Es wurden die Zusammenhänge zwischen den Herstellungsbedingungen und dem nanostrukturellen Aufbau von Multischichten, mit Rücksicht auf das mechanische Verhalten aufgeklärt. Dazu wurden durch plasmaunterstützte Gasphasenabscheidung (PACVD) Hartmetallsubstrate mit Viellagen beschichtet und vorrangig mittels analytischer Transmissionselektronenmikroskopie (TEM) charakterisiert. Als Schichkomponenten wurden hauptsächlich TiN und Al2O3 untersucht, daneben aber auch Schichtsysteme der Komponenten AlON, (TiAl)N, und (Ti,Al)ON. Darüber hinaus wurden noch TiC-aC (TiC mit amorphem Kohlenstoffanteil)-Schichten einbezogen. Ziel waren gleichmäßige Multischichten mit Korngrößen von einigen Nanometern, geringer Testur und geringer Mikrorissdichte, die hart sind und gut haften. Die TEM-Untersuchungen dienten insbesondere der Aufklärung der Nanostruktur in den Interface-Bereichen der Schichtsysteme, wobei an Hand der Elektronenenergie-Verlustspektroskopie (EELS) sowohl element- als auch phasenspezifische Signale ausgewertet wurden. Zur verbesserten Bewertung der anfallenden Datenmengen wurden z. T. faktoranalytische Methoden eingesetzt. Je nach Prozessführung der Schichtherstellung kommt es in den Interface-Bereichen zur Durchmischung der Komponenten. Insbesondere führt diffundierender Sauerstoff zur Bildung von TiO2, was sich nachteilig auf die Qualität der Schichten auswirkt. Die Tiefe der "gestörten" Zonen begrenzt die wünschenswerte Verringerung der Einzelschichtdicken. Als wirkungsvolle Gegenmaßnahme hat sich der Einbau von Kohlenstoff erwiesen, wodurch sich dünnere Einzelschichten verwirklichen lassen.

Abstract: Micro­Raman Spectroscopy Investigation of Hard Coatings Diamond, silicon carbide, and boron nitride have attracted great interest in the last years, due to their excellent material properties. Especially the extreme hardness and the high thermal con­ ductivity of these materials favour them as protective layers. The very large hardness gave these materials, deposited as films on various substrates, their name: hard coatings. In contrast to di­ amond, silicon carbide and boron nitride can be n­ as well as p­doped, making them promising candidates for high speed and high temperature electronic applications. Contrarily to the materials mentioned above, carbon nitride was obtained in crystalline form just very recently. Up to now the deposited films mainly consist of amorphous or nanocrystalline, carbon­rich material. For all these material systems inelastic light scattering (Raman spectroscopy) has been already applied for the material properties investigation. However, these investigations usually were restricted to only one of the various Raman spectroscopy tools, described in this work: Incident laser light energy varia­ tion, temperature variation, utilizing the selection rules, measurements at varying sample positions, two­dimensional mappings and one­dimensional scans in the conventional plane­view and the addi­ tional cross­sectional sample geometry. In contrast to this, this work demonstrates the improvement of the information about the investigated material and/or the sample heterostructure obtained by using the combination of all the above mentioned techniques. In the case of the diamond material system, films deposited on silicon substrates were investigated and an interfacial graphitic layer of 2nm thickness was found by scanning across the interface, which was obscured in the conven­ tional plane­view sample geometry. Similar to this an ultra­thin top layer and buried intermixed regions were identified in the silicon carbide material system utilizing the cross­sectional sample geometry. In addition to this, the temperature and the incident laser light energy dependences for 5 SiC polytypes (3C, 4H, 6H, 15R, and 21R) were measured. A resonance enhancement for the 3C and the 21R polytype was found corresponding to their fundamental bandgaps at 2.46eV and ß2.8eV, respectively. For the other polytypes no resonance enhancement was found, due to their larger fundamental bandgap. In the boron nitride material system the spatial correlation model for Raman lineshape analysis was applied for the first time and the values of the asymmetric broad­ ening and the frequency downshift for decreasing crystal sizes were evaluated. This was measured for single crystals of different size and for films deposited on silicon substrates. The correlation lengths in the ten nanometer region found for the deposited films corroborate the nanocrystalline nature of these films. Additionally incident laser light energy was measured, revealing the 488.0nm (Ar + ) and 482.5nm (Kr + ) laser lines as the optimum laser lines for the boron nitride investigation. Furthermore the dependence of the phonon feature parameters was investigated depending on the incident laser light power. A maximum power of 5­10mW for the micro­Raman spectroscopy setup was found to avoid any laser light induced heating of the investigated material. Two­dimensional mappings of the deposited boron nitride films were performed to improve the information about the material system. In the case of carbon nitride for the first time distinct phonon features were measured in a wide spectral range contrarily to most of the other investigations, which usually show only broad bands.

