20 research outputs found
The effect of anisotropy on residual stress values and modification of Serruys approach to residual stress calculations for coatings such as TiN, ZrN and HfN
No full textThe residual stresses in literature on hard coatings (e.g., TiN, CrN, HfN and ZrN) are usually calculated using the mechanical elastic constants often determined by indentation technique by assuming isotropic behavior. The effect of anisotropy of the hard coatings on residual stress values such as TiN, ZrN and HfN has been documented using classical technique and Thin Film techniques (fixed incidence multiplane (FIM) Technique). Due to lack of the single crystal data, the anisotropy of coatings has been taken into account through XECs determined experimentally for ZrN, HfN and TiN films. Recently, single crystal elastic constants of the ZrN, HfN and NbN have been measured. In the light of single crystal elastic constant data, residual stresses reported in the literature were reevaluated according to Reuss, Voigt, Hill (or mixed) and Kroner models using the best fitting approach after modifying Serruys approach. The modified Serruys approach captures the anisotropic behavior of coatings such as ZrN and Zr(Hf)N. The residual stress calculations were improved and the residual stress values were significantly increased as high as 30% compared to the previously published data. The best fitting approach (modified Serruys approach) was compared to the procedure used by Perry using experimentally determined XECs. (c) 2006 Elsevier B.V. All rights reserved
Fast and low-cost fabrication of 1D hematite photoanode in pure water vapor and air atmosphere: Investigation the effect of the oxidation atmosphere on the PEC performance of the hematite photoanodes
No full textIn this study, hematite photoanodes were successfully fabricated by thermal oxidation of the commercial cold-rolled steel at 500 degrees C in pure water vapor and air atmosphere. The crystal phase structure, surface morphology, and optical properties of the hematite photoanodes were characterized using an X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM) and UV-VIS spectrophotometer, respectively. The results showed that hematite photoanodes had high crystalline phase and the annealing atmosphere influenced the morphology of the hematite photoanodes. Moreover, nanowhisker and nanorod shaped nanostructures were observed on the substrate. The optical band gap values of the hematite photoanodes varied between 2.38 and 2.70 eV. Photoelectrochemical (PEC) studies of the hematite photoanodes were assessed in the 0.1 M NaOH electrolyte solution using the Mott-Schottky analysis and electrochemical impedance spectroscopy techniques. The PEC findings exhibited that the hematite photoanode annealed 15-min in water vapor had best PEC performance achieving photocurrent density 0.244 mA/cm(2) at 1.6 V vs. V-RHE and highest carrier density value (N-D = 1.15 x 10(21) cm(-3)). Furthermore, the photoanodes annealed in water vapor atmosphere revealed at least three times higher PEC performance than that of photoanodes annealed in air. Thermal oxidation method in water vapor is an efficient methods for fabrication of hematite photoanodes. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved
The effect of plasma detonation parameters on residual stresses developed in the plasma modified layer
No full textThe surface modification of the AISI 4140 steel by pulse plasma detonation process resulted in residual stresses. The residual stresses in modified surfaces measured using XRD tilting technique were determined for different process parameters. The results indicated that residual stress developed in modified surface increased from -200 MPa to -1000 MPa with decreasing in nozzle distance and increased from -554 MPa to -823 MPa with increasing in battery capacity. In shortest nozzle distance (60 mm), the increasing in number of pulse from 5 to 10 resulted in decreasing residual stress from -1000 MPa to -340 MPa. It was clearly demonstrated at first time that pulse plasma detonation process parameters significantly influenced the value of residual stress. (C) 2014 Elsevier Ltd. All rights reserved
Heat capacity measurements on BaTa2O6 and derivation of its thermodynamic functions
No full textHeat capacity measurements of barium tantalate (BaTa2O6) were carried out by using a differential scanning calorimeter at temperatures between 323 and 1323 K. From the heat capacity values of BaTa2O6, other thermodynamic functions (enthalpy and entropy increments) were derived between 298.15 and 1323 K. The C (p,m) (298.15) value of BaTa2O6 was computed as 184.857 J mol(-1) K-1. Moreover, fitted heat capacities exhibited good agreement with Neumann-Kopp rule at the temperatures between 298.15 and 1300 K
A new sulfur source for the preparation of efficient Cd(1-x)ZnxS photocatalyst for hydrogen evolution reaction
No full textCd(1-x)ZnxS hexagonal crystals were for the first time synthesized via thermal sulfurization of Cd(1-x)ZnxO particles by using the elemental sulfur as the sulfur source. A temperature profile in the tube furnace was designed to obtain the proposed particle size, crystal structure, and morphology. Synthesized Cd(1-x)ZnxS particles were characterized with scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and diffuse reflectance UV Vis spectroscopy. It was seen that there was a polynomial relationship between the band gap and Cd: Zn ratio in the Cd(1-x)ZnxS. Cd0.58Zn023S has shapeless particles between 250 and 500 nm particle size. It was observed that particle size decreased as Zn ratio increased in the Cd(1-x),ZnxS. Cd(1-x),ZnxS hexagonal crystals had nano step surfaces which were one of the desired factors for achieving high photocatalytic efficiency. Finally, Synthesized Cd(1-x.)ZnxS particles were used as photocatalysts for the photocatalytic hydrogen evolution reaction (HER). Cd0.77Zn0.23S structure behaved the most active one among the different compositions of Cd(1-x)ZnxS nanoparticles. Cd0.77Zn0.23S showed almost high photocatalytic activity for HER with 1927 mu mol g(-1) h(-1) hydrogen evolution rate without using noble co-catalyst such as platinum. This good photocatalytic activity was believed to be due to the nanostep surface structure Cd0.77Zn0.23S which led the separation of the reduction and oxidation reaction sites and inhibited the recombination of the generated electrons and holes. Observation of considerably high photocurrent and open circuit potentials and changes in the electrochemical impedance spectroscopy responses supported the photocatalytic activity of the Cd0.77Zn0.23S particles. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved
