bluuebunny/crossref_metadata_2025_split huggingface dataset:
New Insights into Thermal Chromia Growth on Fe18Cr(10Ni) Model Alloys at 900°C: Scaling Kinetics and Microstructures
Authors: Hänsel Michael , Shemet Vladimir , Markus Torsten 
Published: February 2020

Specimen of Fe-18Cr(-10Ni) (wt.-%) were isothermally oxidized in dry and wet high p(O2) gas at 900°C. The morphology and microstructural evolution of the chromia scales formed were analysed by SEM-EBSD. At high pO2 test gas containing O2 and H2O, the pO2 is independent of the H2O content of the test gas. However, both types of oxygen species, i.e. O2 as well as H2O contribute to the chromia scaling reaction. The effect of specimen thickness on chromia scaling allows the change of the concentration of the intrinsic defects and their diffusivities in thermally grown chromia scales independently from the test gas applied. Chromia scales are under pressure during scale growth. For thermodynamic reasons the concentration and diffusivity of the intrinsic, native defects in oxides under hydro-static pressure varies with the amount of pressure applied. Ion beam polished oxide cross-sections were analysed in terms of oxide grain growth and nucleation rates of new oxide at the oxide-gas interface. Chromia scales formed on the various substrates at high p(O2) test gas grew at different rates, and microstructures formed on Fe18Cr(-10Ni) differ in grain shape and size. The chromia growth kinetic was found to be depending on the thickness of the specimens used, the H2O content of the gas, and its Ni content.
The scale growth mechanism consists of two interlinked levels. At the meta-level oxide nucleation and oxide grain growth are affected by the cation flux in the oxide scale formed and the nature of the oxygen species in the gas. This fixes the number, size and shape of the oxide grains as well as the number of oxide grain boundaries available as short-circuit diffusion paths. The lattice level denotes the atomic level. Hereby the cation flux in the single grain by lattice diffusion and cation vacancy condensation are linked. The defect structure in the oxide lattice is important. The factors affecting it are the Cr diffusion in the substrate and the presence of Ni in the alloy, local p(O2), H-defects and oxide growth stress. The experimental findings will be discussed with strong focus on the oxide growth mechanism, the chromia microstructure of the scales formed under the various conditions and the concentration and mobility of the native defects in the chromia scales and its interactions with H-containing species originating from water vapour in the test gas. Furthermore, the role of Fe as base and Ni as alloying element in the metal substrate will be discussed. This is done by considering the differences between the Ni-Cr-O and Fe-Cr-O phase diagrams and the consequence of the existence of the Fe3+ ion on the miscibility of the oxides formed by the various cations.
Hydrothermal Corrosion of SiC and FeCrAl for Accident Tolerant Fuel Cladding
Authors: Raiman Stephen S , Doyle Peter , Terrani Kurt , Rebak Raul B. 
Published: February 2020

Since the Fukushima incident in 2011, the nuclear industry has sought to replace Zircaloy fuel cladding with a material which will better withstand a beyond-design-basis incident. A suitable material must possess superior oxidation resistance in high temperature steam (1200-1700°) to withstand a loss of coolant accident, while maintaining good hydrothermal corrosion properties for environmental compatibility during normal operating conditions (288-320°C water). In addition to corrosion issues, a suitable material must also demonstrate sufficient mechanical strength, creep resistance, radiation tolerance, and favorable neutronics.
Researchers at Oak Ridge National Laboratory are engaged in testing of two leading candidates for accident tolerant fuel cladding: iron-chomium-aluminum (FeCrAl) alloys, and silicon carbide ceramic matrix composites (SiC/SiC). FeCrAl alloys have shown excellent oxidation resistance due to the formation of a passive alumina film in high temperature steam, and a protective Fe-Cr spinel layer in water. SiC/SiC has shown excellent corrosive properties in high temperature steam, but a tendency to dissolve in LWR water. To improve performance of SiC normal operating conditions, several candidate coatings are being considered, including Cr, CrN, and TiN.
This work presents results of hydrothermal corrosion experiments on FeCrAl alloys and coated SiC in boiling water reactor hydrogen water chemistry (BWR-HWC) and normal water chemistry (BWR-NWC) (288°C with 150 ppb H2 or 2 ppm O2 respectively). FeCrAl samples generally exhibited low corrosion rates. Hydrothermal corrosion properties of current FeCrAl alloys are compared to older generations. CVD-SiC and SiC/SiC exhibited significant mass loss during exposure. SiC samples coated with Cr and CrN adhered well to their substrates, and effectively mitigated dissolution, with acceptable corrosion rates.
This work was funded by the DOE Office of Nuclear Energy Advanced Fuels Campaign
Development of an Advanced Knudsen Effusion Mass Spectrometer for Measurements of Vapor Pressures and Determination of Basic Thermodynamic Data
Authors: Markus Torsten , Henriques David 
Published: February 2020

