Tuneable Piezoresistance of Graphene-Based 2D:2D Nanocomposite Networks

Piezoresistive nanocomposites are an important class of materials that allow the production of very sensitive strain sensors. Herein, a new class of piezoresistive nanocomposites prepared by mixing different types of 2D nanosheets is explored. In this way, three distinct types of nanocomposite are produced by mixing conducting and insulating nanosheets (graphene, Gr and boron nitride, BN), conducting and semiconducting nanosheets (graphene and tungsten diselenide, WSe₂ or tungsten disulfide, WS₂) as well as mixing two different types of conducting nanosheets (graphene and silver, Ag). For each nanocomposite type, a different dependence of composite conductivity on filler volume fraction is observed although all behaviors can be fully described by percolation theory. In addition, each composite type shows different piezoresistive properties. Interestingly, while the conductor insulator composites show the standard monotonic relationship between gauge factor and conductivity, both conductor:semi-conductor and conductor:conductor composites show very unusual behavior, in each case displaying a peak engage factor at the percolation threshold. In each case, percolation theory is used to develop simple equations for gauge factor as a function of both volume fraction and conductivity that fully describes all experimental data. This work expands the understanding of piezoresistive nanocomposites and provides a platform for the engineering of high-performance strain sensors.     

From Meso to Macro: Controlling Hierarchical Porosity in Supraparticle Powders

A drying droplet containing colloidal particles can consolidate into a spherical assembly called a supraparticle. Such supraparticles are inherently porous due to the spaces between the constituent primary particles. Here, the emergent, hierarchical porosity in spray-dried supraparticles is tailored via three distinct strategies acting at different length scales. First, mesopores (<10 nm) are introduced via the primary particles. Second, the interstitial pores are tuned from the meso- (35 nm) to the macro scale (250 nm) by controlling the primary particle size. Third, defined macropores (>100 nm) are introduced via templating polymer particles, which can be selectively removed by calcination. Combining all three strategies creates hierarchical supraparticles with fully tailored pore size distributions. Moreover, another level of the hierarchy is added by fabricating supra-supraparticles, using the supraparticles themselves as building blocks, which provide additional pores with micrometer dimensions. The interconnectivity of the pore networks within all supraparticle types is investigated via detailed textural and tomographic analysis. This work provides a versatile toolbox for designing porous materials with precisely tunable, hierarchical porosity from the meso- (3 nm) to the macroscale (≈10 µm) that can be utilized for applications in catalysis, chromatography, or adsorption.     

Investigation of molecular changes in wine during storage in refrigerated cabinets

Wine is a complex chemical mixture that is bound to change over time. Most wines are produced for consumption within months. Some premium wines are meant to be maturated for several years or even decades after bottling. The post-bottling evolution and the longevity of a wine depends on its initial chemical composition and the storage conditions. Temperature, exposure to light and the closure type are often mentioned as the most important storage influences. Especially elevated temperature is known to cause accelerated aging reactions in wine. Refrigerated wine storage cabinets promise to be the best storage option without the need of a wine cellar. They are available in different sizes and fit in every household. However, the influence of vibrations and low-interval temperature fluctuations caused by compressors are parameters that have been neglected in literature. The aim of this thesis was to investigate if vibrations and low-interval temperature fluctuations, which occur in refrigerated wine storage cabinets, have an influence on the post-bottling evolution of a wine. The influence of both parameters was studied separately from each other. The impact of vibration on oxidation and gas uptake from the headspace of a wine bottle into the wine was investigated using a model wine with saturated O2 and different headspace volumes. The study revealed that vibration promotes the dissolution of O2 from the headspace of bottle into the wine resulting in a faster SO2 consumption. Furthermore, it was shown that horizontal bottle position accelerated the O2 uptake significantly. It was concluded that the increased surface size between headspace and wine accelerates the O2 dissolution in wine. Also, bigger headspace volumes caused an accelerated O2 uptake into the wine. An experiment without any headspace volume revealed that the factors vibration and bottle position did not accelerate the O2 consumption in wine. This proves that vibration and bottle position accelerate only the dissolution of O2 in wine, but not the chemical reaction of O2 with wine constituents. The influence of vibration on the volatile profile of wine was investigated using Riesling sparkling and still wines sealed with different closures that were subjected to vibration for six months. Vibration caused no CO2 losses, SO2 and color changes in all wines indicating that vibration caused by compressors has no impact on the gas permeability of the used closures. However, vibration affected the volatile profile of sparkling wine and Riesling still wine sealed with a screw cap. Similar to the model wine study described earlier, it was shown that the equilibrium of volatile substances between the wine and the headspace in a bottle was influenced by vibration. The gas-liquid-equilibrium of some volatile compounds was shifted towards wine, while others were shifted towards headspace. As a result of this, the concentration of volatile compounds in wine is changed. Besides this indirect influence of vibration, the results of this study also suggested that specific degradation and formation reactions of volatile compounds are directly influenced by vibration. These multiple effects of vibration most likely explain why increasing vibration intensities could not be proportionally related to the observed volatile changes. The investigation of different wine styles revealed that the impact of vibration depends strongly on the initial composition of wine, age, and packaging conditions. Especially, headspace volume, closure type and CO2 pressure are likely to influence the equilibrium of volatile substances between the wine and the headspace in a bottle. Another study investigated the impact of low-interval temperature fluctuations on the volatile profile of wine. For this purpose, a Riesling wine was stored for two years under different temperature fluctuation patterns caused by compressors. Additionally, a model wine with nine volatile substances with known concentrations was stored for eight months under the same fluctuation patterns. The low- interval temperature fluctuations were compared to the mean value of the temperature fluctuations. Chemical and sensory analysis revealed that that low-interval temperature fluctuations accelerate wine aging reactions like ester hydrolysis and monoterpene degradation. Even small temperature amplitudes showed a significant impact on wine aging. The observed effect was explained by the Arrhenius equation which states that reaction rates exponentially increase with rising temperatures. A pump effect of air through the closure was initially assumed but not observed in this study. Small deviations in wine temperature, such as those caused by door openings of a refrigerator were found to be negligible. It was concluded that low-interval temperature fluctuations can accelerate wine aging reactions. The amplitude of the temperature fluctuations should be as small as possible during bottle storage of wine. This thesis showed that both parameters, vibration, and low-interval temperature fluctuations, have been proven to influence the evolution of wine during bottle storage. Regarding storage conditions in a refrigerated wine storage cabinet, those parameters should be monitored. Wine connoisseurs should therefore consider good wine cabinets, since some manufacturers emphasize on the importance to minimize vibrations and temperature fluctuations in their devices. The development of technology should be advanced to reduce both vibration and temperature fluctuations in refrigerated wine storage cabinets. Future research should focus on specific wine compounds in model systems and realistic vibration conditions to reveal the relationship between vibration intensities and reaction rates. The impact of low-interval temperature fluctuations on wine compositional changes should be investigated considering horizontal and vertical bottle positions. The calculated acceleration factors due to temperature fluctuations have to be verified by isotherm storage conditions at higher temperatures.     

