A study of magnetic non-linearity and finite length effects in solid iron subjected to a travelling MMF wave

This thesis describes an experimental and analytic study of the effects of magnetic non-linearity and finite length on the loss and field distribution in solid iron due to a travelling mmf wave. In the first half of the thesis, a two-dimensional solution is developed which accounts for the effects of both magnetic non-linearity and eddy-current reaction; this solution is extended, in the second half, to a three-dimensional model. In the two-dimensional solution, new equations for loss and flux/pole are given; these equations contain the primary excitation, the machine parameters and factors describing the shape of the normal B-H curve. The solution applies to machines of any air-gap length. The conditions for maximum loss are defined, and generalised torque/frequency curves are obtained. A relationship between the peripheral component of magnetic field on the surface of the iron and the primary excitation is given. The effects of magnetic non-linearity and finite length are combined analytically by introducing an equivalent constant permeability into a linear three-dimensional analysis. The equivalent constant permeability is defined from the non-linear solution for the two-dimensional magnetic field at the axial centre of the machine to avoid iterative solutions. In the linear three-dimensional analysis, the primary excitation in the passive end-regions of the machine is set equal to zero and the secondary end faces are developed onto the air-gap surface. The analyses, and the assumptions on which they are based, were verified on an experimental machine which consists of a three-phase rotor and alternative solid iron stators, one with copper end rings, and one without copper end rings j the main dimensions of the two stators are identical. Measurements of torque, flux /pole, surface current density and radial power flow were obtained for both stators over a range of frequencies and excitations. Comparison of the measurements on the two stators enabled the individual effects of finite length and saturation to be identified, and the definition of constant equivalent permeability to be verified. The penetration of the peripheral flux into the stator with copper end rings was measured and compared with theoretical penetration curves. Agreement between measured and theoretical results was generally good.

Electrodeposition of corrosion resistant zinc alloy coatings

With the increase use of de-icing salts on roads for safety, the need for improved corrosion resistance of the traditional galvanized automobile bodies has never been greater. In the present work, Zn alloy coatings (Zn-Ni and Zn-Co) were studied as an alternative to pure Zn coatings. The production of these deposits involved formulation of various acidic (pH of about 5.5) chloride based solutions. These showed anomalous deposition, that is, alloys were deposited much more easily than expected from the noble behaviour of Ni and Co metals. Coating compositions ranging from 0 to about 37% Ni and 20% Co were obtained. The chemical composition of the coatings depended very much on the electrolytes nature and operating conditions. The Ni content of deposits increased with increase in Ni bath concentration, temperature, pH and solution agitation but decreased considerably with increase in current density. The throwing power of the Zn-Ni solution deteriorated as Ni metal bath concentration increased. The Co content of deposits also increased with increase in Co bath concentration and temperature, and decreased with increase in current density. However, the addition of commercial organic additives to Zn-Co plating solutions suppressed considerably the amount of Co in the coatings. The Co content of deposits plated from Zincrolyte solution was found to be more sensitive to variation in current density than in the case of deposits plated from the alkaline Canning solution. The chromating procedures were carried out using laboratory formulated solution and commercially available ones. The deposit surface state was of great significance in influencing the formulation of conversion coatings. Bright and smooth deposits acquired an iridescent colour when treated with the laboratory formulated solution. However, the dull deposits acquired a brownish appearance. The correlation between the electrochemical test results and the neutral salt spray in marine environment was good. Non-chromated Zn-Ni coatings containing about 11-14% Ni increased in corrosion resistance compared to pure Zn. Non-chromated Zn-Co deposits of composition 4-8% were required to show a significant improvement in corrosion resistance Corrosion resistance was improved considerably by conversion coating. However, the type of conversion coating was very important. Samples treated in a laboratory solution performed badly compared to those treated in commercial solutions. Zn alloy coatings were superior to pure Zn, the Schloetter sample (13.8% Ni) had the lowest corrosion rate, followed by the Canning sample (1.0% Co) and then Zincrolyte (0.3% Co).Neither the chromium content of the conversion films nor the chromium state was found to have an effect on corrosion performance of the coatings.

