共查询到20条相似文献,搜索用时 281 毫秒
1.
The formation process of bayerite, from an aqueous solution of sodium aluminate through enforced decomposition of aluminate
ions by introducing CO2 gas and aging with mechanical stirring, was investigated by pH measurements of the mother solution during preparation reaction
and characterization of precipitates obtained at various stages of preparation. An amorphous precipitate, produced initially
by the reaction of introduced CO2, transformed to bayerite via pseudoboehmite during aging. It was found that the crystalline particle size and morphology
of the crystallized bayerite change depending systematically on the preparation conditions. The reaction pathway of the thermal
decomposition of the synthesized bayerite was investigated by using thermoanalytical techniques.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Effect of mechanical grinding of hydromagnesite on the reaction pathway and kinetic behaviors of the thermal decomposition
process was investigated by means of thermoanalytical techniques, together with crystallographic and morphological measurements.
A crystalline hydromagnesite, the as-received sample, was decomposed in two distinguished mass loss steps of overlapped dehydration-dehydroxylation
and dehydroxylation-decarbonation via an amorphous intermediate of carbonate compound. Thermal decomposition of an amorphous
hydromagnesite, obtained by mechanical grinding of the as-received sample, was characterized by three well-separated decomposition
processes of dehydration, dehydroxylation and decarbonation. The kinetic behaviors of the respective decomposition steps were
estimated separately using a mathematical deconvolution of the partially overlapped reaction steps. From the formal kinetic
analyses of the respective reaction processes, it was revealed that the dehydration and dehydroxylation processes indicate
the decelerate rate behaviors controlled by diffusion, while the rate behavior of nucleation limited type is predominant for
the decarbonation process. 相似文献
3.
H. Geßwein A. Pfrengle J. R. Binder J. Haußelt 《Journal of Thermal Analysis and Calorimetry》2008,91(2):517-523
The oxidation kinetics of Zr-disilicide (ZrSi2) powders up to temperatures of 1550°C were studied in flowing air using non-isothermal and isothermal thermogravimetric (TG)
analysis. During the oxidation process two main thermal events were detected. The first stage of the oxidation reaction leads
to the formation of elemental silicon as an intermediate reaction product. Upon further temperature increase the newly formed
silicon is oxidized. Completely oxidized ZrSi2 samples consist of ZrSiO4, amorphous and crystalline SiO2 as well as some residual ZrO2. The experimental TG data were analysed with a model-fitting kinetic method. The gas-solid reaction is complex and can best
be fitted with a multi-step reaction scheme consisting of branching reactions based on 3D diffusion mechanisms and a fractal
order reaction. 相似文献
4.
The reaction pathway of the thermal decomposition of synthetic brochantite, Cu4(OH)6SO4, to copper(II) oxide was investigated through the detailed kinetic characterization of the thermal dehydration and desulferation processes. The dehydration process was characterized by dividing into two overlapped kinetic processes with a possible formation of an intermediate compound, Cu4O(OH)4SO4. The dehydrated sample, Cu4O3SO4, was found first to be amorphous by means of XRD, followed by the crystallization to a mixture of CuO and CuO-CuSO4 at around 776 K. The specific surface area and the crystallization behaviour of the amorphous dehydrated compound depend largely on the dehydration conditions. The thermal desulferation process is influenced by the gross diffusion of the gaseous product SO3, which is governed by the advancement of the overall reaction interface from the top surface of the sample particle assemblage to the bottom. 相似文献
5.
A. I. Kazakov Yu. I. Rubtsov G. B. Manelis L. P. Andrienko 《Russian Chemical Bulletin》1998,47(1):39-45
The kinetic regularities of the thermal decomposition of dinitramide in aqueous solutions of HNO3, in anhydrous acetic acid, and in several other organic solvents were studied. The rate of the decomposition of dinitramide
in aqueous HNO3 is determined by the decomposition of mixed anhydride of dinitramide and nitric acid (N4O6) formed in the solution in the reversible reaction. The decomposition of the anhydride is a reason for an increase in the
decomposition rates of dinitramide in solutions of HNO3 as compared to those in solutions in H2SO4 and the self-acceleration of the process in concentrated aqueous solutions of dinitramide. The increase in the decomposition
rate of nondissociated dinitramide compared to the decomposition rate of the N(NO2)2
− anion is explained by a decrease in the order of the N−NO2 bond. The increase in the rate constant of the decomposition of the protonated form of dinitramide compared to the corresponding
value for neutral molecules is due to the dehydration mechanism of the reaction.
