J. Schnöller

On the effect of Ta on improved oxidation resistance of Ti–Al–Ta–N coatings

Formation of protective oxide scales is the main reason for the high oxidation resistance of TiAlN based coatings. Here the authors report on further improvement in the oxidation resistance of TiAlN by Ta alloying. An industrial-scale cathodic arc evaporation facility was used to deposit Ti–Al–Ta–N coatings from powder metallurgically produced Ti38Al57Ta5 targets. After oxidation in ambient air, a significantly reduced oxide layer thickness in comparison to unalloyed TiAlN reference material was observed. Energy-dispersive x-ray spectroscopy line scans and secondary ion mass spectroscopy depth profiling showed that the oxide scale consists of an Al-rich top layer without detectable amount of Ta and a Ti–Ta-rich sublayer. Transmission electron microscopy investigations revealed α-Al2O3, rutile-type TiO2, and anatase-type TiO2 as the scale forming oxides. Furthermore, the Ti–Ta-rich sublayer consists of a porous layer at the oxide-nitride interface but appears dense toward the Al-rich top layer. The improve...

About the Formation of Basic Silver Carbonate on Silver Surfaces – An In Situ IRRAS Study

Air pollutants such as carbon dioxide play an important role in atmospheric corrosion processes and therefore in the degradation reactions occurring on metal surfaces exposed to an ambient atmosphere. It is known from macroscopic studies that ultraviolet (UV) light influences these surface reactions with respect to the reaction rate and the product for- mation itself even though the exact mechanisms have not been elucidated in situ at a sub-� m level so far. Therefore, the role of CO2 in the humidified ambient atmosphere and the influence of UV light on the initial atmospheric corrosion be- haviour of silver surfaces were investigated under in situ conditions using a combined InfraRed Reflection Absorption Spectroscopy (IRRAS) and Quartz Crystal Microbalance (QCM) set-up. To obtain 3-dimensional information about the depth distribution of the corrosion products formed, ex situ Time of Flight Secondary Ion Mass Spectrometry (TOF- SIMS) measurements were performed additionally. The investigations revealed in situ the main and intermediate reaction products during the formation of basic silver carbonate on a polycrystalline silver surface. Furthermore, a strong depend- ency of the product formation rate with respect to the CO2 concentration and the humidity content in the ambient atmos- phere as well as the influence of UV light irradiation of the surface could be demonstrated.

A portable FTIR-ATR process analyzer - online fermentation control

A mid-IR FT spectrometer equipped with a horizontal attenuated total reflection (ATR) unit has been used for fermentation monitoring. The ATR element has been incorporated in a flow cell connected to the fermentation process under investigation via a flexible computer controlled flow system for online monitoring. Measurement of dissolved components is achieved while pumping the sampled fermentation broth through the flow cell. Upon stopping the flow, the microorganisms can be monitored subsequently as they settle on top of the horizontal ATR element. Because of the surface sensitivity of ATR spectroscopy, the cleanness of the ATR surface must be guaranteed throughout a prolonged operating time. For certain bioprocesses, the formation of bio-films on the ATR surface was identified as an important difficulty as they cannot be removed by simple rinsing with distilled water or simple washing solutions such as NaHCO/sub 3/. Therefore, different chemical solutions have been tested for efficient bio-film removal. Among the studied solutions, the use of oxidizing agents (e.g. H/sub 2/O/sub 2/) in concentrations around 2% proved most effective.

Ultrasonic standing wave accelerates on-line measurement and prevents coating of a FTIR ATR flow cell

It has been shown elsewhere that infrared (IR) spectroscopy can be successfully employed for the on-line monitoring of bio-processes. A horizontal attenuated total reflection (ATR) unit connected to a portable IR-cube was used here to measure the IR absorption spectra of supernatant and microorganisms separately. The common problem of bio-film formation on the ATR was addressed before, e.g. by chemical means. We present a novel method employing the principles of ultrasonic particle manipulation to avoid and potentially remove this coating brought about by the use of fermentation broth. A novel flow cell for a horizontal ATR was developed that decreases measurement time and the undesired formation of bio-films on the ATR surface. An ultrasonic standing wave (/spl sim/2 MHz) is built up between a horizontal transducer and the ATR crystal. Yeast cells in suspension were agglomerated within certain regions by the ultrasound field and therefore settled about 3-4 times faster on the ATR when the field was switched off compared to the slow sedimentation of freely dispersed cells. After the IR spectrum had been measured, the same sound field was used to actively lift the settled material from the optical sensitive surface which therefore could be rinsed away more effectively.

