Moiré patterns and carbon nanotube sorting

Moiré patterns (MPs), arising from the superposition of two lattices with close periods, are tightly related to the physicochemical properties of bilayer nanostructures. Here, we develop the theory of complex MPs emerging in twisted bilayer graphene and planar nets of double-walled nanotubes at significant relative twist and/or deformation of layers. The proposed theory clarifies the physicochemical regularities arising at sorting of single-walled carbon nanotubes (SWCNTs) by organic molecules, which self-assemble in regular coatings on both the tubes and planar graphene. We introduce and consider an outer tubular virtual lattice that is a parent structure for the deposited coating and due to this fact, its existence is crucial for the coating formation. As we show, such outer lattices exist only for successfully sorted SWCNTs and the superposition between the outer lattice and SWCNT forms a specific long-period MP. We explain known experimental results of SWCNT sorting by molecules of flavin group, poly(9,9-dioctylfluorene-2,7-diyl) (PFO), and poly [(m-phenylenevinylene)-alt-(p-phenylenevinylene)] (PmPV). Also, our approach points out other organic molecules and polymers suitable for effective CNT sorting.

Structure of tantalum coatings on NiTi substrate deposited by magnetron sputtering

The paper provides the results of studies of the structural-phase state of tantalum coatings prepared by magnetron deposition. The coatings were deposited on substrates made of titanium nickelide with a shape memory. The NiTi temperature during coating deposition did not exceed 100 °C. The structural-phase state of Ta was determined by X-ray diffraction at different stages of coating formation. It has been shown that at the initial stage of deposition, two-phase coatings (α- and β-Ta) are formed. The synthesis of the coating from Ta leads to the growth of interplanar distance of the B2 austenite phase in the crystallographic direction (100). The growth of interplanar spacing is caused by formation of microstresses during interaction with incident tantalum ions. The lattice parameters of the B19 ‘phase, responsible for appearance of the shape memory effect, do not change during deposition of the tantalum coating.

Material Priority Engineered Metal-Polyphenol Networks: Mechanism And Platform For Multifunctionalities

Engineering the surface of materials with desired multifunctionalities is an effective way to fight against multiple adverse factors during the tissue repair process. Recently, metal-polyphenol networks (MPNs) have gained increasing attention because of their rapid and simple deposition process onto various substrates (silicon, quartz, gold and polypropylene sheets, etc.). However, the coating mechanism has not been clarified, and multifunctionalized MPNs remain unexplored. Herein, the flavonoid polyphenol procyanidin (PC) was selected to form PC-MPN coatings with Fe3+, and assembly parameters, including pH, molar ratio between PC and Fe3+, and material priority during coating formation, were thoroughly evaluated. We found that the material priority (addition sequence of PC and Fe3+) had a great influence on the thickness of the formed PC-MPNs. Various surface techniques (e.g., ultraviolet-visible spectrophotometry, quartz crystal microbalance, X-ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy) were used to investigate the formation mechanism of PC-MPNs, and PC-MPNs were further engineered for multifunctionalities (fastening cellular attachment in the early stage, promoting long-term cellular proliferation, antioxidation and antibacterial activity). We believe that these findings could further reveal the coating formation mechanism of MPNs and guide the future design of MPN coatings with multifunctionalities, thereby greatly broadening their application prospects, such as in sensors, environments, drug delivery, and tissue engineering.

Kinetics of the formation of a diffusion layer on AISI 1045 steel with simultaneous saturation with boron, chromium and titanium

Research has been carried out to determine the kinetics of coating formation on AISI 1045 steel with diffusion saturation with boron, chromium and titanium simultaneously. It was found that the experimental parameters of the thickness of the diffusion layer of borides over time outstrip the calculated values. The diffusion layer has a thickness of 120 μm with a saturation duration of 2.5 h, 155 μm with a saturation duration of 5 h, and 180 μm with a saturation duration of 7.5 h. In addition to studying the kinetics of the formation of a diffusion coating, also studied the distribution of microhardness over the cross section of the diffusion coating. The maximum microhardness of the diffusion coating is observed not on the surface, but at some distance from it. On average, at a depth of 45–60 µm from the surface. In this case, the microhardness on the surface of the diffusion coating, on the contrary, tends to take on a minimum value of about 1800 HV0.1. Such a distribution of microhardness it gives the parts the possibility of minor surface wear.