For Part 1, see Ref. 1.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 41–47, January, 1998. 相似文献
6.
By means of TG, the thermal decomposition of the powdered CaCO3 was tested with its various dispersities, range of size, and the different content of CO2 in flowing nitrogen. Formulae for calculating the rate and time of decomposition were obtained. 相似文献
7.
Fabiana S. Felix L. C. Cides da Silva L. Angnes J. R. Matos 《Journal of Thermal Analysis and Calorimetry》2009,95(3):877-880
The thermal decomposition of salbutamol (β2 — selective adrenoreceptor) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry
(TG/DTG). It was observed that the commercial sample showed a different thermal profile than the standard sample caused by
the presence of excipients. These compounds increase the thermal stability of the drug. Moreover, higher activation energy
was calculated for the pharmaceutical sample, which was estimated by isothermal and non-isothermal methods for the first stage
of the thermal decomposition process. For isothermal experiments the average values were E
act=130 kJ mol−1 (for standard sample) and E
act=252 kJ mol−1 (for pharmaceutical sample) in a dynamic nitrogen atmosphere (50 mL min−1). For non-isothermal method, activation energy was obtained from the plot of log heating rates vs. 1/T in dynamic air atmosphere (50 mL min−1). The calculated values were E
act=134 kJ mol−1 (for standard sample) and E
act=139 kJ mol−1 (for pharmaceutical sample). 相似文献
8.
B. L. Korsounskii V. V. Nedel'ko N. V. Chukanov T. S. Larikova F. Volk 《Russian Chemical Bulletin》2000,49(5):812-818
Thermal decomposition of hexanitrohexaazaisowurtzitane (HNIW) in the solid state and in solution was studied by thermogravimetry,
manometry, optical microscopy, and IR spectroscopy. The kinetics of the reaction in the solid state is described by the first-order
equation of autocatalysis. The rate constants and activation parameters of HNIW thermal decomposition in the solid state and
solution were determined. The content of N2 amounts to approximately half of the gaseous products of HNIW thermolysis. The thermolysis of HNIW and its burning are accompanied
by the formation of a condensed residue. During these processes, five of six nitro groups of the HNIW molecule are removed,
and one NO2 group remains in the residue, which contains amino groups and no C−H bonds.
Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 815–821, May, 2000. 相似文献
9.
Tongshan Sun Yuting Zhao Jaihui Jin Daqing Wang 《Journal of Thermal Analysis and Calorimetry》1995,45(1-2):317-327
Four complexes of rare earth bromides with amino acids, REBr3·3L·3H2O (RE=La, Nd;L=glycine or alanine) were prepared and characterized by means of chemical analysis, elemental analysis, molar conductivity, thermogravimetry, IR spectra and X-ray diffraction. Their thermal decomposition kinetics from ambient temperature to 500°C were studied by means of TG-DTG techniques under non-isothermal conditions. The kinetic parameters (activation energyE and pre-exponential constantA) and the most probable mechanisms of thermal decomposition were obtained by using combined differential and integral methods. The thermal decomposition processes of these complexes are distinguished as being of two different types, depending mainly on the nature of the amino acid. 相似文献
10.
Controlled rate thermal analysis of hydromagnesite 总被引:1,自引:0,他引:1
Veronika Vágvölgyi R. L. Frost M. Hales A. Locke J. Kristóf Erzsébet Horváth 《Journal of Thermal Analysis and Calorimetry》2008,92(3):893-897
The reaction of magnesium minerals such as brucite with CO2 is important in the sequestration of CO2. The study of the thermal stability of hydromagnesite and diagenetically related compounds is of fundamental importance to
this sequestration. The understanding of the thermal stability of magnesium carbonates and the relative metastability of hydrous
carbonates including hydromagnesite, artinite, nesquehonite, barringtonite and lansfordite is extremely important to the sequestration
process for the removal of atmospheric CO2. This work makes a comparison of the dynamic and controlled rate thermal analysis of hydromagnesite and nesquehonite. The
dynamic thermal analysis of synthetic hydromagnesite proves that dehydration takes place in two steps at 135 and 184°C, dehydroxylation
at 412°C and decarbonation at 474°C. Controlled rate thermal analysis shows the first dehydration step is isothermal and the
second quasi-isothermal at 108 and 145°C, respectively. In the CRTA experiment both water and carbon dioxide are evolved in
an isothermal decomposition at 376°C.
