共查询到20条相似文献,搜索用时 31 毫秒
1.
2.
Pontes F. M. L. Oliveira S. F. Espínola J. G. P. Arakaki L. N. H. Fonseca M. G. Airoldi C. 《Journal of Thermal Analysis and Calorimetry》2004,75(3):975-988
Solid adducts SbX3·L-pic (X=Cl, I and L=α-, β- and γ-picolines) were synthesized and characterized by elemental analysis, 1H and 13C NMR, IR spectroscopy and thermal analysis. The infrared spectroscopy and the magnetic resonance for 1H and 13C nuclei of these compounds suggest that the ligands coordinate through nitrogen atom. Kinetic studies were accomplished by
means of thermogravimetric data, through isothermal and non-isothermal techniques. The best adjusting models for adducts thermal
decomposition were R1 for isothermal and R1 and R2 for the non-isothermal methods. The energy of activation values obtained by isothermal method indicate the following orders
of thermal stability for adducts: i) SbCl3·α-pic>SbCl3·β-pic>SbCl3·γ-pic and ii) SbI3·β-pic>SbI3·γ-pic>SbI3·α-pic. The activation energy values obtained by non-isothermal were higher than those from isothermal methods, showing the
order of stability:iii) SbCl3·α-pic<SbCl3·β-pic<SbCl3·γ-pic and iv) SbI3·β-pic>SbI3·α-pic=SbI3··γ-pic. These obtained data through R1 model presented the kinetic compensation effect for trichloride adducts, which could be associated to both isothermal and
non-isothermal processes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
An extracellular thermostable α-galactosidase producing Aspergillus terreus
GR strain was isolated from soil sample using guar gum as sole source of carbon. It was purified to apparent homogeneity by
acetone precipitation, gel filtration followed by DEAE-Sephacel chromatographic step. The purified enzyme showed a single
band after sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The molecular weight of the purified enzyme
after SDS-PAGE was 108 kDa. The enzyme showed optimum pH and temperature of 5.0 and 65 °C, respectively, for artificial substrate
pNPαGal. α-Galactosidase from A. terreus
GR is found to be thermostable, as it was not inactivated after heating at 65 °C for 40 min. The K
m for pNPαGal, oNPαGal, raffinose, and stachyose are 0.1, 0.28, 0.42, and 0.33 mM, respectively. Inhibitors such as 1,10-phenanthroline,
phenylmethylsulfonyl fluoride, ethylenediaminetetraacetic acid, mercaptoethanol, and urea have no effect, whereas N-bromosuccinamide inhibited enzyme activity by 100%. Among metal ions tested, Mg2+, Ni2+, Ca2+, Co2+, and Mn2+ had no effect on enzyme activity, but Ag+, Hg2+, and Cu2+ have inhibited complete activity. 相似文献
4.
Gabriela Vlase T. Vlase Ramona Tudose Otilia Costişor N. Doca 《Journal of Thermal Analysis and Calorimetry》2007,88(3):637-640
Kinetics of thermal decomposition of three structurally similar complexes Co2Cu(C2O4)3 (R-diam)2, where R is ethyl, 1,2-propyl or 1,3-propyl, was studied under non-isothermal conditions and nitrogen dynamic atmosphere at heating
rates of 5, 7, 10, 12 and 15 K min−1.
For data processing the Flynn-Wall-Ozawa and a modified non-parametric kinetic methods were used. By both methods the activation
energy are in the range of 97–102 kJ mol−1. The formal kinetic is r=kα(1−α)2. Also a compensation effect between lnA and E was evidenced. The kinetic analysis lead to the conclusion of an identic decomposition mechanism by a single step process. 相似文献
5.
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
6.
