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Loss Tangent (loss + tangent)
Selected AbstractsImprovement of Microwave Loss Tangent and Tunability of Ba0.55Sr0.45TiO3/MgO Composites Using the Heterogeneous Precipitation MethodJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006Rui-Hong Liang Ba0.55Sr0.45TiO3/MgO composites were successfully prepared by the heterogeneous precipitation method and their structural, surface morphological, tunable properties, and dielectric properties at microwave frequency were systemically investigated. Compared with the sample prepared by the traditional solid-state method, the sample prepared by the heterogeneous precipitation method exhibits a smaller grain size, more uniform microstructure, higher tunability, and lower microwave loss, and these properties are very beneficial to the development of the microwave tunable devices application. Moreover, the effects of La2O3 doping on the dielectric and tunable properties of BST/MgO composites are investigated. The result shows that the La3+ -doped sample has higher tunability and lower microwave loss than the undoped one. [source] Hysteresis measurements and dynamic mechanical characterization of functionally graded natural rubber,carbon black compositesPOLYMER ENGINEERING & SCIENCE, Issue 5 2010S.S. Ahankari Functionally graded polymer composites (FGPCs) were prepared by construction based layering method employing natural rubber (NR) as a matrix and carbon black (CB) in graded form. CB particles were graded along the rectangular geometry polymer matrix comprising the variation of particle volume fraction along thickness direction. These FGPCs were characterized through hysteresis measurements and compared with uniformly dispersed polymeric composites (UDPCs) maintaining the same average amount of filler. Dynamic mechanical properties of these FGPCs and UDPCs were also compared. Dynamic mechanical characterization revealed that FGPCs show much higher storage modulus than the corresponding UDPCs for any given combination of stacking sequence. Loss tangent of FGPCs was also observed to be lesser when compared to UDPCs leading to less hysteretic losses followed by lesser heat buildup in the composite. Hysteresis measurements accorded with the results of dynamic mechanical characterization. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source] Ultrarapid Microwave Synthesis of Superconducting Refractory CarbidesADVANCED MATERIALS, Issue 44 2009Simon R. Vallance Nb1,xTaxC Carbides can be synthesized by high power MW methods in less than 30,s. In situ and ex situ techniques probing changes in temperature and dielectric properties with time demonstrate that the reactions self-terminate as the loss tangent of the materials decreases. The resulting carbides are carbon deficient and superconducting; Tc correlates linearly to unit cell volume, reaching a maximum at NbC. [source] Challenges and Progress in High-Throughput Screening of Polymer Mechanical Properties by IndentationADVANCED MATERIALS, Issue 35 2009Johannes M. Kranenburg Abstract Depth-sensing or instrumented indentation is an experimental characterization approach well-suited for high-throughput investigation of mechanical properties of polymeric materials. This is due to both the precision of force and displacement, and to the small material volumes required for quantitative analysis. Recently, considerable progress in the throughput (number of distinct material samples analyzed per unit time) of indentation experiments has been achieved, particularly for studies of elastic properties. Future challenges include improving the agreement between various macroscopic properties (elastic modulus, creep compliance, loss tangent, onset of nonlinear elasticity, energy dissipation, etc.) and their counterpart properties obtained by indentation. Sample preparation constitutes a major factor for both the accuracy of the results and the speed and efficiency of experimental throughput. It is important to appreciate how this processing step may influence the mechanical properties, in particular the onset of nonlinear elastic or plastic deformation, and how the processing may affect the agreement between the indentation results and their macroscopic analogues. [source] Thermally Stimulated Currents of SiO2/Low-density Polyethylene Micro- and NanocompositesIEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 4 2010Yi Yin Non-member Abstract Composite samples of low-density polyethylene (LDPE)/nano-SiO2 and LDPE/micro-SiO2 were prepared with the method of double-solution mixture. Depolarization currents of all samples were investigated with thermally stimulated depolarization current (TSDC). It was found that the currents of both composites increased with the loading level of nano-SiO2 and/or micro-SiO2, and that the peak width of each composite is greater than that of pure LDPE. In addition, the peak position of the nanocomposite shifts as the loading level increases, while that of the microcomposite does not shift significantly. In order to understand activation energy of both composites and pure LDPE, the initial-rise method was used to analyze the depolarization current. It was found that LDPE has the greatest activation energy among all samples and the activation energy of both composites decreases with increasing loading levels. Moreover, the activation energy of the nanocomposite is less than that of the microcomposite at each of the same loading level. As the nano-SiO2 loading level reaches 5.0%wt, the composite has the lowest activation energy of 0.25 eV. In addition, dielectric spectra of all samples were investigated in the range of 10,4 to 107 Hz, and it was found that the peak position of loss tangent varied consistently with the TSDC curves as the loading levels of nano-SiO2 and/or micro-SiO2 were increased. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source] Starch-lipid composites in plain set yogurtINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 1 2009Mukti Singh Summary Starch-lipid composites (SLC) were used to replace milk solids in yogurt mixes. The effects of the SLC on the yogurt fermentations and rheology were studied. The rate of fermentation was evaluated by the change of pH during the fermentation of yogurt. The syneresis of yogurt was observed over 3 weeks of storage. Small amplitude oscillatory shear flow measurements of the storage modulus, the loss modulus, and the loss tangent were obtained using a vane geometry. Yogurt mixes with milk solids partially replaced by SLC fermented at a similar rate than as with no milk solids replaced. Initial viscosity was higher for yogurt mixes with higher levels of SLC. The higher initial viscosity did not affect the gel structure. The addition of SLC above a level of 3% strengthened the gel and resulted in no syneresis for yogurt samples stored for 3 weeks at 4 °C. [source] Modeling of conductor losses in capacitors with rectangular and circular platesINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 2 2009A. Deleniv Abstract Analytic models are developed for the losses in the plates of MIM capacitors. The formulas are derived for the equivalent loss tangent and resistance of the arbitrary thick rectangular electrodes. An equivalent surface resistance is introduced for an arbitrary thick conductor. The accuracy of the model is demonstrated by comparison with rigorous Sonnet simulation and available alternative approach. The formula for the resistance of electrically thick circular electrodes is obtained. The derived expressions are verified via comparison with rigorous HFSS (high frequency structure simulator) simulations using eigenmode solver. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009. [source] About the activation energies of the main and secondary relaxations in cured styrene butadiene rubberJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2009Ada Ghilarducci Abstract This article studies the influence of the network structure on the activation energies of the , and , relaxations in vulcanized styrene butadiene rubber, SBR. A cure system based on sulphur and TBBS (N-t-butyl-2-benzothiazole sulfenamide) was used in the formulation of several compounds cured at 433 K. The activation energies were evaluated from internal friction (loss tangent) data of the compounds using an automated subresonant forced pendulum in a wide frequency range and between 80 K and 273 K. The internal friction data of the samples reveal two transitions, , and ,, characterized by the temperatures T, and T,, due to the glass transition and the phenyl group rotation of the copolymer, respectively. Although T, increases at higher crosslink density, it shows also a dependence with the amount of polysulphide and monosulphide linkages present in the samples. The highest activation energy for this process is obtained for the samples with high crosslink density and 30% of monosulphides in this structure. In the case of the ,-relaxation, there is a pronounced change in the activation energy between the uncured and the cured samples. The type of structure formed during vulcanization has an important effect in the activation energy of the segmental mode-process. In the case of the ,-process, the cis-trans isomerization that takes place during vulcanization in the butadiene part of the SBR, might be the cause of conformational changes in the surrounding of the phenyl rings that affect the energy barrier associated to the phenyl rotation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Structure,properties relations of the drawn poly(ethylene terephthalate) filament sewing threadJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Andreja Rudolf Abstract This article presents research into draw ratio influence on the structure,properties relationship of drawn PET filament threads. Structural modification influence due to the drawing conditions, i.e., the birefringence and filament crystallinity, on the mechanical properties was investigated, as well as the shrinkage and dynamic mechanical properties of the drawn threads. Increasing draw ratio causes a linear increase in the birefringence, degree of crystallinity, filament shrinkage, and a decrease in the loss modulus. In addition, loss tangent and glass transition temperature, determined at the loss modulus peak, were increased by drawing. The observed structural changes influence the thread's mechanical properties, i.e., the breaking tenacity, elasticity modulus, and tension at the yield point increase, while breaking extension decreases by a higher draw ratio. