Elevated Processing Temperatures Research Articles

Material compatibility and processing challenges in droplet deposition modelling additive manufacturing: A study on pharmaceutical excipients Polyvinylpyrrolidone/vinyl acetate (PVP/VA) and Polycaprolactone (PCL)

Additive manufacturing (AM) enables the production of complex, lightweight, and customized components with superior quality. Selecting the right materials considering their thermal properties, printability, and layer adhesion is crucial in melting-based AM techniques. This study investigates Droplet Deposition Modelling (DDM), an innovative material extrusion process that utilizes thermoplastic granules. DDM is distinguished by its shorter manufacturing times and a wider range of materials, setting it apart from traditional material extrusion methods such as fused filament fabrication. We investigated the printability and part quality in DDM using two common pharmaceutical excipients: Polyvinylpyrrolidone/vinyl acetate 6:4 (PVP/VA), which is highly brittle, and Polycaprolactone (PCL), known for its low solubility and role in controlled drug release. Different ratios of PVP/VA and PCL were compounded via hot melt extrusion (HME) and used in DDM to study the impact of ingredient content on printability and part quality, employing geometrical models to assess material compatibility and printability. The study revealed that increasing PVP/VA content leads to higher viscosity, reduced flowability, and uneven deposition, with formulations of 80 % and 100 % PVP/VA showing poor processability. In contrast, formulations with 60 % and 40 % PVP/VA exhibited smooth processing and compatibility with DDM. We identified processing temperature and Drop Aspect Ratio (DAR) as key factors influencing material printability and part quality. Elevated processing temperatures and reduced DAR were found to increase interface temperatures, reduce diffusion, and potentially cause the 'elephant feet' issue. Additionally, smaller droplet sizes and material characteristics, such as higher interfacial tension in PCL, could lead to coalescence. Our findings highlight the complexities in optimizing DDM processing parameters and material blends, underscoring the need for careful formulation design to achieve high-quality 3D printed products.

Ultrastable Zn3N2 Thin Films via Integration of Amorphous GaN Protection Layers

AbstractZinc nitride (Zn3N2) is a promising semiconductor for a range of optoelectronic and energy conversion applications, offering a direct bandgap of 1.0 eV, large carrier mobilities, and abundant constituent elements. However, the material is prone to bulk oxidation in ambient environments, which has thus far impeded its practical deployment. While previous approaches have focused on stabilizing the material via integration of ZnO surface layers, these strategies introduce additional challenges regarding elevated processing temperatures and limited control of interface properties. In this study, it is shown that amorphous GaN thin films can serve as highly stable protection layers on Zn3N2 surfaces and can be deposited at the same growth temperature and in the same deposition system as the underlying semiconductor. The GaN‐capped Zn3N2 structures exhibit long‐term stability, surviving over 3 years of exposure to ambient conditions with no discernible alterations in composition, structure, or electrical properties. Notably, the amorphous GaN coatings can even impede Zn3N2 oxidation under prolonged aqueous exposure. Thus, this study offers a solution to stabilize Zn3N2 in ambient conditions, providing a viable pathway to its utilization in robust and high‐performance electronic devices, such as thin film transistors and solar energy conversion systems.

PS/PPO foam with excellent comprehensive properties prepared by integrated foaming and sintering strategy with microwave-assisted

Expanded polystyrene (EPS) foam, as the earliest and most common foam part, holds the largest market share in the bead foam industry. However, its poor mechanical and thermal performance significantly hinders its widespread application. Introducing high-performance polymer polyphenylene oxide (PPO), which is well-compatible, can markedly enhance the properties of polystyrene (PS). Nevertheless, the elevated processing temperature poses a challenge for sintering the beads of PS/PPO. In this study, we propose a microwave-assisted polymer integrated foaming and sintering strategy (IFS strategy). Benefiting from the selective heating properties of microwaves, PS/PPO bead foams after rapid depressurization foaming can be sintered into robust foam parts in an extremely short time, with the simultaneous expulsion of microwave absorbers. The compressive performance of PPO-enhanced PS foam is improved by 155 % compared to PS foam and 707 % compared to expanded polystyrene (EPS). Additionally, the foam also has excellent temperature resistance (over 140 °C), flame retardancy, and thermal insulation (thermal conductivity of about 40 mW/m·K). This approach provides a feasible pathway for the green, efficient, safe, energy-saving, and sustainable preparation of high-temperature processing and high-performance polymer bead foam parts.

