TY - GEN A1 - Heinemann, Robert A1 - Schmidt, Peer T1 - Thermodynamic analysis of crystal growth of zinc oxide T2 - Zeitschrift für Anorganische und Allgemeine Chemie N2 - Chemical vapor transport (CVT[1]) is a suitable method for production of single-crystals of high purity. In order to find proper strategies for CVT various tools of thermodynamic calculations and analysis of solid-gas equilibria are available. Those applications are demonstrated for vapor transport of zinc oxide under addition of phosphorous and water. KW - Crystal growth Y1 - 2016 UR - http://onlinelibrary.wiley.com/doi/10.1002/zaac.201690018/full U6 - https://doi.org/10.1002/zaac.201690018 SN - 1521-3749 VL - 642 IS - 18 SP - 1064 ER - TY - GEN A1 - Heinemann, Robert A1 - Schmidt, Peer T1 - Vapor Transport Investigations using the High-temperature Gas-balance T2 - Zeitschrift für Anorganische und Allgemeine Chemie N2 - The High-temperature Gas-balance (HTGB[1]) has been established as a new method for investigations of heterogeneous phase equilibria with volatile components [1,2]. This equipment is notably well suited to analyze reversible heterogeneous equilibria which occur during chemical vapor transport reactions (CVT[3]). Experimental proof has been furnished by vapor transports of germanium and germanium(II) telluride using iodine as a transport addition. Initially the sublimation of iodine has been observed (section a – Fig. 1). The formation of GeI4(g) as the actual transport agent follows (b). Finally, the transport reaction occurs under reversible formation GeI2(g) (c). KW - Crystal growth KW - Chemical vapor transport KW - Chalogenides KW - High-temperature gas-balance Y1 - 2014 UR - http://onlinelibrary.wiley.com/doi/10.1002/zaac.201490026/full U6 - https://doi.org/10.1002/zaac.201490026 SN - 1521-3749 VL - 640 IS - 11 SP - 2338 ER - TY - GEN A1 - Heinemann, Robert A1 - Schmidt, Peer T1 - Crystal Growth by Chemical Vapor Transport: Process Screening by Complementary Modeling and Experiment T2 - Crystal Growth & Design N2 - Despite chemical vapor transport (CVT) being a widely used method for crystal growth of inorganic substances, detailed mechanistic studies on the course of the crystallization process are rather few. In this study, an elaborated experimental screening run combined with sophisticated modeling of the respective heterogeneous equilibria is presented: Crystal growth of germanium by vapor transport with the addition of iodine has been chosen as a model system for validation of the applied method spectrum. In order to record the course and the interplay of heterogeneous equilibrium and non-equilibrium reactions in the system Ge–I, the experimental setup of high-temperature gas-balance (HTGB) is applied. Additionally, the observed evaporation processes are compared with saturation curves of corresponding volatile substances and, thus, can be assigned to individual species within the system. In this experimental screening, a phase sequence means to examine how the condensed phases undergo iodine depletion and how the gaseous phase undergoes a germanium enrichment when the temperature is increased. This phase screening combined with annealing experiments in the course of the phase sequence helps to analyze stepwise non-equilibrium products and to identify the characteristic species. Subsequently, for the evaluation of the composition of the gaseous phase, and for the deduction of the vapor transport mechanism, thermodynamic modeling by the CalPhaD method is performed. For the reference system, it is confirmed that iodine does not act as the transport agent. Instead, GeI4 is responsible for the volatilization of germanium, forming GeI2. Nevertheless, investigations clearly illustrate how GeI4 forms naturally in the phase sequence in the system Ge–I, which makes direct addition of it unnecessary. The recommended temperature range for vapor transport of germanium spans from 460 to 800 °C. Modeling shows that migration rates for germanium reaches a maximum at a mean temperature between 540 and 550 °C. Finally, vapor transport experiments were performed from 565 to 515 °C and from 690 to 590 °C. By increasing the deposition temperature, a slight decrease of the migration rate was observed, though a positive impact on the crystal’s morphology was also found. KW - Crystal growth KW - Chemical vapor transport KW - High-temperature Gas-balance KW - Thermodynamic modeling KW - Phase barogram KW - Germanium Y1 - 2020 UR - https://pubs.acs.org/doi/abs/10.1021/acs.cgd.0c00679 U6 - https://doi.org/10.1021/acs.cgd.0c00679 SN - 1528-7505 SN - 1528-7483 VL - 20 IS - 9 SP - 5986 EP - 6000 ER - TY - GEN A1 - Böhler, Stefan A1 - Rosencrantz, Sophia A1 - Wolf, Karina A1 - Heinemann, Robert A1 - Schmidt, Peer A1 - Ganster, Johannes A1 - Büsse, Thomas A1 - Balko, Jens A1 - Rosencrantz, Ruben R. T1 - Active protease formulation in commodity polymers withstands melt processing into compounds and blown films T2 - Materials Today Communications N2 - Integrating enzymes into thermoplastic polymers is challenging due to their lack of robustness with respect to temperature and shear fields during conventional melt processing. In the present study, blown films from low-density polyethylene (LDPE) were prepared containing a technical protease from Bacillus sp. First, LDPE/protease compounds were produced followed by blown film extrusion, both processes at melt mass temperatures of 130 °C or higher. Enzyme activity was proven, both for the LDPE/protease compound and the blown film. The highest enzyme activity