Precipitation sequence for simultaneous continuous and discontinuous modes in Cu–Be binary alloys

Abstract

The precipitation sequence of the discontinuous and continuous modes in Cu–0·9Be and Cu–1·4Be binary alloys (compositions in wt-%) has been studied primarily via metallographic observations and hardness measurements. A single C curve and triple C curves separated by two temperatures T₁ and T₂ (T₁>T₂) are obtained for the precipitation of discontinuous and continuous modes, respectively. The triple C curves correspond to the formation of γ, γ′, and Guinier–Preston (GP) zones. The precipitation sequence of these two precipitation modes and the cell growth behaviour are different for the following three temperature ranges defined by the triple C curves: (i) above T₁, discontinuous precipitation occurs before the continuous precipitation of γ phase, and the cell growth rate G decreases abruptly; (ii) between T₁ and T₂, the precipitation sequence is similar to that above T₁, but G decreases and interlamellar spacing increases progressively with aging time; (iii) below T₂, GP zones, fine γ″, and/or fine γ′ form before cell growth but the associated variation in G is not observed. The effect of continuous precipitation on the cell growth behaviour is discussed.

MST/1647     

Phase transitions and their co-existence in TlGaSe2–TlCrS2(Se2) systems

Investigation of dielectric properties of layered compound, TlGaSe₂, showed that it is a ferroelectric (T _c  = 105·5 K) with an intermediate incommensurate phase (T _i = 114·5 K). Our magnetic studies of layered compounds, TlCrS₂ and TlCrSe₂, for the first time revealed that the magnetic phase transition in these compounds are quasi two-dimensional ferromagnetic in nature and magnetic characteristics are T _C = 90 K, T $_{C}^{p}$ = 115 K, μ _eff = 3·26 μ _B and T _C = 105 K, T $_{C}^{p}$ = 120 K, μ _eff = 3·05 μ _B , respectively. Using the method of DTA, areas of homogeneous and heterogeneous coexistence of ferroelectric and ferromagnetic phase transitions in the systems, TlGaSe₂–TlCrS₂ and TlGaSe ₂–TlCrSe₂, were identified. The low-dimensional solid solutions and eutectic alloys in these systems can be used as basic materials for plenty of functional recorders.     

Dissolution kinetics and solubility limit of CaF2 in molten KCl–NaCl salt

The interaction between NaCl–KCl salt of an equimolar composition and CaF₂ was investigated in the 1023–1123 K temperature range. The solubility limit was determined as 2.1, 2.5, and 3.4 mol.% for 1023, 1073, and 1123 K, respectively. The linear dependence of the specific weight loss with time and the activation energy of the dissolution (124.6 ± 8.7 kJ/mol) indicate that CaF₂ dissociation of the ions is the limiting stage of the process. Thermodynamic properties (partial enthalpy and entropy) of CaF₂ in a dilute ternary –NaCl–KCl–CaF₂ liquid solution were estimated using the values of the solubility limit and by applying a regular solution approach.     

Microstructure and properties of a composite system for dental applications composed of glass-ceramics in the SiO2–Li2O–ZrO2–P2O5 system and ZrO2-ceramic (TZP)

The objective of the study was to develop a biocompatible composite system which was composed of TZP-ceramic (tetragonal zirconia polycrystals, ZrO₂ stabilized with 3 mol% Y₂O₃) and two glass-ceramics of the SiO₂–Li₂O–ZrO₂–P₂O₅ type. The metal-free composite system would satisfy the translucency, the biocompatibility and the strength requirements of dentistry. The two glass-ceramics of the SiO₂–Li₂O–ZrO₂–P₂O₅ type with a content of 15 and 20 wt% ZrO₂ respectively, were chemically and physically adapted to TZP-ceramic. The glass-ceramics were used as a dentin buildup material. The TZP-ceramic had the function of a root post. The shape of the post was cylindrical with a conical tip. The composite system was easy to process through viscous flow of the glass-ceramic at 900 and 1000°C, respectively. The microstructure and the mechanical properties of two glass-ceramics of the SiO₂–Li₂O–ZrO₂–P₂O₅ type were examined therefore.     

Reaction and diffusion phenomena upon oxidation of a (γ+α2) TiAlNb alloy in air

Abstract

A two-phase fully lamellar titanium aluminide alloy, Ti46Al8Nb, was exposed to air at temperatures ranging from 700 to 900°C. Isothermal and cyclic oxidation tests were conducted for up to 1000 h. Oxidation kinetics was followed by gravimetric measurements. Post-test examination of specimens comprised light microscopy, scanning electron microscopy/energy dispersive X-ray spectrometry (EDS), transmission electron miscoscopy/EDS, X-ray diffraction, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, glow discharge spectrometry, nanoindentation and scratch test. Very thin and perfectly adherent scales were composed of nanometric grains of aluminium oxide with a corundum structure on the surface, followed by a compact layer of titanium dioxide with a rutile structure and a fine-grained porous mixed-oxide layer. Chains of voids appeared locally between the compact and the porous part of the scale after extended exposure. The alloy–scale interface was complex, and contained coarse grains of alumina and Nb-rich precipitates embedded in a Ti-rich matrix. Niobium, as the least mobile element, marked the diffusion front. Major transport processes in the near-surface zone were nitrogen and oxygen inward diffusion and aluminium outward diffusion. The scale was not uniform in thickness, which might be related to grain-boundary diffusion, different orientations of the colonies of lamellae and phase composition of the lamellae on the specimen surface.     

