Synthesis of FeSi-FeAl Composites from Separately Prepared FeSi and FeAl Alloys and Their Structure and Properties.

Composites consisting of iron aluminide and iron silicide phases were studied in this work. Powders of iron aluminide and iron silicide were prepared by mechanical alloying separately. Subsequently, they were blended in three different proportions and sintered by the SPS method under various conditions. After sintering, the composites are composed of FeAl and amounts of other silicides (Fe5Si3 and Fe3Si). Ternary Fe-Al-Si phases were not determined, even though their presence was predicted by DFT calculations. This disagreement was explained by steric factors, i.e., by differences in the space lattice of the present phases. Hardness and tribological properties were measured on composites with various weight ratios of iron aluminide and iron silicide. The results show that sintered silicides with the matrix composed of iron aluminide reach comparable hardness to tool steels. The composites with higher mass ratios of iron aluminide than silicide have higher hardness and better tribological properties.

Multiplexed detection of viral antigen and RNA using nanopore sensing and encoded molecular probes.

We report on single-molecule nanopore sensing combined with position-encoded DNA molecular probes, with chemistry tuned to simultaneously identify various antigen proteins and multiple RNA gene fragments of SARS-CoV-2 with high sensitivity and selectivity. We show that this sensing strategy can directly detect spike (S) and nucleocapsid (N) proteins in unprocessed human saliva. Moreover, our approach enables the identification of RNA fragments from patient samples using nasal/throat swabs, enabling the identification of critical mutations such as D614G, G446S, or Y144del among viral variants. In particular, it can detect and discriminate between SARS-CoV-2 lineages of wild-type B.1.1.7 (Alpha), B.1.617.2 (Delta), and B.1.1.539 (Omicron) within a single measurement without the need for nucleic acid sequencing. The sensing strategy of the molecular probes is easily adaptable to other viral targets and diseases and can be expanded depending on the application required.

Improvement in Abrasive Wear Resistance of Metal Matrix Composites Used for Diamond-Impregnated Tools by Heat Treatment.

This work presents the possibilities of producing a substitute for a commercial matrix material for sintered metal-diamond tools which is characterized by increased tribological properties required in machining natural stones and concrete. In this study, the improvement in wear behavior of sintered pre-alloyed matrix caused by a thermal treatment was investigated. Several mixtures made of commercially available powders were homogenized by ball milling and consolidated at 900 °C using the spark plasma sintering (SPS) method. During cooling down, the specimens were subjected to isothermal holding at 350 or 250 °C for 1 h. After consolidation, all specimens were tested for density and hardness, whereas selected specimens were characterized by scanning electron microscopy (SEM) and flexural strength tests. The specimens made of BDCM50 powder (a mixture of the base and pre-alloyed powders in 50:50 proportion) shows excellent properties including σ0.2 = 1045 MPa in the three-point bending test and HV10 ≈ 380. Resistance to abrasive wear evaluated in both three-body and two-body conditions in the MWT abrasion test was estimated at Ai3=18.1±3.9 µm/20 m and Ai2=95.9±11.8 µm/20 m, respectively. A series of diamond-impregnated specimens (segments) was also produced and tested for wear rate on abrasive concrete. The potential graphitization of the diamond grits was investigated using Raman spectroscopy and X-ray diffraction. As a reference, both the base Fe-Mn-Cu-Sn-C and commercially available Co+20%WC alloy were used to compare selected properties of the investigated materials. It has been proved that heat-treated specimens made of the base mixture modified with pre-alloyed powders are characterized by increased hardness and resistance to abrasive wear. The BDCM50 matrix has a negligible effect on diamond graphitization and shows excellent field performance, which makes it a good potential substitute for replacing Co+20%WC in sintered diamond-impregnated tools.

Processing of Niobium-Alloyed High-Carbon Tool Steel via Additive Manufacturing and Modern Powder Metallurgy.

