G. Papapolymerou

Decomposition of NH3 on Pd and Ir Comparison with Pt and Rh

The unimolecular decompositions of NH3 on polycrystalline wires and foils of Pd and Ir are examined and compared with the corresponding ones on Pt and Rh. The reactions were carried out in a differential flow reactor, at pressures from 0.01 to 1 Torr and temperatures from 500 to 1900 K. It was found that the rates of product formation could be fit by Langmuir-Hinshelwood unimolecular rate expressions, with an accuracy of ±20% under all conditions. Ammonia decomposes to N2 and the rate of decomposition is fastest on Ir by several orders of magnitude when compared with that on the other metals, becoming flux limited above about 750 K. Ir appears to be the choice catalyst for dehydrogenating ammonia. The heats of adsorption of NH3 on Pt, Rh and Pd are similar and equal to 16.7, 16.8 and 17.4 kcal/mol, respectively. The apparent activation energy for this reaction is similar on Pt and Rh and equal to 21 kcal/mol, while for Pd and Ir it is 26.2 and 31.2 kcal/mol, respectively.

Fluorinated ferroelectric liquid crystals1

Abstract The synthesis of fluorinated ferroelectric liquid crystals possessing enhanced smectic behavior over their non-fluorinated analogues are described. The physical properties of these novel fluorinated materials are reported and the effect of fluorination on these physical properties are discussed.

Laminar film flow down a wavy incline

Abstract Laminar flow of a liquid, down an inclined wall with sinusoidal corrugations, is considered. A linear analysis, valid for small-amplitude disturbances but arbitrary wavelength and Re number, leads to an Orr-Sommerfeld type equation with nonhomogeneus boundary conditions. The free-surface amplitude and phase relative to the wall are examined. In a range of Re numbers, a resonance phenomenon is calculated, leading to amplification of the wall corrugations. This behavior has not been encountered in previous analyses of thin film flow, based on the Stokes approximation.

Kinetics of the bimolecular reaction NO+H2 on Pt

Abstract The reaction of NO+H2 on polycrystalline wires and foils is studied from temperatures between 550 and 1800 K, and partial pressures between 10−3 and 1 Torr. N2 and N2O are the main products formed during this reaction. Below about 750 K and above 1500 K, the rates of N2 and N2O formation are about equal. Both rates go through a maximum then a minimum and rise again with increasing temperature above 1500 K and 1200 K respectively. Rate data for the formation of N2 and N2O at low, intermediate and high temperature regimes are fitted with Langmuir-Hinshelwood (LH) bimolecular rate expressions within about ± 30%. Heats of adsorption for NO and H2, obtained from these rate expressions are 25.3 and 12.4 kcal/mol respectively.

Selectivity of the NO+H2 reaction on Pt, Rh and Ir

The selectivity of the NO+H2 reaction towards N2 and N2O was found to vary by more than four orders of magnitude as compared with that on polycrystalline wires and foils of Pt, Rh and Ir. NH3 is also produced during this reaction. Ir is the most selective catalyst towards N2 formation, by more than 3 orders of magnitude below 1000 K, as compared to Pt and Rh.

Decomposition of hydrazine on Ir

The decomposition of N2H4 has been studied on polycrystalline Ir. It was found that hydrazine decomposition is very fast compared with other previously reported unimolecular reactions [3, 4]. Three products were detected, namely N2, H2 and NH3. NH3 formation rates were equal to those of N2 formation up to about 700–800 K, depending on the pressure, but rapidly decreased above that temperature, while those of N2 formation became flux-limited at high temperatures.

Mechanical properties of short oxide fibre-kaolin clay matrix composites

Abstract A series of short fibre ceramic composites was produced by mixing, slip casting, and sintering kaolin clay with Al2O3 or mullite fibres at various volume contents. Sintering was conducted in air at various temperatures. The resulting composites were characterised with respect to chemical and mineralogical composition, microstructure, and mechanical properties. Sintering above 1200 °C changed the microstructure of kaolin from a weak point bonded structure to a strong dense glass ceramic structure, and changed δ-Al2O3 to α-Al2O3. The addition of oxide fibres to kaolin clay resulted in the formation of ceramic matrix composites, the properties of which depended on sintering temperature, matrix and fibre structures and relative volumes, the properties of the fibre/matrix interface, and fibre length. A relative increase in strength and toughness with incorporation of fibres is achieved with limited additions of fibres, and mainly in the weak point bonded structures. The application of linear elastic fracture mechanics to the examined ceramic matrix composites is also discussed.

DYNAMIC BEHAVIOR OF THE NO+H2 REACTION ON PT, RH AND IR

The NO+H2 reaction was found to oscillate on Pt. The oscillations were of the relaxation type and non-isothermal. The temperature amplitude of the oscillation was from 120 to 190 K, and the rate varied between about 5×1015 and 5×1017 molec./cm2.