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Heat insulating moulded refractory materials
Novotný, Radoslav ; Lang, Karel (referee) ; Raschman,, Pavel (referee) ; Havlica, Jaromír (advisor)
Doctoral thesis is focused on the study, research and development of heat insulating moulded refractory materials. The replacement of shaped instead of unshaped refractories is recently and strongly industrially demanded and belongs to ongoing research topics. With the increasing demand of energy savings, the excellent insulation properties are essential. The insulating properties of castables are the result of targeted porosity formation. The porosity is coming from the controlled air intrusion into material resulted to foamed structure. The foaming process was achieved by mixing of separately prepared aqueous foam into raw castable slurry or by in situ foaming of intensively mixed castable slurry with the surfactant additive. Nevertheless, the study of foam behaviour and the influence of additives on binder hydration and setting processes (i.e. calciumaluminate cement) was substantial for successful preparation of the experimental samples. The two types of the experimental samples were prepared. The first one was based on mixing of kaolin slurry with pre-prepared aqueous foam, whereas the de-aglomeration ability of kaolin specie was utilized to water-particle film formation. In situ foaming of multicomponent system is the second one. The both processes brought some negative attributes, so the optimal properties of prepared castables were achieved by their combination.
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Inhibition of Hazardous Compounds in Alumino-Silicate Systems
Koplík, Jan ; Škvára, František (referee) ; Rovnaníková, Pavla (referee) ; Havlica, Jaromír (advisor)
The ability of alumino-silicate systems to immobilize hazardous compounds has been investigated since 1990s. The aim of this work is to develope alumino-silicate system (matrix) based on industrial waste products with ability to immobilize hazardous compounds (heavy metals). This ability of the matrix was confirmed by leaching tests based on the law 294/2005 Sb. Concentration of heavy metals in leachates was determined by ICP-MS method. Alumino-silicate system prepared in this work consists of high-temperature fly ash and blast furnace slag activated by mixture of alkaline activators (hydroxide and water glass). Matrixes were characterized by suitable analytic methods (XRD, SEM, FT-IR, DTA-TGA-EGA). The same analytic methods were used to describe the mechanism of immobilization of selected elements (Ba, Cu, Pb) in prepared systems.
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Investigation and Modelling of Concrete Carbonation
Rovnaníková, Markéta ; Keršner, Zbyněk (referee) ; Bajza, Adolf (referee) ; Havlica, Jaromír (advisor)
The corrosion of steel reinforcement is probably the most frequent type of degradation of reinforced concrete structures. Reinforcing bars are protected from corrosion by a thin iron oxide layer which is formed on their surface due to a high alkalinity of the surrounding concrete. Corrosion may start when this layer is destroyed (i) either by chloride ion penetration (when the concentration of dissolved chloride at the depth of the reinforcing steel exceeds a critical value) or (ii) by a reduction in the pH value of pore solution to values below 9.5. Such a reduction in alkalinity is the result of carbonation of the Ca(OH)2 in the concrete mass, i.e. of its reaction with the atmospheric CO2. The main aim of this work is an experimental investigation and modelling of carbonation process. The effect of relative humidity, curing period and replacement of Portland cement by supplementary cementing materials (SCM - fly ash, blast furnace slag and metakaolin) on carbonation process has been studied. Calcium hydroxide content in the presence of SCM and their pozzolanic activities have been also determined. Furthermore, lots of parametric studies and comparison of carbonation models have been provided. The software tools based on the introduced models and considering the input data to be statistically independent random variables have been described and used for other parametric studies.
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Kinetics of Heterogeneous Processes in Silicate Technologies -Dehydroxylation and Disolution of Clay Minerals
Křečková, Magdaléna ; Kutzendörfer, Jaroslav (referee) ; Kuřitka, Ivo (referee) ; Havlica, Jaromír (advisor)
The first part of the thesis discuss general characterization of heterogeneous processes in silicates. This part is focused on kinetics of heterogeneous processes and mathematical description of reactions time behavior. The other part describes important technologies in silicate industry such as sintering, solid matter decomposition, transition modification, etc. Another chapter deals mineralogy, structure and properties of eminent silicate raw materials. Emphases is given to characterization of clay minerals and their utilising. The experimental part handle the analytic techniques used for investigation of thermal decompostion, dehydroxylation, crystalization of Al-Si spinel phase and sintering process of washed kaolin Sedlec Ia from the region Carlsbad (Czech Republic). Concluding chapter reports on results of experimental work.
