Effect of the structure and charge state on the strength properties of nanocomposites based on PP + <Emphasis Type="Italic">D</Emphasis><Subscript>k2</Subscript> films

In this work, we study the effect of the structure and charge state on the strength properties of nanocomposites prepared on the basis of polypropylene (PP) and D _k2 nanoclays. It is shown that the addition of the D _k2 nanoclay into the PP polymer increases the concentration of the centers of localization of electric charges; that is, interfacial layers are formed at the polymer-nanoclay interface; they can play the role of a trap for charges; this results in an increase in the density and stability of the electret charges. A change in the interfacial interactions and the thickness of the boundary layer can have an effect on the strength properties of the nanocomposite.     

A study of the structure and dielectric properties of nanocomposites based on polypropylene and zirconia nanoparticles

New nanocomposite structures based on isotactic polypropylene and zirconia nanoparticles are developed; the distribution of the zirconia nanoparticles is studied by optical (Motic AE 30/31) and scanning electron microscopy (Carl Zeiss). It is shown that, during the direct introduction of nanopowders into the polymer matrix, the powder nanoparticles form cluster-like fractal structures in the form of dendrites even at the first stage of mixing of the components. The electron microscopy study of the samples shows that the developed technique for preparing nanocomposites makes it possible to obtain a homogeneous distribution of zirconia nanoparticles in the matrix of polypropylene. The dielectric characteristics of nanocomposites based on polypropylene and zirconia are studied. It is found that the dielectric permeability in PP + ZrO₂ nanocomposites varies as a function of the frequency owing to the low-frequency polarization.     

Anisotropy of optical transmission and photoluminescence in ZnIn<Subscript>2</Subscript>S<Subscript>4</Subscript> and ZnIn<Subscript>2</Subscript>S<Subscript>4</Subscript>: Cu single crystals

Significant anisotropy of the optical transmission associated with the exponential increasing of the absorption coefficient and the anisotropy of the photoluminescence were found in ZnIn₂S₄ and ZnIn₂S₄:Cu single crystals. It was shown that the peculiarities of the investigated photoluminescence spectra are associated with optical transitions involving donor and acceptor levels. The possibility was found to control the spectra’s shape and intensity using doping and variation of the technological parameters to allow preparing ZnIn₂S₄ single crystals with alternation of three and one packet polytypes.     

Photoluminescence in nanocomposites based on PVDF + ZnS

The photoluminescence properties of nanocomposite materials based on polyvinylidene fluoride (PVDF) with a filler of ZnS are studied in the wavelength region of λ = 300?1000 nm. PVDF powder with a particle size of 0.5–1.0 μm is used as the matrix. It is shown that an increase in the concentration of the initial solutions leads to an increase in the size of the ZnS nanoparticles in the PVDF; that is, in the process of the cluster formation, the coalescence of the ZnS particles into a nucleation center takes place. It is also found that the composites exhibit a shift of their luminescence bands to shorter wavelengths at a decrease in the concentration of nanoparticles in the matrix and, consequently, in the size. This can be explained by both the reabsorption of the luminescence in the optically dense scattering sample and a change in its spectral composition.     

Electric conductivity of nanocompounds based on polymer and chalcogenide semiconductors CdS,Cu<Subscript>2</Subscript>S

In this work, the temperature dependence of the specific surface resistances of composites on bases of gelatin with different contents of Cu₂S and CdS chalcogenide semiconductor nanoparticles is investigated. It is shown that nanocomposites have a posistor effect. It is found that the posistor effect is the result of the influence of intermolecular interactions at the polymer-nanoparticle phase interface and that the electrotransfer of charges in such systems is caused by tunneling through polymer layer between nanoparticles before the percolation threshold and flow theory after the percolation threshold.     

Radiothermoluminescence of γ-irradiated composites of polypropilene and dispersed oxides

The peculiarities of stabilization of the excess charges in composites based on PP and dispersed metal oxides are investigated using the method of radiothermoluminescence (RTL). It is shown that introduction of fillers such as BeO and ZrO₂ into PP leads to change in the intensity and temperature of realization of the β₁, β, α, and α₁ peaks on the RTL curves, and this can be used to predict the electroactive, dielectric and physical mechanical properties of the composites based on them.     

