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1.
The molecular and physical structures of cellulosic rayon fiber during the stepwise heat treatment for the fabrication of
activated carbon fiber (ACF) were researched by Fourier transform infrared spectroscopy, wide angle X-ray diffraction and
elemental analysis. Dibasic ammonium phosphate (DAP) lowers the dehydration temperature of rayon evidently and acts also as
a reactant besides as a catalyst. Group C=O is generated at 200 °C while group C=C appears at 250 °C. About 220–250 °C is
a key temperature range where the chain, ring and crystal structures of rayon macromolecules are damaged completely to lose
the basic characteristics of cellulose by dehydration. The drastic changes of weight loss, discoloration and shrinkage occur
simultaneously. The bands of chemical groups decrease rapidly and go to disappear during carbonization. The activation at
a lower temperature (750 °C) decreases the contents of oxygen-containing groups, but increases them at a higher temperature
(950 °C). The microcrystalline structures are gradually formed near 800 °C and activation seems to be favor to the crystallization.
A higher usage of the phosphate does not only affect the weight-losses of rayon fiber significantly, it also enhances the
specific surface areas of ACF obviously. 相似文献
2.
Na-montmorillonite (Na-MONT) was loaded with hexadecyltrimethylammonium cations (HDTMA) by replacing 41 and 90% of the exchangeable
Na with HDTMA, labeled OC-41 and OC-90, respectively. Na-MONT, OC-41, and OC-90 were heated in air up to 900 °C. Unheated
and thermally treated organoclays heated at 150, 250, 360, and 420 °C are used in our laboratory as sorbents of different
hazardous organic compounds from waste water. In order to get a better knowledge about the composition and nature of the thermally
treated organoclays Na-MONT and the two organo-clays were studied by thermogravimetry (TG) in air and under nitrogen. Carbon
and hydrogen contents in each of the thermal treated sample were determined and their infrared spectra were recorded. The
present results showed that at 150 °C both organoclays lost water but not intercalated HDTMA cations. At 250 °C, many HDTMA
cations persisted in OC-41, but in OC-90 significant part of the cations were air-oxidized into H 2O and CO 2 and the residual carbon formed charcoal. After heating both samples at 360 °C charcoal was present in both organo clays.
This charcoal persisted at 420 °C but was gradually oxidized by air with further rise in temperature. TG runs under nitrogen
showed stepwise degradation corresponding to interlayer water desorption followed by decomposition of the organic compound,
volatilization of small fragments and condensation of non-volatile fragments into quasi-charcoal. After dehydroxylation of
the clay the last stages of organic matter pyrolysis and volatilization occurred. 相似文献
3.
Emanation thermal analysis, differential thermal analysis, thermogravimetry, X-ray diffraction, scanning electron microscopy
(SEM) and surface area and porosity determination from nitrogen adsorption/desorption measurements were used to characterize
the Mg-Al-CO 3 LDH compound with the Mg:Al ratio 3:1 prepared by re-hydration of the Mg-Al mixed oxide. The mixed oxide was obtained after
heating of the intial Mg-Al-CO 3 LDH compound in air at 500°C for 2 h. The samples were re-hydrated by two ways namely in a distilled water at 20°C for 5
days or by moistening at 60°C in air with RH 80% during 10 days, respectively. The characteristics of the re-hydrated LDH
samples were compared with the initial Mg-Al-CO 3 compound.
The influence of the re-hydration conditions on the microstructure, surface morphology and thermal stability of the regenerated
Mg-Al-CO 3 LDHs samples is discussed.
It was demonstrated that the re-generation of the layered structure by the hydration of the mixed oxide in water or in air,
respectively, took place via the dissolution-crystallization mechanism and that the layered double hydroxide with different
surface area and thermal behavior were formed after re-hydration in water or humid air, respectively. The emanation thermal
analysis revealed differences in the microstructure changes of the re-hydrated sample during heating. XRD patterns and results
of the methods used supported the ETA results. 相似文献
4.
Synthetic iron-manganese glycerates with compositions corresponding to different molar ratios of Fe: Mn, contain large amounts of H 2O (up to 22%). Heating in air at ≈270°C produces a hydrated, disordered Mn-ferrite structure (jacobsite), as shown by XRD and IR spectroscopy. At this temperature no alkoxide groups are detected. TG curves show 45.6% to ≈54% weight losses at 290°C, with a sharp loss from 270° to 290°C for all samples, attributed mostly to the Curie transition of MnFe 2O 4. Further heating of each sample at ≈670°C results in a well-crystallized hematite and variable amounts of bixbyite. At this stage no H 2O is left. Further calcination at ≈1050°C gives qualitatively the same products as at 670°C. Colour changes occur during the heating process. In admixtures of goethite with MnCO 3 or pyrolusite the main difference from the counterpart alkoxide is shown after heating at 270°C, when the Fe?Mn mineral mixture produces mostly protohematite (disordered hematite) instead of disordered jacobsite resulting from the alkoxides. 相似文献
5.
