Showing papers by "DECHEMA published in 2002"

Biotechnological production of 2-phenylethanol

Abstract: 2-Phenylethanol (2-PE) is an important flavour and fragrance compound with a rose-like odour. Most of the world's annual production of several thousand tons is synthesised by chemical means but, due to increasing demand for natural flavours, alternative production methods are being sought. Harnessing the Ehrlich pathway of yeasts by bioconversion of L-phenylalanine to 2-PE could be an option, but in situ product removal is necessary due to product inhibition. This review describes the microbial production of 2-PE, and also summarizes the chemical syntheses and the market situation.

Role of growth stresses on the structure of oxide scales on nickel at 800 and 900°C

Abstract: The development and relief of intrinsic growth stresses in oxide scales on nickel of different purity have been investigated by combining the deflection test in monofacial oxidation (DTMO) with acoustic-emission analysis (AE). Parallel metallographic analysis gave information about the development of the physical- defect structure and all other structural features. The investigations were performed for 100 hr at 800 as well as 900°C in air. The assumption of elastic behavior led to the best correlation between models, literature data, and results of the present investigations. Microcracks are responsible for the relief of growth stress and inward oxygen penetration leads to the typical NiO duplex scale. The growth of the microcracks is initiated at large pore populations at the oxide–metal interface that most probably form due to outward cation-diffusion and vacancy condensation. The pore formation is increased by the presence of impurities. An equilibrium of microcracking and crack healing is finally reached, leading to a continuous growth of the inner and outer NiO layers of the duplex scale. The scale growth stresses are mainly compressive and can reach maximum values of −560 MPa at 900°C. An estimation of the fracture toughness of the oxide–metal interface assuming a wavy interface led to a KIc value of about 2 MNm-3/2 at 900°C

Novel protective coatings for steel based on a combination of self‐assembled monolayers and conducting polymers

Abstract: Investigations for a new primer system for iron or low alloyed steel have led to first results. Several special phosphonic acids with thiophene derivatives as head groups have been synthesized. They form stable self-assembled monolayers ( SAMs ) on passivated iron by dipping the substrates into aqueous phosphonic acid solutions. SAM formation was validated by current potential curves and also by contact angle measurements, which showed an intensive hydrophobisation of the iron surface after the dipping process. Finally cyclovoltammetric ( CV ) experiments after SAM formation indicated the successful polymerisation of the immobilised thiophene derivatives.

Growth Stresses in the Oxide Scales on TiAl Alloys at 800 and 900°C

Abstract: In the oxidation of TiAl alloys, the role of scale-growth stresses formed during oxidation has, thus far, been unknown. In the present paper the oxide-growth stresses were investigated by the deflection-test method in monofacial oxidation (DTMO) accompanied by acoustic-emission measurements. On unmodified surfaces the growth stresses are compressive and reach levels of around −100 MPa. At the same time, significant acoustic emission occurs indicating that even under isothermal conditions, stresses are relieved by a scale-cracking mechanism. For oxide scales on TiAl surfaces, which had been ion implanted with chlorine before oxidation, a very thin protective alumina layer is formed which, however, develops growth stresses in the range of several GPa, accompanied by intensive acoustic emission. In all stress–time curves, a dynamic situation is observed. This consists of phases of stress relief by scale microcracking and phases of stresses increase due to crack healing and further oxide growth. As a result, the level of stress as a function of oxidation time, is characterized by an oscillating course.