Radial-field magnetic electron lenses

This investigation looks critically at conventional magnetic lenses in the light of present-day technology with the aim of advancing electron microscopy in its broadest sense. By optimising the cooling arrangements and heat transfer characteristics of lens windings it was possible to increase substantially the current density in the winding, and achieve a large reduction in the size of conventional magnetic electron lenses. Following investigations into the properties of solenoidal lenses, a new type of lens with only one pole-piece was developed. The focal properties of such lenses, which differ considerably from those.of conventional lenses, have been derived from a combination of mathematical models and experimentally measured axial flux density distributions. These properties can be profitably discussed with reference to "half-lenses". Miniature conventional twin pole-piece lenses and the proposed radial field single pole-piece lenses have been designed and constructed and both types of lenses have been evaluated by constructing miniature electron optical columns. A miniature experimental transmission electron microscope (TEM), a miniature scanning electron microscope (SEM) and a scanning transmission microscope (STEM) have been built. A single pole-piece miniature one million volt projector lens of only lOcm diameter and weighing 2.lkg was designed, built and tested at 1 million volts in a commercial electron microscope. iii. Preliminary experiments indicate that in single pole lenses it is possible to extract secondary electrons from the specimen in spite of the presence of the magnetic field of the probe-forming lens. This may well be relevant for the SEM in which it is desirable to examine a large specimen at a moderately good resolution.

The electron optical limits of performance of single-polepiece magnetic electron lenses

The thesis is concerned with the electron properties of single-polepiece magnetic electron lenses especially under conditions of extreme polepiece saturation. The electron optical properties are first analysed under conditions of high polepiece permeability. From this analysis, a general idea can be obtained of the important parameters that affect ultimate lens performance. In addition, useful information is obtained concerning the design of improved lenses operating under conditions of extreme polepiece saturation, for example at flux densities of the order of 10 Tesla. It is shown that in a single-polepiece lens , the position and shape of the lens exciting coil plays an important role. In particular, the maximum permissible current density in the windings,rather than the properties of the iron, can set a limit to lens performance. This factor was therefore investigated in some detail. The axial field distribution of a single-polepiece lens, unlike that of a conventional lens, is highly asymmetrical. There are therefore two possible physical arrangements of the lens with respect to the incoming electron beam. In general these two orientations will result in different aberration coefficients. This feature has also been investigated in some detail. Single-pole piece lenses are thus considerably more complicated electron- optically than conventional double polepiece lenses. In particular, the absence of the usual second polepiece causes most of the axial magnetic flux density distribution to lie outside the body of the lens. This can have many advantages in electron microscopy but it creates problems in calculating the magnetic field distribution. In particular, presently available computer programs are liable to be considerably in error when applied to such structures. It was therefore necessary to find independent ways of checking the field calculations. Furthermore, if the polepiece is allowed to saturate, much more calculation is involved since the field distribution becomes a non-linear function of the lens excitation. In searching for optimum lens designs, care was therefore taken to ensure that the coil was placed in the optimum position. If this condition is satisfied there seems to be no theoretical limit to the maximum flux density that can be attained at the polepiece tip. However , under iron saturation condition, some broadening of the axial field distribution will take place, thereby changing the lens aberrations . Extensive calculations were therefore made to find the minimum spherical and chromatic aberration coefficients . The focal properties of such lens designs are presented and compared with the best conventional double-polepiece lenses presently available.

