Rozprawy doktorskie na temat „Electrochemical Systhesis”

A green approach is reported for the production of few layered graphenes (FLGs) via electrochemical route utilising the benefits of anodic exfoliation process, wherein electrochemical intercalation of nitrate ions into pyrolytic graphite resulted in electrochemical exfoliation of nitrate ions-intercalated graphite electrode. The role of applied potential in intercalation and concentrations of nitric acid are well defining factors in controlling the number of layers in FLGs. The success of this approach was confirmed by FTIR, wherein smaller particles of intercalated graphite led to broader peaks due to increased interaction with light wave. The SEM images showed several layers of graphene stacked together and slightly twisted at edges. An increased exfoliation in intercalated graphite was revealed by XRD patterns. Desirable conductive properties of the FLGs synthesised makes it a viable option for utility as conductive ink.

There is quiet revolution going on, and its name is nanotechnology. Without much fanfare, a host of innovations are coming our way. Use of electrochemistry, the solid/liquid interface science, in nanoscience and nanotechnology may range from nanosystems, to nanosynthesis, to nanocharacterisation. The characteristic reaction may be ion transfer reaction (ITR) or electron transfer reaction (ETR).The nanoscale electrochemistry covering from metallic and semiconductor based nanoparticles,nanoarrays,nanotubes,nanopits, to self assembled molecule monolayers i.e. bioelectrochemical systems with redox metalloprotein or DNA based molecules, has began to unravel the complexities of these systems. Electrochemistry is a suitable method for coupling particles activity to external circuitry. It has been successfully used in investigating the effects and kinetics of charge transfer at Q-dots using scanning electrochemical microscopy (SECM), by controlled transport reactions. Electrochemical processes i.e. reaction at solid/ liquid interface controlled by an externally applied voltage, are increasingly involved in nanostructured fabrication as a relatively inexpensive superior quality products, easy to handle and a reliable tool.

In recent years, fluids containing suspension of nanometer-sized particles (nano fluids) have been an active area of research due to their enhanced thermal conductivity over the base fluids. This makes them very attractive as heat transfer fluids in many applications such as coolants in the automobile and electronics industries, and manufacturing processes. Stable nano fluids are being investigated for numerous applications, including cooling, manufacturing, chemical and pharmaceutical processes, medical treatments, cosmetics, etc. In a better description, nano fluids are engineered colloidal suspensions of nano particles (<100 nm) in a base fluid. Common base fluids include de-ionized water and organic liquids. In this investigation, the two step method of synthesis of ultra fine Al-Cu alloy powder particles and stable dispersion in base fluid is done. Ultrafine powders were prepared by milling elemental Al and Cu powders for 50 hours in a planetary mill. Aiming at the dispersion of nano-Al-Cu is regarded as the guide of heat transfer enhancement, the stability of Al-Cu alloy particles in de-ionized water were studied under different pH values by using nano zeta meter. It is found from XRD that the crystallite size is around 7 nm and lattice strain value is around 1.4 % for Al-Cu. After 50 hours of milling, particles size has been reduced from 28 m to 300 nm. Transmission electron microscopy (TEM) shows that each particles consists of large number of crystallites of size around 10-15 nm. The stability of nanofluids was also studied by nano zeta meter at different pH of nanofluids for constant ultrasonication time and magnetic stirring. It has been found from Nano zeta meter that the suspension is best stable at pH value of 9.5 corresponding to zeta potential value of -90.60 for Al-Cu alloy with the presence of surfactant.

An effort has been made to synthesize Al-based nanostructure by mechanical alloying (MA). Elemental powder of Al, Si and Ni were blended to obtain nominal composition of Al75Si15Ni10. Alloying was carried out in a high energy planetary ball mill using stainless steel grinding media at 300 r.p.m. up to 50 h. Toluene was used as the process control agent (PCA). The ball to powder weight ratio was maintained at 10:1. The phase evolution of the milled samples was studied by X-ray diffraction (XRD) analysis. The microstructural characterization of the milled powder was followed by scanning electron microscopy (SEM) and XRD. Dissolution of Si and Ni in Al was found to be 15% and 10% respectively along with the formation of some intermetallic phases. SEM micrographs showed that the powder morphology was changed from coarse layered structures obtained by very short period of milling to finer as the milling time increased. XRD and energy dispersive X-ray analysis (EDX) showed the formation of a homogeneous solid solution of the above said blends after milling for 50 h. The crystallite size, lattice strain (%) and lattice parameter were calculated from major XRD peaks. It shows that the crystal size decreased very rapidly up to 25 h of milling and then slowly became almost constant with further milling, whereas, lattice strain (%) increased gradually up to 25 h very rapidly and then very slowly became nearly constant with progress of milling. This suggests that major structural changes and dissolution of the alloying elements almost completed by 25 h, and further milling refined the product by MA. The lattice microstrain of the material increases exponentially. It increases rapidly up to 25 h and then increased slowly as the milling progresses further. The change of lattice parameter of Al-rich solid solution showed a rapid decrease throughout the process of MA. This is because of the entrance of Si and Ni atoms into the lattice of the Al which causes distortion in it. The change in the above mentioned parameters were determined up to 30 h of milling as on further milling Al peaks vanishes because of formation of partially amorphous structure along with some intermetallic phases.

