共查询到20条相似文献,搜索用时 46 毫秒
1.
Influence of γ-irradiation, 0.1–0.75 MGy on the thermal decomposition of (BaC2O4+CuO, 10 mol%) mixture has been studied between the temperature range 678-718 K. It is evident from ‘α-f’ plots that decomposition of both unirradiated and irradiated mixtures follows: (i) initial gas evolution (initial puff of gas), (ii) acceleratory and (iii) decay periods. Irradiation promotes the initial gas evolution (α1), decreases the fractional decomposition (α), the effect being higher at lower doses, without altering the nature of the isotherms. But these effects increase with increasing radiation dose. Analysis of the kinetic data in the light of theories of various kinetic models are found to be well fitted to Prout-Tompkins, Avrami-Erofeyev and contracting square mechanisms. It is found that irradiation diminishes the rate of reaction of both the periods and decreases the energy of activation of the acceleratory stage without affecting the same in the decay period. Plausible mechanism of decomposition and the effect of γ-irradiation thereon has been discussed in detail. 相似文献
2.
P. J. Herley C. S. Wang G. Varsi P. W. Levy 《Journal of Thermal Analysis and Calorimetry》1994,41(2-3):435-448
The thermal decomposition kinetics of irradiated and unirradiated ammonium perchlorate and ammonium perchlorate powder-aluminum
particle mixtures has been studied by determining decomposition gas pressurevs. heating time with samples at a controlled temperature Qualitatively the radiation induced changes are similar to those obtained
in previous studies on ‘pure’ ammonium perchlorate. The induction period is shortened and the acceleratory and decay period
rate constants are increased. The data have been analyzed using Avrami-Erofeev kinetics. The results for pure unirradiated
material are in accord with published results. The activation energies for the induction, acceleratory and decay periods for
pure pellets were found to be 133.5±6.7, 131.8±6.7 and 127.2±6.7 kJ·mol, respectively. Samples were exposed to either a single
gamma-ray irradiation, fission neutron irradiation followed by a gamma-ray irradiation, or to a proton irradiation. When compared
on an equal energy deposited basis, the fast neutron induced changes are appreciably larger than the gamma-ray changes. However,
the proton induced changes are comparable or slightly more than the gamma-ray effects. Some, or all, of the fast neutron effects
can be attributable to the concentrated radiation damage ‘spikes’ along the path of lattice atom recoils. It is likely that
these become thermal decomposition sites when the crystals are heated. Protons create fewer spikes than fast neutrons. Overall,
the results indicate that any ammonium perchlorate-aluminum propellant mixtures that may be exposed to radiation environments,
such as used in this study, should be subjected to a thorough radiation effects analysis if reliable performance is required.
In celebration of the 60th birthday of Dr. Andrew K. Galwey 相似文献
3.
The effect of -irradiation (1.0–4.0 MGy) on the thermal decomposition of barium oxalate hemihydrate has been studied at 723K by a gas evolution method. Decomposition isotherms of unirradiated and irradiated crystals are characterized by (i) rapid initial gas evolution, (ii) acceleratory and (iii) decay stages. Irradiation enhances the rate of decomposition without altering the mechanism of the process, the effect being higher at higher irradiation doses. The analysis of the data reveal that the two-dimensional phase boundary reaction model gives the best fit to the results. 相似文献
4.
S. M. K. Nair T. S. Sahirsh Kumar 《Journal of Radioanalytical and Nuclear Chemistry》1990,146(5):301-310
The thermal decomposition of unirradiated and -irradiated lead nitrate was studied by the gas evolution method. The decomposition proceeds through initial gas evolution, a short induction period, an acceleratory stage and a decay stage. The acceleratory and decay stages follow the Avrami-Erofeyev equation. Irradiation enhances the decomposition but does not affect the shape of the decomposition curve. 相似文献
5.
Catalytic activity of rare earth oxides (REO); La2O3, Sm2O3, Gd2O3 and Ce2O3 on the isothermal decomposition of barium oxalate has been studied at 723 K. The α?t plots for pure salt as well as mixtures indicate that the process follows: initial gas evolution, a short acceleratory and a long decay stages. The results of the kinetic analysis show that Prout-Tompkins relationship and two-dimensional phase boundary reaction give best fit of the data for both pure salt as well as mixtures. The rate constants of acceleratory and decay periods are enhanced remarkably by adding REO admixtures and their catalytical activity is in the order La2O3>Sm2O3>Gd2O3 >Ce2O3. The plausible mechanism of decomposition and the role of admixture there on has been discussed in the light of electron transfer process. 相似文献
6.
