Interaction between laser beam and BaTiO3 powders in selective laser sintering treatments

The research work reported in this paper is an investigation of the behavior of barium titanate powders under selective laser irradiation. Our goal is to determine suitable conditions to sinter the powders and form dense layers usable in some electronic components. On that purpose, compacts of micro/nano BaTiO₃ powder mixes are used for a parametric investigation of the laser scans parameters (power, speed, etc.) with a Nd-YVO₄ laser (23 W). The microstructures obtained after laser treatments are evaluated by XRD, SEM and EDS and compared to a reference specimen manufactured in a conventional way. From this work it can be concluded that a high laser beam power is required to obtain a consolidation of the powder grains and the use of a high scan speed avoids the melting. The scanning speed also influences the final crystallographic state of BaTiO₃. Optimal parameters were founded in order to form a dense and homogeneous tetragonal BaTiO₃ surface.     

Effect of clay type on dispersion and barrier properties of hydrophobically modified poly(vinyl alcohol)–bentonite nanocomposites

The oxygen and water vapor permeability at high relative humidity was studied for composite films formed by incorporation of three different bentonites (MMT) into an ethylene‐modified, water‐soluble poly(vinyl alcohol), EPVOH. The oxygen permeability decreased linearly with an increased addition of hydrophilic MMTs. X‐ray diffraction and Fourier transform infrared spectroscopy suggested a homogeneous distribution in the thickness direction with disordered and probably exfoliated structures for hydrophilic MMTs. In contrast, organophilic modified clay showed an intercalated structure with the clay preferentially located at the lower film surface, a combination which was however efficient in reducing the water vapor‐ and oxygen permeabilities at low addition levels. Composite films of EPVOH and Na⁺‐exchanged MMT resulted in high resistance to dissolution in water, which was ascribed to strong interactions between the components resulting from matching polarities. Annealing the films at 120°C resulted in enhanced resistance to water dissolution and a further reduction in oxygen permeability. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42229.     

Microstress in Reaction‐Bonded SiC from Crystallization Expansion of Silicon

Microstress in reaction‐bonded silicon carbide (RBSiC) has been measured using piezo‐Raman spectroscopy. Compressive microstresses as high as 2 GPa exist in the silicon phase and tensile microstresses as high as 2.3 GPa exist in the SiC phase of RBSiC. This is much larger than expected for thermoelastic microstress from coefficient of thermal expansion mismatch would provide. Instead the microstresses arise from the crystallization of liquid silicon. During the reaction bonding process, not all of the silicon reacts to form SiC and there is liquid free silicon. The phase transformation of the free silicon from liquid to solid has a large volume expansion, which results in large residual microstress within the silicon and SiC phases of RBSiC.     

Kinetic Study of Hydroperoxide Degradation in Edible Oils Using Electron Spin Resonance Spectroscopy

Lipid oxidation is a complex phenomenon involving free radicals which are highly reactive molecular species. The life-time of these radical species is extremely short and their detection is therefore difficult. Several electron spin resonance (ESR) spectroscopy methodologies make it possible to identify, quantify and measure the reactivity of radical species formed during oxidation–reduction reactions. In this study we took advantage of the specificity of ESR spectroscopy to detect radical compounds in order to determine the rate constants of hydroperoxide degradation, a key reaction involved in lipid oxidation. The interaction of 5-doxyl stearic acid and lipid-derived radicals was studied by following the intensity of ESR spectra. A kinetic model was developed to simulate data analysis obtained by ESR and values of rate constants for hydroperoxide degradation were determined at 100 and 110 °C. This quantitative approach of ESR spectroscopy has produced useful information about new rate estimates for hydroperoxide degradation in edible oils.     

A surface-enhanced Raman spectroscopy study of thin graphene sheets functionalized with gold and silver nanostructures by seed-mediated growth

We describe a simple method for decorating graphene (1–5 layers) with Au and Ag nanostructures (nanoparticles, nanorods, and nanoplates). We deposit graphene electrostatically from highly-oriented pyrolytic graphite onto Si/SiO₂ surfaces functionalized with (aminopropyl)trimethoxysilane and grow the metal nanostructures by a seed-mediated growth method from hexanethiolate-coated Au monolayer-protected cluster “seeds” that are attached to graphene by hydrophobic interactions. Scanning electron microscopy reveals the selective growth of Au or Ag nanostructures on the graphene surface. In the case of Au, the low pH 2.8 growth solution causes etching of the graphene and formation of scroll-like structures. For Ag, the high pH 9.3 solution does not seem to affect the graphene. Raman spectroscopy is consistent with the graphene morphology and reveals that the presence of Au and Ag nanostructures increases the Raman scattering from the graphene by a factor of about 45 and 150, respectively. This work demonstrates a simple method for decorating graphene with noble metal nanostructures that may have interesting optical, electronic, and chemical properties for applications in nanoelectronics, sensing, and catalysis.     