Microstructural analysis of surface and interface zones in concrete

Several of OPC paste and concrete specimens, with different mix proportions, were cast against CPF and impermeable formwork (IF) and the profiles of pore structure, microhardness and scratch hardness of the cover zone were established. The chloride ingress and the depth of carbonation of the surface zone of concrete cast against CPF and IF were investigated. The main mechanisms controlling the ECR processes and the factors affecting such treatment were critically reviewed. Subsequently, as a means of restoring passivation of steel embedded in carbonated concrete, such HCP specimens were subjected to ECR. The influence of ECR on the chemistry of the pore solution and the microstructure of the surface and the steel/cement past interface zones were also studied. The main findings of this investigation were as follows: (a) The thickness of the microstructure gradient of cover concrete is significantly decreased with increasing period of water curing but is relatively unaffected by curing temperature, w/e ratio and the use of cement replacement materials. (b) The scratch hardness technique was shown to be potentially useful for characterising the microstructure and microhardness gradients of the surface zone. (c) A relationship between the microstructure gradient and mass transport properties of the surface zone was established. (d) The use of CPF resulted in a significant reduction in porosity of both the cement paste matrix and the aggregate/cement paste transition zone, and a marked improvement in the resistance of the surface zone to carbonation and the ingress of chloride ions. (e) The ECR treatment resulted in a marked densification of the pore structure and in changes to the pore solution chemistry and the cement phases of near-surface and steel/cement paste transition zones. This effect was more pronounced with current density, period of treatment and particularly with the use of sodium phosphate as an electrolyte.

Electrochemical chloride extraction to halt corrosion of reinforcement

This thesis presents results of experiments designed to study the effect of applying electrochemical chloride extraction (ECE) to a range of different hardened cement pastes. Rectangular prism specimens of hydrated cement paste containing sodium chloride at different concentrations were subjected to electrolysis between the embedded steel cathodes and external anodes of activated titanium mesh. The cathodic current density used was in the range of 1 to 5 A/m2 with treatment periods of 4 to 12 weeks. After treatment, the specimens were cut into sections which were subjected to pore-solution expression and analysis in order to determine changes in the distribution of free and total ionic species. The effect of the ECE treatment on the physical and microstructural properties of the cements was studied by using microhardness and MIP techniques. XRD was employed to look at the possibility of ettringite redistribution as a result of the accumulation of soluble sulphate ions in the cement matrix near the cathode during ECE. Remigration of chloride which remains after the ECE treatment and distribution of other ions were studied by analysing specimens which had been stored for several months, after undergoing ECE treatment. The potentials of the steel cathodes were also monitored over the period to detect any changes in their corrosion state. The main findings of this research were as follows: 1, ECE, as applied in this investigation, was capable of removing both free and bound chloride. The removal process occurred relatively quickly and an equilibrium between free and bound chlorides in the specimens was maintained throughout. At the same time, alkali concentrations in the pore solution near the steel cathode increased. The soluble sulphate ionic concentration near the cathode also increased due to the local increase in the pH of the pore solution. 2, ECE caused some changes in physical and microstructural of the cement matrix. However these changes were minimal and in the case of microhardness, the results were highly scattered. Ettringite in the bulk material well away from the cathode was found not to increase significantly with the increase in charge passed.3, Remigration of chloride and other ionic species occurred slowly after cessation of ECE with a resultant gradual increase in the Cl-/OH- ratio around the steel.4, The removal of chloride from blended cements was slower than that from OPC.

Cathodic protection of reinforced concrete:anodic processes in cements and related electrolytes

