Microwave adsorption of core–shell structure polyaniline/SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> composites

Polyaniline/strontium hexaferrites (PANI/SrFe₁₂O₁₉) composites were synthesized by the oxidative chemical polymerization of aniline in the presence of APS. X-ray powder diffraction of ferrites indicated that the structure of core materials is hexagonal with lattice constants around 5.886–5.885 Å. The structural in the character of the sol–gel was investigated with Fourier transform infrared spectrometer analysis. SEM and TEM photographs show that the particle size of core material is around 50–200 nm. After coating with polyaniline, the particle size of the core–shell of PANI/SrFe₁₂O₁₉ has grown up to 100~300 nm. In the magnetization for the PANI/SrFe₁₂O₁₉ composites, it was found that the saturation magnetization (M _s) and coercivity (H _c) decreased after polyaniline coating. The composite under applied magnetic field exhibited the hysteretic loops of the ferromagnetic behavior, such as high saturation magnetization (M _s = 18.9 emu/g) and coercivity (H _c = 3850.0 Oe). The conductivity of the core–shell materials increased with increasing amounts of polyaniline as the temperature increased from 0 to 50 °C, the conductivity increased by about 13%. The polymerization mechanism for the core–shell composites was also investigated. The composite specimens of core–shell PANI/SrFe₁₂O₁₉ and thermal plastic resin (TPR) had band-width microwave absorption due to reflection losses from ?27.3 to ?37.4 dB at frequencies between 10.5 and 11.8 GHz as observed by High-frequency network analyzer.     

Impact of Particle Size on Room Temperature Ferrimagnetism of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>

In this paper, we report the control of important hysteresis parameters, which are useful for memory devices, viz. M _s , H _c and M _r /M _s , by changing the particle size/calcination temperature. An investigation of SrFe₁₂O₁₉ nanopowder from the structural and magnetic aspect is performed using X-ray diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM), Scanning Electron Microscopy (SEM) and Vibrating Sample Magnetometer (VSM). The average particle size (APS) of SrFe₁₂O₁₉(nanopowder) increases from 26 to 600 nm with calcination temperatures of 400 and 1100 °C in air, respectively. With the increase in calcination temperature, saturation magnetization (M _s ) increases with the decrease in coercivity for the respective sample. The change in saturation magnetization and coercive field are explained on the basis of transition from single domain structure to multi-domain geometry with an increase in the heating temperature. The sample heated at 1000 °C shows a minimum coercive field (2.71 kOe) and an appropriate squareness ratio (M _r /M _s ) compared to other calcined samples.     

BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> films produced from BaFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> heterostructures

BaFe₁₂O₁₉ hexaferrite films have been produced on thermally oxidized single-crystal silicon (SiO₂/Si) substrates by sequential ion-beam sputtering of BaFe₂O₄ and α-Fe₂O₃ targets in an argon-oxygen atmosphere. Their crystal structure has been studied, and the origin of the impurity phases forming during heat treatment has been identified. The results show that heat treatment may lead to the formation of eutectic melts. As a result, the hexaferrite films may contain spherulites.     

Morphologies and properties of NiO particles prepared from NiSO<Subscript>4</Subscript>·6H<Subscript>2</Subscript>O and Ni(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>·6H<Subscript>2</Subscript>O by spray pyrolysis

Nickel oxide particles were prepared by spray pyrolysis of aqueous solutions of NiSO₄·6H₂O and Ni(NO₃)₂·6H₂O. In spray pyrolysis reactor hollow salt particles initially formed were collapsed by decomposition to reduce their size. For NiSO₄·6H₂O less hollowness of the primitive particles and its higher decomposition temperature made the oxide particles highly spherical with very smooth surface. On the other hand the particles prepared from Ni(NO₃)₂·6H₂O were so hollow and fragile with rough surface since they were formed on the liquid pool of the salt melt. The particle size decreased with the furnace set temperature while increased with the initial salt concentration. Single oxide particle was composed of many small nuclei without sintering whose size varied with the rate of decomposition. The crystallinity of the particles increased with both temperature and the initial salt concentration. Preliminary drying in diffusion dryer fixed the size of the oxide particles from NiSO₄·6H₂O at that of the primitive particles, independent of the temperature. However, by the preliminary drying the particles from Ni(NO₃)₂·6H₂O became more hollow and fragile, whose sizes decreased with the temperature.     

