Формирование состава и характеристик поверхности хромоникелевой стали 12Х18Н10Т при лазерном модифицировании в слое экспериментальной легирующей обмазки

The results of an experimental study of laser pulsed modification of the surface of stainless steel 12CR18NI10T in a layer of alloying compound made of graphite paste and nanodispersed titanium dioxide powder (anatase) and without coating are presented. A comparative analysis of the effect of the coating on the elemental and phase compositions, morphological characteristics and microhardness of the modified surface is carried out. It was found that as a result of the treatment, the processes of cementation and oxidation of the surface occur, which made it possible to obtain a mixture of iron carbide and high-strength oxides in the surface layer of steel. In the samples that underwent laser treatment in the coating layer, an increase in the intensity of the diffraction peaks of the graphite phase and the formation of iron oxides Fe3O4 and chromium Cr2O3 with the presence of titanium dioxide TiO2 were revealed, which created a mixed heterophase metal oxide structure with increased mechanical strength. An increase in the microhardness of the modified surface after laser pulsed scanning in the layer of the experimental alloying compound is established.

Optical Properties of C−rich (12C, SiC and FeC) Dust Layered Structure of Massive Stars

The composition and structure of interstellar dust are important and complex for the study of the evolution of stars and the interstellar medium (ISM). However, there is a lack of corresponding experimental data and model theories. By theoretical calculations based on ab-initio method, we have predicted and geometry optimized the structures of Carbon-rich (C-rich) dusts, carbon (12C), iron carbide (FeC), silicon carbide (SiC), even silicon (28Si), iron (56Fe), and investigated the optical absorption coefficients and emission coefficients of these materials in 0D (zero−dimensional), 1D, and 2D nanostructures. Comparing the nebular spectra of the supernovae (SN) with the coefficient of dust, we find that the optical absorption coefficient of the 2D 12C, 28Si, 56Fe, SiC and FeC structure corresponds to the absorption peak displayed in the infrared band (5−8) µm of the spectrum at 7554 days after the SN1987A explosion. And it also corresponds to the spectrum of 535 days after the explosion of SN2018bsz, when the wavelength in the range of (0.2−0.8) and (3−10) µm. Nevertheless, 2D SiC and FeC corresponds to the spectrum of 844 days after the explosion of SN2010jl, when the wavelength is within (0.08−10) µm. Therefore, FeC and SiC may be the second type of dust in SN1987A corresponding to infrared band (5−8) µm of dust and may be in the ejecta of SN2010jl and SN2018bsz. The nano−scale C−rich dust size is ∼ 0.1 nm in SN2018bsz, which is 3 orders of magnitude lower than the value of 0.1 µm. In addition, due to the ionization reaction in the supernova remnant (SNR), we also calculated the Infrared Radiation (IR) spectrum of dust cations. We find that the cation of the 2D layered (SiC)2+ has a higher IR spectrum than those of the cation (SiC)1+ and neutral (SiC)0+.

Iron vacancies engineering of FexC@NC hybrids toward enhanced lithium-ion storage properties

Defect engineering have profound influence on the energy storage properties of electrode hybrids by adjusting their intrinsic electronic characteristics. For iron carbide based materials, however, the effect of defect (especially cation vacancies) toward their electrochemical performance are still unclear. Herein, the feasible and scalable synthesis of FexC@NC with 3D honeycomb-like carbon architecture and abundant Fe vacancies via template etching is reported. Such structure enable outstanding lithium-ion storage properties owing to hierarchical pores, improved intrinsic electrochemical activity, as well as the introduction of more active sites. As a result, the FexC@NC-2 presents a high reversible specific capacity of 1079 mAh g−1 after 1000 cycles. Moreover, an excellent cycling stability can be achieved via maintaining a high-capacity retention (689 mAh g−1, 98.4%) over 1000 cycles at 5 A g−1. This study provides a feasible strategy for developing high-performance hybrids with hierarchical pore and rich defects structures.