The amount and composition of vapor pressures over a liquid or solid phase are key physical properties. With the temperature dependency of the partial pressures basic thermodynamic data can be derived such as enthalpy, entropy and Gibbs energy of the vaporization reaction as well as their partial and molar mixing values for the condensed phase. Such high precision thermodynamic data are a basis for designing new materials and predict the corrosion resistance and phase stability of new alloys for technical applications especially at high temperatures.
The vapor pressure (pi) can be measured by the method of Knudsen Effusion Mass Spectrometry (KEMS) in a high vacuum atmosphere. Therefore, a sample is heated up in a Knudsen Cell. The crucible of the Knudsen Cell is closed with a lid which has a small orifice between 0.1 – 1 mm. At constant temperature the gas phase is in equilibrium with the sample. Due to the mean free path in vacuum, the molecules of the gas atmospheres effuse from the Knudsen Cell only stochastically. The molecules effuse out of the Knudsen Cell and will be ionized and then characterized quantitatively and qualitatively by a mass spectrometer. Thereby the equilibrium between gas phase and condensed phase will practically not be disturbed.
With the KEMS method it is possible to measure vapor pressures between 1∙10-7 - 1 mbar. Measurements can be performed between 290 K – 3000 K.
A completely new designed experimental device is set up in our laboratory.
The aim of the project is to build up a new KEMS apparatus which exceeds the current state of the art of measuring vapor pressures in sensitivity and usability. The focus of the new KEMS-device is a user-friendly operation, compact dimensions and self-explanatory evaluation software. Special designed sample carrier will allow measuring samples highly automatical and determination of high precise thermodynamic data.
“White” Photoluminescence of Carbon Nаnoclusters Dispersed in Fumed Silica
Authors: Vasin A. V. , Kysil D. V. , Lajaunie L. , Rudko G. Yu. , Lysenko Vladimir Sergeevitch , Sevostianov S. V. , Tertykh V. A. , Piryatinski Yu. P. , Cannas M. , Vaccaro L. , Arenal R. , Nazarov A. N. 
Published: February 2020

Fumed silica with specific area of 295 m2/g was carbonized by successive procedures of chemical modification by phenyltrimethoxysilane followed by annealing in inert atmosphere up to 650 oC. Strong ultraviolet and visible photoluminescence was observed in the samples after chemical modification and thermal annealing. Emission, excitation, kinetics and photo-induced bleaching effects were investigated by steady state and time-resolved photoluminescence spectroscopy. Interatomic bonds were studied by infrared transmission spectroscopy. It has been shown that ultraviolet photoluminescence in chemically modified fumed silica is associated with phenyl groups while near ultraviolet and visible emission in annealed samples originates from inorganic pyrolytical carbon precipitates dispersed in silica host matrix. Two types of emission bands were identified depending on the annealing temperature: one is in the near UV and another is in the visible range. The relative contribution of these bands depends on samples preparation. All the obtained results have been compared with those observed in fumed silica carbonized using other carbon precursors and treatment procedures. It has been found that these two bands can be observed irrespective to the carbonization procedure. Based on the emission/excitation analysis of these two bands, as well as on correlations with the synthesis conditions, a structural-energy concept of light-emitting centers has been proposed. According to this model, the light-emitting centers are associated with sub-nanometer carbon clusters that can be bonded or adsorbed on the silica surface. It is assumed that the energy of emission photons is determined by the presence or absence of a chemical bond between the emitting clusters and silica surface.
A detailed (S)TEM-EELS study has been performed to check these points. By doing so, we have confirmed the presence of 2-6 nm carbon nanoclusters, which are not evenly distributed at the surface of the silica nanoparticles. These carbon nanoclusters are mostly amorphous although they possess some degree of graphitization and local order; the fraction of sp2 carbon in these nanoclusters has been estimated to be close to 80 %.
Spectral distribution of light emission in visible range of black body at 6000 K (corresponding to natural day-lighting) and PL of the samples annealed at 600 oC (excitation 355 nm) is almost identical. Spectral properties of the emission (in terms of RGB concept - correlated color temperature) can be easily tuned by variation of synthesis procedure. Such light emission properties of environment friendly single component phosphor make them very attractive for artificial white light sources like white LEDs with near-UV excitation or compact fluorescent lamps.
(Invited) Excitation Mechanism of Rare Earth Ions in Nanostructured Silicon Rich Hosts
Authors: Tessler Leandro R. 
Published: February 2020

