Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Terms modified by DSC

  • dsc analysis
  • dsc curve
  • dsc data
  • dsc experiment
  • dsc measurement
  • dsc result
  • dsc studies

  • Selected Abstracts

    Crystal structures and isotope effect on Na5H3(SeO4)42H2O and Na5D3(SeO4)42D2O crystals

    T. Fukami
    Abstract Differential scanning calorimetry (DSC) and X-ray diffraction measurements have been performed on pentasodium trihydrogen tetraselenate dihydrate Na5H3(SeO4)42H2O and deuterated Na5D3(SeO4)42D2O crystals. Any distinct anomaly around 428 K in the DSC curves for both crystals is suggested to be caused by a chemical reaction of thermal decomposition with hydrolysis at high temperature. The space group symmetry (triclinic P) and the structure parameters are determined at room temperature. The hydrogen atom in the centrosymmetric O-H(D)-O hydrogen bond of both crystals is found to be equally distributed at two equivalent sites in the bond. The expansions of two O-H-O hydrogen bonds by the substitution of deuterium are observed to be 0.016(6) and 0.011(4) . The geometric isotope effect on hydrogen bonds is confirmed to be existed in Na5H3(SeO4)42H2O. ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    DC conductivity studies in K3Na(SeO4)2 single crystals

    G. Joseph
    Abstract DC electrical conductivity studies were carried out along the three crystallographic axes for Tripotassium sodium diselenate (K3Na(SeO4)2 or KNSe). Earlier studies of phase transition in this crystal show successive phase transitions at 334 K, 346 K, 730 K, and 758 K. In this paper we report the dc electrical conductivity measurements in the temperature region 303 K , 430 K along a, b and c , axes. An anomaly in conductivity was obtained around 341 K and another one around 333 K. These can be attributed as due to phase transitions in this crystal. A strong anomaly also has been observed along the c-axis and comparatively week one along a and b axes around 395 K for the first time. This can be due to newly observed phase transition in the crystal. DSC taken for the sample also shows endothermic peak supporting the occurrence of newly observed phase transition. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Thermal and EPR investigations of thallium gallium disulphide single crystal

    M. Acikgoz
    Abstract In this research, the results of the differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR) investigations of TlGaS2 single crystal are presented. Specific heat capacity (Cp) anomalies of layered TlGaS2 have been obtained by using a new DSC technique for such crystals. Remarkable heat capacity anomalies have been revealed at the temperatures of 137.7 K, 174.5 K and 238.5 K. It is found that the anomalies appear at maximum with a small deviation (by 3-4%) from the regular values, and Cp discontinuity amounted to approximately 5%. Additionally, EPR spectra of Fe doped TlGaS2 single crystals have been recorded at various temperatures down to 6 K for different orientations of the applied magnetic field. Transformations of present EPR spectra are not sufficient for the confirmation of structural phase transitions, in contrast to the cases in iso structural TlInS2 and TlGaSe2 compounds. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Flux growth and characterization of Ti- and Ni-doped forsterite single crystals

    A. Bloise
    Abstract Forsterite monocrystals doped with Ti and Ni were grown by the flux growth technique. A suitable mixture of flux (MoO3, V2O5, Li2CO3) and nutrient was slowly cooled down to 750 C from 1250 C or 1350 C. The crystals were then characterized by powder and single-crystal X-ray diffraction, scanning electron microscopy and differential scanning calorimetry (DSC). Variations observed in crystal size were attributed by both the varying experimental conditions in which they had been obtained, and to the amount of Ni substituted for Mg in the structure. High abundances of doped forsterite required a cooling rate of 1.8 K h -1. These synthetic, well-characterized Ti and Ni doped forsterite crystals may have potential for exploitation in industrial fields. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Thermal, phase transition and spectral studies in erythromycin pseudopolymorphs: dihydrate and acetone solvate

    Zhanzhong Wang
    Abstract The thermal, phase transition and spectral studies of erythromycin A dihydrate and acetone solvate were performed by Differential Scanning calorimetry (DSC), Thermo Gravimetry (TG-DTA), X-Ray Powder Diffraction (XRPD) and Fourier Transform Infra-Red (FTIR) spectrum. The non-thermal kinetic analysis of erythromycin A dihydrate was carried out by DSC at different heating rates in dynamic nitrogen atmosphere. The result showed that heating rate has substantial influence on the thermal behavior of erythromycin dihydrate. The Arrhenius parameters were estimated according to the Kissinger method. Corresponding to dehydration of dihydrate, melting of dehydrated dihydrate, phase transition from dehydrated dihydrate to anhydrate, and melting of anhydrate, the calculated activation energy were 39.60, 269.85, 261.23, and 582.16 kJmol,1, the pre-exponential factors were 3.46 103, 8.06 1032, 9.23 1030, and 7.29 1063 s,1, respectively. Ozawa method was used to compare activation energy values calculated by Kissinger method. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Phase transition behavior and structure of the thermotropic liquid crystal 6-{[(4,-{[(undecyl)carbonyl]oxy}biphenyl-4yl)carbonyl]oxy}-1-hexyne

