Thermoset IM-LSI-based C/C-SiC: Influence of flow direction and weld lines on microstructure and mechanical properties

The production of ceramic matrix composites (CMC) based on C/C-SiC is still very cost-intensive and therefore only economical for a few applications. The fabrication of the preforms involves many costs that need to be reduced. In this work, the shaping of the CFRP-preforms is realized by thermoset injection molding, which enables large-scale production. The polymeric matrix used is a multi-component matrix consisting of novolak resin, curing agent and lubricant. Six millimeter chopped carbon fiber with a proportion of 50 wt.% were used as a reinforcement. These ingredients are processed by an industrial equipment for compounding and injection molding in order to manufacture a CFRP demonstrator representing a brake disc. Test specimens are cut out of the demonstrator in different directions in order to investigate influences of flow direction and weld lines on microstructural and mechanical properties. Afterward, the CFRP samples were converted to C/C-SiC composites by the liquid silicon infiltration process. The article addresses the flow behavior of the compound during the injection molding and the building of the weld lines in the demonstrator. In addition, results of the directional dependence of the microstructural and mechanical properties within the fabricated disc in the different production steps are presented.     

Intense broadband photoemission from Bi-doped ZrO2 embedded in vitreous aluminoborate via direct melt-quenching

Tuning the optical properties of active species embedded within a glass matrix by modifying the ligand environment is of interest for luminescence-based technologies, for example, in optical sensing, data transmission, or spectral conversion. Here, we discuss a facile synthesis procedure for a glass-crystal composite material comprising of bismuth (Bi)-doped zirconia within an aluminoborate glass phase. The approach offers tunable and broad photoemission characteristics in the visible spectral region from 400 to 750 nm. Incorporation of Bi ions into the crystal phase enhances the photoemission intensity by two orders of magnitude, with an external quantum efficiency of about 29%. At higher ZrO₂ dopant concentration, we observe a red-shift of both the excitation and the emission bands to match commodity ultra-violet light emitting diodes as excitation sources. Encapsulation within the aluminoborate glass phase provides advantageous thermal behavior, with the emission intensity remaining at >80 % of its initial value up to a temperature of 400 K.     

Automated and Continuous Production of Microstructured Metallic Plates via Cold Embossing

Many critical issues need to be addressed when microstructured reactors are manufactured in large unit volumes. The most crucial of these are cost, ease of production, and reliability. The lack of breakthrough manufacturing technology to provide high‐efficiency, low‐cost, high‐precision plates is a hindrance to the early market implementation of systems requiring metallic microstructured plates. This contribution focuses on the development and optimization of a combined embossing and bending tool for the quick and continuous manufacture of easily machined plates.     

A review of varietal change in roots,tubers and bananas: consumer preferences and other drivers of adoption and implications for breeding

This review of the literature on varietal change in sub-Saharan Africa looks in detail at adoption of new varieties of bananas in Uganda, cassava in Nigeria, potato in Kenya, sweetpotato in Uganda and yams in Côte d’Ivoire. The review explored three hypotheses about drivers of varietal change. There was a strong confirmation for the hypothesis that insufficient priority given to consumer-preferred traits by breeding programmes contributes to the limited uptake of modern varieties (MVs) and low varietal turnover. Lack of evidence meant the second hypothesis of insufficient attention to understanding and responding to gender differences in consumer preferences for quality and post-harvest traits was unresolved. The evidence on the third hypothesis about the informal seed system contributing to slow uptake of MVs was mixed. In some cases, the informal system has contributed to rapid uptake of MVs, but often it appears to be a barrier with inconsistent varietal naming a major challenge.     

Gemini Surfactants Foam Formation Ability and Foam Stability Depends on Spacer Length

A series of cationic gemini surfactants containing different spacer length were synthesized and analyzed structurally. It was shown that the surface tension (σ) and critical micelle concentration (CMC), which had a maximum for the n-C₄H₈ spacer depended on the spacer length. The foaming ability and foam stability are high for the gemini surfactants with short spacers (C₂H₄ to n-C₄H₈), while longer spacers lead to a distinct decrease of these foam parameters. Foaming properties are discussed in terms of configuration and conformation of a surfactant molecule and in relation to micellization state kinetic.