Onset Temperature (onset + temperature)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


From monosilane to crystalline silicon, part II: Kinetic considerations on thermal decomposition of pressurized monosilane

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2006
J. O. Odden
Kinetic aspects of the thermal decomposition of monosilane at 690,830 K and initial pressures of 0.1,3.7 MPa in a free-space reactor are considered. Neglecting the preparatory initiation period for the reaction (which is difficult to evaluate under the present dynamic conditions), the onset temperature for the decomposition is stipulated to some 700,710 K, independent of the initial monosilane pressure. The overall reaction appears to be of first order throughout the progressing decomposition process. We observe considerably lower reaction rates under the high-pressure conditions than existing models in the literature suggest. A modified model is proposed that simulates the observed reaction rates within 1% and moreover predicts credible concentrations of the involved gaseous species. A key feature of the modified model is incorporation of two third-body assisted surface reactions, which generate monosilane from disilane and disilane from trisilane. 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 309,321, 2006 [source]


Optimum packing factor of the stack in a standing-wave thermoacoustic prime mover

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2002
Limin Qiu
Abstract A bench consisting of a pulse tube refrigerator driven by a standing-wave thermoacoustic prime mover has been set up to study the relationship among stack, regenerator and working fluids. The stack of the thermoacoustic prime mover is packed with dense-mesh wire screens because of their low cost and easy manufacture. The effect of the packing factor in the stack on onset temperature, refrigeration temperature and input power is explored. The optimum packing factor of 1.15 pieces per millimeter has been found experimentally, which supplies an empirical value to satisfy a compromise for enhancing thermoacoustic effect, decreasing heat conduction and fluid-friction losses along the stack. The pulse tube cooler driven by the thermoacoustic prime mover is able to obtain refrigeration temperatures as low as 138 and 196K with helium and nitrogen, respectively. Copyright 2002 John Wiley & Sons, Ltd. [source]


Cohesive-driven particle circulation in the solids conveying zone of a single-screw extruder

ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2008
Michael R. Thompson
Abstract Aspects of heat transfer within the solids conveying zone of a single-screw extruder were studied by using a specially constructed drum testing apparatus. Experiments were conducted with linear low-density polyethylene, polystyrene (PS), and polypropylene (PP) samples by examining their transient temperature profile while the heated drum was stationary or moving. In accordance with classic solids conveying theory, the granular beds of PP and PS remained as plugs while the drum rotated. In such cases, the dominant modes of heat transfer for these systems are conduction through the contact area of a particle and conduction through the interstitial gas. An exception to this behavior was found with PE, in which the bed temperature increased more rapidly while the drum rotated. Visual observations of the bed showed that the particles circulated in the presence of shear and that this complex flow pattern increased in velocity as the drum temperature approached the onset temperature for melting the PE material. With strong correlation between the rate of circulation and the temperature rise in the bed, the movement of particles was assumed to act in a convective heat transfer mode bringing about more uniform heating of the polymer. The circulation phenomenon was attributed to dominant adhesive forces at the particle,drum interface overcoming the cohesive strength of the bulk. 2009 Wiley Periodicals, Inc. Adv Polym Techn 27:74,88, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20121 [source]


Effect of boron-containing materials on the flammability and thermal degradation of polyamide 6 composites containing melamine

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010
Mehmet Do
Abstract Three different boron-containing substances,zinc borate (ZnB), borophosphate (BPO4), and a boron- and silicon-containing oligomer (BSi),were used to improve the flame retardancy of melamine in a polyamide 6 (PA-6) matrix. The combustion and thermal degradation characteristics of PA-6 composites were investigated with the limiting oxygen index (LOI), the UL-94 standard, thermogravimetric analysis (TGA)/Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). A slight increase was seen in the LOI values of a sample containing BSi (1 wt %). BPO4 at high loadings showed a V0 rating (indicating the best flame retardancy) and slightly lower LOI values in comparison with samples with only melamine. For ZnB and BSi, glassy film and char formation decreased the dripping rate and sublimation of melamine, and this led to low LOIs. According to the TGA,FTIR results, the addition of boron compounds did not change the decomposition product distribution of melamine and PA-6. The addition of boron compounds affected the flame retardancy by physical means. The TGA data showed that boron compounds and melamine reduced the decomposition temperature of PA-6. According to the DSC data, the inclusion of boron compounds increased the onset temperature of sublimation of melamine and also affected the flame retardancy negatively. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]


