bluuebunny/crossref_metadata_2025 huggingface dataset:
In-Vivo and In-Vitro Metabolomics with Porphyrins Based Sensor Arrays
Authors: Capuano Rosamaria , Paolesse Roberto , Di Natale Corrado
Published: February 2020

Porphyrins have been used in the last two decades to prepare sensor arrays for a diversity of applications. The wide chemical interactivity of porphyrins sustains these applications making possible the measurement of complex patterns of volatile compounds.

The interplay between the metal ion, the aromatic ring and the peripheral compounds establishes unique selectivity patterns which are fundamental elements for sensor array design and development.

Porphyrin films can be adequately applied to inorganic surfaces making possible the preparation of different kinds of chemical sensors. Among them mass transducers, such as Quartz Microbalances (QMBs), have been found particularly suitable for several applications. The moderate sensitivity of the transducer avoids unpleasant effects of signal saturation. Furthermore, QMBs do not operate any selection among the interaction mechanisms giving the unique chance to appreciate and to use the whole bouquet of interactions occurring among the volatile compounds and the sensitive layers.

The combination of the intrinsic porphyrins sensitivity and the transduction operated by QMB makes porphyrins sensor array able to discriminate among subtle changes in patterns of volatile compounds produced by living organisms. In-vivo, these sensors have been applied to the measure of volatile compounds released by various body compartments such as skin, breath, and urines.

In breath, the identification of lung cancer has been carried out since 2003 and more recently the relationship between sensor signals and tuberculosis has been studied.

In-vitro applications were concerned with the identification of cancer cells and, more recently, with the identification of the steps of stem cells differentiation has been shown. Finally, it has to be mentioned the use of sensors to study the evolution of xenografted tumors and malaria infection in animal models.

All these results evidence the capability of porphyrin sensor array to capture the differences in volatile compounds patterns elicited by living organisms.

Similar results can be obtained by other sensors technologies; however, porphyrin sensors show a unique character of universal approach to the identification of metabolic volatiles.

A suggestive explanation of this behavior considers the role of oxidative stress to the production of cancer related volatile metabolites and in particular on the role played by natural porphyrins in the oxidative stress promoted by the Cytochrome p450. In practice, a porphyrin may be active in the synthesis of the relevant compounds and other porphyrins are used to detect them.

In this paper, a rationale for the development of porphyrin sensors for metabolomics is presented together with a thorough discussion about the evidences collected so far.
Ion-Pairing Assemblies and Materials Comprising Charged Porphyrins
Authors: Maeda Hiromitsu
Published: February 2020

π-Electronic ions with appropriate geometries and peripheral substituents would provide assemblies through interactions between building subunits, resulting in fascinating electronic properties. Diverse ion-responsive π-electronic systems and π-electronic ions were prepared, affording dimension-controlled ion-pairing assemblies as crystals, supramolecular gels, and thermotropic liquid crystals (LCs).[1] Structures and properties of the assemblies can be controlled by the combined negatively and positively charged species in the assemblies. Highly ordered arrangement of charged species, not only the ion complexes but also charged π-systems, has been found to be a key factor to exhibit the enhanced performance as fascinating electronic materials.[2] Recently, ion pairs based on porphyrin-AuIII complexes as π-electronic cations were prepared with the combination of various anions including a π-electronic anion. Porphyrin-AuIII complexes possessing aliphatic alkyl chains formed dimension-controlled ion-pairing assemblies as thermotropic liquid crystals, whose ionic components were highly organized by electrostatic and π–π stacking interactions.[3,4]

References

A recent review: Haketa, Y.; Maeda, H. Chem. Commun.
2017, 53, 2895.

As an example of an anionic porphyrin: Sasano, Y.; Yasuda, N.; Maeda, H. Dalton Trans.
2017, 46, 8924.

Haketa, H.; Bando, Y.; Yasuda, N.; Hisaki, I.; Maeda, H. to be submitted.