    Leijing Liu
    Abstract The phase transition behaviors and corresponding structures of 6-{[(4,-{[(undecyl)carbonyl]oxy}biphenyl-4yl)carbonyl]oxy}-1-hexyne (A4EE11) were investigated using differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and wide angle X-ray diffraction (WAXD). In comparison with the published homologues, 5-{[(4,-heptoxy-biphenyl-4-yl)carbonyl]oxy}-1-pentyne (A3EO7) which shows a monotropic smectic A (SmA) phase and a metastable monotropic smectic C (SmC) phase; 5-{[(4,-heptoxy-biphenyl-4-yl)oxy]carbonyl}- 1-pentyne (A3E'O7) that exhibits three enantiotropic stable liquid crystalline (LC) phases, SmA phase, SmC phase and smectic X (SmX) phase; 5-{[(4,-heptoxy-biphenyl-4-yl)carbonyl]oxy}-1-undecyne (A9EO7) which has a monotropic SmA phase and a metastable crystal phase, A4EE11 integrates the enantiotropy, monotropy and metastability of the LC phases of those three compounds. Upon cooling from isotropic state to room temperature, in the temperature range of 62.0 to 58.5C, A4EE11 shows an enantiotropic smectic A (SmA) phase with a layer spacing d=32.69. Further lowering the temperature, it enters into a metastable monotropic smectic B (SmB) phase with a longer layer spacing d=34.22 which has a tendency towards crystallization. The metastability of the liquid crystalline phase may associate to the linkage order of the ester bridge between the mesogenic core and the flexible spacer. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Synthesis and characterization of potassium magnesium sulphate hexahydrate crystals

    M. Dhandapani
    Abstract Potassium magnesium sulphate hexahydrate (picromerite) was synthesized and single crystals were obtained from saturated aqueous solution by slow evaporation method at room temperature. The crystals were bright, colourless and transparent having well defined external faces. The grown crystals were characterized through Fourier Transform Infrared (FTIR) spectral studies and thermal analysis. The FTIR data were used to assign the characteristic vibrational frequencies of the various chemical bonds in the compound. The compound crystallizes in monoclinic lattice with the space group P21/c. The thermogravimetry (TG) indicates the removal of only two water molecules around 100 C. A suitable decomposition pattern was formulated based on the percentage weight losses observed in TG of the compound. The results of differential thermal analysis (DTA) conform to the results of TGA. Differential scanning calorimetry (DSC) analysis carried out at high temperature suggests that the occurrence of two phase transitions in the crystal between 140 and 180 C. When the crystal was cooled below the room temperature up to ,170 C, no thermal anomaly was observed. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Inhomogeneity of composition in near-stoichiometric LiNbO3 single crystal grown from Li rich melt

    L. Gao
    Abstract A near-stoichiometric LiNbO3 single crystal has been grown by the Czochralski technique from a melt of 58.5 mol% Li2O. Its composition homogeneity was assessed by measuring the UV absorption edge. It was found that the maximum composition difference is about 0.03 mol% in the radial direction and 0.05 mol% in the axial direction. Differential scanning calorimetry (DSC) analysis was performed on the powder from the synthesized raw material and the frozen melt after crystal growth. The analytical results indicate that, during crystal growth, the magnitude of lithium volatilization from the melt surface is more than the degree of segregation from the crystal. The volatilized lithium diffuses into the crystal to compensate for the lithium segregation in the LiNbO3 crystal. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Synthesis, structural and thermal studies of tetrathioureacopper(I) chloride crystals

