Maria Klimkiewicz

Segregation in YVO4 single crystals grown by Czochralski technique

Abstract SEM-EDS investigations on cleavaged (100) planes of YVO 4 single crystals grown from the melt indirectly indicate a very limited homogeneous solid solution region in the Y 2 O 3 -V 2 O 5 − x phase system around the 50.7 ± 0.2 mol% Y 2 O 3 quasi congruent composition corresponding to the maximum melting (freezing) point at slightly different rates of oxygen deficiency. Two different samples grown by Czochralski technique from stoichiometric starting compositions exhibited either many precipitates with excess V or Y depending upon the sintering and growth conditions employed.

Environmental scanning electron microscopy of activated carbon production from anthracite by one-step pyrolysis-activation

Abstract Experiments were carried out to produce activated carbons from anthracite using one-step steam pyrolysis-activation. Environmental scanning electron microscopy (ESEM) was used to observe the porosity development in real time. The anthracite samples were heated in different gas atmospheres before steam activation. The ESEM observations showed that the activation agent had a significant effect on the porosity of activated carbon produced from anthracite. The activated carbon produced by steam activation at 850°C for 6 h had the highest surface area and a well-developed porous structure. Substantial activation of anthracite surfaces and formation of extensive porosity occurred under the same conditions but with steam at 270 Pa instead of atmospheric pressure. Air treatment at 300°C for 3 h before steam activation also led to production of activated carbon with well-developed porosity. An important advantage of the activated anthracites produced in this study is their microporous structure with a considerable fraction of pores of molecular dimensions. This indicates that molecular sieve materials can be producted from Pennsylvania anthracite by one-step pyrolysis-activation under appropriate conditions.

Kinetics, in situ X-ray diffraction and environmental scanning electron microscopy of activated charcoal gasification catalyzed by vanadium oxide, molybdenum oxide and their eutectic alloy

Mechanisms of carbon oxidation catalyzed by vanadium pentaoxide (V2O5) and molybdenum trioxide (MoO3) have been a subject of controversy. Two complementary in situ techniques, X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM), were used in this work to study the gasification of an activated charcoal catalyzed by the two metal oxides, their eutectic alloy and the binary mixture with the eutectic composition. Gasification experiments were carried out at relatively low temperatures (300–650 °C) in an XRD cell (1 atm) and ESEM (2.2 Torr) to monitor phase transformations and morphological changes of oxide catalysts, respectively. The experimental results showed that MoO3 and V2O5 particles in contact with active carbon surfaces are reduced to oxides with lower oxidation states, e.g. MoO2 and V6O13, respectively. The reduction of MoO3 to MoO2 on the carbon surface prevents the sublimation of MoO3 which takes place readily on a quartz surface under the same conditions. The formation of V6O13, on the other hand, causes more extensive spreading of the catalyst on carbon surfaces, since V6O13 has a lower melting point than V2O5. Based on the XRD and ESEM observations, it is clear that phase transformations of metal oxides during gasification depend on their interactions with carbon surfaces. The phase transformations of the metal oxides, play, in turn, a significant role in carbon gasification, as evident from the kinetic data obtained for the catalytic gasification of the activated charcoal sample. The synergy observed between the components of the eutectic mixture is discussed, comparing the XRD and ESEM observations.

Magnetic alignment of particles in composite films

Films with anisotropic electric properties were created by a processing technique that produces an alignment of μm sized iron particles in a polymer film. The magnetic aligning process was observed to create a formation of iron particle columns parallel to the aligning magnetic field. The degree of alignment can be quantified by measurements of the electrical impedance.

X-Ray Fluorescence Analysis of Obsidian Sources in Arizona and New Mexico

ABSTRACTMajor, minor, and trace element values for 19 obsidian sources located in New Mexico and Arizona have been obtained through energy dispersive X-ray fluorescence analysis. The sample preparation methods and analytical procedures are described. A discriminant analysis on the data indicates that most of the obsidians were correctly assigned to their geological source. Several potential problem areas in the procedure were identified.

Pinhole formation and weight loss during oxidation of industrial graphite and carbon

The performance of graphite or carbon above 400°C depends to a large degree on its resistance to oxidation. In this work oxidation data of graphite and carbon was analyzed using the number of created pinholes for short-term oxidation and weight loss for long-term oxidation. The effect of grain size, purification, and the amount of inorganic impurities was investigated. The migration of vanadium, the formation and morphology of pinholes, and the weight loss were followed in different samples. Short-term oxidation is diminished by the presence of calcium salts and enhanced by the presence of V2O5, but the latter effect is diminished by the presence of Ca3V2O8. Both calcium salts and V2O5 enhance the long-term oxidation.

