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Diffusion von Wasserstoff (H) in Gläsern, Schmelzen und Mineralen spielt eine wichtige Rolle in zahlreichen Anwendungen in verschiedenen wissenschaftlichen Disziplinen wie Geowissenschaften, Archäometrie und Materialwissenschaften. Es wurde eine neuartige Methode entwickelt, die eine Untersuchung von H Diffusion im Tieftemperaturbereich ermöglicht und bisherige experimentelle und analytische Schwierigkeiten umgeht. Die Methode wurde auf Silikat Glas und das Mineral Klinopyroxen (cpx) angewandt, um Diffusionsraten von H zu quantifizieren, die die existierende Datensammlung zu niedrigen Temperaturen deutlich erweitern. Die neuen Diffusionskoeffizienten für H in Silikat Glas zeigen eine Temperaturabhängigkeit mit einer deutlichen Änderung in der Aktivierungsenergie (kein Arrhenius-Gesetz), während die schnellen Diffusionsraten von H in Cpx von Hochtemperaturexperimenten zu niedrigen Temperaturen hin einem Arrhenius Gesetz folgen., Diffusion of hydrogen (H) in glasses, melts, and minerals plays a substantial role in many applications in various scientific disciplines like geosciences, archaeometry, and material sciences. Despite its significant effect on system states and their evolution with time, studying H diffusion at low temperatures (< 400 °C) has been impossible in the past due to experimental and analytical difficulties. A novel method was developed that enables one to study H diffusion in these materials at low temperatures. The method was applied to silicate glass and the mineral clinopyroxene (cpx) to obtain diffusion rates that significantly extend the existing database towards low temperatures (\(\geq\) 150 °C). The newly quantified diffusion coefficients exhibit a non-Arrhenian trend for H in silicate glass, while fast diffusion rates of H in cpx extend from previous high temperature experiments to low temperatures following an Arrhenian law.

Due to their high energy density, Li-ion batteries represent nowadays the most promising electrochemical storage devices for portable electronics, electric vehicles and stationary energy storage application. However, some challenges need to be overcome, especially for automotive applications. These include: the increase of the energy and power densities, decrease the cost, fast charging, safety, aging and recycling of the components, among others. A particular problem regards the sudden degradation due to the many undesired reactions which take place during battery operation. Batteries are complex systems and the effects contributing to capacity fade are still not well understood. One of these undesired reactions is the deposition of metallic lithium on the anode surface during the charging process. This phenomenon, called lithium plating, is not only the main cause for battery degradation when charging at low temperatures, but it may lead to a short circuit, when lithium dendrites deposits in a needle-like form, piercing the battery separator. In large format cells, where temperature and current distributions are not uniform, the lithium deposition process starts locally and it is difficult to detect. A few techniques have been employed to detect and quantify lithium plating, but these are not spatially resolved, and there is still no method that directly detects the deposition of metallic lithium during battery operation. Electrochemical models allow the evaluation of the lithium ions concentration, temperature and potential distribution within the cell, parameters that can be used to identify the plating onset conditions. Experimental parameterization is needed as different parameter combinations lead to the same cell potential curve. Each cell has a specific geometry and the transport parameters depend on the chemistry of the component and on the geometry of the cell. Furthermore, tabulated values for such parameters are scattered and often do not provide information on the electrode geometry. In-operando characterization techniques like optical microscopy and micro-Raman spectroscopy are employed to detect the lithium plating onset in the micro-scale. Intercalation of the plated lithium on the graphite surface was observed during the resting periods after charge and during the constant voltage step. However, at C-Rates higher than C/2 and temperatures below zero degrees, fast capacity decay due to irreversible lithium plating was observed in most commercial cells except in one type. A non-isothermal electrochemical model is used to investigate the lithium plating onset conditions of the commercial Li-ion cell where no plating was found even at very adverse conditions (1C and -10 degrees or 4C and 0 degrees). This model is parameterized experimentally and validated against the individual potentials. Geometry and transport parameters are determined at different temperatures and states of charge. New approaches for a fast parameterization process are introduced and the results are in good agreement with the ones obtained by other techniques. The model can predict well the temperature, potential and current distribution within the cell during charging at high C-rates and low temperatures. This promising model can be used to design new fast charging strategies for Li-ion batteries at low temperature without a detrimental effect on the battery life.

