Crystal structure and thermal behavior of two new organic monosulfates NH3(CH2)5NH3SO4 1.5H2O and NH3(CH2)9NH3SO4 H2O

The chemical preparation, the calorimetric studies and the crystal structure are given for two new organic sulfates NH₃(CH₂)₅NH₃SO₄ 1.5H₂O (DAP-S) and NH₃(CH₂)₉NH₃SO₄·H₂O (DAN-S). DAP-S is monoclinic P2₁/n with unit cell dimensions: a=11.9330(2) Å; b=10.9290(2) Å; c=17.5260(2) Å; β=101.873(1)°; V=2236.77(6) Å³; and Z=8. Its atomic arrangement is described as inorganic layers of units and water molecules separated by organic chains. DAN-S is monoclinic P2₁/c with unit cell parameters: a=5.768(2) Å; b=25.890(10) Å; c=11.177(5) Å; β=115.70(4)°; V=1504.0(11) Å³ and Z=4. Its structure exhibits infinite chains, parallel to the [100] direction where the organic cations are interconnected. In both structures a network of strong and weak hydrogen bonds connects the different components in the building of the crystal.     

Specific heat measurements in pure and in (Cu, Mn, Fe, Ni)-doped single-crystals of l-arginine phosphate monohydrate

The influence of highly diluted impurities (Cu, Mn, Fe, Ni) on the temperature (T) dependence of the specific heat (c_p) of l-arginine phosphate monohydrate (LAP) was investigated in the temperature range 1.8-300 K. The doped samples yielded values for c_p in excess to those obtained for a pure LAP sample. The melting temperatures (T_m≈420 K) obtained by differential scanning calorimetry for pure and doped LAP samples were found not to be significantly affected by the impurities. The T-dependence of c_p was fully accounted for by taking into consideration the Debye contribution, an Einstein term and a contribution due to both Frenkel and Schottky defects. The model fit all c_p versus T data using a single value for both the Debye (θ_D=160 K) and the Einstein (T_E=376.8 K) temperatures, and for the energy (ε_d=157.9 meV) required to create the defects.     

Dielectric and AC ionic conductivity investigations in K3H(SeO4)2 single crystal

Optical observation under the polarizing microscope and DSC measurements on K₃H(SeO₄)₂ single crystal have been carried out in the temperature range 25-200 °C. It reveals a high-temperature structural phase transition at around 110 °C. The crystal system transformed from monoclinic to trigonal. Electrical impedance measurements of K₃H(SeO₄)₂ were performed as a function of both temperature and frequency. The electrical conduction and dielectric relaxation have been studied. The temperature dependence of electrical conductivity indicates that the sample crystal became a fast ionic conductor in the high-temperature phase. The frequency dependence of conductivity follows the Jonscher's universal dynamic law with the relation σ(ω)=σ(0)+Aωⁿ, where ω is the frequency of the AC field, and n is the exponent. The obtained n values decrease from 1.2 to 0.1 from the room temperature phase to fast ionic phase. The high ionic conductivity in the high-temperature phase is explained by the dynamical disordering of protons between the neighboring SeO₄ groups, which provide more vacant sites in the crystal.     

Structure and thermal behaviors of organic crystals based on substituted 1,3,4-thiadiazoles

The crystalline structure of some compounds containing the 1,3,4-thiadiazole moiety, (1) 5-ethyl-2-amino-1,3,4- thiadiazole (EATZ), (2) 5-benzylsulfany-2-amino-1,3,4-thiadiazole (BSATZ) and (3) 2,5-bis-benzylsulfanyl-1,3,4-thiadiazole (BBSTZ) were determined. Both EATZ and BBSTZ show orthorhombic structures with space group Pbca and BSATZ a monoclinic system with space group C2/c. The lattice parameters: a=0.72280 (14), b=1.0811 (2), c=1.6210 (3) nm for 1, a=2.5282 (5), b=0.59083 (12), c=1.5390 (3) nm for 2 and a=0.87530 (18), b=1.0365 (2), c=3.6098 (7) nm for 3. To compare the intra- and intermolecular interactions in thiadiazole containing organic crystals, thermal analysis studies on each crystal is performed using DSC and TG in N₂ atmosphere to describe the thermal behaviors. Based on the results, the changing regularity of melting point and decomposition temperature of these compounds is educed     

