The corrosion behaviour of cast Al-Mg alloy A535 and its composites containing 10 wt.% and 15 wt.% fly ash, and 10 wt.% hybrid reinforcement (5 wt.% fly ash + 5 wt.% SiC) was investigated using weight-loss and electrochemical corrosion tests, optical microscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). The tests were conducted in fresh water collected from the South Saskatchewan River and 3.5 wt.% NaCl solution at room temperature. The pH of the salt solution varied from 3 to 9. For comparison, two other aluminum alloys, AA2618 and AA5083-H116, were tested in the same electrolytes. The results of the weight-loss corrosion test showed that unreinforced A535 alloy had a lower corrosion rate in fresh water and seawater environments than the composites at all the tested pH values. The corrosion rate of the composites increased with increasing fly ash content. As expected, the corrosion rates of A535 alloy and the composites tested in fresh water were lower than those in salt solution. The results of the potentiodynamic and cyclic polarization electrochemical tests showed that the corrosion potential (Ecorr) and pitting potential (Epit) of the alloy were more positive than those of the composites. The corrosion and pitting potentials of the composites became more negative (active) with increasing fly ash content. The composites showed more positive (noble) repassivation or protection potential (Erp) than the matrix alloy, with the positivity increasing with fly ash content. Analysis of the electrochemical noise data showed that pitting corrosion was the dominant mode of corrosion for the alloy in 3.5 wt.% NaCl solution. Optical microscopy and SEM revealed that Mg2Si phase and Al-Mg intermetallics corroded preferentially to the matrix. The EDS data indicated that the protective oxide film formed on A535 contained Al2O3 and MgO.

The corrosion behaviour of cast Al-Mg alloy A535 and its composites containing 10 wt.% and 15 wt.% fly ash, and 10 wt.% hybrid reinforcement (5 wt.% fly ash + 5 wt.% SiC) was investigated using weight-loss and electrochemical corrosion tests, optical microscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). The tests were conducted in fresh water collected from the South Saskatchewan River and 3.5 wt.% NaCl solution at room temperature. The pH of the salt solution varied from 3 to 9. For comparison, two other aluminum alloys, AA2618 and AA5083-H116, were tested in the same electrolytes. The results of the weight-loss corrosion test showed that unreinforced A535 alloy had a lower corrosion rate in fresh water and seawater environments than the composites at all the tested pH values. The corrosion rate of the composites increased with increasing fly ash content. As expected, the corrosion rates of A535 alloy and the composites tested in fresh water were lower than those in salt solution. The results of the potentiodynamic and cyclic polarization electrochemical tests showed that the corrosion potential (Ecorr) and pitting potential (Epit) of the alloy were more positive than those of the composites. The corrosion and pitting potentials of the composites became more negative (active) with increasing fly ash content. The composites showed more positive (noble) repassivation or protection potential (Erp) than the matrix alloy, with the positivity increasing with fly ash content. Analysis of the electrochemical noise data showed that pitting corrosion was the dominant mode of corrosion for the alloy in 3.5 wt.% NaCl solution. Optical microscopy and SEM revealed that Mg2Si phase and Al-Mg intermetallics corroded preferentially to the matrix. The EDS data indicated that the protective oxide film formed on A535 contained Al2O3 and MgO.

