Synthesis of magnetite nanoparticles by thermal decomposition of ferrous oxalate dihydrate

Two different polymorphs of ferrous oxalate dihydrate were synthesized by precipitation of ferrous ions with oxalic acid: α-Fe(C₂O₄) · 2H₂O with a monoclinic unit cell is obtained after precipitation and ageing at 90 °C, whereas the orthorhombic β-type is formed after precipitation at room temperature. The morphology of the oxalate crystals can be tailored from prismatic crystals of the α-polymorph over star-like aggregates of α/β-mixtures to non-agglomerated crystallites of β-oxalate. Thermal decomposition in air gives hematite at T ≥ 250 °C; if the thermolysis reaction is performed at low oxygen partial pressures (e.g., T = 500 °C and p _O2 = 10^?25 atm) magnetite is obtained. The synthesized magnetite is stoichiometric as signaled by lattice parameters of a ₀ = 8.39 Å. The thermal decomposition of ferrous oxalate is monitored by thermal analysis, XRD, and IR-spectroscopy. The morphology of the oxalate crystals is preserved during thermal decomposition; the oxalates are transformed into spinel particle aggregates of similar size and shape. The crystallite size of the magnetite particles increases with temperature and is 40 or 55 nm, if synthesized from β-oxalate at 500 °C or 700 °C, respectively. The saturation magnetization of the magnetite particles decreases with decreasing particle size. Since the particles are larger than the critical diameter for superparamagnetic behavior they display hysteresis behavior at room temperature.     

Size Effects on the Magnetic Properties of ZnFe2O4 Nanoparticles

We report structural and magnetic measurements on ZnFe₂O₄ nanoparticles obtained through coprecipitation chemical method. The Rietveld analysis of X-ray patterns reveals that (i) our samples are single phase, (ii) the average particle size increases with synthesis temperature, and (iii) the cationic disorder increases with decreasing of the mean particle size. The Zero-Field-Cooled (ZFC) and Field-Cooled (FC) magnetization measurements show that the blocking temperature increases with increasing of the particle size and, to the sample grown at T=850?°C, it is possible to observe both Néel temperature to larger particles and blocking effects to smaller particles. Finally, we have observed that the coercive field does not decay with the square root of temperature following the Néel relaxation and Bean–Livingston approaches.     

Effect of the adding of rod-like attapulgite upon the properties of polyimides produced by random copolycondensation

A series of polyimides (PIs) and polyimide/attapulgite (AT) composite films was successfully prepared by random copolycondensation. The polyimides were synthesized based on 4,4′-diaminodiphenyl ether, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), and 4,4′-oxydiphthalic anhydride (ODPA). By adjusting the ratio of BPADA and ODPA, three different types of anhydride group-terminated PIs were obtained. AT was functionalized by chemical modification with γ-aminopropyltriethoxysilane and then chemical bonded with PI via reaction between amino group and anhydride group, resulting in stable PI/AT composites. The structure and properties of PIs and PI/AT composites were characterized by FTIR, XRD, TG, SEM, DSC, DMA, mechanical measure, and so on. Comparison was given between PIs and PI/AT composites. Results showed that all PIs had good thermal stability and mechanical properties with glass translation temperature (T _g) over 210 °C, 5 % weight loss temperature (T _d,5%) over 494 °C and tension strength of 84–89.9 MPa, breaking elongation around 7 %. More stable, flexible, and much stronger films were obtained after adding 5 wt% AT, which showed 535–548.5 °C, 85.8–118.9 MPa, and 10.3–24.7 % in T _d,5%, tension strength, and breaking elongation, respectively. Much interestingly, we found that AT had the greatest effect on PI-2, the yielding of which occurred during mechanical measure, and PI/AT-2 composite displayed excellent comprehensive properties.     