CRTA technology offers better resolution and a more detailed interpretation of the decomposition processes of magnesium carbonates
such as nesquehonite via approaching equilibrium conditions of decomposition through the elimination of the slow transfer
of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of
non-isothermal nature reveal partial nesquehonite structure. 相似文献
11.
The thermal decomposition behavior of hard coal fly ash (HCA2), obtained from the combustion of an Australian hard coal in
thermoelectric power plants, in different atmospheres (air, N2 and N2-H2 mixture), was studied using thermogravimetry (TG), infrared-evolved gas analysis (IR-EGA), differential scanning calorimetry
(DSC) and thermodilatometry (DIL) techniques. It was found that changing of the applied atmosphere affects the carbon content
of the ash which results in different thermal decomposition behaviors. In air, the carbon content was oxidized to carbon dioxide
before the decomposition of carbonate. In N2 or in N2-H2 atmospheres, the carbon content acts as a spacer causing a fewer points of contact between calcium carbonate particles, thus
increasing the interface area which results in a decrease of the carbonate decomposition temperature. Following the carbonate
decomposition, the iron oxide content of the ash undergoes a reductive decomposition reaction with the unburned carbon. This
oxidation-reduction reaction was found to be fast and go to completion in presence of the N2-H2 mixture than in the pure nitrogen atmosphere due to the reducing effect of the hydrogen.
The kinetics of the carbonate decomposition step, in air and N2-H2 mixture was performed under non-isothermal conditions using different integral methods of analysis. The dynamic TG curves
obeyed the Avrami-Erofeev equation (A2) in air, and phase boundary controlled reaction equation (R2) in N2-H2 mixture. The change in the reaction mechanism and the difference in the calculated values of activation parameters with the
change of the atmosphere were discussed in view of effect of the atmosphere on the carbon content of the ash. 相似文献
12.
Z. Hong-Kun T. Cao Zh. Dao-Sen X. Wen-Lin W. Ya-Qong Q. Qi-Shu 《Journal of Thermal Analysis and Calorimetry》2007,89(2):531-536
The non-isothermal decomposition kinetics of 4Na2SO4·2H2O2·NaCl have been investigated by simultaneous TG-DSC in nitrogen atmosphere and in air. The decomposition processes undergo
a single step reaction. The multivariate nonlinear regression technique is used to distinguish kinetic model of 4Na2SO4·2H2O2·NaCl. Results indicate that the reaction type Cn can well describe the decomposition process, the decomposition mechanism
is n-dimensional autocatalysis. The kinetic parameters, n, A and E are obtained via multivariate nonlinear regression. The n
th-order with autocatalysis model is used to simulate the thermal decomposition of 4Na2SO4·2H2O2·NaCl under isothermal conditions at various temperatures. The flow rate of gas has little effect on the decomposition of
4Na2SO4·2H2O2·NaCl. 相似文献
13.
Flammersheim H.-J. Weiß D. Opfermann J. R. 《Journal of Thermal Analysis and Calorimetry》2004,77(3):883-892
Reproducible measurements, reliable results and 1st order kinetics for the whole reaction are obtained during the thermal decomposition of dioxetanes only, if inclusions of impurities in commercial sample pans are blocked by additional thick (magnitude of 100 ?m) and close Al2O3 protective layers. As a rule, nearly the same activation parameters are then found both for the decomposition of solvent-free dioxetanes and diluted solutions in several solvents. Mixtures of different dioxetanes in the same solvent contribute independently to the overall heat flow rate.
相似文献14.