Die vorliegende Arbeit befasst sich mit der Synthese von Ferrocenyloxy- (FcO-; Fc = Fe(η5-C5H4)(η5-C5H5)) substituierten Silanen, Stannoxanen, Titanocen- und Zirkonocen-Komplexen. Weiterhin wurden Titanocen-Komplexe mit Ferrocenyl-sulfanyl- (FcS-) und Ferrocenylselanyl- (FcSe-) Liganden dargestellt. Das elektrochemische Verhalten dieser Verbindungen wurde mittels Cyclovoltammetrie, Square-Wave-Voltammetrie und in situ UV/Vis-NIR-Spektroskopie untersucht. Das drucklose Niedertemperaturfügen von Kupferwerkstoffen und das Generieren dünner MgO- und ZnO-Schichten auf Si-Substraten mittels CVD und Spin-Coating-Prozesse stellen zwei weitere Kernthemen dieser Arbeit dar. Das Niedertemperaturfügen umfasst die Synthese von Ag(I)-Carboxylaten wie [AgO2CCR2OC(O)OMe] (R = H, Me) und deren Verwendung als Basis-Komponenten in der Entwicklung von Fügepasten. Zur Erzeugung von MgO- und ZnO-Schichten wurden Metall-Dialkoholate des Typs [M(OCHMeCH2NMeCH2)2] (M = Mg, Zn) synthetisiert und mit MOCVD- und/oder Spin-Coating-Techniken abgeschieden.

Im Rahmen dieser Arbeit wurden unterschiedliche chirale Systeme mittels IR- und VCD Spektroskopie analysiert. Insbesondere wurde die VCD-Spektroskopie mit der Matrix-Isolations-Spektroskopie gekoppelt, um Moleküle unter kryogenen Temperaturen zu untersuchen. Dabei wurde die Potentialhyperfläche von \(\alpha\)-Phenylethylamin erforscht und "conformational cooling" zum globalen Minimum beobachtet, welches jedoch je nach Matrixumgebung unterschiedliche Konformationen annimmt. Weiterhin wurde ein chiraler E/Z-Photo-Schalter beobachtet und dessen beiden Zustände mittels VCD-Spektroskopie verlässlich zugeordnet. Das Verhalten von Styroloxid wurde unter Zuhilfenahme unterschiedlicher Matrix-Gase ebenfalls untersucht. Abgesehen von Matrix-Isolations-Experimenten wurden auch Experimente in der Flüssigphase durchgeführt: Ein Wirt-Gast-Komplex zeigte die Induktion von Chiralität; weiterhin wurde ein besonderes Augenmerk auf die asymmetrische Katalyse verschiedener Systeme gelegt.

