Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Selected Abstracts

A Linear Model for the Continuous Network Design Problem

S. Travis Waller
A linear programming formulation is introduced based on a dynamic traffic assignment (DTA) model that propagates traffic according to the cell transmission model. The introduced approach is limited to continuous link improvements and does not provide for new link additions. The main contribution of the article is to provide an analytical formulation for network design that accounts for DTA conditions that can be used for further analysis and extensions. The model is tested on a single destination example network, resembling a freeway corridor, for various congestion levels, loading patterns and budget sizes, to demonstrate the simplicity and effectiveness of the approach. [source]

Case,Based Reasoning for Assessing Intelligent Transportation Systems Benefits

Adel Sadek
Existing transportation planning modeling tools have critical limitations with respect to assessing the benefits of intelligent transportation systems (ITS) deployment. In this article, we present a novel framework for developing modeling tools for quantifying ITS deployments benefits. This approach is based on using case,based reasoning (CBR), an artificial intelligence paradigm, to capture and organize the insights gained from running a dynamic traffic assignment (DTA) model. To demonstrate the feasibility of the approach, the study develops a prototype system for evaluating the benefits of diverting traffic away from incident locations using variable message signs. A real,world network from the Hartford area in Connecticut is used in developing the system. The performance of the prototype is evaluated by comparing its predictions to those obtained using a detailed DTA model. The prototype system is shown to yield solutions comparable to those obtained from the DTA model, thus demonstrating the feasibility of the approach. [source]

Effect of NaCl filler on ferroelectric phase and polaron configurations of PVDF films

I. S. ElashmawiArticle first published online: 8 MAR 200
Abstract Polyvinyldene fluoride (PVDF) films filled with NaCl of mass fraction range 1 , W , 6 % were prepared by casting technique. Their crystalline structure, thermal, optical properties and Electron spin resonance (ESR) were examined. X-ray diffraction (XRD) and differential thermal analysis (DTA) measurements indicated a maximum ferroelectric ,-phase increment at 4%. DTA was used to identify the phase transition temperatures, the order of reaction and the activation energy of melting. The UV-Visible optical absorption implied a minimum value of the estimated optical energy gap at W = 4%. ESR spectra contained a Lorentizian signal exhibiting a minimum value of the symmetry factor at W = 4%. The energy levels of the optical gap boundaries were though to contribute to ESR transitions. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Growth and characterization of semiorganic NLO crystals of LAHClBr

P. C. Thomas
Abstract Single crystals of non-linear optical (NLO) LAHClBr were grown by slow evaporation technique from its aqueous solution. Good optical quality crystals having dimensions up to 12 9 7 mm3 were obtained. The lattice parameters and morphology for the grown crystals were determined using single crystal XRD. The crystals were characterized by FT-Raman, optical absorption, thermal (DTA and TGA) and dielectric studies. LAHClBr was found to be thermally stable up to 124.3C. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Influence of the starting powders on the synthesis of nickel ferrite

F. Kenfack
Abstract The thermal decomposition of freeze-dried nickel(II)-iron(III) formate was investigated by means of DTA, TG, mass spectrometry and X-ray powder diffractometry. For the preparation of homogeneous freeze-dried nickel(II)-iron(III) formate precursors, a rigorous control of nickel ion concentration in the precursor solution was required. The decomposition of the reactive nickel(II)-iron(III) formate does not only reflect aspects of single formates, but also an interaction between components which lowers the decomposition temperature. Crystalline nickel ferrite powders were obtained at 600-800C. This temperature is quite lower than 1100C employed for the ceramic method. In the presence of air, the regeneration of nickel ferrite from the taenite phase (,Ni,Fe) is accomplished at 800C. This temperature is also 300C below the temperature employed when the mixtures NiO:,-Fe2O3 or Ni:2Fe are the starting powders. The main reason for the high reactivity of the freeze-dried formates and the taenite alloy is the large homogeneity of these precursors. ( 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]

