Additives, incorporated in film coating formulations, and their process parameters are generally selected using a trial-and-error approach. However, coating problems and defects, especially those associated with aqueous coating systems, indicate the necessity of embracing a quality-by-design approach to identify the optimum coating parameters. In this study, the feasibility of using thermal and rheological measurements to help evaluate and design novel coating formulations has been investigated. Hydroxypropyl methylcellulose acetate succinate (HPMCAS), an enteric coating polymer, was used as the film forming polymer. Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), and Parallel Plate Shear Rheometery (PPSR) were used to evaluate the effect of different plasticisers on the performance of HPMCAS. The results illustrate that, for identical formulations, the DSC and DMA methods yielded up to 40% differences in glass transition temperature (Tg) values. Moreover, Tg measured using loss modulus signals were always 20-30 oC less than those measured using tan delta results in DMA testing. Absolute and relative Tg values can significantly vary depending on the geometry of the samples, clamp size, temperature ramping rate and the frequency of the oscillations. Complex viscosity data for different formulations demonstrated a variable shear thinning behaviour and a Tg independent ranking. It is, therefore, insufficient to rely purely on Tg values to determine the relative performance of additives. In addition, complex viscosity results, obtained using both the DMA and PPSR techniques at similar temperatures, are shown to be comparable. The results from both techniques were therefore used to produce continuous master curves for the HPMCAS formulations. Additionally, step strain tests showed that HPMCAS chains do not fully III disentangle after 105 seconds as predicted by the Maxwell model. Finally, in situ aqueous-based coating experiments proved that mixtures of triethyl acetyl citrate and acetylated monoglyceride (TEAC/AMG), even without cooling of the suspension, do not cause blocking of the spray nozzle whereas triethyl citrate (TEC) based formulae did. TEAC (alone or in a combination with AMG) exhibits superior wettability to HPMCAS than TEC/AMG formulations and can be used to enhance the efficiency and film quality of the dry coating process.

The present thesis is devoted to the investigation of novel superconductors by phase-sensitive terahertz transmission and infrared to ultraviolet spectroscopy. In particular, a nominally undoped Pr2CuO4 superconducting thin film, an FeTe0.5Se0.5 thin film, and a LiFeAs single crystal have been investigated. The emphasis is on the low-frequency part of the optical spectrum (i.e., the terahertz and infrared spectrum), as the goal of the study was to shed light on the size and symmetry of the superconducting gaps and also to determine the temperature dependences as well as the absolute values of the penetration depth, which are key input parameters for models applicable for new superconductors. In addition, niobium has been investigated as a reference, so as to see what is expected from conventional superconductors and to clarify the electrodynamics of niobium. A superconducting Nb thin film with Tc of 8.04 K has been investigated by backward wave oscillator-based (BWO-based) and time-domain terahertz (TDT) spectrometers in the frequency range between 4 and 100 cm−1 for temperatures ranging from 2 to 10 K. From these measurements an energy gap of 22.50 cm−1 = 2.79 meV = 4.02kBTc have been determined. The optical conductivity below Tc could nicely be described by calculations according to the Eliashberg theory, with the electron-phonon interaction evaluated from tunneling measurements. Absolute values of the penetration depth have been calculated from phase-sensitive terahertz measurements. The zero-temperature limit of at T = 0 is found to be 115 ± 5 nm. From this value, a London penetration depth of 43 ± 2 nm has been obtained. The overall temperature dependence of the penetration depth follows a behavior typical for conventional s-wave superconductors. A superconducting Pr2CuO4 film with T0 structure and Tc of 27 K has been investigated by use of optical methods in a wide frequency (5 – 55000 cm−1) and temperature (2 – 300 K) range. A Drude-like peak centered at zero frequency is observed in the optical conductivity below 150 K, above which it shifts to finite frequencies. The detailed analysis of the low-frequency conductivity reveals that the Drude peak and a far-infrared (FIR) peak centered at about 300 cm−1 persist at all temperatures. The FIR spectral weight is found to grow at the expense of the Drude spectral weight with increasing temperature. Absolute values of the penetration depth have been obtained from temperature and frequency-dependent measurements. The zero-temperature limit of is estimated to be 1600 ± 100 nm. The overall temperature dependence of follows a behaviour typical for cuprate superconductors. However, a closer look at the penetration depth at T 12 K reveals a flattening in the temperature dependence. A superconducting FeTe0.5Se0.5 thin film with Tc = 19 K has been investigated using a combination of BWO and TDT spectroscopy in the frequency range 4 - 80 cm−1 and between 3 and 150 K. From such measurements, a superconducting energy gap of 30 cm−1, representing a coupling strength = 2.27, is observed. Further, the penetration depth has been derived from the temperature dependence of the imaginary part of complex conductivity with the penetration depth = 530 ± 10 nm at lowest measured temperature. The temperature-dependent normalized superfluid density, just as is the case with most iron-based superconductors, could nicely be described by the so-called two-gap gamma model. Finally, a superconducting LiFeAs single crystal with Tc = 18 K has been investigated by optical spectroscopy in the frequency range 15 - 55000 cm−1 between 5 and 300 K. From these measurements, no clear signature of the superconducting energy-gap opening could be identified in spite of the spectral weight been suppressed in the infrared frequency regime below Tc. This indicates that LiFeAs single crystal is in a clean limit. With the aid of the Ferrell-Glover-Tinkham (FGT) sum rule, an absolute penetration depth of 215 nm has been calculated from the missing area at 5 K.

