Maghemite, γ-Fe2O3, nanoparticles preparation via carbon-templated solution combustion synthesis

High surface area maghemite, γ-Fe₂O₃, nanoparticles were prepared via carbon-templated solution combustion synthesis, which is a two-step approach. Step one involves the combustion synthesis of maghemite nanoparticles embedded in an amorphous carbon matrix, by using a fuel rich reaction mixture of triethylenetetramine and iron nitrate. Step two consists of residual carbon removal by treating the previously-obtained composite precursor with hydrogen peroxide, which releases the maghemite nanopowder. This approach avoids carbon removal by thermal treatment, thus preserving the nanometric size of maghemite nanoparticles (8–12?nm), yielding a high specific surface area of 191.9?m²/g. At the same time, the final maghemite nanoparticles presented a superparamagnetic behavior and a saturation magnetization of 26.2?emu/g, in relation to the small particle size.     

Structure of zirconium alloy oxides formed in pure water studied with synchrotron radiation and optical microscopy: relation to corrosion rate

A detailed study was undertaken of oxides formed in 360 °C water on four Zr-based alloys (Zircaloy-4, ZIRLO™,¹ Zr-2.5%Nb and Zr-2.5%Nb-0.5%Cu) in an effort to relate oxide structure to corrosion performance. Micro-beam X-ray diffraction was used along with transmitted light optical microscopy to obtain information about the structure of these oxides as a function of distance from the oxide-metal interface. Optical microscopy revealed a layered oxide structure in which the average layer thickness was inversely proportional to the post-transition corrosion rate. The detailed diffraction studies showed an oxide that contained both tetragonal and monoclinic ZrO₂, with a higher fraction of tetragonal oxide near the oxide-metal interface, in a region roughly corresponding to one oxide layer. Evidence was seen also of a cyclic variation of the tetragonal and monoclinic oxide across the oxide thickness with a period of the layer thickness. The results also indicate that the final grain size of the tetragonal phase is smaller than that of the monoclinic phase and the monoclinic grain size is smaller in Zircaloy-4 and ZIRLO than in the other two alloys. These results are discussed in terms of a model of oxide growth based on the periodic breakdown and reconstitution of a protective layer.     

Investigation of the electro-oxidation of artificial Black Sea water by cyclic voltammetry on molybdenum (II)

The electro-oxidation of H₂S in Black Sea water to generate electricity was investigated. MoS₂ exhibited catalytic activity toward the oxidation of H₂S in artificial sea water. The catalytic activity of molybdenum sulfide was found to depend on the electrolyte pH and on the temperature. Cyclic voltammograms taken in the artificial sea water containing hydrogen sulfide at pH = 14 exhibited a peak at 500 mV related to the oxidation of HS⁻. Furthermore, the peak current of the MoS₂ electrode increased to 400 mA g⁻¹ from 250 mA g⁻¹ (approximately 1.6-fold) when the temperature was increased from 353 K to 363 K.     

Development of a power management unit for small portable direct borohydride fuel cell–NiMH battery hybrid system

In this study, a small portable fuel cell/battery hybrid system has been developed. The system consists of a single portable direct borohydride/peroxide fuel cell (DBPFC), NiMH battery and power management unit (PMU). The battery has been used as a primary power source and has been discharged at constant load. When its state of charge is reduced, the DBPFC charges the battery and powers the load simultaneously. A DC–DC Boost converter has been used as a PMU. The DBPFC has provided the total power of 0.21 Wh into the system during the charge. During this experimental study fuel (NaBH₄) efficiency of 37% has been achieved in the hybrid system, while the system efficiency has been calculated as 34.5%.     

Some properties of bacterial cellulose produced by new native strain Gluconacetobacter sp. A06O2 obtained from Turkish vinegar

The aim of the study was to isolate and identify an acetic acid bacterial strain having high cellulose yield and to investigate some physicochemical properties of bacterial cellulose (BC). Acetic acid bacteria were isolated by using 62 samples (vinegar, fruit, vegetable, and soil) from different region of Turkey. The cellulose production ability of 153 isolates was determined. A strain (A06O2) having high and stable cellulose yield was identified by biochemical tests and 16S rRNA gene sequencing and compared with type strain Gluconacetobacter xylinus NRRL B‐759. Based on the results, strain A06O2 was named at the genus level as Gluconacetobacter, however, species level identification could not be made. Celluloses from both strains were purified to investigate the physicochemical properties such as thermal properties, solubility in various solvents, elemental composition, tensile properties, and surface properties by FTIR and SEM. The results showed that the cellulose samples of two bacterial strains differed in the physicochemical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

An example of estimating rock mass deformation around an underground opening using numerical modeling

In rock engineering, rock strength is regarded as an important rock mass parameter and it is widely estimated using the uniaxial compressive strength (UCS) test. A UCS test in laboratory requires sampling and preparation of core samples, which necessitates time consuming and expensive studies. Furthermore, preparation of cores is almost impossible for a weak rock material taken from foliated, laminated or thinly bedded rock masses of low Rock Quality Designation (RQD) values (0–20%). In this case, determination of UCS by laboratory test may be impossible in compliance with ISRM or ASTM standards. To overcome this difficulty, indirect tests, such as Point Load Index (PLI), Schmidt Hammer (SH) Rebound Number tests are often employed to predict the UCS. However, indirect tests are likely to yield UCS values with large standard deviations depending on the geological origin of the rock mass.The Block Punch Index (BPI) has recently been developed to overcome the drawbacks of UCS and indirect tests and to minimize the errors arisen from the structural deficiencies and large standard deviations. In this study, determination of rock mass behavior in laminated–foliated Bornova Melange (yellowish-brown flysch and grayish-black flysch) and well-jointed Yamanlar Volcanics–Altindag Formation, where the second phase of the Izmir Metro tunnels was excavated is aimed. The BPI ratings were directly used in RMR calculations and indirectly used to estimate the UCS values of rock materials. Then, the obtained results were input into numerical models along with the rock mass strength (UCS_RM) and deformation modulus of rock mass (E_RM). The results obtained from the numerical models agreed with that obtained results from inner tunnel convergence and ground settlement measurements.     

