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Ray L Frost - One of the best experts on this subject based on the ideXlab platform.

  • controlled rate thermal analysis and differential scanning calorimetry of sepiolites and palygorskites
    Thermochimica Acta, 2003
    Co-Authors: Ray L Frost, Zhe Ding
    Abstract:

    Abstract A series of sepiolites, palygorskites and “Rocky Mountain Leather” (RML) clay minerals have been analysed by controlled rate thermal analysis and differential scanning calorimetry (DSC). Eight weight loss steps are observed and are structure and composition dependent. Three dehydration steps and five Dehydroxylation steps are observed. The mass spectrometric curve mimicked the differential thermogravimetric (DTGA) curve enabling the detailed determination of the dehydration and Dehydroxylation steps.

  • thermal decomposition of bauxite minerals infrared emission spectroscopy of gibbsite boehmite and diaspore
    Journal of Materials Science, 2002
    Co-Authors: J T Kloprogge, Huada Ruan, Ray L Frost
    Abstract:

    Infrared emission spectroscopy has been used to study the Dehydroxylation behavior over the temperature range from 200 to 750°C of three major Al-minerals in bauxite: gibbsite (synthetic and natural), boehmite (synthetic and natural) and diaspore. A good agreement is found with the thermal analysis and differential thermal analysis curves of these minerals. Loss in intensity of especially the hydroxyl-stretching modes of gibbsite, boehmite and diaspore as function of temperature correspond well with the observed changes in the TGA/DTA patterns. The DTA pattern of gibbsite clearly indicates the formation of boehmite as an intermediate shown by a endotherm around 500°C. Dehydroxylation of gibbsite is followed by a loss of intensity of the 3620 and 3351 cm−1 OH-stretching bands and the corresponding deformation band around 1024 cm−1. Dehydroxylation starts around 220°C and is complete around 350°C. Similar observations were made for boehmite and diaspore. For boehmite Dehydroxylation was observed to commence around 250°C and could be followed by especially the loss in intensity of the bands around 3319 and 3129 cm−1. The DTA pattern of diaspore is more complex with overlapping endotherms around 622 and 650°C. The Dehydroxylation can be followed by the decrease in intensity of the OH-stretching bands around 3667, 3215 and 2972 cm−1. Above 550°C only a single band is observed that disappears after heating above 600°C corresponding to the two endotherms around 622 and 650°C in the DTA.

  • infrared spectroscopy of goethite Dehydroxylation iii ft ir microscopy of in situ study of the thermal transformation of goethite to hematite
    Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2002
    Co-Authors: Huada Ruan, J T Kloprogge, Ray L Frost, Loc V Duong
    Abstract:

    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 (ν1 and ν2), and three bending (νbending-1, 2, 3) and two deformation (νdeformation-1, 2) modes were observed for goethite. The characteristic vibration at 916 cm−1 was observed together with the residuals of the ν1 and ν2 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.

  • Dehydroxylation and the vibrational spectroscopy of aluminum oxo hydroxides using infrared emission spectroscopy part iii diaspore
    Applied Spectroscopy, 1999
    Co-Authors: Ray L Frost, Theo J Kloprogge, S C Russell, Jennifer Szetu
    Abstract:

    Dehydroxylation of diaspore has been followed by a combination of differential thermal analysis (DTA) and infrared emission spectroscopy (IES). The DTA endotherm of diaspore is not simple, and two inflections are observed at 505 and 531 degrees C. Dehydroxylation shows that diaspore loses 15% of its weight upon Dehydroxylation. The Mn-substituted diaspore shows major endotherms at 620 and 649 degrees C with a broad endotherm at 539 degrees C. Infrared absorption bands of diaspore were observed at 3365, 3284, and 3095 cm-1 in the hydroxyl stretching region and at 911, 755, 706, 668, 649, 570, and 544 cm-1 in the low-frequency region. Infrared emission bands were observed at 3239 and 2958 cm-1 in the hydroxyl stretching region. Low-frequency infrared emission bands in agreement with the absorption bands were observed at around 916, 752, 706, 668, 649, 570, and 544 cm-1. The variation of intensity of the hydroxyl stretching frequencies with temperature follows a pattern similar to that for the DTA curves.