The current work aims to improve the thermal conductivity of distilled water by dispersing electrolytic grade iron powder. Thermal conductivity of fluids is an important parameter in deciding their usability in various commercial applications. Nanoparticles dispersed in fluids generally show interesting properties with respect to thermal conductivity. Iron particles were dispersed in distilled water in different volume fractions (1, 2 and 3 percent respectively) and the resultant fluids were analysed in terms of their thermal conductivity. To study the effect of particle size, the as received iron powder was also ball milled and the same set of studies were repeated with the milled powder. All the conductivity measurements were carried out at room temperature the data were compared with the conductivity value of the pure distilled water. The effect of solid powder additions on distilled water results the increase in thermal conductivity with increase in concentration of iron powder. Effect of milled powder was also compared with that of un-milled powder

In this study, few-layer graphene nanosheets (FLGNSs) have been synthesized by electrochemical intercalation followed by exfoliation technique. Three different protic electrolytes such as aq. H2SO4, HClO4 and HNO3 have been used separately. The major intercalants are 2 4 SO  , 4 ClO and 3 NO anions of different sizes, where the rate of impact to the pyrolytic graphite sheet has been monitored by varying the concentration of the electrolytes to 0.5, 1.0, 1.5 and 2.0 M in each case. The effects of sizes of the intercalants and its rate of intercalations on the as-synthesized FLGNSs have been studied. From the in-situ analyses, the exfoliation rates have been significantly increased with the increase in size as well as the concentration of the intercalants. Various physicochemical analyses on the electrochemically exfoliated FLGNSs have been performed in the colloidal as well as solid state. From the colloidal state, the exfoliated FLGNSs dimensions as well as its conductivity have been measured. The thermal stability and yield of FLGNSs flakes have been measured by TGA. The structural properties like phase, lattice spacing, dis-orderness and crystallite sizes of the as-synthesized FLGNSs have been analyzed by XRD and Raman spectroscopy. The (002) and (001) lattice planes of graphene and graphene oxide has been observed at around 24.5° and 11° (2θ) from the XRD spectra respectively. Again, the characteristics peaks at around 1345, 1590 and 2700 cm-1 corresponds to D, G and 2D bands of the FLGNSs in the Raman spectra respectively. This shows the mixture of sp2 and sp3 contents in the electrochemically exfoliated FLGNSs. The qualitative as well as quantitative analyses of the functional endowment on the FLGNSs have been performed by FTIR, XPS and UV-visible spectroscopy. The FTIR analysis depicts the presence of various hydroxylation, carboxylation and aromatic carbon structures in the FLGNSs. The quantification of the functional groups and sp2 content in the FLGNSs has been analyzed by XPS. The UV-visible spectra show the electronic transitions of π-π* and n-π* due to the presence of C=C bond in the aromatic structure and C=O, carbonyl functional groups respectively. The optical band gaps also have been measured from the Tauc plots. The morphological as well as topographical analyses have been performed by FESEM, TEM and AFM. From the FESEM, the domain sizes, agglomerations, curliness at the edges and stratified nature of FLGNSs have been shown. From the TEM analyses, the number of layers in the graphene sheets measured from the lattice fringe analysis. Again the number of layers has been analyzed by the topographic analysis performed by AFM and it varies in between 3-8 layers. The functional application as supercapacitive performance of the as-synthesized FLGNSs have been performed by Swagelok type configured two electrode potentiostat. From the cyclic voltammetry (CV) and charge-discharge (CD) measurements, the FLGNSs synthesized from 1.5 M H2SO4 (S3), 2.0 M HClO4 (C4) and 1.0 M HNO3 (N2) electrolytic conditioned shows maximum capacitance in the respective categories. The Ragone plot shows maximum energy density of 12.35 Wh kg-1 and maximum power density of 3.01 kW kg-1 by S3 and N2 FLGNSs respectively. From the 5000 cycle CD test, it has been observed that the FLGNSs shows ~100 % stability in delivering the power performance. It attributes to the non-faradic EDLC reactions of the materials. The FLGNSs obtained from the extreme electrolytic conditions such as 2.0 M of H2SO4 (S4), HClO4 (C4), and HNO3 (N4) are used as nano-filler in the epoxy (EF) and glass fiber/epoxy (GEF) matrixed polymer composite structures. The nano-fillers have been used 0.1 and 0.3 wt.% in the composite structures. The functional groups present in the FLGNSs act as anchoring agent to the epoxy polymer for enhancement in the mechanical properties. It has been observed that the N4 FLGNSs nano-filler show the maximum enhancement of 42.6 and 28.2 % of flexural strength in EF and GEF polymer composite structures. Similarly, the modulus has been increased to 33.5 and 57.7 % in the EF and GEF polymer composite structures. The fact is attributed to the high extent of the carboxyl-functional endowment in the N4 FLGNSs than S4 and C4 FLGNSs. Again at high concentration of nano-filler to 0.3 wt.%, the mechanical properties of the composites have been drastically reduced. The fact depicts the agglomeration of the FLGNSs in the epoxy matrix, which inhibits the homogeneous bonding in the polymer structures.

