Nitriding and Denitriding of Nanocrystalline Iron System with Bimodal Crystallite Size Distribution

An artificially prepared nanocrystalline iron sample with bimodal crystallite size distribution was nitrided and denitrided in the NH3/H2 atmosphere at 350 °C and 400 °C. The sample was a 1:1 mass ratio mixture of two iron samples with mean crystallite sizes of 48 nm and 21 nm. Phase transformations between α-Fe, γ’-Fe4N and ε-Fe3-2N were observed by the in situ X-ray powder diffraction method. At selected steps of nitriding or denitriding, phase transformations paused at 50% of mass conversion and resumed after prominent variation of the nitriding atmosphere. This effect was attributed to the separation of phase transformations occurring between sets of iron crystallites of 48 nm and 21 nm, respectively. This was due to the Gibbs–Thomson effect, which establishes the dependence of phase transformation conditions on crystallite sizes.

The role of dietary supplements in the meat productivity of rabbits with a dry type of feeding

The role of vitamin-mineral premix and nanocrystalline iron in the meat productivity of young rabbits was studied by classical methods in the scientific and economic experience in the departments of fur farming and Rabbit Breeding of the V. A. Afanasyev Research Institute of Fur Farming and Rabbit Breeding. From 180 heads of young rabbits at the age of 45 days, 3 groups of 60 heads each were formed according to the principle of analogues: the 1-st-control group received a typical full-fledged granulated mixed feed (FGMF) with a vitamin-mineral premix P 90-2T, in the (FGMF) of the 2-nd and 3-rd experimental groups, the premix was absent, but nanocrystalline iron was included in the (FGMF) of the 3-rd group. Control slaughter of rabbits to assess meat productivity was carried out at the age of 90 days. During the experiment, it was found that the feed in all groups was identical in gross caloric content, but slightly different in the ratio of nutrients. In the mixed feed of the experimental groups, there were more nutrients with the highest digestibility coefficient (fat and soluble carbohydrates) and almost 2 times less fiber, which is slightly digested in young rabbits, only by 3-10%. Rabbits of all groups had no significant differences in live weight and average daily gain. But during the fattening period, the rabbits of the experimental groups consumed less feed when feeding freely than in the control group. At the same time, there were no significant differences in the mass of the carcass and the slaughter yield between the groups. But the feed conversion rate in the experimental groups was 1.32 and 1.28 lower than in the control group, which is economically advantageous. Based on the results of the experiment, it can be assumed that the inclusion of biologically active additives in the form of vitamin-mineral premix and nanocrystalline iron in the full-fledged granular feed for young rabbits does not make much sense, since it does not contribute to increasing meat productivity. In the cost of mixed feed, the vitamin and mineral premix accounts for 10%. Optimizing the ratio of nutrients in the diet plays a crucial role in reducing the feed conversion rate.

Study of Phase Transitions Occurring in a Catalytic System of ncFe-NH3/H2 with Chemical Potential Programmed Reaction (CPPR) Method Coupled with In Situ XRD

Nitriding of nanocrystalline iron and reduction of nanocrystalline iron nitride with gaseous mixtures of hydrogen with ammonia were studied at 375 °C and atmospheric pressure using the chemical potential programmed reaction (CPPR) method coupled with in situ XRD. In this paper, a series of phase transitions occurring during the processes is shown, and a detailed analysis of the phase composition and the structure of the material is given. The influence of a variable nitriding potential on the lattice parameters of α-Fe, γ′-Fe4N, and ε-Fe3-2N phases is shown. The α phase interplanar space changes irrelevantly in the one phase area but decreases linearly with average increases in crystallite size when α→γ′ transformation occurs. The nanocrystallite size distributions (nCSDs) were determined, with nCSD of the α phase for nitriding and nCSD of the ε phase for reduction. The reduction of the ε phase can occur directly to α or indirectly with an intermediate step of γ′ formation as a result of ε→γ′→α transformations. The determining factor in the reducing process method is the volume of ε phase nanocrystallites. Those with V < 90,000 nm3 undergo direct transformation ε→αFe(N), and V > 90,000 nm3 transforms to αFe(N) indirectly. It was determined at what value of nitriding potential which fraction of the ε phase nanocrystallites starts to reduce

Корреляция электрических, гальваномагнитных и магнитных характеристик нанокристаллических пленок железа, полученных методом ионно-ассистированного осаждения

Here we present the measurements of the temperature dependence of resistance, transverse and longitudinal magnetoresistance (MR) in nanocrystalline iron films in the temperature range 2-300 K and the sweep of the magnetic field up to 8 T. Thin nanocrystalline films of α- iron phase with 80 nm thickness were obtained by ion-beam assisted deposition on a silicon substrate. In addition to the shape anisotropy, the obtained iron films exhibited perpendicular magnetic anisotropy (PMA), which disappeared after annealing the films at a temperature of 450 oC in a vacuum. The effect of PMA on the sign and magnitude of the MR of iron films, as well as on the magnetic field dependences of the magnetoresistive effect, recorded at different orientations of the external magnetic field with respect to the film plane and current direction, is experimentally shown. The results obtained are discussed in the framework of modern views on the processes of charge transfer in a weakly disordered ferromagnetic films with different magnetic anisotropy and domain structure when a weak (less than the saturation field of magnetization) or strong (higher than the saturation field) external magnetic field is applied.

Thermodynamics of Chemical Processes in the System of Nanocrystalline Iron–Ammonia–Hydrogen at 350 °C

Nanocrystalline iron nitriding and the reduction of nanocrystalline iron nitrides in steady states at 350 °C are described using the chemical potential programmed reaction (CPPR), thermogravimetry (TG), 57Fe Mössbauer spectroscopy (MS), and X-ray diffraction (XRD) methods. It was determined that during the process of nitriding of nanocrystalline iron, larger nanocrystallites formed the γ’ phase and the smallest nanocrystallites (about 4%) were transformed into the α” phase. Both phases were in chemical equilibrium, with the gas phase at the temperature of 350 °C. Stable iron nitride α” was also formed in the ε iron nitride reduction process. Taking the α” phase in the system of nanocrystalline Fe-NH3-H2 into account, it was found that at certain nitriding potentials in the chemical equilibrium state, three solid phases in the nitriding process and four solid phases in the reduction process may coexist. It was also found that the nanocrystallites of ε iron nitride in their reduction process were transformed according to two mechanisms, depending on their size. Larger nanocrystallites of iron nitride ε were transformed into the α-iron phase through iron nitride γ’, and smaller nanocrystallites of ε nitride went through iron nitride α”. In the passivation process of nanocrystalline iron and/or nanocrystalline iron nitrides, amorphous phases of iron oxides and/or iron oxynitrides were formed on their surface.