Mesoporous Co3O4 for low temperature CO oxidation: effect of calcination temperatures on their catalytic performance

Mesoporous Co3O4 particles are prepared by using mesoporous silica KIT-6 (with double gyroid Ia-3d symmetry) as a hard-template and Co(No3)2 x 6H2O as an inorganic precursor. In the former section, we investigate the effect of the calcination temperatures at which the Co salts are converted into Co3O4 inside the mesopores on the textural parameters of the products. The results of N2 adsorption-desorption analysis indicates that the calcination temperatures do not obviously affect the textural parameters such as the surface areas and pore volumes. However, when the calcination temperature reaches 800 degrees C, the mesostructural ordering is dramatically decreased, resulting in the reduction of the surface areas and pore volumes. After 800 degrees C calcination, the formation of large Co3O4 grains is partially confirmed on the particle surface by SEM observation. The grain size is much larger than the mesopore size of the original KIT-6, meaning the crystal growth is continuously occurred by breaking the rigid silica frameworks. In the latter section, we discuss the effect of the calcination temperatures and textural parameters on the catalytic activity for CO oxidation by both steady state and kinetic measurements. All mesoporous Co3O4 particles show a high catalytic activity, for example, -72 degrees C for sample calcined at 450 degrees C. Only 10 degrees C difference in T50 (the temperature of 50% conversion of CO) is found between the samples with the highest and lowest catalytic activity. The values of activation energy (Ea) and pre-exponential factor (A) per unit area are almost the same between two samples calcined at 450 degrees C and 800 degrees C. It is demonstrated that calcination process can not alter the essential catalytic property of mesoporous Co3O4 particles.     

Neural networks for the identification and control of blast furnace hot metal quality

The operation and control of blast furnaces poses a great challenge because of the difficult measurement and control problems associated with the unit. The measurement of hot metal composition with respect to silica and sulfur are critical to the economic operation of blast furnaces. The measurement of the compositions require spectrographic techniques which can be performed only off line. An alternate technique for measuring these variables is a Soft Sensor based on neural networks. In the present work a neural network based model has been developed and trained relating the output variables with a set of thirty three process variables. The output variables include the quantity of the hot metal and slag as well as their composition with respect to all the important constituents. These process variables can be measured on-line and hence the soft sensor can be used on-line to predict the output parameters. The soft sensor has been able to predict the variables with an error less than 3%. A supervisory control system based on the neural network estimator and an expert system has been found to substantially improve the hot metal quality with respect to silicon and sulfur.     

Experimental studies on heat transfer and friction factor characteristics of thermosyphon solar water heater system fitted with spacer at the trailing edge of twisted tapes

Experimental investigation of heat transfer and friction factor characteristics of thermosyphon solar water heater system with full- length twist, twist fitted with rod and spacer fitted at the trailing edge for lengths of 100, 200 and 300 mm for twist ratio 3 and 5 has been carried out and compared with plain tube collector for the same operating conditions. The experimental data for Nusselt number and friction factor for plain tube collector is verified with fundamental equations. Empirical correlations are developed for Nusselt number and friction factor for twist ratio 3 and 5. Results conclude that the decrease in Nusselt number for full length helical twist compared to twist fitted with rod is minimum and is quite significant for twist with spacer. But the decrease in friction factor is maximum in twist fitted with spacer compared to twist fitted with rod. The over all performance for twist fitted with rod is found to be better than twist fitted with spacer.     

Confined growth of Ag2S semiconductor nanocrystals in the presence of PDMAEMA-co-AA polyampholyte co-polymer

Silver sulfide (Ag₂S) nanoparticles were synthesized in the presence of poly(2-(dimethylamino)ethyl methacrylate-co-acrylic acid) co-polymer. It was shown that this polyampholyte can stabilize the growth of the Ag₂S in solution which resulted in formation of nanoparticles with relatively narrow size distribution. The obtained nanoparticles were characterized with structural and optical methods. The results showed that their average size depended on the number of acrylic acid units along the polymer chains.     

