DTA Measurements Research Articles

Experimental Study of Phase Composition of B‐Fe‐Mn‐V Alloys and Thermodynamic Calculations of Phase Equilibria in the B‐Mn‐V and B‐Fe‐Mn‐V Systems

Phase compositions of B‐Fe‐Mn‐V alloys were studied by several experimental methods (DTA measurement, X‐ray diffractions, and scanning electron microscopy). Besides the experimental study of the quaternary system, thermodynamic modelling of the ternary B‐Mn‐V system by the Calphad method and thermodynamic calculations for the quaternary B‐Fe‐Mn‐V system were performed. Calculations for the quaternary system are based on the ternary subsystems (B‐Mn‐V, B‐Fe‐V, B‐Fe‐Mn, and Fe‐Mn‐V). Boron is modelled as an interstitial element in all solid solutions of vanadium, manganese, and iron. Very good agreement between experimental results and thermodynamic calculations was achieved. The created thermodynamic database is suitable for thermodynamic calculations of phase diagrams for all the ternary subsystems and also for the B‐Fe‐Mn‐V quaternary system.

Preparation and characterization of iron(III) 99Mo-molybdate(VI) gels for the assessment of 99mTc elution performance

Abstract New iron(III) 99Mo-molybdate(VI) gels (Fe99Mo) of high Mo content were prepared by the precipitation/filtration method. 99Mo–MoO3 dissolved in NaOH was added to aqueous solutions of Fe(NO3)3 at Mo/Fe mole fractions ~2.21 and 1.99 with continuous stirring at ambient room temperature. Two different Fe99Mo were precipitated from the mixed solutions adjusted at pH 2 and 4.7. The amount of water of hydration increased with the increasing the gel settling time and pH of the mixed solution. The matrices were characterized by radiometric, XRD, SEM, XRF, FT-IR, TGA, and DTA measurements. Small chromatographic columns of 2.0 g Fe99Mo containing ≥800 mg Mo tagged with 740 MBq 99Mo were eluted with 5 mL saline solution. Highly reproducible 99mTc elution indices suitable for preparation of 99Mo/99mTc generators were achieved from generator supported with 0.5 g Al2O3 filter. Elution performance of 99mTc radionuclide was highly dependent on the gel structural properties.

Experimental investigation of the phase equilibria and thermodynamic assessment in the U-Ga and U-Al-Ga systems

The phase relations in the binary U-Ga and ternary U-Al-Ga systems were established as an isopleth section and two isothermal sections at 900 K and 1150 K for the whole concentration range, respectively. They were experimentally determined by means of powder and single crystal XRD, SEM-EDS analyses on both as-cast and heat-treated samples and DTA measurements. Both systems were thermodynamically assessed using the Calphad method based on the available data, i.e. phase relations and thermodynamic properties. The new description of the U-Ga phase diagram improves the composition-temperature description for most of invariant reactions. The U-Al-Ga system is characterized by large ternary extensions of the binary phases and the absence of ternary intermediate phase at both 900 K and 1150 K. These experimental results are nicely reproduced by the Calphad assessment, allowing to extract the thermodynamic parameters further used to calculate the liquidus projection and the invariant reactions along with their temperature.

Effect of Fe2O3 addition on microstructure and dielectric properties of PbO-SrO-Na2O-Nb2O5-SiO2 glass ceramic

Glass ceramic with the addition of 0-2.0 mol% Fe2O3 were synthesized by cast quenching followed by controlled crystallization, and the effect of Fe2O3 addition on the microstructure and dielectric properties of PbO-SrO-Na2O-Nb2O5-SiO2 (PSNNS) glass ceramic were investigated. DTA measurements revealed that the crystallization temperature of (Pb,Sr)Nb2O6 can be decreased by adding Fe2O3, meanwhile, the grain sizes of PSNNS glass ceramic increase with the increasing amount of additives. Dielectric properties of PSNNS glass ceramic were obviously affected by Fe2O3 addition. With 1.5 mol% Fe2O3 addition, the dielectric constant increased from 720 to 917, the dielectric loss increased from 0.012 to 0.0124. The PSNNS glass ceramic with 1.5% Fe2O3 addition show great promise for high voltage capacitors applications.

