Structural and magnetization studies on nanoparticles of Nd doped α-Fe2O3

It has been observed that, compared to bulk form, the nanocrystalline α-Fe₂O₃ is finding application in various areas. Magnetic properties of α-Fe₂O₃ are found to be influenced by the size of particles and are also sensitive to synthesis method employed for sample preparation. In the present work we have prepared a series of Nd doped α-Fe_2−xO₃ samples (x = 0.0–0.5) by combustion method, without using any fuel. The analysis of room temperature neutron diffraction patterns shows that all the compounds of the series form in the hematite (α-Fe₂O₃) structure, space group R−3c. Magnetization measurements show that there is a broad distribution of particle size in the samples. We find that the increase in the Nd content results in the dilution of magnetism of α-Fe₂O₃. From results we believe that inclusion of Nd in α-Fe₂O₃ drastically modifies the magnetic properties.     

Hydrogen rich gas production by the autothermal reforming of biodiesel (FAME) for utilization in the solid-oxide fuel cells: A thermodynamic analysis

The thermodynamics of the autothermal reforming (ATR) of biodiesel (FAME) for production of hydrogen is simulated and evaluated using Gibbs free minimization method. Simulations are performed with water-biodiesel molar feed ratios (WBFR) between 3 and 12, and oxygen-biodiesel molar feed ratio (O_XBFR) from 0 to 4.8 at reaction temperature between 300 and 800 °C at 1 atm. Yields of H₂ and CO are calculated as functions of WBFR, O_XBFR and temperature at 1 atm. Hydrogen rich gas can be produced by the ATR of biodiesel for utilization in solid-oxide fuel cells (SOFCs). The best operating conditions for the ATR reformer are WBFR≥9 and O_XBFR = 4.8 at 800 °C by optimization of the operating parameters. Yields of hydrogen and carbon monoxide are 68.80% and 91.66% with 54.14% and 39.2% selectivities respectively at the above conditions. The hydrogen yield from biodiesel is higher than from unmodified oils i.e., transesterification increases hydrogen yield. Increase in saturation of the esters, results in increase in methane selectivity, while an increase in unsaturation results in a decrease in methane selectivity. Increase in degree of both saturation and unsaturation of esters, increases coke selectivity. Similarly an increase in the linoleic content of esters, increases coke selectivity.     

Study on Precipitation Hardening of C 250 Grade Maraging Steel

The present work reports effect of different heat treatment processes on the microstructure and hardness of C 250 grade maraging steel. Different heat treatment processes have been carried out and the resultant microstructure and hardeness have been characterized. Various structural characterization techniques, such as, optical microscopy, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, etc. have been adopted and the microstructural features thus evaluated have been correlated with the mechanical property, viz. hardness. Presence of Ni₃(Ti,Mo) particles in lath martensitic matrix are revealed in solution treated and aged alloy. It is found that conventional maraging treatment consisting of solution treatment at 850 °C, followed by forced air cooling and finally ageing at 500 °C gives the best hardening response. Grain refinement techniques are not much effective for the improvement of hardness of maraging steel in the age hardened condition.     

Interactions between shrinkage reducing admixtures (SRA) and cement paste's pore solution

Shrinkage reducing admixtures (SRA) have been developed to combat shrinkage cracking in concrete elements. While SRA has been shown to have significant benefits in reducing the magnitude of drying and autogenous shrinkage, it has been reported that SRA may cause a negative side effect as it reduces the rate of cement hydration and strength development in concrete. To examine the influence of SRA on cement hydration, this study explores the interactions between SRA and cement paste's pore solution. It is described that SRA is mainly composed of amphiphilic (i.e., surfactant) molecules that when added to an aqueous solution, accumulate at the solution-air interface and can significantly reduce the interfacial tension. However, these surfactants can also self-aggregate in the bulk solution (i.e., micellation) and this may limit the surface tension reduction capacity of SRA. In synthetic pore solutions, SRA is observed to form an oil-water-surfactant emulsion that may or may not be stable. Specifically, at concentrations above a critical threshold, the mixture of SRA and pore fluid is unstable and can separate into two distinct phases (an SRA-rich phase and an SRA-dilute phase). Further, chemical analysis of extracted pore solutions shows that addition of SRA to the mixing water depresses the dissolution of alkalis in the pore fluid. This results in a pore fluid with lower alkalinity which causes a reduction in the rate of cement hydration. This may explain why concrete containing SRA shows a delayed setting and a slower strength development.     

Electroanalytical studies on cadmium(II) selective potentiometric sensors based on t-butyl thiacalix[4]arene and thiacalix[4]arene in poly(vinyl chloride)

Cd²⁺-selective sensors have been fabricated from poly(vinyl chloride) (PVC) matrix membranes containing t-butyl thiacalix[4]arene (I) and thiacalix[4]arene (II) as electroactive materials. The addition of sodium tetraphenylborate and the plasticizer 2-nitrophenyl octyl ether has been found to improve the performance of the sensors substantially. The membranes of various compositions of the two thiacalixarenes have been investigated and it was found that the best performance was obtained for the membrane of composition II:PVC:NaTPB:NPOE in the ratio 5:120:3:150. The sensor shows a linear potential response for Cd²⁺ over a wide activity range 3.2 × 10⁻⁶ to 1.0 × 10⁻¹ M with Nernstian compliance (29.5 mV decade⁻¹ of activity) in pH range 4.5-6.5 and a fast response time of ∼8 s. The potentiometric selectivity coefficient values determined by matched potential method indicate excellent selectivity for Cd²⁺ ions over mono-, di- and trivalent interfering cations. The sensor exhibits adequate shelf life (∼3 months) with good reproducibility (S.D. ±0.2 mV) and can also be used in partially non-aqueous media having up to 20% (v/v) methanol, ethanol or acetone content with no significant change in the value of slope or working activity range. The sensor has been used in the potentiometric titration of Cd²⁺ with EDTA. The sensor could be successfully used for the quantification of cadmium in river water samples.     

The kinetics of CNT transfer between immiscible blend phases during melt mixing

The complete transfer of multiwalled carbon nanotubes (MWCNTs) from a poly(styrene acrylonitrile) (SAN) precompound into an initially unfilled polycarbonate (PC) phase during 5 min of discontinuous melt mixing in a microcompounder has been observed recently. However, the typical time scale of the occurring transfer is presently still unknown. Morphological investigations within our study revealed that similar results can be obtained when the SAN-MWCNT-precompound is melt blended with neat PC by continuous twin-screw extrusion. Additionally, the kinetics of the CNT transfer was also investigated in a kneading chamber. We found that the CNT transfer rate turned out to be strongly coupled to the development of the interfacial area of the blend. Furthermore, we evaluated the interplay and significance of the possible and presently only insufficiently understood transfer mechanisms. We proposed for the first time a correlation between major processing and blend parameters and the probability of carbon nanotube transfer due to the development of a nanoscaled wetting angle.     

Efficient Implicit Finite-Element Hydrodynamic Model for Dam and Levee Breach

This technical paper presents the development and application of a pseudo-transient continuation (PTC)– inspired flow model for the simulation of dam and levee failure. The unstructured, implicit, Petrov-Galerkin finite-element model relies on computed residuals to automatically adjust the time-step size. The implicit time integration, together with the automatic time-step size selection through PTC, makes the model computationally efficient. The model is verified and applied to several analytic and real-world test cases that exercise model behavior and accuracy for several critical, transcritical, and subcritical flows. The result is an efficient and accurate prediction of both the speed and depth of shock waves as the dam-break flow passes over initially dry and wet land.