Hydroxyl terminated polybutadiene (HTPB) based polyurethanes (PUs) are low modulus materials and degrade easily at low temperature. Polycarbodiimide (PCDI) and polysiloxane (PSi) are reactive-type fillers when formed by carbodimidzation and sol-gel process, respectively. During the combustion, PCDI and PSi give off non-toxic, non-corrosive volatile gases, and finally form carbonaceous and siliceous chars. In this study, modified PUs were prepared by incorporating PCDI or PSi into PUs to give high carbon, nitrogen and silicon materials. These modified PUs are kinds of organic-inorganic hybrids with higher modulus and higher thermal stability than HTPB-based PUs. In addition, new silicone based insulation materials were prepared by mixing two silicone rubber materials LSR-2670 and RTV-627 from GE Silicones, in order to improve the heat insulation and to reduce the ablation rate. These inhibitors can keep the rocket motor from the high temperature ablation for a long time, especially castable silicone based heat insulations for the case of the ramjet engines. The mechanical properties at room temperature and the thermal stability of these modified PUs and silicone rubbers were investigated using a tensile tester and a thermogravimetric analyzer (TGA). ATR/FTIR (Attenuated total reflectance / Fourier transform infrared) technique is applied to monitor the synthesis process of PCDI and to examine the change of surface chemistry of insulator before and after thermal degradation via TGA. TGA coupled with FTIR (TGA/FTIR) was used to analyze the kinetics and the mechanism of thermal degradation under nitrogen and/or air. The Friedman and Kissinger methods of analysis were used for calculating the activation energy of degradation from dynamic TGA. The modified PUs (HIPTD-40%Psi¤ÎHIPTD-30%PMPS-PSi) with average activation energy of 88 and 112 kcal/mole (0.5¡Õ£\¡Õ0.9, under N2) and the modified silicone rubber (LR-5%HTB) with activation energy of 46.2~67.0 kcal/mole (0.1¡Õ£\¡Õ0.9, under N2) and 34.0~59.1 kcal/mole (0.1¡Õ£\¡Õ0.9, under air).The maximum degradation temperature (Tmax) and char yield (CY) of thermal degradation were estimated from a series of experiments with heating rates of 1, 3, 5, 10, 20, 30, 40 and 50 ¢J/min, under nitrogen or air. It is apparent that the maximum degradation temperature is dependent on heating rate. By assuming the heating rate for the insulator used in a rocket operating environment is about 5000¢J/min, Tmax calculated for the modified PUs (HIPTD-40%PSi and HIPTD-30%PMPS-PSi under N2) are found as 538 and 562¢J and for the modified silicone rubber (LR-5%HTB under N2 and air) are found as 576 and 562¢J, respectively. CY calculated for the modified silicone rubber (LR-5%HTB under N2 and air) is found as 71.5% and 66.2%. The morphology of modified PUs and silicone rubbers before and after thermal degradation via TGA was observed by optical and scanning electron microscope (SEM).

In this study the catalytic pyrolysis and combustion characteristics of Turkish coal samples in O2/N2 and O2/CO2 (oxy-fuel conditions) ambient conditions were explored and the evolution of emissions during these tests was investigated using non-isothermal Thermo-gravimetric Analysis (TGA) technique combined with Fourier Transform Infrared (FTIR) spectroscopy. Potassium carbonate (K2CO3), calcium hydroxide (Ca(OH)2), iron (III) oxide (Fe2O3) and iron (III) chloride (FeCl3) were employed as precursors of catalysts to investigate the effects of potassium (K), calcium (Ca) and iron (Fe). Furthermore the effects of these catalysts on calorimetric tests of Turkish coal samples were investigated. TGA-FTIR pyrolysis tests were carried out in 100 % N2 and 100 % CO2 ambient conditions which are the main diluting gases in air and oxy-fuel conditions. Lignite pyrolysis tests revealed that the major difference between pyrolysis in these two ambient conditions was observed beyond 720

Proprietary mixtures of amines and carboxylic acids are used as volatile corrosion inhibitors (VCIs) for the protection of steel and iron components against atmospheric corrosion during storage and transportation. Interactions between amines and carboxylic acids have been comprehensively reported in the literature. However, little is known about the nature of the vapours these mixtures emit. The present study focused on the development of the evolved gas analysis method which will help in the characterisation of the vapours released by VCIs. In the method, the evaporation of various amine-carboxylic acid binary mixtures was monitored by thermogravimetric analysis (TGA). The nature and the composition of the released vapours was followed by Fourier transform infrared (FTIR) spectroscopy. Mixtures consisting of triethylamine (TEA) and acetic acid were studied as a model compound using TGA-FTIR at 50 °C to validate the TGA-FTIR method. As vaporisation progressed, the composition of the remaining liquid and the emitted vapour converged to a