In this dissertation, the minimization of the diffusion bonding temperature during refractory metals’ diffusion bonding process was studied. Two pure refractory metals were used in this study: molybdenum and tungsten. The influence on the joint quality of molybdenum structural conditions, as well as molybdenum surface conditions, was examined. Moreover, diffusion bonding of tungsten to Oxygen Free Electrical copper and copper alloy (CuCr1Zr), without using an interlayer but instead using different bonding parameters, was evaluated. Diffusion bonding of tungsten to Oxygen Free Electrical copper and to CuCr1Zr alloy using titanium and nickel together as intermediate layers was also investigated, as well as the diffusion bonding of tungsten to Oxygen Free Electrical copper and to CuCr1Zr alloy using only nickel as an intermediate layer. The resulting joints were evaluated using optical microscopy, SEM, hardness, shear, and tensile tests. The residual stresses, as well as the deformation, that are generated due to the diffusion bonding process were evaluated through a FEM simulation using the software ANSYS. For pure molybdenum joints, successful results in minimizing bonding temperature were obtained. In tungsten to Oxygen Free Electrical copper and to CuCr1Zr alloy joints contrasting results were achieved. In dieser Arbeit wurde ein Diffusionsschweißverfahren durchgeführt, um zwei Refraktärmetalle zu verbinden. Das erste war Molybdän, das ähnlich diffusionsgeschweißt ist. Das zweite war Wolfram, das diffusionsgeschweißt an OFE-Kupfer und an die CuCr1Zr-Legierung gebunden ist. Aufgrund der hohen Schmelztemperatur von Molybdän und Wolfram erforderten sie eine hohe Diffusionsschweißtemperatur. Das Hauptziel dieser Arbeiten ist es, die erforderliche Temperatur für den Verbindungsprozess zu reduzieren. Die Reduzierung der Molybdän Diffusions-schweißtemperatur ist abhängig von den Bedingungen der Molybdänoberfläche und -struktur. Die Verbindung von Wolfram mit OFE-Kupfer und mit CuCr1Zr-Legierungen erfolgte direkt (ohne Zwischenschicht) sowie unter Verwendung von Titan und Nickel als Zwischenschicht(en). Das Verbinden mit Zwischenschicht(en) ist abhängig von den Interaktionen zwischen der Zwischenschicht und den Grundwerkstoffen. Die Zwischenschichtenmetalle waren Reintitan und Reinnickel. Das Aufbringen der Zwischenschichten in den Verbindungen wurde als Wolfram - Titan - Nickel - Reinkupfer oder CuCr1Zr sortiert. Außerdem wurde nur reines Nickel als Zwischenschicht verwendet, um Wolfram mit Kupfer und der CuCr1Zr-Legierung zu verbinden. Die chemische Zusammenstellung der CuCr1Zr-Legierung ist in der Tabelle 1 dargestellt. Die Eigenspannungen sowie die Verformung, die durch den Diffusionsschweißprozess sowohl für die Refraktärmetalle Molybdän als auch Wolfram erzeugt werden, wurden durch einen Simulationsprozess mit dem Programm ANSYS bewertet. Die resultierenden Verbindungen wurden mittels Lichtmikroskopie, REM, Härte-, Scher- und Zugversuch bewertet. Die Eigenspannungen sowie die Verformung, die durch den Diffusionsschweißprozess erzeugt werden, wurden durch eine FEM-Simulation mit der Software ANSYS bewertet. Für reine Molybdänverbindungen wurden erfolgreiche Ergebnisse bei der Minimierung der Diffusionsschweißtemperatur erzielt. In Wolfram zu OFE-Kupfer und zu CuCr1Zr-Legierungsverbindungen wurden kontrastreiche Ergebnisse erzielt.

Das übergeordnete Ziel dieser Arbeit besteht in der Grundlagenuntersuchung und Optimierung von eutektischen Bondprozessen (auch Anlegieren genannt) für die Befestigung von elektronischen Bauteilen auf flexiblen Substraten. In diesem Zusammenhang sind umfangreiche experimentelle Untersuchungen und zahlreiche Parametervariationen vorgesehen um möglichst stabile mechanische und elektrische Bondverbindung zwischen den Fügepartnern zu erreichen. Dafür werden Chips aus Silizium zunächst auf starren und dann auf flexiblen Substraten durch Anlegieren verbunden. Um eine zuverlässige Bondverbindung auf flexiblen Substraten mit niedrigen Glasübergangstemperaturen zu erzielen, werden die eutektischen Indium-Zinn- und Indium-Bismut-Legierungen zum Einsatz kommen. Die experimentelle Methodik basiert auf der Variation der Bondprozessparameter: Temperatur, Druck und Dauer um die Bondverbindung insbesondere hinsichtlich der mechanischen Stabilität zu optimieren. Hierbei wird diese durch die Scherfestigkeit beurteilt. Ferner wurde ebenfalls der elektrische Widerstand der Verbindung gemessen um die elektrische Eigenschaft der Verbindung zu bewerten.

