Spinodal decomposition of the γ-phase upon quenching in the Ti–Al–Nb ternary alloy system

The γ-TiAl with L1₀ crystal structure shows extensive solubility for Nb at elevated temperatures. Recently (Rios et al., Acta materialia 2009; 57:6243), we have demonstrated that the high-Nb γ-TiAl phase becomes unstable upon rapid cooling into a nano-scale two-phase microstructure. In this paper, using detailed compositional and microstructural analyses, we have demonstrated that this phase goes through a spinodal decomposition that results in the compositionally distinct phases identified as a lower-Nb γ-phase and the h-phase, which is rich in Nb and forms by the ordering of this element in the γ-phase.     

Electrical and magnetic properties of Mg0.85Co0.15Fe2O4 ceramics with V2O5 additives

In this study, magnesium-cobalt ferrite (Mg_0.85Co_0.15Fe₂O₄) powder was synthesized using a solid-state synthesis method, followed by the liquid sintering using 0.50–3.00 wt% vanadium oxide (V₂O₅) at 1050 °C for 2 h. X-ray diffraction (XRD) studies confirmed the formation of spinel ferrite. Microstructure studies revealed that by increasing the amount of V₂O₅ from 0.50 to 3.00 wt%, the average grain size was reduced from 15.9?±?5.9 to 7.0?±?2.5 μm and the samples were highly densified. V₂O₅ promoted the sintering process and reduced the dielectric constant (ε′), loss tangent (tanδ), and increased electrical resistivity. A magnesium-cobalt ferrite sample with 25.4 dielectric constant, 0.078 loss tangent, and 9.0?×?10⁵ Ω.cm resistivity at 1 MHz was achieved using 3.00 wt% V₂O₅. Increasing V₂O₅ content caused increasing coercivity (Hc) from 89 to 129 Oe. Moreover, the maximum saturation magnetization (Ms) value of 26.8 emu/g was obtained for the sample containing 1.50 wt% V₂O₅. The small dielectric loss tangent of the samples at 1 MHz suggests applications of these ceramics in microwave devices.

     

Polysodium N-undecanoyl-L-leucylvalinate: a versatile chiral selector for micellar electrokinetic chromatography

Dipeptide micelle polymers are a new class of polymeric surfactants of which the polysodium undecanoyl-L-leucylvalinate (poly-L-SULV) was found to be a broadly applicable chiral selector for micellar electrokinetic chromatography. This negatively charged dipeptide micelle polymer is a high molecular weight compound with large countercurrent mobility, zero critical micelle concentration, low aggregation number, and high solubility in water or water-organic solvents. In an extensive chiral screening program, enantioseparation of 75 racemic compounds was tested with poly-L-SULV as chiral pseudostationary phase in neutral pH and basic pH background electrolytes. A total of 58 out of 75 racemic compounds could be resolved after choosing an appropriate concentration of poly-L-SULV. Although anionic chiral analytes are difficult to resolve using poly-L-SULV, the percent success rate for chiral resolution of cationic (77%) and neutral (85%) racemates was very high. Aspects regarding electrostatic, steric, hydrophobic, and hydrogen-bonding interactions of this dipeptide micelle polymer with various classes of chiral analytes are discussed.     

Diagnostic pre-treatment procedure for simultaneous cyanide leaching of gold and silver from a refractory gold/silver ore

This study investigates the optimization of simultaneous dissolution of gold and silver from a refractory gold ore through determination of pre-treatment stages. Based on the mineralogical studies (thin layer and polished section) and chemical analysis on the ore sample, a “diagnostic leaching” procedure was designed. Results from diagnostic leaching suggest that the most effective pre-treatment agents for gold and silver are ferric chloride and sulfuric acid media, respectively. Optimum conditions for the simultaneous dissolution of gold and silver were determined using a two factorial design technique. Pre-treatments with sulfuric acid and ferric chloride reagents increased the efficiency of the dissolution of gold from 54.7% to 82% and silver from 37.4% to 81.6%.     

Characterization of CeO2 Promoter of a Nanocrystalline Ni/MgO Catalyst in Dry Reforming of Methane

Ceria‐promoted nickel catalysts supported on nanocrystalline MgO were prepared and employed in methane reforming with CO₂. Their characterization was accomplished by X‐ray diffraction, BET, temperature‐programmed oxidation, and temperature‐programmed reduction (TPR) techniques. Cerium oxide (CeO₂) proved to have a positive effect on catalytic activity, stability, and carbon suppression in methane reforming with CO₂. A higher CeO₂ content increased the catalyst activity and decreased the amount of deposited carbon over the spent catalysts. The suppression of carbon was related to the high oxygen storage capacity of CeO₂. In addition, TPR analysis revealed that the CeO₂ promoter reduced the chemical interaction between nickel and support, resulting in an increase in reducibility and higher dispersion of nickel.     

