660 Chemische Verfahrenstechnik
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Sensoren können verschiedene Aufgaben erfüllen, wie beispielsweise die Optimierung von Prozessen, die Interaktion zwischen Geräten oder die Verbesserung der zivilen Sicherheit. [1–3] Ihr Bedarf für die Industrie oder den Alltag wächst seit Jahren stetig. Besonders mobile Gassensoren sind von großem Interesse. Jedoch ist ihre Anwendung meist durch ihre integrierte Batterie begrenzt. Gassensoren ohne oder mit einem nur sehr geringen Energieverbrauch stehen daher im Interesse bei neuen Anwendungsgebieten, beispielsweise im Brandschutz oder in der Textilindustrie. [4,5] Die Sensoren könnten zum Beispiel in die Textilien einer persönlichen Schutzausrüstung eingearbeitet werden und durch einen Farbumschlag die Anwesenheit eines Gases oder die Überschreitung des Grenzwertes toxischer Substanzen anzeigen.
Design and characterization of geopolymer foams reinforced with Miscanthus x giganteus fibers
(2024)
This paper presents the effects of different amounts of fibers and foaming agent, as well as different fiber sizes, on the mechanical and thermal properties of fly ash-based geopolymer foams reinforced with Miscanthus x giganteus fibers. The mechanical properties of the geopolymer foams were measured through compressive strength, and their thermal properties were characterized by thermal conductivity and X-ray micro-computed tomography. Furthermore, design of experiment (DoE) were used to optimize the thermal conductivity and compressive strength of Miscanthus x giganteus reinforced geopolymer foams. In addition, the microstructure was studied using X-ray diffraction (XRD), Field emission scanning electron microscopy (SEM) and Fourier-Transform Infrared Spectroscopy (FTIR). Mixtures with a low thermal conductivity of 0.056 W (m K)−1 and a porosity of 79 vol% achieved a compressive strength of only 0.02 MPa. In comparison, mixtures with a thermal conductivity of 0.087 W (m K)−1 and a porosity of 58 vol% achieved a compressive strength of 0.45 MPa.
P30 - Das Elektrospinnen von halbleitenden Zinndioxidfasern für die Detektion von Wasserstoff
(2022)
Das Ziel dieser Arbeit ist die Entwicklung von dünnen keramischen Fasern als halbleitendes Sensormaterial zum Nachweis von Wasserstoff, möglichst bei Zimmertemperatur. Die elektrische Leitfähigkeit halbleitender Metalloxide ändert sich durch die Einwirkung von oxidierenden und reduzierenden Gasen auf die Oberfläche des Metalloxids. Dieser Effekt kann zur Messung der Gaskonzentration genutzt werden. Die Reaktion von Zinn(IV)-oxid mit Wasserstoff basiert auf der Reduktion des Zinn(IV)-oxids zum Zinn, wobei die Elektronen des Zinn(IV)-oxids im metallischen Zinn verbleiben und dort im nicht gebundenen Zustand zu einer Leitfähigkeitserhöhung beitragen. Die Reaktion des Wasserstoffes kann sowohl mit den Sauerstoffatomen des Oxids als auch mit adsorbierten Sauerstoffatomen an der Oxidoberfläche stattfinden.[ 6] Da die Reaktionen an der Oberfläche des Oxids stattfinden, sollten Sensoren mit einer großen Oberfläche im Vergleich zu metalloxidischen Bulkmaterialien eine höhere Empfindlichkeit aufweisen. [3] Die Verwendung von Fasern anstelle von Dünn- oder Dickschichten führt dabei zu einer besseren Sensitivität gegenüber Gasen.
