A. Madhan Kumar

A mechanically bendable superhydrophobic steel surface with self-cleaning and corrosion-resistant properties

We present an effective way to develop superhydrophobic steel surface which shows stable superhydrophobicity under harsh mechanical bending. The roughness on the steel surface was created by etching in acid solution and its surface energy was lowered by subsequent hydrophobic silane treatment. The steel etching time in sulfuric acid solution was optimized to 8 h which provides high surface roughness required for superhydrophobicity. A water contact angle of 164 ± 3° and a sliding angle of 9 ± 2° were obtained for the steel surface after surface chemical modification by methyltrichlorosilane. We bent this superhydrophobic steel to 90° and 180° and studied the wetting properties on the bent area, which showed absolutely no change in superhydrophobicity. This superhydrophobic steel surface showed excellent self-cleaning behaviour as well as maintained its superhydrophobic wetting properties under a stream of water jet. Further, the stability of the wetting state was evaluated using a sandpaper abrasion test, adhesive tape peeling test, and under prolonged UV irradiation. Energy-dispersive X-ray spectroscopy was used to confirm the surface chemical composition of the superhydrophobic steel surface. This approach can be applied to steel surfaces of any size and shape to advance their industrial applications.

Fabrication of nitrogen doped graphene oxide coatings: experimental and theoretical approach for surface protection

In this work, we present a simple strategy of fabricating an N-doped graphene oxide (N-GO) coating on stainless steel (SS) for protective applications. Electrochemical, surface analytical and quantum chemical techniques were employed to characterize the synthesized coatings on the SS surface. Graphene oxide (GO) and reduced graphene oxide (rGO) coatings on SS were adopted for comparison. The downshift of the G band in the Raman spectra of N-GO corroborated the incorporation of N atoms and the deconvoluted spectra of N1s revealed that N-GO coatings retain three types of nitrogen. The influence of N doping on the surface roughness and hydrophobicity of GO was investigated using surface topographic and contact angle measurements. An electrochemical corrosion study on the coatings indicated that N doping of GO enhances the corrosion resistance of SS in 3.5% NaCl solution more than GO and rGO. In order to describe the underlying mechanism, the adsorption energies of GO coatings with SS were computed using molecular dynamics simulation (MDS). The MDS results revealed that all the coating systems adsorbed in a parallel orientation on the Fe surface. N-GO coating exhibited the strongest and the most stable chemisorbed interaction on SS when compared to GO and rGO.

Sodium alginate: A promising biopolymer for corrosion protection of API X60 high strength carbon steel in saline medium

Sodium alginate (SA), a polysaccharide biopolymer, has been studied as an effective inhibitor against the corrosion of API X60 steel in neutral 3.5% NaCl using gravimetric and electrochemical techniques (OCP, EIS and EFM). The inhibition efficiency of the SA increased with concentration but was lower at higher temperature (70°C). Electrochemical measurements showed that the SA shifted the steel corrosion potential to more positive value and reduced the kinetics of corrosion by forming an adsorbed layer which mitigated the steel surface wetting, based on contact angle measurement. SEM-EDAX was used to confirm the inhibition of SA on API X60 steel surfaces. The SA adsorbs on the steel surface through a physisorption mechanism using its carboxylate oxygen according to UV-vis and ATR-IR measurements, respectively. This phenomena result in decreased localized pitting corrosion of the API X60 steel in 3.5% NaCl solution. Theoretical results using quantum chemical calculations and Monte Carlo simulations provide further atomic level insights into the interaction of SA with steel surface.