    M. Dhandapani
    Abstract Tetrathioureacopper(I) chloride, hereafter abbreviated as TCC, was synthesised and single crystals were obtained from saturated aqueous solution by slow evaporation (solution growth) method at room temperature. The crystals obtained are bright, colourless and transparent having well defined external faces. The grown crystals were characterized through elemental analysis, single crystal X-ray diffraction study, thermal analysis, electron spin resonance spectroscopy and Fourier Transform infrared spectroscopy. The elemental analysis confirms the stoichiometry of the compound. The single crystal diffraction studies indicate that TCC crystallises in the tetragonal lattice and the unit cell parameters are a = b = 13.4082 , c = 13.8074 , V = 2482.29 3, , = , = , = 90. Space group and the number of molecules per unit cell (Z) are found to be P41212 and 8 respectively. The TG curve of the sample shows a prolonged decomposition from 210 to 628.3 C, from which the decomposition pattern has been formulated. The endothermic peaks in the DTA curve indicate melting and decomposition of the compound at 165.2 and 633.8 C respectively. An exothermic peak in high temperature DSC indicates a phase transition in the compound at 274.8 C. Thermal anomalies observed in the low temperature DSC at ,163.3, ,152.0, ,141.5, ,108.3, 1.0 and 12.1 C in the heating run and ,157.1 and ,153.9 C in the cooling run reveal first order phase transitions in the crystal. The peaks observed at ,146.2 C in both the heating and cooling runs suggest occurrence of a second order phase transition in this compound. The IR spectroscopic data were used to assign the characteristic vibrational frequencies of various groups present in the compound. The ESR study confirms that the copper is in the +1 oxidation state in the complex. ( 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    ,-Blocker use and diabetes symptom score: results from the GEMINI study

    J. B. McGill
    Aim:, The Glycemic Effect in Diabetes Mellitus: Carvedilol,Metoprolol Comparison in Hypertensives (GEMINI) trial compared the metabolic effects of two ,-blockers in people with type 2 diabetes and hypertension treated with renin,angiotensin system (RAS) blockade and found differences in metabolic outcomes. In this paper, we report the results of a prespecified secondary analysis of GEMINI that sought to determine the effect of these two ,-blockers on commonly reported symptoms. Methods:, The Diabetes Symptom Checklist (DSC), a self-report questionnaire measuring the occurrence and perceived burden of diabetes-related symptoms, was completed by GEMINI participants at baseline and at the end of the study (maintenance month 5). The DSC assessed symptoms in eight domains: psychology (fatigue), psychology (cognitive), neuropathy (pain), neuropathy (sensory), cardiology, ophthalmology, hyperglycaemia and hypoglycaemia. Results:, Comparison of the mean change in self-reported diabetes-related symptoms indicated a significant treatment difference favouring carvedilol over metoprolol tartrate in overall symptom score (,0.08; 95% CI ,0.15, ,0.01; p = 0.02) and in the domains for hypoglycaemia symptoms (,0.12; 95% CI ,0.23, ,0.02; p = 0.02) and hyperglycaemia symptoms (,0.16; 95% CI ,0.27, ,0.05; p = 0.005). Carvedilol resulted in fewer perceived diabetes-related symptoms in patients with diabetes and hypertension. Conclusion:, Carvedilol resulted in a lower perceived burden of diabetes-related symptoms in patients with type 2 diabetes and hypertension. The addition of a well-tolerated ,-blocker to RAS blockade may improve hypertension treatment and quality of life in patients with diabetes. [source]

    Improving the dissolution and oral bioavailability of the poorly water-soluble drug aloe-emodin by solid dispersion with polyethylene glycol 6000

    Hao-gang Duan
    Abstract Solid dispersions (SDs) of aloe-emodin (AE) and polyethylene glycol 6000 (PEG6000) with different drug loadings were prepared, characterized by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) and evaluated for solubility and in vitro release. The oral bioavailability of AE from SD in rats was compared with the crystalline drug. Plasma concentrations of AE were determined by HPLC. After administration of crystalline AE (35,mgkg,1) in rats, the AUC0-600 and Cmax were 393.677.1,mgminl,1 and 1.870.30,mgl,1, respectively. For the PEG6000 SD of AE, AUC0-600 and Cmax were boosted to 1310.5111.9,mgminl,1 and 5.860.47,mgl,1, respectively. The results indicated that the oral bioavailability of AE was increased significantly. Simultaneously, the Tmax value of AE for AE crystalline was decreased from 75.617.3,min to 44.814.8,min for SD. The earlier Tmax for AE from SD indicated the higher extent of absorption for SD due to their improved dissolution rate in rat intestine. This SD approach can therefore be used to enhanced dissolution and bioavailability for poorly water-soluble drugs. Drug Dev Res, 2009. 2009 Wiley-Liss, Inc. [source]

    Stability Enhancement of All-Solid-State H+ ISEs with Cross-Linked Silicon-Urethane Matrices

    ELECTROANALYSIS, Issue 8 2005
    Nak-Hyun Kwon
    Abstract An all-solid-state hydrogen-ion-selective electrode (ASHISE) was fabricated using the polymer hybrid membrane. Polymer membranes composed of Tecoflex polyurethane (TPU), polyvinyl chloride (PVC), silicon rubber (SR), and additives (KTpClPB, DOA, and TDDA) were cast on a carbon rod. The TPU/SR hybrid membrane exhibited a longer lifetime and a higher sensitivity in the sensing of the H+ ion compared to conventional TPU/PVC and PVC/SR hybrid membranes. Moreover, the addition of SiCl4 to TPU-based matrices enhanced the potentiometric response and ISE stability, due to the chemical bonding between Si and CO in urethane, in which the cross-linking configuration was confirmed by DSC, FT-IR, and XPS experiments. TPU/SR membranes containing SiCl4 were rendered more stable and showed a pH response over a wide range (i.e., pH,2,11.5) with the slope of 602,mV/pH for more than four months. The ASHISE exhibited a small interfering potential variation in the wide range of the salt concentration (from 1.010,6,M up to 0.1,M). The ASHISE showed a result comparable to a commercial clinical blood analyzer. [source]

