Interface- and diffusion-limited capillary rise of reactive melts with a transient contact angle

The kinetics of unidirectional capillary penetration by a reactive fluid under the limiting cases of diffusion control and interface control has been derived for the reactive infiltration phenomenon characterized by a shrinking capillary radius due to interphase formation and an exponentially decaying contact angle. The computational outcomes for the reactive penetration of Si₃N₄ capillaries by AgCuTi brazes and of carbon capillaries by Si show that greater lengths are attained at lower values of the parabolic rate constant (under diffusion control), and the limiting length is reached earlier at larger values of the linear rate constant (under interface control). A capillary-driven flow analysis (Washburn equation) overestimates the infiltration kinetics, whereas an analysis that considers pore shrinkage but assumes the contact angle and the capillary pressure to be constant during flow underestimates the kinetics. The penetration lengths predicted by the analysis at pore closure due to reaction choking exhibit a slightly better agreement with the recent measurements in the Si/C system than the models of reactive flows currently in vogue.     

Correlations Among Signatures for Detection of Different Types of Fires

One way of overcoming the problem of false alarms encountered in a single parameter detection system due to non-fire stimulii is the simultaneous use of multiple signatures. Researchers have found significant benefits of multi-sensor detection in reducing false triggering. Appreciable interest has been expressed in using carbon monoxide (CO) or carbon dioxide (CO₂) gas sensors in combination with smoke sensors. The present study has been carried out to determine the correlation and inter-dependence between two different fire signatures like CO–OD (optical density), CO–CO₂, CO₂–OD. The signatures have been investigated using experimental measurements of a fire inside a closed compartment measuring 7 x 7 x 4.2 m. A range of fuels are used, and both smouldering and flaming combustion are examined. Attempts have been made to examine whether correlation coefficients between two signatures can form a basis of detection and be exploited as one of the components in multi- criteria fire detection algorithm. The CO/CO₂ ratio as a criterion for detector operation has also been examined and discussed in the light of existing literature and codal provisions.     

Dielectric and electro-optical study of ZnO nano rods doped ferroelectric liquid crystals

Addition of Nano rods results change in the dielectric and electro-optical properties of pure Ferroelectric Liquid Crystal (FLC) considerably. The present study is devoted to characterize the dielectric and electro-optical parameters of the FLC nano rods composite system. The size of nano rods is usually much bigger than that of FLC molecules, therefore, when they are doped in different concentrations, in pure FLC, their volume fraction plays considerable role in deciding the molecular dynamics of the resultant composite system. For the lesser concentrations, the nano rods offer mechanical strength to system geometry while at higher concentration of nano rods, they offer additional constraints on the system. In present report both of these aspects have been analyzed and explained.     

Microstructure and mechanical properties of friction stir welded oxide dispersion strengthened alloy

Effect of friction stir welding (FSW) on microstructure and mechanical properties of oxide dispersion strengthened alloy MA956 was investigated. Fine grained microstructure was developed in the processed region with slight particle coarsening. Tensile behavior of the processed material was compared with that of the as-received material at room temperature. Results indicated that significant grain refinement during FSW compensated for the reduced particle strengthening contribution and enhanced tensile strength by 145 MPa without loss in ductility. Further analysis indicated a good agreement between experimentally measured yield strength and the strength calculated by Pythagorean superimposition of strengthening contribution in FSWed material.     

Need of Alcohol Reference Materials and Reliable Measurement of Alcohol Content by Breath Alcohol Analyzer in India: An Overview

Breath alcohol analyser is used to detect alcohol content in end-expiratory breaths in order to enforce driving regulations under the influence of alcohol legislation. The accuracy and reliability of the routine measurements of alcohol content performed with breath alcohol analyser can be achieved by the calibration of the breath alcohol analyser using standards traceable to SI reference material. Proper calibration is essential for transparency in legal verification for which reference material is needed. At international level, a number of NMIs are active to address this important measurement issue of providing accurate measurements. Several international key comparison programs have been organized so far for the determination of ethanol content in aqueous and in nitrogen/air matrix. NIST, USA; BAM, Germany; IRMM, Belgium, Portugal, INMETRO, Brazil, LGC, UK etc. have developed certain reference materials of ethanol in water solution/air with different concentration ranges. However, no such reference material is introduced in India as an indigenous standard, rather, being procured from abroad or using high purity alcohol for calibration purposes. CSIR-NPL, India, being the NMI is now focusing on establishing the calibration facility and development of SI traceable aqueous alcohol standard to provide test reliability for the testing in breath alcohol analyser. This program has a societal impact which contributes to human health and regulatory needs for the nation.     

