Properties of a melt of the eutectic composition in the NaPO<Subscript>3</Subscript>-Na<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>-LiF system

Physical (density, viscosity) and thermophysical (heat capacity, thermal conductivity) properties of a melt of the eutectic composition (wt %) 84NaPO₃ · 8Na₂B₄O₇ · 8LiF have been investigated. It has been demonstrated that this eutectic mixture is a promising material for the use as a high-temperature heat-transfer agent.     

Thermoelectric Properties of <Emphasis Type="Italic">x</Emphasis>PbTe/Yb<Subscript>0.2</Subscript>Co<Subscript>4</Subscript>Sb<Subscript>12</Subscript> Hot-Pressed Samples

The xPbTe/Yb_0.2Co₄Sb₁₂ compounds were prepared by the ball-milling and hot-pressed process. Electrical conductivity of the composite samples are reduced with a increase in PbTe content; and, their temperature dependence coefficients show the positive values. The maximum electrical conductivity of composite materials is ~80000 Sm⁻¹ at 800 K. The Seebeck coefficient (absolute value) of the composite material is obviously improved with an increase in the dispersed phase (PbTe) content; the Seebeck coefficient (absolute value) of the 10PbTe sample is ~260 μVK⁻¹ at 700 K, which increases by 13.6% relative to that of the Yb_0.2Co₄Sb₁₂ sample. The thermal conductivity of the composite samples is improved due to introduction of PbTe, and the thermal conductivity of the 10PbTe sample is ~3 Wm⁻¹ K⁻¹ at 550 K. The maximum value of ZT is 0.78 at 700 K for the 2.5PbTe sample.     

Viscosity and rheological properties of ethylene glycol+water+Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanofluids at various temperatures: Experimental and thermodynamics modeling

The viscosity and rheological behavior of an ethylene glycol-water mixture based Fe₃O₄ nanofluid have been experimentally investigated. The nanofluids for this study were prepared by a two-step method in which Fe₃O₄ nanoparticles were added to a base fluid mixture consisting of 60% (w/w) ethylene glycol and 40% (w/w) water. The measurements were conducted at temperatures ranging from 288.15 to 343.15 K, and at nanoparticle volume fractions ranging from 0.0022 to 0.0055. Furthermore, the dependency of viscosity of nanofluids on shear rate was examined. The results indicate that increasing the shear rate leads to a reduction in the viscosity (shear thinning behavior). Finally, the obtained experimental data was correlated by both a thermodynamic model and a hybrid GMDH-type polynomial neural network, where the mean absolute relative deviation (MARD) of these models was calculated as 3.64% and 3.88%, respectively.     

Electrical conductivity of CuI-AsI<Subscript>3</Subscript>-As<Subscript>2</Subscript>Se<Subscript>3</Subscript> and CuI-SbI<Subscript>3</Subscript>-As<Subscript>2</Subscript>Se<Subscript>3</Subscript> chalcogenide films prepared by chemical deposition

The electrical conductivity of chalcogenide semiconductor films in the CuI-AsI₃-As₂Se₃ and CuI-SbI₃-As₂Se₃ systems, which have been prepared by chemical deposition from mono-n-butylamine, has been studied as a function of the temperature and film composition. It has been established that the electrical conductivity of the CuI-AsI₃-As₂Se₃ and CuI-SbI₃-As₂Se₃ films is predominantly determined by the copper iodide content. It has been demonstrated that the electrical properties of the chalcogenide glasses and the related films are characterized by the same values to within the experimental error, which is explained by the same model of dissolution of vitreous semiconductors in amines with the retention of the electrical properties of chalcogenide glasses after the deposition of films from their solutions.     