In der Milchindustrie spielt die Auswahl der Starterkulturen eine wichtige Rolle bei der Herstellung fermentierter Produkte mit gewünschter Textur und entsprechenden sensorischen Eigenschaften. Milchsäurebakterien mit der Fähigkeit extrazelluläre Polysaccharide (EPS) zu synthetisieren sind von besonderem Interesse, da auf Grund der in situ gebildeten Hydrokolloide der Einsatz von Zusatzstoffen vermieden werden kann. Die Wirkung von EPS auf die Produkt-eigenschaften ist in der Literatur bereits mehrfach beschrieben, wird jedoch auf Grund der Vielzahl an unterschiedlichen Stämmen und Fermentationsparametern bzw. einer fehlenden Systematisierung immer noch sehr kontrovers diskutiert. Des Weiteren stellt die wissenschaftliche Aufklärung der komplexen Struktur-Funktionsbeziehungen und der Wechselwirkungen mit anderen Produktkomponenten eine große Herausforderung dar. Um die Zusammenhänge besser verstehen zu können, wurde in dieser Arbeit ein neuer Ansatz gewählt: isolierte und aufgereinigte EPS wurden der Milch vor der Säuerung zugesetzt und die daraus hergestellten Milchgele mit jenen mit in situ produzierten EPS verglichen. In Milchgelen aus Einzelstammkulturen von Streptococcus thermophilus oder Lactobacillus delbrueckii ssp. bulgaricus wurden EPS‑Gehalte von 40 - 150 mg/kg ermittelt. Die Gele unterschieden sich hinsichtlich ihrer Viskosität und ihres fadenziehenden Charakters, was erste Hinweise auf die Art der gebildeten EPS liefert. Die Synthese größerer Mengen an EPS zur Charakterisierung und Untersuchung ihrer Funktionalität erfolgte entkoppelt von der Produkt­herstellung mit ausgewählten Stämmen in Batch-Fermentationen mit konstantem pH in komplexen oder semidefinierten Medien. S. thermophilus ST‑143 produzierte ~ 300 mg/L fadenziehende EPS, die durch entsprechende Aufreinigungsschritte als drei EPS‑Fraktionen gewonnen werden konnten: freie EPS (EPSf), kapsuläre EPS (EPSk) und ein Gemisch aus beiden (EPSf+k). EPSf haben eine höhere Molekülmasse (M = 2,6 x 10^6 Da) und eine höhere intrinsische Viskosität (1,14 mL/mg) im Vergleich zu EPSk (M = 7,4 x 10^3 Da, 1,4 x 10^5 Da; intrinsische Viskosität = 0,06 mL/mg) und führten bereits in geringen Mengen zu rheologischen Veränderungen. Allerdings scheinen die EPSk Wechselwirkungen zwischen EPSf Molekülen zu unterstützen. In chemisch gesäuerten Milchgelen konnte durch den definierten Zusatz aufgereinigter Fraktionen von EPSf und EPSf+k vor der Säuerung (c = 0 - 0,35 mg/g) erstmals eine konzentrationsabhängige Wirkung aufgezeigt werden. Mit EPSf stieg der maximale Speichermodul der Milchgele als Maß für die Gelsteifigkeit linear an (457 - 722 Pa). EPSk zeigten hingegen keinen Einfluss. Als Modellpolysaccharid wurde vergleichend das gut beschriebene, ebenfalls ungeladene und nicht gelbildende Homopoly­saccharid Dextran herangezogen (c = 0 - 300 mg/g). EPSf und Dextran veränderten die Gelbildung, erhöhten die Steifigkeit stichfester Gele und die Viskosität gerührter Gele in ähnlichem Maße, es waren jedoch deutlich unterschiedliche Konzentrationen notwendig. Die in den Milchgelen beschriebenen Einflüsse können unter anderem auf Depletionseffekte zwischen gleichgeladenen Polymeren (hier Proteine und Polysaccharide) zurückgeführt werden. / The selection of suitable starter cultures for the production of fermented milk with a desired texture and corresponding sensory attributes is of great importance for the dairy industry. Lactic acid bacteria with the ability to synthesise extracellular polysaccharides (EPS) are of particular interest, because these in situ produced hydrocolloids may allow to omit the use of additives. Many effects of EPS on product properties are already described in the scientific literature, but are still discussed controversially because of the multitude of different strains and fermentation parameters and, hence, a lack of systematisation. Furthermore, research on the mechanisms behind the structure-function relationship and interactions with other product components is a challenging area. To obtain a deeper understanding of this complex system, a new approach was chosen for the present study: EPS were isolated, purified and added to the milk prior to acidification, and the respective milk gels were compared with those with in situ produced EPS. In milk gels acidified by single strains of Streptococcus thermophilus or Lactobacillus delbrueckii ssp. bulgaricus, EPS contents of 40 - 150 g/kg were determined. The gels differed in viscosity and their ropy character, which is a first indicator for the type of the EPS. To allow for their chemical and technofunctional characterisation, the synthesis of higher amounts of EPS was performed by batch-fermentation at constant pH and decoupled from the product manufacturing with selected strains in complex or semidefined media. S. thermophilus ST‑143 synthesised ~ 300 mg/L ropy EPS, which were isolated as three different EPS fractions by applying particular purification steps: free EPS (EPSf), capsular derived EPS (EPSk) and a mixture of both EPS (EPSf+k). EPSf had a higher molecular mass (M = 2.6 x 10^6 Da) and a higher intrinsic viscosity (1.14 mL/mg) compared to EPSk (M = 7.4 x 10^3 Da, 1.4 x 10^5 Da; intrinsic viscosity = 0.06 mL/mg) and affected the rheological properties of aqueous solutions already at low concentration. However, EPSk appear to support interactions between the EPSf molecules. In chemically acidified milk gels a concentration dependent impact of EPSf and EPSf+k, which were added to the milk prior to acidification (c = 0 - 0,35 mg/g), was described for the first time. The maximum of the storage modulus as a measure for stiffness of the milk gels linearly increased with EPSf content (457 - 722 Pa). With EPSk no effects were observed. For the purpose of comparison dextran, a well described also uncharged and non gelling homopolysaccharide, was used as a model polysaccharide (0 - 300 mg/g). EPSf and dextran affected the gelation, increased gel stiffness of set gels and viscosity of stirred gels to a similar way, but the concentrations needed for that found to be completely different. The effects described for milk gels can be ascribed among others to depletion interactions between similar charged polymers (here proteins and polysaccharides).

