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Heating Rate (heating + rate)
Kinds of Heating Rate Selected AbstractsGelatinization kinetics of amaranth starchINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 4 2001Andrea Calzetta Resio Summary The influence of the water:starch ratio and heating rate on the gelatinization of amaranth starch was investigated using differential scanning calorimetry. Onset and peak temperatures did not vary significantly with increase of water content, whereas the completion temperature decreased by more than 14 °C when the water content was in excess. A linear relationship was found between moisture content and gelatinization enthalpy for water:starch ratios between 0.81:1 and 2:1. From this relationship the minimum level of water necessary to initiate gelatinization was calculated. For water::starch ratios over 3:1, the enthalpy of gelatinization reached a maximum value. More rapid heating resulted in an increase of the peak and completion temperatures, as well as the gelatinization energy. Heating rates above 10 °C min,1 gave the maximum energy requirements for the completion of gelatinization in an excess of water. The kinetics of gelatinization of amaranth starch was analysed from the DSC traces. A simple mathematical model was tested to evaluate the kinetic parameters. It was shown that in an excess of water and for heating rates above 10 °C min,1, gelatinization followed first-order kinetics with n varying from 0.91 to 0.93. The activation energy was in the range of 157,185 kJ mol,1. However, the present analysis did not allow for the determination of the kinetic parameter values over the whole gelatinization range. [source] Short-Term Changes in Heat Tolerance in the Alpine Cushion Plant Silene acaulis ssp. excapa [All.] J. Braun at Different AltitudesPLANT BIOLOGY, Issue 6 2000G. Neuner Abstract: The habit of cushion growth positively affects plant temperature but at the same may increase the risk of occasional overheating. In order to determine the adaptive response to short-term heat stress, we exposed S. acaulis cushions at field sites to controlled heat treatments using infrared lamps. Natural diurnal changes in heat tolerance were monitored at alpine sites and at a site distinctly below the natural distribution boundary, where higher temperatures were expected. The range of heat tolerance limits in summer, 45.5 - 54.5 °C (9 K), exceeded that reported for other alpine species (0.1 - 5 K) and even that for total seasonal changes (5 - 8 K). Heat tolerance either increased or decreased on most days (80 %). The maximum diurnal increase was + 4.7 K. Under the experimental conditions heat hardening started at leaf temperatures around 30 °C and proceeded at mean rates of 1.0 ± 0.5 K/h. The onset of functional disturbances in photosystem II also occurred at 30 °C. Heating rates exceeding those naturally found above 30 °C (> 10 K/h) appeared to retard heat hardening. During summer average leaf temperature maxima were 12.4 K (600 m) and 13.0 K (1945 m) higher than air temperature which corroborates the heat trapping nature of cushion plants. At 600 m, as compared to 1945 m, cushions experienced significantly higher leaf temperature maxima (+ 8.8 K) and exceeded 30 °C on most days (80 %). This resulted in a significantly higher heat tolerance (LT50) at 600 m (51.7 ± 0.2 °C) than at 1945 m (49.8 ± 0.2 °C). The fast short-term changes of heat tolerance in summer help S. acaulis to cope with the occasional diurnal short-term heat stress associated with cushion growth. [source] The effect of heating rate on Escherichia coli metabolism, physiological stress, transcriptional response, and production of temperature-induced recombinant protein: A scale-down studyBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2009Luis Caspeta Abstract At the laboratory scale, sudden step increases from 30 to 42°C can be readily accomplished when expressing heterologous proteins in heat-inducible systems. However, for large scale-cultures only slow ramp-type increases in temperature are possible due to heat transfer limitations, where the heating rate decreases as the scale increases. In this work, the transcriptional and metabolic responses of a recombinant Escherichia coli strain to temperature-induced synthesis of pre-proinsulin in high cell density cultures were examined at different heating rates. Heating rates of 6, 1.7, 0.8, and 0.4°C/min were tested in a scale-down approach to mimic fermentors of 0.1, 5, 20, and 100 m3, respectively. The highest yield and concentration of recombinant protein was obtained for the slowest heating rate. As the heating rate increased, the yield and maximum recombinant protein concentration decreased, whereas a larger fraction of carbon skeletons was lost as acetate, lactate, and formate. Compared to 30°C, the mRNA levels of selected heat-shock genes at 38 and 42°C, as quantified by qRT-PCR, increased between 2- to over 42-fold when cultures were induced at 6, 1.7, and 0.8°C/min, but no increase was observed at 0.4°C/min. Only small increases (between 1.5- and 4-fold) in the expression of the stress genes spoT and