METASTABLE STRUCTURE OF AUSTENITIC MANGANESE ALLOY AND PROSPECTS FOR CREATION OF PARTS BASED ON IT

Comparative microstructural studies and mechanical tests of an experimental austenic manganese alloy and typical structural materials have been carried out. As a result of the research, relative data have been revealed, indicating high mechanical properties of the experimental alloy, which makes it possible to recommend it for machine parts operating at high load-speed operating conditions and temperature exposure up to 700 0C.

Effect of F Functional Modification on the Stability and Electronic Structure of Borene

Since the discovery of graphene, two-dimensional materials have quickly won widespread attention in the academic community. Borene is a two-dimensional isomer of boron and the lightest element Dirac material. It becomes the latest and promising two-dimensional material due to its unique structure and electronic properties. In the periodic table, B is a close neighbor of C and has a certain similarity with C. It can also form a hexagonal honeycomb structure. An additional B atom is added to the center of the ring to form a triangular lattice borene. The triangular borene has surplus electrons and belongs to a multi-electron state, which is equivalent to a metastable structure. In this paper, the first principles are used to study the F functionalized modification of the triangular borene. The aim is to transfer the surplus electrons in the system, and probe its structural stability and electronic structure characteristics. The study found that functional modification significantly improved the stability of borene. This can provide feasible ideas and practical guidance for the experimental synthesis of stable boronene.

Preliminary Local Thermal Impact as a Surface Quality Assurance Factor

The article considers the issues of assuring the quality of the surfaces of machine parts by applying a preliminary local thermal impact before their edge cutting machining. In the zone of application of local thermal impact, a zone of metastable structure with respect to the material of the workpiece to be treated occurs. When the cutting plane intersects with the local thermal application line, the formed flow chip is segmented. The created graphs allow assigning of local thermal modes to the surface of the workpiece before edge cutting machining. Application of preliminary local thermal impact will assure the specified quality of the surface of the treated workpiece at semi-finishing and finishing edge cutting machining modes and stable segmentation of the flow chip.

Chemical, Thermal, Time, and Enzymatic Stability of Silk Materials with Silk I Structure

The crystalline structure of silk fibroin Silk I is generally considered to be a metastable structure; however, there is no definite conclusion under what circumstances this crystalline structure is stable or the crystal form will change. In this study, silk fibroin solution was prepared from B. Mori silkworm cocoons, and a combined method of freeze-crystallization and freeze-drying at different temperatures was used to obtain stable Silk I crystalline material and uncrystallized silk material, respectively. Different concentrations of methanol and ethanol were used to soak the two materials with different time periods to investigate the effect of immersion treatments on the crystalline structure of silk fibroin materials. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman scattering spectroscopy (Raman), Scanning electron microscope (SEM), and Thermogravimetric analysis (TGA) were used to characterize the structure of silk fibroin before and after the treatments. The results showed that, after immersion treatments, uncrystallized silk fibroin material with random coil structure was transformed into Silk II crystal structure, while the silk material with dominated Silk I crystal structure showed good long-term stability without obvious transition to Silk II crystal structure. α-chymotrypsin biodegradation study showed that the crystalline structure of silk fibroin Silk I materials is enzymatically degradable with a much lower rate compared to uncrystallized silk materials. The crystalline structure of Silk I materials demonstrate a good long-term stability, endurance to alcohol sterilization without structural changes, and can be applied to many emerging fields, such as biomedical materials, sustainable materials, and biosensors.

Viral Mimicry as a Design Template for Nucleic Acid Nanocarriers

Therapeutic nucleic acids hold immense potential in combating undruggable, gene-based diseases owing to their high programmability and relative ease of synthesis. While the delivery of this class of therapeutics has successfully entered the clinical setting, extrahepatic targeting, endosomal escape efficiency, and subcellular localization. On the other hand, viruses serve as natural carriers of nucleic acids and have acquired a plethora of structures and mechanisms that confer remarkable transfection efficiency. Thus, understanding the structure and mechanism of viruses can guide the design of synthetic nucleic acid vectors. This review revisits relevant structural and mechanistic features of viruses as design considerations for efficient nucleic acid delivery systems. This article explores how viral ligand display and a metastable structure are central to the molecular mechanisms of attachment, entry, and viral genome release. For comparison, accounted for are details on the design and intracellular fate of existing nucleic acid carriers and nanostructures that share similar and essential features to viruses. The review, thus, highlights unifying themes of viruses and nucleic acid delivery systems such as genome protection, target specificity, and controlled release. Sophisticated viral mechanisms that are yet to be exploited in oligonucleotide delivery are also identified as they could further the development of next-generation nonviral nucleic acid vectors.

