Preparation and Characterization of Sandwich Structured Materials with Interesting Insulation and Fire Resistance

A cellular material in the form of 3-layered sandwich structure material was prepared via sole use of mechanical stirring without any use of a foaming agent,while Tween-80 was employed as a foam stabilizer via a developed in-situ mold casting.The resulting structure displayed a good appearance with no visual defects.The 3-layered composition of the sandwish structure,“nonporous resin layer-porous foam layer-nonporous resin layer”,was examined in terms of the microstructure,density&density distribution,pulverization ratio,mechanical strength,insulation and flame retardant performance.It was indicated from the results that the bonding between the resin layer and foam layer was tight,while the tensile rupture always occurred in the porous layer.Also,the density of the sandwich structure material was symmetrical with“saddle”distribution,and a uniform density for any given layer.The increase in the density at the interface layer provided a good interpretation for the tensile rupture never occurred at the interface.The brittleness resistance of the developed material was significantly improved,and the pulverization ratio was sharply decreased from 9.93%to 0.31%.The material acquired a thermal conductivity and limiting oxygen index(LOI)of 0.0241 W/m⋅K and 29.92%,respectively,indicating potential use of such materials broadly in fields of insulation and flame retardancy.

Topological edge states and electronic structures of a 2D topological insulator: Single-bilayer Bi (111)

Providing the strong spin-orbital interaction, Bismuth is the key element in the family of three-dimensional topological insulators. At the same time, Bismuth itself also has very unusual behavior, existing from the thinnest unit to bulk crystals. Ultrathin Bi （111） bilayers have been theoretically proposed as a two-dimensional topological insulator. The related experimental realization achieved only recently, by growing Bi （111） ultrathin bilayers on topological insulator Bi2Te3 or Bi2Se3 substrates. In this review, we started from the growth mode of Bi （111） bilayers and reviewed our recent progress in the studies of the electronic structures and the one-dimensional topological edge states using scanning tunneling microscopy/spectroscopy （STM/STS）, angle-resolved photoemission spectroscopy （ARPES）, and first principles calculations.

Electronic structure of correlated topological insulator candidate YbB6 studied by photoemission and quantum oscillation

Angle-resolved photoemission spectroscopy(ARPES)and torque magnetometry(TM)measurements have been carried out to study the electronic structures of a correlated topological insulator(TI)candidate Yb B6.We observed clear surface states on the[001]surface centered at theГ^- and М^- points of the surface Brillouin zone.Interestingly,the fermiology revealed by the quantum oscillation of TM measurements agrees excellently with ARPES measurements.Moreover,the band structures we observed suggest that the band inversion in Yb B6 happens between the Yb5 dand B2bands,instead of the Yb5dand Yb4fbands as suggested by previous theoretical investigation,which will help settle the heavy debate regarding the topological nature of samarium/ytterbium hexaborides.

Plasmonic Mach-Zehnder interferometric sensor based on a metal-insulator-metal nanostructure

A plasmonic Mach-Zehnder interferometric sensor based on a semicircular aperture-slit nanostructure patterned on a metal-insulator-metal film is proposed and demonstrated by finite difference time domain（FDTD） simulation. Due to the interference between two different surface plasmon polariton modes in this design, the transmission spectra exhibit oscillation behaviors in a broad bandwidth, and can be readily tailored by changing the SPP path length and core layer thickness. Based on this principle, the characteristics of refractive index sensing are also demonstrated by simulation. This structure is illuminated with a collimated light source from the back side to avoid impacts on the interference. Meanwhile,these results show that the proposed structure is promising for portable, efficient, and sensitive biosensing applications.

Temperature-dependent dielectric properties of Au/Si_3N_4/n-Si (metal insulator semiconductor) structures

The dielectric properties of Au/Si3N4/n-Si （MIS） structures are studied using the admittance measurements （C–V and G/ω–V） each as a function of temperature in a range from 80 K to 400 K for two frequencies （100 kHz and 1 MHz）. Experimental results show that both the dielectric constant （ε’） and the dielectric loss （ε＂） increase with temperature increasing and decrease with frequency increasing. The measurements also show that the ac conductivity （σac） increases with temperature and frequency increasing. The lnσac versus 1000/T plot shows two linear regions with different slopes which correspond to low （120 K–240 K） and high （280 K–400 K） temperature ranges for the two frequencies. It is found that activation energy increases with frequency and temperature increasing.

