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Here, we present a study of superconductivity in the Ga-Ag alloy embedded into porous template with pore diameter of 10 nm. The composition was close to the eutectic point in the gallium-rich range. We measured DC and AC magnetizations for temperatures from 1.8 to 10 K and magnetic fields up to 6 T. Three superconducting transitions were found at temperatures 7.05, 6.08, and 2.65 K in contrast to the bulk counterpart. Upper critical field lines were obtained. Activation barriers were evaluated from the AC data. The temperatures of the superconducting transitions were ascribed to emergence of β- and iota-Ga and of an intermetallic different from bulk Ag3Ga2. Keywords: nanostructured Ga-Ag eutectic alloy, superconducting transitions, segregated phases, DC and AC susceptibility.

The discovery of extreme magnetoresistance (XMR) in non-magnetic materials attracted attention to the WTe2 semimetal. We have carried out studies of magnetoresistance in a tungsten ditelluride single crystal in the magnetic field range up to 14 T. Magnetoresistance increased with increasing field following a near quadratic law without saturation. The Shubnikov-de Haas oscillations were observed. Four fundamental frequencies were found in the oscillations spectrum, which correspond to two electron and two hole pockets caused by strong spin-orbit coupling.

AbstractWe study the dc magnetization of a Bi_1.94Fe_0.06Se_3 single crystal in the temperature range of 1.9 to 400 K in applied magnetic fields up to 70 kOe for two sample orientations in the applied field. We register three magnetic phase transitions and observe considerable anisotropy of the magnetic properties. The coercive force varies with temperature in a nonmonotonic manner. For the sample in a paramagnetic state, we estimate its magnetic moment per iron atom; its Curie–Weiss temperature is found to be negative. Arrot–Belov plots are constructed.

We carried out 125Te NMR studies of a WTe2 topological Weyl semimetal at temperatures of 41 and 293 K. Measurements were performed using a pulse Bruker Avance 500 NMR spectrometer. 125Te NMR spectra were obtained for the WTe2 single crystal at the orientation of the crystalline c axis parallel and perpendicular to the quantized field. We ascribed the complex spectra to four non-equivalent tellurium sites in the WTe2 crystalline structure. The recovery of the longitudinal magnetization was studied after the pulse saturation of particular lines in the spectra. We observed the single-exponential relaxation. The frequency shifts and widths of the spectral lines differed insignificantly at two temperatures while the spin-lattice relaxation times at 41 K were by a factor of approximately 30 greater than the relevant times at room temperature. Strong temperature dependence of relaxation was suggested to be due to the contribution of Weyl quasi-particles below the topological phase transition.

The amorphous alloy rods of (Zr53Cu30Ni9Al8)100−xSix (x = 0.25, 0.5, 0.75, 1) with a diameter of 2–6 mm were prepared by drop casting method in an Ar atmosphere. The thermal properties, including glass forming ability (GFA) and thermal stability during isothermal annealing of these amorphous alloys, and the mechanical properties have been systematic investigated by the combination of DSC, XRD, SEM, TEM, and compression test. The result of X-ray diffraction reveals that these entire (Zr53Cu30Ni9Al8)100−xSix alloy rods exhibit a typical amorphous diffraction pattern with only a broad maximum around 2θ around 40 degree. Both Tg (glass transition temperature) and Tx (crystallization temperature) of these (Zr53Cu30Ni9Al8)100−xSix alloys increase with the silicon addition. In addition, both the activation energy of crystallization and the incubation time of isothermal annealing these (Zr53Cu30Ni9Al8)100−xSix amorphous alloys indicate that the (Zr53Cu30Ni9Al8)99.25Si0.75 alloy possesses the best thermal stability in the (Zr53Cu30Ni9Al8)100−xSix alloy system. In parallel, the result of compression test shows that the yield strength increases with the addition of Si content and reaches to a maximum value about 1750 MPa with 3% plastic strain for the (Zr53Cu30Ni9Al8)99.25Si0.75 amorphous alloy.

Mg65Cu20Y10Ag5 Amorphous/ nano ZrO2 composites alloy powder were fabricated through the combination method of melt spinning and mechanical alloying (MA). The melt spun amorphous matrix ribbons are ground into powders and mixed with 3 vol.% ZrO2 nano particles in the planetary mill. After then formed by hot pressing in Ar atmosphere under the pressure of 700 MPa at the temperature of soft point which measured by TMA (Thermal mechanical Analysis). The hot-pressed bulk composite specimens are compression tested at different temperature within the supercooled temperature region. The flow stress was found decrease with increasing temperature dramatically when the temperature exceeds the middle temperature of supercooled region. The specimens after compression test were examined by X-ray diffractometry and SEM to investigate its crystallinity and fracture mechanism.