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Preparation of hystorical geopolymers
Šrámková, Eva ; Šoukal, František (referee) ; Havlica, Jaromír (advisor)
Diploma thesis studies historical bonding agents on the base of geopolymers. The aim of the thesis is to find a proper material composition, especially made of natural clay materials (kaolinite, bentinite) and their modifications (metakaoline). These bonding agents have to have a suitable type of an activator that guarantees good bonding properties. Therefore testing of various kinds of alkaline activating ingredients on the same mineral composition was done. Except of usual hydroxides and a water glass, ancient natrons (mixtures of alkaline carbonate with addition of appropriate chlorides) and a lime mash were used as the activators. From the above mentioned mixtures, series of samples (columns 20 x 20 x 100 mm) stored at the laboratory temperature were prepared. In the prepared mashes, their workableness and moulding were investigated. In the developed samples, their surface appearance was observed together with a number of efflorescence and its types. An indivisible part of the research was formed by determination of mechanical properties of the experimental columns such as a compressive strength and a tensile strength in bending. Furthermore, phase composition of the samples and its changes with a temperature increase were investigated. For these tests, XRD and TG – DTA methods were used. A multi-seat isoperbolic calorimeter was used to study hydratation that was also the important part of the general evaluation of designed mixtures.
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Possibilities of application of phosphate bond in brick abrasion dust treatment
Tmejová, Jana ; Havlica, Jaromír (referee) ; Opravil, Tomáš (advisor)
This bachelor´s thesis deals with possibilities of application of phosphate bond in brick abrasion dust treatment. Brick abrasion dust is produced as a secondary product of brick production during brick grinding. Brick abrasion dust is a relatively fine powder of the same composition as a burnt brick fragment. Since the brick abrasion contains an insufficient amount of the aluminum component, which is crucial for the formation of phosphate bond, the work is primarily concerned with finding a suitable aluminum dopant. The aim of the thesis is to find a suitable admixture that has a sufficient content of aluminum to form a phosphate bond and to determine the ideal amount to be added. Alternative sources of the aluminum component are tested in combination with a commercially available phosphate bond (Alufos 50).
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Corrosion of Nonferrous Metal Materials
Ševčíková, Barbora ; Nový,, František (referee) ; Pacal, Bohumil (referee) ; Havlica, Jaromír (advisor)
In the presented dissertation thesis, I closely focused on corrosion resistance of non-ferrous metals. For full understanding of the possibilities for increasing corrosion resistance, it was vital to initially recognize the influences to the corrosion system of the samples and their surrounding environment. For this purpose, I focused on heat treatment, corrosion, and protective coatings, in the theoretical part of the thesis. For the subsequent research, it was necessary to define several constant variables, first. For this purpose, I have chosen a group of magnesium alloys, namely AZ91 Alloy and 3.5 % NaCl Electrolyte. AZ91 Alloy is of heterogenous structure formed by a solid solution of aluminum in magnesium, intermetallic phase in Mg17Al12, and their eutectic. Local microcells tend to occur in these heterogenities, which leads to faster corrosion. In order to increase corrosion resistance of the alloy, I used a combination of heat treatment and protective phosphate coating. For creating of the desired structure, which further affects compact coating formation, I selected a process involving solution heating with precipitation hardening T6. Secondary goals of the thesis involved optimization of standard technical procedures for the sake of increasing efficiency. With regard to this goal, I introduced optimized heat treatment T6 using accelerated cooling of a sample in water and liquid nitrogen. A modification besides the standard phosphating procedure was carried out with no activation step. For evaluation of corrosion resistance of the samples, I conducted water immersion tests using electrochemical methods; such as potenciodynamic curves combined with electrochemical impedance spectroscopy. In order to streamline the evaluation of the corrosion surface in technical practice, I used automatic detection. Substantial improvement of corrosion resistance of the above mentioned system, compared to heat-untreated samples, was proven through electrochemical methods. Due to accelerated cooling, a more homogeneous structure was achieved, which could be further utilized to create more uniform protective coating. For some phosphate coating, specifically manganese phosphate coating, I identified certain modifications that were in line with the set goals; i.e. skipping the activation phase, and using automatic detection for evaluation of uniform corrosion on the samples.
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