Analysis of the Molecules Structure and Vertical Electron Affinity of Organic Gas Impact on Electric Strength

It is necessary to find an efficient selection method to pre-analyze the gas electric strength from the perspective of molecule structure and the properties for finding the alternative gases to sulphur hexafluoride （SF6）. As the properties of gas are determined by the gas molecule structure, the research on the relationship between the gas molecule structure and the electric strength can contribute to the gas pre-screening and new gas development. In this paper, we calculated the vertical electron affinity, molecule orbits distribution and orbits energy of gas molecules by the means of density functional theory （DFT） for the typical structures of organic gases and compared their electric strengths. By this method, we find part of the key properties of the molecule which are related to the electric strength, including the vertical electron affinity, the lowest unoccupied molecule orbit （LUMO） energy, molecule orbits distribution and negativeion system energy. We also listed some molecule groups such as unsaturated carbons double bonds （C=C） and carbonitrile bonds （C=N） which have high electric strength theoretically by this method.

Symplectic analysis for elastic wave propagation in two-dimensional cellular structures

On the basis of the finite element analysis, the elastic wave propagation in cellular structures is investigated using the symplectic algorithm. The variation principle is first applied to obtain the dual variables and the wave propagation problem is then transformed into two-dimensional （2D） symplectic eigenvalue problems, where the extended Wittrick-Williams algorithm is used to ensure that no phase propagation eigenvalues are missed during computation. Three typical cellular structures, square, triangle and hexagon, are introduced to illustrate the unique feature of the symplectic algorithm in higher-frequency calculation, which is due to the conserved properties of the structure-preserving symplectic algorithm. On the basis of the dispersion relations and phase constant surface analysis, the band structure is shown to be insensitive to the material type at lower frequencies, however, much more related at higher frequencies. This paper also demonstrates how the boundary conditions adopted in the finite element modeling process and the structures＇ configurations affect the band structures. The hexagonal cells are demonstrated to be more efficient for sound insulation at higher frequencies, while the triangular cells are preferred at lower frequencies. No complete band gaps are observed for the square cells with fixed-end boundary conditions. The analysis of phase constant surfaces guides the design of 2D cellular structures where waves at certain frequencies do not propagate in specified directions. The findings from the present study will provide invaluable guidelines for the future application of cellular structures in sound insulation.

Effect of Fly Ash on Drying Shrinkage of Thermal Insulation Mortar with Glazed Hollow Beads

Drying shrinkage of thermal insulation mortar with glazed hollow beads was measured by a vertical length comparator, and the influences of fly ash with different contents（0, 18%, 36%, and 54% were used） on the long-term drying shrinkage were discussed. The mass loss was measured by the weighting method and the pore structure was characterized using three different methods, including the light microscopy, the mercury intrusion porosimetry（MIP）, and the nitrogen adsorption/desorption（NAD） experiments, and the correlations among them were researched. The results show that drying shrinkage process of thermal insulation mortar includes three steps with increasing curing time： the acceleration period（before 7 d）, the deceleration period（7-365 d）, and the metastable period（after 365 d）. Drying shrinkage in the first stage（7 d before） increases quickly owing to the fast water loss, and its development in the last two stages is attributed to the increment of the pore volume of mortar with the radius below 50 nm, especially the increment of the pore volume fraction of the pore radius within the size range between 7.3 nm and 12.3 nm. There is no change in the drying shrinkage development trend of mortar with fly ash addition, and three steps in the service life, but fly ash addition in the mortar restrains its value. There is a linear relationship between the drying shrinkage and fly ash content, which means that drying shrinkage reduces with fly ash addition.

Smart heat isolator with hollow multishelled structures

Safe, green and efficient industrial production has always been the pursuit of the chemical industry. Since thermal energy is the driving force for most of chemical reactions, an ideal reaction tank would have the capacity to automatically regulate heat conduction rate. In detail, this reaction tank should endow an ability that resists the heat loss when the reaction temperature is lower than the target, while accelerating the heat dissipation when the system is overheated. In this case, this smart reactor can not only minimize energy consumption but also reduce safety risks.Hollow structures are known to reduce heat conductivity. Particularly, the hollow structure with multishells can provide more interfaces and thus further inhibit heat transmission, which would be more favorable for heat isolation. Step forward, by coupling HoMSs with temperature-sensitive polymer, a smart heat isolation material has been fabricated in this work. It performs as a good heat isolator at a relatively lower temperature. A heat insulation effect of 6.5℃ can be achieved for the TSPU/3S–TiO_(2)HoMSs with a thickness of 1 mm under the temperature field of 50℃.The thermal conductivity of composite material would be raised under overheating conditions. Furthermore, this composite displays an unusual two-stage phase transformation during heating. Benefiting from the unique multishelled structure, energy is found to be gradually guided into the hollow structure and stored inside. This localized heat accumulation enables the composite to be a potential coating material for intelligent thermal-regulator and site-defined micro-reactor.