En nous concentrant sur les valeurs du module de cisaillement l’équilibre Geq pour le modèle bien connu des polymères vitrifiables (echantillionné par le biais de la MD), nous avons adressé la question générale de en quoi les propriétées méchaniques des couches mince diffères de la phase volumique. Il a été démontrè que dans les deux cas Geq de manière non ambigus sèpare l’état fluide (Geq = 0) de l’état vitreux (Geq > 0). Nous avons aussi insisté sur le fait que Geq pour la couche mince dépend de lépaisseur du film h mais aussi de de la pression tangentielle qui est un résultante de la procédure de préparation de la couche mince / Focusing on the equilibrium shear modulus Geq of well-known glass-forming polymer model system (sampled by means of MD), we have addressed the general question of how the mechanical properties of the thin polymer films differs from the bulk. Using ”stress fluctuation” formalism we obtained Geq(T) for the bulk and films. It has been demonstrated that in both cases Geq unambiguously separates the fluid state (Geq = 0) from the glass (Geq > 0). We also stressed that Geq for the film does not only depend on film thickness h, but also on tangential pressure that is a consequence of the film preparation procedure.

The effect of Laves phase (Fe2Nb) formation on the Charpy impact toughness of the ferritic stainless steel type AISI 441 was investigated. The steel exhibits good toughness after solution treatment at 850°C, but above and below this treatment temperature the impact toughness decreases sharply. With heat treatment below 850°C the presence of the Laves phase on grain boundaries and dislocations plays a significant role in embrittlement of the steel whereas above that temperature, an increase in the grain size from grain growth plays a major role in the impact embrittlement of this alloy. The toughness results agree with the phase equilibrium calculations made using Thermo–Calc® whereby it was observed that a decrease in the Laves phase volume fraction with increasing temperature corresponds to an increase in the impact toughness of the steel. Annealing above 900°C where no Laves phase exists, grain growth is found which similarly has a very negative influence on the steel’s impact properties. Where both a large grain size as well as Laves phase is present, it appears that the grain size may be the dominant embrittlement mechanism. Both the Laves phase and grain growth, therefore, have a significant influence on the impact properties of the steel, while the Laves phase’s precipitation behaviour has also been investigated with reference to the plant’s manufacturing process, particularly the cooling rate after a solution treatment. The microstructural analysis of the grain size shows that there is a steady increase in grain size up to about 950°C, but between 950°C and 1000°C there is a sudden and rapid 60 % increase in the grain size. The TEM analysis of the sample that was annealed at 900°C shows that the Laves phase had already completely dissolved and cannot, therefore, be responsible for “unpinning of grain boundaries” at temperatures of 900°C and higher where this “sudden” increase in grain size was found. The most plausible explanation appears to be one of Nb solute drag that loses its effectiveness within this temperature range, but this probably requires some further study to fully prove this effect. During isothermal annealing within the temperature range of 600 to 850°C, the time – temperature – precipitation (TTP) diagram for the Laves phase as determined from the transformation kinetic curves, shows two classical C noses on the transformation curves. The first one occurring at the higher temperatures of about 750 to 825°C and the second one at much lower temperatures, estimated to possibly be in the range of about 650 to 675°C. The transmission electron microscopy (TEM) analyses show that there are two independent nucleation mechanisms that are occurring within these two temperature ranges. At lower temperatures of about 600°C, the pertaining nucleation mechanism is on dislocations and as the temperature is increased to above 750°C, grain boundary nucleation becomes more dominant. Also, the morphology of the particles and the mis-orientation with the matrix changes with temperature. At lower temperatures the particles are more needle-like in shape, but as the temperature is increased the shape becomes more spheroidal. The effect of the steel’s composition on the Laves phase transformation kinetics shows that by lowering the Nb content in these type 441 stainless steels, had no significance effect on the kinetics on precipitation of the Laves phase. However, a Mo addition and a larger grain size of the steel, retard the formation of the Laves phase, although the optimum values of both parameters still need further quantification. The calculation made for the transformation kinetics of the Laves phase, using the number density of nucleation sites No and the interfacial energy, as the fitting parameters in this work, demonstrated a reasonable agreement with experimental results. / Thesis (PhD)--University of Pretoria, 2010. / Materials Science and Metallurgical Engineering / unrestricted

