Effect of Gr Contents on Wear Properties of Al2024/MgO/Al2O3/Gr Hybrid Composites

In the present study, hybrid metal matrix composites, Al2024/10Al2O3, Al2024/10Al2O3/3MgO, Al2024/10Al2O3/6MgO, Al2024/10Al2O3/3MgO/1.5 Gr, Al2024/10Al2O3/3MgO/3Gr, and reinforcement samples (AA 2024) produced with powder metallurgy process. AA 2024 and reinforcement powders were determined mixture rations and separately mixed during 30 minutes in a three-dimensional Turbula mixer. The mixed compositions were pressed at 300 MPa and sintered at 550°C during 1 h. After that, three materials were extruded at the same temperature. Experimental results show that hybrid metal matrix composites (HMMCs) a better wear resistance than the reinforcement samples because of higher hardness. Gr behave as a lubricant during wear process. The wear resistance of HMMCs can be optimized with controlling of the reinforcement content and type. © 2018 The Authors

Investigation of individual factors impacting the effectiveness of requirements inspections: a replicated experiment

Cataloged from PDF version of article.This paper presents a replication of an empirical study regarding the impact of individual factors on the effectiveness of requirements inspections. Experimental replications are important for verifying results and investigating the generality of empirical studies. We utilized the lab package and procedures from the original study, with some changes and additions, to conduct the replication with 69 professional developers in three different companies in Turkey. In general the results of the replication were consistent with those of the original study. The main result from the original study, which is supported in the replication, was that inspectors whose degree is in a field related to software engineering are less effective during a requirements inspection than inspectors whose degrees are in other fields. In addition, we found that Company, Experience, and English Proficiency impacted inspection effectiveness

Effect of Hygroscopicity of the Metal Salts on the Formation and Air Stability of Lyotropic Liquid Crystalline Mesophases in Hydrated Salt-Surfactant Systems

Cataloged from PDF version of article.It is known that alkali, transition metal and lanthanide salts can form lyotropic liquid crystalline (LLC) mesophases with non-ionic surfactants (such as CiH2i+1(OCH2CH2)(j)OH, denoted as CiEj). Here we combine several salt systems and show that the percent deliquescence relative humidity (%DRH) value of a salt is the determining parameter in the formation and stability of the mesophases and that the other parameters are secondary and less significant. Accordingly, salts can be divided into 3 categories: Type I salts (such as LiCl, LiBr, LiI, LiNO3, LiClO4, CaCl2, Ca(NO3)(2), MgCl2, and some transition metal nitrates) have low %DRH and form stable salt-surfactant LLC mesophases in the presence of a small amount of water, type II salts (such as some sodium and potassium salts) that are moderately hygroscopic form disordered stable mesophases, and type III salts that have high %DRH values, do not form stable LLC mesophases and leach out salt crystals. To illustrate this effect, a large group of salts from alkali and alkaline earth metals were investigated using XRD, POM, FTIR, and Raman techniques. Among the different salts investigated in this study, the LiX (where X is Cl-, Br-, I-, NO3-, and ClO4-) and CaX2 (X is Cl-, and NO3-) salts were more prone to establish LLC mesophases because of their lower %DRH values. The phase behavior with respect to concentration, stability, and thermal behavior of Li(I) systems were investigated further. It is seen that the phase transitions among different anions in the Li(I) systems follow the Hofmeister series. (C) 2014 Elsevier Inc. All rights reserved

A New, Highly Conductive, Lithium Salt/Nonionic Surfactant, Lyotropic Liquid-Crystalline Mesophase and Its Application

Cataloged from PDF version of article.Salty water! Lithium salts (LiCl, LiNO3, and LiClO4) at very high concentrations in water form lyotropic liquid crystalline (LLC) mesophases with a nonionic surfactant (10-lauryl ether) and display high ionic conductivities (10−2–10−4 S cm−1) over a broad temperature range (−10 to 80 °C) with excellent behavior as gel electrolytes in electrochemical applications

Origin of Lyotropic Liquid Crystalline Mesophase Formation and Liquid Crystalline to Mesostructured Solid Transformation in the Metal Nitrate Salt-Surfactant Systems

Cataloged from PDF version of article.The zinc nitrate salt acts as a solvent in the ZnX-C(12)EO(10) (ZnX is [Zn(H(2)O)(6)](NO(3))(2) and C(12)EO(10) is C(12)H(25)(OCH(2)CH(2))(10)OH) lyotropic liquid crystalline (LLC) mesophase with a drastic dropping on the melting point of ZnX. The salt surfactant LLC mesophase is stable down to -52 degrees C and undergoes a phase change into a solid mesostructured salt upon cooling below -52 degrees C; no phase separation is observed down to -190 degrees C. The ZnX-C(12)EO(10) mesophase displays a usual phase behavior with an increasing concentration of the solvent (ZnX) in the media with an order of bicontinuous cubic(V(1))-2D hexagonal(H(1)) - a mixture of 2D hexagonal and micelle cubic(H(1) + I)-micelle cubic(I)-micelle(L(1)) phases. The phase behaviors, specifically at low temperatures, and the first phase diagram of the ZnX-C(12)EO(10) system was investigated using polarized optical microscopy (POM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), and Raman techniques and conductivity measurements

Assembly of Molten Transition Metal Salt-Surfactant in a Confined Space for the Synthesis of Mesoporous Metal Oxide-Rich Metal Oxide-Silica Thin Films

