Properties of the GdTX (T = Mn, Fe, Ni, Pd, X = Al, In) and GdFe6Al6 intermetallics

The magnetic and magnetocaloric properties of GdTX (T = Mn, Fe, Ni, Pd, X = Al, In) and GdFe₆Al₆ ternary compounds for possible applications in magnetic refrigeration have been investigated. Magnetization measurements have been performed in the temperature range of 2-400 K and magnetic field range of 0-7 T. The magnetic entropy changes ΔS_m have been calculated indirectly from the magnetization measurements. The calculated values of entropy change ΔS_m for examined compounds amount −13.63 J/K kg, −13.05 J/K kg, −6.13 J/K kg, −3.72 J/K kg, −1.38 J/K kg and −0.94 J/K kg, respectively, for GdNiAl, GdPdAl, GdPdIn, GdFeAl, GdFe₆Al₆ and GdMnAl at 7 T.     

Effects of rare-earth elements on the glass-forming ability and mechanical properties of Cu46Zr47-xA17Mx （M = Ce, Pr, Tb, and Gd） bulk metallic glasses

Cu₄₆Zr_47−x Al₇M _x (M = Ce, Pr, Tb, and Gd) bulk metallic glassy (BMG) alloys were prepared by copper-mold vacuum suction casting. The effects of rare-earth elements on the glass-forming ability (GFA), thermal stability, and mechanical properties of Cu₄₆Zr_47−x Al₇M _x were investigated. The GFA of Cu₄₆Zr_47−x Al₇M _x (M = Ce, Pr) alloys is dependent on the content of Ce and Pr, and the optimal content is 4 at.%. Cu₄₆Zr_47−x Al₇Tb _x (x = 2, 4, and 5) amorphous alloys with a diameter of 5 mm can be prepared. The GFA of Cu₄₆Zr_47−x Al₇Gd _x (x = 2, 4, and 5) increases with increasing Gd. T _x and T _p of all decrease. T _g is dependent on the rare-earth element and its content. ΔT _x for most of these alloys decreases except the Cu₄₆Zr₄₂Al₇Gd₅ alloy. The activation energies ΔE _g, ΔE _x, and ΔE _p for the Cu₄₆Zr₄₂Al₇Gd₅ BMG alloy with Kissinger equations are 340.7, 211.3, and 211.3 kJ/mol, respectively. These values with Ozawa equations are 334.8, 210.3, and 210.3 kJ/mol, respectively. The Cu₄₆Zr₄₅Al₇Tb₂ alloy presents the highest microhardness, Hv 590, while the Cu₄₆Zr₄₃Al₇Pr₄ alloy presents the least, Hv 479. The compressive strength (σ _c.f.) of the Cu₄₆Zr₄₃Al₇Gd₄ BMG alloy is higher than that of the Cu₄₆Zr₄₃Al₇Tb₄ BMG alloy.     

Ga含量对Al-Mg-Ga-Sn合金组织和降解性的影响

采用电炉熔炼制备了不同Ga含量的Al-Mg-Ga-Sn合金。通过光学显微镜(OM) 、扫描电镜(SEM)和X射线衍射仪(XRD)对其显微组织的形貌和成分进行了表征;在30℃、40℃、70℃、90℃的纯水中进行降解速率的测定;采用电化学工作站测试了室温电化学性能。结果表明：Al-Mg-Ga-Sn合金在Mg+Sn为定值10wt.%的情况下,Ga含量分别为0 wt.%、4 wt.%、8 wt.%、12 wt.%、16 wt.%时,合金组织均有铝基体相和Mg<sub>2</sub>Sn相,且随着Ga含量的增加合金组织中出现了Ga<sub>5</sub>Mg<sub>2</sub>相。Al-Mg-Ga-Sn合金的降解性特点是主要由铝基体相中点蚀开启,由Mg<sub>2</sub>Sn和Ga<sub>5</sub>Mg<sub>2</sub>化合物相的晶间腐蚀加速;不同Ga含量合金的起始降解温度由固溶于铝基体中的低熔点元素(Ga+Sn)的含量决定;相同Ga含量的合金随温度升高降解速率加快,降解反应动力学遵从阿伦尼乌斯公式。室温电化学分析表明：Al-Mg-Ga-Sn合金随Ga含量增加,腐蚀电位不同程度地负移,腐蚀电流逐渐增大。     