Corrosion characteristics of plasma spray, arc spray, high velocity oxygen fuel, and diamond jet coated 30MnB5 boron alloyed steel in 3.5 wt.% NaCl solution

30MnB5 boron alloyed steel surface is coated using different coating techniques, namely 60(Ni-15Cr-4.4Si-3.5Fe-3.2B 0.7C)-40(WC 12Co) metallic powder plasma spray, Fe-28Cr-5C-1Mn alloy wire arc spray, WC-10Co-4Cr (thick) powder high velocity oxy-fuel (HVOF), and WC-10Co-4Cr (fine) diamond jet HVOF. The microstructure of the crude steel sample consists of ferrite and pearlite matrices and iron carbide structures. The intermediate binders are well bonded to the substrate for all coated surfaces. The arc spray coated surface shows the formation of lamellae. The cross-section of HVOF and diamond jet HVOF coated surfaces indicates the formation of WC, W2C Cr, and W parent matrix carbide structures. The corrosion characteristic of the coated steel has been investigated in 3.5 wt.% NaCl solution using electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDAX) techniques. The results reveal that the steel corroded in the medium despite the coatings. However, the extent of corrosion varies. HVOF coated sample demonstrated the highest corrosion resistance while arc spray coated sample exhibited the least. EDAX mapping reveals that the elements in the coatings corroded in the order of their standard electrode potential (SEP). Higher corrosion resistance of HVOF coated sample is linked to the low SEP of tungsten.

Ellinaite, CaCr₂O₄, a new natural post-spinel oxide from Hatrurim Basin, Israel, and Juína kimberlite field, Brazil

Ellinaite, a natural analog of the post-spinel phase β-CaCr2O4, was discovered at the Hatrurim Basin, Hatrurim pyrometamorphic formation (the Mottled Zone), Israel, and in an inclusion within the super-deep diamond collected at the placer of the Sorriso River, Juína kimberlite field, Brazil. Ellinaite at the Hatrurim Basin is confined to a reduced rankinite–gehlenite paralava, where it occurs as subhedral grains up to 30 µm in association with gehlenite, rankinite and pyrrhotite or forms the rims overgrowing zoned chromite–magnesiochromite. The empirical formula of the Hatrurim sample is (Ca0.960Fe0.0162+Na0.012Mg0.003)0.992(Cr1.731V0.1833+Ti0.0683+Al0.023Ti0.0034+)2.008O4. The mineral crystallizes in the orthorhombic system, space group Pnma, unit-cell parameters refined from X-ray single-crystal data: a 8.868(9), b 2.885(3), c 10.355(11) Å, V 264.9(5) Å3 and Z=4. The crystal structure of ellinaite from the Hatrurim Basin has been solved and refined to R1=0.0588 based on 388 independent observed reflections. Ellinaite in the Juína diamond occurs within the micron-sized polyphase inclusion in association with ferropericlase, magnesioferrite, orthorhombic MgCr2O4, unidentified iron carbide and graphite. Its empirical formula is Ca1.07(Cr1.71Fe0.063+V0.06Ti0.03Al0.03Mg0.02Mn0.02)Σ1.93O4. The unit-cell parameters obtained from HRTEM data are as follows: space group Pnma, a 9.017, b 2.874 Å, c 10.170 Å, V 263.55 Å3, Z=4. Ellinaite belongs to a group of natural tunnel-structured oxides of the general formula AB2O4, the so-called post-spinel minerals: marokite CaMn2O4, xieite FeCr2O4, harmunite CaFe2O4, wernerkrauseite CaFe23+Mn4+O6, chenmingite FeCr2O4, maohokite MgFe2O4 and tschaunerite Fe(FeTi)O4. The mineral from both occurrences seems to be crystallized under highly reduced conditions at high temperatures (>1000 ∘C), but under different pressure: near-surface (Hatrurim Basin) and lower mantle (Juína diamond).