Design and preparation of high-performance amine-based poly(ether ketone)s with strong photonic luminescence

Amine-based poly(ether ketone)s (A-PEKs), as novel high-performance functional polymers, have been obtained by the polycondensation of dibromo ketones with aromatic ether diamines via palladium-catalyzed aryl amination reaction. The structures of the polymers are characterized by means of FT-IR, ¹H NMR spectroscopy and elemental analysis, the results show a good agreement with the proposed structures. DSC and TGA measurements exhibit that polymers possess high glass transition temperature (T _g ≥ 175 °C) and good thermal stability with high decomposition temperatures (T ₅ ≥ 400 °C). Based on the hydrogen bonds between the polymer chains, thin films of A-PEKs show great mechanical behaviors with high tensile strength up to 89.5 Mpa. In addition, due to the photoinduced intramolecular charge-transfer (ICT) of A-PEKs, these synthesized polymers are endowed with significantly strong photonic luminescence in N,N′-dimethylformamide.     

Tin fluorophosphate nonwovens by melt state centrifugal Forcespinning

This report describes the direct melt processing of inorganic tin fluorophosphate (TFP) glass fibers with average diameters ranging from 2 to 4 µm via centrifugal Forcespinning. This was accomplished by using a TFP glass with low glass transition temperature (T _g) and the melt processing capability of Forcespinning. The thermal behavior of TFP glass fibers was investigated by differential scanning calorimetry and thermogravimetric analysis, while the compositional evolution of the fibers was studied using energy-dispersive spectrometry and Fourier-transform infrared spectroscopy. These fibers exhibited excellent thermal stability after thermal post-treatment at 300 °C. The T _g of the thermally treated fibers increased by 100 °C compared to the bulk material. The fibers were found to undergo dehydration and loss of fluorine during thermal treatment, resulting in a rigid and crosslinked glass network with enhanced thermal stability and increased T _g. The enhanced thermal stability demonstrated the potential of TFP fibers for high temperature catalysis and chemical filtration applications.     

A dynamic mechanical thermal analysis study of the viscoelastic properties and glass transition temperature behaviour of bioresorbable polymer matrix nanocomposites

The application of bioresorbable polymer nanocomposites in orthopaedics offer the potential to address several of the limitations associated with the use of metallic implants. Their enhanced biological performance has been demonstrated recently, but until now relatively little work has been reported on their mechanical properties. To this end, the viscoelastic properties and T_g of bioresorbable polylactide-co-glycolide/α-tricalcium phosphate nanocomposites were investigated by dynamic mechanical thermal analysis. At room temperature of approximately 20°C, the storage moduli of the nanocomposites were generally higher than the storage modulus of the unfilled polymer due to the stiffening effect of the nano-particles. However at physiological temperature of approximately 37°C, the storage moduli of the nanocomposites decreased from 6.2 to 15.4% v/v nano-particle loadings. Similarly the T_g of the nanocomposites also decreased from 6.2 to 15.4% v/v nano-particle loadings. These effects were thought to be due to weak interfacial bonding between the nano-particles and polymer matrix. The storage moduli at 37°C and T_g increased from the minimum value when the particle loading was raised to 25.7 and 34.2% v/v loadings. SEM and particle size distribution histograms showed that at these loadings, there was a broad particle size distribution consisting of nano-particles and micro-particles and that some particle agglomeration was present. The consequent reduction in the interfacial area and the number of weak interfaces presumably accounts for the rise in the storage modulus at 37°C and the T_g.     

Pure blue light-emitting fluorene-based conjugated polymer with excellent thermal, photophysical, and electroluminescent properties

A functionalized polyfluorene (FPF) with dendritic carbazole and oxadiazole side chains have been successfully designed, synthesized, and characterized. The weight-average molecular weight (M _w) and number-average molecular weight (M _n) were measured by gel permeation chromatography (GPC) to be 71280 and 31185, respectively. The FPF is thermally stable with high decomposition temperature (T _d = 495 °C) and glass transition temperature (T _g = 160 °C), and show good solubility in organic solvents, such as N,N-dimethyl formamide, tetrahydrofuran, CHCl₃, and toluene. The photoluminescent and electroluminescent (EL) emissions and Commission Internationale de L’Eclairage coordinates indicated pure blue light emission of FPF and its device. The luminance–voltage (L–V) and current density–voltage (J–V) characteristics of the devices based on FPF indicated typical diode characteristics with a maximum luminance of 980 cd/m² at a drive voltage of 13.0 V, a maximum current density of 726 mA/cm², and a turn-on voltage of 8.54 V. The maximum EL efficiency of the device based on FPF was measured to be 0.46 % at the current density of 12.5 mA/cm². These results indicate that the FPF polymer could be a promising candidate for pure blue light-emitting polymer with excellent thermal, photophysical, and electroluminescent properties.     