Synthesis and characterization of compounds LixMn1+xFe2,2xO4 with spinel structure in the quasiternary system "LiO0,5 , MnOx , FeOx"

C. Wende
Abstract The thermal decomposition of freeze-dried Li-Mn(II)-Fe(III)-formate precursors was investigated by means of DTA, TG and mass spectroscopy. By the thermal treatment of the prefired precursors between 400 and 1000C, single phase solid solutions LixMn1+xFe2,2xO4 (0 , x , 1) with cubic spinel structure were obtained. To get single phase spinels, special conditions concerning the temperature T and the oxygen partial pressure p(O2) during the synthesis are required. Because of the high reactivity of the freeze-dried precursors, in comparison with the conventional solid state reaction, the reaction temperature can be lowered by 200C. The cation distribution and the properties of the Li-Mn-ferrites were studied by chemical analysis, X-ray powder diffraction and magnetization measurements. It was found that for high substitution rates, almost all lithium occupies the tetrahedral coordinated A-sites of the spinel lattice AB2O4, while at small x-values, lithium ions are distributed over the tetrahedral and octahedral sites. ( 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Assessment of Elastic Properties of the Descending Thoracic Aorta By Transesophageal Echocardiography with Acoustic Quantification in Patients with a Stroke

Seok-Min Kang M.D.
Previous studies have described the use of transesophageal echocardiography (TEE) with acoustic quantification (AQ) in assessing aortic elastic properties. We hypothesized that patients with a prior history of stroke (ST) may have a higher risk of atherosclerotic change in great vessels compared to nonstroke subjects (NST) and thus have decreased elastic properties. We assessed the elastic properties of the descending thoracic aorta (DTA) by TEE in ST patients and compared them with data in NST patients. Subjects included 31 with ST without any evidence of emboli originating from the heart (age 51 10 years, M: F = 20: 11) and 25 age-matched NST (M: F= 8: 17). Patients with significant valvular heart disease including aortic and mitral regurgitation, left ventricular dysfunction (ejection fraction < 55%), and congenital heart disease were excluded. Compliance (C), distensibility (D), and stiffness index (SI) were measured using AQ and M-mode measurement at a level of the left atrium. We scored atherosclerotic risk factors (ARF) such as a history of diabetes, hypertension, smoking, hypercholesterolemia, and the presence of atheroma of DTA. There was no evidence of atheroma of DTA in NST. There were no significant differences in heart rate and systolic and diastolic blood pressure between ST and NST patients. Fractional area change (FAC) of DTA was significantly lower in ST than in NST patients (3.2 1.6 vs 5.4 2.5%, P= 0.000). ST patients had significantly lower C (1.2 0.4 vs 1.5 0.7 times 10 -3 cm2 mmHg -1, P= 0.039), lower D (0.8 0.3 vs 1.5 0.8 times 10 -3 mmHg -1, P= 0.000), and higher SI (10.3 8.8 vs 5.3 2.9, P= 0.006) than NST patients. ST patients without atheroma of DTA (n 21) also had significantly lower C (1.1 0.4 vs 1.5 0.7 times 10 -3 cm -2 mmHg -1, P= 0.038) and lower D (3.5 1.4 vs 4.8 2.4 times 10 -3 mmHg -1, P= 0.021) than NST patients. There was a significant positive correlation between SI and the score of ARF (r= 0.51, P= 0.000). The regional elastic properties of DTA measured by TEE with AQ and M-mode method were abnormal in ST. Therefore, TEE with AQ technique may have a possible clinical application for the detection of early atherosclerotic changes such as alteration of elastic properties in morphological normal DTA. [source]

Synthesis and Crystal Structure of Mercury-Substituted Type-I Clathrates A8Hg4Sn42 (A = K, Rb, Cs)

