Dissertation (PhD)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Silver/Zinc batteries are extensively used for applications where a power source with a high energy density is needed. A reactor was developed to manufacture the zinc electrodes for these batteries. The parameters for the control of this reactor were identified. The interaction and relationships between the set of parameters were established and quantified. The novel design of the reactor includes features such as continuous replenishment of the constituting chemicals, parallel flow of the plating fluid, inert anodes and a serial electrical layout. The controlling parameters consist of both chemical and physical parameters. They are - zincate concentration, hydroxyl concentration, density, temperature, flow rate of the plating fluid, and current density. The unique solubility characteristics of zinc oxide in potassium hydroxide lend themselves to a novel approach for the determination of the zincate concentration in· the plating solution. A set of conditions for the manufacturing of electrodes, with the required characteristics, was identified. The requirements are densely packed zinc dendrite morphology with high porosity and mechanical stability. The designed reactor complies with the industries safety requirements. The batteries were successfully applied in their operational domain (torpedoes) after this extensive research project was completed. / AFRIKAANSE OPSOMMING: Silwer/Sink batterye word intensief aangewend in gebruike waar 'n kragbron met hoë energie digtheid benodig word. 'n Reaktor is ontwikkel wat die sink elektrodes van die tipes batterye vervaardig. Die veranderlikes vir die beheer van die reaktor is bepaal. Die interaksie en verwantskap tussen die stel veranderlikes is verkry en gekwantifiseer. Die unieke ontwerp van die reaktor het die volgende karakteristieke, nl. aaneenlopende vervanging van die chemikalië verbruik, parallelle vloei van die plateringsvloeistof, inerte anodes en elektriese uitleg in serie. Die chemiese en fisiese veranderlikes is beide beherende veranderlikes. Hierdie fisiese en chemiese veranderlikes wat die proses beheer is die sinkaat konsentrasie, hidroksiel konsentrasie, digtheid, temperatuur, vloeitempo van die plateringsvloeistof en die stroomdigtheid. Die unieke oplossingskarakteristieke van sinkoksied in kalsium· hidroksied leen hom tot die unieke proses om die sinkaat konsentrasie in die plateringsvloeistof te bepaal. 'n Steloperasionele kondisies vir die vervaardiging van die elektrodes met die spesifieke spesifikasies soos verlang, is geïdentifiseer. Hierdie kondisies is die diggepakte sinkdendriet morfologie met 'n hoë porositeit en meganiese stabiliteit. Die ontwerpte reaktor voldoen aan die industriële veiligheidsvereistes en die ergonomiese maatstawwe. Die batterye is suksesvol gebruik in hulle industriële aanwending as gevolg van die suksesvolle afhandeling van die stuk navorsing.

Thesis (PhD)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The availability of vast deposits of high-grade ore bodies are rapidly becoming something of the past in the modern mining and metallurgical scenario. Apart from the lower grade content of these ore bodies, complex mineralogy are an even greater obstacle in the recovery of valuable metal species. The development of new technology to deal with these type of ore bodies is therefore critical and worth investigating, as the world's easily exploitable high grade ore deposits are decreasing. Valuable species can be recovered from sparingly soluble solids, which slightly dissociate to give traces of the valuable ions in solution, with the use of ion-exchange resins in a slurry mixture. A dissociation equilibrium exists between the dissolved ions in solution and the solid ore body. Jf the dissolved ions are removed from the solution by ion-exchange, the solid / liquid dissociation equilibrium is continually displaced. According to Le Chatelier's principle further dissolution of the sparingly soluble solid is required to restore the equilibrium concentration of the valuable species in solution. It is possible to recover valuable metal species from metal precipitates, such as metal sulphides, by contacting a slurry of the precipitate with a suitable ion-exchange resin. The resulting ion exchange reaction between the valuable metal species and counter ions creates electrolyte solutions that may facilitate the further dissolution of the metal precipitate. These counter ion electrolyte solutions may easily become significantly concentrated. This occurs in the event of a Resin-in-Leach (RIL) mixture that results in a continuous ion-exchange reaction taking place due to the continually changing electrolyte composition of the mixture, which significantly changes the activities and hence the solubility of the valuable metal species in solution. Complete dissolution and liberation of the metal precipitate can often be achieved provided that a sufficient amount of a suitable high capacity ion-exchange resin is used in a properly engineered Resin-in- Leach (RIL) circuit. The simultaneous dissolution and adsorption of various base metal precipitates were tested. Various interactions that take place in the slurry at molecular level as well as the effects of various variables on the "adsorption by dissolution process" are discussed through the development of fundamental thermodynamic models. These thermodynamic mathematical models are developed for the three phase system that exists in a Resin-in- Leach mixture, i.e. the solid ore body, the electrolyte solution and the ion-exchange resin, and can be used for possible other applications such as the recovery of rare earths from low grade ores in the minerals processing industry. A typical example of an industrial process for the recovery of rare earth species is the percolation leaching of rare earths from low-grade kaolinitic ores, which continually shifts the solid / liquid dissociation