In recent years the steelmaking industry has been subjected to continuous attempts to improve its production route. The main goals has been to increase the competitiveness and to reduce the environmental impact. The development of predictive models has therefore been of crucial importance in order to achieve such optimization. Models are representations or idealizations of reality which can be used to investigate new process strategies without the need of intervention in the process itself. Together with the development of Industry 4.0, Machine Learning (ML) has turned out as a promising modeling approach for the steel industry. However, ML models are generally difficult to interpret, which makes it complicated to investigate if the model accurately represents reality. The present work explores the practical usefulness of applied ML models in the context of the secondary metallurgy processes in steelmaking. In particular, the application of interest is the prediction of the liquid steel temperature after the vacuum treatment step in the Vacuum Tank Degasser (VTD). The choice of the VTD process step is related to its emerging importance in the SSAB Oxelösund steel plant due to the planned future investment in an Electric Arc Furnace (EAF) based production line. The temperature is an important parameter of process control after the vacuum treatment since it directly influences the castability of the steel. Furthermore, there are not many available models which predict the temperature after the vacuum treatment step. The present thesis focuses first on giving a literature background of the statistical modeling approach, mainly addressing the ML approach, and the VTD process. Furthermore, it is reported the methodology behind the construction of the ML model for the application of interest and the results of the numerical experiments. All the statistical concepts used are explained in the literature section. By using the described methodologies, several findings originated from the resulting ML models predicting the temperature of the liquid steel after the vacuum treatment in the VTD.A high complexity of the model is not necessary in order to achieve a high predictive performance on the test data. On the other hand, the data quality is the most important factor to take into account when improving the predictive performance. Itis fundamental having an expertise in both metallurgy and machine learning in order to create a machine learning model that is both relevant and interpretable to domain experts. This knowledge is indeed fundamental for the selection of the input data and the machine learning model framework. Crucial information for the predictions result to be the heat status of the ladle as well as the stirring process time and the temperature benchmarks before and after the vacuum steps. However, to draw specific conclusions, a higher model predictive performance is needed. This can only be obtained upon a significant data quality improvement. / Stålindustrin har under de senaste åren ständigt förbättrat sin produktionsförmåga som i huvudsak har bidragit till ökad konkurrenskraft och minskad miljöpåverkan. Utvecklingen  av  prediktiva  modeller  har  under  denna  process  varit  av  avgörande betydelse för att uppnå dessa bedrifter. Modeller är representationer eller idealiseringar av verkligheten som kan användas för att utvärdera nya processtrategier utan att åberopa  ingrepp  i  själva  processen.    Detta  sparar  industrin  både  tid och pengar.   I takt  med  Industri  4.0  har  maskininlärning  blivit  uppmärksammad  som ett ytterligare modelleringsförfarande inom stålindustrin. Maskininlärningsmodeller är dock generellt svårtolkade, vilket gör det utmanande att undersöka om modellen representerar verkligheten. Detta arbete undersöker den praktiska användningen av maskininlärningsmodeller inom sekundärmetallurgin på  ett  svenskt  stålverk.    Tillämpningen  är  i  synnerhet av   intresse   för   att   kunna   förutspå   temperaturen   hos   det   flytande   stålet   efter vakuumbehandlingssteget  i  VTD-processen. Denna  process  valdes  eftersom den är av  stor  betydelse  för  framtida  ståltillverkning  hos  SSAB  i  Oxelösund. Detta är primärt  på  grund  utav  att  SSAB  kommer  att  investera  i  en ljusbågsugnsbaserad produktionslinje.   Temperaturen är en viktig processparameter eftersom den direkt påverkar   stålets   gjutbarhet. Utöver   detta   har   inga   omfattande   arbeten   gjorts gällande  att  förutspå  temperaturen  efter vakuumbehandlingssteget  med  hjälp av maskininlärningsmodeller. Arbetet presenterar först en litteraturbakgrund inom statistisk modellering med fokus på maskininlärning och VTD-processen.  Därefter redovisas metodiken som använts för att skapa  maskininlärningsmodellerna  som  ligger  till  grund  för  de  numeriska experimenten samt resultaten. Genom att använda de beskrivna metoderna härrörde flera fynd från de skapande maskininlärningsmodellerna. En hög grad av komplexitet är inte   nödvändig   för   att   uppnå   en   hög   prediktiv   förmåga   på   data   som   inte använts  för  att  anpassa  modellens  parametrar.   Å  andra  sidan  är  datakvalitén den viktigaste faktorn om man ämnar att förbättra den prediktiva förmågan hos modellen. Utöver  detta  är  det  av  yttersta  vikt  att  ha  kompetens  inom  både  metallurgi  och maskininlärning för att skapa en modell som är både relevant och tolkbar för experter inom  området  processmetallurgi. Ideligen  är  kunskap  inom  processmetallurgi grundläggande för val av indata och val av maskininlärningsalgoritm. Under analysen av maskininlärningsmodellerna upptäcktes det att skänkens värmestatus, omrörningstiden i processen, samt temperaturriktmärkena före och efter vakuumstegen var de mest avgörande variablerna för modellens prediktiva förmåga. För att kunna dra specifika slutsatser behöver modellen ha en högre prediktiv förmåga. Detta kan endast erhållas efter en betydande förbättring av datakvalitén.