Magnetic properties and tuneable magnetocaloric effect with large temperature span in GdCd1−xRux solid solutions

The magnetic properties and the magnetocaloric effect (MCE) in the GdCd_1−xRu_x (x = 0.1, 0.15, and 0.2) solid solutions have been systematically investigated. A large reversible MCE has been observed in GdCd_1−xRu_x accompanied by a second order magnetic phase transition from paramagnetic to ferromagnetic at T_C ∼ 149, 108, and 73 K for x = 0.1, 0.15, and 0.2, respectively. Under a field change from 0 to 7 T, the maximum values of magnetic entropy change (–ΔS_M^max) are 5.6, 7.8, and 11.0 J/kg K for x = 0.1, 0.15, and 0.2, respectively, the corresponding values of the relative cooling power (RCP) are 889, 852, and 828 J/kg. The considerable reversible MCE and large RCP values together with the tuneable T_M in a wide temperature range make the GdCd_1−xRu_x solid solutions considerable for active magnetic-refrigeration.     

Ru-based bimetallic alloys for hydrogen generation by hydrolysis of sodium tetrahydroborate

The present study contemplates the application of Ru-based bimetallic alloys for hydrogen generation by hydrolysis of sodium tetrahydroborate (NaBH₄). Ru and Pt, RuCu, RuPd, RuAg and RuPt (atomic ratio 1:1), PtAg, and Ru_xPt_y (atomic ratios x:y of 2:1 or 1:2), all supported over titanium oxide, were prepared. Their activity decreased in the order RuRu₂Pt₁ > RuPtRu₁Pt₂ > RuPd > RuAgPt > RuCu > PtAg. Alloying Ru with an inactive metal like Cu, Pd or Ag did not improve the performances of Ru. The catalytic ability of Ru₂Pt₁-TiO₂ is in the range of the highest values reported so far in the literature with a hydrogen generation rate of 15.2 L(H₂) min⁻¹ g⁻¹(RuPt). After separation from the reaction medium and rinsing with deionised water, the used Ru₂Pt₁-TiO₂ catalyst was re-evaluated and almost the same catalytic activities as fresh catalyst were obtained during several cycles.     

Magnetic properties and large magnetocaloric effect in Gd-Ni amorphous ribbons for magnetic refrigeration applications in intermediate temperature range

Amorphous Gd_68−xNi_32+x (x = −3, 0, 3) ribbons were prepared by melt-spinning method. The crystallization onset temperatures T_x1 for Gd_68−xNi_32+x amorphous ribbons with x = −3, 0, and 3 are 561, 568, and 562 K, respectively. All the samples undergo the second-order magnetic transition at temperatures between ∼122 (x = −3 and 3) and 124 K (x = 0). The Curie temperature T_C does not change with the composition significantly. The maximum isothermal magnetic entropy changes (−ΔS_M)_max of Gd₇₁Ni₂₉, Gd₆₈Ni₃₂, and Gd₆₅Ni₃₅ amorphous ribbons for a magnetic field change of 0-5 T were 9.0, 8.0, and 6.9 J kg⁻¹ K⁻¹, respectively. Large values of the refrigerant capacity (RC) were obtained in these ribbons. For example, Gd₇₁Ni₂₉ amorphous ribbon has a maximum RC value of 724 J kg⁻¹. Large magnetic entropy change and RC values together with high stability enable the Gd₇₁Ni₂₉ amorphous alloy a competitive candidate among the magnetic refrigeration materials working at temperatures near 120 K.     

Magnetocaloric effect of （Gd1-xCex）Co2 compounds in low magnetic fields

The phases in the compounds (Gd_1−x Ce _x )Co₂ with x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 were investigated by X-ray diffraction, and the magnetocaloric effect for x = 0–0.4 was studied by magnetization measurements. The samples are almost single phase with a cubic MgCu₂-type structure for x = 0–0.5. The magnetization decreases with an increase in Ce content. There is almost no magnetic transition for x = 0.5 at 100–350 K. The Curie temperature (T _c) of the (Gd_1−x Ce _x )Co₂ compounds with x from 0.1 to 0.4 are 350, 344, 340, and 338 K respectively. The maximum magnetic entropy change is 2.34 J·kg⁻¹·K⁻¹ when x = 0.3. The results of Arrott plots show that the magnetic phase transition is second-order magnetic phase transition in these compounds.     