An investigation over microstructure and HIP processing effects on wear performance of pure chromium parts fabricated by laser powder bed fusion

Chromium (Cr) and its alloys have long been valued for their exceptional properties, including corrosion resistance and high-temperature stability, rendering them indispensable in industrial applications such as chemical processing, energy production, and aerospace. However, due to the difficulties in Cr-based alloy manufacturing, there is a need for novel manufacturing methodologies. Additive Manufacturing (AM) emerges as a promising approach, particularly Laser Powder Bed Fusion (LPBF), which allows for intricate designs, reduced material waste, and simplified assembly. However, certain issues still need to be addressed, including defects like cracks and porosities in the manufactured parts. Post-processing techniques such as Hot Isostatic Pressing (HIP) have gained prominence for enhancing the material properties and quality of AM parts, including those produced using LPBF. HIP treatments are effective in eliminating internal pores, although some challenges remain, notably the presence of trapped argon and grain coarsening side effects of HIP process parameters. This study focuses on LPBF-processed pure chromium parts with crystallographic texture and investigates their properties after HIP treatment, including microstructure, hardness, and tribological performance. According to the obtained results: the HIP process reduced cracks, especially in the center region, but increased gaps in the side region. HIP also hindered grain realignment, limiting grain growth, and resulting in high HAGB density and low MUD values. Elevated HIP processing pressure negatively affected tribological performance due to increased grain size, and reduced hardness. This study, for the first time, realized the effect of HIP conditions on the microstructure and tribological performance of LPBF-processed pure Cr.

Enhancing interfacial solvent resistance and mechanical properties of carbon fiber/polyether ether ketone composites with water‐borne sizing agents based on cross‐linkable polyphthalonitrile

AbstractThe inherent structural properties and elevated processing temperatures of thermoplastic resins present new challenges in the realm of carbon fiber (CF) sizing agents. Consequently, a water‐based cross‐linkable nitro‐phthalonitrile capped polyfluorenyl ether ketone sizing agent was meticulously designed. The sizing agent exhibits superior storage stability, encapsulating particles spanning dimensions from 66.51 to 87.71 nm. The inherent mechanism during the hot‐pressing stage involves a self‐crosslinking of nitrile groups toward stable structures with unparalleled resistance to solvents. The crosslinked sizing agent boasts a remarkable glass‐transition temperature of 290°C. Noteworthy, significance is the consequential 40.1% augmentation in maximum flexural strength, along with a commendable 35% increase in interlaminar shear strength for CF‐1.5/PEEK composites in contrast to their unsized CF/PEEK counterparts. In summary, the focal aspiration of this research endeavor lies in offering a straightforward and viable methodology for the exploration of cross‐linkable sizing agents, strategically catering to both “thermoplastic processing” and “thermosetting applications.”Highlights Bulky fluorenyl unit increases the intermolecular volume of copolymer poly(fluorenyl ether ketone). The introduction of the BPF unit to the molecular elevates the thermal stability of the copolymer. Unique electron‐donating proclivity of the fluorenyl group drastically improved its reactivity. The polymerization was accomplished at a relatively low temperature of 150°C for practical applications. The ILSS, IFSS, and bending strength were noteworthy increased by 35%, 74.02%, and 40.1%

Investigation on the effects of isothermal holding temperature and time on the coarsening mechanism and rheological properties of ADC12 Al semi-solid slurry

