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

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

Na Odontologia, ao se confeccionar peças restauradoras dentárias, pela técnica indireta, o processo mais rotineiramente empregado utiliza um modelo de gesso, obtido a partir de um molde de elastômero, tomado de um dente preparado. Vários fatores podem influenciar na boa precisão de ajustes destas peças como o escoamento do material de vazamento dentro da moldagem, a compatibilidade do material de vazamento com o da moldagem, o tempo de presa, a estabilidade dimensional, a resistência mecânica do material quando da separação moldagem/modelo, a resistência a abrasão e a fidelidade de reprodução de detalhes. Materiais foram introduzidos na odontologia para utilização na confecção de troquéis no intuito de minimizar as desvantagens do gesso, como baixa resistência a abrasão e ligeira expansão de presa. Dentre eles os troquéis metalizados e as resinas epóxicas, que tem vantagens em relação às propriedades mecânicas, porém o primeiro exige técnica demorada e de alto custo e o segundo apresenta contração. O presente trabalho se propõe a testar uma nova composição de poliéster insaturado com estireno adicionado ao carbonato de cálcio em diferentes proporções (10, 20, 30, 40, 50, 60 e 70%) e compará-la ao gesso tipo IV e a resina epoxídica com óxido de alumínio, através de ensaios mecânicos, de abrasão e de alteração dimensional, para avaliar a possibilidade de sua utilização como material de confecção de troquéis para a construção de restaurações indiretas. Para caracterização dos materiais foram feitas análises de espectrometria no infravermelho, Calorimetria de varredura diferencial, termogravimétrica e Microscopia eletrônica de varredura. O compósito a base de poliéster insaturado com 50% de carbonato de cálcio se mostrou viável para utilização como material para troquel. Quando comparado aos materiais de controle mostrou propriedades mecânicas próximas as da resina epoxídica e bem superiores ao gesso, resistência a abrasão superior ao gesso e inferior a resina epoxídica e alteração dimensional próxima a resina epoxídica e maior ao gesso. Sendo a formulação do poliéster/carbonato de cálcio apenas constituída de polímero, catalisador e carga, é possível melhorar a formulação modificando a carga e/ou acrescentando aditivos visando minimizar a contração de polimerização. / In dentistry, the most commonly used procedure to manufacture indirect dental restorations uses a cast of type IV stone. This cast is made from an elastomeric impression of a prepared tooth. Many factors may influence the accuracy of adaptation of these restorations, such as the flow of the pouring material into the mold, the compatibility between the pouring and the impression materials, the setting time, the dimensional stability, the mechanical strength of the material during the mold / cast separation, the abrasion resistance and fidelity to reproduce details. Materials were introduced for preparing dies in order to minimize the disadvantages of the stone, such as its low resistance to abrasion and slight expansion of setting. These materials include metal-plated dies and epoxy resins, which have advantages concerning mechanical properties. However, the first one has a time-consuming technique and requires high costs while the second material shows shrinkage. This study tested a new composition of unsaturated polyester with styrene added to calcium carbonate in different proportions (10, 20, 30, 40, 50, 60 and 70%) and compared it to the type IV stone and to the epoxy resin with aluminum oxide. This comparison was made by mechanical, abrasion and dimensional changes tests in order to evaluate the possibility of using it as material for dies in the process of construction of indirect restorations. The materials were characterized using the analysis of the infrared spectrometry, differential scanning calorimetry, thermogravimetric and scanning electron microscopy. The composite based on unsaturated polyester with 50% calcium carbonate (P5) was considered viable as material for dies. When it was compared to the control materials the following results were found: a) the mechanical properties of P5 are similar to those ones of the epoxy resin and well above the stone ones; b) the abrasion resistance of this new material is lower in relation to the epoxy resin, but higher than the stone one; c) the values for dimensional changes were similar to the epoxy resin ones and superior to those ones found in stone. As the formulation of polyester / calcium carbonate only consists of a polymer, a catalyst and filler particles, it is possible to improve its composition by modifying the filler particles and / or adding additives to minimize the shrinkage of polymerization.