Optimization of Sound Absorption and Insulation Performances of a Dual-Cavity Resonant Micro-Perforated Plate

This study investigates a dual-cavity resonant composite sound-absorbing structure based on a micro-perforated plate.Using the COMSOL impedance tube model,the effects of various structural parameters on sound absorption and sound insulation performances are analyzed.Results show that the aperture of the micro-perforated plate has the greatest influence on the sound absorption coefficient;the smaller the aperture,the greater is this coefficient.The thickness of the resonance plate has the most significant influence on the sound insulation and resonance frequency;the greater the thickness,the wider the frequency domain in which sound insulation is obtained.In addition,the effect of filling the structural cavity with porous foam ceramics has been studied,and it has been found that the porosity and thickness of the porous material have a significant effect on the sound absorption coefficient and sound insulation,while the pore size exhibits a limited influence.

Crystal structures and electronic properties of solid fluorine under high pressure

As the previously proposed structures of C2/m and C2/c possess similar enthalpies and x-ray diffraction patterns, the space group of fluorine at ambient pressure is in controversy. We successfully obtain its thermodynamically stable lowpressure phase, which shares the same structure as the earlier known C2/c. Further investigations on phonon spectra reveal the instability of the C2/m structure with imaginary frequency in the Brillouin zone and confirm the dynamically stable property of the C2/c structure at the same time. Compressing fluorine up to 8 GPa, the C2/c phase is found to undergo a phase transition to a new structure with a space group of Cmca. Electronic energy band structures indicate the insulating feature of C2/c and Cmca with no bands across the Fermi level. The infrared（IR） and Raman spectra of C2/c and Cmca at selected pressures are calculated to provide useful information to future experiments.

In situ electronic structural study of VO_2 thin film across the metal–insulator transition

The in situ valence band photoemission spectrum （PES） and X-ray absorption spectrum （XAS） at V LⅡ-LⅢ edges of the VO2 thin film, which is prepared by pulsed laser deposition, are measured across the metal–insulator transition （MIT） temperature （TMIT=67 ℃）. The spectra show evidence for changes in the electronic structure depending on temperature. Across the TMIT, pure V 3d characteristic d‖ and O 2p-V 3d hybridization characteristic πpd, σpd bands vary in binding energy position and density of state distributions. The XAS reveals a temperature-dependent reversible energy shift at the V LⅢ-edge. The PES and XAS results imply a synergetic energy position shift of occupied valence bands and unoccupied conduction band states across the phase transition. A joint inspection of the PES and XAS results shows that the MIT is not a one-step process, instead it is a process in which a semiconductor phase appears as an intermediate state. The final metallic phase from insulating state is reached through insulator–semiconductor, semiconductor–metal processes, and vice versa. The conventional MIT at around the TMIT=67 ℃ is actually a semiconductor–insulator transformation point.

Numerical Simulation and Experimental Study of Underwater Compound Structures Containing Honeycomb Interlayer

Honeycomb interlayer structure sound wave transferring theory of infinite is introduced into the underwater noise control. Based on the layered elastic or viscoelastic medium, the sound insulation property of a normal incidence plane wave on underwater honeycomb interlayer structure is studied by using the method of the transfer matrix and percentage distribution of sound energy in As a particular kind of complex multilayered rubber compound structures, honeycomb different areas. compound structure has better sound insulation property than rubber interlayer with cylindrical cavities compound structure. Simulation results show that the property of rubber material has great effect on structural sound insulation. Soft and small Poisson＇ s ratio rubber can obviously improve sound insulation performance of the whole structure. Furthermore, the material property of the face layer of the honeycomb interlayer structure has greater effects on the insulation performance. To validate the theoretical analysis, large samples of freedom-field measurement of honeycomb sandwich compound structure is carried out in the anechoic water tank of our university. The measurement result is in good agreement with the theoretical prediction.

Recent Progress of Bionic Hierarchical Structure in the Field of Thermal Insulation Protection

Some living organisms with hierarchical structures in nature have received extensive attention in various fields.The hierarchical structure with multiple pores,a large number of solid-gas interfaces and tortuous conduction paths provide a new direction for the development of thermal insulation materials,making the living creatures under these extreme conditions become the bionic objects of scientific researchers.In this review,the research progress of bionic hierarchical structure in the field of heat insulation is highlighted.Polar bears,cocoons,penguin feathers and wool are typical examples of heat preservation hierarchy in nature to introduce their morphological characteristics.At the same time,the thermal insulation mechanism,fractal model and several preparation methods of bionic hierarchical structures are emphatically discussed.The application of hierarchical structures in various fields,especially in thermal insulation and infrared thermal stealth,is summarised.Finally,the hierarchical structure is prospected.