Effect of the electrothermopolarization on the electret properties and the charge state of polyethylene nanocomposites with Cr and PbCrO4 additives

The results of studying the effect of electrothermopolarization on the electret properties and charge state of PE + Cr and PE + PbCrO₄ composites are described. It is shown that an increase in the polarization field intensity to E _p = 5 × 10⁶ V/m leads to an improvement in the polarization processes in the composites; at E _p > 5 × 10⁶ V/m, the space charge concentration apparently increases, which results in the deterioration of the electret properties. The observed effect can be attributed to the repeated electron capture by deeper traps owing to the internal electric field. In addition, the intensity of the TSD peaks and therefore the number of stabilized charges for the composites polarized at high intensities are higher than for the samples polarized at low intensities.     

Possibility to Use Hydrothermally Synthesized CuFeS<Subscript>2</Subscript> Nanocomposite as an Acceptor in Hybrid Solar Cell

Here we have approached the plausible use of CuFeS₂ nanocomposite as an acceptor in organic–inorganic hybrid solar cell. To produce CuFeS₂ nanocomposite, hydrothermal strategy was employed. The room-temperature XRD pattern approves the synthesized material as CuFeS₂ with no phase impurity (JCPDS Card no: 37-0471). The elemental composition of the material was analyzed from the TEM-EDX data. The obtained selected area electron diffraction (SAED) planes harmonized with the XRD pattern of the synthesized product. Optical band gap (4.14 eV) of the composite from UV–Vis analysis depicts that the synthesized material is belonging to wide band gap semiconductor family. The HOMO (? 6.97 eV) and LUMO (? 2.93 eV) positions from electrochemical study reveal that there is a possibility of electron transfer from MEH-PPV to CuFeS₂. The optical absorption and photoluminescence spectra of MEH-PPV:CuFeS₂ (donor:acceptor) composite were recorded sequentially by varying weight ratios. The monotonic blue shifting of the absorption peak position indicated the interaction between donor and acceptor materials. The possibility of electron transfer from donor (MEH-PPV) to acceptor (CuFeS₂) was approved with photoluminescence analysis. Subsequently, we have fabricated a hybrid solar cell by incorporating CuFeS₂ nanocomposite with MEH-PPV in open atmosphere and obtained 0.3% power conversion efficiency.     

Reversible Polarization Recording in As<Subscript>2</Subscript>S<Subscript>3</Subscript>–Se Multilayer Nanostructures

Polarization holographic recording of diffraction gratings and their subsequent erasure have been investigated on As₂S₃–Se multilayer nanostructures. The work investigates how preexposure to actinic laser radiation up to complete photoinduced changes in the optical properties affects the formation of diffraction gratings in the studied structure. It is shown that the preexposure of an As₂S₃–Se multilayer nanostructure (MNS) leads to photobleaching, and the maximum achievable diffraction efficiency (DE) of 35% does not change; however, the required exposure value is increased. It is also shown that exposure using one laser beam results in complete erasure of the diffraction grating recorded up to the maximum. Seven recording–erasure cycles show that the kinetics of the increase in diffraction efficiency and its maximum value do not change, which indicates that the As₂S₃–Se multilayer structure is capable of reversible holographic recording under orthogonal circular polarization. Study of the gratings recorded with an atomic-force microscope shows that the main factor determining the diffraction efficiency value is modulation of the relief, the depth of which is greater than 200 nm.     

Effect of Ti,Nb, and Ti + Nb Coatings on the Bond Strength-Structure Relationship in Al/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Joints

There is a growing interest in metal-ceramic bonding for wide range of applications in electronic devices and high technology industry for fabrication of metal matrix composites and bonding of ceramic components to metals. The object of the work was to study the effect of Ti, Nb, and Ti + Nb thin films deposited by PVD method on alumina substrates on structure and bond strength properties of Al/Al₂O₃ joints. The joints were fabricated using the results of a wetting experiment and the sessile drop method at a temperature of 1223 K in a vacuum of 0.2 MPa for 30 min of contact. The structure of the metal/ceramic interface was investigated using scanning electron microscopy. The elemental distribution at the metal-ceramic interface was analyzed using energy dispersive x-ray spectroscopy. Transmission electron microscopy was also used to investigate some aspects of the metal/ceramic interface. The bond strength properties of joints were measured using shear test. The shear strength results demonstrated significant improvement of shear strength of Al/Al₂O₃ joints due to the application of Ti + Nb thin film on alumina substrate. Microstructural investigations of the interface indicated that Al/coating/Al₂O₃ couples have diffusion transition interface which influences the strengthening of these joints. A conclusion could be drawn that the presence of thin film layers changes the character of interaction and leads to the formation of new reaction products in the bonding layer.     

