Results 1 - 10 of 418
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[en] The structural, electronic properties and stability of the new MXene compounds—two-dimensional pristine carbonitrides Ti3C2−xNx and their hydroxylated derivatives Ti3C2−xNx(OH)2 are studied by means of DFTB calculations. The genesis of the properties is discussed in the sequence: binary MXenes Ti3C2 (Ti3N2)→hydroxylated forms Ti3C2(OH)2 (Ti3N2(OH)2)→pristine MXene Ti3C2−xNx→hydroxylated Ti3C2−xNx(OH)2. All examined materials are metallic-like. The most favorable type of OH-covering is presented by the occupation of the hollow sites between three neighboring carbon (nitrogen) atoms. Two-dimensional MXene carbonitrides with random distribution of C and N atoms are found to be thermodynamically more favorable. - Graphical abstract: The side views of the optimized atomic structures of some examined hydroxylated derivatives of MXene Ti3CN and their electronic band structures. Display Omitted - Highlights: • Very recently 2D titanium carbonitrides have been synthesized. • Structural, electronic properties and stability for these materials were evaluated. • The hydroxylated derivatives of 2D titanium carbonitrides are examined
[en] In this study, β-Si3(Cx,N1−x)4 Silicon Carbonitride was prepared by Self-Propagation High-Temperature Synthesis (SHS). And the influence of carbon on structure stability, mechanical and tribological properties of β-Si3(Cx,N1−x)4 were investigated. The results showed that the solubility of carbon in β-Si3(Cx,N1−x)4 was about 10 wt%, beyond which cubic-SiC segregated out of β-Si3(Cx,N1−x)4 to form β-Si3N4/cubic-SiC composite. Regarding influences of carbon concentration on mechanical properties, the hardness of β-Si3(Cx,N1−x)4 decreased from 1400 Hv to 1200 Hv with the increase of carbon concentration. Whereas, the fracture toughness of β-Si3(Cx,N1−x)4 increased from 6.5 MPa · m0.5 to 7.6 MPa · m0.5 with the increase of carbon concentration. The tribological property studies revealed the anti-wear performance of β-Si3(Cx,N1−x)4 was enhanced by the increase of carbon concentration. The dominated wear mechanism could be attributed to the abrasive wear by fracture. (paper)
[en] Nanodisperse powders (NDP) of carbonitrides of IV-VI group transition metals (for example, TiCxN1-x, NbCxN1-x, Cr3C1,6N0,4), their hard alloys (for example, TixNb1-xCyN1-y) and mixtures (for example, TiCxN1-x-Cr3C1,6N-0,4) with the medium particle size of 50 - 200 nm have been prepared by the method of plasmachemical synthesis. Due to the dynamic conditions of synthesis (starting products evaporation or decomposition, mixing and condensation of the end product is lasting for some tenths of second) the products is formed in a form of NDP, mainly as a monocrystals with a great concentration of the crystallic lattice defects. This determined high chemical activity of these powders, including increased sintering rate and decreased sintering temperature. Some examples of use of such powders are given. (author)
[en] Full text: The method of carbothermic conversation of uranium dioxide in a stream of nitrogen was chosen as a fundamental technology of carbonitride fuel manufacturing. The processes of producing UCN in the presence of methane and carbon oxide were investigated at carbothermic conversion of UO2 in nitrogen and nitrogen-hydrogenous atmospheres (P=0.1 MPa, T=1673-2073 K). The possibility for realization of UCN (UN) synthesis on compact UO2 samples in the presence of gas-phase transfer of carbon in in the system is demonstrated. Results are reported from reactor tests of coated particles and uranium-graphite fuel elements based on carbonitride fuel at temperatures of 1250 deg. C and 1500 deg.C to burnups if 18.5 % fima and 18.0 % fima. respectively. The specimens under test have shown high serviceability of the fuel developed (R/B) no more (3.5-6.0)·10-6). The technology of manufacturing carbonitride (nitride) fuel created in NSC KIPT and the results of its tests, including reactor tests, allow us to recommend it for using in nuclear power plants. The performance of future experiments will make it possible to realize the potential of the developed technology for producing nitride fuel base on nitrogen-15 isotope
[en] Major difficulties of processing metal-matrix composites by means of conventional powder metallurgy techniques are the lack of dispersion of the phases within the final microstructure. In this work, processing through colloidal techniques of the Fe-based metal-matrix composites, with a high content of a ceramic reinforcement (Ti(C,N) ), is presented for the first time in the literature. The colloidal approach allows a higher control of the powders packing and a better homogenization of phases since powders are mixed in a liquid medium. The chemical stability of Fe in aqueous medium determines the dispersion conditions of the mixture. The Fe slurries were formulated by optimising their zeta potential and their rheology, in order to shape bulk pieces by slip-casting. Preliminary results demonstrate the viability of this procedure, also opening new paths to the microstructural design of fully sintered Fe-based hard metal, with 50 vol. % of Ti(C,N) in its composition. (Author)
[en] Highlights: • A facile method to fabricate BCN microspheres by precursor pyrolysis. • The BCN microspheres have the uniform structure with the size of 2 μm. • This simple technique may contribute to the preparations of other BCN materials. Bulk quantity Boron Carbonitride (BCN) microspheres were successfully synthesized via an organic precursor pyrolysis approach. The organic precursor was synthesized at 90 °C by the polymerization reaction of boron trichloride，aniline and ethylenediamine with a molar ratio of 1:1:1. All particles presented uniform spherical structure with the size of 2 μm. The products have oxidation starting temperature at 624 °C much higher than graphene (404 °C).
[en] For the example of 5ХНМ steel, we show that plasma quenching prior to carbonitriding significantly increases the hardness and thickness of the carbonitride layer. Little change is seen in the parameters of the heterogeneous transition zone.
[en] In as-cast slab steel, dendritic Nb-rich (Ti,Nb)(C,N) carbonitrides were observed which have a thermodynamically stable chemistry at lower than 1000 deg. C. These dendritic carbonitrides were dissolved and then re-precipitated to two kinds of carbonitrides, Ti- and N-rich and Ti- and C-rich (Ti,Nb)(C,N) carbonitrides during reheating