Stephan Barcikowski

Continuous production and online-characterization of nanoparticles from ultrafast laser ablation and laser cracking

Direct ultrafast laser ablation of solids and laser cracking of streaming microparticles is used to fabricate nanocores in a continuous process. Without using any chemical precursors, the nanocores are generated in liquid and gaseous media. Nano-analytical instrumentation is applied for production rate determination and nanomaterial characterization using online-measurement of the particle diameter and optical resonance phenomena. Furthermore, methods to control the nanoparticle size distribution are demonstrated.Direct ultrafast laser ablation of solids and laser cracking of streaming microparticles is used to fabricate nanocores in a continuous process. Without using any chemical precursors, the nanocores are generated in liquid and gaseous media. Nano-analytical instrumentation is applied for production rate determination and nanomaterial characterization using online-measurement of the particle diameter and optical resonance phenomena. Furthermore, methods to control the nanoparticle size distribution are demonstrated.

Adding functionality to metal nanoparticles during femtosecond laser ablation in liquids

This study presents an approach to the in-situ functionalization of metal nanoparticles, established by laser ablation in solution. Additives as polyvinylpyrrolidone (PVP), thiols or alkoxysilanes, that undergo physisorption with the surface of the nanoparticles, can be added to the solution and used as functionalization agents. The concentration of the additive influences the particle size distribution, which leads to plasmon resonance shifts, measurable by UV/VIS spectroscopy. As an example, the size dispersion and stability of generated gold nanoparticles can be controlled by varying the concentration of dodecanthiol as an additive during laser ablation of gold in n-hexane. Moreover, silica shells can be generated to protect metal nanoparticles (gold and copper) against oxidation by in-situ coating and subsequent silica shell formation.In-situ functionalizations of nanoparticles during laser ablation in liquids present a promising approach to the development of nanomaterials for biomedical applications.This study presents an approach to the in-situ functionalization of metal nanoparticles, established by laser ablation in solution. Additives as polyvinylpyrrolidone (PVP), thiols or alkoxysilanes, that undergo physisorption with the surface of the nanoparticles, can be added to the solution and used as functionalization agents. The concentration of the additive influences the particle size distribution, which leads to plasmon resonance shifts, measurable by UV/VIS spectroscopy. As an example, the size dispersion and stability of generated gold nanoparticles can be controlled by varying the concentration of dodecanthiol as an additive during laser ablation of gold in n-hexane. Moreover, silica shells can be generated to protect metal nanoparticles (gold and copper) against oxidation by in-situ coating and subsequent silica shell formation.In-situ functionalizations of nanoparticles during laser ablation in liquids present a promising approach to the development of nanomaterials for biomedical applications.

Protection of the environment and saving costs using electronic nose during laser material processing of polymers and wood composites

The protection against beam and non-beam hazards contributes often more than 10% to the operating costs of laser material processing systems. The decomposition products of laser cut polymers (laser-generated air contaminants: LGACs) have been found to be quite hazardous [1,2,3]. Hence, for laser users handling of emission is obligatory to assure safe laser operation.However, the operation stability of air pollution control systems may be limited with respect to complex mixtures of gaseous LGACs. To use the advantages of the activated carbon systems and to face their inherent problems, an on-line monitoring unit based on the electronic nose concept has been developed and qualified in the frame of a joint research project. In this paper, the improvement of the efficiency of LGACs filtration systems is shown using electronic nose sensing. The on-line monitoring system provides an acceptable compromise of efficiency and costs (invest and running cost) compared to conventional detection technologies for volatile organic compounds [4].The protection against beam and non-beam hazards contributes often more than 10% to the operating costs of laser material processing systems. The decomposition products of laser cut polymers (laser-generated air contaminants: LGACs) have been found to be quite hazardous [1,2,3]. Hence, for laser users handling of emission is obligatory to assure safe laser operation.However, the operation stability of air pollution control systems may be limited with respect to complex mixtures of gaseous LGACs. To use the advantages of the activated carbon systems and to face their inherent problems, an on-line monitoring unit based on the electronic nose concept has been developed and qualified in the frame of a joint research project. In this paper, the improvement of the efficiency of LGACs filtration systems is shown using electronic nose sensing. The on-line monitoring system provides an acceptable compromise of efficiency and costs (invest and running cost) compared to conventional detection technologies for volati...

