Orientador: Assis Vicente Benedetti / Banca: Koshum Iha / Banca: Paulo Olivi / Banca: Sérgio Machado Espíndola / Banca: Nelson Ramos Stradiotto / Resumo: O crômio é o principal elemento de liga, responsável pela alta resistência à corrosão dos aços inoxidáveis. Esta resistência está relacionada com a formação de óxidos e/ou hidróxidos de Cr3+ na superfície. A literatura reporta muitos trabalhos sobre a comportamento eletroquímico do crômio em meio de ácido sulfúrico. Entretanto pouco se conhece sobre o crômio em soluções contendo cloreto. Este conhecimento pode ser muito importante para entender o mecanismo de formação dos filmes e passivação da superfície do crômio e dos aços inoxidáveis. Neste trabalho estudou-se o comportamento eletroquímico do crômio em soluções contento íons cloreto, utilizando-se técnicas eletroquímicas convencionais. Espectroscopia fotoeletrônica e Uv-visível foram também empregadas para analisar, respectivamente, a superfície e espécies de crômio em solução. As curvas de polarização do crômio em soluções mostram três regiões de potenciais: ativa, passiva e transpassiva. Na região ativa verificou-se que o crômio se dissolve como Cr2+ junto com geração de hidrogênio. Para soluções com pH<3 a formação do filme passivo deve ocorrer via dissolução/precipitação enquanto que para soluções com pH>3 o mecanismo deve ser via formação direta do filme. As medidas de espectroscopia de impedância eletroquímica mostraram um circuito equivalente para a interface em solução com pH=0,3 e outro diferente para a interface em soluções com 0,3<pH. As análises por XPS revelaram que o filme é constituído basicamente por Cr2O3. Os resultados das medidas eletroquímicas e de espectroscopia UVvisível mostraram que o crômio e o filme passivante se dissolvem como dicromato na região de transpassivação. / Abstract: Chromium is the main alloying element for stainless steels responsible for their high corrosion resistance. This is due to the formation of Cr3+ surface oxides and/or hydroxides at the chromium surface. In the literature there are many papers reporting studies on the electrochemical behavior of chromium in sulfuric acid. Nevertheless, there is still a lack of knowledge about electrochemical in chloride ions medium. This knowledge can be useful to understand the film formation and passivation mechanisms of chromium and stainless steels. This work reports the influence of the pH dependence on the electrochemical behavior of chromium in aqueous Cl--containing solutions using conventional electrochemical techniques. X-ray Photoelectron and UV-vis Spectroscopies were used to analyze the surface composition and chromium species in solution, respectively. The polarization curves of chromium in acid solutions showed three potential regions: active, passive and the transpassive region. In the active region chromium dissolve as Cr2+ and hydrogen evolution was also observed. It seems that for solutions with pH<3 the formation of a passive layer occurs via a dissolution/precipitation process while for pH>3 the mechanism changes to direct film formation. The electrochemical impedance spectroscopy measurements, performed in the passive region agree with a circuit equivalent at pH=0.3 and another for 0.3< pH. XPS analysis revealed that the passive layer is basically constituted by Cr2O3. For the transpassive region the electrochemical results and UV-vis spectroscopy measurements indicated that both chromium and the passivating film dissolved as dichromate ions. / Doutor