Graphene is a single layer of pure carbon atom that are bonded together in hexagonal or honeycomb lattice structure. The gradual destruction of metal surface by chemical or electrochemical reaction with their environment forms corrosion. The graphene layer has been used as protective thin film on metal surface by electorphoretic depositon (EPD). In the present work, graphene has been synthesized by electrochemical intercalation and exfoliation of pyrolytic graphite sheet by various electrolytes (H2SO4, HNO3, and HCLO4) in varying concentration. The prepared dispersed graphene oxide (GO) solutions were deposited on copper surface with working area of 2cm2 by electrophoretic deposition technique at various (0.1, 0.5, 1 wt %) concentration of graphene. The sodium dodecyl sulfate (SDS) anionic surfactant has been used as binder to increase the thickness of coating. The graphene oxide coatings were used with the aim that it will act as a protective layer for corrosion of Cu substrate. The thickness of the graphene coated thin film was characterized by surface profiler and atomic force microscopy. Morphology of graphene nano sheets and coated graphene was analyzed by FESEM, which has showed clearly microstructure of GNS layer. Topography of graphene coated specimen characterized by AFM and crystal structure, crystalline planes and phases of graphene sheet were characterized by X-ray diffraction. (0 0 2) and (1 0 0) planes showed the graphene sheet has been confirmed by X-ray diffraction. The electrochemical corrosion behavior of graphene coating on Cu in 0.1M NaCl solution has been investigated by potentiodynamic linear sweep voltametry technique. However, the tendency (corrosion potential) is nobler for bare copper substrate. The study needs further experiment and optimization to reach to an affirmative conclusion. The application of GO layer has improved the corrosion resistance property of coated Cu due to better barrierquality of GO layer.

The thin adherent oxide layer formed on the metal surface keeps the surface of metal protective from corrosion i.e. known as passivation.This oxide layer may break due to different types of environmental effects leading to rapid corrosion.Hence the study on breakdown of passivity should permit one for the interpretation of process parameter and environmental restriction for long time of serviceable of the metal.The 304 stainless steel is having the higher percentage of chromium making it corrosion proof literally. In this thesis the study is on the passivity breakdown of 304 stainless steel in deaerated borate buffer solution as a function of pH and Cl ions.The pitting corrosion studies of 304 SS is carried out in borate buffer solution at varying pH(8.3,9.3,10.3)in the presence of varying chloride ions (0.1M, 0.5M, 1M).Corrosion studies were performed by potentiodynamic scans,microscopy techniques and point defect model.The study of the passivity and pitting can be evaluated through a point defect model.As increasing the pH of borate buffer solution, the breakdown potential increases i.e. the pitting tendency decreases whereas it got decreased with increasing chloride ion concentration. The value of breakdown potential was also found to increase with the potential scan rate.After obtaining the potentiodynamic curve pitting studies of the surface is done by optical microscope.The microstructure is shown in above figure at 1M chloride ion and at varying pH.The probability distribution in breakdown potential is the confirmation with the analytical prediction of the breakdown potential distribution obtained from the point defect model.