Andreas Kaltzoglou
Abstract The mercury-substituted type-I clathrates A8Hg4Sn42,with A = K, Rb or Cs, were obtained by fusion of the pure elements at high temperatures. The crystal structures of the compounds were refined from single-crystal X-ray diffraction data. They crystallize in the space group Pmn (No. 223), Z = 1 with a = 12.1255(4) for K8Hg4Sn42 (1), a = 12.1838(4) for Rb8Hg4Sn42 (2) and a = 12.2130(4) for Cs8Hg4Sn42 (3). The 3D framework of four-bonded atoms defines two types of polyhedral cages of different size that are fully occupied by the alkali-metal atoms. All three compounds are considered as formally charge-balanced Zintl phases without any homogeneity range. Differential thermal analysis (DTA) indicates that the stability of the clathrates significantly depends on the size of the encaged cations. The thermal stability of the title compounds and the binary phases A8Sn44 (A = K, Rb, Cs) is discussed. Temperature-dependent magnetic measurements for compound 3 show also the expected diamagnetic behaviour. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Oxidation Resistance of Multilayer SiC for Space Vehicle Thermal Protection Systems,

Claudia Milena Vega Bolivar
The oxidation resistances of different kinds of SiC-based laminates are compared. The materials under investigation are produced by tape casting of green ceramic sheets, followed by stacking of the sheets in a multilayer structure and laminate consolidation by de-binding and sintering. Three kinds of specimens are tested: multilayer SiC with fully dense layers, multilayer SiC integrating porous layers and multilayer composites made by stacking SiC/Cf composite layers. Two kinds of chopped carbon fibres (polyamide coated and uncoated) are used for the manufacture of the composite sheets. The oxidation behaviour is investigated by simultaneous TGA,DTA,MS analysis. Specimens are also submitted to a long-term oxidation treatment (30,h at 1,600,C in flowing air) and their microstructure and mechanical behaviour compared before and after oxidation. This assessment shows that the integration of porous or composite layers in the multilayer architecture does not worsen the oxidation resistance. In every case the formation of a surface passivating layer prevents major degradation phenomena, so that only small changes in the mechanical features are found after oxidation. [source]

Crystallization Kinetics of the (Zr58Ni13.6Cu18Al10.4)Nb1 Bulk Metallic Glass,

D. Qiao
The differential thermal analysis (DTA) curve of the (Zr58Ni13.6Cu18Al10.4)Nb1 bulk metallic glass (BMG) shows that there are two exothermic crystallization peaks and two endothermic melting peaks. The BMG has been completely crystallized in the first crystallization peak. X-ray shows that the quenched BMG only includes the glass single phase. The BMG heated to 823 K (between the first and the second crystallization peak) has the precipitation of the cubic NiZr2. The BMG heated to 1003 K (after the second crystallization peak) has the cubic NiZr2, bct NiZr2, and bct CuZr2. HRTEM shows that there are some nano-crystalline phases for the quenched BMG. [source]

The Experimental and Theoretical Study of Phase Equilibria in the Pd,Zn (-Sn) System,

J. Vizdal
The binary Pd-Zn system was assessed in the scope of this paper. The experimental data from the literature were used for the assessment, together with our own data obtained by SEM-EDS analysis and by the DTA. The paper is focused particularly on the Pd-Zn system, but the Pd-Sn and Sn-Zn systems are also analysed in this paper. Finally, first prediction of the isothermal sections of the ternary Pd-Sn-Zn system was made. [source]

Graft copolymerization modification of silk fabric with an organophosphorus flame retardant

Guan Jinping
Abstract This paper mainly deals with flame retardance of a silk fabric treated with a vinyl phosphate dimethyl 2-(methacryloyloxyethyl) phosphate (DMMEP) onto silk fabric by a graft copolymerization technique. This paper also explores the relationship between limiting oxygen index (LOI) and weight gain of DMMEP treated silk fabric. The paper also investigates the whiteness, handle, tensile strength and laundering durability of treated silk fabric. Microscale combustion calorimetry (MCC) is applied to test the heat release rate of silk fabric. Thermal gravimetric analysis (TG) and differential thermal analysis (DTA) are carried out to investigate the thermal decomposition behavior of DMMEP treated silk fabric. The kinetic parameters, activation energy and pre-exponential factor are determined using the Kissenger method. Copyright 2009 John Wiley & Sons, Ltd. [source]