Effects of niobium on thermal stability and corrosion behavior of glassy Cu-Zr-Al-Nb alloys

The corrosion behavior of Cu_95−xZr_xAl₅ (x=40, 42.5 and 45 at.%) in 1 N HCl, 3 mass% NaCl and 1 N H₂SO₄ solutions was studied. As Zr content increases, the corrosion resistance is slightly enhanced. In order to improve the corrosion resistance of the Cu-Zr-Al glassy alloy, Nb was selected to substitute Cu. Although the supercooled liquid region ΔT_x of the Cu-Zr-Al glassy alloys decreases with increasing Nb content, the alloys still retain high glass-forming ability and bulk glassy samples with 1.5 mm diameter can be obtained when up to 5 at.% Nb was added. It is found that the addition of Nb results in improvement of the corrosion resistance of the glassy Cu-Zr-Al alloys.     

Influence of framework silica-to-alumina ratio on the water adsorption and desorption characteristics of MHI-CaX/CaY zeolite

The influence of the framework SiO₂/Al₂O₃ ratio from 2.0 to 10.0 of commercial faujasite-type CaX/CaY zeolite produced by Mitsubishi Heavy Industries Ltd. (MHI) on the water adsorption and desorption characteristics was investigated. Not only the change in electronegativity of the zeolite but the change in pore-size distribution of the zeolite affects the water adsorption and desorption characteristics of the zeolite. We found great differences in isotherms of water between CaY7.0 (SiO₂/Al₂O₃=7.0) and CaY10.0. The differences are mainly caused by the considerable change in pore-size distribution. A step-wise variation was observed in the desorption isotherm of water from CaY10.0 at approximately P/P₀=0.4. This is due to the pore distribution of CaY10.0 being relatively poor in smaller micropores in zeolite structure, since a similar phenomenon is observed in the case of argon adsorption on CaY10.0. In the experiments using a fixed bed, an apparent dependency of HTO dehydration ratio on the flow rate of the purge gas is measured with the CaY10.0 zeolite, while the water desorption from other tested CaX/CaY zeolite is independent of the flow rate of helium purge gas. This indicates that the transfer step of water diffusion through a laminar film appeared as one of the rate-controlling steps in the water desorption from CaY10.0.     

Molecular alloys as phase change materials (MAPCM) for energy storage and thermal protection at temperatures from 70 to 85 °C

Molecular alloys, that combine a relatively high heat of melting with a suitable melting temperature adapted to the application temperature, are excellent materials for thermal protection and for thermal energy storage. Of special interest is the fact that, by making alloys of molecular materials; the range of melting can be adjusted over a range of temperatures. The present paper reports on the design of MAPCMs to be used for energy storage and thermal protection at temperatures from 70 to 85 °C. The aim is to use these materials for thermal protection in the catering sector in order to avoid proliferation of micro organisms; the minimal temperature required is higher than 65 °C. The work illustrates how some fundamental studies are helpful in choosing the right composition that is able to work at the temperature required for an application. Several molecular alloys using the n-alkanes are elaborated and characterized. The preparation of mixed crystals, their crystallographic and thermodynamic properties and stability, phase change behaviour, and their use in practical applications are reported.     

Hydrogen desorption processes in Li-Mg-N-H systems

Li-Mg-N-H systems composed of Mg(NH₂)₂ and LiH with various ratios can reversibly store a large amount of hydrogen under the temperature condition above 150 °C. These composites with 3:6, 3:8 and 3:12 ratio of Mg(NH₂)₂ and LiH have been independently reported by four groups as promising candidates of high performance hydrogen storage materials possessing the reversibility and the high capacity. In any cases, an interaction between NH₃ and LiH plays an important role for the progress of hydrogen desorbing and absorbing reactions. For the hydrogen desorption process, the NH₃ molecule generated from Mg(NH₂)₂ reacts with LiH, forming LiNH₂ and H₂. Especially, under an equilibrium condition, in situ diffraction results indicated that the single phase of LiNH₂·MgNH (LiMgN₂H₃) could be generated other than the separated two phases. As a next step, the NH₃ molecule generated from LiNH₂ reacts with LiH, desorbing H₂. As a result, the dehydrogenated phase was evaluated to be Li₂NH·MgNH (Li₂MgN₂H₂) or separated two phases, in which the final phase should depend on the experimental conditions. Thus, if the amount of LiH is enough to react with NH₃, the hydrogen desorption processes are described by the NH₃ generation from the corresponding amides and the imide.     

