Laser-based Micro Research Articles

Measurement of tyre-based microplastics using traditional and quantum cascade laser-based infrared spectrometry

BackgroundDespite the potential environmental impact of TWPs (tyre wear particles), there is a lack of reliable analytical methodologies suitable for their routine identification and characterization. The number of papers dealing with this topic is, so far, very reduced and, therefore, there is a need for addressing it, mostly because traditional transmittance-based IR techniques are suboptimal due to scattering caused by black carbon in tyres. ResultsThis study aims to evaluate the most appropriate infrared (IR) spectrometric technique for monitoring TWPs. Macro attenuated total reflectance (ATR), reflectance microscopy, and quantum cascade laser-based micro transflectance (QCL-LDIR) were employed to analyse samples from used car and truck tyres in two sample configurations: small tyre fragments (∼1 cm2) and TWPs (< 1 mm). ATR yielded well-defined spectra with good signal-to-noise ratios, allowing for a straightforward interpretation of the major functional moieties. Despite reflectance measurements on tyre fragments provided good results, those on TWPs offered limited information due to noise and scattering. Transflectance offered clear peaks and enhanced resolution in the fingerprint region –compared to the other techniques-, much faster analysis times and the ability to effectively measure particles down to 20–10 µm, thus, emerging as the most effective technique for TWPs analysis. However, spectral interpretation is not immediate. Further, a proof-of-concept chemometric study was done to evaluate whether the analytical techniques contain information to differentiate types of tyres. An unsupervised pattern recognition and a supervised classification technique (principal components analysis and classification trees, respectively) were used, which were able to differentiate among the tyres, notably the truck tyre from the cars tyres. SignificanceThe study presents first time the use of micro transflectance IR to study tyre particles down to 20 µm. Traditional total attenuated reflectance is demonstrated as a suitable way to analyse bigger microplastics. These two options open pathways to monitor this important emerging contaminant in environmental matrices.

Measurement of Li-Ion Self-Diffusion in Laser Structured Electrodes

It is generally stated that a limiting factor in fast charging and high-power discharging of lithium-ion batteries (LiB) stems from the diffusion kinetics of Li+ in the electrode pore network. Numerous approaches in enabling fast charging of LiBs include active material development, electrolytes with high ionic conductivity and the management of the charging and discharging temperature. Another promising method is laser micro structuring to modify the electrode architecture regarding an enhanced lithium-ion diffusion kinetics. An increased high-rate capability and boost in cell lifetime have been demonstrated with such 3D electrodes [1, 2] but the related mechanisms leading to a substantial impact to diffusion kinetics are still poorly understood. Furthermore, it is imperative to find an optimal ablation pattern with regard to the desired application scenario that minimizes active mass loss in order to create the economic basis for efficient upscaling of the process.Nuclear Magnetic Resonance (NMR) measurements of longitudinal (T1) and transverse relaxation times (T2), as well as the T2/T2 exchange, are routinely used for the identification of different molecular species. The exchange NMR experiment is a well-known technique for studying local environments of nuclei such as liquids in pores and approximating their shapes and sizes [3]. The evolution of the transverse relaxation rate (T2) of a probed nuclei allows to determine if the specie is confined (shorter T2) or in liquid bulk (longer T2). In this work, so-called Exchange Nuclear Magnetic Resonance (T2/T2 exchange or EXSY), is conceptualized to study the impact of laser generated 3D patterns in pore self-diffusion of electrolyte species.Exchange NMR and T1 and T2 measurements were realized at various soaking times and electrolyte amounts for the following electrolyte species: Li+, PF6 -, ethyl carbonate (EC), and ethyl methyl carbonate (EMC), using laser structured, graphite-based electrodes casted on non-metallic substrates (to reduce RF interference). 2D exchange maps show the presence of confined species as well as the approximation of the diffusion properties. Using isotope exchange experiments with 6Li enriched electrolyte, concentration maps revealed the rate of 6LiPF6 intrusion into 7LiPF6 rich pre-soaked electrodes. The impact of laser generated 3D patterns in pore diffusion will be discussed in detail.[1]. Zheng, Y. et al. 3D silicon/graphite composite electrodes for high-energy lithium-ion batteries. Electrochim. Acta 317, 502–508 (2019).[2]. Smyrek, P., Pröll, J., Rakebrandt, J.-H., Seifert, H. J. & Pfleging, W. Manufacturing of advanced Li(NiMnCo)O2 electrodes for lithium-ion batteries . Laser-based Micro- Nanoprocessing IX 9351, 93511D (2015).[3]. Mitchell, J. et al. Validation of NMR relaxation exchange time measurements in porous media. J. Chem. Phys. 127, (2007).

Micro engraving on 316L stainless steel orthopedic implant using fiber laser

It has been seen that there is a growing demand for the production of micron size grooves with a uniform flat surface, minimal heat-affected zone (HAZ) thickness, debris deposition, microcrack, microcavity, and recast layer thickness on orthopedic implants. In the present study, a multi-response optimization approach is adopted for fiber laser-based micro engraving to enhance groove characteristics and implant functionality during fixation. Grey relational analysis (GRA) is applied to analyze the experimental data sets and to decide key input factors' (pulse frequency, scanning speed, number of passes, laser power) level setting. These optimized data sets maintain groove quality (groove width, HAZ, debris deposition, recast layer thickness). Laser power and pulse frequency have been identified as the most significant factors for controlling groove quality. A neural network model has been developed and trained through experimental data sets. During analyzing the model, it has been recognized that the regression analysis score is very nearer to 1, and model performance is 2.45e-18. It represents its adaptability for determining the response quality characteristics when factor level settings are out of defined boundary. Improvements in groove quality are noticed in terms of minimal HAZ thickness, debris deposition, recast layer thickness, microvoids, and microcavity under optimum engraving conditions.

