Um estudo sistemático a respeito da utilização de padrão interno em determinações multielementares por espectrometria de absorção atômica (ETAAS) foi desenvolvido. O objetivo principal do presente trabalho foi verificar a possibilidade de melhorar a precisão e a exatidão dos resultados analíticos, que são obtidos na análise de fluidos biológicos. O pré-tratamento dessas amostras foi simplificado e reduzido a uma única etapa de diluição com surfactante (Triton X-100) e ácido (HNO3). Conseqüentemente, a complexidade da solução diluída de amostra, a ser introduzida no tubo de grafite, apresenta uma elevada quantidade de concomitantes que podem provocar interferências químicas. A seleção preliminar dos elementos a serem testados como padrão interno considerou a semelhança de parâmetros físico-químicos relacionados com o processo de atomização. Desta forma, Ag, Bi, In e Tl foram testados como padrão interno para a determinação simultânea de Cd/Pb em sangue e urina, enquanto Bi, Ge, In, Sb, Sn e Te foram os elementos selecionados para a determinação de Mn/Ni/Se em soro sangüíneo. A melhoria da qualidade dos resultados analíticos obtidos na determinação simultânea de Cd e Pb em sangue foi observada quando Ag foi utilizada como padrão interno, na presença de NH4H2PO4 como modificador químico. Verificou-se uma melhoria na exatidão dos resultados obtidos para Cd e Pb, após a correção com padrão interno. Por outro lado, os resultados obtidos na análise de urina não foram corrigidos por nenhum dos elementos testados. Os melhores resultados para a determinação simultânea de Mn, Ni e Se foram obtidos com a utilização de Bi, Sn e Te como padrão interno. Entretanto, verificou-se que a correção de todos os resultados não seria viável com o uso de um único padrão interno. O melhor desempenho nos testes realizados na presença de soro sangüíneo foi obtido com Bi, que melhorou discretamente a precisão dos resultados obtidos para Se. Desta forma, a padronização interna visando a determinação simultânea de Mn, Ni e Se não foi eficiente. A padronização interna em ETAAS, com a finalidade de melhorar a precisão e a exatidão dos resultados analíticos, é uma estratégia tão complexa, quanto os efeitos interferentes que se pretende corrigir: são necessários mais estudos para compreender melhor como a utilização de uma condição de compromisso afeta os processos de atomização, bem como mais informações a respeito das interferências físicas e químicas causadas por amostras complexas, analisadas por ETAAS após uma simples etapa de diluição. Deve-se considerar com especial atenção o modificador químico e as temperaturas das etapas de pirólise e de atomização empregadas, que são parâmetros críticos para o desempenho de um elemento como padrão interno. / A systematic study involving the use of internal standard for multielement determinations by electrothermal atomic absorption spectrometry was developed. The main objective of this work was evaluate the possibility of improving precision and accuracy of the analytical results for biological fluids. The sample pre-treatment was reduced to a single dilution step with surfactant (Triton X-100) and acid (HNO3), increasing the amount of concomitant introduced into the atomizer. The preliminary selection of the elements to be tested as internal standard considered the resemblance of physico-chemical parameters related with the atomization process. Thus, Ag, Bi, In and Tl were tested as internal standard for the simultaneous determination of Cd/Pb in blood and urine, and Bi, Ge, In, Sb, Sn and Te were the selected elements for the determination of Mn/Ni/Se in blood serum. The correction of the results obtained for the simultaneous determination of Cd and Pb in blood was achieved when Ag was used as internal standard, in presence of NH4H2PO4 as chemical modifier. An improvement for the accuracy of the results was observed for both analytes after their correction with the internal standard. On the other hand, the results obtained for the urine analysis were not corrected by using the tested elements. The best results for the simultaneous determination of Mn, Ni and Se were observed when Bi, Sn and Te were used as internal standard. However, the correction for the results for all analytes was not possible by using only one internal standard. The best performance in presence of the serum was obtained for Bi, which improves slightly the precision for the Se results. Thus, the internal standardization for the simultaneous determination of Mn, Ni and Se was not efficient. The internal standardization in ETAAS, aiming the improvement of precision and accuracy of the analytical results, is a strategy as complex as the interference effects to be corrected: more studies are required in order to better understand how the adoption of a compromised condition disturbs the atomization processes, as well as to get more information about the physical and chemical interference caused by complex samples, analyzed by ETAAS after a single dilution step. The chemical modifier and the selected temperatures for the pyrolysis and atomization steps are critical parameters for the performace of an internal standard and they should be carefully considered.