A Novel Double-Group Crosslinked Hydrogel with High Thixotropy for Water Control in Horizontal Wells

Summary Horizontal wells that are completed with slotted liners often suffer from a severe water-production problem, which is detrimental to oil recovery. It is because the annulus between the slotted liners and wellbore cannot be fully filled with common hydrogels with poor thixotropy, which determines the ultimate hydrogel filling shape in the annulus. This paper presents a novel hydrogel with high thixotropy to effectively control water production in horizontal wells. This study is aimed at evaluating the thixotropic performance, gelation time, plugging performance, and degradation performance. The thixotropic performance of the new hydrogel was also investigated by measuring its rheological properties and examining its microstructures. It was found that the new hydrogel thickened rapidly after shearing. Its thixotropic recovery coefficient was 1.747, which was much higher than those of traditional hydrogels. The gelation time can be controlled in the range of 2 to 8 hours by properly adjusting the concentrations of the framework material, crosslinker, and initiator. The hydrogel could be customized for mature oil reservoirs, at which it was stable for more than 90 days. A series of laboratory physical modeling tests showed that the breakthrough pressure gradient and the plugging ratio of the hydrogel in sandpacks were higher than 9.5 MPa/m and 99%, respectively. At the same time, it was found that the hydrogel has good degradation properties; the viscosity of the hydrogel breaking solution was 4.22 mPa·s. Freeze-etching scanning-electron-microscopy examinations indicated that the hydrogel had a uniform grid structure, which can be broken easily by shear and restored quickly. This led to the remarkable thixotropic performance. The formation of a metastable structure caused by the electrostatic interaction and coordination effect was considered to be the primary reason for the high thixotropy. The successful development of the new thixotropic hydrogel not only helps to control water production from the horizontal wells, but also furthers the thixotropic theory of hydrogel. This study also provides technical guidelines for further increasing the thixotropies of drilling fluids, fracturing fluids, and other enhanced-oil-recovery polymers that are commonly used in the petroleum industry.

Phase Stability of Chloroform and Dichloromethane at High Pressure

Chloroform (CHCl3) and dichloromethane (CH2Cl2) are model systems for the study of intermolecular interactions, such as hydrogen bonds and halogen–halogen interactions. Here we report a joint computational (density-functional perturbation theory (DFPT) modelling) and experimental (Raman scattering) study on the behaviour of the crystals of these compounds up to a pressure of 32 GPa. Comparing the experimental information on the Raman band positions and intensities with the results of calculations enabled us to characterize the pressure-induced evolution of the crystal structure of both compounds. We find that the previously proposed P63 phase of CHCl3 is in fact a metastable structure, and that up to 32 GPa the ambient-pressure Pnma structure is the ground state polymorph of this compound. For CH2Cl2 we confirm the stability of the ambient-pressure Pbcn structure up to 32 GPa. We show that the high-pressure evolution of the crystal geometry of CHCl3 in the Pnma structure is a result of the subtle balance between dipole–dipole interactions, hydrogen bonds and Cl···Cl contacts. For CH2Cl2 (Pbcn structure) the dipole–dipole interactions and hydrogen bonds are the main factors influencing the pressure-induced changes in the geometry.

Some data on the TiC-TiNi system's hard-alloy composite with high performance properties

The data are provided on the composite material of the TiC-TiNi system with increased performance properties, which belong to the group of CM based on refractory titanium compounds called "tungsten-free hard alloys". The concept of a structural-energy transition from the perspective of thermodynamics is involved and developed. Based on this concept, the evolution of the structural-energy state of a composite material in the form of a model with two energy levels is considered. In the process of forming a composite mixture with a stable equilibrium structure, new stress-strain structures with an energy level of E1, which are unstable and have higher mechanical properties, arise. During sintering, the deformed structures with the energy level E1 pass into a more stable state with the energy level E2 due to the formation of energy-winning eutectic structures of the TiNi binding phase and the fine-grained dense structure of TiC carbides, which represent a steady metastable structure of the composite. It is established that depending on the volume concentration of the TiNi binding phase, the development of thermodynamic processes for forming the structure of a hard-alloy composite leads to the production of a final structure of the two different types and performance properties. It is shown that the critical concentration can be considered a volume concentration of 40% (vol). The resonant-acoustic method allowed to determine the visco-elastic characteristics (Young, shear, and compression moduli; Poisson's ratio), as well as their dependence on the concentration of the binding phase. The Young's modulus is theoretically calculated. It was found that the use of TiC-TiNi hard-alloy composite allows to increase the efficiency of the cutting tool and technological equipment by one and a half times compared to a tool made of the known tungsten-free alloys KNT-16, TN-(20, 30) and KTS.