Niobium is recently considered one of the potential alloying elements for tool steels due to the formation of hard and stable carbides of MC type. Its use is limited by the fact that these carbides tend to coarsen during conventional melting metallurgy processing. This work explores the potential of additive manufacturing for processing Nb-alloyed tool steel with a high content of carbon. Directed energy deposition was used as the processing method. It was found that this method allowed us to obtain a microstructure very similar to that obtained after the use of consolidation via spark plasma sintering when subsequent heat treatment by soft annealing, austenitizing, oil quenching and triple tempering for secondary hardness was applied. Moreover, the soft annealing process could be skipped without affecting the structure and properties when machining would not be required. The hardness of the steel was even higher after additive manufacturing was used (approx. 800-830 HV 30) than after spark plasma sintering (approx. 720-750 HV 30). The wear resistance of the materials processed by both routes was almost comparable, reaching 5-7 × 10-6 mm3N-1m-1 depending on the heat treatment.

The reactivity of antimony and bismuth N,C,N-pincer compounds toward K[BEt3H] - the formation of heterocyclic compounds vs. element-element bonds vs. stable terminal Sb-H bonds.

The oxidative addition of CF3SO3CH2Si(CH3)3 (NpSiOTf) toward organopnictogen(I) N,C,N-pincer compounds, i.e. [2,6-(DippNCH)2C6H3]E (1-E, where E = Sb, Bi; Dipp = 2,6-iPr2C6H3) produced compounds [2,6-(DippNCH)2C6H3]E(NpSi)(OTf) (2-E, where E = Sb, Bi). By analogy, the in situ reduction of [2,6-(Me2NCH2)2C6H3]ECl2 (3-E, where E = Sb, Bi) followed by treatment with NpSiOTf or MeI gave compounds [2,6-(Me2NCH2)2C6H3]E(R)(X) (R/X = NpSi/OTf 4-E, where E = Sb, Bi; R/X = Me/I 5-Sb). The reactivity of these compounds toward 1 eq. of K[BEt3H] was examined showing remarkable differences depending both on the ligand backbone and the pnictogen used. Thus in the case of 2-E, the addition of the hydride across the imino-function was achieved thereby yielding azapnicta-heterocyclic compounds [2-(DippNCH2)-6-(DippNCH)C6H3]E(NpSi) (6-E, where E = Sb, Bi). The same reaction of 4-Bi produced dibismuthine {[2,6-(Me2NCH2)2C6H3]Bi(NpSi)}2 (7-Bi), but in the case of 4/5-Sb the analogous distibines {[2,6-(Me2NCH2)2C6H3]Sb(R)}2 (R = NpSi7-Sb, Me 8-Sb) were not formed directly and hydrides [2,6-(Me2NCH2)2C6H3]Sb(R)H (R = NpSi9-Sb, Me 10-Sb) could be isolated instead. Nevertheless, heating of both 9-Sb and 10-Sb led to an activation of a labile Sb-H bond and the formation of distibines 7/8-Sb.

Heat Treatment of Metallic Materials in Modern Industry.

The Heat Treatment of Metallic Materials in Modern Industry is a Special Issue of the journal Materials, which aims to publish original full-length articles and review papers on basic and applied research centered around the given topic, and thereby make the understanding of the metallurgical background of the contemporary state of heat treatment techniques used in the industrial branches in the 21st century [...].

Microstructural Characteristics of Al-Ti-B Inoculation Wires and Their Addition to the AlSi7Mg0.3 Alloy.

Commercially supplied inoculation wires have a guaranteed chemical composition but not the size and distribution of individual phases, which are very important for nucleation. Therefore, two commercial alloys used for the inoculation of Al-Si alloys (AlTi3B1 and AlTi5B1) are investigated in this paper. The emphasis is placed on their structural analysis and the size and distribution of individual intermetallic phases. Furthermore, the grain refinement effect will be tested by adding these alloys to the AlSi7Mg0.3 alloy and testing the optimal amount of added inoculation wires. The results showed that the size and distribution of the individual phases in AlTi3B1 and AlTi5B1 meet the requirements for the successful inoculation of aluminum alloys, the intermetallic phases based on the TiAl3 phase are fine enough, and there is no agglomeration that would reduce the number of nuclei. This assumption was confirmed by adding these inoculants to the AlSi7Mg0.3 alloy, and it was found that the most ideal amount of inoculants added is 0.01 wt % when the structure was refined by approximately 32%.

Stigmatic optical system with corrected third-order spherical aberration for an arbitrary position of the object.

