The structure and magnetic properties of amorphous and nanocrystalline Co56Fe16B20X8 (X=Nb, Ti) alloys have been studied by X-ray diffraction and vibrating sample magnetometry. It is shown that the saturation magnetization of the amorphous Co56Fe16B20Ti8 alloy is higher than that of the Co56Fe16B20Ti8 alloy. The temperature dependence of the saturation magnetization of amorphous alloys is measured and it is shown that the saturation magnetization of the Co56Fe16B20Ti8 alloy decreases with temperature more slowly than the magnetization of the Co56Fe16B20Nb8 alloy. Crystallization of amorphous alloys leads to a decrease in the saturation magnetization of both alloys. During crystallization, BCC nanocrystals are formed in the Co56Fe16B20Nb8 alloy and multiphase structure is formed in the Co56Fe16B20Ti8 alloy. Keywords: amorphous phase, crystallization, nanocrystals, magnetic properties.

The structure and magnetic properties of amorphous and nanocrystalline Co56Fe16B20X8 (X = Nb, Ti) alloys have been studied by X-ray diffraction and vibrating sample magnetometry. It is shown that the saturation magnetization of the amorphous Co56Fe16B20Ti8 alloy is higher than that of the Co56Fe16B20Nb8 alloy. The temperature dependence of the saturation magnetization of amorphous alloys is measured and it is shown that the saturation magnetization of the Co56Fe16B20Ti8 alloy decreases with temperature more slowly than the magnetization of the Co56Fe16B20Nb8 alloy. Crystallization of amorphous alloys leads to a decrease in the saturation magnetization of both alloys. During crystallization, BCC nanocrystals are formed in the Co56Fe16B20Nb8 alloy and multiphase structure is formed in the Co56Fe16B20Ti8 alloy.

The effect of free volume on the process of crystallization of an Al87Ni8Gd5 amorphous alloy is investigated. The deformation of the amorphous alloys leads to the formation of shear bands, which contain an enhanced free volume concentration. To retain the free volume the amorphous alloy was coated with a layer of a refractory metal. The structure of the Al87Ni8Gd5 alloy with a protective Ta coating was studied by X-ray diffraction and transmission electron microscopy methods. The fraction of the nanocrystalline phase formed in the amorphous samples with a protective Ta coating under annealing was found to be larger than that in the uncoated samples. The size of Al nanocrystals formed in the coated and uncoated samples is the same. A higher rate of crystal nucleation in the deformed amorphous samples with a protective coating is caused by a higher diffusion coefficient due to an enhanced free volume concentration.

The crystallization of amorphous alloys of Co-Fe-B-(Ti, Nb) system was studied by differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. It was determined that the alloying of amorphous alloys of Co-Fe-B system with elements having a bcc lattice promotes the formation of a metastable phase with this lattice during crystallization. Nanocrystal size and the fraction of the phase with a bcc lattice depend on the concentration of alloying components. When the concentration of bcc components increases, nanocrystal size decreases. When Nb (an element with a bcc lattice) is replaced by Ti (an element with an hcp lattice), the fraction of the bcc phase decreases, and multiphase crystallization (simultaneous formation of several crystalline phases) occurs. In Co56Fe16B20Ti8 alloy, the first crystallization stage consists of two steps. During the seemingly simultaneous formation of several crystalline phases, first a small quantity of the bcc phase and then Co23B6 and fcc-Co crystals are formed sequentially. All the results obtained indicate heterogeneous nanocrystal formation with the nucleation on structurally related ordered regions (on ordered clusters which consist of alloy components with the structure related to the crystallizing phase).

Phase transformations of silicon clathrate Si-136 under high hydrogen pressure up to 11.5 GPa were studied by in situ Raman spectroscopy and X-ray diffraction at room temperature in a diamond anvil cell. The pressure dependencies of the vibrational mode frequencies of Si-136 agree well with the ab initio calculation results. In addition to the "rigid" one-phonon modes a series of "soft" modes was found in the 300 divided by 400 cm(-1) frequency range, which results from the two-phonon Raman scattering. At the pressure of 10 GPa the silicon clathrate Si-136 transformed into a mixture of the Si-II (beta-Sn-type) and Si-III (BC8-type) phases. During the subsequent decompression down to 9 GPa the Si-II phase transformed to Si-III, which was then recovered to ambient pressure. No interaction between hydrogen and silicon was observed for Si-136 upon compression and for the Si-II and Si-III phases upon decompression.

The nanocrystal formation in Zr55Cu30Al15Ni5 bulk metallic glass was studied under heat treatment and deformation. The activation energy of crystallization under heating is 278 kJ/mol. Different crystalline phases were found to be formed during crystallization under heating and deformation. At the first crystallization stage, the metastable phase with a hexagonal structure (lattice of space group P63/mmc with the parameters a = 8.66 Å, c = 14.99 Å) is formed under heat treatment. When the temperature rises, the metastable phase decays with the formation of stable crystalline phases. The crystalline Zr2Cu phase with the lattice of space group Fd3m is formed during crystallization under the action of deformation. It was determined that during deformation nanocrystals are formed primarily in the subsurface regions of the samples.