This work aims to study the niobium influence in the crystallographic texture and the corrosion resistance of ferritic stainless steels on aerated and de-aerated environments. For this objective the ferritic stainless steels P409, P410, P430A, P430E (Nb stabilized) were used; and austenitic stainless steel, P304, and carbon steel, A36, were used as comparative materials. These materials had a mechanical characterization (hardness and tension test), and the steels P430A and P430E had a crystallographic characterization too. That crystallographic characterization (by EBSD) was analyzed through to inverse pole figure (IPF) and crystal orientation distribution function (CODF). The samples were submitted to anodic potentiodynamic polarization test in solutions: 3.56% NaCl, and 1N H2SO4 on aerated environment, and 3.56% NaCl at de-aerated environment. The samples were examined by SEM after the polarization tests. The analysis of the results clearly showed that the crystallographic texture influence the corrosion resistance. The niobium in the stainless steel reduces the presence of preferential orientation, therefore, the influence of the texture in the corrosion resistance, but helps to increase the corrosion resistance by the formation of niobium carbbonites. Finally it was observed that for polarization tests in aerated environments and de-aerated have a very small variation in behavior that depends on the steel, but this variation is not statistically significant. / O objetivo deste trabalho é estudar a influência do nióbio na textura cristalográfica e resistência à corrosão de aços inoxidáveis ferríticos em ambientes aerados e desaerados. Usou-se para o estudo os aços inoxidáveis ferríticos P409, P410, P430A, P430E (estabilizado ao Nb) e como objetos de comparação usaram-se os aços inoxidáveis austenítico P304 e o aço ao carbono A36. Neles realizou-se uma caracterização mecânica (dureza, ensaio de tração), e para os aços P430A e P430E foi feita uma caracterização cristalográfica (via EBSD) por meio de figura de polos inversa (IPF) e da função de distribuição de orientação cristalina (FDOC). As amostras foram submetidas a ensaios de polarização potenciodinâmica anódica para soluções de 3,56% NaCl e 1N de H2SO4 em ambiente aerado e solução de 3,56% NaCl em ambiente desaerado. As amostras foram examinadas por microscopia MEV após os ensaios de polarização. A análise dos resultados mostrou claramente que a textura cristalográfica influência a resistência à corrosão. O nióbio diminui a presença de orientações preferenciais, e, por consequência, a influência da textura na resistência à corrosão, no entanto aumenta a resistência à corrosão nos aços inoxidáveis pela formação de carbonetos de nióbio. Por último observou-se que para ensaios de polarização em ambientes aerados e desaerados existe uma ligeira variação no comportamento que depende de cada aço, mas que não é estatisticamente significativa. / Mestre em Engenharia Mecânica

This diploma thesis deals with various procedures of surface pretreatment of steel and aluminum alloy for subsequent application of powder coating substance. The work begins with an overview of the general characteristics of the materials used. The core part of the work is then a summary of the individual methods of pretreatment that can be used to modify the material surface. A special chapter is devoted to methodologies for the application of powder substances. Before separate application, the sample must first be carefully pretreated to ensure removal of organic compounds (e.g. oils from primary processing - grinding, cutting), or dust impurities to ensure the correct barrier effect. After dividing the individual methods of surface preparation, a powder paint system with a total thickness of approximately 50 µm is applied to the test material. Samples with different surface pretreatments will be compared both in terms of mechanical properties and in terms of electrochemical properties.

Additive manufacturing (AM) has the potential to overtake the conventional production of pipe systems of stainless steel grade 316L intended for bioprocessing applications by utilising powder bed fusion laser beam (PBF-LB) technologies. However, challenges such as high surface roughness need to be overcome and corrosion properties improved to meet industry standards. This can be done by applying surface post-treatments to the printed parts. Therefore, the first aim of this thesis was to investigate the ability of different post-treatments of PBF-LB 316L samples, including tumbling, electropolishing, chemical milling, Hirtisation®, and DryLyte®, to reduce the surface roughness. One set of samples was left untreated, as-built set, and used as reference. The second aim was to try to correlate the surface roughness with the corrosion properties of the various post-treated samples. Analytical techniques used included needle profilometry, light optical microscopy (LOM), critical pitting temperature (CPT), cyclic potentiodynamic polarisation (CPDP) and immersion in 1M NaCl and 1M NaOH for two different durations for each solution. While some results were expected, others were surprising. Even though tumbled samples resulted in the lowest surface roughness, the results for immersion and CPDP curves tests indicated the lowest corrosion resistance compared to the other post-treatments. On the other hand, electropolishing resulted in the lowest surface roughness reduction among the post-treated samples. However, these samples had comparatively high corrosion resistance in the CPT and CPDP tests. The DryLyte® samples were tested using two DryLyte® medias where one of them resulted in the second lowest surface roughness and showed highest corrosion resistance in all three corrosion