Vistula Marshlands’ muds and peats are lower in comparison with the database of similar soft soils.

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Penetrative convection due to absorption of radiation in a magnetic nanofluid saturated porous layer

Abstract

The present study investigates the onset of penetrative convection in- duced by selective absorption of radiation in a magnetic nanofluid saturated porous medium. The influence of Brownian motion, thermophoresis, and magnetophoresis on magnetic nanofluid treatment is taken into consideration. The Darcy’s model is selected for the porous medium. We conduct a linear stability analysis to examine the onset of instability and evaluate the results for two different configurations, namely, when the layer is heated from below and when the layer is heated from above. The numerical investigations are carried out by applying the Chebyshev pseudospectral method. The effect of the porosity parameter E, parameter Y (represents the ratio of internal heating to boundary heating), Lewis number Le, concentration Rayleigh number Rn, Langevin parameter αL, width of nanofluid layer d, diffusivity ratio η, and modified diffusivity ratio NA is examined at the onset of convection. The results indicate that the convection commences easily with an increase in the value of Y, Le, and NA but opposite in the case with a decrease in the value of E, αL, η and d for both the two configurations. The parameter Rn advances the onset of convection when the layer is heated from below, while delays the onset of convection when the layer is heated from above.

Open access
Slurry shield tunneling in soft ground. Comparison between field data and 3D numerical simulation

Abstract

In urban areas, the control of ground surface settlement is an important issue during shield tunnel-boring machine (TBM) tunneling. These ground movements are affected by many machine control parameters. In this article, a finite difference (FD) model is developed using Itasca FLAC-3D to numerically simulate the whole process of shield TBM tunneling. The model simulates important components of the mechanized excavation process including slurry pressure on the excavation face, shield conicity, installation of segmental lining, grout injection in the annular void, and grout consolidation. The analysis results from the proposed method are compared and discussed in terms of ground movements (both vertical and horizontal) with field measurements data. The results reveal that the proposed 3D simulation is sufficient and can reasonably reproduce all the operations achieved by the TBM. In fact, the results show that the TBM parameters can be controlled to have acceptable levels of surface settlement. In particular, it seems that moderate face pressure can reduce ground movement significantly and, most importantly, can prevent the occurrence of face-expected instability when the shield crosses very weak soil layers. The shield conicity has also an important effect on ground surface settlement, which can be partly compensated by the grout pressure during tail grouting. Finally, the injection pressure at the rear of the shield significantly reduces the vertical displacements at the crown of the tunnel and, therefore, reduces the settlement at the ground surface.

Open access
Investigation of the structural, optical and photoluminescence properties of electrosynthesized hexagonal nanocrystalline Cd0.3Zn0.7S thin film

Abstract

In this paper, Cd0.3Zn0.7S thin film has been electrodeposited from aqueous bath containing CdSO4, ZnSO4, Na2S2O3 and EDTA, having pH ~ 14. The structural, optical, morphological, surface wettability and photoluminescence properties of the film were investigated. The XRD pattern showed that the film consisted of mixed phases of CdS and ZnS with polycrystalline structure. The bandgap of the film was evaluated as 2.69 eV. The AFM study revealed that the Cd0.3Zn0.7S thin film contained spherical grains with root mean square roughness of 6.09 nm. The water contact angle measurement showed that the thin film was hydrophilic in nature. Moreover, the PL study revealed that the excitation wavelength was 460 nm.

Open access