Biocompatible responsive polypyrrole/GO nanocomposite coatings for biomedical applications

Hybrid implant coating materials composed of at least two constituents of different chemistry, functionality, and biocompatibility have attracted attention in a wide range of biomedical applications. One-step electrosynthesis of polypyrrole (PPy)/graphene oxide (GO) nanocomposites on 316L SS implants was achieved by electropolymerization of pyrrole using different amounts of GO. Possible interaction between the PPy chain and GO nanosheet was examined by structural characterizations including UV-visible, X-ray diffraction, Raman, and X-ray photoelectron spectroscopy analyses. Morphological study by scanning electron microscopy and transmission electron microscopy confirmed dispersion of the GO nanosheets within the PPy matrix. Further, in vitro cell culture studies were carried out using MG-63 human osteoblast cells to estimate the biocompatibility of PPy/GO coatings. Noticeable improvements in surface protective and biocompatibility performance suggest possible application as a bioactive coating material on 316L SS implants for biomedical fields.

Electrochemical and in vitro bioactivity of polypyrrole/ceramic nanocomposite coatings on 316L SS bio-implants.

The present investigation describes the versatile fabrication and characterization of a novel composite coating that consists of polypyrrole (PPy) and Nb2O5 nanoparticles. Integration of the two materials is achieved by electrochemical deposition on 316L stainless steel (SS) from an aqueous solution of oxalic acid containing pyrrole and Nb2O5 nanoparticles. Fourier transform infrared spectral (FTIR) and X-ray diffraction (XRD) studies revealed that the existence of Nb2O5 nanoparticles in PPy matrix with hexagonal structure. Surface morphological analysis showed that the presence of Nb2O5 nanoparticles strongly influenced the surface nature of the nanocomposite coated 316L SS. Micro hardness results revealed the enhanced mechanical properties of PPy nanocomposite coated 316L SS due to the addition of Nb2O5 nanoparticles. The electrochemical studies were carried out using cyclic polarization and electrochemical impedance spectroscopy (EIS) measurements. In order to evaluate the biocompatibility, contact angle measurements and in vitro characterization were performed in simulated body fluid (SBF) and on MG63 osteoblast cells. The results showed that the nanocomposite coatings exhibit superior biocompatibility and enhanced corrosion protection performance over 316L SS than pure PPy coatings.

Promising bio-composites of polypyrrole and chitosan: Surface protective and in vitro biocompatibility performance on 316L SS implants

Advanced biomedical materials can potentially be developed from combinations of natural biodegradable polymers and synthetic polymers. We synthesized bioactive composites based on polypyrrole/chitosan through in-situ electrochemical polymerization in oxalic acid medium. Surface characterization results revealed the influence of chitosan inclusion on polypyrrole (PPy) surface morphology. Contact angle results confirmed the enhancement in surface hydrophilicity due to the addition of chitosan into the PPy matrix. Electrochemical corrosion studies revealed that the composite coatings showed enhanced protective performance compared to pure PPy. Further, we investigated the effect of the composite coatings on the growth of MG-63 human osteoblast cells to assess their biocompatibility. Monte Carlo simulations were engaged to assess the interactions between the metal surface and composite coatings. The composite containing equal parts PPy and chitosan was found to be biocompatible; together with the corrosion protection results, the findings indicated that this bioactive coating material has potential for use in 316L SS implants.

A promising nanocomposite from CNTs and nano-ceria: nanostructured fillers in polyurethane coatings for surface protection

The balanced combination of nanostructured carbon materials and metal oxide nanoparticles has been considered as an efficient reinforcement material in developing next-generation multifunctional coatings. Herein, we demonstrate a general approach to fabricate a CNT based nanocomposite with the inclusion of CeO2 nanoparticles that can be effectively implemented as a reinforcement material in surface protective coatings. The synthesized CNT/CeO2 nanocomposite was characterized by spectral and surface morphological analyses, which indicated that the CeO2 nanoparticles were successfully deposited onto the surface of the CNTs. The XRD pattern shows the semi-crystalline nature of the CNTs and the face centered cubic structure of the CeO2 nanoparticles. The prepared nanocomposite has subsequently been used as a nanofiller in polyurethane (PU) coatings for surface protection of steel substrates and a remarkable synergistic effect of nano-ceria and CNTs has been observed. The corrosion resistance of steel coated with a PU coating containing CNT/CeO2 was pointedly higher than with a pure PU coating and a PU coating with CNTs alone. This result suggests a new prospect for solving the corrosion issues encountered on steel structures in industrial applications by using multifunctional hybrid coatings with nanostructured reinforcements.