Stabilization of Superionic δ–Bi2O3 Phase at Room Temperature By Thermal Nanocrystallization of Bismuth Oxide Glasses

INTRODUCTION Crystalline δ–Bi2O3 is the best O2– ion conductor, but it is stable in a relatively narrow temperature range 729–825 °C only. Its very high ionic conductivity (1 S/cm at 750 °C) has motivated many researchers to look for a method to stabilize this fluorite-type structure to lower temperature. So far the successful strategies to achieve the stabilization of the delta phase have included doping (e.g. by rare-earth elements [1]) or synthesis in form of thin films [2]. Our approach to reach the same goal is significantly different from those two strategies. It consists of two steps: i) preparation of the Bi2O3 glass (pure or only slightly doped) and ii) thermal nanocrystallization of the glass prepared in stage i). The advantages of such an approach are as follows: a) the final material is pure or nearly pure Bi2O3 and b) it can be prepared in bulk and is not limited to thin layers only. Our earlier experience with nanocrystallization of glassy analogs of some cathode materials for Li-ion batteries has shown that by the appropriate heat-treatment one can achieve a dramatic (even by a factor of 109) and irreversible enhancement of their electrical conductivity [3,4]. This effect is closely related to changes in the microstructure – namely to formation of nanoscale crystalline grains, with dimensions going down even to a few nanometers, confined in the glassy matrix. EXPERIMENTAL In this research, we firstly obtained a pure Bi2O3 glass and then subjected it to an appropriate thermal treatment. Bismuth (III) oxide was melted at 1100 °C in a furnace and rapidly quenched. As a result, transparent orange glass with ca. 1 mm in thickness was obtained. Thermal events were observed by DTA measurements and the amorphousness of as-quenched material was confirmed by XRD. Crystallization and phase transitions taking place during heating and cooling were observed in-situ by temperature dependent XRD measurements. The microstructure of heat-treated samples was investigated by electron microscopy (both SEM and HRTEM). The total electrical conductivity of nanocrystallized samples as a function of temperature has been determined in preliminary measurements by impedance spectroscopy. RESULTS AND DISCUSSION It was observed by SEM that nanograins (20–40 nm) of δ–Bi2O3 phase were formed in glassy matrix (Fig. 1) upon heating to temperature within the 530–630 °C range, as confirmed by XRD. The phase remained stable after cooling down to room temperature even after ca 1 year of ageing. Heating to higher temperature led to formation of β–Bi2O3 phase, which remained stable down to room temperature. Preliminary electrical measurements showed an increase in the total conductivity at room temperature from 10–19 S/cm (for the initial glass) to 10–12 S/cm (for nanocrystalline samples). Analyses of Nyquist plots revealed the presence of a small arc at high frequencies that may be attributed to the conductivity of the interiors of nanocrystallites with δ–Bi2O3 phase. CONCLUSIONS Synthesis of δ–Bi2O3 phase stable at room temperature in form of nanocrystallites embedded in glassy matrix in bulk samples is an important result, from viewpoints of basic knowledge as well as applications. Further studies will be focused on syntheses of nanocrystallized samples with the highest possible ionic conductivity. References M. Leszczynska, X. Liu, W. Wrobel, M. Malys, J.R. Dygas, S.T. Norberg, S. Hull, F. Krok, I. Abrahams, Journal of Materials Chemistry A 2 (2014) 18624–18634. H.T. Fan, S.S. Pan, X.M. Teng, C. Ye, G.H. Li, L.D. Zhang, Thin Solid Films 513 (2006) 142–147. J.E. Garbarczyk, T.K. Pietrzak, M. Wasiucionek, A. Kaleta, A. Dorau, J.L. Nowiński, Solid State Ionics 272 (2015) 53–59. Figure 1

Thermal properties and formation mechanism of h‐BN nanoneedles synthesized via carbothermic reduction reaction