The (Cu42Zr42Al8Ag8)100-xSix amorphous alloy rods, x =0 to 1, with 3 mm in diameter were prepared by Cu-mold drop casting method. The glass forming ability, thermal properties and microstructure evolution was studied by differential scanning calorimetry (DSC), and X-ray diffractometry (XRD). The XRD result reveals that these as-quenched (Cu42Zr42Al8Ag8)100-xSix alloy rods exhibit a broaden diffraction pattern of amorphous phase. The crystallization temperature and GFA (glass forming ability) of (Cu42Zr42Al8Ag8)100-xSix alloys increase with the silicon additions. The highest Trg (0.59) and γ value (0.405) occurred at the (Cu42Zr42Al8Ag8)99.75Si0.25 and (Cu42Zr42Al8Ag8)99.5Si0.5 alloy. In addition, both of the activation energy of crystallization and the incubation time of isothermal annealing for these (Cu42Zr42Al8Ag8)100-xSix alloys indicates that the (Cu42Zr42Al8Ag8)99.25Si0.75 alloy posses the best thermal stability among the (Cu42Zr42Al8Ag8)100-xSix alloy system.

The results of atmosphere-controlled tensile test in various conditions (with different strain rate at different temperature under vacuum, air, or water vapor atmosphere) revealed that the addition of boron and chromium would improve the elongation as well as ultimate tensile strength (UTS) of the Ni-19Si-3Nb based alloys over a wide range of temperature under air and water vapor atmosphere. The UTS and elongation can reach to 1270 MPa and 14%, respectively at 873K in each kind of atmosphere. On contrary, the alloy without boron addition only presents ductile mechanical behavior in vacuum. This is evident that boron and Cr elements present positive effect on suppressing the environmental embrittlement in air and water vapor atmosphere from room temperature to 1073 K for the Ni-19Si-3Nb base alloy. In addition, both of UTS and elongation present quite insensitive on the strain rate when test at the temperature below 973 K. However, the UTS exhibits very dependent on the strain rate when test temperature above 973 K, decreasing the ultimate tensile strength with decreasing strain rate.

Mg 65 Cu 25− x Gd 10 Ag x ( x = 0–10) amorphous alloy ribbons with 0.1 mm thickness were prepared by melt spinning. The thermal properties and microstructure development during the annealing of amorphous alloys have been investigated by the combination of differential scanning calorimetry (DSC), SEM with EDS capability, X-ray diffractometry (XRD) and TEM techniques. The XRD result reveals that all these as-quenched Mg 65 Cu 25− x Gd 10 Ag x alloy ribbons exhibit broad diffraction patterns of amorphous phase. A clear T g (glass transition temperature) and supercooled region (about 40 K) were revealed for all Mg 65 Cu 25− x Gd 10 Ag x alloy ribbons. In addition, the single stage crystallization of the Mg 65 Cu 25 Gd 10 alloy was found to change into three stage crystallization when the Ag element was added. In parallel, the glass transition temperature for the Mg 65 Cu 25− x Gd 10 Ag x alloys exhibits an increasing trend with Ag content. However, the crystallization temperature T x and supercooled region present a decreasing trend with Ag content.

Recently, the high performance W–Ni–Fe–Co heavy tungsten alloy has become as the major core material of armor piercing ammunition. Since the melting temperature of tungsten element is too high to be fabricated by the melting process, that the W–Ni–Fe–Co alloy only can be synthesized by powder metallurgy process. In this study, two compositions of alloy powders, 93W–3Ni–2Fe–2Co and 93W–3.5Ni–1.5Fe–2Co, were selected for investigating their microstructure and mechanical properties after solid-phase sintering. These pre-alloyed powders with crystal cell size about 16 nm were synthesized by mechanical alloying (MA) the mixture of appropriate composition of pure elements in the Spex mill for 8 h. Then, the MA powders were compressed by cold isostatic pressing (CIP) and vacuum sintered at various temperature below 1400 °C for different time. Microstructure characterization of the sintered tungsten heavy alloys was conducted by means of SEM with EDS capability, X-ray diffraction (XRD), and TEM techniques. The result reveals that the microstructure of these sintered alloys was found to consist of the tungsten matrix phase and the Fe–Ni solid solution phase. The hardness of these sintered tungsten heavy alloy presents a trend with increasing sintering temperature and sintering time.

