共查询到20条相似文献,搜索用时 15 毫秒
1.
Randall K. Weese 《Thermochimica Acta》2005,429(1):119-123
An investigation of the use of modulated differential scanning calorimeter (MDSC) to measure thermal conductivity (κ) of the explosive Tetryl using isothermal and non-isothermal methods. Issues surrounding the use of silicone oil as a heat transfer aid are discussed. Using these methods the calculated isothermal and non-isothermal properties of specific heat capacity were observed to be 0.844 and 0.863 J/(g K) and the calculated thermal conductivity values were found to be 0.165 and 0.186 W/K. Calibration experiments using polystyrene indicate that the non-isothermal method is more reproducible but has a larger offset (35%) from the true value. Our corrected values for Tetryl fall in the middle of the considerable range of values reported in the literature. 相似文献
2.
The effect of thermal history on gel-sol transition was investigated by highly sensitive differential scanning calorimetry (DSC) in order to clarify the non-equilibrium state of κ-carrageenan hydrogels. κ-Carrageenan with a concentration from 0.5% to 5.0% was used. When concentration of solution was lower than 2.0%, homogeneous κ-carrageenan gel was formed when aqueous solution was fully equilibrated. When concentration exceeded 3.0%, a sub-peak could be observed at the low temperature side of the main peak. It was indicated that helices having various sizes and different kinds of defects are present in the junction zone. Thermal histories, such as cooling rate from the sol state or annealing at around gel-sol transition temperature, markedly affect the junction zone formation. A large junction zone is formed at a slow gelation rate, and also that many small junction zones form at a fast gelation speed. 相似文献
3.
Modulated differential scanning calorimetry 总被引:4,自引:0,他引:4
P. S. Gill S. R. Sauerbrunn M. Reading 《Journal of Thermal Analysis and Calorimetry》1993,40(3):931-939
Modulated DSCTM (MDSC) is a new, patent-pending extension to conventional DSC which provides information about the reversing and nonreversing characteristics of thermal events, as well as the ability to directly measure heat capacity. This additional information aids interpretation and allows unique insights into the structure and behaviour of materials., A number of examples of its use are described. 相似文献
4.
Measurement of the sensitization of nitrocompounds by amines using differential scanning calorimetry
We report a new method of making empirical measurements of the sensitization of nitrocompounds by amines based on thermal analysis. The method is sensitive, accurate and reproducible. We have used this method to measure the sensitization of nitromethane, N-methyl-N-(2,4,6-trinitrophenyl) nitramine (tetryl), picric acid and trinitrotoluene (TNT) by a number of aliphatic amines. 相似文献
5.
D. J. Hourston M. Song H. M. Pollock A. Hammiche 《Journal of Thermal Analysis and Calorimetry》1997,49(1):209-218
Modulated-temperature differential scanning calorimetry was used to measure the glass transition temperature,T
g, the heat capacity relaxation in the glassy state and the increment of heat capacity, Cp, in the glass transition region for several polymers. The differential of heat capacity with respect to temperature was used to analyseT
g and Cp simply and accurately. These measurements are not affected by complex thermal histories. 相似文献
6.
Lahu Yang Hua Yin Wehua Zhu Suhua Niu 《Journal of Thermal Analysis and Calorimetry》1995,45(1-2):207-210
Thermal behaviour of codeine phosphate and codeine crystallized at the several solvents system was studied by DSC, and then, the kinetic parameters and thermochemical data have been obtained. We have found that codeine phosphate and codeine exist in a number of polymorphic formes which may inflicence the bio-availability. 相似文献
7.
8.
Differential scanning calorimetry is well suited to record heat productions of chemical and physical processes as data for the following kinetic analysis. To obtain kinetic parameters of complex reactions, nonlinear optimization methods have to be used. Such complex reaction systems are polymerizations. We tried to evaluate measurements of the epoxy cure and the polymerization of β-propiolactame with simple and complex models. In both cases the simple models did not produce satisfactory results. But by using complex models a successful fitting of the measured data was possible. Our investigation shows that the combination of DSC and modern nonlinear evaluation methods presents a suitable tool for the kinetic investigation of polymerizations. 相似文献
9.