The current work's key emphasis is on investigating the influence of isothermal holding temperature and time on the microstructural development and coarsening rate during the directly generated semi-solid slurry of ADC12 Al alloy from the cooling slope process. Additionally, a thorough investigation is conducted to optimize process variables in the rheo-pressure die-casting process to determine the correlation between the non-Newtonian flow behaviour and its morphological characteristics of the quenched slurry of ADC12 Al alloy. The obtained results inferred that with increasing isothermal holding time, average grain size marginally increases initially, then significantly increases with increasing time, while shape factor increases first and then declines. Furthermore, when isothermal temperatures increase, the average grain size rises, while the shape factor rises first before decreasing. As a result of the increase in grain size due to elevated processing temperature and prolonged processing time, the aluminium alloy's hardness deteriorated. The ideal condition for more spheroidization of α-Al in the synthesized semi-solid slurry of ADC12 aluminium alloys was at an isothermal temperature of 565 °C and a holding time of 7 min. Under ideal processing conditions, the alloy's grain size, shape factor, and hardness were 31 μm, 0.89, and 62.32 HV, respectively. The semi-solids of ADC12 Al alloy have a low coarsening coefficient. The coarsening rate constant at 565 °C was calculated using the Lifshitz-Slyozov-Wagner relationship, and a value of 37 μm3/s was discovered. The findings of the isothermal rheology experiment demonstrate that viscosity decreases as the shear rate increases, confirming the existence of shear-thinning actions in semi-solid slurries.

Effects of thermal process conditions on crystallinity and mechanical properties in material extrusion additive manufacturing of discontinuous carbon fibre reinforced polyphenylene sulphide composites

This study investigates the thermal behaviour of discontinuous carbon fibre reinforced polyphenylene sulphide (CF/PPS), additively manufactured by material extrusion, with a focus on the effects of thermal process conditions on the degree of crystallinity, oxidation crosslinking and mechanical properties of CF/PPS from filament fabrication, material extrusion to annealing treatment. The screw extrusion parameters are optimised by performing a thermal analysis of the fabricated filaments. The effect of crosslinking reactions on the crystallinity process in determining the mechanical properties of the printed samples is illustrated by investigating the influence of the printing conditions. Furthermore, the effect of annealing treatment on the semi-crystalline polyphenylene sulphide (PPS) is studied by measuring the degree of crystallinity and viscoelasticity behaviours. Results demonstrate that the flexural properties of the printed CF/PPS composites at elevated processing temperatures are determined by the oxidation crosslinking between PPS chains. These enhance the crystallisation process of semi-crystalline polymers by acting as the nucleating agent first but negatively affect the mechanical properties at higher temperatures because of the detrimental effects of the polymer inter-chain bonding. The maximum flexural strength of printed CF/PPS reached 164.65 MPa when processing at an extrusion temperature of 280°C, a printing temperature of 320°C, and an annealing temperature of 130°C for 6 h. By adjusting the thermal treatment conditions, the degree of the crystallinity and the mechanical properties of the printed CF/PPS composites can be designed, controlled and tailored.

Effect of Temperature on Surface Hardness of Different Acrylic Materials utilized for space maintainer

Aim of the study: surface hardness is essential to avoid the indentation or scratch of space maintainer. Efforts have been made to improve the flexible and cold-cured acrylic's strength, by raising the processing temperature, unless the temperature has a chemical impact on the acrylic's qualities. The aim of this study was to study the effect of elevated temperature on the surface hardness of flexible and cold cured acrylic utilized as space maintainer appliance.
 Methods: Sixty specimens were divided into three groups: flexible acrylic ( Lingchen dental) , cold-cured acrylic (vertex) and (Paladur). Each group was subdivided into two subgroups,10 control and10 experimental . The control group for flexible acrylic was injected at 270 °C ,while for the two types of cold -cure, control groups, the specimens were processed at 37°C . The experimental group for flexible acrylic was injected at 290°C and for the two cold -cure types were processed at 70°C. Hardness was tested by Shore A device for flexible acrylic while for cold -cure specimens, shore D device was used. 
 