equilibrium condition. The rare earth content of these ores is usually between 0.05%and 0.3 %, which is very low by any modern industrial extraction and refining standards. / AFRIKAANSE OPSOMMING: Die beskikbaarheid van ryk mineraal ertsneerslae is spoedig besig om iets van die verlede te word in die huidige mineraalontginning en metallurgiese veredelings industrie. Afgesien van die lae graad van die huidige mineraal ertsneerslae, blyk die komplekse mineralogiese samestelling van hierdie neerslae In veel groter struikelblok te wees in die herwinning en veredeling van die edelmetale teenwoordig in hierdie ertse. Die ontwikkeling van nuwe veredelings en ekstratiewe tegnologie vir die herwinning van edel metale, vanuit hierdie lae graad mineraal ertsneerslae, word dus benodig wat verdere navorsing in hierdie gebied regverdig. Dit is wel moontlik om metaal spesies afkomstig van ertse met 'n baie lae oplosbaarheid in waterige oplossings te herwin met ioon-uitruilings harse vanweë die feit dat die metaal spesies wel teen baie lae konsentrasies in die waterige oplossings teenwoordig is. Die metaal spesies los op in die waterige oplossings volgens hulle karakteristieke oplossings termodinamika. Indien die opgeloste metaal spesies vanuit die waterige oplossing verwyder word, sal die vaste stof / vloeistof ewewigs balans weer herstel word deurdat die vaste stof verder saloplos as gevolg van Le Chatelier se beginsel. Dit is dus moontlik om metaalagtige spesies, soos metaal sulfiedes, te herwin deur 'n waterige oplossing wat die metaal erts bevat in kontak te bring met 'n ioon-uitruilings hars. Die daaropvolgende ioon-uitruilings reaksie tussen die metaalagtige spesies en die spesies teenswoordig op die ioon-uitruilingshars het tot gevolg dat die elektrolitiese samestelling van die waterige oplossing verander. Dit is die gevolg van die migrasie van spesies aanvanklik teenswoordig op die hars wat in die waterige fase eindig. Die veranderende samestelling van die waterige oplossing mag verder tot gevolg hê dat die oplosbaarheid van die metaalagtige spesie verder verhoog mag word. Die gevolg van bogenoemde reaksies is dat die waterige oplossing ionies sterk gekonsentreerd kan word soos meer en meer spesies aanvanklik teenswoordig op die hars migreer na die oplossing. Die ioniese verandering van die waterige oplossing van 'n suiwer waterige fase tot 'n ionies sterk gekonsentreerde oplossing vind plaas tydens die oplos van erste in 'n hars-inpulp (HIP) oplossing. Die nuwe ioniese aktiwiteit in die oplossing kan die oplosbaarheid van die vaste stof drasties verander. Die volledige oplossing van 'n bepaalde kwantiteit van die vaste stof kan bereik word deur die genoegsame toevoeging van 'n geskikte hars tot die waterige oplossing wat die vaste stofbevat. Die gelyktydige oplossing en absorpsie van die metaalagtige vastestowwe vanuit waterige oplossings met behulp van ioon-uitruilings harse is eksperimenteel getoets vir die doeleindes van hierdie werkstuk. Verskeie interaksies wat op molekulêre vlak in die pulp plaasvind asook die adsorpsie proses van die spesies vanuit die waterige oplossing op die harse word bespreek en gemodelleer. Wiskundige modelle wat die termodinamika van die verskillende fases wiskundig verteenwoordig is ontwikkel vanaf bestaande termodinamiese beginsels. Die drie verskillende fases wat in ag geneem is, is die waterige fase met opgeloste metaal spesies, die vaste stof fase wat as die erts in bostaande paragrawe beskryf is en die ioon-uitruilings fase wat 'n komplekse vastestof en water fase gekombineerd is. Die doel van die werkstuk is om die basis te skep vir die ontwikkeling van modelle wat gebruik kan word om die herwinning van skaars-aarde mertale vanuit lae oplosbare erstse te modelleer en beskryf. 'n Tipiese industriële voorbeeld is die herwinning van skaars-aarde metale van lae-graadse kalkagtige erste deur gebruik te maak van perkolerende logings reaksies wat geduring die vastestof / vloeistof ewewig versteur. Die konsentrasie van die skaars-aarde metale in hierde erts gesteentes kan wissel vanaf so laag as 0.05% tot 0.3% per massa. Hierdie konsentrasies is uiters laag gesien vanuit enige industriële herwinnings proses oogpunt.

Thesis (PhD)--Stellenbosch University, 1992. / ENGLISH ABSTRACT: The dissolution of gold from refractory ores is a complex kinetic problem involving a number of chemical, mass transport and mineralogical factors. In most Witwatersrand ores in South Africa more than 97 % of the gold is dissolved in cyanide medium after a residence time of about 16 hours in pachuca tanks. This high percentage may be the reason why so little fundamental research has been done into the mechanism and kinetics of the leaching process. With the increasingly lower grades of ore mined, the introduction of backfill mining, and the reduction of profit margins, it has become imperative to increase the efficiency of gold dissolution. The effects of the chemistry and particle size on the dissolution of gold in each sample of ore were studied in detail. The emphasis in this study is on the effect of the leaching behaviour of various ore constituents on the rate of gold dissolution. Interferences with the leaching of gold in contact with other minerals or metals could be attributed to the galvanic interaction (electrical conductivity) between the gold and the mineral and to the formation of a surface film on the gold surface. Sulphide minerals and their oxidation products cause the largest decrease in gold dissolution rate. Galena enhances the rate of gold dissolution owing to dissolved Pb(II)-ions. Gold in contact with conductive minerals passivates as a result of the enhanced magnitude of the cathodic cu1Tent. In all experiments the rotating disc of gold passivated so that the rate of dissolution was much slower than that predicted by a mass-transport limiting model. The various films that form on the surface of the gold and associated minerals, as well as the galvanic