Na Odontologia, ao se confeccionar peças restauradoras dentárias, pela técnica indireta, o processo mais rotineiramente empregado utiliza um modelo de gesso, obtido a partir de um molde de elastômero, tomado de um dente preparado. Vários fatores podem influenciar na boa precisão de ajustes destas peças como o escoamento do material de vazamento dentro da moldagem, a compatibilidade do material de vazamento com o da moldagem, o tempo de presa, a estabilidade dimensional, a resistência mecânica do material quando da separação moldagem/modelo, a resistência a abrasão e a fidelidade de reprodução de detalhes. Materiais foram introduzidos na odontologia para utilização na confecção de troquéis no intuito de minimizar as desvantagens do gesso, como baixa resistência a abrasão e ligeira expansão de presa. Dentre eles os troquéis metalizados e as resinas epóxicas, que tem vantagens em relação às propriedades mecânicas, porém o primeiro exige técnica demorada e de alto custo e o segundo apresenta contração. O presente trabalho se propõe a testar uma nova composição de poliéster insaturado com estireno adicionado ao carbonato de cálcio em diferentes proporções (10, 20, 30, 40, 50, 60 e 70%) e compará-la ao gesso tipo IV e a resina epoxídica com óxido de alumínio, através de ensaios mecânicos, de abrasão e de alteração dimensional, para avaliar a possibilidade de sua utilização como material de confecção de troquéis para a construção de restaurações indiretas. Para caracterização dos materiais foram feitas análises de espectrometria no infravermelho, Calorimetria de varredura diferencial, termogravimétrica e Microscopia eletrônica de varredura. O compósito a base de poliéster insaturado com 50% de carbonato de cálcio se mostrou viável para utilização como material para troquel. Quando comparado aos materiais de controle mostrou propriedades mecânicas próximas as da resina epoxídica e bem superiores ao gesso, resistência a abrasão superior ao gesso e inferior a resina epoxídica e alteração dimensional próxima a resina epoxídica e maior ao gesso. Sendo a formulação do poliéster/carbonato de cálcio apenas constituída de polímero, catalisador e carga, é possível melhorar a formulação modificando a carga e/ou acrescentando aditivos visando minimizar a contração de polimerização. / In dentistry, the most commonly used procedure to manufacture indirect dental restorations uses a cast of type IV stone. This cast is made from an elastomeric impression of a prepared tooth. Many factors may influence the accuracy of adaptation of these restorations, such as the flow of the pouring material into the mold, the compatibility between the pouring and the impression materials, the setting time, the dimensional stability, the mechanical strength of the material during the mold / cast separation, the abrasion resistance and fidelity to reproduce details. Materials were introduced for preparing dies in order to minimize the disadvantages of the stone, such as its low resistance to abrasion and slight expansion of setting. These materials include metal-plated dies and epoxy resins, which have advantages concerning mechanical properties. However, the first one has a time-consuming technique and requires high costs while the second material shows shrinkage. This study tested a new composition of unsaturated polyester with styrene added to calcium carbonate in different proportions (10, 20, 30, 40, 50, 60 and 70%) and compared it to the type IV stone and to the epoxy resin with aluminum oxide. This comparison was made by mechanical, abrasion and dimensional changes tests in order to evaluate the possibility of using it as material for dies in the process of construction of indirect restorations. The materials were characterized using the analysis of the infrared spectrometry, differential scanning calorimetry, thermogravimetric and scanning electron microscopy. The composite based on unsaturated polyester with 50% calcium carbonate (P5) was considered viable as material for dies. When it was compared to the control materials the following results were found: a) the mechanical properties of P5 are similar to those ones of the epoxy resin and well above the stone ones; b) the abrasion resistance of this new material is lower in relation to the epoxy resin, but higher than the stone one; c) the values for dimensional changes were similar to the epoxy resin ones and superior to those ones found in stone. As the formulation of polyester / calcium carbonate only consists of a polymer, a catalyst and filler particles, it is possible to improve its composition by modifying the filler particles and / or adding additives to minimize the shrinkage of polymerization.