Cataloged from PDF version of article.ABSTRACT: Uniform and homogeneous coating of mesoporous materials with an active (catalytically, photonic, electrical) nanostructure can be very useful for a number of applications. Understanding chemical reactions in a confined space is important in order to design new advanced materials. In this work, we demonstrate that an extensive amount (as high as 53 mol percent) of transition metal salts can be confined between silica walls and two surfactant domains (cetyltrimethylammonium bromide, CTAB, and lauryl ether, C12H25(OCH2CH2)10OH, C12EO10) as molten salts and then converted into sponge-like mesoporous silica metal oxides by thermal annealing. This investigation has been carried out using two different salts, namely, zinc nitrate hexahydrate, [Zn(H2O)6](NO3)2, and cadmium nitrate tetrahydrate, [Cd(H2O)4](NO3)2, in a broad range of salt concentrations. The ZnO (or CdO) layers are as thin as about ∼1.6 nm and are homogenously coated as crystalline nano-islands over the silica pore walls

Chemical abundances of the metal-poor horizontal-branch stars CS 22186-005 and CS 30344-033

We report on a chemical-abundance analysis of two very metal-poor horizontal-branch stars in the Milky Way halo: CS 22186-005 ([Fe/H]=-2.70) and CS 30344-033 ([Fe/H]=-2.90). The analysis is based on high-resolution spectra obtained at ESO, with the spectrographs HARPS at the 3.6 m telescope, and UVES at the VLT. We adopted one-dimensional, plane-parallel model atmospheres assuming local thermodynamic equilibrium. We derived elemental abundances for 13 elements for CS 22186-005 and 14 elements for CS 30344-033. This study is the first abundance analysis of CS 30344-033. CS 22186-005 has been analyzed previously, but we report here the first measurement of nickel (Ni; Z = 28) for this star, based on twenty-two NiI lines ([Ni/Fe]=-0.21$\pm$0.02); the measurement is significantly below the mean found for most metal-poor stars. Differences of up to 0.5 dex in [Ni/Fe] ratios were determined by different authors for the same type of stars in the literature, which means that it is not yet possible to conclude that there is a real intrinsic scatter in the [Ni/Fe] ratios. For the other elements for which we obtained estimates, the abundance patterns in these two stars match the Galactic trends defined by giant and turnoff stars well. This confirms the value of horizontal-branch stars as tracers of the chemical properties of stellar populations in the Galaxy. Our radial velocities measurements for CS 22186-005 differ from previously published measurements by more than the expected statistical errors. More measurements of the radial velocity of this star are encouraged to confirm or refute its radial velocity variability

The effect of cationic surfactant and some organic/inorganic additives on the morphology of mesostructured silica templated by pluronics

Cataloged from PDF version of article.Tri-block copolymers (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), represented as EOxPOyEOx), pluronics (F127=EO106PO70EO106, P65=EO20PO30EO20, P85=EO27PO39EO27, P103= EO17PO55EO17, and P123 = EO20PO70EO20) and cationic surfactants (cethyltrimethylammonium bromide (CTAB)), two surfactant systems, form complex micelles that self-assemble into mesostructured particles with distinct morphology depending on the pluronic type, the concentration of the cationic surfactant and the organic-inorganic ingredients in a siliceous reaction media under acidic conditions. The CTAB-P65 and CTAB-P85 systems form spheres, CTAB-P103 and CTAB-P123 systems form wormlike particles, and CTAB-F127 system form single crystals of mesostructured silica particles under very similar conditions. However addition of various salts (such as KCI and NaNO3) into a CTAB-P103 or CTAB-P123 solution system and cyclohexane and KCI into a CTAB-P85 solution system produces the mesostructured silica spheres and wormlike particles, respectively. By controlling the hydrophilic-hydrophobic character of the pluronics, core-corona interface, by means of additives, such as small organic molecules or salts, one could obtain the desired morphology that is dictated by the shape of the micelles of the pluronic-cationic surfactant complex. The effects of the additives and the formation mechanism of those morphologies have been discussed using spectroscopy (FT-IR and Raman), diffraction (XRD) and microscopy (POM and SEM) data. (c) 2008 Elsevier Inc. All rights reserved

Mechanical properties of polycrystalline ceramics by nanoindentation methods: effect of surface roughness and tip size

Nanoindentation, NI, – mainly with sharp tips - is a powerful method for the mechanical characterization of solids. When the indenters are sharp, however, valuable information concerning the all-important elastic-to-plastic transition is lost. Spherical tips, on the other hand, do not suffer from this problem. In this work, we used 1.4 μm and 5 μm radii, R, spherical diamond indenters to measure the moduli, E, and generate NI stress–strain curves of the polycrystalline sesquioxides Y2O3, Sc2O3 and Er2O3. The moduli - measured from harmonic contact stiffness (S) vs. contact radius (a) curves – were found to be weak functions of R and slightly lower than the moduli measured by ultrasound on the same samples used for the NI measurements.This work also shows that surface finish – that was varied and quantified by measuring the surface roughness - is an important factor in determining both the values of E, and the shapes of the NI stress-strain curves, especially near the origin. In all cases, fine polishing yielded results that were closer to the true values as measured by ultrasound. The values of E measured by the Berkovich indenter were less sensitive to surface roughness.When the hardness values measured using the Berkovich and Vickers indenters were compared with the yield points obtained from the NI stress-strain curves the order was: Berkovich, Vickers followed by the yield point. This conclusion is in agreement with previous work on brittle single crystals.Based on this work, we conclude that S vs. a plots are a powerful method to measure the Young’s moduli of polycrystalline ceramics and other hard solids. The fact that one also obtains NI stress–strain curves is a distinct advantage over the more commonly used load–displacement curves. The influence of surface roughness, tip size and type are important consideration when characterization of mechanical characterization at the nano-scale.M.S., Materials Science and Engineering -- Drexel University, 200