Metal Oxide (MO)semiconductors are one of the most widely used materials in commercial gas sensor devices. The basic principle of chemoresistive gas sensor operation stems on the high sensitivity of electrical resistance to ambient gaseous conditions. Depending on whether the oxide is "p type" or "n type", the resistance increases (or decrease), when placed in atmosphere containing reducing (or oxidizing) gases. The study of conductometric metal oxide semiconductor gas sensors has dual importance in view of their technological device applications and understanding fundamental MO-gas interactions. Metal oxides based sensors offer high thermal, mechanical and chemical stability. A large number of MOs show good sensitivities to various gases like CO, NOX, SOX, NH3, alcohols and other Volatile Organic Compounds (VOCs). VOCs are very common hazardous pollutants in the environment. Gas sensors are in great demand for their various applications such as food quality control, fermentation industries, road safety, defence, environmental monitoring and other chemical industries. The aim of the study is to explore the possibility of advancements in semiconducting MO based gas sensor devices through tuning microstructural parameters along with chemical dopants or additives. And further to investigate the underlying mechanism of conductometric MO gas sensors. The novel synthesis method employed is based on the solution combustion method coupled with ultrasonically nebulized spray pyrolysis technique. The well studied SnO2 and relatively unexplored Cr2O3 oxide systems are selected for the study. The non-equilibrium processing conditions result in unique microstructure and defect chemistry. In addition, using this technique MO - Reduced Graphene Oxide (RGO) nanocomposite films has also been fabricated and its application to room temperature gas sensor devices is demonstrated. The thesis comprises of seven chapters. the following section describe the summery of individual chapters. The Chapter 1 describes the introduction and background literature of this technology. A brief review of developments in gas sensor technology so far has been enlisted. This chapter also gives a glimpse of applications of MO semiconductors based sensors. The underlying mechanism involved in the sensing reaction and the primary factors influencing the response of a gas sensor device are enlisted. Further in the later part of the chapter focused the material selection criteria, effect of additives/dopants and future prospects of the technology. The end of this chapter highlights the objective and scope of the work in this dissertation. In the Chapter 2 the the materials selection, characterization techniques and particularly the experimental setups used are elaborated. This includes the deposition method used, which is developed in our group and the the in house built gas sensing system including its working principles and various issues have been addressed. The Ultrasonic Nebulized Spray Pyrolysis of Aqueous Combustion Mixture (UNSPACM) is a novel deposition method devised, which is a combination of conventional spray pyrolysis and solution combustion technique. Spray pyrolysis is versatile, economic and simple technique, which can be used for large area deposition of porous films. The intention is to exploit the exothermicity of combustion reaction in order to have high crystallinity, smaller crystallite size with high surface area, which are extremely important in gas sensor design and its efficiency. Further the gas sensing system and its operation are discussed in detail including the advantages of vertical sensing chamber geometry, wider analyte concentration range (ppm to percentage) obtained through vapor pressure data and simultaneous multi sensor characterization allowing better comparison. Here in this work, Chromium oxide (Cr2O3) and Tin oxide (SnO2) are selected as gas sensing materials for this work as a p-type and n-type metal oxide semiconductors respectively. Nevertheless Cr2O3 is a less explored gas sensing material as compared to SnO2, which is also being used in many commercially available gas sensor devices. Thus, studying and comparing gas sensing properties of a relatively novel and a well established material would justify the potential of the novel deposition technique developed. In Chapter 3, the effect of exothermic reaction between oxidizer and fuel, on the morphology, surface stoichiometry and observed gas sensing properties of Cr2O3 thin films deposited by UNSPACM, is studied. An elaborative study on the structural, morphological and surface stoichiometry of chromium oxide films is undertaken. Various deposition parameters have been optimized. An extensive and systematic gas sensing study is carried out on Cr2O3 films deposited, to achieve unique microstructure. The crystallinity and microstructure are investigated by varying the deposition conditions. Further, the effect of annealing in oxygen gas atmospheres on the films was also investigated. The gas sensing properties are studied for various VOCs, in temperature range 200 - 375 oC. The possible sensing mechanism and surface chemical processes involved in ethanol sensing, based on empirical results, are discussed. In chapter 4, the effect of 1% Pt doping on gas sensing properties of Cr2O3 thin films prepared by UNSPACM, is investigated. The chemical analysis is done using x-ray photoelectron spectroscopy to find the chemical state of Pt and quantification is done. The gas sensing is done towards gases like NO2, Methane and Ethanol. The enhancement in sensitivity and remarkable reduction in response as well as recovery times have been modeled with kinetic response analysis to study the variation with temperature as well as concentration. Further the analysis of observations and model fittings is discussed. The Chapter 5 deals with the defects induced ferromagnetism and gas sensing studies SnO2 nanoparticles prepared by solution combustion method. The structural, chemical analysis of as-synthesized and annealed SnO2 nanoparticles reveal gradual reduction in defect concentration of as-prepared SnO2. The findings of various characterization techniques along with optical absorption and magnetic studies to investigate the defect structure of the material are presented. As defects play crucial role in gas sensing properties of the metal oxide material, the defect induced room temperature ferromagnetism in undoped SnO2 has been used as a potential tool to probe the evidence of the defects. Finally a correlation is established between observed room temperature ferromagnetism and gas sensing studies and primary role of defects in gas sensing mechanism over microstructure is realized . The Chapter 6 presents the deposition of SnO2 thin films by UNSPACM method on glass substrates for gas sensing application. The readiness of UNSPACM in making sensor materials with unform dopant distribution is demonstrated in order to improve the sensor performance in terms of response and selectivity. The chemical composition, film morphology and gas sensing studies are reported. The SnO2 is doped with Cr and Pt to enhance the sensing properties of the material. The doped Oxide films are found to show enhancement in sensitivity and improve the selectivity of the films towards specific gases like NO2 and CO. Further in Chapter 7 an effort has been made to overcome the problem of high operating temperature of metal oxide gas sensors through use of Reduced Graphene Oxide (RGO) and metal oxide nanocomposite films. Although RGO shows room temperature response towards many toxic and hazardous gases but it exhibits poor sensor signal recovery. This has been successfully solved by making nanohybrids of RGO and SnO2. It not only improves the sensor signal kinetics but it enhances the sensitivity also. Thus this chapter endeavors towards low power consumption gas sensing devices. The key findings and future aspects are summarized in the Chapter 8.

