Efeito do tratamento com gel clareador na relação cálcio-fósforo do esmalte dentário

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Nanopartículas magnéticas de 'FE''CO'@'AU': preparação, caracterização e funcionalização com complexo de 'RU'(II) luminescente

Pós-graduação em Química - IQ

Chemical Modification of Palm Fibres Surface with Zirconium Oxychloride

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Purificação do brometo de tálio pelo refino zonal e análise da segregação das impurezas

Desde o conhecimento da radiação e seus efeitos a necessidade de mensurá-la intriga os cientistas. Os detectores de radiação mais difundidos atualmente fazem o uso de cristais semicondutores. Porém, esses detectores tem uma temperatura ótima de funcionamento que acaba sendo ultrapassada, já que o processo gera calor. Por isso, o resfriamento acaba sendo uma necessidade. O desenvolvimento de detectores de radiação com cristal semicondutor que opere a temperatura ambiente é tema de muitos estudos, já que evitaria o processo de resfriamento, trabalhoso e de alto custo. No Centro de Tecnologia das Radiações (CTR) do Instituto de Pesquisas Energéticas e Nucleares (IPEN) o sal de Brometo de Tálio (TlBr) é estudado para esta finalidade. Até ser um cristal semicondutor este sal deve passar por vários processos, entre eles o de purificação e o de cristalização. A técnica utilizada para purificar este cristal é a de Refino zonal. Após ser purificado por esta técnica o sal estará apto a ser cristalizado e consequentemente integrar um equipamento de detecção de radiação. Portanto, esta monografia teve como objetivo realizar a análise da segregação das impurezas do sal de TlBr através da técnica de espectroscopia de massa em fonte de plasma induzido (ICP-MS) e espectroscopia de emissão atômica (ICP-AES). Determinando assim se o mesmo está apto a ser cristalizado e vir a compor um detector de radiação

High Resolution Paleoceanography of the Guaymas Basin, Gulf of California, During the Past 15 000 Years

Deep Sea Drilling Project Site 480 (27°54.10’N, 111°39.34’W; 655 m water depth) contains a high resolution record of paleoceanographic change of the past 15 000 years for the Guaymas Basin, a region of very high diatom productivity within the central Gulf of California. Analyses of diatoms and silicoflagellates were completed on samples spaced every 40-50 yr, whereas ICP-AES geochemical analyses were completed on alternate samples (sample spacing 80-100 yr). The Bolling-Allerod interval (14.6-12.9 ka) (note, ka refers to 1000 calendar years BP throughout this report) is characterized by an increase in biogenic silica and a decline in calcium carbonate relative to surrounding intervals, suggesting conditions somewhat similar to those of today. The Younger Dryas event (12.9-11.6 ka) is marked by a major drop in biogenic silica and an increase in calcium carbonate. Increasing relative percentage contributions of Azpeitia nodulifera and Dictyocha perlaevis (a tropical diatom and silicoflagellate, respectively) and reduced numbers of the silicoflagellate Octactis pulchra are supportive of reduced upwelling of nutrient-rich waters. Between 10.6 and 10.0 ka, calcium carbonate and A. nodulifera abruptly decline at DSDP 480, while Roperia tesselata, a diatom indicative of winter upwelling in the modern-day Gulf, increases sharply in numbers. A nearly coincident increase in the silicoflagellate Dictyocha stapedia suggests that waters above DSDP 480 were more similar to the cooler and slightly more saline waters of the northern Gulf during much of the early and middle parts of the Holocene (~10 to 3.2 ka). At about 6.2 ka a stepwise increase in biogenic silica and the reappearance of the tropical diatom A. nodulifera marks a major change in oceanographic conditions in the Gulf. A winter shift to more northwesterly winds may have occurred at this time along with the onset of periodic northward excursions (El Nino-driven?) of the North Equatorial Countercurrent during the summer. Beginning between 2.8 and 2.4 ka, the amplitude of biogenic silica and wt% Fe, Al, and Ti (proxies of terrigenous input) increase, possibly reflecting intensification of ENSO cycles and the establishment of modern oceanographic conditions in the Gulf. Increased numbers of O. pulchra after 2.8 ka suggest enhanced spring upwelling.