Imre Miklós Szilágyi Eero Santala Mikko Heikkilä Marianna Kemell Timur Nikitin Leonid Khriachtchev Markku Räsänen Mikko Ritala Markku Leskelä 《Journal of Thermal Analysis and Calorimetry》2011,105(1):73-81
This article demonstrates how important it is to find the optimal heating conditions when electrospun organic/inorganic composite
fibers are annealed to get ceramic nanofibers in appropriate quality (crystal structure, composition, and morphology) and
to avoid their disintegration. Polyvinylpyrrolidone [PVP, (C6H9NO)
n
] and ammonium metatungstate [AMT, (NH4)6[H2W12O40]·nH2O] nanofibers were prepared by electrospinning aqueous solutions of PVP and AMT. The as-spun fibers and their annealing were
characterized by TG/DTA-MS, XRD, SEM, Raman, and FTIR measurements. The 400–600 nm thick and tens of micrometer long PVP/AMT
fibers decomposed thermally in air in four steps, and pure monoclinic WO3 nanofibers formed between 500 and 600 °C. When a too high heating rate and heating temperature (10 °C min−1, 600 °C) were used, the WO3 nanofibers completely disintegrated. At lower heating rate but too high temperature (1 °C min−1, 600 °C), the fibers broke into rods. If the heating rate was adequate, but the annealing temperature was too low (1 °C min−1, 500 °C), the nanofiber morphology was excellent, but the sample was less crystalline. When the optimal heating rate and
temperature (1 °C min−1, 550 °C) were applied, WO3 nanofibers with excellent morphology (250 nm thick and tens of micrometer long nanofibers, which consisted of 20–80 nm particles)
and crystallinity (monoclinic WO3) were obtained. The FTIR and Raman measurements confirmed that with these heating parameters the organic matter was effectively
removed from the nanofibers and monoclinic WO3 was present in a highly crystalline and ordered form. 相似文献
7.
Emilio Bustelo Isaac de los Ríos Manuel J. Tenorio M. Carmen Puerta Pedro Valerga 《Monatshefte für Chemie / Chemical Monthly》2000,131(12):1311-1320
Summary. The solid-state tautomerization of the hydrido-alkynyl derivatives [Cp
*RuH(C&*CR)-(dippe)][BPh4] (Cp* = C5Me5; R = SiMe3, Ph, H; dippe = 1,2-bis-(diisopropylphosphino)-ethane) to their vinylidene isomers [Cp
*Ru*C*CHR(dippe)][BPh4] was studied by IR spectroscopy. Characteristic isothermic αvs. t curves for each individual rearrangement process were recorded. Their shape, and hence the isomerization mechanism, depends
strongly on the nature of the substituent R. The kinetic analysis of the above curves using the Avrami-Erofeev provided some mechanistic information about the isomerization process in the solid.
Received July 7, 2000. Accepted August 29, 2000 相似文献
8.
P. E. Plyusnin E. Yu. Semitut I. A. Baidina S. V. Korenev 《Journal of Structural Chemistry》2011,52(2):383-388
The crystal structures of double complex salts [M(NH3)5Br][AuBr4]2·H2O (M = Ir, Rh) are determined by single crystal XRD. The compounds crystallize in the triclinic system, P-1 space group, Z = 4. Crystallographic characteristics: [Ir(NH3)5Br][AuBr4]2·H2O: a = 8.2982(3) ?, b = 15.3045(4) ?, c = 17.4378(6) ?, α = 73.064(1)°, β = 88.938(1)°, γ = 86.221(1)°, V = 2113.95(12) ?3, d
x = 4.419 g/cm3, R = 0.0469; [Rh(NH3)5Br][AuBr4]2·H2O: a = 8.2855(2) ?, b = 15.2881(3) ?, c = 17.4053(4) ?, α = 73.015(1)°, β = 88.913(1)°, γ = 86.267(1)°, V = 2104.08(8) ?3, d
x = 4.165 g/sm3, R = 0.0480. The crystal structure of [Ir(NH3)5Br]Br2 is determined. The compound crystallizes in the orthorhombic system, Pnma space group, Z = 4. Crystallographic characteristics: a = 13.8521(3) ?, b = 10.8570(2) ?, c = 6.9908(1) ?, V = 1049.31(3) ?3, d
x = 3.273 g/cm3, R = 0.0127. 相似文献
9.