 Results : results showed no significant increase in the hardness of flexible acrylic the mean value of control group is 66.44±0.47 while for experimental group is 66.50±0.48. For vertex and Paladur cold- cured acrylic the surface hardness was increased significantly with increasing processing temperature. The mean values of vertex and Paladur control groups are around 86.14±0.39 and 88.33±0.39 respectively, while for experimental groups are 88.39±0.40 and 88.70±0.25
 Conclusion : elevated processing temperature increased the surface hardness of both types of cold acrylic however; the hardness of flexible acrylic was not affected by temperature elevation.

Process temperature-dependent interface quality and Maxwell-Wagner interfacial polarization in atomic layer deposited Al2O3/TiO2 nanolaminates for energy storage applications.

Considering the excellent tunability of electrical and dielectric properties in binary metal oxide based multi-layered nanolaminate structures, a thermal atomic layer deposition system is carefully optimized for the synthesis of device grade Al2O3/TiO2 nanolaminates with well-defined artificial periodicity and distinct interfaces, and the role of process temperature in the structural, interfacial, dielectric and electrical properties is systematically investigated. A marginal increase in interfacial interdiffusion in these nanolaminates, at elevated temperatures, is validated using X-ray reflectivity and secondary ion mass spectrometry studies. With an increase in deposition temperature from 150 to 300 °C, the impedance spectroscopy measurements of these nanolaminates exhibited a monotonic increment in dielectric constant from ∼95 to 186, and a decrement in dielectric loss from ∼0.48 to 0.21, while the current-voltage measurements revealed a subsequent reduction in leakage current density from ∼2.24 × 10-5 to 3.45 × 10-7 A cm-2 at 1 V applied bias and an improvement in nanobattery polarization voltage from 100 mV to 700 mV, respectively. This improvement in dielectric and electrical properties at elevated processing temperature is attributed to the reduction in impurity content along with the significant enhancement in sublayer densities and the conductivity contrast driven Maxwell-Wagner interfacial polarisation. Additionally, the devices fabricated at 300 °C exhibited a higher capacitance density of ∼22.87 fF μm-2, a low equivalent oxide thickness of ∼1.51 nm, and a low leakage current density of ∼10-7 A cm-2 (at 1 V bias), making this nanolaminate a promising material for high-density energy storage applications. These findings highlight the ALD process temperature assisted growth chemistry of Al2O3/TiO2 nanolaminates for superior dielectric performance and multifaceted applications.

Characterization of linear low‐density polyethylene and halloysite nanotube (LLDPE/HNT) composites based on two‐roll calendering melt fabrication

AbstractIn preparation of polymer nanocomposites, achieving good mixing and uniform distribution of nanofillers is highly desired for property enhancement. Polyethylene (PE) and its nanocomposite with halloysite nanotubes (HNTs) possesses a myriad of potentials for advanced engineering properties. A high nanoparticle loading is preferred to capitalize the nano‐reinforcement, thermal, and barrier properties. The capability of a two‐roll calendaring machine to disperse HNT particles into a linear low‐density polyethylene (LLDPE) matrix at elevated processing temperatures was assessed. Morphological, thermal, mechanical, and rheological behavior of prepared nanocomposites were characterized. A homogeneous distribution of HNTs in concentrations up to 5 wt.% was evidenced by SEM analysis. TGA showed the 10 wt.% composite exhibited an overall outstanding thermal stability. DSC analysis revealed the 30 wt.% sample has the highest Tm and Tc, and the %crystallinity did not change much due to HNT incorporation for all samples. DMA showed the storage and loss moduli increased with increase in HNT loadings. The effect of loading HNTs into the LLDPE matrix on Tg was minimal, implying that LLDPE and HNTs are quite compatible. The results demonstrated that the two‐roll mill fabrication method can efficiently keep HNT particles unagglomerated and disperse them evenly into the LLDPE matrix.

