On the mechanics of the grinding process, Part II—thermal analysis of fine grinding

Thermal analysis of fine grinding is conducted taking into consideration the stochastic nature of the distribution of abrasive grains and its role under fine grinding (dry) conditions to determine the grinding temperatures and the heat partition at the contacting interface. The analysis considers the grain–workpiece interactions at the local level and the wheel–workpiece interactions at the global level. The workpiece temperature in the grinding zone is taken as the sum of the background temperature due to distributed action of all the previous active grains operating in the grinding zone (global thermal analysis) and the localized temperature spikes experienced at the current abrasive grain tip–workpiece interfaces (local thermal analysis), similar to the work reported in the literature. Since the Peclet number, N_Pe, in the case of fine grinding is very high (a few hundred), the heat flow between the work and the contacting abrasive grains can be considered to be nearly one-dimensional. In this paper, we consider the interaction between an abrasive grain and the workpiece at the contact interface. Consequently, the heat source relative to the grain is stationary and relative to the workpiece is fast moving. The interface heat source on the grain side as well as on the workpiece side is equivalent to an infinitely large plane heat source (with the same heat liberation intensity as the circular disc heat source). However, it will be shown in the paper that the contacting times are different. For example, the abrasive grain contacts the heat source, as it moves over the interface, for a longer period of time (˜milliseconds) whereas the workpiece contacts the heat source for a shorter period of time (˜a few microseconds). The equivalent thermal model developed in the present investigation is simple and represents the process more realistically, especially the heat partition. The analytical results reported here are found to be in good agreement with both the analytical and experimental results reported in the literature by other researchers.     

Investigation of 12-Tungstophosphoric Acid Supported on Ce0.5Zr0.5O2 Solid Solution

The nature of the Keggin ions of tungstophosphoric acid interacting with Ce_0.5Zr_0.5O₂ solid solution has been investigated. The vibrational study shows additional IR features at 1051 and 957 cm⁻¹ which are correlated to the primary Keggin anions interacting with Lewis sites involving Ce⁴⁺ and Zr⁴⁺ ions, and thus affecting the P–O and W=O_terminal bonds. The IR study indicates the formation of interfacial Ce⁴⁺–O–W and Zr⁴⁺–O–W bonds. The chemisorbed Keggin molecular layers on Ce_0.5Zr_0.5O₂ show activity towards conversion of acetophenone to styrene by Meerwein–Ponndorf–Verley reduction followed by dehydration. The activity is correlated with the relative intensities of IR peaks at 1051 and 957 cm⁻¹ of the perturbed Keggin molecular layers.     

Optimal cure cycles for the fabrication of thermosetting-matrix composites

Polymer-matrix composites using thermosetting resins as the matrix are increasingly finding use. However, a major impediment to their widespread commercial use is the high cost associated with their manufacture, arising from the long processing cycle times. This paper addresses the problem of determining cure temperature and pressure variations with time for a time-optimal manufacture of thermosetting-matrix composites subject to practical constraints. The optimal cure cycles are determined using the nonlinear programming scheme of sequential quadratic programming combined with a physical model base to simulate the process phenomena. The optimized cycles are shown to improve upon the manufacturer-recomended cycles as well as the improved cycles reported in the literature. The optimization results are reported for a wide range of resin materials, product specifications, and process constraints to illustrate their effects on the optimal cure cycles. Parametric studies are presented in terms of dimensionless groups to assess the combined effects of the product and process variables on the optimal cycles in a generalized manner.     

Swift heavy ion induced phase transition in CdTe films deposited by spray pyrolysis in presence of electric field

CdTe polycrystalline thin films possessing hexagonal phase regions are obtained by spray deposition in presence of a high electric field. Thin film samples are irradiated with 100 MeV Ag ions using Pelletron accelerator to study the swift heavy ion induced effects. The ion irradiation results in the transformation of the metastable hexagonal regions in the films to stable cubic phase due to the dense electronic excitations induced by beam irradiation. The phase transformation is seen from the X-ray diffraction patterns. The band gap of the CdTe film changes marginally due to ion irradiation induced phase transformation. The value changes from 1.47 eV for the as deposited sample to 1.44 eV for the sample irradiated at the fluence 1×10¹³ ions/cm². The AFM images show a gradual change in the shape of the particles from rod shape to nearly spherical ones after irradiation.     