relA were observed at 42°C for cultures induced at 1.7 and 6°C/min, suggesting that cells subjected to slow temperature increases can adapt to stress. mRNA levels of genes from the transcription,translation machinery (tufB, rpoA, and tig) decreased between 40% and 80% at 6, 1.7 and 0.8°C/min, whereas a transient increase occurred for 0.4°C/min at 42°C. mRNA levels of the gene coding for pre-proinsulin showed a similar profile to transcripts of heat-shock genes, reflecting a probable analogous induction mechanism. Altogether, the results obtained indicate that slow heating rates, such as those likely to occur in conventional large-scale fermentors, favored heterologous protein synthesis by the thermo-inducible expression system used in this report. Knowledge of the effect of heating rate on bacterial physiology and product formation is useful for the rational design of scale-down and scale-up strategies and optimum recombinant protein induction schemes. Biotechnol. Bioeng. 2009;102: 468,482. © 2008 Wiley Periodicals, Inc. [source] Screening Breakdown in a Plasma by Two Laser Fields and Strong DC Magnetic FieldCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1 2005D. F. Miranda Abstract The effective static dielectric constant of an electron plasma system in the simultaneous presence of two electromagnetic waves and a strong DC magnetic field is calculated. It is found that as the difference ,, of the two electromagnetic wave frequencies matches the plasma frequency ,, a breakdown in screening occurs thereby increasing the plasma heating rate via the external fields due to inverse Bremmstrahlung. An application is made by considering the typical parameters of a hot plasma. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thermal, phase transition and spectral studies in erythromycin pseudopolymorphs: dihydrate and acetone solvateCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2006Zhanzhong 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] Costs of Refuge Use Affect Escape Decisions of Iberian Rock Lizards Lacerta monticolaETHOLOGY, Issue 6 2000José Martín Theoretical models of anti-predator escape behaviour suggest that prey may adjust their escape response such that the optimal flight distance is the point at which the costs of staying exceed the costs of fleeing. Anti-predatory decisions should be made based also on consequences for long-term expected fitness, such as the costs of refuge use. For example, in lizards, the maintenance of an optimal body temperature is essential to maximize physiological processes. However, if unfavourable thermal conditions of refuges can decrease the body temperature of lizards, their escape decision should be influenced by refuge conditions. Analyses of the variation in flight distances and emergence latency from a refuge for the lizard Lacerta monticola under two different predation risk levels, and their relationship with the thermal environment, supported these predictions. When risk increased, lizards had longer emergence latencies, and thus costs of refuge use increased (a greater loss of time and body temperature). In the low-risk situation, lizards that were farther from the refuge had longer flight distances, whereas thermal conditions were less important. When risk increased, lizards had longer flight distances when refuges were farther off, but also when the external heating rate and the refuge cooling rate were lower. The results suggest that, in addition to the risk of predation, expected long-term fitness costs of refuges can also affect escape decisions. [source] Synthesis and Monitoring of ,-Bi2Mo3O12 Catalyst Formation using Thermo-Raman SpectroscopyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2004Anil Ghule Abstract Thermo-Raman spectroscopy was used to monitor the dehydration and phase transformations of Bi2Mo3O12·5H2O. The hydrated forms Bi2Mo3O12·5H2O, Bi2Mo3O12·4.75H2O, Bi2Mo3O12·3H2O, Bi2Mo3O12·2H2O, and anhydrous Bi2Mo3O12 were observed during dehydration in the wavelength range from 200 to 1400 cm,1. Representative Raman spectra of these compounds are reported for the first time. The thermo-Raman intensity thermogram showed a systematic dehydration in four steps, and the differential thermo-Raman intensity thermogram confirmed this. Thermogravimetry, differential thermogravimetry, and differential scanning calorimetry results were in harmony with the results of the thermo-Raman spectroscopy. Additionally, the dehydration resulting in formation of anhydrous Bi2Mo3O12 (amorphous Bi2Mo3O12 phase) and the final transformation into the ,-Bi2Mo3O12 phase was observed to be a dynamic thermal process. The slow, controlled heating rate produced ,-Bi2Mo3O12 catalyst with a particle size averaging 200 nm. The catalyst formed was further characterized by Fourier transform infrared spectroscopy, X-ray diffraction, time of flight SIMS, transmission electron microscopy, and energy-dispersive X-ray analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Oriented Grain Growth Analyses With In Situ Annealing Experiments Using High Energy Synchrotron RadiationADVANCED ENGINEERING MATERIALS, Issue 3 2010Caterina Elisabetta Tommaseo The development of the recrystallization and annealing textures of Al,Mn alloys with 0.4, 0.7 and 1,wt.