Al-rich region of Al–Pd–Ru at 1000 to 1100 °C

Partial isothermal sections of the Al–Pd–Ru phase diagram at 1000, 1050 and 1100 °C are presented here. The Al–Pd orthorhombic -phases dissolve up to 15.5 at.% Ru, Al₁₃Ru₄ <2.5 at.% Pd and Al₂Ru up to 1 at.% Pd. Between 66 and 75 at.% Al, ternary quasiperiodic icosahedral phase and three cubic phases: C (, a = 0.7757 nm), C₁ (, a = 1.5532 nm) and C₂ (, a = 1.5566 nm) were revealed. An additional complex cubic structure with a ≈ 3.96 nm was found to be formed at compositions close to those of the icosahedral phase.     

Magnetic properties of (Fe)1−x–(Al2O3)x and (Fe50Ni50)1−x–(Al2O3)x nanocomposite magnetic media synthesized using gel like Al2O3 matrix

Composites with ferromagnetic nanoparticles, Fe and Fe₅₀Ni₅₀, dispersed in Al₂O₃ have been synthesized by a solution phase technique. The structure and magnetic properties of these composites with varying fractions of Al₂O₃ have been investigated. Both Fe and Fe₅₀Ni₅₀ nanoparticles are amorphous in the as-prepared state and become crystalline on heat treating with near equilibrium lattice parameters of 0.287 nm and 0.358 nm respectively. The interparticle distance increases with increasing Al₂O₃ from 0 wt.% to 20 wt.%. The size of Fe nanoparticles is 40 nm while the Fe₅₀Ni₅₀ nanoparticles are 20 nm in size. The Fe and Fe₅₀Ni₅₀ nanoparticles dispersed composites are found to be ferromagnetic at room temperature both in the as-prepared and heat treated conditions with clear coercive fields of 5.5–35 × 10³ A m⁻¹. The saturation magnetization increases by orders of magnitude on heat treatment, for e.g. from <1.0 emu g⁻¹ to 143.4 emu g⁻¹ for Fe–15 wt.% Al₂O₃ and 95.6 emu g⁻¹ for Fe₅₀Ni₅₀–15 wt.% Al₂O₃. The Fe-composites exhibit a Curie transition at 1000 K while the Fe₅₀Ni₅₀ composites exhibit a transition at 880 K, both temperatures close to bulk values.     

Amorphous and nanocrystalline sputtered Mg–Cu thin films

Binary Mg–Cu amorphous alloys were first fabricated in 1980s via liquid quenching. In this study, the Mg_1−xCu_x (x varying from 38 at.% to 82 at.%) partially amorphous thin films are prepared via co-sputtering. Upon thermal annealing, the Mg₂Cu or MgCu₂ nanocrystalline phases are induced in the Mg-rich or Cu-rich thin films, respectively. Due to the presence of fine nanocrystalline Mg₂Cu or MgCu₂ particles in the Mg–Cu amorphous matrix, the as-sputtered thin films show satisfactory Young's modulus 100 GPa and hardness 4 GPa.     

Electrochemical behaviour and corrosion performance of Mg–Li–Al–Zn anodes with high Al composition

This study investigated the electrochemical and corrosion performance of Mg–Li–Al–Zn anodes with Al compositions of 3 wt.% and 9 wt.%. Mg–Li–Al–Zn alloy with 9 wt.% Al had a relatively negative open-circuit potential and a high discharge voltage in MgCl₂ electrolyte, owing to the distribution of numerous AlLi particles in the matrix of the alloy. AlLi particles were believed to transform to Al particles during the corrosion of the Mg–Li–Al–Zn anode. The high-Al anode material exhibited good corrosion performance since a dense and continuous Mg(OH)₂/Al composite layer covered the surface of the high-Al anode. Experimentally, increasing the Li⁺ concentration in the electrolyte improved the corrosion performance of the Mg anode.     

Properties of Mn-doped FINEMET

Structural, thermodynamical and magnetic properties of Fe_73.5−xSi_13.5B₉Cu₁Nb₃Mn_x amorphous alloys, with Mn content x=1,3–15, were studied by means of X-ray diffraction (XRD), differential scanning calorimetry (DSC), Mössbauer spectroscopy (MS) and energy-dispersive X-rays (EDX), as-quenched and after annealing. The alloys with x≤7 suffer primary (above 550 °C) and secondary (below 680 °C) crystallisation, whereas the alloys with x≥9 only at 580 °C. Mn doping results in increase (for x≤7) and then (for x≥9) in decrease of grain size. The hyperfine field of the amorphous precursor and remainder substantially decrease with increase of Mn content x, whereas the fields in crystallites remain nearly independent of x. A paramagnetic component appears at x9 and grows with x.     