Effect of Ce, Sb, and Sn on Solarization and Crystallization of an X-Ray-Irradiated Photosensitive Glass

Mohamad Hassan Imanieh
The effect of Ce, Sb, and Sn photosensitive elements, individually and in combination with each other, on solarization and crystallization of an X-ray irradiated and a nonirradiated lithium silicate-based glass were investigated. According to the results, considering the crystallization behavior of the nonirradiated glasses, they were divided into Ce-bearing and Ce-free groups, in which the former group showed a clearer solarization tendency that manifested as an appearance of an absorbance peak at 318 nm in the spectrophotometry experiment. However, the results showed that in the irradiated glasses, the presence of Sb was more important in terms of improvement in crystallization view. Antimony decreased the differential thermal analysis (DTA) crystallization peak temperature from 655C to 594C and, in combination with the two other elements, changed the surface crystallization mechanism to a bulk one. The reactions that seemed to be responsible for the above-mentioned observations were discussed by spectrophotometry, DTA, X-ray diffraction, and scanning electron microscopic methods. [source]

Rheological and curing behavior of aqueous ambient self-crosslinkable polyacrylate emulsion

Xiaohua Liu
Abstract An aqueous ambient crosslinkable polymer acrylic (AACPA) emulsion was obtained by adding adipic acid dihydrazide (ADH) to the polyacrylate emulsion incorporating diacetone acrylamide (DAAM), and this emulsion was synthesized by two feeding materials methods. The AACPA emulsion and its paint film were characterized with rheological measurements, laser light scattering, Fourier transform infrared, torsional braid analysis (TBA), DTA, and so on. The results showed that AACPA emulsion was pseudoplastic fluid and pseudoplasticity increased with increasing of DAAM content. The results also showed that water resistance, solvent resistance, and thermotacky temperature of AACPA paint film increased with increasing of the content of DAAM. The results dealing with curing behavior of the paint film showed that adding organic swelling solvent and organic acid to the AACPA emulsion can accelerate the curing speed of the paint film. 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source]

Role of calcium and ROS in cell death induced by polyunsaturated fatty acids in murine thymocytes

Aparna Prasad
We investigated the mechanisms whereby omega-3 and -6 polyunsaturated fatty acids (PUFAs) cause cell death of mouse thymocytes using flow cytometry, focusing on the respective roles of intracellular calcium concentration, [Ca2+]i and reactive oxygen species (ROS). We applied the C-22, 20, and 18 carbon omega-3 (DHA, EPA, ALA) and omega-6 (DTA, ARA, and LNA) fatty acids to isolated thymocytes and monitored cell death using the DNA-binding dye, propidium iodide. When applied at 20,M concentration, omega-3 fatty acids killed thymocytes over a period of 1,h with a potency of DHA,>,EPA,>,ALA. The omega-6 PUFAs were more potent. The C18 omega-6 fatty acid, LNA, was the most potent, followed by DHA and ARA. Cell death was always accompanied by an increase in the levels of [Ca2+]i and ROS. Both increases were in proportion to the potency of the PUFAs in inducing cell death. Removing extracellular calcium did not prevent the elevation in [Ca2+]i nor cell death. However, the intracellular calcium chelator, BAPTA, almost totally reduced both the elevation in [Ca2+]i and cell death, while vitamin E reduced the elevation in ROS and cell death. BAPTA also prevented the elevation in ROS, but vitamin E did not prevent the elevation in [Ca2+]i. Thapsigargin, which depletes endoplasmic reticulum calcium, blocked the elevation in [Ca2+]i, but CCCP, a mitochondrial calcium uptake inhibitor, did not. These results suggest that the six PUFAs we studied kill thymocytes by causing release of calcium from endoplasmic reticulum, which causes release of ROS from mitochondria which leads to cell death. J. Cell. Physiol. 225: 829,836, 2010. 2010 Wiley-Liss, Inc. [source]