Rare earth doped semiconductors have received much attention in the last decades because of potential applications in photonics and illumination. Because silicon is the most widely employed material in the semiconductor industry, much of this effort is devoted to obtain efficient light emitters involving silicon based alloys. The excitation cross section of rare earth ions is orders of magnitude higher in silicon-rich amorphous alloys than in ordinary oxides. Energy transfer is often very efficient in the presence of silicon nanocrystals or nanoclusters. This has led to energy transfer models involving quantum confinement and the electronic structure of silicon nanocrystals. Although these models are elegant and persuasive, they demand a highly homogeneous nanoparticle size distribution, absence of states associated with surface or strain in very small particles and the excitation of many rare earth ions by a single nanoparticle, all very unlikely in real systems.
We have studied the excitation of Tb3+ doped a-Si3N4:H. Our results show a correlation between the density of silicon dangling bonds and the luminescence efficiency under matrix excitation. These findings lead to a reinterpretation of published results in samples containing silicon nanoparticles. When nanoparticles are formed the density of silicon dangling bonds in fact increase as silicon-silicon, silicon-oxygen, silicon-nitrogen or silicon-hydrogen bonds are broken. Thus, the main effect of the formation of nanoparticles, crystalline or not, to the energy transfer to rare earth ions is through the increase of the density of silicon dangling bonds and consequently of midgap states. A very short range Auger process involving carrier recombination at silicon dangling bonds is most probably the main mechanism for excitation from a silicon rich host to rare earth ions. To optimize the luminescence efficiency, the density of dangling bonds must match the density of active rare earth ions.
(Invited) Plasma Biofilm Decontamination: What Happens to the Underlying Surface?
Authors: Walsh James Leon , Modic Martina , Kovac Janez , Hasan Mohammad , Cvelbar Uros 
Published: February 2020

In natural and manmade environments, bacterial biofilms are ubiquitous, yet the significance of biofilm contamination in a clinical setting is often underestimated [1]. Such contamination presents a particularly virulent form of infection that is shielded from systemic antibiotics, providing ideal conditions for the emergence of multidrug-resistant colonies [2]. There is an unprecedented need to establish new strategies to manage the colonization of clinical surfaces with these complex bacterial communities. This contribution explores the use of cold atmospheric pressure air plasma for the inactivation of clinically relevant biofilms grown on medical grade titanium. Furthermore, the impact of the plasma treatment on the properties of the host surface is investigated.
Using a 1D air plasma model [3], supported by experimental measurements, the chemistry of a Surface Barrier Discharge (SBD) suitable for biofilm inactivation was shown to contain a wealth of long-lived species such as O3, NO2 and N2O. Under the influence of a convective flow, the presence of species that are traditionally considered to be too short-lived to reach a downstream sample are predicted, e.g. OH. [4]
The SBD system, shown in Figure 1, was found to be highly effective for the decontamination of single and mixed species biofilms, achieving a multiple log reduction within 60 seconds of exposure. Given that the surface composition and morphology are key factors influencing biofilm formation, the impact of the plasma decontamination process on the surface characteristics was assessed and shown to induce considerable changes. The impact of these changes on the ability of bacteria to adhere to plasma treated titanium surfaces was examined. It was shown that biofilm formation on surfaces subjected to the plasma treatment was found to be accelerated in comparison to untreated surfaces.
This study demonstrates that cold air plasma is an effective tool for biofilm elimination on clinically relevant surfaces, yet the choice of plasma system must be carefully considered as such treatments can significantly alter the ability of bacteria to attach to the surface.