Our paper is focused on a problem of analysis and design of a stigmatic optical system that has corrected third-order spherical aberration for an arbitrary position of the object. The relations for Seidel aberration coefficients of the system for an object at infinity that must be satisfied to ensure that the third-order spherical aberration does not depend on the position of the object are given. The method for obtaining design parameters of the initial optical system that can serve as a good starting point for further refinement using numerical optimization methods is proposed. Based on the use of modified formulas for third-order aberration coefficients, this method enables one to decide if the individual members of the optical system can be simple lenses or if these should be more complex elements (cemented doublets, triplets, etc.). As a final result, one obtains the design parameters of the above-mentioned optical system (radii of curvature, optical materials, axial separations between individual elements). The analysis is performed for a thin-lens representation of the system. The transition to the thick-lens optical system then can be done by mathematical methods of numerical optimization using commercially available optical design software. The proposed method is shown on a practical example of calculation of parameters of such an optical system.

Heat Treatment of Aluminum Alloys with the Natural Combination of Dopants.

Aluminothermic reduction without the separation of individual metals is currently considered as a possible method for processing ferromanganese sea nodules and creating new alloys. In this study, the product of their reduction-a manganese-based polymetallic mixture-was added to pure aluminum, as a mixture of alloying elements in their natural ratios. After extrusion, two new aluminum alloys with a total percentage of metallic additives ranging from 1 to 6 percent were prepared. The possibilities of the precipitation strengthening of these aluminum alloys, especially those containing Mn, Fe, Si, Ni, and Cu, were investigated under a wide range of heat treatment conditions. After each tested combination of annealing and artificial aging temperatures, the phase composition and the microstructure changes were recorded by X-ray diffraction, optical, and scanning electron microscopy with EDS analysis. Under none of the tested heat treatment conditions is a significant hardening effect observed, even though the precipitate phases are observed by TEM. However, the changes in the morphology of the present intermetallic phases caused by the heat treatment are revealed, which highlights the further possible development of these multicomponent alloys.

Possibilities of a Direct Synthesis of Aluminum Alloys with Elements from Deep-Sea Nodules.

This work investigated the possibility of the direct preparation of aluminum alloys by aluminothermic reduction of deep-sea nodules with a high excess of aluminum. The process was found to be unable to obtain aluminum alloy, but an aluminum-rich manganese-based alloy was obtained instead, being composed of intermetallics. The alloy was characterized in the as-reduced state, as well as after crushing and sintering in the temperature range of 800-950 °C. The sample sintered at 900 °C was also heat-treated by annealing at 800 °C for 3 h and rapidly cooled. It was observed that with the increasing sintering temperature, the original matrix phase Al11Mn14 was transformed into a duplex matrix with a structure corresponding to Al11Mn14 and Al4Cu9, and this mixture was further transformed to the matrix with the structure corresponding to Al4Cu9. Furthermore, the mechanical properties and wear resistance of the samples were described. The highest microhardness was reached in the sample, which was annealed after sintering. Sintered samples reached a lower wear rate because of the fragmentation of brittle intermetallics during crushing.

General method for replacing a thin lens with a thick lens with the same value of Seidel aberration coefficient of spherical aberration or coma.

The paper deals with the problem of replacing a thin lens with a thick lens having similar third-order aberration properties as the thin lens. The equations that make possible the calculation of parameters of the thick lens, which has the same value of focal length (or transverse magnification) and one of the Seidel aberration coefficients (either Seidel aberration coefficient of spherical aberration or Seidel aberration coefficient of coma) as the thin lens for given position of the entrance pupil and object, are derived. The application of the proposed method for calculation of parameters of the thick lens is shown in examples.

Corrosion Properties of Mn-Based Alloys Obtained by Aluminothermic Reduction of Deep-Sea Nodules.