In der vorliegenden Arbeit werden nanopartikelhaltige Suspensionen auf Ag- und Ni-Basis sowie Ag-Precursoren, die während des Erwärmungsprozesses Nanopartikel bilden, bezüglich ihrer Eignung zum Fügen bei niedrigen Temperaturen untersucht. Dabei wird die, im Vergleich zum entsprechenden Massivmaterial, verringerte Schmelz- und Sintertemperatur von Nanopartikeln ausgenutzt. Da nach dem Schmelz- und Sinterprozess der Partikel die thermischen Eigenschaften des Massivmaterials vorliegen, ergibt sich ein großes Potential für die Herstellung hochfester und temperaturbeständiger Verbindungen bei gleichzeitig niedrigen Fügetemperaturen, was für eine Vielzahl von Fügeaufgaben von großem Interesse ist. In der Arbeit wird zunächst eine kommerzielle Ag-Nanopaste insbesondere bezüglich ihres thermischen Verhaltens charakterisiert. In der Folge werden Fügeverbindungen mit Cu-Substraten hergestellt, die in Abhängigkeit verschiedener Prozessparameter bzgl. der Festigkeiten, der Mikrostruktur sowie der Bruchflächen detailliert charakterisiert werden. Dabei zeigt sich, dass insbesondere der Fügedruck einen signifikanten Einfluss auf die erreichbaren Festigkeiten ausübt. Mit hohen Fügedrücken können bei einer Fügetemperatur von 300 °C höhere Verbindungsfestigkeiten als mit einem konventionellen Hartlot auf AgCu-Basis (Löttemperatur: 780 °C) erreicht werden. Weiterhin werden erste Ergebnisse zum Fügen von Stählen mit einer Ni-Nanopaste vorgestellt, mit der hohe Verbindungsfestigkeiten erzielt werden können. Schließlich wird mit Ag-Precursoren eine weitere Klasse möglicher Fügewerkstoffe vorgestellt, die erst während des Erwärmungs- bzw. Fügeprozesses Nanopartikel bilden, was in einer deutlich vereinfachten Handhabbarkeit resultiert. Die Arbeit liefert zudem Ansätze für weitere Forschungstätigkeiten. In this thesis, Ag- and Ni-based nanoparticle-containing suspensions and Ag precursors, which form nanoparticles during heating, are examined with regard to their suitability for joining at low temperatures. Nanoparticles exhibit a decrease in sintering and melting temperature in comparison to the corresponding bulk material. After melting and sintering of the nanoparticles, the material behaves like the bulk material. Therefore, high-strength and temperature-resistant joints can be produced at low temperatures, which is of great interest for various joining tasks. First, a commercially available Ag nanopaste is characterized in particular regarding to its thermal behavior. Subsequently, joints (substrate: Cu) are prepared with the Ag nanopaste. The influence of different process parameters on the strength behavior of the joints, the microstructure and the fracture surfaces is investigated. It is shown, that in particular the joining pressure exerts an essential influence on the achievable strengths. With high joining pressures, the strengths of conventionally brazed joints (AgCu brazing filler metal, brazing temperature: 780 °C) can be exceeded at a joining temperature of only 300 °C. Furthermore, first results for the joining of steels with a Ni nanopaste are presented, whereby high strengths can be achieved. Finally, with Ag precursors, an additional class of possible joining materials is presented, which form nanoparticles only during heating. This results in a significantly simplified handling. The work also provides approaches for further research activities.

The paper reviews a low temperature sol-gel processing of transparent and antiglare conducting Sn doped indium oxide (ITO) coatings. The approach uses already crystalline nanoparticles which can be fully redispersed in an ethanolic sol containing a polymerisable organic binder. Thick single layers up to 600 nm can be deposited by spin and dip coating techniques followed either by a low temperature (

Ink-jet processes using either a drop-on-demand or a dosing system have been applied to the deposition of single lenses and large arrays of high optical property refractive microlenses. The lenses are made of a silica based inorganic-organic material which can be densified either thermally or by UV irradiation at low temperature. Microlense diameter d and height h made with a single drop can be varied between approximately d=50 µm and 2 mm, and h=6.25 and 150 µm, respectively, conferring a focal distance varying between 100 µm and approximately 10 mm, respectively. Large arrays of lenses have been realized with a minimum separation between the lenses as small as 5% of their diameter. Single lenses and arrays of lenses made with multidrops were also obtained. Microdrops (1000) with d=50 µm allow us to obtain lenses with diameter 800 µm, height 56 µm and focal distance of 2.9 mm. All the components have a high optical transparency (92%) within the wavelength range 300 nm-2.7 µm, are highly homogeneous and have very low stress and astigmatism. The index of refraction can be tailored by modifying the sol composition. The lens average surface roughness is Ra≈40 nm. Their shape measured by profilometry and their focusing properties, determined in and near the focal plane, are reported.

