Isothermal section of the Gd–Co–V ternary system at 773 K

The isothermal section of the phase diagram of the Gd–Co–V ternary system at 773 K was investigated by X-ray powder diffraction (XRD), metallographic analysis, electron probe microanalysis, and differential thermal analysis (DTA) techniques. The isothermal section consists of 14 single-phase regions, 26 two-phase regions and 13 three-phase regions. The solid solubilities of V in the compounds Co₁₇Gd₂, Co₃Gd, Co₂Gd, Co₇Gd₁₂ and CoGd₃ were about 10.0, 2.0, 6.0, 1.2 and 5.3 at.% V, respectively. It was found that there are some homogeneity range in the only ternary compound of GdCo_12−xV_x with x = 2.6–3.7 at 773 K. No solubility of Gd in compounds Co₃V, σCoV or CoV₃ was observed. There is no solubility of V in Co₇Gd₂ or Co₃Gd₄ observed at 773 K.     

Microstructure and martensitic transformation of Ni–Fe–Ga–Si ferromagnetic shape memory alloys

The effects of the fourth element Si on the martensitic transformation and magnetic properties of Ni–Fe–Ga magnetic shape memory alloys were investigated. A complete thermoelastic martensitic transformation in Ni–Fe–Ga–Si alloys was observed in the temperature range of 218–285 K. The martensitic transformation temperatures of Ni–Fe–Ga alloys are obviously decreased by the substitution of Si for Ga element, that is, the substitution of 1 at.% Si for Ga leads to a decrease of martensitic transformation temperature of about 39.6 K. Moreover, the substitution of Si for Ga leads to a decrease of the saturation magnetic field and the magnetic anisotropy constant K₁ obviously.     

Phase equilibria on Ni–Al interface under low oxygen pressure

Seventeen phases of the Ni–Al–O system at high temperatures were analyzed using thermodynamic calculations. An Ni–Al–O isothermal stability diagram was obtained from the thermochemical data. The diagram describes the interface equations for Ni/Al intermetallic compounds, Al/Al₂O₃, and Al₂O₃/Al_XNi_Y compounds, and their corresponding regions. Four univariant equilibria points and ten bivariant equilibria lines below 1126 K were obtained. The equations for the coexistence points and interface lines were also obtained. A three-domain diagram of Ni–Al–O phase arrangement at temperatures between 900 and 1191 K is shown. Thermodynamic calculations confirmed that the formation of nickel aluminate spinel (NiAl₂O₄) requires a threshold NiO activity (log a_NiO = −205.3/T − 0.347) and the partial pressure of oxygen (log P_O2=−24622/T+8 atm). In the Ni–Al–O system, a_NiO < 0.266 at 900 K, the compounds in the Ni/Al interface are formed in the order Al₃Ni_(s) → Al₃Ni_2(s) → AlNi_(s) → AlNi_3(s) → Al₂O_3(α). When a_NiO < 0.351 at 1911 K, the compounds in the Ni/Al interface are formed in the order AlNi_(s) → Al₂O_3(α).     

Phase equilibria and chemical vapor transport in the system Mo–Ta–As

The phase diagram Mo–Ta–As was studied in two partial isothermal sections at 1050 °C (in the As-rich corner) and at 1400 °C (As-poor alloys) using powder X-ray diffraction and electron probe microanalysis. A complete solid solution was found to exist between isostructural Mo₅As₄ and Ta₅As₄ and the ternary solubility of Mo in Ta₃As at 1400 °C was determined. A ternary phase Mo_xTa_1−xAs with MnP-type structure was found to exist in the As-rich part of the system. Lattice parameters were investigated as a function of composition for (Mo,Ta)₅As₄ and for Mo_xTa_1−xAs. Additional experiments of chemical vapor transport (CVT) from 1000 °C to 900 °C using different ternary source compositions and I₂ and Br₂ (PtBr₂) as transport agents were performed. Only Ta compounds were found in the sink and no ternary transport was observed.     

Microstructure and grain refining performance of a new Al–Ti–C–B master alloy

A kind of Al–Ti–C–B master alloy with a uniform microstructure is prepared using a melt reaction method. It is found that the average grain size of α-Al can be reduced from 3500 to 170 μm by the addition of 0.2 wt.% of the prepared Al–5Ti–0.3C–0.2B and the refining efficiency does not fade obviously within 60 min. It is considered that the TiC_xB_y and TiB_2−mC_n particles found at the grain center are the effective and stable nucleating substrates for α-Al during solidification, which accounts for the good grain refining performance.     