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Effect of silica reinforcement on natural rubber and butadiene rubber vulcanizates by a sol,gel reaction with tetraethoxysilaneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Kyong-Hwan Chung Abstract The effect of silica reinforcement was studied for natural rubber (NR) and butadiene rubber (BR) vulcanizates by a sol,gel reaction with tetraethoxysilane at different temperatures. The formation of silica in the rubber vulcanizates was investigated analytically with Fourier transform infrared spectroscopy and energy-dispersive X-ray analysis. The variations of the mechanical and dynamic properties were measured in the NR and BR vulcanizates with silica filling. The hardness of the rubber vulcanizates increased with silica filling in the rubber matrix. The tensile strength and elongation at break decreased with silica filling in the NR vulcanizates. The moduli at 50, 100, and 300% elongation increased with silica filling in the rubber matrix. The storage modulus of silica-filled rubber vulcanizates became higher than that of pure rubber vulcanizates. The temperature dependence of the loss modulus also increased with silica filling. The temperature dependence of the loss tangent was maintained, regardless of silica filling in the BR vulcanizates. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Application of a Depth Sensing Indentation Hardness Test to Evaluate the Mechanical Properties of Food MaterialsJOURNAL OF FOOD SCIENCE, Issue 5 2002N. ÖZkan ABSTRACT: A depth sensing indentation hardness test with an associated analysis is described as a convenient and simple technique for characterizing mechanical properties of food materials, such as hardness (H), elastic modulus (E), and an elasticity index (IE), which represents the ratio of elastic to total deformation. Storage modulus (G,) and loss tangent (tan§) of the selected model food material, a whey protein concentrate (WPC) gel, have also been determined using an oscillatory dynamic testing. Fractal dimension (D) and strain rate (or frequency) exponent (n) of the WPC gels were determined using both the indentation and dynamic test results. A good correlation between the results from the indentation and the dynamic tests was established. The effects of protein concentration, deformation rate, and chemical treatment on the mechanical properties of the WPC gels were clearly illustrated using the indentation test. [source] RHEOLOGICAL PROPERTIES, WHEY SEPARATION, AND MICROSTRUCTURE IN SET-STYLE YOGURT: EFFECTS OF HEATING TEMPERATURE AND INCUBATION TEMPERATUREJOURNAL OF TEXTURE STUDIES, Issue 5-6 2003WON-JAE LEE The effects of heat treatment and incubation temperature on the rheological and microstructural properties of yogurt were studied. A central composite experimental design and response surface methodology were used for data analysis. The rheological properties were determined by dynamic low amplitude oscillation and the amount of spontaneous whey separation was quantified by the volumetric flask test. Confocal scanning laser microscopy was used to examine the gel structure. The storage moduli of yogurts increased with an increase in heating temperature and a decrease in incubation temperature. The maximum loss tangent value during gelation, permeability, and amount of spontaneous whey separation of yogurts increased with a decrease in heating temperature and with an increase in incubation temperature. These parameters indicated an increased possibility for rearrangements, which was confirmed by presence of large pores in the gel network. Second order polynomial models successfully predicted the effects of heating temperature and incubation temperature on the rheological properties, permeability, and whey separation of yogurts. Whey separation was negatively correlated with storage modulus (r= -0.66), and was positively correlated with the maximum loss tangent (r= 0.63) and permeability (r= 0.78). This study demonstrates that weak yogurt gels, which have high loss tangent values, favor rearrangements in the network and the resulting network has larger pores (high permeability) and exhibits greater whey separation. [source] Effect of Donor, Acceptor, and Donor,Acceptor Codoping on the Electrical Properties of Ba0.6Sr0.4TiO3 Thin Films for Tunable Device ApplicationsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009Yuanyuan Zhang We have investigated the effects of donor, acceptor, and donor,acceptor codoping on both the dielectric properties and the leakage current behavior of Ba0.6Sr0.4TiO3 thin films prepared by the metalorganic solution deposition technique. La and Co were selected as donor and acceptor dopants, respectively. The electrical properties depend strongly on the type of dopants. Compared with others, codoped BST films have a much