Bulletin of Materials Science最新文献

To deepen the fundamental knowledge on the effect of titanium diboride (TiB₂) particle interface on thermal conductivity of three different composites with polyethylene matrices (HDPE/TiB₂, MDPE/TiB₂ and LDPE/TiB₂), this paper is devoted to a theoretical approach on the analysis of thermal behaviour of polymer-based composites. This study is based on the Hashin and Shtrikman model, which allows us to determine the thermal conductivity considering an idealized interface between the reinforcing molecules. In addition, the Hasselman and Johnson model is used to evaluate thermal conductivity with an imperfect interface. We mainly discuss the difference between two types of interfaces with the aim of improving the thermal conductivity within the composite material used in this study without altering the mechanical and thermal behaviours. This approach creates new opportunities, especially in manufacturing, to use high-quality composite materials at low-cost and non-destructive. To this end, we have investigated the variations in the effective thermal conductivity of different composites, λ_eff as a function of volume fraction of the reinforcement (TiB₂). In particular, we have emphasized the study on the effective thermal conductivity of the composite, taking into account interactions at the interface between the particles and matrix. Definitely, the random dispersion of spherical particles and cylindrical particles oriented perpendicular to the heat flow is considered. The main conclusion is that the form of particles and the type of interface of the reinforcement drastically affect thermal conductivity of the system under consideration.

In the present study, we have confined the smallest water clusters namely, monomer and dimer under various carbon nanotubes and fullerenes using quantum mechanics/molecular mechanics methods. We observed the change in their structural, vibrational, optical and electronic properties as compared to each other as well as against the free monomer and dimer. For monomer, the confinement effect was found to be the greatest for carbon nanotube CNT(7,0) followed by C-60 and then by C-78. However, in the case of the dimer, there was a change in its structure, thus exhibiting different confining effects in each geometry. We also note that, as the diameter of the CNT goes on increasing, the confining effects over the monomer and the dimer go on decreasing. We have also confined a monomer by placing it over one C-60 fullerene, and between two and three C-60 fullerenes at various sites—the hexagon, pentagon and the vertex at different distances from the surface, and compared the extent of confinement. In the vibrational spectra, for short-range interactions, a redshift was observed, whereas a blueshift was seen in the case of long-range interactions as we went from hexagon to pentagon to vertex sites. We have also confirmed the results obtained by studying their structural, vibrational, electronic and optical properties.

A structural study of the transformation of 6√3 reconstruction on the surface of a 4H–SiC substrate into quasi-free epitaxial graphene was carried out by the reflection high-energy electron diffraction (RHEED) method. The conversion was carried out via hydrogen intercalation between the reconstructed layer and the adjacent top layer of SiC. The initial 6√3 reconstruction was obtained during short sublimation annealing of the 4H–SiC substrate in an argon medium. A slight violation of the 6√3 reconstruction layer formation uniformity was found. The results of the study of the crystal structure of quasi-free-standing graphene and single-layer graphene comprising a buffer layer formed on 4H–SiC in the traditional way in an Ar atmosphere without intercalation were compared.

The demand for nanomaterial is increasing day by day due to their wide ranging applications in many areas of science and technology. This has led to a rapid growth of nanotechnology. In this work, a simple route of synthesis for nanoparticle of La₂O₃ has been attempted. The aloe vera gel-assisted precipitation method was used to synthesize nanoparticle of undoped as well as doped La₂O₃. Four down-conversion compounds 1% Pr³⁺: La₂O₃, 1% Eu³⁺: La₂O₃, 1% Tb³⁺: La₂O₃ and 1% Dy³⁺: La₂O₃ were also synthesized by this technique. The aloe vera gel acts as a biosurfactant that controls the particle’s growth, thus minimizing the particle’s size. The structural, elemental, morphological, optical and photoluminescence characterization was carried out on these samples. The XRD and EDAX analysis reveals that the obtained compounds are in the hexagonal phase with high purity having nanocrystallite size. The optical bandgap and refractive index have been calculated using the UV–visible absorption spectra. The size of synthesized particles was from 48 to 64 nm, with a spherical shape, which was confirmed by SEM analysis.

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In this study, calcium titanate (CaTiO₃) doped (0, 15, 25 and 35%) polyaniline (PANI) composites in the presence of dodecylbenzene sulphonic acid (DBSA) were successfully synthesized by the means of in-situ emulsion polymerization of aniline monomer. The structural, morphological and optical characterization of as-prepared composites were determined using X-ray diffraction (XRD), field effect scanning electron microscopy, Fourier-transform infrared spectroscopy, UV–vis analysis, and electronic conductivity was determined using two-point probe method. The structural analysis confirms that PANI–DBSA is amorphous, but sharp peaks present in XRD patterns in composites are of crystalline nature. The morphological study reveals efficacious integration of CaTiO₃ particles into the PANI–DBSA matrix. Further, the integration of CaTiO₃ remarkably reduced the optical bandgap (2.7–2.2 eV) by making composites with PANI–DBSA. Room temperature alternating current conductivity was found to obey universal power law and correlated barrier hopping was found most appropriate model to describe the sample’s charge transport mechanism. With the increasing wt% of CaTiO₃, the dielectric permittivity and loss both varied according to the interfacial polarization law of Maxwell–Wagner. Moreover, the I–V graphs showed augmented electrical conductivity of composites with an increase in CaTiO₃ particle content than that of pure PANI–DBSA. This is a simple way by which PANI–DBSA/CaTiO₃ composites having low optical bandgap, high electrical conductivity and permittivity may be fabricated for a widespread technological application.

The present study was conducted to prepare precursors by rapid hydrolysis method for realizing lower temperature formation of NiFe₂O₄ under hydrothermal conditions. The precursor, obtained from a lower concentration of NiCl₂–FeCl₂ mixed solution, was almost amorphous and could be easily converted to NiFe₂O₄ crystal phase at around 130°C by hydrothermal treatment. On the other hand, when a higher concentration of NiCl₂–FeCl₂ solution or trivalent iron salt (FeCl₃) was used as starting reagents, individual crystal phases such as α-Ni(OH)₂, γ-Fe₂O₃ and α-FeOOH were recognized in precursors owing to the difference in hydrolysis rates between Ni²⁺ and Fe²⁺ (or Fe³⁺). These individual crystal phases involved precursors that could not be converted easily to NiFe₂O₄ crystal phase, but needed to treat at higher temperatures for forming NiFe₂O₄ at least 200°C. Thus, the co-existence of individual crystal phases in precursors might prevent the amorphous precursor from forming NiFe₂O₄ crystal phase. The formation of NiFe₂O₄ at lower temperatures is considered to be taken place preferentially from amorphous precursors than individual certain crystal phases.

ZnO nanorods were prepared by a simple hydrothermal method using Zn(NO₃)₂·6H₂O as a precursor, NaOH as precipitant, anhydrous ethanol as solvent and ethylenediamine as a template. The morphology, size and structure were observed by scanning electron microscope, X-ray diffraction and Raman spectroscopy. The gas sensing response of ZnO nanorods to ethanol vapour was characterized by CGS-8 gas sensitivity analysis system. The results show that the response of ZnO nanorods-based gas sensor increases with the decrease of precursor concentration. The repeatability and concentration characteristics are good. The response of ZnO nanorods-based gas sensor is 33 when the concentration of Zn (NO₃)₂·6H₂O is 0.1 mol·l⁻¹. The optimal working temperature of the gas sensor is 275°C.