The presented diploma thesis is focused on the preparation, characterization and study of membrane properties of liposomal systems which were composed of the neutral phosphatidylcholine (DPPC), cholesterol, negatively charged phosphatidylglycerol (DPPG), polyethylenglycol bounded to phosphatidylethanolamine (PEG5000–PE) and polycation N,N,N-trimethylchitosan (TMC). The influence of individual components and their concentrations on the average particle size, zeta potential and changes in the outer and inner part of the bilayer was investigated. In this matter, methods of dynamic and electrophoretic light scattering and fluorescence spectroscopy with the application of laurdan and DPH probes were used. Based on the above-mentioned parameters, concentrations of components that most suitably influence properties of liposomes in terms of the intended application were selected for the definite complex. It was managed to prepare a liposomal complex stealth liposome–N,N,N-trimethylchitosan, which, due to the optimized composition, could have suitable attributes as a drug delivery system for inhalation administration of biologically active substances.

The diploma thesis is aimed to assesment of the influence of the specimen orientation during the Small Punch Tests (SPT). Steel ČSN 41 0214, or its equivalent steel RFe80, W.-Nr. 1.104 was chosen for experiments. Resulting records from SPT were evaluated using already known correlations which are reported in literature. The correlation values were compared with values obtained by the standard tests like Charpy impact test and tensile test. The influence of axial, radial and tangential test specimens orientation is discussed in relation to Ductile-to-Brittle fracture behaviour of the steel.

The Diploma thesis is focus on polymer modified bitumen for warm mix asphalt. The theoretical part of the thesis describes additives which influence the properties of bitumen for their use and reduction of production and service temperatures. Further, the theoretical part describes the conclusions from the researches. This part also describes empirical and functional tests of bituminous binders. The practical part presents the results of individual tests. Tests were performed on samples of non-aged, aged by RTFOT and RTFOT + PAV methods. The results of the work and the assessment of the suitability of bituminous binders are summarized at the end of the thesis.

The presented diploma thesis deals with an innovative material test, so called Small Punch Test. There are main principles, advantages and limitations of the test stated in the thesis. There are stated also correlation procedures in order to obtain standard mechanical properties. A test fixture design has been done in order to perform test procedures at temperature range from 80 to 25 °C. Twelve experimental curves have been obtained from the test and typical quantities have been evaluated. The different accuracy of correlations with standard mechanical properties has been obtained using different correlation equations.

The present thesis is devoted to the investigation of novel superconductors by phase-sensitive terahertz transmission and infrared to ultraviolet spectroscopy. In particular, a nominally undoped Pr2CuO4 superconducting thin film, an FeTe0.5Se0.5 thin film, and a LiFeAs single crystal have been investigated. The emphasis is on the low-frequency part of the optical spectrum (i.e., the terahertz and infrared spectrum), as the goal of the study was to shed light on the size and symmetry of the superconducting gaps and also to determine the temperature dependences as well as the absolute values of the penetration depth, which are key input parameters for models applicable for new superconductors. In addition, niobium has been investigated as a reference, so as to see what is expected from conventional superconductors and to clarify the electrodynamics of niobium. A superconducting Nb thin film with Tc of 8.04 K has been investigated by backward wave oscillator-based (BWO-based) and time-domain terahertz (TDT) spectrometers in the frequency range between 4 and 100 cm−1 for temperatures ranging from 2 to 10 K. From these measurements an energy gap of 22.50 cm−1 = 2.79 meV = 4.02kBTc have been determined. The optical conductivity below Tc could nicely be described by calculations according to the Eliashberg theory, with the electron-phonon interaction evaluated from tunneling measurements. Absolute values of the penetration depth have been calculated from phase-sensitive terahertz measurements. The zero-temperature limit of at T = 0 is found to be 115 ± 5 nm. From this value, a London penetration depth of 43 ± 2 nm has been obtained. The overall temperature dependence of the penetration depth follows a behavior typical for conventional s-wave superconductors. A superconducting Pr2CuO4 film with T0 structure and Tc of 27 K has been investigated by use of optical methods in a wide frequency (5 – 55000 cm−1) and temperature (2 – 300 K) range. A Drude-like peak centered at zero frequency is observed in the optical conductivity below 150 K, above which it shifts to finite frequencies. The detailed analysis of the low-frequency conductivity reveals that the Drude peak and a far-infrared (FIR) peak centered at about 300 cm−1 persist at all temperatures. The FIR spectral weight is found to grow at the expense of the Drude spectral weight with increasing temperature. Absolute values of the penetration depth have been obtained from temperature and frequency-dependent measurements. The zero-temperature limit of is estimated to be 1600 ± 100 nm. The overall temperature dependence of follows a behaviour typical for cuprate superconductors. However, a closer look at the penetration depth at T 12 K reveals a flattening in the temperature dependence. A superconducting FeTe0.5Se0.5 thin film with Tc = 19 K has been investigated using a combination of BWO and TDT spectroscopy in the frequency range 4 - 80 cm−1 and between 3 and 150 K. From such measurements, a superconducting energy gap of 30 cm−1, representing a coupling strength = 2.27, is observed. Further, the penetration depth has been derived from the temperature dependence of the imaginary part of complex conductivity with the penetration depth = 530 ± 10 nm at lowest measured temperature. The temperature-dependent normalized superfluid density, just as is the case with most iron-based superconductors, could nicely be described by the so-called two-gap gamma model. Finally, a superconducting LiFeAs single crystal with Tc = 18 K has been investigated by optical spectroscopy in the frequency range 15 - 55000 cm−1 between 5 and 300 K. From these measurements, no clear signature of the superconducting energy-gap opening could be identified in spite of the spectral weight been suppressed in the infrared frequency regime below Tc. This indicates that LiFeAs single crystal is in a clean limit. With the aid of the Ferrell-Glover-Tinkham (FGT) sum rule, an absolute penetration depth of 215 nm has been calculated from the missing area at 5 K.

