Abstract
In the present study, a method for the synthesis of gelatin-stabilized copper oxide nanoparticles was developed. Synthesis was carried out by direct chemical precipitation. Copper sulfate, ...chloride, and acetate were used as precursors for the copper oxide synthesis. Gelatin was used as a stabilizer. It was found that the formation of monophase copper oxide II only occurred when copper acetate was used as a precursor. Our results showed that particles of the smallest diameter are formed in an aqueous medium (18 ± 6 nm), and those of th largest diameter—in an isobutanol medium (370 ± 131 nm). According to the photon correlation spectroscopy data, copper oxide nanoparticles synthesized in an aqueous medium were highly stable and had a monomodal size distribution with an average hydrodynamic radius of 61 nm. The study of the pH effect on the colloidal stability of copper oxide nanoparticles showed that the sample was stable in the pH range of 6.8 to 11.98. A possible mechanism for the pH influence on the stability of copper oxide nanoparticles is described. The effect of the ionic strength of the solution on the stability of the CuO nanoparticles sol was also studied, and the results showed that Ca
2+
ions had the greatest effect on the sample stability. IR spectroscopy showed that the interaction of CuO nanoparticles with gelatin occurred through the hydroxyl group. It was found that CuO nanoparticles stabilized with gelatin have a fungicidal activity at concentration equivalent 2.5 · 10
−3
mol/L and as a material for food nanopackaging can provide an increase in the shelf life of products on the example of strawberries and tomatoes. We investigated the possibility of using methylcellulose films modified with CuO nanoparticles for packaging and storage of hard cheese “Holland”. The distribution of CuO nanoparticles in the methylcellulose film was uniform. We found that methylcellulose films modified with CuO nanoparticles inhibited the growth and development of QMAFAM, coliforms, yeast and mold in experimental cheese sa mples. Our research has shown that during the cheese storage in thermostat at 35 ± 1 °C for 7 days, CuO nanoparticles migrated to the product from the film. Nevertheless, it is worth noting that the maximum change in the concentration of copper in the experimental samples was only 0.12 µg/mg, which is not a toxic concentration. In general, the small value of migration of CuO nanoparticles confirms the high stability of the developed preparation. Our results indicated that the CuO nanoparticles stabilized with gelatin have a high potential for use in food packaging – both as an independent nanofilm and as part of other packaging materials.
The сrack growth characteristics are investigated in situ in a scanning electron microscope column during the tension of the welded joints of two-phase (γ + δ) and single-phase (γ) 05Kh22AG16N8M ...steel containing 0.36 and 0.52 wt % N, respectively. A crack in the steel with 0.36% N and its welded joint is shown to form and develop at a low load and strain due to the existence of the σ phase in the steel structure and δ ferrite in the welded joint.
The crack growth characteristics are investigated in situ in a scanning electron microscope column during the tension of nonmagnetic 04Kh18AG20 steel specimens with a overequilibrium nitrogen content ...(0.98 wt % N) and various vanadium contents. The character of crack nucleation and propagation in steel after quenching from 1200°С and after subsequent aging at 650°С for 5 h is shown to be the same. The critical shear crack size at the maximum load is 300 μm in vanadium-free 04Kh18AG20 steel and 120 μm in vanadium-bearing 04Kh18AG20F steel. Corrosion-resistant nickel and vanadium-free austenitic 04Kh18AG20 steel (0.98 wt % N) after quenching from 1200°C is recommended for heavy-duty nonmagnetic structures.
The structure and mechanical properties of martensitic–ferritic nitrogen-bearing 08Kh17N2AF steel after quenching in the temperature range 800–1200°C are studied. This steel after quenching from ...950°C is found to have a high strength (σ
u
= 1290 MPa, σ
0.2
= 850 MPa) and impact toughness at +20°C (
KCU
= 0.8 MJ/m
2
) but a low impact toughness at –70°C (
KCU
= 0.3 MJ/m
2
) as a result of the formation of a martensitic–ferritic–austenitic structure containing ∼82% α, ∼17% δ, ∼1% γ, and a small amount of chromium carbonitrides. The 08Kh17N2AF steel is noted to have the best combination of strength (σ
u
= 950 MPa, σ
0.2
= 800 MPa) and impact toughness at +20 and –70°C (
KCU
+20°C
= 1.65 MJ/m
2
,
KCU
–70°C
= 0.7 MJ/m
2
) after quenching from 800°C and cooling in water as a result of the formation of a martensitic–ferritic–austenitic structure containing 75% martensitic with a high dislocation density, 17% ferrite with grain sizes 2–3 μm, and 8% austenite. The increased impact toughness at +20°C and –70°C is shown to be related to a low content of chromium and vanadium carbonitrides and thin-lamellar martensite having formed from fine austenite grains.
The results of the structure and stacking fault energy (SFE) investigations of low-carbon austenitic steels alloyed with substitutional elements are summarized. An increase in the manganese content ...in the range 7–20 wt % in Fe–Mn alloys is shown to make austenite stable to the γ–α transformation and unstable to the γ–ε transformation. Ferromanganese steel containing 20 wt % Mn has the maximum number (50–55%) of stacking faults after deformation. The SFE of Fe–Mn alloys is inversely proportional to the manganese content at Mn < 14 wt % and directly proportional at higher manganese concentrations. A temperature dependence of the SFE on the manganese content is found for Fe–Mn alloys. The effect of chromium on the SFE depends on the manganese content. A linear dependence of the SFE on the nickel content in Cr–Ni steels with 10–25 wt % Cr is found in the concentration range 10–25 wt %.
