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1.
Ewa Rudnik G. Matuschek N. Milanov A. Kettrup 《Journal of Thermal Analysis and Calorimetry》2006,85(2):279-284
Thermal behaviour of different starch derivatives, i.e. starch esters
and ethers having degree of substitution (DS) in the range of 0.02–0.18
were studied. Potato, maize and wheat starches were used. Measurements were
carried out by coupled thermal analysis/ mass spectrometry method (STA-MS)
in air atmosphere.
The major DTG peak during the investigation
for starch derivatives is observed below 300°C. The mass loss up to a
temperature of 300°C is about 50%. The most abundant ions found areH2O+
and CO2
+. For the studied
starch derivatives with a low degree of substitution (DS<0.18) no correlation
was found between thermal stability and the level of substitution regardless
of the nature of substitution. 相似文献
2.
Zhenhai Liang Yanfa Sun Caimei Fan Xiaogang Hao Yanping Sun 《Journal of solution chemistry》2009,38(9):1119-1127
A Ti/SnO2 + RuO2 + MnO2 electrode was prepared by thermal decomposition of their salts. Results from SEM and XPS analyses, respectively, indicate
that the coating layer exhibits a compact structure and the oxidation state of Mn in the coating layer is +IV. The experimental
activation energy for the oxygen evolution reaction, which increased linearly with increasing overpotential, is about 8 kJ⋅mol−1 at the equilibrium potential (η=0). The electrocatalytic characteristics of the anode are discussed in terms of ligand substitution reaction mechanisms (Sn1
and Sn2). It was found that the transition state for oxygen evolution at the anode in acidic solution follows a dissociative
mechanism (Sn1 reaction). The Ti/SnO2 + RuO2 + MnO2 anode in conjunction with UV illumination was used to degrade phenol solutions, where the concentration of phenol remaining
was determined by high-performance liquid chromatography (HPLC). The results indicate that the degradation efficiency of phenol
on the anode can reach 96.3% after photoelectrocatalytic oxidation for 3 h. 相似文献
3.
Siegfried Menzel Thomas Göbel Stefan Baunack Karl Bartsch Klaus Wetzig 《Mikrochimica acta》2000,133(1-4):215-221
Sputtered (Ti,Al)N hard coatings are successfully used for dry high speed cutting. These films show a lower oxidation rate
than TiN or TiC coatings. In our work (Ti,Al)N films were deposited on WC-6%Co substrates at a temperature of 490°C by plasma-assisted
chemical vapour deposition (PACVD) using a gas mixture of TiCl4/AlCl3/N2/Ar/H2. Investigation of microstructure, crystalline structure and chemical composition was carried out using SEM, WDXS, TEM, AES
and XRD techniques. The chemical composition of the deposited films showed a Al to Ti ratio of 1.33. The film thickness was
5.5 μm. Films showed a fine crystalline size, the metastable fcc crystal structure and a columnar growth. The film surface
was under low compressive stress up to several 100 MPa. For (Ti,Al)N/WC-Co compounds the oxidation behaviour up to 1100°C
(high temperature range) was studied. Therefore, samples were annealed or rapidly heated in air and under high vacuum condition
using the laser shock method. The results show decomposition of the (Ti,Al)N structure to the TiN and the AlN phases at temperature
values above 900°C. Heating in air causes growing of a thin aluminum oxide layer at the film surface, which is a barrier for
further oxygen diffusion to the alumina-film boundary. Additionally, at temperatures above 900°C oxidation of the WC-6%Co
substrate surface was obtained in regions of opened cracks and film delamination. 相似文献
4.
The complex impedance method in the temperature range of 291–660 K was used to study conductivity of oxofluoride BiO0.1F2.8 belonging to the tysonite structural type (LaF3). Bismuth oxofluoride was synthesized using a solid-phase method at 770–870 K for 1–2 h in an argon atmosphere. Heterovalent
substitution of fluoride ions F− by oxygen ions O2− in the anionic BiF3 matrix sublattice results in high ionic conductivity (∼0.1 S/cm at 660 K) of BiO0.1F2.8 ceramic samples. 相似文献
5.
