Dispersion and vaporization of biofuels and conventional fuels in a crossflow pre-mixer

In lean premixed pre-vaporized (LPP) combustion, controlled atomization, dispersion and vaporization of different types of liquid fuel in the premixer are the key factors required to stabilize the combustion process and improve the efficiency. The dispersion and vaporization process for biofuels and conventional fuels sprayed into a crossflow pre-mixer have been simulated and analyzed with respect to vaporization rate, degree of mixedness and homogeneity. Two major biofuels under investigation are Ethanol and Rapeseed Methyl Esters (RME), while conventional fuels are gasoline and jet-A. First, the numerical code is validated by comparing with the experimental data of single n-heptane and decane droplet evaporating under both moderate and high temperature convective air now. Next, the spray simulations were conducted with monodispersed droplets with an initial diameter of 80 mu m injected into a turbulent crossflow of air with a typical velocity of 10 m/s and temperature of around 800K. Vaporization time scales of different fuels are found to be very different. The droplet diameter reduction and surface temperature rise were found to be strongly dependent on the fuel properties. Gasoline droplet exhibited a much faster vaporization due a combination of higher vapor pressure and smaller latent heat of vaporization compared to other fuels. Mono-dispersed spray was adopted with the expectation of achieving more homogeneous fuel droplet size than poly-dispersed spray. However, the diameter histogram in the zone near the pre-mixer exit shows a large range of droplet diameter distributions for all the fuels. In order to improve the vaporization performance, fuels were pre-heated before injection. Results show that the Sauter mean diameter of ethanol improved from 52.8% of the initial injection size to 48.2%, while jet-A improved from 48.4% to 18.6% and RME improved from 63.5% to 31.3%. The diameter histogram showed improved vaporization performance of jet-A. (C) 2011 Elsevier Ltd. All rights reserved.

Reactive pulsed laser deposition and characterization of niobium nitride thin films

We present a systematic study to explore the effect of important process variables on the composition and structure of niobium nitride thin films synthesized by Reactive Pulsed Laser Deposition (RPLD) technique through ablation of high purity niobium target in the presence of low pressure nitrogen gas. Secondary Ion Mass Spectrometry has been used in a unique way to study and fix gas pressure, substrate temperature and laser fluence, in order to obtain optimized conditions for one variable in single experimental run. The x-ray diffraction and electron microscopic characterization have been complemented by proton elastic backscattering spectroscopy and x-ray photoelectron spectroscopy to understand the incorporation of oxygen and associated non-stoichiometry in the metal to nitrogen ratio. The present study demonstrates that RPLD can be used for obtaining thin film architectures using non-equilibrium processing. Finally the optimized NbN thin films were characterized for their hardness using nano-indentation technique and found to be similar to 30 GPa at the deposition pressure of 8 Pa. (C) 2011 Elsevier B.V. All rights reserved.

Investigation on the High Vacuum Tribological Characteristics of Surface Treated Nuclear Grade Stainless Steel Type AISI 316 LN at 25 to 500 degrees C

Although some researchers have published friction and wear data of Plasma Nitride (PN) coatings, the tribological behavior of PN/PN Pairs in high vacuum environment has not been published so far In order to bridge this knowledge gap, tribological tests under dry conditions have been conducted on PN/PN Pairs for varying temperatures of 25, 200, 400 and 500 degrees C in high vacuum (1.6 x 10(-4) bar) environment. The PN coatings showed good wear resistance layer on the ring surface. The PN coatings were removed only from the pin surface for all the tests since it contacts at a point. The friction and wear were low at lower temperatures and it eliminated adhesion between the contact surfaces until the coating was completely removed from the pin surface. (C) 2011 Journal of Mechanical Engineering. All rights reserved.

The influence of Zr layer thickness on contact deformation and fracture in a ZrN-Zr multilayer coating

In order to understand the influence of ductile metal interlayer on the overall deformation behavior of metal/nitride multilayer, different configurations of metal and nitride layers were deposited and tested under indentation loading. To provide insight into the trends in deformation with multilayer spacings, an FEM model with elastic-perfect plastic metal layers alternate with an elastic nitride on top of an elastic-plastic substrate. The strong strain mismatch between the metal and nitride layers significantly alters the stress field under contact loading leading to micro-cracking in the nitride, large tensile stresses immediately below the contact, and a transition from columnar sliding in thin metal films to a more uniform bending and microcracking in thicker coatings.

Hardness and Nitrogen Bonding Structure of A(x)Ti(1-x)N/CrN Multilayer Hard Coating

AlxTi1-xN/CrN multilayer coatings were fabricated by magnetron sputtering and those hardness variations were studied by observing the crack propagation and measuring the chemical bonding state of nitrides by Ti addition. While AlN/CrN multilayer shown stair-like crack propagation, AlxTi1-xN/CrN multilayer illustrated straight crack propagation. Most interestingly, Ti addition induced more broken nitrogen bonds in the nitride multilayers, leading to the reduction of hardness. However, the hardness of Al0.25Ti0.75N/CrN multilayer, having high Ti contents, increased by the formation of many Ti-N bond again instead of Al-N bond. From these results, we found that linear crack propagation behavior was dominated by broken nitrogen bonds in the AlxT1-xN/CrN multilayer coatings.