tests even though the process parameters are still to be developed. The results for samples post-treated by Hirtisation® and chemical milling were inconsistent and need further investigations. The reference as-built set showed high corrosion resistance in its untreated state, indicating post-treatments having minor impact on its performance from a corrosion perspective. / Additiv tillverkning (AM) har möjlighet att konkurrera ut konventionell produktion av rörsystem i rostfritt stål typ 316L avsett för bioprocessapplikationer genom att använda pulverbäddsinfusionslaserstråleteknik (PBF-LB). För tekniken kvarstår dock utmaningar för att uppfylla branschstandarder då tillverkningen medför material med hög ytråhet och sämre korrosionsegenskaper än traditionella metoder. Detta kan åstadkommas genom olika typer av efterbearbetning av de printade ytorna. Ett syfte med denna studie var att utvärdera hur olika typer av efterbehandling av PBF-LB 316L (trumling, elektropolering, kemisk etsning, Hirtisation® och DryLyte®) påverkar ytråheten. Som referensmaterial användes obearbetade printade ytor. Studiens andra huvudmål var att undersöka möjligheten för korrelation mellan ytråhet efter behandling och korrosionsegenskaperna. Analyser gjordes med hjälp av nålprofilometri, ljusoptisk mikroskopi (LOM), bestämning av kritisk gropfrätningstemperatur (CPT), framtagning av cykliska potentiodynamiska polarisationskurvor (CPDP) samt nedsänkning i 1M NaCl och 1M NaOH under två olika tidsperioder per lösning. Resultaten var delvis väntade och delvis överraskande. Trots att de trumlade proverna resulterade i lägst ytråhet, visade de elektrokemiska studierna (CPDP) i de olika lösningarna på att lägre korrosionsbeständighet jämfört med övriga efterbehandlingar. Å andra sidan resulterade elektropolering resulterade i den lägsta minskningen i ytråhet bland de efterbehandlade proverna. Dessa prover visade dock på en jämförelsevis hög korrosionsbeständighet i både CPT och CPDP testerna. DryLyte®-proverna studerades med två olika DryLyte®-medier, varav en av dem gav näst lägst ytråhet samt visade högst korrosionsbeständighet i samtliga korrosionstester trots att processparametrarna inte ännu är optimerade för denna nya teknik. Resultaten för prover som efterbehandlats med Hirtisation® och kemisk etsning var tvetydiga och behöver studeras vidare. De obehandlade referensproverna indikerade hög korrosionsbeständighet, vilket tyder på att efterbehandlingar hade minimal påverkan ur ett korrosionsperspektiv.

The monitoring of pharmaceuticals, heavy metal, pH and free chlorine concentration in drinking water is important for public health and the environment. However, conventional laboratory-based analytical methods are labor-intensive, expensive, and time consuming. This thesis focuses on developing an integrated, highly sensitive, easy-to-use, and low-cost pharmaceuticals, heavy metal, pH and free chlorine sensing system for drinking water quality monitoring. A low-temperature, solution-processed modification of multi-walled carbon nanotubes (MWCNT) with β-cyclodextrin (βCD) on glassy carbon electrode is developed for detecting low levels of acetaminophen. The adsorption properties of βCD are combined with the high surface area of carbon nanotubes towards enhanced electrochemical sensing of acetaminophen with a limit of detection of 11 nM and linear range from 0.05-300 μM. Also, a systematic investigation is carried out using four types of modified MWCNT-βCD. A novel, one-step approach called Steglich esterification modified MWCNT-βCD results in large effective surface area, and fast electron transfer towards sensitive detection of acetaminophen and 17β-estradiol (E2, primary female sex hormone) in the range of 0.005–20 and 0.01–15 μM, with low detection limits of 3.3 and 2.5 nM, respectively. The similar MWCNT-βCD modified electrodes can also detect heavy metal ion (lead, Pb2+) with a limit of detection of <10 ppb. Low frequency noise behavior of these sensors are studied. A spin-coated Pd/PdO based pH sensor, and amine-modified carbon electrode-based free chlorine sensor are fabricated on a common substrate together with the pharmaceuticals and heavy metal sensors. A Wheatstone-bridge temperature sensor is fabricated based on silicon and PEDOT:PSS on another substrate. All the sensors are connected to an Arduino microcontroller based data acquisition system with a smartphone application interface. The integrated sensing system is easy-to-use, low-cost, and can provide accurate monitoring data with real drinking water samples. / Dissertation / Doctor of Philosophy (PhD) / Low-cost, easy-to-use, and sensitive monitoring system for pharmaceuticals, heavy metal, pH and free chlorine in drinking water is crucial for public health safety. In this thesis, we develop solution-based synthesis of multi-walled carbon nanotubes modified by β-cyclodextrin for electrochemical sensing of pharmaceuticals and heavy metal. The modification approaches are compared and characterized to analyze their electrochemical behavior and sensing performances. The developed sensors are highly sensitive toward the detection of acetaminophen (a widely used pain-killer) and estrogen hormone in drinking water. We also develop a modified spin-coating technique to deposit palladium/palladium oxide films for potentiometric pH sensor, a calibration-free free chlorine sensor based on modified carbon electrode, and a resistive temperature sensor. The developed pH, free chlorine and temperature sensors are highly sensitive, and stable with fast response time. All the sensors are integrated and interfaced with a custom-made and smartphone-controlled electronic readout system for accurate and on-site drinking water quality monitoring at low cost.

Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2017-11-09T17:58:22Z No. of bitstreams: 1 2017 - Mariana de Albuquerque Almeida.pdf: 2619920 bytes, checksum: 48c00262629bac9a7779fc4ea9ec94a6 (MD5) / Made available in DSpace on 2017-11-09T17:58:22Z (GMT). No. of bitstreams: 1 2017 - Mariana de Albuquerque Almeida.pdf: 2619920 bytes, checksum: 48c00262629bac9a7779fc4ea9ec94a6 (MD5) Previous issue date: 2017-05-10 / CAPES / This dissertation presents the evaluation of four thiosemicarbazones, from extracts of species of vegetables Talinum triangulare, Physalis angulata e Theobroma cacao L. besides formulation obtained from the combination extract of thiosemicarbazones vegetables as corrosion inhibitor in the presence of carbon steel AISI 1020. Thiosemicarbazones were obtained with good level of purity, satisfactory throughput and identified by NMR of 1H and 13C. The watery extract of Talinum triangulare was obtained using ultrasound device. The extracts of Physalis angulata species were obtained by maceration in water and the other one in ethyl acetate. The watery extracts of Theobroma cacao L. species were obtained using ultrasound device and decoction and hydroalcoholic extract was obtained by maceration in ethanol:water (80:20). The thiosemicarbazones, the vegetable extracts and their formulation were tested in the presence of corrosion of carbon steel AISI 1020 in solution 1 mol. L-1 of HCl. For this evaluation it was used the gravimetric techinique of weight loss and electrochemical techiniques of potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that the presence of thiosemicarbazones, as well as, the formulation increased significantly the resistence of carbon steel AISI 1020 in acidic medium. The results obtained in different used essays (weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy) show that these techniques are complementary in relation to the evaluation of corrosion inhibition. The best anti-corrosion efficiency was observed for thiosemicarbazone chloro and hydroxy-substituted and its formulations with the extract of T. triangulare achieving 88% and 87% of efficiency, by electrochemical impedance spectroscopy, respectively. / Nesta Tese ? apresentada a avalia??o de quatro tiossemicarbazonas, dos extratos das esp?cies vegetais Talinum triangulare, Physalis angulata e Theobroma cacao L., al?m de formula??es obtidas pela combina??o extrato vegetal:tiossemicarbazonas, como inibidores de corros?o frente ao a?o carbono AISI 1020 em meio de ?cido cloridr?co. As tiossemicarbazonas foram obtidas com bom grau de pureza, em rendimentos satisfat?rios e, caracterizadas por IV, RMN de ^1H e ^13C. O extrato aquoso de Talinum triangulare foi obtido em aparelho de ultrassom, os extratos da esp?cie Physalis angulata, foram obtidos sob macera??o em ?gua e o outro em acetato de etila; j? os extratos aquosos da esp?cie Theobroma cacao L. foram obtidos em aparelho de ultrassom e decoc??o e, finalmente, o extrato hidroalco?lico foi obtido por macera??o em etanol:?gua (80:20). As tiossemicarbazonas, os extratos vegetais e suas formula??es foram testadas frente ? corros?o de a?o carbono AISI 1020 em solu??o 1mol.L-1 de HCl. Para tal avalia??o foi utilizada a t?cnica gravim?trica de Perda de Massa e as t?cnicas eletroqu?micas de Polariza??o Potenciodin?mica e Espectroscopia de Imped?ncia Eletroqu?mica. Os resultados mostraram que a presen?a de tiossemicarbazonas, bem como, das formula??es aumentam significativamente a resist?ncia do a?o carbono AISI 1020 em ?cido. Os resultados obtidos nos diferentes ensaios utilizados (Perda de Massa, Polariza??o Potenciodin?mica e Espectroscopia de Imped?ncia Eletroqu?mica) mostraram que estas t?cnicas s?o complementares quanto a avalia??o da inibi??o da corros?o. A melhor efici?ncia anticorrosiva foi observada para as tiossemicarbazonas cloro e hidroxi-substitu?das e, para suas formula??es com o extrato da T. triangulare obtendo-se 88% e 87% de efici?ncia por espectroscopia de imped?ncia eletroqu?mica, respectivamente.