Ultrasonic particle manipulation exploited in on-line infrared spectroscopy of (cell) suspensions

SummaryAn ultrasonic standing wave field of 2 MHz was used to manipulate yeast cells in an on-line flow cell for Fourier transformed mid-infrared spectroscopy (FT-IR) purposes. Results show, that a significant decrease of the undesired formation of biofilms on the attenuated total reflection (ATR) surface was achieved. In addition the time resolution was more than doubled.ZusammenfassungEin 2-MHz-Ultraschallstehwellenfeld wurde verwendet, um Hefezellen in einer Online-Durchflusszelle zu Zwecken der Fourier-transformierten Infrarotspektroskopie (FT-IR) anzuordnen. Die Resultate zeigen, dass eine signifikante Reduktion unerwünschten Biofilms auf der totalreflektierenden (ATR) Oberfläche erreicht wurde. Darüber hinaus konnte die Zeitauflösung mehr als verdoppelt werden.

Sample preparation and biomass determination of SRF model mixture using cryogenic milling and the adapted balance method

The biogenic fraction of a simple solid recovered fuel (SRF) mixture (80 wt% printer paper/20 wt% high density polyethylene) is analyzed with the in-house developed adapted balance method (aBM). This fairly new approach is a combination of combustion elemental analysis (CHNS) and a data reconciliation algorithm based on successive linearisation for evaluation of the analysis results. This method shows a great potential as an alternative way to determine the biomass content in SRF. However, the employed analytical technique (CHNS elemental analysis) restricts the probed sample mass to low amounts in the range of a few hundred milligrams. This requires sample comminution to small grain sizes (<200 μm) to generate representative SRF specimen. This is not easily accomplished for certain material mixtures (e.g. SRF with rubber content) by conventional means of sample size reduction. This paper presents a proof of principle investigation of the sample preparation and analysis of an SRF model mixture with the use of cryogenic impact milling (final sample comminution) and the adapted balance method (determination of biomass content). The so derived sample preparation methodology (cutting mills and cryogenic impact milling) shows a better performance in accuracy and precision for the determination of the biomass content than one solely based on cutting mills. The results for the determination of the biogenic fraction are within 1-5% of the data obtained by the reference methods, selective dissolution method (SDM) and (14)C-method ((14)C-M).

On Chemical and Ultrasonic Strategies to Improve a Portable FT-IR ATR Process Analyzer for Online Fermentation Monitoring

A setup for online fermentation monitoring was tested with suspensions containing yeast cells. A flow cell was equipped with a horizontal attenuated total reflection (ATR) unit for measurements of mid-infrared spectra. The stopped flow principle was employed to separately assess the liquid and the dispersed cells: dissolved components in the supernatant can be assessed while pumping the fermentation broth through the flow cell. Upon stopping the flow the culture can be monitored as the microorganisms settle onto the horizontal ATR diamond. Due to the surface sensitivity of ATR spectroscopy cleanness of the optical element is of particular importance. For yeast fermentations the formation of biofilms on the ATR surface was identified as limitation in regard to long-term stability. Initial experiments showed that the effective removal of residues was impossible by rinsing with water or a NaHCO3 solution. Therefore, various cleaning agents (2%) have been tested for their ability to clear off the biofilm. The problem of biofilm formation was additionally addressed by the exploitation of forces exerted on suspended particles within an ultrasonic standing wave (USW). The USW ( ~2 MHz) was built up between the ATR element and an ultrasonic transducer facing it. This technique of ultrasonic particle manipulation was applied to actively lift the sedimented material from the ATR after the infrared measurement, thus have the rinsing stream carry it away more effectively. Among the studied reagents surfactants and oxidizing agents showed to be most effective, the use of an USW was found to be feasible to remove a biofilm.