Catalytic performance of Brnsted acid sites during esterification of acetic acid with ethyl alcohol over phosphotungestic acid supported on silica

Abd El-Aziz A Said
Abstract Different ratios of phosphotungestic acid supported on silica gel were prepared by an impregnation method with PWA loadings ranging from 1 to 30% w/w and calcined at 350 and 500 C for 4 h in a static air atmosphere. The catalysts were characterized by thermogravimety (TG), differential thermal analysis (DTA), X-ray diffraction, FT-IR spectroscopy and N2 adsorption measurements. The surface acidity and basicity of the catalyst were investigated by the dehydration,dehydrogenation of isopropanol and the adsorption of pyridine (PY) and 2,6-dimethyl pyridine (DMPY). The gas-phase estrification of acetic acid with ethanol was carried out at 185 C in a conventional fixed-bed reactor at 1 atm using air as carrier gas. The results clearly revealed that the catalyst containing 10% w/w PWA/SiO2 is the most active and delivers reaction selectively to ester with 85% yield. The Brnsted acid site resulting from hydroxylation of tungsten oxide plays the main role in the formation of ester. Copyright 2007 Society of Chemical Industry [source]

Structure, texture and surface acidity studies of a series of mixed zinc,aluminum (60,90 molar % Al) phosphate catalysts

Karim Mtalsi
Abstract A series of mixed zinc,aluminum phosphate (ZnAlP) catalysts containing 40,90 aluminum molar % were synthesized by a coprecipitation method and characterized by nitrogen adsorption,desorption, X-ray diffraction, FTIR spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature programmed desorption (TPD) of ammonia. The presence of aluminum greatly affected the surface properties of Zn3(PO4)2 by delaying the crystallization process of Zn3(PO4)2. All amorphous samples were shown to be mesoporous and they contained two types of aluminum surface hydroxyl groups and one type of phosphorus hydroxyl group, as shown by DRIFT spectra. The specific surface area and the acidity of ZnAlP increased on increasing the aluminum content. On the other hand, a great difference in the texture and the concentration of surface acid sites was found by changing the precipitating agent and calcination temperature. Thus these factors also play an important role in the final properties of these catalysts. 2001 Society of Chemical Industry [source]

Structural characterization of anhydrous naloxone- and naltrexone hydrochloride by high resolution laboratory X-ray powder diffraction and thermal analysis

Kunihisa Sugimoto
Abstract The crystal structures of the analgesic compounds anhydrous naloxone and naltrexone hydrochloride were determined ab initio from high resolution laboratory X-ray powder diffraction data. Both compounds crystallize in the orthorhombic space group P212121 with lattice parameters of a,=,14.6588(10) , b,=,17.4363(9) , c,=,7.96200(22) , and V,=,2035.06(23) 3 for naloxone hydrochloride and a,=,15.4560(5) , b,=,14.9809(4) , c,=,7.84121(18) , and V,=,1815.58(11) 3 for naltrexone hydrochloride. The crystal structure of anhydrous naloxone hydrochloride forms one-dimensional chains through hydrogen bonds. In the crystal structure of anhydrous naltrexone hydrochloride, two-dimensional sheets are formed by hydrogen bonds. The dehydration processes of naloxone hydrochloride dehydrate and naltrexone hydrochloride tetrahydrate was analyzed by DTA, DSC, TG, and MG. 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 3316,3323, 2007 [source]

Structural phase transition in [NH3(CH2)5NH3]BiCl5: thermal and vibrational studies