Laser micro- and nano-material processing – Part 2

This special issue of Advanced Optical Technologies (AOT) is dedicated to the field of laser-based micro- and nanostructuring methods.

Laser micro- and nano-material processing – Part 1

This special issue of Advanced Optical Technologies (AOT) is dedicated to the field of laser-based micro- and nanostructuring methods.

Structures for biomimetic, fluidic, and biological applications

Abstract

Process-limiting Factors and Characteristics of Laser-based Micro Welding

Abstract In this study the process of laser-based micro welding was examined using the example of ultra-thin stainless steel foils with total welding depths of 50 μm and 100 μm. For this purpose, focal diameters between 20 μm and 200 μm were applied to the work piece using scanning units with various image scales as well as a single-mode and a multi-mode laser with different fiber core diameters. In order to generate full penetration welds, the process windows were determined applying a power level up to 500 W as well as feeding rates up to 6 m/s. A relational expression concerning related power was defined in order to characterize and predict the lower process boundary. By means of high speed recordings the dependencies of process boundaries with respect to melt pool behavior have been clarified. Furthermore a changeover of welding regime within the process window was revealed and described dependent on the focal diameter.

Process Window for Forming of Micro Preforms at Different Temperatures

Parts, which dimensions do not exceed the micro range are gaining more importance in today´s goods due to miniaturization and function compaction of products. Thus, fabrication methods for these special, very small parts attract notice because whole processes or at least process parameters cannot be transferred into micro range. Nevertheless, this does not necessarily mean, that size-effects are always detrimental as there are some processes which can only be carried out in micro range such as the laser-based micro upsetting process. The basic characteristics of this process are presented in this paper such as its self-aligning capability. Due to the fact that the maximum achievable upset ratio in single stage upsetting decreases with decreasing sample size, the material accumulation represents a very good semi-finished product (preform) being formed in a succeeding upsetting process. A temperature- and time controlled forming unit has been developed which is directly adapted to the laser system which is required to generate the preform. Thus, either a pre-defined temperature of the preform or the down time gives the initial signal to start the forming process. In this paper, a mathematical model is very briefly presented to determine the process window for forming preforms at certain well defined temperatures regarding size-effects.

Investigation on Flow Stress Level of Spherical Preforms Generated by Laser Melting

A laser-based micro upsetting process is presented which takes advantage of scaling effects in order to optimize the conventional multistage upsetting process. Due to the fact that the surface tension exceeds the gravitation force with increasing miniaturization, in the microrange, an accumulation of molten material forms a nearly perfect sphere. This material accumulation can be finally formed in a secondary process step. In former investigations, it has been shown that the laser-based free form heading process improves the upset ratio up to 250 instead of 2.3 commonly achieved by conventional multistage upsetting processes. In this article, the second stage of the upsetting process is examined by investigating the deformation behavior of laser free formed austenitic chromium-nickel steel (1.4301) with a rod diameter of 0.5 mm and head diameters ranging from 1.1 mm to 2.1 mm, using a pneumatic forming machine. The experiments show that the maximum achievable true strain is much higher compared to a conventional multistage upsetting process. Furthermore, the flow stress level of material preforms is compared with values gained in cylinder compression tests.

Upset ratios in laser-based free form heading

A laser-based micro upsetting process is presented which takes advantage of scaling effects in order to optimize the conventional multi-stage upsetting. Due to the fact that the surface tension exceeds the gravitation force with increasing miniaturization, in the micro-range an accumulation of molten material forms a nearly perfect sphere, which can be finally formed in a secondary process step. It is shown that the laser-based free form heading process improves the upset ratio up to 45 instead of 2.3 commonly achieved by conventional multi-stage upsetting processes.

In situ monitoring of material processing by a pulsed laser beam coupled via a lensed fiber into a scanning electron microscope

In this study, a new method coupling laser irradiation into a dual-beam scanning electron microscope (SEM) and focused-ion-beam (FIB) system is developed. By using a lensed fiber, pulsed laser illumination could be successfully delivered onto the sample under SEM imaging, providing in situ monitoring for laser material processing applications including local modification of micro-/nanostructures and laser-assisted chemical vapor deposition. In situ characterization of the laser-induced features by high resolution SEM imaging and energy dispersive x-ray spectrometry was successfully carried out. Furthermore, in situ repair of a contaminated lensed fiber probe during laser-assisted chemical vapor deposition was demonstrated via FIB milling. The results demonstrate the full compatibility of the lensed fiber apparatus with the dual-beam apparatus without disturbing the original functions of the system. The combination of guided laser radiation with SEM and FIB instruments offers a powerful capability for in situ monitoring of multilevel laser-based micro- and nanoscale material processing.

An excimer laser-based micro analytical preparation technique for in-situ oxygen isotope analysis of silicate and oxide minerals

A new excimer laser system for in-situ analysis of oxygen isotope ratios of silicates and oxides is described. In contrast to IR lasers the UV laser does not cause any fractionation during laser ablation due to edge or other effects. Analytical reproducibility and precision is equivalent to the conventional method for sample sizes of 0.1 mg, which is the minimum amount required by our mass-spectrometer system. Refractive minerals like olivine and garnet can be analyzed with a precision comparable with conventional analyses of highly reactive minerals, quartz, however, which is transparent at 248 nm does cause problems. Other advantages and disadvantages of our UV laser system are discussed.