Journal articles and book contributions

The nature of the self-sustained reaction of reactive materials is dependent on the physical, thermal, and mechanical properties of the reacting materials. These properties behave differently at the nano scale. Low-dimensional nanomaterials have various unusual size dependent transport properties. In this review, we summarize the theoretical and experimental reports on the size effect on melting temperature, heat capacity, reaction enthalpy, and surface energy of the materials at nano scale because nanomaterials possess a significant change in large specific surface area and surface effect than the bulk materials. According to the theoretical analysis of size dependent thermodynamic properties, such as melting temperature, cohesive energy, thermal conductivity and specific heat capacity of metallic nanoparticles and ultra-thin layers varies linearly with the reciprocal of the critical dimension. The result of this scaling relation on the material properties can affect the self-sustained reaction behavior in reactive materials. Resultant, powder compacts show lower reaction propagation velocities than bilayer system, if the particle size of the reactants and the void density is decreased an increase of the reaction propagation velocity due to an enhanced heat transfer in reactive materials can be achieved. Standard theories describing the properties of reactive material systems do not include size effects.

In this study, the reversible thickness change of a large-format lithium-ion automotive pouch cell is investigated under precisely monitored cell pressure and temperature using an in-house built actively controlled pneumatic cell press. The quantitative and qualitative contribution of the state-of-the-art NMC811 cathode and the SiOx-graphite composite anode to the total pouch cell expansion is resolved by electrochemical dilatometry and validated. Results show that Ni-rich cathodes have a significant impact on the pouch cell expansion and exhibit highly nonlinear thickness change which is related to the change of the individual lattice parameters of the crystal structure. To resolve the contribution of both anode active materials to the total anode expansion, the capacities of SiOx and graphite are determined by differential voltage analysis and validated with half-cell measurements. Then, the volume expansion of SiOx and graphite as a function of the anode state of charge is calculated. By introducing fitting parameters and applying theories about the interaction of SiOx with the surrounding morphology the correlation between the volume expansion of the active materials and the thickness change of the SiOx-Gr composite anode is investigated. The findings suggest that there is significant nonlinear reduction of pore volume at low state of charge.

Binder- and conducting additive-free Si-O-C composite layers are deposited electrochemically under potentiostatic conditions from sulfolane-based organic electrolyte. Quartz crystal microbalance with damping monitoring is used for evaluation of the layer growth and its physical properties. The sodiation-desodiation performance of the material is afterward explored in Na-ion electrolyte. In terms of specific capacity, rate capability, and long-term electrochemical stability, the experiments confirm the advantages of applying the electrochemically formed Si-O-C structure as anode for Na-ion batteries. The material displays high (722 mAh g^-1) initial reversible capacity at j = 70 mA g^-1 and preserves stable long-term capacity of 540 mAh g^-1 for at least 400 galvanostatic cycles, measured at j = 150 mA g^-1. The observed high performance can be attributed to its improved mechanical stability and accelerated Na-ion transport in the porous anode structure. The origin of the material electroactivity is revealed based on X-Ray photoelectron spectroscopic analysis of pristine (as deposited), sodiated, and desodiated Si-O-C layers. The evaluation of the spectroscopic data indicates reversible activity of the material due to the complex contribution of carbon and silicon redox centers.

Robot polishing is increasingly being used in the production of high-end glass work pieces such as astronomy mirrors, lithography mirrors, laser gyroscopes or high-precision coordinate measuring machines. The quality of optical components such as lenses or mirrors can be described by shape errors and surface roughness. Whilst the trend towards sub nanometre level surfaces finishes and features progresses, matching both form and finish coherently in complex parts remains a major challenge. With increasing optic sizes, the stability of the polishing process becomes more and more important. Polishing agent nozzles supply the polishing process with sufficient polishing agent and it is assumed that this slurry erosion has an influence on the material removal. To investigate this, a static test set-up was built. The primary aim of this paper is to point out and raise awareness of the problem of slurry erosion in glass polishing and the influence of slurry erosion by conventional polishing nozzles is shown. From an angle of 30˚, the nozzle turns into a fluid jet tool and removes material independently.