Study on the Carbonation Behavior of Cement Mortar by Electrochemical Impedance Spectroscopy

A new electrochemical model has been carefully established to explain the carbonation behavior of cement mortar, and the model has been validated by the experimental results. In fact, it is shown by this study that the electrochemical impedance behavior of mortars varies in the process of carbonation. With the cement/sand ratio reduced, the carbonation rate reveals more remarkable. The carbonation process can be quantitatively accessed by a parameter, which can be obtained by means of the electrochemical impedance spectroscopy (EIS)-based electrochemical model. It has been found that the parameter is a function of carbonation depth and of carbonation time. Thereby, prediction of carbonation depth can be achieved

Moving boundary simulation of airflow and micro-particle deposition in the human extra-thoracic airway under steady inspiration. Part I: Airflow

Airflow into the lung is the result of negative alveolar pressure caused by the simultaneous action of diaphragm contraction and rib cage expansion. However, all of the determinate CFD simulations on airflow and particle deposition in the human upper respiratory tract to date have employed a fixed boundary condition, i.e. uniform or axial symmetrical velocity profiles at the mouth inlet and outlet/opening boundary at the end of the airway. In this study, the realistic breathing mechanism, i.e. expansion of the pleural cavity, is mimicked by the fluid-structure interaction employing a junction box routine to assign the motion of the moving wall boundary at the bottom of the extra-thoracic airway model with an extra bell-mouthed tube. The airflow and particle deposition are investigated, particularly for the movable boundary cases, and compared with the fixed cases. In Part I, the flow characteristics which are important factors for particle deposition, i.e. pressure drop, turbulence intensity, secondary intensity and velocity profiles, are illustrated at three flow rates, as well as the detailed recirculation flow in the trachea region. Compared with the fixed boundary cases, several notable differences are found: (i) the velocity profiles at the mouth inlet are not uniform or axially symmetric, but askew with highspeed flow shifted to the upper wall of the mouth inlet tube, and a more evident recirculation zone occurs near the lower wall of the inlet tube; (ii) the pressure drop and turbulence intensity are lower and the secondary intensity is higher than that in the fixed boundary case because of the askew profile in the mouth cavity and modified recirculation flow in the trachea region; ( iii) at three flow rates, the secondary intensities exhibit identical characteristics before the larynx where the turbulence fluctuations are very weak, but discrepancies are evident in the trachea region because of the high level of turbulence intensity and different pattern of recirculation zones; (iv) the length of the recirculation zones increase at three flow rates and the minor separation and reattachment occur in the middle portion of the recirculation flow, while the recirculation flow layer is divided into two parts at higher flow rates; (v) the peaks of the secondary flow intensity in the trachea region are located near the flow separation and reattachment points (both the major and minor) and the peaks of turbulence intensity in the trachea seem to correspond to the major separation and reattachment region.</p

Facile Hydrogels of AIEgens Applied as Reusable Sensors for In Situ and Early Warning of Metallic Corrosion

Early detection of metallic corrosion is one considerable method to reduce imperceptible disasters nowadays. Fluorescent coatings with high sensitivity and long lifetimes for use in the early detection of metallic corrosion are in high demand, but they are presently difficult to prepare. Inspired by the chameleon’s skin, which is capable of switching its color in different atmospheres sensitively and reversibly, we proposed herein a facile and universal all-in-one strategy of combining the fluorescent sensitivity and dynamic hydrogen bonds in a hydrogel to develop a reusable corrosion detection tape to cover metal surfaces. The fluorescent hydrogel tape was constructed using free radical copolymerization of monomers [hydroxyethyl methylacrylate (HEMA) and tetraphenylethene derivatives (TPEPy)]. Due to the aggregation-induced emission (AIE) behavior of TPEPy, the poly(HEMA-co-TPEPy) hydrogel is capable of monitoring the traces of corrosion via the release of ferric ions with a concentration as low as 10–5 M. Moreover, due to the dynamic hydrogen bonds of hydroxyethyl groups in hydrogel networks, the fluorescent hydrogel tape exhibited good adhesion and well reusability for over 10 applications to effectively warn against early corrosion of stainless steel. This non-destructive and reversible method of early corrosion detection can provide valuable signals when maintenance is needed before the metal suffers serious damage