Effect of polymorphic phase transformations in Al2O3 film on oxidation kinetics of aluminum powders

Thermogravimetry was used to study the oxidation of aluminum powders at elevated temperatures. Aluminum powders of various particle sizes and surface morphologies were heated in oxygen up to 1500 °C at different heating rates. Partially oxidized samples were recovered from selected intermediate temperatures and the oxide phases present were analyzed by X-ray diffraction. The experimental data were related to current information on stabilities and phase changes of Al₂O₃ polymorphs. Aluminum powders were observed to oxidize in four distinct stages in the temperature range from 300 to 1500 °C. During stage I, from 300 to about 550 °C, the thickness of the natural amorphous alumina layer on the particle surface increases. The rate of this process is controlled by the outward diffusion of Al cations. At about 550 °C, when the oxide layer thickness exceeds the critical thickness of amorphous alumina of about 4 nm, the oxide transforms into γ-Al₂O₃. The specific volume of γ-Al₂O₃ is less than that of amorphous alumina; therefore, the newly formed γ-Al₂O₃ only partially covers the aluminum surface. The oxidation rate increases rapidly at the onset of stage II, but it decreases when the γ-Al₂O₃ layer becomes continuous. During stage III oxidation, the γ-Al₂O₃ layer grows and partially transforms into the structurally similar θ-Al₂O₃ polymorph. Finally, oxidation stage IV is observed after the transition to stable -Al₂O₃ results in an abrupt reduction of oxidation rate. Qualitative analysis of the rates of oxidation at the different stages enables one to understand the wide range of aluminum ignition temperatures observed for particles of different sizes.     

Discrete time neural network synthesis using input and outputactivation functions

A new very fast algorithm for synthesis of a new structure of discrete-time neural networks (NN) is proposed. For this purpose the following concepts are employed: (i) combination of input and output activation functions, (ii) input time-varying signal distribution, (iii) time-discrete domain synthesis and (iv) one-step learning iteration approach. The problem of input-output mappings of time-varying vectors is solved. Simulation results based on the synthesis of a new structure of feedforward NN of an universal logical unit are presented. The proposed NN synthesis procedure is useful for applications to identification and control of nonlinear, very fast, dynamical systems. In this sense a feedforward NN for an adaptive nonlinear robot control is designed. Finally, a new algorithm for the direct inverse modeling of input/output nonquadratic systems is discussed.     

An application of limited branching in clustering

The technique of limited branching is used to answer an open problem of P. Brucker (1977) arising in a study of computational complexity of clustering problems. This problem is shown to be solvable by a polynomial algorithm.     

Order of complexity of rlc networks containing a reactive gyrator

Using a particular expansion of the network determinant, a simple formula is derived giving the total number of natural frequencies of a passive RLC network containing a reactive gyrator. The order of complexity is expressed in terms of the degrees of the polynomials in the gyration impedance and the alteration in the network topology due to gyrator embedding. Quantitative conditions for the order of complexity of the active network exceeding that of the network without the gyrator are obtained. Formulas are also derived for the number of zero and non-zero natural frequencies.     

Dynamic and Formal Verification of Embedded Systems: A Comparative Survey

Embedded Systems, by their nature, constitute a meeting point for communities with extremely different background. In particular, the high demands for quality and reliability for embedded systems have led to complementary quality assurance efforts: hardware engineers have developed techniques for dynamic verification in terms of co-simulation, which, in particular, addresses the different nature of hardware and software components. Thus these techniques are tailored for the transactional level, which comprises dedicated models for the hardware and the software parts. On the other hand, there is a bulk of work on formal verification techniques, which typically address higher levels of abstraction. These techniques are exhaustive in the sense that they cover all the infinite possible paths of their models, however at the price of neglecting many of the low-level aspects treated by co-simulation. It is the goal of this paper to increase the mutual understanding between these communities and to animate research at this exciting borderline.     

Improving bulk FinFET DC performance in comparison to SOI FinFET

The implementation of FinFET structure in bulk silicon wafers is very attractive due to low-cost technology and compatibility with standard bulk CMOS in comparison with silicon-on-insulator (SOI) FinFET. SOI and bulk FinFET were analyzed by a three-dimensional numerical device simulator. We have shown that bulk FinFET with source/drain-to-body (S/D) junctions shallower than gate-bottom has equal or better subthreshold performance than SOI FinFET. By reducing S/D junction depth, fin width scaling for suppression of short-channel-effects (SCEs) can be relaxed. On-state performance has also been examined and drain current difference between the SOI and bulk FinFET at higher body doping levels has been explained by investigating enhanced conduction in silicon-oxide interface corners. By keeping the body doping low and junctions shallower than the gate-bottom, bulk FinFET characteristics can be improved with no increase in process complexity and cost.     

Crystalline Intermediate Phases in the Sol–Gel-Based Synthesis of La2NiO4+δ

X-ray diffraction and transmission electron microscopy were applied to investigate a sol–gel synthetic process for the mixed oxygen ion and electron conductor La₂NiO_4+δ with a K₂NiF₄ structure type. The development of the La₂NiO_4+δ is elucidated considering the influence of calcination temperatures and dwell times. Following the thermal decomposition of nitrate and organic precursors in an intermediate step, the lanthanum nickel oxide is obtained after a short dwell time above 750°C. This occurs by the transformation of an ultrafinely dispersed powder consisting of lanthanum oxycarbonate, lanthanum oxide, and nickel oxide. The pure La₂NiO_4+δ phase was obtained by similar solid-state reactions between nanocrystalline powder particles at just 950°C.     

Vacuum thermal treated electroless NiP-TiO2 composite coatings

Composite NiP-TiO₂ layers were prepared by simultaneous electroless deposition of Ni-P and TiO₂ on steel substrate, from a solution in which TiO₂ particles were kept in suspension by stirring. Deposits were characterized for its structure, morphology and hardness. It was found that the chemical composition of Ni-P matrix has been influenced by the incorporation of TiO₂ particles. TiO₂ particle incorporation increases with increase in their bath concentrations (0.5-2.0 g/l). An improvement (up to 20%) in microhardness was observed in both as plated and vacuum heat-treated composite coatings compared to Ni-P coatings. Electroless deposited composite coatings exhibit an amorphous structure of the nickel matrix in which crystalline titanium oxide is incorporated. Vacuum heat treatment leads to the formation of a crystalline layer in which the Ni and Ni₃P crystallites appear apart from those of the TiO₂ (anatase). Potentiodynamic polarization measurements made on these deposits in 3.5 wt.% sodium chloride solution showed decrease in the corrosion resistance for the as-plated and heat-treated composite coatings.     

Analysis of TBA‐Based ETBE Production by Means of an Optimization‐Based Process‐Synthesis Approach

The current article presents the extension of a recently developed optimization‐based approach to process synthesis for process intensification. It generates phenomena‐based flowsheet options using superstructure optimization and provides a dedicated translation into equipment‐based flowsheets. The considered case‐study illustrates the application of the method for the analysis of ethyl tert‐butyl ether production, based on the conversion of tert‐butyl alcohol, under consideration of variable configurations of a rector network and a newly introduced pervaporation‐based membrane‐reactor block.