Practical Insights into the Impedance Response of Interdigitated Electrodes: Extraction of Relative Static Permittivity and Electrolytic Conductivity

This work aims to provide a detailed understanding of the challenges related to the computation of the relative static permittivity and electrolytic conductivity of a sample medium from its impedance response recorded with interdigitated electrode (IDE) geometries. Within the scope of the study, impedance data has been measured and evaluated for a total of nine sample media using two distinct IDE geometries. Particular emphasis is laid upon the compensation of parasitic influences affecting the impedance response. With the raw data supporting this study fully disclosed, the reader is offered the opportunity to comprehensively retrace the evaluation procedure proposed in the text

Durability of Cement-Based Materials in Drinking Water Storage

In order to provide a hygienic storage drinking water reservoirs have been coated with mineral mortar linings in all epochs of European history. However, modern cement-based materials often show in this special operational environment an inadequate durability. Even though drinking water is commonly not considered particularly harmful to cementitious systems, the chemical degradation of mortar linings in drinking water storage systems can occur very fast compared to other common deterioration reactions. This results in cost intensive repair measures and thus high life-cycle costs as well associated with an ecological burden. Furthermore, an insufficient understanding of degradation mechanisms and their underlying physical, chemical as well as biological processes currently impedes performance-oriented approaches to improve durability. In this regard a research project aims to unravel the potentially combined multiple deterioration mechanisms, integrating results of case studies and laboratory experiments. In this context a specific issue of this research activity is to evaluate the applicability of an accelerated degradation test that takes advantage of the impact of electrical fields on the stability of cement-based materials in permanent contact to aqueous environments. Laboratory experiments show, that such tests are suitable to compare the resilience against reactive transport processes of materials and to draw conclusions regarding their performance, illustrating material changes in terms of depth and time. Furthermore, the results indicate, that the transport properties of the rim zone of cement-based materials are regulating its sturdiness in aggressive aqueous environments. This approach appears therefore suitable for a performance assessment in material development and provides as well new impulses for quality control in practice paving the path for increased durability of materials applied in drinking water supply infrastructure

On the Integration of Dielectrometry into Electrochemical Impedance Spectroscopy to Obtain Characteristic Properties of a Dielectric Thin Film

We demonstrate a novel impedimetric approach providing unprecedented insight into characteristic properties of dielectric thin films covering electrode surfaces. The concept is based on the joint interpretation of electrochemical impedance spectroscopy (EIS) together with dielectrometry (DEM) whose informative value is mutually interconnected. The advantage lies in the synergistic compensation of individual shortcomings adversely affecting conventional impedimetric analysis strategies relying exclusively on either DEM or the traditional EIS approach, which in turn allows a reliable determination of thickness and permittivity values. The versatility of the method proposed is showcased by an in-situ growth-monitoring of a nanoporous, crystalline thin film (HKUST-1) on an interdigitated electrode geometry

Performance Oriented Functionalisation of Concrete: an Integrated Approach for Prevention in Construction

The long-term preservation and the future-oriented development of the infrastructure are of utmost importance for every country in the world. An increasing failure of infrastructure underpins a tremendous need for action. The reasons for this unsatisfactory situation are various, but certainly among them is often an insufficient performance of the building materials. This holds particularly true for reinforced concrete and its additives, which are nowadays commonly developed by empirical research. Almost all shortcomings of concrete durability are related to the transport of detrimental substances into the pore system. In this regard, a promising approach to prevent chemical deterioration processes is a functionalisation of the pore system by means of organosilicon-based surface treatments in order to hamper the uptake of aggressive aqueous solutions. However, little is known about the reaction mechanisms and the nature of the reaction products associated with such measures. However, this is necessary to obtain reliable information about their performance and ideally to develop these technologies further in a more target-oriented manner. The insufficient understanding of these processes has its origins in the inability of investigations of the reaction course of silicon organic compounds in the pore structure of cement-based systems and their underlying physical and chemical principles. This applies in particular to film-forming reactions in alkaline environments of the pore structure, which lead to functionalization (e.g. hydrophobic effect). The approach of this study is therefore to investigate the reaction products in model systems using mass spectrometry and to explain the course of the reaction by means of computational chemistry. In this way, reaction products of different reaction steps of the condensation of specific components into larger oligomers were characterized and the reaction sequence was explained by molecular modelling. These results contribute to a deeper understanding of the reactions and types of reaction products of organosilicon compounds used to improve the properties of cement-bound materials. This promotes further steps towards the performance-oriented development of such surface protection technologies