The underlying motives of the research undertaken here are twofold: to obtain a deeper understanding of the dewatering mechanisms at the forming section of a papermaking machine and to develop numerical models that describe the flow through forming fabrics. More comprehensive knowledge of dewatering in the forming section allows suggestions to be made for improvements that reduce the amount of energy used in the process without affecting the quality of the end product.   The objective of this thesis is to answer the following questions: How and why does rewetting occur at the high vacuum suction boxes? How does the structure of the forming fabric affect dewatering at the forming section? Is it possible to create accurate numerical models for forming fabrics, and can these be used to predict the dewatering behaviour of new types of fabrics?   Laboratory and pilot studies simulating high vacuum suction boxes were performed together with numerical modelling of the flow of air and water through both the forming fabric and the paper sheet.   The conclusion drawn from the pilot study is that rewetting significantly lowers the dryness of the paper sheet exiting the suction boxes. The phenomenon is extremely rapid and is most likely driven by capillary forces. The high speed at which this rewetting occurs makes it difficult to impede by placing the suction boxes closer to the couch pick-up: the solution is more likely to be the use of new and improved designs of the forming fabric. The structure of the forming fabric has been shown to affect the dewatering rate at certain conditions of vacuum dewatering, and can possibly be connected partly to the fact that fibres penetrate the surface of the fabric to varying degrees and partly to the flow resistance of the different fabric structures. Numerical models of high accuracy can be constructed and used to predetermine how new fabric designs would affect dewatering at the forming section.   This thesis quantifies aspects of dewatering such as rewetting and the influence of the forming fabric. Understanding these dewatering aspects further provides for the potential enhancement of energy efficiency in the forming section, and thereby the entire papermaking process. The forming fabric can play an important role in improving energy efficiency: rewetting after the high vacuum suction boxes occurs more rapidly than was previously known, so its design might be the only possible way of impeding it. The forming fabric can also improve the rate of dewatering: it is therefore likely that its design will be important in the next stage of developing energy efficiency and thereby play a part in achieving a more sustainable future. / This thesis quantifies aspects of dewatering such as rewetting and the influence of the forming fabric. Understanding these dewatering aspects further provides for the potential enhancement of energy efficiency in the forming section, and thereby the entire papermaking process. The forming fabric can play an important role in improving energy efficiency: rewetting after the high vacuum suction boxes occurs more rapidly than was previously known, so its design might be the only possible way of impeding it. The forming fabric can also improve the rate of dewatering: it is therefore likely that its design will be important in the next stage of developing energy efficiency and thereby play a part in achieving a more sustainable future.