Rau María S. Gennero de Chialvo María Rosa Chialvo Abel C. 《Journal of Solid State Electrochemistry》2012,16(5):1893-1900
The carbon monoxide oxidation reaction (COOR) was studied on steady-state conditions by chronoamperometry on polycrystalline
smooth platinum and ruthenium rotating disc electrodes in CO-saturated acid solution. The chronoamperometric response did
not show current oscillations and therefore the current density (j) vs. overpotential (η) curves on steady state could be obtained. In order to interpret these results, kinetic expressions were derived starting
from the mechanism proposed by S. Gilman, which considers two adsorbed reaction intermediates, carbon monoxide (COad) and hydroxyl (OHad). Analytical expressions as a function of overpotential for the current density, the surface coverage of the adsorbed species
(θ
CO and θ
OH) and the CO and CO2 pressures at the electrode surface on steady state were obtained. This set of equations was used for the correlation of the
experimental polarization curves and the evaluation of the corresponding kinetic parameters. From these values, the dependences
of the surface coverage of the adsorbed intermediates on overpotential were simulated, as well as those of the partial pressure
of CO and CO2. Thus, it was demonstrated that the Gilman’s mechanism accurately describes the experimental results on steady state of the
COOR on these metals. 相似文献
6.
Kun Wang Qingbo Yu Wenjun Duan Qin Qin Huaqing Xie 《Journal of Thermal Analysis and Calorimetry》2014,115(2):1163-1172
Chemical looping air separation (CLAS), based on the chemical looping principle, is a novel and energy-efficient method to separate oxygen from air. The oxygen carriers used capture oxygen from air in an oxidation reactor and release oxygen in a reduction reactor. In this work, the adaptability of Cu/Zr oxygen carrier used for CLAS was investigated through thermodynamic analysis and experimental methods. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to measure the phases and surface morphology of oxygen carriers before and after experiments. The results show that CuO has the capability of releasing oxygen when the temperature is higher than 725 °C in the nitrogen atmosphere, and the minimum oxygen reduction temperatures increase with the increasing of oxygen concentrations. The Cu/Zr oxygen carrier has high oxygen reduction and oxidation rates when temperature is higher than a certain values. For reduction, the value is about 860 °C. For oxidation, the value is about 500 °C. The reactivity of oxygen carrier increases significantly with the temperature increasing. On overall, reactivity of oxygen carrier has little difference under different particle sizes. The oxygen carrier exhibits a stable oxygen reduction and oxidation behavior during reduction–oxidation cycles. XRD patterns show that the main phases in reduced samples are Cu2O and ZrO2. The main phases in fresh and oxidized samples are CuO and ZrO2. SEM images show that the fresh and reacted oxygen carriers are porous. The surface of reacted samples is smoother than fresh samples and no agglomeration has been found. 相似文献
7.
SiO2-TiO2 membranes by the sol-gel process 总被引:1,自引:0,他引:1
The use of membranes for gas separation represents an important alternative from the viewpoint of energy conservation in industrial separation processes. Polymeric Si-Ti sols prepared from titanium isopropoxide (Ti(OPri)4) and tetraethoxysilane (TEOS) were used to deposit membranes on α-Al2O3 supports. Acetylacetone (2,4 pentanedione, acacH) and isoeugenol (2-methoxy-4-propenylphenol, isoH) were employed separately to chelate the Ti precursor in order to slow down the chemical reactivity, avoiding precipitation. The radial distribution functions (RDF) of the gels aging at room temperature were obtained. The xerogels were studied by Thermal Gravimetric (TGA) and Differential Thermal (DTA) Analysis in air. The Microporosity of the solids calcined at 773 K was determined by N2-adsorption at 77 K. The membrane thickness was determined from SEM photographs. Preliminary permeance results of the supported membranes on commercial alumina support were obtained for He, N2 and CO2 in a single gas equipment. At 773 K the separation factors α(He/CO2) and α(N2/CO2) for both membranes exceeds the theoretical Knudsen limit. 相似文献
8.
B. Zapata J. Balmaseda E. Fregoso-Israel E. Torres-García 《Journal of Thermal Analysis and Calorimetry》2009,98(1):309-315
Thermal degradation of orange peel was studied in dynamic air atmosphere by means of simultaneous TG-DSC and TG-FTIR analysis.
According to the obtained thermal profiles, the orange peel degradation occurred in at least three steps associated with its
three main components (hemicellulose, cellulose and lignin). The volatiles compounds evolved out at 150–400 °C and the gas
products were mainly CO2, CO, and CH4. A mixture of acids, aldehydes or ketones C=O, alkanes C–C, ethers C–O–C and H2O was also detected. The E
α on α dependence reveled the existence of different and simultaneous processes suggesting that the combustion reaction is
controlled by oxygen accessibility, motivated by the high evolution low-molecular-mass gases and volatile organic compounds.