The nature and kinetics of electrode reactions and processes occurring for four lightweight anode systems which have been utilised in reinforced concrete cathodic protection systems have been studied. The anodes investigated were flame sprayed zinc, conductive paint and two activated titanium meshes. The electrochemical properties of each material were investigated in rapidly stirred de-oxygenated electrolytes using anodic potentiodynamic polarisation. Conductive coating electrodes were formed on glass microscope slides, whilst mesh strands were immersed directly. Oxygen evolution occurred preferentially for both mesh anodes in saturated Ca (OH)2/CaC12 solutions but was severely inhibited in less alkaline solutions and significant current only passed in chloride solutions. The main reactions for conductive paint was based on oxygen evolution in all electrolytes, although chlorides increased the electrical activity. Self-corrosion of zinc was controlled by electrolyte composition and the experimental set-up, chlorides increasing the electrical activity. Impressed current cathodic protection was applied to 25 externally exposed concrete slabs over a period of 18 months to investigate anode degradation mechanisms at normal and high current densities. Specimen chloride content, curing and reinforcement depth were also variables. Several destructive and non-destructive methods for assessing the performance of anodes were evaluated including a site instrument for quantitative "instant-off- potential measurements. The impact of cathodic protection on the concrete substrate was determined for a number of specimens using appropriate methods. Anodic degradation rates were primarily influenced by current density, followed by cemendtious alkalinity, chloride levels and by current distribution. Degradation of cementitious overlays and conductive paint substrates proceeded by sequential neutralisation of cement phases, with some evidence of paint binder oxidation. Sprayed zinc progressively formed an insulating layer of hydroxide complexes, which underwent pitting_ attack in the presence of sufficient chlorides, whilst substrate degradation was minimal. Adhesion of all anode systems decreased with increasing current density. The influence of anode material on the ionic gradients which can develop during cathodic protection was investigated. A constant current was passed through saturated cement paste prisms containing calcium chloride to central cathodes via anodes applied or embedded at each end. Pore solution was obtained from successive cut paste slices for anion and cation analyses. Various experimental errors reduced the value of the results. Characteristic S-shaped profiles were not observed and chloride ion profiles were ambiguous. Mesh anode specimens were significantly more durable than the conductive coatings in the high humidity environment. Limited results suggested zinc ion migration to the cathode region. Electrical data from each investigation clearly indicated a decreasing order of anode efficiency by specific anode material.

Use of ultrasonic agitation in iron group alloy electrodepositions

The effects of ultrasonic agitation on deposition from two iron group alloy plating solutions, nickel-cobalt and bright nickel-iron, have been studied. Comparison has been made with deposits plated from the same solutions using controlled air agitation. The ultrasonic equipment employed had a fixed frequency of 13 KHz but the power output from each transducer was variable up to a maximum of 350 watts. The effects of air and ultrasonic agitation on hardness, ductility, tensile strength, composition, structure, surface topography, limiting current density, cathode current efficiency and macro-throwing power were determined. Transmission and scanning electron microscopy, electron-probe microanalysis and atomic absorption spectrophotometry have been employed to study the nickel alloy deposits produced. The results obtained show that the use of Ultrasonics increased significantly the hardness of both alloy deposits and altered their composition by decreasing the cobalt and iron contents from nickel-cobalt and nickeliron solutions respectively. The ductility of coatings improved but the tensile strength did not change very much. Ultrasonic agitation gave larger grained deposits than air and they seemed to have a lower stress. Dull cobalt-nickel deposits had a similar pyramidal surface topography regardless of the type of agitation but the bright appearance of the nickel-iron was destroyed by ultrasonic agitation; an unusual ribbed pattern was produced. The use of ultrasonic agitation permitted approximately a twofold increase in the plating current density at which sound deposits could be achieved but there was only a slight increase in cathode current efficiency. Macro-throwing power of the solutions was increased slightly by the use of ultrasonic agitation. ultrasonic agitation is an expensive means of agitating plating Solutions and would be worthwhile only if significant improvements in properties could be achieved. The simultaneous improvement in hardness and ductility is a novel feature that should have useful engineering applications.

AlGaInP red-emitting light emitting diode under extremely high pulsed pumping

Efficiency of commercial 620 nm InAlGaP Golden Dragon-cased high-power LEDs has been studied under extremely high pump current density up to 4.5 kA/cm2 and pulse duration from microsecond down to sub-nanosecond range. No efficiency decrease and negligible red shift of the emission wavelength is observed in the whole range of drive currents at nanosecond-range pulses with duty cycles well below 1%. Analysis of the pulse-duration dependence of the LED efficiency and emission spectrum suggests the active region overheating to be the major mechanism of the LED efficiency reduction at higher pumping, dominating over the electron overflow and Auger recombination.