Sasano, Y.; Yasuda, N.; Maeda, H. to be submitted.
C-MEMS Device for Plasma Separation from Whole Blood
Authors: Pramanick Bidhan , Pakira Victor , Chakraborty Suman
Published: February 2020

In this work, we report the fabrication of carbon-microelectromechanical system (C-MEMS) based contactless dielectrophoresis chip for the separation of Red Blood Cell (RBC) and plasma from whole blood. Blood is the most important functional body fluid and it is necessary to separate plasma and RBC for common disease diagnosis. Use of centrifugal force and microfilters are the conventional methods for this separation. To make a portable and cost effective device, researchers found a method of geometry driven separation by means of changing the blood flow channel shapes. This method was not popular because of the pressure driven flow of blood in the channel and the need of the apparatus including syringe pump, tubing, etc. Dielectrophoresis is one of the best methods for this application. But the contact dielectrophoresis (sample is in contact with the electrodes) damages the RBC because of the use of high voltage (more than 100V). It may also cause electrochemical effect, bubble formation and joule heating in the sample.

In our development, one Indium Tin Oxide (ITO) coated glass was used as the bottom substrate. ITO coated side was used as the bottom electrode and microchannel was made in SU-8 by UV photolithography on the other side of the substrate. In a separate process, SU-8 derived carbon electrode was fabricated on Si/SiO2 substrate using the conventional C-MEMS process and transferred to 200µm thick PDMS layer. This polydimethylsiloxane (PDMS) layer was used to cover the microchannel in such a way that the carbon electrode was on the upper side of the device, aligned with the microchannel. These two electrodes (ITO and carbon) were capacitively coupled with the microchannel. The eletrostatic force is induced in the blood cells flow in the channel upon applying high frequency (1MHz) electric field to the electrodes. When blood flows in the channel, the electrostatic force combines with the capillary force and produces velocity difference between RBC and plasma resulting in their separation. In the preliminary experiment, we observed the separation of RBC and plasma at less than 1Vp-p with 1MHz frequency.

Figure 1
Influence of Immersion Conditions on Biocorrosion of Mg Alloys
Authors: Virtanen Sannakaisa
Published: February 2020

Magnesium and its alloys are promising materials for biodegradable implant applications. The degradation behavior strongly depends on the environment of exposure, which can strongly differ for in vitro and in vivo environments. The presentation will describe frequently observed large differences in the corrosion rate of Mg in different types of simulated body fluids and discuss critical factors of biocorrosion of Mg alloys. Electrochemical measurements and surface analysis indicate a strikingly different behavior in SBF (simulated body fluid) as compared with cell culture medium (DMEM), drastically lower corrosion rates are observed in DMEM than in SBF. In both electrolytes the surface becomes covered by Ca-phosphate-rich layers, which mainly differ in their morphology (degree of porosity). In addition, effects of solution flow and temperature on corrosion behavior of Mg in biological environments will be discussed.
Dissolution Behaviors of Dual Phase Steel during Pickling
Authors: Si Yongchao
Published: February 2020

Dual phase steels have been widely used in the automotive industry to produce lighter weight vehicles to meet stringent safety and fuel economy regulations. While the phenomena of steel dissolution in the acidic solution have been reported on carbon steel and stainless steel, little is known about the dissolution behavior of dual phase steel, which could compromise the coating adhesion performance in the subsequent electrogalvanzing line (EGL) or continuous galvanizing line (CGL). A fundamental study was undertaken to understand variables that could affect dissolution of dual phase steel in the acidic solution. The results show that the dissolution kinetics is strongly influenced by temperature, acid concentration and the steel microstructure. Different dissolution mechanism is observed in HCl and H2SO4. Dual phase steel displays a non-uniform dissolution behavior of which the ferrite phase dissolves faster than martensite phase. This selective dissolution phenomenon could be attributed to galvanic corrosion between ferrite and adjacent martensite phase and a higher resistance of martensite phase to dissolution than ferrite phase.
Transient Changes of Corrosion Potentials and Their Correlations with Metal Release During Stagnation and Flow Episodes in Drinking Water Systems
Authors: Korshin Gregory V , Fabbricino Massimiliano
Published: February 2020

