The grades of steel used for automotive bodies are interstitial free steel grades and titanium stabilized ultra-low carbon steel grades. During the manufacturing of these grades, the addition of titanium in liquid steel is achieved in the steel refining units and may cause processing problems. Titanium reacts with the dissolved aluminum and oxygen to form complex solid aluminum titanate type micro-particles (inclusions). During the flow of titanium alloyed steel grades containing solid inclusions (such as aluminum titanate and alumina type inclusions), the clog accompanied by steel skull can be formed at the submerged entry nozzle between the tundish and the mold. To reduce the effects of aluminum titanate type inclusions, they can be either modified or removed. The current study focused on the removal of Al2O3, TiO2, and Al2TiO5 inclusions by dissolving them in slag in the temperature range of 1430 – 1600 °C using a high-temperature confocal scanning laser microscope. In this technique, a single particle (inclusion) is placed on the surface of a solid slag, and the inclusion-slag system is heated to steelmaking temperatures. The dynamic changes in inclusion size are measured to determine dissolution kinetics and mechanism. This work has developed a complex oxide particle synthesis technique and provides the first-ever kinetic data for removal of aluminum titanate inclusions into steelmaking slags. It is found that Al2O3 inclusions have a slower dissolution rate than that of Al2TiO5 inclusions followed by TiO2 inclusions. The rate-controlling steps are investigated using a shrinking core model. It is shown that the rate-controlling step for dissolution of both Al2O3 and Al2TiO5 inclusion types is the mass transfer of alumina. Evidence in support of this finding is the particle-slag interface characterization by line scan analysis and calculated diffusivity values being inversely proportional to the viscosity of slag. The dissolution path of aluminum titanate is proposed in the following steps. First, aluminum titanate dissociates into alumina, titanium oxide and oxygen while slag penetrates through the particle. In the next step, the alumina and titanium oxide dissolves in slag, and the oxygen leaves the system. The existence of gas bubbles enhances the overall rate of Al2TiO5 dissolution. The current work establishes a detailed understanding of the dissolution of Al-Ti-O type inclusions in steelmaking slags. This knowledge will inform steelmakers on which inclusions of different chemistry can be removed preferably and develop strategies on better slag design to produce superior quality steel with reduced operational downtime. / Thesis / Doctor of Philosophy (PhD)

In present thesis, the fundamental studies on the reaction between MgO based refractories and slag were undertaken for the development of a carbon-free bonding MgO lining material. Alumina was selected as a potential binder material. Due to MgO-Al2O3 chemical reaction, the developed refractory was bonded by MgO·Al2O3 spinel phase. To begin with, an investigation of the dissolution process of dense MgO and MgO·Al2O3 spinel in liquid slag was carried out. To obtain reliable information for dissolution study, a new experimental method was therefore developed. In this method, a cylinder was rotating centrally in a special designed container with a quatrefoil profile. This method also showed a good reliability in revealing the dissolution mechanism by quenching the whole reaction system. The experimental results showed that the dissolution process of MgO and spinel was controlled by both mass transfer and chemical reaction. It was found that the rapid dissolution of spinel was mainly because of its larger driving force. To improve the resistance against slag penetration, two aspects were studied to develop carbon-free MgO refractory. First, colloidal alumina was used and the effect of its addition into MgO matrix was investigated. The use of colloidal alumina was to form bonding products in the grain boundary of MgO. The results showed that the alumina addition greatly improved the resistance of MgO based refractory against slag penetration in comparison with the decarburized MgO-carbon refractory. It was found that the improvement of resistance was mainly related to the spinel-slag reaction products of CaO·Al2O3 and CaO·MgO·Al2O3 solid phases at the grain boundaries. Second, the effect of particle size distribution on the penetration resistance of MgO was investigated. The most profound improvement against the slag penetration was obtained by using a proper particle size distribution. The results highlighted the importance of considering the refractory structure. Experiments were undertaken to investigate the dissolution mechanism of different types of MgO based refractories in liquid slag. It was observed that the dissolution of spinel bonded MgO refractory was much slower than the decarburized MgO-carbon refractory. The primary dissolution in spinel bonded MgO refractory occurred at the slag-penetrated layer, and the removal of this layer by peeling off enhanced the dissolution rate rapidly. / <p>QC 20170918</p> / European RFCS LEANSTORY project

<p>The dissolved concentration of an active pharmaceutical ingredient in biological fluids is of significant importance for establishing a therapeutic effect in patients. However, the current pharmaceutical landscape is abundant in poorly soluble drugs that require solubility enhancing techniques to enable their administration. A promising technique, with increasing commercial success, is to molecularly mix drug and polymer to create an amorphous solid dispersion (ASD). While these mixtures provide enhanced drug solubility and dissolution in aqueous solutions, the mechanistic processes by which they release drug into solution are not well understood. Some unexplained behaviors include rapid drug release even at the maximum supersaturated concentration and spontaneous formation of drug-rich nanoparticles. These are beneficial for rapidly achieving and maintaining a highly supersaturated drug concentration during absorption, if crystallization is inhibited. However, the phenomena occur at typically low drug loading and are abruptly lost above a certain threshold termed the ‘limit of congruency’ (LoC), which has been reported to vary based on the drug-polymer system. In this research, the mechanisms underpinning ASD release at low and high drug loading were studied, and the factors affecting LoC were mechanistically explored by performing dissolution experiments and utilizing imaging, separation, thermal analysis, and spectroscopy methods to characterize the materials in the presence and absence of water. The results show that ASDs developed a gel layer on the surface when exposed to aqueous solution. This water-rich environment was thermodynamically unstable and phase separated into hydrophilic and hydrophobic phases. The morphology of the hydrophobic phase was directly related to the ASD release behavior, where ASDs below the LoC exhibited a dispersed and stable hydrophobic phase morphology, and ASDs above the LoC displayed a continuous or aggregated morphology. In cases where thermodynamic factors were rate limiting, LoC was inferred from features on the ternary phase diagram. Moreover, drug-polymer interactions and polymer molecular weight were demonstrated to affect the morphology of the hydrophobic phase and ultimately the LoC. The conclusions from this work provide the basis of a theoretical framework for rationally designing ASDs and optimizing their release. </p>