Aluminum diboride synthesis from elemental powders by mechanical alloying and annealing

In this study, AlB₂ powders were synthesized by using a combined method of mechanical alloying (MA) and annealing of elemental aluminum (Al) and boron (B) powders. Milling was performed in a planetary ball-mill (Fritsch? Pulverisette 7 Premium Line) up to 15 h under argon (Ar) atmosphere. Annealing process was carried out in a tube furnace at 650 °C for 6 h under Ar atmosphere. The effects of MA durations on the annealing process and AlB₂ formation were investigated. The conversion of Al and B powders to AlB₂ starts after only MA for 3 h or after MA for 1 h and subsequent annealing. A slight formation of AlB₁₂ occurs at 242 °C for as-blended powders and it shifts to about 272 °C for MA’d powders. Al–B powder blends MA’d for 9 h and annealed have AlB₂ particles in size between 35 and 75 nm in the presence of Al₁₃Fe₄, Fe₃B and Fe₂B contaminations.     

Synthesis and characterization of (CuO)x(ZnO)1 − x composite thin films with tunable optical and electrical properties

Mixed (CuO)_x(ZnO)_1 − x composite films have been prepared on glass substrates by a sol-gel spin coating method using copper acetate hydrate and zinc acetate dihydrate as precursors. The surface morphology and crystal structure of the films were investigated by field emission scanning electron microscopy and x-ray diffraction, respectively. It was observed that the crystal structure changed from wurtzite (ZnO) to monoclinic (CuO) as the Cu content increased from 0% to 100% in the films. UV-Vis absorption and photoluminescence measurements indicated that the optical properties can be tuned continuously from pure ZnO to pure CuO as the Cu content was increased, following the expected trends for a transition from ZnO to CuO. The resistivity of the films decreased by three orders of magnitude as Cu increased from 0% to 100%. These semiconducting composite oxides with tunable optical and electrical properties have potential applications in electronics and optoelectronics.     

Physico-chemical and sensory properties of chips produced using different lupin (Lupinus albus L.) flour formulations and cooking methods

Development of novel snack foods is an important area of research, and different ingredients are being tested to develop and process new formulations. In this study, lupin chips prepared using different formulations (hulled lupin, whole lupin, wheat and corn flours) were cooked using baking and frying, and changes in the sensory and colour parameters, acrylamide contents, fat absorption, peroxide number and p-anisidine values of the final products were studied. Lupin flour significantly changed p-anisidine value of chips. Addition of lupin flour and cooking methods affected the colour, fat absorption and peroxide values. Significant differences in chemical properties of chips made from whole and hulled lupin flours were also observed. Acrylamide was not detected in all the formulations studied. The lupin chips have increased brightness (L*), no acrylamides, reduced peroxide and p-anisidine values and acceptable sensory quality; hence, this ingredient is recommendable for use in snack foods.     

Electroconductive hyaluronic acid/gelatin/poly(ethylene oxide) polymeric film reinforced by reduced graphene oxide

Novel electroconductive polymeric films with enhanced mechanical performance were fabricated by encapsulating reduced graphene oxide (RGO) at different concentrations (0–50 vol %) into a hyaluronic acid/gelatin/poly(ethylene oxide) (HyA/Gel/PEO) polymeric structure. The obtained RGO-reinforced polymeric films were characterized by Fourier transform infrared and scanning electron microscopy analyses. Mechanical performances were measured with a universal mechanical testing machine. The results verified that the RGO reinforcement significantly enhanced the mechanical performances of the films. To determine the biocompatibility of the polymeric films, L929 (murine fibroblast) cell lines were used. The water uptake capacities were measured using swelling tests. A four-probe method was used to measure conductivity characteristics. The conductivity results indicated that HyA/Gel/PEO film containing 20 vol % RGO has the highest average electrical conductivity (1.832 × 10⁻⁶ S/cm). All of the results demonstrated that the obtained electroconductive films could be used in biomedical fields in the future, especially in controlled drug release systems and tissue engineering. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46905.     