Corrosion and metal release in drinking water systems are affected by the chemistry of ambient water (e.g., pH, concentrations of carbonate and other ions), stagnation/flow transitions associated with diurnal and seasonal changes of water consumption as well as the introduction of alternative water sources, for instance desalinated water. Control of metal release in drinking water is mandated by the EPA within the Lead and Copper Rule (LCR). The current LCR paradigm of copper and lead monitoring is based on measurements of metal concentrations at the end of a predetermined stagnation time (e.g., > 6 hours). While this approach is suitable for the general evaluation of LCR compliance, it does not provide any information concerning metal release in short-term stagnation episodes nor does it allow evaluating effects of short-term changes of water chemistry.

The goal of this study was to address these deficiencies based on the quantitation of transient changes of open circuit corrosion potentials (Ecorr) of metal surfaces during stagnation/flow episodes and examining relationships between such changes and attendant metal release at varying water chemistries. Experimental data demonstrate that Ecorr transients for copper, lead and iron are characterized by several consistently present features. Theoretical interpretation shows that the Ecorr transients are associated with the concurrent processes of release of metal solutes and consumption of oxidants (dissolved oxygen, chlorine species). The former process is dominant in the case of copper or lead while the latter effect is more significant for higher corrosion rates typical for iron. Further modeling shows the presence of the phase of rapid quasi-exponential consumption of the oxidants at the surface followed by a slower phase associated with the development of diffusion controlled fluxes.

These results show that the monitoring of Ecorr transients allows quantitating corrosion and metal release rates in conditions characteristic for drinking water systems, notably when other methods either do not provide relevant data or cannot be deployed.
Corrosion Protection of Pipeline Interior Surface By Sacrificial Metal Coatings in a Natural Gas Environment
Authors: Tylczak Joseph H. , Rodriguez Alvaro , Ziomek-Moroz Margaret
Published: February 2020

While corrosion protection of the exterior of natural gas pipeline has developed to be a routine process, including use of coatings and cathodic impressed current systems; the protection of the inside of the pipe is not as straightforward. This work explores the use of sacrificial metal coatings to protect the pipes inner surface. Coatings, applied by techniques including hot dip, electroplated, and thermally spray, were applied to one side of low carbon steel plates which were similar in composition to an API 5L pipeline steel. Coatings evaluated included Zn, alloys of Zn (95 Zn-5 Al, 85 Zn- 15 Al), Al, and an alloy of 95 Al- 5 Mg. Existing models suggest that any residual water, which often contains chlorides and CO2 from the gas, will be the primary contributors to any corrosion. Gravimetric corrosion tests were conducted in autoclaves to simulate the partial pressure of CO2 found in a natural gas pipeline. A test condition of; immersed samples in a 3 ½ wt. % NaCl brine, with a pressure of 300 kPa (45 psig) of CO2, and a temperature of 40 °C; was used. Tests of 168 h duration with, and without, a nonconductive masking of the steel substrate were conducted. For the tests where the steel surfaces were exposed, on the back side of the coated side of the steel test coupons, did not show significant corrosion after the tests with any of the sacrificial coatings. For the Zn, or Zn alloy, samples; a layer of ZnCO3 formed on coated and uncoated steel surfaces. The results indicated that for these conditions, the thermally sprayed coatings showed less weight loss than the hot dipped or electroplated coatings, and the Zn alloy with 15% Al had less weight loss than either the pure Zn or the Zn with 5 % Al. Visual examination indicated that while AlMg alloy successfully protected the uncoated steel from corrosion, it showed heavy corrosion including pitting in these conditions.
Electrochemical Corrosion Behavior of 316L Stainless Steel in LiBr Solution in the Presence of Na2MoO4 As an Inhibitor
Authors: Zolfaghari Sahar , Rabiei Baboukani Amin , Ashrafi Ali , Saatchi Ahmad , Wang Chunlei
Published: February 2020

The inhibition effect of sodium molybdate (Na2MoO4) at concentrations of 50, 100 and 200­ppm in 60°C on the electrochemical corrosion behavior of 316L stainless steel in LiBr solution at 60°C was studied by polarization curves, electrochemical impedance spectroscopy (EIS) methods and electron microscopy. Polarisation curves indicate that Na2MoO4 acts as mixed-type inhibitor. The corrosion resistance of 316L stainless steel samples increases with the inhibitor concentration up to 200ppm. By increasing the inhibitor concentration from 50ppm to 200ppm, corrosion current density decreases. This result was confirmed by scanning electron microscopy.

