Effect of structural and acidity/basicity changes of CuO–CeO2 catalysts on their activity for water–gas shift reaction

The objective of this work was to investigate the influence of CuO loading and catalyst pretreatment procedure to derive an optimal CuO–CeO₂ catalyst for the water–gas shift reaction (WGS), and to study in detail structure– and surface acidity–activity relationships. Catalyst samples prepared by coprecipitation and a 10, 15 and 20 mol% CuO content were examined by XRD, BET and TPR/TPD analyses and subjected to pulse WGS activity tests in the temperature range of 180–400 °C. Strong structure–activity dependence in the WGS reaction was observed for all catalyst samples. It was established that increasing CuO content has a positive effect on H₂ production during the WGS reaction, due to favored CeO₂ reduction. Increasing calcination temperature on the other hand reduces the BET surface area, induced by CuO sintering and agglomeration of CeO₂ particles, resulting in a negative effect on H₂ production. Distinctive WGS activity dependence on surface acidity was observed and investigated.     

Hydrogen production from raw bioethanol over Rh/MgAl2O4 catalyst: Impact of impurities: Heavy alcohol, aldehyde, ester, acid and amine

The effect of various impurities added in a pure ethanol + water mixture was studied. The impurities chosen were acetic acid, diethylamine, butanol, butanal, ethyl acetate and diethylether. It was shown that the addition of diethylamine or butanal increases the ethanol conversion, compared to that obtained with a pure ethanol + water mixture, without changing the product selectivity. In the presence of the other impurities, butanol, ethylether and ethyl acetate, a strong deactivation of the catalyst with a decreased ethanol conversion was observed. Moreover, the selectivity in hydrogen was also strongly decreased, whereas an increase in intermediate products especially ethylene was observed. The deactivation was explained in terms of coke deposition at the catalyst surface. The poisoning effect induced by the presence of impurities can be classified in the following increasing order: diethylamine  butanal < no impurity < acetic acid < butanol < diethylether  ethyl acetate.     

OPTODYNAMIC DEFORMATION OF A METAL PLATE ILLUMINATED BY A GAUSSIAN LASER PULSE

An analytical model is presented that describes the bending process following the absorption of a Gaussian laser pulse by the surface of a moderately thick metal plate. The model is based on the constitutive equations of thermoelastoplasticity and therefore fundamentally describes this optodynamic process. Assuming relatively short laser pulses, Green's function is used as an approximation for the real plate temperature. The plate is assumed to be made of elastic, linearly hardening material.     

A Self-Mixing NMOS Channel-Detector Optimized for mm-Wave and THZ Signals

A self-mixing terahertz signal detector combined with a low noise amplifier and a properly balanced - folded dipole or slot antenna for concentrating millimeter wave signals to NMOS detectors is described. The detector was optimized to 300 GHz signals. The noise equivalent power (NEP) was estimated to 320 pW/√Hz while the total output referred noise of 2.1 μV/(Hz)^1/2 was measured at amplifier gain of 46 dB. This was achieved by using NMOS mixer devices optimized for resistive mixing that operate in a linear region of operation where the channel voltage is set close to zero by means of regulating the virtual ground level. The NMOS device, which is positioned at the antenna connections, has a minimum channel length that permits a far more precise calculation of the coupling devices. A position like termination of the two symmetrical detector devices was distributed between an antenna area and the amplification stage. The detectors were fully integrated using the 250 nm CMOS technology. Good matching was found between mathematically analyzed and simulated noise performances and prototypes measurements, where comparable measurements were performed on a THz array which consists of four pixels with folded dipole antennas or those with slot type antennas.     

Molecular Auxetic Behavior of Epitaxial Co‐Ferrite Spinel Thin Film

In functional oxide materials so‐called molecular auxetic behavior is extremely rare. Here, it is reported in the CoFe₂O₄ spinel structure. A CoFe₂O₄ epitaxial thin film under compressive axial strain also reduces its cell dimensions in the transverse direction with a Poisson's ratio of ?0.85. A hinge‐like honeycomb network in the spinel structure is identified as being responsible for the negative Poisson's ratio. This phenomenon has a substantial effect on the functional properties of CoFe₂O₄ and enables the construction of a new class of nano‐devices.     