Heat up impact on thermal stresses in SOFC for mobile APU applications: Thermo-structural analysis

Because of its high efficiency, fuel flexibility, and high-quality waste heat for cogeneration requirements, the solid oxide fuel cell (SOFC) is a potential fuel cell type for power generation in a variety of applications. High working temperatures provide these benefits, but they also come with drawbacks, such as restrictions on the operating environment, problems with thermal management, long on/off times, and the issue of selecting appropriate materials to assure compatibility of the physical material properties of the fuel cell stack components. However, the elevated process temperatures of the SOFC system result in technical challenges. The heat-up stage is a critical issue for the SOFC stack, since the transient process conditions lead to thermal gradients which are combined with material gradients. The result is a mismatch in the thermal–mechanical material behavior inducing high thermal stresses, which in turn affect the functionality of the fuel cell stack. In the SOFC stack under consideration, a glass ceramic joint is used to ensure reliable sealing between cells. This region is identified to be at risk, due to high thermal stresses. In this study the computational modeling approach is applied to predict the thermal-structural response of the stack components to different heat-up strategies and investigate the system with respect to fuel cell temperature, thermal gradients, and induced stresses. Computational thermal and structural results for time dependent heat-up speeds are presented and compared. Essentially, running the process with a constant speed would not provide an optimized solution. Instead, the obtained results show that the heat-up speed should be adjusted to achieve the desired state of fuel cell temperature, reduced thermal gradients and stresses. This target can be met by applying mathematical modeling approach, since experimental analysis are time and cost consuming.

Thermally-stable photo-curing chemistry for additive manufacturing by direct melt electrowriting

In the present study, poly(ε-caprolactone) copolymers decorated with the random inclusion of thermally stable and photo-dimerizing cinnamoyl groups were synthesized for an electrically-assisted material extrusion additive manufacturing technique named melt electrowriting (MEW). The absence of thermally-induced reactions between cinnamoyl groups maintained the molten random copolymers processable at the elevated processing temperature while UV curing could improve thermo-mechanical properties of the films in the solid state. Random inclusion of non-crystallizable photo-reactive co-units was shown to enrich the thermodynamic state of the host polymer with the possibility of the formation of various microstructures, which correlated with the emergence of imperfections, such as spherulitic domains over the profile of fibers printed from molten random copolymers.

Relationships between the Decomposition Behaviour of Renewable Fibres and Their Reinforcing Effect in Composites Processed at High Temperatures.

Engineering polymers reinforced with renewable fibres (RF) are an attractive class of materials, due to their excellent mechanical performance and low environmental impact. However, the successful preparation of such composites has proven to be challenging due to the low thermal stability of RF. The aim of the present study was to investigate how different RF behaves under increased processing temperatures and correlate the thermal properties of the fibres to the mechanical properties of composites. For this purpose, hemp, flax and Lyocell fibres were compounded into polypropylene (PP) using a co-rotating twin screw extruder and test specimens were injection moulded at temperatures ranging from 180 °C to 260 °C, with 20 K steps. The decomposition behaviour of fibres was characterised using non-isothermal and isothermal simultaneous thermogravimetric analysis/differential scanning calorimetry (TGA/DSC). The prepared composites were investigated using optical microscopy (OM), colorimetry, tensile test, Charpy impact test, dynamic mechanical analysis (DMA) and melt flow rate (MFR). Composites exhibited a decrease in mechanical performance at processing temperatures above 200 °C, with a steep decrease observed at 240 °C. Lyocell fibres exhibited the best reinforcement effect, especially at elevated processing temperatures, followed by flax and hemp fibres. It was found that the retention of the fibre reinforcement effect at elevated temperatures can be well predicted using isothermal TGA measurements.

