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1.
R. L. Frost W. Martens M. O. Adebajo 《Journal of Thermal Analysis and Calorimetry》2005,81(2):351-355
Summary High resolution TG coupled to a gas evolution mass spectrometer has been used to study the thermal properties of a chromium based series of Ni/Cu hydrotalcites of formulae NixCu6-xCr2(OH)16(CO3)×4H2O where x varied from 6 to 0. The effect of increased Cu composition results in the increase of the endotherms and mass loss steps to higher temperatures. Evolved gas mass spectrometry shows that water is lost in a number of steps and that the interlayer carbonate anion is lost simultaneously with hydroxyl units. Differential scanning calorimetry was used to determine the heat flow steps for the thermal decomposition of the synthetic hydrotalcites. Hydrotalcites in which M2+ consist of Cu, Ni or Co form important precursors for mixed metal-oxide catalysts. The application of these mixed metal oxides is in the wet catalytic oxidation of low concentrations of retractable organics in water. Therefore, the thermal behaviour of synthetic hydrotalcites, NixCu6-xCr2(OH)16CO3×nH2O was studied by thermal analysis techniques in order to determine the correct temperatures for the synthesis of the mixed metal oxides. 相似文献
2.
A combination of high resolution thermogravimetric analysis coupled to a gas evolution mass spectrometer has been used to study the thermal decomposition of synthetic hydrotalcites reevesite (Ni6Fe2(CO3)(OH)16·4H2O) and pyroaurite (Mg6Fe2(SO4,CO3)(OH)16·4H2O) and the cationic mixtures of the two minerals. XRD patterns show the hydrotalcites are layered structures with interspacing distances of around 8.0. Å. A linear relationship is observed for the d(001) spacing as Ni is replaced by Mg in the progression from reevesite to pyroaurite. The significance of this result means the interlayer spacing in these hydrotalcites is cation dependent. High resolution thermal analysis shows the decomposition takes place in 3 steps. A mechanism for the thermal decomposition is proposed based upon the loss of water, hydroxyl units, oxygen and carbon dioxide. 相似文献
3.
R. L. Frost J. M. Bouzaid A. W. Musumeci J. T. Kloprogge W. N. Martens 《Journal of Thermal Analysis and Calorimetry》2006,86(2):437-441
The thermal
stability and thermal decomposition pathways for synthetic iowaite have been
determined using thermogravimetry in conjunction with evolved gas mass spectrometry.
Chemical analysis showed the formula of the synthesised iowaite to be Mg6.27Fe1.73(Cl)1.07(OH)16(CO3)0.336.1H2O
and X-ray diffraction confirms the layered structure. Dehydration of the iowaite
occurred at 35 and 79°C. Dehydroxylation occurred at 254 and 291°C.
Both steps were associated with the loss of CO2. Hydrogen
chloride gas was evolved in two steps at 368 and 434°C. The products of
the thermal decomposition were MgO and a spinel MgFe2O4.
Experimentally it was found to be difficult to eliminate CO2
from inclusion in the interlayer during the synthesis of the iowaite compound
and in this way the synthesised iowaite resembled the natural mineral. 相似文献
4.
N. Voyer A. Soisnard Sara J. Palmer W. N. Martens R. L. Frost 《Journal of Thermal Analysis and Calorimetry》2009,96(2):481-485
Zn-Al hydrotalcites and Cu-Al hydrotalcites were synthesised by coprecipitation method and analysed by X-ray diffraction (XRD)
and thermal analysis coupled with mass spectroscopy. These methods provide a measure of the thermal stability of the hydrotalcite.
The XRD patterns demonstrate similar patterns to that of the reference patterns but present impurities attributed to Zn(OH)2 and Cu(OH)2. The analysis shows that the d003 peak for the Zn-Al hydrotalcite gives a spacing in the interlayer of 7.59 ? and the estimation
of the particle size by using the Debye-Scherrer equation and the width of the d003 peak is 590 ?. In the case of the Cu-Al
hydrotalcite, the d003 spacing is 7.57 ? and the size of the diffracting particles was determined to be 225 ?.
