Oxide films in aluminium melts are unavoidable. A new technology developed by BCAST suggests breaking films into small fragments or particles which play a role as the grain refiner. Mechanical breakage is realised by using a high-shear mixer (HSM) with the rotor-stator impeller. In the presented thesis, the positive role of small oxide particles is shown by the computer modelling. The defragmentation potency of HSM is demonstrated by physical modelling with powders checked by optical analyses (microscopy) and SEM (Scanning Electron Microscopy). The flow has been analysed by optical recording and by PIV (Particle Image Velocimetry) to find the best conditions to cause a satisfying oxides distribution in all volume of liquid metal processed by the HSM. A new model to estimate the mixed volume has been proposed and checked by experiments with liquid metals. The model was checked by the PIV observations and by direct experiments in the liquid metal and is found to be in good agreement with reality. Optimisation methods are considered and a new design of HSM is proposed according to the experimental findings. This design improves the uniformity of mixing in the pseudo-cavern volume and exhibits the dispersion efficiency better than the design used currently by BCAST. Understanding and development of high shear technology for liquid metals processing is an important part of BCAST research and is of great interest for industry. Up to now, this method was found to give good experimental results but it was a lack of information about physical basics behind this process. The goal of this thesis is to answer why and how to apply HSM in metallurgy and to propose new condition and design solutions associated with the specific requirements of the liquid metal process.

Heavy-metal contamination in soils has become a serious environmental problem. Among all metals, excessive amount of zinc was released to soils over the years. Zinc is not only toxic to human being, but also to plants. High concentration of zinc is extremely phytotoxic. Currently, the most popular method to remediate heavy-metal contaminated soils is stabilization/solidification (S/S) technique as it is cheaper, faster and more effective to remediate heavy metals than other remediation methods. Portland cement is the most-used binder in S/S technique. However, the production of Portland cement has released a significant amount of carbon dioxide, which strongly contributes to global warming. In addition, zinc retards the setting and hydration of Portland cement, which would require more Portland cement to remediate zinc-contaminated sites. Therefore, researchers are looking for new materials to improve the performance of Portland cement in zinc-contaminated soils. In recent years, the application of graphene-based materials in concrete had proved to be effective. Due to relative cost-effectiveness and comparable properties, multi-layer graphene, known as graphene nanoplatelets, may show a promising potential in construction. Moreover, research has reported that graphene nanoplatelets can be exfoliated from graphite and potentially scaled up for full-scale applications. At present, there is no application of graphene nanoplatelets in the S/S of contaminated soils and the roles of graphene nanoplatelets in cement-stabilized zinc-contaminated clay remained unknown. In this research, graphene nanoplatelets were dispersed in solution with a high-shear mixing apparatus. Dispersed graphene nanoplatelets solution was then applied to zinc-contaminated soil along with cement. To evaluate the efficacy of this S/S method, various influencing factors such as mixing sequence, graphene nanoplatelets content, zinc content, cement content, and curing time were studied. An optimum graphene nanoplatelets content was determined through the unconfined compressive strength (UCS) of the stabilized/solidified samples. It was found that at the optimum content, the unconfined compressive strength of cement-stabilized zinc-contaminated clay was improved by 22.3% with the addition of graphene nanoplatelets. Also, graphene nanoplatelets were effective at moderate zinc content and low cement content. Graphene nanoplatelets accelerated cement hydration effectively at early ages. Microstructural analyses indicated that more hydration products were developed in samples with graphene nanoplatelets. At current stage, it is still expensive to apply graphene nanoplatelets in S/S technique; however, it is possible to exfoliate graphite into graphene nanoplatelets in future research. / Graduate / 2022-05-12

The thesis deals with study of mechnochemical activation of chemical reactions at interphase of MDF composites. MDF composites are high-perspective composite materials on polymer-cement base. They excel especially in terms of flexural strengths. High flexural stregth is caused by binding interactions between the polymer and the cement. This interactions arise due to mechanochemical activation of raw material mixture at the stage of production. This work focuses on the creation of artificial cement-polymer interphase by contacting the surfaces of two molded tablets (polyvinyl alcohol and monocalcium aluminate), activation of chemical reactions at interphase by means of specially designed appartus, which achieves good plane-parallelism of activation surfaces and good definability of activation conditions (shear rate, pressure). After experiments under different conditions, the activated surfaces are analyzed by SEM, EDS, XPS and FT-IR.