Photoelectrochemical cells based on CdSe films brush plated on high-temperature substrates

CdSe thin films were brush plated on substrates maintained at temperatures in the range 30–90 °C from the precursors. The films exhibited hexagonal crystal structure. Optical band gap of 1.65 eV was obtained. XPS measurements indicated the formation of CdSe. Capacitance–voltage measurements indicated the films to exhibit n-type behaviour. A carrier density of 10¹⁷ cm⁻³ was obtained. Photoelectrochemical cells have exhibited higher efficiency compared to earlier reports on brush-plated films. Spectral response measurements indicated a peak quantum efficiency of 75% at 1.65 eV.     

Application of profiled ejector in chemical lasers

Recently, the use of profiled ejectors based on constant rate of momentum change [I.W. Eames, Applied Thermal Engineering 22 (2002) 121] along the mixing chamber has been proposed for enhancing the recovery ratio across an ejector stage by minimizing shock losses for application in ejector based refrigeration system. Such ejectors can achieve pressure recovery ratio in excess of 150, thus making the system a compact one. Chemical lasers in general and chemical oxygen-iodine laser (COIL) in particular fall in the high power lasers category and find numerous applications in defense and industry. However, these lasers have not been exploited fully because these require pressure recovery systems for their operation and as such the practical systems are extremely voluminous and bulky. The profiled ejectors find direct applications in these lasers and thus can make the system extremely compact. The conventional supersonic COIL systems operate at a typical stagnation pressure of nearly 20 torr and a cavity static pressure of approximately 3 torr, which are amongst the lowest in the class of chemical lasers. Thus, a low-pressure operation of the laser system demands a high capacity vacuum system. Alternatively, efficient ejector based pressure recovery system has been utilized for achieving direct atmospheric exhaust of the lasing medium. However, a minimum of two-stage conventional supersonic ejectors need to be employed for the operation of the laser system. Multiple stages of the ejector are essential on account of the stagnation pressure loss occurring across a normal shock at the exit of the mixing chamber in each ejector stage. The present study presents a general treatment on the design of a profiled ejector for the case of dissimilar motive and suction fluids that are typical of these lasers. Also, determinations for the increase in recovery ratio for various conditions of entrainment ratio over the conventional ejectors have also been presented. Finally, a computational study using McCormack’s method for Euler system of equations has been carried out to numerically validate the analytical studies for a peripheral air ejector system suitable for a 500 W class COIL employing a flow rate of 3 gm/s with an entrainment ratio of 0.025. It has been concluded that a single-stage profiled ejector is sufficient to achieve atmospheric pressure recovery even in the low-pressure systems.     

Zinc ion conducting blended polymer electrolytes based on room temperature ionic liquid and ceramic filler

Zinc ion conducting nanocomposite gel polymer electrolytes (NCGPEs) comprising of poly(vinyl chloride) (PVC)/poly(ethyl methacrylate) (PEMA) blend, zinc triflate [Zn(OTf)₂] salt, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) ionic liquid (IL) and fumed silica (SiO₂) viz. [PVC/PEMA–Zn(OTf)₂–EMIMTFSI–SiO₂] exhibited the highest ionic conductivity value of 6.71 × 10⁻⁴ Scm⁻¹ at room temperature. The ion–filler–polymer interactions and probable conformational changes observed in the structure of the gel composites due to the entrapment of IL and dispersion of nano-sized SiO₂ were confirmed from X-ray diffraction (XRD) and Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. Scanning electron microscopic (SEM) images of NCGPEs demonstrated uniform surface with abundant interconnected micropores. The cationic transport number of NCGPE samples has been found to be appreciably enhanced up to a maximum of 0.69 thus demonstrating a considerable improvement in Zn²⁺ ion conductivity. The NCGPE film possesses an electrochemical stability window up to 5.07 V (vs. Zn/Zn²⁺) and ensures feasible zinc stripping/plating in the redox process. The addition of SiO₂ into the gel polymer electrolyte system has effectively reduced the glass-transition temperature (T_g) of the NCGPE films and also accomplished improved thermal stability up to approximately 180 °C which were ascertained from Differential scanning calorimetry (DSC) and Thermogravimetric (TG) results. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47654.     