    Capillary electrophoresis versus differential scanning calorimetry for the analysis of free enzyme versus enzyme-ligand complexes: In the search of the ligand-free status of cholinesterases

    ELECTROPHORESIS, Issue 2 2006
    Daniel Rochu Dr.
    Abstract Cholinesterases (ChEs) are highly efficient biocatalysts whose active site is buried in a deep, narrow gorge. The talent of CE to discover inhibitors in the gorge of highly purified preparations has fairly altered the meaning of a ChE ligand-free status. To attempt at a description of this one, we investigated the stability of Bungarus fasciatus acetylcholinesterase (AChE), alone or complexed with different inhibitors. Determination of midtransition temperature for thermal denaturation, using differential scanning calorimetry (DSC) and CE, provided conflicting results. Discrepancies strongly question the reality of a ligand-free AChE state. DSC allowed estimation of the stability of AChE-ligands complexes, and to rank the stabilizing effect of different inhibitors. CE acted as a detector of hidden ligands, provided that they were charged, reversibly bound, and thus dissociable upon action of electric fields. Then, CE allowed quantification of the stability of ligand-free AChE. CE and DSC providing each fractional and nonredundant information, cautious attention must be paid for actual estimation of the conformational stability of ChEs. Because inhibitors used in purification of ChEs by affinity chromatography are charged, CE remains a leading method to estimate enzyme stability and detect the presence of bound hidden ligands. [source]

    Electrospun Silk Fibroin Mats for Tissue Engineering

    A. Alessandrino
    Abstract Processing Silk Fibroin (SF) with electrospinning (ES) offers a very attractive opportunity for producing a variety of 2D and 3D matrices with great potential for tissue regeneration and repair due to the superior biocompatibility and mechanical properties of SF. Different combinations of ES parameters were explored to investigate the best experimental set-up related to the dimension and uniformity of the fibers in the electrospun silk fibroin (ES-SF) mats. Using SEM it was found that the ES-SF mats contain uniform fibers with a diameter in the nanometric range obtained by electrospinning a 7.5,% w/v SF solution in formic acid, with an electric field of 2.4,kV/cm and a spinneret-collector distance of 10,cm. FT-IR and DSC analyses were performed to investigate the structure of the ES-SF mats before and after immersion in methanol for different times (5, 10, and 15,min). The methanol treatment was able to promote the crystallization of SF by conformational transition of random coil and other poorly ordered conformations (turns and bends) to the ,-sheet structure. The degree of crystallinity was enhanced as shown by the trend of both the FT-IR crystallinity index and the melting/decomposition peak temperature (from DSC). To study the cytocompatibility of ES-SF mats, tests with L929 murine fibroblasts were carried out. Samples were seeded with the cells and incubated for 1, 3, and 7,days at 37,C. At each time point, SEM investigations and Alamar blue tests were performed. The SEM images showed cell adhesion and proliferation just after 1,day and cell confluence at 7,days. Alamar blue test demonstrated that there were very low differences between cell viability on ES-SF mats and the tissue culture plastic control. [source]

    Nitroamino Triazoles: Nitrogen-Rich Precursors of Stable Energetic Salts

    Yangen Huang
    Abstract 1-Nitroamino-1,2,3-triazole (5) was synthesized and its zwitterionic structure was established using single-crystal X-ray diffraction. The calculated detonation properties for 4-nitroamino-1,2,4-triazole (2) (P = 33.4 GPa, vD = 8793 m/s) and 1-nitroamino-1,2,3-triazole (5) (P = 33.0 GPa, vD = 8743 m/s) are comparable with RDX. A new family of energetic salts 7,21 based on either the 1-nitroamino-1,2,3-triazolate or the 4-nitroamino-1,2,4-triazolate anion were prepared and characterized by vibrational spectroscopy (IR), multinuclear NMR spectra, elemental analyses, density, TGA and DSC. The heats of formation (,fH298) and detonation properties for these stable salts were calculated using Gaussian 03 and Cheetah 4.0, respectively. Comparison of the properties of the 1,2,3- and 1,2,4-triazolate salts indicates that while the 1,2,4-derivatives are more stable thermally, the 1,2,3-analogs invariably have higher heats of formation. In contrast to its salts, 1-nitroamino-1,2,3-triazole (5) is extremely shock-sensitive with an impact sensitivty of <1 J. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Thermal Behavior of Tetrahydropyran-Intercalated VOPO4: Structural and Dynamics Study

