Magnetic nanoparticle clusters (MNCs) are a class of secondary structural materials that comprise chemically defined nanoparticles assembled into clusters of defined size. Herein, MNCs are fabricated ...through a one-pot solvothermal reaction featuring self-limiting assembly of building blocks and the controlled reorganization process. Such growth–dissolution–regrowth fabrication mechanism overcomes some limitations of conventional solvothermal fabrication methods with regard to restricted available feature size and structural complexity, which can be extended to other oxides (as long as one can be chelated by EDTA-2Na). Based on this method, the nanoparticle size of MNCs is tuned between 6.8 and 31.2 nm at a fixed cluster diameter of 120 nm, wherein the critical size for superparamagnetic–ferromagnetic transition is estimated from 13.5 to 15.7 nm. Control over the nature and secondary structure of MNCs gives an excellent model system to understand the nanoparticle size-dependent magnetic properties of MNCs. MNCs have potential applications in many different areas, while this work evaluates their cytotoxicity and Pb2+ adsorption capacity as initial application study.
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•A method was proposed to recover iron from BOF slag and enhance reactivity of the residue as supplementary cementitious materials.•Additives were optimized to recover iron from BOF ...slag and the recovery efficiency was more than 95%.•By replacing 30% mass of cement with residue, the compressive strength of the mortar can reach 52.3MPa.
In this study, a new method for recycling basic oxygen furnace (BOF) slag was proposed. An additive mixture containing kaolin and carbon powder was designed and mixed with BOF slag to induce the reduction of ferric oxides. Iron metal was then recovered from the BOF slag. The additives acted as a component regulator to improve the reactivity of the residue after recovering iron. The results showed that as the basicity of the mixture of BOF slag and additives decreased, the melting temperature of the mixture decreased, whereas the iron recovery efficiency was significantly improved. In fact, when the basicity ranged from 0.97 to 1.31, the iron recovery efficiency reached more than 95%. Additionally, decreasing the basicity of the mixture increased the viscosity of the melt and the extent of the glassy phase formed in the residue during water quenching The maximum percentage of the glassy phase in the residue could reach more than 95%. Accordingly, the reactivity index was high, indicating that the residue from the mixture of BOF slag and the additives after recovering iron can be used as an active supplementary cementitious material.
Mechanism of metal-insulator transition (MIT) in strained VO2 thin films is very complicated and incompletely understood despite three scenarios with potential explanations including electronic ...correlation (Mott mechanism), structural transformation (Peierls theory) and collaborative Mott-Peierls transition. Herein, we have decoupled coactions of structural and electronic phase transitions across the MIT by implementing epitaxial strain on 13-nm-thick (001)-VO2 films in comparison to thicker films. The structural evolution during MIT characterized by temperature-dependent synchrotron radiation high-resolution X-ray diffraction reciprocal space mapping and Raman spectroscopy suggested that the structural phase transition in the temperature range of vicinity of the MIT is suppressed by epitaxial strain. Furthermore, temperature-dependent Ultraviolet Photoelectron Spectroscopy (UPS) revealed the changes in electron occupancy near the Fermi energy EF of V 3d orbital, implying that the electronic transition triggers the MIT in the strained films. Thus the MIT in the bi-axially strained VO2 thin films should be only driven by electronic transition without assistance of structural phase transition. Density functional theoretical calculations further confirmed that the tetragonal phase across the MIT can be both in insulating and metallic states in the strained (001)-VO2/TiO2 thin films. This work offers a better understanding of the mechanism of MIT in the strained VO2 films.
To assess the effect of relative humidity (RH) on drying-induced damage in concrete, the non-uniform strains and microcracks in concrete under different RH conditions were obtained using the digital ...image correlation (DIC) technique and lattice fracture model. The simulated non-uniform displacements were consistent with those captured using DIC. A new damage index was proposed by considering all the subsets with equivalent strain larger than the threshold tensile strength. The calculated damage index showed good correlation with the microcracks' total area and indicated that RH equal or lower than 55% could cause relatively high cracking risk. This work provides an attractive method for quantifying drying-induced damage in concrete using the DIC technique.
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•Drying-induced damage patterns in concrete can be identified using the principal strains determined by the digital image correlation.•Damage index calculated from the principal strains is proportional to the total area of drying-induced microcracks in concrete.•Relative humidity equal or lower than 55% could lead to relatively large damage index and high cracking risk in concrete
Abstract
Designing efficient catalyst for the oxygen evolution reaction (OER) is of importance for energy conversion devices. The anionic redox allows formation of O-O bonds and offers higher OER ...activity than the conventional metal sites. Here, we successfully prepare LiNiO
2
with a dominant 3
d
8
L
configuration (
L
is a hole at O 2
p
) under high oxygen pressure, and achieve a double ligand holes 3
d
8
L
2
under OER since one electron removal occurs at O 2
p
orbitals for Ni
III
oxides. LiNiO
2
exhibits super-efficient OER activity among LiMO
2
,
R
MO
3
(M = transition metal,
R
= rare earth) and other unary 3d catalysts. Multiple in situ/operando spectroscopies reveal Ni
III
→Ni
IV
transition together with Li-removal during OER. Our theory indicates that Ni
IV
(3
d
8
L
2
) leads to direct O-O coupling between lattice oxygen and *O intermediates accelerating the OER activity. These findings highlight a new way to design the lattice oxygen redox with enough ligand holes created in OER process.