Dr. Emilia Wolska 《Monatshefte für Chemie / Chemical Monthly》1976,107(2):349-357
Analysis of the IR spectra reveals that traces of aluminium ions reduce the amount of goethite phase in the products of ageing of amorphous ferric hydroxide. X-ray studies showed that the unit-cell parameters of the hematite decrease during ageing, this decrease ceasing at the composition 0,2 Al2O3· · 0,8 Fe2O3. Electron microscopic examination showed that the hematite grains are always larger in the presence of Al3+. Thermal analysis showed the hydrohematite formed in the presence of 0,03 mole of Al2O3 to be almost anhydrous.In the concentration range 0,2–0,5 mole Al2O3 the processes of ageing show a trend towards the formation of hydrohematite and bayerite, of which the latter could not exist alone at the high ageing temperature. The formation of bayerite is most favoured when the composition is exactly 0,5 Al2O3· · 0,5 Fe2O3, as is proved by IR spectra, X-ray diffraction patterns, differential thermal analysis and electron microscopy. Study of the products of thermal decomposition of such a sample shows that following the decomposition of bayerite no crystalline hydroxide or oxide of aluminium appears until the temperature reaches 900°.When Al3+ predominates in the mixturexAl(OH)3/y
Fe(OH)3 and boehmite is formed, no ferriboehmite can be detected.
Mit 7 Abbildungen 相似文献
Mit 7 Abbildungen 相似文献
15.
Strezov V. Moghtaderi B. Lucas J. A. 《Journal of Thermal Analysis and Calorimetry》2003,72(3):1041-1048
Fears of climate change and increasing concern over the global warming have prompted a search for new, cleaner methods for
electricity power generation. Technologies based on utilising biomass are attracting much attention because biomass is considered
to be CO2 neutral. Co-firing of biomass fuels with coal, for example, is presently being considered as a mean for reducing the global
CO2 emissions. Biomass is also applied in thermal conversion processes to produce fuels with higher calorific values and adsorbents.
In any case, thermal decomposition is essential stage where volatiles and tars are evolved followed by consequent heats of
reactions. In this work sawdust biomass samples were selected in order to study their thermal conversion behaviour. Heats
of decomposition for each sample were measured during continuous heating at a prescribed heating rate under inert atmospheric
conditions. The decomposition generally commenced in all samples at 150°C and was completed at 460°C in a series of endo and
exothermic reactions influenced by its lignin and cellulosic content. Single biomass sample was subjected to heating rates
ranging from 10 to 1000°C min-1 and the effect of heating rate on decomposition was studied. The origin of reactions for each thermal sequence is herein
discussed in detail.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
The kinetics of isothermal decomposition of urea nitrate, an organic secondary explosive with monoclinic structure and chemical formula CO(NH2)2 · HNO3, which melts with decomposition at 152°C, was studied in open air in the temperature range 106-150°C, using a gravimetric method. Gas chromatographic analysis of product gases indicate CO2, N2O and traces of water vapor as product gases. A pasty amorphous product on the basis of wet chemical and infrared analysis was found to be cyanourea. The weight loss-time curve exhibited an acceleratory region extending almost to the end of the main reaction (35% decomposition) and followed a three-dimensional nucleation model obeying the relation x1/3 = K(t—t0 where α = fraction of sample reacted at time t, K = reaction rate constant, and t0 = induction time. On the basis of this model, an enthalpy of activation of 27.6 ± 1.2 kcal/mole was calculated at 95% confidence range. The rate of decomposition was slightly accelerated in He atmosphere and slightly retarded in N2O and CO2 atmospheres, while water vapor drastically reduced the rate. The reaction 3CO(NH2)2 · HNO3 → CNNHCONH2 (cyanourea) + 6H2O+3N2O+CO2 is presented as the most likely one for decomposition of urea nitrate in open air. 相似文献
17.
Alexandra Ioiţescu Gabriela Vlase T. Vlase N. Doca 《Journal of Thermal Analysis and Calorimetry》2007,88(1):121-125
The kinetics of thermal decomposition
of Ca(H2PO4)2·H2O
under non-isothermal conditions was studied. The TG/DTG curves were obtained
at five heating rates: 5, 7, 10, 12 and 20 K min–1.
The kinetic analysis was performed by means of three methods: Friedman,
Budrugeac–Segal and NPK by Sempere and Nomen. An important dependence
of the activation energy vs. the conversion
degree was observed and also a compensation effect. The decomposition consists
of water loss and is due to the elimination of crystallization water and an
intermolecular condensation, respectively. 相似文献
18.
M. A. Mohamed S. A. Halawy M. M. Ebrahim 《Journal of Thermal Analysis and Calorimetry》1994,41(2-3):387-404
The non-isothermal decomposition of cobalt acetate tetrahydrate was studied up to 500°C by means of TG, DTG, DTA and DSC techniques
in different atmospheres of N2, H2 and in air. The complete course of the decomposition is described on the basis of six thermal events. Two intermediate compounds
(i.e. acetyl cobalt acetate and cobalt acetate hydroxide) were found to participate in the decomposition reaction.
