Alkaline hydrothermal kinetics in titanate nanostructure formation

In this study, the mechanism of precursor dissolution and the influence of kinetics of dissolution on titanate nanotube formation were investigated. This comparative study explored the dissolution kinetics for the case of commercial titania powders, one composed of predominantly anatase (>95%) and the other rutile phase (>93%). These nanoparticle precursors were hydrothermally reacted in 9 mol L⁻¹ NaOH at 160 °C over a range of reaction times of between 2 and 32 h. The high surface area nanotube-form product was confirmed using X-ray diffraction, FT-Raman spectroscopy, and transmission electron microscopy. The concentration of nanotubes produced from the different precursors was established using Rietveld analysis with internal and external corundum standardization to calibrate the absolute concentrations of the samples. Interpretation of the dissolution process of the precursor materials indicated that the dissolution of anatase proceeds via a zero-order kinetic process, whereas rutile dissolution is through a second-order process. The TiO₂ nanostructure formation process and mechanism of TiO₂ precursor dissolution was confirmed by non-invasive dynamic light scattering measurements. Significant observations are that nanotube formation occurred over a broad range of hydrothermal treatment conditions and was strongly influenced by the order of precursor dissolution.     

Model for transient behavior of pulse tube cryocooler

This article describes an investigation of the transient behavior of a small (2.0 W at 85 K) pulse tube cryocooler operating at 120 Hz with an average pressure of 3.5 MPa, capable of relatively fast cool-down from ambient to about 60 K. In a series of experiments, the cold end temperature was measured as a function of time in a complete cool-down and subsequent warm-up cycle, with no heat load and different quantities of excess mass at the cold end. A transient heat transfer model was developed, that considers the effects of the cooling power extracted at the cold end and that of the heat gain at the warm end on the cool-down time. The heat gain factor was calculated from warm-up data, and found to be approximately the same for all experiments. Using the same model with cool-down data enables a determination of both the gross and net cooling power as functions of time, but more importantly – as functions of the cold end temperature. An expression was derived for the cold end temperature as a function of time for any amount of excess mass, including zero. The cool-down time of the “lean” cryocooler (with no excess mass) was found to be less than 50 s.This cool-down/warm-up method for evaluating the cooling power of a cryocooler seems simpler than steady-state experiments with a heater simulating load at the cold end. Use of the heat transfer model with data from one or two good experiments conducted in the above manner, can yield both the gross and net cooling powers of a cryocooler as functions of the cold end temperature, and allow the determination of cool-down time with any amount of excess thermal mass. While the net cooling power during cool-down differs somewhat from that under steady-state operation, the former can serve as a good measure for the latter.     

Catalytic reaction in a circulating fluidized bed downer: Ozone decomposition

Catalytic ozone decomposition reaction was used to study the performance of a 76 mm i.d. and 5.8 m high gas–solid circulating fluidized bed (CFB) downer reactor. Optical fiber probes and an ultraviolet (UV) ozone analyzer were used to obtain comprehensive information about local solids holdup and ozone concentration profiles at different axial and radial positions at superficial gas velocity of 2–5 m/s and solids circulation rates of 50 and 100 kg/m² s. Axial ozone concentration profiles significantly deviated from the plug-flow behavior, with most conversion occurring in the entrance region or flow developing zone of the downer reactor. Strong correlation was observed between the spatial distributions of solids and extent of reaction; higher local solids holdups cause lower ozone concentrations due to higher reaction rates. Radial gradients of the reactant (ozone) concentrations increased in the middle section of the downer, and decreased with increasing superficial gas velocity and solids circulation rate. Contact efficiency, a measure of the interaction between gas and solids indicated high efficiency in the flow developing zone and decreased with height in the fully developed region.     

Removal of pyridine from water by pervaporation using filled SBR Membranes

Styrene butadiene rubber (SBR) was efficiently cured (crosslinked) by using sulfur to accelerator ratio less than unity. This cured SBR was further compounded with carbon black filler (grade N330) with three different doses i.e., 5, 10, and 20 wt % of filler to form three different filled and crosslinked membranes, i.e., SBR5, SBR10, and SBR20. These filled rubber membranes and one unfilled but efficiently cured membrane, i.e. SBR0, were used for pervaporative removal of pyridine from its mixtures with water. The filled membranes were found to show better selectivity and mechanical properties but lower flux than the unfilled membrane. All of these membranes showed reasonably good range of flux and pyridine selectivity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Highly Conductive Carbon Nanotube‐Graphene Hybrid Yarn

