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1.
Grygar T. Ruan I. H. D. Gilkes R. J. 《Journal of Thermal Analysis and Calorimetry》1999,55(1):301-309
The kinetics of thermal dehydroxylation of aluminuous goethites [1] synthesised from a ferrous salt has been re-examined using
the general reaction order kinetic law. The utilised data processing was based on the procedures employed by dissolution kinetics.
Recalculation of the activation energies EA of the dehydroxylation yielded the values 130, 132, 128, and 123 kJ mol−1 for pure goethite, goethite with 10, 20, and 30 mol% Al substitution, respectively. The values of EA are in a good agreement with those given for goethite in literature. The EA values are linearly related with the chemically bound excess H2O/OH− in the crystal lattice that is apparently influenced by Al substitution.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
F. Sahnoune N. Saheb B. Khamel Z. Takkouk 《Journal of Thermal Analysis and Calorimetry》2012,107(3):1067-1072
Thermal analysis techniques remain important tools amongst the large variety of methods used for analysis of the dehydroxylation
of kaolinite. In the present study, the kinetics of dehydroxylation of Algerian kaolinite, wet ball milled for 5 h followed
by attrition milling for 1 h, was investigated using differential thermal analysis (DTA) and thermogravimetry (TG). Experiments
were carried out between room temperature and 1350 °C at heating rates of 5, 10 and 20 °C min−1. The temperature of dehydroxylation was found to be around 509 °C. The activation energy and frequency parameter evaluated
through isothermal DTA treatment were 174.69 kJ mol−1 and 2.68 × 109 s−1, respectively. The activation energies evaluated through non-isothermal DTA and TG treatments were 177.32 and 177.75 kJ mol−1, respectively. Growth morphology parameters n and m were found to be almost equal to 1.5. 相似文献
3.
Differential scanning calorimetry shows two endotherms at 75 and 225°C for synthetic goethite. The latter endotherm is strongly
asymmetric on the low temperature side. The endotherms were attributed to the loss of water and the dehydroxylation of the
goethite. The temperature of the endotherms and the enthalpy of the phase change were found to be linear functions of the
percentage of aluminium substitution into the goethite. High-resolution thermogravimetric analysis of goethite showed three
mass loss steps, occurring at ~175, 196 and 263°C. The temperatures of these mass loss steps and the percentage of mass loss
were also linearly related to the degree of Al substitution. The use of infrared emission spectroscopy confirmed the temperature
of dehydroxylation. The observation of the low temperature dehydroxylation of goethite and its relation to ancient aboriginal
cave art is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
The thermal dehydroxylation of natural Al-bearing geothite was investigated by IR spectroscopy. Venezuelan lateritic bauxites (which in addition to goethite contain kaolinite, gibbsite, ilmenite and quartz), as well as chemically isolated samples of Al-goethites, were heated to 300, 600 and 1000°C. The spectral features of the iron oxides formed during the thermal treatment depend on the heating temperature, showing that the first dehydroxylation product is Al-bearing protohematite which at temperatures above 600°C is recrystallized to Al-bearing hematite. Part of the aluminum which is occuled in this hematite originates from the gibbsite and to a smaller extent from the kaolinite. 相似文献
5.
J. Richard Ward 《Thermochimica Acta》1975,13(1):7-14
The kinetics of the dehydroxylation of talc have been measured in the temperature interval 1100–1160 K by means of isothermal weight-change determinations. The reaction follows first-order kinetics. Over the indicated temperature range the enthalpy of activation was found to be 101±4 kcal mol?1, and the entropy of activation was found to be 16±4 cal mol?1 K?1. The error estimates correspond to one standard deviation. The enthalpy necessary to break the MgOH bond was estimated from the heat of reaction for MgOH(g) → Mg(g)+OH(g). This turns out to be 97 kcal mol?1 in reasonable agreement with the measured enthalpy of activation.These activation parameters are consistent with the mechanism proposed for dehydroxylation of talc consisting of MgOH bond scission and subsequent migration of magnesium. These results contradict a previous report on the kinetics of talc dehydroxylation in which a diffusion-controlled expression was claimed to represent the rate of talc weight loss. It is suggested that the presence of adsorbed water on the talc used in the previous investigation is responsible for the discrepancy. 相似文献
6.
