Coal can be converted to different chemical products through processes such destructive distillation. The destructive distillation of coal yields coke as the main product with byproducts such as coal tar pitch (CTP). CTP has a wide range of applications, especially in the carbon-processing industries. Typical applications include the manufacture of anodes used in many electrochemical processes, as well as Söderberg electrodes used in different ferroalloy processes. Söderberg electrodes are made from the thermal treatment of Söderberg electrode paste. The Söderberg electrode paste is a mixture of CTP (binding material) and coke/calcined anthracite (filler). Söderberg electrodes are characterised by a baking isotherm temperature. This temperature is located in the baking zone of the Söderberg electrode system. In the baking zone, the liquid paste is transformed into a solid carbonaceous material. Knowing the baking isotherm temperature is essential as it will ensure the safe, profitable and continuous operation of submerged arc furnaces. Thermomechanical analysis (TMA) was used in this study to determine the baking isotherm temperature of CTP samples. The baking isotherm temperature for all samples was found to lie between 450 and 475 °C irrespective of the initial chemical and physical composition of the CTP. TMA was also used to measure the dimensional changes that take place in the binding material (CTP) at temperatures above the baking isotherm. The dimensional changes of 12 CTP samples when heated from room temperature up to a maximum of 1300 °C were measured. The results indicated that all CTP samples shrank by approximately 14% in the first heating and cooling cycle. The second and third heating and cooling cycles gave a small change in dimensions of approximately 2% for all samples. The significant change in dimensions observed for all CTP samples during the first TMA thermal treatment cycle was attributed to the structural rearrangement that takes place within the carbonaceous material. The structural ordering of all CTP samples thermally treated was evaluated by X-ray diffractometry (XRD). XRD is widely used in the determination of crystallinity/amorphousness of carbonaceous materials, interlayer distance (d-spacing), as well as the degree of ordering (DOG) in a given material. For comparison of structural ordering, XRD analysis was also performed on raw (as-received) CTPs, as well as CTPs thermally treated at 475 and 1300 °C. Prebaked electrode graphite was also analysed. From the XRD results, raw CTP was found to be amorphous with no significant ordering. The interlayer spacing (d002) for all raw CTP samples averaged 3.70 Å, compared to 3.37 Å for prebaked electrode graphite. CTPs thermally treated at 1300 °C had a d-spacing of 3.51 Å. The DOG of raw samples was found to be negative which was indicative of the amorphousness of the raw CTP. The DOG increased with an increase in thermal treatment temperature, as was seen from the DOG of CTPs thermally treated at 1300 °C, which was calculated to be approximately -81% for all 12 samples. The calculated DOG for prebaked electrode graphite was 81%. Prior to determining the baking isotherm temperature, as well as the changes in dimensions during thermal treatment, the chemical compositions of the 12 CTP samples were determined. In the chemical composition determination, fundamental properties such as softening point (SP), coking value (CV), toluene and quinoline insolubles (TI and QI, respectively) were evaluated. This was in addition to proximate and ultimate analysis. The information obtained from this diverse characterisation showed significant differences in the chemical composition of the 12 CTPs. By making use of multi-linear regression analysis (MLR), it was possible to predict or calculate less commonly determined characteristics (CV, TI and QI) from the more commonly obtained parameters (proximate and ultimate analysis parameters). It was found that MLR could be used successfully to calculate CV and TI, but less so for QI. Additional chemical composition of CTP was determined by analytical techniques such as Fourier Transform Infra-Red spectroscopy (FT-IR) and Nuclear Magnetic Resonance spectroscopy (NMR). Results from the FT-IR analysis showed that the spectra for all 12 raw CTPs were similar, with differences only being in the FT-IR band intensities. The differences in FT-IR band intensities were supported by NMR analysis data, which gave quantitative information on the different structural parameters found in all CTPs. The structural composition of CTPs changed during thermal treatment, as was shown by the FT-IR analysis performed on raw CTPs samples, CTPs thermally treated at 475, 700, 1000 and 1300 °C, as well as prebaked electrode graphite. / PhD (Chemistry), North-West University, Potchefstroom Campus, 2014