Adriana Fuliaş Titus Vlase Gabriela Vlase Nicolae Doca 《Journal of Thermal Analysis and Calorimetry》2010,99(3):987-992
The thermoanalytical curves (TA), i.e. TG, DTG and DTA for pure cephalexin and its mixtures with talc, magnesium stearate,
starch and microcrystalline cellulose, respectively, were drawn up in air and nitrogen at a heating rate of 10 °C min−1. The thermal degradation was discussed on the basis of EGA data obtained for a heating rate of 20 °C min−1. Until 250 °C, the TA curves are similar for all mixtures, up this some peculiarities depending on the additive appears.
These certify that between the pure cephalosporin and the excipients do not exists any interaction until 250 °C. A kinetic
analysis was performed using the TG/DTG data in air for the first step of cephalexin decomposition at four heating rates:
5, 7, 10 and 12 °C min−1. The data processing strategy was based on a differential method (Friedman), an integral method (Flynn–Wall–Ozawa) and a
nonparametric kinetic method (NPK). This last one allowed an intrinsic separation of the temperature, respective conversion
dependence on the reaction rate and less speculative discussions on the kinetic model. All there methods had furnished very
near values of the activation energy, this being an argument for a single thermooxidative degradation at the beginning (192–200 °C). 相似文献
10.
T. Kaljuvee I. Rudjak E. Edro A. Trikkel 《Journal of Thermal Analysis and Calorimetry》2009,97(1):215-221
The effect of heating rate on the thermal behavior of ammonium nitrate (AN) and on the kinetic parameters of decomposition
of AN and its blends with limestone and dolomite was studied on the basis of commercial fertilizer-grade AN and several Estonian
limestone and dolomite samples. Experiments were carried out under dynamic heating conditions up to 900 °C at heating rates
of 2, 5, 10 and 20 °C min−1 in a stream of dry air using Setaram Labsys 2000 equipment. For calculation of kinetic parameters, the TG data were processed
by differential isoconversional method of Friedman. The variation of the value of activation energy E along the reaction progress α showed a complex character of decomposition of AN—interaction of AN with limestone and dolomite
additives with the formation of nitrates as well as decomposition of these nitrates at higher temperatures. 相似文献
11.
L. C. Rodrigues M. M. Silva H. I. M. Veiga J. M. S. S. Esperança M. Costa M. J. Smith 《Journal of Solid State Electrochemistry》2012,16(4):1623-1629
In this paper, the preparation and purification of an amorphous polymer network, poly[oxymethylene-oligo(oxyethylene)], designated
as aPEO, are described. The flexible CH2CH2O segments in this host polymer combine appropriate mechanical properties, over a critical temperature range from −20 to 60 °C,
with labile salt-host interactions. The intensity of these interactions is sufficient to permit solubilisation of the guest
salt in the host polymer while permitting adequate mobility of ionic guest species. We also report the preparation and characterisation
of a novel polymer electrolyte based on this host polymer with lithium tetrafluoroborate, LiBF4, as guest salt. Electrolyte samples are thermally stable up to approximately 250 °C and completely amorphous above room temperature.
The electrolyte composition determines the glass transition temperature of electrolytes and was found to vary between −50.8
and −62.4 °C. The electrolyte composition that supports the maximum room temperature conductivity of this electrolyte system
is n = 5 (2.10 × 10−5 S cm−1 at 25 °C). The electrochemical stability domain of the sample with n = 5 spans about 5 V measured against a Li/Li+ reference. This new electrolyte system represents a promising alternative to LiCF3SO3 and LiClO4-doped PEO analogues. 相似文献
12.
Josiane de Lima Souza Marcelo Kobelnik Clóvis Augusto Ribeiro Jorge Manoel Vieira Capela Marisa Spirandeli Crespi 《Journal of Thermal Analysis and Calorimetry》2009,97(2):525-528
Poly(3-hydroxybutyrate), PHB, has been structurally modified through reaction with hydroxy acids (HA) such as tartaric acid
(TA) and malic acid (MA). The crystallization kinetic of the samples was evaluated by isoconversional method through nonlinear
fitting to obtain the estimation for activation energy (E
a
) and pre-exponential (A) values. The thermal behavior of the crystallization temperature, 44.8 and 58.9 °C at 5 °C/min, and results obtained to the
average activation energy, 73 ± 9 kJ mol−1 and 63 ± 1 kJ mol−1, to PHB/MA and PHB, respectively, are suggesting that malic acid may be deriving plasticizer units from its own PHB chain.
