Refractory concretes uniaxial compression behaviour under high temperature testing conditions

Two refractory concretes with the same matrix composition, one based on andalusite aggregate and the other on bauxite aggregate, have been studied at temperatures ranging from room temperature to 1200 °C maximal temperature. Samples dried at 110 °C during 24 h to create dried standard specimens and others, fired at different temperatures, were subjected to several uniaxial compression test conditions conducted at various temperatures. The evolution of the materials’ global behaviour from quasi-brittle to viscous was evidenced and correlated to their microstructure evolution. Loading/unloading, creep, and strain rate jump tests helped define the damageable and viscoplastic nature of the behaviour. The influence of the firing temperature and duration on the materials’ behaviour is also reported and discussed. In conclusion, potential constitutive equations that are able to fit the material recorded behaviour are suggested.     

Crystal chemistry of the monazite structure

The AXO₄ monazite-type compounds form an extended family that is described in this review in terms of field of stability versus composition. All the substitution possibilities on the cationic and anionic sites leading to the monazite structure are reported. The phosphate, vanadate, chromate, arseniate, sulphate and silicate families are described and the unit-cell parameters of pure compounds and solid solutions are gathered. The stability limits of the monazite-type structure are discussed versus several models generally correlated with geometric criteria. The effects of physico-chemical parameters such as pressure, temperature and irradiation on the monazite-type structure stability are also discussed. The structural relationships between the monazite structure and the related structures (zircon, anhydrite, barite, AgMnO₄, scheelite and monoclinic BiPO₄, CaSeO₃, rhabdophane and SrNp(PO₄)₂) are described.     

Silver coated aluminium microrods as highly colloidal stable SERS platforms

We report on the fabrication of a novel material with the ability to remain in solution even under the very demanding conditions required for structural and dynamic characterization of biomacromolecule assays. This stability is provided by the increase in surface area of a low density material (aluminium) natively coated with a very hydrophilic surface composed of aluminium oxide (Al(2)O(3)) and metallic silver nanoparticles. Additionally, due to the dense collection of active hot spots on their surface, this material offers higher levels of SERS intensity as compared with the same free and aggregated silver nanoparticles.     

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.     

Inulin mixed esters crosslinked with 2-ethyl-hexyl-acrylate and their promotion as bio-based materials

New inulin-based materials were obtained by graft-copolymerization of inulin (poly-β(1 → 2)-fructoside) with 2-ethyl-hexyl acrylate. Inulin mixed esters were first synthesized by acylation using methacryloyl and palmitoyl chlorides. Further, these esters were copolymerized with 2-ethyl-hexyl acrylate in order to obtain bio-based crosslinked materials that could be used as commodity plastics and that would have biodegradable properties. The obtained products were characterized using FT-IR and ¹H NMR spectroscopies, thermogravimetry; differential scanning calorimetry, and activation energy for the degradation processes (using Kissinger method) was calculated. These biomaterials were also subjected to density measurement, tensile and torsion tests to evaluate their mechanical properties.     

Fullerene-functionalized carbon nanotubes as improved optical limiting devices

We report the synthesis, characterization and optical limiting behavior of a nanohybrid built by grafting C₆₀-fullerenes on carbon nanotubes (CNTs). The nonlinear optical limiting properties of the CNT-C₆₀ complex were investigated at wavelengths where C₆₀ does not absorb. We found that the nanohybrid had superior performances to those of CNTs and fullerenes, either taken individually or as a mixture. This enhanced optical limitation of the nanohybrid suggests not only cooperative but also synergistic effects between the two carbon forms. A mechanism involving higher excitonic states of the CNTs formed by Auger recombination of low energy excitons is proposed.     

Kinetics study on cnt‐supported RuKCo FTS catalyst in a fixed bed reactor

The rate of syngas (H₂/CO) consumption over a RuKCo/CNT Fischer–Tropsch synthesis (FTS) catalyst was measured in a fixed bed microreactor at 210–225°C, 2–3.5 MPa, H₂/CO feed molar ratios of 1–2.5, and gas hourly space velocity (GHSV) range of 2700–3600 h^?1. The data have been used to model the kinetics of the FTS reactions within the range of the studied conditions. One empirical power law model and four semi‐empirical kinetic models based on Langmuir–Hinshelwood‐type equation have been evaluated. The best fitting was obtained with the equation: similar to that proposed by Brötz et al. The estimated activation energy (E = 80–85 kJ/mol) is lower than that is reported in the literature. The validity of these results are restricted to fixed beds with the given catalyst in the tested conversion regime.     

Cover Feature: A Comparative Study of in vitro Assays for Predicting the Nonspecific Binding of PET Imaging Agents in vivo (ChemMedChem 7/2020)

Nonspecific binding (NSB) is a key parameter in optimizing PET imaging tracers. We compared the ability to predict NSB of three available methods: LIMBA, rat f_u,brain, and CHI(IAM). Even though NSB is often associated with lipophilicity, we observed that logD does not correlate with any of these assays, clearly indicating that lipophilicity, while influencing NSB, is insufficient to predict it. A cross-comparison of the methods showed that all three correlate and are useful predictors of NSB. The three assays, however, rank the molecules slightly differently, illustrating the challenge of comparing molecules within a narrow chemical space. We also noted that CHI(IAM) values more effectively predict V_NS, a measure of in vivo NSB in the human brain. CHI(IAM) measurements might be a closer model of the actual physicochemical interaction between PET tracer candidates and cell membranes, and seems to be the method of choice for the optimization of in vivo NSB.     

Using 15N‐Ammonium to Characterise and Map Potassium Binding Sites in Proteins by NMR Spectroscopy

A variety of enzymes are activated by the binding of potassium ions. The potassium binding sites of these enzymes are very specific, but ammonium ions can often replace potassium ions in vitro because of their similar ionic radii. In these cases, ammonium can be used as a proxy for potassium to characterise potassium binding sites in enzymes: the ¹H,¹⁵N spin‐pair of enzyme‐bound ¹⁵NH₄⁺ can be probed by ¹⁵N‐edited heteronuclear NMR experiments. Here, we demonstrate the use of NMR spectroscopy to characterise binding of ammonium ions to two different enzymes: human histone deacetylase 8 (HDAC8), which is activated allosterically by potassium, and the bacterial Hsp70 homologue DnaK, for which potassium is an integral part of the active site. Ammonium activates both enzymes in a similar way to potassium, thus supporting this non‐invasive approach. Furthermore, we present an approach to map the observed binding site onto the structure of HDAC8. Our method for mapping the binding site is general and does not require chemical shift assignment of the enzyme resonances.