The hydrolysis of niobates in aqueous solutions has been applied to the coprecipitation of PbNb2/3Mg1/3O3 leading to a low temperature synthesis of this ferroelectric relaxor ceramic. The effect of hydrolysis conditions - such as the concentration of bases and acids used, their rates of addition and the nature of the precursors salts - is described. The perovskite phase appears after heating at 350 °C and is obtained as a pure phase at 800 °C after heat treatment for 1 h. Relaxor ferroelectric ceramics with a high dielectric constant can be obtained by sintering at 1000 °C. The process has been also applied to the synthesis of other relaxor ceramic compositions such as PZN (PbNb2/3Zn1/3O3) and PFN (PbNb1/2Fe1/2O3) compounds.

The luminescence was excited by â-radiation from a 90Sr source. Increasing the amt. of bivalent cationic impurity (Ca2+; 30-300 ppm.) considerably increased the intensity, and also reduced the temp. of max. intensity (170 to 156°K.) (Tm). The wavelength of max. emission changed with temp., moving from 4350 A. at 77°K. to 4250 A. at 140° and back to its original value at room temp. Treatment at high temp. (approx. 600-700°K.) increased the intensity, and the presence of Ca2+ and Sr2+ greatly increased the effect; the luminescence disappeared after dissoln. and recrystn. Quenching from 500°C. increased the intensity, showing the influence of Schottky pairs; Tmwas also reduced. The emission bands had profiles corresponding to Gaussian curves.

In der Arbeit wird untersucht, inwieweit zwei Epitaxieverfahren (LPCVD- und RPCVDVerfahren) geeignet sind, Bor-dotierte Si/SiGe/Si-Heteroschichtstapel mit guter Homogenität und Reproduzierbarkeit herzustellen. Die Bewertung der Epitaxieverfahren erfolgte anhand von HBT-Parametern, deren Streuungen von Wafer zu Wafer und über den Wafer ermittelt und mit publizierten Referenzdaten des etablierten UHVCVD-Verfahrens verglichen wurden. Die besten Ergebnisse wurden für RPCVD-basierte Si/SiGe/Si-Schichstapel ermittelt. Schichtstapel beider Epitaxieverfahren haben eine geringe Dichte elektrisch aktiver Defekte. Als kritischer Epitaxieprozeßparameter wurde die Abscheidetemperatur ermittelt. Im Fall des LPCVD-Verfahrens hat die Trägergasgeschwindigkeit einen großen Einfluß auf die Homogenität des Boreinbaus. Mit dieser Arbeit wurde nachgewiesen, daß das RPCVDEpitaxieverfahren eine Alternative zum etablierten UHVCVD-Verfahren ist. In this thesis it is investigated how far two epitaxial methods (LPCVD and RPCVD) are applicable for the homogeneous and reproducible deposition of boron doped Si/SiGe/Si hetero layer stacks. The methods were evaluated by means of wafer to wafer and within wafer spread of HBT parameters as well as by comparison of these data with published data of the established UHVCVD epitaxial method. The best results were achieved for RPCVD based Si/SiGe/Si-layer stacks. It was found that layer stacks of both investigated epitaxial methods possess low densities of electrically active defects. The most critical process parameter is the deposition temperature. The carrier gas velocity influenced strongly the boron incorporation in the case of the LPCVD reactor. In result of this thesis it was found that the RPCVD method is an alternative to the established UHVCVD method.

