Tailored nitrogen dioxide sensing response of three-dimensional graphene foam

Ultralight and macroporous three-dimensional reduced graphene oxide (rGO) foams are prepared by lyophilization (freeze-drying) technique to avoid a conventional template method. This method allows tailoring the porosity of the foams by varying the weight percentages of graphene oxide dispersions in water. Three different rGO foams of 0.2, 0.5 and 1.0 wt% are used for NO2 sensing. Sensing response from the tailored structure of rGO is found to be directly related to the density. A maximum of 20% sensing response is observed for a higher porosity of the structure, better than the known results so far on graphene foams in the literature. (C) 2015 Elsevier B.V. All rights reserved.

A novel in-situ polymer derived nano ceramic MMC by friction stir processing

Fiction stir processing (FSP) is a solid state technique used for material processing. Tool wear and the agglomeration of ceramic particles have been serious issues in FSP of metal matrix composites. In the present study, FSP has been employed to disperse the nanoscale particles of a polymer-derived silicon carbonitride (SiCN) ceramic phase into copper by an in-situ process. SiCN cross linked polymer particles were incorporated using multi-pass ESP into pure copper to form bulk particulate metal matrix composites. The polymer was then converted into ceramic through an in-situ pyrolysis process and dispersed by ESP. Multi-pass processing was carried out to remove porosity from the samples and also for the uniform dispersion of polymer derived ceramic particles. Microstructural observations were carried out using Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM) of the composite. The results indicate a uniform distribution of similar to 100 nm size particles of the ceramic phase in the copper matrix after ESP. The nanocomposite exhibits a five fold increase in microhardness (260HV(100)) which is attributed to the nano scale dispersion of ceramic particles. A mechanism has been proposed for the fracturing of PDC particles during multi pass FSP. (C) 2015 Elsevier Ltd. All rights reserved

Effect of combined treatment with zoledronic acid and propranolol on mechanical strength in an rat model of disuse osteoporosis

Objectives: A model that uses right hind-limb unloading of rats is used to study the consequences of skeletal unloading during various conditions like space flights and prolonged bed rest in elderly. This study was aimed to investigate the additive effects of antiresorptive agent zoledronic acid (ZOL), alone and in combination with propranolol (PRO) in a rat model of disuse osteoporosis. Methods: In the present study, 3-month-old male Wistar rats had their right hind-limb immobilized (RHLI) for 10 weeks to induce osteopenia, then were randomized into four groups: 1-RHLI positive control, 2-RHLI plus ZOL (50 mu g/kg, i.v. single dose), 3-RHLI plus PRO (0.1 mg/kg, s.c. 5 days per week), 4-RHLI plus PRO (0.1 mg/kg, s.c. 5 days per week) plus ZOL (50 mu g/kg, i.v. single dose) for another 10 weeks. One group of non-immobilized rats was used as negative control. At the end of treatment, the femurs were removed and tested for bone porosity, bone mechanical properties, and bone dry and ash weight. Results: With respect to improvement in the mechanical strength of the femoral mid-shaft, the combination treatment with ZOL plus PRO was more effective than ZOL or PRO monotherapy. Moreover, combination therapy using ZOL plus PRO was more effective in improving dry bone weight and preserved the cortical bone porosity better than monotherapy using ZOL or PRO in right hind-limb immobilized rats. Conclusions: These data suggest that this combined treatment with ZOL plus PRO should be recommended for the treatment of disuse osteoporosis. (C) 2014 Elsevier Editora Ltda. All rights reserved.

Simulation of Effective Thermal Conductivity of Metal Hydride Packed Beds

Several mathematical models are available for estimation of effective thermal conductivity of nonreactive packed beds. Keeping in view the salient differences between metal hydride beds in which chemisorption of hydrogen takes place and conventional nonreactive packed beds, modified models are proposed here to predict the effective thermal conductivity. Variation in properties such as solid thermal conductivity and porosity during hydrogen absorption and desorption processes are incorporated. These extended models have been applied to simulate the effective thermal conductivity of the MmNi(4.5)Al(0.5) hydride bed and are compared with the experimental results. Applicability of the extended models for estimation of the effective thermal conductivity at different operating conditions such as pressure, temperature, and hydrogen concentration is discussed.