Green Synthesis of Carbon-Encapsulated Magnetic Fe3O4 Nanoparticles Using Hydrothermal Carbonization from Rattan Holocelluloses

How to design a simple and scalable procedure for manufacturing multifunctional carbon-based nanoparticles using lignocellulosic biomass directly is a challenging task. Based on the green chemistry concept, we developed a novel one-pot solution-phase reaction to prepare carbon-encapsulated magnetic nano-Fe3O4 particles (Fe3O4@C) with a tunable structure and composition through the hydrothermal carbonization (HTC) of Fe2+/Fe3+ loaded rattan holocelluloses pretreated with ionic liquids (EmimAc and AmimCl). The detailed characterization results indicated that the Fe3O4@C synthesized from the holocelluloses pretreated with ionic liquids (ILs) under alkaline conditions tends to have a higher saturation magnetization, probably due to the increased iron ions loading. Moreover, increasing the HTC temperature led to an increased abundance of hydroxyl groups on the surface of the synthesized particles and an elevated saturation magnetization. When EmimAc-treated holocelluloses were used as the carbon precursors, well-encapsulated Fe3O4@C nanoparticles were obtained with a maximum saturation magnetization of 42.6 emu/g. This synthetic strategy, coupled with the structure of the iron carbide-based composite and the proposed mechanism, may open a new avenue for the development of carbon-encapsulated iron oxide-based magnetic nanoparticles.

Solution-Phase Synthesis of Nanoparticles and Growth Study

<p>This thesis is concerned with solution-phase synthesis of nanoparticles and growth of nanoparticles in solution. A facile synthesis route was developed to produce nanoparticles of iron, iron carbide and ruthenium. In general, the synthesis involved the reaction/decomposition of a metal precursor in solution, in the presence of a stabilising agent, in a closed reaction vessel, under a hydrogen atmosphere. The crystallinity, crystal structure, morphology and chemical composition of the nanoparticles obtained were studied primarily by transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDS). Scanning quantum interference device magnetometry (SQUID) was used to characterise the magnetic properties of iron and iron carbide nanoparticles. In situ synchrotron-based XRD was employed to investigate the growth of platinum nanoparticles of different morphologies. The synthesis of iron and iron carbide nanoparticles was investigated at temperatures 80-160 °C. Syntheses at 130 °C and above produced mainly single-crystal α-Fe nanoparticles, whereas those at lower temperatures yielded products consisting of α-Fe and Fe₃C nanoparticles. Nanoparticles of larger than 10 nm oxidised on the surface leading to core/shell structures, and those of smaller size oxidised completely upon exposure to air. Core/shell nanoparticles of larger than 15 nm were observed to be stable under ambient conditions for at least a year, whereas those smaller in size underwent further oxidation forming core/void/shell structures. The magnetic properties of selected samples were characterised. The core/shell nanoparticles were shown to exhibit ferromagnetic behaviours, and saturation magnetisations were obtained at the range of 100-130 emu g⁻¹. Nanoparticle size and size distribution, and morphology were found to be a result of combined effect of precursor concentration and the relative stabiliser concentration. In general, high-precursor concentration resulted in less controlled reaction and produced large nanoparticle size and size distribution. Under the high-concentration condition, the use of stabilisers in reduced amount then led to a diverse range of morphologies, which include dimer, porous and branched structures. As for the synthesis of ruthenium nanoparticles, reactions of different precursors were investigated at temperatures ranging from room temperature to 140 °C. Highly crystalline ruthenium nanoparticles of different sizes and morphologies were obtained through different experimental conditions. The increase in nanoparticle size was found to be a result of increasing reaction temperature and/or decreasing stabiliser to ruthenium ratio. This trend was observed to be independent of the type of stabilisers and precursors used. The use of stabilisers with different binding characteristics has facilitated the formation of non-spherical nanoparticles; these include rod-like structures with high aspect ratios (of up to 12), hexagonal and truncated triangular plate-like structures, and tripods. The growth of faceted and branched structures of platinum nanoparticles was investigated by employing in situ XRD techniques. TEM was used to examine the intermediate structures. The two different morphologies were previously shown to be governed by precursor concentration. It was found that the growth in the low-concentration reaction was characteristic of a thermodynamically controlled regime, whereas that in the high-concentration reaction occurred at much greater rates under a kinetically controlled regime. Based on the observations obtained, different growth mechanisms were proposed and discussed. The former involved an oriented attachment mechanism, while the latter, a novel mechanism involving selective growth and etching processes. The results are followed by an overall discussion comparing and contrasting the various syntheses involved, and relating the results of syntheses to those of the growth studies.</p>