Electroless Ni-W-P Coating and Its Nano-WS2 Composite: Preparation and Properties

The ternary alloy Ni-W-P and its WS2 nanocomposite coatings were successfully obtained on low-carbon steel using the electroless plating technique. The sodium tungstate (Na2WO4) concentration in the bath was varied to obtain Ni-W-P deposits containing various Ni and P contents. WS2 composite was obtained with a suitable concentration of Na2WO4 in Ni-P coating. These deposits were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX) studies. The corrosion behavior was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies in 3.5 wt % NaCl solutions, and the corrosion rates of the coatings for Ni-P, Ni-W-P, and Ni-W-P-WS2 were found to be 2.571 x 10(-5), 8.219 x 10(-7), and 7.986 x 10(-7) g/h, respectively. An increase in the codeposition of alloying metal tungsten (W) enhanced the corrosion resistance and microhardness and changed the structure and morphology of the deposits. Incorporation of WS2 nanoparticles to Ni-W-P alloy coating reduced the coefficient of friction from 0.16 to 0.11 and also helped in improving the corrosion resistance of the coating further.

Dual functional performance of fiber Bragg gratings coated with metals using flash evaporation technique

Metallic and other type of coatings on fiber Bragg grating (FBG) sensors alter their sensitivity with thermal and mechanical stress while protecting the fragile optical fiber in harsh sensing surroundings. The behavior of the coated materials is unique in their response to thermal and mechanical stress depending on the thickness and the mode of coating. The thermal stress during the coating affects the temperature sensitivity of FBG sensors. We have explored the thermal response of FBGs coated with Al and Pb to an average thickness of 80 nm using flash evaporation technique where the FBG sensor is mounted in a region at room temperature in an evacuated chamber having a pressure of 10(6) Torr which will minimize any thermal stress during the coating process. The coating thickness is chosen in the nanometer region with the aim to study thermal behavior of nanocoatings and their effect on FBG sensitivity. The sensitivity of FBGs is evaluated from the wavelengths recorded using an optical sensing interrogator sm 130 (Micron Optics) from room temperature to 300 degrees C both during heating and cooling. It is observed that the sensitivity of the metal coated fibers is better than the reference FBG with no coating for the entire range of temperature. For a coating thickness of 80 nm, Al coated FBG is more sensitive than the one coated with Pb up to 170 degrees C and it reverses at higher temperatures. This point is identified as a reversible phase transition in Pb monolayers as the 2-dimensional aspects of the metal layers are dominant in the nanocoatings of Pb. On cooling, the phase transition reverses and the FBGs return to the original state and for repeated cycles of heating and cooling the same pattern is observed. Thus the FBG functions as a sensor of the phase transitions of the coatings also. (C) 2012 Elsevier Inc. All rights reserved.

Friction between a Steel Ball and a Steel Flat Lubricated by MoS2 Particles Suspended in Hexadecane at 150 degrees C

A steel ball was slid on a steel flat lubricated by molybdenum disulfide (MoS2) particles suspended in hexadecane oil at 150 degrees C. The friction data is compared with that obtained when the ball was slid on the flat sprayed apriori with nominally dry MoS2 particles. The friction in the dry experiment was found to increase with temperature while the friction in wet condition was found to decrease with increasing temperature. Micro-Raman and Fourier transform IR spectroscopy are used to explore the roles of environmental moisture and chemical degradation of oil on the formation of antifriction film on the steel substrate.

A new method for fracture toughness determination of graded (Pt,Ni)Al bond coats by microbeam bend tests

A novel method is proposed for fracture toughness determination of graded microstructurally complex (Pt,Ni)Al bond coats using edge-notched doubly clamped beams subjected to bending. Micron-scale beams are machined using the focused ion beam and loaded in bending under a nanoindenter. Failure loads gathered from the pop-ins in the load-displacement curves combined with XFEM analysis are used to calculate K-c at individual zones, free from substrate effects. The testing technique and sources of errors in measurement are described and possible micromechanisms of fracture in such heterogeneous coatings discussed.