Colloidal particles with various glass transition temperatures: preparation, assembly, and the properties of stop bands under heat treatment

Monodisperse P(St-co-nBA-co-AA) colloidal microspheres with various glass transition temperatures (T _gs), whose average particle sizes were about 300 nm, were prepared using soap-free emulsion polymerization by adjusting the ratio of styrene and n-butyl acrylate. Colloidal photonic crystals were assembled with these microspheres by vertical deposition method. Stop bands of colloidal crystals under different temperatures have been characterized. The relationship between the stop band and temperature was indicated. The microstructure and reflectance spectra of photonic crystals were characterized by SEM and fiber spectrometer, respectively. Results showed that as the temperature increased, only a little red shift of stop band appeared in the vicinity of T _g and the intensity of the maximum reflection peak decreased until the stop bands disappeared. Furthermore, enough heating time at the T _g ±2 °C could also lead to the disappearance of stop bands. What’s more, colloidal crystal films with certain connection strength were obtained by simple heating.     

Synthesis of multi-walled carbon nanotube/silica nanoparticle/polystyrene microsphere/polyaniline based hybrids for EMI shielding application

Novel polystyrene microsphere (PSMS)-based PSMS/Si and polystyrene/silica nanoparticle/multi-walled carbon nanotube (PS/Si/MWCNT) nanocomposite has been prepared using in situ sol-gel and chemical amalgamation methods. Aniline monomer was introduced by in situ route to form PSMS/PANI, PSMS/PANI/Si and PSMS/PANI/Si/MWCNT nanocomposite. FESEM of nanocomposite indicated core-shell spherical and tubular morphology. Glass transition temperature (T_g) and maximum decomposition temperature (T_max) of PSMS/PANI/Si/MWCNT nanocomposite were found as 295°C and 524°C, respectively, which were higher than the PSMS/PANI (T_g = 245°C; T_max = 387°C) and PSMS/PANI/Si (T_g = 257°C; T_max = 388°C) nanocomposite. For nanocomposite dispersion, tetrahydrofuran was studied as fine solvent. XRD depicted amorphous nature of PSMS/Si and PSMS/PANI/Si; however MWCNT reduced amorphous character of PSMS/PANI/Si/MWCNT. Electromagnetic interference (EMI) shielding effectiveness improved from 0.1 dB (PSMS) to 12.3 dB (PSMS/PANI/Si) to 24.5 dB (PSMS/PANI/Si/MWCNT). The increase in EMI shielding effectiveness was also observed with variation in log of conductivity from ?14 mho m^?1 (PSMA) to 1.17 mho m^?1 (PSMS/PANI/Si/MWCNT).     

Novel green-emitting polymer containing fluorene and 1-(2-benzothiazolyl)-3,5-diphenylpyrazoline

Novel electroluminescent (EL) polymer based on fluorene having benzothiazolylpyrazoline unit in the main chain was synthesized. The result polymer possessed satisfactory thermal stability with onset decomposition temperature (T _d) of 401 °C and glass-transition temperature (T _g) of 213 °C. The polymer emits green fluorescence with high photoluminescence (PL) quantum yield of 47%. Polymer light-emitting diode (PLED) was fabricated with the configuration of ITO/PEDT 40 nm/PVK 40 nm/polymer(80 nm)/Ba(4 nm)/Al(160 nm) showed turn-on voltage of 4.5 V, and it can emit green light with maximum brightness of 1726 cd m⁻² with the maximum external quantum efficiency of 1.59%.     