Device fabrication on multi walled carbon nanotubes (MWCNTs) using electrical beam lithography (EBL), electron beam induced deposition (EBID), ion beam induced deposition (IBID) methods was carried out, followed by device electrical characterization using a conventional probe station. A four-probe configuration was utilized to measure accurately the electrical resistivity of MWCNTs with similar results obtained from devices fabricated by different methods. In order to reduce the contact resistance of the beam deposited platinum electrodes, single step vacuum thermal annealing was performed. Microscopy and spectroscopy were carried out on the beam deposited electrodes to follow the structural and chemical changes occurring during the vacuum thermal annealing. For the first time, a core-shell type structure was identified on EBID Pt and IBID Pt annealed electrodes and analogous free standing nanorods previously exposed to high temperature. We believe this observation has important implications for transport properties studies of carbon materials. Apart from that, contamination of carbon nanostructure, originating from the device fabrication methods, was also studied. Finally, based on the observations of faster processing time together with higher yield and flexibility for device preparation, we investigated EBID to fabricate devices for other discrete carbon nanostructures.

Submitted by Maria Eneide de Souza Araujo (mearaujo@ipen.br) on 2015-09-01T18:02:01Z No. of bitstreams: 0 / Made available in DSpace on 2015-09-01T18:02:01Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2016-12-08T17:19:39Z (GMT). No. of bitstreams: 1 Capa-Introducao.pdf: 151731 bytes, checksum: 85462ba1c7359a14191412d891696a53 (MD5) Previous issue date: 2011-07-26 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Secondary graphitization in ductile cast iron occurs in quenched and tempered irons for long times. Usually the phenomenon is prevented since decreases mechanical properties of the material. On the other hand, cast irons with high graphite particles number present good resistance to hydrogen embrittlement.This work presents the development of secondary graphitization in gray cast iron. Samples of special compositions of gray iron, with high silicon content and low Cr content (2,56% Si and 0,025% Cr; 2,80% Si and 0,03% Cr), were casted. The heat treatment for graphitization consisted in austenitizing and quenching, in order to obtain a martensite matrix, susceptible to secondary graphite nodule development, and then tempering. For each composition, two austenitizing temperatures were defined, for the higher Si composition, 850° and 900°C and, for the lower Si composition, 900° and 950°C. The tempering temperatures were 600° and 650°C for periods of 2, 5 and 7 hours. The highest secondary graphite nodule number found were 261 nodules per mm2, from the higher Si composition sample, austenitized at 950°C and tempered at 650°C for 5 hours. The results show higher number of graphite nodules and secondary graphite volume for higher austenitizing temperatures. As the tempering time increased, martensite tempers and, then, a ferrite matrix takes place with spheroidal cementite particles. Cementite transforms to ferrite and small graphite particles. In the sequence, the particles grow and coalesce, aggregating higher graphite volume. The reaction controlling factor is the carbon diffusion. The nodules morphology is similar to the morphology of malleable iron graphite particles. The nodule numbers reveals a peak at about 5 hours of tempering for the majority of composition and heat treating combinations. After this time, small nodules reprecipitate over the larger ones. The preferable sites for secondary graphite nodules formation were regions far from primary graphite veins, interdendritic and inside the eutectic cells. The secondary graphite precipitation over the primary graphite was also observed. The secondary graphite volume increases with tempering time. / A grafitização secundária em ferro fundido nodular é obtida após tratamento de têmpera seguido de revenido por longos períodos. Geralmente, o fenômeno é