PITTING CORROSION OF TiN-COATED STAINLESS STEEL IN 3 % NaCl SOLUTION
No full textTiN coatings deposited by arc PVD were characterized by XRD and SEM. In-situ measurements of the corrosion of the substrate and the TiN-coated substrate were made using the corrosion potential (Cor.Pot.), the polarization resistance (PR) method and electrochemical impedance spectroscopy (EIS) in a 3 % NaCl solution as a function of the immersion time. The semiconductor scale formed on the TiN was identified using a Mott-Shottky analysis as an n-type semiconductor with a flat band potential of -0.83 V vs. SCE. The TiN coating (0.5 mu m thick) consisted of cubic TiN exhibiting columnar grains, pin holes, voids and porosities. The pitting corrosion of the TiN, observed visually between I h and 2 h, was captured by EIS and PR. The electrical circuit (EC) model used for the EIS data supported the degradation of the coating through pitting corrosion, in agreement with the visual observations. The corrosion resistance (polarization resistance) determined by the polarization resistance method (R-p) and the EIS (R-total) decreased suddenly during the pitting corrosion. The corrosion resistance of the TiN-coated substrate was greater than the corrosion resistance of the substrate during the approximately 24 h of exposure
CORROSION OF CrN-COATED STAINLESS STEEL IN A NaCl SOLUTION (w=3 %)
No full textA CrN coating deposited by arc PVD was characterized by XRD and SEM. The in-situ measurement of the corrosion of the CrN-coated substrate was made by corrosion potential (Cor. Pot.), the polarization resistance (PR) method and electrochemical impedance spectroscopy (EIS) in a NaCl solution w = 3 % as a function of the immersion time (about 24 h). A semiconductor scale that formed on the CrN was identified by Mott-Shottky analysis as a p-type semiconductor with flat band potentials, 0.49 V (SCE). The CrN coating (0.5 mu m thick) consisted of a mixture of cubic Cr and hexagonal Cr2N phases exhibiting equiaxed grains and a dense coating with a small quantity of pinholes, voids and porosities. The transition in corrosion resistance for the CrN coatings at an early stage was found based on Cor. Pot., PR and EIS data. The CrN did not exhibit any pitting for about 24 h, while the corrosion resistance (R-p and R-total) decreased rapidly with time after 5 h of incubation. The transition from high resistance (3 M Omega cm(2)) to low resistance (0.24 M Omega cm(2)) was explained as a result of the penetration of the electrolyte through the Cr2O3 oxide layer to the Cr2O3/CrN interface. The resistance of the CrN against pitting corrosion was explained based on the blocking character of the equiaxed, dense, CrN coating against the penetration of the electrolyte
Analysis of XRD stress measurement data of naturally grown oxide films Al2O3 and Cr2O3 based on existing Reuss, Voigt, and Hill models
No full textThe resistance of naturally grown alumina (Al2O3) and chromia (Cr2O3) scales to cracking and spalling under influence of growth and thermal stresses is a critical aspect of the environmental resistance of high temperature alloys such as Fe and Ni based alloys. The driving force for scale failure is the residual stress developed in the scale. In this study, strain and stress measurement techniques by XRD were reviewed. XRD data for Al2O3 and Cr2O3 films were analysed and discussed with respect to existing models. It was experimentally found that the Reuss model provided the best description of the measured strain data for these films. Strain and stress states of Al2O3 and Cr2O3 films here determined. (C) 2002 IoM Communications Ltd
Corrosion behaviour of twin-roll cast 8006 aluminium alloy foil with different thicknesses for the food packaging industry
No full textPurpose The purpose of this paper is to investigate and find out the surface and electrochemical behaviours of twin roll cast (TRC) 8006 aluminium alloy with different thicknesses due to the cold rolling rates after the TRC process. Design/methodology/approach The 8006 aluminium alloys are mostly used for the food packaging industry, as they are corrosion resistant, lightweight and shapable materials. The present work investigates the surface and corrosion behaviours of 8006 aluminium alloys at different thicknesses. TRC aluminium alloys were cold-rolled at two different reduction rates before investigation. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDX) tests were used to examine the phase and elemental analyses. FE-SEM and 3D profilometry also used to observe surface morphology. Open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy tests (EIS) were carried out to find out corrosion behaviours. The results show that the more cold rolling reduction (CRR), the more corrosion rate and surface affection of the TRC 8006 aluminium alloys. Findings According to the electrochemical tests (OCP, potentiodynamic polarization test and EIS) and surface morphology results (such as SEM, 3D profilometry and XRD) the more the rolling rate the less the corrosion resistance. Originality/value First corrosion behaviour investigation of twin-rolled 8006 Al alloys using electrochemical techniques. First investigation of CRR effects on electrochemical corrosion behaviour of 8006 Al alloys with 3.5 wt.% NaCl solution using EIS. First investigation of 8006 Al alloys as a food packaging material with electrochemical ways