Figure 1
Electrochemical Corrosion Studies of Molybdenum Disulfide, Boron Nitride, and Tungsten Disulfide– Coated Stainless Steel
Authors: Arreola Diana Jaqueline , Mukherjee Santanu , Abass Monsur , Singh Gurpreet
Published: February 2020

There has been a significant rise in the use of stainless steel structures, especially because of its improved corrosion resistance properties in natural water when compared to carbon steels. However, also there has been reports of corrosion failures in these steels especially at weld points and other heat affected zones, some of which can have large scale socio-economic consequences. Coatings with nanomaterials have been proposed to stabilize the surface and prevent the failure. 2 dimensional (2D) materials e.g. graphene has recently elicited a lot of interest due to their improved corrosion resistance properties. This work investigates the corrosion resistance properties of a commercial grade stainless steel in 3.5 wt. % aqueous NaCl solution, coated with 3 different types of 2D nanomaterials; molybdenum disulfide (MoS2), boron nitride (BN) and tungsten disulfide (WS2). Coatings of these materials on the tested stainless steel were made via drop casting method from a previously prepared slurry of each. The electrochemical behavior of the coated stainless steel was studied with bare stainless steel as control, using open circuit potential and Tafel plots. The MoS2 coated stainless steel displayed a superior corrosion resistance than the BN and WS2 coated stainless steel samples. Scanning electron microscopy (SEM) images demonstrate uniform coating for the MoS2 coated stainless steel sample, which provides a reduced number of defect sites for diffusion of corrosive ions and explains its superior corrosion resistance compared to the other coated samples It is postulated that MoS2 showed a higher corrosion resistance vis-à-vis the bare sample due to its higher open circuit potential as well as a lower corrosion rate.
Terahertz Spectrum Measurement of Corrosion Products on Coated Steel Sheet Surface
Authors: Hasegawa Ryo , Kimura Takashi , Tanabe Tadao , Nishihara Katsuhiro , Taniyama Akira , Oyama Yutaka
Published: February 2020

Our research group has developed a terahertz light source with high luminance and broadband, and is developing research on non-destructive inspection technology. As a nondestructive inspection technology for hot-dip galvanized steel sheets, we have built a terahertz spectrum database for corrosion products that may exist there. In this research, we aim to newly obtain spectral data of β-FeOOH. Absorption Spectrum is shown in Figure.1. Optical system is shown in Figure.2. The terahertz wave was generated by difference frequency mixing using a GaP crystal which is a nonlinear optical crystal. The standard powder sample was diluted with polyethylene powder and pelletized, and it was measured at room temperature by a permeation method. As a result of spectroscopic measurement, an absorption peak was obtained around 3.06 THz. On the day of the presentation, in addition to discussions on attribution of peaks, report together with ATR-FTIR results.

Figure 1
Microstructure and Corrosion Behavior of Fe-Cr-Ni-Co-Mn High Entropy Alloys
Authors: Chang Jun-Kai , Hsu Kuo-Min , Lin Chao-Sung
Published: February 2020

High entropy alloys (HEAs) consisting of five or more principle elements are known as an emerging novel material because of superior properties resulting from the alloy effects of mixing elements. Several HEAs systems have been developed by adjusting the compositions. Among them, an equiatomic Fe-Cr-Ni-Co-Mn alloy (also known as the Cantor alloy) is a single FCC structure and has good resistance against brittleness at low temperatures. Several HEAs studies have detailed the microstructure, processing, and related mechanical properties. However, the materials scales only limit in the laboratory. The knowledge of microstructure and corrosion resistance of the Fe-Cr-Ni-Co-Mn alloy for industry application scales is still absent nowadays.

