The major aim of this research was to provide quantitative data about the pyrolytic "behaviour of a series of coals from the South Y>,ales Coalfield using thermogravimetry as the major experimental technique. It is hoped that this data will (1) provide information of value to the development of coal conversion technologies, (2) provide information about the kinetics of coal pyrolysis, (3) provide information about the effect upon the kinetic results by the addition of some transition metal elements to two of the coal samples. An extensive literature survey revealed that work of this nature had not been done previously. It was also revealed that a computer interfaced to the thermogravimetric apparatus to collect and manipulate data would aid the research. An extra aim of the research was added: to interface a i.iodel B BBC Microcomputer to the apparatus and to develop the necessary programs. This aim was successfully realised. Hot-Stage- Microscopy was used to provide qualitative information about the physical changes the samples underwent during pyrolysis. This information was used to aid the interpretation of the thermogravimetric results. Thermogravimetric studies of the coals at three heating rates revealed distinct trends in behaviour with rank. The computerised data recording system also revealed more information about the pyrolysis of coals and allowed the tentative suggestion of a system of fingerprinting the pyrclytic behaviour of the coals. One avenue of further research could be the expansion and validation of this system. The kinetic analysis of the thermogravimetric results revealed that for each sample there are a series of temperature regions with their own activation energy. These regions and activation energies vary with the heating rate. It is suggested that each activation energy relates to a different kind of pyrolysis reaction, and although some suggestions have been made, further research incorporating other techniques is necessary to identify these reactions. The effect of the addition of some transition metal elements upon the activation energies for two of the samples was then investigated. It was found that most of the metals affected the activation energies in some way - either inhibiting or promoting the reactions. No general trends in behaviour were observed. Another possible avenue of further research is apparent here - to find out the ways in which these metals affect the production of the products of pyrolysis, particularly the gaseous products.

YBa2Cu3O7-d (YBCO) was one of the first high temperature superconductors discovered, and its superconducting properties are strongly dependent on oxygen stoichiometry. A large amount of work has been done on the variation of stoichiometry and its effect on the superconducting properties of the material. However, in spite of all the work done, the results published in the literature are very scattered. This thesis presents a thermogravimetric study of oxygen diffusion in YBCO under isothermal and non-isothermal conditions and tries to reconcile the data available based on the results obtained and taking into account the factors that may have affected the data presented by other groups, such as the effects of the microstructure and the different diffusion coefficients measured with the techniques used. An Arrhenius expression for the chemical diffusion of oxygen has been calculated from the analysis of isothermal oxygenation data, and it has been corroborated by a study of the nonisothermal experiments carried out. This work includes the development of a macroscopic model for oxygen diffusion in YBCO based on the diffusion coefficient calculated from experimental data. The model is used to simulate for the first time oxygenations under both isothermal and non-isothermal conditions. The study of non-isothermal oxygenations has led directly to the design of novel cooling procedures that can be introduced at the end of the processing stage of YBCO samples, producing highly oxygenated specimens in shorter times than for conventional isothermal and ramped oxygenation procedures. The final section of this dissertation presents a study of the Direct Current Zoning effect. The generation of a mobile hot zone in a polycrystalline YBCO bar when passing a current across it is directly linked to the diffusion of oxygen ions in the material. A mechanism for the motion of the zone along the sample has been suggested. A computer model has been developed to reproduce this process taking into account the motion of ions due to chemical diffusion and the potential difference established. The results from this model have corroborated the mechanism suggested and give for the first time the opportunity to study this phenomenon in more detail.

<p> The main objective of this study was to gain an understanding of the oxidation properties of iron at low oxygen pressures and at high temperature. </p> <p> A thermogravimetric technique was employed to investigate the oxidation of iron in oxygen over the pressure range 2.5×10⁻³ - 3.0×10⁻¹ torr at temperatures ranging between 750ºC and 1000ºC. The oxidation curves exhibited distinct intervals of linear kinetics followed by transition to intervals of parabolic kinetics during exposures extending to 125 min. Linear kinetics governing the growth of uniformly thick wustite scales; the linear rate constants showed a proportional dependence on oxygen pressure due to reaction control by a phase boundary reaction involving non-dissociation adsorption of oxygen. Parabolic kinetics governed growth of wustite-magnetite scales containing magnetite as outermost layers. The value of the parabolic rate constants were independent of oxygen pressure since scale growth was directly dependent on the iron vacancy gradient in wustite established by the oxygen activities at the Fe/FeO and FeO/Fe₃O₄ interfaces. </p> <p> Scanning electron microscopy techniques were used to gain information on the growth of magnetite and hematite layers in the multilayer scale consisting largely of wustite formed at high temperature in the pressure range 2.5×10⁻³ to 760 torr. </p> / Thesis / Master of Science (MSc)

No description available.