An alternative finite element model for simulation of frictional gap

This study is an attempt to modeling a frictional gap in a crack closure process under compressive loading conditions in which the crack surfaces are in touch and the effects of friction between them are significant. An iterative finite element (FE) solution is developed to model a finite crack in an interfacial layer with varying material properties. A mere application of a Lagrange multiplier formulation (node-to-node, NTN, or node-to-segment, NTS) in a developed FE framework to fulfill the contact constraints between contacting surfaces is discussed which improves the penalty formulation used in ANSYS. We then argue that the penalty formulation allows for a certain amount of crack surface interpenetration whereas the Lagrange multiplier formulation fulfils the contact constraints more accurately. This technique is easy to implement and offers higher accuracy than the equivalent FE solution, available in commercial FE software such as ANSYS 9.0, to the same system.     

Effect of laser preparation on adhesion of a self‐adhesive flowable composite resin to primary teeth

The aim of the study was to evaluate the adhesion of a self‐adhering flowable composite resin to primary tooth enamel and dentin after silicon carbide paper (SiC) and laser pretreatment. Adhesive properties were evaluated as shear bond strength (SBS) and scanning electron microscopic (SEM) characteristics. A total 120 primary canine teeth were randomly divided into two groups to study enamel and dentin. Each group was divided into 6 subgroups (n = 10) according to type of surface preparation (SiC or Er:YAG laser) of enamel or dentin. Three methods were used to build cylinders of restoration on tooth surface: OptiBond All‐In‐One + Premise Flowable composite, OptiBond All‐In‐One + Vertise Flow and Vertise flow. After restoration, samples were tested for SBS and failure mode. Twenty eight samples were examined by SEM. The results of the study showed SBS of Vertise Flow was lower than others in enamel and dentin samples pretreated with SiC and in dentin samples pretreated with laser (P < 0.001). Compared to SiC pretreatment, laser pretreatment led to a significantly higher SBS with Vertise Flow on enamel (P < 0.001). Vertise Flow associated with the adhesive led to a higher SBS in enamel and dentin compared to Vertise Flow alone. Adhesive and mixed failure modes were observed more frequently in Vertise Flow groups. SEM images showed that Vertise Flow led to more irregularities on enamel and more open dentinal tubules after laser ablation compared SiC pretreatment. Microsc. Res. Tech. 79:334–341, 2016. © 2016 Wiley Periodicals, Inc.     

Preparation,morphological and thermal characterization of novel nanocomposites based on poly (amide-ester-imide) containing amino acid and nano-Mg-doped fluorapatite surface modified with biodegradable diacid N-trimellitylimido-L-leucine

In this investigation, we prepared novel nanocomposites (NC) s based on poly (amide-ester-imide) (PAEI) containing L-leucine moiety and surface modified nano-Mg-doped fluorapatite (Mod-MgFA) with biodegradable diacid, via ultrasound irradiation. First, surface of nanocystalline Mg-doped fluorapatite was functionalized with biodegradable optically active diacid N-trimellitylimido-L-leucine (TML) by ultrasonic irradiation, so as to increase the compatibility and dispersity in the PAEI matrix. After modification via diacid TML, the Mg-doped fluorapatite was altered from a hydrophilic state to an organophilic one. At that time, the obtained functionalized Mod-MgFA was investigated as reinforcing agent for the synthesis of the PAEI NCs. The resulting NCs were characterized by Fourier transform infrared (FT-IR), transmission electron microscopy, field emission-scanning electron microscopy (FE-SEM), X-ray diffraction, and thermogravimetric analysis (TGA) techniques. TGA data showed an increasing in thermal stability of the aforementioned NCs when compared to the neat PAEI. FE-SEM results presented a rather good amount of dispersion of Mod-MgFA in the polymer matrix.     

Design of a reversible structure for memory in quantum-dot cellular automata

Complementary metal oxide semiconductor (CMOS) technology has limitations in reducing the area and size of circuits. The disadvantages of this technology include high power consumption and temperature problems. Quantum-dot cellular automata (QCA) is a new technology that can overcome these shortcomings. Reversible logic is technology used to reduce the power loss in QCA. QCA can be used to design memories that require high operating speed. In this paper, we propose a structure for the reversible memory in QCA. The proposed structure utilizes three-layer technology, which has a significant impact on circuit size reduction. The proposed structure for the reversible memory has 63% improvement in cell number, a 75% improvement in area occupancy, and a 60% reduction in delay compared to the previous best structure.