Microwave synthesis and characterization of Zn-doped nickel ferrite nanoparticles

Microwave assisted combustion method was used to synthesize nanocrystalline Zn_xNi_1−xFe₂O₄ from a stoichiometric mixture of corresponding metal nitrates and urea powders. The structural, chemical and magnetic properties of Ni–Zn ferrite was determined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM) and DC conductivity measurements. Results showed that the material was spinel structure with a high purity with an estimated crystallite size of 20 nm by X-ray line profile fitting. TEM analysis showed necked near-spherical particles with an average size of 20 nm, reflecting highly crystalline nature of these nanoparticles. Magnetic properties showed anomalities as the Zn doping level increased. This has been explained and attributed to the relative positions of Ni, Zn, and Fe ions in the crystal lattice.     

Synthesis, characterization and low temperature studies of iron chalcogenide superconductors

We have synthesized tetragonal iron selenide and telluride superconductors through solid state reaction at 450 °C and 550 °C, respectively. These synthesis temperatures have been established by optimization. Electrical resistivity and magnetic susceptibility measurements (4.2–300 K) confirm superconductivity with T_C of around 8.5 K in all selenide samples of nominal composition Fe_1+δSe (δ = 0.02–0.22). However, Scanning Electron Microscopy/Energy Dispersive Spectroscopy studies clearly indicate that the actual stoichiometric ratio of Fe:Se for all the samples synthesized is around 1:1. Also all the samples exhibit identical phase transition temperatures from tetragonal to orthorhombic structure below 100 K implying identical phase composition. The partial substitution of Se by Te leads to an enhancement of T_C to 13 K. The non-superconducting telluride Fe_1.09Te exhibits a metal–insulator phase transition at 82 K. Substitution studies of this telluride system by S and Si have in addition been carried out to investigate if chemical pressure induces superconductivity.     

Creep feed grinding of gamma titanium aluminide and burn resistant titanium alloys using SiC abrasive

Following a brief introduction to titanium alloys and their machinability, the cutting performance of a gamma titanium aluminide intermetallic (γ-TiAl) alloy: Ti–45Al–8Nb–0.2C wt% and a burn resistant titanium (BuRTi) alloy: Ti–25V–15Cr–2Al–0.2C wt%, is compared with creep feed grinding using SiC abrasive. The work utilised 2 separate L9 Taguchi fractional factorial arrays. Typically G-ratios were a factor of 10× greater for γ-TiAl than BuRTi, with on average 10% lower maximum power and 25% lower maximum specific energy for the γ-TiAl alloy. A combination of a moderately high wheel speed: 35 m/s, low depth of cut: 1.25 mm and low feed rate: 150 mm/min, produced the lowest average workpiece surface roughness (Ra1.4 μm). Workpiece surface integrity evaluation indicated that with lower operating parameter levels, in particular a wheel speed of 15 m/s, surfaces free of burn and cracks could be produced, while at higher wheel speeds: 35 m/s, extensive workpiece surface burn was evident, with the γ-TiAl alloy suffering extensive cracking. Microhardness measurements showed in some instances slightly increased workpiece surface hardness of around 50–60HK_0.025 for the BuRTi alloy and 200HK_0.025 for the γ-TiAl material over respective bulk hardness values of 375HK_0.025 and 400HK_0.025.     

Effects of C particle size on the ignition and combustion characteristics of the SHS reaction in the 20 wt.% Ni–Ti–C system

C particle size plays an important role in the ignition and combustion characteristics of the SHS reaction in the 20 wt.% Ni–Ti–C system. When coarse C particles (38 and 75 μm) are used, the SHS reactions consist of two different combustion stages with different brightness intensity of the combustion wave; XRD results indicate that the first and second combustion stages mainly correspond to the formation of Ni–Ti compounds and TiC ceramics, respectively. However, the final reaction is incomplete with a few Ni–Ti compounds and unreacted C. In contrast, when the fine C particle (1 μm) is used, the SHS reaction consists of only one combustion stage with high brightness intensity of the combustion wave; XRD result indicates that final products consist of TiC and Ni, without any intermediate phase. With the decrease of C particle size, the wave velocities increase, and the ignition time becomes shorter. In addition, the morphology of TiC particulate changes to near-spherical, as C particle size decreases.     

Micro-forming of Zr65Al10Ni10Cu15 metallic glasses under superplastic condition

Micro-formability behavior of the Zr₆₅Al₁₀Ni₁₀Cu₁₅ alloy sheet fabricated by using squeeze casting method, which exhibited Newtonian behavior in the supercooled liquid region, was examined by finite element methods and experiments. In micro-forming simulation on a single V-groove, micro-formability index increased with time and nearly completed die-filling was achieved in 100 s when deformed under a constant pressure of 52.6 MPa at 696 K. In micro-forming on the die with multiple V-grooves in array along its width, the degree of die-filling was predicted to depend on the V-groove position. The V-grooves near the center of the die exhibited the high degree filling ratio of 1 but it was only 0.1 near the free end. This trend was confirmed to agree with the experimental results. According to the simulation result, higher friction coefficient and longer loading time could improve the die-filling ability near the free end.     