In vitro assessment of degradation and bioactivity of robocast bioactive glass scaffolds in simulated body fluid

In this study porous three-dimensional scaffolds of borate (13-93B3) bioactive glass were prepared by robocasting and in vitro degradation and bioactivity was evaluated. Grid like scaffolds with interconnected pores was assembled using robotic deposition technique which is a direct ink writing method. After binder burnout, the constructs were sintered for 1 h at 560 °C to produce scaffolds (porosity≈60%) consisting of dense glass struts (300±20 μm in diameter) and interconnected pores of width 580±20 μm. Hydroxyapatite formation on borate bioactive glass scaffolds was investigated in simulated body fluid (SBF) using three different scaffold/SBF (S/S) ratios (1, 2 and 10 mg/ml) at 37 °C. When immersed in SBF, degradation rate of the scaffolds and conversion to a calcium phosphate material showed a strong dependence to the S/S ratio. At high solid concentration (10 mg/ml) surface of the glass scaffolds converted to the calcium rich amorphous calcium phosphate after 30 days. At lower solid concentrations (2 and 1 mg/ml) an amorphous calcium phosphate layer formation was observed followed by the conversion to hydroxyapatite.     

Flow behavior of hydroxypropyl methyl cellulose/polyacrylic acid interpolymer complexes in aqueous media

The intermolecular complexation of non‐ionic polymers with weak acids having chemically complementary structures is an important approach to modify the viscosity of polymer solutions. In this study intermolecular complexation of hydroxypropyl methyl cellulose (HPMC) with polyacrylic acid (PAA) in an aqueous medium was studied. The study focuses on the factors affecting the complexation and rheological behavior of the HPMC/PAA system including the stoichiometric ratio of the two polymers, the molecular weight of the PAA, and the pH and ionic strength of the medium. Results showed that interpolymer complexation occurred between HPMC and PAA at low pH. It was attributed to hydrogen bonding between the ? COOH group of the PAA and the ? OH group of the HPMC. Under basic conditions (above the critical pH) the viscosity of the interpolymer complex increased accompanied by a transition from a compact interpolymer complexation structure to an extended conformation of interpolymer associates. Introduction of monovalent and multivalent salts (at > pH_critical) decreased the viscosity of the HPMC/PAA interpolymer associates and favored the formation of interpolymer complexes between the two polymers. Copyright © 2012 Society of Chemical Industry     

Direct-write assembly of silicate and borate bioactive glass scaffolds for bone repair

Silicate (13-93) and borate (13-93B3) bioactive glass scaffolds were created by robotic deposition (robocasting) of organic solvent-based suspensions and evaluated in vitro for potential application in bone repair. Suspensions (inks) were developed, characterized, and deposited layer-by-layer to form three-dimensional scaffolds with a grid-like microstructure (porosity ≈50%; pore width 420 ± 30 μm). The mechanical response of the scaffolds was tested in compression, and the conversion of the glass to hydroxyapatite (HA)-like material in a simulated body fluid (SBF) was evaluated. As fabricated, the 13-93 scaffolds had a compressive strength 142 ± 20 MPa, comparable to the strength of human cortical bone, while the strength of the 13-93B3 scaffolds (65 ± 11 MPa), was far higher than that for trabecular bone. When immersed in SBF, the borate 13-93B3 scaffolds converted faster than the silicate 13-93 scaffolds to an HA-like material, but they also showed a sharper decrease in strength with immersion time. Based on their high compressive strength and bioactivity, the scaffolds fabricated in this work by robocasting could have potential application in the repair of load-bearing bone.     

Effect of different modified atmosphere packaging on microbial quality,oxidation and colour of a seasoned ground beef product (meatball)

The effects of different modified atmosphere packaging (MAP) on microbial quality, oxidation and colour of meatballs were investigated. Meatballs were prepared in our laboratory and packaged in vacuum or in different gases: combinations of O₂ (0, 2, 21%) and CO₂ (0, 33, 66, 100%) with N₂ as balance gas. Total microbial count, thiobarbituric acid reactive substances and colour were determined during storage at 3°C for 3 weeks. Total microbial count remained unchanged at around 6.3 LogCFU/g in vacuum and 100% CO₂ packages after 7 days, and slightly increased afterwards. The microbial count was higher in other packages and increased to 7.6 LogCFU/g after 21 days storage. Oxidation was inhibited by reduced O₂ and increased CO₂ in the packages. Packages with low O₂ maintained colour (a‐values) to a greater extent than the packages with higher O₂ levels. MAP containing 1–3%O₂ with 33%CO₂ inhibited microbial growth, oxidation and colour change in meatballs. Copyright © 2009 John Wiley & Sons, Ltd.