Determination of buffer sizes for drum–buffer–rope (DBR)-controlled production systems

The present paper describes an analytical approach based on reliability analysis to determine the sizes of constraint buffer and assembly buffer in a drum–buffer–rope-controlled production system. Every machine in the system is modelled as a two-state named as up and down canonical model. Then, with these canonical models and the relationships between the feeder and fed machines, the models for determining constraint buffer and assembly buffer are constructed. To illustrate the approach's practical usefulness, a numerical example is presented. Based on the data analysis, we find that, for constraint buffer, the more feeder machines, the smaller the buffer size needed. And for assembly buffer, the more feeder machines the larger the buffer size needed. Then, two pieces of advice for the production managers to effectively use production-controlling policies are proposed.     

Preparation and study of in vitro bioactivity of PMMA–co–EHA composites filled with a Ca3(PO4)2–SiO2–MgO glass

The nature of the orthopaedic implant surface affects the interaction with cells and subsequent bone formation. The bone/cement interface in cement-held prostheses is considered to be the main cause of fracture leading to implant revision. It is thought that the introduction of a bioactive phase, such as bioglass, in the cement may permit a more stable interface by encouraging direct bone apposition rather then encapsulation of the implant by fibrous tissue. In this work new poly(methylmethacrylate) (PMMA) based composites filled with 0, 30, 40 and 50 (wt.%) of a Ca₃(PO₄)₂–SiO₂–MgO glass, were processed. The prepared composites consist of a poly(methylmethacrylate)–co–(ethylhexylacrylate) (PMMA–co–EHA) matrix filled with a glass (G7), with nominal composition 33.26CaO, 28.07P₂O_5, 23.03SiO_2, 15.64MgO (wt.%). The in vitro bioactivity of the composites was assessed by determining the changes in surface morphology and composition, by X-ray diffraction (XRD) and scanning electron microscopy coupled with X-ray energy dispersive spectroscopy (SEM-EDS), after soaking in a simulated body fluid (SBF) for periods of up to 21 days at 37 °C. Inductively coupled plasma (ICP) was used to assess the evolution of ionic concentrations in the SBF solution. The results obtained confirmed the growth of a hydroxyapatite (HA)-like layer on the surface of the prepared composites. As expected, HA layer formation was faster for composites prepared with higher glass content.     

Solid-liquid phase equilibria of (α-methylnaphthalene + β-methylnaphthalene) and (chlorobenzene + bromobenzene) systems under high Pressures

Solid-liquid phase equilibria of the (-methylnaphthalene + -methylnaphthalene) and the (chlorobenzene + bromobenzene) systems have been investigated at temperatures from 278 to 343 K and pressures up to 500 MPa using a high-pressure optical vessel. The uncertainties of the measurements of temperature, pressure, and composition were within ±0.1 K, ±0.5 MPa, and ±0.001 mole fraction, respectively. In both systems, the freezing and melting pressures at a constant composition increase almost linearly with increasing temperatures. In the former system, where the two components can form a solid solution with one another to a limit extent, the eutectic point shifts to a higher temperature and to a -methylnaphthalene-rich composition with increasing pressures. In the latter system, where the two components are completely soluble in each other in the solid phase, the freezing points of all mixtures lie between those of the pure components at each pressure. It is found that the coexistence curves obtained can be expressed by a quadratic equation in pressure.     

Glass formation in the GeSe2 (As2Se3)–Sb2Se3–CdTe systems

Glass-forming regions in GeSe₂–Sb₂Se₃–CdTe (I) and As₂Se₃–Sb₂Se₃–CdTe (II) systems have been determined by visual, X-ray diffraction and electron microscope analyses. Glasses have been obtained in the GeSe₂-rich region in system I and As₂Se₃-rich region in system II, respectively. Glassformation has been observed along the tie-lines GeSe₂–Sb₂Se₃-line (30–100 mol% GeSe₂) and As₂Se₃–CdTe-line (45–100 mol% As₂Se₃). In the binary GeSe₂–CdTe and As₂Se₃–CdTe systems, glasses has found homogeneous in the concentration ranges 0–5 mol% CdTe (I) and 0–7 mol% CdTe (II), respectively. Up to 15 mol% CdTe are dissolved in the system GeSe₂–Sb₂Se₃ and in the system As₂Se₃–Sb₂Se₃, up to 12 mol% CdTe are dissolved. The basic physical–chemical characteristics of the glasses are investigated—density, microhardness, transformation temperature, crystallization temperature, melting temperature. A compositional dependence of these properties is shown. IR spectra of the samples are investigated.     