Synthesis and characterization of poly(silphenylenesiloxane)s containing functional side groups,a study to high-temperature elastomer

Poly(silphenylenesiloxane)s containing hydride or vinyl functional side groups were successfully synthesized by deaminative polycondensation of bis(aminosilane)s having the functional groups with monomeric or polymeric bis(silanol). The bis(silanol) prepolymer was prepared by palladium-catalyzed dehydrocoupling polymerization of 1,4-bis(dimethylsilyl)benzene with water. ¹H, ¹³C, and ²⁹Si NMR revealed that the polymers have exactly alternating structure of the starting component units. The poly(silphenylenesiloxane)s containing functional side groups have low T_gs ranging from −23 to −40 °C, and exhibit good thermal stability in both nitrogen and air atmosphere. For example, the most thermally stable polymer 3b-alt, having vinyl side groups on half silicon atoms, has T_g at –33°C which is 11°C lower than that of the all-methyl substituted PTMPS, and shows the highest degradation temperature at 498°C in nitrogen and 521°C in air. The TGA residues at 800°C are 67% in nitrogen and 54% in air. Isothermal studies revealed 3b-alt only lost 2.5% weight after 5h at 400°C in nitrogen.     

Synthesis, IR, crystallization and dielectric study of (Pb, Sr)TiO 3 borosilicate glass–ceramics

Eleven glass compositions were prepared by melt and quench method with progressive substitution of SrO for PbO (0?≤?x?≤ 1·0) with a step-wise increment of 0·10 in the glass [(Pb _x Sr_1???x )OTiO₂]–[(2SiO₂B₂O₃)]–[BaO·K₂O]·Nb₂O₅ (mol percentage) system. The infrared spectra (IR) of various glass compositions in the above mentioned glass system was recorded over a continuous spectral range 400–4000 cm^???1 to study their different oxides structure systematically. Differential thermal analysis (DTA) was recorded from room temperature (~27 °C) to 1400 °C employing a heating rate of 10 °C /min to determine glass transition temperature, T _g and crystallization temperature, T _c. The melting temperature, T _m, of these glass compositions was found to be in the range 597–1060 °C depending on the composition under normal atmospheric conditions. T _g and T _m of glasses were found to increase with increasing SrO content. X-ray diffraction analysis of these glass–ceramic samples shows that major crystalline phase of the glass–ceramic sample with x ≤ 0·5 was found to have cubic structure similar to SrTiO₃ ceramic. Scanning electron microscopy has been carried out to see the surface morphology of the crystallites dispersed in the glassy matrix.     

Compressive Strength of Notched Poly(Phenylene Sulfide) Aerospace Composite: Influence of Fatigue and Environment

The purpose of this work is to evaluate the influences of fatigue and environmental conditions (?55 °C, 23 °C, and 82 °C/Wet) on the ultimate compression strength of notched carbon-fiber-reinforced poly(phenylene sulfide) composites by performing open-hole compression (OHC) tests. Analysis of the fatigue effect showed that at temperatures of ?55 and 23 °C, the ultimate OHC strengths were higher for fatigued than for not-fatigued specimens; this could be attributed to fiber splitting and delamination during fatigue cycling, which reduces the stress concentration at the hole edge, thus increasing the composite strength. This effect of increasing strength for fatigued specimens was not observed under the 82 °C/Wet conditions, since the test temperature near the matrix glass transition temperature (T _g) together with moisture content resulted in matrix softening, suggesting a reduction in fiber splitting during cycling; similar OHC strengths were verified for fatigued and not-fatigued specimens tested at 82 °C/Wet. Analysis of the temperature effect showed that the ultimate OHC strengths decreased with increasing temperature. A high temperature together with moisture content (82 °C/Wet condition) reduced the composite compressive strengths, since a temperature close to the matrix T _g resulted in matrix softening, which reduced the lateral support provided by the resin to the 0° fibers, leading to fiber instability failure at reduced applied loads. On the other hand, a low temperature (?55 °C) improved the compressive strength because of possible fiber-matrix interfacial strengthening, increasing the fiber contribution to compressive strength.     