GaAsBi is a relatively unexplored alloy with interesting features such as a large bandgap reduction for a given lattice mismatch with GaAs substrates and good photoluminescence which make it promising for long wavelength light detection and emission applications. In this research, the molecular beam epitaxy (MBE) method was used to grow epi-layers and hetero-structures. A Vertical-external-cavity surface-emitting-laser (VECSEL) was grown as a part of collaboration with Tampere University in Finland. The process of laser growth promoted the writer’s skills in the growth of hetero-structures and led into an investigation of the effect of growth conditions on GaAsBi optical properties with important results. For instance, when the substrate temperature during growth was reduced from 400°C to 300°C and all other growth conditions were fixed, the Bi concentration in the deposited films increased from 1% to 5% and the photoluminescence (PL) intensity decreased by more than a factor of 1000. This is an indication of the importance of growth temperature in GaAsBi crystal quality. n+/p junctions were grown for the deep level transient spectroscopy (DLTS) experiments in collaboration with Simon Fraser University. The DLTS measurements showed that lowering the GaAsBi growth temperature increases the deep level density by a factor of 10. These deep levels are the source of non-radiative recombination and decrease the PL intensity. The structural properties of GaAsBi were investigated by high resolution x-ray diffraction and polarized PL and revealed long distance atomic arrangement (Cu-Pt ordering) in GaAsBi. The measurements showed that the ordering is more probable at high growth temperature. This can be due to the larger mobility of the atoms on the surface at high growth temperatures that allows them to find the ordered low energy sites. / Graduate

Vacuum polarization by electric fields is a well established fact. Assuming that anti-matter has negative gravitational properties, the fluctating electric dipoles from the quantum vacuum may also have gravitational dipolar properties. A model is developed that describes how electric fields could gravitationally polarize the vacuum causing gravitational screening or anti-screening effects. This leads to a violation of the Weak Equivalence Principle or a general mass change most notabily for elementary particles, such as the electron or positron, below but close to measured boundaries. Also a gravitational vacuum torque is predicted to act on a charged capacitor perpendicular to a gravitational field. The predictions could be verified by future laboratory experiments that could contribute on our understanding of the gravitational properties of anti-matter.

The aim of the present work was to get an overview of the steel cleanness in tool steel. Plant trial studies of three steel grades were done with different focuses. Firstly the change of the inclusion characteristics during the vacuum degassing in the ladle was looked upon. The top slag composition was altered and sampling was made before and after vacuum degassing and the results showed that the top slag composition has an effect on the inclusion composition. Thermodynamic calculations indicated that the oxygen activity for the steel/inclusion was twice as large as that of the steel/top slag before vacuum degassing. However, after vacuum degassing the oxygen activity values were close. In order to study the inclusion characteristics during vacuum degassing the process was interrupted at five pre-determined time points for sampling. During vacuum the number of the smaller inclusions was decreased. However, for the larger inclusions (&gt;11.2µm) the number of inclusions had increased. Throughout the degassing process the inclusion composition was found to approach the top slag composition and at the end of the process only one type of inclusion composition was found. The removal of hydrogen, nitrogen and sulphur was studied. Samples were taken before and after vacuum degassing. It was found that the removal kinetics of hydrogen and nitrogen can be described with first-order reactions. When 10 minutes of vacuum degassing have passed, the removal of hydrogen and nitrogen is more or less finished for the studied steel grades. Two steel grades with similar process route and with only a few differences in steel composition were studied. The sum of FeO and MnO was found to be a clear indicator for when reoxidation had taken place. The results from oxygen activity calculations indicate that calculations of oxygen activities with multivalence slag species such as Fe and Cr requires measurements for validations