An efficient procedure for the fabrication of highly conductive carbon nanotube/graphene hybrid yarns has been developed. To start, arrays of vertically aligned multi‐walled carbon nanotubes (MWNT) are converted into indefinitely long MWNT sheets by drawing. Graphene flakes are then deposited onto the MWNT sheets by electrospinning to form a composite structure that is transformed into yarn filaments by twisting. The process is scalable for yarn fabrication on an industrial scale. Prepared materials are characterized by electron microscopy, electrical, mechanical, and electrochemical measurements. It is found that the electrical conductivity of the composite MWNT‐graphene yarns is over 900 S/cm. This value is 400% and 1250% higher than electrical conductivity of pristine MWNT yarns or graphene paper, respectively. The increase in conductivity is asssociated with the increase of the density of states near the Fermi level by a factor of 100 and a decrease in the hopping distance by an order of magnitude induced by grapene flakes. It is found also that the MWNT‐graphene yarn has a strong electrochemical response with specific capacitance in excess of 111 Fg^?1. This value is 425% higher than the capacitance of pristine MWNT yarn. Such substantial improvements of key properties of the hybrid material can be associated with the synergy of MWNT and graphene layers in the yarn structure. Prepared hybrid yarns can benefit such applications as high‐performance supercapacitors, batteries, high current capable cables, and artificial muscles.     

Self‐Healing Reduced Graphene Oxide Films by Supersonic Kinetic Spraying

The industrial scale application of graphene and other functional materials in the field of electronics has been limited by inherent defects, and the lack of simple deposition methods. A simple spray deposition method is developed that uses a supersonic air jet for a commercially available reduced graphene oxide (r‐GO) suspension. The r‐GO flakes are used as received, which are pre‐annealed and pre‐hydrazine‐treated, and do not undergo any post‐treatment. A part of the considerable kinetic energy of the r‐GO flakes entrained by the supersonic jet is used in stretching the flakes upon impact with the substrate. The resulting “frozen elastic strains” heal the defects (topological defects, namely Stone‐Wales defect and C₂ vacancies) in the r‐GO flakes, which is reflected in the reduced ratio of the intensities of the D and G bands in the deposited film. The defects can also be regenerated by annealing.     

Synthesis of Nanocrystalline FeS2 with Increased Band Gap for Solar Energy Harvesting

In this paper,we have reported the synthesis of FeS2 of higher band gap energy（2.75 eV） by using capping reagent and its successive application in organic-inorganic based hybrid solar cells.Hydrothermal route was adopted for preparing iron pyrite（FeS2） nanoparticles with capping reagent PEG-400.The quality of synthesized FeS2 material was confirmed by X-ray diffraction,field emission scanning electron microscopy,transmission electron microscopy,Fourier transform infrared,thermogravimetric analyzer,and Raman study.The optical band gap energy and electro-chemical band gap energy of the synthesized FeS2 were investigated by UV-vis spectrophotometry and cyclic voltammetry.Finally band gap engineered FeS2 has been successfully used in conjunction with conjugated polymer MEHPPV for harvesting solar energy.The energy conversion efficiency was obtained as 0.064%with a fill-factor of 0.52.     

Dispersion of nanoplatelets of graphite on PMMA matrix by in situ polymerisation technique

Poly(methyl methacrylate)/expanded graphite (PMMA/EG) composites were prepared by the incorporation of EG in various proportions (1%, 2%, 3%, 4% and 5%) with PMMA by in situ polymerisation technique. The polymer composites were characterised by ultraviolet–visible (UV–vis) and Fourier transform infra-red spectroscopies. The structural property of PMMA/EG nanocomposites was studied by X-ray diffraction. The scanning electron microscopy and transmission electron microscopy of synthesised composites were taken in order to study their morphological properties. The conductivity of composites was measured as function of EG concentration. It was found that conductivity of composites gradually increased with the increase in EG loading. Oxygen permeability of PMMA/EG nanocomposites was calculated and it was found that the property was reduced substantially with rise of EG proportion. The thermal stability of PMMA/EG nanocomposites was improved by dispersion of EG with PMMA matrix.     

Analysis of fatigue crack growth in reinforced concrete beams

Mechanical behavior of reinforced concrete members is influenced by the action of unknown crack bridging reactions of rebars. Under cyclic loading, due to progressive growth of cracks, this bridging action contributes to the overall strength, stiffness and hysteretic behavior of the member. In this work, fatigue behavior of reinforced concrete beams are studied using a crack propagation law, developed using dimensional analysis for plain concrete with the effect of reinforcement being simulated through constraint exerted on the crack opening. The parameters considered in the model are fracture toughness, crack length, loading ratio and structural size. A numerical procedure is followed to compute fatigue life of RC beams and the dissipated energy in the steel reinforcement due to the shake down phenomenon under cyclic loading. Through a sensitivity study, it is concluded that the structural size is the most sensitive parameter in the fatigue crack propagation phenomenon. Furthermore, the residual moment carrying capacity of an RC member is determined as a function of crack extension by including the bond-slip mechanism.