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The movement of the construction industry towards sustainable development has drawn attention to the revision of concrete. In addition to reducing pollution, the use of nano-materials should lead to the provision of higher quality concrete in terms of regulatory items (workability, resistance characteristics, durability characteristics, microstructure). The present study investigates 15 key characteristics of concrete modified with nano-CaCO3, nano-clay, nano-TiO2, and nano-SiO2. The results of the study showed that nanomaterials significantly have a positive effect on the hydration mechanism and the production of more C-S-H gel. The evaluation of resistance characteristics also indicates the promising results of these valuable materials. The durability characteristics of nano-containing concrete showed significant improvement despite high dispersion. Concrete in coastal areas (such as bridges or platforms), concrete exposed to radiation (such as hospitals), concrete exposed to impact load (such as nuclear power plants), and concrete containing recycled aggregate (such as bricks, tiles, ceramics) can be effectively improved by using nanomaterials. It is hoped that the current review paper can provide an effective image and idea for future applied studies by other researchers. [ABSTRACT FROM AUTHOR]

Normal mode decomposition of atomic vibrations has been used to provide microscopic understanding of thermal transport in amorphous solids for decades. In normal mode methods, it is naturally assumed that atoms vibrate around their equilibrium positions, and that individual normal modes are the fundamental vibrational excitations transporting heat. With the abundance of predictions from normal mode methods and experimental measurements now available, we carefully analyze these calculations in amorphous silicon, a model amorphous solid. We find a number of discrepancies, suggesting that treating individual normal modes as fundamental heat carriers may not be accurate in amorphous solids. Furthermore, our classical and ab initio molecular dynamics simulations of amorphous silicon demonstrate a large degree of atomic diffusion, especially at high temperatures, leading to the conclusion that thermal transport in amorphous solids could be better described starting from the perspectives of liquid physics rather than from crystalline solids. [ABSTRACT FROM AUTHOR]

Biochar is commonly used for soil amendment, due to its excellent water-holding capacity. The Cr(VI) contamination of water is a current environmental issue in industrial regions. Here, we evaluated the effects of two-step modifications on boosting biochar's performance in terms of the removal of aqueous hexavalent chromium (Cr(VI)), along with investigating the alterations to its surface properties. The first modification step was heat treatment under air at 300 °C, producing hydrophilic biochar (HBC). The resulting HBC was then impregnated with zero-valent iron nanoparticles (nZVI), creating an HBC/nZVI composite, adding a chemical reduction capability to the physical sorption mechanism. Unmodified biochar (BC), HBC, and HBC/nZVI were characterized for their physicochemical properties, including surface morphology and elemental composition, by SEM/EDS, while functional groups were ascertained by FTIR and surface charge by zeta potential. Cr(VI) removal kinetic studies revealed the four-time greater sorption capacity of HBC than BC. Although unmodified BC showed faster initial Cr(VI) uptake, it rapidly worsened and started desorption. After nZVI impregnation, the Cr(VI) removal rate of HBC increased by a factor of 10. FTIR analysis of biochars after Cr(VI) adsorption showed the presence of Cr(III) oxide only on the used HBC/nZVI and demonstrated that the carbonyl and carboxyl groups were the main groups involved in Cr(VI) sorption. Modified biochars could be considered an economical substitute for conventional methods. [ABSTRACT FROM AUTHOR]

Elastic properties of amorphous solids remain a topic of intense interest due to their important roles in a wide range of applications. Prior works have focused on short-range, local structural features, such as number density and coordination number, to elucidate the underlying mechanism of elastic moduli in glasses. Here, we report strong correlations among the spatial extension of the interatomic potential, elastic moduli, and the coherence lengths of the medium-range structural order through molecular dynamics simulations for single element glasses. Our findings demonstrate an unconventional design principle to engineer elastic properties by extending the medium-range order and provide insights into the microscopic origin of elastic properties in amorphous solids. [ABSTRACT FROM AUTHOR]

