Search Results
researches are focused on phase transitions of (1-C 12 H 25 NH 3 ) 2 CuCl 4 , (1-C 14 H 29 NH 3 ) 2 CuCl 4 , and (1-C 16 H 33 NH 3 ) 2 CuCl 4 . However, the crystal structure, lattice potential energy, and some basic thermochemical data of (1-C 8 H 17 NH 3
Abstract
The crystal structure of a manganese(II) 1-allylimidazole complex ([Mn(1-AIm)3(NO3)2], where 1-Aim=1-allylimidazole), was characterized by X-ray diffraction (XRD) using SHELX-97. The thermal behaviour of the complex was investigated by thermogravimetry (TG) coupled with an FTIR unit. The complex showed a multi-step decomposition related to the release of the ligand molecules, followed by oxidation. The final residue at 1073 K was found to be manganese(II) oxide. Evolved gas analysis allowed to prove the oxidative decomposition pattern of the examined complex, initially proposed by the percentage mass loss data. Finally, a kinetic analysis of the oxidative decomposition steps was made using the Kissinger equation, while the complex nature of the decomposition kinetics was revealed by the isoconversional Ozawa-Flynn-Wall method.
Summary The size effect on the crystal structure including the chemical bonding nature has been investigated for several kinds of BaTiO3 nanopowder with the particle sizes down to 50 nm in diameter, by means of powder diffraction using high-energy synchrotron radiation. The Rietveld refinement reveals that the BaTiO3 nanopowder consists of tetragonal and cubic structure components at 300 K. The feature of coexistence can be illustrated by the core/shell model for the particle, in which the shell with a cubic structure covers the core with a tetragonal structure. The thickness of the cubic shell is almost constant irrespective of the particle sizes, and is estimated as approximately 8 nm. Hence, the critical particle-size, where the entire particle is covered with the cubic shell, is suggested as 16 nm. The charge density distributions of the BaTiO3 nanopowder in the cubic phase at 410 K are revealed by the maximum entropy method. Changes in the bonding electron density and the ionic valence expected are not observed clearly even in the 50 nm crystal compared with the bulk crystal.
Three aromatic polyimides based on 3,3′,4,4′-biphenyl-tetracarboxylic dianhydride (BPDA) and three different diamines 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), 2,2′-dimethyl-4, 4′-diaminophenyl (DMB) or 3,3′-dimethylbenzidine (OTOL) have been synthesized. These polyimides are soluble in hotp-chlorophenol,m-cresol or other phenolic solvents. Fibers have been spun from isotropic solutions using a dry-jet wet spinning method. The as-spun fibers generally exhibit low tensile properties, and can be drawn at elevated temperatures (>380° C) up to a draw ratio of 10 times. Remarkable increases in tensile strength and modulus are achieved after drawing and annealing. The crystal structures of highly drawn fibers were determinedvia wide angle X-ray diffraction (WAXD). The crystal unit cell lattices have been determined to be monoclinic for BPDA-PFMB and triclinic for both BPDA-DMB and BPDA-OTOL. Thermomechanical analysis (TMA) was used to measure thermal shrinkage stress and strain. A selfelongation has been found in the temperature region around 450°C. This phenomenon can be explained as resulting from the structural development in the fibers as evidencedvia WAXD observations.
Abstract
The phase behavior of semicrystalline, aliphatic nylons is analyzed on the basis of differential scanning calorimetry, DSC, and quasi-isothermal, temperature-modulated DSC, TMDSC. The data of main interest are the apparent heat capacities, C p, in the temperature range from below the glass transitions to above the isotropization. Based on the contributions of the vibrational motion to C p, as is available from measurements in our laboratory, the ATHAS Data Bank, and multifaceted new TMDSC results, as well as on information on the crystal structures, NMR, molecular dynamics simulation of paraffin crystals, and quasi-elastic neutron scattering, the following observations are made: (a) In semicrystalline nylons the glass transition of the mobile-amorphous phase is broadened to higher temperature. The additionally present rigid-amorphous phase, RAF, undergoes a separate, broad glass transition at somewhat higher temperature. (b) The transition of the RAF, in turn, overlaps usually with an increase in large-amplitude motion of the CH2-groups within the crystals and latent heat effects due to melting, recrystallization, and crystal annealing. (c) Above the glass transitions of the two non-crystalline phases, C p of the crystals approaches and exceeds that of the melt. This effect is due to additional entropy contributions (disordering) within the crystals, which may for some nylons lead to a mesophase. In case a mesophase is formed, the C p drops to the level of the melt as is common for mesophases. (d) Some locally reversible melting is present on the crystal surfaces, but seems to be minimal for the mesophase. (e) The increasing amount of large-amplitude motion in the crystals is described as a third glass transition, occurring over a broad temperature range below the melting or disordering transition from crystal to mesophase. The assumption of a separate glass transition in ordered phases was previously discovered on analyzing aliphatic poly(oxide)s such as poly(oxyethylene), POE, and in the broad class of mesophase-forming small and large molecules. To attain a full description of the globally-metastable, semicrystalline phase-structure of nylons and to understand its properties, one needs quantitative information about the glass transitions of the two non-crystalline phases and that of the crystal, as well as the various irreversible and locally reversible order/disorder transitions and their kinetics. Finally, with different substitutions in the α-position of the backbone structure of nylon 2, one describes poly(amino acid)s which on proper copolymerization yield proteins. This links the present study to the earlier thermal analyses of all naturally occurring poly(amino acid)s, a number of copoly(amino acid)s, and globular proteins in their dehydrated states. It will be of importance to check by quantitative thermal analysis if similar glass transitions and phase structures as seen in the aliphatic nylons are also present in the poly(amino acid)s to possibly gain new information about the nanophase structure of proteins.