EPR studies of (Bi, Pb)-2223 phase substituted by Ruthenium ions

This work studied X-ray powder diffraction (XRD), electrical resistivity and electron paramagnetic resonance (EPR) measurements for Bi_1.8Pb_0.4Sr₂Ca_2.1Cu_3−xRu_xO_10+δ (0.0 ≤ x ≤ 0.4) superconducting samples. XRD analysis and electrical resistivity data showed that the low-content of Ru, x ≤ 0.05, enhanced both the phase formation and the superconducting transition temperature of (Bi, Pb)-2223 phase. A phase change from (Bi, Pb)-2223 phase to (Bi, Pb)-2212 phase was reported for x ≥ 0.15. Two EPR lines were observed for 0.0 ≤ x ≤ 0.075, indicating the presence of both (Bi, Pb)-2223 and (Bi, Pb)-2212 phases. While, one EPR line was observed for x ≥ 0.15, corresponding to the (Bi, Pb)-2212 phase formation. The number of spins (N) participating in the resonance and its spin paramagnetic susceptibility (χ), for the two phases, were calculated as a function of both Ru-content and temperature. In addition, we reported the variation of activation energy (E_a), Curie constant (C), Curie temperature (θ) and effective magnetic moment (μ) with Ru-content.     

Metal Dusting of Fe–Cr and Fe–Ni–Cr Alloys Under Cyclic Conditions

Metal dusting is the disintegration of alloys into carbon and metal particles during high-temperature exposure to carbon-bearing gases. Model Fe–Cr and Fe–Ni–Cr alloys were studied to test the hypothesis that M₃C formation is necessary for metal dusting to occur. The alloys were exposed to a 68% CO–26% H₂–6% H₂O gas mixture at 680°C (a_c=2.9) under thermal cycling conditions. Equilibrium calculations predicted the formation of M₃C at the surface of Fe–25Cr, but not Fe–60Cr. All compositions were expressed in w/o, weight percent. Alloys of Fe–25Cr with 2.5, 5, 10, and 25 w/o nickel additions were also exposed to the same conditions to study the role of nickel in destabilizing the precipitation of M₃C and, hence, altering the resistance to metal dusting. Metal dusting was observed on all the alloys except Fe–60Cr. For Fe–25Cr, Fe–25Cr–2.5Ni, and Fe–25Cr–5Ni, the carbonization and dusting process was localized, and its incidence decreased in Fe–25Cr–2.5Ni, consistent with the increased destabilization of M₃C precipitation. However, Fe–25Cr–10Ni and Fe–25Cr–25Ni both underwent extensive dusting in the absence of protective Cr₂O₃ formation. The carbon deposits formed consisted of carbon filaments, which contained particles at their tips. These were shown by electron diffraction to be exclusively Fe₃C in Fe–25Cr, Fe–25Cr–2.5Ni, and Fe–25Cr–5Ni, and a mixture of austenite and (Fe,Ni)₃C in Fe–25Cr–10Ni and Fe–25Cr–25Ni.     

Synthesis and conductivity of heptadecatungstovanadodiphosphoric heteropoly acid with Dawson structure

A new solid high-proton conductor, heptadecatungstovanadodiphosphoric heteropoly acid H₇P₂W₁₇VO₆₂·28H₂O with Dawson structure was synthesized by the stepwise acidification and the stepwise addition of element solutions. The optimal proportion of component compounds in the synthesis reaction was given. The product was characterized by chemical analysis, potentiometric titration, IR, UV, XRD, ³¹P NMR, TG-DTA and electrochemical impedance spectroscopy (EIS). The results indicate that H₇P₂W₁₇VO₆₂·28H₂O possesses the Dawson structure. EIS measurements show a high conductivity (3.10 × 10⁻² S cm⁻¹ at 26 °C and 75% relative humidity), with an activation energy of 32.23 kJ mol⁻¹ for proton conduction. The mechanism of proton conduction for this heteropoly acid is Vehicle mechanism.     

