Quantitative microstructural evaluation of 12 Cr creep aged steels after welding

This dissertation focuses on the quantitative microstructural evaluation of new and creep aged X20 (12 Cr) stainless steel after welding. X20 stainless steel has been widely used in the high temperature and pressure pipework of coal-fired power plants. Consequently, this material has to withstand extreme conditions of high temperature and stress during service exposure. Under these conditions, creep deteriorates the strength of the material. The material’s resistance to creep damage due to its microstructure can be quantitatively described by the back-stress. There are four microstructural contributions to the back-stress: Precipitate Hardening, Sub-Boundary Hardening, Solid-Solution Hardening and Dislocation Hardening. Fusion welding is performed on creep aged materials when a component needs to be replaced. This high temperature process results in the formation of different microstructural regions within the weldment. These creep damaged components have a weldability limit as set by the life management strategy of the power plant company. Measuring techniques capable of quantifying the microstructural contributions (precipitates, subgrains and dislocations) were developed and evaluated in this study. These techniques were then used to characterise the different microstructural regions within a new and creep aged X20 steel weldment. Differences in the microstructure of the new and creep aged X20 steel was illustrated by the results of this study. The measured size and number densities of the precipitates in the creep aged X20 material showed that there is a decrease in PH during creep exposure. There was a decrease in SBH and DH stress for the creep aged X20 material due to coarsening of the subgrains and annealing of dislocations during creep exposure. The quantitative techniques demonstrated in this study opens up the possibility to perform life assessment on weldments with inhomogeneous microstructures by following a microstructural based approach

Nanomechanical testing of ODS steels irradiated with 1 MeV/amu heavy ions

Heavy ion beams with high damage production rate are widely used to evaluate radiation tolerance of promising nuclear reactor materials, such as oxide dispersion strengthened (ODS) alloys, including their mechanical properties. Since typical ion projected ranges do not exceed 1 micron, nanoindentation technique is the most convenient method for examination of irradiated materials. In present work we report data on radiation hardening of several ODS steels irradiated with 107 MeV Kr and 167 MeV Xe ions. Some samples were irradiated trough the special Al-foil filter in order to obtain the unfolding damage profile on the surface. The post-irradiation testing steels included conventional nanoindentation measurements and CSM for determination of possible size effects associated with indentation size effect as well as soft surface effect. Swift heavy ion induced changes in microstructure evolution were studied by transmission electron microscopy (TEM). It was found that hardening of the ODS steels irradiated with krypton and xenon ions of fission fragment energy for damage dose about 1 dpa level is in the range 5-25% (figure 1). TEM examination have revealed complete amorphization of carbide and (Y,Ti) oxide particles in ferritic matrices as a result of multiple amorphous latent track overlapping. At the same time no dissolution of nano-oxide particles was observed. This implies that radiation hardening is not due to changes in morphology of nanoparticles

Characterisation of solid hydrodynamics in a three-phase stirred tank reactor with positron emission particle tracking (PEPT)

It is challenging to measure the hydrodynamics of stirred tank reactors when they contain multiphase flows comprising liquid, gas bubbles and particles. Radioactive particle tracking techniques such as positron emission particle tracking (PEPT) are the only established techniques to determine internal flow behaviour due to the inherent opacity and density of fluid and the vessel walls. The profiles of solids flow are an important tool for robust reactor design and optimisation and offer insight into underlying transport processes and particle–fluid–bubble interactions for applications such as froth flotation. In this work, measurements with PEPT were performed with two tracer particles differing in surface hydrophobicity to characterise the solids hydrodynamics in a baffled vessel agitated with a Rushton turbine. The location data from PEPT were averaged with time to estimate the probability density function (PDF) of particle velocity in individual voxels. The peaks of these voxel distributions were used to produce profiles of solids flow in different azimuthal and horizontal slices. Bimodal vertical velocity distributions were observed in the impeller radial jet which suggest the particles experienced trajectory crossing effects due to inertia. Statistical tests were performed to compare the velocity distributions of the hydrophilic and hydrophobic tracer particles, which indicated similar average flow behaviour in the liquid or pulp phase of the vessel and differences near the air inlet, in the impeller discharge stream and pulp–froth interface. With tracers designed to represent gangue and valuable mineral species, the differences in velocity reveal interactions such as bubble–particle attachment and entrainment