Phase formation and structures of quasicrystals and approximants in the Zn–Mg–(Ti, Zr, Hf) system

The compositional regions for primitive (P) and face-centered (F) icosahedral quasicrystals (iQc) have been determined to be around Zn₈₄Mg₉Zr₇ and Zn₇₅Mg₁₈Zr₆, respectively. A 1/1 approximant of the F-type iQc was found to have a composition around Zn₇₇Mg₁₈Zr₅. A similar tendency has been verified for the Zn–Mg–Hf system. No stable iQc was observed in the Zn–Mg–Ti system. High-resolution X-ray measurements performed with synchrotron radiation showed that the stable iQcs are highly ordered and contain less phason disorder. High-angle annular dark field (HAADF) scanning transmission electron microscopy observation of the 1/1 Zn–Mg–Hf approximant effectively revealed the Hf positions in the structure, whose local contrasts can be reasonably interpreted by a structural model where icosahedral and dodecahedral Hf clusters are mutually interpenetrated. Similar appearances of local contrasts were frequently observed in HAADF images of the F-type iQc, indicating that the iQc structure is also build up of icosahedral clusters that are almost identical to those in the 1/1 approximant.     

Influence of the borohydride concentration on the composition of the amorphous Fe–B alloy produced by chemical reduction of synthetic, nano-sized iron-oxide particles: Part I: Hematite

Amorphous Fe–B alloys can be prepared at room temperature by reduction with borohydride of iron-oxide particles in suspension. By varying the borohydride concentration, amorphous Fe–B alloys with boron contents between 2 and 13 at.% have been produced by reduction of synthetic (nano-sized particles) and natural (micro-sized) hematite (α-Fe₂O₃) using sodium borohydride (NaBH₄). The results presented in this paper were obtained from a systematic study of the effect of borohydride concentration on the resulting reaction products using a variety of experimental techniques, such as X-ray diffraction, wet chemical analyses, thermal analyses, scanning electron microscopy, transmission Mössbauer spectroscopy (TMS) and integral low-energy electron Mössbauer spectroscopy (ILEEMS). Three distinct NaBH₄ concentrations have been applied. Beside unreacted hematite, amorphous Fe_1−xB_x alloys have been identified from the TMS spectra recorded at various temperatures between 15 K and room temperature. The amount of Fe_1−xB_x increases strongly with increasing NaBH₄ concentration, and for a given concentration with increasing specific surface area (SSA). Thermal analyses have suggested that for any given reduction condition, the boron content x in the formed amorphous alloy has a bimodal distribution. This is found to be consistent with the finding that the contribution of the Fe_1−xB_x phase to the total Mössbauer spectra consists of a superposition of a broad sextet and doublet. ILEEMS has further revealed that especially the surface layers of the hematite grains are affected by the reduction processes.     

The infrared absorption and dielectric properties of Li–Ga ferrite

The investigated compositions of the Li–Ga ferrite system Li_0.5Fe_2.5−xGa_xO₄ (where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) were studied by means of infrared (IR) spectroscopy. The analysis of IR spectra indicates the presence of splitting in the absorption band due to the presence of Fe²⁺ ions in ferrite. The dielectric constant ′, the dielectric loss ″ and the loss tangent tan δ were measured at elevated temperatures ranging from room temperature up to 850 K as a function of frequency (f = 10²–10⁶ Hz) for the investigated compositions. Maximum peak in tan δ and inverse peaks in ′ appeared for some samples due to the resonance phenomenon. The obtained data were discussed based on the valence exchange between (Fe³⁺ and Fe²⁺) and (Ga³⁺ and Ga²⁺), i.e. hopping mechanism.     

The poisoning of Pd–Y alloy membranes by carbon monoxide

We have explored the poisoning mechanism of CO on Pd–Y alloy membranes by means of thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS). TDS results show the total deuterium content sharply decreases and the desorption peak shifts to higher temperature with the increasing concentration of CO (from 0% to 26%) in gaseous deuterium. XPS results show that there are YO_x, carbon, carbonate and adsorbed molecular CO on Pd–Y alloy surfaces after reaction with the mixture of D₂ + 26%CO at 623 K followed by cooling to room temperature. But no carbides and PdO_x are detected.     

Formation of nanoparticles and nanorods via UV irradiation of AgNO3 solutions

The synthesis of silver nanoparticles via UV irradiation of AgNO₃ solutions was controlled by using UV–vis absorption spectra and TEM (transmission electron microscope) images. The UV–vis absorption method is good enough for the general control of synthesis process, and TEM images give us information about size of formed species. For investigated solutions of silver nitrate in ethanol and water, we observed formation of large nanoparticles (size about 100 nm) and nanorods (100 nm in length). Moreover, there was effort to confirm evidence of formation of these particles by using TOF mass spectrometer. Due to laser desorption/ionization process there is only evidence of small silver nanoparticles Ag_x, x ≤ 4 (clusters), and variety of silver compounds Ag_xN_yO_z (x ≤ 5, y ≤ 2, z ≤ 3).     