In this study, a 50-kg-bulk Fe-Cr-Ni-Co-Mn alloy was melted and casted. The alloy was homogenized, forged, and rolled. The as-cast bulk and deformed bulk alloys had different microstructures. The as-cast ingot with a diameter of approximately 120 mm was sliced using wire electrical discharge machining. The as-cut disk showed brown color on the rim of the disk and dark len-shaped in the middle. The XRD results showed different patterns from the distinct regions. The microstructure and the related corrosion properties of the specific was compared. The effect of segregation of the as-cast bulk was re-constructed with the related corrosion resistance. The in-situ corrosion observation system was also built and employed to study the corrosion behavior of the Fe-Cr-Ni-Co-Mn alloy in comparison to 316 stainless steel.

Key Words: high-entropy alloys, Fe-Cr-Ni-Co-Mn alloys, corrosion, segregation, as-casted
Alloy Corrosion in Direct-Fired CO2 Power Cycle Environments
Authors: Oleksak Richard P. , Tylczak Joseph H. , Holcomb Gordon R. , Doğan Ömer N.
Published: February 2020

Power cycles using supercritical CO2 (sCO2) as the working fluid are expected to offer significantly improved conversion efficiency and lower levelized cost of electricity over current power systems. In addition, sCO2 power cycles operated in a direct-fired configuration (where the combustion gases are used to turn the turbine) may allow for capture of 100% of the CO2 produced by combustion at almost no additional energy penalty. A broad materials evaluation effort is underway at the National Energy Technology Laboratory (NETL) to help enable direct-fired sCO2 power cycles as a promising next-generation energy conversion technology. Of primary interest is the corrosion behavior of structural alloys in the complex multi-oxidant environments expected for this application. In this study, the corrosion behavior of several candidate structural alloys was evaluated by simulating the conditions expected for the high-temperature regime of a direct sCO2 power cycle. Several commercial Fe (grades 22 and 91, 304, 310, 347H) and Ni (617, 230, 625, 740H, 282, 263) alloys were exposed at 1 atm and 550 °C (Fe alloys) or 750 °C (Ni alloys) to CO2 containing 4 vol% H2O and 1 vol% O2, with and without 0.1 vol% SO2. The alloys were massed at 500 h increments up to 2500 h to determine the oxidation kinetics. At 2500 h samples were removed from the test and characterized by XRD, SEM, and EDS, while duplicate samples continue to be exposed for longer times to assess for possible breakaway oxidation. Ni alloys all exhibited relatively low oxidation rates to 2500 h (<1 mg/cm2 in all cases) and XRD and SEM analyses revealed that Cr-rich oxides were the primary reaction products. For Fe alloys (current exposure time of 1500 h with tests ongoing), 304, 310, and 347H show minimal mass gains (<0.2 mg/cm2), while grade 91 and 22 show similar and more substantial mass gains (≈10 mg/cm2). In general, the presence of SO2 led to approximately twice the mass gain as the SO2-free condition for both Ni and Fe alloys. The results are used to assess the influence of impurities on the oxidation behavior of structural alloys in high-temperature CO2, and to evaluate the suitability of these alloys for direct sCO2 power cycles.
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.
Surface Pretreatment of Alumina Forming Alloy and Its Implication on Cr Evaporation
Authors: Aphale Ashish N , Ravi Narayan Lakshmi , Hu Boxun , Pandey Amit , Singh Prabhakar
Published: February 2020

