The objectives of the Reactive Spraying division under the direction of Prof. Dr.-Ing. habil. Lutz Mädler include the design of spray processes that enable the synthesis of complex particulate materials through reactions in the gas and liquid phase. At the same time, the in-process processing of these materials is investigated (e.g. functionalization, mixing, coating) and the synthesis routes are linked to process optimization and design for specific application requirements.
Thus, the area of Reactive Spray Technology comprises the following research foci in theory and experiment:
- Synthesis of functional nanoparticles and nanostructured surfaces
- Preparation and characterization of disperse materials and porous layers
- Reactor design and development for reactive spray applications for the synthesis of functional materials and layers
- High-throughput methods and material-process data for experimental material development
Single-drop experiments are used to investigate the scientific basis of the mechanisms involved in the combustion of and explosion in single drops. In the established process of flame spray pyrolysis, organometallic fluids (precursors) are atomized into fine droplets in the first step, which react in a flame and synthesize into nanoparticles in the second step. A deep understanding of the processes and the interplay of atomization, reaction kinetics, nucleation, coagulation and condensation in multiphase flows is necessary for a tailor-made end product.
Multi-flame systems, which have been developed in the field in recent years, can be used to produce multicomponent systems in a targeted manner by synthesizing in two or more flames. The properties of the new material can be adjusted by defined interaction of the particles.
Many years of expertise in this field, starting with the conceptual idea and the reactor development, have made it possible to produce new materials and products that are used in catalysis, gas sensor technology, as multifunctional fillers (e.g. dental prostheses), optical materials and in flexible electronic coatings. These applications are always researched in theory and with simulations (DEM, DSMSC, CFD and corresponding couplings). In addition, the working group produces nanomaterials with defined properties and investigates their bio-nano interactions in numerous collaborations with research institutes and industry in Germany, Europe, USA and Australia.
Projects of Reactive Spray Deposition Technology
Iron-steam process for the transport and storage of hydrogen (Me2H2)
Hydrogen is essential for industrial decarbonization, but the large quantities required cannot be met solely by domestic renewable energy. Therefore, environmentally friendly methods for large-scale hydrogen transport and storage are crucial. The iron-steam process offers a promising solution by enabling the cyclic production of hydrogen, heat and electricity through metal oxidation and reduction reactions.
At the point of consumption, metals are oxidized with steam to produce hydrogen, while the resulting oxide can be returned to regions with abundant renewable energy for reduction. The scientific and technical goal of this collaborative project is to further develop the iron-steam technology for largescale applications, with the development of a suitable process technology seen as a core task. To address the problem of decreasing reactivity of the iron carrier in the classical iron-steam process, iron alloys with varying Mn contents (3, 5, 10, and 20 wt%) were tested, and the alloy containing 10 wt% Mn was identified as the optimum material system under the current experimental conditions, which include temperatures of 800 °C, 700 °C, and 600 °C.
Cooperation: Universität Duisburg-Essen, Institut für Technologien der Metalle (ITM), Lehrstuhl für Metallurgie der Eisen- und Stahlerzeugung, Technische Universität Clausthal, Institut für Metallurgie (IMET), Metallurgische Prozesstechnik, thyssenkrupp Steel Europe AG, SMS group GmbH
Funding: BMBF 03SF0658C (Me2H2)
Contact:
Dr.-Ing. Andree Irretier
Tel.: +49 421 218 51419
E-Mail: irretier@mpa-bremen.de
M.Sc. Carolina Souza Santiago
Tel.:+49 421 218 64511
E-Mail: c.santiago@iwt.uni-bremen.de
Engineered Artificial Minerals (EnAM) – Exploration of the compositional phase space of metallurgical slag models for a rational design of processes of refractory metal recovers through smelting and recrystallization
Metallurgical slags contain small, yet significant amounts of rare, valuable elements such as Co and Ta which are commonly lost during downstream processing due to a lack of efficient recycling technologies.
This project aims at contributing to a novel recovery approach called “Engineered Artificial Minerals” which foresees the enrichment of target elements in crystalline phases.
