Catalytic effect of potassium carbonate on carbothermic production of hexagonal boron nitride

Effect of potassium carbonate addition on the carbothermic formation of hexagonal boron nitride (hBN) was investigated by keeping the K₂CO₃ added B₂O₃+C mixtures in nitrogen atmosphere at 1400 °C for 40–160 min. K₂CO₃ amount was varied in the range of 10–60 wt% of the B₂O₃+C mixture. Products were subjected to XRD and quantitative analyses, SEM and TEM observations, and particle size measurement. Amount of hBN increased considerably with K₂CO₃ addition; also particle size and crystallinity improved. Catalytic role of K₂CO₃ was suggested as forming a potassium borate melt in which hBN particles form, in addition to carbothermic formation reaction. Effect of K₂CO₃ on increasing the hBN amount decreased when it was used over 40%. This was attributed to the rapid evaporation of the formed potassium borate liquid.     

Development of a metallic/ceramic composite for the deposition of thin-film oxygen transport membrane

Asymmetric perovskite membranes have an attractive potential in the application of O₂/N₂ gas separation for future membrane-based power plants using oxyfuel technology. In this study – a metal-supported membrane structure with a thin-film perovskite layer and porous ceramic interlayers was developed. Porous NiCoCrAlY sintered at 1225 °C in H₂ was selected as the substrate based on a sufficient permeability and corrosion resistance in co-firing conditions. According to the oxidation behaviour of NiCoCrAlY, the temperature for co-firing of the substrate and the interlayers was defined as 1100 °C for 5 h in air. Two interlayers of La_0.58Sr_0.4Co_0.2Fe_0.8O_3?δ were applied by screen printing. The top layer was deposited by magnetron sputtering with a thickness of 3.8 μm. While gas-tightness was improved considerably, significant air-leakage was still detected. In summary, the successful development of a metal-perovskite-composite is shown, which acts as a basis for further development of a gas-tight metal-supported oxygen transport membrane structure.     

Sintering of porous alumina obtained by biotemplate fibers for low thermal conductivity applications

In this research report, a sintering process of porous ceramic materials based on Al₂O₃ was employed using a method where a cation precursor solution is embedded in an organic fibrous cotton matrix. For porous green bodies, the precursor solution and cotton were annealed at temperatures in the range of 100–1600 °C using scanning electron microscopy (SEM) and thermogravimetric (TG) analysis to obtain a porous body formation and disposal process containing organic fibers and precursor solution. In a structure consisting of open pores and interconnected nanometric grains, despite the low porosity of around 40% (calculated geometrically), nitrogen physisorption determined a specific surface area of 14 m²/g, which shows much sintering of porous bodies. Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analytical methods revealed a predominant amount of α-Al₂O₃ in the sintered samples. Thermal properties of the sintered Al₂O₃ fibers were obtained by using the Laser Flash which resulted in the lower thermal conductivity obtained by α-Al₂O₃ and therefore improved its potential use as an insulating material.     

LAS glass–ceramic scaffolds by three-dimensional printing

Highly porous (>60% open porosity) glass–ceramic scaffolds with remarkable mechanical properties (compression strength of ～15 MPa) were produced by indirect 3D printing. Precursor glass powders were printed into 3D ordered structures and then heat treated to sinter and develop crystalline phases. The final glass–ceramic contained a β-spodumene solid solution together with a secondary phase of lithium disilicate.The precision of the printed geometry and the density of the struts in the scaffold depended on several processing parameters (e.g. powder size and flowability, layer thickness) and were improved by increasing the binder saturation and drying time. Two types of powders with different particle size distribution (PSD) and flowability were used. Powders with a larger PSD, could be processed within a wider range of printing parameters due to their good flowability; however, the printing precision and the struts density were lower compared to the scaffolds printed using the powder in a smaller average PSD.     

Laser-induced desorption of small molecules from oxide surfaces: A first-principles study

Recent efforts in the theoretical simulation of laser-induced desorption of small molecules from surfaces are summarized. As a representative example, photodesorption of CO molecules from a Cr₂O₃(0001) surface is investigated since detailed quantum state resolved experimental results are available for this system. In particular, vectorial properties such as the alignment of the desorbing species are considered. Furthermore, the influence of surface temperature as a control parameter is investigated, and lateral velocity distributions are calculated and compared with experimental results. All simulations presented in the present study are based on ab initio potential energy surfaces (PESs) for the electronic ground state as well as electronically excited states involved in the desorption process. These PESs provide the prerequisite for extensive high-dimensional quantum mechanical simulations of the dynamics of nuclear motion based on a stochastic wave packet scheme. These wave packet calculations allow for a detailed microscopic understanding of experimental results and provide a perspective for future experiments.     

Ultra-trace Analysis of Enantiomeric Impurities in Proteinogenic N-Fmoc-Amino-acid Samples on Cinchona Alkaloid-based Chiral Stationary Phases

The enantiomeric purity of N_α-Fmoc-protected amino acids is crucial from the viewpoint of peptide synthesis; therefore, a sensitive high-performance liquid chromatographic protocol was developed for the identification and quantification of enantiomeric impurities of commercially available N_α-Fmoc-protected amino acids on Cinchona alkaloid quinine- and quinidine-based weak anion exchanger-type chiral stationary phases. In the course of the evaluation of the chiral chromatographic method, the effect of the mobile phase composition, nature, and concentration of different additives were optimized. The specific phenomenon that quinine- and quinidine-based chiral stationary phases behave as pseudo-enantiomers permits that the sequence of elution of the enantiomers might be reversed by simple column switching. This is quite advantageous as regards the separation of the minor component in the presence of the major one. The method developed permits detection of less than 0.01 % enantiomeric impurity in the presence of the major enantiomer.     

Pore Analysis and the Behaviour of the Unreacted Metakaolin Particles in the Networks of Geopolymer Cements Using Metakaolins From Kaolinitic and Halloysitic Clays

Silicon - This work aims to study the pore analysis and the behaviour of the unreacted metakaolin particles in the geopolymer cements from halloysitic and kaolinitic clays. The XRD patterns of the...     

Chemical Attraction of Gall Midge Pollinators (Cecidomyiidae: Cecidomyiinae) to Anthurium acutangulum (Araceae)

Flowering plants often use chemical signals to attract their pollinators, and compounds that elicit attraction are known for several groups of pollinators. For other pollinators such as gall midges, however, compounds responsible for their attraction to flowers are largely unknown. Here, we describe the pollination biology of Anthurium acutangulum, a Neotropical aroid species found to be attractive to gall midges. We collected and analyzed its floral scent by dynamic headspace collections and gas chromatography coupled to mass spectrometry, and identified compounds responsible for pollinator attraction. The inflorescences were almost exclusively visited by gall midges (females; Cecidomyiidae: Cecidomyiinae) and released a strong scent reminiscent of freshly cut cucumber, mainly (5S,7S)-trans-conophthorin, (E2,Z6)-2,6-nonadienal, and cis-conophthorin. Behavioral assays with the two most abundant compounds identified (E2,Z6)-2,6-nonadienal as being highly attractive to the female gall midge pollinators, whereas (5S,7S)-trans-conophthorin was not attractive. Overall, we introduce a new specialized gall midge pollination system and identify the chemical mediating communication between the pollinators and their host plants.