In-depth characterisation of metal-support compounds in spent Co/SiO2 Fischer-Tropsch model catalysts

Only little is known about the formation and morphology of metal-support compounds (MSCs) in heterogeneous catalysis. This fact can be mostly ascribed to the challenges in directly identifying these phases. In the present study, a series of Co/SiO2 model catalysts with different crystallite sizes was thoroughly characterised with focus on the identification of cobalt silicate, which is the expected metal-support compound for this particular catalyst system. The catalysts were exposed to simulated high conversion Fischer-Tropsch environment, i.e. water-rich conditions in the presence of hydrogen. The transformation of significant amounts of metallic cobalt to a hard-to-reduce phase has been observed. This particular MSC, Co2SiO4, was herein identified as needle- or platelet-type cobalt silicate structures by means of X-ray spectroscopy (XAS) and high-resolution scanning transmission electron microscopy (HRSTEM) in combination with elemental mapping. The metal-support compounds formed on top of fully SiO2-encapsulated nanoparticles, which are hypothesised to represent a prerequisite for the formation of cobalt silicate needles. Both, the encapsulation of cobalt nanoparticles by SiO2 via creeping, as well as the formation of these structures, were seemingly induced by high concentrations of water

Characterization of multifunctional β-NaEuF4/NaGdF4 core–shell nanoparticles with narrow size distribution

We characterized NaEuF4/NaGdF4 core–shell nanoparticles

Improved survival of children and adolescents with classical Hodgkin lymphoma treated on a harmonised protocol in South Africa

Funding: CANSA, Wits Faculty Research Committee Individual Research Grant, Carnegie Corporation Research Funding, Crowdfunding through Doit4Charity Backabuddy and the Ride Joburg Cycle Race.Background Historic South African 5-year overall survival (OS) rates for Hodgkin lymphoma (HL) from 2000 to 2010 were 46% and 84% for human immunodeficiency virus (HIV)-positive and HIV-negative children, respectively. We investigated whether a harmonised treatment protocol using risk stratification and response-adapted therapy could increase the OS of childhood and adolescent HL. Methods Seventeen units prospectively enrolled patients less than 18 years, newly diagnosed with classical HL onto a risk-stratified, response-adapted treatment protocol from July 2016 to December 2022. Low- and intermediate-risk patients received four and six courses of adriamycin, bleomycin, vinblastine, and dacarbazine (ABVD), respectively. High-risk patients received two courses of ABVD, followed by four courses of cyclophosphamide, vincristine, prednisone, and dacarbazine (COPDac). Those with a slow early response and bulky disease received consolidation radiotherapy. HIV-positive patients could receive granulocyte colony-stimulating factor and less intensive therapy if stratified as high risk, at the treating clinician's discretion. Kaplan–Meier survival analysis was performed to determine 2-year OS and Cox regression to elucidate prognostic factors. Results  The cohort comprised 132 patients (19 HIV-positive, 113 HIV-negative), median age of 9.7 years, with a median follow-up of 2.2 years. Risk grouping comprised nine (7%) low risk, 36 (27%) intermediate risk and 87 (66%) high risk, with 71 (54%) rapid early responders and 45 (34%) slow early responders, and 16 (12%) undocumented. Two-year OS was 100% for low-risk, 93% for intermediate-risk, and 91% for high-risk patients. OS for HIV-negative (93%) and HIV-positive (89%) patients were similar (p = .53). Absolute lymphocyte count greater than 0.6 × 109 predicted survival (94% vs. 83%, p = .02). Conclusion In the first South African harmonised HL treatment protocol, risk stratification correlated with prognosis. Two-year OS of HIV-positive and HIV-negative patients improved since 2010, partially ascribed to standardised treatment and increased supportive care. This improved survival strengthens the harmonisation movement and gives hope that South Africa will achieve the WHO Global Initiative for Childhood Cancer goals.Publisher PDFPeer reviewe

