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1.
Manik Pavan Maheswaram Dhruthiman Mantheni Indika Perera Hareesha Venumuddala Alan Riga Kenneth Alexander 《Journal of Thermal Analysis and Calorimetry》2013,111(3):1987-1997
Morphological and thermodynamic transitions in drugs as well as their amorphous and crystalline content in the solid state have been distinguished by thermal analytical techniques, which include dielectric analysis (DEA), differential scanning calorimetry (DSC), and macro-photomicrography. These techniques were used successfully to establish a structure versus property relationship with the United States Pharmacopeia standard set of active pharmaceutical ingredient (API) drugs. A distinguishing method is the DSC determination of the amorphous and crystalline content which is based on the fusion properties of the specific drug and its recrystallization. The DSC technique to determine the crystalline and amorphous content is based on a series of heat and cool cycles to evaluate the drugs ability to recrystallize. To enhance the amorphous portion, the API is heated above its melting temperature and cooled with liquid nitrogen to ?120 °C (153 K). Alternatively a sample is program heated and cooled by DSC at a rate of 10 °C min?1. DEA measures the crystalline solid and amorphous liquid API electrical ionic conductivity. The DEA ionic conductivity is repeatable and differentiates the solid crystalline drug with a low conductivity level (10?2 pS cm?1) and a high conductivity level associated with the amorphous liquid (106 pS cm?1). The DSC sets the analytical transition temperature range from melting to recrystallization. However, analysis of the DEA ionic conductivity cycle establishes the quantitative amorphous and crystalline content in the solid state at frequencies of 0.10–1.00 Hz and to greater than 30 °C below the melting transition as the peak melting temperature. This describes the “activation energy method.” An Arrhenius plot, log ionic conductivity versus reciprocal temperature (K?1), of the pre-melt DEA transition yields frequency dependent activation energy (E a, J mol?1) for the complex charging in the solid state. The amorphous content is inversely proportional to the E a where the E a for the crystalline form is higher and lower for the amorphous form with a standard deviation of ±2%. There was a good agreement between the DSC crystalline melting, recrystallization, and the solid state DEA conductivity method with relevant microscopic evaluation. An alternate technique to determine amorphous and crystalline content has been established for the drugs of interest based on an obvious amorphous and crystalline state identified by macro-photomicrography and compared to the conductivity variations. This second “empirical method” correlates well with the “activation energy” method. 相似文献
2.
H. M. J. C. Pitawala M. A. K. L. Dissanayake V. A. Seneviratne B.-E. Mellander I. Albinson 《Journal of Solid State Electrochemistry》2008,12(7-8):783-789
A new plasticized nanocomposite polymer electrolyte based on poly (ethylene oxide) (PEO)-LiTf dispersed with ceramic filler (Al2O3) and plasticized with propylene carbonate (PC), ethylene carbonate (EC), and a mixture of EC and PC (EC+PC) have been studied for their ionic conductivity and thermal properties. The incorporation of plasticizers alone will yield polymer electrolytes with enhanced conductivity but with poor mechanical properties. However, mechanical properties can be improved by incorporating ceramic fillers to the plasticized system. Nanocomposite solid polymer electrolyte films (200–600 μm) were prepared by common solvent-casting method. In present work, we have shown the ionic conductivity can be substantially enhanced by using the combined effect of the plasticizers as well as the inert filler. It was revealed that the incorporating 15 wt.% Al2O3 filler in to PEO: LiTf polymer electrolyte significantly enhanced the ionic conductivity [σ RT (max)?=?7.8?×?10?6 S cm?1]. It was interesting to observe that the addition of PC, EC, and mixture of EC and PC to the PEO: LiTf: 15 wt.% Al2O3 CPE showed further conductivity enhancement. The conductivity enhancement with EC is higher than PC. However, mixture of plasticizer (EC+PC) showed maximum conductivity enhancement in the temperature range interest, giving the value [σ RT (max)?=?1.2?×?10?4 S cm?1]. It is suggested that the addition of PC, EC, or a mixture of EC and PC leads to a lowering of glass transition temperature and increasing the amorphous phase of PEO and the fraction of PEO-Li+ complex, corresponding to conductivity enhancement. Al2O3 filler would contribute to conductivity enhancement by transient hydrogen bonding of migrating ionic species with O–OH groups at the filler grain surface. The differential scanning calorimetry thermograms points towards the decrease of T g , crystallite melting temperature, and melting enthalpy of PEO: LiTf: Al2O3 CPE after introducing plasticizers. The reduction of crystallinity and the increase in the amorphous phase content of the electrolyte, caused by the filler, also contributes to the observed conductivity enhancement. 相似文献
3.