Chemically-derived CuO/In2O3-based nanocomposite for diode applications

Nowadays, oxide-based semiconducting nanostructures are widely regarded as one of the most essential elements of the modern semiconductor industry and for a number of advanced technological functions in electronics and optoelectronic platforms. In this regard, a CuO-based nanocomposite was synthesized through a facile surfactant-free wet chemical strategy, and its potential for photoelectronic applications has been demonstrated. The nature of the composite phase and its other structural characteristics were studied in detail using Raman and X-ray photoelectron spectroscopic tools. The particulate characteristics of the composite were inferred using transmission electron microscopic measurements. Room temperature luminescence measurements revealed that the optical activity of the composite spreads across the red and near-infrared region of the electromagnetic spectrum through corresponding transitions. The optoelectronic capabilities of the processed composite were investigated through fabricating a CuO composite/ZnO nanowire-based p–n heterostructure and studying its associated current–voltage (I–V) characteristics under photon illumination. The nature of charge carriers, flat band potential, charge transfer resistance and carrier density were also studied individually and collectively for each component comprising the heterostructure through Mott–Schottky and Nyquist type impedance plots.

Ultrasonic-assisted synthesis of ZnTe nanostructures and their structural, electrochemical and photoelectrical properties

Colloidal zinc telluride (ZnTe) nanostructures were successfully processed through a simple and facile ultrasonic (sonochemical) treatment for photoelectronic applications. The particle-like morphological features, phase and nature of valence state of various metal ions existing in ZnTe were examined using electron and X-ray photoelectron spectroscopic tools. Raman spectroscopic measurements revealed the dominance of exciton-phonon coupling and occurrence of TeO2 traces in ZnTe through the corresponding vibrations. Optical bandgap of the ZnTe suspension was estimated to be around 2.15eV, authenticating the direct allowed transitions. The p-type electrical conductivity and charge carrier density of ZnTe were additionally estimated from the Bode, Nyquist and Mott-Schottky type impedance plots. The photoelectrical properties of ZnTe were investigated by fabricating p-ZnTe/n-Si heterostructures and studying their corresponding current-voltage characteristics under dark and white light illumination. The diodes revealed excellent rectifying behaviour with significant increase in reverse current under illumination. The stability of the devices were also affirmed through the time-dependent photoresponse characteristics, which actually suggested the improved and effective separation of photo generated electron hole pairs across the integrated heterojunctions. The obtained results also augment the potential of sonochemically processed ZnTe for application in photo detection and sensor related functions.

Blue luminescence and Schottky diode applications of monoclinic HfO2 nanostructures

Schottky diodes based on metal–semiconductor (MS) and metal–insulator–semiconductor (MIS) configurations are nowadays widely regarded as key components for the realization of a number of improved electronic and optoelectronic functions. In this regard, hafnium dioxide (HfO2) nanostructures were processed through a facile chemical route for application in MIS Schottky diodes. Their monoclinic phase and micro-structural characteristics were studied in detail using the X-ray diffraction, Raman and electron microscopic measurements. The nanostructures were studied to evolve in form of particulate structures at an average scale of 8–10 nm. The low-temperature photoluminescence measurements revealed the optical activity of HfO2 to spread across the blue region of electromagnetic spectrum. And their origin has been related to the transitions taking place across the intermediary energy levels established by the oxygen related vacancies. The power of incident laser irradiation was also noted to have a significant influence on the surface-state related defect emissions. The electrical properties of HfO2 were studied using the Bode, Nyquist and Mott–Schottky type plots extracted from the impedance spectroscopic measurements. MIS Schottky diode architectures were finally fabricated using the HfO2 thin films that were spin cast on n-Si. A significant improvement in the diode characteristics were noted for the heat treated devices, suggesting the improved tunnelling and limiting of charge leakages across the integrated heterojunctions.