AbstractHexagonal boron nitride (BN) was synthesized through the carbothermic reduction reaction (CRR) of boric acid using lactose as a carbon source under the nitrogen atmosphere at 1500°C for 3 hours. The boron/carbon (B/C) molar ratio was controlled during the CRR, and the produced samples were investigated by XRD diffraction pattern, FTIR analysis, and Raman spectra. Boron carbide (B4C) was formed in samples that have a higher carbon content, in addition to boron nitride. While boron nitride pure sample was produced from lower carbon content samples. Formation of B4C was found to depend on the B/C molar ratio. The morphology of the produced powder was also investigated by SEM and TEM, which revealed that the samples consist of nanoneedles of BN and hexagonal particles of B4C. The vapor‐solid (VS) reaction mechanism was processed greatly with increasing boron amount, producing boron nitride nanoneedles, which compete with the liquid‐solid (LS) reaction mechanism. The physicochemical properties of the produced samples were studied by DTA, UV, PL, and AC impedance measurements, and revealed that the samples are promising to many proper applications.

Interdependence of Structure, Morphology, and Phase Transitions in CVD Grown VO2 and V2O3 Nanostructures

Phase selective chemical vapor deposition of nanostructured vanadium dioxide (VO2) and sesquioxide (V2O3) was achieved by deploying [V(OR)4]n (R = tBu, n = 1 (1), R = Et, n = 3 (2), R = Me, n = 4 (3)). Use of [V(OtBu)4] (1) produced thin films of monoclinic VO2 (M1) at 700 and 800 °C consisting of anisotropic nanostructures with high crystallinity and small hysteresis in the metal-to-semiconductor transition (MST). Film morphologies manifested strong dependence on growth temperatures and exhibited pronounced texturing effects at high temperatures (>700 °C). The microstructure of the films was found to significantly affect the MST behavior of VO2 films. DTA measurements of VO2 films showed MST at 63 °C (700 °C) and 65 °C (800 °C), much lower than the transition temperature observed in single crystal material (68 °C). Precursors were characterized in the solid state (XRD) and solution state (temperature dependent EPR, NMR) to reveal an association–dissociation equilibrium in solution (complexes 2 and 3), in...

Thermooxidative stability of polypropylene/TiO2 and polypropylene/layered silicate nanocomposites

Thermooxidative stability of polypropylene (PP), PP/TiO2 and PP/Cloisite 10A nanocomposites was studied using non-isothermal DTA measurements. The effect of various concentrations of both nanofillers on the stability of pristine PP was evaluated. Moreover, the influence of additional processing cycles on the stability of all samples was investigated. For the treatment of the experimental results, our method for the evaluation of the induction periods of thermal oxidation using non-Arrhenian temperature functions was employed. Values of the induction periods were taken as a measure of the samples stability. The results obtained clearly demonstrate that both TiO2 and Cloisite 10A nanoparticles accelerate thermooxidative degradation of PP. Stability of nanocomposites decreases drastically in comparison with pristine PP, especially at lower concentrations of both nanofillers. The lifetime of all PP samples decreases with additional processing cycles. The steepest decrease is observed after first and second additional passes through the extruder, and then, the stability remains almost constant up to five passes.

Effect of Strontium the phase structure of Ba1−xSrxCe0.65Zr0.2Y0.15O3−δ (0 ≤ x ≤ 0.25) proton conductor by citrate–EDTA complexing sol–gel method

Proton conducting oxides Ba1−xSrxCe0.65Zr0.2Y0.15O3−δ (0 ≤ x ≤ 0.25) are prepared using the citrate–EDTA complexing sol–gel method. The effect of strontium and yttrium doping on the material properties is systematically investigated. The phase formation, thermal analysis, morphology, stability and conductivity measurements are performed on the sintered powders through TG–DTA, XRD, SEM, EDAX, FTIR, Raman and LCR measurements. The results indicated a single-phase orthorhombic system. Strontium incorporation helped in increasing the grain size up to 20% of strontium doping while reducing the lattice parameters and unit cell volume. The ionic conductivities of the Ba1−xSrxCe0.65Zr0.2Y0.15O3−δ sintered oxides increased with increase in the concentration of Sr2+ along with the co-doping strategy of trivalent Y3+ in the B site. Among the synthesized samples, Ba0.8Sr0.2Ce0.65Zr0.2Y0.15O3−δ pellet with orthorhombic structure showed highest conductivity with a value of 2.35 × 10−1 S/cm and 2.41 × 10−1 S/cm at 500 °C due to its smaller lattice volume, larger grain size and lower activation energy that led to excessive increase in conductivity. All pellets exhibited good chemical stability when exposed to air and H2O atmospheres. These results indicate that this composition can be used as a potential electrolyte if synthesis conditions and temperature are well maintained.