Impact of donor, acceptor, and blocking layer thickness on power conversion efficiency for small-molecular organic solar cells

We investigated the dependency of the power conversion efficiency on the thickness of donor (copper phthalocyanine; CuPc), acceptor (fullerene; C₆₀), and hole/exciton blocking (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline; BCP) layers in the OPV devices fabricated with double small-molecular layers. The power conversion efficiency peaked at a specific layer thickness, 12.7 nm for the donor layer, 17.5 nm for the acceptor layer, and 8.0 nm for the hole/exciton blocking layer. This trend of power conversion efficiency was determined by short-circuit-current rather than open-circuit-voltage after light absorption. In addition, the donor layer thickness was more sensitive than the thickness of the acceptor or hole/exciton blocking layers in improving power conversion efficiency; i.e., 330% for the donor layer, 118% for the acceptor layer, and 112% for the hole/exciton blocking layers.     

Chromism and molecular weight of polyaniline derivatives

The striking solvatochromic shift observed in polyaniline derivatives correlates with two solvent polarity scales, donor number (DN) and hydrogen bond acceptor scale (Taft's β-scale). The large shift is caused by conformational changes in solution that result in dramatic differences in relative molecular weight values obtained by gel permeation chromatography (MW_GPC) in different solvents. For example, for poly-o-toluidine base in the emeraldine oxidation state, a low transition energy solvent like NMP (excitonic transition, λ_max 608 nm) yields a very high molecular weight value (M_w  15,000 g mol⁻¹) whereas a high transition energy solvent like CHCl₃ (excitonic transition, λ_max 570 nm) yields an absurdly low value (M_w  650 g mol⁻¹). An absolute molecular weight value, M_w  4700 g mol⁻¹, was obtained for the first time using laser light scattering (MW_LS) suggesting that CHCl₃ promotes a highly coiled chain conformation whereas NMP promotes a more expanded, rod-like conformation. A similar trend is observed for poly-o-toluidine base in the fully oxidized pernigraniline oxidation state (Pierels transition). This suggests that even though the Pierels and excitonic transitions have different molecular origins their conformation driven solvatochromic shifts trend in a similar fashion which is different from thermochromic trends reported in previous studies.     

Temperature dependent conductivity and thermoelectric power of the iodine doped poly(vinyl alcohol)–Cu chelate

We have investigated the temperature dependence of electrical conductivity and thermoelectric power (TEP) at 1.7 K < T < 300 K in an organo metallic complex, the iodine doped poly(vinyl alcohol)–Cu²⁺ chelate. We observed intrinsic metallic temperature dependence of resistivity from room temperature to 68 K with a broad minimum [ρ(68 K)/ρ(300 K) 0.75], which has not been observed previously in similar organo metallic complexes. There occurs an unusual metal-insulator transition at T 68 K and the resisitivity increases upon cooling below 68 K. However, the low temperature resistivity becomes finite (instead of going to infinity), [ρ(1.7 K)/ρ(300 K) 0.98] indicating that a quantum mechanical tunneling conduction is dominant at this low temperature. It is remarkable that the resistivity at 1.7 K is as small as that of room temperature. Such unusual temperature dependence of conductivity could be understood as thermally assisted hopping conduction between metallic islands. However, the observed intrinsic metallic temperature dependence of resistivity implies that such hopping conduction barrier is not important at high temperature (T > 68 K). The intrinsic metallic characteristics are confirmed by the quasi-linear temperature dependence of TEP for the whole measured temperature range (1.7 K < T < 300 K) with a small slope change at low temperature, T < 68 K, which is understood as an effect of variable range hopping (VRH) conduction at low temperature. The results of magneto resistance (MR) and magneto thermoelectric power (MTEP) are consistent with the above interpretation.     

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.     

A theoretical interpretation of the pressure–composition isotherms of RNi5 (, Pr, Nd and Sm) systems based on statistical mechanics

A simple model to understand the phase behavior of RNi₅–H (R=La, Pr, Nd and Sm) systems is proposed based on the statistical mechanics. The essential parameters in the present model, hydrogen site energies and lattice relaxation term, were optimized so as to reproduce the experimentally determined pressure–composition isotherms (PCIs) of these four alloys. The qualitative difference in the PCI of LaNi₅ from other alloys – at room temperature the former tends to show a single plateau while the latter have two plateaux – is explicable in terms of hydrogen site energies as follows. In case of LaNi₅, four hydrogen sites, which are considered to belong to 3f, 12n, 6m and 12o sites, are stable in α phase, leading to a wide single plateau upto N6 where N is in RNi₅H_N below room temperature. At higher temperature, small differences in site energies for these sites brings the appearance of the second plateau. In case of other three alloys, on the other hand, the 6m site (or 12o) is less stable than LaNi₅ in the α phase. After obtaining enough lattice relaxation energy by around N=4 through hydrogenation, the 6m site becomes favorable for hydrogen, bringing the sencond plateau spanning from N4 to N6. Predicted T–C phase diagrams are also shown.     