Cooperation: Hybrid Materials Interfaces Group, Universität Bremen
Funding: DFG (SPP 2315)
Contact:
M.Sc. Manuel Vollbrecht
Tel.: +49 421 218 51210
E-Mail: m.vollbrecht@iwt.uni-bremen.de
1D modeling of single droplet combustion in Flame Spray Pyrolysis
This study presents a one-dimensional single-droplet model to simulate the combustion of multicomponent droplets, focusing on precursor reactions and solid particle formation. The model examines precursor decomposition and solid phase formation in tin 2-ethylhexanoate and m-xylene droplets.
A notable feature is the formation of a viscous shell from less-volatile precursors and reaction products, encapsulating volatile species and often causing microexplosions or puffing. These events are predicted by calculating vapor pressure under specific Damköhler, Arrhenius, and Liquid Lewis numbers. The model provides a robust framework for optimizing precursor and process design and can integrate into multiphase turbulent flame simulations for advanced modeling of flame spray pyrolysis.
Cooperation: Universität Bremen (FB04)
Funding: ERC (ReSuNiCo 786487)
Contact:
M.Tech. Arvind Chouhan
Tel.:+49 421 218 64507
E-Mail: a.chouhan@iwt.uni-bremen.de
Combustion of single droplets in a confined microreactor
With the support of single droplet experiments, physicochemical mechanisms in nanoparticle producing spray flames can be deduced. Here, the single burning droplets themselves can be viewed as spatially confined microreactors, with numerous mechanistic pathways involved in attaining the particle size, composition, and morphology.
Studying the burning droplets in a confined microfluidic channel enables a novel arrangement of a microreactor within a microreactor and allows precise control and fundamental investigation of combustion dynamics for burning droplets. Flame and droplet histories for varying ratios of gap distance (H) to droplet size (D) were analyzed using high-speed imaging.
Cooperation: Rutgers University, USA
Funding: DFG-NSF
Contact:
M.Sc. Arne Witte
Tel.:+49 421 218 51216
E-Mail: a.witte@iwt.uni-bremen.de
Single droplet flame emission spectroscopy
A novel method based on flame emission spectroscopy combined with high-speed imaging has been developed to analyse nanoparticle formation during single droplet combustions, providing fundamental insights into the smallest unit of the flame spray pyrolysis process: the droplet.
This method allows for direct observation of metal release and combustion dynamics, revealing the micro-explosions as a critical step for the metal release and nanoparticle synthesis. This insight enhances understanding of flame spray pyrolysis processes for tailored nanoparticle production.
Cooperation: Universität Bremen (FB04)
Funding: ERC (ReSuNiCo 786487)
Contact:
M.Sc. Jan Derk Groeneveld
Tel.:+49 421 218 51217
E-Mail:j.groeneveld@iwt.uni-bremen.de
Process parameter optimization of metal sulfide production in Flame Spray Pyrolysis (FSP)
The project investigates how process parameters such as precursor-solvent interaction, fuel-to-oxygen ratio, precursor flow rate, co-flow rate, and metal-to-sulfur ratios affect flame spray pyrolysis (FSP) synthesized metal sulfide properties.
The parameters can be optimized to synthesize tailored metal sulfide nanoparticles with certain phase composition, crystallinity, and particle diameter to bring metal sulfide into a new application field. This study will help to perform in situ coating, doping, mixing, and functionalizing the metal sulfide nanoparticle in a reducing environment.
Funding: ERC (ReSuNiCo 786487)
Contact:
M.Sc. Muhammad Ali Martuza
Tel.: +49 421 218 64508
E-Mail: m.martuza@iwt-bremen.de
Tin doped Indium sulfide solid solutions as potential photocatalysts water splitting
A novel reactive-spray system for synthesizing metal sulfides in reducing flames offers advancements in photocatalysis for solar energy and water splitting. By gas-phase reactions and doping strategies, Sn doped In2S3 solid solutions with enhanced photo-catalytic activity and structural stability were synthesized.
Characterization techniques, including XRD and TEM, confirmed high crystallinity, while Sn doping improved photoexcitation and redox potential. These materials demonstrated suitable band gaps (1.9–1.1 eV) and flat band potentials for water oxidation. This innovative approach addresses material degradation issues and supports future industrial and research applications in visible light-driven catalysis.
Funding: ERC (ReSuNiCo 786487)
Contact:
Prof. Dr. habil. Suman Pokhrel
Tel.: +49 421 218 51218
E-Mail: spokhrel@iwt.uni-bremen.de