H. Jeghnou
Abstract An x-ray diffraction study carried out on the pentylenediammonium pentachlorobismuthate (III) compound [NH3(CH2)5NH3]BiCl5 indicated that it is orthorhombic with a P212121(Z = 4) space group. Differential scanning calorimetry (DSC), differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were also made, which showed that this compound undergoes a unique phase transition at high temperatures. The infrared and Raman spectra recorded at room temperature were interpreted on the basis of data published in the literature. The Raman bands observed below 300 cm,1 are very characteristic of the anions, which are made of isolated (BiCl52, )n units composed of BiCl63, octahedra. Raman spectra recorded at various temperatures confirmed the contribution to the phase-transition mechanism of both the anion and cation motions. Copyright 2005 John Wiley & Sons, Ltd. [source]

Synthesis of Yttrium,Aluminum,Garnet Hollow Microspheres by Reverse-Emulsion Technique

Minati Chatterjee
Yttrium,aluminum,garnet (YAG, Y3Al5O12) hollow microspheres were synthesized by reverse-emulsion (w/o) technique starting with aqua-based precursors of oxides. The non-ionic surfactant was used as the emulsifying agent. The gel powders were calcined at 700,1200C. The synthesized powders were characterized by differential thermal analysis (DTA), thermogravimetry, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The appearance of an exothermic peak at 932C in the DTA curve revealed the crystallization of YAG, which was further confirmed by XRD and FTIR studies. SEM confirmed the formation of hollow microspheres. [source]

Zirconia,Silica,Carbon Coatings on Ceramic Fibers

Emmanuel E. Boakye
Precursors for zircon,carbon mixtures were made to coat fibers for ceramic-matrix composites. Precursors were characterized using XRD, TGA, and DTA. Zircon formed from vanadium- or lithium-doped precursors after heat treatments at ,900C in air, but it did not form at 1200,1400C in argon when large amounts of carbon were added. Some precursors were used to coat Nextel 720 and Hi-Nicalon fibers. The coatings were characterized using SEM and TEM, and coated-fiber tensile strengths were measured. Although zircon formed in powders, only tetragonal-zirconia,silica mixed phases formed in fiber coatings at 1200C in air. Loss of vanadium oxide flux to the fibers may have caused the lack of conversion to zircon. The strengths of the coated fibers were severely degraded after heat treatment at ,1000C in air, but not in argon. The coated fibers were compared with zirconia,carbon-coated fibers made using similar methods. Mechanisms for fiber strength degradation are discussed. [source]

Effect of B2O3 Addition on the Thermal Stability of Barium Phosphate Glasses for Optical Fiber Devices

Takashi Harada
The effect of B2O3 addition on the thermal stability of BaO,P2O5 glasses is studied by differential thermal analysis (DTA), X-ray diffraction (XRD) analysis, scanning electron microscopy, and micro-Raman spectroscopy. The difference between glass-transition and onset-crystallization temperatures increases monotonically with increasing B2O3 concentration. The DTA result reveals that no exothermic peak due to surface crystallization exists in the BaO,P2O5 glass doped with 3 mol% B2O3. A single-mode BaO,P2O5 -B2O3 glass fiber could be fabricated by a rod-in-tube technique. The modification of glass structure due to B2O3 addition is qualitatively discussed. [source]

Effect of Oligosaccharide Alcohol Addition to Alumina Slurry and Translucent Alumina Produced by Slip Casting

Yuji Hotta
A slurry used to produce dense green compacts by slip casting should exhibit low viscosity, high solids content, and good dispersion. Slurries with good characteristics were produced in the present study by adding oligosaccharide alcohol to an Al2O3 slurry with an NH4+ salt of poly(methacrylic acid) (NH4+ -PMA). The role of NH4+ -PMA and oligosaccharide alcohol in the Al2O3 slurry was examined by DTA, ,-potential measurement, high-pressure liquid chromatography, and viscometry. The viscosity of the slurry with NH4+ -PMA and oligosaccharide alcohol was lower than that of the slurry with NH4+ -PMA at a high solids content. Oligosaccharide alcohol did not interact with the Al2O3 surface. However, the Al2O3 slurry with NH4+ -PMA was influenced by the addition of oligosaccharide alcohol. We found that the dispersibility of the slurry was greatly improved by adding oligosaccharide alcohol. The transmittance of the Al2O3 ceramics produced by slip casting using the slurry with both NH4+ -PMA and oligosaccharide alcohol was higher than that of ceramics produced by slip casting using the slurry with NH4+ -PMA alone. The increased optical property resulted from low viscosity, which was attributed to the addition of oligosaccharide alcohol, at a high solids content. [source]