Synthesis and photopolymerizations of phosphate-containing acrylate/(di)methacrylate monomers from 3-(acryloyloxy)-2-hydroxypropyl methacrylate

Summary Novel phosphorus-containing acrylate/(di)methacrylate monomers based on 3-(acryloyloxy)-2-hydroxypropyl methacrylate (AHM) were prepared by two different methods. The first method involved reaction of AHM with diethylchlorophosphate to produce a phosphate-containing acrylate/methacrylate monomer followed by Michael addition of this monomer with dihexyl amine. In the second method, a hydroxyl-containing dimethacrylate monomer was prepared via Michael addition of hydroxyl amine to AHM followed by its reaction with diethylchlorophosphate. The photopolymerization kinetics of the synthesized monomers were investigated using a differential scanning calorimeter. It was shown that changing the monomer structure allows control of polymerization reactivity and new phosphorus-containing polymers can be obtained.     

Effect of an Er,Cr:YSGG laser preparation on dentin bond strength of a universal adhesive

The aim of this study was to evaluate the bond strength of a universal adhesive system to dentin prepared with SiC paper or an Er,Cr:YSGG laser using different bonding strategies (etch-and-rinse versus self-etch mode). Ninety-six extracted caries-free, sound human molars were used. The teeth were longitudinally sectioned in the mesiodistal direction and were wet polished with 600-grit SiC paper to obtain a standardized flat dentin surface. All prepared teeth were randomly divided into two groups, according to the surface preparation method: GroupI:an erbium, chromium:yttrium,scandium, gallium, garnet laser; Group II: silicon carbide paper[SiC] (n = 48). Each group was then assigned into three subgroups according to the universal adhesive’s (Single Bond Universal) bonding strategies: (a) etch-and-rinse mode with phosphoric acid, (b) etch-and-rinse mode with a laser, (c) self-etch mode (n = 16). For surface preparation, the Er,Cr:YSGG laser was used at 3 W, 30 Hz with 140 μs pulse duration for 25 s. For etching mode, the laser was used at 1.5 W (60% air, 70% water). Cylinders of composite were fabricated on the bonding area and shear bond strength was determined using a universal testing machine. Failure modes were evaluated using a stereomicroscope. The data were analyzed using two-way ANOVA followed by the Bonferroni test (p < 0.05). Bonding strategies showed statistically significant differences in both the SiC-and laser-prepared groups (p < 0.05).Universal adhesive used in etch-and-rinse mode with acid showed significantly higher bond strength values than in self-etch mode (p < 0.05). The bond strength values did not differ according to the surface preparation method (p > 0.05). Irrespective of preparation method, using universal adhesive in etch-and-rinse mode with acid might improve dentin bond strength. Laser preparation did not affect the bond strength of the universal adhesive tested.     

Effect of (Ta/Nb) co-doping on the magnetoresistivity and flux pinning energy of the BPSCCO superconductors

In the present work, the effect of co-doping of Ta and Nb with nominal composition of (BiPb)₂Ta_xSr₂Ca₃Cu_4?yNb_yO_12+δ where x = 0.1 and y = 0.0, 0.025, 0.05, 0.075, and 0.1 were investigated. The samples were prepared by using the well-known conventional standard solid-state reaction method. The magnetoresistance measurements were studied for different values of the applied magnetic field. The activation energies, irreversibility fields (H _irr ), upper critical fields (H _c2 ) and coherence lengths at 0 K (ζ(0)) were calculated from the resistivity versus temperature (ρ-T) curves, under DC magnetic fields up to 6 T. The thermally activated flux flow (TAFF) model has been applied in order to calculate the flux pinning energies. The results have shown that the upper critical magnetic field, H _c2 (0), and the flux pinning energies vary from ~113 to 74 T and ~384 to 101 meV at 0 T, with the Nb-content, respectively.