interaction, depend largely on the pretreatment of the ore. Pre-elimination of host minerals from the gold bearing ore increases the dissolution rate of gold, and explains the kinetics of reaction on the gold surface to a large extent. The selective destruction of the various minerals with oxidative acid leaches destroys and/or decomposes certain minerals which may form films on the gold surface by precipitation. The chemical composition of these films and precipitates depends on the mineralogy of the sample. These films may be oxides, sulphides, carbonates and cyanide complexes. The complexes can be destroyed, depending on the nature of the film, by interstage dilute acid and/or cyanide washes in an agitated vessel. The destruction of the films exposes the gold surface for cyanidation. A simple distribution function similar to the King liberation model is proposed and tested to describe the dissolution step in the multi-step leaching mechanism. For the King model, good agreement is shown with experimental results. For the liberation results obtained by leaching in this study, the trend is co1Tect, but calibration is required for a close fit. A potentially important use for the liberation model by leaching is to predict the leachable or free gold in an ore from the free gold in the complete sample. This approach for studying the leaching behaviour of different gold bearing minerals has provided reasons why some ores leach better than others. / AFRIKAANSE OPSOMMING: Die loging van goud vanuit weerbarstige ertse is 'n komplekse kinetiese probleem wat verskeie faktore soos massa-oordrag, chemiese aspekte en mineralogiese ingeweefdheid insluit. Goud ekstraksies so hoog as 97 % in sianied oplossings in Pachuca reaktore na ongeveer 16 uur logingstyd word behaal in die meeste Witwatersrand ertse in Suid-Afrika. Hierdie hoë ekstraksies mag dalk die rede wees vir die min fundamentele navorsing oor die ekstraksie van goud vanuit minerale in 'n spesifieke erts. Die dalende erts grade, die verlaging van winsgrense en die terugplaas van geloogde erts in die myn noodsaak verbeterde goud ekstraksie. Verkeie faktore nl., chemie, diffusie, partikelgrootte en oplosbaarheid van goud in elke monster erts is in hierdie studie ondersoek. Die sentrale tema was om die logingsgedrag van goud vanuit verskeie minerale in 'n erts te bepaal. Galvaniese interaksie (hou verband met elektriese geleidingsvermoeë) en film vorming is die belangrikste faktore wat die loging van goud in kontak met minerale nadelig beïnvloed. Sulfied minerale en hul oksidasie produkte speel die grootste rol in die verlaging van die tempo van goudloging. Galena verhoog die tempo van goudloging as gevolg van die Pb (II)- ione in oplossing. Goud in kontak met geleidende minerale passiveer as gevolg van die verhoogde katodiese stroomdigtheid. In alle eksperimente met die roterende skyf (goudskyf) apparaat, passiveer die goudskyf in so 'n mate dat die logingstempo baie stadiger is as wat voorspel word met die massa-oordrags model. Die onderskeie films wat vorm op die goud- en geassosieerde minerale se oppervlaktes, asook die galvaniese interaksies, is 'n funksie van die voorafbehandeling van die erts. Die selektiewe eliminering van minerale vanuit 'n gouddraende erts verhoog die tempo van goudloging drasties en dit beskryf die kinetika van goudloging op die goudoppervlak in 'n groot mate. Die selektiewe eliminering van minerale deur gebruik te maak van oksiderende suurlogings, vernietig sekere van die minerale wat films op die goudoppervlakte kan veroorsaak deur middel van presipitasie. Die chemiese samestelling van hierdie films hang af van die mineralogie van die monster. Dit bestaan meestal uit oksiedes, sulfiedes, karbonate en sianiedkomplekse en hulle kan vernietig word deur middel van inter-stadia verdunde suur-en/of sianied wasse. 'n Eenvoudige distribusiefunksie, soortgelyk aan die King bevrydingsmodel word voorgestel en eksperimenteel getoets om die logingstap in die multi-stadia logingsmeganisme te beskryf. Vir bevryding deur loging, is die neiging van King se model korrek, maar kalibrasie word benodig vir goeie passing. 'n Potensiele gebruik van die aangepaste model is om vrye of loogbare goud in 'n spesi fieke partikel grootte fraksie van 'n erts te voorspel as die vry goud in die totale fraksie bekend is. Die resultate uit hierdie studie kan gebruik word om die logingsgedrag van gouddraende minerale te voorspel en te beskryf, en dus veduidelik hoekom goud uit sekere ertse beter loog as uit ander.

Thesis (MScIng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Physical systems encountered in process engineering are invariably ill-defined, multivariate, and exhibit complex nonlinear dynamical behaviour. The increasing demands for better process efficiency and high product quality have led to the development and implementation of advanced control strategies in process plants. These modern control strategies are based on the use of a mathematical model defined for the process. Traditionally, linear models have been used to approximate the dynamics of processes whereas most processes are governed by nonlinear mechanisms. Since linear systems theory is well-established whereas nonlinear systems theory is not, recent developments in nonlinear dynamical systems theory present opportunities for improved approaches in modelling these process systems. It is now known that a nonlinear description of a process can be obtained from using time-delayed copies reconstructed from measurements taken from the process. Due to low signal to noise ratios associated with measured data it is logical to exploit redundant information in multivariate time signals taken from the systems in reconstructing the underlying dynamics. This study investigated the extension of univariate nonlinear time series analysis to the situation where multivariate measurements are available. Using simulated data from a coupled continuously stirred tank reactor and