Synthesis of thorn-like Ca<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>·H<Subscript>2</Subscript>O by hydrothermal method

Thorn-like polycrystalline Ca₂B₂O₅·H₂O microspheres with nano-sized slices were synthesized using boric acid and calcium hydroxide as reactants by a facile catalyst-free hydrothermal method at low temperature. The products were characterized by means of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The XRD pattern reveals that the Ca₂B₂O₅·H₂O is a monoclinic phase polycrystalline with cell parameters a = 0·6702, b = 0·5419 and c = 0·3558 nm. SEM also reveals that the monoclinic phase polycrystalline are thorn-like microspheres composed of many flakes with an average thickness of <100 nm. Possible reaction and growth mechanism were also discussed.     

Investigation of solid solution of ZrP<Subscript>2</Subscript>O<Subscript>7</Subscript>–Sr<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

In this study, ZrP₂O₇ was synthesized by the solid state reaction of ZrO₂ and NH₄H₂PO₄ at 900 °C. Then, in set 1; 10, 5, 1, 0.5, 0.1, 0.05, 0.03% previously prepared Sr₂P₂O₇ were doped into ZrP₂O₇, and Sr₂P₂O₇ slightly affect the unit cell parameter of cubic ZrP₂O₇ (a = 8.248(6)–8.233(8) Å). The reverse of this process was also applied to Sr₂P₂O₇ system (set 2). ZrP₂O₇ changes the unit cell parameters of orthorhombic Sr₂P₂O₇ in between a = 8.909(5)–8.877(5) Å, b = 13.163(3)–13.12(1) Å, and c = 5.403(2)–5.386(4) Å. Analysis of the vibrations of the P₂O ₇ ^4? ion and approximate band assignments for IR and Raman spectra are also reported in this work. Some coincidences in infrared and Raman spectra both sets were found and strong P–O–P bands were observed. Surface morphology, EDX analysis, and thermoluminescence properties of both sets were given the first time in this paper.     

Microstructure,interfaces and creep behaviour of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> (ZrO<Subscript>2</Subscript>) eutectic ceramic composites

New compositions in the melt-grown eutectic ceramics field are investigated for thermomechanical applications. This paper is focused on the Al₂O₃–Sm₂O₃–(ZrO₂) system. The studied compositions give rise to interconnected microstructures without anisotropy along the growth direction. At variance with the binary eutectic Al₂O₃–SmAlO₃, the homogeneity of the microstructure of the Al₂O₃–SmAlO₃–ZrO₂ ternary eutectic is less sensitive to the growth rate. Interfaces between the alumina and perovskite phases are investigated by high-resolution transmission electron microscopy (TEM). They are semi-coherent. In stepped interfaces, the facets are parallel to dense planes of each phase. The steps have a dislocation character and may accommodate both misfits. The ternary eutectic displays a very good creep behaviour with strain rates very close to those obtained on other previously studied eutectics in the Al₂O₃–RE₂O₃(RE = Y, Gd, Er)–ZrO₂ systems. The deformation micromechanisms are analysed by TEM in the three eutectic phases. After creep, dislocations are present in every phase. The activation of unusual slip systems (pyramidal slip in the alumina phase) shows that high local stresses can be reached. The presence of dislocation networks with low energy configurations is consistent with predominance of dislocation climb processes controlled by bulk diffusion.     

Variable—Range hopping in Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> glasses

The dc conductivity of the glasses in the Fe₂O₃-Bi₂O₃-K₂B₄O₇ system was studied at temperatures between 223 and 393 K. At temperatures from 300 to 223 K, T^–1/4 (T is temperature) dependence of the conductivity was found, however, both Mott variable-range hopping and Greaves intermediate range hopping models are found to be applicable. Mott and Greaves parameters analysis gave the density of states at Fermi level N (E_F) = 3.13 × 10²⁰–21.01 × 10²⁰ and 1.93 × 10²¹–16.39 × 10²¹ cm^–3eV^–1 at 240 K, respectively. The variable-range hopping conduction occurred in the temperature range T = 300–223 K, since W_D was found to be large (W_D = 0.08–0.14 eV for these glasses) and dominated the conduction at T < 300 K.     

Growth of bulk β-BaB<Subscript>2</Subscript>O<Subscript>4</Subscript> crystals of high optical quality in the BaB<Subscript>2</Subscript>O<Subscript>4</Subscript>-NaBaBO<Subscript>3</Subscript> system

Phase equilibria along the BaB₂O₄-NaBaBO₃ join of the BaO-B 2 O 3 -Na 2 O system are studied by differential thermal analysis and modified visual thermal analysis. The join is shown to be suitable for growing - BaB₂O₄ crystal of high optical quality.Translated from Neorganicheskie Materialy, Vol. 41, No. 1, 2005, pp. 64–69. Original Russian Text Copyright © 2005 by Kokh, Kononova, Fedorov, Bekker, Kuznetsov.     

