Rahul Sharma

Electroless Ni‐P Based Nanocoating Technology—A Review

An advancement of electroless, (EL) Ni‐P based coatings from micro to nano level is being discussed in this present review. This paper provides a coherent understanding of the EL coatings in terms of systems, bath composition for metal/alloy and composite coatings. The elements of the EL composite bath have been discussed. The studies on the second phase nanosized particles dispersed in the Ni‐P matrix have been illustrated. The bonding mechanisms of EL coatings with the substrates have been discussed. The morphology, physical and mechanical properties of the Ni‐P‐X (X the second phase particles added into EL Ni‐P matrix) composite coatings have discussed. A few applications have also been outlined that may reveal the capabilities of the EL Ni‐P based nanocomposite coating technology to the relevant industries with the emphasis on tribological, corrosion, and magnetic behavior.

Development of Radar Absorbing Nano Crystals under Thermal Irradiation

Single phase W-type barium hexaferrite nano crystals of radar absorbing material (RAM) i.e., BaMe2Fe16O27 (Me2+=Fe2+) were synthesized by a modified flux method that combines the controlled chemical co-precipitation process for nucleation and complete uniform growth during in-situ annealing with NaCl flux under vacuum furnace. Uniform structure morphological transformation of nano crystals from spherical to prism faces were noticed after annealing with increasing temperatures from 200 to 1200 oC for 4 h in vacuum. XRD results showed the single phase nanocrystals of BaFe18O27 with increasing crystallanity and size from 10 to 90 nm during annealing. FESEM and TEM were used to investigate the systematic growth processes of various morphologies of nano crystals. The effect of such systematic morphological transformation of nanocrystals was observed in dielectric, dynamic magnetic and refection loss (RL) properties in Kuband (12.4 -18.0 GHz). A significant increment from -15.23 dB to -43.65 dB with wide range of bandwidth in RL loss is noticed due to the symmetric morphological growth of single phase nano crystals of RAM during annealing. This process of crystal growth, morphology evolution and RL enhancement with respect to increasing temperature were also explained in terms of ostwald ripening and quantum size effect.

A Comparative Study on Process-Properties Correlation of Nano Radar Absorbing Heat Treated Materials

Single phase M-type barium hexaferrite nano radar absorbing material (NRAM) i.e., BaFe12O19 were synthesized by modified flux method that combines the controlled chemical co-precipitation process for nucleation and complete uniform growth during annealing with NaCl flux under microwave annealing (MWA) and vacuum annealing (VA). Uniform morphological transformation of nano crystals from spherical (~ 10 nm) to prism faces (~ 35 nm) were observed under TEM during annealing. The effect of such systematic nano morphological transformation of NRAM was observed on magnetic and reflection loss (RL) properties. Maximum reflection loss (RL) was improved to 37.15 dB at 16.00 GHz for MWA at 760 watt and 27.56 dB at 15.75 GHz for VA at 1200 oC with continuous increasing absorption range under −10 dB for 2 mm thick coating layer in the Ku Band (12.4-18.0 GHz).. Excellent microwave absorption properties are a consequence of accurate EM match in the nano morphological planes, a strong natural resonance, as well as multipolarization. This process of crystal growth, morphology evolution and RL enhancement with respect to the heat treatments were also explained in terms of Ostwald ripening and quantum size effect.

Electroless Ni‐P Nano Coating Technology

This study ascribes advancement of electroless Ni‐P coatings of nano level by controlling the process by controlling bath composition for the coating of metal/alloy or nanocomposite. Effect of Ni‐P coating on different substrates with parameters like coating thickness, deposition rate, Ni‐P globule size, etc. have been extensively analyzed by using different characterizations techniques. Various second phase nanosized particles (ZrO2‐Al2O3‐Al3Zr, hexaferrites, ferrites, ZnO, Al2O3‐TiO2, etc.) dispersed in the Ni‐P matrix have been illustrated. A few applications have also been outlined, which may reveal the capabilities of the EL Ni‐P based nanocomposite coatings for relevant industrial applications with emphasis on tribological, corrosion, magnetic properties, etc.

Development of Electroless Ni-P/NRAM Nanocomposite Powder with Enhanced Microwave Absorption Properties

Nano radar absorbing material (NRAM) i.e. BaMe2Fe16O27 (Me2+=Fe2+) powder (10 nm) is coated with amorphous Ni-P nano layer (5-10 nm) by using electroless (EL) technology to develop EL Ni-P/NRAM nanocomposite powder. The experimental processes parameters and EL Ni-P bath composition were optimized to obtain the deposition. As-deposited nanocomposite powder was microwave annealed (MWA) with increasing radiation power from 160 to 760 watts for 5 minutes. The surface morphology, elemental contents, phase transformation and magnetic properties of NRAM powders were examined under field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) respectively. Maximum reflection loss (RL) 33.75 dB at 15.80 GHz for nanocomposite powder MWA at 760 watt was obtained the absorption range under −15 dB is from 13.76 to 16.77 GHz with 2 mm thickness layer in Ku Band. Excellent microwave absorption properties due to accurate electromagnetic (EM) match in the nanocomposite microstructure, a strong natural resonance and multipolarization. Such (Ni+ Ni3P)/NRAM nanocomposite powders may be attractive candidates for EM absorption.