measured data from a flotation process system, the comparative advantages of using multivariate and univariate state space reconstructions were investigated. With respect to detection of nonlinearity multivariate surrogate analysis were found to give potentially robust results because of preservation of cross-correlations among components in the surrogate data. Multivariate local linear models showed a deterministic structure in both small and large neighbourhood sizes whereas for scalar embeddings determinism was defined only in smaller neighbourhood sizes. Non-uniform multivariate embeddings gave local linear models that resembled models from a trivial reconstruction of the original state space variables. With regard to global nonlinear modelling, multivariate embeddings gave models with better predictability irrespective of the model class used. Further improvements in the performance of models were obtained for multivariate non-uniform embeddings. A relatively new statistical learning algorithm, the least-squares support vector machine (LSSVM), was evaluated using multilayer perceptrons (MLP) as a benchmark in modelling nonlinear time series using simulated and plant data. It was observed that in the absence of autocorrelations in the variables and sparse data LSSVMs performed better than MLPs. Simulation of trained models gave consistent results for the LSSVMs, which was not the case for MLPs. However, the computational costs incurred in training the LSSVM model was significantly higher than for MLPs. LSSVMs were found to be insensitive to dimensionality reduction methods whereas the performance of MLPs degraded with increasing complexity of the dimension reduction method. No relative merits were found for using complex subspace dimension reduction methods for the data used. No general conclusions could be drawn with respect to the relative superiority of one class of models method over the other. Spatiotemporal structures are routinely observed in many chemical systems, such as reactive-diffusion and other pattern forming systems. We investigated the modelling of spatiotemporal time series using the coupled logistic map lattice as a case study. It was found that including both spatial and temporal information improved the performance of the fitted models. However, the superiority of spatiotemporal embeddings over individual time series was found to be defined for certain choices of the spatial and temporal embedding parameters. / AFRIKAANSE OPSOMMING: Fisiese stelsels wat in prosesingenieurswese voorkom is dikwels nie goed gedefinieer nie, multiveranderlik en vertoon komplekse nie-lineˆere gedrag. Toenemende vereistes vir ho¨e prosesdoeltreffendheid en produkgehalte het gelei tot die ontwikkeling en implementering van gevorderde beheerstrategie¨e vir prosesaanlegte. Hierdie morderne beheerstrategie¨e is gebaseer op die gebruik van wiskundige prosesmodelle. Lineˆere modelle word gewoonlik ontwikkel, al is die onderliggende prosesmeganismes in die algemeen nie-lineˆere, aangesien lineˆere stetselteorie goed gevestig is, en nie-line¨ere stelselteorie nie. Onlangse verwikkelinge in die teorie van nie-lineˆeredinamiese stelsels bied egter geleenthede vir verbeterde modellering van prosesstelsels. Dit is bekend dat ‘n nie-lineˆere beskrywing van ‘n progses verkry kan word deur tydvertraagde kopie¨e van metings van die prosesse te rekonstrueer. Met die lae seintot- geraasverhoudings wat met gemete data geassosieer word, is dit logies om die oortollige informasie in meerveranderlike seine te benut tydens die rekonstruksie van die onderliggende prosesdinamika. In die tesis is die uitbreiding van enkel-veranderlike nie-lineˆere tydreeksontleding na meer-veranderlike stelsels ondersoek. Met data van twee aaneengeskakelde gesimuleerde geroerde tenkreaktore en werklike data van ‘n flottasieproses, is die meriete van enkel- en meerveranderlike rekonstruksies van toestandruimtes ondersoek. Meerveranderlike surrogaatdata-ontleding het nie-lineariteite in die data op ‘n meer robuuste wyse ge¨ıdentifiseer, a.g.v. die behoud van kruis-korrelasies in die komponente van die data. Meerveranderlike lokale lineˆere modelle het ‘n deterministiese struktuur in beide klein en groot naasliggende omgewings ge¨ıdentifiseer, terwyl enkelveranderlike metodes dit slegs vir klein naasliggende omgewings kon doen. Nie-uniforme meerveranderlike inbeddings het lokale lineˆere modelle gegenereer wat soos globale modelle afkomstig van triviale rekonstruksies van die data gelyk het. M.b.t globale nie-lineˆere modellering, het meerveranderlike inbedding deurgaans beter modelle opgelewer. Verdere verbetering in die prestasie van modelle kon verkry word d.m.v. meerveranderlike nie-uniforme inbedding. ‘n Relatief nuwe statistiese algoritme, die kleinste-kwadrate-steunvektormasjien (KKSVM) is ge¨evalueer teenoor multilaag-perseptrons (MLP) as ‘n standaard vir die modellering van nie-lineˆere tydreekse, deur gebruik te maak van gesimuleerde en werklike aanlegdata. Daar is gevind dat die KKSVM beter presteer het as die MLPs wanneer die opeenvolgende waarnemings swak gekorreleer en min was relatief tot die aantal veranderlikes. Die KKSVMs het beduidend langer geneem as die MLPs om te ontwikkel. Hulle was ook minder sensitief vir die metodes wat gevolg is om die dimensionaliteit van die data te verlaag, anders as die MLPs. Ook is gevind dat meer komplekse metodes tot die verlaging van die dimensionaliteit weinig nut gehad het. Geen algemene gevolgtrekkings kan egter gemaak word m.b.t die verskillende modelle nie. Ruimtelik-temporale strukture word algemeen waargeneem in baie chemiese stelsels, soos reaktiewe diffusie e.a. patroonvormende sisteme. Die modellering van ruimtelik-temporale stelsels is bestudeer aan die hand van ‘n gekoppelde logistiese projeksierooster. Insluiting van beide die ruimtelike en temporale inligting het tot beduidend beter modelle gelei, solank as wat di´e inligting op die regte wyse ontsluit is.