Silicon orientation effects on surface blistering characteristics due to hydrogen ion implantation

This study attempted to examine surface blistering characteristics induced by room-temperature implantation of 5 × 10¹⁶ cm^− 2 40 keV hydrogen ions into Si<111> wafers followed by furnace annealing treatments at various temperatures for a duration of 1 h. The results obtained in our previous work [1], in which Si<100> wafers were used, were adopted for making comparisons. A comparison of Si<111> and Si<100> resulted in blister distributions with greater areal number densities, smaller diameters, similar covered-area fractions, higher threshold and saturation post-annealing temperatures, larger apparent activation energy levels, smaller hydrogen-trapping and oxygen-gettering depths, higher threshold post-annealing temperatures for hydrogen trapping and oxygen gettering, and lower SIMS peak intensities at hydrogen-trapping and oxygen-gettering depths. Furthermore, the K values for Si<111> were less than those for Si<100> when post-annealing temperatures ranged from 200 to 450 °C. Conversely, just the opposite was true when post-annealing temperatures ranged from 450 to 550 °C. In addition, the crater distributions achieved in Si<111> had lower areal number densities and covered-area fractions, higher threshold and saturation post-annealing temperatures, and smaller crater depths compared to Si<100>. In both Si<111> and Si<100>, areal number densities and covered-area fractions in the crater distributions were lower than those in the blister distributions.     

A contribution to the Al–Ni–Cr phase diagram

The Al–Ni–Cr phase diagram was specified at 1000 °C and partially at 900 °C. The results concerning the region below 60 at.% Al agreed qualitatively with the literature data. The binary Al–Cr phases μ and γ dissolve up to 1 and 3 at.% Ni, respectively, and Al₃Ni₂ up to 2.5 at.% Cr. Two ternary phases were revealed: hexagonal ζ (a ≈ 1.77, c ≈ 1.24 nm) in a wide range between Al₈₁Ni₃Cr₁₆, Al_76.5Ni₃Cr_20.5, Al_76.5Ni₉Cr_14.5 and Al_71.5Ni₉Cr_19.5, and high-temperature orthorhombic (a ≈ 1.26, b ≈ 3.48, c ≈ 2.02 nm) around Al_76.5Ni_2.0Cr_21.5.     

Effect of manganese on the microstructure of Mg–3Al alloy

The effect of manganese on the microstructure of Mg–3Al alloy, especially the nucleation efficiency of Al–Mn particles on primary Mg, has been investigated in this paper. Mg–0.72Mn was used to fabricate Mg–3Al–xMn (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) alloys, and the grain sizes of these alloys fluctuate at 390 μm indicating addition of manganese does not evidently influence the grain size of Mg–3Al alloy. Through XRD, FESEM and TEM detection, it is found that Al_0.89Mn_1.11 compound is the dominant Al–Mn phase in Mg–3Al–0.3Mn, Mg–3Al–0.4Mn and Mg–3Al–0.5Mn, and distributes in primary Mg matrix and interdendritic regions with an angular blocky morphology. The number of Al_0.89Mn_1.11 increases gradually with increasing manganese content while the grain sizes of primary Mg are nearly the same in Mg–3Al, Mg–3Al–0.3Mn, Mg–3Al–0.4Mn and Mg–3Al–0.5Mn, indicating Al_0.89Mn_1.11 has low nucleation efficiency on primary Mg.     