Im Fraunhofer-Institut für Silizium-Technologie ISIT in Itzehoe wurde ein mikromechanischer Hochfrequenzschalter (RF-MEMS-Schalter - Micro-Electro-Mechanical System (MEMS)) entwickelt und in die Fertigung überführt. Der Aufbau und die Funktionsweise werden beschrieben und anhand von zwei Bildern dargestellt. Bei dem für die HF-Bauteile verwendeten oberflächenmikromechanischen Verfahren mit metallischer Aufbaustruktur werden Siliziumwafer in einem Niedertemperaturprozess hintereinander mit Metall- und Isolationslayer beschichtet und mit Belichtungs- und Ätzmethoden strukturiert. Als Basismaterial wird eine Kombination aus Nickel und Gold benutzt. Kritischer Punkt bei der Entwicklung des Packaging-Verfahrens war die Limitierung der Prozesstemperatur auf maximal 300 Grad C. Ein weiteres Packaging-Verfahren für HF-MEMS-Schalter wurde im Rahmen des EU-Forschungsprojekts 'RF PLATFORM' entwickelt, bei dem keramische Deckel aus LTCC (Low Temperature Cofired Ceramics) einzeln auf ein komplett mit RF-Schaltern prozessierten Wafer montiert werden. Fehlerhafte Deckel werden vor dem Einhäusen ausgesondert. Der Einsatz der HF-MEMS-Schalter ist für folgende Anwendungen vorgesehen: Mobilfunkgeräte, Basisstationen, drahtlose Breitbandkommunikationssysteme und Automobil-Radarsysteme (Abstandsregelung, Einparkhilfe).

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Das Ziel der Arbeit war, das Verständnis von induktiv gekoppelten Plasmen in Wasserstoff zu verbessern. Dazu wurden zahlreiche Diagnostikmethoden eingesetzt und ein Modell entwickelt, das die Mechanismen der Leistungseinkoppelung, Plasmaerzeugung und Schichtausbildung berücksichtigt. Experimentelle Untersuchungen wurden mit Langmuir- Sondenmessungen, Messungen des elektrischen Feldes im Schichtbereich, massenaufgelöste Ionenenergieanalyse an der Elektrodenoberfläche und zeitaufgelöster optischer Emissionsspektroskopie in einer modifizierten GEC-Referenz-Zelle durchgeführt. Das ICP-Entladungsmodell besteht aus drei Modulen. Das „Plasmamodell” erlaubt die Berechnung von Elektronendichte und Elektronentemperatur. Das „elektrische Modell“ verknüpft die Eingangs-RF-Leistung mit der im Plasma kapazitiv oder induktiv dissipierten Leistung. Das „Schichtmodell“ berechnet die Felder, die Potentiale, die Ströme und die Ionenenergie-Verteilungsfunktion. Das Modell ist konsistent mit den Messungen.

In2O3:Sn (ITO) transparent conducting coatings of high optical quality have been obtained on glass and several plastic substrates by spin and dip coating processes followed by a low temperature processing (T < 130°C). The sols are made of crystalline nanoparticles redispersable in an alcohol and modified by adding a binder to favour the coalescing of the particles and to allow the deposition of thick single layers (>400 nm). The smallest stable resistivity so far obtained is ρ = 9

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Investigations on selected oxidation hair dyes - which are normally applied in the form of gels and pastes - have shown that it is possible to use these dyes on wool in commercial wool dyeing procedure. The precursors are applied at low low temperatures (e.g. 60oC) and short treatment times (20 min). For the subsequent oxidation with H2O2 temperatures of 40oC are sufficient together with a development time of 40 min. Therefore, this colouring method offers a genuine low temperature colouring potential for wool, saving energy and time with a significant improvement of the wool quality in comparison to commercial wool dying at substantially higher temperatures (98oC). At the same time the oxidation hair dyes offer a substitution potential for the heavymetalliferous chrome colouring dyes, since they are free from toxicological alarming heavy metals. With the system 2,5-diaminotoluene sulfate/2-amino-4-hydroxyethyl aminoanisole sulfate a black coloured wool could nearly be realized. The use of 4 % oww precursor and a dye bath exhaustion up to 96 % results in a deep blue-black coloured wool. The small molecule size of the resulting chromophor together with its good water solubility turned out as a disadvantage for the fastness. With the system 1,10-bis-(2,5-diaminophenyl)-1,4,7,10-tetraoxadecane/1,3-bis-(2,4-di-aminophenoxy)propane a deep dark-blue black colour could be achieved. The structure of the high-molecular oligomers of this dye could not be determined. Investigations on the sorption of the precursors 1,10-bis-(2,5-diamino-phenyl)-1,4,7,10-tetraoxadecane and 1,3-bis-(2,4-di-aminophenoxy)propane on wool showed that the bath exhaustion of the precursor can be increased significantly from 60 to over 85% by addition of surfactants such as sodiumdodecyl sulfate or dodecylbenzene sulfonic acid or by the use of plasma-treated wool. The alkaline fastness to perspiration with values of 3-4 and the (dry/wet) fastness to rubbing with values of 4 and 3-4 are satisfactory. The requirements of the Wollmark spezification for fabrics are almost met. The fastness to light with values of 4 fulfills the minimum requirements of the Wollmark federation for fabrics.