Nanoparticles - Potential risk during pulsed laser ablation

Nanoparticles are generated as by-products during laser ablation with an amount of 50 – 90% of the overall particulate emissions. The quantity and size of particulate emission depends strongly on the laser type, feed rate and process gas. Laser ablation using ultrashort laser pulses leads to the highest relative release of nanoparticles. In order to provide safety-related statements on nanoparticles generated during laser materials processing, the particle size distribution during laser ablation of ten materials (metal, ceramic, polymer) is studied. The number frequency of nanoparticles may increase up to over 99% if nitrogen is used as process gas. Based on data of the concentration and particle size distribution, a risk assessment is carried out. The number concentration and the particle surface area of nanoparticles in the workplace area are compared with indicators of toxicological effects available in the literature. The number concentration after an 8 hour shift is up to 100 times higher than the background condition. Although the assessment shows that the nanoparticle concentrations are negligible compared to toxicological thresholds, sufficient capturement during laser ablation processes is strongly recommended.Nanoparticles are generated as by-products during laser ablation with an amount of 50 – 90% of the overall particulate emissions. The quantity and size of particulate emission depends strongly on the laser type, feed rate and process gas. Laser ablation using ultrashort laser pulses leads to the highest relative release of nanoparticles. In order to provide safety-related statements on nanoparticles generated during laser materials processing, the particle size distribution during laser ablation of ten materials (metal, ceramic, polymer) is studied. The number frequency of nanoparticles may increase up to over 99% if nitrogen is used as process gas. Based on data of the concentration and particle size distribution, a risk assessment is carried out. The number concentration and the particle surface area of nanoparticles in the workplace area are compared with indicators of toxicological effects available in the literature. The number concentration after an 8 hour shift is up to 100 times higher than the ba...

Putting fundamentals on multiphase material balance of laser-based cutting polymers and natural fiber composites to practical use

Laser-based cutting and drilling of polymers and natural fiber composites has already covered a market niche, even though fundamentals of heat transfer and multiphase material balances are not well characterized up to now. Discussing the decomposition and vaporization balance, a recommendation on process parameters is given. Within this paper, criteria for laser-based production are given as well as requirements of the material. The investigation focus on strategies to control the pyrolysation and decomposition of the material as well as the prognosis of the process ability derived from laser Micropyrolysis-GC/MS correlated with industrial applications.

Laser cladding of metal-ceramic nanocomposite layers for cutting applications

The laser cladding process can be used for the generation of complex, near-net-shape geometries on a multitude of different substrate materials. By adding ceramic particles, the mechanical and tribological properties of the matrix material can be improved, and hence, optimization of tool manufacturing for various applications is possible. In metallic matrices, these particles act as a reinforcing phase and lead to a higher wear resistance. To avoid stress peaks in the material, ceramic nanoparticles instead of microparticles may be used. In this context, a homogeneous distribution of the particles and the prevention of ceramic agglomerates in the matrix are essential to achieve optimized properties. A method for the integration of nanoparticles in the laser cladding process has been developed, and has thus enabled the fabrication of steel-ceramic nanocomposite structures. Cutting tools, for example in the paper-converting industries, could be manufactured by applying the generative laser cladding process developed in this work, using powder as an additive material. These high precision tools have so far been produced using etching techniques. Here, the generation of metal-ceramic nanocomposite layers could lead to a significantly longer tool lifetime, and a more efficient material utilization.The laser cladding process can be used for the generation of complex, near-net-shape geometries on a multitude of different substrate materials. By adding ceramic particles, the mechanical and tribological properties of the matrix material can be improved, and hence, optimization of tool manufacturing for various applications is possible. In metallic matrices, these particles act as a reinforcing phase and lead to a higher wear resistance. To avoid stress peaks in the material, ceramic nanoparticles instead of microparticles may be used. In this context, a homogeneous distribution of the particles and the prevention of ceramic agglomerates in the matrix are essential to achieve optimized properties. A method for the integration of nanoparticles in the laser cladding process has been developed, and has thus enabled the fabrication of steel-ceramic nanocomposite structures. Cutting tools, for example in the paper-converting industries, could be manufactured by applying the generative laser cladding process ...

