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- ItemLight emission intensities of luminescent Y2O3:Eu and Gd2O3:Eu particles of various sizes(Basel : MDPI, 2017) Adam, Jens; Metzger, Wilhelm; Koch, Marcus; Rogin, Peter; Coenen, Toon; Atchison, Jennifer S.; König, PeterThere is great technological interest in elucidating the effect of particle size on the luminescence efficiency of doped rare earth oxides. This study demonstrates unambiguously that there is a size effect and that it is not dependent on the calcination temperature. The Y2O3:Eu and Gd2O3:Eu particles used in this study were synthesized using wet chemistry to produce particles ranging in size between 7 nm and 326 nm and a commercially available phosphor. These particles were characterized using three excitation methods: UV light at 250 nm wavelength, electron beam at 10 kV, and X-rays generated at 100 kV. Regardless of the excitation source, it was found that with increasing particle diameter there is an increase in emitted light. Furthermore, dense particles emit more light than porous particles. These results can be explained by considering the larger surface area to volume ratio of the smallest particles and increased internal surface area of the pores found in the large particles. For the small particles, the additional surface area hosts adsorbates that lead to non-radiative recombination, and in the porous particles, the pore walls can quench fluorescence. This trend is valid across calcination temperatures and is evident when comparing particles from the same calcination temperature.
- ItemMechanisms of bonding effected by nanoparticles in zirconia coatings applied by spraying of suspensions(Saarbrücke : Leibniz-Institut für Neue Materialien, 2008) Adam, Jens; Aslan, Mesut; Drumm, Robert; Veith, MichaelZirconia coatings consisting of a mixture of coarse and fine grained zirconia powders prepared by spraying of suspensions and subsequent thermal treatment at limited temperatures (up to 500°C) are poor in adherence and in intrinsic mechanical strength. We have shown elsewhere that mechanical properties of these coatings can be improved clearly by adding a small amount of nanoscaled zirconia. Here, the structural and the chemical development of this coating material and of the nanoparticles is examined to gain information about the underlying bonding mechanisms. The applied temperature is relatively low in comparison to the usual onset temperature of accelerated sintering. Nevertheless, the results show that diffusion controlled material transport mechanisms play their role in bonding. The condensation of surface OH groups may participate in bonding, too. These first results confirm the potential of nanoparticles to act as inorganic binder. Additional research effort to clarify the underlying mechanisms in detail is of interest. For the practical side, it can be concluded that the resulting effect of mechanical consolidation of ceramic structures at relatively low temperatures enables new ceramic applications, for example a new type of ceramic coatings on metallic substrates.
- ItemPreparation of acoustic lenses by mechano-chemical synthesis and electrophoretic deposition of lead zirconium titanate (PZT) films(Saarbrücke : Leibniz-Institut für Neue Materialien, 2008) Bender, Michael; Drumm, Robert; Adam, Jens; Jakob, Annette; Lemor, Robert; Veith, MichaelPZT powders has been synthesized via reactive dry milling using PbZrO3 and PbTiO3 as starting materials. Stabel suspensions of the PZT particles in ethanol (d50(Vol) = 115 nm) were obtained by a chemomechanical dispersion step. Teh electrophoretic deposition has been optimized varying the cell voltage and the PZT solid content in the suspension. PZT films have been deposited on platinum coated saphire. After drying, the films are densely packed and free of cracks. By using lithium acetate and lead acetate as a sinter aid it was possible to reduce the sintering temperature to 1050°C. A good electrode has been sputtered onto the piezoelectric films which then have been poled by the corona method. The circular PZT dots (...) with a thickness of 1 µm show the expected oscillation resonance at about 2 GHz and can be used in acoustic lenses, for example in acoustic microscopes.
- ItemSensor placement technique using BaTiO3/epoxy resin piezoelectric composite sensors based on differential imaging method for damage detection in structural health monitoring(Cambridge : arXiv, 2016) Taltavull Cazcarra, Adrià; Bareiro Ferreira, Oscar; Sridaran Venkat, Ramanan; Adam, Jens; Boller, ChristianStructural Health Monitoring (SHM) is an emerging technology in many engineering disciplines that aims at designing systems being able to continuously monitor ageing of structures throughout their life span. Damage monitoring using guided waves (GWs) is one promising approach in that regard. Principally a network of integrated piezoelectric transducer patches (actuators and sensors) on a structure generates GWs, where the GWs propagate through the structure and relative information about the damage is finally obtained. Based on damage mechanics principles and damage tolerance criteria, the structure’s remaining useful life is then be determined from the data recorded by the transducers and the need for structural maintenance actions can finally be derived accordingly. The detectability of the growing structural damage is highly dependent on the placement of actuators and sensors. This therefore requires an optimum placement of those transducers to be found, which is obtained through simulation. This need for simulation becomes specifically relevant when structures are large and complex. A new approach presented within the paper proposed has therefore been developed, which is based on differential imaging/signals, where the differential is determined from the difference of the wave patterns between an undamaged and a damaged condition. The resulting topology of the differential signal is considered to define the shape/pattern of the respective piezoelectric transducers, which will be placed on the structural component considered using a defined coating process. The coating and monitoring process applied using a BaTiO3/epoxy resin will be demonstrated on a thin aluminium test coupon with three holes where a crack of tolerable length has originated from one of the holes due to fatigue loading and the coated piezoelectric composite transducer pattern for monitoring the crack has been defined from the output of guided wave FEM simulations.
- ItemDevelopment of the fabrication process and characterization of piezoelectric BaTiO3/epoxy composite used for coated ultrasonic transducer patterns in structural health monitoring(Cambridge : arXiv, 2016) Bareiro Ferreira, Oscar; Sridaran Venkat, Ramanan; Adam, Jens; Boller, ChristianStructural health monitoring (SHM) is based on integrating and/or adapting a sensor system into a structure such that a tolerable damage to occur can be monitored. This requires a network of transducers specifically when this SHM approach is considered as a monitoring system such as based on guided waves. A desirable solution would be to get a transducer network simply ‘printed’ on the structure considered once the network has been designed such as through a simulation approach. In the paper proposed the fabrication process and characterization of a piezoelectric composite to be used as an ultrasonic transducer for damage sensing of structures based on SHM using guided waves is first considered. The composite consists of piezoelectric BaTiO3 particles homogenously distributed in an epoxy resin matrix. A paste with a solid volume fraction of up to 50 vol% was prepared by the direct mechanical mixing of the piezoelectric particles in the epoxy matrix. Due to the ferroelectric properties of BaTiO3 the polarization of the composite is required with a high electric field prior to use. Two electrodes placed on both sides of the samples are required to measure the dielectric and electromechanical properties of the composite in the form of a thick film. The influence of the volume fraction of BaTiO3 on the dialectic properties and piezoelectric transversal constant (d33) of the piezoelectric composite will be shown. Beyond this more materials processing related work performance of those transducers will be demonstrated. This will be done in terms of getting those coated as a transducer pattern/network on a hosting structure after having had the transducer network determined through simulation. Validation of the approach will be done by looking at the transducer network’s performance in terms of detecting guided acoustic waves.
- ItemLangzeitstabile Formtrennschichten auf BN-Basis für metallurgische Anwendungen : Schlussbericht(Hannover : Technische Informationsbibliothek (TIB), 2004) Schwetz, Karl; Adam, Jens; Drumm, Robert; Ehlen, Frank; Grossman, Kai; Hareesh, Nair[no abstract available]