Electrochemical systems such as SOFC, SOEC and OTM, operating in 600-1000°C temperature range, can effectively utilize alumina scale forming alloys and coatings for the construction of air handling system (heat exchanger, pipe, manifolds) to prevent or minimize chromium evaporation and related electrode poisoning. Experimental observations on chromium evaporation from alumina forming alloys (Haynes 214 and Carpenter AFA 25) in humidified air (3%H2O) indicate reduction in chromium evaporation when compared to chromia forming alloys (RA602). Pretreatment under controlled oxidation conditions to allow for the formation of predominantly alumina surface scale, on the other hand, significantly reduces chromium evaporation. Mechanism for reduction in chromium evaporation from the alloy surface is presented. Oxide morphology and chemistry developed during surface pretreatment are also presented.
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.
Real-Time Analysis on Structural Variations of Alumina-Supported Cu/Fe Spinel and Natural Hematite Particles in Cyclic Redox Environments
Authors: Nakano Jinichiro , Nealley William , Nakano Anna , Bennett James P
Published: February 2020

Oxygen carrier materials in chemical looping applications exhibit physical and chemical variations during cyclic oxidation-reduction exposure at elevated temperature, which often lead to material degradation. While ideal chemical reactions of pure components may be predicted thermodynamically, structural changes of materials in chemical looping systems are complex and continuous due to the redox nature of the process. In this work, structural variations in two types of oxygen carrier particles (alumina-supported Cu/Fe spinel and natural hematite) during repeated redox exposures at 800°C were investigated in situ using a customized heat chamber attached to a confocal scanning laser microscope. Volume changes of the micron particles corresponding to each exposure cycle were recorded real time. Volume changes along with other structural degradation influence oxygen accessibility into the particles; impacting the oxygen exchange capability of a material. Structural degradation will be discussed based on a lattice structure changes, void formation in inner grains and particles, diffusion of the constituents, and sintering/densification with different structures.
“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) RF Pump-Probe Modulation Spectroscopy of Silicon Nanocrystals: Determination of the Carrier Dynamics and Quantum Efficiency
Authors: Crowe Iain F , Halsall Matthew P
Published: February 2020

We present our latest work on the development of an all-optical (pump-probe) technique for estimating the quantum efficiency (QE) of silicon nanocrystals. Our experiment combines measurement of micro-photoluminescence and reflectivity when driven with an RF frequency modulated pump. By varying this frequency over a wide (5 decade) range, we are able to determine the dynamics of the free carrier concentration (multi-component in these systems) and thus retrieve the PL decay rate(s). Interestingly, we find that, in addition to the dominant (10’s-us) component (typically noted from direct measurement of the PL decay), a very slow component persists (in the ms regime), which we attribute to the recombination of ‘trapped’ charges. The technique provides a method for estimating the relative QE as a function of carrier concentration, providing clues as to the efficiency limiting processes in these materials. We present our most recent data for silicon nanocrystals formed in glass cover-slips after ion implantation and thermal annealing, and we discuss how the technique can be applied to luminescent materials more generally, e.g. to study the efficiency ‘droop’ mechanism observed at high carrier concentration in nitride based LED materials.
Effects of the Heat Treatment on the Photoluminescence Properties for La1-XPrxVO4 Phosphor Prepared by a Hydrothermal Method
Authors: Chen Hao-Long , Tsai Mu-Tsun , Young Sheng - Joue , Chang Yee-Shin
Published: February 2020

A hydrothermal method had been employed firstly for the preparation of La1-xPrxVO4 (x=0—0.05) nano-crystal phosphors, and then they were annealed at 600 oC for 4 h. The x-ray diffraction profiles show that the La1-xPrxVO4 phosphors still keep the tetragonal structure. The SEM results show that phosphor particles were increased from 60 nm to 80 nm after annealing process, and the surface morphology gradually changed from reunion to uniform distribution. The excitation spectra show that an absorption band between 200 ~ 330 nm is due to the charge transfer from the oxygen ligands to the central vanadium atom inside the VO4
3- anionic group, and the Pr3+ ion 4f-5d characteristic transition is located between in the 440 ~ 500 nm and 580 ~ 620 nm region. By 315 nm excitation, the main emission band still retains the characteristics for Pr3+ ion-doped LaVO4
phosphor, belonging to the host luminescent, and the 1D2→3H4, 3P0→3H6 electron transition of the Pr3+ ion, respectively. As the Pr3+ ion concentration increases, the color tone changes from blue ( 0 mol% Pr3+ ion doping ) to white (for 0.2-1 mol% Pr3+ ion doping), to blueish (for 5 mol% Pr3+ ion doping). Therefore, the color of the emission for (Y1-xPrx)InGe2O7 phosphors can be tuned by adjusting the Pr3+ ion concentration, without doping other color centers in a single phased host lattice. When the Pr3+ ion concentration of x=0.005, it possesses the strongest emission behavior, and is located in the white light region with a CIE chromaticity coordinates of x=0.299, y=258.
(Invited) AlGaN Nanowire Deep Ultraviolet Photonics
Authors: Mi Zetian
Published: February 2020

