Thermal shock characteristics of plasma sprayed mullite coatings

Commercially available mullite (3Al(2)O(3). 2SiO(2)) powders containing oxides of calcium and iron as impurities, have been made suitable for plasma spraying by using an organic binder. Stainless steel substrates covered with Ni-22Cr-10Al-1.0Y bond coat were spray coated with mullite, The 425 mu m thick coatings were subjected to thermal shock cycling under burner rig conditions between 1000 and 1200 degrees C and less than 200 degrees C with holding times of 1, 5, and 30 min. While the coatings withstood as high as 1000 shock cycles without failure between 1000 and 200 degrees C, spallation occurred early at 120 cycles when shocked from 1200 degrees C, The coatings appeared to go through a process of self erosion at high temperatures resulting in loss of material. Also observed were changes attributable to melting of the silicate grains, which smooth down the surface. Oxidation of the bond coat did not appear to influence the failure, These observations were supported by detailed scanning electron microscopy and quantitative chemical composition analysis, differential thermal analysis, and surface roughness measurements.

Chicken prealbumin: Nature of its heterogeneity and binding of plasma retinol-binding protein and thyroid hormones

The heterogeneity of chicken prealbumin (PA) has been shown to be due to the occurrence of three different plasma proteins (PA1 PA2 and PA3). Equilibrium dialysis studies revealed that the thyroid hormones bind specifically to PA2. These hormones bind at the same site on PA2. Circular dichroism studies failed to reveal conformational changes on interaction of retinol-binding protein and thyroid hormone with PA2. Both retinol-binding protein and thyroid hormone are independently transported by PA2.

Homeostatic regulation of free retinol-binding protein and free thyroxine pools of plasma by their plasma carrier proteins in chicken

The mechanism underlying homeostatic regulation of the plasma levels of free retinol-binding protein and free thyroxine, the systemic distribution of which is of great importance, has been investigated. A simple method has been developed to determine the rate of dissociation of a ligand from the binding protein. Analysis of the dissociation process of retinol-binding protein from prealbumin-2 reveals that the free retinol-binding protein pool undergoes massive flux, and the prealbumin-2 participates in homeostatic regulation of the free retinol-binding protein pool. Studies on the dissociation process of thyroxine from its plasma carrier proteins show that the various plasma carrier proteins share two roles. Of the two types of protein, the thyroxine-binding globulin (the high affinity binding protein) contributes only 27% of the free thyroxine in a rapid transition process, despite its being the major binding protein. But prealbumin-2, which has lower affinity towards thyroxine, participates mainly in a rapid flux of the free thyroxine pool. Thus thyroxine-binding globulin acts predominantly as a plasma reservoir of thyroxine, and also probably in the �buffering� action on plasma free thyroxine level, in the long term, while prealbumin-2 participates mainly in the maintainance of constancy of free thyroxine levels even in the short term. The existence of these two types of binding protein facilitates compensation for the metabolic flux of the free ligand and maintenance of the thyroxine pool within a very narrow range.

A simple method for the preparation of plasma-sprayable powders based on ZrO2

Plasma-sprayable powders of calcia, magnesia and yttria-stabilized zirconia have been prepared by using polyvinyl alcohol binders. The powders have been characterized for sprayability by spray coating on steer plates previously coated with an NiAl bond coat. The suitability of these coatings for thermal barrier applications have been examined. Thermal barrier and related properties, along with phase stability and mechanical properties, have been found to be good. Failure of the thermal barrier coating has been observed to occur at the interface between the bond coat and the substrate, due to the formation of a pile-up layer consisting of Fe-Zr-Al-O compound.

Experimental study and optimization of Plasma Actuators for Flow control in subsonic regime

Experimental study and optimization of Plasma Ac- tuators for Flow control in subsonic regime PRADEEP MOISE, JOSEPH MATHEW, KARTIK VENKATRAMAN, JOY THOMAS, Indian Institute of Science, FLOW CONTROL TEAM | The induced jet produced by a dielectric barrier discharge (DBD) setup is capable of preventing °ow separation on airfoils at high angles of attack. The ef-fect of various parameters on the velocity of this induced jet was studied experimentally. The glow discharge was created at atmospheric con-ditions by using a high voltage RF power supply. Flow visualization,photographic studies of the plasma, and hot-wire measurements on the induced jet were performed. The parametric investigation of the charac- teristics of the plasma show that the width of the plasma in the uniform glow discharge regime was an indication of the velocity induced. It was observed that the spanwise and streamwise overlap of the two electrodes,dielectric thickness, voltage and frequency of the applied voltage are the major parameters that govern the velocity and the extent of plasma.e®ect of the optimized con¯guration on the performance characteristics of an airfoil was studied experimentally.