Competitive plasticization in ternary plasticized starch biopolymer system

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010
Deeptangshu S. Chaudhary
Abstract Two plasticizers namely, glycerol and xylitol, based on their similar molecular diameter (, 6.3 ) but different molecular weights (glycerol-92; xylitol-152) were selected were selected for studying the plasticization of starch biopolymer containing 70% amylopectin structure via glass transition measurements carried over a wide range of water activity. A standard calorimetry was used to determine the onset temperature of polymeric viscous flow. For both glycerol and xylitol, typical antiplasticization was evident at low plasticizer concentrations, whereas at higher concentration, there was significant reduction in glass transition temperature. Water activity isotherms showed that equilibrium moisture content of the starch biopolymer (no plasticizer) steadily increases up to 11%, however, for plasticized biopolymer, the moisture content was nearly double than that of biopolymer. We used a modified Gordon-Taylor model, using a new interaction parameter, to understand the competitive plasticization of glycerol and xylitol in presence of water, and determined 8 wt % water as a threshold amount of matrix water for strong three-way interactions: starch-plasticizer, plasticizer-plasticizer/water and starch-water. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]


Thermal and dielectric properties of bismaleimide-triazine resins containing octa(maleimidophenyl)silsesquioxane

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008
Hongwei Cao
Abstract Octa(maleimidophenyl)silsesquioxane (OMPS) was synthesized, characterized, and employed to modify the BT resin which composed of 4,4,-bismaleimidodiphenylmethane (BMI) and 2,2,-bis(4-cyanatophenyl)propane (BCE). The curing reaction between OMPS and BT resin was first investigated. It was found that OMPS accelerate the curing reaction of BCE, and the onset temperature of the cyclotrimerization was reduced up to 95.5C (by DSC). As demonstrated by DSC and FTIR, there was no evidence that indicated the coreaction between maleimide and cyanate ester. 2,2,-diallyl bisphenol A (DBA) and diglycidyl ether of bisphenol A (E-51) (Wuxi Resin Factory, Jiangsu Province, China) were also used to enhance the toughness of BT resin, and the formulated BTA (containing DBA) and BTE (containing E-51) resins were obtained. The thermal properties of BT, BTA, and BTE resins incorporated with OMPS were then investigated. The results of DMA and TG showed that the BT, BTA, and BTE resins containing 1 wt % of OMPS exhibit enhanced thermal properties in comparison with their pristine resins respectively, while more contents of OMPS may impair the thermal properties of the polymer matrix, though the effect of OMPS was slight. Finally, the dielectric constant of these hybrid materials were detected, and their dielectric constant were distinctly reduced by the incorporation of OMPS, while overmuch contents of OMPS were disadvantageous for dielectric constant because of the aggregation of OMPS. 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source]


Effect of heat treatment after accelerated aging on phase transformation in 3Y-TZP

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2010
I. L. Denry
Abstract Our purpose was to investigate the effect of heat treatment on the reversibility of the tetragonal to monoclinic transformation in 3Y-TZP, and associated surface roughness. The goals were to determine the onset temperature of the reverse transformation, and characterize surface roughness after accelerated aging, and after aging followed by heat treatment. 3Y-TZP disc-shaped specimens were sintered at temperatures from 1300 to 1550C. The reversibility of the transformation was investigated by X-ray diffraction (XRD) after accelerated aging, followed by heat treatment at temperatures from 350C up to 850C. The surface roughness (Rrms) was measured by atomic force microscopy after polishing, after accelerated aging for 1 or 10 h, and after aging followed by heat treatment. XRD showed that the fraction of m -phase increased linearly with grain size after aging for 10 h (1.0,29.8%). The transformation was reversed for all groups after heat treatment at 850C/min., with only trace amounts of m -phase remaining for the group sintered at 1550C. A significant increase in mean surface roughness was observed after accelerated aging (1.59,7.45 nm), compared to polished groups (0.83,1.0 nm). However, the mean surface roughness after accelerated aging for either 1 or 10 h, followed by heat treatment at 850C/min. (1.18,2.1 nm), was not significantly different from that of the polished groups. This was attributed to the reverse transformation. XRD revealed that the monoclinic to tetragonal transformation, was complete after heat treatment at 500C for 1 min, for specimens sintered at 1550C and aged 10 h. 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010 [source]