Dehydrogenation of ammonia borane aided by hydrophobic ionic liquids

The beneficial effect on the dehydrogenation of ammonia borane due to mixing with hydrophobic ionic liquids (ILs) is investigated by means of detailed combined TG–DTA and IR measurements. Desorption of several mixtures of ammonia borane with hydrophobic ILs having bis(trifluoromethanesulfonyl)-imide or trifluorosulfonyl-imide anions was studied in both isothermal and non-isothermal conditions. The addition of hydrophobic liquids lowers the dehydrogenation temperatures and allows the observation of the decomposition process without any induction time even at temperatures below 90 °C. The IR data of the products of the decomposition confirm that ILs do not react with AB but provide an highly polar medium which promotes the decomposition reaction. Furthermore, the proposed method to enhance hydrogen release from ammonia borane provides the possibility of working in air avoiding any protective atmosphere.

Synthesis, characterization and electrochemical properties of poly(phenoxy-imine)s containing carbazole unit

Several new Schiff base polymers were synthesized via oxidative polymerization method in an aqueous alkaline medium in the presence of NaOCl as an oxidant and were confirmed by FT-IR, 1H-NMR, 13C-NMR and UV–Vis spectroscopic techniques. Furthermore, cyclic voltammetry measurements were carried out and the HOMO–LUMO energy levels and electrochemical band gaps (Eg′) were calculated. Additionally, the optical band gaps (Eg) were determined using their UV–Vis spectra of the materials. The morphologic properties of the polymers were investigated by scanning electron microscopy. In addition, the number average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity index values of the polymers were determined by gel permeation chromatography technique. Electrical conductivity measurements of the doped (with iodine) and undoped polymer related to doping time were carried out by four-point probe technique using a Keithley 2400 electrometer. Their thermal behaviors were determined by TG–DTA and DSC measurements. The synthesized compounds were soluble in common solvents such as DMF, THF and DMSO. Photoluminescence properties of the polymers were determined in different concentrations of DMF solvent.

Phase equilibria study and characterization of the alloys in the BiCu0.5Ni0.5 section of the Bi-Cu-Ni system

The Bi-Cu-Ni system is a very significant, because its alloys belong to the group of potential Cu-Ni-based advanced lead-free solder materials for high temperature application. The results of phase equilibria investigation and characterization of the alloys selected in the Bi-Cu0.5Ni0.5 section from bismuth corner with molar ratio Cu:Ni = 1:1, are presented in this paper. The investigations were performed using different experimental methods - DTA, DSC, SEM-EDS, hardness and electrical conductivity measurements, while thermodynamic calculation was done according to the CALPHAD method using PANDAT software.

Enzymatic synthesis of 5-amino quinoline oligomers and evaluation of their free radical scavenging activity

The compound 5-aminoquinoline (AQ) was treated with horseradish peroxidase (HRP) and H2O2 in a reaction medium containing a dioxane:phosphate buffer mixture (70:30). Products (OAQ) with a degree of polymerization ranging from 4 to 12 were obtained. 1H NMR, FTIR, UV–vis, SEM, TG–DTA, DSC, XRD analysis, and conductivity measurements were conducted for characterization of OAQ. Compared with a monomer, OAQ showed higher thermal stability. After heating to 1000 °C, 46% of the initial weight of the OAQ remained. The antioxidant efficiencies of the monomer and oligomer were evaluated by the typical spectrophotometric method such as the bleaching of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals. OAQ showed improved DPPH activity compared with the AQ monomer.