Thermoelectric properties of novel skutterudites with didymium: DDy(Fe1−xCox)4Sb12 and DDy(Fe1−xNix)4Sb12

In order to improve the thermoelectric properties via efficient phonon scattering Didymium (DD), a mixture of Pr and Nd, was used as a new filler in ternary skutterudites (Fe_1−xCo_x)₄Sb₁₂ and (Fe_1−xNi_x)₄Sb₁₂. DD-filling levels have been determined from combined data of X-ray powder diffraction and electron microprobe analyses (EMPA). Thermoelectric properties have been characterized by measurements of electrical resistivity, thermopower and thermal conductivity in the temperature range from 4.3 to 800 K. The effect of nanostructuring in DD_0.4Fe₂Co₂Sb₁₂ was elucidated from a comparison of both micro-powder (ground in a WC-mortar, 10 μm) and nano-powder (ball-milled, 150 nm), both hot pressed under identical conditions. The figure of merit ZT depends on the Fe/Co and Ni/Co-contents, respectively, reaching ZT > 1. At low temperatures the nanostructured material exhibits a higher thermoelectric figure of merit. The Vickers hardness was measured for all samples being higher for the nanostructured material.     

Using friction stir processing to fabricate MgAlZn intermetallic alloys

Friction stir processing (FSP) is applied in mixing elemental thin sheets of Mg, Al, and Zn in various portions, resulting in hard intermetallic alloys with Vicker’s hardness in excess of 350. The Mg₃Al₂Zn₃ τ phase formed at 360 °C during FSP, coupled with some other binary or ternary phases of nano size, accounts for the high hardness.     

The ultimate sharpness of single-crystal diamond cutting tools—Part II: A novel efficient lapping process

As the theoretical predictions presented in Part I, the ultimate sharpness of (1 1 0)–(1 0 0) oriented diamond cutting tool can reach up to 16 nm, and the (1 0 0)–(1 0 0) oriented cutting tool up to 25 nm [W.J. Zong, K. Cheng, D. Li, T. Sun, Y.C. Liang, The ultimate sharpness of single-crystal diamond cutting tools—Part I. Theoretical analysis and predictions, International Journal of Machine Tools and Manufacture 2005, submitted]. In order to validate the theoretical predictions, a novel efficient lapping process, namely thermo-mechanical lapping, is developed in the present work, which is regarded as an effective extension of the traditional mechanical lapping process. By this developed lapping method, a large number of lapping experiments are carried out on the (1 1 0)–(1 0 0) oriented cutting tools. AFM measurement results illustrate that lapping time has little effects, but both lapping compression force and lapping velocity have enormous influences on the finished cutting-edge radius. Furthermore, based on the optimized lapping compression force and lapping velocity, an elegant diamond cutting tool oriented along (1 1 0)–(1 0 0) is sharpened. Atomic force microscope (AFM) and scanning electron microscope (SEM) measurement results indicate the cutting-edge radius has been sharpened down to 29 nm, which agrees well with the theoretical predicted value, i.e. 16 nm.     

Phase equilibria on the ternary Mg–Mn–Ce system at the Mg-rich corner

Three isopleths at the Mg-rich corner of Mg–Mn–Ce ternary system were investigated via thermal analysis, SEM/EPMA and XRD. A ternary eutectic reaction was observed at 1 wt.% Mn and 23 wt.% Ce and 592 °C. A solid-solution type ternary intermetallic compound, (Mg,Mn)₁₂Ce, was observed with 0.5 at% solid solubility of Mn in the tetragonal Mg₁₂Ce. With the aid of thermodynamic modeling and experiments, a revised phase diagram for the binary Mg–Ce system and the isopleths of 0.6, 1.8 and 2.5 wt.% Mn were proposed up to 25 wt.% Ce.     

dc-Magnetic susceptibility and EPR studies of vapour phase grown Cd1−xCoxTe crystals

Cd_1−xCo_xTe crystals (x = 0.001, 0.003, 0.005, 0.007 and 0.009) were grown by vapour phase technique. The grown diluted magnetic semiconducting (DMS) crystals were subjected to magnetization and dc-magnetic susceptibilities at room temperature. EPR spectra were recorded at 20 K for samples of all compositions. EPR spectra exhibited a broad resonance band around g  5.43. All the studies indicated the paramagnetic nature of the samples.