to ensure that reliable results are obtained. / Syftet med denna studie var att få en överblick av verktygsståls renhet. Studier på tre olika stålsorter utfördes. Inneslutningsbilden under vakuumbehandling undersöktes. Resultaten är baserade på industriförsök likväl som termodynamiska beräkningar. Försöken gjordes på två olika stålsorter där toppslaggens sammansättning varierades och stål- och slaggprover tog ut före och efter vakuumbehandling. Proverna analyserades för att bestämma den kemiska sammansättningen på stål och slagg, men inneslutningsbilden undersöktes också. Med hjälp av termodynamiska beräkningar beräknades syreaktiviteten för jämvikterna stål/inneslutning och stål/toppslag. Beräkningarna jämfördes sinsemellan samt med uppmätt syreaktivitet från stålsmältan. Resultaten visar att toppslaggens sammansättning har en påverkan på inneslutningarnas sammansättning. Specifikt så fanns att när CaO-halten i toppslaggen ökar syns en ökning av CaO i inneslutningssammansättningen. De termodynamiska beräkningarna visar att syreaktiviten för jämvikten stål/inneslutning är dubbelt så stor som den för jämvikten stål/topplagg före vakuumbehandling. Dock är syreaktiviteterna för de olika jämvikterna lika efter vakuumbehandlingen. För att studera hur inneslutningsbilden utvecklas under vakuumbehandling avbröts vakuumbehandlingen vid fem förutbestämda tidpunkter. Vid varje avbrott av vakuumbehandlingen togs stål- och slaggprover som analyserades för att bestämma totalsyre, inneslutningsmängd och inneslutningssammansättning. Före vakuumbehandlingen var antalet inneslutningar stort, medan antalet små inneslutningar minskade under vakuumbehandlingen. Däremot konstaterades att antalet stora inneslutningarna (&gt;11.2μm) ökade under avgasningen. Vad beträffar inneslutningssammansättningen syntes en variation i analys före vakuumbehandlingen som sedan förändrades till att likna toppslaggens sammansättning under vakuumbehandlingstiden. I slutet av processen märktes endast en typ av inneslutningssammansättning i stålsmältan. Vad som också noterades var att efter ungefär 10 minuter av vakuumbehandling så hade inneslutningsantalet nått sitt minimumvärde. För att erhålla rent stål är väte-, kväve- och svavelreningen också av stor vikt under vakuumbehandlingen. Dessa tre element studerades genom att prover togs vid olika tillfällen i processen; före, under (vid fem olika förutbestämda tidpunkter) och efter vakuumbehandling. De kemiska sammansättningarna för stål- och slaggproverna användes för att beräkna väte-, kväve- och svavelreningarna. Beräkningarna visade att för väte och kväve så kan kinetiken beskrivas med en förstagradsekvation. Specifikt så gäller detta för stålsorten i studien, samt under förutsättningen att svavelhalten är lägre än 0,003 vikts-%. Dessutom så visade resultaten att väte- och kvävereningen är i stort sett klar för den studerade stålsorten efter 10 minuters vakuumbehandling. När det gäller svavel så kan en förstagradsekvation inte användas vid beräkningarna Istället uppvisar svavel en tendens att följa jämviktshalten av svavel genom hela avgasningsprocessen. Genom att kontrollera processen finns stora möjligheter att erhålla en bra renhet på stålet. Två stålsorter studerades i denna specifika studie, där de hade en liknande processväg samt endast ix några små skillnader i stålanalysen. Stål- och slaggprover samlades in och analyserades. Summan av FeO och MnO visade sig vara en klar indikation på när reoxidation har skett, men mängden "carry-over" slagg från ljusbågsugnen kunde inte predikteras med hjälp av någon specifik indikator. Dessutom så beräknades syreaktiviten och beräkningarna jämfördes sedan med uppmätt syre i stålet. Resultaten indikerar att beräkningar av syreaktivitet med toppslagger som innehåller multivalenselement, såsom Fe och Cr, kräver valideringar med mätningar för att trovärdiga predikteringar ska erhållas. / <p>QC 20160523</p>

In current production systems, automation and handling of workpieces is often solved by use of vacuum technology. Most production systems use vacuum ejectors which generate vacuum from compressed air by means of the Venturi effect. However, producing vacuum with compressed air is significantly less efficient than using other principles. To minimize the energy costs of pneumatic vacuum generation or to make full use of the energy available, it is important that the inner contour of the nozzle is shaped precisely to suit the specific application - also the system\'s flow conduction needs to be optimal and the flow losses have to be minimized. This paper presents a method for optimally designing pneumatic vacuum generators and producing them economically even at very low lot sizes in order to keep the operation costs low and address other concerns (such as noise emissions) as well.