-% manganese is analyzed using specific techniques that allow the detection of changes in grain orientation during in situ annealing. In order to investigate the evolution of texture components during annealing, highly rolled samples were annealed from room temperature to 500,°C at a constant heating rate. The advantage of in situ annealing experiments using synchrotron radiation is the detection of grain orientations over time, which allows observation of the development of the recrystallization and annealing textures in a sample. In fact, the recrystallization and annealing textures in the Al,0.4Mn are characterized by an interruption in the detection of most of the grain orientations between 380 and 425,°C and by competition between the cube {001}<100>, {011}<1-33>, {011}<0-11> and rotated-cube {001}<110> grain orientations, where the latter is detected until the end of the experiment. In the Al,0.7Mn sample a competition between the cube {001}<100>, {011}<100>, and rotated cube {001}<110>, {011}<0,11> grain orientations is observed. In the sample with the highest manganese concentration (1,wt.-%) an unhindered grain growth of all possible grain orientations with a high amount of the {011}<0-11> grain orientation is observed. The evolution of the resulting local textures is discussed in terms of preferentially oriented grain growth depending on the temperature and manganese concentration. [source] A Screening Design Approach for the Understanding of Spark Plasma Sintering Parameters: A Case of Translucent Polycrystalline Undoped AluminaINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2010Yann Aman An experimental screening design was used to evaluate the effects of spark plasma sintering (SPS) parameters such as heating rate, sintering temperature, dwell duration, and green-shaping processing on the relative density, grain size, and the optical properties of polycrystalline alumina (PCA). It is shown that heating rate and sintering temperature are the most critical factors for the densification of PCA during SPS. Green-shaping processing could prevent grain growth at low SPS sintering temperatures. No predominant SPS parameters are observed on the optical properties. Hence, the optical properties of PCA are controlled by microstructural evolution during the SPS process. [source] Gelatinization kinetics of amaranth starchINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 4 2001Andrea Calzetta Resio Summary The influence of the water:starch ratio and heating rate on the gelatinization of amaranth starch was investigated using differential scanning calorimetry. Onset and peak temperatures did not vary significantly with increase of water content, whereas the completion temperature decreased by more than 14 °C when the water content was in excess. A linear relationship was found between moisture content and gelatinization enthalpy for water:starch ratios between 0.81:1 and 2:1. From this relationship the minimum level of water necessary to initiate gelatinization was calculated. For water::starch ratios over 3:1, the enthalpy of gelatinization reached a maximum value. More rapid heating resulted in an increase of the peak and completion temperatures, as well as the gelatinization energy. Heating rates above 10 °C min,1 gave the maximum energy requirements for the completion of gelatinization in an excess of water. The kinetics of gelatinization of amaranth starch was analysed from the DSC traces. A simple mathematical model was tested to evaluate the kinetic parameters. It was shown that in an excess of water and for heating rates above 10 °C min,1, gelatinization followed first-order kinetics with n varying from 0.91 to 0.93. The activation energy was in the range of 157,185 kJ mol,1. However, the present analysis did not allow for the determination of the kinetic parameter values over the whole gelatinization range. [source] Effects of storage aging on the cure kinetics of bismaleimide prepregsADVANCES IN POLYMER TECHNOLOGY, Issue 4 2005M. Frigione The effects of room temperature aging on the subsequent polymerization kinetics of a bismaleimide (BMI) matrix prepreg, for high performance composites, have been characterized by different time and storage conditions. The study has focused on the stability of BMI matrix carbon fiber prepregs, when exposed to controlled environmental conditions before being used in composite manufacturing. The effects of aging on glass transition temperature, reactivity, and processability have been investigated by calorimetry through dynamic, isothermal, and cure-simulating tests. A theoretical kinetic model for epoxy matrix prepregs, developed in previous studies, has been applied to the polymerization of both aged and unaged BMI matrix. The model is able to satisfactorily describe the effect of processing variables such as temperature and degree of reaction during the curing of the composite under different conditions (curing temperature and heating rate). The effects of diffusion-controlled phenomena on the