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Metallurgical processes are often high dimensional and non-linear making them difficult to understand, model and control. Whereas the human eye has extensively been used in discerning temporal patterns in historical process data from these processes, the systematic study of such data has only recently come to the forefront. This resulted predominantly from the inadequacy of previously used linear techniques and the computational power required when analysing the non-linear dynamics underlying these systems. Furthermore, owing to the recent progress made with regard to the identification of non-linear systems and the increased availability of computational power, the application of non-linear modelling techniques for the development of neural network models to be used in advanced control systems has become a potential alternative to operator experience. The objective of this study was the development ofa non-linear, dynamic model of an autogenous mill for use in an advanced control system. This was accomplished through system identification, modelling and prediction, and application to control. For system identification, the attractor was reconstructed based on Taken's theorem making use of both the Method Of Delays and singular spectrum analysis. Modelling consisted of the development of multi-layer perceptron neural network, radial basis function neural network, and support vector machine models for the prediction of the power drawn by an autogenous mill. The best model was subsequently selected and validated through its application to control. This was accomplished by means of developing a neurocontroller, which was tested under simulation. Initial inspection of the process data to be modelled indicated that it contained a considerable amount noise. However, using the method of surrogate data, it was found that the time series representing the power drawn by the autogenous mill clearly exhibited deterministic character, making it suitable for predictive modelling. It was subsequently found that, when using the data for attractor reconstruction, a connection existed between the embedding strategy used, the quality of the reconstructed attractor, and the quality of the resulting model. Owing to the high degree of noise in the data it was found that the singular spectrum analysis embeddings resulted in better quality reconstructed attractors that covered a larger part of the state space when compared to the method of delays embeddings; the data embedded using singular spectrum analysis also resulting in the development of better quality models. From a modelling perspective it was found that the multi-layer perceptron neural network models generally performed the best; a multi-layer perceptron neural network model having an appropriately embedded multi-dimensional input space outperforming all the other developed models with regard to free-run prediction success. However, none of the non-linear models performed significantly better than the ARX model with regard to one-step prediction results (based on the R2 statistic); the one-step predictions having a prediction interval of 30 seconds. In general the best model was a multi-layer perceptron neural network model having an input space consisting of the FAG mill power (XI), the FAG mill load (X2), the FAG mill coarse ore feed rate (X3), the FAG mill fine ore feed rate (X4), the FAG mill inlet water flow rate (X7) and the FAG mill discharge flow rates (X9, XIO). Since the accuracy of any neural network model is highly dependent on its training data, a process model diagnostic system was developed to accompany the process model. Linear principal component analysis was used for this purposes and the resulting diagnostic system was successfully used for data validation. One of the models developed during this research was also successfully used for the development of a neurocontroller, proving its possible use in an advanced control system. / AFRIKAANSE OPSOMMING: Metallurgiese prosesse is gewoonlik hoogs dimensioneel en nie-lineêr, wat dit moeilik maak om te verstaan, modelleer, en te beheer. Alhoewel die menslike oog alreeds wyd gebruik word om temporale patrone in historiese proses data te onderskei, het die sistematiese studie van hierdie tipe data eers onlangs na vore gekom. Dit is hoofsaaklik na aanleiding van die onvoldoende resultate wat verkry is deur van voorafgaande lineêre tegnieke gebruik te maak, asook die beperkende berekenings vermoë wat beskikbaar was vir analise van onderliggend nie-lineêre dinamiese stelsels. 'n Verder bydraende faktor is die onlangse vordering wat gemaak is met betrekking tot die identifikasie van nie-lineêre stelsels en die toename in beskikbaarheid van rekenaar-vermoë. Die toepassing van nie-lineêre modellerings tegnieke vir die ontwikkeling van neurale netwerke om gebruik te word in gevorderde beheerstelsels, het 'n potensiële alternatief geword tot operateur ondervinding. Die doelwit van hierdie studie was die ontwikkeling van 'n gevorderde beheerstelsel vir 'n outogene meul gebaseer op 'n nie-lineêre, dinamiese model. Dit is bereik deur middel van stelsel-identifikasie, modellering en voorspelling, en laastens implementering van die beheerstelsel. Vir stelsel-identifikasie is die attraktor van die stelsel bepaal soos gebaseer op Taken se teorema deur gebruik te maak van beide die metode van vertraging en enkelvoudige spektrum analise. Modellering van die stelsel vir die voorspelling van krag-verbruik deur die outogene meul het bestaan uit die ontwikkeling van multilaag-perseptron-neurale netwerke, radiaalbasisfunksie-neurale netwerke, en steunvektor-masjien-modelle. Die beste model is daarna gekies vir validasie deur middel van toepassing vir beheer. Dit is bereik deur 'n neurobeheerder te ontwikkel en te toets deur middel van simulasie. Die aanvanklike inspeksie van proses data wat gebruik sou word vir modellering het egter getoon dat die data 'n aansienlike hoeveelheid geraas bevat. Nietemin, deur die gebruik van 'n surrogaat-data-metode, is dit bevind dat die tyd-reeks wat die krag verbruik van die outogene meul beskryf, duidelik deterministiese karakter toon en dat dit dus wenslik is om 'n nie-lineêre voorspellings-model, soos 'n neurale netwerk te gruik. Gevolglik is gevind dat, wanneer die data vir attraktor hersamestelling gebruik word, 'n verband bestaan tussen die ontvouing-strategie wat gebruik word, die kwaliteit van die gerekonstrueerde attraktor, en die kwaliteit van die daaropvolgende model. As gevolg van die geraas in die data is gevind dat die ontvouing gebaseer op enkelvoudige spektrum analise 'n beter kwaliteit attraktor hersamestelling lewer. So ook is gevind dat 'n groter deel van die toestandruimte gedek word in vergelyking met die metode van vertraging-ontvouing. Deur gebruik te maak van enkelvoudige spektrum-analise, het die dataontvouing ook beter kwaliteit modelle opgelewer. Vanuit 'n modellerings-perspektief is gevind dat die multilaag-perseptron-neurale netwerk-modelle in die algemeen die beste gevaar het. 'n Multilaag-perseptronneurale netwerk met 'n gepaste ontvoude multidimensionele invoer-spasie het die beste gevaar van al die ontwikkelde modelle met betrekking tot vryloopvoorspellings. Geen van die nie-lineêre modelle het egter beduidend (op 'n R2 basis) beter gevaar as die ARX model wanneer daar na die eenstap-voorspellings (oor 'n 30 sekonde interval) gekyk word nie. Die multilaag-perseptron-neurale netwerk met 'n invoer-spasie bestaande uit die meul krag-verbruik (XI), die meullading (X2), die meul growwe-erts voertempo (X3), die meul fyn-erts voertemp ('4), die meul inlaat-water vloeitempo (X7) en die meul uitlaat vloeitempo's (X9, XIO) het in die algemeen die beste gevaar. Aangesien die akkuraatheid van emge neurale netwerk afhanklik is van die data waarmee dit aanvanklik opgestel is, is 'n diagnostiese proses modelontwikkel om die proses-model te vergesel. Lineêre hoofkomponent analise is vir hierdie doel aangewend en die gevolglike diagnostiese stelsel is suksesvol aangewend vir datavalidasie. Een van die modelle ontwikkel gedurende hierdie navorsing is ook suksesvol gebruik vir die ontwikkeling van 'n neurobeheerder wat dien as bewys dat die model goed gebruik kan word in 'n gevorderde beheerstelsel.