Optical and electrical properties of ZrSe3 single crystals grown by chemical vapour transport technique

Single crystals of the lamellar compound, ZrSe₃, were grown by chemical vapour transport technique using iodine as a transporting agent. The grown crystals were characterized with the help of energy dispersive analysis by X-ray (EDAX), which gave confirmation about the stoichiometry. The optical band gap measurement of as grown crystals was carried out with the help of optical absorption spectra in the range 700–1450 nm. The indirect as well as direct band gap of ZrSe₃ were found to be 1.1 eV and 1.47 eV, respectively. The resistivity of the as grown crystals was measured using van der Pauw method. The Hall parameters of the grown crystals were determined at room temperature from Hall effect measurements. Electrical resistivity measurements were performed on this crystal in the temperature range 303–423 K. The crystals were found to exhibit semiconducting nature in this range. The activation energy and anisotropy measurements were carried out for this crystal. Pressure dependence of electrical resistance was studied using Bridgman opposed anvils set up up to 8 GPa. The semiconducting nature of ZrSe₃ single crystal was inferred from the graph of resistance vs pressure. The results obtained are discussed in detail.     

Ion beam-assisted planarization of chemically vapor deposited diamond thin films using electron cyclotron resonance plasma

The high inherent surface roughness of as-deposited polycrystalline diamond films has made effective planarization processing of these films essential for most industrial applications. We have investigated the efficacy of ion beam sources for planarization in an electron cyclotron resonance plasma system using both direct substrate biasing and an accelerating grid system. Rough polycrystalline diamond films were synthesized using hot filament chemical vapor deposition. Both the etching rates and the resultant surface roughnesses were found to decrease as the angle of incidence (relative to the substrate surface normal) of the ion beam was increased. In the case of direct biasing of the sample, acicular features were observed following processing at higher incident angles. The use of double ion-extraction grids in conjunction with concomitant sample rotation was found to produce more uniform planarization of the diamond films. The rate of surface roughness reduction was found to be nonlinear and decreased with time. For both ion extraction methods investigated, the average film roughness (R_a) was significantly reduced from 0.2 to 0.05–0.06 μm.     

Thermo-mechanical model with adaptive boundary conditions for friction stir welding of Al 6061

Thermo-mechanical simulation of friction stir welding can predict the transient temperature field, active stresses developed, forces in all the three dimensions and may be extended to determine the residual stress. The thermal stresses constitute a major portion of the total stress developed during the process. Boundary conditions in the thermal modeling of process play a vital role in the final temperature profile. The heating and cooling rates with the peak temperature attained by the workpiece determine the thermal stress. Also, predicting realistic peak temperature becomes important as the operating temperature at the interface of tool-workpiece is very close to the solidus temperature of the aluminum workpiece.The convection heat-transfer coefficients of the surfaces exposed to air can be theoretically determined using Newton's law of cooling. Contact conductance depends on the pressure at the interface and has a non-uniform variation. The actual pressure distribution along the interface is dependent on the thermal stress from local temperature and non-linear stress–strain state. Therefore, applying an adaptive contact conductance can make the model more robust for process parameter variations.A finite element thermo-mechanical model with mechanical tool loading was developed considering a uniform value for contact conductance and used for predicting the stress at the workpiece and backplate interface. This pressure distribution contours are used for defining the non-uniform adaptive contact conductance used in the thermal model for predicting the thermal history in the workpiece. The thermo-mechanical model was then used in predict stress development in friction stir welding.