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: A tunable narrow-bandwidth vacuum ultra violet laser source was developed and characterised. Two-photon resonant four-wave sum-frequency mixing of two pulsed dye laser beams in magnesium vapour was used to generate the VUV laser light. A heat pipe oven with a concentric design was incorporated to provide a magnesium vapour column of around 30 cm in length with a sufficiently stable temperature and appropriate vapour pressure for efficient VUV production. This is a longer nonlinear medium length than previously produced in our laboratory using a crossed heat pipe oven. The longer medium facilitated the production of VUV laser light of higher intensity than was previously obtainable. High resolution laser induced fluorescence spectra of carbon monoxide in a supersonic gas jet was recorded using the tunable VUV laser light produced in the crossed heat pipe oven. Experimental parameters were optimised and adjusted for the selective detection of the forbidden singlet-triplet transitions which typically have longer lifetimes than singlet-singlet transitions. Transitions from the X¹Σ⁺(v = 0) ground state to the e³Σ⁻( v = 5) triplet state were recorded, and accurate wavelength for the spectral lines were determined. Laboratory wavelengths for these lines have not been measured previously. Accurate wavelength for the weak forbidden spectral lines of CO are important in astrophysical applications, for example determining column densities of interstellar gas clouds. / AFRIKAANSE OPSOMMING: 'n Afstembare smal bandwydte vakuum ultraviolet laser bron is ontwikkel en gekarakteriseer. Twee-foton resonante vier-golf som-frekwensie vermenging van twee gepulseerde kleurstoflaserbundels in 'n magnesium damp is gebruik om die VUV laser lig te produseer. 'n Hittepyp oond met 'n konsentriese ontwerp is in gebruik geneem om a magnesium damp kollom van ongeveer 30 cm in lengte te voorsien waarvan die temperatuur voldoende stabiel is en die dampdruk toepaslik is vir effektiewe VUV produksie. Dit is 'n langer nie-liniêre medium as wat in die verlede deur 'n kruis-hittepyp oond voorsien is. Die langer medium het dit moontlik gemaak om VUV laser lig van hoër intensiteit te produseer as wat tot dusver bereikbaar was. Hoë resolusie laser geinduseerde fluoresensie spektra van koolstof monoksied in a supersoniese gasstraal is opgeneem met die hulp van die afstembare VUV laser lig geproduseer in die kruis-hittepyp oond. Eksperimentele parameters is geoptimeer en verstel vir die selektiewe waarneming van die verbode singlet-triplet oorgange wat tipies langer leeftye besit in vergelyking met singlet-singlet oorgange. Oorgange vanaf die X¹Σ⁺(v = 0) grond toestand na die e³Σ⁻( v = 5) triplet toestand is opgeneem en akkurate golflengtes vir die spektrale lyne is bepaal. Laboratorium golflengtes het tot dusver nie bestaan vir hierdie lyne nie. Akkurate golflengtes vir die swak verbode spektrale lyne van CO het belangrike toepassings in astrofisika soos die bepaling van die kollom digtheid van interstellêre gas wolke.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The large band gap (approximately 11.5-12.1 eV) and high transmission of calcium fluoride (CaF2) crystal in the ultraviolet (UV) and vacuum ultraviolet (VUV) region makes it an important material for optics for laser applications in UV. However, CaF2 degrades during long exposure to UV irradiation due to defect generation. The formation of selftrapped excitons (STE) is considered the first step in defect generation. In this project the possibility of observing STE states in CaF2 using a narrow bandwidth tunable VUV laser source is investigated. This is the first spectroscopy study of an alkaline earth fluoride using VUV tunable laser radiation instead of a fixed wavelength laser. The use of a VUV tunable laser source has potential for determining the energies of the STE states, which are unknown. Our main objective is addressed by developing techniques to measure absorption spectra of pure and doped CaF2 samples, using a VUV scanning monochromator and a tunable VUV laser, and by doing a literature study. The results obtained with the scanning monochromator show absorption features in 126-180 nm range of all our samples. These vary for different samples and correlate with information from the supplier on the samples’ fluorescence spectra. Total absorption of the VUV light by CaF2 in the 115-126 nm range is observed. With the narrow bandwidth tunable laser