Please read the abstract in the section 00front of this document / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / unrestricted

This research project investigated the option of steelmaking with the ESS furnace by using computational modelling to estimate steady state decarburisation rates. It focused on understanding metallurgical phenomena that would dictate refining rates of molten pig iron with iron ore. The results obtained are aimed at designers and potential users of the furnace technology to improve their understanding of the expected steady-state process behaviour. A mass-and-energy-balance model with a decarburisation sub-model was developed to estimate feed material requirements for steady state operation. Modelling and simulation results suggest that it may not be possible to produce steel under the conditions proposed. However, the furnace still holds potential if ideal operational conditions are understood and applied. Modelling also gave insight into which areas areas of concern, such as bubble formation in the furnace’s channel induction heaters, and necessity for a well designed refractory lining to contain heat and allow the process to operate at a stable condition under the conditions proposed. Keywords: ESS furnace, steelmaking, metallurgical analysis, modelling, mass and energy balance, decarburisation kinetics / Dissertation (MEng)--University of Pretoria, 2020. / Materials Science and Metallurgical Engineering / MEng / Unrestricted

Thesis (MScIng)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Due to economic and environmental constraints mining operations are placed under increasing pressure to effectively manage and operate tailings disposal operations. Restrictions imposed on water usage and tailings operations footprint have led to higher density and wider particle size distribution slurries conveyed to tailings areas. One means of efficiently disposing the tailings is co-disposal. In this method a concentrated fine vehicle slurry is used to convey a coarser fraction. This produces a higher density of tailings, with a number of advantages both upstream and downstream of the tailings process. Limited research has been conducted on the effect of coarse particles on the non-Newtonian rheological properties of these slurries. This lack of information complicates the design and reliable operation of these systems. This project aims at gaining a clearer understanding as to the mechanisms involved in the addition of coarse particles to a fine clay slurry vehicle; and to provide a means of estimating the measured slurry rheological properties. A number of experiments were designed to test the slurry (both Kaolin only, and Kaolin-coarse particle mixtures) rheological properties using a Couette viscometer (for the dynamic flow properties of yield stress and plastic viscosity) and a vane instrument (for the static yield stress measurements). The slurries were prepared in varying Kaolin clay solids concentrations with reverse osmosis water. Glass beads and two types of industrial sand were used as the coarse fractions. All of the coarse particles had a similar size but varied significantly in shape. Slurry pH and temperature readings were monitored throughout the tests. Tests were done initially on clay only slurries. The rheological properties of these slurries were repeatable, and no noticeable variations of properties with time were observed. The yield stress (both static and dynamic) and plastic viscosity data were well correlated with established relationships. Coarse particles were added to the clay only slurries, and then removed. The remaining clay only slurry exhibited the same rheological properties as the initial clay only slurry. The presence of coarse particles increased all the measured rheological properties (i.e. dynamic yield stress, Bingham viscosity, and static vane yield stress) in a fashion resembling the effect of adding clay to a clay only slurry. In addition, the change in measured rheological property by addition of coarse particle was independent of the clay fraction in the clay slurry. Furthermore, with both the clay only slurries and clay and coarse sand slurries, a constant linear relationship existed between the static and dynamic yield stress. Several correlations from the literature were found to provide reasonable prediction of the rheological property variations observed. These empirical and semi-empirical models however did little to explain the mechanisms involved in coarse particle addition. A new correlation has been proposed, Residual Clay Concentration, which predicts the change in rheological property based on an additional clay concentration, which in turn is a linear function of the coarse particle concentration. The accuracy of this model further strengthens the belief that the coarse particle acts in a similar fashion to a floc. By means of a case study example the importance of selecting an appropriate model for design was illustrated. The Residual Clay Concentration method provided the most conservative results. This combined with its theoretical basis strengthens the models recommendation for use in design. / AFRIKAANSE OPSOMMING: As gevolg van ekonomiese en omgewings beperkinge word mynwese nywerhede onder toenemende druk geplaas om doeltreffende afvalstroom bestuur en operasie toe te pas. Beperkinge geplaas op water gebruik en afvalstroom area-groote ly tot hoër digthede en wyer partikel-grooteverspreidings van flodders vervoer na afval areas. Een manier om van die afval doeltreffend ontslae te raak en te berg is deur medeberging. In die metode word ‘n gekonsentreerde fyn flodder gebruik as draer van ‘n growwer partikel-fraksie. Dit ly tot ‘n hoër digtheid flodder, met verskeie voordele in beide die op – en afstroom prosesse. Beperkte navorsing is gedoen op die effek van growwe partikels op die nie-Newoniese rheolgiese eienskappe van hierdie flodders. Hierdie tekort aan informasie maak die effektiewe, betroubare bedryf en operasie van die sisteme meer ingewikkeld. Hierdie projek is daarheen gemik om ‘n beter begrip te