Effect of spark plasma sintering temperature on the phase equilibria and dielectric properties of BaTi2O5 ceramics

The effect of sintering temperature (ranging from 1055 to 1200 °C) on the phase ingredient and dielectric property of the nominal BaTi₂O₅ ceramics (starting with the Ba/Ti of 1:2) fabricated by a spark plasma sintering method were systematically studied. At the first stage, BaTi₂O₅ component was enhanced in the sintering temperature range of 1055–1120 °C; it turned out to be the dominant phase. For these BaTi₂O₅ phase dominated ceramics, the Curie temperature T _c rised on increasing the sintering temperature and saturated around 440 °C with the maximum dielectric constant of 500. Further increasing the sintering temperature, the decomposition of the obtained BaTi₂O₅ into BaTiO₃ extensively happened; the ceramics turned to be the BaTi₂O₅ and BaTiO₃ coexisting state. These ceramics can be characterized by two dielectric anomalies. One at ~420 °C stood for the phase transition of BaTi₂O₅ while the other at ~150 °C stood for the transition of BaTiO₃, which is exceptionally high as the normal BaTiO₃ ceramics. Further increasing the sintering temperature (until 1200 °C) would dramatically enhance the BaTiO₃ phase; the ceramics showed T _c at 130 °C with the maximum dielectric constant of 1800.     

Synthesis of the RuSr2GdCu2O8±z Compound at Ambient Pressure Through a Solid State Reaction, Melts and Sol-Gel by Acrylamide Polymerization Methods

The RuSr₂GdCu₂O_8±z (Ru-1:2:1:2) compound, was synthesized at ambient pressure by solid-state reaction, melts, and sol-gel by acrylamide polymerization methods with the following intervals of temperature reaction: T= 960–1015°C, T=1450°C, 135–980°C respectively. Differential Thermal Analysis (DTA) result gave us an idea about the temperature interval where the Ru-1:2:1:2 compound was formed. Results of X-Ray powder Diffraction (XRD) data show the formation of the Ru-1:2:1:2 phase, which crystallizes in a tetragonal structure with a space group P4/mmm. The synthesis of the Ru-1:2:1:2 compound by the melts route was found to be faster than the other synthesis methods. Studies by the Scanning Electron Microscopy (SEM) technique gives a particle size around 1–6 μm. The chemical compositions of the samples were obtained by Energy Dispersive X-ray (EDX) spectroscopy. The resistance vs. temperature data of the samples annealed in oxygen flux for 6, 12, 41 and 64 h, at T=960°C, shows a semiconductor behavior.     

Isothermal solid–liquid transitions in the (Ni,B)/ZrB2 system as revealed by sessile drop experiments

In the framework of joining processes of ultrahigh temperature ceramics (UHTCs), sessile drop experiments were performed in the Ni–B/ZrB₂ system in the range 1110° ≤ T ≤ 1200 °C. They show that, at temperatures between 1110 and 1150 °C, isothermal solid–liquid transitions occur in a sequence; while in fact at T ≥ 1200 °C, the drop melts without any further phase transition, at lower temperatures, complete melting is followed by a solidification stage and final remelting. This complex behavior, which can be very relevant when utilizing Ni–B alloys for brazing processes (e.g., by the transient liquid phase bonding technique), is successfully interpreted on the basis of the complete B–Ni–Zr phase diagram newly computed by CALPHAD: Isothermal sections, calculated between 1110 and 1150 °C, show that the composition of the drop enters, crosses, and leaves the primary solidification region of the Zr₂Ni₂₁B₆ ternary compound. The use of thermodynamic modeling for the explanation of experimental data sets a link between wetting and joining experiments and phase diagrams assessment.     