Polyethersulfone-expanded graphite nanocomposites: Charge transport and impedance characteristics

Polyethersulfone (PES)-expanded graphite nanocomposites have been prepared by solution blending route after sonicating expanded graphite in dichloromethane. It has been observed that ultrasonication results in nanosheets formation leading to a low percolation threshold of 3 wt.%. At 5 wt.% filler loading the conductivity is of the order of 10⁻² S/cm. Hopping type of charge transport occurs at 3.2 wt.% expanded graphite in PES below which capacitive effects couple. The effective dielectric constant at low frequency increases with filler concentration. Impedance measurement has been carried out to evaluate interfacial capacitance which, for 3.2 wt.% expanded graphite addition in PES, increases to 110 pF from 32 pF for 1 wt.% expanded graphite in the polymer. DSC analysis shows an increment of 12 °C in the T_g of PES with 3 wt.% expanded graphite suggesting interaction between the polymer and filler.     

Structure-property correlation of two Cu-bearing high-strength low-alloy steels

Structure and mechanical properties of two copper bearing high-strength low-alloy steels (HSLA)—one similar to HSLA 80 and the other to HSLA 100—are studied in different aging conditions. Elemental copper precipitates of nanometer size have been found to play an important role in the formation of different types of microstructures and in enhancing the strength and toughness of the alloys. Other alloying elements such as Ti, Nb, and V result in fine precipitates of carbides and nitrides, which improve the mechanical strength.     

Demonstration of aluminum-free metamorphic InP/In0.53Ga0.47As/InP double heterojunction bipolar transistors on GaAssubstrates

We report, for the first time, the successful fabrication of aluminum-free metamorphic (MM) InP/In_0.53 Ga_0.47 As/InP double heterojunction bipolar transistors (DHBTs) on GaAs substrates with a linearly graded In_xGa_1-xP buffer grown by solid-source molecular beam epitaxy (SSMBE). Devices with 5×5 μm² emitters display a peak current gain of 40 and a common-emitter breakdown voltage (BV_CE0) higher than 9 V, a current gain cut-off frequency (f_T) of 48 GHz and a maximum oscillation frequency (f_max) of 42 GHz. A minimum noise figure of 2.9 dB and associated gain of 19.5 dB were measured at a collector current level of 2.6 mA at 2 GHz. Detailed analysis suggests that the degradation of the base-emitter heterojunction interface and the increase of bulk recombination are the most probable causes for the poorer device performance of current metamorphic HBTs compared with lattice-matched HBTs     

Development of electromagnetic shielding materials from the conductive blends of polyaniline and polyaniline-clay nanocomposite-EVA: Preparation and properties

Electromagnetic interference shielding composite materials were developed from the conductive blends of nanostructured polyaniline (PANI) and polyaniline-clay nanocomposite (PANICN) with ethylene vinyl acetate (EVA) as host matrix. Electrically conducting nanostructured PANI and PANICNs were prepared using amphiphilic dopants, 3-pentadecyl phenol 4-sulphonic acid (3-PDPSA) derived from cashew nut shell liquid, a low cost renewable resource based product and dodecyl benzene sulfonic acid (DBSA). Effects of type and quantity of conductive fillers on the electrical conductivity, mechanical properties, thermal stability, morphology and electromagnetic shielding efficiency were investigated. The presence of exfoliated nanoclay and interaction between the conductive filler–host matrix in conductive films containing PANICNs manifested from the measurement on rheological property. Films with conductive filler (～15% loading) showed a shielding effectiveness of ～40–80 dB at 8 GHz which makes these conducting composites potential candidate for the encapsulation as EMI shielding materials for electronic devices.     

Thermal Degradation Studies of Polythiophenes Containing Hetero Aromatic Side Chains

Thiophene monomer structures containing different hetero aromatic rings (containing five-member/six-member, varying electronegativity, functional groups) were designed and synthesized. The influence of structural components of the side chain on the thermal stability of the polymers of the above monomers was analyzed using thermogravimetric analysis. The results show that thiophene-containing hetero aromatic side chains linked through six-member ring show high thermal stability.