Design of Magnesia–Spinel Bricks for Improved Coating Adherence in Cement Rotary Kilns

It is well known that doloma bricks present better coating adherence than magnesia–spinel bricks when applied in cement rotary kilns, which is related to the different coating formation mechanism. The coating has an essential role in prolonged operation by protecting the refractory lining; thus, it is important to improve its adherence on magnesia–spinel refractories. The objective of this investigation is to study different compositions of magnesia–spinel bricks, achieved by varying additives used (calcined alumina, limestone, hematite and zirconia) and firing temperature (1500 °C and 1700 °C), to enhance the coating adherence measured by the sandwich test. The results have pointed out that the use of higher firing temperature contributes positively to physical adherence due to well-sintered refractory structure and elevated permeability, attaining coating strength superior to 2 MPa. For the chemical adherence, the addition of 2 wt.% of limestone increased the coating strength to 3 MPa, but resulted in a drop in hot properties. In this context, the most suitable approach to improve adherence of clinker coating and maintain hot properties in suitable levels is to increase the firing temperature.

Two-stage PVD method for protective coating formation

The CVD methods are typically used for the formation of aluminum oxide coatings since aluminum oxide is a dielectric. The adhesion between the protective coating and the substrate material is normally improved by growing thin intermediate layers based on titanium oxides and nitrides. These intermediate layers are mainly formed using the PVD methods. In this paper, we propose a two-stage PVD method for forming a layered structure on the titanium substrate. The formation of intermediate layers was carried out by the magnetron method (first stage), and the main protective layer was deposited at the second stage using a fore-vacuum electron source. The dense beam plasma generated during the electron beam transport in a fore-vacuum gas medium compensates for the negative electrical charge accumulating on the surface of the aluminum oxide target and facilitates its effective evaporation. The electrical properties of the intermediate layers and the resulting layered coatings have been investigated, including the tangent of dielectric loss angle, the real and imaginary parts of the conductivity and the dielectric constant dependencies on frequency.

Study of the titanium VT1-0 surface degradation after cyclic loading in different structural states, including ones when coatings are formed by Micro-Arc Oxidation

This article considers the results of the study of the titanium VT1-0 surface degradation (Grade-4 equivalent) for recrystallized- and ultrafine-grained states after fatigue testing. Comparative analysis of peculiarities of the titanium samples degradation was performed after coating formation by Micro-Arc Oxidation. It was found, that the coating formed by Micro-Arc Oxidation shows different degradation behaviors for recrystallized and ultrafine-grained states

Developing technology of creating wear-resistant ceramic coating for internal combustion engine cylinder sleeve

This paper presents the results of testing a wear-resistant ceramic coating on the work surface of an internal combustion engine (ICE) cylinder’s sleeve. A combined coating formation technology is described that consists in applying an aluminum layer to the sleeve’s work face by gas dynamic spraying and then covering this face with a ceramic layer by microarc oxidation (MAO). A tenfold reduction in the reinforced sleeve has been determined by the accelerated comparative wear rig tests of reference (new) sleeve-piston ring coupling specimens and reinforced specimens with a combined coating. The supplementation of nanoparticle admixture to MAO coating reduces the friction factor between the cylinder sleeve face and the piston ring by 25-30%. The proposed technology can be used to reinforce work surfaces of new cylinder sleeves and recover worn out ones.

Physical–Chemical Exfoliation of n-Alkylamine Derivatives of Layered Perovskite-like Oxide H2K0.5Bi2.5Ti4O13 into Nanosheets

In the present work, we report the results on exfoliation and coating formation of inorganic–organic hybrids based on the layered perovskite-like bismuth titanate H2K0.5Bi2.5Ti4O13·H2O that could be prepared by a simple ion exchange reaction from a Ruddlesden–Popper phase K2.5Bi2.5Ti4O13. The inorganic–organic hybrids were synthesized by intercalation reactions. Exfoliation into nanosheets was performed for the starting hydrated protonated titanate and for the derivatives intercalated by n-alkylamines to study the influence of preliminary intercalation on exfoliation efficiency. The selected precursors were exfoliated in aqueous solutions of tetrabutylammonium hydroxide using facile stirring and ultrasonication. The suspensions of nanosheets obtained were characterized using UV–vis spectrophotometry, dynamic light scattering, inductively coupled plasma spectroscopy, and gravimetry. Nanosheets were coated on preliminarily polyethyleneimine-covered Si substrates using a self-assembly procedure and studied using atomic force and scanning electron microscopy.