Crystal structures and thermal properties of some rare earth alkoxides with tertiary alcohols
Possible precursors for atomic layer deposition of rare earth oxides
thermal analysis (SDTA) measurements and vacuum sublimation experiments. Crystal structures of four new compounds, [Y(OCEt 2 t Bu) 3 ] 2 , [La(OCEt 2 t Bu) 3 ] 2 , [Gd(OC i Pr 3 ) 3 ] 2 , and [La(OC i Pr 3 ) 3 ] 2 were solved. In addition, some ALD
Effect of carbon nanotubes’ crystal structure on adsorption kinetics of small molecules
An experimental study utilizing ultra-high vacuum thermal analysis techniques
’s group at Clemson University, in order to correlate CNT’s crystal structure and chemical activity [ 6 ]. In addition, for the first time, molecular beam scattering data have been collected on CNTs in collaboration with Turro’s group at Columbia University
Abstract
A novel complex, [Pr(5-nip)(phen)(NO3)(DMF)] (5-nip: 5-nitroisophthalic acid; phen: 1,10-phenanthroline, DMF: N,N-dimethylformamide), was prepared and characterized by single crystal X-ray diffraction, elemental analysis, IR spectrum and DTG-DSC techniques. The results show that the crystal is monoclinic, space group P2(1)/n with a=11.0876(6) Å, b=12.8739(7) Å, c=16.9994(8) Å; β=91.193(4)°, Z=4, D c=1.822 Mg m–3, F(000)=1320. Each Pr(III) ion is nine-coordinated by one chelating bidentate and two monodentate bridging carboxylate groups, one chelating bidentate nitryl group, one DMF molecule and one 1,10-phenanthroline molecule. The complex is constructed with one-dimensional ribbons featuring dinuclear units and the one-dimensional ribbons are further assembled into two-dimensional networks by strong π–π stacking interactions. The complex has high stability up to 500°C. The enthalpy change of formation of the compound in DMF was measured using an RD496-III type microcalorimeter with the value of –9.214±0.173 kJ mol–1.
Abstract
A new complex, diaquadi(1,2,4-triazol-5-one)zinc(II) ion nitrate formulated as {[Zn(TO)2(H2O)2](NO3)2}n (1) (1,2,4-triazole-5-one, abbreviated as: TO) was synthesized and characterized by elemental analysis, X-ray single crystal diffraction, infrared spectrum (IR), differential scanning calorimetry (DSC), thermogravimetric analysis and differential thermogravimetric analysis (TG-DTG). The X-ray structure analysis reveals that the complex is orthorhombic with space group Pbca and unit-cell parameters a=6.9504(2) �; b=10.6473(3) �; c=17.8555(5) �. Based on the result of thermal analysis, the thermal decomposition process of the compound was derived. From measurement of the enthalpy of solution in water in 298.15 K, the standard molar enthalpy of solution of lignand TO and the complex were determined as 15.43�0.18 and 52.64�0.42 kJ mol−1, respectively. In addition, the standard molar enthalpy of formation of TO(aq) was calculated as −126.97�0.72 kJ mol−1.
Crystal structures together with enthalpies and temperatures of fusion of two substituted amino acids, N-acetylsarcosinamide (NASarA) and N-acetyl-L-isoleucinamide (NAIA), were determined by single crystal X-ray analysis and differential scanning calorimetry, respectively. The results were compared with those of some analogous amino acid derivatives previously studied. The detailed knowledge of crystallographic parameters is undoubtedly useful for discussing the thermodynamic results and rationalizing the fusion behaviour, owing to the rather poor knowledge of the molecular interactions occurring in the melt.