Nano-enamel: a new way to produce glass-like protective coatings for metals

Abstract: Nanoparticles and nanostructured films have gained an increasing interest for industrial application in the last years. Based on chemical nanotechnology glass-like protective coatings thermally processed at comparatively lower temperatures around 500°C were developed for metal substrates by two different ways. Starting from polymeric sols (suspension consisting of branched macromolecules) containing multicomponent oxide of the SiO2-B2O3-P2O5-Na2O system produced by hydrolysis and polycondensation of an alkoxide mixture under acidic condition, thin, hard, transparent, crack-free and corrosion resistant coatings could be applied to aluminium and steel. Coatings from particulate sols (suspension consisting of solid particles) containing multicomponent oxide synthesized under basic condition by electrophoretic deposition (EPD) proved to be a promising method when very thick coatings are required. Both routes offer the potential of a new type of purely inorganic coatings for corrosion and abrasion protection. Nano-Email: ein neuer Weg zur Erzeugung glasartiger Schutzschichten fur Metalle In jungerer Zeit haben nanotechnologisch basierte Herstellungsverfahren fur Oberflachenschutzschichten zunehmend an Bedeutung gewonnen. In der vorliegenden Arbeit wurden solche Schichten auf zwei Wegen erzeugt, wobei in beiden Fallen eine thermische Nachbehandlung bei vergleichsweise niedrigen Temperaturen um 500°C zur thermischen Verdichtung und Uberfuhrung in eine rein anorganische Schicht durchgefuhrt wurde. Im ersten Fall wurde mit Polymer-Solen gestartet, die durch Hydrolyse und Polykondensation von Alkoxiden unter saurer Katalyse hergestellte Multikomponentenoxide des Systems SiO2-B2O3-P2O5-Na2O enthalten. Auf diese Weise konnten dunne, harte, transparente, risfreie und korrosionsbestandige Schichten auf Aluminium und Stahl aufgebracht werden. Im zweiten Fall wurden Sole mit festen Multikomponenten-Nanopartikeln verwendet, die sol-gel-technisch unter basischer Katalyse synthetisiert wurden. Schichten wurden mit Hilfe der elektrophoretischen Abscheidung auf Metallsubstrate aufgebracht. Diese Methode war besonders fur die Aufbringung dicker Schichten geeignet. Beide Methoden besitzen das Potential fur die Entwicklung neuartiger Schutzschichten gegen Korrosion und Abrasion.

Detection of the microbial activity of aerobic heterotrophic, anoxic heterotrophic and aerobic autotrophic activated sludge organisms with an electrochemical sensor

Abstract: The microbial activity of aerobic heterotrophic, anoxic heterotrophic and aerobic autotrophic microorganisms in biological wastewater treatment was determined by means of an electrochemical bioactivity sensor. The development of the sensor resulted in a system which can determine the microbial activities that are relevant for effective wastewater treatment. The signals of the sensor system are proportional to the substrate degradation and it can show inhibiting effects on the biomass. The most important advantages of the system are: it is independent of O2 consumption, the three most important types of metabolic activities in wastewater technology can be measured with one sensor, furthermore the measurement is suitable for automation and it is on-line. The result is a potential for the optimization of processes based on microbial activity.

Characterization of starter cultures by determining microbial activity using an electrochemical gel cell

Abstract: The application of starter cultures in the food industry is a widely used method of deliberately initiating fermentations of foodstuffs. Batch-dependent fluctuations in the activity of starter cultures can have an adverse effect on the quality of the products to be made using them. The amperometric sensor system presented in this study is able to detect deficiencies in the quality of starter cultures, thus enabling the end-user to adapt production steps according to the culture applied. The principle of the sensor system is current measurement by way of a three-electrode system. The current signal is based on a mediator, which has been reduced by microorganisms, immobilised in a gel together with the microorganisms.

Preparation of inorganic coatings on metal surfaces for corrosion protection under aggressive conditions having higher flexibility, resistance to crack formation, and higher hardness at lower treatment temperatures

Abstract: A process for preparation of corrosion protecting inorganic coatings for industrial materials in which a layer forming gel is obtained by hydrolysis or polycondensation of one or more OH group containing silanes is new. A process for preparation of corrosion protecting inorganic coatings for industrial materials in which a layer forming gel is obtained by hydrolysis or polycondensation of one or more silanes of formula H-Si(-OR)-3, where the -(OR)- groups can be the same or different.

Electrochemical method for the determination of the cell count and the biological activity

Abstract: An electrochemical measurement cell combining an anode, a cathode, and leads with voltage- and current measurement instrumentation, with a redox mediator immobilized in the framework of a gel substrate, is new.

Corrosion-resistant inorganic coating producing process involves electrostatically depositing non-metallic inorganic nanometric particles on surface of material

Abstract: The inorganic coating producing process involves depositing non-metallic inorganic nanometric particles on the surface of the material electrostatically. The deposited particles are subsequently sintered at 200-1500[deg]C to produce a sealing layer. The material surface should be degreased before the particles are deposited on it.