Structural properties of Li–borate glasses doped with Sm and Eu ions

A Li–borate glass system doped with samarium and europium has been prepared by a conventional melt quenching technique. Europium content was kept constant at 0.01 mol%. The general formula was

xSm₂O₃ + (100 − x) [0.84B₂O₃ + 0.15Li₂O + 0.01Eu₂O₃]

where x = 0.1, 0.2, 0.5, 0.6 and 0.7 mol%. The density was measured and the corresponding molar volume was evaluated .The former was found to increase by increasing Sm while the later exhibits opposite trend. The average optical basicity, Λ_th, electron negativity χ_2av and electron polarizability α²⁻ were calculated for the prepared compositions. Infrared spectra were obtained at room temperature for the prepared glasses before and after γ irradiation. The results showed that the three main appeared bands are most likely due to the bending and/or stretching vibration of both tetrahedral BO₄ and triagonal BO₃ borate units. ESR spectra were recorded at room temperature before and after γ-irradiation. It was found that the oxygen atoms of BO₃ units are responsible for the formation of the hole paramagnetic centers after irradiation in the glass matrix.     

Preparation of W–15 wt%Ti prealloyed powders

W–15 wt%Ti prealloyed powders were prepared by high-energy milling W and TiH₂ powders, and the prealloyed powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The size of W and TiH₂ grains was estimated by Williamson–Hall formula from width of XRD peaks. The results show that the grain size decreases with increasing milling time, while the lattice parameter increases. After milling for 40 h, nanocrystalline β-W_xTi_1−x solid solution with the form of thin laminar exists in the W–TiH₂ prealloyed powders.     

Magnetic properties and microstructural characteristics of bulk Nd–Al–Fe–Co glassy alloys

Bulk Nd–Al–Fe–Co glassy alloys with diameter up to 5 mm were investigated by magnetic measurements, magnetic force microscopy (MFM) and high resolution electron microscopy (HREM) at room temperature. The results from the measurement of vibrating sample magnetometer show that these samples with compositions Nd₆₅Al₁₀Fe_25-xCo_x (x=0–10 at.%) and Nd₆₀Al₁₀Fe₂₀Co₁₀ display hard magnetic properties with H_C of 300 kAm⁻¹, M_S of 10 Am² kg⁻¹, and M_r of 7 Am² kg⁻¹. The MFM measurements of the Nd₆₀Al₁₀Fe₂₀Co₁₀ bulk metallic glass (BMG) reveal the existence of magnetic domains with a period of about 0.36 μm, and the ordered clusters with the averaged size of about 5 nm was observed by the HREM on the sample. The domain structure or cluster is believed to be associated with the appearance of hard-magnetic properties in this alloy system. The existence of the large-size domains demonstrates that magnetic moment of a great deal of ordered atomic clusters in the BMG has been aligned by exchange-coupling.     

Mechanical alloyed Ti–Cu–Ni–Si–B amorphous alloys with significant supercooled liquid region

This study examined the glass formation range of Ti_94–x–yCu_xNi_ySi₄B₂ alloy powders synthesized by mechanical alloying technique. According to the results, after 5–7 h of milling, the mechanically alloyed powders were amorphous at compositions with (x+y) equal to 20–40%. For the compositions with (x+y) larger than 45% or smaller than 10%, the structure of ball-milled powders is a partial amorphous single phase or coexistent partial amorphous and crystalline phases, respectively. The thermal stability of the amorphous powders was also investigated by differential thermal analysis. As the results demonstrated, several amorphous powders were found to exhibit a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region defined by the difference between T_g and T_x, i.e. ΔT(=T_x–T_g), are 52 K for Ti₇₄Ni₂₀Si₄B₂, 74 K for Ti₆₄Ni₃₀Si₄B₂, 58 K for Ti₆₄Cu₂₀Ni₁₀Si₄B₂, and 61 K for Ti₇₄Cu₁₀Ni₁₀Si₄B₂.     