Thermal analysis of the binary system KCl-LiCl in the composition range 0.368–0.812 mol fraction of LiCl was studied by differential scanning calorimetry (DSC). On the basis of the DSC curves, the experimental data for the phase-diagram, the latent heat of fusion, and the average specific heat in the liquid and solid states are presented as a function of the composition of the mixture. The experimental results compared with literature data. The following empirical correlation between the heat of fusion (H) and of compositions of the mixture in mol fraction of LiCl (x) was obtained: ·GH=26.95–50.20x+43.06x2 with a minimum value of 11.8 kJ(g mol)–1 at the eutectic point of 0.587 mol fraction of LiCl at 354.4°C. These results are required as basic data to develop thermal energy storage materials, based on the phase change of a molten mixture of KCl-LiCI. 相似文献
10.
The specific heat capacities of some triglycerides commonly found in palm oil were determined with a heat-flux differential scanning calorimeter. The specific heat capacity measurements were made under the optimum operating conditions determined earlier: scan rate 17 deg·min?1, sample mass 21 mg and purge gas (nitrogen) flow rate 50 ml/min. Pure triglycerides (four simple and four mixed) were used in the experiments. The four simple triglycerides were trilaurin, trimyristin, tripalmitin and tristearin, and the mixed triglycerides were 1,2-dimyristoyl-3-oleoyl, 1,2-dimyristoyl-3-palmitoyl, 1,2-dipalmitoyl-3-oleoyl and 1,2-dioleoyl-3-palmitoyl. The results of this study are compared with literature values and also with values obtained by using estimation methods. The experimental specific heat capacities are within ±1% precision with a 95% confidence level. 相似文献
11.
A procedure is described to determine the limit of detection of DSC instruments by using tiny signals from spontaneous polymorphic transitions of CsCl, K2Cr2O7 and Na2SO4. It is shown how such signals can be found well-resolved in DSC diagrams of powder samples. To distinguish them from the baseline noise they should exhibit a height at least twice that of the baseline width. For the instrument employed the corresponding smallest amount of heat, i.e., the limit of detection, was found to be 0.1 mJ.The authors thank Mr. H. Maltry for technical help and the Deutsche Forschungsgemeinschaft for support. 相似文献
12.
Kinetics
of polyurethane formation between several polyols and isocyanates with dibutyltin
dilaurate (DBTDL) as the curing catalyst, were studied in the bulk state by
differential scanning calorimetry (DSC) using an improved method of interpretation.
The molar enthalpy of urethane formation from secondary hydroxyl groups and
aliphatic isocyanates is 72±3 kJ mol-1
and for aromatic isocyanates it is 55±2 kJ mol-1
. In the case of a single second order reaction for aliphatic isocyanates
reaction, activation energy is 70±5 kJ mol-1
with oxypropylated polyols and 50±3 kJ mol-1
with Castor oil. For aromatic isocyanates and oxypropylated polyols the activation
energy is higher around 77 kJ mol-1 .
In the case of two
parallel reactions (situation for IPDI and TDI 2-4) best fits are observed
considering two different activation energies. 相似文献
13.
14.
B. E. I. Abdelrazig S. D. Main D. V. Nowell 《Journal of Thermal Analysis and Calorimetry》1992,38(3):495-504
Thermal methods are used extensively in investigating cements and effects of additives on their hydration behaviour. Calcium chloride is the most effective and widely used accelerator for cement hydration, but the result is largely dependent on the rate at which it is added. In this study the influence of calcium chloride dosage on the hydration behaviour of OPC pastes aged for different periods has been investigated by means of differential scanning calorimetry (DSC), thermogravimetry (TG) and X-ray diffraction (XRD) methods. The results are discussed in relation to the relative amounts of calcium hydroxide and total reaction product formed. Chloroaluminate was a product of hydration in the samples dosed with greater than 1% calcium chloride. XRD was unable of itself to differentiate between monochloroaluminate and the calcium aluminate hydrate C4AH13 when present in small amounts. Thermal methods proved effective in characterising the products of hydration in the presence of chloride.
