The synthesis of nanostructured NiCrAlY powders for plasma sprayed thermal barrier coatings

Thermal barrier coatings (TBCs) are used to protect hot sections of industrial gas turbine blades against high temperature corrosion and oxidation. They usually consist of a thermally insulating ceramic top layer (Yittria Stabilized Zirconia or YSZ) and an oxidation resistant metallic bond coat (MCrAlY) thermally sprayed onto the nickel-based superalloy substrate surfaces. Currently MCrAlY powders, up to 100µm in diameter are used in the production of thermal barrier coatings by the industrial gas turbine component manufacturers. It has been found that the nanocrystalline MCrAlY layer provide better oxidation behavior than the currently used microstructured MCrAlY layer at elevated temperatures. In this research work, nanocrystalline NiCrAlY powders were manufactured using a conventional Ni22Cr10Al1.0Y powder as the base material using a planetary ball mill device. The microstructural characterization of NiCrAlY powders before and after milling were explored using X-ray diffraction, scanning electron microscope equipped with energy dispersive spectrometer. The results indicated that the synthesized NiCrAlY powders mainly consists of two phases: ? (Ni,Cr-rich) and ?’ (Ni3Al) . Key words: MCrAlY powders, High temperature oxidation, Ball milling, Air-plasma sprayed coatings

Inhibiting sulphate attack on concrete by hydrophobic green plant extract

Organic base (Amine) and inorganic base (Nitrite) have been known for protection of concrete structures but are not commercially indigenous to most developing economies due to manufacturing difficulties and are toxic to the environment. Also inhibitors are not known to stop sulphate attack in concrete. Hence, the objective of the present investigation was to study a novel, eco-friendly and hydrophobic green plant extracts inhibitor and compares its effectiveness with established calcium nitrite and ethanolamine inhibitors. Bambusa Arundinacea (Green plant extracts), calcium nitrite and ethanolamine corrosion inhibitors were selected for the present investigation. Compressive strength of 100×100×100mm concrete cubes after 7, 28 and 90 days of curing test was used. The results of the inhibitors studied showed that Bambusa Arundinacea has superior compressive strength compared to calcium nitrite and ethanolamine. Bambusa Arundinacea may be considered a better substitute for nitrite and amine- based corrosion inhibiting admixtures for durable concrete structures due its pore blocking effects

Nd:YAG laser welding of stainless steel 304 for photonics device packaging

Although pulsed Nd:YAG laser welding has been widely used in microelectronics and photonics packaging industry, a full understanding of various phenomena involved is still a matter of trials and speculations. In this research, an ultra compact pulsed Nd:YAG laser with wavelength of 1.064 µm has been used to produce a spot weld on stainless steel 304. The principal objective of this research is to examine the effects of laser welding parameters such as laser beam peak powers, pulse durations, incident angles, focus point positions and number of shots on the weld dimensions: penetration depth and bead width. The ratio of the penetration depth to the bead width is considered as one of the most critical parameters to determine the weld quality. It is found that the penetration depth and bead width increase when the laser beam peak power, pulse duration and number of shot increase. In contrast, the penetration depth decreases when the laser beam defocus position and incident angle increase. This is due to the reduction of the laser beam intensity causing by the widening of the laser spot size. These experimental results provide a reference on an optimal laser welding operations for a reliable photonics device packaging. The results obtained shows that stainless steel 304 is suitable to be used as a base material for photonics device packaging employing Nd:YAG laser welding technique

Electroforming a process for macro/nano-manufacturing

This paper describes the application of electroforming in the synthesis of nanocrystalline nickel by very high speed movement of the electrolyte; the principles and mechanisms of electroforming in the production of nanocrystalline structured metallic objects in combination with high speed movement of electrolyte are also described. Nanocrystalline nickel components were formed at a speed exceeding 600 µm per hour; the grain size of the electrodeposited nickel was considerably reduced by high speed movement of the plating solution. When requirements specify high-tolerances, complexity, lightweight and miniature geometry, electroforming is a serious contender and in certain cases may be the only economically viable manufacturing process. AFM characterisation showed that the crystalline/particle sizes of the electroformed objects were less than 30 nm. The nickel deposits were characterised further using SEM/EDAX. The focus of this study is primarily in the application of nanomaterials in industrial gas turbines