An analysis of the regional economic development functionality of selected SEZs in the Eastern Cape, South Africa

PhD (Economics), North-West University, Vanderbijlpark CampusSpecial economic zones are selected geographical regions reserved for selected economic activities whereby these regions enjoy benefits such as limited corporate taxes, limited labour market regulations and relief from trade tariffs. These special economic zones do not only help the organisations or businesses situated within the geographical regions but also influences the local economy by creating more work opportunities, economic growth as well as Foreign Direct Investments (FDIs). The study of special economic zones and how it influences the regional economy is a critical aspect in modern economics because it may be seen as a growth pole for regional development in underdeveloped regions. If special economic zones are “well-planned” it will have a positive effect on the comparative and locational advantages, which will boost the local economy and can also be regarded as “engines for growth.” The total number of special economic zones grew significantly over the past 21 years with more than 4500 new established special economic zones established worldwide. Countries in Africa have only 237 special economic zones, while the world total is more than 5300 SEZ, showing that the continent only has only 4.40% of the total established special economic zones in the world, which contributes to lower regional economic development. However, it is said that the continents share in proportion to the world trade is below 3%, which suggests that the continent only focuses on natural resources as the main commodity for the exportation of products. The establishment of special economic zones can come a long way to encourage economic growth and development with the attraction of investment for the African continent and more specifically South Africa. In South Africa at the start of the new democracy in 1994 the government started to approach a new horizon in its industrialisation and manufacturing sector and the focus was drawn on an export driven tactic. The objective of the South African government was to apply policy, which reduced high unemployment rates and poverty, however, the main focus was to integrate into value regional and global value chains due to the past sanctions imposed on the country in terms of importation and exportation. The South African government imposed industrial development zones to curb the inequalities in the manufacturing and industrialisation sector and consequently to encourage export and overall trade activities within the country. The South African government followed the same approach as other developing countries such as Latin America and East Asia, which were successful in adopting inward looking policies Favourably, South Africa had some major potential in the macroeconomic surrounding and comparative advantages in terms of market intensity and natural reserves, indicating that the potential for economic development was significant. The plan to implement the industrial development zones in South Africa started in 1996 with the GEAR (Growth, Employment and Redistribution), however, the establishment of the zones was not as successful as initially expected. In South Africa, there are a total of ten established special economic zones while only six of these special economic zones are fully operational, which causes the existing special economic zones to be less competitive and insignificant in terms of local economic growth. While the special economic zones can contribute significantly towards economic growth and development, the question remained whether special economic zones in South Africa are functioning well enough to be sustainable in the long term and to contribute towards the local economies of South Africa. Limited studies have directed their exploration on how functional and successful operational special economic zones influence regional economic development within a specific region or area and some of the problems include aspects such as “insufficient knowledge” and the capability to use the inventive of special economic zones in Africa, which are limitless and unclear. The gap in the research of special economic zones in developing countries is tremendous. The main goal of the study is to evaluate and analyse the level of regional economic development in areas of functional special economic zones in South Africa. Two of the most successful industrial development zones in South Africa, the East London IDZ and the COEGA IDZ situated in the Eastern Cape was selected as the region where the study will take place, mostly due to its success since it was first established. The primary objective of this study is to evaluate the regional economic development functionality of selected special economic zones in the Eastern Cape of South Africa. This is a mixed-method study including both qualitative and quantitative data analysis. The qualitative part involved setting up and finding the success factors of special economic zones with the support of several case studies and sources and these success factors were divided into three broad categories namely microclimate, mesoclimate (region specific) and macroclimate. Moreover, the success factors of special economic zones identified were utilised in an interview schedule with various stakeholders from the industrial development zones in the Eastern Cape. The main categories within the interview schedule included basic information, physical features of