Wear behavior of plasma electrolytic oxidation (PEO) and hybrid coatings of PEO and laser on MRI 230D magnesium alloy

Wear resistant coatings were produced on a permanent mould cast MRI 230D Mg alloy by (a) PEO in silicate based electrolyte, (b) PEO in phosphate based electrolyte, (c) hybrid coatings of silicate PEO followed by laser surface alloying (LSA) with Al and Al(2)O(3), and (d) hybrid coatings of phosphate PEO followed by LSA with Al and Al(2)O(3). Microstructural characterization of the coatings was carried out by scanning electron microscopy (SEM) and X(ray diffraction. The tribological behavior of the coatings was investigated under dry sliding condition using linearly reciprocating ball-on-flat wear test. Both the PEO coatings exhibited a friction coefficient of about 0.8 and hybrid coatings exhibited a value of about 0.5 against the AISI 52100 steel ball as the friction partner, which were slightly reduced with the increase in applied load. The PEO coatings sustained the test without failure at 2 N load but failed at 5 N load due to micro-fracture caused by high contact stresses. The hybrid coatings did not get completely worn off at 2 N load but were completely removed exposing the substrate at 5 N load. The PEO coatings exhibited better wear resistance than the hybrid coatings and silicate PEO coatings exhibited better wear resistance than the phosphate PEO coatings. Both the PEO coatings melted/decomposed on laser irradiation and all the hybrid coatings exhibited similar microstructure and wear behavior irrespective of the nature of the primary PEO coating or laser energies. SEM examination of worn surfaces indicated abrasive wear combined with adhesive wear for all the specimens. The surface of the ball exhibited a discontinuous transfer layer after the wear test. (C) 2011 Elsevier B.V. All rights reserved.

A Laboratory Analysis of Plasma Based Hybrid Techniques for Treating Engine Exhaust

A detailed study on the removal of pollutants (NOx, aldehydes and CO) from the exhaust of a stationary diesel engine is carried out using barrier discharge hybrid plasma techniques. The objective of the study is to make a comparative analysis. For this purpose, the exhaust treatment was carried out in two stages. In the first stage, the exhaust was treated with plasma process and plasma-adsorbent hybrid process. The effectiveness of the two processes with regard to NOx removal and by-product reduction was discussed. In the second stage, the exhaust was treated by plasma and plasma-catalyst hybrid process. The effectiveness of the two processes with regard to pollutants (NOx, CO) removal and by-product reduction was analyzed. Finally, a comprehensive comparison of different techniques has been made and feasible plasma based hybrid techniques for stationary and non-stationary engine exhaust treatments were proposed.

Sliding wear behavior of plasma nitrided Austenitic Stainless Steel Type AISI 316LN in the temperature range from 25 to 400 degrees C at 10(-4) bar

There is a research knowledge gap for the dry wear data of nitride treated Stainless Steel in high temperature and high vacuum environment. In order to fill this gap, plasma nitriding was done on austenitic Stainless Steel type AISI 316LN (316LN SS) and dry sliding wear tests have been conducted at 25 degrees C, 200 degrees C and 400 degrees C in high vacuum of 1.6 x 10(-4) bar. The two different slider material (316LN SS and Colmonoy) and two different sliding speeds (0.0576 m/s and 0.167 m/s) have been used. The tribological parameters such as friction coefficient, wear mechanism and volume of metal loss have been evaluated. Scanning Electron Microscopy (SEM) was used to study the surface morphology of the worn pins and rings. Electronic balancing machine was used to record the mass of metal loss during wear tests. The 2D optical profilometer was used to measure the depth of the wear track. The Plasma Nitride treated 316LN SS rings (PN rings) exhibit excellent wear resistance against 316LN SS pin and Colmonoy pin at all temperatures. However, PN ring vs. Colmonoy pin Pair shows better wear resistance than PN ring vs. 316LN SS pin Pair at higher temperature. (C) 2012 Elsevier B.V. All rights reserved.