reaction kinetics, associated with changes in glass transition temperature as a function of the degree of polymerization and cross-linking, have been taken into account in the formulation of an nth-order kinetic model. © 2005 Wiley Periodicals, Inc. Adv Polym Techn 24: 253,265, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20048 [source] Structure and metal type effects on cure kinetics of DGEBA with benzil bisthiosemicarbazone complexesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Mousa Ghaemy Abstract The curing reaction kinetics of the diglycidyl ether of bisphenol A- (DGEBA) based epoxy was investigated according to the change of curing agents. Complex curing agents based on Ni(II) and Cu(II) chelates with benzil bisthiosemicarbazone (LH6) as a ligand was studied using differential scanning calorimetry. The curing reaction was characterized by high-activation energies (Ea), cure onset (Ti), and peak maximum (Tp) temperatures. Dynamic kinetic parameters were calculated by using Kissinger and Ozawa methods. For the NiLH6Cl2, CuLH6Cl2, and LH6 the average values of Ea were calculated to be 165.16, 165.92, and 115.75 kJ/mol, respectively. For the NiLH6Cl2 systems, their activation energies at 40 and 30 phr are equal. The Ti and Tp of the DGEBA/NiLH6Cl2 system are lower than those of DGEBA/CuLH6Cl2 system. These results indicate that NiLH6Cl2 has a higher reactivity toward epoxy resin at the beginning of the curing reaction. The effect of hardener concentration, heating rate, and type of metal ion on the cure kinetic parameters and the shape of DSC thermograms were investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Effect of quasi-carbonization processing parameters on the mechanical properties of quasi-carbon/phenolic compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Donghwan Cho Abstract In this work, quasi-carbon fabrics were produced by quasi-carbonization processes conducted at and below 1200°C. Stabilized polyacrylonitrile (PAN) fabrics and quasi-carbon fabrics were used as reinforcements of phenolic composites with a 50 wt %/50 wt % ratio of the fabric to the phenolic resin. The effect of the quasi-carbonization process on the flexural properties, interfacial strength, and dynamic mechanical properties of quasi-carbon/phenolic composites was investigated in terms of the flexural strength and modulus, interlaminar shear strength, and storage modulus. The results were also compared with those of a stabilized PAN fabric/phenolic composite. The flexural, interlaminar, and dynamic mechanical results were quite consistent with one another. On the basis of all the results, the quasi-static and dynamic mechanical properties of quasi-carbon/phenolic composites increased with the applied external tension and heat-treatment temperature increasing and with the heating rate decreasing for the quasi-carbonization process. This study shows that control of the processing parameters strongly influences not only the mechanical properties of quasi-carbon/phenolic composites but also the interlaminar shear strength between the fibers and the matrix resin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Kinetic study of the thermal degradation of poly(aryl ether ketone)s containing 2,7-naphthalene moietiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Si-Jie Liu Abstract The degradation of poly(aryl ether ketone) containing 2,7-naphthalene moieties was subjected to dynamic and isothermal thermogravimetry in nitrogen and air. The dynamic experiments showed that the initial degradation temperature, temperature for 5% weight loss, and temperature corresponding to the maximum degradation rate of poly(aryl ether ketone) containing 2,7-naphthalene moieties were a little higher than those of poly(ether ether ketone) and almost independent of the 2,7-naphthalene moiety content. The thermal stability of poly(aryl ether ketone) containing 2,7-naphthalene moieties in air was substantially less than that in nitrogen, and the degradation mechanism was more complex. The results obtained under the isothermal conditions were in agreement with the corresponding results obtained in nitrogen and air under the dynamic conditions. In the dynamic experiments, the apparent activation energies for the degradation processes were 240 and 218 kJ/mol in nitrogen and air for the second reaction stage as the heating rate was higher than 5°C/min. In the isothermal experiments, the apparent activation energies for the degradation processes were 222 and 190 kJ/mol in nitrogen and air, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Synthesis, characterization, and electrical properties of diazophenylene bridged Co, Ni, Cu, Ce, and Er phthalocyanine polymersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Cemil Alkan Abstract In this research, diazophenylene bridged metal-phthalocyanine (Pc) polymers were produced from diazonium salt of 1,4-diaminophenylene and presynthesized 1,8,15,22-tetraamino metal-Pcs. 1,8,15,22-Tetraamino metal-Pc complexes of Co, Ni, Cu, Ce, and Er were obtained by reducing 1,8,15,22-tetranitro metal-Pc complexes synthesized from 3-nitrophthalic