IR spectroscopy, mass spectrometry and X-ray diffraction analysis were used to identify the solid products of calcination
at different temperatures and in different atmospheres. CoO was identified as the final solid product in N2, and Co3O4 was produced in air. A hydrogen atmosphere, on the other hand, produces cobalt metal. Scanning electron microscopy was used
to investigate the solid decomposition products at different stages of the reaction. Identification of the volatile gaseous
products (in nitrogen and in oxygen) was performed using gas chromatography. The main products were: acetone, acetic acid,
CO2 and acetaldehyde. The proportions of these products varied with the decomposition temperature and the prevailing atmosphere.
Kinetic parameters (e.g.E and lnA) together with thermodynamic functions (e.g. °H, C
p and °S) were calculated for the different decomposition steps.
In celebration of the 60th birthday of Dr. Andrew K. Galwey 相似文献
19.
Research of thermal decomposition kinetic characteristic of emulsion explosive base containing Fe and Mn elements 总被引:1,自引:0,他引:1
X. H. Wang X. J. Li H. H. Yan Y. D. Qu G. L. Sun X. H. Xie Y. J. Zhang 《Journal of Thermal Analysis and Calorimetry》2008,91(2):545-550
The kinetic characteristic of thermal decomposition of the Emulsion Explosive Base Containing Fe and Mn elements (EEBCFM)
which was used to prepare nano-MnFe2O4 particles via detonation method was investigated by means of non-isothermal DSC and TG methods at various heating rates of
2.5, 5 and 7.5°C min−1respectively under the atmosphere of dynamic air from room temperature to 400°C.
The results indicated that the EEBCFM was sensitive to temperature, especially to heating rate and could decompose at the
temperature up to 60°C. The maximum speed of decomposition (dα/dT)m at the heating rate of 5 and 7.5°C min−1 was more than 10 times of that at 2.5°C min−1 and nearly 10 times of that of the second-category coal mine permitted commercial emulsion explosive (SCPCEE). The plenty
of metal ions could seriously reduce the thermal stability of emulsion explosive, and the decomposition reaction in the conversion
degree range of 0.0∼0.6 was most probably controlled by nucleation and growth mechanism and the mechanism function could be
described with Avrami-Erofeev equation with n=2. When the fractional extent of reaction α>0.6, the combustion of oil phase primarily controlled the decomposition reaction. 相似文献
20.
R. Nikolic S. Zec V. Maksimovic S. Mentus 《Journal of Thermal Analysis and Calorimetry》2006,86(2):423-428
This study reports experimental investigations by non-isothermal TG/DSC
analysis of Zn(NO3)2·4H2O,
Cu(NO3)2·4H2O
and their mixtures of known compositions in the temperature range 30–1200°C.
Solid/liquid transitions in the sealed samples of the hexahydrate salts and
their mixtures were also studied by DSC in the temperature range 0–60°C.
The mixture with composition 0.85Zn(NO3)2·6H2O+0.15Cu(NO3)2·6H2O showed single
melting peak at 29°C. This mixture was chosen for detailed studies. Melting
temperature and heat of fusion of single salt hexahydrates and of the mixture
were calculated from DSC endotherms.
The different stages in the
thermal decomposition processes have been established. The intermediate and
the final solid products of the thermal decomposition were analyzed by XRD.
The scheme and the decomposition temperature depended on the composition of
the starting material. The final decomposition products were CuO (monoclinic),
Cu2O (cubic), ZnO (hexagonal) and their mixtures with
the defined crystalline structures. Possible influence of the addition of
CuCl2·2H2O into the mixture
0.85Zn(NO3)2·6H2O+0.15Cu(NO3)2·6H2O and a gel combustion technique of the
precursor preparation, on the composition and morphology of the solid decomposition
products, were also studied. The gel combustion technique, using citric acid
added to a mixture of 0.85Zn(NO3)2·6H2O+0.15Cu(NO3)2·6H2O, was applied
in an attempt to obtain mixed Zn/Cu oxides of a particular mole ratio. The
morphology of the solid decomposition products was examined by SEM. 相似文献