In‐situ techniques for studying deterioration of C/C composite aircraft brakes by catalytic oxidation

Recent use of potassium acetate as a runway deicer fluid at the airports leads to rapid wear of aircraft brakes. In this study, the deterioration of carbon/carbon composite aircraft brakes by oxidation was studied using samples of new and used brake materials. In-situ techniques, including Environmental Scanning Electron Microscopy (ESEM) and in-situ X-Ray Diffraction (ISXRD) were used together with thermal gravimetric analysis (TGA) to study the oxidation mechanisms and kinetics of oxidation. The new brake samples impregnated with potassium acetate showed high oxidation reactivity at relatively low temperatures, indicating catalysis of carbon oxidation by potassium species. Samples of used brake were more resistant to weight loss in air probably because the more reactive carbon components had already been gasified. ESEM experiments showed that particles of potassium oxides are very effective in catalysing the gasification of isotropic carbon fibers in the CVD composite. Potassium oxides identified by in situ XRD experiments seem to be present as molten phase, suggesting that an oxidation-reduction cycle with the intermediate formation of peroxide, or a higher oxide of potassium, is responsible for the observed catalytic effect. In-situ Methoden zur Untersuchung der Zerstorung von C/C-Verbundwerkstoff-Flugzeugbremsen durch katalytische Oxidation In letzter Zeit wurde Kaliumacetat zum Enteisen von Startbahnen auf Flughafen eingesetzt, was zum schnellen Verschleis von Flugzeugbremsen fuhrte. In dieser Arbeit wurde die Zerstorung von Flugzeugbremsen aus Kohlenstoff/Kohlenstoffverbundwerkstoffen durch Oxidation untersucht, wobei Proben von neuen und gebrauchten Bremsmaterialien eingesetzt wurden. In-situ Methoden, darunter in-situ-Rasterelektronenmikroskopie (ESEM) und in-situ Rontgenbeugung wurden gemeinsam mit thermogravimetrischer Analyse eingesetzt, um die Oxidationsmechanismen und die Kinetik der Oxidation zu studieren. Die neuen Bremswerkstoffe, die mit Kaliumacetat impragniert waren, zeigten hohen Oxidationsangriff bei relativ niedrigen Temperaturen, was eine Katalyse der Kohlenstoffoxidation durch Kaliumverbindungen anzeigt. Die Proben von gebrauchten Bremswerkstoffen waren bestandiger gegenuber Masseverlust in Luft, wahrscheinlich weil die reaktiveren Kohlenstoffkomponenten bereits oxidiert waren. ESEM Experimente zeigten, das Partikel von Kaliumoxiden sehr effektiv die Oxidation von isotropen Kohlenstofffaden aus dem CVD Verbundwerkstoff katalysieren. Die Kaliumoxide, die durch in-situ Rontgenbeugungsexperimente nachgewiesen wurden, scheinen als geschmolzene Phase vorzuliegen, woraus sich schliesen last, das ein Oxidations-Reduktionskreislauf unter intermediarer Bildung von Peroxid oder eines hoheren Oxids von Kalium verantwortlich ist fur die beobachteten katalytischen Effekte.

Deep lateral anhydrous HF/methanol etching for MEMS release processes

As demonstrated earlier, gas-phase etching of sacrificial oxide with a vapor mixture of anhydrous HF (AHF) and methanol (CH3OH) offers a clean, stiction-free, effective etching technique for microelectromechanical systems (MEMS) release. The use of AHF/methanol process in MEMS release operations is explored in the deep lateral etching of patterned silicon-on-insulator (SOI) substrates using a 200 mm multiwafer commercial module, which assures adequate process throughput. It was determined that highly selective, with respect to both Si and Si3N4, etching of SiO2 can be accomplished by controlling pressure and wafer temperature. It was also observed that the vertical etch rates for both the AHF/methanol and the HF: H2O solution was higher than the rates of lateral etches in confined geometries. Furthermore, the AHF/methanol and 1:10 HF: H2O etch chemistries were directly compared in releasing silicon cantilevers up to 500 µm in length and a significantly faster, stiction-free process was observed in the former case. Adequate process reproducibility from wafer to wafer as well uniformity across the wafer was demonstrated.