► The concentric expansion method is proposed to process the strip delineation. ► The overflow criterion is employed for pore segmentation. ► A typical excess of porosity is found in the vicinity of ...aggregate. ► The ITZ porosity differs as sand content.
The interfacial transition zone (ITZ) needs to be assessed since its excess of porosity could bring a negative impact on the overall material behavior. An intention of current research is to investigate porosity characteristics of ITZ in hardened Portland cement-based composites, by means of backscattered electron–scanning electron microscope (BSE–SEM). Emphasis is laid on presenting an elaborative illustration of image analysis with regard to ITZ porosity characteristic. Specifically, a new method named ‘concentric expansion’ is proposed to process the strip delineation for analyzing porosity profile from aggregate surface. The overflow criterion is employed to determine the upper threshold for pore segmentation. Such procedure was applied on two kinds of mortars with 10% and 50% sand volume fractions. Image analysis results indicated that a typical excess of porosity took place in the vicinity of aggregate for designed mortars, which is considered as a sign for ITZ in conventional cementitious composites. Furthermore, the average porosity level (36.32%) of ITZ in mortar with 10% sand content was higher than the value (21.37%) in mortar with 50% sand content. Such discrepancy came from varied effective water binder ratio and air content.
This study investigated the strength and toughness of reactive powder concrete (RPC) made with various steel fiber lengths and concrete strengths. The results indicated that among RPC samples with ...strength of 150 MPa, RPC reinforced with long steel fibers had the highest compressive strength, peak strength, and toughness. Among the RPC samples with strength of 270 MPa, RPC reinforced with short steel fibers had the highest compressive strength, and peak strength, while RPC reinforced with medium-length steel fibers had the highest toughness. As a result of the higher bond adhesion between fibers and ultra-high-strength RPC matrix, long steel fibers were more effective for the reinforcement of RPC with strength of 150 MPa, while short steel fibers were more effective for the reinforcement of RPC with strength of 270 MPa.
Both the discrete and continuous particle packing models are used to design UHPC, but the influences of a water film covering the particle surfaces on the compactness of the particle system were not ...considered in these models. In fact, the water film results in a certain distance between solid particles (DSP), which affects the compactness of the particle system, especially for cementitious materials with small particle sizes. In the present study, the mixture design method for UHPC was proposed based on the Fuller distribution model modified using the DSP. Then, the components of cementitious materials and aggregates were optimized, and the UHPC matrices with high solid concentrations were obtained. The results showed that the solid concentration, slump flow, and compressive strength of the UHPC matrix reached 77.1 vol.%, 810 mm, and 162.0 MPa, respectively. By replacing granulated blast furnace slag (GBFS) with quartz powder (QP), the flexural strength of the UHPC matrix was increased without reducing its compressive strength. When the steel fiber with a volume fraction of 1.5% was used, the slump flow, compressive strength, tensile strength, and flexural strength of the UHPC reached 740 mm, 175.6 MPa, 9.7 MPa, and 22.8 MPa, respectively. After 500 freeze-thaw cycles or 60 dry-wet cycles under sulfate erosion, the mechanical properties did not deteriorate. The chloride diffusion coefficients in UHPCs were lower than 3.0 × 10
m
/s, and the carbonation depth of each UHPC was 0 mm after carbonization for 28 days. The UHPCs presented ideal workability, mechanical properties, and durability, demonstrating the validity of the method proposed for UHPC design.
► The BSE image analysis with regard to ITZ is well implemented by two new algorithms. ► Local water binder ratio and water transport are two critical factors for the numerical simulation of ITZ. ► A ...typical higher porosity and lower anhydrous fraction is found in the vicinity of aggregate.
In this paper, some results are presented referring to experiment and simulation on the characterization of the ITZ microstructure in ternary blended cement based composites. The backscattered electron (BSE) imaging technique is used to acquire images in experiment. Image analysis is applied based on two new algorithms: concentric expansion for strip delineation and overflow criterion for phase segmentation. Besides, a continuum integrated model HYMOSTRUC has been extended to simulate the coupled aggregate-ITZ-bulk paste microstructure. In particular, local water binder ratio and water transport have been incorporated to account for variable hydration conditions of cementitious particles in ITZ and bulk paste. Results indicate that a good agreement has been reached between experiment and simulation. The proposed image processing procedure is well implemented in the ITZ analysis of ternary blended composites, while local water binder ratio and water transport are two critical factors for the simulation of ITZ. For the designed ternary blended mortar, ITZ has been well differentiated from bulk paste quantitatively, i.e., higher porosity and lower anhydrous fraction, whilst the capillary pore connectivity does not seem to be different between ITZ and bulk paste in the current simulation.
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