Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Erscheinungsjahr
- 2016 (207) (entfernen)
Dokumenttyp
- Zeitschriftenartikel (177)
- Beitrag zu einem Tagungsband (27)
- Buchkapitel (3)
Referierte Publikation
- ja (207) (entfernen)
Schlagworte
- Mechanochemistry (8)
- Corrosion (5)
- Nanocomposite (5)
- Hydrogen embrittlement (4)
- Wear (4)
- XRD (4)
- Additive manufacturing (3)
- Duplex stainless steel (3)
- Dye (3)
- EBSD (3)
Visualization of surface modifications may be very challenging for coating/substrate systems of either almost identical optical constants, e.g. transparent films on substrates of the same material, or minor film thickness, substance quantity and affected area, e.g. ultra-thin or island films. Methods for visualization are optical microscopy (OM), imaging ellipsometry (IE), and referenced spectroscopic ellipsometry (RSE). Imaging ellipsometry operates at oblique incidence near Brewster angle of the bare, clean or unmodified substrate. In this configuration, reflected intensities are rather weak. However, the contrast to add-on and sub-off features may be superior. Referenced spectroscopic ellipsometry operates in a two-sample configuration but with much higher intensities. In many cases, both ellipsometric techniques reveal and visualize thin films, printed-pattern, laser-induced changes, and impurities better than optical microscopy. In particular for stratified homogeneous modifications, ellipsometric techniques give access to modelling and hence thickness determination. Modifications under investigation are polymer foil residue on silicon, laser-induced changes of ta-C:H coatings on 100Cr6 steel, imperfections of ta-C:H on thermal silicon oxide, degradation of glass, thin film tin oxide pattern on silicon, printed and dried pattern of liquids such as deionized water, cleaning agents, and dissolved silicone. © 2016 Elsevier B.V. All rights reserved.
In coal-fired power plants using oxyfuel combustion process with carbon capture and sequestration, instead of air, a mixture of oxygen and recirculated flue gas is injected in the boiler. A series of steels were exposed to CO2-SO2-Ar-H2O gas mixtures at 600 °C for 1000 h to compare their high temperature corrosion behavior. During the corrosion process, carburization, decarburization and recrystallization were observed underneath the oxide scale depending on the gas mixture and alloy composition. The conditions that lead to carburization are not yet completely understood, but decarburization can be simulated using thermodynamic and kinetic models. In this work, the results of these simulations are compared with measured values for one of the alloys that displayed a decarburized region. Since the mobility of carbon in the scale is not known, two strategies were adopted: simulation of alloy-atmosphere contact; and estimation of the carbon flux to produce the observed decarburization. The second approach might give an insight on how permeable to carbon the scale is.
Hydroxyapatite (HA) is a bioceramic material with excellent biological properties. However, these properties are strongly dependent of ist crystallinity degree, with high values of crystallinity associated to poor resorption rates and bioactivity. This work evaluates the properties of HA samples produced by two different free-forming conformation methods, CNC machining and 3D printing. In both cases, porous gypsum samples were produced and subsequently converted into HA in a reaction with di-ammonium hydrogen phosphate at 100°C and pH 8. A total conversion of the samples was achieved after 36 h independently of the conformation method used. The microstructure, however, before and after the conversion is showed to be dependent on the method used. After conversion the machined samples achieved a Maximum compressive strength of 3.5 MPaforporosities of circa 80%, while 3D printed samples achieved a tensile strength of 2.0 MPa by porosities of 61%.
It has been shown that selected types of substituents are able to vary the oxidative behavior of multi-walled carbon nanotubes. Such substituents investigated were sterically hindered secondary amino groups bonded in grafted piperidine units and covalently bonded bromine groups. Their interference and activity was preliminary determined in the model cumene and then in oil diesel fraction and low density polyethylene oxidation reactions. Results obtained indicate that chemical linking of amine moieties containing –NH groups directly to the carbon nanotubes core significantly increases their intrinsic anti-oxidative capacity while the grafting of Br-groups provokes the opposite functioning of the pristine samples. This inference was proved by thermogravimetric and differential thermal analysis of the polyethylene composites and experiments on profound aerobic oxidation of petroleum naphthenic fraction derived from the commercial Baku oils blend diesel cut.
Quality control requirements imposed on assays used in clinical diagnostics and point-of-care-diagnostic testing (POCT), utilizing amplification reactions performed at elevated temperatures of 35 to 95 °C are very stringent. As the temperature of a reaction vessel has a large impact on the specificity and sensitivity of the amplification reaction, simple tools for local in situ temperature sensing and monitoring are required for reaction and assay control. We describe here a platform of stem-and-loop structured DNA hairpins (molecular beacons, MBs), absorbing and emitting in the visible and red spectral region, rationally designed for precise temperature measurements in microfluidic assays for POCT, and their ap-plication for temperature measurements in a common DNA-based molecular biological assay utilizing thermophilic helicase-dependent amplification (tHDA). Spectroscopic studies of these MBs, rationally designed from DNA se-quences of different thermal stabilities, chosen not to interact with the DNA probes applied in the nucleic acid amplification assay, and temperature-dependent fluorescence measurements of MB-assay mixtures revealed the suitability of these MBs for temperature measurements directly in such an assay with a temperature resolution of about 0.5 °C without interferences from assay components. Combining two spectrally distinguishable MBs provides a broader response range and an increase in temperature sensitivity up to 0.1 °C. This approach will find future application for temperature monitoring and quality control in commercialized diagnostics assays using dried reagents and microfluidic chips as well as assays read out with tube and microplate readers and PCR detection systems for temperature measurements in the range of 35 to 95 °C.