The two-dimensional material graphene possesses many impressive properties such asextraordinary carrier mobility, mechanical stiffness and optical transmittance. However,the properties of pristine graphene do not always complement the requirements of applications. Of particular interest, a band gap is needed for electronic logic devices. Recent research shows that using few-layer hexagonal boron nitride as a substrate for graphene-based electronic devices can open a band gap in graphene. Also, introducing impurities such as hydrogen atoms, transition metals or silicon atoms on or within graphene can control the electronic properties according to recent studies. Furthermore, ion irradiation is an alternative option to tailor the properties of graphene by introducing defects. In this thesis, pristine, impure or defective graphene and few-layer boron nitride were characterised by scanning transmission electron microscopy (STEM) and electron energy loss (EEL) spectroscopy. Through STEM and EEL spectroscopy, lattice structures and electronic properties of these two-dimensional materials could be investigated at the atomic scale. This thesis focuses on the frontier studies of theoretical and experimental EEL spectroscopy of graphene and few-layer boron nitride with impurities. In the EEL spectra of pristine graphene and boron nitride two prominent peaks were observed, which are attributed to the plasmon excitations of π- and π+σ-electrons. By introducing impurities such as hydrogen adatoms on graphene and substitutional oxygen and carbon atoms within single-layer boron nitride, our experimental and simulated EEL spectra show that their π-plasmon peaks are modified. The concentrations of these impurities were then evaluated via EEL spectra and atomic-resolution images. If other impurities, such as various transition metals and silicon atoms, are introduced on or within single-layer graphene, our simulated EEL spectra demonstrate that the geometry of these impurity clusters affects the π-plasmon peak in graphene and some impurities even enhance it. Finally, experiments on in-situ transmission electron microscopy and ex-situ STEM and Raman spectroscopy were conducted to investigate ion irradiated graphene. Many topological defects were, for the first time, observed in atomic-resolution STEM images of ion irradiated graphene. Simulated EEL spectra of defective graphene are also reported, which suggests that corrugations and dangling bonds in defects can modify out-of-plane EEL spectra and introduce intraband transitions, respectively.