Microstructure and dry sliding wear resistance evaluation of plasma nitrided austenitic stainless steel type AISI 316LN against different sliders

In this work, Plasma Nitriding was carried out at a temperature of 570 degrees C on nuclear grade austenitic stainless steel type AISI 316 LN (316LN SS) in a gas mixture of 20% N-2-80% H-2 to improve the surface hardness and thereby sliding wear resistance. The Plasma Nitride (PN) treated surface has been characterized by Vickers microhardness measurements, Scanning Electron Microscopic (SEM) examination, X-ray Diffraction (XRD) and sliding wear assessment. The average thickness of the PN layer was found to be 70 mu m. Microhardness measurements showed a significant increase in the hardness from 210 HV25g (unnitrided sample) to 1040 HV25g (Plasma Nitrided sample). The XRD reveals that PN layer consists of CrN, Fe4N and Fe3N phases along with austenite phase. The tribological parameters such as the friction coefficient and wear mechanism have been evaluated at ambient conditions for PN treated ring (PN ring) vs. ASTM A453 grade 660 pin (ASTM pin), PN ring vs. Nickel based alloy hard faced pin (Colmonoy pin), PN ring vs. 316LN SS pin and 316LN SS ring vs. 316LN SS pin. The wear tracks have been analyzed by SEM, Energy Dispersive X-ray Analysis (EDX) and Optical Profilometry. The untreated 316LN SS ring vs. 316LN SS pin produced severe wear and was characterized by a combination of delamination and adhesion wear mechanism, whereas wear mechanism of the PN rings reveals mild abrasion and a transfer layer from pin materials. (C) 2012 Elsevier B.V. All rights reserved.

Effect of electrical parameters on morphology and in-vitro corrosion resistance of plasma electrolytic oxidized films formed on zirconium

The objective of the present work is to study the effect of electrical process Parameters (duty cycle and frequency) on morphological, structural, and in-vitro corrosion characteristics of oxide films formed on zirconium by plasma electrolytic oxidation in an electrolyte system consisting of 5 g/L of trisodium orthophosphate. The oxide films fabricated on zirconium by systematically varying the duty cycle and frequency are characterized for its phase composition, surface morphology, chemical composition, roughness, wettability, surface energy, scratch resistance, corrosion resistance, apatite forming ability and osteoblast cell adhesion. X-ray diffraction pattern of all the oxide films showed the predominance of m-ZrO2 phase. Dense and uniform films with thickness varying from 9 to 15 mu m and roughness in the range of 0.62 to 1.03 mu m are formed. Porosity of oxide films is found to be increased with an increase infrequency. The water contact angle results demonstrated that the oxide films exhibited similar hydrophilicity to zirconium substrate. All oxide films showed improved corrosion resistance, as indicated by far lower corrosion current density and passive corrosion potential compared to the zirconium substrate in simulated body fluid environment, and among the four different combinations of duty cycle and frequency employed in the present study, the oxide film formed at 95% duty cycle and 50 Hz frequency (HDLF film) showed superior pitting corrosion resistance, which can be attributed to its pore free morpholOgy. Scratch test results showed that the HDLF oxide film adhered firmly to the substrate by developing a notable scratch resistance at 19.5 +/- 1.2.N. Besides the best corrosion resistance and scratch retistance, the HDLF film also showed good apatite forming ability and osteo sarcoma cell adhesion on its surface. The HDLF oxide film on zirconium with superior surface characteristics is believed to be useful for various types of implants in the dental and orthopedic fields. (C) 2015 Elsevier B.V. All rights reserved.

Effect of current density on the microstructure and corrosion properties of plasma electrolytic oxidation (PEO) coatings on AM50 Mg alloy produced in an electrolyte containing clay additives