This thesis examines the use of electrochemically treated viscose rayon based activated carbon cloth (ACC) for the removal of metal ions from aqueous effluent streams. Two types of treatment were performed: (i) electrochemical oxidation and (ii) electrochemical reduction to enhance cation and anion sorption capacities of the ACC, respectively. Electrochemical oxidation resulted in a loss of 61% BET surface area due to blockage of pores through formation of carboxylic acidic groups but its cation exchange capacity and oxygen content increased by 365% and 121%, respectively. The optimum constant current at which a combination of applied current and oxidation time at any extent of oxidation to produce ACC of maximum cation exchange capacity was found to be 1.1 A, with voltage of 4.2 V and current density of 0.8 mA/m2. Batch sorption experiments showed that the maximum copper and lead sorption capacities for electrochemically oxidised ACC increased 17 and 4 times, respectively, for noncompetitive sorption and 8.8 and 8.6 times, respectively for competitive sorption. Therefore, electrochemically oxidised ACC is an effective adsorbent for treating aqueous solution contaminated with copper/lead in both single component and multi-component systems. Industrial wastewaters are multicomponent systems, therefore, electrochemical oxidation of ACC is an efficient way of enhancing lead and copper ions sorptive capacity for industrial wastewater treatment. Electrochemical reduction resulted in a loss of 28% BET surface area due to formation of ether groups but its anion exchange capacity increased by 292%. The optimum constant current at which a combination of applied current and reduction time at any extent of reduction to produce ACC of maximum anion exchange capacity was found to be 5.5 A, with voltage of 9.8 V and current density of 6.4 mA/m2. Batch sorption experiments showed that the maximum chromium(VI) sorption capacity for electrochemically reduced ACC increased 2.12 times, with highest maximum chromium(VI) sorption capacity of 3.8 mmol/g at solution pH 4. Most industrial wastewaters contaminated with chromium(VI) are highly acidic, therefore, electrochemical reduction of ACC is an efficient way of enhancing chromium(VI) sorptive capacity for industrial wastewater treatment.

