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Degradation of nanocomposites
Polách, Ondřej ; Rozsívalová, Zdenka (referee) ; Polsterová, Helena (advisor)
The present work deals with the electrical properties of nanocomposite materials. Samples for the practical part consisting of epoxy resin as matrix and SiO2 as nanofillers and were made in four different percentage performance. There is investigated the influence of thermal degradation of nanocomposite materials change resistivity, loss factor and relative permitivity.
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Effect of colloidal silicon dioxide on selected properties of cement pastes and mortars
Barek, Jaroslav ; Žižková, Nikol (referee) ; Rovnaníková, Pavla (advisor)
The presented diploma thesis deals with the potential use of colloidal silica in cement composites. Investigation is focused primarily on selected properties of cement pastes and mortars with colloidal silica content. Two selected types of colloidal silica (particles with average size of 14 nm) have been used as a cement addition and partial replacement of cement, respectively. The experimental program for cement pastes with colloidal silica included tests for isothermal calorimetry (the study of cement hydration) and thermal analysis (determining the portlandite content). Hardened cement pastes have been studied through measurements of compressive strength. The microstructure was examined by scanning electron microscopy. Hardened mortars with colloidal silica have been studied through measurements of compressive strength, flexural strength, modulus of elasticity and fracture mechanics parameters. Fracture mechanics tests show that 5 % and 20 % addition of colloidal silica can enhance after 28 days of curing fracture energy up to 18,4 % and 32,7 %, respectively. For the compressive strength enhancing effect of colloidal silica, it was found to be more pronounced in the early age, while rate of strength gain can be lower than the control in the later ages. Our investigations revealed that the silica sol will coagulate immediately when the cement is mixed into the water containing sol. The ionic composition of pore fluid significantly influences the stability of colloidal silica and lead to their aggregation. After additional tests it has been found that small addition of calcium hydroxide greatly improved the compressive strength of the resulting cement pastes with colloidal silica content. Addition of calcium hydroxide in conjunction with modified cement paste preparation can enhance compressive strength after 3 days of curing up to 64,4 % in comparison with the blank paste.
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Optimization of Working Mass Composition for Dense Silica Bricks Production.
Maňák, Jan ; Lang,, Karel (referee) ; Nevřivová, Lenka (advisor)
A silica bricks is a refractory material which is used mainly in coke industry, glass industry and metallurgy. This material constitute of the quartz modifications. Compact silica is an irreplaceable part of the coke battery and its compactness and robustness is important for quality and long endurance. Very important for large compactness is a grain curve of work matter. This thesis deals with influence of different grain of work matter.
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Hybrid titania-silica layers on polymeric supports
Bednárková, Jana ; Pekárková, Jana (referee) ; Dzik, Petr (advisor)
This bachelor thesis deals with titania-silica photocatalytic layers on polymeric supports. The theoretical part involves the study of properties and possibilities of preparing the layer and it is mainly focused on the influence of silica on the nature of layers. The experimental part of this thesis investigates the influence of layer thickness on the degradation rate of 4 different dyes.
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Mineralizers Using in the Silica Materials Production Process
Maňák, Jan ; Sokolář, Radomír (referee) ; Nevřivová, Lenka (advisor)
Silica bricks is a refractory material whitch is used mainly in glass furnaces, coke oven bateries and hot blast stoves. Silica bricks constitute of the crystalline phases cristobalite, tridymite, glass phase and unconverted quartz. Content of these phases influences eventual properteis of silica bricks. This thesis deals with influence of the different kind of mineralizers, method of homogenization and length of firing on the content of these phases and eventual properties of silica bricks.
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Pozzolanic Activity of Silicon Dioxide
Barek, Jaroslav ; Žižková, Nikol (referee) ; Rovnaníková, Pavla (advisor)
The aim of this bachelor's thesis is to investigate and identify the present status of resources with dominant amorphous silicon dioxide content and summarize feasible test methods to assess pozzolanic activity. The use of pozzolan as a partial replacement of Portland cement reduces the carbon dioxide emitted per tonne of product and can also improve various physical properties of the resulting cementitious composites. Assessment of the pozzolanic activity of cement replacement materials is increasingly important because of the economic sustainability of cementing materials. The pozzolanic activity of wheat straw ash, silica fume, nanosilica, two diatomites, glass powder and expanded perlite have been investigated and compared using the strength activity index test, the modified Chapelle test and the pozzolanicity test in accordance with the European Standard EN 196-5. From an experimental investigation of seven different pozzolans, the following main conclusions can be drawn. In the case of an acid-base titration (determination of [OH–], the procedure specified in EN 196-5) is better to use Tashiro (mixed indicator) instead of required methyl orange, Tashiro changes color at the endpoint of a titration distinctly. Strength activity index: the procedure used was based on EN 450-1. In its current form, this procedure is misleading because of two other significant properties of the pozzolan, namely its density and its water-reducing/increasing capabilities. Based on the results of our experimental investigation, the current testing procedure is evaluated against an alternative in which the 25% pozzolan replacement for cement is performed on a volumetric basis and the volume fraction of water is held constant.
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Preparation of photocatalytically active layers of titanium dioxide
Šeffer, Lukáš ; Jančovičová, Viera (referee) ; Veselý, Michal (advisor)
This bachelor work gives an overview about preparation of titanium dioxide and silicon dioxide thin films by sol-gel process, using coating methods as spin coating, dip coating, capillary and cell coating, flow coating, spray coating, pyrosol process, chemical vapour deposition and printing. The procedures of composite films preparation obtained by mixed sols of titanium dioxide and silica dioxide are also discussed together with preparation of double layer films, when titanium dioxide is coated on glass substrate covered by a silica dioxide layer. The methods of photocatalytic activity testing are the important part of this work.
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