Carbon nanotube based systems for high energy efficient applications

In the current age of fast-depleting conventional energy sources, top priority is given to exploring non-conventional energy sources, designing highly efficient energy storage systems and converting existing machines/instruments/devices into energy-efficient ones. ‘Energy efficiency’ is one of the important challenges for today’s scientific and research community, worldwide. In line with this demand, the current research was focused on developing two highly energy-efficient devices – field emitters and Li-ion batteries, using beneficial properties of carbon nanotubes (CNT). Interface-engineered, directly grown CNTs were used as cathode in field emitters, while similar structure was applied as anode in Li-ion batteries. Interface engineering was found to offer minimum resistance to electron flow and strong bonding with the substrate. Both field emitters and Li-ion battery anodes were benefitted from these advantages, demonstrating high energy efficiency. Field emitter, developed during this research, could be characterized by low turn-on field, high emission current, very high field enhancement factor and extremely good stability during long-run. Further, application of 3-dimensional design to these field emitters resulted in achieving one of the highest emission current densities reported so far. The 3-D field emitter registered 27 times increase in current density, as compared to their 2-D counterparts. These achievements were further followed by adding new functionalities, transparency and flexibility, to field emitters, keeping in view of current demand for flexible displays. A CNT-graphene hybrid structure showed appreciable emission, along with very good transparency and flexibility. Li-ion battery anodes, prepared using the interface-engineered CNTs, have offered 140% increment in capacity, as compared to conventional graphite anodes. Further, it has shown very good rate capability and an exceptional ‘zero capacity degradation’ during long cycle operation. Enhanced safety and charge transfer mechanism of this novel anode structure could be explained from structural characterization. In an attempt to progress further, CNTs were coated with ultrathin alumina by atomic layer deposition technique. These alumina-coated CNT anodes offered much higher capacity and an exceptional rate capability, with very low capacity degradation in higher current densities. These highly energy efficient CNT based anodes are expected to enhance capacities of future Li-ion batteries.

Carbon nanostructure based electrodes for high efficiency dye sensitized solar cell

Synthesis and functionalization of large-area graphene and its structural, electrical and electrochemical properties has been investigated. First, the graphene films, grown by thermal chemical vapor deposition (CVD), contain three to five atomic layers of graphene, as confirmed by Raman spectroscopy and high-resolution transmission electron microscopy. Furthermore, the graphene film is treated with CF4 reactive-ion plasma to dope fluorine ions into graphene lattice as confirmed by X-ray photoelectron spectroscopy (XPS) and UV-photoemission spectroscopy (UPS). Electrochemical characterization reveals that the catalytic activity of graphene for iodine reduction enhanced with increasing plasma treatment time, which is attributed to increase in catalytic sites of graphene for charge transfer. The fluorinated graphene is characterized as a counter-electrode (CE) in a dye-sensitized solar cell (DSSC) which shows ~ 2.56% photon to electron conversion efficiency with ~11 mAcm−2 current density. Second, the large scale graphene film is covalently functionalized with HNO3 for high efficiency electro-catalytic electrode for DSSC. The XPS and UPS confirm the covalent attachment of C-OH, C(O)OH and NO3- moieties with carbon atoms through sp2-sp3 hybridization and Fermi level shift of graphene occurs under different doping concentrations, respectively. Finally, CoS-implanted graphene (G-CoS) film was prepared using CVD followed by SILAR method. The G-CoS electro-catalytic electrodes are characterized in a DSSC CE and is found to be highly electro-catalytic towards iodine reduction with low charge transfer resistance (Rct ~5.05 Ωcm 2) and high exchange current density (J0~2.50 mAcm -2). The improved performance compared to the pristine graphene is attributed to the increased number of active catalytic sites of G-CoS and highly conducting path of graphene. We also studied the synthesis and characterization of graphene-carbon nanotube (CNT) hybrid film consisting of graphene supported by vertical CNTs on a Si substrate. The hybrid film is inverted and transferred to flexible substrates for its application in flexible electronics, demonstrating a distinguishable variation of electrical conductivity for both tension and compression. Furthermore, both turn-on field and total emission current was found to depend strongly on the bending radius of the film and were found to vary in ranges of 0.8 - 3.1 V/μm and 4.2 - 0.4 mA, respectively.