Real-Time Interactive Navigation on Input-Output Data Sets in Chemical Processes

Input-output data sets are ubiquitous in chemical process engineering. We introduce a real-time interactive navigation framework that provides several capabilities to the decision maker (DM). Once a surrogate model is trained the DM can perform what-if analyses in both input and output spaces by manipulating sliders. An approximated convex hull spanned in the input space supports both a reliable surrogate prediction and a navigation close to the data set. The framework has been tested on data sets obtained with a flowsheet simulator modeling a real steam methane reforming process.     

Gas- und Flüssigkeitsanalysatoren auf der ACHEMA 2022

ACHEMA, the world's largest trade fair for measurement and automation technology in industrial production, once again showcased innovations in the field of gas and liquid analysis. Due to the pandemic, there was a decrease of 41 % in the number of exhibitors and 56 % in the number of visitors compared to 2018. It was noticeable that two big names in the industry were missing with their own booths: ABB and Siemens. ACHEMA organizers said exhibitors had been satisfied with the show and visitor contacts; the next ACHEMA will be held in June 2024. This report provides information on the trends and product innovations observed.     

In Situ Observations of the Microstructural Evolution during Heat Treatment of a PH 13-8 Mo Maraging Steel

The standard heat treatment of PH 13-8 Mo maraging steels consists of solution annealing and subsequent aging. Herein, it is investigated how an additional intercritical annealing step prior to aging affects the microstructure, and, consequently, the mechanical properties of a PH 13-8 Mo maraging steel. In situ techniques by means of high-temperature electron backscatter diffraction and high-temperature X-ray diffraction are applied to study the microstructural changes during intercritical annealing and subsequent aging. In addition, high-resolution investigation methods, such as transmission electron microscopy and atom probe tomography supplemented by transmission Kikuchi diffraction, are used for an in-depth characterization of the microstructure. The results reveal that a diffusion-controlled martensite to austenite transformation accompanied by partitioning of the substitutional atoms Cr, Ni, and Mo takes place during intercritical annealing. As a result of partitioning during intercritical annealing, an inhomogeneous distribution of Ni remains in the microstructure after the martensitic transformation. Consequently, the formation of reverted austenite is facilitated during subsequent aging due to existing Ni-enriched zones in martensite. Since the fracture toughness is significantly enhanced compared to the standard heat treatment, it is suggested that this improvement is related to the increased phase fraction of reverted austenite.     

Novel transfer learning schemes based on Siamese networks and synthetic data

Neural Computing and Applications - Transfer learning schemes based on deep networks which have been trained on huge image corpora offer state-of-the-art technologies in computer vision. Here,...     

Production Scheduling Using Deep Reinforcement Learning and Discrete Event Simulation

Scheduling in the process industry is a highly demanding task. Having access to optimal production schedules at short notice, for instance, after spontaneous changes, offers numerous advantages in terms of robustness, economics, and ultimately customer satisfaction, as delays are minimized. In this work, we describe our initial efforts to apply and evaluate deep reinforcement learning (DRL) for optimized scheduling in a typical fill-and-finish batch production plant in the chemical industry. Our pilot study demonstrates how DRL can be implemented using an approach based on discrete event simulation. We discuss the results and benefits of DRL, compare it to mathematical programming approaches, and outline a potential path forward. Our study suggests that the application of DRL in the chemical industry is a promising research direction and that DRL can complement established methods such as process simulation and mathematical programming.     

Complex validation of novel mullite-based ceramic filters for microfiltration purposes

The goal of this paper is to investigate a complex validation, developed by Rauschert in Poland, of casted ceramic filters for microfiltration. For disc manufacturing, a self-developed material RaFo-MF-401e with a filtration membrane was used. The presented experiment was conducted on component, subsystem, and system levels. Component level analysis consisted of the investigation of mechanical strength, hardness, rough lifetime, and resistance against acids and alkalis. Annealing at high temperature and humidity was used to test the subsystem. The final system test was executed on the real filtration system. The final aim of the tests was to verify the filtration efficiency of a complete module (core and membrane) in a real filtration device. The filtration quality of the whole setup was very good and the particles in the permeate (filtrated solution) were smaller than 10 μm (defined as D99). Thus, the developed discs provide the expected filtration quality in the range of microfiltration.