The thermal decomposition steps can be broken down into 4 sections for both of these hydrotalcites. The first step decomposition
below 100°C is caused by the dehydration of some water absorbed. The second stage shows two major steps attributed to the
dehydroxylation of the hydrotalcite. In the next stage, the gas CO2 is liberated over a temperature range of 150°C. The last reactions occur over 400°C and involved CO2 evolution in the decomposition of the compounds produced during the dehydroxylation of the hydrotalcite. 相似文献
5.
J. M. Bouzaid R. L. Frost A. W. Musumeci W. N. Martens 《Journal of Thermal Analysis and Calorimetry》2006,86(3):745-749
The thermal
stability and thermal decomposition pathways for synthetic woodallite have
been determined using thermogravimetry in conjunction with evolved gas mass
spectrometry. Chemical analysis showed the formula of the synthesised woodallite
to be Mg6.28Cr1.72Cl(OH)16(CO3)0.36⋅8.3H2O and X-ray diffraction confirms the layered
LDH structure. Dehydration of the woodallite occurred at 65°C. Dehydroxylation
occurred at 302 and 338°C. Both steps were associated with the loss of
carbonate. Hydrogen chloride gas was evolved over a wide temperature range
centred on 507°C. The products of the thermal decomposition were MgO and
a spinel MgCr2O4. Experimentally
it was found to be difficult to eliminate CO2 from
inclusion in the interlayer during the synthesis of the woodallite compound
and in this way the synthesised woodallite resembled the natural mineral. 相似文献
6.
Thermal analysis increasingly being used to obtain kinetic data relating to sample decomposition. This work involves a comparative study of several methods used to analyse DSC and TG/DTG data obtained on the oxidation of Beypazari lignite. A general computer program was developed and the methods are compared with regard to their accuracy and the ease of interpretation of the kinetics of thermal decomposition. For this study, the ratio method was regarded as the preferred method, because it permits the estimation of reaction order, activation energy and Arrhenius constant simultaneously from a single experiment.The experimental part of this research was supported in part by NATO-SFS Project TU-Energy II. The authors express their appreciation to the NATO-SFS program for providing financial support for this project. 相似文献
7.
R L Frost R A Wills J T Kloprogge W N Martens 《Journal of Thermal Analysis and Calorimetry》2006,83(1):213-218
Thermogravimetry combined
with mass spectrometry has been used to study the thermal decomposition of
a synthetic hydronium jarosite. Five mass loss steps are observed at 262,
294, 385, 557 and 619°C. The mass loss step at 557°C is sharp and
marks a sharp loss of sulphate as SO3 from the hydronium
jarosite. Mass spectrometry through evolved gases confirms the first three
mass loss steps to dehydroxylation, the fourth to a mass loss of the hydrated
proton and a sulphate and the final step to the loss of the remaining sulphate.
Changes in the molecular structure of the hydronium jarosite were followed
by infrared emission spectroscopy. This technique allows the infrared spectrum
at the elevated temperatures to be obtained. Infrared emission spectroscopy
confirms the dehydroxylation has taken place by 400 and the sulphate loss
by 650°C. Jarosites are a group of minerals formed in evaporite deposits
and form a component of the efflorescence. The minerals can function as cation
and heavy metal collectors. Hydronium jarosite has the potential to act as
a cation collector by the replacement of the proton with a heavy metal cation. 相似文献
8.
Summary A combination of high resolution thermogravimetric analysis coupled to a gas evolution mass spectrometer has been used to
study the thermal decomposition of liebigite. Water is lost in two steps at 44 and 302°C. Two mass loss steps are observed
for carbon dioxide evolution at 456 and 686°C. The product of the thermal decomposition was found to be a mixture of CaUO4 and Ca3UO6. The thermal decomposition of liebigite was followed by hot-stage Raman spectroscopy. Two Raman bands are observed in the
50°C spectrum at 3504 and 3318 cm-1 and shift to higher wavenumbers upon thermal treatment; no intensity remains in the bands above 300°C. Three bands assigned
to the υ1 symmetric stretching modes of the (CO3)2- units are observed at 1094, 1087 and 1075 cm-1 in agreement with three structurally distinct (CO3)2- units. At 100°C, two bands are found at 1089 and 1078 cm-1. Thermogravimetric analysis is undertaken as dynamic experiment with a constant heating rate whereas the hot-stage Raman
spectroscopic experiment occurs as a staged experiment. Hot stage Raman spectroscopy supports the changes in molecular structure
of liebigite during the proposed stages of thermal decomposition as observed in the TG-MS experiment. 相似文献
9.