Raman spectroscopy of particles in suspension concentrated by an ultrasonic standing wave

SummaryAn ultrasonic standing wave field of 2MHz was used to manipulate yeast cells and theophylline crystals in suspension to control the local concentration of solid material in the focus of a Raman spectroscope to improve the signal quality of such measurements for suspensions. In case of agglomerated yeast cells the signal-to-noise ratio was significantly increased in comparison to Raman spectra of the suspension. The spectra corresponded well with yeast dried on glass used as reference. Measurements of theophylline suspensions confirmed these results. Furthermore, it was possible to show the absence of theophylline crystals between the pressure nodal planes of the ultrasonic standing wave. This opens the possibility to specifically measure the solid fraction and the pure liquid of a suspension almost simultaneously by only changing the optical focus of the Raman microscope in respect to the location of the ultrasonic standing waves nodes.ZusammenfassungEin 2-MHz-Ultraschallstehwellenfeld wurde verwendet, um suspendierte Hefezellen und Theophylline Kristalle im optischen Fokus eines Raman-Spektroskops zu konzentrieren, mit dem Ziel, die Signalqualität solcher Messungen für Suspensionen zu verbessern. Das Signal-Rausch-Verhältnis konnte für die Raman-Spektren von agglomerierten Hefezellen im Vergleich zu Hefesuspensionen signifikant verbessert werden. Die Spektren zeigten auch eine hohe Übereinstimmung mit Referenzspektren von auf Glas getrockneten Zellen. Diese Resultate bestätigten sich bei Messungen mit Theophylline Suspensionen. Hier war es zudem möglich, die Abwesenheit von Theophylline Kristallen zwischen den Druckknoten der Ultraschallstehwelle zu zeigen. Dies eröffnet die Möglichkeit, die Partikel und die reine Flüssigkeit einer Suspension beinahe gleichzeitig spezifisch zu messen, indem man den optischen Fokus des Raman-Mikroskops relativ zum Ort der Knoten des Ultraschallstehwellenfeldes verschiebt.

Sample preparation and determination of biomass content in solid recovered fuels: A comparison of methods

The biomass content of material from pulp and paper production (a mixture of waste and paper and thin layer packaging plastics) is determined by the adapted balance method. This novel approach is a combination of combustion elemental analysis (CHNSO) and a data reconciliation algorithm based on successive linearisation for evaluation of the analysis results. It also involves less effort and expense than conventional procedures. However, the CHNSO technique only handles small mass amounts (few hundred milligrams), so cryogenic impact milling was applied for particle size reduction below 200 µm in order to generate homogeneous, representative analysis samples. The investigation focuses on the parameters biogenic content as a percentage of the total mass xB and xBTC, which is the biomass stated as a fraction of the total carbon value. The results are within 1%–5% of the data obtained by the reference methods, namely the selective dissolution method and 14C- method. Additionally, advantages and drawbacks of the adapted balance method in comparison with standard methods are discussed, showing that the adapted balance method is a method to be considered for the determination of biomass content in solid recovered fuels or similar materials.

Ultrasonic particle manipulation exploited for infrared and Raman spectroscopy of suspensions

Ultrasonic separation techniques are based on the so-called acoustic radiation forces exerted on suspended particles within an ultrasonic standing wave in the megahertz frequency range. Among the systems employing the aggregation effects caused by sonication, acoustic cell filters are successfully applied in biotechnology. In this work, an ultrasonic standing wave field of 2 MHz was used to concentrate particles in the light path of a confocal Raman microscope. Due to the increased spatial concentration of matter in the focus of the laser beam, an increase of the signal-to-noise ratio of the recorded Raman spectra of the particles was achieved. The utilized biomodel suspensions of yeast cells are important, e.g., for on-line monitoring of bioprocesses. Spectra are presented taken by the Raman microscope pointing at cell aggregates induced by ultrasound. As an indication of feasibility, this data are compared to measurements taken when no means of concentration were at work and to measurements of dried yeast cells, respectively. A further field of application was identified in the control of crystallisation processes with emphasis to discriminate polymorphs. Therefore, suspensions of theophylline crystals were investigated following a similar protocol as with the yeast cells. Here, the data show significant differences in the spectroscopic feature structure between dried matter and crystals in contact with water. In addition, SNR is increased by several orders of magnitude.