H D Ruan R L Frost J T Kloprogge 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2001,57(13):2575-2586
The behavior of the hydroxyl units of synthetic goethite and its dehydroxylated product hematite was characterized using a combination of Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) during the thermal transformation over a temperature range of 180-270 degrees C. Hematite was detected at temperatures above 200 degrees C by XRD while goethite was not observed above 230 degrees C. Five intense OH vibrations at 3212-3194, 1687-1674, 1643-1640, 888-884 and 800-798 cm(-1), and a H2O vibration at 3450-3445 cm(-1) were observed for goethite. The intensity of hydroxyl stretching and bending vibrations decreased with the extent of dehydroxylation of goethite. Infrared absorption bands clearly show the phase transformation between goethite and hematite: in particular. the migration of excess hydroxyl units from goethite to hematite. Two bands at 536-533 and 454-452 cm(-1) are the low wavenumber vibrations of Fe-O in the hematite structure. Band component analysis data of FTIR spectra support the fact that the hydroxyl units mainly affect the a plane in goethite and the equivalent c plane in hematite. 相似文献
7.
T. Zaremba A. Krząkała J. Piotrowski D. Garczorz 《Journal of Thermal Analysis and Calorimetry》2010,101(2):479-485
This article reports the possibility of detoxification of chrysotile asbestos through a low temperature heating and grinding
treatment. The effect of thermal treatment at different temperatures in the range from 500 to 725 °C for 3 h on raw natural
asbestos was characterized by thermal analysis, X-ray diffraction, and scanning electron microscopy. It was found that an
isothermal treatment at 650 °C caused the complete dehydroxylation of chrysotile Mg3Si2O5(OH)4. Transformation of the dehydroxylated phase to forsterite Mg2SiO4 was obtained by heat treatment in the range 650–725 °C. The study of microstructure changes of heated asbestos show the destruction
of characteristic fibers of chrysotile and formation of strips of forsterite. It is easily milled to pulverulent-shape material
by mechanical milling in vibratory mill. 相似文献
8.
H. Bayram M. Önal G. Üstünışık Y. Sarıkaya 《Journal of Thermal Analysis and Calorimetry》2007,89(1):169-174
An industrial raw material taken from Sivrihisar (Eskişehir, Turkey) region was heat-treated at different temperatures in
the range of 100–1000°C for 2 h. The volumetric percentage of the particles having a diameter below 2 μm after staying in
an aqueous suspension of the material was determined as 67% by the particle size distribution analysis. The mineralogical
composition of the material was obtained as mass% of 32% palygorskite, 10% metahalloysite, 35% magnesite, 20% dolomite and
3% interparticle water by using the acid treatment, X-ray diffraction and thermal analysis (TG, DTA) data.
The temperature ranges were determined for the endothermic dehydrations for the interparticle water as 25–140°C, for the zeolitic
water as 140–320°C, and for the bound water as 320–480°C, in the palygorskite. The temperature range for the endothermic dehydroxylation
and exothermic recrystalization of the palygorskite is 780–840°C. The temperature range for the endothermic dehydroxylation
of the metahalloysite and calcinations of magnesite are coincided at 480–600°C. Dolomite calcined in the temperature range
of 600–1000°C by two steps. The zig-zag changes in the specific surface area (S/m2 g−1) and specific micro and mesopore volume (V/cm3 g−1) as the temperature increases were discussed according to the dehydrations in the palygorkskite, dehydroxylation of palygorskite
and metahalloysite, and calcinations in magnesite and dolomite. 相似文献
9.
The thermal transformations of muscovite flakes are a key point in many applications because besides dehydroxylation a significant
exfoliation process occurs. Dehydroxylation kinetic is experimented by isothermal TG analyses in the 700–850°C temperature
range and described with the Avrami theory. Hydroxyl condensation predominates at the onset of the process, but water diffusion
is the most important process when the transformed fraction is high. The progressive transition between the two transformation
stages contrast with the more accentuated transition for a ground muscovite. The activation energy varies weakly (190–214
kJ mol−1) in the whole transformation process that supports the co-existence of hydroxyl condensation and diffusion phenomena. Dehydroxylation
kinetic increases strongly with temperature and decreases with the reaction advancement. Exfoliation is correlated with dehydroxylation
kinetic and occurs in a narrow transformation and temperature ranges. An in-situ combination process of hydroxyls occurs and
water vapor favors the layer expansion. 相似文献
10.