Synthesis of Highly Substituted Imidazo[1,5‐a]quinoxalines Through a Multicomponent Reaction Followed by Deprotection–Cyclization

An operationally simple and efficient, one‐pot, two‐step methodology has been developed for the assembly of medicinally important imidazo[1,5‐a]quinoxalines. The protocol involves the multicomponent reaction of aryl aldehydes, ortho‐N‐Boc‐phenylenediamines and azidochalcones in the presence of erbium triflate as a Lewis acid catalyst, followed by deprotection–cyclization with 10% trifluoroacetic acid, furnishing the desired compounds in moderate to good yields. By virtue of their convergence, two aromatic rings and four new bonds are generated during the course of this reaction protocol. The structure of one of the compounds was proved by X‐ray crystallography.

     

Hydrogen-enriched non-premixed jet flames: Analysis of the flame surface,flame normal,flame index and Wobbe index

A non-premixed impinging jet flame is studied using three-dimensional direct numerical simulation with detailed chemical kinetics in order to investigate the influence of fuel variability on flame surface, flame normal, flame index and Wobbe index for hydrogen-enriched combustion. Analyses indicate that the fuel composition greatly influences the H₂/CO syngas combustion, not only on the important local stoichiometric iso-mixture fraction surface distribution but also on the vortical structures in the flow field. As a result of CO addition to hydrogen-rich combustion, changes of the reaction zone in the flammable layer, shift of peak flame surface density distribution, shift of non-premixed regions, formation of widely populated scalar dissipation distribution rate with respect to tangential strain and reduction of global heat release are all found to appear. In particular, the CO addition induces a micromixing process which appears to be an important factor for the modelling investigation of turbulence/chemistry interaction especially for combustion modelling of H₂-rich syngas fuels.     

Urchin and sheaf-like NiCo2O4 nanostructures: Synthesis and electrochemical energy storage application

Spinel NiCo₂O₄ in different morphologies is of current interest in the design and development of electrochemical supercapacitors. In this work, we synthesized two different morphologies of NiCo₂O₄ by facile hydrothermal method employing CTAB as a soft template and urea as hydrolysis controlling agent. This study has been undertaken to determine the effect of synthesis temperature on the morphology and pseudocapacitance behavior of the NiCo₂O₄. We find that the temperature variation in the synthesis procedure has a strong effect on the morphology of NiCo₂O₄, producing urchin-like morphology at 120 °C (NiCoO-120-cal) and sheaf-like morphology at 200 °C (NiCoO-200-cal) with hierarchical porous textures. The effect of morphology on the electrochemical pseudocapacitance behavior was studied by CV, CP and EIS techniques. Both NiCo₂O₄ samples show higher electrochemical performance than the parent NiO and Co₃O₄ synthesized under similar conditions. The maximum specific capacitance values obtained for NiCoO-120-cal and NiCoO-200-cal are 636 and 504 F g⁻¹ respectively, at a current density of 0.5 A g⁻¹. The capacitance retention of NiCoO-120-cal and NiCoO-200-cal samples, respectively, are 76% and 69% after 1000 charge–discharge cycles at a current density of 1 A g⁻¹.     

Infrared reflection absorption study of water interaction with H-terminated Si(100) surfaces

Water adsorption on clean and hydrogenated Si(100) surfaces was studied under ultra high vacuum conditions using surface infrared spectroscopy. The study shows that H-Si-Si-OH and SiH₂ species are formed on Si(100)-(2 × 1) and Si(100)-(2 × 1)-H surfaces, respectively. The reactivity behaviour of Si(100)-(3 × 1)-H and Si(100)-(1 × 1)-H is similar, both stabilizing oxygen inserted silicon dihydrides.     

Fluorescence properties of Ho3 doped fluorophosphate glasses

This paper reports the formation of a new series of Ho³⁺ -doped fluorophosphate optical glasses in the chemical formulae: 50 (NaPO₃)₆ + 18 BaF₂ + 10 ZnF₂ + 20 RF + 2 HoF₃ where RF = LiF, NaF, KF, (LiF-NaF), (NaF-KF) and (KF-LiF). The physical properties, absorption and photoluminescene spectra have been measured to understand the optical behaviours of these Ho³⁺ -glasses as a function of the alkali content changes in the host glass matrices.     

Polarization‐independent modulation for projection displays using small‐period LC polarization gratings

Abstract— Progress in the use of liquid‐crystal polarization grating (LCPG) to modulate unpolarized (and polarized) light with a grating period as small as 6.3 μm is reported. Similar to LCPGs formed at larger periods (11 μm) reported previously, polarization‐independent switching, predominantly three diffraction orders, maximum contrast ratios of ～100:1 for unpolarized broadband light, very low scattering, and diffraction efficiencies >98% continue to be observed. The smaller period led to an expected lower threshold voltage, even though the thickness was greater. Because the smaller grating period enables a brighter result from a Schlieren projection scheme for a microdisplay using the LCPG light valve, the inherent tradeoffs involved with both material and design parameters are discussed, and prospects for a polarization‐independent projection display are commented upon.