Elimination of irreversible effects during first charging of lithium battery anodes

The irreversible capacity of negative electrode in a lithium-ion cell is a widely described the phenomenon. Irreversible capacity losses are connected with formation of a solid electrolyte interface layer. This layer is growing on the electrode-electrolyte interface during first several charging cycles. The layer is indispensable for proper functioning of a lithium-ion cell. However, during this layer formation, the atoms of lithium are consumed in a range from 18 to 45% of the total amount of lithium atoms presented in cell. Demonstration of possibilities to suppress this phenomenon that occurs on a negative electrode interface is the main aim of this paper.     

The goal specificity effect on strategy use and instructional efficiency during computer-based scientific discovery learning

Using a computer-based scientific discovery learning environment on buoyancy in fluids we investigated the effects of goal specificity (nonspecific goals vs. specific goals) for two goal types (problem solving goals vs. learning goals) on strategy use and instructional efficiency. Our empirical findings close an important research gap, because in earlier studies the goal specificity effect either was restricted to one goal type or goal type was confounded with goal specificity. In addition, there is hardly a study with empirical evidence for the goal specificity effect on strategy use, which counts even more for a cognitive cost-benefit ratio as a dependent variable. Instead, in earlier studies the goal specificity effect has been attributed to differences in strategy use and cognitive cost-benefit ratio in a rather theoretical way. In the present study for strategy use an interaction was found between goal specificity and goal type, indicating that the goal specificity effect occurs only in case of problem solving goals, but not in case of learning goals. Compared to students provided with specific problem solving goals, students who worked on nonspecific problem solving goals, used a control of variables-strategy more frequently. Additionally, we found a main effect of goal specificity on instructional efficiency for both of the goal types, pointing at a more favorable relationship between performance gain and cognitive load caused by nonspecific goals.     

Characterization of glow‐discharge–treated cellulose acetate membrane surfaces for single‐layer enzyme electrode studies

Cellulose acetate membranes (CA) were modified by means of plasma polymerization of ethylene diamine (EDA) and n‐butylamine (n‐BA). The motivation for this work was the application of a modified membrane for the single‐layer enzyme electrode. A tubular reactor with the external radiofrequency (13.56 MHz) excitation was used. Surface modification was performed at 5, 10, and 15 W power (at 27 Pa working pressure) for 5, 10, 15 min. Modified surfaces were characterized in detail by FTIR–ATR, XPS (ESCA), contact angle, and enzyme immobilization activity. The best treatment results were obtained for EDA with 5 W and 30 min and 15 W and 10 min. These results are discussed using surface analysis data. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1341–1352, 2001     

Structure and properties of plasma sprayed BaTiO3 coatings

Plasma spraying enables to create layers with thickness in a millimeter range adhering on various substrates. This paper provides a study of electric and mechanical properties of BaTiO₃ coatings prepared by atmospheric plasma spraying. The spraying was carried out by a direct current gas-stabilized plasma gun. BaTiO₃ was fed into the plasma jet as a feedstock powder prepared by a reactive sintering of micrometer-sized powders of BaCO₃ and TiO₂. Microstructure and phase composition are reported and discussed in connection with electric and mechanical properties. The ability of the used techniques to detect precisely the phase transformation temperatures of BaTiO₃ plasma sprayed coatings is discussed as well. A depth-sensing indentation measurement was done between 290 and 520 K to provide local mechanical characterization. The elastic modulus has shown slightly higher values than that reported typically in papers focused on BaTiO₃ ferroelectric thin films. The average Vickers microhardness is tested to characterize the samples in larger scale. A wear resistance in a slurry environment is reported as well. Dielectric properties are reported for the temperature window of existence of the tetragonal ferroelectric phase. Relative permittivity and loss factor are studied at frequency from 50 Hz to 1 MHz and temperature from 260 to 400 K.     

A new technique to derive particle size distributions and aerosol number concentrations directly from thermophoretic data

The manufacture of many high value-added powders takes place by the decomposition of gaseous precursors in aerosol tube reactors. Historically, process improvements were achieved by making changes on the outside of the reactor and observing what comes out at the end of the pipe. The development of increasingly accurate aerosol dynamics models based on engineering first principles has been limited because models were typically validated on integral properties of ex situ product, instead of particle properties measured at multiple positions inside the reactor. In this study, a model reactor was equipped to capture samples thermophoretically from 15 internal positions. Additional in-line measurements were achieved with a multi-stage inertial impactor and by traditional analysis of ex situ product. Calculations were performed to verify that thermophoresis was the dominant mechanism of particle capture. The thermophoretic samples were analyzed by electron beam microscopy and image analysis to develop particle size distributions at each of the internal positions inside the reactor. An approximation of Talbot's Equation for thermophoretic velocity allowed experimental measurements to be combined with thermophoretic sample data to give predictions of particle number concentration corresponding to the precise sampling locations. The combinations of particle size distributions and number concentrations provide powerful insights on particle nucleation and growth dynamics.     

On the use of peak-force tapping atomic force microscopy for quantification of the local elastic modulus in hardened cement paste

A surface of epoxy-impregnated hardened cement paste was investigated using a novel atomic force microscopy (AFM) imaging mode that allows for the quantitative mapping of the local elastic modulus. The analyzed surface was previously prepared using focussed ion beam milling. The same surface was also characterized by electron microscopy and energy-dispersive X-ray spectroscopy.We demonstrate the capability of this quantitative nanomechanical mapping to provide information on the local distribution of the elastic modulus (from about 1 to about 100 GPa) with a spatial resolution in the range of decananometers, that corresponds to that of low-keV back-scattered electron imaging. Despite some surface roughness which affects the measured nanomechanical properties it is shown that topography, adhesion and Young's modulus can be clearly distinguished.The quantitative mapping of the local elastic modulus is able to discriminate between phases in the cement paste microstructure that cannot be distinguished from the corresponding back-scattered electron images.     

Comparative analysis of microstructure and fracture surfaces of blade roots

Samples of chromium stainless steel were loaded to investigate fatigue crack growth in roots of steam turbine blades. Images of the material microstructure and fracture surfaces were subjected to textural image analysis. The main steps were normalization, enhancement of fiber structures and 2D Fourier transforms. By means of analysis of spectra in the space of periods, characteristic dimensions of both image sets were investigated. The locations of three peaks of spectral functions are very close in both image sets. It may be concluded that the material microstructure is projected onto the morphology of fracture surfaces much more than was expected.     

Complexing agent assisted synthesis of high aspect ratio Fe3 +/Mg2 + layered double hydroxides

A new, facile synthesis for Fe^3 +/Mg^2 + LDHs is developed and investigated. The crucial feature of the synthesis is the usage of a complexing agent (diethylenetriamine, DETA) to increase the solubility of iron phases precipitated intermediately. The influences of different synthesis parameter like DETA concentration, pH value, and temperature are investigated. The optimized synthesis route yields high aspect ratio Fe^3 +/Mg^2 + LDHs which are expected to be interesting filler materials for flame retardant nanocomposites.