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To construct their shells, molluscs are able to produce a large array of calcified materials including granular, prismatic, lamellar, fibrous, foliated, and plywood-like microstructures. The latter includes an aragonitic (the crossed-lamellar) and a calcitic (the crossed-foliated) variety, whose modes of formation are particularly enigmatic. We studied the crossed-foliated calcitic layers secreted solely by members of the limpet family Patellidae using scanning and transmission electron microscopy and electron backscatter diffraction. From the exterior to the interior, the material becomes progressively organized into commarginal first-order lamellae, with second and third order lamellae dipping in opposite directions in alternating lamellae. At the same time, the crystallographic texture becomes stronger because each set of the first order lamellae develops a particular orientation for the c-axis, while both sets maintain common orientations for one {104} face (parallel to the growth surface) and one a-axis (perpendicular to the planes of the first order lamellae). Each first order lamella shows a progressive migration of its crystallographic axes with growth in order to adapt to the orientation of the set of first order lamellae to which it belongs. To explain the progressive organization of the material, we hypothesize that a secretional zebra pattern, mirrored by the first order lamellae on the shell growth surface, is developed on the shell-secreting mantle surface. Cells belonging to alternating stripes behave differently to determine the growth orientation of the laths composing the first order lamellae. In this way, we provide an explanation as to how plywood-like materials can be fabricated, which is based mainly on the activity of mantle cells.

Abstract: Planktonic gastropods of the suborder Euthecosomata (order Pteropoda) secrete a unique microstructure made of tightly interlocked, space-filling helically coiled aragonite fibers. This material has a high degree of ordering because all fibers are in phase at a given growth plane. The recognition of the helical nature from mere scanning electron micrographs is somewhat uncertain. In addition, three-dimensional (3D) reconstructions of individual helices are hindered by the small dimensions of fibers, and the virtual absence of intervening organic interphases. Here, we (1) reexamine the morphological characteristics of the fibers in fracture and find them compatible with a helical model, (2) provide direct evidence of the helical mode of coiling in the form of anaglyphs, and (3) develop a 3D model, which is fully consistent with the patterns observed in fractures and polished sections. Proposals based on motifs different from helices are not congruent with the observations. Graphical abstract: Impact statement: Some planktonic gastropods of the order Pteropoda secrete a unique microstructure that was originally described as made of tightly interlocked helically coiled continuous aragonite fibers. Despite this material having been described 50 years ago, there is still debate as to the helical design of such fibers. We provide additional unambiguous evidence that fibers describe true helical trajectories during growth. Establishing their true nature is essential in order to know the spectrum of calcified biomaterials produced by molluscs. This is also a prerequisite for future biomimetic studies aiming at producing bioinspired highly functional materials.

The European Union Fit For 55 program plans to cease the production and sales of vehicles with the internal combustion engines in 2035, although fuel powered vehicles will remain on the road for many more years to come.

Water is the basis of life in the world. Unfortunately, resources are shrinking at an alarming rate. The lack of access to water is still the biggest problem in the modern world. The key to solving it is to find new unconventional ways to obtain water from alternative sources. Fog collectors are becoming an increasingly important way of water harvesting as there are places in the world where fog is the only source of water. Our aim is to apply electrospun fiber technology, due to its high surface area, to increase fog collection efficiency. Therefore, composites consisting of hydrophobic and hydrophilic fibers were successfully fabricated using a two-nozzle electrospinning setup. This design enables the realization of optimal meshes for harvesting water from fog. In our studies we focused on combining hydrophobic polystyrene (PS) and hydrophilic polyamide 6 (PA6), surface properties in the produced meshes, without any chemical modifications, on the basis of new hierarchical composites for collecting water. This combination of hydrophobic and hydrophilic materials causes water to condense on the hydrophobic microfibers and to run down on the hydrophilic nanofibers. By adjusting the fraction of PA6 nanofibers, we were able to tune the mechanical properties of PS meshes and importantly increase the efficiency in collecting water. We combined a few characterization methods together with novel image processing protocols for the analysis of fiber fractions in the constructed meshes. The obtained results show a new single-step method to produce meshes with enhanced mechanical properties and water collecting abilities that can be applied in existing fog water collectors. This is a new promising design for fog collectors with nano- and macrofibers which are able to efficiently harvest water, showing great application in comparison to commercially available standard meshes.