AlGaN-based deep ultraviolet (UV) light emitting diodes (LEDs) and lasers are important for a broad range of applications, including water purification, disinfection, surface treatment, and chemical and biochemical sensing. To date, the performance of AlGaN quantum well UV LEDs and laser diodes has been limited by the presence of large densities of defects and dislocations, large polarization field, and extremely inefficient p-type doping. In this context, we have developed nearly defect-free AlGaN nanowire heterostructures. We have achieved highly efficient p-type conduction of Mg-doped AlN and Al-rich AlGaN nanowires. With the use of AlGaN nanowires, we have further demonstrated, for the first time, electrically pumped semiconductor lasers operating in the UV-B and UV-C bands. The AlGaN nanowires are grown on Si substrate under N-rich conditions by plasma-assisted molecular beam epitaxy. Detailed structural characterization suggests the presence of strong compositional modulation. The Ga-rich AlGaN clusters have dimensions of 0.25 to 2 nm along the growth direction and of 2 to 10 nm along the lateral direction. The localized variations in the Ga-concentration are estimated to be ~10%, thereby providing strong quantum-confinement of charge carriers. By changing alloy composition, the emission can be widely tuned in the UV-C band from 207 nm to 280 nm. We have demonstrated AlN nanowire LEDs with a small turn on voltage of ~6 V, which is significantly smaller than previously reported AlN epilayers LEDs (> 20 V). This excellent electrical performance is largely ascribed to the significantly enhanced Mg-dopant incorporation in nanowire structures and the resulting efficient impurity band conduction. For ternary AlGaN nanowire UV LEDs, the device structure consists of n+-GaN/Al/p+-AlGaN tunnel junction, which can remove the resistive p-contact layer and improve hole transport. Compared to devices without tunnel junction, the output power is improved by 2 orders of magnitude. For the device operating at 274 nm, the maximum output power is > 20 mW. It is further envisioned that, with the use of AlGaN nanowires, UV-C LEDs with efficiency >70% can be potentially achieved. By further exploiting Anderson localization of light in such nearly defect-free AlGaN nanowires, we have demonstrated, for the first time, electrically injected lasers operating in the UV-B and UV-C bands. For lasers operating at 239 nm, the threshold current is ~0.3 mA at room-temperature. These studies provide a viable path to achieve high efficiency semiconductor laser diodes operating in the UV-C band that was not previously possible.
(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.
(Invited) Advanced Aqueous Electrolytes for Li-ion Batteries
Authors: Wang Chunsheng , Xu Kang
Published: February 2020

Current technologies for electric vehicles and other applications require high energy, power density, and long cycle life. However, the energy density and safety of current batteries still need to be improved to satisfy these requirements. Typical Li-ion batteries consist of organic electrolytes that are toxic, flammable, and pose significant safety concerns in the events of thermal runaway and improper operation and handling. In recent years, we have explored advanced materials for Li-ion, Na-ion, Zn-ion and Mg-ion batteries that address these key challenges. A new revolutionary concept of an aqueous electrolyte for Li-ion batteries, termed water-in-salt electrolyte, has been developed, extending the electrochemical voltage stability window of aqueous electrolytes to >4.0V and significantly enhancing the energy density. Use of the water-in-salt gel electrolytes, a robust flexible Li-ion battery that can be cut open, exposed to air, and continue to operate despite the mechanical damage has been demonstrated.