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- Femtosecond laser ablation (9)
- Laser-induced periodic surface structures (LIPSS) (9)
- Double-pulse experiments (4)
- Femtosecond laser (4)
- Polycondensation (4)
- Silicon compounds (4)
- Ultrafast optical techniques (4)
- High-speed optical techniques (3)
- Laser ablation (3)
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- Laser-induced periodic surface structures, LIPSS (3)
- MALDI (3)
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- Laser-induced periodic surface strcutures (LIPSS) (1)
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- Steel (1)
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- Ti6Al4V alloys (1)
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- Ultrashort pulse laser processing (1)
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- behaviour (1)
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Organisationseinheit der BAM
- 6 Materialchemie (4)
- 6.2 Material- und Oberflächentechnologien (4)
- 8 Zerstörungsfreie Prüfung (4)
- 7 Bauwerkssicherheit (3)
- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (3)
- 7.1 Baustoffe (2)
- 2 Prozess- und Anlagensicherheit (1)
- 2.1 Sicherheit von Energieträgern (1)
- 3 Gefahrgutumschließungen; Energiespeicher (1)
- 3.1 Sicherheit von Gefahrgutverpackungen und Batterien (1)
Glass-ceramics are noted for their unusual combination of properties and manifold commercialized products for consumer and specialized markets. Evolution of novel glass and ceramic processing routes, a plethora of new compositions, and unique exotic nano- and microstructures over the past 60 years led us to review the Definition of glass-ceramics. Well-established and emerging processing methods, such as co-firing, additive manufacturing, and laser patterning are analyzed concerning the core requirements of processing glass-ceramics and the Performance of the final products. In this communication, we propose a revised, updated definition of glass-ceramics, which reads “Glass-ceramics are inorganic, non-metallic materials prepared by controlled crystallization of glasses via different processing methods. They contain at least one type of functional crystalline phase and a residual glass. The volume fraction crystallized may vary from ppm to almost 100%”.
Die Mikro- und Nanotechnologie gehört zu den Schlüsseltechnologien des 21. Jahrhunderts mit hohen Wachstumsprognosen, wie auch die im Auftrag des BMBF durchgeführte Studie “Nanotechnologie als wirtschaftlicher Wachstumsmarkt” von 2004 ausführlich darstellt. Aus diesem Trend resultiert ein steigender Bedarf an Messsystemen, die Nanostrukturen prozessnah bzw. im Fertigungsprozess charakterisieren können. Virtuelle Messgeräte liefern Erkenntnisse zur Entwicklung neuartiger Messsysteme, Analyse und Optimierung bestehender Verfahren sowie die Bestimmung der Messunsicherheit und modellbasierten Korrektur systematischer Fehler. Der virtuelle Messprozess umfasst neben dem Messmittel auch die Probe und die Wechselwirkungen zwischen beiden. In diesem Beitrag werden virtuelle Messgeräte vorgestellt sowie deren Anwendung diskutiert.
The inhalationof smoke gases is awell-established cause of poisoning and leads to the death of fire victims. Carbonmonoxide(CO) and Hydrogen cyanide (HCN) are two of the main noxious gases,whereby HCN is formed by an incomplete combustion of materials containing nitrogen. These materials may be natural materials, such as wool, silk and feathers or synthetic plastics, such as polyacrylonitrile (PAN), polyamide and polyurethane. These materials are very common in modern household furnishings; therefore, notonlyCObutalsoHCN can be produced during home fires. Up tonowonly a fewstudieshave been carried out on the generation of HCN as the fire proceeds, e. g. by Crewe et al. The data from such analyses are useful for forensic purposes. This enables the possibility to more accurately assess the events at the fire location, the Situation in which the fire victims are found as well as the cause of death. One way to analyze the gas composition of smoke is to perform bench scale fire tests, where various fire scenarios can be simulated on a smaller scale (e. g. using a smoke density chamber). The results from such experiments were compared with the results obtained in an enclosed room fire test.