Nilgün Yener Müşerref Önal Gökçe Üstünışık Y. Sarıkaya 《Journal of Thermal Analysis and Calorimetry》2007,88(3):813-817
An industrial raw material taken from Beypazarı (Ankara, Turkey) region was heated at different temperatures in the 100–1100°C
interval for 2 h. The volumetric percentage of particles having diameter below 2 μm in an aqueous suspension of the material
held 24 h were determined as 85% by the particle size distribution analysis. The mineralogical composition of the material
was obtained as mass% of 81% sepiolite, 15% dolomite, and 4% interparticle water by using the X-ray diffraction (XRD) and
thermal analysis (TG, DTA) data. The temperature ranges were determined for the dehydrations of the interparticle water and
the zeolitic water as 25–340°C, for the dehydration of the bound water as 340–580°C, and for the dehydroxylation of the hydroxyls
as 800–833°C in the sepiolite. The zig-zag changes in the specific surface area (S/m2 g−1) and specific micro-and mesopore volume (V/cm3 g−1) with the temperature increases were discussed according to the dehydrations and dehydroxylation of the sepiolite. 相似文献
11.
Ruan HD Frost RL Kloprogge JT Duong L 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(5):967-981
Fourier transform infrared microscopy has been used to investigate in situ dehydroxylation of goethite to form hematite. The characterisation was based on the behaviour of hydroxyl units, which were observed in the hydroxyl stretching and hydroxyl deformation and water bending regions, and the Fe-O vibrations of the newly formed hematite during the thermal dehydroxylation process. Two hydroxyl stretching modes (v1 and v2), and three bending (V(bending-1, 2, 3)) and two deformation (V(deformation-1, 2)) modes were observed for goethite. The characteristic vibration at 916 cm(-1) was observed together with the residuals of the v1 and v2 bands in hematite spectrum. The structural transformation between goethite and hematite through thermal dehydroxylation was interpreted in order to provide criteria that can be used for the characterisation of thermally activated bauxite and their conversion to activated alumina phases. 相似文献
12.
Tanveer Hussain Bokhari A. Mushtaq Islam Ullah Khan 《Journal of Radioanalytical and Nuclear Chemistry》2010,285(2):389-398
In this work, sorption of Ni(II) from aqueous solution to goethite as a function of various water quality parameters and temperature
was investigated. The results indicated that the pseudo-second-order rate equation fitted the kinetic sorption well. The sorption
of Ni(II) to goethite was strongly dependent on pH and ionic strength. A positive effect of HA/FA on Ni(II) sorption was found
at pH < 8.0, whereas a negative effect was observed at pH > 8.0. The Langmuir, Freundlich, and D-R models were applied to
simulate the sorption isotherms at three different temperatures of 293.15 K, 313.15 K and 333.15 K. The thermodynamic parameters
(ΔH
0, ΔS
0 and ΔG
0) were calculated from the temperature dependent sorption, and the results indicated that the sorption was endothermic and
spontaneous. At low pH, the sorption of Ni(II) was dominated by outer-sphere surface complexation or ion exchange with Na+/H+ on goethite surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. 相似文献
13.
Thermal differential diagnosis of mica mineral group 总被引:1,自引:0,他引:1
The following criteria can be used for differential diagnosis of mica mineral group: weight loss < 350°C; weight loss during dehydroxylation (500–1000°C); peak temperature of structural decomposition and formation of high temperature phases; course of dilatometric curves during dehydroxylation and structural decomposition interval (Fig. 1).Using the single criteria by stepwise comparing a complete thermal differentiation is possible between the members of mica mineral group.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthday 相似文献
14.