In recent decade growing concerns of CO2 emissions from power plants have increased, which led to development of technologies like oxy-fuel combustion process. P91 steel is profoundly used in power plants, but oxy fuel combustion exacerbates corrosion due to recycling of flue gas. This paper studied the kinetics of the corrosion rate on the boiler tubes and furnace and help achieve a corrosion resistant coating over it. Refractory metal diffusion coating is created and tested at high temperature in corrosive atmosphere. This was done by forming Ti and Zr diffusion coating on P91 steel using pack cementation. Coating thickness of 12 and 20 µm were obtained for Ti and Zr respectively. These samples were tested in thermo-gravimetric system by heating at 950˚C for 24 hours in 5% oxygen in Helium gas. Heating in an oxidizing environment lead to exfoliation corrosion on uncoated P91 steel. TGA procedure confirmed less mass change of Ti and Zr coated samples, than that of uncoated P91 steel sample. SEM and depth profiling confirms oxygen penetration is 2.7mm in uncoated P91 steel sample, whereas the Ti and Zr Coated samples oxygen penetration is just 16 and 56 µm respectively.

Coal is a chemical compound with a complex composition. Proximate and ultimate analysis as well as physical and mechanical tests which are available do not furnish all the information required by industry. Information regarding e.g. the burning properties of coal is required by furnace and boiler designers. Thermal analysis can be used for studying these properties using small masses of coal. Differential thermal analysis (DTA) where temperature variations are measured which result from reactions which occur when coal is heated and thermogravimetric analysis, (TGA) where similarly mass variations are measured, are regarded as important. Results from eg. TGA tests are usually interpreted without unified and formally accepted prescripts. It is desirable to investigate how the best use can be made of thermal analysis of coal, using DTA and TGA, and to devise a procedure for interpreting the results. The problem is approached by studying DTA and TGA results obtained from a specially selected group of coals for which other analytic data are available. The samples were prepared according to the standard procedure for the laboratory analysis of coal. At first, related information published by other researchers were integrated and parameters used by them identified and assessed in terms of fundamental scientific principles. Special experiments were conducted to probe the situation regarding orthodox kinetics of reactions and its related theory and observed discrepancies with regard to coal and its decomposition characteristics. It was found, along with other observers, that eg. activation energy values which are derived from TGA data should be used with extreme caution. In general an empirical approach for interpretation of results has much to offer. A system is developed by which various thermal techniques, executable by a single instrumental arrangement can be identified by expressing them in matrix format using as indexes, heating arrangement, reactant type and reaction environment. 5(1,1,2) e.g. designates a linearly heated mass of coal in air at atmospheric pressure. To enhance the comparison of TG characteristics of similar coals they should be classified according to a matrix arrangement C(g,t,r) which is based on three index parameters namely, grade ie. the ash content, type ie. the vitrinite content and rank. A TG test provides the basic requirements for computing the indexes using formulae provided by the originators. Information which can only be derived from a TG experiment e.g. 5(1,1,2), are referred to as specification parameters. The information consists of e.g. a series of temperatures which identify specific reaction changes in the coal. Several other parameters can be derived. Coals are assessed by comparing their specification parameters. Only two of the S(i,j,k) techniques are described in detail namely TG dispersion 5(1,1,2) and drop furnace burnout 5(3,1,2). The dispersion technique requires a linear increasing furnace temperature while the near sample temperature is also measured. This technique shows the decomposition stages of coal from dehydration to complete burnout. The drop furnace technique, involves a sudden exposure of the coal to a hot furnace environment with free air access: Actual burnout of coal is emulated. The model is not perfect for combustion but the best that can conveniently be acquired for comparing the burning responses of coals. To illustrate the type of information which can be obtained with other S(i,j,k) techniques experimental results of eg. a devolatilization test are presented. Brief reference is made to the role that particle size plays during combustion and the importance of the composition of volatiles which are released is indicated by presenting relevant information from external sources. The chemical composition and structure of the coals could not be determined but relevant information from an external source was presented which has a bearing on the practical analytic procedure which was described. After a study of the group TG characteristics of the various coals and discussion of the conclusions which are justified a practical procedure is described according to which the equipment can be used both for routine or special purpose analysis of coal. / Thesis (PhD)--University of Pretoria, 2013. / Geology / unrestricted

No description available.

M.Tech (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Dithiocarbamate ligands and their complexes has been a subject of interest in various fields but they found much interest in medical applications as potential anti-microbial agents. The dithiocarbamate ligands were used to prepare complexes of copper and zinc. All the prepared ligands and complexes were characterized using techniques such as IR and 13CNMR spectroscopy and thermogravimetric analysis (complexes). The data obtained from the spectroscopies was consistent with the coordination of the ligand to the metal ion through the sulfur atoms of the dithiocarbamate or thioureide moiety. The thermal analysis of the prepared complexes gave a final residue of metal sulfide, thus indicating the potential of the prepared complexes as single molecular precursor for the synthesis of metal sulfide nanoparticles. The prepared complexes were then used to synthesize metal sulfide nanoparticles. The nanoparticles were successfully prepared by thermal decomposition of a single-source precursor (dithiocarbamate complexes) in a solution of hexadecylamine (HDA) or tri-n-octylphosphine oxide (TOPO). The investigated parameters were the capping molecule (HDA and TOPO), and capping molecule concentration (3 g and 6 g) to see their effect on the shape and size of the synthesized nanomaterials. The synthesized metal sulfide nanoparticles were characterized using techniques such as UV-vis spectroscopy, photoluminescence spectroscopy, X-ray diffraction analysis and transmission electron microscopy. The absorption study showed some interesting features in the prepared nanomaterials. The first was the red-shifted spectra of the ZnS nanoparticles which was attributed to the impurities and that assumption was further confirmed by the XRD analysis that showed a sulfur impurity and other amorphous peaks. The second was the localized surface plasmon resonances on the copper sulfide nanoparticles that suggested the formation of electron deficient copper sulfide stoichiometry that was further confirmed by XRD analysis that gave hexagonal phase copper sulfide covellite. The TEM images of the prepared nanoparticles showed that the concentration and the capping molecule has an effect on the size and shape of the synthesized nanoparticles. The increase in capping concentration gave a decrease in particle size in most of the prepared nanoparticles, while they were few exceptions. The capping molecule effect showed that most of the nanoparticles prepared from TOPO were spherical in shape and were well dispersed compared to the mixed morphological nanoparticles prepared from HDA. There were also exceptions of the well dispersed HDA-capped nanoparticles.