Investigation on the crystal growth, molecular structure and nonlinear optical susceptibilities of 2-[2-(4-Ethoxy-phenyl)-vinyl]-1-ethyl-stilbazolium iodide (EESI) by Z-scan technique using He–Ne laser for third-order nonlinear optical applications

Organic 2-[2-(4-Ethoxy-phenyl)-vinyl]-1-ethyl-stilbazolium iodide (EESI), a derivative of the stilbazolium family single crystal was synthesized by condensation method. Nearly perfect as-gown single crystals of EESI structure was confirmed by single-crystal X-ray diffraction studies. The crystal has a triclinic system with the space group P-1, the molecule consists of one pyridinium cation, one iodide anion, and 0·5H2O molecules. The nature of charge transfer, molecular properties, electrostatic potential map, and HOMO-LUMO energy gap of EESI have been theoretically investigated by Sparton’10 V1.0.1 program. The optical transparency of EESI was studied by Uv–Visible spectral analysis. The growth features were observed during the etching studies using a Carl Zeiss optical microscope (50X magnification). The mechanical behavior of the crystal was estimated by Vickers microhardness test, which shows reverse indentation size effect (RISE) with good mechanical stability. Both the dielectric constant and dielectric loss increases with the increasing temperature and attain almost constant at higher frequencies, which justify the crystal quality and essential parameter for electro-optic device applications. The complex impedance analysis explains the electrical property of EESI. TGA and DTA measurements determined the thermal stability of the grown crystal. Laser-induced damage threshold energy measurements exhibit that the excellent resistance with good threshold energy up to 2.08GW/cm2 that was found to be more than that of some known organic and inorganic NLO crystals. Photoconductivity of EESI crystal confirms that the positive photoconductivity nature. Also, the third-order nonlinear optical (NLO) properties of EESI were investigated by using the single beam Z-scan technique under the Visible light (632.8nm) region. The results show that EESI has effective third-order nonlinear optical property with the nonlinear refractive index n2 =1.787×10-11m2/W, third-order nonlinear optical susceptibility χ(3) =4.229×10-6esu and second-order hyperpolarizability (γ) =1.468×10–33 esu. It is found to be larger than that of some organic NLO materials. All the obtained results are making it a potential candidate as useful non-linear optical (NLO) applications.

The Reagent‐depending Nitration of 1,3‐Dihydroxyacetone Dimer

Two highly energetic nitric acid esters were synthesized from the dimer of dihydroxyacetone. 1,3‐Dinitratoacetone (1) and its dimer 2,5‐bis(nitratomethyl‐2,5‐nitrato)‐1,4‐dioxane (2) were characterized by single‐crystal X‐ray diffraction, vibrational spectroscopy (IR and Raman), multinuclear NMR spectroscopy, and elemental analysis. The thermal behavior was investigated with DTA measurements. Although showing the same atomic stoichiometry, dimer 2 shows significantly higher sensitivities measured by BAM methods (drophammer and friction tester). Due to the high oxygen content of 62.2 %, 1 and 2 were evaluated as potential high energy dense oxidizers.

Hydrogen Induced Abrupt Structural Expansion at High Temperatures of a Ni32Nb28Zr30Cu10 Membrane for H₂ Purification.

Ni-Nb-Zr amorphous membranes, prepared by melt-spinning, show great potential for replacing crystalline Pd-based materials in the field of hydrogen purification to an ultrapure grade (>99.999%). In this study, we investigate the temperature evolution of the structure of an amorphous ribbon with the composition Ni32Nb28Zr30Cu10 (expressed in atom %) by means of XRD and DTA measurements. An abrupt structural expansion is induced between 240 and 300 °C by hydrogenation. This structural modification deeply modifies the hydrogen sorption properties of the membrane, which indeed shows a strong reduction of the hydrogen capacity above 270 °C.

Li2ADC·2H2O and Li2ADC: Two new Coordination Polymers with the Acetylenedicarboxylate Dianion (ADC2–)

Single crystals of dilithium‐acetylenedicarboxylate‐dihydrate, Li2ADC·2H2O (1), were isolated from a solid product formed by isothermal evaporation of an aqueous solution of LiOH und acetylenedicarboxylic acid (H2ADC). 1 crystallizes in the triclinic space group P1 with Z = 2. LiO4 tetrahedra are interconnected by ADC2– anions and water molecules to form a 3D polymeric structure. Coupled TGA and DTA measurements show that 1 loses its two water molecules above 100 °C. Heating a polycrystalline sample of 1 at 140 °C for 2 h in an argon atmosphere leads to a significant change of the powder diffraction pattern indicating the formation of the new anhydrous coordination polymer dilithium‐acetylenedicarboxylate, Li2ADC (2). Its crystal structure was solved and refined from X‐ray powder diffraction data. 2 crystallizes in the orthorhombic space group Fddd (Z = 8). LiO4 tetrahedra are interconnected by ADC2– anions to form a 3D polymeric structure.