in the compound was determined for processing at 132 °C and a screw speed of 75 rpm. The influence of melt temperature and shear fields was studied in detail. Enzyme activities were determined for melt temperatures up to 160 °C and for screw speeds ranging from 75 to 300 rpm during compounding by twin-screw extrusion. The process was also applied for biobased and biodegradable polyesters, where similar protease activity after compounding was verified. Electron microscopy, X-ray diffraction, nuclear magnetic resonance spectroscopy and differential scanning calorimetry served to analyze components and morphology of the enzyme formulation used here. It is proposed that the porous morphology of the protease particles is beneficial for the enzyme to remain active after processing. Additionally, the polymer matrix surrounding the particles protects the protease at elevated temperatures, which can be attributed to thermal insulation. Thus, the right combination of a suited technical enzyme formulation with appropriate mild melt compounding conditions allows enzymes to be incorporated into thermoplastics and retain their activity. This opens the way to use the abundant biological functions of enzymes in thermoplastic applications. KW - Thermal analysis KW - X-ray diffraction KW - Crystal structure Y1 - 2023 UR - https://www.sciencedirect.com/science/article/pii/S2352492822018591 U6 - https://doi.org/10.1016/j.mtcomm.2022.105018 SN - 2352-4928 VL - 34 SP - 1 EP - 9 ER - TY - RPRT A1 - Schmidt, Peer A1 - Giese, Marie A1 - Heinemann, Robert A1 - Nawdiyal, Amruta A1 - Knorr, Monika A1 - Breitkopf, Cornelia A1 - Schneegans, Marcel Felix A1 - Pinnau, Sebastian A1 - Lorenz, Tommy A1 - Mickoleit, Erik A1 - to Baben, Moritz A1 - Keuter, Philipp A1 - Müller, Michael A1 - Sergeev, Dmitry A1 - Ewaznezhad Fard, Darya A1 - Morsa, Amedeo A1 - Rhys, Dominic Jacob A1 - Yazhenskikh, Elena T1 - PCM-Screening-2 : Evaluierung eutektischer Gemische für den Einsatz als PCM : thermodynamische Modellierung und experimentelle Methoden - 2 T2 - Deutsche Forschungsberichte N2 - Durch den Einsatz von Wärme- und Kältespeichern in Gebäuden, Industrieanlagen und Kraftwerken können Lastschwankungen reduziert und die Anlageneffizienz verbessert werden. Latentwärmespeicher (PCM) ermöglichen durch Ausnutzung einer fest-flüssig Phasenumwandlung hohe Speicherdichten bei geringen Temperaturdifferenzen. Die Verfügbarkeit geeigneter und kostengünstiger PCM’s ist derzeit noch eingeschränkt. Ein Screening geeigneter Stoffsysteme zur Bildung multinärer Eutektika durch thermodynamische Modellierung der Phasengleichgewichte erlaubt fundierte Vorhersagen zur Zusammensetzung eutektischer Gemische, ihren Schmelztemperaturen und -enthalpien. Auf Basis der Literatur, umfangreicher experimenteller Untersuchungen und Simulationen wurde im Projekt eine im Temperaturbereich nicht eingeschränkte thermochemische Datenbank für das komplexe Stoffsystem Na+, K+, Ca2+, Mg2+ // Cl−, NO3−, SO4_2−, CO3_2− // H2O geschaffen, die eine Auswahl neuer PCM mit optimalen thermodynamischen Eigenschaften für spezifische Prozessanforderungen auf Basis von in Deutschland in großen Mengen verfügbaren, preiswerten Rohstoffen ermöglicht. Weiterhin wurde ein CalPhaD-basiertes Viskositätsmodell, ein Screening-Verfahren inkl. Webserver und intuitive Visualisierungsmöglichkeiten hochkomponentiger Systeme entwickelt. Mittels eines Screenings erfolgte eine Vorauswahl von potentiell als PCM geeigneten Gemischen, die umfangreich charakterisiert wurden. Auf Basis der vielversprechenden Speicherdichten und der niedrigen Materialkosten wird erwartet, dass ein oder mehrere dieser identifizierten PCMs in die Anwendung als thermische Speicher gebracht werden können. N2 - The use of heat and cold storage systems in buildings, industrial plants, and power stations can reduce load fluctuations and improve plant efficiency. Latent heat storage systems (phase change materials - PCM) enable high storage densities with low temperature differences by exploiting a solid-liquid phase transition. The availability of suitable and cost-effective PCMs is currently still limited. Screening suitable material systems for the formation of multinary eutectics through thermodynamic modeling of phase equilibria allows well-founded predictions to be made about the composition of eutectic mixtures, their melting temperatures, and enthalpies. Based on the literature, extensive experimental investigations, and simulations, the project created a thermochemical database for the complex material system Na+, K+, Ca2+, Mg2+ // Cl−, NO3−, SO4_2−, CO3_2− // H2O was created, which enables the selection of new PCMs with optimal thermodynamic properties for specific process requirements based on inexpensive raw materials available in large quantities in Germany. Furthermore, a CalPhaD-based viscosity model, a screening procedure including a web server, and intuitive visualization options for highly component systems were developed. A screening process was used to preselect mixtures potentially suitable as PCMs, which were then extensively characterized. Based on the promising storage densities and low material costs, it is expected that one or more of these identified PCMs can be put into application as thermal storage. KW - PCM KW - Latenwärmespeicher KW - Eutektische Gemische KW - Thermodynamische Daten KW - Thermodynamische Modellierung KW - Anorganische Salzhydrate KW - Anorganische Salze Y1 - 2026 UR - https://oa.tib.eu/renate/handle/123456789/29435 U6 - https://doi.org/10.34657/28504 ER -