{"id":{"repo_id":"aachen","oai_identifier":"oai:publications.rwth-aachen.de:50142"},"canonical_url":"https://search.dev.ndltd.org/etd/aachen/oai:publications.rwth-aachen.de:50142","repository":{"repo_id":"aachen","name":"RWTH Aachen University","base_url":"https://publications.rwth-aachen.de/oai2d"},"display":{"title":"Untersuchungen zur Dehydroxilierung dioktaedrischer Smectite","abstract":"Due to their special features smectites, dioctahedral smectites in particular, are widely used in a broad spectrum of technical applications and processes. They seem to be one of the most important indsutrial minerals. By using smectites in thermal technology processes their behaviour plays an important role. So far many questions concerning these characteristics are still open. This study was carried out to gain detailed insight of mineralogical features and changes during thermal changes in smectites. The main focus of this work is the dehydroxylation process of dioctahedral semctites. In a first chapter the seven utilised bentonites, as well as the extracted smectites were investigated by conventional methods. Accordingly they were characterised as different types of dioctahedral smectites, presenting three montmorillonites, one montmorillonitic beidellite, one beidellite and two nontronites. Dehydroxylation of dioctahedral smectites is strongly linked with changes in smectite-structure. This encompasses changes in cation coordination (Wardle and Brindley, 1972) and possibly migration of octahedral cations (Drits et al., 1995; Heller-Kallai and Rozenson, 1980). By keeping this in mind for interpretation of different behaviour during dehydroxylation, the octahedral sheets of the seven smectites were characterised by Monte Carlo Simulation in a second chapter. Both, trans- and cis-vacant smectites, display a preferred orientation of AlAl and FeFe pairs along the OH-bonding direction. They rather show local segregation of lonely cation-pairs than large-area clusters. A preferred incorporation of Fe or Al to special positions is not observable. In cis-vacant smectites AlFe pairs appear more and AlMg pairs less frequently than expected for random distributed cations. Nontronites display strong undersaturation of AlFe pairs compared to random distributed cations. Whereas segregation of AlAl and FeFe pairs can be explained by different size and charge of individual cations, the preferred orientation along OH-bonded directions seems to be created during the formation of the structure. Thereby hydration and hydrolysis energy of the respective cations may deliver an essential contribution to develop a trans- or cis-vacant constitution. Investigations of structural changes during the dehydroxylation process was carried out at FTIR-spectra of isothermal heated material and is discussed in a third chapter. Substitutions within the tetrahedral sheet show effects on the position of the v SiO band at 1027-1045 cm-1 as well as on the position of the delta AlFe und delta AlMg band. The process of dehydroxylation is not homogeneous. Hydroxyl groups linked with AlMg and FeFe pairs show lower activation energy for breaking up than hydroxyl groups linked with AlFe and AlAl pairs. Within all smectites dehydroxylation proceeds very fast and the process is completed closely above the initial dehydroxylation temperature (mainly before the dehydroxylation peak in DSC/TG measurements). An additional supply of energy to the smectitic structure initiates continous transformation. New absorption bands develop which only cease by achieving a fully water free structure. Thus the dehydroxilation process can be regarded as a two step process. Fully water free cis-vacant structures seem to be more ordered than respective trans-vacant structures. In a fourth chapter the kinetic of dehydroxylation was investigated. Since it is impossible to resolve each reaction on atom level an overall kinetic was measured. This reaction gets more and more controlled by diffusion during temperature increase and shows a rate-determining step during the structures loss of water molecules. Differences between cis- and trans-vacant smectites are not observable. The investigated smectites can be divided with respect to the temperature dependency of the kinetic reaction. Montmorillonites show an Ea > 140 kJ/mol and montmorillonitic beidellite, beidellite and nontronites show an E-a < 70 kJ/mol. Du to an increase of water molecules within the interlayer sheet of the smectites bacause of an increased turnover, the activation energy also increases with respect to the reaction progress.","abstract_html":"Due to their special features smectites, dioctahedral smectites in particular, are widely used in a broad spectrum of technical applications and processes. They seem to be one of the most important indsutrial minerals. By using smectites in thermal technology processes their behaviour plays an important role. So far many questions concerning these characteristics are still open. This study was carried out to gain detailed insight of mineralogical features and changes during thermal changes in smectites. The main focus of this work is the dehydroxylation process of dioctahedral semctites. In a first chapter the seven utilised bentonites, as well