Laser-induced periodic surface structures (LIPSS) were generated on two types of steel (100Cr6, X30CrMoN15-1) and two types of titanium (Ti, Ti6A14V) surfaces upon irradiation with multiple linear polarized femtosecond laser pulses in air environment (pulse duration 30 fs, central wavelength 790 nm, pulse repetition rate 1 kHz, Gaussian beam shape). Teh conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning geometry for the processing of large surface areas covered homogeneously by two different types of LIPSS - either near wavelength or sub-100 nm structures. The tribological performance of the nanostructured surfaces was characterized under reciprocating sliding at 1 Hz against a ball of hardened steel using different lubricants and normal forces. After 1000 cycles the corresponding wear tracks were characterized by optical and scanning electron microscopy. For specific conditions, the wear was strongly reduced and laser-generated nanostructures endured the tribological treatment. Simultaneously, a significant reduction of the friction coefficient was observed in the laser-irradiated LIPSS-covered areas, indicating the benefit of laser surface structuring for tribological applications. The spatially Gaussian shaped beam used for the laser processing was transformed via beam shaping into a top hat distribution at the surface of the samples for optimization. The tribological performance of the laser-induced nanostructures is discussed on the basis of different physical and chemical mechanisms.
The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica with multiple irradiation sequences consisting of five Ti:sapphire femtosecond (fs) laser pulse pairs (150 fs, 800 nm) is studied experimentally. A Michelson interferometer is used to generate near-equal-energy double-pulse sequences with a temporal pulse delay from -20 to +20 ps between the cross-polarized individual fs-laser pulses (~0.2 ps resolution). The results of multiple double-pulse irradiation sequences are characterized by means of Scanning Electron and Scanning Force Microscopy. Specifically in the sub-ps delay domain striking differences in the surface morphologies can be observed, indicating the importance of the laser-induced free-electron plasma in the conduction band of the solids for the formation of LIPSS.
Pulmonary surfactant contains two extremely hydrophobic proteins, SP-B and SP-C. We present a novel HPLC method for the preparation of these hydrophobic proteins. It is based on size-exclusion chromatography using the apolar stationary-phase butyl silica gel and isocratic elution with acidified chloroform/methanol. Samples for HPLC were prepared from sheep lung lavage fluid by centrifugation and extraction with chloroform/methanol. Amino acid analyses of the two protein fractions revealed sequences that are consistent with SP-B and SP-C, respectively. MALDI-TOF-MS analyses of the SP-B fraction showed one major peak of dimeric SP-B with m/z 17,361, and additional peaks of monomeric and oligomeric forms, which are predominantly even numbered. The SP-C fraction showed a peak at m/z 4200, consistent with the theoretical mass of the dipalmitoylated form of this protein. The biophysical activity of pure sheep SP-B and SP-C was evaluated by measuring the surface tension using axisymmetric drop shape analysis for captive bubbles. We found distinct surface pressure versus surface area isotherms of SP-B and SP-C indicating different biophysical activities for these surfactant proteins. The new preparative HPLC method is able to replace the established, time-consuming low-pressure liquid chromatography method for the isolation of SP-B and SP-C from lipids.
Poly(ether-sulfone)s having an identical backbone were prepared by four different methods. First, silylated bisphenol A (BSBA) was polycondensed with 4,4'-difluorodiphenyl sulfone (DFDPS) and K2CO3 in N-methylpyrrolidone with variation of the temperature. Second, analogous polycondensation were conducted using CsF as catalyst (and no K2CO3). Third, CsF-catalyzed polycondensations BSBA and DFDPS were conducted in bulk up to 290 C. Fourth, free bisphenol was polycondensed with DFDPS or 4,4'-dichlorodiphenyl sulfone and K2CO3 in DMSO with azeotropic removal of water. MALDI-TOF mass spectroscopy revealed that the first method mainly yielded cyclic poly(ether-sulfone)s which were detected up to masses around 13 000 Da. These and other results suggest that these polycondensations take a kinetically kontrolled course at tempeatures 145 C. This interpretation is also valid for the fourth method where high yields of cycles were obtained with DFDPS. With the less reactive 4,4'-dichlorodiphenyl sulfone lower conversions, lower molecular weights and lower fractions of cycles were found. In contrast to KF (resulting from K2CO3) CsF cleaves the poly(ether sulfone) backbone at temperatures > 145 C. Smaller amounts of smaller cycles were found in these CsF-catalyzed polycondensations which were in this case the result of thermodynamically controlled "back-biting degradation".