These results could explain the non-autocatalytic character of the reactions during the decomposition process. 相似文献
9.
S. A. Grabovski D. V. Kazakov N. N. Kabalnova S. L. Khursan V. V. Shereshovets 《Reaction Kinetics and Catalysis Letters》1997,62(1):179-183
Dimethyldioxirane decomposition in oxygen atmosphere follows a first-order kinetic law. Decomposition rate constant (k, s−1) in acetone in the temperature range from 30 to 50°C has been determined as lgk=(7.1±0.9)−(16.0±1.4)/θ, θ=2.303RT kcal/mol. 相似文献
10.
A. Al-Kahlout S. Heusing T. Mueller N. Aldahoudi M. Quilitz P. W. de Oliveira 《Journal of Sol-Gel Science and Technology》2011,59(3):532-538
Transparent semiconducting ITO:Ti thin films, prepared by a sol–gel process, has been deposited by spin-coating technique
onto alkali-free glass substrates. The as-coated films were annealed in ambient air at 550 °C for 1 h and further annealed
in a reducing atmosphere. The influences of the Ti content in the sol on the surface morphology, microstructure, optical properties
and electrical resistivity have been investigated. These properties were found to depend on the Ti content in the coating
sol. Ti addition led to dense smooth layers with larger crystallite size (20–30 nm). Double layers synthesized with Ti:ITO = 0.53 wt%
and submitted to reducing treatment in forming gas exhibited the lowest sheet resistance R□ = 60 Ω□ with an average transmittance of 87% at 550 nm. 相似文献
11.
Lech Nowicki Anna Antecka Tomasz Bedyk Paweł Stolarek Stanisław Ledakowicz 《Journal of Thermal Analysis and Calorimetry》2011,104(2):693-700
Gasification of char derived from sewage sludge was studied under different oxidizing atmospheres containing CO2, O2 or H2O. The gasification tests were carried out in thermobalance at different temperatures and oxidizing reagent concentrations.
The most efficient were the gaseous mixtures containing oxygen. The reaction took place at temperature 400–500 °C, whilst
in the case of CO2 and steam much higher temperatures (700–900 °C) were necessary to complete the conversion. Two rate models for gas–solid
reaction were applied to describe the effect of char conversion on reaction rate. The shrinking core model for reaction-controlled
regime was found to be the best for predicting the rate of char gasification in CO2 and O2 atmosphere. The experimental data for steam gasification of the char were fitted best by the first-order kinetics. The kinetic
parameters estimated from the experimental data are in accordance with the literature for lignocellulosic char gasification
and are the first published for sewage sludge char gasification. 相似文献
12.
Gülbanu Koyundereli Çılgı Halil Cetişli Ramazan Donat 《Journal of Thermal Analysis and Calorimetry》2014,115(2):2007-2020
Thermal decomposition of U(C2O4)2·6H2O was studied using TG method in nitrogen, air, and oxygen atmospheres. The decomposition proceeded in five stages. The first three stages were dehydration reactions and corresponded to removal of four, one, and one mole water, respectively. Anhydrous salt decomposed to oxide products in two stages. The decomposition products in nitrogen atmosphere were different from those in air and oxygen atmospheres. In nitrogen atmosphere UO1.5(CO3)0.5 was the first product and U2O5 was the second product, while these in air and oxygen atmospheres were UO(CO3) and UO3, respectively. The second decomposition products were not stable and converted to stable oxides (nitrogen: UO2, air–oxygen: U3O8). The kinetics of each reaction was investigated with using Kissinger–Akahira–Sunose and Flynn–Wall–Ozawa methods. These methods were combined with modeling equations for thermodynamic functions, the effective models were investigated and thermodynamic values were calculated. 相似文献
13.
YBaCo4O7 compound is capable to intake and release a large amount of oxygen in the temperature range of 200–400°C. In the present
study, the effect of Zn, Ga and Fe substitution for Co on the oxygen adsorption/desorption properties of YBaCo4O7 were investigated by thermogravimetry (TG) method. Due to fixed oxidation state of Zn2+ ions, the substitution of Zn2+ for Co2+ suppresses the oxygen adsorption of YBaCo4−xZnxO7. The substitution of Ga3+ for Co3+ also decreases the oxygen absorption capacity of YBaCo4−xGaxO7. This can be explained by the strong affinity of Ga3+ ions towards the GaO4 tetrahedron. Compared with Zn- and Ga-substituted samples, the drop of oxygen adsorption capacity is smallest for Fe-substituted
samples because of the similar changeability of oxidation states of Co and Fe ions. 相似文献
14.