Subsolidus phase equilibria in the CaO-poor part of the RuO2-CaO-SiO2 system

During firing the conductive phase based on CaRuO₃ in lead-free thick-film resistors decomposes, presumably due to interactions with the silica-rich glass phase. Subsolidus equilibria in the CaO-poor part of the RuO₂-CaO-SiO₂ diagram were studied with the aim of investigating possible interactions between the conductive phase and silica-rich glasses in thick-film resistors. The tie lines are between CaRuO₃ and CaSiO₃, and between RuO₂ and CaSiO₃. This indicates that the calcium ruthenate is not stable in the presence of the silica-rich glass phase.     

Investigation on electrical and microstructural properties of Thick Film Lead-Free resistor series under various firing conditions

The paper presents investigation of four lead free thick film resistor pastes, developed at ITME, denoted R-100, R-1k, R-10k and R-100k with sheet resistivities of 0.1, 1, 10 and 100 kΩ/□, respectively. The resistors were based on RuO₂ as the conductive phase. The aim of the work was to evaluate the influence of firing conditions of the resistive pastes on a sintering process. The pastes were screen printed onto alumina substrate with prefired AgPd lead-free terminations. They were fired at several temperatures from 750 to 950 °C for 10 min at peak temperature, as well as fired at the highest temperature for 6 h, in order to bring the sintering process into the equilibrium. The properties of the resistors, i.e , sheet resistivity and temperature coefficient of resistance (TCR), microstructure changes, glass crystallization upon firing, etc., were examined. Dried and fired resistor samples were evaluated by X-Ray diffraction analysis and by the scanning electron microscopy. The RuO₂ conductive phase maintained the same crystal structure regardless of the firing conditions. No devitrification was observed in lead-free resistors glasses. The lattice constants of RuO₂ were uniform after firing at temperatures over 800 °C. The resistors matched the desired resistivity and the TCR was the least temperature dependent at the firing temperatures around 850 °C.     

An investigation of thick PZT films for sensor applications: A case study with different electrode materials

Lead zirconate titanate (PZT) is a piezoelectric material that can sense or respond to mechanical deformations and can be used in ceramic micro-electro-mechanical systems (C-MEMS). A thick-film paste was prepared from a pre-reacted PZT powder (PbZr_0.53Ti_0.47O₃) and thick-film technology (screen-printing and firing) was used to deposit the PZT layers on LTCC tapes and on alumina substrates. The microstructural, electrical and piezoelectric characteristics of the thick PZT films on relatively inert alumina substrates and on LTCC tapes were studied. Preliminary experiments indicated that due to the interaction between the printed PZT layers and the LTCC substrates during firing the electrical characteristics deteriorate significantly. To minimise the influence of substrate-film interactions different electrode materials and the use of additional intermediate layers as a barrier were evaluated. The dielectric permittivities, dielectric losses, and piezoelectric coefficients (d ₃₃) were measured. The dielectric permittivities of the thick films fired on LTCC substrates were lower (210 with gold electrodes and 430 with silver electrodes) than those measured on alumina substrates (500). The piezoelectric coefficients d₃₃ were measured with a Berlincourt piezometer. The d ₃₃ values measured on the LTCC substrates were relatively low (60–80 pC/N) compared with the values obtained for the alumina substrates (around 140 pC/N). The lower dielectric constants and piezoelectric coefficients d ₃₃ of the films on LTCC substrates are attributed to the formation of phases with a lower permittivity. This was a result of the diffusion of SiO₂ from the LTCC into the active PZT layer. The diffusion of silica was confirmed by the SEM and EDS analyses.     

Video-based learners’ observed attention estimates for lecture learning gain evaluation

Multimedia Tools and Applications - A significant problem in the field of higher education is maintaining learners’ attention during lectures, which is known to significantly affect their...