Effect of PbTe on Thermoelectric Properties of Co<Subscript>0.88</Subscript>Ni<Subscript>0.12</Subscript>Sb<Subscript>2.91</Subscript>Sn<Subscript>0.09</Subscript>

The Co_0.88Ni_0.12Sb_2.91Sn_0.09 compound was synthesized by a metallurgical route, and PbTe powder was prepared by the low-temperature aqueous chemical method. Composite materials (xPbTe/Co_0.88Ni_0.12Sb_2.91Sn_0.09) were prepared by the ball-milling and the hot-pressed process. Electrical conductivities of xPbTe/Co_0.88Ni_0.12Sb_2.91Sn_0.09 hot-pressed samples decrease with increase of PbTe content, but their thermal conductivities were effectively improved due to induction of disperse phase. Due to agglomeration of the disperse phase, little thermal conductivity improvement occurs for composite material with low PbTe content. The ZT values of xPbTe/Co_0.88Ni_0.12Sb_2.91Sn_0.09 samples were hardly enhanced due to the negative contribution of electrical conductivity.     

Thermoelectric properties of Cu-dispersed bi<Subscript>0.5</Subscript>sb<Subscript>1.5</Subscript>te<Subscript>3</Subscript>

A novel and simple approach was used to disperse Cu nanoparticles uniformly in the Bi_0.5Sb_1.5Te₃ matrix, and the thermoelectric properties were evaluated for the Cu-dispersed Bi_0.5Sb_1.5Te₃. Polycrystalline Bi_0.5Sb_1.5Te₃ powder prepared by encapsulated melting and grinding was dry-mixed with Cu(OAc)₂ powder. After Cu(OAc)₂ decomposition, the Cu-dispersed Bi_0.5Sb_1.5Te₃ was hot-pressed. Cu nanoparticles were well-dispersed in the Bi_0.5Sb_1.5Te₃ matrix and acted as effective phonon scattering centers. The electrical conductivity increased systematically with increasing level of Cu nanoparticle dispersion. All specimens had a positive Seebeck coefficient, which confirmed that the electrical charge was transported mainly by holes. The thermoelectric figure of merit was enhanced remarkably over a wide temperature range of 323-523 K.     

Synthesis and Characterization of Ferromagnetic BaFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanocrystals Using Novel Ionic Precursor Complex [Fe(opd)<Subscript>3</Subscript>]<Subscript>2</Subscript>[Ba(CN)<Subscript>8</Subscript>]

The following investigation reports the synthesis of novel complex [Fe(opd)₃]₂[Ba(CN)₈] and preparation of BaFe₂O₄ nanoparticles through thermal decomposition without using any surfactant. The complex was characterized via Furrier transform infrared spectroscopy (FT-IR), ultra violet-visible spectroscopy (UV–vis), conductivity measurement and elemental analysis. The synthesized crystals of inorganic precursor complex was transferred to furnace, where they were calcined under normal atmosphere condition at 900 °C for 4 h. Formation of BaFe₂O₄ was supported by FT-IR and energy-dispersive X-ray analysis. Hexagonal structure of nano-oxide was confirmed on powder X-ray diffraction. Furthermore, uniform morphology of nanocrystals were reported by scanning electron microscopy. The saturation magnetization (22 emu/g), remanent magnetization (6 emu/g) and coercivity (400 Oe) reported on vibrating sample magnetometer curve illustrates the promising industrial and medicinal applications of prepared mixed oxide.     

Synthesis and Characterization of Superparamagnetic NiBaO<Subscript>2</Subscript> Nano-Oxide Using Novel Precursor Complex [Ba(H<Subscript>2</Subscript>O)<Subscript>8</Subscript>][Ni(dipic)<Subscript>2</Subscript>]

In this paper, for the first time, synthesis of [Ba(H₂O)₈][Ni(dipic)₂] complex and preparation of NiBaO₂ nano-oxide are reported through thermal decomposition under surfactant free condition. This novel complex was characterized by Fourier transform infrared spectroscopy (FT-IR), ultra violet–visible spectroscopy, conductivity measurement and elemental analysis. Formation of novel nanoparticles was supported by FT-IR and energy-dispersive X-ray spectroscopy and the orthorhombic structure of nanocrystals was confirmed by powder X-ray diffraction analysis. In addition, size distribution as well as uniform morphology of prepared nano-oxide were recorded by dynamic light scattering analysis and field-emission scanning electron microscopy, respectively. Magnetic features measured by vibrating sample magnetometer, illustrate superparamagnetic behavior of the oxide.     

