Papers by Author: Dora Kroisová

Abstract: Rice husks are among the world's most significant agricultural waste. On the one hand, their use is related to solving an environmental problem; on the other hand, they use this material as a potential advanced material for many applications. Due to their chemical composition, rice husks can be a source of cellulose fibers and silica nanoparticles. The present text presents the essential characteristics of fibers and nanoparticles that were obtained from the treated shells at the same time. The fibers released from the rice husks have diameters ranging from 5 to 10 μm, the length being in the hundreds of micrometers. The surface of the fibers is not smooth, a sub-micrometer structure is visible, which indicates the potential possibility of further pulping into nanofiber formations. Silica nanoparticles are found on the surface of fibers released from rice husks and beyond. Nanoparticles form clusters of tens of nanometers; the sizes of individual particles are at the level of nanometer units. In the modified hulls, the accompanying technique did not identify the accompanying elements found in the original rice hulls.

Abstract: Rice husks (RH) are characterized by a high content of silicon dioxide up to 23 wt. %. Silica in the form of nanoparticles creates surface layers formed in various plant parts which ensure protective properties and mechanical stability. These nanoparticles with a dimension in the range of tens of nanometers, are formed during biochemical processes and photosynthesis. Individual nanoparticles are interconnected between themselves and between layers with organic phase via cellulose fibres. Accompanying ions mainly potassium, calcium, sodium, magnesium and aluminium extremely important for plant growth have also been identified in rice husks. In this research paper we investigated mechanical properties of composite epoxy resin material, which was composed of ChS Epoxy 520 filled with silica obtained from rice husks. Nanoparticles of silicon dioxide with the size in dozen of nanometers were prepared by calcination of raw plant parts. We found that the 0.1 phr of filling (0.01 g of filler + 10 g of epoxy) demonstrated a significant increase of wear resistance and decrease of coefficient of friction. An excellent adhesion between epoxy resin and silica nanoparticles was also observed. The silicon dioxide in epoxy resin plays the role of the hard phase, which transfers part of the load and protects the surface of polymer against wear. The presence of this filler does not change the mechanical properties of the original resin.

Abstract: This paper deals with description of properties of selected natural materials mainly theirs shelter function. The investigated materials are horsetail and walnut shell. Both natural materials have porous shell/tubular structure. Walnut shell provides natural shield cover for fruit with gradient distribution of porosity and membrane function. In case of horse tail, except the gradient distribution of porosity there is also the gradient change of chemical composition along the cross-section.

Abstract: Protection and safety of workers in plants with the danger of fire is always the first place. They are currently used in devices that are designed to quickly separate the fire residues from workers such as steel fire doors filled with non-combustible materials that insulate the prescribed time up to 600 ° C. As the demands for safety was the requirement for resistance to temperatures higher than 600 ° C. [1, 2]. Post relates to improvements refractory properties of steel gates based geopolymer matrix composites. They are analyzed the properties of different materials such as fillers geopolymer matrix, durability and affinity to steel parts of the door structure.

Abstract: Geopolymer matrice Composites are fabricated at room temperature or thermoset in a simple autoclave. After approximately four hours of curing, composite materials exhibit excellent properties. Finding applications of geopolymeric composites in all fields of industry are the hot topics. This paper covers: (i) mechanical properties of fibers: carbon, Saint-Gobain Cemfil/CFV alkali resistance glass (various types), ARG-NEC (Nippon electric Columbia) alkali resistance glass, E-glass for pultrusion, AR glass for pultrusion were evaluated in accordance with Japanese Industrial Standard (JIS R 7601). (ii) properties of geopolymeric matrices: geopolymeric matrices are fabricated from various types of geopolymeric resins that were made at Research Institute of Inorganic Chemistry, Inc., Czech Republic and testing for mechanical properties, and by SEM for structure characterization. (iii) fabrication procedures of geopolymer matrix composites with carbon and other fiber reinforcements. (iv) results of mechanical testing of geopolymer composites, SEM for adhesion between the matrix and reinforcement, and (v) Results and discussion.