Effects of Arabinoxylans on Thermal Behavior of Frozen Wheat Doughs as Measured by DSC, DMA, and DEA

JOURNAL OF FOOD SCIENCE, Issue 1 2002
T. J. Laaksonen
ABSTRACT: The effects of water extractable arabinoxylans (WEA) on physical state of frozen wheat dough with added sucrose, NaCl, and their mixture were investigated using DSC, DMA, and DEA. DSC thermograms were obtained for annealed samples, and they showed only an endothermic peak of ice melting. Annealed samples were also analyzed using DMA and DEA with both dynamic heating and isothermal steps. Added sucrose and NaCl decreased the onset temperature of ice melting and it decreased with increasing WEA concentration. Isothermal measurements showed an a-relaxation peaks, taken as the Tg,. Added NaCl had a great depressing effect on the Tg, at low frequencies as measured by DEA. [source]


Preparation of Dense MgB2 Bulk Superconductors by Spark Plasma Sintering

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2003
Soo-Yong Lee
Fully dense MgB2 bulk specimens (,higher than 99% dense) were prepared using spark plasma sintering (SPS) at 1250C for 15 min. Microstructure analyses revealed that faceted MgO particles of ,8% volume fraction were dispersed in the MgB2 matrix. A sharp superconducting transition with an onset temperature of 38.5 K was confirmed by both magnetization and resistivity measurements. [source]


Effect of starch on the thermal kinetics and transmittance properties of lysozyme,

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 3 2005
Abdellatif A Mohamed
Abstract Lysozyme is being tested for use as a preservative in the food industry. The interaction between starch and lysozyme will help in recommending starch or starch fractions as carriers for lysozyme. The effect of starch fractions on the folding and unfolding of lysozyme was estimated by differential scanning calorimetry (DSC), kinetics and transmittance turbidometry. Lysozyme was unfolded (heated to 90 C) and folded (cooled to 20 C) five times in the presence of starch fractions. Starch was added at 1 and 2%. Overall, a trend of higher onset temperature (To) values occurred at 2% addition of all starch fractions except amylose. The increase in the number of cycles influenced the effect of starch on lysozyme denaturation. The percentage of lysozyme's ,H values decreased as a new heating and cooling cycle was performed (ie 74.4% of the ,H remained from the first cycle). The effect of amylose (AM) and amylopectin (AP) on the kinetics of lysozyme unfolding and folding was found to be different based on the assumption that the peak DSC temperature is the fastest step of the reaction. The unfolding showed higher activation energy (Ea) in the presence of both AM and AP, while the folding was not significantly changed. The turbidity of the solution containing lysozyme and potato starch showed transmittance in between that of lysozyme and starch. Stirring of the blend kept the transmittance unchanged while an increase in the transmittance was noticed when stirring ceased. Copyright 2004 Society of Chemical Industry [source]


Functional properties and retrogradation behaviour of native and chemically modified starch of mucuna bean (Mucuna pruriens)

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2003
Kayode O Adebowale
Abstract Mucuna bean (Mucuna pruriens) starch was isolated and subjected to chemical modification by oxidation and acetylation. The proximate analysis of the non-starch components of the native starch on a dry weight basis was 92 g kg,1 moisture, 5 g kg,1 ash, 2 g kg,1 fat, 7 g kg,1 crude fibre and 19 g kg,1 protein. Chemical modification reduced the values for all the non-starch components except the moisture level. For all the samples, swelling power and solubility increased as the temperature increased in the range 50,90 C. The swelling power of mucuna native starch (MNS) and mucuna acetylated starch (MAS) increased with increasing acidity and alkalinity, while that of mucuna oxidised starch (MOS) only increased with increasing pH in the acidic range. The maximal solubility of all the starches was observed at pH 12. All the starch samples absorbed more oil than water. The lowest gelation concentration followed the trend MAS < MNS < MOS. Chemical modification reduced the gelatinisation temperature (Tp), while peak viscosity (Pv), hot paste viscosity (Hv) and cold paste viscosity (Cv) decreased after oxidation but increased following acetylation. The setback tendency of the native starch was reduced significantly after chemical modification. However, the breakdown value of MNS, 65 BU (Brabender units), was lower than that of MOS (78 BU) but higher than that of MAS (40 BU). Differential scanning calorimetry studies of gelatinisation and retrogradation revealed that chemical modification reduced the onset temperature (To), peak temperature (Tp) and conclusion temperature (Tc). Oxidation and acetylation reduced the gelatinisation and retrogradation enthalpies of the native starch. The enthalpy of retrogradation of the starches increased as the length of storage increased. Copyright 2003 Society of Chemical Industry [source]