Supercapacitor characteristic of La-doped Ni(OH)<Subscript>2</Subscript> prepared by electrode-position

Samples of lanthanum-doped nickel hydroxide were prepared by electrodeposition method. The structure and electrochemical properties of the samples were studied by X-ray diffraction and a home-made open three-electrode cell system, respectively. The results show that the deposition process of Ni(OH)₂ and La(OH)₃ is mainly controlled by electrochemical polarization, which makes it easy to form uniform fine crystals. In addition, La(OH)₃ is not a separate phase and lanthanum ions are doped into Ni(OH)₂ crystal lattices. When V(0.5 mol/L Ni(NO₃)₂)/V(0.25 mol/L La(NO₃)₃) was 9:1, the lanthanum-doped nickel hydroxide reached the highest discharge capability of 840 F/g with a good cyclic reversibility. The capability still retains 670 F/g when the discharge current reaches 1000 mA/g.     

Corrosion Behavior of Novel Al-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Composites in Aerated 3.5% Chloride Solution

The corrosion behavior of novel Al-Al₂O₃ MMCs was evaluated in aerated 3.5% NaCl solution through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). These materials corrode almost spontaneously by pitting in aerated 3.5% NaCl solution. Observations indicate that intermetallic particles in these composites appear to play an important role in this pitting corrosion behavior. Addition of Al₂O₃ particles to the base alloys did not appear to increase their corrosion resistance significantly, although corrosion rate was affected by these reinforcement particles. In cyclic polarization experiments, the small difference between the pitting potentials and the repassivation potentials for these MMCs indicated their low resistance to pitting corrosion. EIS measurements indicate adsorption/diffusion phenomena at the interface of the composites. Electrically equivalent circuits are proposed to describe and substantiate the corrosion processes occurring in these materials.     

A Study of a Novel Nanocomposite Material Based on Reduced Graphene Oxide and Poly(<Emphasis Type="Italic">o</Emphasis>-Phenylenediamine)

The formation of a nanocomposite coating based on reduced graphene oxide (RGO) and poly(o-phenylenediamine) (PPD) in the chemical reaction of graphene oxide (GO) and o-phenylenediamine (OPD) has been studied by cyclic voltammetry (CVA), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). It has been shown that the action of cyclic polarization provides a more uniform structure of the nanocomposite films (decrease in the corrugation effect). In addition, it has been found that the polarization of GO films containing the OPD monomer distributed inside to the PPD synthesis potentials leads to the formation of uniformly distributed globular structures, which most probably correspond to a polymer electrochemically synthesized in the space between the GO nanosheets.     

Plasma-electrolytic oxidation of titanium in Zr(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>-containing electrolyte

It is shown that anodic oxide coatings with a thickness of several to 300 νm can be obtained on titanium by varying the charge spent on (Q). The prevailing phase in the coatings is ZrO₂ in monoclinic and tetragonal modifications. The content of zirconium in the layers is up to 20 at %. Distributions of titanium, zirconium, and oxygen in the cross sections of the coatings are obtained, and the effect of Q on the formation and elementary and phase compositions of the coatings is studied. Tentative experiments clarifying the effects of bipolar anodic-cathodic polarization and electrolyte aging on the composition of coatings are carried out. The coatings are shown to be stable at temperature variations in the range of 20–700°C and to decrease the contact corrosion current at the (titanium + coating)—St3 steel interface by a digit of 10–15 in 3% NaCl.     

Upconversion luminescence properties of Er<Superscript>3+</Superscript> doped GeS<Subscript>2</Subscript>-Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>-KCl chalcohalide glasses

Er3+ ions doped chalcohalide glasses with the composition of 56GeS2-24Ga2S3-20KCl were fabricated by a melt-quenching method.Under 800 nm laser excitation,strong green emissions centered at 525 nm and 550 nm and weak red emission centered at 660 nm were observed,which were assigned to 2H11/2→4I15/2,4S3/2→4I15/2,and 4F9/2→4I15/2 transitions,respectively.The intensity reached maximum when the Er3+ ions concentration was 0.1 mol%.The possible upconversion luminescence mechanism was proposed from the discussion...     