lower loss tangent, higher figure of merit, and lower leakage current. The electronic conduction mechanisms of the three types of dopants are reported. [source] Microwave Dielectric Properties of Sintered Alumina Using Nano-Scaled Powders of , Alumina and TiO2JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2007Cheng-Liang Huang The microstructure and the microwave dielectric properties of nano-scaled , alumina (,-Al2O3) ceramics with various added amounts of nano-scaled TiO2 have been investigated. The sintering temperature of nano-scaled , alumina can be effectively lowered by increasing the TiO2 content. The Q×f values of nano-scaled , alumina could be tremendously boosted by adding an appropriate amount of TiO2. However, introducing excessive TiO2 into the alumina ceramics would instead lead to a decrease in the Q×f values. The phases of TiO2 and Al2TiO5 co-existed at 1350°C, and the maximum Q×f value appeared right after the eradication of TiO2 phase at 1400°C. Consequently, increasing the TiO2 content to 0.5 wt% yielded a Q×f value of 680 000 GHz (measured at 14 GHz) for nano-scaled , alumina prepared at 1400°C for duration of 4 h. In addition, a very low loss tangent (tan ,) of 2 × 10,5 was also obtained at 14 GHz. The ,f value is strongly correlated to the compositions and can be controlled through the existing phases. In fact, ,f could be adjusted to near zero by adding 8 wt% TiO2 to , alumina ceramics. A dielectric constant (,r) of 10.81, a high Q×f value of 338 000 GHz (measured at 14 GHz), and a temperature coefficient of resonant frequency (,f) of 1.3 ppm/°C were obtained for nano-scaled , alumina with 8 wt% TiO2 sintered at 1350°C for 4 h. Sintered ceramic samples were also characterized by X-ray diffraction and scanning electron microscopy. [source] Structural, Dielectric, and Thermal Properties of Strontium Barium Niobate-Doped Fused Silica NanocompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2003Sheng-Guo Lu Ferroelectric strontium barium niobate (SBN)-doped Na2O,B2O3,SiO2 (NBS) glass nanocomposites were prepared by dispersing sol,gel-derived SBN powder into fused NBS glass. Their structures were characterized by X-ray diffractometry and Raman spectroscopy. The dielectric constants were measured as functions of frequency and temperature using an impedance analyzer. The ferroelectric-to-paraelectric-phase transition was studied by differential scanning calorimetric analysis. Our results revealed that the embedded SBN has lower phase transition temperature and phase transition heat than those of SBN bulk materials. Their activation energy, however, is larger than that of SBN ultra-fine powders. Pure tetragonal-phase SBN nanocomposites can be obtained at annealing temperatures of 750°,1000°C. Their dielectric constants are ,32,46 and ,20,25 at low frequencies and radio frequencies, respectively, and the loss tangent is <0.1 at room temperature in the radio frequencies range. Our studies suggested that additional reduction in the loss properties must be made before these systems can be considered for application as microwave dielectric materials. [source] Lead Zirconate Titanate Thin Films on Base-Metal Foils: An Approach for Embedded High-Permittivity Passive ComponentsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2001Jon-Paul Maria An approach for embedding high-permittivity dielectric thin films into glass epoxy laminate packages has been developed. Lead lanthanum zirconate titanate (Pb0.85La0.15(Zr0.52Ti0.48)0.96O3, PLZT) thin films were prepared using chemical solution deposition on nickel-coated copper foils that were 50 ,m thick. Sputter-deposited nickel top electrodes completed the all-base-metal capacitor stack. After high-temperature nitrogen-gas crystallization anneals, the PLZT composition showed no signs of reduction, whereas the base-metal foils remained flexible. The capacitance density was 300,400 nF/cm2, and the loss tangent was 0.01,0.02 over a frequency range of 1,1000 kHz. These properties represent a potential improvement of 2,3 orders of magnitude over currently available embedded capacitor technologies for polymeric packages. [source] Effect of EPDM on Morphology, Mechanical Properties, Crystallization Behavior and Viscoelastic Properties of iPP+HDPE BlendsMACROMOLECULAR SYMPOSIA, Issue 1 2007Nina Vranjes Abstract Summary: Blends of isotactic polypropylene (iPP) and high density polyethylene (HDPE) with and without ethylene-propylene-diene (EPDM) terpolymer as compatibilizer were systematically investigated to determine the influence of the EPDM on blends properties. The morphology was studied by Scanning Electron Microscopy (SEM). Mechanical properties of investigated systems: tensile strength at break, elongation at break, yield stress and Izod impact strength were determined. Crystallization behavior was determined by Differential Scanning Calorimetry (DSC). Dynamic Mechanical Analysis (DMA) was used to determined the storage modulus (E,), loss modulus (E,), and loss tangent (tan ,). The PP+HDPE blend revealed poor adhesion between PP and HDPE phases. Finer morphology was obtained by EPDM addition in PP+HDPE