fixed amine content of ca. 27 mol %. This is just above the composition expected for the 1:3 amine: carboxylic acid complex. Mixtures close to this composition also featured the lowest volatility. TGA-FTIR proved to be a convenient method for studying the evaporation of TEA-acetic acid mixtures, and the nature and composition of the released vapours. Amine addition leads to the dissociation of carboxylic acid dimers in favour salt formation. The formation of an ion pair between the amine and carboxylic acid was confirmed by the FTIR spectra of the liquid phase. The resulting amine-carboxylic acid mixtures showed a slow mass loss rate on TGA when compared with the pure amines and pure carboxylic acids. This indicated that the mixtures have low volatility, hence low vapour pressure compared with the pure components. The low vapour pressure of the mixtures was confirmed by the calculated gas permeability values. These values were much higher for the pure amines and the pure carboxylic acids. However, they dropped significantly on amine addition. The strong amine-carboxylic acid interaction is responsible for the suppressed volatility of the mixtures. No interaction is observed between amine and carboxylic acid molecules in the vapour phase at 230 °C. The method developed was applied to characterise the model compounds simulating the amine-carboxylic acid-based volatile corrosion inhibitors. These model systems contained the primary, secondary and tertiary amines (hexylamine, morpholine and triethylamine), as well as carboxylic acids with different chain lengths (acetic, propanoic, hexanoic and octanoic). These systems are usually employed as equimolar mixtures to protect ferrous metals against atmospheric corrosion. The key finding of the study was that the vapours released by such equimolar mixtures initially contain almost exclusively free amine. After prolonged vaporisation, a steady-state “azeotrope”-like composition is approached. It contains excess acid and features impaired corrosion-inhibition efficiencies according to the Skinner test. In part, this behaviour can be attributed to the mismatch between the volatilities of the amine and carboxylic acid constituents. / Thesis (PhD)--University of Pretoria, 2013. / gm2013 / Chemical Engineering / unrestricted

Oxy-fuel combustion technology, which is based on burning coal in a mixture of oxygen and recycled flue gas (RFG), is suggested as one of new promising technologies for capturing CO2 from power plants. In this thesis study, the pyrolysis and combustion behaviour of various fuels including imported coal, petroleum coke, two different types of indigenous lignites, olive residue and their blends with different proportions in air and oxy-fuel conditions were investigated by using non-isothermal thermogravimetric method (TGA) coupled with Fourier-transform infrared (FTIR) spectrometer. Pyrolysis tests were carried out in nitrogen and carbon dioxide environments, which are the main diluting gases of air and oxy-fuel environment, respectively. Pyrolysis results reveal that weight loss profiles are similar up to high temperature zone in both pyrolysis environments, indicating that CO2 behaves as an inert gas in this temperature range. However, further weight loss takes place in CO2 atmosphere v after 700oC due to CO2-char gasification reaction which is observed in pyrolysis of all fuel samples. Combustion experiments were carried out in four different atmospheres / air, oxygen-enriched air environment (30 % O2 &ndash / 70 % N2), oxy-fuel environment (21 % O2 &ndash / 79 % CO2) and oxygen-enriched oxy-fuel environment (30 % O2 &ndash / 70 % CO2). Combustion experiments show that replacing nitrogen in the gas mixture by the same concentration of CO2 does not affect the combustion process significantly but leads to slight delay (lower weight loss rate and higher burnout temperature) in combustion. Overall comparison of weight loss profiles shows that higher oxygen content in the combustion environment is the dominant factor affecting the combustion rather than the diluting gas. As O2 concentration increases profiles shift through lower temperature zone, peak and burnout temperatures decrease, weight loss rate increases and complete combustion is achieved at lower temperatures and shorter times. Pyrolysis and combustion behaviour of three different fuel blends were also investigated. Results reveal synergistic interactions in combustion tests of all blends in all combustion environments. During pyrolysis and combustion tests gaseous products CO2, CO, H2O, CH4, SO2 and COS were identified in flue gas and analyzed by using FTIR. Results indicate that higher CO and COS formation take place during pyrolysis tests due to gasification reaction in CO2 atmosphere at high temperature zone. Gaseous species evolution trends in combustion tests are found specific for each fuel. However, evolution trends slightly shift to lower temperatures in oxygen-enriched conditions.