light, absorption spectra were obtained in the range of 143-146.7 nm of all our CaF2 samples. No significance peaks which can be related to the STE states in CaF2 were observed in the VUV laser absorption spectra, but the results are valuable to improve the technique. The conclusion is that either a different spectral range or fluorescence detection can be investigated in future. / AFRIKAANSE OPSOMMING: Die groot bandgaping (ongeveer 11.5-12.1 eV) en hoë transmissie van kalsiumfluoried (CaF2) kristal in die ultraviolet (UV) en die vakuum ultraviolet (VUV) gebied maak dit ’n belangrike materiaal vir optika vir laser toepassings in die UV. CaF2 degradeer egter gedurende langdurige blootstelling aan UV lig as gevolg van die generering van defekte. Die vorming van ’n elektron-holte paar wat deur die kristalstuktuur gestabiliseer word teen rekombinasie (self-trapped excitons, afgekort STE) word beskou as die eerste stap in defek generering. In hierdie projek word die moontlikheid ondersoek om STE toestande in CaF2 waar te neem deur die gebruik van ’n afstembare VUV laserbron met emissie in ’n smal spektrale band. Dit is die eerste spektroskopiese studie van ’n aardalkali-fluoried deur die gebruik van afstembare VUV laserlig in plaas van ’n vaste golflengte laser. Die gebruik van ’n afstembare VUV laserbron het potensiaal vir die bepaling van die energieë van die STE teostande, wat onbekend is. Ons hoofdoel word aangespreek deur die ontwikkeling van tegnieke vir die meet van absorpsie spektra van suiwer en gedoteerde CaF2 monsters met behulp van ’n VUV skanderende monochromator en ’n afstembare VUV laser, en deur ’n literatuurstudie. Die resultate wat behaal is met die skanderende monochromator toon die absorpsieprofiele van al ons monsters in die 126-180 nm spektrale gebied. Die absopsieprofiele varieer vir die verskillende monsters en korreleer met die inligting van die verskaffer oor die fluoressensie spektra van die monsters. Totale absorpsie van die VUV lig deur CaF2 in die 115-126 nm gebied is waargeneem. Met die smalband afstembare laserlig is absorpsie spektra in die 143-146.7 nm gebied vir al ons CaF2 monsters verkry. Geen beduidende pieke wat verband hou met die STE toestande in CaF2 is waargeneem in die VUV laser absorpsie spektra nie, maar die resultate is waardevol vir die verbetering van die tegniek. Die gevolgtrekking is dat of ’n ander spektraalgebied of fluoressensiedeteksie in die toekoms ondersoek kan word.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: According to recent studies, biochar has the potential to improve soil fertility, mitigate climate change, reduce off-site pollution and assist in managing wastes. The application of biochar to soil is not a new concept; Amazonian dark earths are carbon-rich soils with high soil fertility that were created before 1541. Vacuum pyrolysis is a thermo-chemical conversion technique in which biomass is transformed into bio-oil, biochar and non-condensable gas. The objective of this work was to investigate the chemical and physical properties of biochar produced from vacuum pyrolysis of black wattle, vineyard annual prunings and sugar cane bagasse for their potential as soil amendment and adsorbent. The vacuum pyrolysis of black wattle, vineyard prunings and sugar cane bagasse (pyrolysis temperature: 460°C, pressure: 8kPaabs, heating rate: 17°C/min) resulted in biochar yields of 23.5%, 31.0% and 19.7% on a weight basis, respectively. The nature of the biomass had a substantial effect on yields of the products. High ash content combined with high lignin composition led to higher biochar yields for vineyard prunings. The highest surface acidity was observed for sugar cane bagasse (2.3 mmol/g), whereas the lowest surface acidity was observed for vineyard biochar (1.67 mmol/g). Consequently, the pH of the biochars was in the order: vineyard (10.43)> black wattle (9.74)> sugar cane bagasse (6.56). The cation exchange capacities (CEC) of biochars were 122 cmol/kg, 101 cmol/kg and 65 cmol/kg for sugar cane bagasse, black wattle and vineyard, respectively. The electrical conductivities (EC) were highly correlated with feedstock nature. The Ca and K rich vineyard biochar resulted in the highest EC (0.83 dS/m), whilst EC values of black wattle and sugar cane bagasse were 0.67 dS/m and 0.17 dS/m, respectively. Biochars contained substantial amounts of plant-available nutrients, while being low in toxic inorganic content (Pb, As, Cd). The BET surface areas of sugar cane bagasse, black wattle and vineyard were 259 mª/g, 241 mª/g and 91 mª/g, respectively. The adsorption capacity was found to increase with increased contact time and initial solution