Analysis of thin-slab casting by the compact-strip process: Part II. Effect of operating and design parameters on solidification and bulging

The mathematical model to compute the thermal evolution and solidification of thin slabs, previously presented in Part I of this article, was used in combination with a three-dimensional (3-D) finite-element thermomechanical model to analyze how actual operation conditions can lead to excessive deflection and jamming of the slab shell at the pinch rolls. The models suggest that these phenomena arise from a sudden loss of control of the metallurgical length stemming from the coupling of inappropriate steel superheats and casting velocities to deficient heat-extraction conditions at the mold or secondary cooling system. The bulging deformation was calculated with an elastic and creep model that takes into account the temperature distribution across the shell thickness and the different times that shell elements have to creep exposure, i.e., according to the time that rows of elements require to reach their current position in the casting direction at a given casting speed. The last point was simulated by varying the duration of application of the ferrostatic load to the inside surface of each row of elements. The conditions forecast by the models as being responsible for excessive bulging agree very well with those present during the occurrence of these events in the plant. Since bulging after the last containment roll is a major limitation to productivity, this article also presents a parametric evaluation of the casting-speed limits that two compact-strip process (CSP) casters with different supported lengths may have as a function of steel superheat, mold heat-extraction level, water flow rate of the spray and air-mist nozzles, and slab thickness.     

Effect of SnO2 on the photocatalytical properties of TiO2 films

TiO₂/SnO₂ thin films with different tin atomic percentages were successfully prepared on glass substrates by the spray pyrolysis method from an alcoholic solution of TiO[C₅H₇O₂]₂ with different concentrations of SnCl₄. The TiO₂/SnO₂ thin films prepared at 450 °C presented the anatase phase in polycrystalline configuration from %Sn = 0 in the starting solution up to %Sn = 20, at higher tin content the films present an amorphous configuration. The resulting thin films have a homogeneous surface structure with some porosity. The photocatalytical properties of the films were evaluated with the degradation of methylene blue. The products of the degradation reaction were identified by ¹H nuclear magnetic resonance and the film properties were studied by atomic force microscopy, scanning electron microscopy, UV–Vis spectroscopy, and X-ray diffraction.     

Integral sliding mode design for robust filtering and control of linear stochastic time‐delay systems

This paper presents an integral sliding mode technique robustifying the optimal controller for linear stochastic systems with input and observation delays, which is based on integral sliding mode compen‐sation of disturbances. The general principles of the integral sliding mode compensator design are modified to yield the basic control algorithm oriented to time‐delay systems, which is then applied to robustify the optimal controller. As a result, two integral sliding mode control compensators are designed to suppress disturbances in state and observation equations, respectively, from the initial time moment. Moreover, it is shown that if certain matching conditions hold, the designed compensator in the state equation can simultaneously suppress observation disturbances, as well as the designed compensator in the observation equation can simultaneously suppress state disturbances. The obtained robust control algorithm is verified by simulations in the illustrative example, where the compensator in the observation equation provides simultaneous suppression of state and observation disturbances. Copyright © 2005 John Wiley & Sons, Ltd.     

Extrinsic conducting and superconducting polymer systems. III. Electrical properties of PVDF/PS blends containing copper,carbon black,and YBaCuO fillers

In this work, the electrical characterization of three extrinsic polymeric conducting systems was carried out using complex impedance spectroscopy. These systems were obtained by the incorporation of conducting fillers (carbon black and metallic copper), on the one hand, and, on the other hand, by blending with a superconducting ceramic (YBaCuO). The experimental results prove that the electrical characteristics of these systems vary as a function of the nature of the filler added. In the case of metallic copper, the resulting composites posses a conductivity which is intermediate between insulating materials and semiconductors. When carbon black is incorporated in concentration above 10%, the composites may be considered as metalliclike from the point of view of conductivity. Finally, when the filler is YBaCuO, the low conductivity values obtained are indicative of insulating materials regardless of their composition. © 1996 John Wiley & Sons, Inc.     