El carácter adictivo del tabaco se debe fundamentalmente a la nicotina, mientras que su toxicidad se debe a una serie de sustancias tales como el monóxido de carbono, 1,3-butadieno, hidrocarburos policíclicos aromáticos (PAH) y las nitrosaminas específicas del tabaco (TSNAs), entre otros. La reducción de la toxicidad del humo del tabaco a través de la reducción de la emisión de los productos más problemáticos o la modificación de su composición en conjunto resultan alternativas muy interesantes, mientras se consigue la eliminación de este hábito. Se han localizado trabajos en la literatura encaminados a este fin. Con este objetivo, nuestro grupo de investigación lleva más de quince años estudiando el efecto que ciertos materiales micro y mesoporosos mezclados con el tabaco producen sobre la composición del humo obtenido en el proceso de fumado. En este sentido, en los últimos años se ha puesto de manifiesto la eficacia que presentan algunos silicatos mesoporosos, tales como SBA-15 y MCM-41 en la reducción de los alquitranes y la mayoría de los compuestos presentes en el humo del tabaco. Es por ello que se ha considerado que conocer el comportamiento de determinados compuestos específicos presentes en el humo de tabaco, como son la nicotina y dos nitrosaminas específicas del tabaco (NNK y NNN), los productos que se generan en su pirólisis y combustión, así como el efecto de los materiales mesoporosos mencionados en los procesos que tienen lugar durante el fumado del tabaco, sería de gran interés, y permitiría ayudar a diseñar productos de toxicidad reducida y menor carácter adictivo. A este respecto se han localizado muy escasos artículos en la bibliografía. Por todo ello, en el presente trabajo se aborda esta problemática y se plantea el estudio de la pirólisis de las dos nitrosaminas específicas del tabaco más cancerígenas, como son la 4-(N-metilnitrosoamino)-1-(3-piridinil)-butanona (NNK) y la N-nitrosonornicotina (NNN) mediante dos técnicas, TGA/FTIR y EGA/PY-GC/MS que son capaces de realizar experimentos a las velocidades de calefacción tan dispares que se dan en el proceso de fumado y tanto atmósfera inerte como atmósfera oxidante. También se estudia el comportamiento de la nicotina en EGA/PY-GC/MS, con objeto de completar el ya realizado por nuestro grupo de investigación la técnica de TGA/FTIR. Se estudia el efecto que producen tres silicatos mesoporosos (dos SBA-15 y un MCM-41) que presentan propiedades texturales y morfológicas diferentes, en la pirólisis catalítica de los tres compuestos anteriormente mencionados. Además, se analiza el efecto de la temperatura y la atmósfera (inerte y oxidante), en la degradación de la nicotina y las dos nitrosaminas mencionadas, y en la composición de los gases generados tras su descomposición. Se ha comprobado que en atmósfera oxidante los procesos de descomposición suceden a temperaturas más bajas, siendo especialmente notable este efecto en el caso de la nicotina. Así mismo, la presencia de los tres catalizadores favorece los procesos de descomposición de estos compuestos en ambas atmósferas, modifican la distribución de productos y favorecen la formación de residuo carbonoso. Los principales productos de descomposición de la nicotina en atmósfera inerte son la 3-etil-piridina, la miosmina y, especialmente la 3-vinilpiridina, que aumentan su contribución al aumentar la temperatura. Algunos compuestos como la miosmina presentan un máximo en su evolución, lo que indica que experimentan procesos de craqueo. En atmósfera oxidante se produce un cambio muy significativo en la distribución de productos, además de la mayor reactividad ya mencionada. Los productos mayoritarios pasan a ser la 3-cianopiridina, la nicotirina, la miosmina, el dióxido de carbono y el agua. La 3-cianopiridina y la 3-hidroxipiridina, muestran una tendencia creciente con la temperatura, mientras que el resto de los compuestos presentan evidencias de reacciones secundarias, poniendo de manifiesto que la presencia de oxígeno en el medio favorece