Non-beam hazards during laser machine

Laser material processing is gaining increasing importance in micro and macro machining. During laser processing of polymers and metals dangerous air pollutants have to be considered with regard to occupational safety. Moreover, technical measures for the handling of Laser Generated Air Contaminants (LGACs) often contribute to more than 10 % of the operating costs of laser machinery. Therefore, data are required for an adequate design and scaling of emission capturing systems. An overview on the characterization, handling, and filtration of non-beam hazards during laser processing as well as a consideration of economic aspects is given. Based on these data we introduce the Laser Micropyrolysis-GC/MS as a novel method for emission prognosis. Finally, technical precaution measures for a variety of laser machining processes are evaluated.Laser material processing is gaining increasing importance in micro and macro machining. During laser processing of polymers and metals dangerous air pollutants have to be considered with regard to occupational safety. Moreover, technical measures for the handling of Laser Generated Air Contaminants (LGACs) often contribute to more than 10 % of the operating costs of laser machinery. Therefore, data are required for an adequate design and scaling of emission capturing systems. An overview on the characterization, handling, and filtration of non-beam hazards during laser processing as well as a consideration of economic aspects is given. Based on these data we introduce the Laser Micropyrolysis-GC/MS as a novel method for emission prognosis. Finally, technical precaution measures for a variety of laser machining processes are evaluated.

Intelligent, low-cost system for fume control during laser material processing

This paper describes an intelligent filter system for laser machinery. To avoid contamination of the workplace, laser generated air contaminants (LGACs) have to be efficiently minimized. Especially for LGACs generated during laser processing of organic materials, up to now, there is no system available which provides information on the condition of the filter system (concentration of LGACs in the clean gas, resp. degree of filter saturation) which controls exhaust streams and which meets the requirements of laser users (a.o. reliable, not expensive). With the on-line sensor system the filter system will be more reliable, economic and meets the requirements by the laser users.The sensor system is based on a semiconductor array which is integrated in a control unit. Since a very complex mixture of gaseous LGACs is emitted during laser processing of organic materials, the sensor array is addressed to the specific main components of the LGACs. To overcome cross-sensitivities, software algorithms have been dev...

Microshaping of densely sintered zirconia ceramic using femtosecond lasers

For dental restorations, very dense and hard ceramics – especially hot isostatically pressed forms of zirconia ceramics like HIP Y-TZP – have the potential of superseding conventional dental material. Structuring such ceramics with lasers avoids strong tool wear that is unavoidable when using mechanical processes. Another important issue is the crystal structure transformation in the bulk material during the process. For this reason, femtosecond lasers are intended as the key tool for HIP ceramic dental restoration manufacturing units.We demonstrate why lasers in the femtosecond regime are most suitable for these demands and search for optimal structuring approaches to be implemented in dental crown processing. Applications of such processes in connection with dental crowns and bridges include the complete production by shape cutting from solid material, finishing steps, as well as surface structuring for the purpose of optimized cement adhesion.For dental restorations, very dense and hard ceramics – especially hot isostatically pressed forms of zirconia ceramics like HIP Y-TZP – have the potential of superseding conventional dental material. Structuring such ceramics with lasers avoids strong tool wear that is unavoidable when using mechanical processes. Another important issue is the crystal structure transformation in the bulk material during the process. For this reason, femtosecond lasers are intended as the key tool for HIP ceramic dental restoration manufacturing units.We demonstrate why lasers in the femtosecond regime are most suitable for these demands and search for optimal structuring approaches to be implemented in dental crown processing. Applications of such processes in connection with dental crowns and bridges include the complete production by shape cutting from solid material, finishing steps, as well as surface structuring for the purpose of optimized cement adhesion.