Self-healing by design: universal kinetic model of strength recovery in self-healing ceramics

We propose a new theoretical kinetic model of strength recovery by oxidation-induced self-healing of surface cracks in composites containing a healing agent (HA). The kinetics is a key parameter in the design of structural components that can self-heal the damage done in service. Based on three-dimensional (3D) observations of crack-gap filling, two crack-gap filling models, i.e., a bridging model and a tip-to-mouth filling model, are incorporated in the proposed kinetic model. These crack-gap filling models account for the microstructural features of the fracture surfaces, crack geometry, and oxidation kinetics of the healing-agent. Hence, the minimum and maximum remaining flaw sizes in the healed crack gaps are estimated for various healing temperatures, times, and oxygen partial pressure conditions. Further, the nonlinear elastic fracture mechanics suitable for small-sized remaining flaws, together with a statistical analysis of the original Weibull-type strength distribution, enables the prediction of upper and lower strength limits of the healed composites. Three sintered alumina matrix composites containing silicon carbide (SiC)-type HAs with various volume fractions and shapes, together with monolithic SiC ceramics, are considered. The strength of the healed-composite predicted by our model agrees well with the experimental values. This theoretical approach can be applied to HAs other than SiC and enables the design of self-healing ceramic components for various applications

Rapid Dispersive Micro-Solid Phase Extraction Using Mesoporous Carbon COU-2 in the Analysis of Cloxacillin in Water

Abstract Purpose A new microextraction technique termed COU-2 dispersive micro-solid phase extraction (COU-2-D-μ-SPE) has been developed. The proposed method utilized synthesized mesoporous carbons, COU-2, as sorbent for sample pretreatment in the determination of cloxacillin (CLOX) in water. Methods The optimized conditions involved the use of 100 mg of COU-2 as adsorbent, 50 mL of water sample at pH 2 containing 10 % (w/v) sodium chloride in a sample tube, 1 min of extraction time, methanol as desorption solvent, and 5 min of desorption time. After extraction, COU-2 was collected on a filter and CLOX was desorbed with 300 µL of methanol and dried under a gentle stream of nitrogen. The extract was then reconstituted to 60 µL with distilled water. Results Under the optimized conditions, the method showed excellent detection and quantification limits for CLOX (0.06 and 0.17 µg L −1 , respectively) with good reproducibility (relative standard deviation <8 %) for both intra-and inter-day analyses. The method provided acceptable extraction recoveries for drinking water samples in the range of 89.7-113.6 %. The extraction of blank samples indicated that both samples were free from CLOX contamination. The high recoveries and good precision for CLOX suggest that the COU-2-D-μ-SPE is potentially a good alternative microextraction technique for the monitoring of pharmaceuticals in water samples

Experimental Verification for Numerical Flow Analysis in Mixing Vessel

Visualization of a streak line pattern in a mixing vessel is quite useful for understanding the mixing mechanism and designing an optimal mixing vessel. However, conventional experimental methods for visualizing streak lines require a lot of time to construct impellers and prepare solutions. Although various commercial fluid analysis software has been developed, there are still no examples of its use for calculating streak lines in mixing vessels. A simulation method was developed to quickly evaluate the streak line pattern in a laminar mixing vessel by numerical analysis with commercial code. A commercial CFD code can calculate streak line patterns in a laminar mixing vessel. It was found that a lattice method was more suitable than a particle method for the simulation of the streak line

Dispersive micro-solid phase extraction combined with high-performance liquid chromatography for the determination of three penicillins in milk samples

A simple, rapid, and environmentally friendly microextraction termed COU-2-D-μ-SPE has been developed for the analysis of three penicillins (i.e., oxacillin, cloxacillin, and dicloxacillin) in milk samples. An ordered mesoporous carbon, COU-2, was synthesized and used as the sorbent in dispersive micro-solid phase for the extraction of selected penicillins prior to high-performance liquid chromatography-ultraviolet detection (HPLC-UV). Several important parameters, namely, pH value, salt addition, desorption solvent, extraction time, desorption time, and amount of COU-2, were investigated and optimized. Under the optimum extraction conditions, the method showed good linearity in the range of 10–5,000 μg L−1 (r2 ≥ 0.9994), low limits of detection (2.0–3.3 μg L−1), acceptable reproducibility (relative standard deviation (RSD) 6.2–8.8 %, n = 9), and satisfactory relative recoveries (80.3–99.5 %) for studied penicillins in milk. The proposed COU-2-D-μ-SPE method has been successfully applied to six commercial milk samples, and the extraction of blank samples indicated that all samples were free from selected penicillin contamination

Vinyl-functionalized mesoporous carbon for dispersive micro-solid phase extraction of azole antifungal agents from aqueous matrices

A simple, rapid and sensitive vinyl-functionalized mesoporous carbon-based dispersive micro-solid phase extraction method has been developed for the preconcentration and quantification of azole antifungal drugs in aqueous matrices. The effects of type of adsorbent, desorption solvent, amount of adsorbent, pH, desorption time, salt addition and extraction time were investigated. Under the optimized conditions, the method demonstrated good linearity over the range of 1–300 µg L−1 for water sample and 5–400 µg L−1 for biological samples, low limits of detection (0.4 µg L−1 to 1.6 µg L−1), good analyte recoveries (89.8–113.9%) and acceptable RSDs (7.5–13.4%)