Deep-sea manganese nodules are polymetallic oxidic ores that can be found on a seabed. Aluminothermic reduction is one of the possibilities of manganese nodules processing. This process obtains the polymetallic alloy with a high content of Mn and a varying content of Al, depending on the ratio between aluminum and nodules. The corrosion behaviors of three experimental Mn-based alloys produced by aluminothermic reduction with a content of Mn > 50 wt % were studied. The electrochemical testing in potable water and model seawater was used to explain the corrosion mechanism of Mn-based alloys. The results showed that the corrosion rate of experimental Mn-based alloy decreases with the increase in aluminum content in both potable water and model seawater. It was observed that the uniform corrosion of experimental Mn-based alloys is changed with an increase in aluminum content in alloy to localized corrosion, which was caused by microcells in an environment of model seawater. In contrast, the formation of a semi-protective layer of corrosion products was observed on the surface of Mn-based alloys with a higher content of aluminum in potable water. Moreover, the pitting corrosion of tested Mn-based alloys was observed neither in potable water nor in model seawater.

First-principles calculations of magnetic properties for analysis of magnetization processes in rare-earth permanent magnets.

It has been empirically known that the coercivity of rare-earth permanent magnets depends on the size and shape of fine particles of the main phase in the system. Also, recent experimental observations have suggested that the atomic-scale structures around the grain-boundaries of the fine particles play a crucial role to determine their switching fields. In this article, we review a theoretical attempt to describe the finite temperature magnetic properties and to evaluate the reduction of the switching fields of fine particles of several rare-earth permanent magnetic materials based on an atomistic spin model that is constructed using first-principles calculations. It is shown that, over a wide temperature range, the spin model gives a good description of the magnetization curves of rare-earth intermetallic compounds such as R 2Fe14B (R= Dy, Ho, Pr, Nd, Sm) and SmFe12. The atomistic spin model approach is also used to describe the local magnetic anisotropy around the surfaces of the fine particles, and predicts that the rare-earth ions may exhibit planar magnetic anisotropy when they are on the crystalline-structure surfaces of the particles. The dynamical simulation of the atomistic spin model and the corresponding micromagnetic simulation show that the planar surface magnetic anisotropy causes a reduction in the switching field of fine particles by approximately 20-30%, which may be relevant to the atomic-scale surface effects found in the experimental studies.

Novel High-Entropy Aluminide-Silicide Alloy.

Novel high-entropy (multi-principal elements) alloy based on Fe-Al-Si-Ni-Ti in equimolar proportions has been developed. The alloy powder obtained by mechanical alloying is composed of orthorhombic FeTiSi phase with the admixture of B2 FeAl. During spark plasma sintering of this powder, the FeSi phase is formed and the amount of FeAl phase increases at the expense of the FeTiSi phase. The material is characterized by a high compressive strength (approx. 1500 MPa) at room temperature, being brittle. At 800 °C, the alloy is plastically deformable, having a yield strength of 459 MPa. The wear resistance of the material is very good, comparable to the tool steel. During the wear test, the spallation of the FeSi particles from the wear track was observed locally.

Noncontact Nanoscale Imaging of Cells.

The reduction in ion current as a fine pipette approaches a cell surface allows the cell surface topography to be imaged, with nanoscale resolution, without contact with the delicate cell surface. A variety of different methods have been developed and refined to scan the topography of the dynamic cell surface at high resolution and speed. Measurement of cell topography can be complemented by performing local probing or mapping of the cell surface using the same pipette. This can be done by performing single-channel recording, applying force, delivering agonists, using pipettes fabricated to contain an electrochemical probe, or combining with fluorescence imaging. These methods in combination have great potential to image and map the surface of live cells at the nanoscale.

Mapping mechanical properties of living cells at nanoscale using intrinsic nanopipette-sample force interactions.

Mechanical properties of living cells determined by cytoskeletal elements play a crucial role in a wide range of biological functions. However, low-stress mapping of mechanical properties with nanoscale resolution but with a minimal effect on the fragile structure of cells remains difficult. Scanning Ion-Conductance Microscopy (SICM) for quantitative nanomechanical mapping (QNM) is based on intrinsic force interactions between nanopipettes and samples and has been previously suggested as a promising alternative to conventional techniques. In this work, we have provided an alternative estimation of intrinsic force and stress and demonstrated the possibility to perform qualitative and quantitative analysis of cell nanomechanical properties of a variety of living cells. Force estimation on decane droplets with well-known elastic properties, similar to living cells, revealed that the forces applied using a nanopipette are much smaller than in the case using atomic force microscopy. We have shown that we can perform nanoscale topography and QNM using a scanning procedure with no detectable effect on live cells, allowing long-term QNM as well as detection of nanomechanical properties under drug-induced alterations of actin filaments and microtubulin.