Plasma electrolytic oxidation coatings were produced on AM50 Mg alloy in alkaline phosphate based electrolyte with montmorillonite clay additives employing current densities of 30, 60, and 120 mA/cm(2). The effect of current density on the microstructure and corrosion properties of the coating was investigated. The clay additives got melted and reactively incorporated into the coating forming an amorphous phase, at all the current densities. However, the coating was predominantly amorphous only at 30 mA/cm(2) and with increasing current density, increasing fractions of crystalline phases were formed. Higher current densities resulted in increased thickness of the coating, but reduced the compactness of the coatings. Electrochemical impedance spectroscopy tests in 0.5 wt.% (0.08 M) and 3.5 wt.% (0.6 M) NaCl solution revealed that the coatings processed at 30 mA/cm(2) exhibited a relatively better initial corrosion resistance owing to its relatively defect-free barrier layer and compactness of the coating. However, the presence of amorphous phases in significant amounts and lack of MgO in the coating resulted in increased rate of dissolution of the coatings and degradation of corrosion resistance. Coatings produced at higher current densities exhibited initial inferior corrosion resistance due to a more defective barrier layer and increased porosity in pore band and outer porous layer. However, the increased amount of crystalline phases and an increased amount of MgO, which resisted dissolution, counterbalanced the negative effects of defective barrier and increased porosity resulting in a relatively lower rate of the degradation of the corrosion resistance. Thus, the corrosion resistance of all the coatings continuously decreased with time and became similar after prolonged immersion in NaCl solution. Increasing current density, therefore, did not prove to be beneficial for the improvement of the corrosion performance of the PEO coatings. (C) 2016 Elsevier B.V. All rights reserved.

Response And Stability Of A Stochastic Beam-Column Using Stochastic Fem

A beam-column resting on continuous Winkler foundation and discrete elastic supports is considered. The beam-column is of variable cross-section and the variation of sectional properties along the axis of the beam-column is deterministic. Young's modulus, mass per unit length and distributed axial loadings of the beam-column have a stochastic distribution. The foundation stiffness coefficient of the Winkler model, the stiffnesses of discrete elastic supports, stiffnesses of end springs and the end thrust, are all considered as random parameters. The material property fluctuations and distributed axial loadings are considered to constitute independent, one-dimension uni-variate homogeneous real stochastic fields in space. The foundation stiffness coefficient, stiffnesses of the discrete elastic supports, stiffnesses of end springs and the end thrust are considered to constitute independent random variables. Static response, free vibration and stability behaviour of the beam-column are studied. Hamilton's principle is used to formulate the problem using stochastic FEM. Sensitivity vectors of the response and stability parameters are evaluated. Using these statistics of free vibration frequencies, mode shapes, buckling parameters, etc., are evaluated. A numerical example is given.

Generation of hydrogen peroxide on oxidation of NADH by hepatic plasma membranes

The oxidation of NADH by mouse liver plasma membranes was shown to be accompanied by the formation of H2O2. The rate of H2O2 formation was less than one-tenth the rate of oxygen uptake and much slower than the rate of reduction of artificial electron acceptors. The optimum pH for this reaction was 7.0 and theK m value for NADH was found to be 3×10–6 M. The H2O2-generating system of plasma membranes was inhibited by quinacrine and azide, thus distinguishing it from similar activities in endoplasmic reticulum and mitochondria. Both NADH and NADPH served as substrates for plasma membrane H2O2 generation. Superoxide dismutase and adriamycin inhibited the reaction. Vanadate, known to stimulate the oxidation of NADH by plasma membranes, did not increase the formation of H2O2. In view of the growing evidence that H2O2 can be involved in metabolic control, the formation of H2O2 by a plasma membrane NAD(P)H oxidase system may be pertinent to control sites at the plasma membrane.

On the Purity of Atmospheric Glow-Discharge Plasma

Purity of the glow-discharge plasma at atmospheric pressure for surface modification applications is always debatable, since it works at ambient atmosphere. We have demonstrated on the use of optical emission spectroscopy to test the purity of this kind of plasma. The effect of gas flow pattern, nature of gas, and its flow rate on the plasma chemistry was studied. The importance of proper system design in maintaining a uniform flow of heavy and inert gases as carrier gas in atmospheric glow-discharge plasma was confirmed. The surface of a plasma-treated PET sample was analyzed using X-ray photoelectron spectroscopy to verify the studies on plasma purity done using emission spectrum.

Effect of ionic temperature on propagation of ion-acoustic solitary waves in a collisionless plasma of warm-ion fluid and non-isothermal electrons

Using a perturbation technique, we derive Modified Korteweg—de Vries (MKdV) equations for a mixture of warm-ion fluid (γ i = 3) and hot and non-isothermal electrons (γ e> 1), (i) when deviations from isothermality are finite, and (ii) when deviations from isothermality are small. We obtain stationary solutions for these equations, and compare them with the corresponding solutions for a mixture of warm-ion fluid (γ i = 3) and hot, isothermal electrons (γ i = 1).