The mechanism of preferential CO oxidation in H2-rich gas (PROX) is investigated over three different catalyst systems: supported platinum (in particular Pt/gamma-Al2O3), a supported bimetallic catalyst (Pt3Sn/Vulcan) and supported gold (in particular Au/alpha-Fe2O3). Compared to standard Pt catalysts which require temperatures above 150°C to operate at reasonable rates, the latter low temperature PROX catalysts are characterized by a combination of facile oxygen adsorption and largely inhibited hydrogen adsorption under reaction conditions. This can be achieved either by an active material that is inert for both, hydrogen and oxygen adsorption, but allows CO adsorption, and where oxygen adsorption proceeds on the support material (i.e., Au/Fe2O3), or by a material that would be active for adsorption of all reaction partners, but which is blocked for hydrogen and consequently also for oxygen adsorption by a CO adlayer. In all of these cases the oxidation reactions will take part at the interface between the different areas, or via a spill-over process and the reaction is not limited by CO desorption, which is the limiting factor for the Pt catalysts at temperatures below 150°C. On Pt/gamma-Al2O3 the rather constant selectivity is explained by a saturation coverage of COad which is maintained over a large range operation conditions. For the low-temperature catalysts the selectivity is also very high due to the high activation barrier for the dissociative adsorption of hydrogen. However, on the latter systems the selectivity decreases very fast at decreasing pCO or increasing temperatures as a result of the reduced CO surface coverage. All investigated systems show a more or less severe tendency for deactivation during time on-stream, but the reasons and also the degree of reversibility are very different. In experiments with more realistic simulations of methanol reformer gas (i. e., containing CO2 and H2O), it is found that the platinum-based systems suffer from large H2O-contents, which decrease the selectivity significantly, wheras Au/alpha-Fe2O3 is more sensitive to CO2.For Pt and Au various support materials are compared, but none of them appears to be significantly superior to the originally employed Pt/gamma-Al2O3 or Au/alpha-Fe2O3 catalysts.

A new wet chemical concept to produce coatings by dip, spin or spray processes is presented. It is based on the preparation of solutions made of crystalline nanoparticles fully redispersable in a solvent. It is exemplified for the preparation of SnO2 : Sb (ATO) and In2O3 : Sn (ITO) transparent conducting coatings. The process combines the advantages of using particles having already a low resistivity and the possibility to sinter the coatings at low temperature. The particles are prepared using an in-situ monitoring of the surface energy to control the growth of the particles and to avoid their agglomeration. The dried powders can be fully redispersed in alcohol (ITO) or water (ATO). Single layers with thickness up to 200 nm (ATO) and 400 nm (ITO) have been fabricated. The sheet resistance of the coatings decreases with the sintering temperature. Typical values are 430 Ω(open square) for ATO (550°C) and 380 Ω(open square) for ITO (550°C). Sols made by redispersing the powders in organosilanes allow to produce coatings at low temperature with antistatic (R(open square) > 100 kΩ(open square)) and anti-glare properties (R(open square) > 100 kΩ(open square), 60 to 80 gloss units).

In this overview we describe some recent developments of technological interest realized at INM in the processing of sol-gel coatings. Nanoscale crystalline particles, fully redispersed in aqueous solutions, have been developed to produce thin ceramic layers at low temperature. As an example, antistatic optical coatings and conducting membranes based on SnO2:Sb material are reported. New wet chemical processes have been developed to extend the sol-gel basic principles for the coating of oxide compounds on plastic (biomimetic process) and sulfide materials (MoS2). Also ink-jet and pad printing processes, well established in other fields, have been adapted for the development of micro structured coatings. As examples, the realization of single and arrays of spherical and cylindrical refractive microlenses is presented. Finally non conventional sintering process using high power CO2 laser is exemplified for the obtention of optical quality transparent conducting coatings under high sintering rate (30 cm2/s).