Thermodynamic properties of Dy<Subscript>2</Subscript>O<Subscript>3</Subscript> · 2ZrO<Subscript>2</Subscript> and Ho<Subscript>2</Subscript>O<Subscript>3</Subscript> · 2ZrO<Subscript>2</Subscript> in the range 10–340 K

The low-temperature heat capacity of Dy₂O₃ · 2ZrO₂ and Ho₂O₃ · 2ZrO₂ has been determined by adiabatic calorimetry in the temperature range 10–340 K. The results have been used to calculate the entropy, enthalpy increment, and reduced Gibbs energy of the zirconates without taking into account their low-temperature magnetic transformations.     

Fabrication of Yb<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> Optical Fibers with a Perfect Step-Index Profile by the MCVD Process

An all-vapor phase MCVD process has been proposed for the fabrication of fiber preforms with a Yb₂O₃–Al₂O₃–P₂O₅–SiO₂ multicomponent glass core. We have investigated the tubular preform collapse into a rod and demonstrated approaches capable of preventing P₂O₅ losses in the central part of the core during the collapse process. Preforms with a flat, perfect step-index profile have been fabricated.     

Effect of sintering temperatures on properties of BaO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass/silica composites for CBGA package

BaO–B₂O₃–SiO₂–Al₂O₃ (BBSA) glass/silica composites synthesized by solid-state reaction method were developed for CBGA packages, and the effects of sintering temperature (900–950 °C) on the phase transformation, microstructure, thermal, mechanical and electrical properties were investigated. XRD results show that the major phases quartz and cristobalite, and the minor phase BaSi₂O₅ are detected in BBSA composites. Furthermore, it was found that the quartz phase transforms to cristobalite phase at 930–940 °C. The formation of cristobalite phase with higher coefficient of thermal expansion (CTE) led to the increase of CTE value of BBSA composites. However, excessive cristobalite phase content would degrade the mechanical properties and the linearity of thermal expansion of the ceramics. BBSA composites sintered at 920 °C exhibited excellent properties: low dielectric constant and loss (ε_r = 6.2, tanδ = 10^?4 at 1 MHz), high bending strength (179 MPa), high CTE (12.19 ppm/°C) as well as superior linearity of the thermal expansion.     

High- and low-temperature X-ray diffraction studies of aluminate spinels in the CoAl<Subscript>2</Subscript>O<Subscript>4</Subscript>–NiAl<Subscript>2</Subscript>O<Subscript>4</Subscript> system

Co _x Ni_1–x Al₂O₄ (x = 0, 0.25, 0.5, 0.75, 1) aluminate spinels have been prepared by solid-state reactions and their crystal structures have been refined by the Rietveld method. We have analyzed whether the results are consistent with theoretical relationships stemming from the hard sphere model. Using high- and low-temperature X-ray diffraction measurements, we have obtained the temperature dependences of the unit-cell parameters for the synthesized compounds and determined their thermal expansion coefficients. The rate of cation exchange reactions has been shown to be very slow at temperatures below 200°C.     

Enhanced antibacterial performance of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–Ag and MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>–Ag nanocomposites

In this work, we have described the antibacterial activities of Fe₃O₄ nanoparticles with different organic parts, including Humic acid (HA), Nicotinic acid (Nico) and Histidine (His), and the antibacterial activity of MnFe₂O₄ nanoparticles coated with PANI and SiO₂ against different bacteria and some standard antibacterial drugs. The present study revealed that the newly fabricated various Fe₃O₄ and MnFe₂O₄ nanocomposites, when combined with some different organic parts, are superiour antibacterial agents. Also, the synthesized nanocomposites can be easily separated from aqueous solution by magnetic filtration without any contamination of the medium.     

Enthalpy of Formation of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> · 0.793Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nonstoichiometric Spinel at 1900 K from High-Temperature Mass Spectrometry Data

The composition and partial pressures of vapor species over the pseudobinary system Al₂O₃–MgO have been determined by high-temperature mass spectrometry. The data obtained have been used to evaluate the standard enthalpy of formation of nonstoichiometric spinel with the composition MgAl₂O₄ · 0.793Al₂O₃ from its constituent oxides by third-law calculations. The entropy of MgAl₂O₄ · 0.793Al₂O₃ has been evaluated using a regular-solution model with allowance for cation inversion.     

Chemical interaction of InAs,InSb, GaAs,and GaSb with (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>Cr<Subscript>2</Subscript>O<Subscript>7</Subscript>–HBr–C<Subscript>4</Subscript>H<Subscript>6</Subscript>O<Subscript>6</Subscript> etching solutions

This paper presents results on the kinetics and mechanism of the physicochemical interaction of InAs, InSb, GaAs, and GaSb semiconductor surfaces with (NH₄)₂Cr₂O₇–HBr–C₄H₆O₆ etching solutions under reproducible hydrodynamic conditions in the case of laminar etchant flow over a substrate. We have identified regions of polishing and nonpolishing solutions and evaluated the apparent activation energy of the process. The surface morphology of the crystals has been examined by microstructural analysis after chemical etching. The results demonstrate that the presence of C₄H₆O₆ in etchants helps to reduce the overall reaction rate and extend the region of polishing solutions.     