Crystallization Behavior of Amorphous Zr<Subscript>55</Subscript>Cu<Subscript>20</Subscript>Ni<Subscript>10</Subscript>Al<Subscript>10</Subscript>Ti<Subscript>5</Subscript> Alloy

In the present study, the crystallization behavior and thermal stability of amorphous Zr₅₅Cu₂₀Ni₁₀Al₁₀Ti₅ alloy, obtained by melt-spinning, have been investigated using X-ray diffraction (XRD), differential thermal analysis (DTA) and transmission electron microscopy (TEM). The activation energy for crystallization has been evaluated by the Kissinger method, and it has been found that E _x obtained from the crystallization onset temperature (T _x) is lower than E _p determined by the crystallization peak temperature (T _P). During the continuous annealing process, ZrO and h-Al₃Zr₅ phases firstly precipitate from the amorphous matrix, then Zr₂Ni_0.66O_0.33 phase forms continuously and its relative content increases with increasing annealing temperature. However, no crystalline phases have been observed during the isothermal annealing process at 733 K (below T _x) for 90 min. The atomic clusters can keep the stability state through adjusting the short-range ordering.     

Electrical conductivity of CuI-Cu<Subscript>2</Subscript>Se-As<Subscript>2</Subscript>Se<Subscript>3</Subscript> chalcogenide films prepared by chemical deposition

The electrical conductivity of CuI-Cu₂Se-As₂Se₃ chalcogenide semiconductor films prepared through the chemical deposition from an organic solvent has been investigated as a function of the temperature and composition of the films. It has been established that the electrical properties of the chalcogenide glasses and related films are characterized by the same values within the limits of the experimental error. This result is in agreement with the model of dissolution of vitreous semiconductors in organic bases (amines), according to which the main properties of bulk (cast) chalcogenide glasses are retained in films prepared from these glasses.     

Structure and properties of solid solutions of La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Pr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>BaCuFeO<Subscript>5 + δ</Subscript>

The effect of replacing lanthanum with praseodymium on the crystal chemistry parameters of solid solutions of La_{1 − x} Pr _x BaCuFeO_{5 + δ} has been investigated using X-ray powder diffraction analysis and IR spectroscopy. The thermal expansion, electroconductivity, and thermopower of these phases have been studied in air in the temperature range 300–1100 K. The values of linear thermal expansion coefficients (LTEC) of ceramics in different temperature ranges have been determined, and the values of electric transfer parameters in the above oxides have been calculated. It has been established that replacing lanthanum with praseodymium resulted in the compression of the elementary oxide unit La_{1 − x} Pr _x BaCuFeO_{5 + δ}, decrease in the content of labile oxygen in them (δ), decrease in nonmonotonic electroconductivity, increase in thermopower, decrease in LTEC, and difficulties in charge transfer in these phases.     

Melt-spinning and thermal stability behavior of TiO<Subscript>2</Subscript> nanoparticle/polypropylene nanocomposite fibers

The elongational flow properties of TiO₂ nanoparticle/polypropylene (PP) nanocomposite fibers were studied via melt spinning. The diameter, tension, and flow rate of fibers were directly measured and used to calculate the apparent elongational viscosity and apparent elongational strain rate using Cogswell’s theory. Thermal gravimetric analysis (TGA) was used to demonstrate that the TiO₂ nanoparticles improved the thermal stability of the PP fibers. With a 1–3 wt % loading of the TiO₂ nanoparticles, the PP fiber decomposition temperatures ranged from 338 °C for the pristine polymer to 342, 349, and 367 °C; the decomposition was accompamied by an initial 95 wt % weight loss. In addition, the well-distributed morphology of the TiO₂ nanoparticles on the side surface of the PP matrix was observed using atomic force microscopy (AFM). At 1 wt % loading of the TiO₂ nanoparticles, the surfaces of the PP nanofibers contained mono-disperse nanoparticles with sizes of 20–50 nm. Furthermore, the TiO₂ nanoparticle/PP nanocomposite fibers were shown to be thermally stable and are suitable for application as an antibacterial polymer.     

