Evaluation of dynamic modulus measurement for C/C-SiC composites at different temperatures

The determination of elastic properties at application temperature is fundamental for the design of fibre reinforced ceramic composite components. An attractive method to characterize the flexural modulus at room and high temperature under specific atmosphere is the nondestructive Resonant Frequency Damping Analysis (RFDA). The objective of this paper was to evaluate and validate the modulus measurement via RFDA for orthotropic C/C-SiC composites at the application temperature. At room temperature flexural moduli of C/C-SiC with 0/90° reinforcement were measured under quasi-static 4-point bending loads and compared with dynamic moduli measured via RFDA longitudinally to fibre direction. The dynamic modulus of C/C-SiC was then measured via RFDA up to 1250°C under flowing inert gas and showed an increase with temperature which fitted with literature values. The measured fundamental frequencies were finally compared to those resulting from numerical modal analyses. Dynamic and quasi-static flexural moduli are comparable and the numerical analyses proved that bending modes are correctly modeled by means of dynamic modulus measured via RFDA. The nondestructive RFDA as well as the numerical modeling approach are suitable for evaluation of C/C-SiC and may be transferred to other fibre reinforced ceramic composite materials.     

Acid Value,Polar Compounds and Polymers as Determinants of the Efficient Conversion of Waste Frying Oils to Biodiesel

The cost of starting materials for the production of biodiesel is typically 75 % of the final retail price. Oils previously used for frying, waste frying oils (WFO), are a very suitable resource. Repetitive use of oil for frying foods involves high temperature, moisture and aeration for extended periods. The most important deterioration processes triggered by these conditions are hydrolysis and oxidation. In this study, 24 WFO samples of different origins were analyzed and classified as potential starting materials for biodiesel production using three quality parameters representing the main factors that affect the conversion of WFO. These parameters were: acid value, content of polar compounds and content of polymers, which varied in the ranges from 0.2 to 7.6, 14.9 to 43.2 and 0.9 to 15.2 %, respectively. Ester content obtained using conventional transesterification (TE) for WFO conversion decreased with increased levels of WFO deterioration determined by any of the three parameters noted above. TE products obtained had ester content between 81.4 and 95.7 %. Total ester content of a WFO sample with relatively low %AV could be increased to 96.5 % using a two-stage base catalysis TE. Finally, conversion of WFO samples resulted in ester contents of 89.0 and 91.3 %, respectively, when transesterified by conventional TE. After blending up to 10 % with refined oil, the ester content achieved was near 96.5 %. Thus, the blending represents an alternative for obtaining a product with suitable ester content.     

Optimization of post-combustion CO2 process using DEA-MDEA mixtures

This paper presents optimal operating conditions for the post-combustion CO₂ capture process utilizing aqueous amine solutions obtained using a process simulator (HYSYS). Three alkanolamine solutions (Methyldiethanolamine MDEA, DiEthanolAmine DEA and MDEA-DEA mixture) are considered to study the performance of the capture process.The design problem addressed in this paper requires specifying the optimal operating conditions (inlet and outlet temperature of the lean solution stream on the absorber, CO₂ loading, amine composition and flow rates, among others) to achieve the given CO₂ emission targets at a minimum total annual cost. A detailed objective function including total operating costs and investment is considered.The influence of the variation of CO₂ reduction targets and the mixing proportion of amines on the total annual cost is analyzed in detail. Numerical results are presented and discussed using different case studies.The results demonstrate that process simulators can be used as a powerful tool not only to simulate but also to optimize the most important design parameters of the post-combustion CO₂ capture process.     

Effects of the nature of the doping salt and of the thermal pre-treatment and sintering temperature on Spark Plasma Sintering of transparent alumina

A slurry of α-Al₂O₃ was doped with Mg, Zr and La nitrates or chlorides, in various amounts in the range 150-500 wt ppm and then freeze-dried to produce nanosized doped powder (∼150 nm). The powder was sintered by SPS to yield transparent polycrystalline alpha alumina. The influence of the nature of the doping element and the starting salt, the thermal treatment before sintering and the sintering temperature on the transparency of the ceramics were investigated. The transparency of the ceramics of nanosized Al₂O₃ was shown to depend mainly on the way the powder was prepared, the nature of the doping salt also had an effect. Finally, a high real inline transmittance, reaching 48.1% was achieved after optimization.     