Thermo-chemical conversion of cucumber peel waste for biobased energy and chemical production
(2022)
The cube in cube approach was used by Paul and Ishai-Cohen to model and derive formulas for filler content dependent Young´s moduli of particle filled composites assuming perfect filler matrix adhesion. Their formulas were chosen because of their simplicity, recalculated using an elementary volume approach which transforms spherical inclusions to cubic inclusions. The EV approach led to expression for the composites moduli that allow for introducing an adhesion factor kadh ranging from 0 and 1 to take into account none perfect reduced filler matrix adhesion. This adhesion factor scales the edge length of the cubic inclusions, thus, reducing the stress transfer area between matrix and filler. Fitting the experimental data with the modified Paul model provides reasonable kadh for PA66, PBT, PP, PE-LD and BR which are in line with their surface energies. Further analysis showed that stiffening only occurs if kadh exceeds <span class="math-tex">\( { \ \sqrt{E^M/E^F} \ }\) and depends on the ratio of matrix modulus and filler modulus. The modified model allows for a quick calculation of any particle filled composites for known matrix modulus EM, filler modulus EF, filler volume content vF and adhesion factor kadh. Thus, finite element analysis (FEA) simulations of any particle filled polymer parts as well as materials selection are significantly eased. FEA of cubic and hexagonal EV arrangements show that stress distributions within the EV exhibit more shear stresses if one deviates from the cubic arrangement. At high filler contents the assumption that the property of the EV is representative for the whole composite, holds only for filler volume contents up to 15 or 20 % (corresponding to 30 to 40 weight %). Thus, for vast majority of commercially available particulate composites, the modified model can be applied. Furthermore, this indicates that the cube in cube approach reaches two limits: i) the occurrence of increasing shear stresses at filler contents above 20 % due to deviations of EV arrangements or spatial filler distribution from cubic arrangements (singular), and ii) increasing interaction between particles with the formation of particle network within the matrix violating the EV assumption of their homogeneous dispersion.
Introduction of Matrix-Filler Adhesion to Modelling of Elastic Moduli of Particulate Composites
(2022)
Cube in cube elementary volume (EV) concept serves to predict a filler-content dependent Young´s moduli of particle filled composites using moduli of a matrix EM and a filler EF. Paul and Ishai-Cohen derived formulas for composites moduli considering different load transfer boundaries in the EV assuming a complete filler-matrix adhesion. In this paper it is confirmed that their models represent the upper and lower bounds, respectively, with the respect to the experimental data. However, in vast majority of composites a filler-matrix adhesion is not complete. Therefore, an adhesion factor kadh gaining values between 0 and 1 was introduced into Paul´s model to consider the reduced adhesion as the reduction of the filler-matrix contact area for glass beads filled in polar and unpolar thermoplastic matrices as well as elastomer. The evaluation of these composite systems provides reasonable adhesion coefficients of PA66 > PBT > PP > PE-LD >> BR. It was also found that stiffening only occurs if kadh exceeds the minimum value adhesion of root square of E(M) divided by E(F). The determined kadh correspond to scanning electron microscopy observations of the composites fracture surfaces. Additionally, finite element analysis of the cubic and hexagonal arrangements of the EV show that the stress distributions are different, but they affect the calculated moduli only for the filler volume contents exceeding 20 %. The introduction of the filler-matrix adhesion provides more reliable predictions of Young´s moduli of particulate composites.
Process-dependent thermo-mechanical viscoelastic properties and the corresponding morphology of HDPE extrusion blow molded (EBM) parts were investigated. Evaluation of bulk data showed that flow direction, draw ratio, and mold temperature influence the viscoelastic behavior significantly in certain temperature ranges. Flow induced orientations due to higher draw ratio and higher mold temperature lead to higher crystallinities. To determine the local viscoelastic properties, a new microindentation system was developed by merging indentation with dynamic mechanical analysis. The local process-structure-property relationship of EBM parts showed that the cross-sectional temperature distribution is clearly reflected by local crystallinities and local complex moduli. Additionally, a model to calculate three-dimensional anisotropic coefficients of thermal expansion as a function of the process dependent crystallinity was developed based on an elementary volume unit cell with stacked layers of amorphous phase and crystalline lamellae. Good agreement of the predicted thermal expansion coefficients with measured ones was found up to a temperature of 70 °C.