We review the status of research on thermal/phonon transport in disordered materials. The term disordered materials is used here to encompass both structural and compositional disorder. It includes structural deviations ranging from an ideal crystal with disordered arrangements of defects all the way to fully amorphous materials, as well as crystals with impurities up through multi-component random alloys. Both types of disorder affect phonons by breaking the symmetry of an idealized crystal and changing their character/mode shapes. These effects have important implications with regard to phonon–phonon interactions, phonon transport and phonon interactions with other quantum particles, which are being actively investigated. Herein, we synthesize the current theoretical understanding, identify the aspects of the problem that require more work, and pose open questions. Abbreviations: BTE: Boltzmann transport equation; DFT: Density functional theory; EPP: Eigenvector periodicity parameter; FAFDTR: Fiber-aligned frequency domain thermoreflectance; GK: Green–Kubo; GKMA: Green–Kubo modal analysis; HCACF: Heat current autocorrelation function; IXS: Inelastic X-ray scattering; LD: Lattice dynamics; LJ: Lennard–Jones; MD: Molecular dynamics; MFP: Mean free path; NEMD: Non-equilibrium molecular dynamics; NMD: Normal-mode dynamics; PDL: Propagon, diffuson, locon; PGM: Phonon gas model; PR: Participation ratio; SCLD: Supercell lattice dynamics; SED: Spectral energy density; TDTR: Time-domain thermoreflectance; VCA: Virtual crystal approximation; [ABSTRACT FROM AUTHOR]

Metallic glasses exhibit fast mechanical relaxations at temperatures well below the glass transition, one of which shows little variation with temperature known as nearly constant loss (NCL). Despite the important implications of this phenomenon to deformation, the origin of the relaxation is unclear. Through molecular dynamics simulations of a model metallic glass, C u 64.5 Z r 35.5 , we implement molecular dynamics dynamical mechanical spectroscopy (MD-DMS) with system stress decomposed into atomic-level stresses to identify the group of atoms responsible for NCL. This work demonstrates that NCL relaxation is due to transient groups of atoms that revert to the typical atomic-level viscoelastic behavior over picosecond timescales. They are homogenously distributed throughout the glass and have no outstanding features, rather than having defect-like local structure as previously reported. [Display omitted] [ABSTRACT FROM AUTHOR]

Concentrating solar power is becoming an increasingly important part of the renewable energy portfolio. However, further cost reduction is desired to make CSP competitive with traditional energy technologies. Higher operating temperature is considered an attractive avenue leading to higher power conversion efficiency and lower cost, but tremendous technical challenges exist with higher temperature operation of CSP, with one of the main issues being the lack of a high-performance solar absorbing material that is durable at 750 °C or above. In this work, a black oxide material, made of cobalt oxide nanoparticles, is synthesized and utilized as a high-temperature solar absorbing material. The nanoparticles are embedded in a dielectric matrix through a scalable spray coating process. The top layer of the coating is further improved with light-trapping structures using sacrificial fillers introduced from the same coating process. After the surface modification of cobalt oxide coating, we achieved a high thermal efficiency of 88.2%. More importantly, the coating shows no degradation after 1000-h annealing at 750 °C in air, while the existing commercial light absorbing coating was reported to degrade by long-term exposure at high temperature. Our findings suggest that the materials and processes developed here are promising for solar absorbing coating for future high-temperature CSP systems. [ABSTRACT FROM AUTHOR]

