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Ptacek P.,Brno University of Technology | Opravil T.,Brno University of Technology | Soukal F.,Brno University of Technology | Havlica J.,Brno University of Technology | Holesinsky R.,Research Institute of Building Materials
Solid State Sciences

The kinetics and mechanism of formation of gehlenite, Al-Si spinel phase, wollastonite and anorthite from the mixture of kaolinite and calcite was investigated by differential thermal analysis under the heating rate from 283 to 293 K min-1 using Kissinger equation. The changes in the phase composition of the sample during the thermal treatment were investigated via simultaneous TG-DTA, in situ high-temperature x-ray diffraction analysis and high-temperature heating-microscopy. The crystallizations of gehlenite and Al-Si spinel phase show apparent activation energy of (411 ± 5) kJ mol -1 and (550 ± 9) kJ mol-1, respectively. The value of kinetic exponent corresponds to the process limited by the decreasing nucleation rate for gehlenite while constant nucleation rate is determined for Al-Si spinel phase. Anorthite crystallizes from the eutectic melt and the process shows the apparent activation energy of (1140 ± 25) kJ mol -1. The process is limited by the constant nucleation rate of a new phase. © 2013 Elsevier Masson SAS. All rights reserved. Source

Soukal F.,Brno University of Technology | Ptacek P.,Brno University of Technology | Masilko J.,Brno University of Technology | Opravil T.,Brno University of Technology | And 2 more authors.
Journal of Thermal Analysis and Calorimetry

The macro-defect-free composites belong to the well-known group of promising materials consisting of inorganic binder and organic polymer. MDF composites exhibit unusual mechanical properties, especially the flexural strength that can reach over 200 MPa. Moreover, the MDF composites based on calcium aluminate cement have a good temperature resistance because of the Al2O3 content in the cement. This paper deals with the preparation and high temperature characterization of MDF composite based on calcium aluminate cement combined with polyvinyl alcohol that could enable its utilization as a refractory material in industrial kilns. The composition of the MDF mixture has been optimized for an easy high-shear processing and flexural strength of the resulting 7-days cured material has been studied under laboratory condition and after heating at 240, 300, 600, 1,000, and 1,500 C. The structure changes during the heating have been observed by SEM and the course of processes during the heating has been investigated by TG-DTA-EGA, TMA and heating microscopy. © 2013 Akadémiai Kiadó, Budapest, Hungary. Source

Stanek T.,Research Institute of Building Materials | Sulovsky P.,Palacky University
34th International Conference on Cement Microscopy 2012

The article is focused on the influence of P2O5 in combination with other minor oxides (SO3, MgO, K2O a Na2O) on the formation and phase composition of Portland clinker. The research was performed using methods of optical microscopy, electron microscopy and microanalysis, and X-ray diffraction. It was found that some oxides and their combinations partially eliminate the negative influence of P 2O5 on the phase composition of clinker, especially on alite formation. Cements prepared from clinkers with selected combination of minor oxides have shown positive influence on technological properties in comparison with cement with adequate addition of P2O5, but without additional minor oxides. Apparent improvement was in accelerated hydration and increase in initial strengths thanks to higher share of alite and positive influence of increased sulfate modulus and content of soluble alkalis. Source

Bohac M.,Brno University of Technology | Palou M.,Brno University of Technology | Novotny R.,Brno University of Technology | Masilko J.,Brno University of Technology | And 2 more authors.
Construction and Building Materials

The paper investigates the hydration of ternary blends comprising Portland cement, blast-furnace slag and metakaolin. The isothermal calorimetry and "in situ" X-ray diffraction was used to evaluate the effect of metakaolin and blast-furnace slag on the early hydration of blends. XRD, DTA and SEM were used to analyze the hardened paste after 1 month of hydration. Metakaolin influences significantly the kinetics, mechanism and products of hydration at initial period of hydration causing the rapid formation of ettringite. Hemicarbonate aluminate hydrate is formed as a product of ettringite conversion due to the presence of reactive calcite in Portland cement. © 2014 Elsevier Ltd. All rights reserved. Source

Bohac M.,Research Institute of Building Materials | Stanek T.,Research Institute of Building Materials | Urbanek P.,Research Institute of Building Materials
Advanced Materials Research

Paper deals with testing of surface photoactivity of fibre-cement composites. Self-cleaning ability, de-NOX activity, visual stability and weathering resistance were tested. Carriers of photoactivity were four different nano-powders with high content of anatase; crystalline form of TiO2. Photocatalytic properties of TiO2 particles are maintained even after mixing with cement in composite matrix. Natural photolysis as reaction of material and UV light is accelerated in presence of a proper form of TiO2 as a catalyst which by producing free radicals is able to oxidize organic matter and even small inorganic particles. Oxidized material is mostly less harmful considering the de-NOX process and decomposition of other gaseous pollutants. By this reaction the surface of composites containing large number of TiO2 particles is able to maintain its original appearance by so called self-cleaning ability. © (2014) Trans Tech Publications Switzerland. Source

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