With the cost of green hydrogen production decreasing year by year, methanation, a carbon dioxide hydrogenation reaction, is becoming a more critical technology for the realization of a carbon-neutral society. Here, we show the procedure of membrane preparation for a distributor-type membrane reactor that simultaneously captures and recycles CO2together with experimental tests of the proposed reactor design. To decrease the temperature gradient in the reactor and to improve methane recovery from the inlet gas mixture, a three-dimensional computational fluid dynamics simulation of the reactor was conducted. The numerical results suggest that the distributed feed design results in a uniform distribution of carbon dioxide, preventing localized reactions at the reactor inlet. In addition, it reduces the temperature rise in the reactor by up to about 300 K compared to the case where the carbon dioxide and hydrogen gas mixture is fed from a single inlet. The effect of the feed CO2concentration on reactivity is also discussed. Simulation results show that the membrane reactor with inlet concentration of about 15 %, such as those emitted from industrial boilers, is capable of recovering methane at concentrations about 1.5 times higher in comparison to 100 % CO2concentration at the inlet in a classical reactor.

Magnesium is particularly challenging material, when formed from liquid phase because of high flammability risk. An alternative process for casting, which eliminates above mentioned disadvantage, is thixoforming, which involves a lower temperature of process and operation in the partially solidified state. Influence of semi-solid metal processing on EZ33A magnesium alloy (Mg–Zn–RE–Zr) microstructure and mechanical properties was studied. Ingot microstructure revealed globular grains with coarse eutectic mixture consisting of Mg7Zn3RE, T-phase – RE(Mg,Zn)11and α(Mg). Heterogeneous nucleation of magnesium solid solution allowed obtaining structure appropriate for thixoforming. Using differential scanning calorimetry, temperature of process was determined to be 622°C, which corresponded to about 30% of the liquid phase. Thixo-cast microstructure consisted of α(Mg) globular grains with a size of 76±1.1 surrounded by fine eutectic mixture in a volume of 35%. T6 heat treatment (solution at 500°C for 6h and ageing at 190°C for 33h) caused increase of grain size to 92μm and the precipitation of two kinds of phases within the α(Mg): β′1and β′2responsible for the increase of yield strength to 135MPa, compression strength to 383MPa and hardness to 73HV5.

This work shows the effect on the soldering process of the addition of Ag and Cu to Sn–Zn alloys. Soldering of Al/Cu and Al/Al joints was performed for a time of 3 min, at a temperature of 250°C, with the use of flux. Aging was carried out at 170°C for Al/Cu and Al/Al joints for 1 and 10 days. During the aging process, intermetallic layers grew at the interface of the Al/Cu joint at the Cu substrate. Intermetallic layers were not observed during wetting of Al/Al joints. On the contrary, dissolution of the Al substrate and migration of Al-rich particles into the bulk of the solder were observed. The experiment was designed to demonstrate the effect of Ag and Cu addition on the dissolution of Al substrate during the soldering and aging processes. In the solder alloys, small precipitates of AgZn3and Cu5Zn8were observed.

ABSTRACTThis work shows the effect on the soldering process of the addition of Ag and Cu to Sn–Zn alloys. Soldering of Al/Cu and Al/Al joints was performed for a time of 3 min, at a temperature of 250°C, with the use of flux. Aging was carried out at 170°C for Al/Cu and Al/Al joints for 1 and 10 days. During the aging process, intermetallic layers grew at the interface of the Al/Cu joint at the Cu substrate. Intermetallic layers were not observed during wetting of Al/Al joints. On the contrary, dissolution of the Al substrate and migration of Al-rich particles into the bulk of the solder were observed. The experiment was designed to demonstrate the effect of Ag and Cu addition on the dissolution of Al substrate during the soldering and aging processes. In the solder alloys, small precipitates of AgZn3and Cu5Zn8were observed.