  • Dehydroxylation of aluminum oxo hydroxides using infrared emission spectroscopy part ii boehmite
    Applied Spectroscopy, 1999
    Co-Authors: Ray L Frost, Theo J Kloprogge, S C Russell, Jennifer Szetu
    Abstract:

    The Dehydroxylation of boehmite has been studied by the application of infrared emission spectroscopy over the 200 to 750 C temperature range. The Dehydroxylation is followed by the loss of intensity of the hydroxyl stretching frequencies observed at 3478, 3319, and 3129 cm-1 and by the loss of intensity of the hydroxyl deformation modes at 1140 and 1057 cm-1. Dehydroxylation starts at 250 C and is complete by 450 C. No difference was found between the synthetic and natural boehmite Dehydroxylation. The hydroxyl stretching frequencies show a pronounced blue shift, while the hydroxyl deformation modes show a pronounced red shift. Infrared absorption bands were observed at 3413, 3283, and 3096 cm- 1 for the hydroxyl stretching frequencies and at 1161 and 1071 cm-1 for the hydroxyl deformation frequencies. Low-frequency infrared absorption bands are observed at 749, 635, and 542 cm-1 and infrared emission bands at 811, 716, 611, and 456 cm-1. The infrared emission low-frequency bands moved to higher frequencies upon thermal treatment. Spectral changes in the low-frequency bands confirm that Dehydroxylation commenced at 250 C. Infrared emission spectroscopy allows the phase changes of the Al2O3-H2O alumina system to be studied in situ at the elevated temperatures.

Hongfei Cheng - One of the best experts on this subject based on the ideXlab platform.

  • thermal analysis and infrared emission spectroscopic study of halloysite potassium acetate intercalation compound
    Thermochimica Acta, 2010
    Co-Authors: Hongfei Cheng, Jing Yang, Jinshan Zhang
    Abstract:

    Abstract The thermal decomposition of halloysite–potassium acetate intercalation compound was investigated by thermogravimetric analysis and infrared emission spectroscopy. The X-ray diffraction patterns indicated that intercalation of potassium acetate into halloysite caused an increase of the basal spacing from 1.00 to 1.41 nm. The thermogravimetry results show that the mass losses of intercalation the compound occur in main three main steps, which correspond to (a) the loss of adsorbed water, (b) the loss of coordination water and (c) the loss of potassium acetate and Dehydroxylation. The temperature of Dehydroxylation and dehydration of halloysite is decreased about 100 °C. The infrared emission spectra clearly show the decomposition and Dehydroxylation of the halloysite intercalation compound when the temperature is raised. The dehydration of the intercalation compound is followed by the loss of intensity of the stretching vibration bands at region 3600–3200 cm −1 . Dehydroxylation is followed by the decrease in intensity in the bands between 3695 and 3620 cm −1 . Dehydration was completed by 300 °C and partial Dehydroxylation by 350 °C. The inner hydroxyl group remained until around 500 °C.

Douglas K Mccarty - One of the best experts on this subject based on the ideXlab platform.

  • nature of rehydroxylation in dioctahedral 2 1 layer clay minerals
    American Mineralogist, 2012
    Co-Authors: Arkadiusz Derkowski, Victor Drits, Douglas K Mccarty
    Abstract:

    Rehydroxylation of the previously dehydroxylated dioctahedral 2:1 layer clay mineral occurs preferentially in specific sites within the former octahedral sheet. The rehydroxylation of dehydroxylated Al-rich and Al,Mg-rich 2:1 layers occurs as trans -vacant ( tv ) structural arrangements, regardless of whether the initial structure was tv or cis -vacant ( cv ). In nontronite (Fe-rich 2:1 layer clay), the dehydroxylate pseudo-cv structure is probably directly reconstructed into the rehydroxylated cv structure without migration of octahedral cations. Rehydroxylation occurs preferentially in the R 3+ -O r -R 3+ former octahedral structural arrangements (O r = residual oxygen) over R 2+ -O r -R (R = R 3+ or R 2+ = Al 3+ , Fe 3+ or Mg 2+ , Fe 2+ ). In the case of the R 2+ octahedral substitution, the interlayer cation is attracted to the electrostatically undersaturated residual oxygen of the R 2+ -O r -R arrangement, which blocks the ability of water molecules to pass through the ditrigonal cavity and rehydroxylate the previously dehydroxylated local arrangement. The pyrophyllite-like type of octahedral R 3+ -O r -R 3+ arrangements, formed due to the lack of tetrahedral substitution and resulting in the absence of interlayer cations, is thus favored for rehydroxylation over the mica-like R 3+ -O r -R 3+ arrangements where Al occurs in the tetrahedral sheet. The valence of the interlayer cation and the charge density of the 2:1 layer clay mineral, which controls the interlayer cation content, also affect the degree of rehydroxylation. Dehydroxylated 2:1 layer minerals with a high-rehydroxylation potential, including beidellite and illite, use all the adsorbed water molecules that persist above 200 °C for rehydroxylation; the water vapor from the ambient environment also becomes a source of H 2 O molecules for rehydroxylation. The high demand for water molecules to use for rehydroxyltion results in a noticeable gain of mass in the temperature interval between 200 and 350 °C even during heating.

  • kinetics of thermal transformation of partially dehydroxylated pyrophyllite
    American Mineralogist, 2011
    Co-Authors: Victor Drits, Arkadiusz Derkowski, Douglas K Mccarty
    Abstract:

    A multi-cycle heating and cooling thermogravimetric (TG) method was used to study the kinetic behavior of two partially dehydroxylated pyrophyllite samples. In the original state, the S076 sample contains only trans -vacant ( tv ) layers, whereas in sample S037 tv and cis- vacant ( cv ) layers are randomly interstratified. The method consists of consecutive heating cycles (rate 2 °C/min) separated by intervals of cooling to room temperature, with the maximum cycle temperature set (MCT) incrementally higher than in each previous cycle. The activation energy ( E a ) values were calculated for the S037 and S076 samples for all cycles in terms of a homogeneous zero-order reaction with the regression coefficients r2 ≥ 0.9997. The S076 sample had E a values that varied from 40 to 42 kcal/mol within a partial Dehydroxylation ( D T ) range from 19 to 63%. However, at D T values 63% the E a values are slightly lower at 38–39 kcal/mol and drop below 30 kcal/mol at D T = 90%. A bimodal distribution of the S037 sample E a values exists with increasing MCT and D T . In the first cycles of intense Dehydroxylation from tv layers the E a values increase sharply from 34 kcal/mol at D T = 7% to 45 kcal/mol within the MCT interval from 525 to 575 °C and then decrease to 36–38 kcal/mol at the cycles with MCT = 650–700 °C. In the second portion of cycles corresponding to the Dehydroxylation of cv layers, the E a values increase from 36–37 kcal/mol at MCT = 700 °C to 44–46 kcal/mol at MCT = 775 °C. These results show that both tv and cv layers require exactly the same energy for Dehydroxylation and have similar variation of the E a values with MCT and D T . The pyrophyllite particle size distribution is a major factor that is likely responsible for a broad interval of Dehydroxylation temperature. This implies that the lower the temperature, the smaller the particles that can be dehydroxylated. Therefore, the activation energy values at the beginning of the reaction are lower than those at higher degrees of Dehydroxylation because of the combination of a slow experimental heating rate and thin crystallites, which both contribute to lower temperatures at which the reaction starts. The decrease in activation energy observed at the end of the Dehydroxylation reaction of sample S076, and of the tv layer portion of sample S037 is accompanied by an increase in the “induction” temperature interval during which an accumulation of additional thermal energy decreases the activation energy. The kinetic parameters determined for the samples in this study correspond to a homogeneous reaction and are used to predict a general pattern of the structural transformations of pyrophyllite at different stages during Dehydroxylation.

Jing Yang - One of the best experts on this subject based on the ideXlab platform.