Estudo da participação das espécies fortemente oxidantes produzidas durante a oxidação eletroquímica de corantes usando eletrodo de diamante dopado com boro: função das propriedades eletroquímicas do eletrodo e condições experimentais

The textile industry is one of the most polluting in the world (AHMEDCHEKKAT et al. 2011), generating wastewater with high organic loading. Among the pollutants present in these effluents are dyes, substances with complex structures, toxic and carcinogenic characteristics, besides having a strong staining. Improper disposal of these substances to the environment, without performing a pre-treatment can cause major environmental impacts. The objective this thesis to use a technique of electrochemical oxidation of boron doped diamond anode, BDD, for the treatment of a synthetic dye and a textile real effluent. In addition to studying the behavior of different electrolytes (HClO4, H3PO4, NaCl and Na2SO4) and current densities (15, 60, 90 and 120 mA.cm-2 ), and compare the methods with Rhodamine B (RhB) photolysis, electrolysis and photoelectrocatalytic using H3PO4 and Na2SO4. Electrochemical oxidation studies were performed in different ratio sp3 /sp2 of BDD with solution of RhB. To achieve these objectives, analysis of pH, conductivity, UV-visible, TOC, HPLC and GC-MS were developed. Based on the results with the Rhodamine B, it was observed that in all cases occurred at mineralization, independent of electrolyte and current density, but these parameters affect the speed and efficiency of mineralization. The radiation of light was favorable during the electrolysis of RhB with phosphate and sulfate. Regarding the oxidation in BDD anode with different ratio sp3 /sp2 (165, 176, 206, 220, 262 e 329), with lower carbon-sp3 had a longer favoring the electrochemical conversion of RhB, instead of combustion. The greater the carbon content on the anodes BDD took the biggest favor of direct electrochemical oxidation

Estudo da densidade de corrente crítica para reversão da magnetização de nanoelementos ferromagnéticos

The discovery that a spin-polarized current is capable of exerting a torque in a ferromagnetic material, through spin transfer, might provide the development of new technological devices that store information via the direction of magnetization. The reduction of current density to revert the magnetization is a primary issue to potential applications on non volatile random access memories (MRAM). We report a theorical study of the dipolar and shape effects on the critical current density for reversal of magnetization, via spin transfer torque (STT), on ferromagnetic nanoelements. The nanostructured system consists on a reference layer, in which the current will be spin-polarized, and a free layer of magnetization reversal. We observed considerable changes on the critical current density as a function of the element’s reversion layer thickness (t = 1.0 nm, 1.5 nm, 2.0 nm e 2.5 nm) and geometry (circular and elliptical), the material kind of the system free layer (Iron and Permalloy) and according to the orientation of the magnetization and the spin polarization with the major axis. We show that the critical current density may be reduced about 50% by reducing the Fe free layer thickness and around 75% when we change the saturation magnetization of circular nanoelements with 2.5 nm of thickness. We still observed a reduction as much as 90% on the current density of reversion for thin nanoelements magnetized along the minor axis direction, using in-plane spin polarization parallel to the magnetization.

Aplicação de tecnologias eletroquímicas (oxidação via radicais hidroxila, oxidação mediada via cloro ativo e eletrocoagulação) para o tratamento de efluentes reais ou sintéticos