The effect of heat treatment at temperatures above 300°C on the low temperature relaxation of poly(4,4′-oxydiphenylenepyromellitimide) (Kapton H-film) was studied by wide-line nuclear magnetic resonance (NMR), mechanical, and dielectric measurements. In the NMR line spectrum of the as-received film, a narrow component above ?60°C and a broad component which begins to narrow at about ?100°C were observed. It is proposed that the narrow component is associated with absorbed water, because it disappeared in the heat-treated film at 300°C in N 2. On the other hand, the behavior of the broad component was not influenced by heating to 300°C in N 2. Mechanical and dielectric loss peaks were observed at ?75°C (11 Hz) and ?65°C (1 kHz), respectively, in the as-received film. These loss peaks did not change in intensity with heating to 300°C in N 2. It is proposed that the mechanical and dielectric loss peaks corresponding to the narrowing of the NMR broad component are associated with the local-mode motion of the diphenylether portion of the polypyromellitimide chain. It was found that crosslinks are formed by heating to 374°C in air through coupling of the diphenylether portions of the molecular chains. With the formation of crosslinks the dielectric loss peak shifted toward higher temperature and the intensity decreased through restriction of the local-mode motion of the diphenylether portion of the molecular chain. 相似文献
6.
A simple water sorption/retention ( WS/WR) test, followed by stepwise static heating, was applied to the study of cement quality and the reactivity of its grain surface.
The physically bound water and hence the specific surface both in the unhydrated and in the hydrated state were estimated
as a function of the hydration time. Rehydration after heating at 220°C and contact with air was different in WS from that in WR samples, which indicates a difference in microstructure. XRD proved the formation of portlandite during the sorption test
and eventual heating at 200°C, and its transformation into carbonates on contact with air, especially on heating at 400°C.
The contents of these compounds were estimated from the mass difference between 400 and 800°C, which was compatible with the
mass change between 220 and 400°C and this indicates surface reactivity. The test may serve for the routine study of cement.
Dedicated to Professor Lisa Heller-Kallai on the occasion of her 65 th birthday 相似文献
7.
Investigations on the Thermal Degradation of Keggin-Heteropolytungstoacids by Means of High-temperature X-ray-Powder-Photographs and I.R. Spectroscopy The termal degradations of 12-tungstoboric acid ( I ), 12-tungstosilicic acid ( II ) and 12-tungstiphosphoric acid ( III ), recorded with a high temperature powder camera (heating rate: 4°C/min, atmosphere: air) are observed at 420, 530, and 620°C, respectively. These doped WO 3-phases are stable at room temperature and forms either a monoclinic distorted lattice ( I ) or a tetragonal one ( II and III ). Above 850°C in all cases a tetragonal phase is formed with a diagram typical for pure WO 3. Investigation by means of I.R. spectroscopy (250—1300 cm ?1) are in agreement with those of X-ray results. 相似文献
8.
The characteristics of bioaragonite of shells of recent T. decussatus during heating were studied by the means of TG-DTA-EGA (FTIR), XRD, XRF and FTIR. The mass loss recorded up to 2.5% appeared
with the higher rates at 110–150, 200–250, 295–300, and 390–415°C at heating of 10°C min −1 up to 500°C. IR analysis of the evolved gases revealed the emission of water and CO 2. The lattice constants tend to change with anisotropy character (parameters a and c diminish whilst b tends to grows) and with an overall contraction of cell volume (from 227.36 to 226.84 ? 3) during heating was established. The peculiarity of bioaragonite was explained by substitution of H 2O and sulphate ion into the lattice. In spite of those substitutions, bioaragonite reveals an orthorhombic structure, which
is preserved during the changes up to calcite formation above 380°C. 相似文献
9.
The thermal decomposition of basic copper carbonate (malachite; CuCO 3·Cu(OH) 2) in a dynamic atmosphere of air or nitrogen was studied via TG, DTA and DSC at different heating rates. The non-isothermal kinetic and thermodynamic parameters were estimated. The decomposition course was thoroughly followed by examining the structural and morphological consequences of calcining the material at elevated temperatures by IR, XRD and SEM. The results obtained showed that in air CuCO 3·Cu(OH) 2 released 0.5 H 2O at 195°C, transforming into the azurite structure 2CuCO 3·Cu(OH) 2. Decomposition then commenced, through two endothermic steps maximized at 325 and 430°C. The resultant product maintained the water released from the decomposition process up to 650–750°C. A schematic decomposition pathway has been proposed in terms of the thermal and physicoanalytical results. 相似文献
10.