The aim of this work is electrochemical exfoliation of pyrolytic graphite for mass production of few-layer graphene nano sheets. It is synthesized by intercalation of graphite sheets in the electrolyte of two different types of concentrations, one molar and two molar concentrations of nitric acid by application of positive bias. The voltage is gradually increased with an increment of 0.5V upto 8V and an interval of 3 minutes. The X-ray diffraction peaks corresponding to graphene sheet ((002) plane) were observed at 2θ positions of 26.35°. The morphology of as-synthesized FLGNSs is characterized by field emission scanning electron microscopy. The transparent layers of FLGNSs are observed in transmission electron microscopy. The number of layers in transparent graphene sheets is confirmed by the HRTEM. Through FTIR studies, the presence of functional groups of O-H and C-O has been identified. AFM topography revealed that the thickness of the single layer is in the range of 1 nm, and for few-layer graphene nano sheets are in the range of 5-6 nm only. However, FLGNSs could be readily distinguished through phase imaging of tapping-mode AFM, because of differences in hydrophobicity arising from their different oxygen contents. STM studies of graphene nanosheets revealed atomic scaled periodicity at very low tunneling currents (∼1 pA). Phase imaging showed distinct contrast difference between FLGNSs to the graphite substrate (HOPG), a result that was attributed to their extremely low conductivity. The atomically flatness of the graphene nano sheets and electronic properties were measured by scanning tunneling microscopy. Scanning probe spectroscopy revealed the electronic properties like the density of states (DOS) and Dirac point (DP) of graphene sheets. The synthesized material can be used as a base material for the future applications such as desalination of sea water, supercapacitors, sensors, solar cells, and coatings.

Nanostructured tungsten based alloys with nominal composition of W80Ni10Nb10,W79Ni10Nb10(Y2O3)1, W78Ni10Nb10(Y2O3)2, W72Ni10Nb15(Y2O3)3 (all in wt.%) are synthesized by mechanical alloying of elemental powders of tungsten (W), Nickel (Ni), Niobium (Nb) and Yittrium oxide (Y2O3) in high energy planetary ball milling machine followed by compaction at 500 MPa pressure for 5 mins and sintering at 1500o C for 2 h in Argonatmosphere. Investigation of phase and microstructure of milled powder and consolidatedsamples are carried out by X-ray diffraction (XRD), Scanning electron microscopy (SEM),Energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM).Minimum crystallite size of 20 nm is achieved in 20 h milled powder ofW72Ni10Nb15(Y2O3)3. The dislocation density for all the investigated alloys increases at 10 h of milling owing to hydrostatic pressure exerted by the nano-crystallites due to severe plastic deformation,however the rate of increase of dislocation density reduces after 10 h of milling due to formation of solid solution. The lattice parameter of W in W80Ni10Nb10 and W79Ni10Nb10(Y2O3)1, W78Ni10Nb10(Y2O3)2, W72Ni10Nb15(Y2O3)3 alloy expands at 10 h and 5h of milling and contracts thereafter respectively. The SEM micrograph reveals the presence of ultrafine particles at 20 h of milling for all alloys. Formation of hard, brittle NbNi intermetallic and Y2O3 disperoids is evident from XRD and SEM study of sintered alloys. Hardness, wear, oxidation, and compression test has been conducted to investigate the mechanical behaviour of oxide dispersion strengthened (ODS) and non-ODS sintered alloys. Increased Y2O3 content results in enhanced compressive strength, sinterability, oxidation resistance and wear resistance. Higher hardness and strength in Y2O3 dispersed alloys as compared to W80Ni10Nb10 can be attributed to dispersion strengthening mechanism by Y2O3.Maximum sinterability, hardness, of 93.38%, 6 GPa, has been achieved in W72Ni10Nb15(Y2O3)3 owing to the presence of high Y2O3 content and NbNi intermetallic.W79Ni10Nb10(Y2O3)1 shows superior oxidation resistance at 8001000°C as compared to restof the alloys.

Due to their small size and thickness, nanostructured thin films exhibit novel properties which largely differ from the bulk materials. Due to their significant properties it can be used as microelectronic materials, bacteriostatic materials, catalytic materials or magnetorecording materials, antibacterial materials, cryogenic superconducting materials, biosensor materials. Generally the shape, size, and size distribution of particulates and grains can be controlled by adjusting the reaction condition such as external and internal parameters like temperature, electrolyte concentration, current density, PH of the solution. Sonoelectrochemistry is the study of the effects of the combination of ultrasonic radiation with electrode processes occurring at surfaces of electrodes immersed in a solution in an electrochemical cell. The ultrasound plays an important role to produce cavitation bubbles inside the electrolyte by rupturing the chemical bonds between molecules and electrolyte. The cavitation bubbles implosively collapse within a very short time after undergoing the formation growth and contraction. Synthesis under low temperature may avoid undesirable interdiffusion between adjacent layers and structures and allows uniform modification of surfaces and structures with reduced grain size. In this work we prepare the copper thin film by sonoelectrosynthesis method. The grain size, mechanical and electrical properties of the electrodeposited metal thin film depends upon various parameters like temperature, PH, current density, and concentration of electrolyte and also ultrasound has many numerous effects on the grain size, hardness, porosity and brightness of the deposits. This particle can characterized by XRD, SEM, AFM, DSC and study the mechanical properties by nanaoidentation. v