  • thermal analysis and infrared emission spectroscopic study of kaolinite potassium acetate intercalate complex
    Journal of Thermal Analysis and Calorimetry, 2011
    Co-Authors: Jing Yang, Qinfu Liu, Zhiliang Zhang
    Abstract:

    The thermal behavior and decomposition of kaolinite–potassium acetate intercalation complex was investigated through a combination of thermogravimetric analysis and infrared emission spectroscopy. Three main changes were observed at 48, 280, 323, and 460 °C which were attributed to (a) the loss of adsorbed water, (b) loss of the water coordinated to acetate ion in the layer of kaolinite, (c) loss of potassium acetate in the complex, and (d) water through Dehydroxylation. It is proposed that the potassium acetate intercalation complex is stability except heating at above 300 °C. The infrared emission spectra clearly show the decomposition and Dehydroxylation of the kaolinite intercalation complex when the temperature is raised. The dehydration of the intercalation complex is followed by the loss of intensity of the stretching vibration bands at region 3600–3200 cm−1. Dehydroxylation is followed by the decrease in intensity in the bands between 3695 and 3620 cm−1. Dehydration is completed by 400 °C and partial Dehydroxylation by 650 °C. The inner hydroxyl group remained until around 700 °C.

  • thermal analysis and infrared emission spectroscopic study of halloysite potassium acetate intercalation compound
    Thermochimica Acta, 2010
    Co-Authors: Hongfei Cheng, Jing Yang, Jinshan Zhang
    Abstract:

    Abstract The thermal decomposition of halloysite–potassium acetate intercalation compound was investigated by thermogravimetric analysis and infrared emission spectroscopy. The X-ray diffraction patterns indicated that intercalation of potassium acetate into halloysite caused an increase of the basal spacing from 1.00 to 1.41 nm. The thermogravimetry results show that the mass losses of intercalation the compound occur in main three main steps, which correspond to (a) the loss of adsorbed water, (b) the loss of coordination water and (c) the loss of potassium acetate and Dehydroxylation. The temperature of Dehydroxylation and dehydration of halloysite is decreased about 100 °C. The infrared emission spectra clearly show the decomposition and Dehydroxylation of the halloysite intercalation compound when the temperature is raised. The dehydration of the intercalation compound is followed by the loss of intensity of the stretching vibration bands at region 3600–3200 cm −1 . Dehydroxylation is followed by the decrease in intensity in the bands between 3695 and 3620 cm −1 . Dehydration was completed by 300 °C and partial Dehydroxylation by 350 °C. The inner hydroxyl group remained until around 500 °C.

Victor Drits - One of the best experts on this subject based on the ideXlab platform.

  • STRUCTURAL TRANSFORMATION OF 2:1 DIOCTAHEDRAL LAYER SILICATES DURING Dehydroxylation-REHYDROXYLATION REACTIONS
    2016
    Co-Authors: Fabrice Muller, Victor Drits, Alain T Plan~on, Jean-louis Robert
    Abstract:

    Abstract--The structural transformation f dioctahedral 2:1 layer silicates (illite, montmorillonite, glau-conite, and celadonite) during a dehydoxylation-rehydroxylation pr cess has been studied by X-ray dif-fraction, thermal analysis, and infrared spectroscopy. The layers of the samples differ in the distribution of the octahedral cations over the cis- and trans-sites as determined by the analysis of the positions and intensities of the 11l, 02l reflections, and that of the relative displacements of adjacent layers along the a axis (c cos ~3/a), as wei1 as by Dehydroxylation-temperature valu s. One illite, glauconite, and celadonite consist of trans-vacant (tv) layers; Wyoming montmorillonite is composed of cis-vacant (cv) layers, where-as in the other illite sample ta, and cv layers are interstratified. The results obtained show that the rehy-droxylated Al-rich minerals (montmorillonite, illites) consist of tv layers whatever the distribution of octahedral cations over cis- and trans-sites in the original structure. The reason for this is that in the dehydroxylated state, both tv and cv layers are transformed into the same layer structure where the former trans-sites are vacant. The Dehydroxylation of glauconite and celadonite is accompanied by a migration of the octahedral cations from former cis-octahedra to empty trans-sites. The structural transformation of these minerals during rehydroxylation depends probably on their cation composition. The rehydroxylation f celadonit

  • STRUCTURAL TRANSFORMATION OF 2:1 DIOCTAHEDRAL LAYER SILICATES DURING Dehydroxylation-REHYDROXYLATION REACTIONS
    2016
    Co-Authors: Fabrice Muller, Victor Drits, Jean-louis Robert
    Abstract:

    Abstract—The structural transformation of dioctahedral 2:1 layer silicates (illite, montmorillonite, glau-conite, and celadonite) during a dehydoxylation-rehydroxylation process has been studied by X-ray dif-fraction, thermal analysis, and infrared spectroscopy. The layers of the samples differ in the distribution of the octahedral cations over the cis- and trans-sites as determined by the analysis of the positions and intensities of the 11l, 02l reflections, and that of the relative displacements of adjacent layers along the a axis (c cos b/a), as well as by Dehydroxylation-temperature values. One illite, glauconite, and celadonite consist of trans-vacant (tv) layers; Wyoming montmorillonite is composed of cis-vacant (cv) layers, where-as in the other illite sample tv and cv layers are interstratified. The results obtained show that the rehy-droxylated Al-rich minerals (montmorillonite, illites) consist of tv layers whatever the distribution of octahedral cations over cis- and trans-sites in the original structure. The reason for this is that in the dehydroxylated state, both tv and cv layers are transformed into the same layer structure where the former trans-sites are vacant. The Dehydroxylation of glauconite and celadonite is accompanied by a migration of the octahedral cations from former cis-octahedra to empty trans-sites. The structural transformation of these minerals during rehydroxylation depends probably on their cation composition. The rehydroxylation of celadonit

  • nature of rehydroxylation in dioctahedral 2 1 layer clay minerals
    American Mineralogist, 2012
    Co-Authors: Arkadiusz Derkowski, Victor Drits, Douglas K Mccarty
    Abstract:

    Rehydroxylation of the previously dehydroxylated dioctahedral 2:1 layer clay mineral occurs preferentially in specific sites within the former octahedral sheet. The rehydroxylation of dehydroxylated Al-rich and Al,Mg-rich 2:1 layers occurs as trans -vacant ( tv ) structural arrangements, regardless of whether the initial structure was tv or cis -vacant ( cv ). In nontronite (Fe-rich 2:1 layer clay), the dehydroxylate pseudo-cv structure is probably directly reconstructed into the rehydroxylated cv structure without migration of octahedral cations. Rehydroxylation occurs preferentially in the R 3+ -O r -R 3+ former octahedral structural arrangements (O r = residual oxygen) over R 2+ -O r -R (R = R 3+ or R 2+ = Al 3+ , Fe 3+ or Mg 2+ , Fe 2+ ). In the case of the R 2+ octahedral substitution, the interlayer cation is attracted to the electrostatically undersaturated residual oxygen of the R 2+ -O r -R arrangement, which blocks the ability of water molecules to pass through the ditrigonal cavity and rehydroxylate the previously dehydroxylated local arrangement. The pyrophyllite-like type of octahedral R 3+ -O r -R 3+ arrangements, formed due to the lack of tetrahedral substitution and resulting in the absence of interlayer cations, is thus favored for rehydroxylation over the mica-like R 3+ -O r -R 3+ arrangements where Al occurs in the tetrahedral sheet. The valence of the interlayer cation and the charge density of the 2:1 layer clay mineral, which controls the interlayer cation content, also affect the degree of rehydroxylation. Dehydroxylated 2:1 layer minerals with a high-rehydroxylation potential, including beidellite and illite, use all the adsorbed water molecules that persist above 200 °C for rehydroxylation; the water vapor from the ambient environment also becomes a source of H 2 O molecules for rehydroxylation. The high demand for water molecules to use for rehydroxyltion results in a noticeable gain of mass in the temperature interval between 200 and 350 °C even during heating.