Partially stabilized zirconia (PSZ) is an attractive material for thermal barrier coatings. Zirconia exists in three crystallographic phases: cubic, tetragonal and monoclinic. In particular, the phase transformation of tetragonal to monoclinic is accompanied by significant volume expansion, so this transition generally results in cracking and contributes to the failure of the TBC system. Both plasma-sprayed ZrO2–8Y2O3 (YSZ) and ZrO2–25CeO2–2.5Y2O3 (CYSZ) coatings were isothermally heat-treated at 1300 and 1500 °C for 100 h and cooled at four different cooling rates. The monoclinic phase was not evident in all CYSZ samples annealed at 1300 and 1500 °C. In the 1500 °C heat-treated specimens, YSZ contains some monoclinic phase, while none exists in the 1300 °C heat-treated YSZ coating. The difference in phase transformation behavior between YSZ and CYSZ results from the degree of stabilization of the initial composition and the various cation radii. For YSZ, the different phase transformation behavior at the two temperatures is due to the stabilizing concentration of high-temperature phases and grain growth. For YSZ annealed at 1500 °C for 100 h, the amount of monoclinic phase increased with the slower cooling rate. High oxygen vacancy, formed during high-temperature holding, remained at room temperature due to a fast cooling rate. The extra oxygen vacancy at room temperature displaces an oxygen ion from the equilibrium position in the tetragonal phase and functions as a cubic stabilizer, so the tetragonal–monoclinic transformation is suppressed. [Copyright &y& Elsevier]

Customized engineered fibers are currently being used extensively in the aerospace and automobile industries due to the ability to 'design in' specific engineering characteristics. Understanding the thermal conductivity of these new fibers is critical for thermal management and design optimization. In the current investigation, a steady-state dc thermal bridge method (DCTBM) is developed to measure the thermal conductivity of individual poly(ether ketone) (PEK)/carbon nanotube (CNT) fibers. For non-conductive fibers, a thin platinum layer was deposited on the test articles to serve as the heater and temperature sensor. The effect of the platinum layer on the thermal conductivity is presented and discussed. DCTBM is first validated using gold and platinum wires (25 μm in diameter) over a temperature ranging from room temperature to 400 K with ±11% uncertainty, and then applied to PEK/CNT fibers with diverse CNT loadings. At a 28 wt. % CNT loading, the thermal conductivity of fibers at 390 K is over 27 Wm-1K-1, which is comparable to some engineering alloys. [ABSTRACT FROM AUTHOR]

The thermal atomic vibrations of amorphous solids can be distinguished by whether they propagate as elastic waves or do not propagate due to lack of atomic periodicity. In a -Si, prior works concluded that nonpropagating waves are the dominant contributors to heat transport, with propagating waves being restricted to frequencies less than a few THz and scattered by anharmonicity. Here, we present a lattice and molecular dynamics analysis of vibrations in a -Si that supports a qualitatively different picture in which propagating elastic waves dominate the thermal conduction and are scattered by local fluctuations of elastic modulus rather than anharmonicity. We explicitly demonstrate the propagating nature of waves up to around 10 THz, and further show that pseudoperiodic structures with homogeneous elastic properties exhibit a marked temperature dependence characteristic of anharmonic interactions. Our work suggests that most heat is carried by propagating elastic waves in a -Si and demonstrates that manipulating local elastic modulus variations is a promising route to realize amorphous materials with extreme thermal properties. [ABSTRACT FROM AUTHOR]

Concentrated Solar Power (CSP), a promising renewable energy technology, involves methods to concentrate the sun's energy onto receiver systems that generate steam, activate turbines, and consequently generate electrical power. To ensure CSP technologies remain cost-competitive, absorber coatings on CSP receiver systems require performance enhancements for increasing solar-thermal energy conversion efficiency. In this work, black metal-oxide nanoparticles comprising copper-cobalt oxides ( Cu x Co 3 − x O 4 ) and copper-manganese oxides ( Cu x Mn 3 − x O 4 ) are synthesized for solar absorptive potential by hydrothermal syntheses – selected for low-cost, energy-efficient fabrication capable for bulk manufacturability. The material is deposited onto high-temperature, durable Inconel substrates by a flexible spray-coating method, and characterization is performed by Scanning Electron Microscopy (SEM), Energy-Dispersive X-Ray Spectroscopy (EDS), and X-Ray Powder Diffraction (XRD) analyses, as well as measurements to gauge thermal performance. High temperature stability of a model solar receiver surface using these synthesized materials are assessed by comparing spectral reflectance and a figure-of-merit efficiency metric before and after high temperature exposure beyond 1000 h. To extend spectrally-selective absorbance capability, the coating surfaces are geometrically-textured using sacrificial polymer beads that are jointly implemented in the spray-coating process. This study ultimately showcases materials produced with high figure-of-merit conversion efficiency, demonstrating solar absorber coatings capable of interfacing with next-generation CSP receiver systems. [ABSTRACT FROM AUTHOR]