Multilayers have received increasing attention in recent years because of their unique properties. These materials comprised of alternating layers of different metals and/or alloy is expected unusual and enhanced electrical, optical, magnetic and mechanical properties when the sublayer thickness is confined to the nanometer scale. In this work we tried to Cu/Ni multilayer by varying the concentration of the bath with changing potential for alternate deposition of nano multilayer. Our conclusions are the result of combining experimental work with chraterization with XRD, SEM, AFM and and nanoindentation with special concentration of the different growth texture of the multilayers grains and growth mechanism with GMR studies. We argue that this approach is the best avenue to obtain accurate information about the texture and quality of metallic multilayers. The study of physical properties of multilayers (structural, elastic, magnetic, and transport) is one of the most prosperous and rich branches of materials science today.

Thin films are deposited onto bulk materials (substrates) to achieve properties unattainable or not easily attainable in the substrates alone. The film thickness usually varies from few nanometers to a maximum value of 1 μm. Cavitation, irradiation of liquid with high intensity ultrasound, as a means of altering the crystallization process is achieved by the repeated creation and collapse of microscopic bubbles inside the solution. It is at the solid-liquid interface that electrochemical techniques may be employed to detect the possible influence of sonication on electrochemical nucleation and growth of clusters. In this work we prepare the copper thin film by sonoelectrosynthesis method at different temperature, acid and concentration of electrolyte. Films are characterized by XRD, SEM, AFM, and study of the mechanical properties is done by nanaoidentation. Scahifker and Hills model was used for study of nucleation and growth phenomena for electrochemically deposited thin film by cyclic voltammetry and chronoamperometry. A potential of 450 mV (100 mV negative than the Nernst potential) was selected for the deposition procedure for all the conditions. The sole impact of sonication was experimented before the study of the coupling effect and was found to favor nucleation ahead of growth. The evidence of secondary nucleation in ultrasonic condition was also observed. The thickness of films lies in the range of 400-500 nm. The phases of the deposits are confirmed by the XRD analysis. The nucleation population density got increased from a low value to high value of acid concentrations. Comparison with the theoretical models, it is apparent that copper follows progressive nucleation mode in increasing acid concentration. Hydrogen evolution was also imperative at increasing acid concentrations, however, ultrasound capable of degassing produced hydrogen free adherent surfaces. The facts are also confirmed by the morphological analysis by SEM and AFM. The same trend is observed for the films with low temperatures. Among all the depositions copper films at – 4 °C is the smoothest. Increasing metal ion concentrations produces finer and harder deposits. Films are rougher at 0.1 M as compared to that of 0.025 M. The grains are found to vary from 400 nm to 50 nm at various conditions with the average roughness factors from 300 nm to 14 nm.

Temperature is an excellent tool for tuning the phase formation kinetics and hence structure and properties of synthesized materials. The effect of the said parameter with added sonication impact on the electrochemical synthesis of copper thin films has been investigated in the present study. Copper was electroplated on graphite and aluminum substrates from a simple aqueous binary sulfate electrolyte at sub-ambient temperatures in presence of an ultrasonic horn of 20 KHz frequency and 20% output of the total power. The prepared films were characterized by X-ray diffraction and electron microscopic methods i.e. atomic force microscopy (AFM) and scanning electron microscopy (SEM). Reaction kinetics and nucleation mechanism of film formation was investigated by cyclic voltammetry and chronoamperometry.Mechanical properties and thermal stability of the films were analyzed by nano-indentation and differential scanning calorimetry.

In the present study (Cr) and (Cr-ZrO2) composite coatings were deposited on low carbon steel substrate by pulse electroplating (PED) technique to enhance tribology and mechanical properties of conventional chromium coating. Zeta potential of ZrO2 particles in electrolytes was investigated and from the Iso-electric point obtained, the bath pH was maintained at a fixed value. The effect of PED parameter such as frequency and duty cycle on the morphology of the coating was investigated. The structure and morphology of the coating were evaluated using (SEM) and (XRD). Microhardness tester and ball-on-plate type wear tester were used to access the microhardness and wear resistance of coatings. Finally along with the PED parameters the effect of dispersed ZrO2 particles on coating properties such as hardness, wear resistance were correlated and it was observed that the change in property was due to dispersion hardening and favourable crystallographic orientations. The crystallite size was averagely 30-50 nm and a strong (220) texture was obtained in composite coatings and in unreinforced Cr coatings a strong (210) texture was determined from the XRD data. The composition and surface morphology of coatings were studied by using EDS and SEM. Hardness and Wear resistance of the coatings were determined by using microhardness tester and ball on plate wear tester, improved hardness and wear resistance of composite coatings were observed compared to the unreinforced chromium coatings. The wear loss behaviour of the coatings developed at different frequency and duty cycle follows the general trend i.e wear loss decreases with increase in frequency and duty cycle. The microhardness values obtained for the composite coatings are higher than the pure Cr coating hardness, the improvement is attributed to dispersion strengthening caused by the embedded second phase particles, texture and modified microstructure of chromium matrix.