PHB/TA show increase in the medium value of E
a, 119 ± 2 kJ mol−1 and T
c = 48.2 °C (at 5 °C/min), indicating that tartaric acid is probably interacts in different way to the of PHB chain (E
a=73 ± 9 kJ mol−1, T
c = 44.8 °C at 5 °C/min). 相似文献
13.
We have investigated tension wood cellulose obtained from Populus maximowiczii using X-ray diffraction at temperatures from room temperature to 250 °C. Three equatorial and one meridional d-spacings showed a gradual linear increase with increasing temperature. For temperatures above 180 °C, however, the equatorial
d-spacing increased dramatically. Thus, the linear and volume thermal expansion coefficients (TECs) below 180 °C were determined
from the d-spacings. The linear TECs of the a-, b-, and c-axes were: α
a
= 13.6 × 10−5 °C−1, α
b
= −3.0× 10−5 °C−1, and α
c
=0.6× 10−5 °C−1, respectively, and the volume TEC was β = 11.1× 10−5 °C−1. The anisotropic thermal expansion in the three coordinate directions was closely related to the crystal structure of the
wood cellulose, and it governed the macroscopic thermal behavior of solid wood. 相似文献
14.
X. F. Wang J. Gao J. Wang Zh. H. Zhang Y. F. Wang L. J. Chen W. Sun X. D. Zhang 《Journal of Structural Chemistry》2008,49(4):724-731
The title compounds, (NH4)2[MnII(edta)(H2O)]·3H2O (H4edta = ethylenediamine-N,N,N′,N′-tetraacetic acid), (NH4)2[MnII(cydta)(H2O)]·4H2O (H4cydta = trans-1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid) and K2[MnII(Hdtpa)]·3.5H2O (H5dtpa = diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid), were prepared; their compositions and structures were determined
by elemental analysis and single-crystal X-ray diffraction technique. In these three complexes, the Mn2+ ions are all seven-coordinated and have a pseudomonocapped trigonal prismatic configuration. All the three complexes crystallize
in triclinic system in P-1 space group. Crystal data: (NH4)2[MnII(edta)(H2O)]·3H2O complex, a = 8.774(3) ?, b = 9.007(3) ?, c = 13.483(4) ?, α = 80.095(4)°, β = 80.708(4)°, γ = 68.770(4)°, V = 972.6(5) ?3, Z = 2, D
c = 1.541 g/cm3, μ = 0.745 mm−1, R = 0.033 and wR = 0.099 for 3406 observed reflections with I ≥ 2σ(I); (NH4)2[MnII(cydta)(H2O)]·4H2O complex, a = 8.9720(18) ?, b = 9.4380(19) ?, c = 14.931(3) ?, α = 76.99(3)°, β = 83.27(3)°, γ = 75.62(3)°, V = 1190.8(4)?3, Z = 2, D
c = 1.426 g/cm3, μ = 0.625 mm−1, R = 0.061 and wR = 0.197 for 3240 observed reflections with I ≥ 2σ(I); K2[MnII(Hdtpa)]·3.5H2O complex, a = 8.672(3) ?, b = 9.059(3) ?, c = 15.074(6) ?, α = 95.813(6)°, β = 96.665(6)°, γ = 99.212(6)°, V = 1152.4(7) ?3, Z = 2, D
c = 1.687 g/cm3, μ = 1.006 mm−1, R = 0.037 and wR = 0.090 for 4654 observed reflections with I ≥ 2σ(I).
Original Russian Text Copyright ? 2008 by X. F. Wang, J. Gao, J. Wang, Zh. H. Zhang, Y. F. Wang, L. J. Chen, W. Sun, and X.
D. Zhang
The text was submitted by the authors in English. Zhurnal Strukturnoi Khimii, Vol. 49, No. 4, pp. 753–759, July–August, 2008. 相似文献
15.
