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Polymer-cement composites for refractory aplications
Zbončák, Marek ; Ptáček, Petr (referee) ; Šoukal, František (advisor)
This bachelor thesis deals with preparation of high-strength polymer-cement composites based on the calcium aluminate cement and polyvinylalcohol. MDF composites are interesting because of their mechanical properties which exceed strengths of the common materials based on the cement and inorganic binders. So they represent perspective kind of material which could be used for construction purposes. Thermal degradation of the polymer leads to structure changes of the composite and reduction of mechanical properties. Therefore thesis is aimed to characterize the influence of the temperature on mechanical properties, structural changes and material composition. Temperature dependence of flexural strength was examined during the work. Changes of composition and structure were characterized by XRD, DTA-TGA in combination with EGA, SEM and EDS analyses. Due to requirement of the material refractoriness there were also tested options of preparation of MDF composites based on phosphates binders which are used in refractory manufacture.
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STRAIN ENGINEERING OF THE ELECTRONIC STRUCTURE OF 2D MATERIALS
del Corro, Elena ; Peňa-Alvarez, M. ; Morales-García, A. ; Bouša, Milan ; Řáhová, Jaroslava ; Kavan, Ladislav ; Kalbáč, Martin ; Frank, Otakar
The research on graphene has attracted much attention since its first successful preparation in 2004. It possesses many unique properties, such as an extreme stiffness and strength, high electron mobility, ballistic transport even at room temperature, superior thermal conductivity and many others. The affection for graphene was followed swiftly by a keen interest in other two dimensional materials like transition metal dichalcogenides. As has been predicted and in part proven experimentally, the electronic properties of these materials can be modified by various means. The most common ones include covalent or non-covalent chemistry, electrochemical, gate or atomic doping, or quantum confinement. None of these methods has proven universal enough in terms of the devices' characteristics or scalability. However, another approach is known mechanical strain/stress, but experiments in that direction are scarce, in spite of their high promises.\nThe primary challenge consists in the understanding of the mechanical properties of 2D materials and in the ability to quantify the lattice deformation. Several techniques can be then used to apply strain to the specimens and thus to induce changes in their electronic structure. We will review their basic concepts and some of the examples so far documented experimentally and/or theoretically.
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