The prospects for expanding the mineral resource base in many countries are linked with the exploration of stranded sites localized at unexplored areas with complex natural and landscape conditions ...that make any ground survey, including magnetic prospecting, difficult and expensive. The current level of geology requires high-precision and large-scale data at the first stages of geological exploration. Since 2012, technologies of aeromagnetic surveying with unmanned aircraft vehicles (UAV) enter the market, but most of them are based on big fixed-wing UAV and do not allow to substantially increase the level of survey granularity compared with traditional aerial methods. To increase the scale of survey, it is necessary to reduce the altitude and speed of flight, for which the authors develop the methodical and technical solutions described in this article. To obtain data at altitudes of 5 m above the terrain even in a rugged relief, we created heavy multirotor UAVs that are stable in flight and may be used in a wide range of environmental conditions (even a moderate snowfall), and develop a special software to generate flight missions on the basis of digital elevation models. A UAV has special design to reduce magnetic interference of the flight platform; the magnetic sensor is hung below the aircraft. This technology was conducted in a considerable amount of magnetic surveys in the mountainous regions of East Siberia between 2014 and 2016. The results of the comparison between airborne and ground surveys are presented, which show that the sensitivity of the developed system in conjunction with low-altitude measurements can cover any geologically significant anomalies of the magnetic field. An unmanned survey is cheaper and more productive; the multirotor-based technologies may largely replace traditional ground magnetic exploration in scales of 1:10,000−1:1000.
—The structure and mechanical properties of rods of low-alloy martensitic steels with an overequilibrium nitrogen content, which are melted in a vacuum induction furnace with subsequent electroslag ...remelting under nitrogen pressure and are manufactured by free forging, are studied. The distribution of alloying elements and the hardness along the rod length is found to be uniform. The α → γ transformation temperature on hearting,
Ac
1
= 662°C and
Ac
3
= 838°C, of the steels are determined by differential scanning calorimetry. The structure of these steels contains a small amount of disperse particles of manganese sulfides and vanadium nitrides. Quenching and low tempering of the steels are shown to lead to a good combination of a high strength (σ
u
= 2150–2170 MPa, σ
0.2
= 1450–1480 MPa), ductility (δ = 12–14%, ψ = 35–40%), and impact toughness (KCU = 0.6–0.7 MJ/m
2
) as a result of formation of a fine-grained structure consisting of 85–87% lath martensite and 13–15% retained austenite, thin layers of which are placed between martensite laths.
The works on the structure and mechanical properties of aluminum-alloyed austenitic steels are analyzed. Aluminum in aging high-nitrogen Cr–Mn–Ni–V nonmagnetic steels is shown to decrease the ...strength due to a decrease in the amount of dispersed VN nitrides having precipitated during aging because of the formation of coarse AlN particles hard to dissolve on quenching heating. An additional increase in the strength of aging nonmagnetic Mn–Ni–V–C steels is reached by their alloying with aluminum, which does not form hard to dissolve compounds with carbon. A significant increase in the surface hardness and the wear resistance during nitriding is reached as a result of separate or complex alloying of Mn–Ni–V steels with chromium up to 3% and aluminum up to 1.2%, which increase the nitrided layer thickness. The best combination of the properties of the nitrided layer is achieved after nitriding these steels containing 2.5–3.5% V at 700°C (12 h) in a 80% N
2
+ 20% HN
3
medium. In this case, the hardening of the core during aging is related to the precipitation of VC carbides, and that of the nitrided layer, to the formation of VN nitrides. A significant increase in the volume fraction of strengthening phases in manganese steels is reached by complex alloying with Al, Ni, Cu, and V in the amounts that provide the simultaneous precipitation of the VC carbide and NiAl intermetallics during aging. Nonmagnetic 50G17N10Yu4F2 steel with a combined carbide–intermetallic hardening is highly competitive in strength (σ
u
> 1600 MPa, σ
0.2
> 1400 MPa) with high-strength 18Kh2N4VA ferromagnetic steels and significantly surpasses the well-known aging nonmagnetic high-nitrogen alloys.
We bring together two topics that, until now, have been the focus of intense but non-overlapping research efforts. The first concerns high-harmonic generation in solids, which occurs when an intense ...light field excites a highly non-equilibrium electronic response in a semiconductor or a dielectric. The second concerns many-body dynamics in strongly correlated systems such as the Mott insulator. We show that high-harmonic generation can be used to time-resolve ultrafast many-body dynamics associated with an optically driven phase transition, with accuracy far exceeding one cycle of the driving light field. Our work paves the way for time-resolving highly non-equilibrium many-body dynamics in strongly correlated systems, with few femtosecond accuracy.
The structure and the mechanical properties of low-carbon low-alloy 10Kh3A steel with an overequilibrium nitrogen content (0.20 wt %) are studied after heat treatment under various conditions. The ...quenching (950°C) and tempering (400°C) temperatures that result in significant hardening of the steel (σ
u
= 1680 MPa, σ
0.2
= 1550 MPa) at the retained plasticity (δ = 11%, ψ = 44%) that is high enough for practical application are determined. The strength of the 10Kh3A steel is higher than that of low-alloy nitrogen-free low-carbon 18Kh2N4VA steel, which is alloyed with nickel and tungsten and is widely used for heavily loaded structural members.
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