as the extracted smectites were investigated by conventional methods. Accordingly they were characterised as different types of dioctahedral smectites, presenting three montmorillonites, one montmorillonitic beidellite, one beidellite and two nontronites. Dehydroxylation of dioctahedral smectites is strongly linked with changes in smectite-structure. This encompasses changes in cation coordination (Wardle and Brindley, 1972) and possibly migration of octahedral cations (Drits et al., 1995; Heller-Kallai and Rozenson, 1980). By keeping this in mind for interpretation of different behaviour during dehydroxylation, the octahedral sheets of the seven smectites were characterised by Monte Carlo Simulation in a second chapter. Both, trans- and cis-vacant smectites, display a preferred orientation of AlAl and FeFe pairs along the OH-bonding direction. They rather show local segregation of lonely cation-pairs than large-area clusters. A preferred incorporation of Fe or Al to special positions is not observable. In cis-vacant smectites AlFe pairs appear more and AlMg pairs less frequently than expected for random distributed cations. Nontronites display strong undersaturation of AlFe pairs compared to random distributed cations. Whereas segregation of AlAl and FeFe pairs can be explained by different size and charge of individual cations, the preferred orientation along OH-bonded directions seems to be created during the formation of the structure. Thereby hydration and hydrolysis energy of the respective cations may deliver an essential contribution to develop a trans- or cis-vacant constitution. Investigations of structural changes during the dehydroxylation process was carried out at FTIR-spectra of isothermal heated material and is discussed in a third chapter. Substitutions within the tetrahedral sheet show effects on the position of the v SiO band at 1027-1045 cm-1 as well as on the position of the delta AlFe und delta AlMg band. The process of dehydroxylation is not homogeneous. Hydroxyl groups linked with AlMg and FeFe pairs show lower activation energy for breaking up than hydroxyl groups linked with AlFe and AlAl pairs. Within all smectites dehydroxylation proceeds very fast and the process is completed closely above the initial dehydroxylation temperature (mainly before the dehydroxylation peak in DSC/TG measurements). An additional supply of energy to the smectitic structure initiates continous transformation. New absorption bands develop which only cease by achieving a fully water free structure. Thus the dehydroxilation process can be regarded as a two step process. Fully water free cis-vacant structures seem to be more ordered than respective trans-vacant structures. In a fourth chapter the kinetic of dehydroxylation was investigated. Since it is impossible to resolve each reaction on atom level an overall kinetic was measured. This reaction gets more and more controlled by diffusion during temperature increase and shows a rate-determining step during the structures loss of water molecules. Differences between cis- and trans-vacant smectites are not observable. The investigated smectites can be divided with respect to the temperature dependency of the kinetic reaction. Montmorillonites show an Ea &gt; 140 kJ/mol and montmorillonitic beidellite, beidellite and nontronites show an E-a &lt; 70 kJ/mol. Du to an increase of water molecules within the interlayer sheet of the smectites bacause of an increased turnover, the activation energy also increases with respect to the reaction progress.","abstract_has_math":false,"creators":["Marchel, Christian Willy"],"institution":"Publikationsserver der RWTH Aachen University","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":["Stanjek, Helge"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2008,"date_issued":"2008","date_published":"2008","updated_at":"2026-07-30T19:40:16Z","subjects":["info:eu-repo/classification/ddc/550","Kinetik","Geowissenschaften","Smektit","Dehydroxilierung","Kationenverteilung","IR-Spektroskopie","smectite","dehydroxylation","cation distribution","kinetic","IR-spectroscopy"],"languages":["ger"],"rights":["info:eu-repo/semantics/openAccess"],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-112697%22"],"render_values":[{"text":"https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-112697%22","href":"https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-112697%22","code":true}]}]},"links":{"outbound_url":"https://publications.rwth-aachen.de/record/50142","outbound_label":"Repository record","outbound_source":"dc:identifier"},"source_record":{"url":"https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A50142","prefix":"oai_dc"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Stanjek, Helge"]},{"key":"dc:creator","label":"Author","values":["Marchel, Christian Willy"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:coverage","label":"Dc Coverage","values":["DE"]},{"key":"dc:date","label":"Dc Date","values":["2008"]},{"key":"dc:publisher","label":"Institution","values":["Publikationsserver der RWTH Aachen University"]},{"key":"dc:relation","label":"Dc Relation","values":["info:eu-repo/semantics/altIdentifier/urn/urn:nbn:de:hbz:82-opus-23890"]},{"key":"dc:type","label":"Dc