Corrosion inhibitors for steel reinforcement in concrete: a review

Inhibitors are added to concrete to improve its quality and integrity. In recent years the use of these inhibitors in producing high performance concrete has increased significantly as a result of aggressive environment. This report is based on the corrosion inhibitors used in concrete and also on the published literatures. Most authors agreed that reinforcement corrosion is the most important causes of premature failure of reinforced concrete structure worldwide and generate a great research concern due to its effects on global economy. The report presents information related to basic mechanism of corrosion protection methods to extend the service life of reinforced concrete structures which include inhibitors, sealers and barriers. Environmental sustainability issues concerning the present inhibitors being used were examined, viability and versatility of green inhibitors to concrete was also x-rayed

Nano-sized agglomerated Ni particles synthesized by a phase transformation method

Nano-sized nickel particles have been prepared by using a 'phase transformation' method. Nickel chloride was used as a precursor, hydrazine as a reducing agent in the presence of an anionic surfactant sodium-dodecyl-sulphate (SDS) and PVP (polyvinylpyrrolidone – a cationic polymer) in a strong basic medium. Initially the effect of SDS and SDS-PVP on the particle size formation was studied, then hydrazine only and then followed by the effect of adding SDS to the solution. SEM characterisation showed that in the absence of SDS-PVP the Ni particles were almost spherical but when SDS and SDS-PVP were present the particles showed very spiky morphology. Much finer particles were produced when SDS was used on its own. However, the combination of SDS-PVP had produced the finest particles in our research work. Froth contained Ni particles; TEM characterisation showed these Ni particles were much finer than the particles collected from the precipitated particles

The role of formation of continues thermally grown oxide layer on the nanostructured NiCrAlY bond coat during thermal exposure in air

In recent years, the life expectancy of thermal barrier coatings is expected to be improved by applying the nanostructured NiCrAlY bond coat. The present paper reviews the main technique used in the synthesis of nano-crystalline NiCrAlY powders using a planetary ball mill and investigates the microstructural evolution of thermally grown oxide (TGO) layer on the conventional and nanostructured atmospheric plasma sprayed (APS) NiCrAlY coatings in thermal barrier coating (TBC) systems during oxidation. Microstructural characterization showed that the growth of Ni(Cr,Al) 2O 4 (as spinel) and NiO on the surface of Al 2O 3 layer (as pure TGO) in nano TBC system was much lower compared to that of normal TBC system during thermal exposure at 1150 °C. These two oxides play a detrimental role in causing crack nucleation and growth, reducing the life of the TBC in air. This microstructure optimization of TGO layer is primarily associated with the formation of a continuous, dense, uniform Al 2O 3 layer (at first 24 h of isothermal oxidation at 1000 °C) over the nanostructured NiCrAlY coating

Synthesis of nano-sized nickel particles by a bottom-up approach in the presence of an anionic surfactant and a non-ionic polymer

Nano-sized nickel particles have been synthesized by a bottom-up approach, using hydrazine as the reducing agent in the presence of an anionic surfactant - sodium-dodecyl sulphate (SDS). The effect of adding a nonionic polymer -polyvinyl pyrrolidone (PVP) with an anionic surfactant has been studied at two different temperatures; the rate of reduction increased as the reaction temperature was increased from 60 to 100°C. These nano-aggregated nickel particles were characterized by using SEM with EDX facilities and TEM. TEM characterization showed the presence of spherical Ni particles as fine as 10nm in diameter. However, the SEM images showed a very spiky morphology, very small spherical shaped objects were clearly observed within these spiky structures. The combination of SDS/PVP reaction produced nano-sized nickel particles which were much finer than the reactions where SDS was used on its own. PVP has shown some dispersion power, and was found to be capable of preventing nickel particles from gradual agglomeration

Inhibition of corrosion of mild steel in hydrochloric acid by bambusa arundinacea

The inhibitive property of green plant inhibitor (Bambusa Arundinacea) on the corrosion of mild steel strip in 1M HCl were studied using weight loss technique. Inhibition efficiency of 72.84% at 10% v/v of extract concentration for 72 hours exposed time for Bambusa arundinacea was achieved. Adsorption of the inhibitor molecules on mild steel strip surfaces was consistent with Langmuir adsorption isotherm