[1] D. Lindsay, A. von Holy, Journal of Hospital Infection. 64, (2006), 313-25.
[2] J. Davies, D. Davies, Microbiol Mol Biol Rev. 74, (2010) 417.
[3] M. Hasan, J. L. Walsh, J. Appl. Phys. 119, (2016), 203302.
[4] M. Hasan, J. L. Walsh, Appl. Phys. Lett. 110, (2017), 134102.
[5] Y. Ni, Y., M.J. Lynch, M. Modic, R.D. Whalley, J.L. Walsh. Journal of Physics D: Applied Physics, 49 (35), 355203 (2016).

Figure 1
Effect of Cathodic Current on the Microstructure and Characteristics of Micro-Arc Oxidation Ceramic Coatings on 7075 Aluminum Alloy
Authors: Wang Ting-Yi , Lin Hsin-Chih 
Published: February 2020

Micro arc oxidation (MAO), also known as plasma electrolytic oxidation (PEO), which is applied to obtain hard oxide coatings on aluminum alloys. The coatings formed during the MAO process are superior to anodic oxide coatings on plenty of properties, such as strong coating-substrate adhesion, adequate thickness, high hardness, excellent corrosion and wear resistance. There are several parameters affecting the properties of MAO coating, including composition of the substrate and electrolyte, process time, applied voltage and current density, but few works study the influence of cathodic current on MAO coating.
This study investigated the effect of cathodic current density on the structures and properties of the coatings. The MAO coatings on 7075 Al alloys were obtained in aluminate-based electrolyte by using a bipolar pulsed power supply. The morphology, microstructure and compositions of the MAO coatings were characterized by using scanning electron microscope (SEM), X-ray diffraction (XRD), electron probe micro-analyzer (EPMA). The measurements of surface roughness, thickness, and microhardness were also conducted. Furthermore, the ball-on-disk tribometer and potentiodynamic polarization were used to evaluate the wear and corrosion resistance, respectively.
Experimental results showed that the ceramic coatings are mainly composed of α-Al2O3 and γ-Al2O3. The microstructural observations of the MAO coatings revealed that with increasing cathodic current, the presence of pancake-like structure and the size of micro-pores are significantly reduced, meaning the coatings became smoother and more compact. Moreover, due to the low porosity and the phase composition, the microhardness of the ceramic coatings can reach ~1400 HV. With increasing cathodic current, the MAO coatings are nearly pore-free and crack-free. Therefore, the coatings exhibit an obvious improvement in corrosion and wear resistance.
Interconnected Nickel Nanowires – the Missing Link between Metallic High Surface Area Catalysts and High Porosity Foams
Authors: Zankowski Stanislaw Piotr , Vereecken Philippe M. 
Published: February 2020

Porous and electrically conductive materials having extended surface area are attractive for wide range of applications, such as catalysis, sensing or energy storage. High surface area of the material provides higher reaction rates and lower electrode resistance. For instance, metallic sponges such as Raney nickel, having surface areas up to 100 m2/g show high catalytic activity during water electrolysis or heterogenous organic synthesis. However, low porosity and small average pore diameter limit their application for devices utilizing additional functional layers (e.g. active electrode materials in batteries). On the other hand, highly porous nickel foams are commonly used as current collectors for Ni- and Zn-based batteries, where sufficient loading of active material can be realized inside of the porous network. However, the surface area of such foams is more than three orders of magnitude smaller than that of the metallic sponges, lowering the potential for e.g. high rate operations of their parent devices.
In this talk we will present a recently developed material composed of interconnected nickel nanowires of controllable diameter and distance. The nanowires assembly offers a unique combination of high surface area of metallic sponges and high porosity of metallic foams. The material is conveniently obtained by cheap and up-scalable electrochemical techniques. The unique nanostructural properties of the interconnected nanowires allow for high flexibility of the material and applications in e.g. flexible electronics or wearable sensors. As a proof-of-concept, we will present the performance of our structure for hydrogen generation during water electrolysis. Compared to nickel foams, the high surface area interconnected nanowires offers significantly higher hydrogen evolution currents, showing their potential for next generation electrolyzers and energy devices.