Measurement of electrical conductivity, differential scanning calorimetry and viscosity of starch and flour suspensions during gelatinisation process

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2001
Saiwarun Chaiwanichsiri
Abstract Electrical conductivity measurements were applied to analyse the gelatinisation process of 12 starch or flour suspensions. The electrical conductivity of starch suspensions was found to increase upon gelatinisation because of the release of ions from starch granules. The initiation temperature of ion release, Ti, correlated well with the onset temperature in the DSC thermogram (R,=,0.868), while the completion temperature of ion release, Tf, correlated with the temperature at the start of viscosity increase (R,=,0.865). Thus Ti and Tf corresponded to the beginning and ending temperatures of gelatinisation respectively. The electrical conductivity measurement will be used as an on-line technique to monitor the whole process of starch gelatinisation. 2001 Society of Chemical Industry [source]


Thermostability of Lyocell Dopes Modified with Surface-Active Additives

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 8 2005
Frank Wendler
Abstract Summary: Cellulose/N -methylmorpholine- N -oxide monohydrate (NMMO) spinning solutions were modified with surface-active additives to yield Lyocell fibers with functional properties. Based on cellulose fibers, a new class of materials with tailored adsorption characteristics are produced. Activated charcoal and carbon black used as additives significantly affect the thermostability of the spinning solutions. Considering the degree of filling three general tendencies become evident. It is most obvious that the onset temperature of dope decomposition is shifted towards lower values accompanied by viscosity reduction after annealing at elevated temperatures and an enhanced formation of degradations products. Morpholine, N -methylmorpholine and formaldehyde as the main degradation products were detected in aqueous distillates by means of HPLC. To study the rate of by-product formation during preparation of the solution kinetic measurements were carried out. Thermal instabilities are not only initiated by heavy metal ions, especially Fe(II), but also by the particle size and porosity of the charcoal. The nano-scaled carbon black used causes autocatalytic reactions as revealed by calorimetric measurements. Relationships between amount of Acc versus onset temperature (Ton) and concentration of N -methylmorpholine. [source]


Crystallization study of amorphous Pd43Ni10Cu27P20 alloy by internal friction measurement

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2007
K. W. Yang
Abstract We have successfully measured the internal friction and electrical resistivity of Pd43Ni10Cu27P20 bulk metallic glass during a constant heating process. The results of electrical resistivity suggest that the position of the internal friction peak is the onset temperature of crystallization. The dependence of internal friction on frequencies show both linear and nonlinear relations. The internal friction at 623 K in the supercooled liquid region decreases monotonously with the increase of annealing time, indicating structural relaxation and subsequent crystallization occurs during isothermal annealing near the crystallization temperature. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Hazard ratings for organic peroxides

PROCESS SAFETY PROGRESS, Issue 2 2008
Yih-Shing Duh
Abstract Nine of commercially available organic peroxides were assessed with differential scanning calorimeter (DSC) and adiabatic calorimeters. These organic peroxides are cumene hydroperoxide (CHP), di- tert -butyl peroxide (DTBP), methyl-ethyl-ketone peroxide (MEKPO), tert -butyl hydroperoxide (TBHP), benzoyl peroxide (BPO), hydrogen peroxide, lauroyl peroxide (LPO), tert -butyl peroxybenzoate (TBPBZ), and dicumyl peroxide (DCPO). Exothermic onset temperatures, self-heat temperature and pressure rates, and heats of decomposition were measured and assessed. Adiabatic runaway reaction characteristics were determined by using ARC (accelerating rate calorimeter) and VSP2 (vent sizing package). Incompatibility, tests with several potential contaminants, was made using DSC, VSP2, and microcalorimeter. An incompatibility rating was developed using onset temperature, lowering of the onset temperature, heat of decomposition, maximum self-heat rate, adiabatic temperature rise, maximum pressure of decomposition, and maximum pressure rising rate, etc. 2008 American Institute of Chemical Engineers Process Saf Prog 2008 [source]


A heuristic approach of calculating spray water flux needed to avert fire-induced runaway reactions,,