blends and better interfacial adhesion. Addition of HDPE to PP decreased tensile strength at break, elongation and yield stress. Decrease of tensile strength and yield stress is faster with EPDM addition in PP+HDPE blends. Elongation at break and impact strength was significantly increased with EPDM addition. The addition of EPDM in PP+HDPE blends did not significantly change melting points of PP phase, while melting points of HDPE phase was slightly decreased in PP+HDPE+EPDM blends. The EPDM addition increased the percentage of crystallization (Xc) of PP in PP+HDPE blends. The increase of Xc of HDPE was found in the blend with HDPE as matrix. Dynamical mechanical analysis showed glass transitions of PP and HDPE phase, as well as the relaxation transitions of their crystalline phase. By addition of EPDM glass transitions (Tg) of HDPE and PP phases in PP+HDPE blends decreased. Storage modulus (E,) vs. temperatures (T) curves are in the region between E,/T curves of neat PP and HDPE. The decrease of E, values at 25,°C with EPDM addition in PP+HDPE blends is more pronounced. [source] A modified expression for determining the wall thickness of monolithic half-wave radomesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2001S. Sunil Abstract A comparison of the wall thickness for a monolithic half-wave radome at different incidence angles is made by considering the loss tangent of the material used. It is seen that, for large incidence angles and for moderately low-loss radome materials, the computed wall thickness is different from the values obtained by neglecting the loss tangent of the material. The above context seems to be important, particularly for variable thickness radomes for aerospace applications where the thickness from nose to base varies with the angle of incidence and angle of polarization so as to achieve the optimum design of the radome. An expression for computing the wall thickness is given which is valid for both moderately lossy and very low-loss radome materials. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 350,352, 2001. [source] Influence of Ca[(Li1/3Nb2/3)0.8Ti0.2]O3-, filler on the microwave dielectric properties of polyethylene and polystyrene for microelectronic applicationsPOLYMER ENGINEERING & SCIENCE, Issue 3 2010Sumesh George Ceramic reinforced polyethylene and polystyrene composites were prepared by melt mixing and hot molding techniques. Temperature stable low-loss Ca[(Li1/3Nb2/3)0.8Ti0.2]O3-, (CLNT) ceramic was used as the filler to improve the dielectric properties of the polymers. The relative permittivity and dielectric loss in the microwave frequency range were increased with increase in the ceramic loading. As the filler content increased from 0 to 0.50 volume fraction, the relative permittivity increased from 2.3 to 9 and dielectric loss tangent from 0.0006 to 0.005 for polyethylene-CLNT composite. In the case of polystyrene-CLNT composite, the relative permittivity and dielectric loss tangent increased from 2.1 to 10.5 and 0.0005 to 0.0032 respectively with increase in filler content from 0 to 0.50 volume fractions. The thermal stability of the relative permittivity of polymer ceramic composites was also investigated. The experimentally observed relative permittivity was compared with theoretical models. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source] The effect of crystallinity and water absorption on the dynamic mechanical relaxation behaviour of polycaprolactonePOLYMER INTERNATIONAL, Issue 9 2004Kate L Harrison Abstract The effect of the degree of crystallinity on the dynamic mechanical relaxation behaviour (flexural storage modulus and loss tangent) of polycaprolactone has been investigated. The degree of crystallinity was found to determine the temperature of the ,-relaxation process and the relaxation strength of the ,-relaxation. The increase in temperature of the ,-process has been ascribed to constrainment of the amorphous regions of the sample by the crystallites. In accordance with the observed effect of the degree of crystallinity, the origin of the dynamic mechanical ,-relaxation has been ascribed to the amorphous regions of the material. The intensity of the ,-process has also been found to depend on the moisture content, becoming more prominent when moisture is present. In addition, moisture has been shown to penetrate the crystalline regions of the sample over a relatively short timescale, as shown by infrared spectroscopy. Copyright © 2004 Society of Chemical Industry [source] Preparation and characterization of a polyimide nanofoam through grafting of labile poly(propylene glycol) oligomerPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2004Sang Hyub Han Abstract Preparation of a polyimide nanofoam (PI-F) for microelectronic applications was carried out using a polyimide precursor synthesized from poly[(amic acid)-co-(amic ester)] and grafted with a labile poly(propylene glycol) (PPG) oligomer. Polyimide precursor was synthesized by partial esterification of poly(amic acid) (PAA) derived from pyromellitic dianhydride (PMDA) and 4,4,-oxydianiline (ODA). The precursor was then