Chemical and structural induced ductile-to-brittle transition in electrospun silica nanofiber membranes

Electrospun silica nanofiber membranes show a high potential in many advanced environmental applications. However, little is known about their mechanical performance which could be a limiting factor for further innovation. It is shown in this work that silica nanofiber membranes have a completely different deformation behavior compared to conventional polymeric/thermoplastic nanofiber membranes, resulting from their significant differences in chemical and physical properties such as fiber interactions and porosity. Furthermore, storage at room temperature initiates remarkable changes in failure mechanisms, depending on the storage humidity, which can be accelerated via a thermal treatment. These changes are linked to the structural changes of the membrane resulting from its chemical reactivity towards moisture in the air. Additional interactions and crosslinks are observed, leading to fiber shrinkage and rearrangement. As a result, more contact points are created between nanofibers, creating additional friction forces and, as such, a complete shift in mechanical properties towards a stronger, stiffer, and more brittle material (tensile strength of 14.0 ± 3.8 MPa vs. 3.1 ± 0.4 MPa and failure strain of 0.9 ± 0.2% vs. 24.2 ± 1.0%). The silica nanofiber membranes thus allow mechanical tunability via altering the storage or treatment conditions.     

High electric field-induced strain properties in La-doped Pb(In1/2Nb1/2)O3–PbZrO3–PbTiO3 relaxor ferroelectric ceramics

Piezoelectric ceramics with high strain response and low hysteresis are highly in demand for high-performance actuator applications. Unfortunately, the trade-off relationship between large field-induced strain and low hysteresis in piezoelectric ceramics is a key challenge for designing high-performance piezoelectric actuators. Herein, ymol%La-doped 0.10 Pb(In_1/2Nb_1/2)O₃-xPbZrO₃-(0.90–x)PbTiO₃ [0.10PIN-xPZ-(0.90-x)PT: ymol%La] ternary relaxor ferroelectric ceramics were prepared by conventional solid-state reaction technique. Pb(In_1/2Nb_1/2)O₃ (PIN) as a relaxor end member was introduced into (Pb,La) (Zr,Ti)O₃ (PLZT) system to improve relaxor characteristics and strain properties. A giant strain of 0.23% was obtained in 0.10PIN-0.59PZ-0.31 PT: 8mol%La ceramic at the electric field of 20 kV/cm, with a high piezoelectric d₃₃* of 1150 pm/V and low hysteresis H_y of 6.4%, exhibiting a potential application in high-performance piezoelectric actuators. Furthermore, the effects of La ion doping and components on the ferroelectric, dielectric and electric field-induced strain properties were investigated, and provides a new way for improve the strain properties of piezoelectric materials.     

Evolution mechanism of pore structure in sintered coal gangue ceramsites

Preparation of high-strength densified ceramsites and porous water-retaining ceramsites to replace part of the original gravel aggregates and natural moisturizing materials, respectively, is an effective way for the resource utilization of coal gangue (CG). The pore structure of ceramsites affects their strength, density, porosity, etc. In this paper, CG was used as the sole raw material to prepare ceramsites at different temperatures (600–1220 °C). By using methods of thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscope (SEM), element analysis (EA), heating microscope (HM), and density tester (DT), the evolution mechanism of pore structure in sintered coal gangue ceramsites (CGCs) was discussed. The results showed that there were two key temperatures: 950 °C and 1160 °C. Below 950 °C, the pore structure of CGCs was in a stable state, and the true, apparent, and closed porosity remained around 45%, 32%, and 12%, respectively. At 950–1160 °C, the true and apparent porosity decreased, and the closed porosity and compressive strength increased. Above 1160 °C, its performance deteriorated. During the heating process, the loss of carbon-containing components, phase transition, high-temperature diffusion and densification would change the pore structure. The appropriate temperature range for the preparation of porous water-retaining CGCs was about 950 °C, while that for preparing high-strength densified CGCs was about 1000–1160 °C. It was proved that qualified CGC products with different prospective applications could be prepared in different temperature regimes.     

Experimental investigation of cell generation in an expanding spherical hydrogen-air flame front

This paper reports on the cellular structure formation on the front of a spherically expanding hydrogen-air flame. The hydrogen-air mixture was considered with hydrogen concentration in experiments from 10 to 50 vol%. This paper aims to analyze cell cascade formation, which occurs due to diffusional-thermal and hydrodynamics instabilities. Using experimentally obtained schlieren images, the flame front radius as the function of an angle was obtained. The cell amplitude dependencies on the normalized time were also analyzed. The values corresponding to cell splitting were obtained by the discrete Fourier transform method. The cell split criterion, which allows taking into account the known instability mechanisms, was formulated.     

Bioactive membranes of tricalcium phosphate and hydroxyapatite containing manganese for bone regeneration

In this study, we produced bioactive ceramic membranes of tricalcium phosphate (TCP) and hydroxyapatite (HA) incorporated with manganese (Mn) with osteogenic and antibacterial properties for applications in bone regeneration. Membranes were prepared by tape casting technique using PVA as a binder between molecules. The incorporation of manganese favors the reticulation of the membranes, providing more excellent resistance in aqueous media. Furthermore, the HA-Mn membrane exhibits the lowest optical density values and, therefore, the most significant difference from the negative control, presenting the lowest cellular viability. Between the membranes without manganese, HA shows the highest efficiency in improving cellular viability. Through bioactivity analysis, we observed that the TCP-Mn membrane presents the most significant formation of amorphous calcium phosphate precipitates, making the material more bioactive. Thus, our results become fascinating for applications in biomaterials.