• pNDA reduction susceptibility was investigated for the first time using nZVI/SBA-15. • nZVI/SBA-15 synthesis was optimized for the greatest pNDA bleaching efficiency. • FTIR showed differences in pNDA molecules bleached in low and high DO solutions. • pNDA bleached significantly faster under the reduction-favored conditions. • Results implied that pNDA is not a fully selective ●OH compound. Use of p -nitroso dimethylaniline (pNDA) as a selective hydroxyl radical (OH) probe compound has been extensively reported in the literature for evaluating the performance of the catalysts used in Advanced Oxidation Processes (AOPs). Some recent studies speculated that pNDA might be oxidized by other oxidizing species, and might also be directly reduced. This study, for the first time, investigates pNDA bleaching mechanism by an Fe0-containing composite, capable of causing both reduction and Fenton-like oxidation. The composite consisted of Santa Barbara-15 (SBA-15) mesoporous silica as the supporting medium for nZVI immobilization (nZVI/SBA-15). The quantity of iron in the composite was optimized by synthesizing four various nZVI/SBA-15 samples with different iron to silica weight ratios and comparing their pNDA bleaching efficiency. Kinetic studies showed a pseudo-second-order model for pNDA bleaching using all nZVI/SBA-15 samples. The effects of OH scavengers and dissolved oxygen concentration on pNDA bleaching rate were examined. FTIR analysis of pNDA solutions showed different molecular structures for pNDA bleached under different DO conditions, leading to the conclusion that pNDA is susceptible to reductive bleaching. Results demonstrated that when using pNDA as a probe for free radicals' generation assessment, the reductive potential of the catalysts needs to be considered. [ABSTRACT FROM AUTHOR]

Developing microscopic understanding of the thermal properties of liquids is challenging due to their strong dynamic disorder, which prevents characterization of the atomic degrees of freedom. There have been significant research interests in the past few decades to extend the normal mode analysis for solids to instantaneous structures of liquids. However, the nature of normal modes that arise from these unstable structures is still elusive. In this paper, we explore the instantaneous eigenmodes of dynamical matrices of various Lennard-Jones argon liquid and gas systems at high temperatures and show that the normal modes can be interpreted as an interpolation of T→∞ (gas) and T=0 (solid) mode descriptions. We find that normal modes become increasingly collisional and translational, recovering atomistic gaslike behavior rather than vibrational with increase in temperature, suggesting that normal modes in liquids may be described by both solidlike and gaslike modes.

Flexible thermoelectric (TE) materials, which are devices that convert thermal gradients to electrical energy, have attracted interest for practical energy-harvesting/recovery applications. However, as compared with p-type materials, the progress on the development of n-type TE flexible materials has been slow due to difficulties involved in n-type doping techniques. This study used high mobility carbon nanotubes (CNTs) to a uniformly mixed hybrid-composite, resulting in an enhanced power factor by increasing electrical conductivity. The energy filtering effect and stoichiometric composition of the material used, bismuth telluride (Bi 2 Te 3 ) correlated to a significant enhancement in TE performance, with a power factor of 225.9 μW m -1 K -2 at room temperature: a factor of 65 higher than as-fabricated composite film. This paper describes a simplified synthesis for the preparation of the composite film that eliminates time-intensive and cost-prohibitive processing, traditionally seen during extrusion and dicing inorganic manufacturing. The resulting post-annealed composite film consisting of Bi 2 Te 3 nanowire and CNTs demonstrate a promising candidate for material that can be used for an n-type TE device that has improved energy conversion efficiency.