The effect of strain rate and environment on the mechanical behavior at different temperatures of the Ni–19Si–3Nb–0.15B–0.1C alloy is investigated by atmosphere-controlled tensile testing under various conditions at different strain rates and different temperatures). The results reveal that the Ni–19Si–3Nb–0.15B–0.1C alloy exhibits ductile mechanical behavior (UTS ∼ 1250 MPa, e ~ 14%) at temperatures below 873 K under different atmosphere conditions. However, the alloy without boron and carbon addition shows ductile mechanical behavior only when the sample is tested in vacuum. This indicates that the microalloying of boron and carbon does overcome the environmental embrittlement from water vapor at test temperatures below 873 K for the Ni–19Si–3Nb base alloy. However, the boron and carbon doped alloy still suffers from embrittlement associated with oxygen at a medium high temperature (i.e. 973 K). In parallel, both of the ultimate tensile strength and elongation exhibit quite insensitive response with respect to the loading strain rate when tests are held at temperatures below 873 K. However, the ultimate tensile strength exhibits high dependence on the strain rate in air at temperatures above 873 K, decreasing the ultimate tensile strength with decreasing strain rate.

The Mg65Cu25Gd10-xNdx (x=0 ~ 10) amorphous alloy rods with 3~6 mm in diameter were prepared by Cu-mold injection method. The thermal properties and mechanical properties of these amorphous alloys have been investigated by DSC, SEM with EDS capability, X-ray diffractometry (XRD) and Vickers hardness test. The XRD revealed that these entire as-quenched Mg65Cu25Gd10-xNdx alloy rods exhibit a broaden diffraction pattern of amorphous phase. A clear Tg (glass transition temperature) and supercooled region (about 30~60 K) were revealed for all of those Mg65Cu25Gd10-xNdx alloys. In addition, the single stage crystallization of the Mg65Cu25Gd10 alloy was found to change into two stages crystallization when the Nd element was added into this alloy. In parallel, the crystallization temperature (Tx) and supercooled region (Tx) presents a decreasing trend with increasing Nd content. The lowest liquidus temperature (Tl, about 721 K) occurs at the Mg65Cu25Gd8Nd2 alloy. In addition, The Mg65Cu25Gd8Nd2 alloy exhibits the high γ value (0.416, defined as γ= Tx/Tg+Tl), a relatively high Trg (0.59, defined as Trg = Tg/Tl) and the highest hardness in these alloys.

The Zr60Al7.5Cu17.5Ni10Si4B1 (numbers indicate at.%) amorphous alloy was selected for an investigation of its crystallization kinetics and thermal stability because of its high activation energy of 370 kJ/mol for crystallization and its extended incubation time during isothermal annealing in the supercooled temperature region. The crystallization behavior and microstructure development during isothermal annealing were examined by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy (TEM). When annealing the Zr60Al7.5Cu17.5Ni10Si4B1 alloy isothermally at 714 K, Zr2Cu crystals with average size about 5 nm were first observed at the early stage of 1% crystallization by TEM. The Zr2Cu crystal size increases with annealing time, then reaches an average size of about 25 nm at the stage of 72% crystallization. In addition, the grain growth time as a function of the cube of particle size of the Zr2Cu type crystalline phases presented a good linear relationship. This indicates that the crystal growth of the Zr60Al7.5Cu17.5Ni10Si4B1 alloy is a thermally activated process. The activation energy for growth of Zr2Cu particles in the Zr60Al7.5 Cu17.5Ni10Si4B1 amorphous alloy is found to be 210 ± 25 kJ/mol. The lower activation energy of crystal growth during crystallization in comparison with 440 kJ/mol for crystallization in Zr65Cu35 corresponds to the rearrangement of other smaller atoms in the glass, such as Al or Si (compare to Zr).

Mg-based composites are fabricated through mechanical alloying (MA) the Mg65Cu20Y10Ag5 amorphous alloy spun and mixed with 1-5 vol.% spherical nano-sized ZrO2 particles in the planetary mill, after then formed by hot pressing in Ar atmosphere under different pressures at the temperature 5 K above the glass transition temperature (Tg). The microstructure characterizations of the resulting specimens are conducted by means of XRD, FEG-SEM, and TEM techniques. It is found that the nano-sized ZrO2 dispersed Mg-based composite alloy powders can reach to a homogeneous size distribution (about 80 nm) after 50-hour mechanical alloying. After hot pressing of these composite alloy powders under the pressure of 1100 MPa at 409K, a 96% dense bulk specimen can be formed. Throughout the MA and hot pressing, the amorphous nature of the Mg65Cu25Y10Ag5 matrix is maintained. The hardness of the formed bulk Mg-based composites (with 3 vol.% nano-sized ZrO2 particles) can reach to 370 in Hv scale. In addition, the toughness of the formed bulk Mg-based composites presents an increasing trend with the content of nano-sized ZrO2 particles and can reach to 8.9 MPa m .