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
11.
The process of shrinkage of calcium silicate hydrate was investigated by dilatometry up to 350 °C. The properties of this material are based on the formation of C–S–H phases during the reaction at temperatures between 180 and 205 °C and water vapor pressure lower than 16 bars. The main C–S–H phases are 11.3 Å tobermorite and xonotlite. 11.3 Å tobermorite converts to 9.3 Å tobermorite on air at temperatures around 300 °C. The hydrosilicate materials were prepared from quicklime and finely ground sand with different CaO/SiO2 ratios under different hydrothermal conditions. The reaction time was 24 h. Materials based on xonotlite and tobermorite were produced, and the calcium silicate phases were characterized by XRD and TG/DTA methods. Dilatometry measurements were used to study the effect of heating conditions on sample shrinkage. Dehydration of hydrated calcium silicate minerals occurred during heating. The results show that sample shrinkage is dependent on the type and amount of C–S–H phases, the amount of bound water and formation of 9.3 Å tobermorite. All samples showed shrinkage after heating up to 350 °C, but this change was not irreversible for all samples after cooling to room temperature. 相似文献
12.
Thermal behaviour of Er 2(SO 3) 3· 3H 3O has been studied by means of TG, DTG, DTA, DSC and EGA techniques. Experimental conditions were also varied, sample size, heating rate and the atmosphere.The dehydration starts slowly above 150°C but the release of water is rapid around 250°C. SO 2 gas is evolved slowly and simultaneously with H 2O. The anhydrous sulphite is formed below 300°C after which it decomposes through several reactions accompanied by a release of mainly SO 2, but also a small amount of SO 3 near 650°C. In air, there is a clear plateau in the TG curve between 600 and 800°C; the weight loss involved depends strongly on the sample size and heating rate, however. A plausible explanation for the plateau is the formation of a mixture of Er 2(SO 4) 3, Er 2O(SO 4) 2 and Er 2O 2SO 4. The next plateau around 900 – 1000°C corresponds to Er 2O(SO 4) 2 and Er 2O 2SO 4. In nitrogen atmosphere, the first plateau after the anhydrous sulphite appears later in the weight scale as compared to air. Although the position of the plateau corresponds to the sesquisulphide, it is according to X-ray diffraction results a mixture of Er 2O 2(SO 4) and Er 2O 3. In both air and nitrogen, the final reaction step above 1000°C is the formation of Er 2O 3. 相似文献
13.
Optically clear monolithic (OCM) gels of microporous aluminosilicates have been prepared by slow hydrolysis-polycondensation of alkoxides. Subsequent heating induces transformations into OCM microporous glasses. The surface area (∼610 m 2/g after drying at 300°C) and the pore volume (∼0.35 cc/g at 300°C) decrease monotonously with increasing annealing temperature. However, after heat treatment at 600°C under air (glass state) the monoliths are still microporous. Modifications of the xerogel pore distribution by an impregnation process and metal aggregate formation with pyrolysis are studied by N 2 adsorption-desorption analysis and small-angle X-ray scattering (SAXS). The microporous structure becomes mesoporous. A model of microporous impregnation in the gel or glass state is proposed. 相似文献
14.
Ultrahigh temperature composite materials HfB 2-SiC containing 25, 35, and 45 vol % SiC were produced by spark plasma sintering. Modeling of heating under the action of a dissociated air flow for selected samples using a VGU-4 induction plasma generator showed that these materials do not degrade even while keeping at a surface temperature of more than 2000°C (up to 2600°C) for 11 min. A combination of optical microscopy, scanning electron microscopy (with EDX analysis), and X-ray computed microtomography were used for investigating the microstructure and composition of the oxidized layer before and after heating. 相似文献
15.
The thermal behaviour of H 4SiW 12O 40·24.8H 2O (SiW 12) was investigated by using DTA, TG and FTIR. Endothermic effects were observed at 40, 98 and 217°C, corresponding to the fusion of SiW 12 in its own crystallization water, boiling of the solution and decomposition of the remaining tetrahydrate into anhydrous SiW 12, respectively. The mass of the sample remained constant on heating from about 250 to 400°C. Subsequently, it slowly decreased and reached a constant value at about 500°C. At 526°C a DTA peak appeared. There was an abrupt change in the FTIR spectrum of the sample heated to 550°C. The typical spectrum of the Keggin unit vanished and new bands at 807.5 and 1030 cm ?1 indicated the presence of free WO 3 and SiO 2, respectively. 相似文献
16.
