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Adsorption-induced deformation of a series of silica samples with hierarchical porosity has been studied by in situ small-angle neutron scattering (SANS) and in situ dilatometry. Monolithic samples consisted of a disordered macroporous network of struts formed by a 2D lattice of hexagonally ordered cylindrical mesopores and disordered micropores within the mesopore walls. Strain isotherms were obtained at the mesopore level by analyzing the shift of the Bragg reflections from the ordered mesopore lattice in SANS data. Thus, SANS essentially measured the radial strain of the cylindrical mesopores including the volume changes of the mesopore walls due to micropore deformation. A H2O/D2O adsorbate with net zero coherent neutron scattering length density was employed in order to avoid apparent strain effects due to intensity changes during pore filling. In contrast to SANS, the strain isotherms obtained from in situ dilatometry result from a combination of axial and radial mesopore deformation together with micropore deformation. Strain data were quantitatively analyzed with a theoretical model for micro-/mesopore deformation by combining information from nitrogen and water adsorption isotherms to estimate the water–silica interaction. It was shown that in situ SANS provides complementary information to dilatometry and allows for a quantitative estimate of the elastic properties of the mesopore walls from water adsorption.

Mechanical properties of hierarchically structured nanoporous materials are determined by the solid phase stiffness and the pore network morphology. We analyze the mechanical stiffness of hierarchically structured silica monoliths synthesized via a sol–gel process, which possess a macroporous scaffold built of interconnected struts with hexagonally ordered cylindrical mesopores. We consider samples with and without microporosity within the mesopore walls and analyze them on the macroscopic level as well as on the microscopic level of the mesopores. Untreated as-prepared samples still containing some organic components and the respective calcined and sintered counterparts of varying microporosity are investigated. To determine Young’s moduli on the level of the macroscopic monoliths, we apply ultrasonic run time measurements, while Young’s moduli of the mesopore walls are obtained by analysis of the in situ strain isotherms during N2 adsorption at 77 K. For the latter, we extended our previously reported theoretical approach for this type of materials by incorporating the micropore effects, which are clearly not negligible in the calcined and most of the sintered samples. The comparison of the macro- and microscopic Young’s moduli reveals that both properties follow essentially the same trends, that is, calcination and sintering increase the mechanical stiffness on both levels. Consequently, stiffening of the monolithic samples can be primarily attributed to stiffening of the backbone material which is consistent with the fact that the morphology on the mesopore level is mainly preserved with the post-treatments applied.

The goal of this work is to understand adsorption-induced deformation of hierarchically structured porous silica exhibiting well-defined cylindrical mesopores. For this purpose, we performed an in situ dilatometry measurement on a calcined and sintered monolithic silica sample during the adsorption of N2 at 77 K. To analyze the experimental data, we extended the adsorption stress model to account for the anisotropy of cylindrical mesopores, i.e., we explicitly derived the adsorption stress tensor components in the axial and radial direction of the pore. For quantitative predictions of stresses and strains, we applied the theoretical framework of Derjaguin, Broekhoff, and de Boer for adsorption in mesopores and two mechanical models of silica rods with axially aligned pore channels: an idealized cylindrical tube model, which can be described analytically, and an ordered hexagonal array of cylindrical mesopores, whose mechanical response to adsorption stress was evaluated by 3D finite element calculations. The adsorption-induced strains predicted by both mechanical models are in good quantitative agreement making the cylindrical tube the preferable model for adsorption-induced strains due to its simple analytical nature. The theoretical results are compared with the in situ dilatometry data on a hierarchically structured silica monolith composed by a network of mesoporous struts of MCM-41 type morphology. Analyzing the experimental adsorption and strain data with the proposed theoretical framework, we find the adsorption-induced deformation of the monolithic sample being reasonably described by a superposition of axial and radial strains calculated on the mesopore level. The structural and mechanical parameters obtained from the model are in good agreement with expectations from independent measurements and literature, respectively.

