Tunable Microwave Dielectric Properties in Rare-Earth Niobates via a High-Entropy Configuration Strategy To Induce Ferroelastic Phase Transition.

In this study, (La0.2Nd0.2Sm0.2Ho0.2Y0.2)(Nb1-xVx)O4 (0.1 ≤ x ≤ 0.4) ceramics were prepared using a high-entropy strategy via the solid-phase method. The crystal structure, microstructure, vibration modes, and phase transition were studied by X-ray diffraction, scanning electron microscopy/transmission electron microscopy (SEM/TEM), and Raman spectroscopy techniques. The phase of ceramics was confirmed to be a monoclinic fergusonite in the range of x ≤ 0.28, a tetragonal scheelite was in the range of 0.3 ≤ x ≤ 0.32, a complex phase of tetragonal scheelite, and zircon was observed in the ceramics when x ≥ 0.35. A zircon phase was also detected by TEM at x = 0.4. The ceramic at x = 0.25 exhibited outstanding temperature stabilization with εr = 18.06, Q × f = 56,300 GHz, and τf = -1.52 ppm/°C, while the x = 0.2 ceramic exhibited a low dielectric loss with εr = 18.14, Q × f = 65,200 GHz, and τf = -7.96 ppm/°C. Moreover, the permittivity, quality factor, and the temperature coefficient of resonance frequency were related to the polarizability, packing fraction, density, and the temperature coefficient of permittivity caused by phase transition. This is an effective method to regulate near-zero τf by the synergism of the high-entropy strategy and substituting Nb with V in LnNbO4 ceramics.

Effects of Infill Line Multiplier and Patterns on Mechanical Properties of Lightweight and Resilient Hollow Section Products Manufactured Using Fused Filament Fabrication.

Fused Filament Fabrication (FFF) is a popular additive manufacturing process for creating prototypes and end-use products. Infill patterns, which fill the interior of hollow FFF-printed objects, play a crucial role in determining the mechanical properties and structural integrity of hollow structures. This study investigates the effects of infill line multipliers and different infill patterns (hexagonal, grid, and triangle) on the mechanical properties of 3D printed hollow structures. Thermoplastic poly lactic acid (PLA) was used as the material for 3D-printed components. Infill densities of 25%, 50%, and 75% were chosen, along with a line multiplier of one. The results indicate that the hexagonal infill pattern consistently demonstrated the highest Ultimate Tensile Strength (UTS) of 1.86 MPa across all infill densities, out-performing the other two patterns. To maintain a sample weight below 10 g, a two-line multiplier was utilised for a 25% infill density sample. Remarkably, this combination exhibited a UTS value of 3.57 MPa, which is comparable to samples printed at 50% infill density, which were 3.83 MPa. This research highlights the importance of line multiplier in combination with infill density and infill pattens to ensuring the achievement of the desired mechanical properties in the final product.

In Situ Printing and Functionalization of Hybrid Polymer-Ceramic Composites Using a Commercial 3D Printer and Dielectrophoresis-A Novel Conceptual Design.

Three-dimensional printing-based additive manufacturing has emerged as a new frontier in materials science, with applications in the production of functionalized polymeric-based hybrid composites for various applications. In this work, a novel conceptual design was conceived in which an AC electric field was integrated into a commercial 3D printer (-based fused filament fabrication (FFF) working principle) to in situ manufacture hybrid composites having aligned ceramic filler particles. For this work, the thermoplastic poly lactic acid (PLA) was used as a polymer matrix while 10 vol% KNLN (K0.485Na0.485Li0.03NbO3) ceramic particles were chosen as a filler material. The degree of alignment of the ceramic powders depended upon print speed, printing temperature and distance between electrodes. At 210 °C and a 1 kV/mm applied electric field, printed samples showed nearly complete alignment of ceramic particles in the PLA matrix. This research shows that incorporating electric field sources into 3D printing processes would result in in situ ceramic particle alignment while preserving the other benefits of 3D printing.

Solution Blow Spinning of Polyvinylidene Fluoride Based Fibers for Energy Harvesting Applications: A Review.

Polyvinylidene fluoride (PVDF)-based piezoelectric materials (PEMs) have found extensive applications in energy harvesting which are being extended consistently to diverse fields requiring strenuous service conditions. Hence, there is a pressing need to mass produce PVDF-based PEMs with the highest possible energy harvesting ability under a given set of conditions. To achieve high yield and efficiency, solution blow spinning (SBS) technique is attracting a lot of interest due to its operational simplicity and high throughput. SBS is arguably still in its infancy when the objective is to mass produce high efficiency PVDF-based PEMs. Therefore, a deeper understanding of the critical parameters regarding design and processing of SBS is essential. The key objective of this review is to critically analyze the key aspects of SBS to produce high efficiency PVDF-based PEMs. As piezoelectric properties of neat PVDF are not intrinsically much significant, various additives are commonly incorporated to enhance its piezoelectricity. Therefore, PVDF-based copolymers and nanocomposites are also included in this review. We discuss both theoretical and experimental results regarding SBS process parameters such as solvents, dissolution methods, feed rate, viscosity, air pressure and velocity, and nozzle design. Morphological features and mechanical properties of PVDF-based nanofibers were also discussed and important applications have been presented. For completeness, key findings from electrospinning were also included. At the end, some insights are given to better direct the efforts in the field of PVDF-based PEMs using SBS technique.

Solution Blow Spinning of High-Performance Submicron Polyvinylidene Fluoride Fibres: Computational Fluid Mechanics Modelling and Experimental Results.

Computational fluid dynamics (CFD) was used to investigate characteristics of high-speed air as it is expelled from a solution blow spinning (SBS) nozzle using a k-ε turbulence model. Air velocity, pressure, temperature, turbulent kinetic energy and density contours were generated and analysed in order to achieve an optimal attenuation force for fibre production. A bespoke convergent nozzle was used to produce polyvinylidene fluoride (PVDF) fibres at air pressures between 1 and 5 bar. The nozzle comprised of four parts: a polymer solution syringe holder, an air inlet, an air chamber, and a cap that covers the air chamber. A custom-built SBS setup was used to produce PVDF submicron fibres which were consequently analysed using scanning electron microscope (SEM) for their morphological features. Both theoretical and experimental observations showed that a higher air pressure (4 bar) is more suitable to achieve thin fibres of PVDF. However, fibre diameter increased at 5 bar and intertwined ropes of fibres were also observed.