A. S. Ulikhin N. F. Uvarov K. B. Gerasimov A. A. Iskakova Yu. G. Mateishina 《Russian Journal of Electrochemistry》2017,53(8):834-837
Composite solid electrolytes were synthesized from the organic salt dimethylammonium chloride (1–x)C2H8NCl–xAl2O3. Their physicochemical properties were studied. In the starting C2H8NCl salt, there is a phase transition at 39°C accompanied by an increase in conductivity by two orders of magnitude. The conductivity of the high-temperature phase is 9.3 × 10–6 S/cm at 160°C. A differential scanning calorimetry study showed that the salt in the composites spreads over the oxide surface and at x > 0.6 the salt melting enthalpy decreases to zero. The conductivity of the resulting composites was studied by impedance spectroscopy. It was shown that heterogeneous doping leads to a sharp increase in ion conductivity to 7.0 × 10–3 S/cm at 160°C and a decrease in the activation energy to 0.55 eV. 相似文献
4.
The main aim of this research is to investigate the effect of salt concentration on the dielectric properties(AC (σAC),permittivity(ε′),dielectric loss(ε″),and dielectric relaxation process) and melting behavior of polyethylene oxide (PEO)/CdCl2 complexes.The dielectric study was carried out over a frequency range 10-335 kHz and a temperature range 25-45℃.The AC conductivity,permittivity and dielectric loss of the PEO/CdCl2 complexes increase with increasing salt concentration and temperature.Also,it was found that the addition of CdCl2 salt to PEO host reduced the melting temperature of PEO host.Dielectric results reveal that the relaxation process of these complexes is due to viscoelastic relaxation or non-Debye relaxation at room temperature.Additionally,it was found that relaxation behavior remained viscoelastic at different temperatures and salt concentrations. 相似文献
5.
Non-isothermal and isothermal crystallization behaviors of polystyrene-b-poly(ethylene-co-butene) (PSt-b-PEB) block copolymers with different compositions and chain lengths were investigated by differential scanning calorimetry (DSC). The results show that crystallization of PEB block is strongly dependent on the composition. Crystallization temperature (Tc), melting temperature (Tm) and fusion enthalpy (ΔHf) increase rapidly with PEB volume fraction (VE) for block copolymers with VE below 50%, but there is little change when PEB block becomes the major component. Glass transition temperature (Tg) of the PSt block and order-disorder transition temperature (TODT) of block copolymers also have a weak effect. The isothermal crystallization kinetics results show that Avrami exponent (n) was strongly dependent on the composition and crystallization temperature. For the block copolymers with VE below 38.7 vol%, the values of n vary between 0.9 and 1.3, indicating that crystallization is confined. For the PSt-b-PEB block copolymers with VE higher than 50%, fractionated crystallization behavior is usually observed. A two-step isothermal crystallization procedure is applied to these block copolymers. It is found that breakout crystallization occurs at higher Tc, but confined at lower Tc. Two overlapped melting peaks are observed for the block copolymers with fractionated crystallization behavior after two-step crystallization, and only the higher melting peak corresponding to breakout crystallization can be used to derive equilibrium melting temperature. 相似文献
6.
A. A. Abd El-Rahman K. K. Tahoon Abd El-Salam M. Abousehly Abd Elwahab A. El-Sharkawy 《Journal of Thermal Analysis and Calorimetry》1996,47(6):1719-1728
The specific heat (C p), thermal conductivity (λ), thermal diffusivity (a), and electrical conductivity (σ) were measured for polycrystalline HgS and Sb2S3 in the temperature range 300–600 K. The measurements were performed with an experimental apparatus based on a socalled flash method. The results showed that the mechanism of heat transfer is mainly due to phonons, whereas the contribution of electrons and bipolars is very small indeed. The energy gap of the samples was also calculated. 相似文献
7.