This study is aimed at investigating the feasibility of using the radiometric technique as an alternative to traditional methods for determining soil physico-chemical parameters which are important for terroir characterization. In-situ and ex-situ radiometric analyses of soil from three vineyard blocks of Simonsig Wine Estate in the Stellenbosch district (Western Cape, South Africa) were studied. A mobile MEDUSA gamma-ray detection system comprising a CsI(Na) crystal (length 15 cm, diameter 7 cm) and associated electronics mounted on a portable trolley were used for partial terroir characterisation. Thereafter activity concentrations of 40K, 232Th series and 238U series in soil (top ~30 cm) from the measured MEDUSA spectra (0 – 3 MeV) were extracted by means of the full-spectrum analysis (FSA) method. A lead-shielded HPGe detector was used for analyzing collected soil samples while soil physico-chemical parameters were analysed using standard methods at research and commercial laboratories.

An importantmatter in the field of building physics is the questioning of how wellbuildings sustain ageing, and how their overall efficiency evolves over their lifetime.Many causes for degradation are carried by moisture transfer through these porousmaterials. Indeed, infiltratedwatermay transport chemicals, altermechanical properties,and cause freeze thaw damage or mould development. It may also affect thermalproperties and energetic efficiency, as well as the health and comfort of the occupants.The understanding of how moisture transfer properties evolve during the lifespan ofbuildingmaterials is however far fromcomplete. The pore structure of amaterial itselfmay change over time, or be altered by cracks and defects caused bymechanical loadingand aggravated bymoisture-induced degradation. All sizes of fracturesmay have astrong impact on heat and moisture flow in the building envelope, and their influenceis to be accounted for in any long-termperformance assessment, not only of buildingand building components,but of any built structure in general. A considerable amountof work has already been performed in order to allow predicting the hygrothermal behaviourof buildings over longer periods of time. However, an accurate prediction of allranges of damage in a building component, from microscopic to macroscopic cracks,supposes an extensive knowledge of all damage-inducing, time-varying boundary conditionsof the problem during the simulation time. This also implies high computationalcosts, as well as important needs formaterial characterisation.As a complement to these predictive methods, a new approach was undertaken,combining experimental characterisation of crack patterns and numerical simulationsof coupled heat and moisture transfer. First, a preliminary study was conducted, consistingof measurements of the water vapour permeability of diffusely damaged constructionmaterials.This allowed identifying the experimental and numerical requirementsof the remainder of the work, which aimed at providing measurements of fracturenetwork geometries for their explicitmodelling in heat andmoisture transfer simulations.Digital image correlation and acoustic emission monitoring were then performedduring the degradation of cementitiousmaterials, in order to obtain quantitativedata on crack pattern geometries, and to assess the possibilities for damagemonitoringat the building scale. The optical technique, along with an appropriate imageprocessing procedure, was found suitable for providing precisemeasurements of fracturenetworks. Amethodwas also proposed for the interpretation of acoustic emissionrecordings in terms of damage quantification, localisation and identification.Then, a newmodel for coupled heat andmoisturemodelling in cracked porousmediawas developed, that allows including such measurements of fracture patterns intoa finite element mesh, and simulating flow accordingly. This model was validated onthe basis of experimentalmeasurements: digital image correlationwas performed duringthe fracturing of concrete samples, in which moisture uptake was then monitoredusing X-ray radiography. A good accordance was found between experimental and numericalresults in terms of 2-dimensional moisture concentration distributions. The validated code was then used for the simulation of test cases, in order to assess the hygrothermalperformance of damagedmulti-layered building components subjected toreal climatic conditions. The consequences of fractures on themoisture accumulationin walls, on the amplitude of sorption/desorption cycles and on the thermal performance,were observed.