Barium bromate decomposes in the solid state through various stages: (i) initial gas evolution, (ii) induction period, (iii) slow linear reaction, (iv) acceleratory and decay stages. Rare earth semiconductors (p-type), Gd2O3 and Dy3O3 facilitate the acceleratory and decay stages without affecting the induction and linear periods. The extent of decomposition is higher in the case of mixture than that of the pure salt. The data are discussed in the light of theories of Prout—Tompkins and Avarami-Erofeev mechanisms exploring that nucleation occurs in a chain branching manner and there is two dimensional growth of nuclei.
Zusammenfassung Bariumbromat zersetzt sich im festen Zustand über verschiedene Schritte: (i) anfängliche Gasentwicklung, (ii) Induktionsperiode, (iii) langsame lineare Reaktion, (iv) Beschleunigungs- und Abschlußschritt. Seltenerdenhalbleiter (vomp-Typ) erleichtern die Beschleunigungs- und Abschlußschritte, ohne die Induktions- und die lineare Periode zu beeinflussen. Das Ausmaß der Zersetzung ist im Falle von Gemischen höher als bei reinen Salzen. Die Angaben wurden im Hinblick auf die Mechanismentheorien von Prout-Tompkins und Avarami-Erofeev besprochen, die besagen, daß die Keimbildung auf kettenverzweigende Weise erfolgt und daß ein zweidimensionales Keimwachstum stattfindet.相似文献
7.
Role ofγ-irradiation and Ba2+ doping on the isothermal decomposition of caesium bromate has been investigated gasometrically. It is seen that decomposition proceeds in a molten/semi-molten state presumably due to formation of an eutectic between the product bromide and the host material, i.e., bromate. The process exhibits stages: (i) initial gas evolution (initial puff) (ii) short acceleratory and (iii) long decay. The data are analysed in the light of theories of different kinetic models like Prout-Tompkins, Avrami-Erofeev and explore that irradiation as well as doping enhance decomposition. 相似文献
8.
Structural defects were introduced into the potassium bromate (PB) lattice in the form of SO2−
4 and Cl− ions in the process of crystal growth. It was assumed that these doped crystals PB(Cl−) and PB(SO2−
4) are composed of a two phase system, one being the perfect PB lattice and the other distorted regions due to induced defects.
Isothermal decomposition of doped and normal PB samples was carried out gasometrically between the temperature range 653–663
K. The α-t plots reveal that the process occurs through initial gas evolution, acceleratory and decay stages. It also confirmed
that doping enhances the rate of the reaction, the effect being more pronounced in the case of PB(SO2−
4). The data are found to be well fitted to the Prout-Tompkins and Avrami-Erofe'ev mechanisms.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Ms. S. Mishra K. K. Sahu D. Bhatta 《Journal of Radioanalytical and Nuclear Chemistry》1994,177(2):357-363
Decomposition of barium perchlorate occurs through various stages: (i) initial gas evolution, (ii) induction period, (iii) short acceleratory, and (iv) long decay. Effect of pre-irradiation with60Co -rays (5 to 100 Mrad) on the decomposition process between 703.0 to 733.0 K shows that irradiation reduces the duration of induction periodI to the onset of reaction conforming to the relation:I=C
1-C2 log dose. The experimental data forI are very close to the theoretical values obtained by using the induction period-dose relationship. The topochemical aspects of the validity of the above relation has been considered to be due to the linear growth of nuclei during irradiation and subsequent exponential growth during the induction period. Irradiation enhances the rate of reaction in the acceleratory stage but decreases the duration of the decay period. 相似文献
10.
Anbalagan G. Rajakumar P. R. Gunasekaran S. 《Journal of Thermal Analysis and Calorimetry》2009,97(3):917-921
Single crystals of pure and neodymium doped calcium hydrogen phosphate were grown in sodium meta silicate gels, by the single
diffusion gel method. Platelet and needle shaped crystals were obtained. The grown crystals were characterized by different
techniques. The thermal behaviour of the crystals was studied using the thermo analytical techniques, which included TG, DTA,
DTG and DSC. These studies reveal that the decomposition of the material occurs in one or more stages. The enthalpy value
is also calculated. 相似文献
11.
Shivani Suri K. K. Bamzai Vishal Singh 《Journal of Thermal Analysis and Calorimetry》2011,105(1):229-238
Non-isothermal kinetic parameter of pure and cadmium-doped barium phosphate single crystal grown by room temperature solution
technique have been investigated. Single crystal X-ray diffraction establishes grown crystal to be orthorhombic in nature.
