Mechanism and kinetics of wollastonite fibre dissolution in the aqueous solution of acetic acid

The dissolution of fibrous wollastonite (CaSiO₃) in the aqueous solution of acetic acid (3 mol dm^− 3) was investigated in the temperature interval from 25 to 50 °C using mixed batch-type reactor. An incongruent dissolution of wollastonite proceeds under applied acidic condition. The pH of solvent was increasing during leaching of calcium and its actual value depended on the concentration of Ca²⁺ ions in the solution according to the Henderson buffer equation. That enabled the monitoring of dissolution kinetics via concentration of Ca in the dispersion medium of suspension of wollastonite measurement. The kinetic parameter of the process was evaluated from measured dissolution rates of wollastonite at constant temperature using the empirical Arrhenius equation. The apparent activation energy and pre-exponential factor estimated from the Arrhenius plot are 47 ± 1 kJ mol^− 1 and (1.8 ± 0.9) × 10³ s^− 1. The kinetics analysis of the process indicates that the process is driven by the stationary two-dimensional diffusion (D₂).     

The kinetic analysis of the thermal decomposition of kaolinite by DTG technique

The thermal decomposition of kaolinite was studied by differential thermogravimetry (DTG) technique under non-isothermal conditions. Samples of industrially treated (washed) kaolin with high content of the medium ordered kaolinite were calcined using a heating rate from 1 to 40 K min^− 1. The apparent activation energy and frequency factor for the dehydroxylation of kaolinite was evaluated by Kissinger method as 195 ± 2 kJ × mol^− 1 and (8.58 ± 0.33) × 10¹⁴ s^− 1, respectively. Avrami exponent of the process was estimated using Kissinger empirical kinetic models and Carne equation.     

The influence of the local current density on the electrochemical exfoliation of graphite in lithium-ion battery negative electrodes

The local current density related to the exfoliation process of graphite negative electrodes in mixed ethylene carbonate/propylene carbonate electrolytes was controlled by a variation of the current applied to lithium half-cells containing either single type graphite electrodes or electrodes consisting of mixtures of an exfoliating and a non-exfoliating graphite. The partial local current density attributed to graphite passivation and its distribution within the volume of the electrode was found to be a key parameter to explain differences in the exfoliation behaviour observed for graphite electrodes. The local current density is related with a local overpotential which may suppress one of several possible electrochemical processes. In a negative electrode consisting of a mixture of a non-exfoliating and an exfoliating graphite component, the exfoliation of the exfoliation-sensitive graphite component can be completely suppressed when increasing the partial local current density attributed to the graphite exfoliation process above a certain threshold, by either decreasing the amount of exfoliating graphite particles in the electrode or by increasing the total current density, i.e., the specific current. The consideration of the local current density distribution for the electrochemical processes throughout the electrode leads to a more general concept for the graphite passivation behaviour during the first lithium insertion in lithium-ion batteries.     

Mixed bi-material electrodes based on LiMn2O4 and activated carbon for hybrid electrochemical energy storage devices

The performance of mixed bi-material electrodes composed of the battery material, LiMn₂O₄, and the electrochemical capacitor material, activated carbon, for hybrid electrochemical energy storage devices is investigated by galvanostatic charge/discharge and pulsed discharge experiments. Both, a high and a low conductivity lithium-containing electrolyte are used. The specific charge of the bi-material electrode is the linear combination of the specific charges of LiMn₂O₄ and activated carbon according to the electrode composition at low discharge rates. Thus, the specific charge of the bi-material electrode falls between the specific charge of the activated carbon electrode and the LiMn₂O₄ battery electrode. The bi-material electrodes have better rate capability than the LiMn₂O₄ battery electrode. For high current pulsed applications the bi-material electrodes typically outperform both the battery and the capacitor electrode.     

Electrochemical and spectroscopic characterization of lithium titanate spinel Li4Ti5O12

Herein we describe electrochemical and spectroscopic properties of lithium titanate spinel as well as an easy method based on colorimetry to determine the lithium content of electrodes containing lithium titanate spinel as active material. Raman microspectrometry measurements have been performed to follow lithium insertion into and extraction from the active material, respectively. The Raman signals display a pronounced fading of intensity already at low levels of lithium intercalation and disappear at a SOC higher than ∼10%. However, the colorimetric method can be used up to a SOC of 50%.     

Ferroceneboronic acid for the electrochemical probing of interactions involving sugars

Ferroceneboronic acid (FcBA) was used as a redox-active probe suitable for monitoring of diol–boronate interactions. Voltammetric and amperometric measurements allowed to detect FcBA forms – free and bound in the boronate complex. In this way, the complexation interaction was studied for a set of saccharide molecules as model diols and the corresponding affinity equilibrium constants were determined. A shift of the peak potential on voltammograms accompanying formation of the boronate complex with FcBA was proposed as a probe for electrochemical characterization of surface-confined diol-containing structures. The model experiments were carried out using sorbitol- and 1,6-hexandiol-modified polyepichlorhydrin conjugates deposited on the electrodes; the former compound was able to form the boronate complex while no change of the peak potential for the latter conjugate was observed. This approach seems promising for artificial bioelectronic affinity receptors and technology of reagentless biosensors where the binding interaction directly stimulates a measurable electrochemical event.     

Morphology and mechanical properties of polypropylene/organoclay nanocomposites

Polypropylene (PP) nanocomposites were prepared by melt intercalation in an intermeshing corotating twin‐screw extruder. The effect of molecular weight of PP‐MA (maleic anhydride‐ modified polypropylene) on clay dispersion and mechanical properties of nanocomposites was investigated. After injection molding, the tensile properties and impact strength were measured. The best overall mechanical properties were found for composites containing PP‐MA having the highest molecular weight. The basal spacing of clay in the composites was measured by X‐ray diffraction (XRD). Nanoscale morphology of the samples was observed by transmission electron microscopy (TEM). The crystallization kinetics was measured by differential scanning calorimetry (DSC) and optical microscopy at a fixed crystallization temperature. Increasing the clay content in PP‐ MA330k/clay, a well‐dispersed two‐component system, caused the impact strength to decrease while the crystallization kinetics and the spherulite size remained almost the same. On the other hand, PP/PP‐MA330k/clay, an intercalated three‐component system containing some dispersed clay as well as the clay tactoids, showed a much smaller size of spherulites and a slight increase in impact strength with increasing the clay content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1562–1570, 2002     

A novel method for biopolymer surface nanostructuring by platinum deposition and subsequent thermal annealing

A novel procedure for biopolymer surface nanostructuring with defined surface roughness and pattern dimension is presented. The surface properties of sputtered platinum layers on the biocompatible polymer poly(l-lactic acid) (PLLA) are presented. The influence of thermal treatment on surface morphology and electrical resistance and Pt distribution in ca. 100 nm of altered surface is described. The thickness, roughness and morphology of Pt structures were determined by atomic force microscopy. Surface sheet resistance was studied by a two-point technique. It was the sequence of Pt layer sputtering followed by thermal treatment that dramatically changed the structure of the PLLA’s surface. Depending on the Pt thickness, the ripple-like and worm-like patterns appeared on the surface for thinner and thicker Pt layers, respectively. Electrokinetic analysis confirmed the Pt coverage of PLLA and the slightly different behaviour of non-annealed and annealed surfaces. The amount and distribution of platinum on the PLLA is significantly altered by thermal annealing.