evitado, pois reduz as propriedades mecânicas do material. Por outro lado, ferros fundidos com grande número de partículas de grafita apresentam boa resistência à fragilização por hidrogênio. O presente trabalho trata do estudo da formação de grafita secundária em ferro fundido cinzento Duas composições de ferro fundido cinzento com alto teor de Si e baixo teor de Cr (2,56% de Si e 0,025% de Cr; 2,80% de Si e 0,03% de Cr), foram fundidas. O tratamento térmico para a grafitização consistiu em austenitização e têmpera, para a obtenção de matriz martensítica, mais propensa à formação de nódulos de grafita secundária, e posterior revenido. Para cada material, duas temperaturas de austenitização foram escolhidas, a saber, para o material de menor teor de Si, 850° e 900°C e, para o de maior, 900° e 950°C. As temperaturas de revenido foram definidas como 600° e 650°C por tempos de 2, 5 e 7 horas. O maior número de nódulos de grafita secundária encontrado foi o de 261 nódulos por mm2, da amostra de composição de maior teor de Si, austenitizada a 950°C, revenida a 650°C, por 5 horas. Os resultados mostram maior formação de nódulos de grafita secundária, bem como maior volume grafitizado, para maiores temperaturas de austenitização. Com o passar do tempo do revenido, tem-se martensita revenida e, então, esta dá lugar à matriz ferrítica com carbonetos esferoidizados. A cementita transforma-se em ferrita e pequenas partículas de grafita. Com o tempo, as partículas crescem e coalescem, agregando maior volume grafitizado. O mecanismo controlador dessa reação de grafitização é a difusão de carbono. A morfologia dos nódulos é similar à das partículas de grafita de ferro maleável. O número de nódulos mostra um pico em cerca de 5 horas de revenido para a maioria das combinações de composição e tratamento térmico. Após esse período, os pequenos nódulos reprecipitam sobre os maiores. Os locais preferenciais para a formação de nódulos de grafita secundária são regiões distantes de lamelas de grafita, interdendríticas e no interior de células eutéticas. Foi possível observar a precipitação de grafita secundária também sobre as lamelas de grafita primária. O volume grafitizado é crescente com o tempo de revenido.

Submitted by Maria Eneide de Souza Araujo (mearaujo@ipen.br) on 2015-09-01T18:02:01Z No. of bitstreams: 0 / Made available in DSpace on 2015-09-01T18:02:01Z (GMT). No. of bitstreams: 0 / As indústrias que desenvolvem motores de combustão interna têm como preocupação atual prover motores que sejam cada vez menos poluentes, uma vez que a preocupação com a preservação do meio ambiente é intensa em todo o mundo. No entanto, com o desenvolvimento de novas tecnologias destinadas à redução das emissões, a condensação dos gases, provenientes da combustão, está sendo promovida dentro das câmaras de combustão dos veículos. Ácidos, como sulfúrico e nítrico, são gerados pela condensação destes gases. Esta condensação está associada às altas taxas de recirculação de gases de escape, conhecido como EGR, (termo em inglês para Exhaust Gas Recirculation). Consequentemente, problemas de corrosão nos componentes do motor estão aumentando, especialmente em camisas de cilindro em ferro fundido. Neste estudo, foi investigada a resistência à corrosão de dois ferros fundidos, um de microestrutura perlítica e o outro com microestrutura bainítica, em soluções de condensado natural e sintético de motores movidos a diesel. Os resultados foram associados às microestruturas e as composições químicas dos materiais estudados. Resultados de testes de imersão e ensaios de espectroscopia de impedância eletroquímica, bem como de curvas de polarização potenciodinâmicas, indicaram que os dois materiais não apresentam resistência à corrosão nos meios de ensaio adotados. O ataque intenso da matriz observado em ambos os materiais observado pelos ensaios de imersão, mostraram a atuação do mecanismo eletroquímico de corrosão por grafitização. Este mecanismo causa o ataque localizado e destrutivo da matriz de ferrita (-Fe), que funciona como anodo enquanto as grafitas atuam como áreas catódicas. Enquanto em meio ácido não foi possível observar uma diferenciação entre os dois tipos de ferros fundidos estudados, em meio neutro e aerado, o ferro fundido bainítico mostrou resistência à corrosão superior à do ferro fundido perlítico. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Les fontes à graphite sphéroïdal sont aujourd’hui très largement utilisées en raison de leurs bonnes propriétés mécaniques. La forme sphéroïdale du graphite est obtenue le plus souvent par l’ajout de magnésium ou de cérium lors de l’élaboration des fontes. Le graphite sphéroïdal peut être obtenu par graphitisation à l'état solide des fontes totalement ou partiellement solidifiées dans le système métastable. L’objectif de ce travail est d’étudier l’effet du traitement de graphitisation à l’état solide sur la croissance du graphite nodulaire d’une fonte à paroi mince qui présente une structure truitée à l'état brut de coulée. Cette fonte a été étudiée par microscopie optique, microscopies électronique à balayage et en transmission, spectroscopie Raman et spectroscopie de perte d'énergie des électrons. Des traitements thermiques assurant une graphitisation totale et partielle pour décomposer la cémentite formée à la solidification en graphite et en austénite ont été réalisés. Les nodules deviennent plus nombreux et leur taille augmente en fonction du temps de graphitisation. La microstructure après traitement thermique est composée de nodules de graphite et de ferrite. La spectroscopie Raman a été utilisée pour caractériser les nodules de graphite d’échantillons ayant été entièrement graphitisés à différentes températures dans le domaine austénitique. L’analyse par spectroscopie Raman ne montre aucune différence significative entre les spectres Raman enregistrés sur le graphite formé lors de la solidification et à l’état solide. Les caractérisations microstructurales par microscopie électronique en transmission montrent que le graphite à l’état brut de coulée présente une structure caractérisée par une zone interne où le graphite est désorienté. Une déformation mécanique due à la contraction lors de la solidification métastable induit la formation de cette zone. Cette zone disparaît par recristallisation après traitement de graphitisation totale pour former à la fin des secteurs coniques rayonnant à partir du germe et se développant vers la périphérie. Les résultats de ces travaux ont permis une meilleure compréhension de la structure de graphite nodulaire à l’état solide et montre aussi que le mécanisme de croissance du graphite nodulaire est le même lors de la solidification et de la transformation à l'état solide. / Spheroidal graphite iron castings are today widely used because of their good mechanical properties. The spheroidal shape of graphite is most often obtained by the addition of magnesium or cerium during the casting process. Spheroidal graphite can be formed at the solid-state by graphitization of cast irons which solidified partly or totally in the metastable system. The purpose of this work is to study the effect of solid-state graphitization treatment on the growth of nodular graphite of a thin wall casting which has a mottled structure at the as-cast state. This cast iron was studied using optical microscopy, scanning and transmission electron microscopy, Raman spectroscopy and electron energy loss spectroscopy. Heat treatments ensuring a total and partial graphitization to decompose the cementite formed at the solidification in graphite and austenite were realized. The nodules become more numerous and their size increases according to the time of graphitization. The microstructure after heat treatment is composed of graphite nodules and ferrite. Raman spectroscopy has been used to characterize graphite nodules in as-cast state and in samples having been fully graphitized at various temperatures in the austenite field. The results show no significant difference between Raman spectra recorded on these various samples, suggesting graphite grows with the same mechanism during either solidification or hightemperature (so-called first stage) graphitization. Transmission electron microscopy characterizations show that nodules in the as-cast material presents a multi-fold structure characterized by an inner zone where graphite is misoriented and an outer zone where it is well crystallized. In heat-treated samples, graphite nodules consist of well crystallized sectors radiating from the nucleus. These observations suggest that the misoriented zone appears because of mechanical deformation when the liquid contracts during its solidification. During heat-treatment, this zone disappears by recrystallization. The results of the present work lead to a better understanding of the nodular graphite structure in the solid state and also show that nodular graphite growth mechanism is the same during solidification and solid-state transformation.