Photocatalytic degradation of gaseous toluene by using immobilized titania/silica on aluminum sheets

The aim of this study was to prepare a highly active immobilized titania/silica photocatalyst and to test its performance in situ toward degradation of toluene as one of the major toxic indoor contaminants. In this work, two different titania layers immobilized on Al sheets were synthesized via low temperature sol-gel method employing presynthesized highly active titania powders (Degussa P25 and Millennium PC500, mass ratio 1:1): (a) with a silica/titania binder and a protective layer and (b) without the binder. The photocatalysts were characterized by X-ray diffraction, nitrogen sorption measurements, scanning electron microscopy (SEM), infrared spectroscopy, and UV-vis diffuse reflectance spectroscopy (DRS). The in situ photocatalytic degradation of gaseous toluene was selected as a probe reaction to test photocatalytic activity and to verify the potential application of these materials for air remediation. Results show that nontransparent highly photocatalytically active coatings based on the silica/titania binder and homogeneously dispersed TiO2 powders were obtained on the Al sheets. The crystalline structure of titania was not altered upon addition of the binder, which also prevented inhomogeneous agglomeration of particles on the photocatalyst surface. The photoactivity results indicate that the adsorption properties and photocatalytic activity of immobilized photocatalysts with the silica/titania binder and an underlying protective layer were very effective and additionally, they exhibited considerably improved adhesion and uniformity. We present a new highly photocatalytically active immobilized catalyst on a convenient metallic support, which has a potential application in an air cleaning device.

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.

Pressure induced structural phase transformation in TiN: a first-principles study

Titanium nitride (TiN), which is widely used for hard coatings, reportedly undergoes a pressure-induced structural phase transformation, from a NaCl to a CsCl structure, at similar to 7 GPa. In this paper, we use first-principles calculations based on density functional theory with a generalized gradient approximation of the exchange correlation energy to determine the structural stability of this transformation. Our results show that the stress required for this structural transformation is substantially lower (by more than an order of magnitude) when it is deviatoric in nature vis-a-vis that under hydrostatic pressure. Local stability of the structure is assessed with phonon dispersion determined at different pressures, and we find that CsCl structure of TiN is expected to distort after the transformation. From the electronic structure calculations, we estimate the electrical conductivity of TiN in the CsCl structure to be about 5 times of that in NaCl structure, which should be observable experimentally. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4798591]

Investigations on high enthalpy shock wave exposed graphitic carbon nanoparticles

The impact of high enthalpy shock wave on graphitic carbon nanoparticle (GCNP) films has been investigated and discussed in view of space and chemical engineering applications. The GCNP films were developed by using spray method and exposed to high enthalpy shock wave under an inert atmosphere. Upon shock wave treatment, two typical amendments such as weight loss in the deposited material and growth of second order nanostructures (SONS) have been observed. While increasing test gas pressure, the loss of material and density of SONs are gradually increased. Most of the shock wave induced SONS are highly crystalline and belong to the cubic diamond structure. Upon shock treatment as well as with increase of test gas pressure, a considerable improvement in the quality of GCNP films has been observed. Further, ablation of GCNPs exclusively on the top surface of the coatings and formation of hierarchical NPs (diamond NPs on GCNPs) has been observed.

Low temperature and rapid deposition of ZnO nanorods on Si(100) substrate with tunable optical emissions

This research article describes the large scale fabrication of ZnO nanorods of various shapes on Si(100) substrate, by using metalorganic precursor of Zn in solutions with microwave as the source of energy. This is a low temperature, environmental friendly and rapid thin film deposition process, where ZnO nanorods (1-3 mu m length) were grown only in 1-5 min of microwave irradiation. All as-synthesized nanorods are of single crystalline grown along the < 0001 > crystallographic direction. The coated nanorods were found to be highly dense having a thickness of similar to 1-3 mu m over the entire area 20 mm x 20 mm of the substrate. The ZnO thin film comprising of nanorods exhibits good adhesion with the substrate. A possible mechanism for the initial nucleation and growth of ZnO is discussed. A cross over from a strong visible light emission to an enhanced UV emission is observed, when the nature of the surfactants are varied from polymeric to ionic and nonionic. The position of the chromaticity coordinates in yellow region of the color space gives an impression of white light generation from these coatings by exciting with a blue laser.

Fretting studies on self-mated stainless steel and chromium carbide coated surfaces under controlled environment conditions

Adhesive wear has been widely accepted as the type of wear which is most frequently encountered under fretting conditions. Present study has been carried out to study the mode of failure and mechanisms associated under conditions where strong adhesion prevails at the contact interface. Mechanical variables such as normal load, displacement amplitude, and environment conditions were controlled so as to simulate adhesion as the governing mechanism at the contact interface. Self-mated Stainless Steel (SS) and chromium carbide with 25% nickel chrome binder coatings using plasma spray and high-velocity oxy-fuel (HVOF) processes on SS were considered as the material for contacting bodies. Damage in the form of plastic deformation, fracture, and material transfer has been observed. Further, chromium carbide with 25% nickel chrome binder coatings using HVOF process on SS shows less fretting damage, and can be considered as an effective palliative against fretting damage, even under high vacuum conditions. (C) 2013 Elsevier B.V. All rights reserved.