The need to characterise a PEM electrolyser is motivated by a South African hydrogen company. One of two electrochemical characterisation methods, namely the current interrupt method or electrochemical impedance spectroscopy, is investigated to characterise the PEM electrolyser. Various literature sources can be found on the electrochemical characterisation methods. In this study the current interrupt method is used for the electrochemical characterisation of a PEM electrolyser. The current interrupt method is an electrical test method that will be used to obtain an equivalent electric circuit model of the PEM electrolyser. The equivalent electric circuit model relates to various electrochemical characteristics such as the activation losses, the ohmic losses and the concentration losses. Two variants of the current interrupt method, namely the natural voltage response method and the current switching method, are presented. These methods are used to obtain two different equivalent electric circuit models of the PEM electrolyser. The parameters of the first equivalent electric circuit, namely the Randles cell, will be estimated with the natural voltage response method. The parameters of the second equivalent electric circuit, namely the Randles-Warburg cell, will be estimated with the current switching method. Simulation models of the equivalent electric circuits are developed and tested. The simulation models are used to verify and validate the natural voltage response method and the current switching method. The parameters of the Randles cell simulation model is accurately calculated with the natural voltage response method. The parameters of the Randles-Warburg cell simulation model is accurately calculated with the current switching method. The natural voltage response method and the current switching method are also practically implemented. The results is used to indicate the various electrochemical characteristics of the PEM electrolyser. A Nafion 117 type membrane was tested with the current interrupt method. The membrane resistance parameters of Randles cell were estimated with the natural voltage response method. These values are validated with conductivity measurements found in literature. The results of the Randles- Warburg cell is validated with a system identification validation model. / Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013

The need to characterise a PEM electrolyser is motivated by a South African hydrogen company. One of two electrochemical characterisation methods, namely the current interrupt method or electrochemical impedance spectroscopy, is investigated to characterise the PEM electrolyser. Various literature sources can be found on the electrochemical characterisation methods. In this study the current interrupt method is used for the electrochemical characterisation of a PEM electrolyser. The current interrupt method is an electrical test method that will be used to obtain an equivalent electric circuit model of the PEM electrolyser. The equivalent electric circuit model relates to various electrochemical characteristics such as the activation losses, the ohmic losses and the concentration losses. Two variants of the current interrupt method, namely the natural voltage response method and the current switching method, are presented. These methods are used to obtain two different equivalent electric circuit models of the PEM electrolyser. The parameters of the first equivalent electric circuit, namely the Randles cell, will be estimated with the natural voltage response method. The parameters of the second equivalent electric circuit, namely the Randles-Warburg cell, will be estimated with the current switching method. Simulation models of the equivalent electric circuits are developed and tested. The simulation models are used to verify and validate the natural voltage response method and the current switching method. The parameters of the Randles cell simulation model is accurately calculated with the natural voltage response method. The parameters of the Randles-Warburg cell simulation model is accurately calculated with the current switching method. The natural voltage response method and the current switching method are also practically implemented. The results is used to indicate the various electrochemical characteristics of the PEM electrolyser. A Nafion 117 type membrane was tested with the current interrupt method. The membrane resistance parameters of Randles cell were estimated with the natural voltage response method. These values are validated with conductivity measurements found in literature. The results of the Randles- Warburg cell is validated with a system identification validation model. / Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013

The correct administration of insulin is a constant challenge for type 1 diabetics. The correct insulin regime leads to fewer complications and an easier way of life. The amount of insulin administered must take into account the meals eaten, previous administered insulin, exercise etc. A rapid process for determining insulin regimes that is accessible to type 1 diabetics will greatly reduce diabetic complications later in life. This study researches such a process. Software is developed to use the ets-concept to simulate blood glucose levels. From these simulations blood glucose characterisation can be done to propose insulin regimes. Data gathered in previous studies is used to verify the results of this process. These results are compared to factors that describe the accuracy of a person's blood glucose control. The effects the new regimes will have are used to make recommendations to the end-user. Accurate characterisation leads to insulin regImes that will Improve the control performance of type 1 diabetes. / Thesis (M.Ing. (Electronical Engineering)--North-West University, Potchefstroom Campus, 2008.

The correct administration of insulin is a constant challenge for type 1 diabetics. The correct insulin regime leads to fewer complications and an easier way of life. The amount of insulin administered must take into account the meals eaten, previous administered insulin, exercise etc. A rapid process for determining insulin regimes that is accessible to type 1 diabetics will greatly reduce diabetic complications later in life. This study researches such a process. Software is developed to use the ets-concept to simulate blood glucose levels. From these simulations blood glucose characterisation can be done to propose insulin regimes. Data gathered in previous studies is used to verify the results of this process. These results are compared to factors that describe the accuracy of a person's blood glucose control. The effects the new regimes will have are used to make recommendations to the end-user. Accurate characterisation leads to insulin regImes that will Improve the control performance of type 1 diabetes. / Thesis (M.Ing. (Electronical Engineering)--North-West University, Potchefstroom Campus, 2008.