Nucleation and Crystallization of a Lead Halide Phosphate Glass by Differential Thermal Analysis

Hongsheng Zhao
The nucleation and crystallization mechanisms of a lead halide phosphate glass [40P2O530PbBr230PbF2 (mol%)] were investigated by differential thermal analysis (DTA) and X-ray diffraction analysis. There were two crystalline phases in the crystallized samples: the major phase was PbP2O4, and the minor phase was PbP2O6. The average activation energy for crystallization, E, for two different particle sizes of this glass was determined to be 119 4 kJ/mol by the Kissinger method and 124 4 kJ/mol by the Augis,Bennett method. The Avrami constants were determined to be 1.6 and 2.5 for particle sizes of 203 and 1040 ,m, respectively, by the Ozawa equation, and 1.7 and 2.4 for particle sizes of 203 and 1040 ,m, respectively, by the Augis,Bennett equation. The decrease in the crystallization peak height in the DTA curve with increasing particle size suggested that the particles crystallize primarily by surface crystallization. A nucleation-rate type curve was determined by plotting either the reciprocal of the temperature corresponding to the crystallization peak maximum, 1/Tp, or the height of the crystallization peak, (,T)p, as a function of nucleation temperature, Tn. The temperature where nucleation can occur for this glass ranges from 360,450C and the maximum nucleation rate is at 420 10C. [source]

Effects of Dry Grinding on the Structural Changes of Kaolinite Powders

Pedro J. Snchez-Soto
The present study examined the effects of dry grinding, using ball-milling, on the structure of reference well-crystallized (KGa-1) and poorly crystallized (KGa-2) kaolinite powders from Georgia. Grinding produced a strong structural alteration, mainly along the c axis, resulting in disorder and total degradation of the crystal structure of the kaolinite and the formation of an amorphous product. The surface area increased with grinding time, mainly in KGa-2 (maximum value 50.27 m2/g), a result associated with particle-size reduction. These particles became more agglomerated with grinding, and the surface area decreased after 30 min, as confirmed by scanning electron microscopy and particle-size-distribution analysis. There was a limit to particle-size reduction with grinding time. When grinding time was increased, the original endothermic differential thermal analysis (DTA) effects of dehydroxylation in both samples shifted to lower temperatures, decreased in intensity, then disappeared completely after 120 min of grinding. The temperature of the characteristic first exothermic effect shifted slightly to lower temperatures with grinding, although the DTA effects did not increase with grinding time in either kaolinite sample, at least up to 325 min. The amorphous, mechanically activated kaolinite converted into low-crystalline mullite nuclei at a lower temperature than did the unground samples, as deduced by thermal and X-ray observations. This effect was especially important for the KGa-2 sample. Grinding did not seem to influence the formation of silicon-aluminum spinel from kaolinite. The present results may explain why ground kaolinite samples prepared via different routes,e.g., with differences in grinding,behave differently during high-temperature transformations, as reported in the related literature. [source]