Results of electrical conductivity measurements, thermal analysis, and X-ray diffraction studies indicate the existence of four phases, between 295 K and the melting points, in the system (Cs1?yRby)Cu4Cl3I2. These phases are designated α, á β, γ in order of decreasing temperature. The α phase is isostructural with α-RbAg4I5; the á phase is also cubic and very likely belongs to space groupP213, a subgroup ofP4132 andP4332 to which the α phase belongs. There is a high probability that the á → α transition is continuous. The á → α transition is not discernible in the conductivity measurements or thermal analysis; therefore the line of á-α transitions is presently unknown. The β phase transforms to the á and the γ phase transforms to the β phase wheny ≤ 0.36; the γ phase transforms to the α phase wheny ≥ 0.36. That is, there is a triple point aty = 0.36, T = 399K. The γ-β, β-α′, and γ-α transitions are all hysteretic and are therefore first order. The conductivities of the β phases are relatively low and the enthalpies of activation relatively high. The conductivity of the β phase decreases with increasingy. The β phase probably belongs to space groupR3, in which the Cu+ ions can be ordered. The α and á phases are the true solid electrolytes; the conductivities are high, >0.73 Ω?1cm?1 at 419 K, and the enthalpies of activation of motion of the Cu+ ions low, 0.11 eV.In the system CsCu4Cl3(I2?xClx), 0 ≤ x ≤ 0.25, the Cl? for I? substitutions affect the transitions to only a small extent relative to the stoichiometric compound. The β phase occurs for allx and transforms to á. 相似文献
8.
Mohamed Mahmoud Nasef 《European Polymer Journal》2002,38(1):87-95
Structural investigation of polystyrene grafted and sulfonated poly(tetrafluoroethylene) (PTFE) membranes prepared by radiation-induced grafting of styrene onto commercial PTFE films and subsequent sulfonation was carried out by differential scanning calorimetry and X-ray diffraction. The effect of the structural changes taking place in the membranes during the preparation procedure (grafting and sulfonation) and the variation of the degree of grafting on melting temperature (Tm), glass transition temperature (Tg), heat of melting (ΔHm), and degree of crystallinity was studied. The melting temperature (Tm) was found to be independent of the degree of grafting unlike glass transition temperature (Tg), which was found to be a function of the degree of grafting. Moreover, the degree of crystallinity of the membranes was found to decrease with the increase in the degree of grafting. The results of this work suggest that grafting takes place in the entire amorphous region without any significant disruption in the crystalline structure of PTFE film and the decrease in the degree of crystallinity is mainly attributed to the dilution effect. 相似文献
9.
《Solid State Sciences》2012,14(10):1496-1502
The magnetization M(T,H), specific heat Cp(T,H), electrical resistivity ρ(T), magnetoresistance MR(T,H), thermal conductivity κ(T) and thermopower S(T) measurements were performed on the antiferromagnetic compound Ce5Ni2Si3 with the Néel temperature TN = 5.7 K. The estimated effective moment μeff is close to the free ion value of Ce in its trivalent state. The negative sign of the paramagnetic Curie temperature θp indicate the antiferromagnetic nature of the magnetic ordering. The variation of magnetic resistivity ρmag with temperature in Ce5Ni2Si3 can be explained by a competition of the crystal electric field (CEF) splitting, the Kondo effect and the magnetic order. Based on the thermopower and employing a simple single-ion Kondo model the Kondo temperature have been estimated. Magnetocaloric effect is small but shows a sign change, which may be caused by a metamagnetic behavior. 相似文献
10.
The superionic properties of the compounds RbAg4I5, KAg4I5 and KCu4I5 have been investigated by powder neutron diffraction and complex impedance spectroscopy. RbAg4I5 and KAg4I5 have room-temperature ionic conductivities of σ=0.21(6) and 0.08(5) Ω−1 cm−1, respectively, which increase gradually on increasing temperature. KCu4I5 is only stable in the temperature range between 515(5) K and its melting point of 605 K, and its ionic conductivity is σ=0.61(8) Ω−1 cm−1, at T=540 K. At lower temperatures, KCu4I5 disproportionates into KI+4CuI and the ionic conductivity falls by over three orders of magnitude. Least-squares refinements of the powder neutron diffraction data for RbAg4I5 at ambient temperature confirm the reported structure (space group P4132, Z=4, a=11.23934(3) Å), though with some differences in the preferred locations of the mobile Ag+. KAg4I5 and KCu4I5 are found to adopt the same basic structure as RbAg4I5, with the I− forming a β-Mn-type sublattice, with the K+ located in a distorted octahedral environment and the Ag+(Cu+) predominantly distributed over two sites which are tetrahedrally co-ordinated to I−. The implications for the conduction mechanism within these compounds are discussed, using a novel maximum entropy difference Fourier technique to map the distribution of the Ag+(Cu+) within the unit cell. 相似文献
11.