Fluorinated polymers of substantial high performance such as perfluorocyclobutyl (PFCB) and fluorinated aryl vinyl ether (FAVE) polymers can readily be synthesized by thermal [2+2] cyclopolymerization as a melt or by classical polycondensation. These fluoropolymers naturally possess high thermal and chemical resistance, low conductivity properties, and other mechanical properties. In this work, a method using 0th order kinetics is proposed and thermal degradation studies were conducted on six different aromatic ether-based polymers to gauge trends in activation energy barrier and differences in thermal stability by 0th order degradation kinetics. The activation barrier (E_a) obtained can give accurate insight into the stability of the polymer based only on structure for external applications. Activation energies ranging from 17 to 41 kcal/mol were obtained for the various polymers. Overall, this study provides an established method using TGA for thermal stability studies through 0th order kinetics that can be potentially used for future lab applications.

Šioje daktaro disertacijoje pirmoje dalyje nustatyta šiuolaikinės, o antroje dalyje – archeologinės keramikos gaminių elementinė ir fazinė sudėtis, bei ištirta morfologija. Šiuolaikinės ir archeologinės keramikos pavyzdžių elementinė sudėtis nustatyta Rentgeno spindulių dispersinės analizės (EDX), liepsnos atominės absorbcinės spektrometrijos (LAAS), titrimetrinės ir spektrofotometrinės analizės metodais. Parodyta, kad visų keraminių pavyzdžių kokybinė bei kiekybinė sudėtis yra skirtinga Nustatyta, kad visuose keramikos mėginiuose pagrindiniai elementai yra silicis ir aliuminis. SiO2 sudaro 46 – 60% keramikos sudėties, Al2O3 – apie 17 – 33%. Fe, Na, Mg, K, Ca ir Ti mėginiuose rasta kelis kartus mažiau. EDX analizė gali būti sėkmingai naudojama nustatant pagrindinius elementus, kurių kiekiai viršija 0,5 % bendros elementinės sudėties. Norint nustatyti tikslią keramikos sudėtį ir pėdsakinius elementus reikia naudoti LAAS analizės metodą. Aliuminio kiekį keramikoje patikimai galima nustatyti titrimetriniu, o silicio ir titano kiekį – spektrofotometriniais metodais. Ištyrus šiuolaikę ir archeologinę keramiką Rentgeno spindulių difrakcine analize (XRD), nustatyta, kad visų keramikų pagrindinė fazė yra vienoda – silicio dioksidas SiO2, tačiau jų bendra fazinė sudėtis skiriasi. Skirtinguose kermikos pavyzdžiuose buvo aptikos šios fazės: kvarcas, dolomitas, kaolinas, albitas, mikroklinas, muskovitas, mulitas, hematitas, rutilas, diopsidas, korundas, titanitas, natrio anortitas... [toliau žr. visą tekstą] / The elemental composition of the samples of modern and archaeological ceramics was determined using the energy dispersive X-ray analysis, flame atomic absorption spectrometry, titrimetric and spectrophotometric analysis methods. It has been shown that the qualitative and quantitative composition of all the samples is different. It has been established that silicon and aluminium are the main elements in all the samples. SiO2 accounts for 46–60 % of the composition of the ceramics, Al2O3 – for some 17–33%. The amounts of Fe, Na, Mg, K, Ca and Ti discovered in the samples are several times lesser. EDX analysis can successfully be used in determining the main elements whose amounts exceed 0.5% of the overall elemental composition. In order to determine the exact composition of ceramics one has to employ the FAAS analysis method. To determine in a credible manner the amount of aluminium in ceramics, one can use the titrimetric method, and the amount of silicon and titanium – spectrophotometric methods. Upon examination of the modern and archaeological ceramics by diffraction analysis it has been established that the main phase of all the samples is the same – quartz SiO2, however their phase composition varies. In different samples the following phases have been discovered: calcite, dolomite, kaolinite, albite, microcline, muscovite, mullite, hematite, rutile, diopside, corundum, titanite, and sodium anorthite. Being aware of the phase composition, it has been established that the... [to full text]