Disintegration on heating of a Brazilian manganese lump ore

This pioneering study characterized the chemical, physical and mineralogical aspects of the Urucum Standard manganese ore typology, and evaluated some of its metallurgical characteristics, such as the main mineral heat decompositions, and the particle disintegration at room temperature and under continuous heating. A one-ton sample of ore was received, homogenized and quartered. Representative samples were collected and characterized with the aid of techniques, such as ICP-AES, XRD, SEM-EDS, BET and OM. Representative samples with particle sizes between 9.5 mm and 15.9 mm were separated to perform tumbling tests at room temperature, and thermogravimetry tests for both air and nitrogen constant flow at different temperatures. After each heating cycle, the mechanical strength of the orewas evaluated by means of screening and tumbling procedures. The Urucum Standard typology was classified as an oxidized anhydrous ore, with a high manganese content (~47%). This typology ismainly composed of cryptomelane and pyrolusite; however there is a significantamount of hematite. The Urucum Standard particles presented low susceptibility to disintegration at room temperature, but as temperature increased, susceptibility increased. No significant differences were observed between the tests done with the air or nitrogen injections.

Dati geochimici ed ecologici di foraminiferi planctonici. Implicazioni paleoceanografiche in due aree chiave: Oceano Meridionale e Mare Mediterraneo.

La studio della distribuzione spaziale e temporale della associazioni a foraminiferi planctonici, campionati in zone con differente regime idrografico, ha permesso di comprendere che molte specie possono essere diagnostiche della presenza di diverse masse d’acqua superficiali e sottosuperficiali e di diversi regimi di nutrienti nelle acque oceaniche. Parte di questo lavoro di tesi si basa sullo studio delle associazioni a foraminiferi planctonici attualmente viventi nel Settore Pacifico dell’Oceano Meridionale (Mare di Ross e Zona del Fronte Polare) e nel Mare Mediterraneo (Mar Tirreno Meridionale). L’obiettivo di questo studio è quello di comprendere i fattori (temperatura, salinità, nutrienti etc.) che determinano la distribuzione attuale delle diverse specie al fine di valutarne il valore di “indicatori” (proxies) utili alla ricostruzione degli scenari paleoclimatici e paleoceanografici succedutisi in queste aree. I risultati documentano che la distribuzione delle diverse specie, il numero di individui e le variazioni nella morfologia di alcuni taxa sono correlate alle caratteristiche chimico-fisiche della colonna e alla disponibilità di nutrienti e di clorofilla. La seconda parte del lavoro di tesi ha previsto l’analisi degli isotopi stabili dell’ossigeno e del rapporto Mg/Ca in gusci di N. pachyderma (sin) prelevati da pescate di micro zooplancton (per tarare l’equazione di paleo temperatura) da un box core e da una carota provenienti dalla zona del Fronte Polare (Oceano Pacifico meridionale), al fine di ricostruire le variazioni di temperatura negli ultimi 13 ka e durante la Mid-Pleistocene Revolution. Le temperature, dedotte tramite i valori degli isotopi stabili dell’ossigeno, sono coerenti con le temperature attuali documentate in questa zona e il trend di temperatura è paragonabile a quelli riportati in letteratura anche per eventi climatici come lo Younger Dryas e il mid-Holocene Optimum. I valori del rapporto Mg/Ca misurato tramite due diverse tecniche di analisi (laser ablation e analisi in soluzione) sono risultati sempre molto più alti dei valori riportati in letteratura per la stessa specie. La laser ablation sembra carente dal punto di vista del cleaning del campione e da questo studio emerge che le due tecniche non sono comparabili e che non possono essere usate indifferentemente sullo stesso campione. Per quanto riguarda l’analisi dei campioni in soluzione è stato migliorato il protocollo di cleaning per il trattamento di campioni antartici, che ha permesso di ottenere valori veritieri e utili ai fini delle ricostruzioni di paleotemperatura. Tuttavia, rimane verosimile l’ipotesi che in ambienti particolari come questo, con salinità e temperature molto basse, l’incorporazione del Mg all’interno del guscio risenta delle condizioni particolari e che non segua quindi la relazione esponenziale con la temperatura ampiamente dimostrata ad altre latitudini.