In this study, unalloyed titanium (Gr.1) and deoxidized high phosphorus copper plates were joined through explosive welding process. Different stand-off distances were used to investigate their influence on the microstructure and mechanical properties of the clad fabricated at the same amount of explosive charge. Microstructures near-the-interface were examined with the use of scanning electron microscope equipped with energy dispersive X-ray spectrometer and then microhardness measurements were carried out on the clad. Microstructure examinations showed that with increasing stand-off distance the length and amplitude of the waviness and the quantity of melted zones in areas near-the-interface increase. The inclusions of the melted zones are formed behind the wave crests on titanium side or within the wave vortex. Microhardness measurements indicate a significant increase of both plates microhardness, especially near-the-interface.

The conditions for manganese with tin electrodeposition from aqueous citrate electrolytes were studied. Partial polarization curves were determined. The influence of applied potential, electrolyte composition and pH level, hydrodynamic conditions and quantity of charge passed, on the electrodeposition of Sn-Mn layers were determined. The surface composition of deposits was ascertained by chemical analysis (WDXRF). The morphology of coatings was studied by SEM. The phase composition of Sn-Mn samples was determined by X-ray diffractometry and Raman spectroscopy. The electrolysis parameters allowing electrodeposition of Sn-Mn coatings containing various amounts of Mn (in the range from about 0.5 wt% to 42 wt%) were selected. The morphology of deposits depends significantly on the content of manganese and on the parameters of electrolysis. The surface morphology of samples with Mn content of about 27 wt% is not uniform, two types of areas with significant differences in chemical composition are observed. XRD studies indicate that four crystallographic phases are formed in the deposits (b-Sn), MnO, Mn(OH)2, and MnSn2, while Raman spectroscopy revealed also the presence of a-MnO2, MnOOH, and SnO2, which are the products of chemical processes taking place simultaneously with electrolysis. The mechanism of the co-deposition of manganese with tin has been proposed.

Early stages of recrystallization were observed for the technical purity aluminium alloy (AA1050). The samples were severely deformed by equal channel angular pressing and then annealed to obtain the state of partial recrystallization. The nucleation of new grains and the changes in ‘density’ of low- and high- angle boundaries were analysed using scanning electron microscopy equipped with high resolution EBSD system. After deformation in six passes along route A the alloy contained a structure of flat grains. On annealing, the structure coarsened and got transformed into nearly equiaxed grains by both discontinuous and continuous recrystallization. A particular role in the rise of nuclei and the structure spheroidization is attributed to migration of low-angle boundaries.

The nanocrystalline silver powder and the amorphous powders of composition Ni49,5Ti20,5Nb15Zr15 (numbers indicate at%) were prepared by ball milling in the planetary Fritsch mill for 40 hours. TEM studies confirmed almost complete amorphization of milled alloys powders allowed to detect a small fraction of a small intermetallic inclusions within the amorphous matrix. The erosion of composites during contact cycling was similar as in Ag-W composites known as a good contact materials. SEM and TEM studies have shown a low solubility of tungsten in silver after ball milling and no solubility of silver in tungsten. The grain size of silver crystals within powders drastically decreased after milling down to about 30 nm and only a small increase in the grain size up to 200 nm was observed after hot pressing. These results were confirmed using TEM studies of composites after hot pressing. TEM microstructures have shown very narrow transition layer at the amorphous/silver interface (between 10-30 nm thick) containing all elements from the amorphous powders plus silver due to short time of hot pressing. The amorphous part has shown growth of intermetallic phases there, however diffused ring from the amorphous part was still visible. The composites prepared from silver and tungsten have shown presence of coherent tungsten rich precipitates showing typical strain field contrast within fine grains near 100 nm formed most probably during hot pressing of silver solid solution formed during mechanical alloying. The structure of tungsten has shown less defects and consequently less grain refinement than silver particles. SEM studies of the compression tested samples of silver-amorphous composites have shown crack formation at the interfaces of both components most probably due to presence of a brittle transition phase containing all elements.