anhydride, urea, metal salt, and ammonium molybdate catalyst. Complexes and polymers were characterized by Fourier transform infrared (FTIR), ultraviolet,visible (UV,vis), and X-ray powder diffraction spectroscopes. X-ray analysis of the polymers showed that there were short-range orientations in the polymers. Thermal analysis of the complexes and the polymers were done by differential scanning calorimeter (DSC) and thermal gravimetric analysis (TGA) at a heating rate of 10°C min,1 under nitrogen atmosphere. Ash analysis was performed to determine the metal content of the polymers. Viscosimetry and ebullioscopy measurements of the soluble part of the polymers were done for molecular weight analysis of the soluble part in tetrahydrofuran (THF) at 25°C. Four-probe conductivity measurements on isothermal conditions revealed that the polymer samples showed 104 fold increases in their electrical conductivities when doped with iodine. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Thermal oxidative degradation kinetics of PP and PP/mg (OH)2 flame-retardant compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007Xiaolang Chen Abstract The thermal stability and thermal oxidative degradation kinetics of polypropylene (PP) and flame-retardant PP composites filled with untreated and treated magnesium hydroxide (MH) in air were studied by thermogravimetric analysis (TGA). The effect of the heating rate in dynamic measurements (5°C,30°C/min) on kinetic parameters such as activation energy was also investigated. The Kissinger and Flynn,Wall,Ozawa methods were used to determine the apparent activation energy for the degradation of neat PP and flame-retardant PP composites. The results of TGA showed that the addition of untreated or treated MH improved the thermal oxidative stability of PP in air. The kinetic results showed that the apparent activation energy for degradation of flame-retardant PP composites was much higher than that of neat PP, suggesting that the flame retardant used in this work had a great effect on the mechanisms of pyrolysis and combustion of PP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1978,1984, 2007 [source] Synthesis of Mo,W carbide via propane carburization of the precursor sulfide: Kinetic analysisJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2004Tuan-Huy Nguyen Abstract Thermogravimetric analysis (TGA) has been used to investigate the carburization kinetics of Mo,W sulfide using an H2:C3H8 feed mixture. The effect of heating rate over the range 1,10 K min,1 showed that up to four different carburized products may be formed but the critical (peak) temperature for formation of these species and the amount (peak height) of each species formed are highly dependent on the heating rate employed. The critical temperature increased linearly with heating rate for each of the four products. The four TGA peaks corresponding to the four phase transformation species are consistent with XRD identifiable species, namely; ,-Mo2C, ,-Mo2C, W and MoC1,x. Isothermal conversion,time data at three different temperatures are described by a reaction-controlled shrinking core model implicating a first-order dependency on the H2:C3H8 ratio. The reaction exhibited fractional order dependence on the metal sulfide concentration, the associated global activation energy estimated as 227 kJ mol,1 is representative of a non-catalytic gas,solid reaction. Copyright © 2004 Society of Chemical Industry [source] Pyrolysis of tetra pack in municipal solid wasteJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2001Chao-Hsiung Wu Abstract The pyrolysis of tetra pack in nitrogen was investigated with a thermogravimetric analysis (TGA) reaction system. The pyrolysis kinetics experiments for the tetra pack and its main components (kraft paper and low-density poly(ethene) (LDPE)) were carried out at heating rates (,) of 5.2, 12.8, 21.8,K,min,1. The results indicated that the one-reaction model and two-reaction model could be used to describe the pyrolysis of LDPE and kraft paper respectively. The total reaction rate of tetra pack can be expressed by the summation of the individual class of LDPE and kraft paper by multiplying the weighting factors. The pyrolysis products experiments were carried out at a constant heating rate of 5.2,K,min,1. The gaseous products were collected at room temperature (298,K) and analyzed by gas chromatography (GC). The residues were collected at some significant pyrolysis reaction temperatures and analyzed by an elemental analyzer (EA) and X-ray powdered diffraction (XRPD). The accumulated masses and the instantaneous concentrations of gaseous products were obtained under the experimental conditions. The major gaseous products included non-hydrocarbons (CO2, CO, and H2O) and hydrocarbons (C1,5). In the XRPD analysis, the results indicated that pure aluminum foil could be obtained from the final residues. The proposed model may be supported by the pyrolysis mechanisms with product distribution. © 2001 Society of Chemical Industry [source] Application of the distributed activation energy model to biomass and biomass constituents devolatilizationAICHE