Ronny Kleinhempel Gunar Kaune Matthias Herrmann Hartmut Kupfer Walter Hoyer Frank Richter 《Mikrochimica acta》2006,156(1-2):61-67
Indium tin oxide (ITO) thin films were deposited by mid frequency pulsed dual magnetron sputtering using a metallic alloy
target with 10 wt.% tin in an atmosphere of argon and oxygen. The aim of the work was to study the interdependence of structural,
electrical and optical properties of ITO films deposited in the reactive and transition target mode, respectively. The deposition
rate in the transition mode exceeds the deposition rate in the reactive mode by a factor of six, a maximum value of 100 nm·m min−1 could be achieved. This corresponds to a static deposition rate of 200 nm min−1. The lowest electrical resistivity of 1.1·10−3 Ω cm was measured at samples deposited in the high oxygen flow range in the transition mode. The samples show a good transparency
in the visible range corresponding to extinction coefficients being below 10−2. X-ray diffraction was used to characterise crystalline structure as well as film stress. ITO films prepared in the transition
mode show a slightly preferred orientation in (211) direction, whereas films deposited in the reactive mode are strongly (222)
oriented. Compared to undoped In2O3 all samples have an enlarged lattice. The lattice strain perpendicular to the surface is about 0.8% and 2.0% for films grown
in the transition and the reactive mode, respectively. Deposition in the transition mode introduces a biaxial film stress
in the range of −300 MPa, while stress in reactive mode samples is −1500 MPa. 相似文献
15.
Wolfgang Preis Michael Holzinger Werner Sitte 《Monatshefte für Chemie / Chemical Monthly》2001,132(4):499-508
Summary. The van der Pauw method has been applied to conductivity relaxation experiments on YBa2Cu3O6+δ at 600°C in order to determine the chemical diffusion coefficient as a function of the oxygen partial pressure in the surrounding
atmosphere (100 > p
O
2/bar > 10−3). It is shown that the van der Pauw technique is suitable for monitoring the conductivity relaxation when the oxygen diffusion is perpendicular to the direct
current flowing through the sample in accordance with the van der Pauw geometry using thin tablets as samples. The oxygen partial pressure is changed stepwise (generally Δlogp
O
2 ≤ 0.5) by employing appropriate gas mixtures as well as an electrochemical oxygen pump device. An evaluation formula is given
for the determination of the chemical diffusion coefficient neglecting slow surface processes. In addition, the electronic
conductivity of YBa2Cu3O6+δ has been measured at 600°C as a function of oxygen partial pressure of the ambient atmosphere (100 > p
O
2/bar > 10−5) by means of the van der Pauw method applying the same experimental set-up. Typical values of the chemical diffusion coefficient are in the range of 10−6 cm2·s−1; the results of the conductivity measurements are interpreted in terms of an appropriate defect model.
Received May 30, 2000. Accepted June 8, 2000 相似文献
16.
A. M. Kalinkin 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2008,82(2):263-268
Processes that occur during the mechanical activation of CaTiO3 perovskite in a centrifugal-planetary mill in the atmosphere of CO2 and in air were studied. Mechanical activation in CO2 was accompanied by substantial chemisorption of carbon dioxide with perovskite with the formation of carbonate groups not only on the surface but also in the volume of structurally disordered calcium titanate particles. The content of CO2 in perovskite samples reached 12.8% after 50 min of mechanical activation. Carbon dioxide atmosphere contributed to a more intense accumulation of structure imperfections in perovskite under mechanical actions, whereas the dispersion of the compound was more effective in air. 相似文献
17.