In this work the degradation of real and synthetic wastewater was studied using electrochemical processes such as oxidation via hydroxyl radicals, mediated oxidation via active chlorine and electrocoagulation. The real effluent used was collected in the decanter tank of the Federal University of Rio Grande do Norte (ETE-UFRN) of Effluent Treatment Plant and the other a textile effluent dye Ácido Blue 113 (AB 113) was synthesized in the laboratory. In the electrochemical process, the effects of anode material, current density, the presence and concentration of chloride as well as the active chlorine species on site generated were evaluated. Electrodes of different compositions, Ti/Pt, Ti/Ru0,3Ti0,7O2, BDD, Pb/PbO2 and Ti/TiO2-nanotubes/PbO2 were used as anodes. These electrodes were subjected to electroanalytical analysis with the goal of checking how happen the anodic and cathodic processes across the concentrations of NaCl and supporting electrolyte used. The potential of oxygen evolution reaction were also checked. The effect of active chlorine species formed under the process efficiency was evaluated by removing the organic matter in the effluent-ETE UFRN. The wastewater treatment ETE-UFRN using Ti/Pt, DDB and Ti/Ru0,3Ti0,7O2 electrodes was evaluated, obtaining good performances. The electrochemical degradation of effluent-UFRN was able to promote the reduction of the concentration of TOC and COD in all tested anodes. However, Ti/Ru0,3Ti0,7O2 showed a considerable degradation due to active chlorine species generated on site. The results obtained from the electrochemical process in the presence of chloride were more satisfactory than those obtained in the absence. The addition of 0.021 M NaCl resulted in a faster removal of organic matter. Secondly, was prepared and characterized the electrode Ti/TiO2-nanotubes/PbO2 according to what the literature reports, however their preparation was to disk (10 cm diameter) with surface area and higher than that described by the same authors, aiming at application to textile effluent AB 113 dye. SEM images were taken to observe the growth of TiO2 nanotubes and confirm the electrodeposition of PbO2. Atomic Force Microscope was also used to confirm the formation of these nanotubes. Furthermore, was tested and found a high electrochemical stability of the electrode Ti/TiO2-nanotubes/PbO2 for applications such as long-term indicating a good electrocatalytic material. The electrochemical oxidation of AB 113 using Ti/Pt, Pb/PbO2 and Ti/TiO2-nanotubes/PbO2 and Al/Al (electrocoagulation) was also studied. However, the best color removal and COD decay were obtained when Ti/TiO2-nanotubes/PbO2 was used as the anode, removing up to 98% of color and 92,5% of COD decay. Analysis of GC/MS were performed in order to identify possible intermediates formed in the degradation of AB 113.

Tecnologia eletroquímica como tratamento alternativo de efluentes derivados da indústria têxtil e petroquímica

In this work, the treatment of wastewater from the textile industry, containing dyes as Yellow Novacron (YN), Red Remazol BR (RRB) and Blue Novacron CD (NB), and also, the treatment of wastewater from petrochemical industry (produced water) were investigated by anodic oxidation (OA) with platinum anodes supported on titanium (Ti/Pt) and boron-doped diamond (DDB). Definitely, one of the main parameters of this kind of treatment is the type of electrocatalytic material used, since the mechanisms and products of some anodic reactions depend on it. The OA of synthetic effluents containing with RRB, NB and YN were investigated in order to find the best conditions for the removal of color and organic content of the dye. According to the experimental results, the process of OA is suitable for decolorization of wastewaters containing these textile dyes due to electrocatalytic properties of DDB and Pt anodes. Removal of the organic load was more efficient at DDB, in all cases; where the dyes were degraded to aliphatic carboxylic acids at the end of the electrolysis. Energy requirements for the removal of color during OA of solutions of RRB, NB and YN depends mainly on the operating conditions, for example, RRB passes of 3.30 kWh m-3 at 20 mA cm-2 for 4.28 kWh m-3 at 60 mA cm-2 (pH = 1); 15.23 kWh m-3 at 20 mA cm-2 to 24.75 kWh m-3 at 60 mA cm-2 (pH 4.5); 10.80 kWh m-3 at 20 mA cm-2 to 31.5 kWh m-3 at 60 mA cm-2 (pH = 8) (estimated data for volume of treated effluent). On the other hand, in the study of OA of produced water effluent generated by petrochemical industry, galvanostatic electrolysis using DDB led to the complete removal of COD (98%), due to large amounts of hydroxyl radicals and peroxodisulphates generated from the oxidation of water and sulfates in solution, respectively. Thus, the rate of COD removal increases with increasing applied current density (15-60 mAcm-2 ). Moreover, at Pt electrode, approximately 50% removal of the organic load was achieved by applying from 15 to 30 mAcm-2 while 80% of COD removal was achieved for 60 mAcm-2 . Thus, the results obtained in the application of this technology were satisfactory depending on the electrocatalytic materials and operating conditions used for removal of organic load (petrochemical and textile effluents) as well as for the removal of color (in the case of textile effluents). Therefore, the applicability of electrochemical treatment can be considered as a new alternative like pretreatment or treatment of effluents derived from textiles and petrochemical industries.