Elda Markovic Kim Nguyen Stephen Clarke Kristina Constantopoulos Janis Matisons George P. Simon 《Journal of polymer science. Part A, Polymer chemistry》2013,51(23):5038-5045
A series of polyurethane hybrid networks have been synthesized using octakis(m‐isoprenyl‐α,α′‐dimethylbenzylisocyanato dimethylsiloxy) octasilsesquioxane (Q8M8TMI) as a crosslinking agent. The formation of the urethane linkages within the polyurethane hybrids was confirmed by photoacoustic FTIR spectroscopy. The TGA and DSC studies demonstrated that the incorporation of the POSS crosslinking agents altered the thermal properties of the polyurethanes, and that this was dependent on the length of the polyethylene glycol chain. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5038–5045 相似文献
10.
11.
Complex mixtures of long chain organic compounds often show overlapping glass transition temperatures (T
gs) when analyzed by differential scanning calorimetry (DSC) or modulated DSC (MDSC). In such cases, subjective and inconsistent
smoothing of data acquired under different conditions can lead to the misinterpretation of results. A quantitative method
for the selection of smoothing factors for the analysis and comparison of (M)DSC results is presented. The method is most
useful for the analysis of the derivative of the heat capacity, dC
p/dt or dC
p/dT, plots which best highlight overlapping T
gs. Four equations are shown to relate the heating rate and the smoothing factor. The equations allow a comparison of data
acquired i) at different heating rates and plotted vs. temperature, ii) at a single heating rate and plotted vs. both time and temperature, i.e., dC
p/dt vs. dC
p/dT, iii) at different heating rates and plotted vs. both time and temperature, and iv) at different heating rates, and shown exclusively in the time domain. Examples of the use of the equations are provided
for the analysis of bitumen, a complex mixture of natural origin. 相似文献
12.
Differential
scanning calorimetry (DSC) is applicable to studying the thermal properties
of bacteria when treated with heat, cold, or antibiotics. Foodborne pathogens
are inactivated by heat, and denaturation transitions observed by DSC indicate
potential sites of cellular injury. Ribosomes, which are the sites for messenger
RNA translation, are one critical component of thermal damage as evidenced
by characteristic denaturation transitions in the 66-74°C range.
These transitions disappear when cells of Clostridium
perfringens are subjected to heat, suggesting structural or conformational
changes to ribosomal proteins, and when cells of Listeria
monocytogenes are cold-shocked by refrigeration, indicating ribosomal
dissociation. DSC can be used to show that refrigeration followed by heat
treatment improves the killing of dangerous microorganisms. 相似文献
13.
Thermal decomposition of jarosites of potassium,sodium and lead 总被引:1,自引:0,他引:1
Summary Jarosites are a group of minerals formed in evaporite deposits and form a component of efflorescence. As such the minerals
can function as cation and heavy metal collectors. Thermogravimetry coupled to mass spectrometry has been used to study three
Australian jarosites which are predominantly K, Na and Pb jarosites. Mass loss steps of K-jarosite occur over the 130 to 330
and 500 to 622°C temperature range and are attributed to dehydroxylation and desulphation. In contrast the behaviour of the
thermal decomposition of Na-jarosite shows three mass loss steps at 215 to 230, 316 to 352 and 555 to 595°C. The first mass
loss step for Na-jarosite is attributed to deprotonation. For Pb-jarosite two mass loss steps associated with dehydroxylation
are observed at 390 and 418°C and a third mass loss step at 531°C is attributed to the loss of SO3. Thermal analysis is an excellent technique for the study of jarosites. The analysis depends heavily on the actual composition
of the jarosite. 相似文献
14.
15.