Ziel der Arbeit ist die theoretische Analyse von Kohlenstoff-Clustern der Größe 100 - 500 Atome. Die experimentellen Beobachtungen sind bei dieser geringen Anzahl der Atome schwierig. Anderseits sind Kenntnisse über solche Cluster sehr wichtig, z.B. für die Keimbildung von Diamant auf Substraten, oder für die Kohlenstoff-Nanotechnologie (Fullerene, Nanotubes), oder für strukturelle Defekte in Kohlenstoff-Systemen. Es wurden gekrümmte Grenzflächen im Diamant simuliert. Zuerst mit einem empirischen Potential. Es wurde danach eine Methode entwickelt, bei der die schwach gestörten Gebiete einem empirischen Potential gehorchen, und die stark gestörten Gebiete, wo eine genaue Berechnung erforderlich ist, durch eine quantenmechanische Näherung beschrieben wurden. Somit kann man mit guter Genauigkeit große Systeme, bestehend aus einigen 10 (hoch)4 Atomen, simulieren, bei denen nur lokal quantenmechanische Methoden erforderlich sind. Mit diesem Hybrid-Code wurden weiterhin Diamantkeime auf Silizium gerechnet. Es wurden Aussagen bezüglich der Stabilität des Diamants auf dem Siliziumsubstrat, der kritischen Keimgröße, der Änderungen, die der Keim erfährt, gemacht. Ein anderes Gebiet ist die molekulardynamische Simulation bezüglich der Stabilität und des Transformationsverhaltens von Kohlenstoff-Nanoteilchen. Es wurden als »Rohstoffe» sowohl Diamant- und Graphitkristalle sphärischer, ellipsoidischer oder quadratischer Form benutzt, als auch amorpher Kohlenstoff. Es wurde demonstriert, daß sich Diamant unter höherer Temperatur und Bestrahlung in Kohlenstoffzwiebeln transformiert. Es wurde der innere Kern, bestehend aus zwei Schalen, der Kohlenstoffzwiebel simuliert. Es wurde, nach meinem Wissen, zum ersten Mal gezeigt, daß zwischen den Schalen der Kohlenstoffzwiebel Quer-Verbindungen (cross-links) existieren. Diese waren von den Experimentatoren vermutet worden. Sie bilden die Initiatoren der Diamantkeime der Kohlenstoffzwiebel bei ihrer ohne äußeren Druck möglichen Transformation in Diamant. Die Zentren der Kohlenstoffzwiebeln befinden sich bereits in der Entstehung der Zwiebel unter einem Selbstdruck. Bei den größeren Kohlenstoffzwiebeln beträgt der experimentell bestimmte Abstand zwischen den Schalen von außen nach innen von 3.34 Å bis 2.2 Å. Anlagen: nano1.mpg (91,8 MB); nano2.mpg (131 MB) Nutzung: Referat Informationsvermittlung der SLUB / The scope of this work is the analysis of carbon clusters of about 100 - 500 atoms. The experimental studies are at such small clusters heavy. Knowledges about thus clusters are very important, for example in the field of the nucleation of diamond on substrates, or for the carbon nano-technology (fullerene, nanotubes), or for local defects in carbon systems. There were simulated curved interfaces in diamond. Firstly with an empirical potential. Than I developed a method, in wich the defects and the structure around them are treated by a quantum mechanical algorithm and the rest with a near to ideal structure with an empirical potential. So, it is possible an accurate calculation of great systems of about 10 (high)4 atoms on wich only locally quantum mechanical methods are necessary. With this hybrid-code diamond nuclei on silicon substrate were simulated. The stability of the diamond nuclei on the silicon substrate, the critical radius of the nuclei and the changes of the nuclei during his transformation was investigated. Another field of investigations is the molecular dynamics simulation of free carbon clusters. The initial structures had spherical, ellipsoidical or square form and consists of diamond and graphite or a free form in the case of amorphous carbon. It was demonstrated that diamond transforms at higher temperatures and under irradiation in carbon onions. The genesis of the nucleus of a carbon onion with two shells was here for the first time simulated. The existence of the cross-links between the shells of a carbon onion was demonstrated. These existence was expected from the experimentators. The cross-links are the initiators of the transformation of carbon onions to diamond. The center of carbon onions is under self-pressure, because the distance between the outer shells is about 3.34 Å and between the inner shells about 2.2 Å. Appendix: nano1.mpg (91,8 MB); nano2.mpg (131 MB) Usage: Referat Informationsvermittlung/ SLUB

Presented work investigates the problem of secondary lithium-ion cells and the different available cathode materials. We have prepared samples of LiFePO4 with the addition of different kinds of carbon materials such as Super P, Vulcan and expanded graphite. We have always created the sample with and without surfactant. Developed samples were compared by measuring electrochemical methods (cyclic voltammetry, charge and discharge cycles and impedance spectroscopy). We also modeled the three-point cell for measuring electrochemical electrode materials.