    Klra Melnov
    Abstract The thermal behavior of tetrahydropyran-(THP-)intercalated VOPO4 was probed by an extensive combination of experimental methods (XRD, DSC, FTIR, solid-state NMR) and quantum chemical calculations. Two temperature-induced transitions were detected and all polymorphs exhibit a high degree of molecular order and tight packing of THP in VOPO4. The first reversible thermal transition at around 100 C was attributed to boat/chair conformation changes of the THP molecules. Most probably, a low-temperature boat conformation of the guest molecules present in the interlayer space of VOPO4 changes to a high-temperature chair conformation. This rearrangement of the THP molecules was confirmed by variable-temperature 13C CP/MAS NMR spectroscopy. Quantum chemical calculations using a B3LYP functional and 6-31G(d) basis set also support this idea. The second change at around 140 C is probably caused by a weakening of the donor,acceptor bond between the oxygen molecule of THP and the vanadium atom of the host and the formation of a disorder in packing of the THP molecules. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Calorimetric study of milk fat/rapeseed oil blends and their interesterification products

    Mario Aguedo
    Abstract Milk fat (MF) and rapeseed oil (RO) blends were analyzed by differential scanning calorimetry (DSC). It was shown that peak and onset temperatures can be used to determine the percentage of each fat in the blend and that the relative enthalpy of one peak assigned to low-melting triacylglycerols (TAG) can also be used to determine the percentage of RO in the blend. A linear relation was also established between MF content of the blend and its dropping point (DP), indicating that DP can be linearly related with the above DSC data. A blend of MF/RO 70,:,30 (wt/wt) was then chosen as a model system for enzymatic interesterification (EIE). The applicability of DSC analyses to EIE products was checked and a correct correlation could be established between DSC values and the interesterification degree and DP. Among the data from the DSC profiles, the peak associated with low-melting TAG was the best indicator of the reaction course. In the same way, a high-melting MF stearin fraction was interesterified with RO. In that case, onset temperatures and peak "a" were better reaction indicators than for the interesterified MF/RO blend. We therefore suggest that values from DSC endotherms could be used to monitor EIE of fat blends. [source]

    Comparative analysis of triacylglycerol composition, melting properties and polymorphic behavior of palm oil and fractions

    Sabine Braipson-Danthine
    Abstract Palm oil is without doubt the most widely fractionated oil. Dry fractionation is based on differences in the melting points of triacylglycerols (TAG) which will crystallize selectively during the cooling process. Unfortunately, limitations due to intersolubility, closely linked to polymorphism, induce formation of co-crystals at each crystallization step. For this reason, only restricted TAG enrichments are observed. In this work, a series of samples (24) of palm oil, solid and liquid fractions (stearins, mid fractions, oleins and superoleins) have been selected and examined in terms of TAG composition (by HPLC), differential scanning calorimetry (DSC) melting profile and variable temperature powder X-ray diffraction pattern. Three major endotherms [low-melting, high-melting and very high-melting peaks (LMP, HMP and VHMP)] are detected in the DSC melting profiles (5,C/min). The VHMP is only recorded for palm stearin which contains more SSS components. The HMP contribution is weak for palm olein and even not observed for palm super oleins. The LMP is usually made up of UUU, SUU and SUS components; SUS components are observed in both LMP and HMP; the HMP is also made up of some SSS, except for palm oleins and super oleins. Sub-,2, sub-,1, ,, ,'2, ,'1 and , polymorphic forms are recorded; the LMP components preferentially crystallize in sub-,2, sub-,1 and ,,forms; the HMP components generally crystallize in ,'2 and ,'1, with a tendency to exhibit ,,crystals, depending on the SSS content. Components of the VHMP have an increased tendency to stabilize in the ,,form; in view of the results, we can assume that there is a clear relationship between TAG composition, melting properties and polymorphic behavior and of palm oil and fractions. [source]

    Rheological behavior of crystallizing palm oil

    Veerle De Graef
    Abstract The static isothermal crystallization of palm oil was studied by oscillatory rheology. The phase angle, complex modulus, storage modulus and loss modulus were followed as a function of the crystallization time. Various crystallization temperatures were applied, and the results obtained by oscillatory rheology were compared with crystallization data obtained by more classical techniques like differential scanning calorimetry (DSC) and pulsed nuclear magnetic resonance (pNMR). It was shown that oscillatory rheology is a valuable complementary method to DSC and pNMR to evaluate primary crystallization. Like DSC and pNMR, oscillatory rheology is capable of differentiating whether crystallization occurs in a two-stage or a single-stage process. In addition, oscillatory measurements also allow the evaluation of aggregation, network formation and post-hardening events like sintering and thus provide information on the crystal network and the final macroscopic properties of the crystallized sample. [source]