Nickel and its alloy films have versatile applications including metal coatings for its high strength, surface finishing and corrosion resistance, use in microelectronics, integrated optoelectronics and data storage technologies also used in decoration, electroplating industry and protection industries. Most properties of thin films are influenced by some factors such as crystalline structure, texture, or internal/residual stresses. The present research revolves around the residual stresses evolved during film synthesis. Residual stresses are stresses that remain after the original cause of the stresses (external forces) has been removed, which can have strong effects on film performance. These stresses are basically caused by interface coherency, thermal cycling and change in deposition parameters. Hence an understanding of the evolution of the same during synthesis will be a great avenue to thin film technologists. In the present study, an emerging technique sono-electroplating (electroplating plus ultrasound), has been used to synthesize Ni thin films at room temperature for four different electrolyte baths i.e. sulphate, chloride, Watts and sulphamate. And the aim of this study is to find the effect of ultrasonic vibration on evolution of residual stresses along with analysis of various parameters and properties including hardness, stress, surface finish and basic behavior of the depositing system in terms of cyclic voltammetry and chronoamperometry. The in-process analysis includes the electrochemical techniques and post-synthesis analysis followed by morphological studies includes SEM, AFM, XRD, hardness, residual stress and film thickness from surface profilometer. The same is solicited for electroplated and sonoelectroplated nickel thin films in four different aqueous solutions.

Passivation is the process of temporary or permanent halt in degradation or corrosion rate of a metal due to the formation of different types of surface layers or films that protects the underlying metal. Pitting corrosion is the breakdown of the surface film due to presence of aggressive ions such as chloride ions. The breakdown of the passivity film is characterized by breakdown potential (Vc) which is dependent on the pH of the solution, concentration of the aggressive ions and the potential sweep rate. This study used the Point Defect Model to characterize the breakdown potential with respect to varying pH and concentration. The pH of the solution was kept a constant at 10.4. The breakdown potential is found to decrease with increasing chloride concentration and decrease with increasing pH. The cumulative distribution of the breakdown potential was found to be in well agreement with the experimentally obtained data. Optical micrographs showed stable and Meta stable pitting. The parameters from point defect model was found to be in well agreement with the experimental data.

This project work presents a Molecular dynamics(MD) simulation study on radiation damage of Nano copper single crystal and its effect on the deformation behavior and underlying deformation mechanism.At first,perfect Nano copper models will be created using MD simulations.Then the models will be subjected to radiation and the damaged samples will be tested for mechanical characterization by tensile studies at a temperature 300K and strain rate 1010s-1.The MD simulation was performed by using LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator).In this,we studied Irradiated Nano copper-cascade interactions caused by 0.2KeV to 3KeV primary knock-on atoms(PKA)respectively.We found the displacement of atoms(dpa) from its lattice structure that caused for the creation of various defects within the lattice structure.The mechanical properties of the Irradiated Nano copper single crystal are analyzed and both the elastic properties and yields under tension is analyzed.Defects like point(vacancy) and stacking faults,appears in the irradiated Nano copper depending on the incident energy. The Young modulus is significantly reduced by the incident irradiation energy,and the reduction magnitude depends on the vacancy number,which is determined by the incident radiation energy.The mechanism for these changes are also discussed.

Molecular dynamics (MD) simulations are carried out for cyclic nano-indentation on sintered metal (Al)-metallic glass (Cu66Zr34) reinforced composites termed as composite-I and on sintered alloy(Al-4%Cu)-metallic glass (Cu66Zr34)termed as composite-II to measure the hardness, stiffness and reduced young modulus.I ndenter radius, and indentation speed effects on the load-displacement behavior, hardness, stiffness, and young modulus has been studied. Depth-sensing cycling nano-indentation is studied to assess depth-dependent plastic deformation of the composite at room temperature. The results showed that the plastic deformation continued to take place and the continuous displacement increased as the number of indentation increased. We have found that composite-II sample shows high mechanical properties like hardness, stiffness and reduced young modulus than composite-I.But, there was reduction in the plasticity of the composite-II to enhance other mechanical properties such as Hardness and stiffness.Furthermore, the initial hardness is seen to slightly increase with increase in indenter radius, indentation speed and alloying element. After each cyclic nano-indentation, the loading curve overlapped with the previous unloading curve and had a small displacement after each reloading cycle. From the first loading-unloading cycle, plastic deformation continued to take place and the continuous displacement increased as the number of indentations increased. The stiffness was seen to remain constant for a constant cycle and increased with increase in number of cycles and was seen to remain constant after few cycles.