  • kinetics of thermal transformation of partially dehydroxylated pyrophyllite
    American Mineralogist, 2011
    Co-Authors: Victor Drits, Arkadiusz Derkowski, Douglas K Mccarty
    Abstract:

    A multi-cycle heating and cooling thermogravimetric (TG) method was used to study the kinetic behavior of two partially dehydroxylated pyrophyllite samples. In the original state, the S076 sample contains only trans -vacant ( tv ) layers, whereas in sample S037 tv and cis- vacant ( cv ) layers are randomly interstratified. The method consists of consecutive heating cycles (rate 2 °C/min) separated by intervals of cooling to room temperature, with the maximum cycle temperature set (MCT) incrementally higher than in each previous cycle. The activation energy ( E a ) values were calculated for the S037 and S076 samples for all cycles in terms of a homogeneous zero-order reaction with the regression coefficients r2 ≥ 0.9997. The S076 sample had E a values that varied from 40 to 42 kcal/mol within a partial Dehydroxylation ( D T ) range from 19 to 63%. However, at D T values 63% the E a values are slightly lower at 38–39 kcal/mol and drop below 30 kcal/mol at D T = 90%. A bimodal distribution of the S037 sample E a values exists with increasing MCT and D T . In the first cycles of intense Dehydroxylation from tv layers the E a values increase sharply from 34 kcal/mol at D T = 7% to 45 kcal/mol within the MCT interval from 525 to 575 °C and then decrease to 36–38 kcal/mol at the cycles with MCT = 650–700 °C. In the second portion of cycles corresponding to the Dehydroxylation of cv layers, the E a values increase from 36–37 kcal/mol at MCT = 700 °C to 44–46 kcal/mol at MCT = 775 °C. These results show that both tv and cv layers require exactly the same energy for Dehydroxylation and have similar variation of the E a values with MCT and D T . The pyrophyllite particle size distribution is a major factor that is likely responsible for a broad interval of Dehydroxylation temperature. This implies that the lower the temperature, the smaller the particles that can be dehydroxylated. Therefore, the activation energy values at the beginning of the reaction are lower than those at higher degrees of Dehydroxylation because of the combination of a slow experimental heating rate and thin crystallites, which both contribute to lower temperatures at which the reaction starts. The decrease in activation energy observed at the end of the Dehydroxylation reaction of sample S076, and of the tv layer portion of sample S037 is accompanied by an increase in the “induction” temperature interval during which an accumulation of additional thermal energy decreases the activation energy. The kinetic parameters determined for the samples in this study correspond to a homogeneous reaction and are used to predict a general pattern of the structural transformations of pyrophyllite at different stages during Dehydroxylation.

  • Structural transformation of 2:1 dioctahedral layer silicates during Dehydroxylation-rehydroxylation reactions.
    Clays and Clay Minerals, 2000
    Co-Authors: Fabrice Muller, Victor Drits, Alain Plançon, Jean-louis Robert
    Abstract:

    The structural transformation of dioctahedral 2:1 layer silicates (illite, montmorillonite, glauconite, and celadonite) during a dehydoxylation-rehydroxylation process has been studied by X-ray diffraction, thermal analysis, and infrared spectroscopy. The layers of the samples differ in the distribution of the octahedral cations over the cis- and trans-sites as determined by the analysis of the positions and intensities of the 11l, 02l reflections, and that of the relative displacements of adjacent layers along the a axis (c cos ß/a), as well as by Dehydroxylation-temperature values. One illite, glauconite, and celadonite consist of trans-vacant (tv) layers; Wyoming montmorillonite is composed of cis-vacant (cv) layers, whereas in the other illite sample tv and cv layers are interstratified. The results obtained show that the rehydroxylated Al-rich minerals (montmorillonite, illites) consist of tv layers whatever the distribution of octahedral cations over cis- and trans-sites in the original structure. The reason for this is that in the dehydroxylated state, both tv and cv layers are transformed into the same layer structure where the former trans-sites are vacant. The Dehydroxylation of glauconite and celadonite is accompanied by a migration of the octahedral cations from former cis-octahedra to empty trans-sites. The structural transformation of these minerals during rehydroxylation depends probably on their cation composition. The rehydroxylation of celadonite preserves the octahedral-cation distribution formed after Dehydroxylation. Therefore, most 2:1 layers of celadonite that rehydroxylate (~75%) have cis-vacant octahedra and, only in a minor part of the layers, a reverse cation migration from former trans-sites to empty octahedra occurred. In contrast, for a glauconite sample with a high content in IVAl and VIAl the rehydroxylation is accompanied by the reverse cation migration and most of the 2:1 layers are transformed into tv layers.