Structure and electrochemical properties of the Fe substituted Ti–V-based hydrogen storage alloys

To elucidate the effects of Fe on the Ti–V-based hydrogen storage electrode alloys, the Ti_0.8Zr_0.2V_2.7−xMn_0.5Cr_0.8Ni_1.0Fe_x (x = 0.0–0.5) alloys were prepared and their structures and electrochemical properties were systematically investigated. XRD results show that all the alloys consist of a C14 Laves phase with hexagonal structure and a V-based solid solution phase with bcc structure. With increasing Fe content, the abundance of the C14 Laves phase gradually decreases from 43.4 wt% (x = 0.0) to 28.5 wt% (x = 0.5), on the contrary, that of the V-based solid solution phase monotonously increases from 56.6 wt% to 71.5 wt%. In addition, SEM observation finds that the grain size of the V-based solid solution phase is first gradually reduced and then enlarged with increasing x. Electrochemical investigations indicate that the substitution of Fe for V markedly improves the cycling stability and the high rate dischargeability of the alloy electrodes, but decreases the maximum discharge capacity and the activation performance. Further electrochemical impedance spectra, the linear polarization curve and the potentiostatic step discharge measurements reveal that the electrochemical kinetics of the alloy electrodes should be jointly controlled by the charge-transfer reaction rate on the alloy surface and the hydrogen diffusion rate in the bulk of the alloys. For the alloy electrodes with the lower Fe content (x = 0.0–0.2), the hydrogen diffusion in the bulk of the alloys should be the rate-determining step of its discharge process, and while x increases from 0.3 to 0.5, the charge-transfer reaction on the alloy surface becomes to the rate-determining step, which induces that the electrochemical kinetics of the alloy electrodes is firstly improved and then decreased with increasing Fe content.     

Thermodynamic analysis of alloys Ti–Al, Ti–V, Al–V and Ti–Al–V

Thermodynamic analysis of three binary Ti-based alloys: Ti–Al, Ti–V, and Al–V, as well as ternary alloy Ti–Al–V, is shown in this paper. Thermodynamic analysis involved thermodynamic determination of activities, coefficient of activities, partial and integral values for enthalpies and Gibbs energies of mixing and excess energies at four different temperatures: 2000, 2073, 2200 and 2273 K, as well as calculated phase diagrams for the investigated binary and ternary systems. The FactSage is used for all thermodynamic calculations.     

Structural and magnetic susceptibility studies of samarium substituted magnesium–zinc ferrites

Polycrystalline soft ferrites Mg_1−x–Zn_x–Fe_2−y–Sm_y–O₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0; y = 0.0, 0.05 and 0.1) were prepared by usual ceramic method. The samples were characterized by X-ray diffraction and IR techniques. Magnetic properties have been studied from magnetization and (a)–(c) susceptibility measurements. The XRD patterns of all the samples reveal the formation of single-phase cubic spinel. The IR spectra show two strong absorption bands in the frequency range 300–800 cm⁻¹. The magnetization measurements exhibit the Neel's collinear ferrimagnetic behavior for x ≤ 0.2 and suggest non-collinear Y–K (Yaffet–Kittel) type magnetic ordering for x ≥ 0.4. The samples with x ≥ 0.8 are paramagnetic at and above the room temperature. Variation of ac susceptibility with temperature exhibit the single domain structure (SD) with x = 0.0 and multi-domain (MD) structure with x ≥ 0.2 on substitution of Zn²⁺ content. On substitution of Sm³⁺ content, the samples exhibit SD for x = 0.0, MD for x = 0.2 and MD to SP transition for x ≥ 0.4.     

Dependence of coercivity on the intergranular phase for nanocrystalline Nd–Fe–B magnet

Assume that the intergranular phase (IP) existing between adjacent grains is a weak magnetic phase, and could weaken or interrupt the intergrain exchange-coupling interaction (IECI). Using our proposed cubic-grain anisotropy model, we investigate the effects of IP's thickness d, and its anisotropy constant K₁(0) on the coercivity of nanocrystalline Nd–Fe–B magnet. Calculation results indicate that the coercivity increases with increasing d, but decreases with increasing K₁(0). When d = 1.2 nm and K₁(0) = 0.5K₁ (K₁ is the common anisotropy constant of the bulk Nd–Fe–B material), our calculated results are consistent with available experimental data.     

Al–Ti–B grain refiners via powder metallurgy processing of Al/K2TiF6/KBF4 powder blends

The response to thermal exposure of ball-milled Al/K₂TiF₆/KBF₄ powder blends was investigated to explore the potential of PM processing for the manufacture of Al–Ti–B alloys. K₂TiF₆ starts to be reduced by aluminium as early as 220 °C when ball-milled Al/K₂TiF₆/KBF₄ powder blends are heated. The reaction of KBF₄ with aluminium follows soon after. The Ti and B thus produced are both solutionized in aluminium before precipitating out as Al₃Ti and TiB₂. All these reactions take place below the melting point of aluminium. The ball-milled Al/K₂TiF₆/KBF₄ powder blends heat treated at approximately 525 °C can be compacted to produce Al–Ti–B pellets with in situ formed Al₃Ti and TiB₂ particles. These pellets are shown to be adequate grain refiners for aluminium alloys.