The Mg 58 Cu 31 Y 11-x Nd x (x = 0 ∼ 11) amorphous alloy rods with 3∼10 mm in diameter were prepared by Cu-mold injection method. The XRD result reveals that these entire Mg 58 Cu 31 Y 11-x Nd x alloy rods exhibit a broaden diffraction pattern of amorphous phase. A clear Tg (glass transition temperature) and supercooled region (about 70 K) were revealed for all of those Mg 58 Cu 31 Y 11-x Nd x amorphous alloy rods. The single stage crystallization of the Mg 58 Cu 31 Y 11 alloy was found to change into two stages crystallization when large amount of Nd element was added into this alloy. In parallel, the crystallization temperature (T x ) and supercooled region (ΔT x ) present a decreasing trend with increasing Nd content. The highest y value of 0.414 occurs at the alloy compositions of Mg 58 Cu 31 Y 4 Nd 7 and Mg 58 Cu 31 Y 6 Nd 5 in this alloy system. Therefore, suitable addition of Nd element can obviously increase the glass forming ability for the Mg 58 Cu 31 Y 11-x Nd x alloy system.

The amorphous Zr 65− x − y Al 7.5 Cu 17.5 Ni 10 Si x B y alloy ribbons, x =1–4 and y =1–2, with 0.1 mm thickness were prepared by melt spinning. The thermal properties and microstructure development during the annealing of amorphous alloys were investigated by the combination of differential thermal analysis, differential scanning calorimetry, X-ray diffractometry, and TEM. Both of the glass transition temperature and the crystallization temperature for Zr 65− x − y Al 7.5 Cu 17.5 Ni 10 Si x B y alloys increases with the silicon and boron additions and reaches 674 and 754 K, respectively for Zr 60 Al 7.5 Cu 17.5 Ni 10 Si 4 B 1 alloy. The highest T rg (0.62) and γ value (0.43) occurred at the Zr 60 Al 7.5 Cu 17.5 Ni 10 Si 4 B 1 alloy. In addition, the Zr 60 Al 7.5 Cu 17.5 Ni 10 Si 4 B 1 alloy was revealed to have the highest activation energy of crystallization (about 370 kJ/mol as determined by the Kissinger plot). This value is about 20% higher than the activation energy of crystallization for the Zr 65 Al 7.5 Cu 17.5 Ni 10 based alloy (314 kJ/mol). In parallel, the alloy 4Si1B also performs a longer incubation time at higher isothermally annealing temperature. All of the evidence implies that Zr 60 Al 7.5 Cu 17.5 Ni 10 Si 4 B 1 alloy exhibits the highest thermal stability among those alloys in this study. The crystallization behavior for the alloy 4Si1B isothermally annealed at the supercooled temperature region for different time has also been examined by TEM and discussed.

Mg-based composites are fabricated through mechanical alloying (MA) in the planetary mill, using amorphous Mg65Cu25KxY10Agx (xZ0, 5, 10) matrix alloy prepared by melt spun and 1–5 vol.% spherical nano-sized ZrO2 particles. The melt spun amorphous matrix ribbons are ground into powders and mixed with the ZrO2 nano particles in the planetary mill, after then formed by hot pressing in Ar atmosphere under different pressures at the temperature 5 K above the glass transition temperature (Tg). The microstructure characterizations of the resulting specimens are conducted by means of XRD, FEG-SEM, and TEM techniques. It is found that the nano-sized ZrO2 dispersed Mg-based composite alloy powders can reach to a homogeneous size distribution (about 80 nm) after 50 h mechanical alloying. After hot pressing of these composite alloy powders under the pressure of 1100 MPa at 409 K, a 96% dense bulk specimen can be formed. Throughout the MA and hot pressing, the amorphous nature of the Mg65Cu25KxY10Agx matrix is maintained. The hardness of the formed bulk Mg-based composites (with 5 vol% nano-sized ZrO2 particles) can reach to 360 in Hv scale. In addition, the microstructure near the interface between the matrix and nano particles presents a well-bonded condition.