    Influence of whitening on the degree of conversion of dental adhesives on dentin

    Milena Cadenaro
    The aim of this study was to analyze the extent of polymerization of different adhesive systems on whitened dentin. One adhesive of each class was investigated: Adper Scotchbond Multi Purpose (3M ESPE); One-Step (Bisco); Clearfil Protect Bond (Kuraray); and Xeno III (Dentsply DeTrey). Dentin disks were treated with Opalescence Xtra Boost (Ultradent) for 30 min and bonded immediately after 24 h or after 14 d of storage in 100% humidity at 37C. Unbleached dentin disks were prepared as controls. The extent of polymerization of bonded interfaces was obtained with differential scanning calorimetry (DSC) at 20, 40 and 60 s, and the data were statistically analyzed. The extent of polymerization obtained from DSC exotherms of adhesives applied immediately after whitening was significantly lower compared with controls. An increased extent of polymerization after storage was confirmed for all adhesives, and no difference with controls was found after 14 d. A prolonged irradiation time increased the curing rate for all the tested adhesives. This study supports the hypothesis that polymerization of the adhesive is reduced after dentin whitening and that delayed adhesive application reverses the polymerization inhibition. Prolonged polymerization intervals may counteract the inhibition of polymerization caused by the whitening procedure. Nevertheless, further in vivo studies should validate this issue. [source]

    Degree of conversion and permeability of dental adhesives

    Milena Cadenaro
    The aim of this study was to analyse the extent of polymerization of different adhesive films in relation to their permeability. One adhesive of each class was investigated: OptiBond FL; One-Step; Clearfil Protect Bond; and Xeno III. Adhesive films were prepared and cured with XL-2500 (3M ESPE) for 20, 40 or 60 s. Polymerization kinetic curves of the adhesives tested were obtained with differential scanning calorimetry (DSC) and data were correlated with microhardness. The permeability of the adhesives under the same experimental conditions was evaluated on human extracted teeth connected to a permeability device and analysed statistically. The results showed that the extent of polymerization obtained from DSC exotherms was directly correlated with microhardness. An increased level of polymerization after prolonged light-curing was confirmed for all adhesives. Simplified adhesives exhibited a lower extent of polymerization and showed incomplete polymerization, even after 60 s. An inverse correlation was found between the degree of cure and the permeability. This study supports the hypothesis that the permeability of simplified adhesives is correlated with incomplete polymerization of resin monomers and the extent of light exposure. These adhesives may be rendered less permeable by using longer curing times than those recommended by the respective manufacturer. [source]

    The Effects of Casting Temperature on the Glass Formation of Zr-Based Metallic Glasses,

    Jie Mao
    Abstract The glass1-forming ability of two alloys, Zr64.9Al7.9Ni10.7Cu16.5 and Zr47Cu37.5Ag7.5Al8, prepared by arc-melting a mixture of Zr, Cu, Al, Ni and Ag elements is studied as a function of casting temperature. Other processing parameters such as the alloy melt mass, and the vacuum and injection pressures during the copper-mold-casting process are kept constant so just the influence of the casting temperature is considered. The casting temperature determines the characteristics of the liquid melt and the cooling rate. The glass-forming ability is discussed in terms of dissipation of pre-exiting, metastable local-ordering clusters that act as nucleation sites promoting crystallization, the cooling rate at high casting temperatures, and the presence of oxygen in the alloys, which is increased at high casting temperatures. It is found that the glass-forming ranges of alloys shrink as the glass-forming size approaches a critical value. The optimum temperatures are around 1450,K and 1550,K for Zr64.9Al7.9Ni10.7Cu16.5 and Zr47Cu37.5Ag7.5Al8 alloys respectively. The alloys were studied by XRD, TEM, oxygen-level determination, and DSC. [source]

    The Coupling Effect of Small Nanocrystals and Free Volume on the Ductility of Cu46Zr47Al7 Bulk Metallic Glass Alloy,

    Feng Jiang
    Cu46Zr47Al7 bulk metallic glass (BMG) and its composite containing small in situ precipitated nanocrystals were prepared through copper mold casting. Different free volume states of these Cu46Zr47Al7 alloys were obtained through thermal treatment such as annealing and quenching. Three-point bending tests for these alloys were undertaken to evaluate their plastic deformation ability. Free volume changes were measured indirectly but quantitatively with differential scanning calorimetry (DSC) method. The results show that, the ductility of Cu46Zr47Al7 alloys is closely related with the free volume states and the ductility of thermally embrittled Cu46Zr47Al7 alloys samples can be partially recovered by restoring free volume through quenching process. The presence of small nanocrystals is more efficient than free volume to enhance the ductility. However, only with the concurrence of the small nanocrystals and the free volume, the Cu46Zr47Al7 BMG alloys will present excellent ductility. [source]