JOURNAL, Issue 10 2009María V. Navarro Abstract In this study, an investigation about the thermal behavior of four different woods was carried out. The distributed activation energy model was applied to study the effect of heating rate on the reaction of single solids. Results obtained were used in the curve prediction of fraction of mass remaining and rate of mass loss vs. temperature at more realistic heating rates. The possible calculation of biomass samples behavior in pyrolysis conditions as the summation of their constituents, lignin, cellulose, and hemi-cellulose is also explored. All the samples show a weak interaction between the constituents which produce slight differences between experimental and calculated behavior. However, differences between experimental and calculated data lower than 2% offer a robust test of the applicability of the model on kinetic studies of a wide range of biomass samples, heating rates, data input format and equipment layout. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Effect of sample size on microwave power absorption within dielectric materials: 2D numerical results vs. closed-form expressionsAICHE JOURNAL, Issue 6 2009S. Curet Abstract This study deals with the analytical and numerical solutions of the heat source term because of microwave heating for high and low dielectric materials in 1D and 2D configurations. The authors compare closed-form expressions dedicated to microwave power calculation to numerical simulations. A comprehensive and accurate analysis of the microwave power reflected from the surface of the sample is also carried out during microwave heating. The influence of sample length is studied using an original numerical procedure. The study highlights that 1D closed-form expressions can be extended to 2D configurations in the case of sufficiently high dielectric properties. Examples of heating rate during 2D microwave heating in TE10 mode are finally presented. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Strain rates from snowball garnetJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2003C. Biermeier Abstract Spiral inclusion trails in garnet porphyroblasts are likely to have formed due to simultaneous growth and rotation of the crystals, during syn-metamorphic deformation. Thus, they contain information on the strain rate of the rock. Strain rates may be interpreted from such inclusion trails if two functions are known: (1) The relationship between rotation rate and shear strain rate; (2) the growth rate of the crystal. We have investigated details of both functions using a garnetiferous mica schist from the eastern European Alps as an example. The rotation rate of garnet porphyroblasts was determined using finite element modelling of the geometrical arrangement of the crystals in the rock. The growth rate of the porphyroblasts was determined by using the major and trace element distributions in garnet crystals, thermodynamic pseudosections and information on the grain size distribution. For the largest porphyroblast size fraction (size L=12 mm) we constrain a growth interval between 540 and 590 °C during the prograde evolution of the rock. Assuming a reasonable heating rate and using the angular geometry of the spiral inclusion trails we are able to suggest that the mean strain rate during crystal growth was of the order of =6.6 × 10,14 s,1. These estimates are consistent with independent estimates for the strain rates during the evolution of this part of the Alpine orogen. [source] Effect of heating rate on kinetics of high-temperature reactions: Mo-Si systemAICHE JOURNAL, Issue 1 2005Suren L. Kharatyan Abstract By using the Computer Assisted Electrothermography (CAE) method and taking the molybdenum-silicon system as an example, the influence of preheating rate on the kinetics of gasless reactions at high temperatures (above Si melting point, 1683 K) is studied. It is shown that an increase of heating rate Vh in the range 10,105 K/s, leads to a substantial increase in the rate of chemical reaction. At high heating rates (>103 K/s), the first stage of interaction involves rapid reaction due to the direct dissolution of Mo in the Si melt. Furthermore, the formation of MoSi2 phase, owing both to crystallization from eutectic (MoSi2 -Si) melt and reaction-diffusion mechanism, is primarily responsible for the observed intensive heat release under these conditions. At lower Vh, a thin layer of Mo5Si3 phase formed at earlier stages (solid-solid interaction) significantly retards reaction at higher temperatures and changes the mechanism of interaction. Some methodological aspects of using the CAE technique for kinetic studies are also discussed. © 2004 American Institute of Chemical Engineers AIChE J, 51: 261,270, 2005 [source] Dielectric study of equimolar acetaminophen,aspirin, acetaminophen,quinidine, and benzoic acid,progesterone molecular alloys in the glass and ultraviscous states and their relevance to solubility and stabilityJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2010G.P. Johari Abstract Equimolar mixtures of acetaminophen,aspirin, acetaminophen,quinidine, and benzoic acid,progesterone