Mechanical properties of hierarchically structured nanoporous materials are determined by the solid phase stiffness and the pore network morphology. We analyze the mechanical stiffness of hierarchically structured silica monoliths synthesized via a solgel process, which possess a macroporous scaffold built of interconnected struts with hexagonally ordered cylindrical mesopores. We consider samples with and without microporosity within the mesopore walls and analyze them on the macroscopic level as well as on the microscopic level of the mesopores. Untreated as-prepared samples still containing some organic components and the respective calcined and sintered counterparts of varying microporosity are investigated. To determine Youngs moduli on the level of the macroscopic monoliths, we apply ultrasonic run time measurements, while Youngs moduli of the mesopore walls are obtained by analysis of the in situ strain isotherms during N2 adsorption at 77 K. For the latter, we extended our previously reported theoretical approach for this type of materials by incorporating the micropore effects, which are clearly not negligible in the calcined and most of the sintered samples. The comparison of the macro- and microscopic Youngs moduli reveals that both properties follow essentially the same trends, that is, calcination and sintering increase the mechanical stiffness on both levels. Consequently, stiffening of the monolithic samples can be primarily attributed to stiffening of the backbone material which is consistent with the fact that the morphology on the mesopore level is mainly preserved with the post-treatments applied. (VLID)3424545

Adsorption-induced deformation of a series of silica samples with hierarchical porosity has been studied by in situ small-angle neutron scattering (SANS) and in situ dilatometry. Monolithic samples consisted of a disordered macroporous network of struts formed by a 2D lattice of hexagonally ordered cylindrical mesopores and disordered micropores within the mesopore walls. Strain isotherms were obtained at the mesopore level by analyzing the shift of the Bragg reflections from the ordered mesopore lattice in SANS data. Thus, SANS essentially measured the radial strain of the cylindrical mesopores including the volume changes of the mesopore walls due to micropore deformation. A H2O/D2O adsorbate with net zero coherent neutron scattering length density was employed in order to avoid apparent strain effects due to intensity changes during pore filling. In contrast to SANS, the strain isotherms obtained from in situ dilatometry result from a combination of axial and radial mesopore deformation together with micropore deformation. Strain data were quantitatively analyzed with a theoretical model for micro-/mesopore deformation by combining information from nitrogen and water adsorption isotherms to estimate the watersilica interaction. It was shown that in situ SANS provides complementary information to dilatometry and allows for a quantitative estimate of the elastic properties of the mesopore walls from water adsorption. (VLID)4402442

The goal of this work is to improve the understanding of adsorption-induced deformation in nanoporous (and in particular microporous) materials in order to explore its potential for material characterization and provide guidelines for related technical applications such as adsorption-driven actuation. For this purpose this work combines in-situ dilatometry measurements with in-depth modeling of the obtained adsorption-induced strains. A major advantage with respect to previous studies is the combination of the dilatometric setup and a commercial sorption instrument resulting in high quality adsorption and strain isotherms. The considered model materials are (activated and thermally annealed) carbon xerogels, a sintered silica aerogel, a sintered hierarchical structured porous silica and binderless zeolites of type LTA and FAU; this selection covers micro-, meso- and macroporous as well as ordered and disordered model materials. All sample materials were characterized by scanning electron microscopy, gas adsorption and sound velocity measurements. In-situ dilatometry measurements on mesoporous model materials were performed for the adsorption of N2 at 77 K, while microporous model materials were also investigated for CO2 adsorption at 273 K, Ar adsorption at 77 K and H2O