nÃo hà / A exposiÃÃo ocupacional em ambientes de curtumes tem sido objeto de estudo e de investigaÃÃes cientÃficas. As informaÃÃes controversas sobre a toxicidade do cromo III e sua relaÃÃo com a epidemiologia do curtume serviram de subsÃdio para esta pesquisa. O objetivo deste estudo foi avaliar os possÃveis efeitos genotÃxicos e mutagÃnicos da exposiÃÃo de trabalhadores de curtume de Teresina (PI) à substÃncias quÃmicas contendo cromo III atravÃs do uso de biomarcadores de danos ao DNA e aos cromossomos.Trata-se de uma investigaÃÃo transversal, observacional e quantitativa. Foram coletadas amostras de mucosa, sangue e urina de 43 trabalhadores de curtume para anÃlise de micronÃcleo em mucosa (20 trabalhadores), micronÃcleo em linfÃcitos (30 trabalhadores), cometa em mucosa (20 trabalhadores), cometa em linfÃcitos (43 trabalhadores), aberraÃÃes cromossÃmicas (30 trabalhadores) e mensuraÃÃo de cromo na urina (27 trabalhadores) . As mesmas anÃlises foram realizadas em trabalhadores nÃo expostos ao ambiente do curtume, para fins de comparaÃÃo estatÃstica. AlÃm disso, foi aplicado um questionÃrio de saÃde pessoal recomendado pela International Comission for Protection Against Environmental Mutagens and Carcinogens-ICPEMC com intuito de correlacionar suas informaÃÃes aos dados obtidos nos testes. Os resultados indicaram aumentos significativos (p<0,05) do nÃmero (8,100  3,905 vs1,200 1,609) e frequÃncia de micronÃcleo em mucosa (0,403 0,1513vs 0,060 0,04887), do nÃmero (17,73  9,44vs10,90 7,092) e frequÃncia de micronÃcleos em linfÃcitos(0,886 0,472vs 0,306 0,202), para o total (16,3 3,38 vs 0,60  0,16) e frequÃncia (8,01  1,82 vs 0,403 0,09) de aberraÃÃes cromossÃmicas(teste T Student). AlÃm disso, foi observado aumento sigficativo (ANOVA p<0,05 ) para o todas as classes de danos e frequÃncia de danos no teste de cometa em mucosa e em linfÃcitos. O cromo na urina indicou que os trabalhadores estavam com maior concentraÃÃo deste metal na urina que os nÃo expostos (p<0,05 ) ( 1,108  1,277vs 0,089  0,027). As correlaÃÃes (Pearson) entre o cromo na urina e as anÃlises genotÃxicas indicaram forte relaÃÃo positiva com a frequÃncia de aberraÃÃes cromossÃmicas (r=0,841 p= 0,018 ) e frequÃncia de micronÃcleo em linfÃcitos (r=0,730 p < 0,0001).Conclui-se que os trabalhadores de curtume apresentam riscos de toxicidade e de instabilidade genÃtica associados à exposiÃÃo ocupacional a misturas quÃmicas contendo crmo III. / Occupational exposure in tannery environments has been the subject of study and scientific research. Controversial information about the toxicity of chromium III and its relationship with the epidemiology of the tannery employees served as a subsidy for this research. The objective of this study was to evaluate the possible genotoxic and mutagenic effects of the exposure of tannery workers in Teresina (PI) to chemicals containing chromium III through the use of biomarkers of DNA and chromosomal damage. This was a cross-sectional, observational and quantitative study. Samples were taken from the mucosa, blood and urine of 43 tannery workers to analyze mucosal micronuclei (20 workers), lymphocytic micronuclei (30 workers), mucosal comet assays (20 workers), lymphocytic comet assay (43 workers) and chromosomal aberrations (30 workers); the level of urinary chromium was also measured (27 employees).The same analyses were carried out in non-exposed workers of the tannery environment for statistical comparison. In addition, personal health questionnaires were administered as recommended by the International Commission for Protection Against Environmental Mutagens and Carcinogens-ICPEMC with the aim of correlating their information with data obtained in the tests. The results indicated significant increases (p <0.05) in: the number (8.100  3.905 vs 1.200  1.609) and frequency (0.403  0.060 vs. 0.1513  0.04887) of mucosal micronuclei; the number (17.73  9.44 vs 10.90  7.092) and frequency (0.886  0.472 vs 0.306  0.202) of lymphocytic micronuclei; and the total (16.3  3.38 vs 0.60  0.16) and frequency (8.01  1.82 vs 0.403  0.09) of chromosomal aberrations (Studentâs t test). There was a significant increase (ANOVA, p <0.05) for all types of damage and frequency of damage to the mucosal and lymphocytic COMET assay. Urine chromium levels was higher in exposed workers than in non-exposed workers (p <0.05) (1.108  1.277 vs 0.089  0.027).Pearson correlations between the level of chromium in the urine and genotoxic analyses indicated a strong positive correlation with the frequency of chromosomal aberrations (r = 0.841, p = 0.018) and frequency of lymphocytic micronuclei (r = 0.730, p <0.0001). It was concluded that the tannery workers are at risk of toxicity and genetic instability associated with occupational exposure to chemical mixtures containing chromium III.