concentration. The experimental equilibrium time were found to be 3505 min, 1350 min and 150 min for adsorption of 20 mg/L methylene blue solution for vineyard, black wattle and sugar cane bagasse, respectively. Equilibrium data were well fitted to Langmuir and Freundlich isotherms. The maximum adsorption capacities were found to be 15.15 mg/g, 14.49 mg/g and 19.23 mg/g for vineyard, black wattle and sugar cane bagasse when modelled with Langmuir isotherms. The adsorption kinetics was found to follow the pseudo-second order kinetic model. In summary, biochar from sugar cane bagasse is a promising adsorbent for the removal of basic dyes due to its high surface area and microporous structure. This biochar can be applied to slightly acidic soils for nutrient retention and the exchange of nutrients. On the other hand, possessing high amounts of nutrients, biochars from black wattle and vineyard are potential soil amendentment agents. Biochar from black wattle is more beneficial compared to biochar from vineyard due to its higher surface area, microporosity and cation exchange capacity. / AFRIKAANSE OPSOMMING: Volgens onlangse studies, het houtskool die potensiaal om grond vrugbaarheid te verbeter, klimaat verandering te versag, besoedeling te verlaag en ondersteuning te verleen in die bestuur van afval. Die toevoeging van houtskool in grond is nie ‘n nuwe konsep nie; Amazone donker gronde is koolstof ryk gronde met hoë vrugbaarheid wat voor 1541 geskep is. Vakuum pirolise is ‘n termo-chemiese omskakelings tegniek waarin biomassa afgebreek word na bio-olie, houtskool en nie-kondenseerbare gasse. Die doelwit van hierdie werk was om die chemiese en fisiese eienskappe van houtskool, wat geproduseer is deur die vakuum pirolise van swart wattel, jaarlikse wingerd snoeisels, en suikerriet bagasse, vir hulle potensiaal vir grond verbetering en adsorpsie toepassings te ondersoek. Die vakuum pirolise van swart wattel, jaarlikse wingerd snoeisels, en suikerriet bagasse (pirolise temperatuur: 460°C, druk: 8kPaabs, verhittingstempo: 17°C/min) het houtskool opbrengste van 23.5%, 31.0% en 19.7% op massa basis, respektiewelik tot gevolg. Die tipe biomassa het ‘n beduidende effek op die opbrengs van die produkte. Hoë as-inhoud, gekombineer met hoë lignien inhoud, lei tot hoër houtskool opbrengste vir wingerd snoeisels. Die hoogste oppervlak suurheid is gevind vir suikerriet bagasse (2.3 mmol/g), terwyl die laagste waarde gevind is vir die wingerd snoeisels (1.67 mmol/g). Gevolglik, is die pH van die houtskole in die volgorde van: wingerd (10.43) > swart wattle (9.74) > suikerriet bagasse (6.56). Die katioon uitruiling vermoë (CEC) van die houtskole was 122 cmol/kg, 101 cmol/kg and 65 cmol/kg vir suikerriet bagasse, swart wattel en wingerd snoeisels respektiewelik. Die elektriese konduktiwiteite (EC) is gekorreleer met die eienskappe van die biomassas. Die Ca en K ryke wingerd snoeisel houtskool het die hoogste EC waarde (0.83 dS/m) tot gevolg, terwyl die EC waardes vir swart wattel en suikerriet bagasse bepaal is as 0.67 dS/ 0.16 dS/m respektiewelik. Die houtskole het groot hoeveelhede plant-beskikbare voedingstowwe bevat, terwyl dit laag was in toksiese anorganiese stowwe (Pb, As, Cd). Die BET oppervlak areas van suikerriet bagasse, swart wattel en wingerd snoeisels was 259 mª/g, 241 mª/g en 91 mª/g respektiewelik. Daar is gevind dat die adsorpsie kapasiteit toeneem met toenemende kontak tyd met die aanvanklike oplossing. Die eksperimentele ewewigs tye is gevind as 350 min, 1350 min en 150 min vir die adsorpsie van ‘n 20 mg/L metileen blou oplossing vir wingerd snoeisels, swart wattel en suikerriet bagasse, respektiewelik. Die ewewigs data het die Langmuir en Freundlich isoterme goed gepas. Die maksimum adsorpsie kapasiteite is gevind as 15.15 mg/g, 14.9 mg/g en 19.23 mg/g vir wingerd snoeisels, swart wattel en suikerriet bagasse wanneer dit gemodeleer is met Langmuir isoterme. Daar is bevind dat die adsorpsie kinetika ‘n pseudo-tweede orde kintika model volg. In opsomming, houtskool van suikerriet bagasse is ‘n veelbelowende adsorpsie middel vir die verwydering van basiese kleurstowwe, as gevolg van die hoë oppervlak area en mikroporie-struktuur van hierdie houtskool. Dié houtskool kan gebruik word op effense suur gronde vir voedingstof behoud en uitruiling. Aan die ander kant, houtskole van swart wattel en wingerd snoeisels wat hoë hoeveelhede voedingsstowwe bevat, is potensiële grond verbeterings middels. Houtskool afkomstig van swart wattel is meer voordelig as die van wingerd snoeisels, as gevolg van die hoër oppervlak area, mikroporositeit en katioon uitruilings vermoë van die swart wattel houtskool.