A series of Mg-based alloys with composition of Mg65Y10Cu25-XAgX, x = 0, 5, 10, were selected for investigating the microstructure evolution of the Mg-based nano/amorphous-composite alloy powder synthesized by the combination method of melt-spinning and mechanical alloying (MA). The microstructure characterization of the alloy powders was conducted by means of DSC, XRD, FEG-SEM, and TEM techniques. The result of XRD reveals that the entire as-quenched alloy ribbons exhibit a broaden diffraction pattern of amorphous phase. After 50 hours milling the mixture of amorphous alloy ribbons with 5 vol.% of nano-sized ZrO2 by planetary mill, the ZrO2 dispersed magnesium composite alloy powder can reach to a homogeneous size distribution. In parallel, the MA composite Mg-based alloy powders still remain an amorphous state by the characterization of X-ray diffraction and the DSC analysis. A clear Tg (glass transition temperature) and most wide supercooled region (about 44 K) were revealed for both the Mg65Y10Cu20Ag5 alloy ribbon and the MA magnesium composite powder. In addition, the result of TEM observation also revealed that the ZrO2 with average particle size of 80 nm distributed homogeneously in the amorphous matrix of the Mg65Y10Cu20Ag5 /5 vol.% ZrO2 composite alloy powder. The interface between the ZrO2 dispersoid and the amorphous matrix of the composite alloy powder exhibits a very good bonding condition.

The crystallization behavior and microstructure development of the Zr 61 Al 7.5 Cu 17.5 Ni 10 Si 4 alloy during annealing were investigated by isothermal differential scanning calorimetry, X-ray diffractometry and transmission electron microscopy. During isothermal annealing of the Zr 61 Al 7.5 Cu 17.5 Ni 10 Si 4 alloy at 703 K, Zr 2 Cu crystals with an average size of about 5 nm were first observed during the early stages (30% crystallization) of crystallization by TEM. The Zr 2 Cu crystal size increased with annealing time and attained an average size of 20 nm corresponding to the stage of 80% crystallization. In addition, the change in particle size with increasing annealing time exhibited a linear relationship between grain growth time and the cube of the particle size for the Zr 2 Cu type crystalline phase. This indicates that the crystal growth of the Zr 61 Al 7.5 Cu 17.5 Ni 10 Si 4 alloy belongs to a thermal activated process of the Arrhenius type. The activation energy for the grain growth of Zr 2 Cu is 155 ± 20 kJ/mol in the Zr 61 Al 7.5 Cu 17.5 Ni 10 Si 4 amorphous alloy. The lower activation energy for grain growth in compared to that for crystallization in Zr 65 Cu 35 440 kJ/mol crystal corresponds to the rearrangement of smaller atoms in the metallic glass, Al or Si (compare to Zr).

The crystallization behavior of Zr 63 Al 7.5 Cu 17.5 Ni 10 B 2 amorphous Alloy was studied by means of scanning differential calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). A single stage transformation of the amorphous phase forming a Zr 2 Cu-type crystalline phase was observed. Kinetics for such single stage crystallization was analyzed by means of Johnson–Mehl–Avrami equation and discussed regarding to the value of Avrami exponent. In addition, the cube of crystal size presents a linear relationship with isothermal annealing time. This indicates that the crystallization process of Zr 63 Al 7.5 Cu 17.5 Ni 10 B 2 amorphous alloy belongs to thermally activated process of Arrhenius type. From the HRTEM analysis, small amount of Zr 2 Cu-type crystals in the nano-scale dimension (10–20 nm) were observed to precipitate from the amorphous matrix upon the early stage of isothermal annealing the amorphous alloy at the temperature between the glass transition ( T g ) and the onset crystallization temperature ( T x ).

The crystallization behavior of amorphous Zr 65− x Al 7.5 Cu 17.5 Ni 10 Si x alloys, x = 0–10, was studied by means of differential scanning calorimetry, X-ray diffractometry, and TEM. The calculated T rg ( T g / T l ) for these amorphous alloys increases with increasing silicon content from 0.55 to 0.60, which indicates that the silicon addition, could improve the GFA for the Zr 65− x Al 7.5 Cu 17.5 Ni 10 Si x alloys. The activation energy of crystallization of the alloy 4Si was about 365 ± 5 kJ mol −1 , both determined by the Kissinger and Avrami plot. This value is about 20% higher than the base alloy (314 kJ mol − ), which implies that the silicon addition can increase the thermal stability for the Zr-based alloy. The average value of the Avrami exponent n were calculated to be 1.7–2.5 for the alloys in this study. In addition, the cube of crystal size as a function of isothermal annealing time presents a linear relationship for the Zr 61 Al 7.5 Cu 17.5 Ni 10 Si 4 alloy. During isothermal annealing the Zr 61 Al 7.5 Cu 17.5 Ni 10 Si 4 alloy at 698 K, the Zr 2 Cu crystal with average size of 105 nm was first observed at the early stage (30% crystallization ratio) of crystallization. In addition, both nano-crystals of the ZrCu (∼100 nm) and the Zr 3 Al (∼30 nm) were also observed to precipitate from the amorphous matrix upon the middle stage (50% crystallization ratio) of crystallization. The fracture surface presents typical ductile vein pattern for 4Si amorphous alloy ribbon after bended to 180°. However, a ductile–brittle transition phenomenon occurs at the amorphous ribbon after 50% crystallization ratio of isothermal annealing at the temperature between T g and T x .