Performance evaluation of a constant speed IC engine on CNG,methane enriched biogas and biogas

This paper presents the performance results of a 5.9 kW stationary diesel engine which was converted into spark ignition mode and run on compressed natural gas (CNG), methane enriched biogas (Bio-CNG) and biogas produced from biomethanation of jatropha and pongamia oil seed cakes. The performance of the engine with 12.65 compression ratio was evaluated at 30°, 35° and 40° ignition advance of TDC. The maximum brake power produced by the engine was found at ignition advance of 35° TDC for all the tested fuels. In comparison to diesel as original fuel, the power deteriorations of the engine was observed to be 31.8%, 35.6% and 46.3% on compressed natural gas, methane enriched biogas and raw biogas, respectively, due to its conversion from CI to SI mode. The methane enriched biogas showed almost similar engine performance as compared to compressed natural gas in terms of brake power output, specific gas consumption and thermal efficiency.     

Effect of Al2O3 content on the adsorptive properties of Cu/ZnO/Al2O3 for removal of odorant sulfur compounds

Cu/ZnO/Al₂O₃ adsorbents for removal of odorant sulfur compounds were prepared with various Al/Cu molar ratios by co-precipitation method. The sulfur removing ability as a function of Al/Cu molar ratio of the adsorbents for t-butyl mercaptan (TBM), tetrahydro thiophene (THT), dimethyl disulfide (DMS) and H₂S were investigated at 250 °C and 6000 h⁻¹ space velocity. Based on the results of adsorption capacity and characterization by various techniques, the optimum Al/Cu ratio for maximum sulfur removal capacity is found to be at Al/Cu molar ratio of 0.15 which possesses the well-dispersed Cu species with high reducibility. The adsorption capacity is highest for H₂S followed by TBM, DMS and THT. The main role of Al₂O₃ component is to provide the dispersion of CuO species homogeneously with small particle formation and high reducibility.     

Preparation and properties of silica filled PTFE flexible laminates for microwave circuit applications

Micron and nano size silica fillers are incorporated in the PTFE matrix to prepare flexible composite substrates. A proprietary process comprising of sigma mixing, extrusion, calendering followed by hot pressing (SMECH process) has been employed to obtain nearly isotropic and dimensionally stable filled PTFE substrates. Theoretical modeling has been employed to predict the effective dielectric constant of the composite system and validated the results with experimental data. The distribution of particulate filler in the PTFE matrix has been studied using scanning electron microscopy. The linear coefficient of thermal expansion and ultimate tensile strength of the composite systems with respect to filler loading have been found out. Dielectric properties of the composite substrates at X-band frequency (8.2–12.4 GHz) are measured using waveguide cavity perturbation technique. Moisture absorption of fused silica filled substrates is found out conforming to IPC-TM-650 2.6.2.     

Synthesis of Catalytically Active Porous Platinum Nanoparticles by Transmetallation Reaction and Proposition of the Mechanism

A facile method for the synthesis of porous platinum nanoparticles by transmetallation reactions between sacrificial nickel nanoparticles and chloroplatinic acid (H₂PtCl₆) in solution, as well as at the constrained environment of the air–water interface, using a Langmuir–Blodgett instrumental setup is presented. To carry out the transmetallation at the air–water interface hydrophobized nickel nanoparticles are assembled as a monolayer on the sub phase containing platinum ions. The porous Pt nanoparticles obtained as a result of the reaction are found to act as extremely good catalysts for hydrogenation reaction. The products are well characterized by TEM, HRTEM, EDAX, and STEM. Attempts are made to postulate the plausible mechanism of this reaction to generate this kind of nanoparticle with controllable geometric shape and structure. This simple strategy has the potential to synthesize other nanomaterials of interest too.     

Characterization of petroleum pitch using steady shear experiments

Asphalt for highway and runway construction is processed by either air blowing or blending with different petroleum streams. In the blending process, petroleum pitch, a by-product of solvent deasphalting of the vacuum residue is mixed with heavy extract to produce asphalt of the desired specifications. The rheological response of blended asphalt hence depends to a large extent on the constitutive property of petroleum pitch. In an aim to develop robust models for blended asphalt, modeling the mechanical behavior of petroleum pitch hence becomes necessary.In this work reported here, petroleum pitch from crude sources such as Basrah Light, Arab Mix and Arab Light are subjected to steady shear for 99 min at temperatures ranging from 70 to 120 °C for different shear rates. Each of these material exhibited different stress overshoot and decay during steady shear depending on the temperature and shear rate. A viscoelastic fluid model of the rate type is selected to model the response of the material. Using the recent thermodynamic framework based on Gibbs potential proposed by Rajagopal and Srinivasa [27], restrictions on the proposed model are obtained. The rotational flow problem is solved and the material parameters are estimated. The model predictions are corroborated with the experimental observations and they are found to be reasonably good.