Modern scanning electron microscopes (SEMs) increase the ability to study a wide range of materials. Especially, an application of low vacuum conditions enables characterization of nonconductive samples without complicated preparation procedure. However, the operator must be aware of several problems he may encounter collecting electron diffractions in the SEM with variable pressure. The charge control and quality of the surface are the challenges when running experiments on insulators. Specimen charging obscures forward scatter electrons images and decreases the EBSD pattern quality making indexing difficult or even impossible. Another crucial question is how to limit the influence of so called "skirt effect" caused by ionization of gas molecules followed by electron beam broading above the sample. The influence of several important parameters (gas pressure, a type of gas, working distance and energy of electron beam) on the EBSD pattern quality must also be considered. When it is properly done, a coupling of crystallographic information with the chemical data obtained from Energy Dispersive Spectroscopy (EDS) in the LV-SEM allows to perform phase identification of insulators. The paper presents some ideas how to deal with the (Pb, La)(Zr, Ti)O3 ceramics in high resolution Quanta 3D SEM (with thermally assisted Schottky type FEG) equipped with EDAX-TSL system in low vacuum environment. The problems occurring during EBSD analysis of the PLZT ceramics are discussed and some solutions are suggested. Paper summarizes the results obtained from PLZT ferroelectric ceramics in the low vacuum FEGSEM and shows how to optimise experimental parameters in order to achieve the best quality of orientation maps acquired from nonconductive samples.

A novel approach to fabricate magnetic elements made from nanocomposite materials by material extrusion is proposed. Flexibility in the shape and dimensions of this technology leads to the possibility to overcome the restrictions in the design and manufacturing of complex-shaped bulk magnets. The nanocomposites discussed here were fabricated by the addition of magnetite (Fe3O4) nanoparticles into a polymeric matrix: PEG-PVB and silicone gel. Composites with nanoparticles to polymer blend weight concentrations varying from 20% to 60% were prepared. The rheological behaviour of the suspensions was studied using rotational rheometry. The 3D prints were performed with and without an externally applied magnetic field. Microstructure, morphology and magnetic properties of the synthesised nanocomposites were confirmed by Fourier-transform infra-red spectroscopy (FT-IR), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM), respectively. The composites showed a uniform morphology with nanoparticles embedded homogeneously in the matrix. Magnetic response, namely remanence, saturation, coercive field and squareness, depend substantially on the type of polymeric matrix and nanoparticles concentration. Composites based on silicone have around 20–25% lower squareness ratio than the PEG-PVB-Fe3O4ones. The elements printed from selected composites exhibit weak but well pronounced magnetic shape anisotropy – a feature characteristic for bulk magnets.

The conditions for manganese with tin electrodeposition from aqueous citrate electrolytes were studied. Partial polarization curves were determined. The influence of applied potential, electrolyte composition and pH level, hydrodynamic conditions and quantity of charge passed, on the electrodeposition of Sn-Mn layers were determined. The surface composition of deposits was ascertained by chemical analysis (WDXRF). The morphology of coatings was studied by SEM. The phase composition of Sn-Mn samples was determined by X-ray diffractometry and Raman spectroscopy. The electrolysis parameters allowing electrodeposition of Sn-Mn coatings containing various amounts of Mn (in the range from about 0.5 wt% to 42 wt%) were selected. The morphology of deposits depends significantly on the content of manganese and on the parameters of electrolysis. The surface morphology of samples with Mn content of about 27 wt% is not uniform, two types of areas with significant differences in chemical composition are observed. XRD studies indicate that four crystallographic phases are formed in the deposits (β-Sn), MnO, Mn(OH)2, and MnSn2, while Raman spectroscopy revealed also the presence of α-MnO2, MnOOH, and SnO2, which are the products of chemical processes taking place simultaneously with electrolysis. The mechanism of the co-deposition of manganese with tin has been proposed.

The calcitic prismatic units forming the outer shell of the bivalve Pinctada margaritiferahave been analysed using scanning electron microscopy–electron back-scatter diffraction, transmission electron microscopy and atomic force microscopy. In the initial stages of growth, the individual prismatic units are single crystals. Their crystalline orientation is not consistent but rather changes gradually during growth. The gradients in crystallographic orientation occur mainly in a direction parallel to the long axis of the prism, i.e. perpendicular to the shell surface and do not show preferential tilting along any of the calcite lattice axes. At a certain growth stage, gradients begin to spread and diverge, implying that the prismatic units split into several crystalline domains. In this way, a branched crystal, in which the ends of the branches are independent crystalline domains, is formed. At the nanometre scale, the material is composed of slightly misoriented domains, which are separated by planes approximately perpendicular to the c-axis. Orientational gradients and splitting processes are described in biocrystals for the first time and are undoubtedly related to the high content of intracrystalline organic molecules, although the way in which these act to induce the observed crystalline patterns is a matter of future research.