Influence of the Degree of Dehydroxylation of Kaolinite on the Properties of Aluminosilicate Glasses
The degree of dehydroxylation of kaolinite, DTG and DIR, respectively, is characterized by thermogravimetric analysis (TG) and Fourier transform infrared spectroscopy (FTIR). The
relation between DTG and DIR based on the infrared absorptions at 3600–3700, 915, 810, and 540 cm−1 is established. Three regions can clearly be distinguished: the dehydroxylation region (DTG<0.9), the metakaolinite region (0.9<DTG<1) and the ‘spinel’ region(DTG=1). The effect of the degree of dehydroxylation of kaolinite on the amount of reactive material is measured by the reaction
enthalpy, ΔH, of the low-temperature reaction of the dehydroxylated kaolinite with a potassium silicate solution using differential scanning
calorimetry (DSC). |ΔH| increases almost linearly with DTG in the dehydroxylation region. In the metakaolinite region, ΔH and thus the amount of reactive material, becomes constant. |ΔH| is sharply decreasing when metakaolinite transforms into other phases in the ‘spinel’ region. No significant differences
in the reactivity of the dehydroxylates is detected with DSC. According to FTIR, the use of partially dehydroxylated kaolinite
is not influencing the molecular structure of the low-temperature synthesized aluminosilicates, but residual kaolinite is
retrieved as an additive.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
15.
I. L. Lapides 《Journal of Thermal Analysis and Calorimetry》1997,50(1-2):269-277
The equation for calculation of the activation energy of the diffusion of the evolved products through the matrix (E) from a single TG curve were proposed by solving Fick's laws. The solution is based on the similarly theory by utilizing a Fourier number.The proposed method was examined by using mass loss data for the dehydroxylation of some micas with and without FeO (muscovite and its varieties and lepidolite) as determined from their TG curves. TheE values for the first stage of the dehydroxylation of these micas areE
1,=85±10 kJ mol–1; for the final stageE
2=380±40 kJ mol–1 and for the mass loss connected with fluorineE
F=85±10 kJ mol–1.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthdayPart of this work was carried out in the Institute of Geochemistry of the USSR Academy Science (Irkutsk). I wish to thank Dr. S. B. Brandt for helpful discussions.I am pleased to express my gratitude to Prof. S. Yariv for his important comments.I am grateful to the Ministry of Absorption of the Government of Israel for financial support of this work. 相似文献
16.
A kinetic study on decomposition processes of some penicillin and some commercial drugs was carried out. As expected by the
complex structures of penicillins, several steps with different activation energies occurred in their decomposition processes.
Model-fitting and model-free kinetic approach were applied to non-isothermal and isothermal data.
In the model-fitting methods the kinetic triplets (f(α), A and E
a) that defines a single reaction step resulted in being at variance with the multi-step nature of penicillins decomposition.
The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation
energies on the extent of conversion. The complex nature of the multi-step process of the studied compounds was more easily
revealed using a broader temperature range in non-isothermal isoconversional method. The failure in the model fitting method
did not allow calculating storage times. Model-fitting and model-free methods, both isothermal and non-isothermal, showed
that F1 mechanism is able to describe decomposition processes for drugs (having Phosphomycin salts as active component) for
which a single decomposition process occurs. Statistical analysis allowed us to select reliable kinetic parameters related
to the decomposition processes for these last compounds. This procedure showed that the values obtained by extrapolation,
outside the temperature range where the processes occurred must be used with caution. Indeed half-life and shelf-life values,
commonly extrapoled at room temperature, seemed to be unrealistic.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
Heider Nasser ákos Rédey Tatiana Yuzhakova Zsolt Németh Tóth Tamás Ollár 《Reaction Kinetics and Catalysis Letters》2007,92(2):329-335
CO adsorption at low temperature has been used to probe Lewis acid sites created upon dehydroxylation of γ-Al2O3 and reduction of Mo/Al2O3 catalysts, using Fourier Transform Infrared spectroscopy (FTIR).
Carbon-monoxide adsorption on γ-Al2O3 and Mo/Al2O3 catalysts dehydroxylated and reduced at different temperatures was studied at 78 K by IR spectroscopy. However, our results
indicate that there is an approximately linear correlation between the increase either of dehydroxylation or the extent of
reduction of the catalysts and the increasing absorbance of CO due to CO adsorption on Lewis acid sites created upon dehydroxylation
of γ-Al2O3 and reduction of Mo/Al2O3. 相似文献
18.