    Multiuser detection techniques with decision statistics combining for layered space-time coded CDMA systems

    Slavica Marinkovic
    This paper considers a low-complexity iterative multiuser detection/decoding algorithm in single user layered space-time coded (LST) systems and LST coded code division multiple access (CDMA) systems. We concentrate on the iterative multiuser receiver based on parallel interference cancellation (PIC) and compare it to the iterative PIC with the minimum means square error (MMSE) detection, as these two approaches seem to be most efficient in meeting the performance-complexity trade-off required by practical systems. In iterative PIC structures, a decision statistics bias severely limits the system performance for a large number of multiple access (MA) or multiple-input multiple-output (MIMO) interferers. A decision statistics combining (DSC) method, originally proposed for iterative PIC receivers in CDMA systems, is used to minimize the bias effect in space-time coded systems for iterative PIC receivers. Significant performance improvements have been confirmed with the iterative PIC receiver with DSC (PIC-DSC) relative to the standard iterative PIC receivers in LST systems for both flat and frequency selective fading channels. This advantage is retained in layered coded CDMA systems as well. The proposed iterative PIC-DSC detector approaches the performance of the much more complex iterative PIC-MMSE receiver. Copyright 2006 AEIT. [source]

    Thermally induced conformational changes in horseradish peroxidase

    FEBS JOURNAL, Issue 1 2001
    David G. Pina
    Detailed differential scanning calorimetry (DSC), steady-state tryptophan fluorescence and far-UV and visible CD studies, together with enzymatic assays, were carried out to monitor the thermal denaturation of horseradish peroxidase isoenzyme c (HRPc) at pH 3.0. The spectral parameters were complementary to the highly sensitive but integral method of DSC. Thus, changes in far-UV CD corresponded to changes in the overall secondary structure of the enzyme, while that in the Soret region, as well as changes in intrinsic tryptophan fluorescence emission, corresponded to changes in the tertiary structure of the enzyme. The results, supported by data about changes in enzymatic activity with temperature, show that thermally induced transitions for peroxidase are irreversible and strongly dependent upon the scan rate, suggesting that denaturation is under kinetic control. It is shown that the process of HRPc denaturation can be interpreted with sufficient accuracy in terms of the simple kinetic scheme where k is a first-order kinetic constant that changes with temperature, as given by the Arrhenius equation; N is the native state, and D is the denatured state. On the basis of this model, the parameters of the Arrhenius equation were calculated. [source]

    An evaluation of the self-heating hazards of cerium(IV) nitrated treated towels using differential scanning calorimetry and thermogravimetric analysis

    FIRE AND MATERIALS, Issue 6 2007
    J. R. Hartman
    Abstract This study measured the Arrhenius kinetic parameters and heat of reaction using thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) for the combustion of untreated towels and towels treated with cerium(IV) nitrate. These parameters were used to calculate the self-heating parameters, M and P (Self-heating: Evaluating and Controlling the Hazard. Her Majesty's Stationery Office: London, 1984) and the critical pile sizes of the towels at several temperatures. The results from the TGA/DSC experiments support the conclusions by Beyler et al. (Fire and Materials 2005; 30:223,240) that the cerium(IV) nitrate treatment of towels significantly enhances the ignitability of the towels but that self-heating is not a hazard for normal temperature storage scenarios other than bulk storage. It was found that the kinetic reaction data measured by TGA and DSC are only useful for predicting the specific reaction hazard for materials stored above 100C. A comparison of the self-heating parameters measured by oven and kinetic reaction data methods for a number of materials suggests that the kinetic reaction data overestimate the critical pile size at temperatures below 100C. In addition, it was found that the kinetic reaction data measured by TGA can be used to determine the relative self-heating hazards for modified materials. TGA testing with towels saturated with a 0.5 N solution of cerium(IV) nitrate (Ce(NO3)4) in a 2.0 N solution of nitric acid, a 2.0 N solution of sodium nitrate in 2.0 N nitric acid and simple 2.0 N nitric acid, showed that the sodium nitrate and nitric acid treated samples reacted at the same temperatures as the untreated towels, while cerium(IV) nitrate markedly reduced the reaction temperature. These tests clearly point to the importance of the cerium(IV) ion as an oxidizing agent. Thus, the TGA testing provided in a matter of days, insights that would have required months of oven testing. Copyright 2006 John Wiley & Sons, Ltd. [source]