las reacciones de descomposición de la nicotina y de muchos de los productos generados. La nicotina genera cianuro de hidrógeno en ambas atmósferas. Los tres catalizadores estudiados aceleran el proceso de descomposición de la nicotina y conducen a una mayor formación de residuo carbonoso, siendo el MCM-41 el material que ocasiona un mayor efecto, probablemente debido a su mayor superficie específica y buena accesibilidad de su porosidad debida a su morfología (aunque presente un menor tamaño de poro que los otros catalizadores). En atmósfera inerte la presencia de SBA-15f (SBA-15 fibras), apenas modifica el comportamiento de la nicotina, mientras que tanto MCM-41 como SBA-15p (SBA-15 platelet) se reduce la formación de algunos compuestos como la 3-vinilpiridina, incrementándose la formación de otros como quinolina e isoquinolina. En atmósfera oxidante los cambios son más significativos, ya que todos los catalizadores favorecen las reacciones de oxidación y descarboxilación, incrementando la generación de dióxido de carbono y disminuyendo la formación de agua, especialmente MCM-41 y SBA15p. MCM-41 reduce notablemente la formación de 3-cianopiridina y de nicotirina al aumentar la temperatura, a diferencia de lo observado en la nicotina, tanto sola como en presencia de los dos SBA-15. Ambas nitrosaminas han presentado unos resultados en la línea de los comentados para la nicotina. Se ha observado que la degradación completa de ambos compuestos sucede a temperaturas ligeramente inferiores para atmósfera oxidante, y presenta variaciones en la composición de los gases generados. Se ha podido comprobar cómo, de los tres materiales estudiados, el MCM-41 es el que provoca mayor modificación de la degradación térmica de ambas nitrosaminas, favoreciendo la generación de residuo en atmósfera inerte. En cuanto a la composición de los productos generados tras la pirólisis de NNK, ambos SBA-15 han mostrado una modificación clara de la distribución de los mismos. También se ha podido observar como en el caso de la NNN, algunos de sus productos de descomposición reducen su contribución a máxima temperatura, observándose tendencias decrecientes y algún máximo en función de la temperatura. Por otro lado, los resultados de termogravimetría para ambas nitrosaminas se han ajustado a un sencillo modelo cinético que permite estimar las áreas de cada uno de los procesos de pérdida de peso observados, pudiéndose realizar de esta forma un análisis más claro del efecto de los catalizadores utilizados basado en las distintas fracciones asociadas a cada uno de los procesos. El caso de la NNK presenta tres procesos de pérdida de peso a 194, 299 y 368 ºC en atmósfera inerte y tres procesos a 208, 299 y 648 ºC en atmósfera oxidante, siendo el principal el que tiene lugar a 299 ºC con un 81.8 y 66.4 % de contribución relativa para atmósfera inerte y oxidante, respectivamente. La NNN ha mostrado dos procesos de pérdida de peso, a 190 y 218 ºC en atmósfera inerte y a 180 y 207 ºC en oxidante. Los tres materiales mesoporosos estudiados han mostrado, para ambas nitrosaminas, modificaciones en la temperatura e intensidad de los procesos observados. Este efecto se hace más notable en aire donde se observa un nuevo proceso térmico a altas temperaturas, siendo especialmente notable este efecto con MCM-41. El experimento con este material para la NNK ha presentado cuatro procesos de pérdida de peso a 197, 232, 281, 414 ºC para atmósfera inerte y oxidante, variando la contribución relativa entre ellos. En el caso de la NNN, el experimento con MCM-41 ha mostrado tres procesos a 190, 218 y 260 ºC para atmósfera inerte y a 180, 207 y a 610 ºC en atmósfera oxidante. Para ambas nitrosaminas en atmósfera oxidante, los gases analizados para los tres materiales han mostrado un aumento considerable (principalmente por el MCM-41) de las bandas de CO2 y CO a temperaturas elevadas, respecto al experimento sin catalizador. Este aumento se ha debido a la degradación oxidativa del residuo carbonoso generado.