Migration processes in the glass forming melts of the Na<Subscript>2</Subscript>O–BaO–Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> system

The specific conductivity and tracer of diffusion of sodium and barium ions have been determined and the values of the transport numbers and correlation factor for diffusion have been calculated in two melts of the Na₂O–BaO–Ga₂O₃–SiO₂ system.     

Influence of Cobalt Doping on the Physical Properties of Zn<Subscript>0.9</Subscript>Cd<Subscript>0.1</Subscript>S Nanoparticles

Zn_0.9Cd_0.1S nanoparticles doped with 0.005–0.24 M cobalt have been prepared by co-precipitation technique in ice bath at 280 K. For the cobalt concentration >0.18 M, XRD pattern shows unidentified phases along with Zn_0.9Cd_0.1S sphalerite phase. For low cobalt concentration (≤0.05 M) particle size, d _XRD is ~3.5 nm, while for high cobalt concentration (>0.05 M) particle size decreases abruptly (~2 nm) as detected by XRD. However, TEM analysis shows the similar particle size (~3.5 nm) irrespective of the cobalt concentration. Local strain in the alloyed nanoparticles with cobalt concentration of 0.18 M increases ~46% in comparison to that of 0.05 M. Direct to indirect energy band-gap transition is obtained when cobalt concentration goes beyond 0.05 M. A red shift in energy band gap is also observed for both the cases. Nanoparticles with low cobalt concentrations were found to have paramagnetic nature with no antiferromagnetic coupling. A negative Curie–Weiss temperature of −75 K with antiferromagnetic coupling was obtained for the high cobalt concentration.     

Effects of adding TiO<Subscript>2</Subscript> nanoparticles to a water-based varnish for wood applied to nine tropical woods of Costa Rica exposed to natural and accelerated weathering

The addition of titanium dioxide nanoparticles (TiO₂ nanoparticles) to a water-based varnish used for finishing tropical woods was studied. Three different concentrations of TiO₂ nanoparticles (0%, 1.0%, and 1.5%) were evaluated. The nanoparticles were characterized by means of the transmission electron microscopy and an X-ray diffractometer. The varnish prepared was evaluated for its viscosity, adhesion of the film to the wood, water absorption, and the effects of natural weathering on the color and quality of the varnish. It was found that viscosity decreases as the concentration of TiO₂ nanoparticles increases, while no variation was found in the thickness of the film. Except for Gmelina arborea and Tectona grandis, the adhesion was not statistically affected. It was found that, in the 9 species tested, incorporation of TiO₂ nanoparticles decreased the values of water absorption. The evaluation of natural weathering showed that the varnish with no added TiO₂ nanoparticles degraded completely after 1 year of weathering exposure, while the modified varnish film endured. Less color change was observed in lumber treated with the varnish containing TiO₂ nanoparticles. The best performance of the varnish in the nine tropical woods used was observed when TiO₂ nanoparticles were added at 1.5% concentration.     

NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> Nanoparticles Stabilized by Porous Silica Shells

Abstract  

NiFe₂O₄ nanoparticles stabilized by porous silica shells (NiFe₂O₄@SiO₂) were prepared using a one-pot synthesis and characterized for their physical and chemical stability in severe environments, representative of those encountered in industrial catalytic reactors. The SiO₂ shell is porous, allowing transport of gases to and from the metal core. The shell also stabilizes NiFe₂O₄ at the nanoparticle surface: NiFe₂O₄@SiO₂ annealed at temperatures through 973 K displays evidence of surface Ni, as verified by H₂ TPD analyses. At 1,173 K, hematite forms at the surface of the metallic cores of the NiFe₂O₄@SiO₂ nanoparticles and surface Ni is no longer observed. Without the silica shell, however, even mild reduction (at 773 K) can draw Fe to the surface and eliminate surface Ni sites.     