Crystal structure of a Np(V) sesquioxalate,Na<Subscript>4</Subscript>(NpO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>3</Subscript>·2H<Subscript>2</Subscript>O

The crystal structure of a previously unknown Np(V) sesquioxalate, Na₄(NpO₂)₂(C₂O₄)₃·2H₂O was studied. The crystal structure consists of neptunyl(V) cations, sodium cations, oxalate anions, and water molecules of crystallization. Neptunyl(V) cations and oxalate ions form anionic chains [(NpO₂)₂(C₂O₄)₃] _n ^4n? . The coordination polyhedron (CP) of Np (pentagonal bipyramid) contains two apical “yl” oxygen atoms and five equatorial O atoms of three oxalate ions. The CP of Na(1) and Na(2) cations are combined through the common edges into zigzag chains in the [010] direction. Two independent oxalate ions are tridentate and tetradentate ligands.     

Syntheses and proton conductivity of mesoporous Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> and NdOCl–SiO<Subscript>2</Subscript> composites

Two mesoporous oxide composites of Nd₂O₃–SiO₂ and NdOCl–SiO₂ were synthesized using SBA-15 as a template and neodymium nitrate or neodymium chloride as a precursor. The porous Nd₂O₃–SiO₂ with a SBA-15-like structure has amorphous walls and the porous NdOCl–SiO₂ with a replicated structure of SBA-15 has crystalline walls. These porous materials were characterized by X-ray diffraction, transmission electron microscopy and nitrogen adsorption/desorption. They exhibited significant proton conductivities in the presence of moisture at low temperatures and the highest conductivity observed was 4.55 × 10⁻⁴ S/cm at 47 °C in wet air (RH = 28.6%).     

Atomistic structure and energetics of interface between Mn-doped γ-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript>

The interface between an Mn-doped γ-gallium oxide (Ga₂O₃) thin film and an MgAl₂O₄ (001) substrate has been investigated using high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and first-principles calculations. A high-quality Mn-doped γ-Ga₂O₃ film with a defective spinel structure has been epitaxially grown by pulsed laser deposition. The γ-Ga₂O₃ crystal shows an uniform tetragonal distortion with a tetragonality of 1.05 throughout the film thickness of 75 nm. HRTEM and HAADF-STEM observations reveal that the γ-Ga₂O₃ and MgAl₂O₄ crystals form a coherent interface without any interfacial layers or precipitates. The atomistic structure and energies are theoretically evaluated for the interfaces with two types of termination plane, i.e., Mg- and Al₂O₄-termination of MgAl₂O₄. The cation sublattice is found to be continuous for both interfaces despite the defective spinel structure of Mn-doped γ-Ga₂O₃ with some vacant cation sites. The Al₂O₄-termination shows a lower interfacial energy than the Mg-termination under most conditions of the chemical potentials. This behavior is attributed to the energetic preference of the Mn–Al₂O₄ local configuration at the interface.     

Reaction of CaAl<Subscript>4</Subscript>O<Subscript>7</Subscript> with (0001)-oriented α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Reactions between thin films of CA₂ and (0001)-oriented α-Al₂O₃ have been studied using a combination of microscopy techniques. Thin films of amorphous CA₂ were deposited on sapphire substrates by pulsed-laser deposition at 900 °C in an oxygen ambient atmosphere. After deposition, the reaction couples were heat treated in air for various times either at 1300 or 1400 °C. Atomic-force microscopy was used to monitor changes in the microstructure of the films. Interfaces between the different regions were examined by transmission electron microscopy (TEM) of cross-sectional samples prepared by focused ion-beam milling. The CA₂ films had dewetted the substrate surface as a result of the heat treatment. An interfacial reaction layer was observed between the dewetted CA₂ droplets and the substrate. The structure of this reaction layer was found to be consistent with γ-Al₂O₃ by computer analysis of high-resolution TEM images. There is a perfect epitaxy between the interfacial layer and the substrate. For the samples heat treated for longer times, hexagonal features were found on the substrate surface. The presence of these features on (0001)-oriented α-Al₂O₃ suggests that CA₆ platelets form by the transformation of the interfacial reaction layer. The results are discussed in relation to the crystallization behavior of the various calcium aluminate phases and the equilibrium-phase diagram of the CaO–Al₂O₃ system.