K. Ashok

Bio: K. Ashok is an academic researcher from Vikram Sarabhai Space Centre. The author has contributed to research in topics: Dielectric & Ceramic. The author has an hindex of 10, co-authored 21 publications receiving 297 citations. Previous affiliations of K. Ashok include SRM University & Center for Advanced Materials.

Synthesis and properties of α‐Fe2O3 nanorods

Abstract: We report synthesis of α-Fe2O3 (hematite) nanorods by reverse micelles method using cetyltrimethyl ammonium bromide (CTAB) as surfactant and calcined at 300 °C. The calcined α-Fe2O3 nanorods were characterized by X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). The result showed that the α-Fe2O3 nanorods were hexagonal structure. The nanorods have diameter of 30-50 nm and length of 120-150 nm. The weak ferromagnetic behavior was observed with saturation magnetization = 0.6 emu/g, coercive force = 25 Oe and remanant magnetization = 0.03 emu/g. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Evaluation of corrosion and wear resistance titanium nitride (TiN) coated on mild steel (MS) with brush plated nickel interlayer

Abstract: Titanium nitride (TiN) coatings were deposited on mild steel (MS) by direct current reactive magnetron sputtering. With the aim of improving the corrosion resistance of TiN, an additional nickel interlayer was brush plated on the steel substrates before TiN film formation. The phases have been identified with X-ray diffraction analysis. The hardness values of TiN layers were found to increase with the increase in thickness of the Ni interlayer. The wear track investigations of TiN layers showed that the TiN/MS system was worn out by abrasive wear mechanism while on the film with Ni interlayer is by adhesive wear. It was found that the TiN/Ni/MS stack had a weaker tendency towards corrosion and higher corrosion resistance in 3·5%NaCl than the bare MS substrate, Ni/MS and TiN/MS specimen.

Thermal management of LEDs: Package to system

Abstract: Light emitting diodes, LEDs, historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs with white light and monochromatic colors have led to a movement towards general illumination. The increased electrical currents used to drive the LEDs have focused more attention on the thermal paths in the developments of LED power packaging. The luminous efficiency of LEDs is soon expected to reach over 80 lumens/W, this is approximately 6 times the efficiency of a conventional incandescent tungsten bulb. Thermal management for the solid-state lighting applications is a key design parameter for both package and system level. Package and system level thermal management is discussed in separate sections. Effect of chip packages on junction to board thermal resistance was compared for both SiC and Sapphire chips. The higher thermal conductivity of the SiC chip provided about 2 times better thermal performance than the latter, while the under-filled Sapphire chip package can only catch the SiC chip performance. Later, system level thermal management was studied based on established numerical models for a conceptual solid-state lighting system. A conceptual LED illumination system was chosen and CFD models were created to determine the availability and limitations of passive air-cooling.