Inhibition of polyphenoloxidase from apple by Maillard reaction products prepared from glucose or fructose with l-cysteine under various conditions of pH and temperature

The effects of Maillard reaction products (MRPs), synthesized from equimolar glucose or fructose with l-cysteine (1 mol l⁻¹) aqueous model mixtures, by modulating pH and temperature of heating, according to a two-factor and five-level experimental design, were investigated on polyphenoloxidase (PPO) activity from apple. Final pH and absorbance measurements at 350 nm were also selected as indicators of the Maillard reaction development and checked. In general, inhibitory potency (IP) of the mixtures increased with the increase in temperature (80-120°C) and the decrease in pH (pH 2.0-12.0) of the reaction medium. A linear relationship between the IP and heating time (0-48 h) or Abs.350 nm (0-70 AU) was demonstrated for glucose/cysteine system heated from 80°C to 120°C. Polarographic and spectrophotometric data were used to calculate kinetic constants and activation energy (Ea) values of inhibitory MRPs formation versus PPO activity and of those compounds absorbing at 350 nm. Ea values for these reactions were close, being 191 and 124 kJ mol⁻¹, respectively. The experimental design allowed to conclude that linear effects of both factors as well as a quadratic effect of pH were significant, leading to optimum conditions for the production of glucose-derived MRPs inhibitors. In most cases, glucose produced MRPs with higher IP compared to counterpart fructose-cysteine MRPs.     

Potential influence of microorganisms on the corrosion of carbon steel in the French high- and intermediate-level long-lived radioactive waste disposal context

In the context of the high-level radioactive waste disposal CIGEO, the corrosion rate due to microbially influenced corrosion (MIC) has to be evaluated. In France, it is envisaged to dispose of high- and intermediate-level long-lived radioactive waste at a depth of 500 m in a deep geological disposal, drilled in the Callovo-Oxfordian claystone (Cox) formation. To do so, a carbon steel casing will be inserted inside disposal cells, which are horizontal tunnels drilled in the Cox. A specific cement grout will be injected between the carbon steel casing and the claystone. A study was conducted to evaluate the possibility of MIC on carbon steel in the foreseeable high radioactive waste disposal. The corrosiveness of various environments was investigated at 50°C and 80°C with or without microorganisms enriched from samples of Andra's underground research laboratory. The monitoring of corrosion during the experiments was ensured using gravimetric method and real-time corrosion monitoring using sensors based on the measurements of the electrical resistance. The corrosion data were completed with microbiological analyses including cultural and molecular characterizations.     

The Multifunctional Sactipeptide Ruminococcin C1 Displays Potent Antibacterial Activity In Vivo as Well as Other Beneficial Properties for Human Health

The world is on the verge of a major antibiotic crisis as the emergence of resistant bacteria is increasing, and very few novel molecules have been discovered since the 1960s. In this context, scientists have been exploring alternatives to conventional antibiotics, such as ribosomally synthesized and post-translationally modified peptides (RiPPs). Interestingly, the highly potent in vitro antibacterial activity and safety of ruminococcin C1, a recently discovered RiPP belonging to the sactipeptide subclass, has been demonstrated. The present results show that ruminococcin C1 is efficient at curing infection and at protecting challenged mice from Clostridium perfringens with a lower dose than the conventional antibiotic vancomycin. Moreover, antimicrobial peptide (AMP) is also effective against this pathogen in the complex microbial community of the gut environment, with a selective impact on a few bacterial genera, while maintaining a global homeostasis of the microbiome. In addition, ruminococcin C1 exhibits other biological activities that could be beneficial for human health, as well as other fields of applications. Overall, this study, by using an in vivo infection approach, confirms the antimicrobial clinical potential and highlights the multiple functional properties of ruminococcin C1, thus extending its therapeutic interest.     

Influence of chemical composition on mechanical properties of spark plasma sintered boron carbide monoliths

Fully dense boron carbide monoliths exhibiting fine microstructure (i.e., submicrometric grain size) are sintered by Spark Plasma Sintering. Two different commercial powder batches, exhibiting different stoichiometries (i.e., B/C ratio and oxygen content) and various amounts of secondary phases (i.e., boric acid and free carbon), are used. Their chemical composition is well‐defined by coupling different methods (Transmission Electron Microscopy associated with XRD analyses, and Instrumental Gas Analysis), and are correlated with their mechanical properties, characterized from meso‐ to macro‐scopic scales by nano‐indentation and ultrasonic pulse echography. The presence of secondary phases (graphite and boric acid) is evidenced in various proportions in each powder batch. If the boric acid disappears during sintering, the graphite remains. However, for the considered amounts of graphite (lower than 1 wt%), the low variations in graphite content have no significant effect on hardness and elasticity values. At the opposite, the presence of oxygen in boron carbide lattice, leading to a boron oxycarbide phase, induces a decrease in both hardness and elasticity properties.