Type","values":["info:eu-repo/semantics/doctoralThesis","info:eu-repo/semantics/publishedVersion"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["info:eu-repo/classification/ddc/550","Kinetik","Geowissenschaften","Smektit","Dehydroxilierung","Kationenverteilung","IR-Spektroskopie","smectite","dehydroxylation","cation distribution","kinetic","IR-spectroscopy"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["ger"]},{"key":"dc:rights","label":"Dc Rights","values":["info:eu-repo/semantics/openAccess"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://publications.rwth-aachen.de/record/50142","https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-112697%22"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Due to their special features smectites, dioctahedral smectites in particular, are widely used in a broad spectrum of technical applications and processes. They seem to be one of the most important indsutrial minerals. By using smectites in thermal technology processes their behaviour plays an important role. So far many questions concerning these characteristics are still open. This study was carried out to gain detailed insight of mineralogical features and changes during thermal changes in smectites. The main focus of this work is the dehydroxylation process of dioctahedral semctites. In a first chapter the seven utilised bentonites, as well as the extracted smectites were investigated by conventional methods. Accordingly they were characterised as different types of dioctahedral smectites, presenting three montmorillonites, one montmorillonitic beidellite, one beidellite and two nontronites. Dehydroxylation of dioctahedral smectites is strongly linked with changes in smectite-structure. This encompasses changes in cation coordination (Wardle and Brindley, 1972) and possibly migration of octahedral cations (Drits et al., 1995; Heller-Kallai and Rozenson, 1980). By keeping this in mind for interpretation of different behaviour during dehydroxylation, the octahedral sheets of the seven smectites were characterised by Monte Carlo Simulation in a second chapter. Both, trans- and cis-vacant smectites, display a preferred orientation of AlAl and FeFe pairs along the OH-bonding direction. They rather show local segregation of lonely cation-pairs than large-area clusters. A preferred incorporation of Fe or Al to special positions is not observable. In cis-vacant smectites AlFe pairs appear more and AlMg pairs less frequently than expected for random distributed cations. Nontronites display strong undersaturation of AlFe pairs compared to random distributed cations. Whereas segregation of AlAl and FeFe pairs can be explained by different size and charge of individual cations, the preferred orientation along OH-bonded directions seems to be created during the formation of the structure. Thereby hydration and hydrolysis energy of the respective cations may deliver an essential contribution to develop a trans- or cis-vacant constitution. Investigations of structural changes during the dehydroxylation process was carried out at FTIR-spectra of isothermal heated material and is discussed in a third chapter. Substitutions within the tetrahedral sheet show effects on the position of the v SiO band at 1027-1045 cm-1 as well as on the position of the delta AlFe und delta AlMg band. The process of dehydroxylation is not homogeneous. Hydroxyl groups linked with AlMg and FeFe pairs show lower activation energy for breaking up than hydroxyl groups linked with AlFe and AlAl pairs. Within all smectites dehydroxylation proceeds very fast and the process is completed closely above the initial dehydroxylation temperature (mainly before the dehydroxylation peak in DSC/TG measurements). An additional supply of energy to the smectitic structure initiates continous transformation. New absorption bands develop which only cease by achieving a fully water free structure. Thus the dehydroxilation process can be regarded as a two step process. Fully water free cis-vacant structures seem to be more ordered than respective trans-vacant structures. In a fourth chapter the kinetic of dehydroxylation was investigated. Since it is impossible to resolve each reaction on atom level an overall kinetic was measured. This reaction gets more and more controlled by diffusion during temperature increase and shows a rate-determining step during the structures loss of water molecules. Differences between cis- and trans-vacant smectites are not observable. The investigated smectites can be divided with respect to the temperature dependency of the kinetic reaction. Montmorillonites show an Ea > 140 kJ/mol and montmorillonitic beidellite, beidellite and nontronites show an E-a < 70 kJ/mol. Du to an increase of water molecules within the interlayer sheet of the smectites bacause of an increased turnover, the activation energy also increases with respect to the reaction progress."]