Direct Cloning, Genetic Engineering, and Heterologous Expression of the Syringolin Biosynthetic Gene Cluster in E. coli through Red/ET Recombineering

The reconstruction of a natural product biosynthetic pathway from bacteria in a vector and subsequent heterologous expression in a technically amenable microbial system represents an efficient alternative to empirical traditional methods for functional discovery, yield improvement, and genetic engineering to produce "unnatural" derivatives. However, the traditional cloning procedure based on genomic library construction and screening are complicated due to the large size (>10 kb) of most biosynthetic pathways. Here, we describe the direct cloning of a partial syringolin biosynthetic gene cluster (sylCDE, 19 kb) from a digested genomic DNA mixture of Pseudomonas syringae into a plasmid in which sylCDE is under the control of an inducible promoter by one step linear-plus-linear homologous recombination (LLHR) in Escherichia coli. After expression in E. coli GB05-MtaA, two new syringolin derivatives were discovered. The complete syringolin gene cluster was assembled by addition of sylAB and exchange of a synthetic bidirectional promoter against the native promoter to drive sylB and sylC expression by using Red/ET recombineering. The varying production distribution of syringolin derivatives showed the different efficiencies of native and synthetic promoters in E. coli. The successful reconstitution and expression of the syringolin biosynthetic pathway shows that Red/ET recombineering is an efficient tool to clone and engineer secondary metabolite biosynthetic pathways.     

Potential of <Emphasis Type="Italic">Jatropha curcas</Emphasis> as a Biofuel,Animal Feed and Health Products

Jatropha curcas is a multipurpose plant with numerous attributes. It can potentially become one of the world’s key energy crops. Its seed weighs 0.53–0.86 g and the seed kernel contains 22–27% protein and 57–63% lipid indicating good nutritional value. The seeds can produce crude vegetable oil that can be transformed into high quality biodiesel. Several methods for oil extraction have been developed. In all processes, about 75% of the weight of the seed remains as a press cake containing mainly carbohydrates, protein and residual oil and is a potential source of livestock feed. The highly toxic nature of whole as well as dehulled seed meal due to the presence of high levels of shells, toxic phorbol esters and other antinutrients prevents its use in animal diet. The genetic variation among accessions from different regions of the world and rich diversity among Mexican genotypes in terms of phorbol ester content and distinct molecular profiles indicates the potential for improvement of germplasm of Jatropha through breeding programs. The extracts of Jatropha display potent cytotoxic, antitumor, anti-inflammatory and antimicrobial activities. The possibilities on the exploitation potential of this plant through various applications have been explored.     

Deformation behaviour of an advanced nickel-based superalloy studied by neutron diffraction and electron microscopy

Deformation mechanisms under tensile loading at room temperature have been studied in a polycrystalline nickel-based superalloy containing close to 50 vol.% γ′. In order to identify the effect of γ′ particle size on deformation mechanisms, model microstructures with unimodal γ′ size distributions were developed. The investigations were carried out by combining in situ loading experiments using neutron diffraction and two-site elasto-plastic self-consistent plasticity modelling with detailed post-mortem electron microscopy. The microscopy work also includes results for samples strained at 500 °C. During early plastic deformation, the diffraction data demonstrate that γ and γ′ display the same elastic strain response, indicating that at this stage γ′ is cut by dislocations regardless of the γ′ particle size. Scanning electron microscopy studies showed an abundance of shearing processes in all three microstructures, hence supporting the conclusions drawn from the diffraction experiment. As the material is further deformed, elastic load transfer from γ to γ′ was observed in the medium (130 nm) and coarse (230 nm) γ′ microstructures but not in the fine (90 nm) γ′ microstructure. The load transfer can be explained by assuming that Orowan looping becomes an additional operative deformation mode. Transmission electron microscopy confirmed that in the fine γ′ microstructure deformation takes place by strongly coupled dislocations cutting the γ′, while the medium and coarse γ′ microstructures showed additional signs of Orowan looping.     

Molybdenum Oxycarbide and Tungsten Oxycarbide Coatings on Silicon Carbide Fibers

The strength and toughness of fibrous composites depend on the interface properties which control the bonding between the fibers and matrices. One method of controlling the interface involves coating the fiber with an appropriate material. In a previous study, it was found that there is a definite advantage in using low coating temperatures to prevent fibers from degrading. We therefore were interested in a report that Mo₂C could be deposited from Mo(CO)₆ at temperatures as low as 300° to 475°C. Our studies indicated that the material was not Mo₂C, but an oxycarbide, which, with an analogous tungsten oxycarbide coating, was applied to SiC yarns. Both oxycarbides could be converted to the metals by heat-treating in N₂.     

A comparison of the determination of macromolecular orientation in polypropylene by attenuated total-reflection fourier-transform infrared spectroscopy and X-ray diffraction

Attenuated total reflection-infrared (ATR-IR) spectroscopy and wide-angle x-ray diffraction (WAXD) were used to determine the macromolecular orientation of a series of six uniaxially oriented polypropylene sheets with elongations of 0% to 500%. The orientation functions were expressed as fractions of chains oriented along the machine, trasverse, and normal directions in the sheets. Good agreement was found between the orientation functions for the two techniques. Sources of potential difference between the two techniques were discussed. The ATR-IR technique is surface sensitive to a depth of about 5 or 10 μm into the surface while the WAXD technique is bulk sensitive. The ATR-IR technique is sensitive to both the crystalline and noncrystalline material while the XRD technique is sensitive only to the crystalline material.