Characterization of explosives traces by the Nanocalorimetry

Thermal characterization of energetic materials is often a non-trivial task. Experiments on such materials employing differential scanning calorimetry (DSC) have been mainly performed using special high-pressure crucibles, in which the pressure uncontrollably changes during the measurement. Conducting constant pressure experiments would allow addressing the decomposition reaction kinetics in a more quantitative way. In addition, the explosives detection requires sensing much smaller amounts of samples than those used in the DSC measurements. Explosives in the state of traces typically provide the sample sizes in the nano-gram to pico-gram range.The present work has been carried out with the Nanocalorimeter (www.nanotlab.com), which can safely measure nano-gram-size samples. The Nanocalorimeter is operational in both DC and AC modes. In the DC mode, the device can perform heating ramps at ultra-fast heating rates (10³-10⁶ K/s) that are up to 1 million times faster than the conventional DSC. In the AC mode, which is analogous to the Modulated-DSC, the interval of the temperature modulation frequencies is also unmatched: the upper frequency bound reaches 3.0-10.0 kHz. Similar to the experimental setups described in the literature, the Nanocalorimeter employs a commercial gas sensor with integrated heating elements and thermocouples.In this work, a series of energetic materials of practical interest such as hexogen (cyclotrimethylenetrinitramine) and pentrite are characterized for the first time using ultra-fast heatings. The samples have been deposited on the sensor membrane using either micro-manipulation or spin-coating. Coupling of the Nanocalorimeter to a fast CCD camera was found quite useful to simultaneously visualize the processes occurring on a micro-second time-scale.     

Calorimetric study of characteristic temperatures and crystallization behavior in Ge-As-Se-Te glass system

Results of differential scanning calorimetry of high purity Ge_xAs_40−xSe₄₀Te₂₀ (x=0-40) chalcogenide glasses are reported. The glass transition temperatures and crystallization behavior were studied under non-isothermal conditions at different heating rates (2.5-35 K/min). The glass transition temperature changes from 140 °C up to 320 °C with increasing the Ge content in Ge_xAs_40−xSe₄₀Te₂₀ glass. The studied glasses with x≤35 have no exothermal peaks of crystallization, indicating their high glass-forming ability. The glass of Ge₄₀Se₄₀Te₂₀ composition has one-stage glass transition and double-stage crystallization process during phase change. The activation energy of the glass transition (E_g), the activation energy of crystallization (E_c), the Avrami exponent (n), the frequency factor (K₀) and the crystallization criteria of Ge₄₀Se₄₀Te₂₀ glass were determined.     

Thermal stability and reaction properties of passivated Al/CuO nano-thermite

Thermal stability and reaction properties of Al-CuO system, a mixture of 50-200 nm aluminum nanoparticles passivated by nitrocellulose and 12 nm copper (II) oxide, were investigated with microstructure characterization, differential thermal analysis (DTA), and thermogravimetric analysis (TGA). Transmission electron microscopy observation confirmed that the passivation coating successfully hinders the oxidization. TGA revealed that the passivation shell does not influence the ignition temperature of the thermite reaction. Reaction chemistry of the nano-thermite was elucidated by heating the composite both in inert ambient and vacuum. It was found that the thermite reaction composes of three continuing steps: At 570 °C, Al is oxidized into Al₂O₃ by reacting with CuO, which forms Cu₂O and produces a significant amount of heat. Subsequently two endothermic reactions occur. Starting at 800 °C, alumina reacts with Cu₂O and forms CuAlO₂. Above this temperature CuAlO₂ will decompose and eventually produce alumina, Cu, and O₂ at 1000 °C. Since the nano-thermite reaction pathway differs greatly from bulk thermite reactions, these results are important to develop a nano-thermite platform that can be used for a novel low cost, low temperature, and copper based microjoining and advance IC packaging.     