Infrared Signature of Novel Super-Thermite (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/Mg) Fluorocarbon Nanocomposite for Effective Countermeasures of Infrared Seekers

Infrared (IR) guided missiles are real threat; they caused 90% of aircraft damage. Fluorocarbon polymer nanocomposite based on super-thermites can offer superior thermal signature to countermeasure IR guided missile seekers. This study reports on the sustainable fabrication of mono-dispersed colloidal Fe₂O₃ nanoparticles with 3 nm average particle size. Fe₂O₃ nanoparticles were dispersed in acetone for subsequent integration in fluorocarbon polymer. The impact of Fe₂O₃ content on thermal signature was evaluated using (FT-MIR 2–6 μm) spectrophotometer. Nanocomposite polymer with 8 wt% Fe₂O₃ offered an increase in the average intensity of α (2–3 μm) and β (4–5 μm) bands by 50 and 85% respectively to that of reference formulation. Quantification of stimulated emitting species in the combustion flame was conducted using ICT thermodynamic code. The developed nanothermite particles extended the primary reaction zone by 183%. Full discussions about combustion zones with associated exothermic chemical reactions have been represented.     

Electrical conductivity and structure of glasses in the Na<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>S-P<Subscript>2</Subscript>O<Subscript>5</Subscript> and Na<Subscript>2</Subscript>S-P<Subscript>2</Subscript>S<Subscript>5</Subscript> systems

The glasses, in which oxygen was partially replaced with sulfur, have been synthesized in the Na₂O-P₂O₅-Na₂S system. The chemical and chromatographic analyses of the glasses synthesized have been performed. The temperature-concentration dependences of electrical conductivity of the glasses have been studied over a wide temperature range; the glass transition temperatures and the nature of charge carriers have been determined. The IR spectra and Raman spectra have been recorded at room temperature; the density and microhardness of the glasses and ultrasound velocity have been measured. A comparison of the electrical conductivities of the investigated glasses with those of the earlier studied glasses in the Na₂O-P₂O₅ system has shown their fair coincidence. The introduction of sodium sulfide into the Na₂O-P₂O₅ system is accompanied by an approximately threefold increase in electrical conductivity, although the concentrations of charge carriers (sodium ions) in the glasses amount to ∼17 and ∼26 mmol/cm³, respectively. The rise in electrical conductivity has been assumed to be caused by the increase in the degree of dissociation of polar structural chemical units including sulfide ions and by the higher mobility of sodium ions in the oxygen-free matrix.     

Structure and electrical conductivity of glasses in the Na<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> system

The temperature-concentration dependence of the electrical conductivity of glasses in the Na₂SO₄-NaPO₃ and Na₂O-P₂O₅ systems has been investigated. Based on the obtained experimental data (IR spectra, density, microhardness, sound velocity, and paper chromatography), it has been demonstrated that SO₄²⁻ ions form terminal groups through the incorporation into polyphosphate fragments of the structure of glasses in the Na₂SO₄-NaPO₃ system. An increase in the electrical conductivity of glasses in this system by a factor of ∼1000 (as compared to NaPO₃) at 25°C and a decrease in the activation energy for electrical conduction from 1.40 to 1.10 eV have been interpreted from the viewpoint of the decrease in the dissociation energy E _d of polar sulfate phosphate structural chemical fragments formed in the glass bulk upon introduction into sodium metaphosphate Na₂SO₄. This leads to an increase in the number of dissociated sodium ions, which are charge carriers, and to a decrease in the energy (E _a) of their activation shift in the sublattice formed by sulfate phosphate fragments of the structure.     

Modification of Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> nanotubes by magnetite nanoparticles

The magnetite nanoparticles and nanocomposite “Nanotube of hydrosilicate Mg—magnetite nanoparticles—Mg-ChR-NT/Fe₃O₄-NP” were obtained by coprecipitation. The composition of the synthesized samples has been established by X-ray diffraction. Using transmission electron microscopy, the presence of magnetite nanoparticles has been detected both inside the NTs and at the external surface of the NT walls. The specific surface of the NTs, nanoparticles, and composite is determined.