Tree‑Inspired Structurally Graded Aerogel with Synergistic Water,Salt,and Thermal Transport for High‑Salinity Solar‑Powered Evaporation

Solar-powered interfacial evaporation is an energy-efficient solution for water scarcity.It requires solar absorbers to facilitate upward water transport and limit the heat to the surface for efficient evaporation.Furthermore,downward salt ion transport is also desired to prevent salt accumulation.However,achieving simultaneously fast water uptake,downward salt transport,and heat localization is challenging due to highly coupled water,mass,and thermal transport.Here,we develop a structurally graded aerogel inspired by tree transport systems to collectively optimize water,salt,and thermal transport.The arched aerogel features root-like,fan-shaped microchannels for rapid water uptake and downward salt diffusion,and horizontally aligned pores near the surface for heat localization through maximizing solar absorption and minimizing conductive heat loss.These structural characteristics gave rise to consistent evaporation rates of 2.09 kg m^(-2) h^(-1) under one-sun illumination in a 3.5 wt%NaCl solution for 7 days without degradation.Even in a high-salinity solution of 20 wt%NaCl,the evaporation rates maintained stable at 1.94 kg m^(-2) h^(-1) for 8 h without salt crystal formation.This work offers a novel microstructural design to address the complex interplay of water,salt,and thermal transport.

A lightweight and high compressive resistance thermal insulation material with dual-network structure

Ceramic fibrous aerogels are highly desirable for thermal management materials due to their high porosity,excellent elasticity,thermal conductivity,and good thermal resistance.However,the fabrication of nanofibrous aerogel with super-elasticity and good shape retention at the same time has remained challenging.To meet the requirements,a novel anisotropy nanofibrous-granular aerogel with a quasi-layered multi-arch-like and hierarchical-cellular structure is designed and prepared by vacuum-filtration-assisted freeze-drying and sintering.The quasi-layered multi-arch and flexible nanofibers endowed the aerogels with excellent mechanical robustness(ultimate stress up to 60 kPa with strain 60%)and super-elasticity with recoverable compression strain up to 60%.The introduced SiO_(2) aerogel nanoparticles and nanofibers are assembled into an arch-like structure and become the connection point of adjacent nanofibers,which endows low thermal conductivity(0.024 mW/(m·K))of composite aerogel.This novel strategy provides a fresh perspective for the preparation of nanofibrous aerogel with robust mechanical in thermal insulation and other fields.

MOISTURE AND FLEXURAL BEHAVIOUR OF HEMP MAT FOAM STRUCTURAL INSULATED PANEL SPECIMENS

The use of structural insulated panels(SIPs)for wall and roof assemblies in residential and commercial buildings is a well-known construction technique.SIPs typically use a combination of either expanded polystyrene foam(EPS)or polyurethane foam(PUR)as the core material.The covering or skin is predominantly oriented strand board(OSB).The OSB is either bonded to the foam with adhesive in the case of EPS,while polyurethane is used to provide adhesion with PUR SIPs.This paper presents the results of research that investigated the use of industrial hemp mat used as a skin for soy-based polyurethane foam panels.A series of tests were conducted to investigate moisture resistance and flexural behaviour on hemp mat foam panels.Moisture absorption behaviour was evaluated on three specimen types:uncoated,earth plaster and tung oil treated hemp mat.The absorption coefficient Aw was determined for all specimens.The tung oil treated specimens exhibited a water absorption coefficient that was 5.3%of that for untreated hemp mat panel specimens.Flexural tests were conducted on dry specimens with earth-plastered hemp mat,tung oil coated hemp mat,OSB and,untreated hemp mat skins.Tung oil provided resistance to tension failure and increased capacity to withstand considerable deformation without tensile failure in flexural specimens.Compared with pure foam specimens,untreated hemp mat improved flexural performance by 16.3%.

Analysis of Soundproof Technology of Assembled Steel Structure Houses

The problem of noise has always been highlighted in assembled steel structure houses.Therefore,it is necessary to use effective soundproof measures where steel beams intersect with the reserved line pipe openings,doors,windows,elevator shafts,and other locations.In this paper,we will investigate the areas with subpar soundproof performance in an assembled steel structure residential project and propose suitable noise control measures to address this issue.

The Influence of Different Type Irradiations on the Surface States Parameters of Si-SiO₂Structures

The results of experimental research of some effects in metal-insulator-semiconductor (MIS) structures induced by different types of radiation (50 MeV electrons, 12 keV gamma-quanta, 10 and 40 keV arsenic ions) are presented. It is found that there is a significant difference between the characters of radiation surface states (SS) formed by ionization and impact actions of the MIS structure irradiation at the insulator-semiconductor (I-S) interface. It is shown that the SS generation rate is increased in electric fields and depends on the MIS structure field electrode material.