Solidification morphology and phase selection in drop-tube processed Ni–Fe–Si intermetallics

Drop-tube processing was used to rapidly solidify droplets of Ni_64.7Fe₁₀Si_25.3 and Ni_59.7Fe₁₅Si_25.3 alloys. In the larger droplets, and therefore at low cooling rates, only two phases, γ-Ni₃₁Si₁₂ and β₁-Ni₃Si were observed. Conversely, in the smaller droplets, and therefore at higher cooling rates, the metastable phase Ni₂₅Si₉ was also observed. The critical cooling rate for the formation of Ni₂₅Si₉ was estimated as 5 × 10³ K s⁻¹. SEM and TEM analysis reveals three typical microstructures: (I) a regular structure, comprising single-phase γ-Ni₃₁Si₁₂ and a eutectic structure between γ-Ni₃₁Si₁₂ and β₁-Ni₃Si; (II) a refined lamellar structure with a lamellar spacing <50 nm comprising γ-Ni₃₁Si₁₂ and β₁-Ni₃Si; (III) an anomalous structure with a matrix of Ni₂₅Si₉ and only a very small proportion of a second, and as yet unidentified, phase. These results indicate that there is an extended stability field for Ni₂₅Si₉ in the Ni-rich part of the Ni–Fe–Si ternary system in comparison to the Ni–Si binary system. With an increase of cooling rate, an increasing fraction of small droplets experience high undercoolings and, therefore, can be undercooled into the Ni₂₅Si₉ stability field forming droplets consisting of only the anomalous structure (III). The Fe atoms are found to occupy different substitutional sites in different phase, i.e. Fe substitutes for Ni in the γ phase and Si in the L1₂ (β₁) phase respectively.     

Experimental investigation of the Ce-Cu phase diagram

The binary Ce-Cu system has been re-investigated via the selected eighteen key alloys by means of the differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM) with energy dispersive X-ray analysis techniques. Five intermetallic compounds, Cu₆Ce, Cu₅Ce, Cu₄Ce, Cu₂Ce, and CuCe, have been confirmed. Cu₆Ce and Cu₂Ce melt congruently at 947 °C and 810 °C, respectively. Cu₅Ce, Cu₄Ce, and CuCe are formed through peritectic reactions, L + Cu₆Ce ↔ Cu₅Ce at 799 °C, L + Cu₅Ce ↔ Cu₄Ce at 792 °C, and L + Cu₂Ce ↔ CuCe at 492 °C, respectively. Three eutectic reactions, L ↔ (Cu) + Cu₆Ce at 879 °C, L ↔ Cu₄Ce + Cu₂Ce at 753 °C, and L ↔ CuCe + (γCe) at 407 °C, have been observed. One catatectic reaction, (δCe) ↔ L + (γCe) at 702 °C, was determined. According to the present experimental results, the Ce-Cu phase diagram is revised.     

A new type of molecular packing in the conducting complex of tetrathiofulvalene C6H4S4 (TTF) with pyromellitic dianhydride C10H2O6 (PMDA)

The structure of the tetrathiofulvalene-pyromellitic dianhydride complex, TTF-PMDA (C₆H₄S₄?C₁₀H₂O₆), has been determined (a = 0.72550, b = 0.76317, c = 1.71905 nm, α = 106.226, β = 108.580, γ = 70.493°, $\text{space group}\text{, P}\text{I}\text{, N}{}_{\mathrm{I}}\text{= 1538, Z = 2, R}{}_{\mathrm{<mtext>F</mtext>}}\text{= 8.5\%)}$. The 1:1 TTF-PMDA complex is the first compound where TTF molecules do not form stacks. Instead, the structure contains quasi-one-dimensional strips of donor molecules where π-orbitals overlap π-like. With the actual degree of charge transfer, the donor strips are conducting (the conductivity of pellet samples is about 0.1 $\text{Ω}{}^{\mathrm{?1}}$ m^?1). The TTF strips showing no Peierls distortions are stabilized by close contact with PMDA strips.     

Sulfidation Properties of Ni–20Cr and Ni–13.5Co–20Cr Alloys at 873 K under Low Sulfur Pressures in H2S-H2 Atmospheres