Scanning electron microscopy supplemented with energy dispersive X-ray analysis was used to study the surface features and
to find the exact stoichiometric composition of the grown crystal. Fourier transform infrared spectroscopy studies confirm
the presence of various functional groups. The effect of cadmium doping on pure barium phosphate single crystal was studied
using thermogravimetry analysis. Thermogravimetry studies shows that the pure crystal was stable up to a temperature of 330 °C
whereas doped crystal was stable up to a temperature of 240 °C, i.e., pure crystals were more stable than doped ones. Various
solid-state reaction kinetics, i.e., activation energy (E
a), frequency factor (Z), and entropy (ΔS*) was calculated out to find the mechanism of thermal decomposition at different stages for pure and cadmium doped barium
phosphate. 相似文献
12.
S. Parthiban H. Anandalakshmi S. Senthilkumar V. Karthikeyan S. C. Mojumdar 《Journal of Thermal Analysis and Calorimetry》2012,108(3):881-885
We have prepared pure and divalent vanadyl ion-doped magnesium rubidium sulfate hexahydrate crystals by using slow evaporation solution growth technique. It is interesting to observe that Vo(II) doping influences the physical properties of MRSH. Presence of Vo(II) ions in the doped specimen was confirmed by energy dispersive spectroscopy and electron paramagnetic resonance spectroscopy. FTIR studies reveal that the doping of vanadium ion has not altered the basic structure of MRSH. Scanning electron microscope studies of doped sample reveals that structure defect centers are formed in the crystals. Gradual decomposition patterns were observed for pure and doped specimens in thermogravimetry and differential thermogravimetry. The grown crystals were also characterized by powder X-ray diffraction. The second harmonic generation efficiency tested using Kurtz powder technique is not influenced by the added dopant. 相似文献
13.
El-Said N. Sayed M. S. Mikhail A. S. 《Journal of Thermal Analysis and Calorimetry》2000,63(2):525-532
The thermal stability of solidified NaNO3 salts in bitumen and cement has been investigated for safety considerations in the field of solidification of radioactive
waste. The thermal decomposition of bitumen and cement in presence of NaNO3 in a temperature range 22–650°C has been studied. The fraction decomposed of the pure samples and mixtures showed slow linear
reactions followed by acceleratory and decay stages. Data are analyzed according to both Freeman-Carroll and Coats-Redfern
kinetics to evaluate the activation energy and the order of reactions of all mixtures. It is found that the activation energies
of bitumen and cement were 594 and 203 kJ mol-1, respectively. The order of reactions of bitumen and cement was 2 and 4, respectively. The addition of NaNO3 shortens the duration of the induction period in all mixtures. It was concluded that solidification of radioactive waste
containing NaNO3 in bitumen and cement should be applied in the temperature range 22–300°C. At temperature higher than300°C
solidification should be in cement.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
Yuriy Garbovskiy 《Liquid crystals》2017,44(6):948-955
Typically, ionic species in thermotropic liquid crystals are nearly fully ionised. Therefore, the concentration of mobile ions practically does not depend on the temperature. Interestingly, the same liquid crystals doped with nanoparticles exhibit totally different behaviour. The concentration of mobile ions become temperature dependent. This paper reports the effects of the temperature on the concentration of ions in liquid crystal nanocolloids. Liquid crystals doped with both 100% pure and contaminated nanoparticles are considered. Regardless the ionic purity of nanodopants, the concentration of mobile ions in liquid crystal nanocolloids increases towards the saturation as their temperature goes up. The magnitude of this saturation level equals the initial concentration of ions in liquid crystals doped with 100% pure nanoparticles. The temperature induced release of ions by contaminated nanoparticles in liquid crystals increases the above-mentioned saturation level. While the dispersion of 100% pure nanoparticles in liquid crystals leads to the temperature-dependent purification only, the use of contaminated nanoparticles results in the temperature-driven switching between the purification and contamination regimes enabling thermal control of ions. 相似文献
15.
Catalytic activities exerted by the lanthanide oxides Ln2O3 (Ln=La, Sm, Gd and Dy) (0.25 mol%) on the thermal decomposition of barium perchlorate were studied gasometrically at 718 K. The
α vs. t plot for the salt alone displays (i) initial gas evolution (ii) an induction period, (iii) a short acceleratory stage and
(iv) a long decay stage. For the mixtures with Ln2O3, phenomena (i) and (ii) are not observed. Ln2O3 enhances the rate of reaction in both the acceleratory and the decay stage, and increases the fraction decomposed, α, in
the sequence La2O3>Gd2O3>Sm2O3,>Dy2O3.