Vulcanisation of rubber compounds was studied by DSC under isothermal and non-isothermal conditions. The parameters of an
Arrhenius-like equation describing the temperature dependence of induction period have been obtained both from isothermal
and non-isothermal measurements. A new method for obtaining the kinetic parameters from non-isothermal measurements, based
on the dependence of onset temperature of vulcanisation peak on heating rate, is presented. Also, a procedure for the evaluation
of temperature difference between the furnace and sample is proposed. It has been shown that the treatment of non-isothermal
DSC measurements gives the kinetic parameters free of systematic errors. The new method can also be used for studying other
reactions exhibiting the induction period.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
R. Ciach W. Kapturkiewicz W. Wolczynski A. M. Zahra 《Journal of Thermal Analysis and Calorimetry》1992,38(9):1949-1957
A general mathematical treatment for heat-flux differential scanning calorimetry is given. It combines equations derived for heat transfer in the calorimeter cell with an approach to the solidification of metal or alloy carried out in this type of instrument. The differences are discussed between temperature evolution, kinetics of latent heat and undercooling evolution within the sample, and temperature evolution, recorded signal and measured undercooling at the monitoring station.
Zusammenfassung Es wird ein allgemeine mathematische Behandlung von Wärmefluß-DSC gegeben. Es verbindet Gleichungen für den Wärmetransport in der Kalorimeterzelle mit einer Annäherung der Verfestigung von Metall oder Legierung, die in diesem Gerätetyp durchgeführt werden. Es werden die Unterschiede zwischen: Temperaturevolution, Kinetik latenter Wärme und Unterkühlungsevolution innerhalb der Probe und zwischen: Temperaturevolution, aufgezeichnetes Signal und gemessene Unterkühlung an der Monitorstation diskutiert.相似文献
17.
The results of determination of activation energies (EA) of polymeric cable insulations obtained by conventional methods (usually based on the evaluation of changes of mechanical
properties of insulations after their ageing in thermal chamber at different temperatures) have been compared with results
obtained by methods employing the differential scanning calorimetry (DSC). Three DSC methods have been tested: the method
according the ASTM E 698; measuring of DSC characteristics in the isothermal mode at several different temperatures; and the
method based on evaluation of DSC characteristics of insulations after their thermal ageing in thermal chamber. The last method
— which can be called as a modified conventional method, because instead of mechanical properties, the DSC characteristics
are determined — has been found as most acceptable and giving similar values of EA as the other conventional methods.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
Different
methods have been used by various workers to determine the activation energy
of thermal crystallization (Ec)
in chalcogenide glasses using non-isothermal DSC data. In the present work,
the crystallization kinetics of two important binary alloys Se80Te20
and Se80In20 is studied using
non-isothermal DSC data. DSC scans of these alloys have been taken at five
different heating rates. The values of activation energy of crystallization
(Ec) have been determined
by four different methods, i.e., Kissinger's method, Matusita-Sakka
method, Augis-Bennett's method and Ozawa's method, have
been used to calculate Ec.
The results obtained have been compared with each other to see the effect
of using different methods in the determination of Ec. 相似文献
19.
Degradation of polymeric materials used in nuclear power plants (NPP), especially polymeric cable insulation materials, in
the course of their service can be monitored by measuring their properties by DSC, mainly oxidative induction time — OIT.
The studied materials were in-laboratory aged by applying main stressors that act in NPP — ionising radiation and temperature.
The dependence of OIT on radiation and thermal degradation of polymeric material was determined. The OIT values have been
compared to elongation at break as a property that directly reflects the functionality of the studied material. The comparison
of monitored OIT of real cable samples taken from NPP with dependencies on how the OIT values change with the elongation at
break, makes possible to establish the extent of cable degradation. This method can be considered as a suitable and effective
technique for lifetime assessment not only of cable insulations but also of many other plastics.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
DSC曲线各特征点的物理意义以及相变热焓的广义Speil公式的推导 总被引:1,自引:0,他引:1
按目前差示扫描量热法(DSC)公认的Gray-Speil理论,由于对实际的过程过于简化,以致不能很好地解释DSC曲线上的每个特征点;就相变前后试样的热容量发生改变的普遍情况下,如何定量计算相变潜热,目前尚未有严格的计算理论。本文对差示扫描量热法的基本理论做了一些较深入的探索,通过考虑容器及试样内存在温度梯度这一实际情况,成功地解释了实际DSC曲线上各个特征点具体的物理意义,并就相变前后试样的热容量发生变化且热容量是温度的函数这一普遍情况,推广出广义的Speil公式和热焓计算的普遍法则,得到了与实验更加接近的结果。 相似文献