PROCESS SAFETY PROGRESS, Issue 3 2006
BChE (Honors), Dilip K. Das BSc (Honors), MSChE
In general all reactions have some heat effects. When the ability of the equipment to remove the heat is exceeded by the heat generated by a reaction, a hazardous situation called a runaway reaction may take place. Sometimes the exothermicity of runaway reactions is so high that the size of an emergency vent becomes impractical to install. A water spray system can sometimes be used to avert a fire-induced runaway reaction. Because the water spray system has a finite activation time, insulation helps to prolong the time required to reach the decomposition temperature. This article concludes that the required water flux to avert the fire-induced runaway reaction may be conservatively estimated by adding the water flux necessary to maintain an unbroken water film on the external surface of the equipment and the water flux necessary to absorb the fire heat after allowing for the splash loss and the in-flight loss. When adequate spray water is used, the metal temperature of the insulation jacket cannot theoretically exceed the boiling point of water thereby ensuring the avoidance of fire-induced runaway reactions whose adjusted onset decomposition temperature exceeds 100 C. Fire-induced runaway reactions with lower onset temperature can also be avoided depending on the initial temperature of the contents, mass of the contents and equipment, insulation thickness, and fire duration, for example, but a detailed calculation including dynamic simulation is necessary and the burden of proof lies with the designer. The reliability of the spray water system must be maintained high to include its credit as an environmental factor defined according to NFPA 30 to avoid the fire-induced runaway reaction as a scenario. Although API RP 521 does not allow any credit for sprinkler water, it allows credit, unlike NFPA 30, for insulation thickness and thus a runaway reaction can be avoided by using insulation alone according to API RP 521. 2006 American Institute of Chemical Engineers Process Saf Prog, 2006 [source]


Method for estimating decomposition characteristics of energetic chemicals

PROCESS SAFETY PROGRESS, Issue 4 2003
Sima Chervin
Experimental data on the decomposition characteristics of approximately400 chemicals, representing various classes of energetic materials, were summarized by chemical class and statistically analyzed. Average decomposition characteristics, such as energy of decomposition and decomposition onset temperature, were determined for chemical classes containing the following energetic groups: nitro, nitroso, N-oxide, oxime, hydroxylamine, tetrazole, azide, triazene, triazole, diazo, azo, hydrazine, and perchlorate. Additional statistical information is presented for each chemical class, such as number of chemicals analyzed, ranges, and standard deviations for the decomposition parameters analyzed. For chemical classes containing an energetic group attached to an aromatic ring, the presence and position of another substituting group in the ring can significantly influence the decomposition onset temperature. The study summarizes the list of activating and deactivating functional groups, and the positions in the ring where the strongest activation or deactivation occurs. The authors also recommend a method for estimating decomposition parameters of new chemicals. [source]


Effect of genipin-crosslinked chitin-chitosan scaffolds with hydroxyapatite modifications on the cultivation of bovine knee chondrocytes

BIOTECHNOLOGY & BIOENGINEERING, Issue 1 2006
Yung-Chih Kuo
Abstract Chitin and chitosan were hybridized in various weight percentages by genipin crosslinkage under various prefreezing temperatures to form tissue-engineering scaffolds via lyophilization. In addition, deposition of hydroxyapatite (HA) on the surface of the porous scaffolds was performed by precipitation method to achieve modified chemical compositions for chondrocyte attachments and growths. The experimental results revealed that a lower prefreezing temperature or a higher weight percentage of chitin in the chitin-chitosan scaffolds would yield a smaller pore diameter, a greater porosity, a larger specific surface area, a higher Young's modulus, and a lower extensibility. Moreover, a higher chitin percentage could also result in a higher content of amine groups after crosslink and a lower onset temperature for the phase transition after thermal treatment. A decrease in the prefreezing temperature from ,4C to ,80C, an increase in the chitin percentage from 20% to 50%, and an increase in the cycle number of alternate immersion for HA deposition from 1 to 5 generated positive effects on the cell number, the content of glycosaminoglycans, and the collagen level over 28-day cultivation of bovine knee chondrocytes. 2006 Wiley Periodicals, Inc. [source]


Promoted H2 Generation from NH3BH3 Thermal Dehydrogenation Catalyzed by Metal,Organic Framework Based Catalysts

CHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2010
Dr. Yaoqi Li
Abstract The application of ammonium borane (AB) as a hydrogen storage material is limited by the sluggish kinetics of H2 release. Two catalysts based on metal,organic frameworks (MOFs) have been prepared either by applying MOF as precursors or by the in situ reduction method. In the release of H2 from AB, the high H2 content of the whole system, the remarkably lower reaction onset temperature, the significantly increased H2 release rates at ,90,C, and the decreased reaction exothermicity have all been achieved with only 1.0,mol,% MOF-based catalyst. Moreover, the clear catalytic diversity of three catalysts has been observed and discussed. The in situ synthesized Ni0 sites and the MOF supports in the catalysts were proven to show significant and different effects to promote the catalytic activities. With MOF-based catalysts, both the enhanced kinetics and the high H2 capacity of the AB system present great advantages for future use. [source]


Thermal Behavior and Non-isothermal Decomposition Reaction Kinetics of NEPE Propellant with Ammonium Dinitramide

CHINESE JOURNAL OF CHEMISTRY, Issue 5 2010
Weiqiang Pang
Abstract Thermal decomposition behavior and non-isothermal decomposition reaction kinetics of nitrate ester plasticized polyether NEPE propellant containing ammonium dinitramide (ADN), which is one of the most important high energetic materials, were investigated by DSC, TG and DTG at 0.1 MPa. The results show that there are four exothermic peaks on DTG curves and four mass loss stages on TG curves at a heating rate of 2.5 Kmin,1 under 0.1 MPa, and nitric ester evaporates and decomposes in the first stage, ADN decomposes in the second stage, nitrocellulose and cyclotrimethylenetrinitramine (RDX) decompose in the third stage, and ammonium perchlorate decomposes in the fourth stage. It was also found that the thermal decomposition processes of the NEPE propellant with ADN mainly have two mass loss stages with an increase in the heating rate, that is the result of the decomposition heats of the first two processes overlap each other and the mass content of ammonium perchlorate is very little which is not displayed in the fourth stage at the heating rate of 5, 10, and 20 Kmin,1 probably. It was to be found that the exothermal peak temperatures increased with an increase in the heating rate. The reaction mechanism was random nucleation and then growth, and the process can be classified as chemical reaction. The kinetic equations of the main exothermal decomposition reaction can be expressed as: d,/dt=1012.77(3/2)(1,,)[,ln(1,,)]1/3 e,1.723104/T. The critical temperatures of the thermal explosion (Tbe and Tbp) obtained from the onset temperature (Te) and the peak temperature (Tp) on the condition of ,,0 are 461.41 and 458.02 K, respectively. Activation entropy (,S,), activation enthalpy (,H,), and Gibbs free energy (,G,) of the decomposition reaction are ,7.02 Jmol,1K,1, 126.19 kJmol,1, and 129.31 kJmol,1, respectively. [source]


Synthesis, characterization and impedance spectroscopy of the new material [(CH3) (C6H5) 3P] 2CoBr4: a member of the A2BX4 family

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2008
M. F. Mostafa
Abstract The crystal structure of bis-(methyltriphenylphosphonium) tetrabromocobaltate (II), [(C19H18P)2 CoBr4] is determined: Mr = 933.203, monoclinic, P21, a = 9. 6977 (3) , b = 12.5547 (4), c = 16.4503 (6), , = 105.603 (2), V = 1929.04 (11)3, Z = 2, Dx = 1.607 Mg m -3, T = 298 K. Differential thermal analysis at high temperatures shows three endothermic peaks characterizing four phases, with onset temperatures at T1= 3132 K, T2 = 3204 K and T3= 3601 K. The structural instability detected via the temperature dependence of permittivity at T1 is ascribed to order-disorder transition associated with cation dipole reorientation. Permittivity and ac conductivity studies as a function of temperature (295 K-375 K) and frequency (0.11 kHz < f <100 kHz) are presented. The results indicate the importance of the cation size and shape on the phase transitions in the system. Bulk conductivity behavior is thermally activated. The associated activation energies are in the range 2.9 to 1.0 eV depending on the temperature regime. Two contributions to the ac conductivity, one dominating at low temperatures and high frequencies which are characterized by superlinear frequency exponent and the second dominates at high temperatures characterized by a sublinear frequency exponent. The behavior is interpreted in terms of the jump relaxation model. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


