Series resistance effects in thin oxide capacitor evaluation

The effects of undesired series resistance in thin oxide capacitors are studied. Thin dielectric reliability is usually evaluated by means of accelerated tests (ramped or constant voltage or current stress). It is shown that the breakdown electric field can be highly overestimated due to the series resistance associated with the test structure: the larger the resistance, the bigger the error. Moreover, breakdown detection criteria in automatic test routines become more critical. It is also demonstrated that a nonuniform stress is applied to the dielectric whenever the series resistance is position-dependent, as it usually is. Erroneous breakdown-related defect distributions could be inferred as a consequence of neglecting the series resistance effect. It is therefore suggested that workers pay much attention to the test structure layout definition in order to minimize these problems     

Methods of isolation and identification of volatile compounds in lipids

Techniques are described for the collection, separation and identification of the volatile compounds produced in lipids by oxidation or irradiation. Methods employed are high vacuum distillation followed by wide range programmed temperature gas chromatography and rapid scanning mass spectrometry. Efficacy of the methods is discussed.     

Basic Evaluation of the Catalytic Pattern of the CuCeO x System in the Wet Oxidation of Phenol with Oxygen

The working mechanism of a ceria-supported Cu (Cu_at:Ce_at = 1:10) system in the Catalytic Wet Oxidation (CWO) of phenol with O₂ (T_R, 130–170 °C; P_O2, 7 atm) has been thoroughly assessed. Basic relationships amongst pH, extent of leaching and rate of phenol and TOC conversion prove the major contribution of a homogeneous catalytic path by Cu ions on the peculiar CWO pattern of supported copper catalyst. In addition, gas-phase reduction/oxidation tests signal the lack of reversibility of the redox cycle of the CuCeO_x system under typical reaction conditions.     

Comparison among structured and packed-bed reactors for the catalytic partial oxidation of CH4 at short contact times

Three types of catalyst support (foams, honeycomb monoliths with square channels and spheres with approximately equal values of specific geometric surface a_v) were examined and compared by simulation with a 1D, dynamic heterogeneous mathematical model for application to the autothermal partial oxidation of methane. Both cold start-up and steady-state behaviours were investigated.

It was found that mass and, particularly, heat transfer properties markedly affect the reactor behaviour, both at start up and at steady state. Thus, the choice of the catalyst support can lead to greatly different reactor performances. Concerning the reactor start-up, simulations revealed that better interphase heat transport properties and lower bed heat capacity are useful to minimize the total start-up time; on the other hand, more favourable transport properties reduce the maximum flow rate which allows to achieve and maintain an ignited steady state. At steady state, oxygen conversion is strictly governed by interphase mass transfer, while methane conversion depends on a more complex, mixed chemical-diffusional regime.     

Surface characterization of Ba-β-alumina

The surface properties of a Ba-β-alumina sample (Ba ∶ Al ratio 1∶ 12) very stable to sintering (15 m²/g after calcination at 1670 K for 10 h) have been investigated by FT-IR spectroscopy of adsorbed probe molecules (water, pyridine and CO₂) and by measuring the isoelectric point. The surface has a medium-strong basic character, justified by the preferential exposition of Ba-O-containing “mirror planes”, parallel to 0001 planes, on the surface of plate-like particles. This behavior has been associated to the resistance to sintering, typical of this material, possibly originated by the difficulty of the very big Ba²⁺ ions to migrate into the spinel-type alumina blocks. This should imply the blocking of the crystal growth along the crystallographicc axis.     

Effect of hydrogen sulphide on the deactivation of alumina-supported ruthenium methanation catalysts

The deactivation of a 0.5% ruthenium-alumina catalyst for the methanation reaction has been studied at 250 and 400 °C in the absence and presence of small concentrations of hydrogen sulphide (H₂S). The adequacy of a suggested mechanistic model for the methanation reaction has been confirmed and the model has been applied to the deactivation in the absence of H₂S, which is significantly improved with respect to an empirical methanation rate equation. The effect of the presence of 10 mg dm^?3 H₂S in the reactant stream on the catalyst deactivation rate has also been investigated.     

Mechanism of the Reduction by Ammonia of Nitrates Stored onto a Pt–Ba/Al2O3 LNT Catalyst

The mechanism involved in the formation of N₂ and of N₂O during the reduction of nitrates stored onto a Pt–Ba/Al₂O₃ LNT catalyst is investigated using labeled NO and unlabeled ammonia, in the presence and in the absence of NO in the gas phase. The reduction of the stored NO _x species (labeled nitrates) with NH₃ leads to the selective formation of N₂. Based on the isotopic distribution, it appears that N₂ formation occurs primarily through the statistical coupling of N-atoms formed by dissociation of NO and NH₃ at metal Pt sites. When the reduction of the stored nitrates is carried out in the presence of NO in the gas phase, NO is preferentially reduced. This implies that the rate determining step of the reduction of nitrates by ammonia is likely associated with the release of stored NO _x . Negligible amounts of nitrous oxide have been observed during the NH₃-TPSR with adsorbed nitrates, whereas relevant quantities of N₂O have been detected at low temperatures (below 180 °C) in the runs performed in the presence of NO in the gas phase. The data converge to indicate that N₂O formation involves the presence of gaseous NO and this suggests that the formation of nitrous oxide occurs either through the coupling of two adsorbed NO molecules or the recombination of an adsorbed NO molecule with an adsorbed NH _x species.     

Ethanol and glycerin processor systems coupled to solid oxide fuel cells (SOFCs). Optimal operation and heat exchangers network synthesis

This paper is aimed at presenting a methodology for the simultaneous synthesis of solid oxide fuel cell (SOFC) based systems and their associated heat exchangers network (HEN). The optimization model is formulated as a mixed integer nonlinear mathematical programming (MINLP) problem. The optimization goal is to maximize the overall net efficiency of the integrated system.     

Higher Alcohol Synthesis

It has been known for many years that it is possible to produce mixtures of methanol and higher alcohols from synthesis gas by alkali promotion of the methanol synthesis catalysts and by appropriate modification of the reaction conditions [l]. From 1927 to 1945 plants were in operation in the United States and Germany, that were dismantled with the coming of different feedstocks and the necessity of obtaining pure alcohols for chemical use. In the last decade the chemical and petroleum industry has shown a renewed and growing interest in the use of mixtures of methanol and higher aliphatic alcohols. The original goal in the late '70s was mainly to reduce oil dependence by producing synthetic components for gasoline blends. More recently the trend to lead phase-down due to environmental protection has focused the attention on the product performances of such alcohol mixtures as high octane blending stock for gasoline. It has been shown that the addition of higher alcohols to methanol increases the water tolerance in respect to phase separation, reduces the fuel volatility and the vapor lock tendency, and also results in higher volumetric heating values.