Switchable friction properties induced by shape memory effect

In this study, the thermal-responsive polymer networks based on poly(vinyl butyral) (PVB) are prepared, and their friction properties in response to external stimuli are investigated. Under dry sliding condition, the materials show low friction (COF ~0.14) at room temperature, but show ultra-high friction (COF ~1.09) at 100 °C above the glass transition temperature of PVB. This marked variation is due to the effect of recovery stress caused by the shape memory effect of polymer networks. Additionally, the recovery stress would increase with the increase of cross-linked density and test temperature above T _g, leading to a higher COF. The polymer networks also show excellent mechanical strength with tensile modulus and elongation at break over 60 MPa and 100 %, respectively. To the best of our knowledge, this is the first paradigm about tunable friction properties realized by shape memory polymer. These interesting properties would enable the polymer networks with potential application in the design of intelligent device in future.     

Fine tuning of glass transition temperature in monolithic organic photorefractive material

In order to study the effect of T_g on the photorefractivity in organic monolithic system, we designed and synthesized photorefractive homopolymer (PCzBO) and organic glass (EHCzBO), consisting of the same monolithic chromophore. Photorefractive polymer composites were prepared by blending them. T_g of PCzBO and EHCzBO were 106 and 29 °C, respectively. T_g of polymer composite could be controlled precisely by the compositional ratio of PCzBO and EHCzBO in the range from 29 to 40 °C. Since both the polymer and the organic glass contained the same chromophore structure, all the samples had nearly the same chromophore concentration even though compositional ratios of them were different, as was confirmed by UV–visible spectroscopy. Frequency-dependent ellipsometric technique showed that the birefringence contribution through the orientation enhancement effect was dominant in the refractive index modulation of our low T_g composites. It was found that the reorientation of chromophore according to the modulated voltage was more limited for the higher T_g composite, which consequently reduced the birefringence contribution. The diffraction efficiency and two beam coupling coefficient were decreased with the increase of T_g.     

Ag5Pb2O6/CuO Composite, an Approach to Ambient Temperature Superconductivity

Byström?CEvers compound Ag₅Pb₂O₆ is highly conducting oxide, and it was prepared from the components Ag₂O and PbO₂ fired in a 300 bar O₂ atmosphere and 623 K. Compound was milled, and particles were dispersed in a powdered CuO matrix. For low concentrations of metallic particles (<38 w/w percents), the composite is semiconductor or insulator, while for concentrations >48 w/w percents material is metallic down to liquid helium temperatures. For intermediate concentrations, the composite exhibits properties characteristic for superconductors with transition temperatures 178 K<T _c<356 K, dependent on the size of dissolved metallic particles and their mutual distance. Magnetic data support a presumption of novel superconductivity. Samples were prepared with SC transition temperature T _c=138 K, and in the temperature range 145?C800 K electric resistance obeys the temperature dependence ln?R??(T ₀/T)^1/2, and this indicates a possible 1-dimensional conduction mechanism.     

The effect of ZrO2 and TiO2 on solubility and strength of apatite–mullite glass–ceramics for dental applications

The effect of ZrO₂ and TiO₂ on the chemical and mechanical properties of apatite–mullite glass–ceramics was investigated after sample preparation according to the ISO (2768:2008) recommendations for dental ceramics. All materials were characterized using differential thermal analysis, X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. X-ray fluorescence spectroscopy was used to determine the concentrations of elements present in all materials produced. The chemical solubility test and the biaxial flexural strength (BFS) test were then carried out on all the samples. The best solubility value of 242 ± 61 μg/cm² was obtained when HG1T was heat-treated for 1 h at the glass transition temperature plus 20 °C (T_g + 20 °C) followed by 5 h at 1200 °C. The highest BFS value of 174 ± 38 MPa was achieved when HG1Z and HG1Z+T were heat-treated for 1 h at the T_g + 20 °C followed by 7 h at 1200 °C. The present study has demonstrated that the addition of TiO₂ to the reference composition showed promise in both the glass and heat-treated samples. However, ZrO₂ is an effective agent for developing the solubility or the mechanical properties of an apatite–mullite glass–ceramic separately but does not improve the solubility and the BFS simultaneously.