Crystal structure,ionic conductivity and dielectric relaxation studies in the (C5H10N)2BiBr5 compound

The synthesis and crystal structure of the bis (3-dimethylammonium-1-propyne) pentabromobismuthate(III) salt are given in the present paper. After an X-ray investigation, it has been shown that the title compound crystallizes at 298 K in a centrosymmetric monoclinic system, in the space group C₂/c with the following lattice parameters a=12.9034(3) Å, b=19.4505(6) Å, c=8.5188(2) Å, β=102.449(2). Not only were the impedance spectroscopy measurements of (C₅H₁₀N)₂BiBr₅ carried out from 209 Hz to 5 MHz over the temperature range of 318 K–373 K, but also its ac conductivity evaluated. Besides, the dielectric relaxation was examined using the modulus formalism. Actually, the near values of activation energies obtained from the impedance and modulus spectra confirms that the transport is of an ion hopping mechanism, dominated by the motion of the H⁺ ions in the structure of the investigated material.     

Morphology and properties of poly(methyl methacrylate)/clay nanocomposites by in-situ solution polymerization

Poly(methyl metacrylate)/montmorillonite (PMMA)/(MMT) nanocomposites were prepared by in-situ solution polymerization of methyl methacrylate monomer in the presence of the organic modified MMT-clay. After the organic modification by ionic exchanging with amine salts, the organoclay becomes more hydrophobic and compatible then pristine clay with methyl methacrylate monomer. The modified clays are characterized by wide angle X-ray diffraction (WAXRD). The powdered X-ray diffraction and transmission electron microscopy (TEM) techniques were employed to study the morphology of the PMMA/clay nanocomposites which indicate that the modified clays are dispersed in PMMA matrix to form both exfoliated and intercalated PMMA/modified clay nanocomposites. The thermo-mechanical properties were measured by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC). Gas permeability analyzer (GPA) shows the excellent gas barrier property of the PMMA nanocomposites which is in good agreement with the morphology. The optical property was measured by UV-vis spectroscopy which shows that these materials have good optical clarity, and UV resistance.     

Microwave synthesis and textural property of europium substituted mesoporous molecular sieves

Using cetyltrimethyl ammonium bromide (CTAB) as the template and sodium silicate as the silicon source, the MCM-41 mesoporous molecular sieves with Eu incorporated in the framework were synthesized under microwave irradiation condition and the influence of the Si/Eu molar ratio on the crystalline structure, textural properties and the long-range ordering of the resulting sample was investigated by various physicochemical techniques such as X-ray diffraction (XRD), transmission electron microscope (TEM), diffuse reflectance ultraviolet-visible spectroscopy (UV-vis), thermal gravimetric-differential scanning calorimeter (TG-DSC) and N₂ physical adsorption. The results of N₂ adsorption and XRD reveal that the synthesized sample has the ordered hexagonal mesoporous structure. UV-vis spectra provide the strong evidences that most of europium ions were incorporated into the framework of the MCM-41 sample. The crystalline structure, textural properties and mesoporous ordering of the resultant mesoporous materials are related to the amount of europium incorporation. Small amount europium incorporated into the silica-based MCM-41 does not strongly modify the structure of mesoporous molecular sieve. An increase of the Eu content in sample led to reduction of the specific surface area and the deterioration of the long-range ordering.     

Polystyrene-co-maleic acid/CdS nanocomposites: Preparation and properties

Composites of CdS nanoparticles confined in a polystyrene-co-maleic acid (PS-co-MAc) matrix have been prepared and characterized. It was shown that the acid groups of the co-polymer could be successfully used to control the aggregation of the nanoparticles, because they act as coordinate sites for Cd ions. UV-VIS measurements showed a blue shift of the absorption threshold, proving the presence of nanoparticles. An average size of the nanoparticles of about 4 nm is estimated from the change in band gap energy. Although the FTIR spectrum of the nanocomposite showed the presence of C-S bonds, a broad emission originating from surface recombination sites are noticed. DSC and TGA measurements revealed changes in thermal properties upon incorporation of nanoparticles. No thermal transition was observed in the nanocomposite, while the pure co-polymer exhibits a glass transition at 190 °C. In the presence of nanoparticles the onset of the thermal decomposition of the matrix is also shifted by 50 °C towards a higher temperature.     