ontwikkel met betrekking tot die meganismes betrokke in die byvoeging van growwe partikels aan ‘n fyn klei-agtige flodder draer; en om ‘n manier te voorsien wat die rheologiese eienskappe kan beraam. Verskeie eksperimente was ontwerp om die flodders (beide slegs Kaolien, en Kaoliengrowwe partikel mengsels) se rheologiese eienskappe te toets deur die gebruik van ‘n Couette-viskometer. Die Couette viskometer was gebruik om die dinamiese eienskappe (van grens-spanning, en plastiese viskositet) te meet. ‘n Vaan apparaat is gebruik om die eienskap van statiese grens-spanning te meet. Die flodders was voorberei in verskeie Kaolien konsentrasies met tru-osmosis water. Glas krale en twee tipes industriële sand is gebruik as die growwe fraksies. Al die growwe partikels het soortgelyke groottes gehad, maar het grootliks verskil in vorm. Die flodder pH en temperatuur lesings is deurentyd nagegaan. Toetse was aanvanklik gedoen op die klei-alleenlike flodders. Die gemete reologiese eienskappe van die flodders was herhaalbaar, en geen opmerkbare veranderinge van die eienskappe met betrekking tot tyd is gemeet nie. Die grens-spanning (beide statiese en dinamiese) en plastiese viskositeit is goed gekorrelleer met gevestigde verhoudinge. Growwe partikels is aan die klei-alleenlike flodders bygevoeg, en daarnae verwyder. Die oorblywende klei-alleenlike flodder het dieselfde gemete rheologiese eienskappe getoon as die oorspronklike klei-allenlike flodder. Die teenwoordigheid van growwe partikels het na ‘n toename van al die gamete rheologiese eienskappe gelei wat fisies baie soortgelyk is aan die byvoeging van klei tot ‘n klei-alleenlike flodder. Verder, met beide die klei-alleenlike en klei-growwe partikel flodders het ‘n konstante liniëre funksie tussen die statiese en dinamiese grens-spannings bestaan. Verskeie verhoudings uit die literatuur het goeie korrelasie bewerkstellig met die waargenome rheologie veranderinge. Hierdie empiriese en semi-empiriese modelle doen egter min om die megansimes betrokke in die toevoeging van growwe partikels te verduidelik. ‘n Nuwe korrelasie is voorgestel, naamlik die Residu Klei Konsentrasie. Hierdie model voorspel die verandering in reologiese eienskappe gebaseer op ‘n addisionele klei konsentrasie, wat ‘n liniëre funkise is van die growwe partikel konsentrasie. Die goeie korrelasie gesien met die model versterk die idée dat die growwe partikel in ‘n soortgelyke manier as ‘n flok gedra in die teenwoordigheid van ander flokke. Deur middel van ‘n tipiese industriële voorbeeld is die belangrikheid in die keuse van die regte korrelasie geillustreer. Die Residu Klei Konsentrasie metode het die mees konservatiewe resultate gelewer. Hierdie feit gekombineerd met die model se soliede teoreitiese beginsels versterk dit as voorgestelde korrelasie vir ontwerp.

Este trabalho consiste em uma pesquisa experimental comparativa entre o zircônio puro e a liga comercial de aplicação nuclear Zircaloy-4, com ênfase nas características de encruamento, recristalização e textura cristalográfica. Foram utilizadas várias técnicas complementares de análise microestrutural tais como microscopia óptica, microscopia eletrônica de varredura com análise química de microrregiões por dispersão de energia de raios X característicos, difração de raios X, calorimetria exploratória diferencial, medidas de dureza e de condutividade elétrica. Para as determinações de macrotextura foi utilizado um goniômetro dedicado de raios X. No estado como recebido, enquanto o zircônio puro apresentava grãos recristalizados com diâmetro médio de aproximadamente 50μm, a liga apresentava granulação alfa em plaquetas grosseiras com diâmetro médio do pré-grão beta de aproximadamente 1,1mm. Experiências de laminação e a determinação de curvas de limite de redução sem a presença de trincas em função da temperatura mostraram que enquanto o zircônio puro apresentou níveis altos de plasticidade na temperatura ambiente, a liga Zircaloy-4 apresentou baixa ductilidade e muitas trincas. As ductilidades dos dois materiais, especialmente da liga Zircaloy-4, aumentaram significativamente a partir de 300°C. A 500°C as ductilidades de ambos são idênticas. Utilizando-se deformações e recozimentos diferenciados foram obtidas tiras de mesma espessura, com grãos equiaxiais e diâmetros médios de grão de aproximadamente 9µm para os dois materiais. Os estudos de recristalização revelaram que, enquanto para o zircônio puro a recuperação contribui significativamente para o amolecimento, no caso da liga Zircaloy-4, o amolecimento ocorre quase que exclusivamente por recristalização. As temperaturas de recristalização do zircônio puro foram mais baixas que as da liga. Os átomos de soluto em solução sólida foram responsáveis pelos dois efeitos concorrentes; aumento da energia armazenada na deformação e aumento da resistência à recristalização. Além da caracterização microestrutural mencionada, foram realizadas determinações de textura cristalográfica para os dois materiais em diferentes condições. Com relação às texturas de laminação do zircônio puro, para uma mesma temperatura, em cerca de 50% de redução a textura de laminado a frio {1 1 2 2} já estava plenamente formada e se alterou muito pouco a partir desta redução, até cerca de 90%. Com o aumento de temperatura de deformação para a mesma redução, a textura de laminado a frio se manteve estável até 300°C. A amostra de Zircaloy-4 preparada para possuir um tamanho de grão de 9 m tinha uma textura próxima de {0 0 0 2} , demonstrando que os tratamentos térmicos e mecânicos utilizados para obtenção dessa amostra foram eficientes na redução da textura de laminado a frio {1 1 2 2} . Recozimentos com duração de uma hora a 550 e 575°C, tanto em zircônio puro como na liga Zircaloy-4, foram suficientes para provocar recristalização estática. A 600°C, uma mudança na orientação cristalográfica foi verificada em Zircaloy-4, tendendo a {0 0 0 2} , enquanto em zircônio puro os planos basais continuam estáveis. O uso de funções de distribuição de orientação cristalográfica (FDOC) auxiliaram na detecção de um segundo grupo