The present masters's thesis informs about the development and application of low-temperature sintering pastes in the manufacture and assembly of PCB components of the enclosing lead-free using nanoparticles of metals and their compounds. Lead-free brazing technology which s using in the present time, which has its drawbacks, however, and thus gaining other appropriate alternatives that seek to replace or further refined lead brazing. The introduction of the theoretical part inform about retrieval method of the type, composition and properties of low-temperature sintering pastes consisting of metal nanoparticles and their compounds. This section describes and explains the reaction mechanisms taking place during the sintering process. The end of the first chapter is dedicated to nanotechnology and production of nanoparticles and their compounds for the needs of the low-temperature sintering and possible related problems. Folowing section is devoted to examples of practitioners of the application and use of low-temperature sintering pastes and tests with which to assess the characteristics and quality of the related sintering conection. At the end of the thesis is a summary perspective and the use of low-temperature sintering technology nanoparticle past into the future. The experimental part is devoted to the application of conductive ink on the base of graphite for the production of 1V, 2V and 4V structures and their electroplated by the copper. There were created technological processes of 2V and 4V structures and test proposed methodologies resistance conductive theme to environmental influences. Filling pasta was tested in implementing 4V structure. There were made microsections various technological applications and their results were processed and evaluated.

This diploma work is engaged in replacement of gasket main dividing plane of reactor coolant pumps in nuclear power plant Paks. Of the newly suggested gasket is kammprofile gasket with expanded graphite layer. This work contain suggestion and calculation of new sealing a knot and calculation existing sealing the knot. Results are confrontacion and sequentially is discussed influence on main dividing plane HCČ 317 by use the new and the existing gasket. In this work is contained description brief of legislation. This legislation must keep by design components dedicated for nuclear equipment. Next this work contain view of the most important sealing knots used in primary system of Nuclear Power Plant type VVER 440.

This diploma thesis is engaged in replacement of gasket ion filter used in the ion filter of continuous cleaning TC SV01 of rector coolant in nuclear power plants with VVER 440 reactor. Original nickel gasket is replaced by kammprofile gasket with expanded graphite. Calculation results are compared with each other and are described as suggestions for further calculation. The first part included a detailed description of the primary coolant water chemistry, along with a description of the function and structure of ion filter.

This work reports on the cobalt pyridinoporphyrazinate (CoTmtppa) as a platinum-group metal-free catalyst for hydrogen evolution and oxidation reactions with the possibility of use in hydrogen energy and hydrogen potentiometric sensing. A different interaction of CoTmtppa with various electrode substrates, highly oriented pyrolytic graphite (HOPG) and annealed gold (Au(111)), affects its electrocatalytic behaviour in hydrogen reactions. The formation of a hydride-type complex with the bonding of hydrogen atoms to cobalt centre is supposed to be the rate-determining step. In the case of hydrogen evolution, the maximum catalytic activity of mediator was reached at pH = 11,0, when the HOPG/CoTmtppa showed overpotential decrease by 300 mV and an almost 60-fold increase of current densities compared to HOPG. The electrocatalytic activity of Au(111)/CoTmtppa resulted in a further decrease of overpotential by 175 mV in comparison with HOPG/Co(I)Tmtppa. The electrochemical oxidation of hydrogen was found to depend on hydrogen source which was electrochemically generated on-site or molecular hydrogen supplied from an external source. In the case of electrochemically generated hydrogen, the maximum activity of HOPG/CoTmtppa was reached at pH = 2.1 and an additional it was observed 50 % increase in current...

In this work, the application of boron-doped diamond electrodes with various surface pre- treatment were tested on selected oxidizable and reducible model compounds, specifically para and ortho cresols and 2'-deoxycytidine and 7-deazaadenosine labeled by 4-nitrophenyl triazole. The aim of the study was the investigation of electrochemical and adsorptive processes with respect to the development of electroanalytical methods of detection of the selected compounds, or utilization of boron-doped diamond electrodes as detectors in liquid-flow systems. Cresols were used as the model oxidizable compound. On O-terminated and polished boron- doped diamond electrodes, cresols provide oxidation signal owing to their oxidation to methylphenoxy radical at comparable potentials as on other carbon-based electrodes used as a reference in this work, i.e., glassy carbon electrode, pyrolytic graphite electrode, and carbon paste electrode. These carbon electrode materials show relatively high propensity to adsorption of reaction products, while such adsorption is minimal on boron-doped diamond. In situ anodic activation allows for a rapid regeneration of boron-doped diamond surface prior to each scan. A differential pulse voltammetric method that was developed with a detection limit of 0.61 mol∙l-1 to 2.97 mol∙l-1...