adsorption at 298 K. Within this work the available in-situ dilatometry setup was revised to improve resolution and reproducibility of measurements of small strains at low relative pressures, which are of particular relevance for microporous materials. The obtained experimental adsorption and strain isotherms of the hierarchical structured porous silica and a micro-macroporous carbon xerogel were quantitatively analyzed based on the adsorption stress model; this approach, originally proposed by Ravikovitch and Neimark, was extended for anisotropic pore geometries within this work. While the adsorption in silica mesopores could be well described by the classical and analytical theory of Derjaguin, Broekhoff and de Boer, the adsorption in carbon micropores required for comprehensive nonlocal density functional theory calculations. To connect adsorption-induced stresses and strains, furthermore mechanical models for the respective model materials were derived. The resulting theoretical framework of adsorption, adsorption stress and mechanical model was applied to the experimental data yielding structural and mechanical information about the model materials investigated, i.e., pore size or pore size distribution, respectively, and mechanical moduli of the porous matrix and the nonporous solid skeleton. The derived structural and mechanical properties of the model materials were found to be consistent with independent measurements and/or literature values. Noteworthy, the proposed extension of the adsorption stress model proved to be crucial for the correct description of the experimental data. Furthermore, it could be shown that the adsorption-induced deformation of disordered mesoporous aero-/xerogel structures follows qualitatively the same mechanisms obtained for the ordered hierarchical structured porous silica. However, respective quantitative modeling proved to be challenging due to the ill-shaped pore geometry of aero-/xerogels; good agreement between model and experiment could only be achieved for the filled pore regime of the adsorption isotherm and the relative pressure range of monolayer formation. In the intermediate regime of multilayer formation a more complex model than the one proposed here is required to correctly describe stress related to the curved adsorbate-adsorptive interface. Notably, for micro-mesoporous carbon xerogels it could be shown that micro- and mesopore related strain mechanisms superimpose one another. The strain isotherms of the zeolites were only qualitatively evaluated. The result for the FAU type zeolite is in good agreement with other experiments reported in literature and the theoretical understanding derived from the adsorption stress model. On the contrary, the strain isotherm of the LTA type zeolite is rather exceptional as it shows monotonic expansion over the whole relative pressure range. Qualitatively this type of strain isotherm can also be explained by the adsorption stress model, but a respective quantitative analysis is beyond the scope of this work. In summary, the analysis of the model materials' adsorption-induced strains proved to be a suitable tool to obtain information on their structural and mechanical properties including the stiffness of the nonporous solid skeleton. Investigations on the carbon xerogels modified by activation and thermal annealing revealed that adsorption-induced deformation is particularly suited to analyze even small changes of carbon micropore structures., Ziel dieser Arbeit ist es, dass Verständnis der adsorptionsinduzierter Deformation von nanoporösen (insbesondere mikroporösen) Materialien zu erweitern, um ihr Potenzial für die Materialcharakterisierung zu erforschen. Zusätzlich sollen Orientierungshilfen für technische Anwendungen, wie z.B. adsorptionsgetriebene Aktuatoren, bereitgestellt werden. Hierfür kombiniert diese Arbeit in-situ Dilatometriemessungen und detaillierte Modellierung der gemessenen adsorptionsinduzierten Dehnungen. Der wesentliche Vorteil dieser Arbeit gegenüber vorherigen Studien ist die Kombination des dilatometrischen Messaufbaus mit einer kommerziellen Gasadsorptionsanlage, was die Messung qualitativ hochwertiger Adsorptions- und Dehnungsisothermen erlaubt. Die betrachteten Materialsysteme sind (aktivierte und geglühte) Kohlenstoffxerogele, ein gesintertes Silica-Aerogel, ein gesintertes, hierarchisch strukturiertes, poröses