Solution-Phase Synthesis of Nanoparticles and Growth Study

<p>This thesis is concerned with solution-phase synthesis of nanoparticles and growth of nanoparticles in solution. A facile synthesis route was developed to produce nanoparticles of iron, iron carbide and ruthenium. In general, the synthesis involved the reaction/decomposition of a metal precursor in solution, in the presence of a stabilising agent, in a closed reaction vessel, under a hydrogen atmosphere. The crystallinity, crystal structure, morphology and chemical composition of the nanoparticles obtained were studied primarily by transmission electron microscopy (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDS). Scanning quantum interference device magnetometry (SQUID) was used to characterise the magnetic properties of iron and iron carbide nanoparticles. In situ synchrotron-based XRD was employed to investigate the growth of platinum nanoparticles of different morphologies. The synthesis of iron and iron carbide nanoparticles was investigated at temperatures 80-160 °C. Syntheses at 130 °C and above produced mainly single-crystal α-Fe nanoparticles, whereas those at lower temperatures yielded products consisting of α-Fe and Fe₃C nanoparticles. Nanoparticles of larger than 10 nm oxidised on the surface leading to core/shell structures, and those of smaller size oxidised completely upon exposure to air. Core/shell nanoparticles of larger than 15 nm were observed to be stable under ambient conditions for at least a year, whereas those smaller in size underwent further oxidation forming core/void/shell structures. The magnetic properties of selected samples were characterised. The core/shell nanoparticles were shown to exhibit ferromagnetic behaviours, and saturation magnetisations were obtained at the range of 100-130 emu g⁻¹. Nanoparticle size and size distribution, and morphology were found to be a result of combined effect of precursor concentration and the relative stabiliser concentration. In general, high-precursor concentration resulted in less controlled reaction and produced large nanoparticle size and size distribution. Under the high-concentration condition, the use of stabilisers in reduced amount then led to a diverse range of morphologies, which include dimer, porous and branched structures. As for the synthesis of ruthenium nanoparticles, reactions of different precursors were investigated at temperatures ranging from room temperature to 140 °C. Highly crystalline ruthenium nanoparticles of different sizes and morphologies were obtained through different experimental conditions. The increase in nanoparticle size was found to be a result of increasing reaction temperature and/or decreasing stabiliser to ruthenium ratio. This trend was observed to be independent of the type of stabilisers and precursors used. The use of stabilisers with different binding characteristics has facilitated the formation of non-spherical nanoparticles; these include rod-like structures with high aspect ratios (of up to 12), hexagonal and truncated triangular plate-like structures, and tripods. The growth of faceted and branched structures of platinum nanoparticles was investigated by employing in situ XRD techniques. TEM was used to examine the intermediate structures. The two different morphologies were previously shown to be governed by precursor concentration. It was found that the growth in the low-concentration reaction was characteristic of a thermodynamically controlled regime, whereas that in the high-concentration reaction occurred at much greater rates under a kinetically controlled regime. Based on the observations obtained, different growth mechanisms were proposed and discussed. The former involved an oriented attachment mechanism, while the latter, a novel mechanism involving selective growth and etching processes. The results are followed by an overall discussion comparing and contrasting the various syntheses involved, and relating the results of syntheses to those of the growth studies.</p>