    Flame retardancy finish with an organophosphorus retardant on silk fabrics

    FIRE AND MATERIALS, Issue 6 2006
    Jin-Ping Guan
    Abstract The paper mainly deals with flame retardancy of silk fabrics treated with a commercial organophosphorus flame retardant [N-hydroxymethyl (3-dimethyl phosphono) propionamide (HDPP), also known as Pyrovatex CP], using the pad-dry-cure-wash method. The structures and properties of the treated and control sample are discussed. The Limiting Oxygen Index (LOI) value of the modified sample is above 30%. After 50 laundry cycles, it still has some flame retardancy left. HDPP and a cross-linking agent (HMM) were bound to silk fabrics which is confirmed by FT-IR spectra and amino analysis. The reaction degree of the flame retardant with silk is also high; almost all the tyrosine units have reacted, which can be confirmed by amino acid analysis. The reaction between flame retardant and silk only occurs in the amorphous region of silk fibre, which is confirmed by X-ray diffraction analysis and amino acid analysis. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis show that the flame retardant causes silk fabrics to decompose below its ignition temperature (600C) and formed carbonaceous residue or char when exposed to fire. The char behaves as a thermal barrier to fire, so silk fabrics show good flame retardancy. The treatment has a little effect on the whiteness of the silk fabrics and the tensile strength of treated silk fabrics slightly decreased; both effects are negligible. Copyright 2006 John Wiley & Sons, Ltd. [source]

    Fire-resistant cyanate ester,epoxy blends

    FIRE AND MATERIALS, Issue 4 2003
    Richard N. Walters
    Abstract The cure chemistry, thermal stability and fire behaviour of a series of fire-resistant cyanate ester,epoxy blends were examined. The dicyanate and diepoxide of 1, 1-dichloro-2, 2-bis(4-hydroxyphenyl)ethylene (bisphenol-C, BPC) were combined in various molar ratios and the reaction chemistry was monitored using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The fire behaviour of the BPC cyanate,epoxy blends was studied in flaming and non-flaming combustion, using OSU calorimetry and pyrolysis-combustion flow calorimetry (PCFC), respectively. Published in 2003 by John Wiley & Sons, Ltd. [source]

    Hydrophilic Sparse Ionic Monolayer-Protected Metal Nanoparticles: Highly Concentrated Nano-Au and Nano-Ag "Inks" that can be Sintered to Near-Bulk Conductivity at 150,C

    Bibin T. Anto
    Here, monolayer-protected gold and silver nanoparticles with extremely high solvent dispersibility (over 200,mg mL,1 in water and glycols) and low coalescence temperature (approximately 150,C, measured by the percolation transition temperature Tp) are developed, to reach conductivities better than 1,,105,S cm,1. These materials are suitable for inkjet and other forms of printing on substrates that may be solvent- and/or temperature-sensitive, such as for plastic electronics, and as bus lines for solar and lighting panels. This is achieved using a new concept of the sparse ionic protection monolayer. The metal nanoparticles are initially protected by a two-component mixed ligand shell comprising an ,-functionalized ionic ligand and a labile ligand. These are selectively desorbed to give a sparse shell of the ,-ionic ligands of ca. 25% coverage. Through a systematic study of different monolayer-protected Au nanoparticles using FTIR spectroscopy, supported by XPS and DSC, it is shown that Tp is not determined by thermodynamic size melting or by surface area effects, as previously thought, but by the temperature when ca. 80% of the dense monolayer is eliminated. Therefore, Tp depends on the thermal stability and packing density of the shell, rather than the size of the metal core, while the solubility characteristics depend strongly on the exposed terminal group. [source]

    SPEEK/Polyimide Blends for Proton Conductive MembranesPresented at the 1st CARISMA Conference, Progress MEA 2008, La Grande Motte, 21st,24th September 2008.

    FUEL CELLS, Issue 4 2009
    H. Maab
    Abstract A series of membranes, based on sulphonated poly(ether ether ketone) (SPEEK)/polyimide (PI) blends, was prepared at different casting conditions. They were characterised by SEM, FTIR, DMTA, DSC, TGA, water/methanol pervaporation and impedance spectroscopy. The membranes prepared at 130,C from blends with 10, 20 and 30,wt.-% of PI are homogeneous, and the methanol permeabilities decreased from 28,,10,10,kg,m,s,1,m,2 (plain SPEEK) to 7.21, 2.61 and 0.55,,10,10,kg,m,s,1,m,2, respectively. This corresponds to a 4- to 57-fold methanol crossover reduction. With this improvement, by the introduction of PI, the power density of SPEEK-based membranes in DMFC tests could be greatly improved. [source]