Cluster-derived Gold/Iron catalysts for environmental applications

During the last years we assisted to an exponential growth of scientific discoveries for catalysis by gold and many applications have been found for Au-based catalysts. In the literature there are several studies concerning the use of gold-based catalysts for environmental applications and good results are reported for the catalytic combustion of different volatile organic compounds (VOCs). Recently it has also been established that gold-based catalysts are potentially capable of being effectively employed in fuel cells in order to remove CO traces by preferential CO oxidation in H2-rich streams. Bi-metallic catalysts have attracted increasing attention because of their markedly different properties from either of the costituent metals, and above all their enhanced catalytic activity, selectivity and stability. In the literature there are several studies demostrating the beneficial effect due to the addition of an iron component to gold supported catalysts in terms of enhanced activity, selectivity, resistence to deactivation and prolonged lifetime of the catalyst. In this work we tried to develop a methodology for the preparation of iron stabilized gold nanoparticles with controlled size and composition, particularly in terms of obtaining an intimate contact between different phases, since it is well known that the catalytic behaviour of multi-component supported catalysts is strongly influenced by the size of the metal particles and by their reciprocal interaction. Ligand stabilized metal clusters, with nanometric dimensions, are possible precursors for the preparation of catalytically active nanoparticles with controlled dimensions and compositions. Among these, metal carbonyl clusters are quite attractive, since they can be prepared with several different sizes and compositions and, moreover, they are decomposed under very mild conditions. A novel preparation method was developed during this thesis for the preparation of iron and gold/iron supported catalysts using bi-metallic carbonyl clusters as precursors of highly dispersed nanoparticles over TiO2 and CeO2, which are widely considered two of the most suitable supports for gold nanoparticles. Au/FeOx catalysts were prepared by employing the bi-metallic carbonyl cluster salts [NEt4]4[Au4Fe4(CO)16] (Fe/Au=1) and [NEt4][AuFe4(CO)16] (Fe/Au=4), and for comparison FeOx samples were prepared by employing the homometallic [NEt4][HFe3(CO)11] cluster. These clusters were prepared by Prof. Longoni research group (Department of Physical and Inorganic Chemistry- University of Bologna). Particular attention was dedicated to the optimization of a suitable thermal treatment in order to achieve, apart from a good Au and Fe metal dispersion, also the formation of appropriate species with good catalytic properties. A deep IR study was carried out in order to understand the physical interaction between clusters and different supports and detect the occurrence of chemical reactions between them at any stage of the preparation. The characterization by BET, XRD, TEM, H2-TPR, ICP-AES and XPS was performed in order to investigate the catalysts properties, whit particular attention to the interaction between Au and Fe and its influence on the catalytic activity. This novel preparation method resulted in small gold metallic nanoparticles surrounded by highly dispersed iron oxide species, essentially in an amorphous phase, on both TiO2 and CeO2. The results presented in this thesis confirmed that FeOx species can stabilize small Au particles, since keeping costant the gold content but introducing a higher iron amount a higher metal dispersion was achieved. Partial encapsulation of gold atoms by iron species was observed since the Au/Fe surface ratio was found much lower than bulk ratio and a strong interaction between gold and oxide species, both of iron oxide and supports, was achieved. The prepared catalysts were tested in the total oxidation of VOCs, using toluene and methanol as probe molecules for aromatics and alchols, respectively, and in the PROX reaction. Different performances were observed on titania and ceria catalysts, on both toluene and methanol combustion. Toluene combustion on titania catalyst was found to be enhanced increasing iron loading while a moderate effect on FeOx-Ti activity was achieved by Au addition. In this case toluene combustion was improved due to a higher oxygen mobility depending on enhanced oxygen activation by FeOx and Au/FeOx dispersed on titania. On the contrary ceria activity was strongly decreased in the presence of FeOx, while the introduction of gold was found to moderate the detrimental effect of iron species. In fact, excellent ceria performances are due to its ability to adsorb toluene and O2. Since toluene activation is the determining factor for its oxidation, the partial coverage of ceria sites, responsible of toluene adsorption, by FeOx species finely dispersed on the surface resulted in worse efficiency in toluene combustion. Better results were obtained for both ceria and titania catalysts on methanol total oxidation. In this case, the performances achieved on differently supported catalysts indicate that the oxygen mobility is the determining factor in this reaction. The introduction of gold on both TiO2 and CeO2 catalysts, lead to a higher oxygen mobility due to the weakening of both Fe-O and Ce-O bonds and consequently to enhanced methanol combustion. The catalytic activity was found to strongly depend on oxygen mobility and followed the same trend observed for catalysts reducibility. Regarding CO PROX reaction, it was observed that Au/FeOx titania catalysts are less active than ceria ones, due to the lower reducibility of titania compared to ceria. In fact the availability of lattice oxygen involved in PROX reaction is much higher in the latter catalysts. However, the CO PROX performances observed for ceria catalysts are not really high compared to data reported in literature, probably due to the very low Au/Fe surface ratio achieved with this preparation method. CO preferential oxidation was found to strongly depend on Au particle size but also on surface oxygen reducibility, depending on the different oxide species which can be formed using different thermal treatment conditions or varying the iron loading over the support.