Demand for high-quality graphite is expected to experience an extraordinary growth rate, in large part due to its wide range of industrial applications such as adsorbents, lubricants, electrodes, etc. This thesis developed a novel sustainable approach to produce green-graphite materials by applying biochar, acarbon-rich valuable by-product obtained from biomass, as a carbon precursor. Meanwhile, iron-based catalysts are applied to enable the graphitization at a relatively lower temperature. This study focuses on the different parameters which could affect the evolution of carbon structure. The samples were mixed with catalyst in two ways, dry mixing and wet impregnation. Aside from the addition method, several parameters including temperature, heating duration, and iron loading amount were varied from 800 to 1300 ℃, 1 to 6 hours, and 0 to 33.6% respectively, to figure out an optimum graphitization process. The samples were characterized by X-ray diffraction, Raman scattering, SEM and particle size distribution analysis. Based on the characterization results, it was confirmed that with the increase of the graphitization temperature, duration and amount of iron loading, synthetic graphite performs a better graphitization and a higher conversion rate. Meanwhile, a detailed dissolution-precipitation mechanism was introduced and discussed in the context of iron-carbon equilibrium phase diagram to explain this catalytic process. / Efterfrågan på högkvalitativ grafit förväntas uppleva en extraordinär tillväxttakt, till stor del på grund av dess breda utbud av industriella applikationer som adsorbenter, smörjmedel, elektroder etc.  Denna avhandling utvecklar ett nytt hållbart tillvägagångssätt för att producera grön-grafit genom att använda biokol, en kolrik värdefull biprodukt erhållen från biomassa, som en kolprekursor. Även järnbaserade katalysatorer används för att möjliggöra grafitisering vid relativt lägre temperaturer. Denna  studie fokuserar på  de olika  parametrar  som  kan  påverka  bildandet  av kolstrukturen. Proverna blandades med katalysatormaterialet på två sätt, torrblandning och våtimpregnering. Förutom tillsatsmetoden justeras flera andra parametrar, inklusive temperatur, uppvärmningstid och mängd järnbelastning för  att  få  en optimal  grafitiseringsprocess.  Proverna karakteriserades därefter genom röntgendiffraktion, Ramanspridning, SEM och  partikelstorleksfördelningsanalys. Baserat på karakteriseringsresultaten bekräftades det att med en ökande grafitiseringstemperatur, varaktighet och mängd av järnbelastning, får syntetisk grafit en bättre grafitisering och en högre omvandlingsgrad. Även en detaljerad upplösnings-utfällningsmekanism introducerades och diskuterades i sammanhanget av järn-kol jämviktsfasdiagrammet  för  att förklara den katalytiska processen.

Graphite materials are vital industrial products. The rapid development of the battery and electronic computer industries has incentivized a great demand for graphite materials. However, today, graphite materials are commercially produced via thermal treating fossil oil or coal derived coke at a temperature higher than 2500℃. Both of the fossil-based feedstock and the energy-intensive production process are contrary to the concept of sustainable development. This thesis proposes a sustainable low-temperature catalytic graphitization process to produce graphite materials with highly ordered crystallinity by using commercial biomass pyrolysis biochar as the feedstock. Iron nitrate was selected as the graphitization catalyst. The effect of the graphitization temperature and the iron loading amount on the properties of the produced carbon products was studied. Produced graphite materials were characterized by performing X-ray diffraction, Nitrogen adsorption-desorption, and elemental analysis. Results show that the average graphitic crystalline size and the degree of graphitization of the product increased with the increase of the graphitization temperature and the iron loading amount. However, the increase of the iron loading amount reduced the catalyst removal efficiency of the acid washing process. When the graphitization temperature is higher than 1100℃ and the iron loading amount is higher than 11.2 wt.%, the crystallinity of the produced graphite material is better than that of the commercial graphite. The graphite material with the best crystallinity, which was produced at a temperature of 1300℃ and an iron loading of 33.6 wt.