Various dibutyltin derivatives were polycondensed with aliphatic ,-dicarboxylic acids having chain lengths from 4 (succinic acid) to 22 carbon atoms. White crystalline products were obtained from all experiments, and the structure of the products was independent of the synthetic method. Viscosity measurements revealed low molecular weights (n 1 500 Da) in all cases. Vapor pressure osmometry (VPO) measurements and matrix-assisted laser desorption time-of-flight (MALDI-TOF) mass spectrometry proved that cyclic dimers and trimer were formed from dicarboxylic acids having 6 to 16 carbons, but mainly the monomeric cycle from docosane dioic acid. Heating to 250°C did not change the structure. Therefore, the results indicate that the macrocycles are the result of a thermodynamically controlled ring-closing polycondensation. This means that linear high-molecular weight poly(dibutyltin dicarboxylate)s cannot exist above room temperature.
Various dibutyltin derivatives were polycondensed with aliphatic ,-dicarboxylic acids having chain lengths from 4 (succinic acid) to 22 carbon atoms. White crystalline products were obtained from all experiments, and the structure of the products was independent of the synthetic method. Viscosity measurements revealed low molecular weights (n 1 500 Da) in all cases. Vapor pressure osmometry (VPO) measurements and matrix-assisted laser desorption time-of-flight (MALDI-TOF) mass spectrometry proved that cyclic dimers and trimer were formed from dicarboxylic acids having 6 to 16 carbons, but mainly the monomeric cycle from docosane dioic acid. Heating to 250°C did not change the structure. Therefore, the results indicate that the macrocycles are the result of a thermodynamically controlled ring-closing polycondensation. This means that linear high-molecular weight poly(dibutyltin dicarboxylate)s cannot exist above room temperature.
Three new aromatic polyazomethines have been synthesized by solution polycondensation reactions of terephthalic dialdehyde with fluorine containing aromatic diamines. The polymers were obtained in high yields. The investigation of these polymers by means of matrix-assisted laser desorption ionizationtime-of-flightmass spectrometry (MALDITOFMS) proved the initial members of the four theoretical possible series of the corresponding oligomers with 210 repeating units per molecule.
The role of 1,1-diphenylethylene (DPE) in radical emulsion polymerization of methyl methacrylate is investigated. The presence of DPE causes a strong decrease in both the rate of polymerization and the molecular weight. According to the results of structure analysis by means of MALDI-TOF mass spectrometry, UVvis spectroscopy, and 1HNMR spectroscopy, DPE is incorporated in the copolymer chain exclusively as a reactive recombinant ?,p-dimer, underlining the peculiar role of DPE in radical polymerizations.
Hydrolytic condensation of different methacrylate groups containing alkoxy silanes yielded resins which showed interesting properties as a matrix for dental composites. For this purpose, resins of low viscosity are desired resulting in composites with a high amount of inorganic fillers. Our investigations demonstrated that the viscosity of the obtained polycondensates was predominantly influenced by the kind of organic spacer between the methacrylate group and the silicon atom. In addition, the viscosity also significantly changed in dependence of the kind of structure units built. NMR spectroscopic investigations as well as size exclusion chromatography (SEC) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry showed that the formed structures depended both on the kind of catalyst used for hydrolysis/condensation and the bulkiness of the organic substituent at the silicon atom.