T. Bashir A. Shakoor E. Ahmed N. A. Niaz Shahid Iqbal Muhammad Saeed Akhtar Mohammad Azad Malik 《Polymer Science Series A》2017,59(6):902-908
This research paper comprises of the synthesis of polypyrrole (PPy)-Fe2O3 nanocomposites by employing the in situ chemical oxidative polymerization method. The concentration of the filler material was adjusted between 10–50 wt % of PPy. The synthesized nanocomposites were characterized by using X-ray diffraction (XRD). Magnetic analysis and DC electrical conductivity of the samples were carried out using vibrating sample magnetometer (VSM) and two probe DC conductivity method, point towards magnetically active and electrically conductive samples. The magnetic parameters under applied magnetic field demonstrated that the values of coercivity (H c ), saturation magnetization (M s ) and remanence (M r ) can be tailored by carefully controlling the amount of dopant material into the nanocomposites indicating their suitability for controllable switching devices and microwave absorption applications. The DC electrical conductivity showed an increase up to 20 wt % of filler material and thereafter a decrease in the conductivity of nanocomposites with increase in filler content is observed. Thermogravimetric analysis (TGA) showed an increase in thermal stability with an increase in ferrite content in nanocomposites. 相似文献
12.
Bioactive glasses prepared in SiO2–CaO–Na2O and P2O5 system are used as biomaterials in orthopaedic and maxillofacial surgery. Zn presents high physiological interest. It enhances physiological effects of implanted biomaterials. In this work, the thermal characteristics (T g, T c and T f) of pure bioactive glass elaborated with different amounts of CaO, Na2O in pure glass and with different amounts of introduced Zn in glass (ranging from 0.1 to 10 in mass%), were studied. The excess entropy was calculated for different compounds. Glasses were prepared by the melting process. The thermal behaviour of obtained bioactive glasses was determined using differential thermal analysis. Therefore, the glass transition (T g), the crystallization (T c) and the melting temperatures (T f) were revealed. Moreover, according to Dietzel formula, the thermal stability (TS) of the studied bioactive glasses has been calculated. The first results concerning the impact of different oxides, revealed a decrease of the TS, T g, T c and T f when the SiO2/CaO increases and revealed an increase of these thermal characteristics when the SiO2/Na2O and CaO/Na2O ratios increase. Introducing Zn into the bioactive glasses induces a decrease of T f and an increase of TS. Contrary to crystals, prepared glasses have entropy different to zero at T = 0 K and vary versus T f. The excess entropy of pure glasses and Zn-doped glasses were calculated. The significant variations were registered. 相似文献
13.
A. Yu. Shaulov 《Polymer Science Series B》2006,48(6):308-323
Monoelemental polymers with various chemical constitutions and different spatial structures (linear Te n , Se n , and S n ; planar graphite C n , black phosphorus P n , As n , Sb n , and Bi n ; and chemically bonded three-dimensional diamond C n , B n , Si n , and Ge n ) were considered and categorized as a class of covalent macromolecular compounds. Quantitative expressions relating the thermal (melting point, thermal expansion coefficient, heat conductivity) and elastic (microhardness, bulk compression modulus of elasticity) properties of polymers to the energy of intra-and intermolecular interactions and the equilibrium length of chemical bonds in the crystalline and glassy states are given. A numerical correlation between the spatial structure of polymers and their thermal and elastic properties was obtained. The hypothetical melting point of diamond at normal pressure was calculated as T f = 3155 K. 相似文献
14.
Analysis of the literature data allows one to correlate the melting parameters and the activation enthalpy H0 of the charge carrier formation in an ionic crystal. The melting enthalpy Hm and H0 values are connected by the basic relation H0 = 9.2 Hm. The well-known Barr-Lidiard relation is shown to be a particular case of this basic relation. It is demonstrated that the conductivity jump at the melting temperature of an ionic crystal may be predicted from the melting entropy. Correlations of the form mentioned above may be useful in predicting the conductivity values of ionic crystals as well as in looking for new types of superionic conductors. 相似文献
15.