Zhiqiang Guo Dapeng Xu Donglin Zhao Shouwei Zhang Jinzhang Xu 《Journal of Radioanalytical and Nuclear Chemistry》2011,287(2):505-512
This work contributed to the adsorption of radiocobalt on goethite as a function of contact time, pH, ionic strength and foreign
ions in the absence and presence of fulvic acid (FA) under ambient conditions. The results indicated that adsorption of Co(II)
was dependent on ionic strength and foreign ions at low pH values (pH < 7.8), and independent of ionic strength and foreign
ions at high pH values (pH > 7.8). Outer-sphere surface complexation and/or ion exchange were the main mechanisms of Co(II)
adsorption on goethite at low pH values, whereas inner-sphere surface complexation was the main adsorption mechanism at high
pH values. The presence of FA enhanced Co(II) adsorption at low pH values, but reduced Co(II) adsorption at high pH values.
The thermodynamic data (ΔH
0, ΔS
0, ΔG
0) were calculated from the temperature dependent adsorption isotherms, and the results suggested that adsorption process of
Co(II) on goethite was spontaneous and endothermic. The results are crucial to understand the physicochemical behavior of
Co(II) in the nature environment. 相似文献
19.
A modified first-order kinetic law which takes into account defect decay during an ordering process was employed to predict the short-range-order kinetics of a quenched and a quenched-deformed Cu—5 at.% Zn alloy, in conjunction with experiments performed by isothermal calorimetry. The effective activation energy of point defect migration and its temperature dependence strongly suggest the contribution of bound vacancies to the ordering process. An estimate of 91.2 kJ mol–1 was made for the activation energy of solute—vacancy migration by applying an effective rate constant, a value in very good agreement with that obtained from previous non-isothermal experiments. The isothermal curves were utilized to determine the ordering energy: w=–2.90 kJ mol–1. In conjunction, a parametric study of the defect sink density was performed in order to assess its influence on the calculated isothermal curve profiles.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
20.
The mineralogical composition of the Kütahya calcium bentonite (CaB) from Turkey was obtained as mass% of 60% calcium rich
smectite (CaS), 30% opal-CT (OCT), trace amount illite (I), and some non-clay impurities by using chemical analysis (CA),
X-ray diffraction (XRD), and thermal analysis (TG-DTA) data. The crystallinity, porosity, and surface area of the samples
heated between 25–1300°C for 2 h were examined by using XRD, TG, DTA and N2-adsorption-desorption data. The position of the 001 reflection which is the most characteristic for CaS does not affect from
heating between 25–600°C and then disappeared. The decrease in relative intensity (I/I
0) from 1.0 to zero and the increase in full width at half-maximum peak height (FWHM) from 0.25 to 1.0° of the 001 reflection
show that the crystallinity of the CaS decreased continuously by rising the heating temperature from 25 to 900°C and then
collapsed. The most characteristic 101 reflection for opals intensifies greatly between 900 and 1100°C with the opal becoming
more crystalline.
The total water content of the natural bentonite after dried at 25, 105 and 150°C for 48 h were determined as 8.8, 5.0 and
2.5%, respectively. The mass loss occurs between 25 and 400°C over two steps with the maximum rate at 80 and 150°C, respectively.
The exact distinction of the dehydration temperatures for the adsorbed water and interlayer water is seen almost impossible.
The temperature interval, maximum rate temperature, and mass loss during dehydroxylation are 400–800°C, 670°C and 4.6–5.0%,
respectively. The maximum rate temperatures for decrystallization and recrystallization are 980 and 1030°C, respectively.
The changes in specific micropore volume (V
mi), specific mesopore volume (V
me), specific surface area (S) were discussed according to the dehydration and dehydroxylation of the CaS. The V
mi, V
me and S reach to their maxima at around 400°C with the values of 0.045, 0.115 cm3 g−1 and 90 m2 g−1, respectively. The radii of mesopores for the bentonite heated at 400°C are distributed between 1–10 nm and intensified approximately
at 1.5 nm. 相似文献