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1.
Differential Scanning Calorimetry combined with Fourier transform infrared spectroscopy, was applied to the study of a number of fulvic and humic acids extracted from soils, peat, river and seawater. The thermal patterns obtained were related to the nature and origin of samples. The low-temperature endotherms were attributed to dehydration and loss of peripheral polysaccharide chains. The endotherm at 250°C observed for soil FA was ascribed to partial decarboxylation of more labile surface COOH groups, whereas the high-temperature exotherms at about 500°C were related to the degree of polycondensation of the aromatic network of the humic molecules.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
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Mrevlishvili G. M. Sottomayor M. J. Ribeiro da Silva M. A. V. Mdzinarashvili T. D. Al-Zaza M. Tediashvili M. Tushishvili D. Chanishvili N. 《Journal of Thermal Analysis and Calorimetry》2001,66(1):103-113
Journal of Thermal Analysis and Calorimetry - Bacterial viruses genome- ds-DNA -expulsion from the phage capsid is induced by temperature and is not accompanied by heat effects (temperature... 相似文献
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微管系统在细胞中执行许多重要功能山.微管在细胞中呈现高度的时间和空间有序性,并与构成它的结构单元—一微管蛋白(土。l})lllil。)保持动态平衡,而且这种平衡是局域的和暂时的,Mit(Jlisou和Krscllner根据他们的微管体外实验及体内微管聚合特性称之为微管生长的动态不稳定性*1.微管的生理功能正是与它的这种根本特性有关.另有研究发现微管是许多药物包括许多抗癌药物作用的靶子问.如紫杉醇(TaX01)*等.因此国际上研究微管蛋白的聚合过程以及药物分子的作用是微管研究中的热点问题之一.生理状态下微管蛋白以。月异二聚体… 相似文献
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Chris Holland Nicholas Hawkins Martin Frydrych Peter Laity David Porter Fritz Vollrath 《Macromolecular bioscience》2019,19(3)
Native silk proteins, extracted directly from the silk gland prior to spinning, offer access to a naturally hydrated protein that has undergone little to no processing. Combined with differential scanning calorimetry (DSC), it is possible to probe the thermal stability and hydration status of silk and thus investigate its denaturation and solidification, echoing that of the natural spinning process. It is found that native silk is stable between ?10 °C and 55 °C, and both the high‐temperature enthalpy of denaturation (measured via modulated temperature DSC) and a newly reported low‐temperature ice‐melting transition may serve as useful quality indicators in the future for artificial silks. Finally, compared to albumin, silk's denaturation enthalpy is much lower than expected, which is interpreted within a recently proposed entropic desolvation framework which can serve to unveil the low‐energy aquamelt processing pathway. 相似文献
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The reproducibility and reliability of the TA Instruments Modulated Differential Scanning Calorimeter (MDSC) was tested over a range of conditions. The equipment base line was found to be fairly constant with a very small fluctuation (10 W), which means a 0.1 % fluctuation on the scale of a normal polymer MDSC curve. The excellent stability of the base line and the reasonable reproducibility of the curves (5%) suggest that frequent calibration is not required.The heat capacities calculated from the modulated response to the variable temperature depend on the frequency for a given cell constant. The heat capacity cell constant is a unique function of the modulation frequency:k
c
=K
c
o
p/(p–6.3) wherep is the time of the periodicity expressed in seconds and K
c
o
is the heat capacity cell constant measured on a standard material and reduced to zero frequency. The cell constants depend on the flow rate of the helium according to:K(He)=K
o(1.298–0.004424He+1.438·10–5
He
2) whereHe is the flow rate of helium in ml min–1 andK
o represents a constant at 100 cm3 min–1. There is a strong dependence of cell constant on the flow rate ranges from 10 to 80 cm3 min–1, while above this rate (up to 135 ml min–1) the cell constant approaches a plateau. 相似文献
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采用示差扫描量热仪研究了稀土顺式聚丁二烯(PB)等温过程的结晶及其熔融行为. 结果表明,在等温结晶的后期存在晶型完善的过程,而且随着等温结晶温度的提高,结晶速率均下降. PB的熔融总是在比等温结晶温度高约2 ℃处开始,而且在10 ℃/min的升温速率下,DSC曲线不仅显示出很宽的熔融温度范围,而且在低温处还出现了小肩峰,说明等温结晶后体系中具有在该升温速率下不同稳定性的晶体. 通过不同温度下的等温结晶曲线,分别采用结晶度趋于零(Xc=0)时的熔点和结晶时间无限长(t-1c=0)时的熔点,用Hoffman-Weeks方法得到顺式聚丁二烯的平衡熔点T∞m位于9~17.6 ℃之间. 相似文献
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New approaches to the analysis of differential scanning calorimetry (DSC) data relating to proteins undergoing irreversible
thermal denaturation have been demonstrated. The experimental approaches include obtaining a set of DSC curves at various
scanning rates and protein concentrations, and also reheating experiments. The mathematical methods of analysis include construction
of a linear anamorphosis and simultaneous fitting of a theoretical expression for the dependence of the excess heat capacity
on temperature to a set of experimental DSC curves. Different kinetic models are discussed: the one-step irreversible model,
the model including two consecutive irreversible steps, the Lumry and Eyring model with a fast equilibrating first step, and
the whole kinetic Lumry and Eyring model.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Identification of Polyethylene by Differential Scanning Calorimetry: Application to forensic science
Tsukame T. Kutsuzawa M. Sekine H. Saitoh H. Shibasaki Y. 《Journal of Thermal Analysis and Calorimetry》1999,57(3):847-851