The ribbons of amorphous Zr61Al7.5Cu17.5Ni10Si4 alloy were studied by means of differential scanning calorimetry (DSC), X-ray diffractometry (XRD), high-temperature optical microscope and transmission electron microscopy (TEM). The activation energy for such the crystallization of the amorphous phase was about 360 and 370 kJ mole−1 calculated by Kissinger and Avrami plots, respectively. Kinetics for the crystallization was analyzed by means of Johnson–Mehl–Avrami equation and discussed regarding to the value of Avrami exponent. The average value of the Avrami exponent n was measured about 2.43 at the range from 698 to 713 K. In addition, the cube of crystal size as a function of isothermally annealing time presents a linear relationship for the Zr61Al7.5Cu17.5Ni10Si4 alloy. When the Zr61Al7.5Cu17.5Ni10Si4 alloy was isothermally annealed at 698 K, a Zr2Cu crystal with an average size of 105 nm was first observed at the early stage (30% crystallization) of crystallization. In addition, both nano-crystals of ordered fcc ZrCu (∼100 nm) and ordered fcc Zr3Al (∼30 nm) were observed to precipitate from the amorphous matrix upon the middle stage (50% crystallization) of crystallization.

Ribbons of amorphous Zr 65− x Al 7.5 Cu 17.5 Ni 10 B x alloys with 0.1 mm thickness were prepared by melt-spinning. The thermal properties and microstructural development during the annealing of amorphous alloys have been investigated by the combination of differential thermal analysis (DTA), differential scanning calorimetry (DSC), high-temperature optical microscope, X-ray diffractometry (XRD), and transmission electron microscopy (TEM). The glass transition temperature for the Zr 65− x Al 7.5 Cu 17.5 Ni 10 B x alloys were measured around 645 K. The crystallization temperature increased with increasing boron content to 4 at.% and obtained a relative large temperature interval Δ T x of around 88 K. The calculated T rg for Zr 65 Al 7.5 Cu 17.5 Ni 10 alloy, Zr 63 Al 7.5 Cu 17.5 Ni 10 B 2 alloy, and Zr 61 Al 7.5 Cu 17.5 Ni 10 B 4 alloy exhibit the same value of 0.57. The activation energy of crystallization for the Zr 61 Al 7.5 Cu 17.5 Ni 10 B 2 alloy was about 360 or 380 kJ/mol, as determined by the Kissinger or Avrami plot, respectively. These values are about 20% higher than the activation energy of crystallization for the base alloy (314 kJ/mol as determined by the Kissinger plot). The average value of the Avrami exponent n were calculated to be 1.96±0.25 for Zr 65 Al 7.5 Cu 17.5 Ni 10 alloy, 1.75±0.15 for Zr 63 Al 7.5 Cu 17.5 Ni 10 B 2 alloy, and 1.9±90.45 for Zr 61 Al 7.5 Cu 17.5 Ni 10 B 4 alloy. This indicates that these three alloys exhibit similar crystallization process, a diffusion controlled growth process with a decreasing nucleation rate.

The effect of chromium addition to the Ni–19Si–3Nb–0.15B based alloy on the environment embrittlement at different temperature was investigated by the atmosphere-controlled tensile test in various conditions. Our experimental result reveals that the addition of chromium results in destabilizing the β phase (Ni 3 Si) and forming the hard Ni 5 Si 2 plate phase. These hard Ni 5 Si 2 plates play a major role of ductility deterioration of those alloys in this study. The elongation tested in vacuum, air and water vapor for the Ni–18Si–3Nb–0.15B–1Cr alloy exhibits a significantly increase with temperature from 973 to 1073 K. In addition, fracture surfaces tested at 1073 K in vacuum, water vapor, and air atmosphere present a typical ductile fracture surface, a fully dimpled fracture pattern. This observation appears to be well correlated with those results of tensile elongation and indicates that the addition of chromium may suppress the environmental embrittlement at high temperature (i.e. 1073 K).