Macropores generated during shrinkage in two paddy soils using X-ray micro-computed tomography

Soil shrinkage curve represents a decrease of total porosity or an increase of bulk density with water loss. However, our knowledge of the dynamics of pores and their geometry during soil shrinkage is scarce, partially due to lack of reliable methods for determining soil pores in relation to change in soil water. This study aimed to investigate the dynamics of macropores (>30 mu m) of paddy soils during shrinkage. Two, paddy soils, which were sampled from one paddy field cultivated for 20 years (YPF) and the other one for over 100 years (OPF), represented difference in crack geometry in the field. Macropore parameters (volume, connectivity, and orientation of pores) and soil shrinkage parameters were determined on the same undisturbed soil cores by X-ray microtomography and shrinkage curve, respectively. Macroporosity was on average four times larger in the YPF than in the OPF whereas the shrinkage capacity was lower in the YPF as compared to the OPF (0.09 vs. 0.15 COLE). Soil shrinkage increased the volume of pores by 3.7% in the YPF and by 1.6% in the OPF as well as their connectivity. The formation of macropores occurred mostly in the proportional shrinkage phase. As a result, the slope of the proportional shrinkage phase was smaller in the YPF (0.65) than in the OPF (0.89). New macropores were cracks and extended pre-existing pores in the range of 225-1215 pm size without any preferential orientation. This work provides image evidences that in paddy soils with high shrinkage capacity more macropores are generated in the soil presenting a smaller proportional shrinkage slope. (C) 2015 Elsevier B.V. All rights reserved.

Flower-like porous cobalt(II) monoxide nanostructures as anode material for Li-ion batteries

In the present study, a microwave-assisted, solution-based route has been employed to obtain porous CoO nano structures. Detailed characterization reveals that the flower-like nanostructures comprise petal-like sheets, each of which is made of an ordered, porous arrangement of crystallites of CoO measuring about 6 nm. TEM analysis shows that each ``petal'' is an oriented aggregate of CoO nanocrystals, such aggregation promoted by the hydroxyl moieties derived from the solution. The structure provides a large specific area as well as the porosity desirable in electrodes in Li-ion batteries. Electrochemical measurements carried out on electrodes made of nanostructured CoO show excellent Li ion-storing capability. A specific capacitance of 779 mAh g(-1) has been measured at a specific current of 100 mA g(-1). Measurements show also excellent cyclability and coulombic efficiency. Impedance spectroscopy provides evidence for charge transfer occurring in the porous networks. (C) 2015 Elsevier B.V. All rights reserved.

Conceptual design of three-dimensional scaffolds of powder-based materials for bone tissue engineering applications

Purpose - The purpose of this paper is to investigate the possibility to construct tissue-engineered bone repair scaffolds with pore size distributions using rapid prototyping techniques. Design/methodology/approach - The fabrication of porous scaffolds with complex porous architectures represents a major challenge in tissue engineering and the design aspects to mimic complex pore shape as well as spatial distribution of pore sizes of natural hard tissue remain unexplored. In this context, this work aims to evaluate the three-dimensional printing process to study its potential for scaffold fabrication as well as some innovative design of homogeneously porous or gradient porous scaffolds is described and such design has wider implication in the field of bone tissue engineering. Findings - The present work discusses biomedically relevant various design strategies with spatial/radial gradient in pore sizes as well as with different pore sizes and with different pore geometries. Originality/value - One of the important implications of the proposed novel design scheme would be the development of porous bioactive/biodegradable composites with gradient pore size, porosity, composition and with spatially distributed biochemical stimuli so that stem cells loaded into scaffolds would develop into complex tissues such as those at the bone-cartilage interface.

Hierarchically porous Li1.2Mn0.6Ni0.2O2 as a high capacity and high rate capability positive electrode material

Layered composite samples of lithium-rich manganese oxide (Li1.2Mn0.6Ni0.2O2) are prepared by a reverse microemutsion route employing a soft polymer template and studied as a positive electrode material. The product samples possess dual porosity with distribution of pores at 3.5 and 60 nm. Pore volume and surface area decrease on increasing the temperature of preparation. Nevertheless, the electrochemical activity of the composite increases with an increase in temperature. The discharge capacity value of the samples prepared at 800 and 900 degrees C is about 240 mA h g(-1) at a specific current of 25 mA g(-1) with a good cycling stability. The composite sample heated at 900 degrees C possesses a high rate capability with a discharge capacity of 100 mA h g(-1) at a specific current of 500 mA g(-1). The high rate capability is attributed to porous nature of the composite sample.