The sol-gel method which features a low-temperature wet-chemical process opens vast possibilities to incorporating organic dyes into solid matrices for various optical applications. In this paper we present our experimental results on the sol-gel derived photochromic organic-inorganic composite (ORMOCER) materials follwoing an introductory description of the sol-gel process and a brief review on the state of the art of the photochromic solids prepared using this method. Our photochromic spirooxazine-Ormocer gels and coatings possess better photochromic response and colour-change speed than the corresponding photochromic polymer coatings and similar photochemical stability to the latter. Further developments are proposed as to tackle the temperature dependence problem and further tap the potentialities of the photochromic dye-Ormocer material for practical applications.

We present a new sol-gel method to prepare gels of mullite (3Al2O3∙2SiO2) using as precursors a mixture of Si and Al alkoxides and a slow hydrolysis process. The gels have a polymeric structure with a high chemical homogeneity and crystallize at low temperature (980°C). X ray diffraction data indicate, at this temperature, the presence of a mixture of mullite and Al-Si spinel phases. The Al-Si spinel phase disappears at 1180°C and pure, well organized orthorhombic mullite is obtained at 1450°C. Ceramics prepared under uniaxial or isostatic pressing and sintered at 1550°C present, however, poor mechanical properties with apparent densities of the order of 70 to 80% of the theoretical density (3.17 g cm(-2)).

For the synthesis of composites on a nano or molecular level, chemical or physical methods have to be used since mechanical procedures cannot be employed for these systems. If organics have tobe included, low temperature processing has to be used for the synthesis of the inorganic component in order not to damage the organic component. Sol-gel techniques are an appropriate means to synthesize oxidic networks by soft chemistry, and various systems of organically modified ceramics (ORMOCERs) have been developed so far. It has been shown that the synthesis parameter can be used to tailor the material properties of ORMOCERs and several examples of material developments will be given.

An amorphous solid, precursor to BaTiO3, has been prepared by the sol-gel route and its structural organization studied by LAXS as a function of temperature. In the low-temperature solid, the barium atoms keep the same environment as in barium acetate. The titanium alkoxide reacts with acetic acid to give an hexanuclear molecule.

The sol-gel route to glass offers considerable advantages. Among these the control of composition, low processing temperatures, organical modifications of inorganic polymers leading to a new a class of glass-like materials, the processing of sols to coatings or powders, and the possibilities to structurize glasses are interesting for optoelectronic glasses. Future perspectives of sol-gel processing of optoelectronic glasses as well as some experimental results concerning the state of the art are given.

Organisch-anorganische Netzwerke können, wie Sol-Gel-Prozeße, bei so niedrigen Temperaturen aufgebaut werden, daß auch der organische Anteil "überlebt". Diese neuen Polymere sind für empfindliche Kunststoffoberflächen als Beschichtungsmaterialien interessant. Ein Scaling Up zum industriellen Maßstab ist problemlos möglich.

The non-luminescent and spin-dependent disexcitation process observed in F-center pairs in alkali halides at low temperature is explained by a covalent bond within the pair. Exchange effects give a negative contribution to the lattice potential energy. If the pair separation is small, local modes become unstable and spontaneous lattice distortions bring back the pair in its ground state.

Concentration quenching plays an important role in luminescence phenomena, and is generally accounted for by pair interactions. In alkali halides containing F centers, whenever a member of an F center pair is optically excited at low temperature, it can return to its ground state either radiatively or by the formation of an intermediate F' center. In this case, the excited electron is transferred by fast tunnelling to a neighboring center. This process depends on the spin symmetry of the pair, which is determined by the inhomogeneity of the hyperfine field. Effects of applied magnetic field, spin lattice relaxation and spin-spin interaction on the tunnelling probability are investigated. Experimental confirmation of the theory is presented for the case of KCl.