Zusammenfassung Bei der Untersuchung von Zement und des Einflusses von Additiven auf das Hydratationsverhalten von Zement finden thermoanalytische Methoden eine breite Anwendung. Der effektivste und meistbenutzte Beschleuniger für die Hydratation von Zement ist Calciumchlorid, aber die Ergebnisse hängen stark von der Dosiergeschwindigkeit ab. In vorliegender Studie wird mittels DSC-, TG- und Röntgendiffraktionsmethoden der Einflu\ der Dosierung von Calciumchlorid auf das Hydratationsverhalten von verschieden alten OPC-Zementbreiproben untersucht. Die Ergebnisse wurden in Bezug auf die relativen Mengen Calciumhydroxid und das gebildete Gesamtreaktionsprodukt gewertet.Bei Dosen von mehr als 1% Calciumchlorid konnte als Hydratationsprodukt Chloraluminat festgestellt werden. Sind Monochloraluminat und das Calciumaluminathydrat C4AH13 in geringen Mengen vorhanden, kann man zwischen den beiden mittels Röntgendiffraktion nicht unterscheiden. Thermoanalytische Methoden erwiesen sich als effektives Hilfsmittel bei der Charakterisierung der Produkte der Hydratation in Gegenwart von Chlorid.相似文献
15.
W. M. Leung 《Colloid and polymer science》1985,263(10):818-821
Fusion behaviour of solution-grown low molecular weight polyethylene single crystals was studied by differential scanning calorimetry at different heating rates. The results were correlated to the polymer chain conformation in the crystal. It was found that in the molecular weight range studied, crystals of shorter chain length and fewer foldings per chain are less stable and more susceptible to heat annealing. Melting endotherms of the crystals of the lowest molecular weight fraction grown at various temperatures indicate that during crystallization, a fractional stem at the end of a folding chain will be rejected outside the lamellae of the crystal. 相似文献
16.
Danièle Clausse 《Journal of Thermal Analysis and Calorimetry》1998,51(1):191-201
This article is a review about the ways in which solidification and the melting may occur within emulsions submitted to steady
cooling and heating performed in a differential scanning calorimeter. Simple, multiple and mixed emulsions are considered.
Due to nucleation phenomena creating supercooled and supersaturated liquids, the DSC curves obtained during cooling and heating
are quite different. The influence of a solute in the disperse phase is described in detail. Some implications about the instabilities
of emulsions due to mass transfer phenomena are described. 相似文献
17.
The kinetic investigation of thermoanalytical curves for the ethyl acetate and alkaline hydrolysis, requires tedious calculations of several mathematical expressions, to establish the correlation between the thermochemical and kinetic parameters. Using the DSC measured data for the heat flow-temperature dependence of the studied reactions, we have obtained the kinetic bulk parameters and the dependencek=k(T) for the basic and acid hydrolysis of ethyl acetate. 相似文献
18.
A differential scanning calorimetry study of the thermal behaviour of haemin in N,N-dimethylformamide solution was carried
out. The samples were scanned with different scan rates in the temperature range 25-130°C. The UV VIS spectrophotometry was
used as assistant measurement method. The scan rate dependent and irreversible exothermic peaks were found. The activation
energies of observed transitions were calculated assuming kinetically controlled process. The nature of thermal behaviour
of haemin in DMF solutions is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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20.
J. F. Turner A. Riga A. O'Connor J. Zhang J. Collis 《Journal of Thermal Analysis and Calorimetry》2004,75(1):257-268
Poly-L-lactic acid (PLLA) is an optically active, biocompatible and biodegradable polymer that has been widely investigated as an artificial cell scaffold material. In its most crystalline form, PLLA is highly anisotropic and is one of the most piezoelectric polymers known. Conversely, amorphous PLLA exhibits little, if any, piezoelectric behavior. Compression molded PLLA films can be endowed with varying amounts of crystalline character and piezoelectricity by uniaxially stretching the polymer in a hot air bath. Understanding the precise crystalline architecture of PLLA that results from tensile drawing is important for constructing cell scaffolds that have highly tailored biodegradation and cell guiding properties. In our work here, we investigate the changes in the thermal properties of PLLA at draw ratios between 1.0 and 5.5 using differential scanning calorimetry (DSC). The crystallinity of the compression molded undrawn starting material is characterized using X-ray diffraction. Our DSC results show an increase in percent crystallinity with increasing draw up to a draw ratio of 4.0. At greater draw ratios, there is a decrease in the crystalline character exhibited by PLLA.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献