Figure 1
(Invited) Electrochemically Synthesized High Density Chemical Sensor Arrays
Authors: Myung Nosang Vincent 
Published: February 2020

Electronic detection of molecules is rapidly emerging as an alternative to the tranditional optical and electrochemical methods because of the small size, low-power consumption, improved sensing performance and most of all possibility of developing high density arrays for simulatenous analyses of multiple species in small sample volumes. Recently, one-dimensional nanostructures (e.g., carbon nanotubes (CNTs), inorganic, and organic nanowires) as conduction channels of field effect transistors (FETs) have been developed for detection of a variety of gaseous molecules with excellent low detection limit, sensitivity, and selectivity. These features are a consequence of dramatic decrease in characteristic length and increase in the ratio of surface to volume atoms, allowing for rapid diffusion into the bulk and for a more significant fraction of the atoms to participate in surface processes such as chemical and biochemical binding interactions. One-dimensional geometries also enhance response times by virtue of their two-dimensional mass transfer profile. Furthermore, nanowires are heralded for device miniaturization and sensor arrays, enabling duplicate elements to reduce false positives/negatives and pattern recognition systems termed electronic noses where each sensor in the array has a unique response to every analyte creating a fingerprint type response that increases sensitivity and selectivity. Finally, sensors are also attractive for their proven commercial viability, as this approach uses a single material behaving as both the sensitive layer and transducer to directly covert chemical information into an electronic signal without the need for labels, allowing for real-time, continuous monitoring.
In this presentation, synthesis, functionalization, and assembly of various nanoengineered materials including CNTs and conducting polymer nanowires will be discussed to create “true” high density gaseous sensor arrays with superior sensing performance in cost-effective manner. Finally, Android based smartphone integratable sensor will be demonstrated.
Annealing-Free Copper Foil Due to Ultra-Large Grain Sizes after Electroplating
Authors: Dow Wei-Ping , Chan Po-Fan 
Published: February 2020

Copper electroplating has been widely used in the fabrication of electronic products. For semiconductor fabrication, damascene copper process needs copper electroplating;1 for IC chip packaging, 2.5D, 3D TSV and FOWLP need copper electroplating;2 for HDI PCB fabrication, microvias and through holes also need copper electroplating.3 Regarding the 3D IC chip packaging and FOWLP, copper pillars are necessary components, which are used as conducting pillars or heat conductors. Currently, copper pillars are made by electroplating, so that they are a polycrystalline structure. In other words, there are many grain boundaries in the copper pillars, which lead to a high electric resistance and, usually, need to be annealed at high temperature to obtain large grain sizes and reduce their electric resistance simultaneously. Moreover, if the copper pillar is polycrystalline, it is easily to form IMC with tin-containing solder and induce Kirkendall voids.4, 5 Many papers have demonstrated that the formation of Kirkendall void depends on the grain boundary of the electroplated copper. The more grain boundaries in the electroplated copper, the more Kirkendall voids will be observed.5 Impurities from plating additives, empty space between two grains and active copper atoms exist at the grain boundaries will lead to vacancies. Once these vacancies aggregate together, voids will be observed. Therefore, if there is no grain boundary instead of nano-twinned boundary or single crystal without boundary after copper electroplating, no void will be observed even after a long ageing time at a high temperature. Herein, a copper foil is obtained by electroplating and it has an ultra-large grain size (i.e., 10~20 μm) after electroplating. Hence, it needn’t annealing after electroplating. Of course, there is no Kirkendall void at the interface between copper/tin joint for a long ageing time at a high temperature.
References:
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2. V.-H. Hoang and K. Kondo, J. Electrochem. Soc., 164, D795 (2017).
3. T.-C. Chen, Y.-L. Tsai, C.-F. Hsu, W.-P. Dow and Y. Hashimoto, Electrochimica Acta, 212, 572 (2016).
4. T. C. Liu, C. M. Liu, Y. S. Huang, C. Chen and K. N. Tu, Scripta Mater., 68, 241 (2013).
5. L. Yin and P. Borgesen, J. Mater. Res., 26, 455 (2011).