orientado, que tende à orientação {1 0 1 1} , além do grupo que reforça as fibras D0 e Rf . A mudança de textura ocorreu durante o crescimento de grão em ambos os materiais. De um modo geral, os resultados mostraram que o zircônio puro tende a ser mais suscetível à recristalização e ao crescimento de grão do que a liga Zircaloy-4. Entretanto, tanto zircônio como a liga são resistentes à modificação de textura, sendo que esta ocorreu principalmente com o crescimento de grão, em temperaturas após a completa recristalização primária. / This work shows a comparative experimental research between pure zirconium and the nuclear-grade zirconium alloy Zircaloy-4. This work emphasizes the characteristics of strain hardening, recrystallization, and crystallographic texture. Was used several complementary techniques for microstructural analysis such as optical microscopy, scanning electron microscopy with chemical analysis (EDS), X-ray diffraction, differential scanning calorimetry, indentation hardness and electrical conductivity. For measurements of macrotexture was used a dedicated X-ray goniometer. In the as received state, while pure zirconium showed grains recrystallized with an average diameter of about 50µm, the alloy had rough alpha plates with average diameter of beta pregrain of about 1,1mm. Rolling experiments and determination of reduction limit curves without cracks as a function of temperature showed that while zirconium pure showed high levels of plasticity at room temperature, the alloy zircaloy-4 showed low ductility and many cracks. The ductilities of the two materials, mainly zircaloy-4, significantly increased from 300°C. At 500°C, the ductilities were identical. Using different strains and annealing were obtained strips of equal thickness, with equiaxed grains and grain average diameters of about 9µm for both materials. Recrystallization studies revealed that recovery contributes significantly to softening of pure zirconium. In the case of the alloy zircaloy-4, the softening occurs almost exclusively by recrystallization. The temperature of recrystallization of the pure zirconium were lower than the alloy. The solute atoms in the solid solution were responsible for the two competing effects, the increase of the strain energy stored and the increasing of recrystallization resistance. Crystallographic texture measurements were made for both materials under different conditions. With respect to the rolling textures of pure zirconium, in about 50% reduction of the cold-rolled texture {1 1 2 2} was already fully formed and changed very little from this reduction to about 90%. With the increase of temperature strain to the same reduction, texture cold rolled remained stable up to 300°C. The sample of zircaloy-4 prepared to have a grain size of 9m had a texture close to {0 0 0 2} , demonstrating that the thermal and mechanical treatments used to obtain this sample were effective in reducing texture of cold-rolled {1 1 2 2} . One hour annealings at 550 and 575°C, in pure zirconium and Zircaloy-4, were suffcient to cause static recrystallization. At 600 °C a change in crystallographic orientation was seen in zircaloy-4, tends to {0 0 0 2} , while in pure zirconium the basal planes remains stable. The use of orientation distribution functions (ODF) aided in the detection of a second oriented group, which tends to orientation {1 0 1 1} , besides the group that reinforced D0 and Rf fibers. The change in texture occurred during the grain growth in both materials. In general, the results showed that pure zirconium tends to be more susceptible to recrystallization and grain growth than Zircaloy-4. Nevertheless, Both zinconium and Zircaloy-4 are resistant to texture changes. The texture changes occurred mainly in grain growth, at temperatures after complete recrystallization.

Este trabalho consiste em uma pesquisa sobre aços inoxidáveis ferríticomartensíticos de ativação reduzida (RAFM): EUROFER (9Cr-1W) e ODS-EUROFER (9Cr-1W-0,3Y2O3), envolvendo o encruamento e a recristalização destas duas ligas com o objetivo de estudar a influência de uma dispersão de partículas nanométricas na recristalização de aços inoxidáveis. O conceito de materiais de ativação reduzida é discutido e é apresentada a aplicação destes aços tanto na estrutura de diversor do ITER quanto na primeira parede no módulo de câmara fértil do reator DEMO. As placas, no estado revenido, foram laminadas a frio em um laminador de pequeno porte. As curvas de encruamento de ambos os materiais mostram um comportamento quase linear. Os tratamentos isócronos de uma hora, entre 300 e 750 °C, resultaram curvas de amolecimento que indicam uma forte resistência à recristalização da liga ODS-EUROFER, em concordância com os modelos teóricos. A liga EUROFER-97 apresentou recristalização muito similar a liga comercial 430, mas com maior dureza inicial, devido a maior quantidade de elementos intersticiais. / This work studies reduced activation ferritic-martensitic (RAFM) stainless steels: EUROFER (9Cr-1W) and ODS-EUROFER (9Cr-1W-0,3Y2O3), and their work hardening and recrystallization behaviour to better understand the influence of a dispersion of nanometric particles on the recrystallization process of stainless steels. The concept of reduced activation materials is discussed and the application of these steel alloys, such as in the divertor structure of ITER (International Thermonuclear Experimental Reactor) and as in the DEMO reactor breeding blanket first wall is shown. The plates, in the as-tempered condition, were cold rolled in a laboratory rolling mill. The work hardness curves of both materials presented an approximately linear behavior with strain increase. One hour isochronal treatments, in the temperature range from 300 to 750 °C, resulted in softening curves that indicated a strong resistance to recrystallization of the alloy ODS-EUROFER, supporting the theorical models. The EUROFER-97 recrystallization showed a similar behaviour to the commercial 430 alloy, however with higher initial hardness, due to the larger amount of interstitial elements.