grafted with bromide-terminated poly(propylene glycol) in the presence of K2CO3 in hexamethylphosphoramide and N -methylpyrrolidone, imidized at 200°C in nitrogen and the product was subsequently decomposed in air at 300°C to eliminate the labile PPG oligomer to produce PMDA/ODA polyimide nanofoam. Nuclear magnetic resonance spectroscopy (1H-NMR) and Fourier transform infrared spectroscopy (FT-IR) techniques were used to characterize the formation of polyimide precursor and extent of grafting of PPG with polyimide. The results of thermogravimetric analysis (TGA) showed three step decomposition of nanofoam with the removal of PPG at 350°C and decomposition of polyimide at around 600°C. The polyimide nanofoams were also characterized by small angle X-ray scattering (SAXS), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The morphology showed nanophase-separated structures with uniformly distributed and non-interconnected pores of 20,40,nm in size. Dynamic mechanical analysis (DMA) indicated higher storage modulus for the foamed structure compared to the pure PI with reduction in loss tangent for the former system. Copyright © 2004 John Wiley & Sons, Ltd. [source] A novel route to perovskite lead zirconate titanate from glycolate precursors via the sol,gel processAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2008N. Tangboriboon Abstract A perovskite lead zirconate titanate was synthesized by the sol-gel process, using lead glycolate, sodium tris(glycozirconate) and titanium glycolate as the starting precursors. For the mole ratio Pb:Zr:Ti of 1:0.5:0.5 [Pb(Zr0.5Ti0.5)O3], TGA-DSC thermal analysis indicated that the percentage of ceramic yield was 55.8, close to the calculated chemical composition value of 49.5. The exothermic peak occurred at 268 °C below the theoretical Curie temperature of 400 °C. The pyrolysis of Pb(Zr0.5Ti0.5)O3 of the perovskite phase was investigated in terms of calcination temperature and time. The structure obtained was of the tetragonal form when calcined at temperatures below 400 °C; it transformed to the tetragonal and the cubic forms of the perovskite phase on calcination above the Curie temperature, as verified by X-ray data. The lead zirconate titanate synthesized and calcined at 400 °C for 1 h had the highest dielectric constant, the highest electrical conductivity and the dielectric loss tangent of 10 190, 0.803 × 10,3 (,.m),1 and 1.513 at 1000 Hz, respectively. The lead zirconate titanate powder synthesized has potential applications as an electronic material. Copyright © 2008 John Wiley & Sons, Ltd. [source] Microwave-based alkali pretreatment of switchgrass and coastal bermudagrass for bioethanol productionBIOTECHNOLOGY PROGRESS, Issue 3 2010Deepak R. Keshwani Abstract Switchgrass and coastal bermudagrass are promising lignocellulosic feedstocks for bioethanol production. However, pretreatment of lignocelluloses is required to improve production of fermentable sugars from enzymatic hydrolysis. Microwave-based alkali pretreatment of switchgrass and coastal bermudagrass was investigated in this study. Pretreatments were carried out by immersing the biomass in dilute alkali reagents and exposing the slurry to microwave radiation at 250 W for residence times ranging from 5 to 20 min. Simons' stain method was used to quantify changes in biomass porosity as a result of the pretreatment. Pretreatments were evaluated based on yields of total reducing sugars, glucose, and xylose. An evaluation of different alkalis identified sodium hydroxide as the most effective alkali reagent for microwave-based pretreatment of switchgrass and coastal bermudagrass. 82% glucose and 63% xylose yields were achieved for switchgrass and 87% glucose and 59% xylose yields were achieved for coastal bermudagrass following enzymatic hydrolysis of biomass pretreated under optimal conditions. Dielectric properties for dilute sodium hydroxide solutions were measured and compared with solid losses, lignin reduction, and reducing sugar levels in hydrolyzates. Results indicate that dielectric loss tangent of alkali solutions is a potential indicator of the severity of microwave-based pretreatments. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Polymeric composites for use in electronic and microwave devicesPOLYMER ENGINEERING & SCIENCE, Issue 3 2004Alexandre Moulart The dielectric and conductive properties of thermoplastic (ABS) composites filled with ceramic powder (barium titanate), conductive powders (carbon black, copper) and conductive fibers (carbon, steel) were investigated for use in electromagnetic crystals and microwave devices. Barium titanate/ABS composites were produced that had dielectric constants over 8 and loss tangents of 0.01, which are the requirements for electromagnetic crystals. Carbon black/ABS and steel fiber/ABS composites were obtained with conductivities suitable for electromagnetic shielding (over 10,3 S/cm). Fused decomposition modeling was tested as a method for building electromagnetic crystals and showed promising results. Polym. Eng. Sci. 44:588,597, 2004. © 2004 Society of Plastics Engineers. [source] | ||||||||||||||||