The sulfidation properties of Ni–20Cr and Ni–13.5Co–20Cralloys as well as a nickel-base superalloy AISI685 were investigated at873 K in H₂S–H₂ gas mixtures with sulfur partial pressures of10^–4, 10^–5.5, and 10^–7Pa by mass-gain measurements,electron-probe microanalysis (EPMA), and X-ray diffraction (XRD)analysis. Sulfidation obeyed the parabolic rate law, and the parabolic rateconstants decreased in the order Ni–20Cr, Ni–13.5Co–20Cr,and AISI685 at each sulfur pressure. With decreasing sulfur pressure, therate constants first decreased slowly and then rapidly at a 10–7 Pasulfur pressure. At both 10^–4 and 10^–5.5 Pa sulfur pressures,Ni–20Cr formed a surface scale with a duplex structure of inner(Cr₃S₄) and outer (Ni₃S₂) layers, while Ni–13.5Co–20Cr formeda triplex structure of inner (Cr₃S₄), intermediate(Ni,Co)Cr₂S₄, and outer[Ni₃S₂+(Co,Ni)₉S₈] layers. Thesurface scale formed on AISI685 was verycomplex, comprising at least four layers, a fibrous (Co,Ni)₉S₈ top surface,outer [Ni₃S₂+(Co,Ni)₉S₈], and intermediate [(Cr,Ti)₃S₄] layers, as well asan inner layer containing Cr, Ti, Mo, Al, and S. At the 10^–7 Pa sulfurpressure, which is lower than the dissociation pressure of Ni₃S₂, bothNi–20Cr and Ni–13.5Co–20Cr formed a surface scale ofCr₃S₄ covered by a thin NiCr₂S₄ layer, accompanied by copious internalsulfidation of Cr₃S₄ and/or CrS. On AISI685 there was a surface scale of(Cr,Ti)₃S₄ accompanied by the usual internal sulfidation. It is discussedthat diffusion of cations in the inner Cr₃S₄ layer is the rate-determiningstep for the growth of the multilayer structures. At the 10^–7 Pasulfur pressure, diffusion of Cr and S contribute to form a thin surfacescale and internal sulfidation, respectively.     

BGA焊点界面化合物纳米压痕力学行为

利用纳米压痕法对BGA焊点(Cu,Ni)₆Sn₅,Cu₆Sn₅,Cu₃Sn界面化合物(IMC)进行了压痕试验.基于Oliver-Pharr法确定了(Cu,Ni)₆Sn₅,Cu₆Sn₅,Cu₃Sn的弹性模量和压痕硬度,研究了加载速率对IMC纳米压痕力学行为的影响及其变化规律.结果表明,锯齿流变效应与加载速率的大小是相关的.在加载速率较小的情况下(Cu,Ni)₆Sn₅,Cu₆Sn₅,Cu₃Sn都具有锯齿流变效应,但程度不同;在加载速率较大的情况下(Cu,Ni)₆Sn₅,Cu₃Sn锯齿流变效应不明显,而Cu₆Sn₅的锯齿流变效应相对明显.(Cu,Ni)₆Sn₅,Cu₆Sn₅,Cu₃Sn界面IMC的弹性模量分别为126,118,135 GPa;压痕硬度分别为6.5,6.3,5.8 GPa;含镍的(Cu,Ni)₆Sn₅化合物弹性模量和压痕硬度均比Cu₆Sn₅的值要高.     

Complex impedance analysis of (Y2O3 + CeO2)-YCr0.5Mn0.5O3 composite NTC ceramics

Ceramic compositions based on (aY₂O₃ + bCeO₂)-0.4YCr_0.5Mn_0.5O₃ (a + b = 0.6) were prepared by conventional solid state reaction at 1200 °C, and sintered under air atmosphere at 1600 °C. For 0 ≤ a < 0.6, XRD patterns have shown that the major phases presented in the calcined powders are Y₂O₃, CeO₂ and orthorhombic perovskite YCr_0.5Mn_0.5O₃ phase, respectively. SEM and EDAX observations confirm the YCr_0.5Mn_0.5O₃ phases mostly exist at the grain, whereas the Y₂O₃ and CeO₂ phases mainly exist at the grain boundaries. Complex impedance analysis shows that, for 0 < a ≤ 0.6, single semicircular arc whose shape does not show any change with temperature. Nevertheless, for a = 0, two overlapping semicircular arcs are observed at and above 300 °C. The grain boundary properties exhibit thermistor parameters with a negative temperature coefficient characteristic. The relaxation behavior and conduction for the grain boundary could be due to a space-charge relaxation mechanism and oxygen vacancies, respectively.