The microstructural change of the Ni–19Si–3Nb-0.15B alloys after different heat treatment was examined by scanning electron microscopy with energy dispersive spectrum. In addition, Vickers’s hardness test was used to measure the variation of mechanical properties for each heat-treated alloy. The results reveal that the typical dendritic microstructure of the heat-treated alloys (comprised of dendritic β-phase, α–β eutectic, and the Nb-rich precipitates) remained almost the same microstructure as the as-cast alloy. However, the morphology of the sharp-edged Nb-rich precipitate (identified to be the cubic Nb3Ni2Si by electron diffraction of TEM) would be blunted by homogenization. In addition, the size of precipitates seemed to grow with increased aging temperature and aging time. Correlating the result of microhardness measurement with the microstructure observation, an aging temperature of 700 °C and an aging time of 10 h is found to be the optimum treating condition for the Ni–19Si–3Nb–0.15B alloy. In addition, the precipitate growth is revealed dominating by an interfacial-controlled kinetics with a thermal activation process of Arrhenius type. The strengthening effect of the heat treatment is not obvious from the hardness test. However, the effect of heat treatment exhibited significant improvement on the ductility of the Ni–19Si–3Nb–0.15B alloy (e ∼3% for as-cast alloy and 12% for heat-treated alloy).

The implementation in Julich of 3He spin filters for neutrons has progressed substantially. Apparatus for polarization via metastable 3He atoms in an RF-excited plasma has been constructed and polarization of 3He above 60% has been achieved. The compressors now in construction have been designed with the major goal of bringing of all components containing polarized gas as close as possible, thereby, minimizing the length of connecting lines which otherwise contribute excessively to polarization losses on account of their unfavorable ratio of surface to volume. The compressors are the result of a cooperative effort between groups at HMI (Berlin) and IFF (Julich). For the spin-exchange method we are working on a new approach, namely, the use of potassium instead of the standard choice, rubidium, as the alkali metal. We expect a much higher polarization of the 3He nuclei due to the much higher efficiency of K–3He spin transfer. In addition, we plan tests of filter cells including two separate chambers. One chamber is where the 3He is continuously optically polarized while the filter is in the neutron beam while the other chamber is the actual neutron spin filter. In this way, we can achieve a better environment for each of these vital functions. The transfer of the polarization will be by diffusion and convection.

The Ni–19Si–3Nb base alloy was microalloyed with different combinations of boron and carbon for modifying its precipitate microstructure as well as improving its ductility. The microstructural evolution in the Ni–19Si–3Nb–xB–yC alloys was characterized by X-ray diffraction, DTA, SEM, Auger analysis, and TEM. The results of X-ray diffraction and DTA could not reveal any phase change in the Ni–19Si–3Nb based alloys with different carbon and boron contents. However, the morphology of the Nb-rich precipitate (which was confirmed to be a cubic Nb3Ni2Si phase by selected area diffraction of TEM) changes from plate-like shape to discrete equiaxial shape when the boron and carbon additions increase to 100 ppm or more. Meanwhile, the fracture behavior of the Ni–19Si–3Nb alloy with different carbon and boron additions changes significantly from brittle mode to ductile mode. In addition, the results of Auger analysis revealed that the boron and carbon elements would segregate on the grain boundaries and the interface between Nb-rich precipitates and matrix. The additions of boron and carbon are suggested to improve the adhesion of grain boundaries to the matrix, and to re-modify the shape of the precipitates to resist crack propagation and improve the ductility of the Ni–19Si–3Nb-based alloy.

Проведены исследования методом ЯМР 125Te топологического изолятора теллурида висмута Bi2Te3 в широком диапазоне от комнатной температуры до 12.5 K. Измерения проводились на импульсном ЯМР-спектрометре Bruker Avance 400. Спектры ЯМР были получены для порошка, приготовленного из монокристалла Bi2Te3, и для монокристаллических пластин в ориентациях c|| B и c normal B. Спектры при комнатной температуре состояли из двух линий, которые были отнесены к двум неэквивалентным позициями ядер теллура Te1 и Te2. Параметры тензора сдвига частоты ЯМР были найдены из спектра для порошка. Температурные зависимости спектров для порошка и пластин в ориентации c normal B согласовывались между собой. Изменения положения линий с понижением температуры объяснялись уменьшением сдвига Найта. Была оценена энергия термоактивации носителей заряда. Спектры для пластин в ориентации c|| B демонстрировали особенности ниже 91 K. Измерены времена спин-решеточной релаксации для порошка и монокристаллических пластин в обеих ориентациях при комнатной температуре. Данная работа была поддержана Российским фондом фундаментальных исследований (гранты N 14-02-92012 и 16-57-52009), ФАНО России (программа "Спин" N 01201463330), правительством Российской Федерации (государственный контракт N 02.A03.21.0006) и Национальным научным советом Тайваня. ЯМР-измерения и рентгеновская дифракция проводились в Научном парке СПбГУ. DOI: 10.21883/FTT.2017.12.45225.170