Study of a Layered Au, Pt-YSZ Mixed-Potential Sensing Electrode by ESEM, XRD and GD-OES with Relation to Its Electrochemical Behaviour

Morphological and structural properties of layered Au, Pt-YSZ mixed-potential gas sensing electrodes (APE) prepared under different temperature treatments were studied by environmental scanning electron microscope (ESEM) and glow-discharge optical emission spectroscopy (GD-OES), and correlated with open-circuit potential (OCP) and cyclic voltammetry (CV) measurements under gas exposures at elevated temperatures. The OCP response of the APE sintered at 1050 °C is clearly higher than that of the APE sintered at 850 °C, and can be well correlated with a smaller oxygen reduction reaction (ORR) observed in the related CV diagrams. Moreover, a transition from the charge transfer reaction kinetics to the diffusional transport controlled mixed-potential formation was found between 550 °C and 650 °C

Reactivity of Gypsum-Based Materials Subjected to Thermal Load: Investigation of Reaction Mechanisms

The thermal stability of gypsum-based materials, and in this context, especially their long-term behavior, is the background of our current research activities. A comprehensive investigation program was compiled in which detailed examinations of various model materials exposed to thermal loads were carried out. The understanding of the partly not entirely consistent state of knowledge shall be sharpened especially by in situ observations of the thermally induced conversion reaction of gypsum into hemihydrate. The temporal course of the reaction was investigated non-destructively by in situ investigations in a high-resolution X-ray computed tomography setup, and the experiment was accompanied by detailed characterizations of the microstructure and composition. In this contribution, selected results of experiments with a high-purity natural gypsum rock as the model substance are presented. Studying the influence of temperature on the reaction showed that, even under supposedly dry conditions, the reaction could take place at much lower temperatures than usually reported in the literature. It was demonstrated that the transformation of gypsum into hemihydrate could take place at a temperature of already 50 °C. The results indicated that even under “classical” heating conditions in a conventional oven, the dissolution and crystallization processes in water films on the mineral surfaces could be suggested to be a driving force for the reaction. A corresponding reaction model, which took these aspects into account, was proposed in this work

Identification of Zirconia Particle Uptake in Human Osteoblasts by ToF-SIMS Analysis and Particle-Size Effects on Cell Metabolism

As the use of zirconia-based nano-ceramics is rising in dentistry, the examination of possible biological effects caused by released nanoparticles on oral target tissues, such as bone, is gaining importance. The aim of this investigation was to identify a possible internalization of differently sized zirconia nanoparticles (ZrNP) into human osteoblasts applying Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and to examine whether ZrNP exposure affected the metabolic activity of the cells. Since ToF-SIMS has a low probing depth (about 5 nm), visualizing the ZrNP required the controlled erosion of the sample by oxygen bombardment. This procedure removed organic matter, uncovering the internalized ZrNP and leaving the hard particles practically unaffected. It was demonstrated that osteoblasts internalized ZrNP within 24 h in a size-dependent manner. Regarding the cellular metabolic activity, metabolization of alamarBlue by osteoblasts revealed a size- and time-dependent unfavorable effect of ZrNP, with the smallest ZrNP exerting the most pronounced effect. These findings point to different uptake efficiencies of the differently sized ZrNP by human osteoblasts. Furthermore, it was proven that ToF-SIMS is a powerful technique for the detection of zirconia-based nano/microparticles that can be applied for the cell-based validation of clinically relevant materials at the nano/micro scale

Stability of monolithic mof thin films in acidic and alkaline aqueous media

In the context of thin film nanotechnologies, metal-organic frameworks (MOFs) are currently intensively explored in the context of both, novel applications and as alternatives to existing materials. When it comes to applications under relatively harsh conditions, in several cases it has been noticed that the stability of MOF thin films deviates from the corresponding standard, powdery form of MOFs. Here, we subjected SURMOFs, surface-anchored MOF thin films, fabricated using layer-by layer methods, to a thorough characterization after exposure to different harsh aqueous environments. The stability of three prototypal SURMOFs, HKUST-1, ZIF-8, and UiO-66-NH2 was systematically investigated in acidic, neutral, and basic environments using X-ray diffraction and electron microscopy. While HKUST-1 films were rather unstable in aqueous media, ZIF-8 SURMOFs were preserved in alkaline environments when exposed for short periods of time, but in apparent contrast to results reported in the literature for the corresponding bulk powders- not stable in neutral and acidic environments. UiO-66-NH$_{2}$ SURMOFs were found to be stable over a large window of pH values