Microstructure-property connections for porous ceramics: The possibilities offered by micromechanics
(2016)
Microstructure of porous ceramics is highly “irregular”: it comprises pores and microcracks of diverse shapes and orientations.
This makes their quantitative modeling challenging, and one
often resorts to empirical relations containing Fitting Parameters and having somewhat uncertain range of applicability. We review the substantial progress made in modeling of “irregular” microstructures that does not seem to have been sufficiently utilized in the context of ceramics. We discuss the possibilities offered by micromechanics in developing microstructure–property relations for porous microcracked ceramics. After an overview of relevant micromechanics topics, we focus on several issues of specific interest for ceramics: nonlinear stress–strain behavior, effective elastic properties, and thermally induced microcracking. We discuss extraction of microscale Parameters (such as strength of the intergranular cohesion, density of cracks and pores, etc.) from macroscopic data and identify the extent of uncertainty in this process. We also argue that there is no quantitative correlation between fracturing process and the loss of elastic stiffness.
Texture formation in amorphous Al86Ni6Y4.5La1.5Co2 splats by thermal and mechanical treatment
(2016)
The crystallization behavior of amorphous Al86Ni6Y4.5La1.5Co2 splats was analyzed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Rietveld refinement was used to analyze the preferred orientation of fcc aluminum nanocrystals in the residual amorphous matrix after annealing. Fiber textures in [200] and [220] directions were found after heating to 360 C. The influence of cold rolling on the preferred crystal orientation was studied as a function of the thickness reduction of the specimen. It was found that cold rolling significantly increases the (220) texture, while the (200) texture remains unchanged. Based on the experimental results the formation of (220) and (200) texture during the crystallization of the amorphous splats was ascribed to two different processes, internal stresses induced during splat formation or cold-rolling.
3-Aminovinylquinoxalines are readily accessible from (hetero)aryl glyoxylic acids or heterocyclic π-nucleophiles by consecutive four- and fivecomponent syntheses in the sense of an activation-alkynylation-cyclocondensation-addition sequence or glyoxylation-alkynylation-cyclocondensation-addition sequence in good yields. The title compounds are highly fluorescent with pronounced emission solvatochromicity and protochromic fluorescence quenching. Time-resolved fluorescence spectroscopy furnishes radiative and nonradiative fluorescence decay rates in various solvent polarities. The electronic structure is corroborated by DFT and TD-DFT calculations rationalizing the observed spectroscopic effects.
Designing artificial macromolecules with absolute sequence order represents a considerable challenge. Here we report an advanced light-induced avenue to monodisperse sequencedefined functional linear macromolecules up to decamers via a unique photochemical approach. The versatility of the synthetic strategy—combining sequential and modular concepts—enables the synthesis of perfect macromolecules varying in chemical constitution and topology. Specific functions are placed at arbitrary positions along the chain via the successive addition of monomer units and blocks, leading to a library of functional homopolymers, alternating copolymers and block copolymers. The in-depth characterization of each sequence-defined chain confirms the precision nature of the macromolecules. Decoding of the functional information contained in the molecular structure is achieved via tandem mass spectrometry without recourse to their synthetic history, showing that the sequence information can be read.We submit that the presented photochemical strategy is a viable and advanced concept for coding individual monomer units along a macromolecular chain.
In-line laser thermography for crack detection at elevated temperature: A Numerical modeling study
(2016)
The detection and characterization of cracks prior to damage is a technologically and economically highly significant task and is of very importance when it comes to safety-relevant structures. The evaluation of a components life is closely related to the presence of cracks in it. Laser thermography has already high capability for the detection of surface cracks and for the characterization of the geometry of artificial surface flaws in metallic samples. Crack detection in metallic samples at high temperature is highly significant in present manufacturing scenario. During the casting process of billets, surface cracks form, due to the suboptimal cooling rates. These cracks reduce value of the billet and must be removed using machining process after cooling. This secondary process increases cost of manufacturing. In this work we developed a heat transfer model for laser thermography to study the thermal contrast variation with increase in surface temperature using finite element method (FEM). Here we are mainly concentrating the capability of the scanning laser thermography in crack detection which are in elevated temperature and numerical modeling study of thermal contrast variation of crack with respect increase in metal surface temperature. This study is important to prove the capability of laser thermography for crack detection in elevated temperature. Since we are using High power CW Laser to local heating of the metal surface which can give relatively high thermal contrast even at elevated temperature compare to other heating source. Here we are modeled and simulated 2D laser scanning across a surface breaking crack and developed an algorithm to produce the vicinity of crack. The algorithm we developed applied for various surface temperature data. And validated the credibility of the algorithm with experimental data.