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

EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 4 2009
Mario Aguedo
Abstract Milk fat (MF) and rapeseed oil (RO) blends were analyzed by differential scanning calorimetry (DSC). It was shown that peak and onset temperatures can be used to determine the percentage of each fat in the blend and that the relative enthalpy of one peak assigned to low-melting triacylglycerols (TAG) can also be used to determine the percentage of RO in the blend. A linear relation was also established between MF content of the blend and its dropping point (DP), indicating that DP can be linearly related with the above DSC data. A blend of MF/RO 70,:,30 (wt/wt) was then chosen as a model system for enzymatic interesterification (EIE). The applicability of DSC analyses to EIE products was checked and a correct correlation could be established between DSC values and the interesterification degree and DP. Among the data from the DSC profiles, the peak associated with low-melting TAG was the best indicator of the reaction course. In the same way, a high-melting MF stearin fraction was interesterified with RO. In that case, onset temperatures and peak "a" were better reaction indicators than for the interesterified MF/RO blend. We therefore suggest that values from DSC endotherms could be used to monitor EIE of fat blends. [source]


Synthesis and characterization of novel Schiff base polyurethanes,

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2009
A. V. Raghu
Abstract Eight different types of novel polyurethanes (PUs) were synthesized through the polyaddition reaction of 4,4,-(ethane-1,2-diylidenedinitrilo)diphenol and 4,4,-(pentane-1,5-diylidenedinitrilo)diphenol with four different diisocyanates: 4,4,-diphenylmethane diisocyanate, toluene 2,4-diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate. The resulting PUs were soluble in polar, aprotic solvents. Structures of the diols and PUs were established with ultraviolet,visible, fluorescence, Fourier transform infrared (FTIR), 1H-NMR, and 13C-NMR spectroscopy data. FTIR and NMR spectral data indicated the disappearance of both hydroxyl and isocyanate groups in the PUs. The thermal properties were investigated with thermogravimetry and differential scanning calorimetry. The weight losses, glass transitions, onset temperatures, and crystalline melting temperatures were measured. All the PUs exhibited semicrystalline and amorphous morphologies, as indicated by X-ray diffraction. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009. [source]


Thermal Properties, Heat Sealability and Seal Attributes of Whey Protein Isolate/ Lipid Emulsion Edible Films

JOURNAL OF FOOD SCIENCE, Issue 7 2001
S-J. Kim
ABSTRACT: From 5% w/v whey protein isolate (WPI), whey protein/lipid emulsion edible films were produced that were sorbitol- or glycerol-plasticized, containing butterfat (0.2% w/v) or candelilla wax (0.8% w/v). Thermal properties of the films determined by Differential Scanning Calorimetry (DSC) showed onset temperatures (To) of 126 to 127 C for sorbitol- and 108 to 122 C for glycerol-plasticized films. To values were used as the basis for heat sealing temperatures. Temperature (110, 120, 130 C), pressure (296,445 kPa), and dwell time (1,3 s) affected seal strength. Optimum heat sealing temperature was 130 C for sorbitol- and 110 C for glycerol-plasticized films. All films were heat sealable with an impulse heat-sealer. Electron Spectroscopy for Chemical Analysis (ESCA) of the surfaces of both sealed and unsealed films showed increase in hydrogen and covalent bonds involving C-O-H and N-C, which may be the main forces responsible for the sealed joint formation of the films. [source]


Hazard ratings for organic peroxides

PROCESS SAFETY PROGRESS, Issue 2 2008
Yih-Shing Duh
Abstract Nine of commercially available organic peroxides were assessed with differential scanning calorimeter (DSC) and adiabatic calorimeters. These organic peroxides are cumene hydroperoxide (CHP), di- tert -butyl peroxide (DTBP), methyl-ethyl-ketone peroxide (MEKPO), tert -butyl hydroperoxide (TBHP), benzoyl peroxide (BPO), hydrogen peroxide, lauroyl peroxide (LPO), tert -butyl peroxybenzoate (TBPBZ), and dicumyl peroxide (DCPO). Exothermic onset temperatures, self-heat temperature and pressure rates, and heats of decomposition were measured and assessed. Adiabatic runaway reaction characteristics were determined by using ARC (accelerating rate calorimeter) and VSP2 (vent sizing package). Incompatibility, tests with several potential contaminants, was made using DSC, VSP2, and microcalorimeter. An incompatibility rating was developed using onset temperature, lowering of the onset temperature, heat of decomposition, maximum self-heat rate, adiabatic temperature rise, maximum pressure of decomposition, and maximum pressure rising rate, etc. 2008 American Institute of Chemical Engineers Process Saf Prog 2008 [source]