Copper and Nickel multilayer composites have been prepared by electrodeposition of nickel on copper substrate from Watt’s bath, producing Ni layer of low thickness and then subsequent deposition of copper on Ni by acidic sulfate bath, leading to electroplating of a thin Cu layer. Since adherent Nickel deposit cannot be deposited directly from conventional baths, copper substrate serves as an ideal undercoat for obtaining adherent Ni layer deposit with improved metal distribution and reduced critical cleaning & polishing requirements. Plating parameters such as current density and plating time are kept constant whereas the other bath compositions differ. This is done alternatively to generate alternate Cu-Ni metal multilayer. Magnetic stirring was applied during deposition process in order to produce homogeneous, smooth and adherent coatings of nickel. Characterization and surface morphology analysis is done using FESEM and optical imaging and thus, the thickness of the layers is obtained. The Cu-Ni multilayered composite is then subjected to vacuum heating so as to obtain the Time Temperature profile and the extent of interlayer diffusion. This vacuum furnace heating was carried out in the presence of Argon gas, at different temperatures (773K, 973K, 1173K) and the samples are held at these temperatures each for different time intervals (1 hr, 2hrs, 3hrs). The resultant hardness, microstructure and the diffusion effects are then investigated and studied. The diffusion coefficients for Cu in Ni and Ni in Cu at the above mentioned temperatures was studied from theoretical calculation and subsequently compared with actual diffusion coefficients measured from the Energy Dispersive Spectroscopy (EDS) line scan.

The quest for searching alternative energy resource is of current interest due to the scarcity of the conventional energy sources, which are major pollutants of the atmosphere. Research on renewable energy has gained attention due to its advantageous features sides like no noise, impollutant, static working parts and long life time. The much matured technology in solar cells is silicon (Si). Thought it have gained a dominant place in commercial aspects, it recedes in terms of cost effective purification process, defect tolerance, Indirect band gap nature (less absorption coefficient), which made researchers to thin for a better alternative direct band gap semiconducting materials like CIGS and CdTe. CIGS have gained much attention in last two decades due to their high absorption coefficient (direct band gap nature). Photovoltaics utilizing CIGS (Copper indium gallium Selenide) material is considered to be the most efficient solar energy converter of any thin film device. They exhibit the potential to reduce the device fabrication cost when compared to Si-based solar devices. The high efficiency CIGS thin film solar cells 20.5% were reported by NREL (National Renewable energy laboratory,USA) for an aperture area of 1 cm2. Very recently, featuring news release of Center for Solar Energy and Hydrogen Research Baden-Württemberg) of Stuttgart, Germany have reported 21.7% (0.5 Cm2) as confirmed by Fraunhofer Institute for Solar Energy Systems ISE. Impressive efficiencies were also reported for mini-modules of CIGS devices of efficiency 18.7% (15cm2). The efficiency percentage motivates to give an impressive scope to explore about the material. All the reported high efficiency devices were fabricated by co-deposition technique (Physical Vapor Techniques). Inspite of high efficiency, the cost of production and mass production are the hurdles for the PVD technique. Electrodeposition is one of the promising deposition techniques, have achieved an efficiency of 12.25% and 10% for an area of 102 cm2 and 1.07 m2. The work pertains to the electrodeposition of CIS/CIGS absorber layer using two and three electrode systems. From the linear sweep voltammetry (LSV), the bath composition and deposition potential were optimized for ternary system (CIS). Similar approach was extended to quaternary systems using cyclic voltammetry (CV). Using sodium dodecyl sulphate (SDS) as surfactant , it was found to be beneficial in obtaining crystalline and dense CIS/CIGS thin films which is confirmed by XRD and FE-SEM studies. From the preliminary experiments for CIS electrodeposition in a neutral electrolyte without any complexing agents, it was found that CIS can be conveniently co-deposited between the potential of -1 to -1.3 V. This proposed simplified bath scheme reduces the complexity in bath chemistry. The compositional analysis by EDS for CIS/CIGS absorbers deposited using two electrode system revealed that a potential higher than -2 V is required to obtain near stoichiometric CIS/CIGS films.