Проведены исследования методом ЯМР 125Te порошкового образца и монокристаллических пластинок топологического изолятора Bi2Te3 при комнатной температуре и при низких температурах в интервале 12.5-16.5 K. Спектры монокристаллических пластинок исследовались в ориентации, в которой кристаллографическая ось c была параллельна или перпендикулярна магнитному полю. Для получения спектров регистрировались сигналы спинового эха и строилась их огибающая. Показано, что спектр ЯМР для порошка теллурида висмута и для пластинок с ориентацией c normal B состоит из двух линий, которые предположительно обусловлены ядрами теллура в двух кристаллографических позициях в объеме образца. Положение и форма линий определяются химическим сдвигом и сдвигом Найта. Для ориентации пластинок c|| B в спектре имеется дополнительная компонента в области высоких частот, которая не может появиться за счет угловой зависимости сдвигов линий, обусловленных ядрами теллура в объеме топологического изолятора. При низкой температуре дополнительная линия доминирует в спектре. Работа выполнена при поддержке РФФИ (гранты N 14-52-12010, 16-57-52009 МНТ, 14-02-92012), в рамках государственного задания ФАНО России (тема "Спин", N 01201463330) при частичной поддержке Комплексной программы УрО РАН (проект N 15-17-2-12), правительства РФ (контракт N 02.A03.21.0006) и Национального научного совета (Тайвань, гранты N 104-2811-M-006-029 и 104-2811-M-006-031). DOI: 10.21883/FTT.2017.05.44368.370

Проведены измерения спектра ЯМР и восстановления продольной ядерной намагниченности после инвертирующего импульса для изотопов 69Ga и 71Ga в жидком эвтектическом сплаве Ga-In-Sn, внедренном в пористые стекла с размером пор 25 и 7 nm в сравнении с объемным расплавом в полях 9.4, 11.7 и 17.6 T. Обнаружено различие формы и положения линий ЯМР в различных полях и для разных изотопов галлия в расплаве, внедренном в пористое стекло с размером пор 7 nm. Полученные в этом образце данные интерпретированы на основе теоретической модели динамического квадрупольного сдвига, в рамках которой найдено время корреляции атомного движения. Показана согласованность характеристик атомного движения, рассчитанных на основе модели динамического сдвига и на основе измерений спиновой релаксации. Работа выполнена при поддержке РФФИ (грант N 16-57-52009). Измерения частично проводились в Ресурсном центре "Центр диагностики функциональных материалов для медицины, фармакологии и наноэлектроники" Санкт-Петербургского государственного университета. DOI: 10.21883/FTT.2017.12.45247.160

Contamination of groundwater by petroleum-hydrocarbons is a serious environmental problem. The Monitored Natural Attenuation (MNA) approach is a passive remediation to degrade and dissipate groundwater contaminants in situ. In this study, a full-scale natural bioremediation investigation was conducted at a gasoline spill site. Results show that concentrations of major contaminants (benzene, toluene, ethylbenzene, and xylenes) dropped to below detection limit before they reached the downgradient monitor well located 280 m from the spill location. The results also reveal that natural biodegradation was the major cause of the observed contaminant reduction. The calculated natural first-order attenuation rates for BTEX and 1,2,4-trimethylbenzene (1,2,4-TMB) ranged from 0.051 (benzene) to 0.189 1/day (1,2,4-TMB). Evidence for the occurrence of natural attenuation includes the following: (1) depletion of dissolved oxygen, nitrate, and sulfate; (2) production of dissolved ferrous iron, sulfide, and CO2; (3) decreased BTEX concentrations and BTEX as carbon to TOC ratio along the transport path; (4) increased alkalinity and microbial populations; (5) limited spreading of the BTEX plume; and (6) preferential removal of certain BTEX components along the transport path. Additionally, the biodegradation capacity (44.73 mg/L) for BTEX and 1,2,4-TMB was much higher than other detected contaminants within the plume. Hence, natural attenuation can effectively contain the plume, and biodegradation processes played an important role in contaminant removal.

For combustion processes, it is important to monitor gases such as NO, in exhaust streams. Traditional approaches for such emission monitoring use analytical instruments, which are usually very expensive to install. Soft sensor techniques can provide a lower cost alternative to analyzers. In this paper we discuss using neural network partial least squares (NNPLS) and nonlinear principal components analysis (NLPCA) to build soft sensors for emission monitoring using data from an industrial heater. Several issues which are very important for the soft sensor approach are discussed, such as variable selection, sensor validation, and missing sensor replacement.