Solutions of Critical Raw Materials Issues Regarding Iron-Based Alloys.

The Critical Raw Materials (CRMs) list has been defined based on economic importance and supply risk by the European Commission. This review paper describes two issues regarding critical raw materials: the possibilities of their substitution in iron-based alloys and the use of iron-based alloys instead of other materials in order to save CRMs. This review covers strategies for saving chromium in stainless steel, substitution or lowering the amounts of carbide-forming elements (especially tungsten and vanadium) in tool steel and alternative iron-based CRM-free and low-CRM materials: austempered ductile cast iron, high-temperature alloys based on intermetallics of iron and sintered diamond tools with an iron-containing low-cobalt binder.

Development of TiAl-Si Alloys-A Review.

This paper describes the effect of silicon on the manufacturing process, structure, phase composition, and selected properties of titanium aluminide alloys. The experimental generation of TiAl-Si alloys is composed of titanium aluminide (TiAl, Ti3Al or TiAl3) matrix reinforced by hard and heat-resistant titanium silicides (especially Ti5Si3). The alloys are characterized by wear resistance comparable with tool steels, high hardness, and very good resistance to oxidation at high temperatures (up to 1000 °C), but also low room-temperature ductility, as is typical also for other intermetallic materials. These alloys had been successfully prepared by the means of powder metallurgical routes and melting metallurgy methods.

Structure and Properties of Cast Ti-Al-Si Alloys.

Intermetallic compounds based on Ti-Al- (Si) are attractive materials with good thermal stability and low density. However, the production of these materials is quite complicated. Partially modified conventional methods of melting metallurgy are most often used due to availability, possible high productivity, and relatively low production costs. Therefore, some technologies for the production of intermetallics based on Ti-Al are currently available, but with certain disadvantages, which are caused by poor casting properties or extreme reactivity of the melt with crucibles. Some shortcomings can be eliminated by modifying the melting technology, which contributes to increasing the cost of the process. The work deals with the preparation of Ti-Al-Si intermetallic compounds with different contents of aluminum and silicon, which were produced by centrifugal casting in an induction vacuum furnace Linn Supercast-Titan. This process could contribute to the commercial use of these alloys in the future. For this research, the TiAl15Si15(in wt.%) alloy was selected, which represents a balanced ratio of aluminides and silicides in its structure, and the TiAl35Si5 alloy, which due to the lower silicon content allows better melting conditions, especially with regard to the melting temperature. This alloy was also investigated after HIP ("Hot Isostatic Pressing") treatment.

Exchange interactions in ε-Fe2O3: GGA+U calculations.

We have studied the origin of magnetic interaction in ε-Fe2O3by ab-initio electronic structure calculations. The exchange integrals of the Heisenberg hamiltonian have been calculated using the methods based on the density functional theory (DFT) employing generalized gradient approximation with orbital dependent potential extension for 3d electrons of Fe (GGA+U method). The calculations confirm the ground antiferromagnetic (AFM) state with two Fe3+sublattices oriented up (Fe2 and Fe3) and two Fe3+sublattices oriented down (Fe1 and Fe4). The calculated exchange integrals, including also the intra-sublattice ones, are all of AFM type. Their strength weighted by the number of neighbors is larger between the Fe sublattices with opposite spins than between the sublattices with equal spin directions. The notable exception is a strong exchange integral between theneighboring tetrahedrally-coordinated sites within the Fe4 sublattice, which effectively decreases the molecular field imposed on Fe4 sites by neighboring sites of other sublattices, namely the antiparallelly oriented Fe2 and Fe3. For this reason, the ordered magnetic moment of Fe4 exhibits the fastest decrease with increasing temperature among the sublattices, leading to an uncompensated AFM arrangement in ε-Fe2O3. Considering the competition of the inter- and intra-sublattice exchange integrals and applying symmetry arguments, we infer that the collinear AFM ground state of ε-Fe2O3is prone to an intrinsic canting within the sublattices, retaining at the same time the magnetic group symmetry Pna'21'.