Shimin Xu Lawrence S. Bartell 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,31(1):117-123
Molecular dynamics simulations of the behavior of molecules in crystalline clusters of TeF6 were carried out on systems of 100, 150, 250, and 350 molecules. Several diagnostic functions were applied to investigate whether rotational melting occurred before translational melting. These functions included the coefficient of rotational diffusionD θ(T), the “orientational Lindemann index” δθ(T), the “orientational angular distribution function”Q(θ,T), and the “orientational pair-correlation function”g θ(r, T). All indicators implied that rotational melting occurred before translational melting, that it began with the outermost molecules, and that its onset for smaller clusters was at lower temperatures than for larger clusters. Results also showed that the rotational transition coincided with the transition from a lower symmetry phase (monoclinic) to cubic, a phenomenon that had been noted by others to occur with some regularity for systems of globular molecules. 相似文献
16.
S. Budak C. SmithM. Pugh K. HeidaryT. Colon R.B. JohnsonC. Muntele D. ila 《Radiation Physics and Chemistry》2012,81(4):410-413
The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT=S2σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and K is the thermal conductivity. ZT can be increased by increasing S, increasing σ, or decreasing K. We have prepared the thermoelectric generator device of SiO2/SiO2+Ge multilayer superlattice films using the ion beam assisted deposition (IBAD). The 5 MeV Si ion bombardments have been performed using the AAMU Pelletron ion beam accelerator at five different fluences to make quantum structures (nanodots and/or nanoclusters) in the multilayer superlattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric generator devices before and after MeV Si ions bombardments at the different fluences we have measured the cross-plane Seebeck coefficient, the cross-plane electrical conductivity, and the cross-plane thermal conductivity, Raman spectra to get some information about the sample structure and bond structures among the used elements in the superlattice thin film systems. 相似文献
17.
In this study, we have studied the effect of elements Ag, Cd, and Sn as chemical modifiers on some thermal transport properties (thermal conductivity, diffusivity, and specific heat per unit volume) of amorphous Se. Concurrent measurements of thermal transport properties such as effective thermal conductivity (??e), thermal diffusivity (??e), and specific heat per unit volume (??C v) are used at room temperature for twin pellets of pure Se- and Se-based binary Se98M2 (M?=?Ag, Cd, and Sn) alloys using transient plane source technique. We have also determined the thermal inertia I T using the experimental values of thermal conductivity and specific heat per unit volume for present amorphous alloys. The increasing sequence of measured thermal transport properties is also discussed. 相似文献
18.
E. I. Burmakin G. V. Nechaev G. Sh. Shekhtman 《Russian Journal of Electrochemistry》2008,44(12):1386-1392
New solid electrolytes with high potassium cationic conductivity based on potassium monoaluminate were synthesized and studied in the K1?2x Ba x AlO2 and K1?2x Pb x AlO2 systems. A partial substitution of potassium cations with double charged positive cations results in a considerable increase in the conductivity of KAlO2 in the whole studied range of temperatures. The electric characteristics are somewhat higher in the bariumcontaining system, which is in all probability connected with the effect of the size factor: the size of the Ba2+ ion is higher than that of Pb2+, which must correlate with the increase of the effective dimensions of the migration channels in the electrolyte structure. The main cause of the conductivity increase at the introduction of the studied additives is the formation of potassium vacancies at the substitution of 2K+ → Ba2+(Pb2+) + V′K. 相似文献
19.
W.W. Wendlandt 《Thermochimica Acta》1980,37(1):89-96
The thermal dissociation of the [Co(NH3)6]X3 (X = Cl?, Br?, I?, and NO?3), [Co(en)3]X3 (X = Cl?, Br?, I?, NO?3, HSO?4 and C2O2?4), cis- [Co(en)2Cl2]Cl, and trans-[Co(en)2ClBr]NO3 complexes was investigated by an electrical conductivity (EC) technique. During the thermal dissociation reactions, liquid or semi-liquid phases are formed which cause large increases in the EC of the compound. The effect of concentration of the complex in a matrix medium as well as the composition of the matrix material on the EC curves were also determined. 相似文献
20.
Dongling Han Longxiao Liu Xinghua Wang 《Journal of Thermal Analysis and Calorimetry》1995,45(1-2):247-254
The thermal properties of caprolactam/long chain lactam copolymer were studied with a Perkin-Elmer DSC 7. The melting point (T m), heat of fusion (δH m), crystalline degree (X c), crystallization temperature (T c) and glass transition temperature (T g) of the copolymers increase with decrease of the content of the log chain lactam. From the changes in the mechanical properties with corresponding changes in the thermal properties, it is clear that the copolymers are thermal plastic and elastic. In addition, it is found that the results at a heating rate of 10 deg·min?1 are almost the same as that at 20 deg·min?1 after thermal history is erased. 相似文献