Investigation on the Sodium and Potassium Tetrasalts of 1,1,2,2‐Tetranitraminoethane

With respect to high-energy dense materials with high oxygen-content, the tetrasodium salt of 1,1,2,2-tetranitraminoethane as monohydrate Na(4)TNAE center dot H2O (4) and the tetrapotassium salt as dihydrate K(4)TNAE center dot 2H(2)O (5) were synthesized and reported for the first time together with their crystal structures at 173 K. Whilst 4 cannot be dehydrated the crystal water content of 5 can be removed irreversibly at 160 degrees C to obtain K(4)TNAE (6) as demonstrated by DTA and TGA measurements. K(4)TNAE (6) was demonstrated using the small scale reactivity test to be a inferior explosive to RDX and CL-20. However the anionic nitramine compound was measured to be less toxic against Vibrio fischeri than RDX (EC50: 240 mg.L-1) with respect to its EC50 value above 15070 mg.L-1. This demonstrates that the introduction of anionic nitramine moieties is a promising concept for the stabilization of energetic materials with lower toxicity.

Effect of Solvent Variations in the Alcothermal Synthesis of Template-Free Mesoporous Titania for Dye-Sensitized Solar Cells Applications.

A series of 14 mesoporous titania materials has been synthesized using the simple alcothermal template-free method and various alcohols, such as methanol, propanols and butanols, as solvents. All materials were characterized by both wide and small angle XRD, which exhibited the anatase phase with short-range ordered mesoporous structure that is still forming during post synthetic temperature treatment in most of the investigated materials. Nitrogen adsorption–desorption isotherms confirmed the mesoporous structure with surface area ranging from 241 to 383 m2g- 1 and pore volumes from 0.162 to 0.473 m3g-1, UV-Vis diffuse reflectance showed the redshift of the absorption edge and the bandgap decrease after post synthetic calcination of the materials presented. The TEM, FT-IR, DTA and TG measurements have been made to well characterize the materials synthesized. The mesoporous samples obtained were applied as anode materials for dye-sensitized solar cells and showed good activity in photon-to-current conversion process with efficiency values ranging from 0.54% to 4.6% and fill factors in the 52% to 67% range. The photovoltaic performances were not as high as those obtained for the materials synthesized by us earlier employing ethanol as a solvent. The differences in the electron lifetime, calculated from electrochemical impedance spectroscopy results and varying between 4.3 to 17.5 ms, were found as a main factor determining the efficiency of the investigated photovoltaic cells.

Structural, thermal, electrical and morphological characterization of (Bi2O3)1−x−y(Sm2O3)x(Yb2O3)y nanostructures prepared by solid state synthesis

In the present work, the ternary system of (Bi2O3)1−x−y(Sm2O3)x(Yb2O3)y was investigated. For the production and stabilization of the fcc-type solid solution, nano-Sm2O3 and nano-Yb2O3 were doped into nano-Bi2O3 by solid-state synthesis techniques. The XRD results showed that the crystallographic structure of the samples had displayed a fluorite type face-centered cubic δ-Bi2O3 phase. The phase stability was also checked by the DTA measurements. The temperature dependent electrical conductivity results revealed that the maximum electrical conductivity observed for the sample of the nanostructure-(Bi2O3)0.8(Sm2O3)0.1(Yb2O3)0.1 system was 5.39 × 10−2 (ohm.cm)−1 at 650 °C. The results also show that the lowest activation energy was 0.7062 eV and the lowest crystallite size was 31.62 nm for the nanostructure-(Bi2O3)0.75(Sm2O3)0.1(Yb2O3)0.15 system. Consequently, the face-centered cubic stable δ-phase-(Bi2O3)0.8(Sm2O3)0.1(Yb2O3)0.1 is the optimal dopant amount due to the relatively good stability and oxygen ionic conductivity obtained, which are two of our major concerns for the electrolyte layer of solid oxide fuel cells (SOFCs).