have been vitrified and dielectric properties of their glassy and ultraviscous alloys have been studied. For 20,K/min heating rate, their Tgs are 266, 330, and 263,K, respectively. The relaxation has an asymmetric distribution of times, and the distribution parameter increases with increase in temperature. The dielectric relaxation time varies with T according to the Vogel,Fulcher,Tammann equation, log10(,0),=,AVFT,+,[BVFT/(T,,,T0)], where AVFT, BVFT, and T0 are empirical constants. The equilibrium permittivity is highest for the aspirin,acetaminophen and lowest for the benzoic acid-progesterone alloy, indicating a substantial interpharmaceutical hydrogen bonding that makes the alloy more stable against crystallization than the pure components. The benzoic acid,progesterone alloy is thermodynamically the most nonideal. It showed cold crystallization on heating, which is attributed to its relatively greater magnitude of the JG relaxation in relation to its ,-relaxation. It is argued that the difference between the free energy of an alloy and the pure components would have an effect on the solubility. Studies of solution thermodynamics of a glassy molecular alloy may be useful for optimizing choice of components and composition to form molecular alloys and to impact drug delivery. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1358,1374, 2010 [source] Characterization of amorphous solids with weak glass transitions using high ramp rate differential scanning calorimetryJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2008Derrick S. Katayama Abstract Measurement of the glass transition temperature (Tg) of proteins and other high molecular weight polymers in the amorphous state is often difficult, since the transition is extremely weak, that is, the ,Cp at the glass transition temperature is small. For example, little is known about the solid-state properties of hydroxyethyl starch (HES), which is beginning to become more commonly evaluated as a bulking agent in pharmaceutical products. For weak thermal events, such as the change in heat capacity at the Tg of a pure protein or large synthetic polymer, increased heating rate should produce greater sensitivity in terms of heat flow. Recent innovations in rapid scanning technology for differential scanning calorimetry (DSC) allow measurements on materials where the thermal events are difficult to detect by conventional DSC. In the current study, measurements of the Tg of proteins in the solid state, amorphous pharmaceutical excipients which have small ,Cp at the glass transition temperature, and bacterial spores, have all been made using high ramp rate DSC, providing information on materials that was inaccessible using conventional DSC methods. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:1013,1024, 2008 [source] Solid state characterization of mometasone furoate anhydrous and monohydrate formsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2005Xiaoming (Sean) Chen Abstract Mometasone furoate is a potent glucocorticoid anti-inflammatory agent. Its anhydrous Form 1 and monohydrate form were characterized by X-ray crystallography, X-ray powder diffraction at ambient and elevated temperature, thermal analysis, FT-IR, and dynamic moisture adsorption. In Form 1, mometasone furoate molecules pack tightly with molecules interlocked in a space group of P212121. The monohydrate form crystallizes in space group P1. The unit cell of the monohydrate contains one water molecule and one mometasone furoate molecule. The water molecules form channels along the a axis and mometasone furoate molecules pack in layers in the same direction. Dehydration was observed between 60 and 100°C by thermogravimetric analysis with a heating rate of 10°C/min. It corresponds to a broad endotherm over the same temperature range in the differential scanning calorimetry with the same heating rate. Variable temperature X-ray powder diffraction reveals that a new anhydrous form (Form 2) was fully produced above 90°C. This crystalline form was converted to Form 1 after being heated above 150°C; and was totally converted to the monohydrate after 1 day at 23°C, 45% RH. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2496-2509, 2005 [source] Aggregation kinetics of recombinant human FVIII (rFVIII)JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2005Karthik Ramani Abstract The physical phenomenon of aggregation can have profound impact on the stability of therapeutic proteins. This study focuses on the aggregation behavior of recombinant human FVIII (rFVIII), a multi-domain protein used as the first line of therapy for hemophilia A, a bleeding disorder caused by the deficiency or dysfunction of factor VIII (FVIII). Thermal denaturation of rFVIII was investigated using circular dichroism (CD) spectroscopy and size exclusion chromatography (SEC). The dependence of unfolding on heating rate indicated that the thermal denaturation of the protein was at least partly under kinetic control. The data was interpreted in terms of a simple two-state kinetic model, , where k is a first-order kinetic constant that changes with temperature, as given by the Arrhenius equation. Analysis of the data in terms of the above scheme suggested that under the experimental conditions used in this study, the rate-controlling step in the aggregation of rFVIII may be a unimolecular reaction involving conformational changes. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:2023,2029, 2005 [source] Growth and Mechanism of Network-Like Branched Si3N4 NanostructuresJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2010Zhijian Peng The high-yield synthesis of network-like branched silicon nitride (Si3N4) nanostructures by a simple template catalyst-assisted pyrolysis of a polymer precursor, perhydropolysilazane, was reported. The templates were silicon wafers deposited with Fe films of 5,20 nm in thickness. The processes simply involved thermal cross-linking of the preceramic polymer, crushing of the solidified polymer chunks into fine powder, and thermal pyrolysis of the powder under flowing high-purity nitrogen. The collected white network-like branched nanostructures are ,-Si3N4 of hexagonal phase, and their microstructures, in which the diameters of each linear part of the network-like nanostructure varied in a very wide range from tens of nanometers to hundreds of nanometers, strongly depend on the applied growth parameters, where the key factors are the heating rate and catalyst thickness for change in the diameters. It was proposed that the Si3N4 nanonetworks were formed through "metal-absorption on the surface of nanostructures" model by vapor,liquid,solid mechanism. The reaction mechanism of Si3N4 nanonetworks was also discussed. [source] Pressureless Rapid Sintering of UO2 Assisted by High-frequency Induction Heating ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2008Jae Ho Yang Heat generation of uranium dioxide (UO2) powder and its pressureless rapid sintering behaviors have been studied using a high-frequency induction heating apparatus. The porous graphite housing has been used to prevent heat loss and to preheat the uranium oxides, simultaneously. At an elevated temperature, UO2 powder generated extra heat by itself. The synergism of individual heat generation between the graphite and UO2 powder could effectively heat the UO2 to the sintering temperature of 1700°C. Using this process, densification behavior of cylindrical and disk-type UO2 green pellets according to the heating rate and grain structure of sintered UO2 pellets were investigated. Rapid sintering caused a large crack around the circumference of the sintered pellet. The formation of cracks could be avoided when the heating rate or sample dimension are properly reduced. A dense and crack-free UO2 pellet with a relative density of up to 96% was produced within 5 min of the process time. The induction heat sintering process can be a potential candidate for the rapid fabrication of ceramics and composites. [source] Densification of the PLZT Films Derived from Polymer-Modified Solution by Tailoring Annealing ConditionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2007Z. H. Du The Pb0.91La0.09(Zr0.65,Ti0.35)0.9775O3 films were prepared from the solution containing polyvinylpyrrolidone, with Mw of 360 000. A fast heating rate of 40°C/min was used to heat our samples to temperatures in the range of 550°,750°C for different durations. Both a rapid heating rate and isothermal holding at a proper temperature are found to be essential for obtaining dense and crack-free PLZT films. The TG-DTA and Fourier-transform infrared results indicated that the fast heating rate could keep a certain amount of polyvinylpyrrolidone residues undecomposed to a higher temperature (<700°C), which was found to be beneficial for the densification of the films during subsequent isothermal hold. The possible mechanisms responsible for the enhanced densification have been discussed. In addition, the effects of annealing temperature on the electrical and optical properties were also investigated. [source] Sintering Behavior and Properties of Iron-Rich Glass-CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2004Alexander Karamanov Iron-rich glass-ceramics were obtained by the sintering of two glass powders, labeled G1 and G2, at heating rates of 5° and 20°C/min followed by an isothermal step in the 850°,1050°C temperature interval. The sintering process was evaluated by the linear shrinkage; the closed porosity was estimated by density measurements; the structure and the morphology of the glass ceramics were observed by scanning electron microscopy. The bending strength, the Young modulus, and Vickers hardness of the glass-ceramics materials were evaluated. The results showed that the sintering process and morphology of the glass-ceramics depends on the amount of magnetite and pyroxene formed. With a low percentage of crystal phase formed (25%,30% typical of G1) the structure is characterized by closed porosity; at higher crystallization (45%,50% typical of G2) open porosity is mainly formed. The properties of the glass-ceramics were not influenced by the heating rate but improved with an increase in the degree of crystallization. [source] | |||||||||||||||||||||||||||||||||||||