At room and lower temperatures, hydrogen atoms occupy octahedral (O) interstitial sites in all known monohydrides of d-metals with close-packed metal lattices (fcc, hcp or double hcp) (see [1] and references therein). On the other hand, the ground-state energy of the H atom sitting on an alternative tetrahedral (T) interstitial site is not much higher. This opens the possibility of a partial Boltzmann occupancy of the Tsites at elevated temperatures. A considerable T-occupancy reaching about 1/3 of all D atoms has for the first time been found in fcc deuterides of palladium by in situ neutron diffraction at 310 °C and deuterium pressures up to 9 MPa [2, 3]. A few years later, another in situ ND investigation showed that about 1/6 of D atoms are likely to occupy the T-sites in fcc deuteride of iron at T = 715 °C and P = 6.3 GPa [4]. The subtle difference between the profile fits using the O-model and O+T model was not however sufficient to establish the presence of D atoms on the T-sites with certainty. At the same time, modeling this pattern assuming that D atoms could fill only the O-sites and allowing them to occupy both Oand T-sites gave noticeably different total D/Fe ratios of 0.47 and 0.64, respectively [4]. In order to examine which of the two predicted D/Fe values better agrees with experiment, we constructed an isobar of deuterium solubility in iron at P = 6.3 GPa and temperatures from 100 to 800 °C using a quenching technique [5]. The point (6.3 GPa, 715 °C) chosen for the experiment in Ref. [4] and the temperature interval of the isobar constructed in the present work are shown on the T-P diagram of the Fe-H system (Fig. 1) copied from Ref. [6]. The isobar is presented in Fig. 2. As one can see from Fig. 2, our experiment confirms the value of D/Fe = 0.64(3) resulting from the O+T model [4]. Such a value corresponds to the deuteriuminduced volume expansion of fcc iron dVa/dx = 2.21(4) Ǻ3/atom D [4], and therefore this estimate of Ref. [4] is also confirmed. The isobar in Fig. 2 also demonstrates a step-wise decrease in the deuterium solubility in iron from D/Fe =1 to D/Fe ≈ 0.9 at T0 ≈ 260 °C due to the transition from the low-temperature stoichiometric dhcp (ε′) FeD phase to the high-temperature fcc (γ) Fe-D phase with a variable composition. Since the direct synthesis of single-phase samples of ε′-FeD from α-Fe at a pressure of 6.3 GPa is not possible for kinetic reasons, the points shown by the solid blue triangles were obtained with the samples first transformed to γ-FeDx at 500 °C. Figure 1. T-P diagram of the Fe-H system [4]. α – dilute H solutions in bcc Fe; γ – hydrogen solutions in fcc Fe with the H/Fe ratio varying from x = 0 to x ≈ 1 depending on the temperature and pressure; ε ́ a stoichiometrc hydride FeH with a double hcp metal lattice.

Samples of the clathrate Na x Si 136 were saturated with hydrogen to 100 atm at 25°C in a Sievertstype apparatus and at pressures of 6 and 28 kbar in lentil-type high-pressure apparatuses at 100 and 250°C. X-ray powder diffraction analysis and Raman spectroscopy of the samples quenched after the saturation with hydrogen showed that the phase composition of the clathrates did not change. Heating of the quenched samples to room temperature in a thermal desorption setup produced not hydrogen, but hydrogen-containing gases, as we assumed, silanes. Heating to 650°C leads to decomposition of these compounds to form hydrogen.

Aminoborane NH3BH3 is proposed as an appropriate material to produce hydrogen in the high-pressure cells designed for the synthesis of hydrides in sizeable amounts at pressures of a few GPa and elevated temperatures. Aminoborane is a non-hydroscopic material and it does not noticeably react with air that permits assembling the high-pressure cells under ambient conditions without any precautions. If heated to 300 degrees C at any pressure from 0.6 to 9 GPa, aminoborane decomposes to H-2 gas and chemically inert amorphous BN and does not further absorb the liberated hydrogen. Experiments using NH3BH3 and AIH(3) alternatively as the internal hydrogen source gave coinciding isotherms of hydrogen solubility in rhodium at 600 degrees C and pressures up to 9 GPa therefore demonstrating that the partial pressure of impurities (if any) in the H-2 gas generated by NH3BH3 is well below the accuracy +/- 0.3 GPa of determination of the total gas pressure. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

The T-P phase diagram of the Mo-H system studied earlier at hydrogen pressures up to 5.3 GPa and temperatures up to 1200 degrees C by in-situ X-ray diffraction [Y. Fukai et al. Mater. Trans. 44 (2003) 1359] is re-examined at P <= 6 GPa and T <= 800 degrees C using a quenching technique. The formation of the high-temperature fcc MoH hydride at T > 480-570 degrees C is not confirmed. Instead, the stability region of the low-temperature hcp MoH1.1 hydride is found to grow with pressure. The temperature of its boundary with the region of diluted Mo-H solutions rises with pressure and reaches 800 degrees C at P approximate to 5.5 GPa. (C) 2016 Elsevier B.V. All rights reserved.

The rule of triple joints has recently been proved for two-dimensional phase diagrams and two-dimensional sections of phase diagrams of a higher dimension (Antonov, 2013). The present paper is extending this rule to phase diagrams of binary metal-hydrogen systems composed of a metal immersed in a hydrogen gas. The rule is shown to be valid for every triple point in the temperature-pressure phase diagrams of these systems, including the points with the intersecting boundary lines tangent to each other. The paper also considers the sufficient conditions for the application of the rule to triple points in the projections of phase diagrams onto the temperature-concentration plane. (C) 2015 Elsevier B.V. All rights reserved.