Performance measures and metrics in logistics and supply chain management: a review of recent literature (1995–2004) for research and applications

Performance measures and metrics are essential for effectively managing logistics operations, particularly in a competitive global economy. The global economy is featured with global operations, outsourcing and supply chain and e-commerce. The real challenge for managers of this new enterprise environment is to develop suitable performance measures and metrics to make right decisions that would contribute to an improved organizational competitiveness. Now the question is whether traditional performance measures can be used and out of them which ones should be given priority for measuring the performance in a new enterprise environment. Some of the traditional measures and metrics may not be suitable for the new environment wherein many activities are not easily identifiable. Measuring intangibles and nonfinancial performance measures pose the greater challenge in the so-called knowledge economy. Nevertheless, measuring them is so critical for the successful operations of companies in this environment. Considering the importance of nonfinancial measures and intangibles, an attempt has been made in this paper to determine the key performance measures and metrics in supply chain and logistics operations. This is based on a literature survey and some of the reported case experiences. Suggestions for future research directions are also indicated.     

Microstructure and texture assessment of Al–Mn–Fe–Si (3003) aluminum alloy produced by continuous and semicontinuous casting processes

Aluminum sheets are currently produced by the direct-chill process (DC). The need for low-cost aluminum sheets is a challenge for the development of new materials produced by the twin roll caster (TRC) process. It is expected that sheets produced from these different casting procedures will differ in their microstructure. These differences in microstructure and in the crystallographic texture have great impact on sheet mechanical properties and formability. The present study investigated microstructure and evaluated texture of two strips of Al–Mn-Fe–Si (3003) aluminum alloy produced by TRC and by hot-rolling processes. It was possible to notice that the microstructure, morphology, and grain size of the TRC sample were more homogenous than those found in hot-rolled samples. Both strips, obtained by the two processes, showed strong texture gradient across the thickness.     

Development and in vitro–in vivo evaluation of a water-in-oil microemulsion formulation for the oral delivery of troxerutin

Objective: The main objective of this study was to develop and evaluate a W/O microemulsion formulation of troxerutin to improve its oral bioavailability.

Methods: The W/O microemulsion was optimized using a pseudo-ternary phase diagram and evaluated for physical properties. In vitro MDCK cell permeability studies were carried out to evaluate the permeability enhancement effect of microemulsion, and in vivo absorption of troxerutin microemulsion in the intestine was compared with that of solution after single-dose administration (56.7?mg/kg) in male Wistar rats.

Results: The optimal formulation consisted of lecithin, ethanol, isopropyl myristate and water (23.30/11.67/52.45/12.59 w/w) was physicochemical stable and the mean droplet size was about 50.20?nm. In vitro study, the troxerutin-loaded microemulsion showed higher intestinal membrane permeability across MDCK monolayer when compared with the control solution. The W/O microemulsion can significantly promote the intestinal absorption of troxerutin in rats in vivo, and the relative bioavailability of the microemulsion was about 205.55% compared to control solution.

Conclusion: These results suggest that novel W/O microemulsion could be used as an effective formulation for improving the oral bioavailability of troxerutin.     

Optimal design of a novel tuned mass-damper–inerter (TMDI) passive vibration control configuration for stochastically support-excited structural systems

This paper proposes a novel passive vibration control configuration, namely the tuned mass-damper–inerter (TMDI), introduced as a generalization of the classical tuned mass-damper (TMD), to suppress the oscillatory motion of stochastically support excited mechanical cascaded (chain-like) systems. The TMDI takes advantage of the “mass amplification effect” of the inerter, a two-terminal flywheel device developing resisting forces proportional to the relative acceleration of its terminals, to achieve enhanced performance compared to the classical TMD. Specifically, it is analytically shown that optimally designed TMDI outperforms the classical TMD in minimizing the displacement variance of undamped single-degree-of-freedom (SDOF) white-noise excited primary structures. For this particular case, optimal TMDI parameters are derived in closed-form as functions of the TMD mass and the inerter constant. Furthermore, pertinent numerical data are furnished, derived by means of a numerical optimization procedure, for a 3-DOF classically damped primary structure base excited by stationary colored noise, which exemplify the effectiveness of the TMDI over the classical TMD to suppress the fundamental mode of vibration for MDOF structures. It is concluded that the incorporation of the inerter in the proposed TMDI configuration can either replace part of the TMD vibrating mass to achieve lightweight passive vibration control solutions, or improve the performance of the classical TMD for a given TMD mass.     

Interface interaction and wetting in the Er2O3/(Cu–Al) and Er2O3/(Cu–Ti) systems

The wetting behavior and metal-oxide interface interactions in the Er₂O₃/(Cu–Al) and Er₂O₃/(Cu–Ti) systems were investigated at 1,423 K in order to evaluate the compatibility of ceramic crucibles with liquid metals, containing active elements. Pure Cu does not wet Er₂O₃ (Θ ≈ 140°) but the wettability is significantly improved by the addition of Al or Ti. It was established that Er₂O₃ reacts with Ti and Al dissolved in liquid Cu and the wettable spinel ErAlO₃ and ErTiO₃ is formed at the interface. The amount of the released Er from the substrate as a result of the reaction and the depth of the reaction zone beneath the drop are controlled by the thermodynamic properties of liquid solutions.