Influence of ECAP processing temperature and number of passes on hardness and microstructure of Al-6063

ABSTRACT Equal-channel angular pressing (ECAP) is one the most efficient techniques of severe plastic deformation for grain refinement and improving mechanical properties. In this study, aluminium alloy 6063 is used due to its wide range of applications. The ECAP process depends on die geometry, number of passes, processing temperature, following routes, plunger speed, strain and frictions. In this study, cylindrical billets of Al-6063 are processed at two different temperatures, at room temperature and at elevated temperature (250°C) through route BC. In the present research, specimens deformed after first pass, third pass and the sixth pass are considered for analysing the microstructure evolution and hardness values. Optical microscopy and electron back scattered diffraction (EBSD) techniques are used for microstructural study. Hardness test is carried out for hardness measurement with test load 100 g. The hardness is increased up to 85 HV after six passes at room temperature. Hardness increases up to 83% only after one pass at room temperature. EBSD result shows the low-angle grain boundaries are 91.06% where high-angle grain boundaries are only 8.9% of sample with one pass at 250°C. The elevated processing temperature influences both hardness and microstructure.

Characterization of the dynamic mechanical properties of sisal fiber reinforced PET composites; Effect of fiber loading and fiber surface modification

Dynamic mechanical analysis (DMA) is an essential procedure for characterizing the performance of composites and effectively simulate with the real-world applications. This research work aims to characterize the dynamic mechanical (DM) properties of sisal fiber reinforced polyethylene terephthalate (PET) composites as a factor of fiber content and fiber surface modification. The effect of elevated processing temperature (>260°C) on the thermal degradation of sisal fibers is also analyzed. To study the effect of sisal fiber loading, PET composite specimens; one with 25% by weight fraction of raw sisal fiber (w/w), abbreviated as 25% RSC and the other with 40% by weight fraction (w/w) of raw sisal fiber, hereafter abbreviated as 40% RSC, were prepared by injection molding. Similarly, to analyze the impact of fiber surface modifications, PET composite samples containing 40% by weight fraction (w/w) of alkali-treated sisal, hereafter abbreviated as (40% Al-SC), and 40% by weight fraction (w/w) of a combined alkali/acetylation-treated sisal, hereafter abbreviated as (40% Al-ASC), were prepared. It was found that the fiber volume fraction and fiber surface modifications affected the DM properties of the produced composites. The improved storage module and glass transition temperature (Tg) with minimized damping has been demonstrated by increasing fiber content. With the same 40% fiber content, the composites produced from modified fibers enhanced the storage modulus and Tg values. However, with increasing temperature, the storage modulus decreased, the loss modulus increased, and the damping factor increased with composites containing higher fiber content and surface modified fibers. This indicates the low thermal stability of the sisal fiber and the interface damage at elevated temperatures.

3D-printing on textiles \u2013 an investigation on adhesion properties of the produced composite materials

The actual paper is related to adhesive properties of 3D objects printed on cotton textile fabrics. For practical applications of 3D prints in the textile sector, the adhesion of the printed object on the textile substrate is an important issue. In the current study, two different types of polymers are printed on cotton – polylactide acid (PLA) and polyamide 6.6 (Nylon). Altogether six cotton fabrics differing in structure, weight and thickness are evaluated. Also, the effect of washing and enzymatic desizing is investigated. For printing parameters, best results are gained for elevated process temperatures, intermediate printing speed and low Z-distance between printing head and substrate. Also, a textile treatment by washing and desizing can improve the adhesion of an afterwards applied 3D print. The presented results are quite useful for future developments of 3D printing applications on textile substrates, e.g. to implement new decorative features or protective functions.