Luminescence properties of red-emitting Ca<Subscript>2</Subscript>Al<Subscript>2</Subscript>SiO<Subscript>7</Subscript>:Eu<Superscript>3+</Superscript> nanoparticles prepared by sol-gel method

A series of red-emitting Ca2-xAl2SiO7:xEu3+(x = 1 mol.%-10 mol.%) phosphors were synthesized by the sol-gel method.The effects of annealing temperature and doping concentration on the crystal structure and luminescence properties of Ca2Al2SiO7:Eu3+ phosphors were investigated.X-ray diffraction(XRD) profiles showed that all peaks could be attributed to the tetragonal Ca2Al2SiO7 phase when the sample was annealed at 1000℃.Scanning electron microscopy(SEM) micrographs indicate that the phosphors have an irregularly rounded morphology with particles of about 200 nm.Excitation spectra showed that the strong broad band at around 258 nm and weak sharp lines in 350-490 nm were attributed to the charge transfer band of Eu3+-O2-and f-f transitions within the 4f6 configuration of Eu3+ ions,respectively.Emission spectra implied that the red luminescence could be attributed to the transitions from the 5D0 excited level to the 7FJ(J = 0,1,2,3,4) levels of Eu3+ ions with the main electric dipole transition 5D0→7F2(618 and 620 nm),and Eu3+ ions prefer to occupy a lower symmetry site in the crystal lattice.Moreover,the photoluminescence(PL) intensity was strongly dependent on both the sintering temperature and doping concentration,and the highest PL intensity was observed at an Eu3+ concentration x = 7 mol.% after annealing at 1100℃.The obtained Ca2Al2SiO7:Eu3+ phosphor may have potential application for the red lamp phosphor.     

Effect of water intercalation on the structure and electrophysical properties of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6.9</Subscript>

The influence of water vapors and plastic deformation on the structure and electrophysical properties of YBa₂Cu₃O_6.9 (123) has been studied. It has been established that, at T = 200°C, the introduction of water into the structure of YBa₂Cu₃O_6.9 leads to its transition into a defect tetragonal phase of the 124 type as a result of the formation of planar stacking faults. After annealing at T = 930°C, these defects are partially retained and are efficient centers of pinning in the magnetic fields applied perpendicularly to the c axis, which makes it possible to increase (by an order of magnitude) the critical current density in the high-textured ceramics at 77 K in the external magnetic field of 5–10 T. The plastic deformation of the hydrated ceramics favors the reverse transition of the arising 124 phase to the 123 phase at T = 930°C and is accompanied by a recrystallization of the material, which leads to the appearance of a texture and an increase the critical current density.     

SnO<Subscript>2</Subscript>-core/SiO<Subscript>x</Subscript>-shell coaxial whiskers with a needle-like morphology

Needle-shaped structures of tin oxide (SnO₂) were coated with a shell layer of SiO_x via a sputtering method. The diameters of the SiO_x-coated structures gradually became thinner, leading to the formation of sharp tips. The whiskers consisted of a crystalline SnO₂ core surrounded by an amorphous SiO_x shell. The photoluminescence (PL) spectrum with a Gaussian fitting exhibited yellow-green and orange light emission bands, and the overall shape and intensity of the PL spectrum were not changed by the SiO_xcoating. The results of this study suggest that sputtering can be employed to achieve the layered growth of shell layers on a variety of nanostructures.     

Influence of anions in phosphate and tetraborate electrolytes on growth kinetics of microarc oxidation coatings on Ti6Al4V alloy

The growth kinetics of microarc oxidation (MAO) coatings on Ti6Al4V alloy was studied by designing an electrolyte with low content and high content, using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and potentiodynamic polarization. The results showed that increased the spark intensity and dissolved most of the oxides at high temperatures. Then, a thicker barrier layer at the coating/substrate interface was produced, which increased the polarization resistance of the coating. at a low concentration also promoted the uniform growth of the MAO coating and the formation of hat-shaped holes in the outer deposition layer. The thickness of the MAO coatings obtained in Na₂B₄O₇ electrolytes exhibited an exponential increase with time at spark discharge stage, while that of the MAO coating obtained in phosphate–tetraborate electrolytes showed a linear trend as the content increased.     

Electrical Conductivity of Nanocomposites Based on Low-Density Polyethylene and Cu<Subscript>2</Subscript>S Nanoparticles

The temperature dependences of the electrical conductivity of nanocomposites based on low-density polyethylene (LDPE) and Cu₂S nanoparticles are studied. It is shown that, starting from a certain temperature, the temperature dependence of the electrical conductivity is described by the following Arrhenius equation: σ = σ₀exp(–E/kT); the logσ = f(10³/T) dependence has several linear portions with different activation energy values. The observed behavior of the logρ = f(1/T) dependence of the LDPE/Cu₂S nanocomposites suggests that an increase in temperature is accompanied by an increase in the mobility of the structural units of the polymer matrix in the bulk and on the surface of the sample. The polymer–filler interfacial interactions decrease the electrical resistance of the boundary layer and thereby lead to a decrease in the activation energy of the charge carriers and an increase in the electrical conductivity of the nanocomposite.