Syfte: Syftet med denna systematiska litteraturöversikt var att analysera litteraturen avseende dimensionsförändringar av det buckala benet efter implantatkirurgi samt att undersöka vilka resultat som beskrevs i studier som mätte det buckala benets tjocklek. Material och metoder: Databaserna Medline, Cochrane Library och ISI Web of Science genomsöktes för att identifiera relevanta humanstudier som mätte det buckala benets tjocklek vid implantatkirurgi och följde resultaten i åtminstone 12 månader efter implantatplaceringen. Resultat: Från 834 identifierade publikationer, inkluderades totalt 3. 2 av dessa var prospektiva kliniska studier och 1 en systematisk litteraturöversikt. Den inkluderade systematiska litteraturöversikten kunde inte ge någon ytterligare information till frågeställningen. Horisontell och vertikal resorption av det buckala benet visades i båda observationsstudierna. Resultat av hård- och mjukvävnadsförändringar beskrevs liksom det inflammatoriska tillståndet i mjukvävnaden runt implantatet. Slutsats: Mer forskning behövs om dimensionella förändringar av det buckala benet efter implantatkirurgi på grund av metodologisk heterogenitet och bristen på studier. Angående den buckala bentjockleken kunde inget tröskelvärde identifieras avseende vilken dimension som bidrog till minst andel resorption. Dock verkar det som om viss horisontell och vertikal resorption av det buckala benet kan ske inom loppet av 12 månader efter implantatkirurgi. / Purpose: The purpose of this systematic review was to analyze the literature on alterations of the buccal bone dimensions following implant surgery, and what outcomes that were described in studies measuring the buccal bone thickness. Materials and methods: Medline, the Cochrane Library and the ISI Web of Science databases were searched to identify eligible human studies that measured the buccal bone thickness at delayed implant placement and followed the outcomes at least 12 months following implant placement.Results: From 834 identified publications, 3 were included. 2 of these were prospective clinical studies and 1 a systematic review. The included systematic review did not yield any additional information to the focused questions. Horizontal and vertical resorption of the buccal bone was demonstrated in both observational studies. Outcomes of hard and soft tissue changes were described as well as inflammatory state of the peri-implant mucosa.Conclusion: More research is needed concerning dimensional alterations of the buccal bone following implant placement due to methodological heterogeneity and lack of studies. No threshold regarding the buccal bone thickness and the degree of resorption could be identified. However, within the limitations of this review, results suggests that some horizontal and vertical buccal bone resorption may take place during the first 12 months following implant placement.

O intuito deste trabalho foi avaliar as alterações dimensionais das arcadas dentárias de crianças portadoras de fissuras labiopalatinas na fase de dentição decídua completa, comparando-as entre si com um grupo controle. As dimensões estudadas foram: distância intercaninos, distância intermolares, perímetro do arco e comprimento do arco, tanto na arcada superior quanto na inferior. Selecionou-se 64 (sessenta e quatro) crianças portadoras de fissuras de lábio e/ou palato, formando o Grupo de Estudo, e 20 (vinte) crianças sem deformidades, formando o Grupo Controle. O Grupo de Estudo foi distribuído em quatro tipos de fissura: Fissura Labiopalatina Unilateral, Fissura Labiopalatina Bilateral, Fissura de Lábio e Fissura de Palato. Após a obtenção de modelos em gesso, foram demarcados os pontos necessários para que as mensurações pudessem ser realizadas. Utilizou-se um paquímetro digital da marca Mytutoio para a determinação das medidas, que foram executadas duas vezes pelo mesmo operador em oportunidades diferentes, sendo registrada a média aritmética. Os resultados obtidos foram tabelados e submetidos à análise estatística, permitindo concluir que a arcada dentária maxilar de indivíduos fissurados apresentou maiores alterações dimensionais no sentido transversal, enquanto a arcada dentária mandibular não demonstrou alterações significativas; o tipo de fissura com as maiores alterações dimensionais foi a fissura labiopalatina bilateral, e a que mostrou menor comprometimento da morfologia das arcadas dentárias foi a fissura de lábio; a fissura de palato foi a que mais apresentou relativa alteração compensatória na arcada dentária inferior. / The aim of this work was to evaluate the dimensional changes in dental arches of cleft lip and palate children during the complete deciduous dentition phase, comparing one to each other and with a group control. The studied dimensions were: intercanine distance, intermolar distance, perimeter and length arch both in superior and inferior arches. The studied group was constituted through the selection of 64 (sixty four) cleft lip and/or cleft palate children and 20 (twenty) children without deformities which constituted the control group. The study group was distributed in four types: unilateral cleft lip and palate, bilateral cleft lip and palate, cleft lip and cleft palate. After the obtaining of plaster models, points were demarcated in order to allow measurements. A digital pachymeter (Mytutoio) was used for measure determination, that was performed twice by the same operator in different opportunities, being registered the arithmetic mean value. The obtained results were registered and submitted to statistical analysis being possible to conclude that maxillary dental arch presented larger dimensional changes in the traverse direction while mandibular dental arch didn't demonstrate significant change. The largest dimensional change was observed in bilateral cleft lip and palate and the smaller compromising in dental arch morphology was verified in cleft lip. The palate cleft presented larger relative compensatory change in the inferior dental arch.