A forensic sample consisting of melt-recrystallized polymers that was recovered from the scene of a fire in a factory was identified by differential scanning calorimetry. The factory commonly used two kinds of film sheets, A and B, made by different manufacturers. It was necessary to decide whether the forensic sample related to material A or B. The forensic sample and reference samples of materials A and B were subjected to infrared spectroscopy and pyrolysis gas chromatograph mass spectrometry measurements, which revealed their polyethylene nature. The thermal behaviour of the samples was examined by differential scanning calorimetry (DSC) and they were found to be blends of two kinds of polyethylenes, low-density polyethylene and linear low-density polyethylene. The samples could be identified and distinguished from each other via the DSC measurements.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
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Lammert A. M. Lammert R. M. Schmidt S. J. 《Journal of Thermal Analysis and Calorimetry》1999,55(3):949-975
The physical aging characteristics of maltose glasses aged at two temperatures below the glass transition temperature, Tg, (Tg-10°C and Tg-20°C) from 5 to 10 000 min were measured by standard differential scanning calorimetry (SDSC) and modulated differential
scanning calorimetry (MDSC). The experimentally measured instrumental Tg, the calculated Tg, and the excess enthalpy values were obtained for aged glasses using both DSC methods. The development of excess enthalpy
as a function of aging time, as measured by both SDSC and MDSC, was fit using the Cowie and Ferguson and Tool-Narayanswamy-Moynihan
models. The change in the Tg values and the development of the excess enthalpy resulting from physical aging measured by the two DSC methods are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Mohamed Bechir Chebab Memia Benna Malika Trabelsi-Ayadi 《Journal of Dispersion Science and Technology》2013,34(1):67-76
In this work, we have tested various formulations in order to get emulsions containing pure water, Tunisian olive oil, Tunisian clays, and an ammonium salt. Two different types of clays: smectite and kaolinite and the cethyltrimethylamonium bromide (CTAB) were tested. CTAB is used as surfactant and a compound modifying the clays properties. The amount of CTAB being fixed at 0.66 w/w, the proportions of clays were varied from 0 to 9% for each of the following proportions of water: 10, 20, 30%. To the aqueous phase obtained by mixing two separate aqueous phases: water + CTAB and water + clay, the oil was added drop by drop, the agitation being maintained at 5000 rpm. The obtained mixtures were analyzed by Differential Scanning Calorimetry (DSC), optical microscopy and bottle tests. An optimized formulation containing water (30%), smectite clay (5.3%) and CTAB (0.66%) was found to give W/O emulsions which kinetic stability is greater than 75 days regarding coalescence and greater than 700 hours regarding sedimentation. 相似文献
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Summary. The primary crystallization of molten alloy systems at high undercooling is studied by a precise quantitative analysis of
the calorimetric signal obtained during the transformation in terms of the reaction rate under isothermal and continuous heating
regimes. It is shown that, under specific conditions, namely, stoechiometric primary precipitates, generalized relationships
for the crystallization enthalpy and the reaction rate may be obtained. 相似文献
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差示扫描量热法中相变潜热公式的推导 总被引:3,自引:0,他引:3
通过考虑热分析过程中存在于试样内的温度梯度,就相变前后试样的比热容发生变化、并且是温度的函数这一普遍情况,推导得到了普遍的用差示扫描量热法求相变潜热的公式 相似文献
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应用差示扫描量热法(DSC)研究了衣康酸(IA)、气氛、升温速率对丙烯腈-衣康酸共聚物[P(AN-IA)]热稳定化的影响. IA能够显著降低放热峰起始温度、放热量和放热速率. P(AN-IA)共聚物的放热峰起始温度受气氛影响不大, 却随着IA含量的增加而明显降低, 表明在热稳定化过程中它可能首先以离子机理发生氰基环化反应, 再发生氧化反应. 提高升温速率会导致放热峰向高温偏移和放热速率加快. 采用Kissinger法计算了不同IA含量共聚物的热稳定化活化能, 结果表明IA可以有效降低活化能. 相似文献
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Modulated-temperature differential scanning calorimetry (M-TDSC) is becoming a useful tool in the characterisation of thermal
behaviour of polymers. In this paper, we discuss whether the non-reversing M-TDSC signal can be used, quantitatively and directly,
to study the process of physical ageing in polymers. Difference exists between the values of relaxation enthalpy determined
by using average heat capacity, <C
p>, signal as for conventional DSC and non-reversing heat capacity, C
n
p, signal. When the signal of reversing heat capacity of unaged sample is considered as baseline for <C
p> and C
n
p signals, the difference disappears. It is concluded that non-reversing M-TDSC signal can be used to observe the process of
physical ageing semi-qualitatively and directly. With increasing annealing time, the peak of the imaginary part, C″p, of the complex heat capacity becomes narrow, but peak area changes little. This indicated that C″p is not correlated with relaxation enthalpy. It may be related to entropy change during the modulation. However, the entropy
change is quite small.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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The thermal denaturation of superoxide dismutase (SOD) from bovine erythrocytes was studied at various pH values of different buffers and at various concentrations of solutions of two neutral salts by differential scanning calorimetry. The experiments performed indicate that the PIPES is a buffer non-coordinating with the SOD, and that the binding of the anions studied influences more or less the thermal denaturation of SOD, but the effect on the oxidation form of SOD is more apparent. A new conformer of SOD with lower thermostability was discovered by the experiments performed in different buffers at certain pH values higher than the isoelectric point of SOD, or at higher concentrations of neutral salt solutions. The new conformer may be converted irreversibly into the usual conformer with high thermostability during heating. Based on the thermodynamic parameters obtained in distilled water and by thermodynamic analysis using the Ooi's model, it is revealed that the large enthalpy △Hdc contributed by 相似文献