Photophysical and electrochemical properties of monoporphyrin rare earth liquid crystalline materials

The synthesis and characterization of [5-(p-alkacyloxy ) phenyl-10,15,20-tri-phenyl] porphyrin (APTPP) and its lanthanide complexes(lanthanide ions: Ho(III), Dy(III), Er(III), Yb(III)) are reported. They form hexagonal columnar discotic columnar (Col_h) liquid crystals over an extended domain of temperature. Luminescence spectra of the compounds are discussed. Quantum yields of Q band are in the region 0.004570-0.05847. The electrochemical property is studied by cyclic voltammetry. The synthesized APTPP and its lanthanide complexes exhibit two one-electron reversible redox reactions and three redox reactions, respectively. The photovoltaic properties and charge-transfer process of the liquid crystalline compounds are investigated by surface photovoltage spectroscopy (SPS) and electric-field-induced surface photovoltaic spectroscopy (EFISPS) techniques, and the bands are analogous with the ultraviolet (Uv) -visible absorption spectra, which reveal that all compounds are P-type semiconductors. All of compounds are nonelectrolytes.     

Reversibility window in as-quenched Ge-As-S glasses

Thermoanalytical characteristics and Raman scattering of high purity sulfur and ternary bulk glasses Ge_xAs_xS_(100−2x) for x=4-22 at. % were studied. The intermediate phase characterized by vanishing of non-reversing heat flow ΔH_nr, i.e. so-called the thermally reversing window was found between mean coordination number 〈r〉∼2.28-2.47. Separated phase of non-crystalline cycloocta-S, manifesting itself by λ-transition at ∼155 °C, was found for glasses with sulfur content higher than ∼80 at.%. Raman spectra of studied Ge-As-S glasses showed different shapes in three different areas according to three distinct phases of network glasses-floppy, intermediate, rigid.     

Effect of plasticizer on ionic transport and dielectric properties of PVA-H3PO4 proton conducting polymeric electrolytes

Solid polymer electrolytes have attracted considerable attention due to their wide variety of electrochemical device applications. The present paper is focused on the effect of plasticizer to study the structural, electrical and dielectric properties of PVA-H₃PO₄ complex polymer electrolytes. XRD results show that the crystallinity decreases due to addition of plasticizer up to particular amount of polyethylene glycol (PEG) and thereafter it increases. Consequently, there is an enhancement in the amorphicity of the samples responsible for process of ion transport. This characteristic behavior can be verified by the analysis of the differential scanning calorimetry results. FTIR spectroscopy has been used to characterize the structure of polymer and confirms the complexation of plasticizer with host polymeric matrix. Electrical and dielectric properties have been studied for different wt% of plasticizer and their variations have been observed. The addition of PEG has significantly improved the ionic conductivity. The optimum ionic conductivity value of the plasticized polymer electrolyte film of 30 wt% PEG has been achieved to be of the order of 10⁻⁴ S cm⁻¹ at room temperature and corresponding ionic transference number is 0.98. The minimum activation energy is found to be 0.25 eV for optimum conductivity condition.     

Structural, sorption and thermodynamic correlations from a layered barium phenylarsonate/n-alkyldiamine system

The barium phenylarsonate compound, Ba(HO₃AsC₆H₅)₂·2H₂O, has the ability to intercalate n-alkyldiamine molecules, H₂N(CH₂)_nNH₂ (n=2-5). The amount intercalated (n_f) from a batchwise procedure and the variation of the original basal distance (d) of 1245 ppm determined through X-ray diffractions, gave linear correlations as a function of the number of carbon atoms in the aliphatic chain (n_c): n_f=(2.66±0.06)−(0.13±0.02)n_c and d=(2168±65)+(114±14)n_c. The intercalation process was calorimetrically followed to give exothermic enthalpy and negative Gibbs energy, reflecting spontaneous intercalation reactions at the solid/liquid interface. The displacement of solvent molecules bonded to amine and of those on the matrix during the intercalation increases the disorder to result in positive entropy, giving a favorable set of thermodynamic data for this system.