Three-dimensional plotted hydroxyapatite scaffolds with predefined architecture: comparison of stabilization by alginate cross-linking versus sintering

Scaffolds for bone tissue engineering are essentially characterized by porous three-dimensional structures with interconnected pores to facilitate the exchange of nutrients and removal of waste products from cells, thereby promoting cell proliferation in such engineered scaffolds. Although hydroxyapatite is widely being considered for bone tissue engineering applications due to its occurrence in the natural extracellular matrix of this tissue, limited reports are available on additive manufacturing of hydroxyapatite-based materials. In this perspective, hydroxyapatite-based three-dimensional porous scaffolds with two different binders (maltodextrin and sodium alginate) were fabricated using the extrusion method of three-dimensional plotting and the results were compared in reference to the structural properties of scaffolds processed via chemical stabilization and sintering routes, respectively. With the optimal processing conditions regarding to pH and viscosity of binder-loaded hydroxyapatite pastes, scaffolds with parallelepiped porous architecture having up to 74% porosity were fabricated. Interestingly, sintering of the as-plotted hydroxyapatite-sodium alginate (cross-linked with CaCl2 solution) scaffolds led to the formation of chlorapatite (Ca9.54P5.98O23.8Cl1.60(OH)(2.74)). Both the sintered scaffolds displayed progressive deformation and delayed fracture under compressive loading, with hydroxyapatite-alginate scaffolds exhibiting a higher compressive strength (9.5 +/- 0.5MPa) than hydroxyapatite-maltodextrin scaffolds (7.0 +/- 0.6MPa). The difference in properties is explained in terms of the phase assemblage and microstructure.

Facile synthesis of Graphene Oxide/Double-stranded DNA composite liquid crystals and Hydrogels

Investigation of the interactions between graphene oxide (GO) and biomolecules is very crucial for the development of biomedical applications based on GO. This study reports the first observation of the spontaneous formation of self-assembled liquid crystals and three-dimensional hydrogels of graphene oxide with double-stranded DNA by simple mixing in an aqueous buffer media without unwinding double-stranded DNA to single-stranded DNA. The GO/dsDNA hydrogels have shown controlled porosity by changing the concentration of the components. The strong binding between dsDNA and graphene is proved by Raman spectroscopy.

Effect of current density on the microstructure and corrosion properties of plasma electrolytic oxidation (PEO) coatings on AM50 Mg alloy produced in an electrolyte containing clay additives

Plasma electrolytic oxidation coatings were produced on AM50 Mg alloy in alkaline phosphate based electrolyte with montmorillonite clay additives employing current densities of 30, 60, and 120 mA/cm(2). The effect of current density on the microstructure and corrosion properties of the coating was investigated. The clay additives got melted and reactively incorporated into the coating forming an amorphous phase, at all the current densities. However, the coating was predominantly amorphous only at 30 mA/cm(2) and with increasing current density, increasing fractions of crystalline phases were formed. Higher current densities resulted in increased thickness of the coating, but reduced the compactness of the coatings. Electrochemical impedance spectroscopy tests in 0.5 wt.% (0.08 M) and 3.5 wt.% (0.6 M) NaCl solution revealed that the coatings processed at 30 mA/cm(2) exhibited a relatively better initial corrosion resistance owing to its relatively defect-free barrier layer and compactness of the coating. However, the presence of amorphous phases in significant amounts and lack of MgO in the coating resulted in increased rate of dissolution of the coatings and degradation of corrosion resistance. Coatings produced at higher current densities exhibited initial inferior corrosion resistance due to a more defective barrier layer and increased porosity in pore band and outer porous layer. However, the increased amount of crystalline phases and an increased amount of MgO, which resisted dissolution, counterbalanced the negative effects of defective barrier and increased porosity resulting in a relatively lower rate of the degradation of the corrosion resistance. Thus, the corrosion resistance of all the coatings continuously decreased with time and became similar after prolonged immersion in NaCl solution. Increasing current density, therefore, did not prove to be beneficial for the improvement of the corrosion performance of the PEO coatings. (C) 2016 Elsevier B.V. All rights reserved.