The influence of Dy2O3 (0.25–2.0 mol%) on the decomposition of Ba(ClO4)2 at 718 K indicates that such admixture facilitates the process and the effect increases with increasing concentration.
The salt alone and the mixtures decompose through the same stages in the temperature range 703–733 K as at 718 K. The data
on both types of samples fit well to the Prout-Tompkins and the Avrami-Erofeev mechanism, suggesting that nucleation takes
place in a chain-branching manner and that the two-dimensional growth of the nuclei occurs during the process. Admixture enhances
the rate of reaction marked without affecting the energy of activation
.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
Single crystals of pure triglycine sulfate (TGS) and potassium chloride (KCl)-doped TGS with different concentrations (0.2, 0.4, 0.6, and 1?mol%) were grown from aqueous solutions by natural evaporation process at room temperature. Thermal stability of the grown crystals was investigated by differential thermal analysis (DTA) and thermogravimetric (TG) studies. DTA curve shows a lower decomposition temperature for KCl-doped TGS crystal than that of pure TGS crystal. The dielectric properties of pure TGS and KCl-doped TGS crystals were performed in the frequency range of 1?C500?kHz at 30?°C and this study showed that the dielectric constant was increased due to KCl concentration. DC electrical conductivity measurements were made in the temperature range from 35 to 100?°C and showed that the DC conductivity was increased with the increase of temperature as well as doping concentrations of KCl. The etching feature of the surface of the grown crystals was studied in water etchant. 相似文献
17.
A. Ortiz S. Ramos-Bernal A. Negrón-Mendoza T. Martínez G. Sanchez-Mejorada 《Journal of Radioanalytical and Nuclear Chemistry》2007,273(3):573-575
The thermoluminescense (TL) behavior of solid solutions of cadmium and manganese doped single crystals under γ-irradiation
is reported. Various compositions of single crystals of NaCl doped with Cd2+ and Mn2+ have been irradiated with ionizing radiation. The increase in the glow curve was followed as a function of the F-centers
produced by the dose. The analysis shows the potential use of these materials as dosimeters. 相似文献
18.
19.
A. M. Amorim da Costa A. M. Amado M. Becucci Carola Kryschi 《Journal of Molecular Structure》1997,416(1-3):69-73
Phase transition in crystalline pure p-terphenyl and p-terphenyl: tetracene doped crystals was studied with Raman spectroscopy, for temperatures from 295 to 10 K. In particular, the torsional Raman vibrational mode with a “hard-core frequency” of 230.8 cm−1 was investigated in its frequency and bandwidth dependence upon temperature. The results were analyzed based on an order-disorder model allowing the determination of the activation energies and orientational correlation times of the molecular diffusive process in the monoclinic (above 193 K) and triclinic (below 193 K) phases of the crystals. The activation energy is observed to decrease from the monoclinic to the triclinic phase, whereas the orientational correlation times increase, both in the undoped and the doped crystals. The doping of p-terphenyl with tetracene appears to affect the activation energy and the orientational correlation times in a different way in each phase. 相似文献
20.
The oxidation of pure V(2)O(3) and Pd/V(2)O(3) films was studied by Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED) in the temperature range 673-773 K. Thin films of V(2)O(3) were prepared by reactive deposition of V metal in 10(-2) Pa O(2) on NaCl(001) cleavage faces. Pd particles were epitaxially grown on NaCl(001) and subsequently embedded in V(2)O(3). Oxidation of both pure V(2)O(3) and Pd/V(2)O(3) at 673 K transforms V(2)O(3) into a platelet-like V(2)O(5) structure. At temperatures T>or= 773 K, a reconstruction of the platelet-like V(2)O(5) structure into an array of oblong and needle-type V(2)O(5) nanocrystals of different size occurs. Subsequent reduction of the so-prepared structures in 1 bar H(2) at 573-673 K results in the formation of the cubic VO phase, whereby the external shape of the original crystals is partially maintained. Upon oxidation at 723 K, Pd is transformed into PdO, but its formation is suppressed in comparison with Pd supported on Al(2)O(3) and occurs only at an about 100 K higher temperature than on Pd/Al(2)O(3). The Pd particles are stabilized against oxidation up to 673 K, PdO decomposes upon reduction in hydrogen between 573 and 673 K. 相似文献