Silica und binderlose Zeolithe der Typen LTA und FAU. Diese Auswahl umfasst mikro-, meso- und makroporöse ebenso wie geordnete und ungeordnete Modellmaterialien. Alle Modellmaterialien wurden mit Rasterelektronenmikroskopie, Gasadsorption und Schallgeschwindigkeitsmessungen charakterisiert. In-situ Dilatometriemessungen an mesoporösen Modellsystemen wurden für N2-Adsorption bei 77 K durchgeführt, während alle mikroporösen Modellsysteme zusätzlich bei CO2-Adsorption (273 K), Ar-Adsorption (77 K) und H2O-Adsorption (298 K) untersucht wurden. Der verfügbare Messaufbau für in-situ Dilatometrie wurde im Rahmen dieser Arbeit weiterentwickelt, um Auflösung und Reproduzierbarkeit der Messungen von kleinen Dehnungen zu verbessern, was insbesondere für mikroporöse Materialien von Bedeutung ist. Die experimentellen Adsorptions- und Dehnungsisothermen des hierarchisch strukturierten, porösen Silicas und des mikro-makroporösen Kohlenstoff-Xerogels wurden mit dem adsorption-stress-Modell quantitativ ausgewertet. Hierfür wurde das adsorption-stress-Modell, ursprünglich eingeführt von Ravikovitch et al., für die Verwendung von anisotropen Porengeometrien erweitert. Während die der Deformation zu Grunde liegende Adsorption im Fall des mesoporösen Silicas gut mit der klassischen und analytischen Theorie von Derjaguin, Broekhoff und de Boer beschrieben werden konnte, erforderte die Adsorption in den Kohlenstoffmikroporen umfassende Berechnungen mittels nichtlokaler Dichtefunktionaltheorie. Um die adsorptionsinduzierten Spannungen mit entsprechenden Dehnungen zu korrelieren, wurden zusätzlich mechanische Modelle für die untersuchten Materialien entworfen. Das resultierende theoretische Konstrukt aus Adsorptions-, adsorption-stress- und mechanischem Modell wurde auf die ermittelten experimentellen Daten angewandt und strukturelle und mechanische Eigenschaften der Modellmaterialien bestimmt, d.h. Porengröße bzw. Porengrößenverteilung sowie die mechanischen Module der porösen Matrix und des unporösen Festkörperskeletts. Es konnte gezeigt werden, dass die ermittelten Materialeigenschaften konsistent mit unabhängigen Messungen und/oder Literaturwerten sind. Hierbei ist zu beachten, dass sich die Erweiterung des adsorption-stress-Modells für eine korrekte Auswertung der experimentellen Daten als zwingend erforderlich erwies. Des Weiteren konnte gezeigt werden, dass die adsorptionsinduzierte Deformation von ungeordneten mesoporösen Aero-/Xerogelstrukturen qualitativ denselben Mechanismen folgt, die für das geordnete, hierarchisch strukturierte, poröse Silica identifiziert wurden. Die entsprechende quantitative Modellierung erwies sich allerdings als schwierig, da die Poren in Aero-/Xerogelstrukturen geometrisch schlecht zu fassen sind. Gute Übereinstimmung zwischen Modell und Experiment konnte nur für das Stadium gefüllter Poren und den relativen Druckbereich der Monolagenbildung erzielt werden. Der Zwischenbereich der Multilagenadsorption erfordert ein komplexeres Modell, um die Spannung quantitativ korrekt zu beschreiben, die sich auf Grund der gekrümmten Adsorbat-Adsorptiv-Grenzfläche im Material ausbildet. Mit Hinblick auf mikro-mesoporöse Kohlenstoffxerogele konnte gezeigt werden, dass sich dort Deformationsmechanismen von Mikro- und Mesoporen überlagern. Die Dehnungsisothermen der Zeolithe wurden nur qualitativ ausgewertet. Das Ergebnis für den Zeolithen vom Typ FAU stimmt gut mit anderen in der Literatur beschriebenen Experimenten und dem theoretischen Verständnis überein, das sich aus dem adsorption-stress-Modell ergibt. Im Gegensatz dazu ist die gemessene Dehnungsisotherme des Zeolithen vom Typ LTA eher ungewöhnlich, da sie monotone Expansion des LTA-Zeolithen über den gesamten Druckbereich zeigt. Qualitativ kann dieses Ergebnis ebenfals mit dem adsorption-stress-Modell erklärt werden, aber eine detaillierte, quantitative Analyse übersteigt den Rahmen dieser Arbeit. Insgesamt erweist sich die Analyse der adsorptionsinduzierten Dehnungen der Modellmaterialien als geeignetes Mittel, um Informationen über deren strukturelle und mechanische Eigenschaften zu erlangen, was auch die Steifigkeit des unporösen Festkörperskeletts miteinschließt. Desweiteren zeigen Untersuchungen an aktivierten und geglühten Kohlenstoffxerogelen, dass adsorptionsinduzierte Deformation insbesondere geeignet ist, um kleine Änderungen an Mikroporenstrukturen zu analysieren.