Thermal transport in multilayers (MLs) has attracted significant interest and shows promising applications. Unlike their single-component counterparts, MLs exhibit a thermal conductivity that can be effectively engineered by both the number density of the layers and the interfacial thermal resistance between layers, with the latter being highly tunable via the contrast of acoustic properties of each layer. In this work, we experimentally demonstrated an ultralow thermal conductivity of 0.33 ± 0.04 W m(-1) K(-1) at room temperature in MLs made of Au and Si with a high interfacial density of ∼0.2 interface nm(-1). The measured thermal conductivity is significantly lower than the amorphous limit of either Si or Au and is also much lower than previously measured MLs with a similar interfacial density. With a Debye temperature ratio of ∼3.9 for Au and Si, the Au/Si MLs represent the highest mismatched system in inorganic MLs measured to date. In addition, we explore the prior theoretical prediction that full phonon dispersion could better model the interfacial thermal resistance involving materials with low Debye temperatures. Our results demonstrate that MLs with highly dissimilar Debye temperatures represent a rational approach to achieve ultralow thermal conductivity in inorganic materials and can also serve as a platform for investigating interfacial thermal transport.

We experimentally studied the thermoelectric power factor of hole gas in individual Ge-Si core-shell nanowires with Ge core diameters ranging from 11 to 25 nm. The Ge cores are dopant-free, but the Fermi level in the cores is pinned by surface and defect states in the epitaxial Si shell thereby doping the cores into the degenerate regime. This doping mechanism avoids the high concentration of dopants usually encountered in bulk thermoelectric materials and provides a unique opportunity to enhance the carrier mobility with suppressed ionized impurity scattering. Moreover, the carrier concentration in small diameter nanowires has also been effectively modulated by field effect, allowing one to probe the electrical conductivity and thermopower within a wide range of carrier concentrations, which is crucial to understand the thermoelectric transport behavior. We found that the thermopower of nanowires with Ge core diameters down to 11 nm still follows the behavior of bulk Ge. As a result, the power factor is found to be closely correlated with the carrier mobility, which is higher than that of bulk Ge in one of the core-shell nanowires studied here.

Heterostructure core-shell semiconductor nanowires (NWs) have attracted tremendous interest recently due to their remarkable properties and potential applications as building blocks for nanodevices. Among their unique traits, thermal properties would play a significant role in thermal management of future heterostructure NW-based nanoelectronics, nanophotonics, and energy conversion devices, yet have been explored much less than others. Similar to their electronic counterparts, phonon spectrum and thermal transport properties could be modified by confinement effects and the acoustic mismatch at the core-shell interface in small diameter NWs (<20 nm). However, fundamental thermal measurement on thin core shell NWs has been challenging due to their small size and their expected low thermal conductivity (κ). Herein, we have developed an experimental technique with drastically improved sensitivity capable of measuring thermal conductance values down to ∼10 pW/K. Thermal conductivities of Ge and Ge-Si core-shell NWs with diameters less than 20 nm have been measured. Comparing the experimental data with Boltzmann transport models reveals that thermal conductivities of the sub-20 nm diameter NWs are further suppressed by the phonon confinement effect beyond the diffusive boundary scattering limit. Interestingly, core-shell NWs exhibit different temperature dependence in κ and show a lower κ from 300 to 388 K compared to Ge NWs, indicating the important effect of the core-shell interface on phonon transport, consistent with recent molecular dynamics studies. Our results could open up applications of Ge-Si core shell NWs for nanostructured thermoelectrics, as well as a new realm of tuning thermal conductivity by "phononic engineering".