Synthesis and characterization of Cu3TaIn3Se7 and CuTa2InTe4

P. Grima-Gallardo
Abstract Polycrystalline samples of Cu3TaIn3Se7 and CuTa2InTe4 were synthesized by the usual melt and anneal technique. X-ray powder diffraction showed a single phase behavior for both samples with tetragonal symmetry and unit cell parameter values a = 5.794 0.002 , c = 11.66 0.01 , c /a = 2.01, V = 391 1 3 and a = 6.193 0.001 , c = 12.400 0.002 , c /a = 2.00, V = 475 1 3, respectively. Differential thermal analysis (DTA) measurements suggested a complicated behavior near the melting point with several thermal transitions observed in the heating and cooling runs. From the shape of the DTA peaks it was deduced that the melting is incongruent for both materials. Magnetic susceptibility measurements (zero-field cooling and field cooling) indicated an antiferromagnetic character with transition temperatures of T = 70 K (Cu3TaIn3Se7) and 42 K (CuTa2InTe4). A spin,glass transition was observed in Cu3TaIn3Se7 with Tf , 50 K. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Study of the mechanical and thermal properties of Sn,5 wt% Sb solder alloy at two annealing temperatures

M. M. EL-Bahay
Abstract Sn,5 wt% Sb alloy is one of the materials considered for replacing lead-containing alloys for soldering in electronic packaging. Differential thermal analysis (DTA) and specific heat of the sample were studied. Wetting contact angle measurements of the alloy on different substrates were carried out at high temperature. Microhardness tests as a function of temperature were performed to calculate the effective activation energy of the solder alloy Sn,Sb and compared with the pure elements Sn and Sb. Isothermal creep curves for alloy samples were obtained under different constant applied stresses at different working temperatures ranging from 463 K to 503 K, followed by annealing the samples at two different temperatures before and above the threshold value (Tm/2). The transient creep parameters and the values of the stress exponent n were calculated for the two annealing temperatures. Microstructure examinations of the as-cast alloy at room temperature and after the two annealing treatments with the effect of the cold work deformation and creep test on the structure change and properties of Sn,Sb alloys were reported. The stress rupture test was also measured. [source]

Effects of Zn doping on YBaCuO superconductor

M. Mahtali
Abstract In this work we present a study of Zn impurity effects on the YBa2Cu3O7,, high Tc superconducting ceramics prepared by the solid state reaction method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA) techniques, and resistivity measurements are used to characterize the YBa(Cu1,xZnx)3O7,, samples. The obtained results show that, for example, the value of the transition critical temperature is decreasing up to 80 K caused by the substitution of Zn for Cu in the interval 0 , x , 0.01. Also, the peritectic transformation of superconducting phase undergoes a displacement to lower temperatures compared with pure YBaCuO. On the basis of the obtained results, the effects of Zn doping on the structural and electronic properties are explained. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effects of synthesis conditions on crystal morphological structures and thermal degradation behavior of hydrotalcites and flame retardant and mechanical properties of EVA/hydrotalcite blends

Longchao Du
The effects of synthesis methods and reaction conditions on the crystal morphological structures and thermal degradation behavior of hydrotalcites have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), particle size analysis (PSA), and differential thermal analysis (DTA). The flame retardant and mechanical properties of ethylene,vinyl acetate (EVA) blends with the corresponding hydrotalcites have been estimated by limiting oxygen index (LOI), UL-94, and mechanical measurements. The results from the XRD, TEM, and PSA demonstrate that the hydrotalcites synthesized by ultrasound method have larger crystal sizes and particle size distribution than those by mechanical stirring method. Higher reaction temperature, longer dripping time, and lower solution concentration can increase the crystal and particle sizes of ultrasound-synthesized hydrotalcites, whereas the longer ultrasound aging time can increase the crystal sizes and decrease the particle sizes of hydrotalcites because of the smashing conglomeration. The DTA data give a positive evidence that the hydrotalcite samples prepared by mechanical stirring method with longer alkaline dripping time have higher thermal degradation temperature than those by ultrasound method, since the ultrasound-synthesized hydrotalcites have more lattice defects than stirring-prepared hydrotalcites. The data from LOI, UL-94, and mechanical tests show that the ultrasonic-synthesized hydrotalcites have better flame retardant properties, whereas the stirring-synthesized hydrotalcites have better tensile strength in the EVA/hydrotalcite blends. POLYM. COMPOS., 28:131,138, 2007. 2007 Society of Plastics Engineers [source]