The mechanisms and kinetics of combustion of waste wood as well as the phases during combustion processes are important to eliminate these wastes without any possible damage to environment. In the present study, combustion mechanisms, activation energy and pre-exponential constants, and phases of combustion were investigated for untreated natural pine and treated Medium Density Fiberboard (MDF), plywood and particleboard samples that involve some chemicals and additives. Waste wood samples were heated in air at 10, 20 and 30oC/min heating rates in a Thermo Gravimetric Analyzer (TGA) from room temperature to 900oC. Thermogravimetry (TG) and Derivative Thermogravimetry (DTG) curves for all samples were obtained. The gases formed during combustion reactions were directly fed to a Fourier Transform Infrared Spectroscopy (FTIR) instrument coupled to TGA. Emission characteristics of the samples were determined in-situ by using the FTIR spectrums. As a result of TG analysis, thermal decomposition of treated samples was observed at lower temperatures as compared to the untreated pine sample because of the catalyzing effects of the chemicals in the treated samples. Therefore, there were less flammable products, lower weight losses in the main oxidation region, decrease in the max. weight loss temperatures and formation of more char for treated samples as compared to untreated pine sample. In other words, chemicals used during production of these samples lead to decrease in the combustibility of the treated samples. Thermal kinetic constants for the samples were calculated by using Coats Redfern and Broido Methods. In order to find out the mechanisms responsible for the oxidation of the waste wood samples in different regions, six solid state mechanisms of Coats Redfern Method were tested. As a result of FTIR analysis of the emitted gases from TG analysis, several chemical groups were detected from pine and treated samples. Combustion of all samples revealed some gases containing aromatics, C-H groups, CO2 and CO. However, there were some toxic and carcinogenic gases like formaldehyde, isocyanate group, ammonia, phenyl group and benzoylbromide among the emissions of treated samples which need utmost attention when recovering energy from treated waste woods.

Pour répondre aux problématiques d’usure précoce des pièces mécaniques causée par des pressions et températures élevées d’utilisation, des nanolubrifiants constitués de nanocarbones fluorés, connus pour leurs faibles coefficients de frottement et haute stabilité thermique ont été synthétisés. Pour améliorer ces propriétés, des précurseurs nanocarbonés de dimensionnalités différentes, et des procédés de synthèse gaz-solide variés ont été employés. Ainsi, une structure fermée comme les nanofibres de carbone NFCs (1D, tubulaire), ouverte comme le mélange nanodisques / nanocônes de carbone NDCs (majoritairement 2D, discotique) et intermédiaire avec les noirs de carbone graphitisés NCGs (0D, sphérique) ont été fluorés, d’une part avec le fluor moléculaire gazeux et d’autre part avec le fluor atomique produit par décomposition thermique d’un agent solide. Les mécanismes de fluoration / défluoration ont été proposés à l’aide de différentes techniques de caractérisation complémentaires (RMN du solide, MEB, MET, AFM, DRX) pour l’ensemble des matrices étudiées. Des matériaux présentant un gain de stabilité thermique de plusieurs dizaines de degrés comparativement aux matériaux fluorés de la littérature ont été élaborés, et une nouvelle méthode de synthèse dite « fluoration flash » a été mise au point pour étendre encore cette tenue en température. Les bonnes propriétés tribologiques de ces matériaux ont également été démontrées, notamment à 160°C et ceci quel que soit le mode de fluoration. Par la suite, des vernis à base de résines siliconées et chargés en nanofibres de carbone fluorées ont été formulés. Le revêtement composite présente une stabilité thermique supérieure à 400°C comme démontré par l’étude de son mécanisme de dégradation en température, notamment par couplage ATG-FTIR. D’un point de vue tribologique, les coefficients de frottement mesurés à température ambiante et 160°C sont inférieurs à 0,1 et les tribofilms obtenus ont été caractérisés par analyse MEB et EDX. / To address some issues to premature wear caused by high pressures and temperatures used on aircraft parts, nanolubricants made of fluorinated nanocarbons were synthesized. They are known for their low friction coefficients and high thermal stability in air. To improve these properties, carbonaceous nanomaterial precursors with different dimensionalities, and various gaz-solid synthesis methods were investigated. Thus, a closed structure such as carbon nanofibres (1D, tubular), opened such as carbon nanodiscs/nanocones (2D in majority, discotic) and intermediate with graphitized carbon blacks(0D, spherical) were fluorinated, firstly with molecular fluorine gas, and secondly with atomic fluorine released by the thermal decomposition of a solid fluorinating agent. Mechanisms of fluorination/defluorination were proposed thanks to complementary characterization techniques (solid NMR, SEM, TEM, AFM, XRD) for all the studied compounds. Materials with a gain of thermal stability of several tens of degrees compared to fluorinated materials of the litterature were prepared, and a new synthesis way called “flash fluorination” has been developed to further expand the thermal stability in air. Good tribological properties of these materials have been also demonstrated, including high temperature (160°C) regardless of the fluorination method. Then, polysiloxane resins loaded with fluorinated carbon nanofibres were formulated. The composite coatings exhibit thermal stability above 400°C as demonstrated by the study of the degradation mechanism as a function of the temperature, in particular by coupling TGA-FTIR. From a tribological point of view, friction coefficients measured at room temperature and 160°C are below 0.1 and the tribofilms obtained were characterized by SEM and EDX analysis.