Analisi geochimica ed ambientale di sedimenti ed acque del lago di Veovaca (Vares- Bosnia ed Erzegovina)

Il lavoro svolto nella zona di Vareš, in particolare nella zona del lago di Veovača ha investigato diverse matrici ambientali (sedimenti, suoli, acque) per valutare le loro caratteristiche e la loro qualità. Nella zona è stata presente in passato attività estrattiva e di lavorazione dei minerali estratti, da qui la necessità di questo studio esplorativo. Il lavoro svolto si divide in tre fasi: campionamento, svolto in quattro giorni passati in campagna; analisi dei campioni raccolti e interpretazione dei risultati. Sono state campionate acque e sedimenti in punti interni al lago, altri in corrispondenza delle sue sponde e punti lungo la diga. Sul materiale solido sono state svolte analisi di spettrometria di fluorescenza a raggi X, mentre sulle acque sono state applicate tecniche di spettrometria di assorbimento atomico (AAS), spettrometria di emissione al plasma induttivamente accoppiato (ICP-AES) e cromatografia ionica oltre che a misure di parametri chimico-fisici in campo. Sono stati poi valutati i risultati, attraverso il confronto con banche dati di riferimento ed elaborazioni statistiche e grafiche. Si tratta di uno studio preliminare effettuato su un piccolo numero di campioni e perciò solo indicativo e non in grado di fornire risposte definitive sulla condizione ambientale dell'area. Tuttavia queste prime informazioni consentono di delineare un quadro nel quale future indagini potranno approfondire aspetti e problemi critici per la qualità ambientale.

Quantum dot cytotoxicity in vitro: An investigation into the cytotoxic effects of a series of different surface chemistries and their core/shell materials

Abstract The aim of this study was to assess the effects of a series of different surface coated quantum dots (QDs) (organic, carboxylated [COOH] and amino [NH(2)] polytethylene glycol [PEG]) on J774.A1 macrophage cell viability and to further determine which part of the QDs cause such toxicity. Cytotoxic examination (MTT assay and LDH release) showed organic QDs to induce significant cytotoxicity up to 48 h, even at a low particle concentration (20 nM), whilst both COOH and NH(2) (PEG) QDs caused reduced cell viability and cell membrane permeability after 24 and 48 h exposure at 80 nM. Subsequent analysis of the elements that constitute the QD core, core/shell and (organic QD) surface coating showed that the surface coating drives QD toxicity. Elemental analysis (ICP-AES) after 48 h, however, also observed a release of Cd from organic QDs. In conclusion, both the specific surface coating and core material can have a significant impact on QD toxicity.