Made available in DSpace on 2014-10-09T12:23:18Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:21Z (GMT). No. of bitstreams: 1 01037.pdf: 935328 bytes, checksum: ff8c1531e582a0ca8cc764019d7db537 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Biociencias, Universidade de Sao Paulo - IB/USP

M.Sc. (Experimental Physics) / Please refer to full text to view abstract

The chemistry of co-ordination compounds in general has played an important role in the development of the modern theory of valency, but the properties of complex salts between chromium and organic compounds containing carboxyl and amino- groups are of additional interest because of their bearing on the theory of certain technological processes such as chromium plating and, in particular, chrome-tanning. Owing to the rapid development of valence theory over the last two decades the technological chemist finds himself at a disadvantage vis-a-vis his academic counterpart in attempting to interpret the results of researches relating to these compounds as he must rely on the less powerful "classical" approach to his problems. Hence the need was felt for a brief survey of modern concepts of valency in terms of wave mechanics. For a more extended study the reader may consult the appropriate references and text books.

The kinetic behaviour of anhydrous CrCl₃ in gaseous oxidising atmospheres has been examined in the temperature range 350 to 630°C in order to identify optimum reaction conditions and to establish the mechanism by which the reaction is controlled. The reaction under consideration is CrCl₃ (s) + ¾ O₂ (g) → ½ Cr₂O₃ (s) + ³/₂ Cl₂ (g). The main experimental techniques used were isothermal and programmed-temperature thermogravimetry, supplemented by scanning electron-microscopy, surface-area determinations and porosity measurements. The effects of sample pelletisation, gas flowrate, temperature, oxygen partial pressure, pellet porosity and the addition of other oxide species on the rate and extent of reaction have been studied. The reaction is shown to occur in a single step, starting at -350°C under non-isothermal conditions, and exhibiting a deceleratory rate over most of the reaction. Isothermal thermogravimetric curves were fitted to a number of kinetic rate expressions, and a series of statistical analyses used to identify the rate equation which best describes the experimental data. Supporting evidence was provided by scanning electron-microscopic examination of partially-reacted samples. It is concluded that the reaction is under chemical control, and that reaction occurs by means of a linearly-advancing reactant-product interface. The reaction kinetics can be described by a contracting-geometry rate expression. / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

In this work physical and analytical methods have been used to investigate the potassium salts of certain dioxalato chromium (III) complexes. The solid potassium salts of the trioxalatochromiate and the cis and trans dioxalatodiaquochromiates together with a salt corresponding to potassium dioxalatosulphatoaquochromiate were prepared. The mono- and dihydroxo derivatives of the cis and trans dioxalatochromiates were also obtained in aqueous solution. The methods of preparation and analysis used are described. Spectrophotometric absorption curves obtained on solutions of these salts using a Beckman Spectrophotometer are in agreement with results of previous workers, and the new absorption curve obtained from a solution of the solid cis dioxalatodiaquochromia salt shows that it is pure and gives additional proof of the completeness of the trans - cis isomerisation. Summary, p. i.

Ph.D. (Physics) / Please refer to full text to view abstract.

New preparative routes to chromyl fluoride were sought. It was found that chlorine monofluoride reacts with chromium trioxide and chromyl chloride to produce chromyl fluoride. Attempts were made to define a mechanism for the reaction of ClF and Cr03 in light of by-products observed and previous investigations. Carbonyl fluoride and chromium trioxide react to form chromyl fluoride and carbon dioxide. A mechanism was also proposed for this reaction. Chromium trioxide with MoF6 or WF6 to produce chromyl fluoride and the respective oxide tetrafluoride.

No description available.