I. Blanco L. Abate F. A. Bottino P. Bottino 《Journal of Thermal Analysis and Calorimetry》2012,108(2):807-815
Six polyhedral oligomeric silsesquioxanes (POSSs) with general formula R7 R′1 (SiO1.5)8, where R- was an isobutyl group and R′- a variously substituted phenyl group, namely hepta isobutyl polyhedral oligomeric
silsesquioxane (hib-POSS), were prepared and their composition was checked by elemental analysis and 1
H NMR spectroscopy. The degradation of compounds obtained was studied by simultaneous differential thermal analysis/thermogravimetry
(DTA/TG) technique, in both inert (flowing nitrogen) and oxidative (static air atmosphere) environments, in order to draw
useful information about their thermal stability. Experiments, performed in the 35–700 °C temperature range, showed different
behaviour between the two used atmospheres. The formation of volatile compounds only, with an about complete mass loss, was
observed under nitrogen, while a solid residue (≈40–50% in every case), due to the formation of SiO2, as indicated by the FTIR spectra, was obtained in static air atmosphere. The results obtained were discussed and compared,
and the classifications of resistance to thermal degradation in the studied environments were made. A comparison between the
thermal stabilities of hib-POSSs and analogous cyclopentyl POSSs previously studied was also performed. 相似文献
18.
A.Z. Simões M.A. Ramírez A.H.M. Gonzalez C.S. Riccardi A. Ries E. Longo J.A. Varela 《Journal of solid state chemistry》2006,179(7):2206-2211
Ferroelectric CaBi4Ti4O15 (CBTi144) thin films were deposited on Pt/Ti/SiO2/Si substrates by the polymeric precursor method. The films present a single phase of layered-structured perovskite with polar axis orientation after annealing at 700 °C for 2 h in static air and oxygen atmosphere. The a/b-axis orientation of the ferroelectric film is considered to be associated with the preferred orientation of the Pt bottom electrode. It is noted that the films annealed in static air showed good polarization fatigue characteristics at least up to 1010 bipolar pulse cycles and excellent retention properties up to 104 s. On the other hand, oxygen atmosphere seems to be crucial in the decrease of both, fatigue and retention characteristics of the capacitors. Independently of the applied electric field, the retained switchable polarization approached a nearly steady-state value after a retention time of 10 s. 相似文献
19.
Carbon dioxide evolution from poly(ethylene terephthalate) (PET) films during ultraviolet (UV) exposure has been monitored using FTIR interrogation of the atmosphere surrounding the test pieces. Measurement periods as little as 4 h could easily discriminate between CO2 emission rates when tests were conducted to investigate the effect of using different reaction atmospheres or of including UV absorber in the PET samples. Samples containing UV absorbers either homogeneously distributed through the film or in thin surface layers (∼0.7 μm thick) were also tested. Relatively small reductions in CO2 emission rates were observed with samples containing UV absorbers but the rates were not very sensitive to the distribution and concentration of the absorbers. A thin surface layer containing only 2% stabiliser (equivalent to 0.23% stabiliser when averaged over the whole film thickness) provided oxidation reduction similar to that observed when 1% stabiliser was distributed evenly throughout the sample. Tests were conducted in wet oxygen, dry oxygen and dry nitrogen. For as-received bi-axially drawn PET film containing no absorber, the CO2 emission rate under UV illumination in wet oxygen was much higher than in dry oxygen or dry nitrogen. For as-received PET the difference between the rates observed in dry oxygen and dry nitrogen was small. For PET films that had been pre-exposed to UV (for 9 days) prior to insertion into the in situ CO2 measurement cell the rate of CO2 generation in oxygen was significantly larger than that in nitrogen. In both nitrogen and oxygen the presence of UV absorbers significantly decreased the rate of CO2 generation. 相似文献
20.
Anca Mihaela Mocanu Lucia Odochian N. Apostolescu C. Moldoveanu 《Journal of Thermal Analysis and Calorimetry》2011,103(1):283-291
The article is devoted to a comparative study on the thermal degradation of some new diazoaminoderivatives under both air
and nitrogen atmosphere by TG-FTIR analysis. The TG–DTG–DTA curves show the thermal degradation in air to present two temperature
domains: an endothermic one identical to the case of the degradation under nitrogen and an exothermic one which is not to
be found under nitrogen atmosphere. The identification of the gaseous species released by degradation in air within the endothermic
domain made evident the presence of the same components of the degradation in nitrogen atmosphere. In the exothermic domain
of the sample degradation in air, the CO2, H2O, SO2 species result by the burning of the molecular residues of the first domain. The obtained results afforded a degradation
mechanism to be advanced that coincide for the endothermic domain with that of degradation under nitrogen atmosphere. Due
to the importance of these compounds as possible reaction initiators and also as potentially bioactive substances (herbicides,
acaricides, fungicides), the study on their thermal degradation could give useful information on the environmental impact
of the degradation products resulting by the thermal processing of the plants which could possible retain these compounds,
when the initial degradation temperature is exceeded. 相似文献