A constant rate method involving the control of the concentration of evolved CO 2 at a constant level was used to study the air activation of pure and copper-doped carbon prepared from sodium carboxymethylcellulose.
Whereas under a linear heating regime, both types of carbon reacted suddenly and quickly with O 2, under constant rate conditions this violent reaction was avoided and oxidation proceeded steadily at a lower temperature
until complete burn off of the carbon was achieved. The catalytic effect of the copper on carbon gasification was noted with
lower reaction temperatures for both linear heating (380°C compared to 500°C) and for the constant rate experiments (320°C
compared to 400°C).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Summary TG-DSC-MS (thermogravimetry-differential scanning calorimetry-mass spectrometry) coupling techniques were used to make a simultaneous
characterizing study for the thermal decomposition process of the carbon nanotube (CNT)/SiO 2precursor powders prepared by rapid sol-gel method. The thermal stability of the CNT and the SiO 2pure gel were investigated by TG-DSC. The results showed that the oxidation of CNT began from 530 and combusted at about 678°C
at the heating rate of 10°C min -1in air. Moreover, the faster the heating rate, the higher the temperature of CNT combustion. The appropriate calcinations
temperature of the CNT/SiO 2precursor powders should be held for 1 h at 500°C. 相似文献
18.
Triniobium hydroxide heptaoxide, Nb 3O 7(OH), was prepared hydrothermally by treating niobic acid or triniobium chloride heptaoxide with 3.0 mol/dm 3 sulfuric acid at 250–350°C and 15 MPa. The hydroxide oxide was isomorphous with the low-pressure form of triniobium fluoride heptaoxide which is built up of 3 X ∞ blocks of the ReO 3 structure with crystallographic shear in one dimension. When heated in air, Nb 3O 7(OH) dehydrated up to 460°C to give poorly crystallized Nb 2O 5, which, on further heating, changed slowly into a less ordered precursor of M? Nb 2O 5( 1). Hydrothermal treatment of Nb 3O 7(OH) with pure water at 400–500°C afforded P? and R? Nb 2O 5; the conversion of Nb 3O 7(OH) is explained in terms of the close structural relation among these three forms. 相似文献
19.
The course of the reaction CuSO 4 · 5 H 2O ? CuSO 4 · H 2O + 4 H 2O was studied by non-isothermal thermogravimetry with various heating rates ranging from 1 to 300° h ?. The measurements were made either in static air, in a dry nitrogen stream, or in water vapor at a reduced pressure (9 mm Hg). In static air, the shape of the TG curve changed drastically at a heating rate of 13 to 15° h ?, and this change was explained by considering the nature of the plateaus and inflections present. In a dry nitrogen stream, the dehydration is made much easier at slow heating rates and occurs almost in one step at 2° h ?; in water vapor at 9 mm Hg, on the other hand, a very distinct two-step curve is obtained at 1° h ?. This can reasonably be compared with the phase diagram of copper sulfate. 相似文献
20.
Na-montmorillonite (Na-MONT) was loaded with hexadecyltrimethylammonium cations (HDTMA) by replacing 41 and 90% of the exchangeable
Na with HDTMA. The organoclays were labeled OC-41 and OC-90, respectively. Freeze-dried Na-MONT, OC-41, and OC-90 were heated
in air at 150, 250, 360, 420, 550, 700, and 900 °C. The thermally treated samples were suspended in water, air-dried, and
desiccated over silica during 40 days. All samples were diffracted by X-ray and fitting calculations were performed on each
diffractogram. These calculations gave information on basal spacings, relative concentrations, and homogeneity of the different
tactoids obtained at each temperature, before and after suspending and desiccating. HDTMA-MONT tactoids with spacing ≥1.41 nm
appeared between 25 and 250 °C. OC-41 or OC-90 intercalated monolayers or bilayers of HDTMA, respectively. At 250 °C OC-41
was air-oxidized to a smaller extent than OC-90, resulting in charcoal-MONT tactoids. With further heating the organic matter
was gradually oxidized and at 700 °C both clays were collapsed. During the thermo-XRD-analysis of both organoclays three types
of charcoal-MONT complexes appeared: (1) LTSC-MONT tactoids with a basal spacing 1.32–1.39 nm, between 250 and 420 °C in both
clays; (2) HTSC-α-MONT tactoids with spacing 1.22–1.28 nm, between 360 or 250 and 500 or 550 °C in OC-41 or OC-90, respectively;
(3) HTSC-β-MONT with spacing 1.12–1.18 nm, between 360 and 550 °C in both clays, where LTSC and HTSC are low- and high-temperature
stable charcoal, respectively. HTSC-β-MONT differs from HTSC-α-MONT by having carbon atoms keying into the ditrigonal holes
of the clay-O-planes. 相似文献
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