The present research provides a comprehensive investigation in understanding the effects of the addition of exfoliated graphite nanoplatelets (xGnPs) and multiwalled carbon nanotubes (MWCNTs) on the microstructure and mechanical properties of two types of ceramic matrices, namely, polycrystalline alumina (Al2O3) matrix and amorphous silica (SiO2) matrix. The main objective of this work is to understand the difference in the properties of ceramic matrix nanocomposites (CMNCs) reinforced with xGnPs and MWCNTs, due to the different characteristics of both nanofillers. xGnPs and MWCNTs when used as nano-reinforcements, can extensively improve the mechanical properties like hardness, fracture toughness and wear resistance of the brittle Al2O3 and SiO2-based materials, which can be further used for various mechanical and structural engineering applications. For the fabrication of xGnP and MWCNT reinforced Al2O3 and SiO2-based nanocomposites, efforts have been made on three major aspects, namely (i) production of good quality xGnPs and MWCNTs, (ii) homogeneous dispersion of xGnPs and MWCNTs in the ceramic matrices, and (iii) preservation of the graphitic structure of both nanofillers during high temperature processing. xGnPs were synthesised from a graphite intercalation compound (GIC) by rapid evaporation of the intercalant at an elevated temperature and its subsequent ultrasonication in acetone. The synthesis of MWCNTs was done by low pressure chemical vapour deposition (LPCVD) method. In order to solve the problem of xGnP/MWCNT agglomeration at higher loading levels in the ceramic matrices, powder metallurgy route was adopted and processing techniques like ultrasonication and surface modification were employed. Al2O3-xGnP, Al2O3-MWCNT, SiO2-xGnP and SiO2-MWCNT powder mixtures were prepared by blending the monolithic powders of pure Al2O3 and pure SiO2 with desired volume fractions of xGnPs and MWCNTs by ball milling. To avoid thermal degradation of the carbonaceous nanofillers during high temperature processing, sintering of the nanocomposites was carried out at optimised parameters. Al2O3-0.2, 0.5, 0.8, 3, 5 vol.% xGnP, Al2O3-0.2, 0.5, 0.8, 3, 5 vol.% MWCNT, SiO2-0.5, 1, 3, 5 vol.% xGnP and SiO2-0.5, 1, 3, 5 vol.% MWCNT nanocomposites were fabricated and analyzed. Conventional sintering of nanocomposites was carried out in vacuum whereas spark plasma sintering (SPS) was done in Ar atmosphere. In the case of conventionally sintered nanocomposites, green compacts of Al2O3-xGnP and Al2O3-MWCNT nanocomposites were prepared under uniaxial load of ~390 MPa and later sintered at 1650oC for the period of 2, 3, 4 h and 1, 2, 3 h respectively, whereas for SiO2-xGnP and SiO2-MWCNT nanocomposites the cold compaction was achieved at ~310 MPa and the nanocomposites were sintered at 1350oC for a period of 2 h and 4 h. For the SPSed samples, Al2O3-xGnP and Al2O3-MWCNT nanocomposites were prepared at 1450oC under 50 MPa pressure for the duration of 5 min and 10 min respectively. For the development of various SiO2-xGnP and SiO2-MWCNT nanocomposites, SPS was carried out at 1350oC under 40 MPa pressure for the duration of 10 min. Near full densification was achieved for all the SPSed Al2O3-xGnP, Al2O3-MWCNT, SiO2-xGnP and SiO2-MWCNT nanocomposites. The microstructural characterization and analysis of mechanical properties of developed nanocomposites was carried out. A significant improvement in the mechanical properties like relative density, hardness, wear resistance and indentation toughness was observed for various Al2O3 and SiO2 based CMNCs. The loading level of nanofillers play a vital role in effecting the properties of the nanocomposites. A remarkable improvement in the mechanical properties of various conventionally sintered and SPSed nanocomposites, upto an optimum loading level of both nanofillers was observed. The indentation toughness of various Al2O3-xGnP and Al2O3-MWCNT nanocomposites showed an improvement only upto the addition of 0.8 vol. % of xGnPs and MWCNT, whereas for the SiO2-xGnP and SiO2-MWCNTs nanocomposites, an improvement in the fracture toughness value was observed up to the loading level of 3 vol. % of both the nanofillers. The toughening mechanisms such as crack bridging, crack deflection and crack branching attributed to the improvement of the fracture toughness of the nanocomposites. An increase in the content of xGnPs and MWCNTS up to 5 vol. % deteriorated the mechanical properties of various CMNCs due to the agglomeration of both the nanofillers. The wear mechanism in the various nanocomposites was found to involve abrasion, galling and pullout of the nanofillers. Results suggest that the Al2O3-xGnP and SiO2-xGnP nanocomposites possess better mechanical attributes as compared to Al2O3-MWCNT and SiO2-MWCNT nanocomposites when prepared under similar conditions. Furthermore, SPSed nanocomposites were found to possess superior mechanical properties as compared to the conventionally sintered nanocomposites.