O intuito deste trabalho foi avaliar as alterações dimensionais das arcadas dentárias de crianças portadoras de fissuras labiopalatinas na fase de dentição decídua completa, comparando-as entre si com um grupo controle. As dimensões estudadas foram: distância intercaninos, distância intermolares, perímetro do arco e comprimento do arco, tanto na arcada superior quanto na inferior. Selecionou-se 64 (sessenta e quatro) crianças portadoras de fissuras de lábio e/ou palato, formando o Grupo de Estudo, e 20 (vinte) crianças sem deformidades, formando o Grupo Controle. O Grupo de Estudo foi distribuído em quatro tipos de fissura: Fissura Labiopalatina Unilateral, Fissura Labiopalatina Bilateral, Fissura de Lábio e Fissura de Palato. Após a obtenção de modelos em gesso, foram demarcados os pontos necessários para que as mensurações pudessem ser realizadas. Utilizou-se um paquímetro digital da marca Mytutoio para a determinação das medidas, que foram executadas duas vezes pelo mesmo operador em oportunidades diferentes, sendo registrada a média aritmética. Os resultados obtidos foram tabelados e submetidos à análise estatística, permitindo concluir que a arcada dentária maxilar de indivíduos fissurados apresentou maiores alterações dimensionais no sentido transversal, enquanto a arcada dentária mandibular não demonstrou alterações significativas; o tipo de fissura com as maiores alterações dimensionais foi a fissura labiopalatina bilateral, e a que mostrou menor comprometimento da morfologia das arcadas dentárias foi a fissura de lábio; a fissura de palato foi a que mais apresentou relativa alteração compensatória na arcada dentária inferior. / The aim of this work was to evaluate the dimensional changes in dental arches of cleft lip and palate children during the complete deciduous dentition phase, comparing one to each other and with a group control. The studied dimensions were: intercanine distance, intermolar distance, perimeter and length arch both in superior and inferior arches. The studied group was constituted through the selection of 64 (sixty four) cleft lip and/or cleft palate children and 20 (twenty) children without deformities which constituted the control group. The study group was distributed in four types: unilateral cleft lip and palate, bilateral cleft lip and palate, cleft lip and cleft palate. After the obtaining of plaster models, points were demarcated in order to allow measurements. A digital pachymeter (Mytutoio) was used for measure determination, that was performed twice by the same operator in different opportunities, being registered the arithmetic mean value. The obtained results were registered and submitted to statistical analysis being possible to conclude that maxillary dental arch presented larger dimensional changes in the traverse direction while mandibular dental arch didn't demonstrate significant change. The largest dimensional change was observed in bilateral cleft lip and palate and the smaller compromising in dental arch morphology was verified in cleft lip. The palate cleft presented larger relative compensatory change in the inferior dental arch.

This diploma thesis deals with the problem of wax patterns manufacturing in investment casting technology (lost wax process). This technology is very sensitive to the exact execution in each phase of the whole process, from concept design up to the final casting expedition. During most operations, dimensional changes occur, which is affecting the accuracy of the final casting. No matter how big these changes are, but especially if they occur with the least variance. One of the first phases in this technology is making wax patterns. There are several ways of making the wax patterns and this thesis is describing two different methods used in the Alucast foundry. One is based on using “soft waxes” enabling using low pressure machines, the other one on the “hard waxes” where the injection machine with higher presses is being used (SOM). These two above mentioned technologies are compared in this work.

The diploma thesis is focused on polymercement materials with dispersed reinforcement. The aim of this work is development of suitable polymercement mixture and monitoring of the impact of dispersed reinforcement on the course of maturation of these materials and physico-mechanical properties. The effect of high temperatures on the properties of the mortar is also examined. Emphasis is placed on the use of alternative resources and byproducts. Mixed binder of cement and slag and admixture of microsilica was used. Recycled cellulose was used as dispersed reinforcement and was compared with commercial polypropylene fibers.