On the Temperature-Induced Equilibration of Phase Distribution and Microstructure in a Gas-Atomized Titanium Aluminide Powder

Powder production by gas atomization of γ-TiAl based alloys typically yields a highly nonequilibrium material regarding the occurring phases and their microstructural appearance. In particular, the equilibration of the powder and the associated phase transformations during heating are of great importance for the subsequently applied densification techniques. The present work employs in situ high-energy X-ray diffraction to investigate how this thermodynamic equilibration manifests itself in the resulting phase distribution, the ordering behavior of the disordered α and β phase, both evidenced in the powder, and the change of the γ lattice parameters during heating of a Ti–46.3Al–2.2W–0.2B (at%) powder up to 850 °C. Complementary microstructural characterization of the gas-atomized powder and the heat-treated material condition reveals that the temperature exposure predominately affects the dendritic parts of the microstructure, especially when the α phase is transformed into γ phase with small embedded grains of α₂ and β_o.     

Design and Analysis of Charge-Reduced Refrigerant Cycles Using R290

R290 is one of the most promising refrigerants for heat pumps and cooling processes working in a temperature range of –15 to 70 °C. The nearly neglectable global warming potential and attractive thermodynamic properties allow the design of climate-friendly and efficient refrigeration systems and heat pumps. However, R290 is flammable, and the use of charge-reduced components and designs should be the first central step to reduce safety risks. Whereas the prediction of heat capacity, temperatures and pressure drops are sufficiently precise the prediction of refrigerant charge is not very accurate when using computer-aided design tools. The article presents a method to enhance accuracy for refrigerant cycles with less than 500 g of R290.     

Tethered Ribosomes: Toward the Synthesis of Nonproteinogenic Polymers in Bacteria

The ribosome is the core element of the translational apparatus and displays unrivaled fidelity and efficiency in the synthesis of long polymers with defined sequences and diverse compositions. Repurposing ribosomes for the assembly of nonproteinogenic (bio)polymers is an enticing prospect with implications for fundamental science, bioengineering and synthetic biology alike. Here, we review tethered ribosomes, which feature inseparable large and small subunits that can be evolved for novel function without interfering with native translation. Following a tutorial summary of ribosome structure, function, and biogenesis, we introduce design and optimization strategies for the creation of orthogonal and tethered ribosomes. We also highlight studies, in which (rational) engineering efforts of these designer ribosomes enabled the evolution of new functions. Lastly, we discuss future prospects and challenges that remain for the ribosomal synthesis of tailor-made (bio)polymers.     

Novel Additive Manufacturing Materials for Waste Heat Deduction

Herein, three material approaches, for the fabrication of thermally conductive and yet electrically insulating parts via additive manufacturing (AM) technologies, are described. Samples are prepared from light-curable resins, sol–gel-hybrid polymers, and thermoplastic materials using thermally conductive particles as fillers. AM sample preparation is done using vat photo-polymerization and material extrusion with subsequent measurements of thermal conductivity and electrical insulation properties. The main goal herein in addition to material development is the demonstration of manufacturing applicability including usage properties. Use cases are heat sinks for power electronics, which have to be thermally conductive to spread the generated heat and electrically insulating to ensure general functionality and long-term operation.     

Parameter Optimization of the ARBURG Plastic Freeforming Process by Means of a Design of Experiments Approach

Additive manufacturing finds more applications every day, especially in medical devices, ranging from models, tools, to implants. The fabricated parts have to withstand the mechanical loading applied during their lifetime. Hence, optimization of process parameters must be performed to reach the best performance of the manufactured part with the given polymer. A fractional design of experiments is performed with the ARBURG plastic freeforming using a medical-grade poly (methyl methacrylate) to improve the overall mechanical performance. Tensile specimens are produced, tested, and the impact of different parameter settings is analyzed to identify the factors with the highest impact on the mechanical performance. Based on the results, further parameter optimization is performed. A direct correlation between the density and the tensile properties of the printed parts is observed. Further, an influence of the processing pressure resulting from changes in the processing temperature is detected. Optimization for good mechanical performance is performed, and a relation between the filling of the parts, the nozzle temperature, and the discharge pressure on to the tensile properties is found. This investigation reveals that shrinkage due to changes in temperature and pressure has an essential role in determining the tensile properties of specimens produced by ARBURG plastic freeforming.     

Stabilizing Antiferroelectric-Like Aluminum-Doped Hafnium Oxide for Energy Storage Capacitors

Herein, a systematic study of aluminum-doped hafnium oxide to utilize its antiferroelectric-like (AFE) properties for energy storage applications is done. The doping concentration of aluminum is optimized to obtain the AFE-like phase. In addition, the impact of the postmetallization annealing temperature on the energy storage properties of the materials is studied. Metal–insulator–metal capacitors are fabricated by varying the doping concentration of the Al in HfO₂ from 1.9 to 6.2 at% with a constant thickness of 10 nm by atomic layer deposition. The devices are rapid thermal annealed by varying the annealing temperature from 650 to 800 °C for 20 s. Polarization measurements indicate a clear phase transformation from ferroelectric (FE) to AFE to paraelectric phase with the increase of doping concentration in the polarization measurements. The planar antiferroelectric devices have an energy storage density of 30 J cm⁻³ with 76% efficiency after 10⁵ cycles. The storage density can be further increased by a factor of 16.5 using area-enhanced substrates to 500 J cm^{− 3} at 73% efficiency. The endurance characteristics are studied for both planar and 3D capacitors which are found to be stable up to 10⁸ cycles.     

Secondary-Phase-Induced Charge–Discharge Performance Enhancement of Co-Free High Entropy Spinel Oxide Electrodes for Li-Ion Batteries

High entropy oxide (HEO) has emerged as a new class of anode material for Li-ion batteries (LIBs) by offering infinite possibilities to tailor the charge–discharge properties. While the advantages of single-phase HEO anodes are realized, the effects of a secondary phase are overlooked. In this study, two kinds of Co-free HEOs are prepared, containing Cr, Mn, Fe, Ni, and Zn, for use as LIB anodes. One is a plain cubic-structure high entropy spinel oxide HESO (C) prepared using a solvothermal method. The other HESO (C+T) contains an extra secondary phase of tetragonal spinel oxide and is prepared using a hydrothermal method. It is demonstrated that the secondary tetragonal spinel phase introduces phase boundaries and defects/oxygen vacancies within HESO (C+T), which improve the redox kinetics and reversibility during electrode lithiation/delithiation. Density functional theory calculation is performed to assess the phase stability of cubic spinel, tetragonal spinel, and rock-salt structures, and validate the cycling stability of the electrodes upon charging–discharging. The secondary-phase-induced rate capability and cyclability enhancement of HEO electrodes are for the first time demonstrated. A HESO (C+T)||LiNi_0.8Co_0.1Mn_0.1O₂ full cell is assembled and evaluated, showing a promising gravimetric energy density of ≈610 Wh kg⁻¹ based on electrode-active materials.