%, has crystallinity very close tothe pure graphite. / Grafitmaterial är viktiga industriprodukter. Den snabba utvecklingen av batteri- och elektronikdatorindustrin har stimulerat en stor efterfrågan på grafitmaterial. Idag framställs emellertid grafitmaterial kommersiellt via termisk behandling av fossil olja eller kol härledd koks vid en temperatur högre än 2500℃. Både det fossilbaserade råvaran och den energikrävande produktionsprocessen strider mot begreppet hållbar utveckling. Denna avhandling föreslår en hållbar katalytisk grafitiseringsprocess vid låg temperatur för att producera grafitmaterial med högt ordnad kristallinitet genom att använda kommersiell biomassapyrolysbiokol som råmaterial. Järnnitrat valdes som grafitiseringskatalysator. Effekten av grafitiseringstemperaturen och järnbelastningsmängden på egenskaperna hos de producerade kolprodukterna studerades. Framställda grafitmaterial kännetecknades av utförande av röntgendiffraktion, kväve-adsorptionsdesorption och elementaranalys. Resultaten visar att den genomsnittliga grafitiska kristallina storleken och graden av grafitisering av produkten ökade med ökningen av grafitiseringstemperaturen och järnbelastningsmängden. Ökningen av järnbelastningsmängden minskade emellertid katalysatorns avlägsnande effektivitet för syratvättprocessen. När grafitiseringstemperaturen är högre än 1100℃ och järnbelastningsmängden är högre än 11,2 viktprocent, är kristalliniteten hos det producerade grafitmaterialet bättre än den för den kommersiella grafiten. Grafitmaterialet med den bästa kristalliniteten, som producerades vid en temperatur av 1300℃ och en järnbelastning på 33,6 viktprocent, har kristallinitet mycket nära den rena grafiten.

Cette thèse est focalisée sur la contribution de l'étude couplée de l’organisation multi-échelle et de la composition isotopique de C et N des carbones de météorites différenciées (acapulcoites – lodranites (A-L)), pour mieux comprendre l’histoire de leur corps-parent. Nous avons systématiquement combiné observations des carbones de ces météorites avec des analogues expérimentaux. Nous avons développé une méthodologie originale couplant l'étude de l'organisation des échelles micrométriques à nanométriques (par Microscopie Electronique par Transmission et Microspectrométrie Raman) et l'analyse isotopique des carbones (par SIMS) sur rigoureusement les mêmes plages de dimensions micrométriques. La comparaison avec les mélanges expérimentaux indique que le graphite d’Acapulco s’est formé par un mode de graphitisation "catalysée par le fer". L’absence de graphitisation des carbones de Lodran dans un environnement riche en fer et chaud est apparemment paradoxale. Toutes nos observations peuvent être réconciliées si nous considérons une collision tardive du corps-parent des A-L avec un corps chondritique apportant matière organique insoluble et chaleur d'impact. Ce scénario est conforté par les analyses isotopiques qui indiquent une formation des carbones des A-L par carbonisation d’un précurseur chondritique et une migration d’effluents carbonés au sein du corps-parent / This thesis is focused on the contribution of the coupling of multi-scale organization and C, N isotopic composition of carbons in differentiated meteorites (acapulcoites – lodranites (A-L)), in order to better understand the history of their parent body. We systematically combined observations of carbons from these meteorites with experimental analogues. We developed an original methodology associating the study of the organization at the micrometre to nanometre scales (by Transmission Electron Microscopy and by Raman Microspectrometry), and the analysis of the isotopic composition of carbons (by SIMS) on strictly the same areas of micrometre dimensions. The comparison with experimental analogues indicates that the Acapulco graphite was formed by a "catalytic" graphitization mode. The absence of graphite in Lodran, in an iron-rich and hot environment, is apparently paradoxical. All our observations can be reconciled if we consider a late collision of the A-L parent body with a chondritic body bringing insoluble organic matter and impact heat. This scenario is strengthened by isotopic analyses, which indicate formation of A-L carbons by carbonization of a chondritic precursor and migration of carbonaceous effluents within the parent-body

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