the special economic zones, policy framework perceptions, policy framework constraints, incentives’ perceptions, enabling environment perceptions, economic leverage perceptions and the role of government. The standardised/structured interviews with close-ended questions were used in the qualitative approach of the study. A total of 12 people were interviewed within the East London industrustrial development zone and the COEGA industrustrial development zone. The results obtained from the interviews showed that the stakeholders had an optimistic view with regard to the physical features of the industrial development zone and that the infrastructure is of high quality. Most of the respondents also agreed that the industrial development zone is situated in a strategic location, which makes it easier for trade and efficiency in logistics. Green energy and renewable energy are being implemented within the industrial development zone and the long-term strategic plan is to have a leading eco-industrial park on the African continent. With regard to the policy framework perceptions, it was noticed that unemployment remains a huge concern within the local communities, however, the industrial development zones did create a substantial number of new jobs in the past few years. The shortage of skilled labour remains a huge concern, which hampers the firms’ abilities to employ new workers especially within the manufacturing sector, however, the industrial development zones do have science and technology parks which are able to provide the necessary skills. The industrial development zones contribute significantly towards the local economy since they are able to attract sufficient local and foreign investments and the industrial development zones themself use local material in their production processes. The stakeholders feel that more investments are needed for the industrial development zones to have a certain level of success, hence, South Africa should sharpen its value propositions so that it is in line with international standards. The stakeholders also agree that the industrial development zones provide investor-friendly and pro-business policies that are crucial for any economic zone. In terms of the policy constraints, it is noted that the stakeholders feel that the firms operating within the industrial development zones should focus more on sourcing products and materials from the local business community. With references to the respondents’ perceptions, it was noted that the industrial development zones do provide effective incentives. However, the firms operating within these industrial development zones should make more use of the incentives provided to them in order for them to get the full benefits provided by the industrial development zones. In terms of the enabling environment perceptions, it was noted that the industrial development zones do interact with the local communities, however, more can be done in terms of creating efficient and effective synergies between government, people and the local businesses. The influence of government in terms of financial and business support are adequate and the various departments do play a key role in terms of skills development and the provision of services. Some stakeholders feel that the DTIC can do more in terms of the industrial development zone programme since they lead from a policy perspective regarding infrastructure development funds. Skills development from the national government is fragmented and the different spheres between the different national departments need to improve to have a more integrated approach in terms of collaborations. The stakeholders had a positive feeling about the future of industrial development zones in South Africa, however, government should focus on aspects such as value proposition, the market, capital resources as well as human resources in order for the industrial development zones to be successful. The record of industrial development zones in South Africa shows that they do not perform as well as initially expected and if government do decide to establish new industrial development zones they will need capable management for the industrial development zones to operate effectively, however, the market should demand industrial development zones and there should be a need within the region to establish an industrial development zone. It was noted that if the industrial development zones are dependent on money from government in terms of funding in the long term, the industrial development zones will fail because the government does not have capital to sustain industrial development zones in the short and long term. Overall this study found that only a small number of special economic zones perform well, while the majority of the special economic zones in South Africa are not functioning well or they are not operative and this is due to the special economic zones’ location (inland), the inability of government to drive the projects and plans for the zones and the lack of co-ordination between the various departments of government. For the industrial development zones in South Africa to function well it is important that these zones create labour intensive manufacturing jobs to create more employment, focusing more on skills development as a priority to achieve sustainable work opportunities, a more integrated approach between the different government departments, a focus on policy direction, the creation of capable value chains, fiscal independence and the focus on creating excellent value propositions.Doctora