Structural hierarchy, porosity, and isotropy/anisotropy are highly relevant factors for mechanical properties and thereby the functionality of porous materials. However, even though anisotropic and hierarchically organized, porous materials are well known in nature, such as bone or wood, producing the synthetic counterparts in the laboratory is difficult. We report for the first time a straightforward combination of solgel processing and shear-induced alignment to create hierarchical silica monoliths exhibiting anisotropy on the levels of both, meso- and macropores. The resulting material consists of an anisotropic macroporous network of struts comprising 2D hexagonally organized cylindrical mesopores. While the anisotropy of the mesopores is an inherent feature of the pores formed by liquid crystal templating, the anisotropy of the macropores is induced by shearing of the network. Scanning electron microscopy and small-angle X-ray scattering show that the majority of network forming struts is oriented towards the shearing direction; a quantitative analysis of scattering data confirms that roughly 40% of the strut volume exhibits a preferred orientation. The anisotropy of the materials macroporosity is also reflected in its mechanical properties; i.e., the Youngs modulus differs by nearly a factor of 2 between the directions of shear application and perpendicular to it. Unexpectedly, the adsorption-induced strain of the material exhibits little to no anisotropy. I 1605-N20 (VLID)3547199

Große Stegöffnungen werden in Stahlverbundträgern immer dann erforderlich, wenn in Trägerebene Leitungen quer zur Trägerachse geführt werden sollen. Die Attraktivität der Stahlverbundbauweise steigt mit der Möglichkeit, die Tragfähigkeit im Bereich großer Stegöffnungen rechnerisch nachweisen zu können. Bisher war es aber nicht möglich, eine Verstärkung des Betongurtes durch Einbau von Dübelleisten in einem Nachweiskonzept nutzbar zu machen. Bei Dübelleisten handelt es sich um Doppelkopfanker, die in einer Reihe meist auf ein Lochblech aufgeschweißt werden. Sie werden von mehreren Herstellern als Querkraft- und Durchstanzbewehrungselemente vertrieben. In der vorliegenden Arbeit wird der Einfluss von Dübelleisten auf das Querkrafttragverhalten des Stahlbetongurts von Verbundträgern im Bereich von großen Stegöffnungen untersucht. Dazu wurden 28 Versuche sowie rechnerische Untersuchungen durchgeführt. Dabei konnte in einzelnen Versuchen durch den Einsatz von Dübelleisten eine Traglaststeigerung von mehr als 50 % erzielt werden. Unter anderem wurde der Effekt der Querbiegung untersucht, bei dem durch die vertikale Belastung des Betongurts außerhalb der Verbundträgerachse ein negatives Biegemoment in Querrichtung entsteht. Es wurde ein Nachweiskonzept erarbeitet, mit dem die Querkrafttragfähigkeit eines Betongurts unter Berücksichtigung von im Betongurt angeordneten Dübelleisten wirklichkeitsnah bestimmt werden kann. Das erstellte Konzept ermöglicht es, bei der Bemessung von Verbundträgern, die durch Stegöffnungen geschwächt sind, durch einen geringen Mehreinsatz von Bewehrung in Form von Dübelleisten eine deutliche Traglaststeigerung zu erzielen. Der Einfluss von Querbiegemomenten wird durch eine konservative Abschätzung der Lasteinzugsfläche berücksichtigt. Large web openings of composite beams are necessary if cables and pipes of the building services cross the axis of the steel girder. Composite construction becomes more attractive with the possibility to calculate the load-bearing capacity of the composite beam in the area of a large web opening. However, in previous design models the reinforcement of the concrete chord with shear rails was not included. Shear rails consist of double headed studs which are welded on perforated metal strips to fix their position. Several producers sell these shear rails as shear and punching reinforcement. As part of the following thesis, the influence of shear rails on the laod bearing behaviour of the concrete chord of composite beams with large web openings was investigated. For this purpose 28 experiments as well as finite-element calculations were carried out. Several tests showed that the ultimate load capacity can be increased by 50 % by introducing shear rails. Furthermore, the effect of a negative bending moment orthogonal to the axis of the composite girder was investigated. The moment results from vertical loads beside the girder axis. In order to determine the shear laod capacity of a concrete chord reinforced with shear rails, a design model was set up. The model allows the structural design of composite girders in the area of web openings. By the arrangement of shear rails alongside large web openings, the shear load capacity can be improved significantly. The influence of a bending moment orthogonal to the composite girder axis is taken into consideration by conservatively evaluating the loaded area.