},{"key":"dc:source","label":"Dc Source","values":["Aachen : Publikationsserver der RWTH Aachen University 142 S. : Ill., graph. Darst. (2008). = Aachen, Techn. Hochsch., Diss., 2008"]},{"key":"dc:title","label":"Title","values":["Untersuchungen zur Dehydroxilierung dioktaedrischer Smectite"]}]}],"canonical_facts":{"dc:contributor":["Stanjek, Helge"],"dc:coverage":["DE"],"dc:creator":["Marchel, Christian Willy"],"dc:date":["2008"],"dc:description":["Due to their special features smectites, dioctahedral smectites in particular, are widely used in a broad spectrum of technical applications and processes. They seem to be one of the most important indsutrial minerals. By using smectites in thermal technology processes their behaviour plays an important role. So far many questions concerning these characteristics are still open. This study was carried out to gain detailed insight of mineralogical features and changes during thermal changes in smectites. The main focus of this work is the dehydroxylation process of dioctahedral semctites. In a first chapter the seven utilised bentonites, as well as the extracted smectites were investigated by conventional methods. Accordingly they were characterised as different types of dioctahedral smectites, presenting three montmorillonites, one montmorillonitic beidellite, one beidellite and two nontronites. Dehydroxylation of dioctahedral smectites is strongly linked with changes in smectite-structure. This encompasses changes in cation coordination (Wardle and Brindley, 1972) and possibly migration of octahedral cations (Drits et al., 1995; Heller-Kallai and Rozenson, 1980). By keeping this in mind for interpretation of different behaviour during dehydroxylation, the octahedral sheets of the seven smectites were characterised by Monte Carlo Simulation in a second chapter. Both, trans- and cis-vacant smectites, display a preferred orientation of AlAl and FeFe pairs along the OH-bonding direction. They rather show local segregation of lonely cation-pairs than large-area clusters. A preferred incorporation of Fe or Al to special positions is not observable. In cis-vacant smectites AlFe pairs appear more and AlMg pairs less frequently than expected for random distributed cations. Nontronites display strong undersaturation of AlFe pairs compared to random distributed cations. Whereas segregation of AlAl and FeFe pairs can be explained by different size and charge of individual cations, the preferred orientation along OH-bonded directions seems to be created during the formation of the structure. Thereby hydration and hydrolysis energy of the respective cations may deliver an essential contribution to develop a trans- or cis-vacant constitution. Investigations of structural changes during the dehydroxylation process was carried out at FTIR-spectra of isothermal heated material and is discussed in a third chapter. Substitutions within the tetrahedral sheet show effects on the position of the v SiO band at 1027-1045 cm-1 as well as on the position of the delta AlFe und delta AlMg band. The process of dehydroxylation is not homogeneous. Hydroxyl groups linked with AlMg and FeFe pairs show lower activation energy for breaking up than hydroxyl groups linked with AlFe and AlAl pairs. Within all smectites dehydroxylation proceeds very fast and the process is completed closely above the initial dehydroxylation temperature (mainly before the dehydroxylation peak in DSC/TG measurements). An additional supply of energy to the smectitic structure initiates continous transformation. New absorption bands develop which only cease by achieving a fully water free structure. Thus the dehydroxilation process can be regarded as a two step process. Fully water free cis-vacant structures seem to be more ordered than respective trans-vacant structures. In a fourth chapter the kinetic of dehydroxylation was investigated. Since it is impossible to resolve each reaction on atom level an overall kinetic was measured. This reaction gets more and more controlled by diffusion during temperature increase and shows a rate-determining step during the structures loss of water molecules. Differences between cis- and trans-vacant smectites are not observable. The investigated smectites can be divided with respect to the temperature dependency of the kinetic reaction. Montmorillonites show an Ea > 140 kJ/mol and montmorillonitic beidellite, beidellite and nontronites show an E-a < 70 kJ/mol. Du to an increase of water molecules within the interlayer sheet of the smectites bacause of an increased turnover, the activation energy also increases with respect to the reaction progress."],"dc:identifier":["https://publications.rwth-aachen.de/record/50142","https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-112697%22"],"dc:language":["ger"],"dc:publisher":["Publikationsserver der RWTH Aachen University"],"dc:relation":["info:eu-repo/semantics/altIdentifier/urn/urn:nbn:de:hbz:82-opus-23890"],"dc:rights":["info:eu-repo/semantics/openAccess"],"dc:source":["Aachen : Publikationsserver der RWTH Aachen University 142 S. : Ill., graph. Darst. (2008). = Aachen, Techn. Hochsch., Diss., 2008"],"dc:subject":["info:eu-repo/classification/ddc/550","Kinetik","Geowissenschaften","Smektit","Dehydroxilierung","Kationenverteilung","IR-Spektroskopie","smectite","dehydroxylation","cation distribution","kinetic","IR-spectroscopy"],"dc:title":["Untersuchungen zur Dehydroxilierung dioktaedrischer Smectite"],"dc:type":["info:eu-repo/semantics/doctoralThesis","info:eu-repo/semantics/publishedVersion"]},"updated_at":"2026-07-30T19:40:16Z"}