Extrinsic conducting and superconducting polymer systems. IV. Superconducting properties of YBaCuO composites based on PVDF/PS/carbon black and PVDF/PS/copper polymer systems

In this work, the critical temperature (T_c) of a series of polymeric superconducting systems is determined which, sintered or not, are obtained through the incorporation of the superconducting ceramic YBaCuO into two extrinsic conducting polymer systems: PVDF/PS/carbon black and PVDF/PS/copper. In addition, the diamagnetic characteristics of these systems are studied on the basis of susceptibility measurements as a function of temperature. As regards the unsintered systems and according to the experimental results, copper-based composites can be termed as insulating materials and the samples with the highest carbon black content as reaching metalliclike conductivities. In no case, however, is an abrupt leap in conductivity observed as a function of temperature, indicating the superconducting nature of these systems from an electrical point of view. On the contrary, magnetic susceptibility measurements as a function of temperature detect in all cases a superconducting transition, i.e., a shift in the critical temperature range, bringing it close to that of pure YBaCuO (≈100 K). After sintering, the samples retained their original shape as well as reasonable mechanical properties. The electrical conductivity study confirmed the absence of superconductivity as a consequence of polymer combustion during sintering and thereby implying the disappearance of the orthorhombic phase of YBaCuO, which X-ray evidence proved to be accountable for superconductivity in this ceramic material. © 1996 John Wiley & Sons, Inc.     

Characterization of cathodes for rechargeable lithium batteries based on new vanadium oxides and PEO/PPz polymer blends

Three new vanadium oxides were synthesized and characterized using an X-ray. Once incorporated into different polymer systems containing either poly(ethylene oxide) or a poly(ethylene oxide)–polyphosphazene (PPz), together with carbon black (CB) as an electronic crosslinker, kinetic isothermal and nonisothermal crystallization studies were conducted, as well as an electrical characterization study through complex impedance spectroscopy for the purpose of examining, on the one hand, the effects exerted by the different vanadium compounds on the microstructure of the systems into which they are incorporated, and, on the other hand, of determining which of the synthesized vanadium compounds possesses the best conducting properties. © 1996 John Wiley & Sons, Inc.     

Dynamic mechanical analysis of polypropylene composites based on surface-treated sepiolite

The dynamic mechanical properties in terms of the storage modulus G′, loss modulus G″, and loss tangent δ have been studied for polypropylene-sepiolite composites. The effect of surface treatment on the relaxation spectra has been elucidated, and quantitative values indicating the extent of polymer-filler interaction have been given. Analysis of the results show that the addition of sepiolite leads to an increase in the values of the modulus, a value of the glass transition temperature lower than that of unfilled polypropylene, and displacement towards higher temperatures of the α_c relaxation associated with the crystalline regions. Surface treatment of the sepiolite, by esterification with organic acids of different chain length, does not have a marked effect on the relaxation spectra of the composites, even though the polymer-filler interaction parameter decreases with respect to untreated sepiolite.     

Formulation of ultralow interfacial tension systems using extended surfactants

Inspired by the concept of lipophilic and hydrophilic linkers, extended surfactants have been proposed as highly desirable candidates for the formulation of microemulsions with high solubilization capacity and ultralow interfacial tension (IFT), especially for triglyceride oils. The defining characteristic of an extended surfactant is the presence of one or more intermediate-polarity groups between the hydrophilic head and the hydrophobic tail. Currently only limited information exists on extended surfactants; such knowledge is especially relevant for cleaning and separation applications where the cost of the surfactant and environmental regulations prohibit the use of concentrated surfactant solutions. In this work, we examine surfactant formulations for a wide range of oils using dilute solutions of the extended surfactant classes sodium alkyl polypropyleneoxide sulfate (R-(PO) _x −SO₄Na), and sodium alkyl polypropyleneoxide-polyethyleneoxide sulfate (R-(PO) _y -(EO) _z −SO₄Na). The IFT of these systems was measured as a function of electrolyte and surfactant concentration for polar and nonpolar oils. The results show that these extended surfactant systems have low critical micelle concentrations (CMC) and critical microemulsion concentrations (CμC) compared with other surfactants. We also found that the unique structure of these extended surfactants allows them to achieve ultralow IFT with a wide range of oils, including highly hydrophobic oils (e.g., hexadecane), triolein, and vegetable oils, using only ppm levels of these extended surfactants. It was also found that the introduction of additional PO and EO groups in the extended surfactant yielded lower IFT and lower optimum salinity, both of which are desirable in most formulations. Based on the optimum formulation conditions, it was found that the triolein sample used in these experiments behaved as a very polar oil, and all other vegetable oils displayed very hydrophobic behavior. This unexpected triolein behavior is suspected to be due to uncharacterized impurities in the triolein sample, and will be further evaluated in future research.