Die Erfindung betrifft eine Filtervorrichtung zur Anreicherung gasförmiger und/oder partikelgebundener Stoffe. Erfindungsgemäß weist Filtervorrichtung eine wenigstens abschnittsweise luftdurchlässige Umhüllung (1, 3) und ein innerhalb der Umhüllung (1, 3) vorgesehenen Adsorbens (2) zur Anreicherung gasförmiger und/oder partikelgebundener Stoffe aus durch die Umhüllung (1, 3) hindurchgetretener Luft auf, zur nachfolgenden Überprüfung mittels eines lebenden olfaktorischen Detektors und/oder eines thermodesorptionsgekoppelten Analysegeräts auf Geruchsstoffe und/oder Zielanalyten, wobei ein Teil der Umhüllung (1, 3) einen in das Adsorbens (2) hineinführend, an nur einer Seite offenen Kanal (7) ausbildet, an dem offenen Ende des Kanals (7) eine Anschlusseinrichtung (8) zum Anschluss an ein Ansaugsystem angeordnet ist und die Umhüllung (1, 3) und das Adsorbens an Luft bis wenigstens 400 °C thermostabil sind. Auf diese Weise wird eine einfache und verlässliche Möglichkeit bereitgestellt, mit einer gemeinsamen Filtervorrichtung (9) sowohl eine Überprüfung mittels eines lebenden olfaktorischen Detektors sowie nachfolgend eine Überprüfung mittels eines thermodesorptionsgekoppelten Analysegeräts auf Geruchsstoffe und/oder Zielanalyten durchführen zu können.
Analytical pyrolysis
(2019)
Analytical pyrolysis deals with the structural identification and quantitation of pyrolysis products with the ultimate aim of establishing the identity of the original material and the mechanisms of its thermal decomposition. The pyrolytic process is carried out in a pyrolyzer interfaced with analytical instrumentation such as gas chromatography (GC), mass spectrometry (MS), gas chromatography coupled with mass spectrometry (GC/MS), or with Fourier-transform infrared spectroscopy (GC/FTIR). By measurement and identification of pyrolysis products, the molecular composition of the original sample can often be reconstructed.This book is the outcome of contributions by experts in the field of pyrolysis and includes applications of the analytical pyrolysis-GC/MS to characterize the structure of synthetic organic polymers and lignocellulosic materials as well as cellulosic pulps and isolated lignins, solid wood, waste particle board, and bio-oil. The thermal degradation of cellulose and biomass is examined by scanning electron micrography, FTIR spectroscopy, thermogravimetry (TG), differential thermal analysis, and TG/MS. The calorimetric determination of high heating values of different raw biomass, plastic waste, and biomass/plastic waste mixtures and their by-products resulting from pyrolysis is described.
Influence of design of extrusion blow molding (EBM) in terms of extrusion direction set-up and draw ratio as well as process conditions (mold temperature) on storage modulus of high density polyethylene EBM containers was analyzed with dynamic mechanical analysis. All three parameters - mold temperature, flow direction and draw ratio - are statistically significant and lead to relative and absolute evaluation of storage modulus. Furthermore, flow induced changes in crystallinity was analyzed by differential scanning calorimetry. Obtained data on deformation properties can be employed for more sophisticated finite element simulations with the aim to reach more sustainable extrusion blow molding production.
Pyrolysis–Gas Chromatography
(2018)
The methodology of analytical pyrolysis-GC/MS has been known for several years, but is seldom used in research laboratories and process control in the chemical industry. This is due to the relative difficulty of interpreting the identified pyrolysis products as well as the variety of them. This book contains full identification of several classes of polymers/copolymers and biopolymers that can be very helpful to the user. In addition, the practical applications can encourage analytical chemists and engineers to use the techniques explored in this volume.
The structure and the functions of various types of pyrolyzers and the results of the pyrolysis–gas chromatographic–mass spectrometric identification of synthetic polymers/copolymers and biopolymers at 700°C are described. Practical applications of these techniques are also included, detailing the analysis of microplastics, failure analysis in the automotive industry and solutions for technological problems.
Raman-microspectroscopy was used for the non-destructive characterization and differentiation of six different meat spoilage associated microorganisms, namely Brochothrix thermosphacta DSM 20171, Micrococcus luteus, Pseudomonas fluorescens DSM 4358, Escherichia coli Top10 and K12 and Pseudomonas fluorescens DSM 50090. To evaluate and classify the Raman-spectroscopic data at species and strain level an adequate preprocessing and subsequent principal component analysis was used. The same procedure was extended to an independent test data set, which could be successfully assigned to the correct bacterial species and even to the right strain. The evaluation was not only successful in differentiation of gram-positive and gram-negative bacteria but also the discrimination between the different bacterial species and strains was possible. This means that the training data set, the preprocessing method and the evaluation of the data lead to a robust principal component analysis. Even the correct assignment of unknown samples is possible. The results show that Raman-microspectroscopy in combination with an appropriate chemometric treatment can be a good tool for a rapid examination and classification of microbial cultures.