I. I. Seifullina L. Kh. Minacheva E. A. Chebanenko E. E. Martsinko V. S. Sergienko A. V. Churakov 《Russian Journal of Inorganic Chemistry》2011,56(12):1886-1893
Bis(citrato)hydroxogermanic(IV) acid was obtained for the first time in the complex [H5O2][Ge(H2Cit)(H2.5Cit)(OH)]2 · 2CH3COOH · 2H2O (H4Cit is citric acid). The complex was characterized by chemical analysis, X-ray powder diffraction, TGA, and IR spectroscopy.
Complex I was studied by X-ray crystallography. The crystals are triclinic; a = 10.0651(4) ?, b = 10.1918(4) ?, c = 10.5838(4) ?, α = 85.0110(10)°, β = 85.2170(10)°, γ = 86.7670(10)°, V = 1076.50(7) ?3, Z = 1, space group P[`1]P\bar 1, R1 = 0.0353 for 5709 reflections with I > 2σ(I). Complex I is composed of centrosymmetric dimeric complex anions [Ge2(H2Cit)2(H2.5Cit)2(OH)2]−, dioxonium cations [H5O2]+, and acetic acid and water molecules of crystallization. The coordination polyhedron of the Ge atom is a trigonal bipyramid.
Its equatorial plane comprises two O atoms of the deprotonated alcohol groups of two ligands H2Cit (A) and H2.5Cit (B) and the O atom of the terminal OH group (Ge-O, 1.7585–1.7754 ?; OeqGe(1)Oeq, 116.26°–127.64°). The axial positions are occupied by the carboxy O atom of the deprotonated carboxylate group of the α
branch of ligand A (α-Ge-O(C)(carb), 1.8882(12) ?)) and the carbonyl O atom of the hemiprotonated acetate α branch of ligand
B (α-Ge-O(C) 1.9615(12) ?, O(1)Ge(1)O(8) 170.47(5)°). In structure I, the complex dianion, the cation, and acetic acid and water molecules are united through hydrogen bonds into a three-dimensional
framework. 相似文献
16.
A. F. Santos L. Polese M. S. Crespi C. A. Ribeiro 《Journal of Thermal Analysis and Calorimetry》2009,96(1):287-291
The non-isothermal data given by TG curves for poly(3-hydroxybutyrate) (PHB) were studied in order to obtain a consistent
kinetic model that better represents the PHB thermal decomposition. Thus, data obtained from the dynamic TG curves were suitably
managed in order to obtain the Arrhenius kinetic parameter E according to the isoconversional F-W-O method. Once the E parameters is found, a suitable logA and kinetic model (f(α)) could be calculated. Hence, the kinetic triplet (E±SD, logA±SD and f(α)) obtained for the thermal decomposition of PHB under non-isothermal conditions was E=152±4 kJ mol−1, logA=14.1±0.2 s−1 for the kinetic model, and the autocatalytic model function was: f(α)=αm(1−α)n=α0.42(1−α)0.56. 相似文献
17.
Hernani S. Barud Clóvis A. Ribeiro Jorge M. V. Capela Marisa S. Crespi Sidney. J. L. Ribeiro Younes Messadeq 《Journal of Thermal Analysis and Calorimetry》2011,105(2):421-426
Cellulose can be obtained from innumerable sources such as cotton, trees, sugar cane bagasse, wood, bacteria, and others.
The bacterial cellulose (BC) produced by the Gram-negative acetic-acid bacterium Acetobacter xylinum has several unique properties. This BC is produced as highly hydrated membranes free of lignin and hemicelluloses and has
a higher molecular weight and higher crystallinity. Here, the thermal behavior of BC, was compared with those of microcrystalline
(MMC) and vegetal cellulose (VC). The kinetic parameters for the thermal decomposition step of the celluloses were determined
by the Capela-Ribeiro non-linear isoconversional method. From data for the TG curves in nitrogen atmosphere and at heating
rates of 5, 10, and 20 °C/min, the E
α
and B
α
terms could be determined and consequently the pre-exponential factor A
α as well as the kinetic model g(α). The pyrolysis of celluloses followed kinetic model
g(a) = [ - ln(1 - a)]1 \mathord