Microstructural analysis of forged Al-11Si-2.5Cu-0.6Fe alloy at different processing conditions

Present investigations demonstrate the microstructural analysis of complex eutectic Al-Si alloy namely Al-11Si-2.5Cu-0.6Fe during forging at different processing conditions. The alloy forged through converging die with reduction ratios (R) 1.5 and 2.0 at 300, 400 and 500 °C elevated processing temperatures. X-Ray diffractometer was used to evaluate the various phases present in the alloy. Optical microscopy was executed to characterize the microstructural features induced during process (forging). The obtained results are critically observed to investigate the interaction of different processing parameter. The diffraction patterns confirmed that various complex intermetallic phases (β-Al4.5FeSi and Al2Cu) were formed due to the higher temperature during casting. Significant microstructural refinement observed during forging due to precipitation of fine particles while the coarse particulates fractured and fragmented during the process. The present study delivers valuable insight into microstructural development during forging of Al-11Si-2.5Cu-0.6Fe alloy.

Recyclable Polymethacrylate Networks Containing Dynamic Dialkylamino Disulfide Linkages and Exhibiting Full Property Recovery

Reprocessable polymer networks with dynamic covalent bonds exhibit thermoplastic-like properties at elevated processing temperatures while maintaining thermoset responses under service conditions, ...

Wafer-Level Vacuum-Packaged Translatory MEMS Actuator with Large Stroke for NIR-FT Spectrometers.

We present a wafer-level vacuum-packaged (WLVP) translatory micro-electro-mechanical system (MEMS) actuator developed for a compact near-infrared-Fourier transform spectrometer (NIR-FTS) with 800–2500 nm spectral bandwidth and signal-nose-ratio (SNR) > 1000 in the smaller bandwidth range (1200–2500 nm) for 1 s measuring time. Although monolithic, highly miniaturized MEMS NIR-FTSs exist today, we follow a classical optical FT instrumentation using a resonant MEMS mirror of 5 mm diameter with precise out-of-plane translatory oscillation for optical path-length modulation. Compared to highly miniaturized MEMS NIR-FTS, the present concept features higher optical throughput and resolution, as well as mechanical robustness and insensitivity to vibration and mechanical shock, compared to conventional FTS mirror drives. The large-stroke MEMS design uses a fully symmetrical four-pantograph suspension, avoiding problems with tilting and parasitic modes. Due to significant gas damping, a permanent vacuum of ≤3.21 Pa is required. Therefore, an MEMS design with WLVP optimization for the NIR spectral range with minimized static and dynamic mirror deformation of ≤100 nm was developed. For hermetic sealing, glass-frit bonding at elevated process temperatures of 430–440 °C was used to ensure compatibility with a qualified MEMS processes. Finally, a WLVP MEMS with a vacuum pressure of ≤0.15 Pa and Q ≥ 38,600 was realized, resulting in a stroke of 700 µm at 267 Hz for driving at 4 V in parametric resonance. The long-term stability of the 0.2 Pa interior vacuum was successfully tested using a Ne fine-leakage test and resulted in an estimated lifetime of >10 years. This meets the requirements of a compact NIR-FTS.

Controlled Atomic Layer Deposition of Aluminum Oxide to Improve the Performance of Lithium–Sulfur Batteries

The high capacity of sulfur makes lithium–sulfur (Li–S) batteries the most promising next‐generation battery systems. With a significantly higher theoretical specific energy than conventional lithium‐ion batteries, this technology is intensely investigated. However, currently used cathodes have some critical drawbacks which affect the performance of Li–S batteries. Atomic layer deposition (ALD) demonstrates its power for solving some emerging issues in energy‐storage systems. The application of alumina (Al2O3) to the cathode surface improves the morphology and/or chemistry, providing a solution for some of the most common issues of Li–S batteries. Herein, the cathode of Li–S batteries is coated with alumina by ALD. In addition, the optimal parameters for ALD application to sulfur‐based electrodes are reported. It is demonstrated that alumina deposition results in an improved capacity of the system. The process temperature plays an important role, in particular for few‐cycle ALD processes, aiding better cell performance. Higher numbers of ALD cycles, especially at elevated process temperatures, result in considerable sulfur loss, which significantly lowers the cell performance. Cathodes coated with alumina at low process temperatures and with low numbers of ALD cycles are promising alternatives for conventional Li–S cathodes as they increase the capacity of the system considerably.