Bei der Beurteilung der Sicherheit bestehender Konstruktionen aus altem Baustahl (i. A. Flussstahl) und der Entscheidung über notwendige Instandsetzungs- und Verstärkungsmaßnahmen ist der Nachweis ausreichender Werkstoffzähigkeit (der Sicherheit gegen ein sprödes Versagen) von wesentlicher Bedeutung. Die in DIN EN 1993-1-10 normativ geregelten Nachweismethoden zur Beurteilung der Sprödbruchgefährdung wurden basierend auf umfangreichen bruchmechanischen Untersuchungen entwickelt. Sie gelten für Schweißkonstruktionen und „Stähle aus neuerer Zeit“ mit in der Regel hohen Zähigkeitswerten. Die Quantifizierung der Zähigkeit in Werkstoffnormen erfolgt durch Kerbschlagbiegeversuche. Die Beziehung zwischen der Übergangstemperatur der Kerbschlagarbeit und der Referenztemperatur der Bruchzähigkeit wird durch die modifizierte Sanz-Korrelation hergestellt, die nur für diese Stähle abgeleitet wurde. Das in der Norm verankerte Verfahren ist für alte Flussstahlkonstruktionen mit Lochschwächung durch Niet- und Schraubenverbindungen nicht geeignet. Einerseits unterscheiden sich Kerbwirkung und Eigenspannungszustand von geschweißten und genieteten Konstruktionen und damit die Zähigkeitsanforderungen wesentlich voneinander. Auf der anderen Seite unterliegen die Zähigkeitseigenschaften von Flussstählen deutlich größeren Streuungen. In der vorliegenden Arbeit werden experimentelle und rechnerische Untersuchungen zum Sprödbruchverhalten gelochter Konstruktionen aus altem Flussstahl vorgestellt. Wesentlicher Bestandteil sind dabei die umfangreichen Werkstoffanalysen zur Ermittlung der bruchmechanischen Werkstoffzähigkeit im spröd-duktilen Übergangsbereich nach dem Master-Curve-Konzept (ASTM E1921). Die Auswertungen belegen, dass in Abhängigkeit des Herstellungsverfahrens unterschiedliche Werkstoffgüten definiert werden können. Um den Einfluss des Stanzens von Löchern auf das Sprödbruchverhalten alter Flussstähle zu beurteilen, werden Gefügeuntersuchungen und Mikrohärtemessungen durchgeführt. Ausgehend von einer umfassenden Analyse typischer Konstruktionsformen bestehender Tragwerke des Stahlhochbaus erfolgen bruchmechanische FE-Berechnungen an Anschlüssen von Winkelprofilen zur Bestimmung der Zähigkeitsanforderungen. Die dabei gewonnenen Ergebnisse des Spannungsintensitätsfaktors werden durch Modifikation bekannter Lösungen aus der Fachliteratur für die weitere Anwendung aufbereitet. Darauf aufbauend wird für die untersuchten Konstruktionsdetails im Rahmen einer bruchmechanischen Sicherheitsanalyse ein praxisgerechtes Verfahren zur Beurteilung der Sprödbruchgefährdung genieteter und geschraubter Bauteile abgeleitet. Mit Hilfe statistischer Methoden werden Streuungen der Festigkeits- und Zähigkeitskennwerte der Flussstähle erfasst und nach der Verifizierung durch Bauteilversuche in ein semi-probabilistisches Nachweiskonzept überführt.