Thesis (PhD (Physics))--University of Stellenbosch, 2006. / Carbon monoxide (CO) is a diatomic molecule of particular interest in astrophysics, due to its high abundance in interstellar space. The Fourth Positive System A1Π−X1Σ+ of CO is an important feature in the vacuum ultraviolet (VUV) region of the electromagnetic spectrum in astronomical observations, especially in high-resolution spectra recorded by satellite-based spectrographs. The interpretation of these astronomically detected spectra requires accurate laboratory wavelengths to serve as rest wavelengths and to resolve possible Doppler-shifts. Such rest wavelengths are known for the 12C16O, 13C16O and 12C18O isotopomers for all astronomically observed spectral lines of the Fourth Positive System. The only laboratory wavelengths currently available for the Fourth Positive System of the 12C17O isotopomer have been determined in a previous work carried out in our laboratory for the vibronic band A1Π(v0 = 3)−X1Σ+(v00 = 0). The present study continues this work for the other vibronic bands which have been detected astronomically, namely A1Π(v0 = 2 − 5)−X1Σ+(v00 = 0). The A1Π(v0 = 0− 1)−X1Σ+(v00 = 0) vibronic bands have also been investigated due to their probability for future astronomical detection. Rotationally-resolved spectra of these six vibronic bands were obtained by selective rovibronic laser excitation, and subsequent detection of the undispersed fluorescence, observed as a function of the excitation wavelength in the VUV. A tunable narrow-bandwidth VUV laser source is used for excitation, and the CO gas sample is introduced by supersonic expansion. Flow-cooling in the supersonic expansion to rotational temperatures roughly corresponding to temperatures in the interstellar medium simplifies and aids the spectral analysis of the spectral lines of interest. The cold conditions in the supersonic expansion facilitates a high sensitivity for detection of the low-J lines, and allows the detection of rare isotopomers of CO in natural abundance. The experimental setup has been improved in the present study by the addition of a vacuum monochromator, facilitating an improved characterisation of the VUV source. Furthermore, a number of experimental conditions have been optimised for the detection of rare CO isotopomers, significantly increasing the signals of these lines in the spectra. The combination of this increase in sensitivity and the addition of the vacuum monochromator to the experimental setup, allowed the simultaneous detection of absorption spectra with the fluorescence spectra as an additional source of information in spectral analysis. The increased sensitivity also contributed to the detection of a large number of spectral lines of interest, with some additional lines identified in the previously studied vibronic band. Spectral lines of 12C16O, 13C16O, 12C18O and 12C17O were detected in each vibronic band, allowing accurate calibration of the spectra. A total of 29 new lines of 12C17O were recorded in the six vibronic bands investigated. Additionally, 10 new singlet-triplet lines of 12C16O were recorded in the wavelength regions investigated. The new wavelengths of 12C17O have been applied to calculate consistent heliocentric velocities of a gas cloud toward the star X Persei, obtained from spectra of the different CO isotopomers taken by the Hubble space telescope.