EFFETS DE L’INCORPORATION D’ADJUVANTS MINÉRAUX SUR LES PROPRIÉTÉS DE CIMENTS GÉOPOLYMÈRES A BASE DE SCORIES VOLCANIQUES

Volcanic ashes are raw materials from geological deposits with a range of chemical compositions. When combined with suitable alkali activators they can be converted to geopolymers cement at ambient temperature. In this work we have investigated the possibility of use bauxite and oyster shells as mineral admixture in volcanic ashes, to enhance the properties of geopolymers synthesized. Different methods of analyses such as Fourier Transform Infrared spectroscopy (FTIR), X-ray diffractometry (XRD), and Scanning Electron Microscopy (SEM) were used to assess the variation of setting time, linear shrinkage and 28 days compressive strength of geopolymers paste. The bauxite and the oyster shells were characterized using inductively coupled plasma (ICP-AES), thermal analyses (DSC/ATG), FTIR and X-ray diffractometry. The results of these analyses has showed that bauxite and oyster shells are respectively source of Al2O3 and of CaO, and can compensate the deficiencies of these oxides in volcanic ashes. Adding mineral admixture dissolve slowly in high alkaline medium. Addition of about 20% of bauxite or 10% of oyster shells is seen to decrease the setting time respectively from 415 to 275 min and 195 min. Linear shrinkage decrease with percentage of bauxite or of oyster shells added. Efflorescence is reduced by adding 10% of bauxite. 28 days compressive strength of geopolymeric materials increase respectively for 4.77 and 7.52% for 10% of bauxite or 20% of oyster shells added. More than these percentage additive has a deleterious effect on compressive strength due to crystalized mineralogical phases of the admixture.

Eruptive history of Maderas volcano using new 40Ar/39Ar ages and geochemical analyses

Maderas volcano is a small, andesitic stratovolcano located on the island of Ometepe, in Lake Nicaragua, Nicaragua with no record of historic activity. Twenty-one samples were collected from lava flows from Maderas in 2010. Selected samples were analyzed for whole-rock geochemical data using ICP-AES and/or were dated using the 40Ar/39Ar method. The results of these analyses were combined with previously collected data from Maderas as well as field observations to determine the eruptive history of the volcano and create a geologic map. The results of the geochemical analyses indicate that Maderas is a typical Central American andesitic volcano similar to other volcanoes in Nicaragua and Costa Rica and to its nearest neighbor, Concepción volcano. It is different from Concepción in one important way – higher incompatible elements. Determined age dates range from 176.8 ± 6.1 ka to 70.5 ± 6.1 ka. Based on these ages and the geomorphology of the volcano which is characterized by a bisecting graben, it is proposed that Maderas experienced two clear generations of development with three separate phases of volcanism: initial build-up of the older cone, pre-graben lava flows, and post-graben lava flows. The ages also indicate that Maderas is markedly older than Concepción which is historically active. Results were also analyzed regarding geologic hazards. The 40Ar/39Ar ages indicate that Maderas has likely been inactive for tens of thousands of years and the risk of future volcanic eruptions is low. However, earthquake, lahar and landslide hazards exist for the communities around the volcano. The steep slopes of the eroded older cone are the most likely source of landslide and lahar hazards.

Stable oxygen isotope record and Sr/Ca ratios of corals from IODP Holes M0009D and M0023A

We present monthly resolved records of strontium/calcium (Sr/Ca) and oxygen isotope (d18O) ratios from well-preserved fossil corals drilled during the Integrated Ocean Drilling Program (IODP) Expedition 310 'Tahiti Sea Level' and reconstruct sea surface conditions in the central tropical South Pacific Ocean during two time windows of the last deglaciation. The two Tahiti corals examined here are uranium/thorium (U/Th)-dated at 12.4 and 14.2 ka, which correspond to the Younger Dryas (YD) cold reversal and the Bølling-Allerød (B-A) warming of the Northern Hemisphere, respectively. The coral Sr/Ca records indicate that annual average sea surface temperature (SST) was 2.6-3.1 °C lower at 12.4 ka and 1.0-1.6 °C lower at 14.2 ka relative to the present, with no significant changes in the amplitude of the seasonal SST cycle. These cooler conditions were accompanied by seawater d18O (d18Osw) values higher by ~0.8 per mill and ~0.6 per mill relative to the present at 12.4 and 14.2 ka, respectively, implying more saline conditions in the surface waters. Along with previously published coral Sr/Ca records from the island [Cohen and Hart (2004), Deglacial sea surface temperatures of the western tropical Pacific: A new look at old coral. Paleoceanography 19, PA4031, doi:10.1029/2004PA001084], our new Tahiti coral records suggest that a shift toward lower SST by ~1.5 °C occurred from 13.1 to 12.4 ka, which was probably associated with a shift toward higher d18Osw by ~0.2 per mill. Along with a previously published coral Sr/Ca record from Vanuatu [Corrège et al. (2004), Interdecadal variation in the extent of South Pacific tropical waters during the Younger Dyras event. Nature 428, 927-929], the Tahiti coral records provide new evidence for a pronounced cooling of the western to central tropical South Pacific during the Northern Hemisphere YD event.