Solid State Phenomena Vol. 244

Abstract: The purpose of this research is to identify influence of natural pozzolana - opoka additive on hydration properties of the composite cement consisting of clinker, slag, opoka and gypsum. Recipes are created by reducing the amount of clinker from 60% to 20% to meet the requirements of cement composition according EN 197-1 standard (table 3).It was estimated that slag and opoka are increasing strength properties of the samples and accelerates the hydration of C₃S, moreover, participate in pozzolanic reaction in the composite cement. Slag has a greater effect on the compressive strength of samples after 1 month of hydration and opoka - after 3 months. It was found that opoka additive accelerates the hydration of C₃S more to compare with slag.

Abstract: In this work hydrothermal synthesis was carried out at 175 and 200 °C for 2, 8, 16, 24 and 48 h when using a stoichiometric composition (CaO/SiO₂=2.0) mixtures consisting of amorphous SiO₂·nH₂O and CaO or Ca (OH)₂. It was determined that α-C₂SH forms only after 16 h of the hydrothermal synthesis at 175 °C when using CaO. It starts to recrystallize to hilebrandite after 48 h. The temperature increase to 200 °C vividly fastens the formation of α-C₂SH as a noticeable amount of this calcium silicate hydrate was identified in the product already after 2 h and it became the dominant compound after 8 h. In case of using Ca (OH)₂, only negligible traces of α-C₂SH were identified after 2 h and the growth of its amount in the product, while prolonging the synthesis, was much slower as it prevailed only after 16 h. In addition, considerable amounts of unreacted portlandite were identified in the product even after 48 h.

Abstract: Aluminum powders are used in porous concrete constructional elements production, in coating compositions and varnish media industry, introduction of printing inks and finally but not less in chemical and pyrotechnical production. The purpose of atypical grinding processes is to obtain fine metal powders of extremely high specific surface which should be evaluated by the parameter of hiding power ability of pigment materials. This paper shows the development of this basic parameter of metal pigment products under the wet process of milling using a pilot-plant ball mill, as a function of milling time and turns of mill drum as one of the basic parameters.

Abstract: The parameters of α-C₂SH substituted with Al³⁺ ions hydrothermal synthesis was determined. α-C₂SH was synthesized in the primary mixtures with CaO/(SiO₂+Al₂O₃) = 1.75 and Al₂O₃/(SiO₂+Al₂O₃) = 0; and 0.025. The hydrothermal synthesis has been carried out in unstirred suspensions under saturated steam pressure in argon atmosphere at 175 °C temperature for 4; 8; 16; 24; 48; 72 hours by applying extra argon gas (10 bar). It was determined that in unstirred CaO–SiO₂·nH₂O–H₂O suspensions, the additive of Al₂O₃ changes the formation mechanism of synthesis products as well as their stability during the isothermal curing. It should be noted that in the mixtures with Al₂O₃, within 4 hours of isothermal curing at 175 °C all Al³⁺ ions were incorporated in the synthesis products structure. However, Al₂O₃ additive has negative influence on the formation of calcium silicate hydrates because even after 24 h of isothermal curing quite intensive diffraction peaks of unreacted portlandite were identified. When hydrothermal synthesis is extended to 48 hours, Ca (OH)₂ fully reacted and dibasic calcium silicate hydrates start dominate in the products.

Abstract: This article summarizes the main topics related to the issue of particle size analysis. It provides a discussion of the term ’particle’ and briefly describes the advantages and disadvantages of the most important particle size analysis methods.

Abstract: For a correct estimation of the energy demands of particulate systems mixing it is necessary to know the stress in the particulate material situated in front of the mixing element. Despite the theoretical knowledge of the overall stress in front of the homogenizer blade, so far there is no experimental verification in the literature, due to the current absence of a suitable measuring system. This study focuses on an understanding of the distribution of the force interactions between the particulate material and the blade along its height during the mixing process. The theoretical background of this process results from the theory of equilibrium limit of the particulate material, and this state may by described by Mohrʼs circle theory. The Novosad model is the theoretical model which enables an approximate calculation of the force acting on the blade. This model takes into account the effect of the mechanical and physical properties of the particulate material. By modifying the fundamentals of the Novosad model, it will be possible to identify the force distribution along the height of the blade. For the verification of this theoretical study, a new patented measuring system was designed and implemented in the homogenizer blade.

Abstract: This paper proposes the evaluation of material coefficient of heat dissipation rate for building materials, in particular using partial entropies, a temporal change in entropy upon heating a sample of a studied material and a temporal change in entropy upon overheating a sample of a studied material, in order to evaluate the rate of heat dissipation on samples of building materials with thermal insulating properties. From a physical point of view, the material parameter “specific heat capacity” generally refers to the ability of material to “conceive heat” so it can be said that the illustrated material Ytong has a slightly higher specific heat capacity than that of polyurethane. From a physical point of view, the material parameter “thermal conductivity” generally refers to the ability of a given material to “conduct heat through the material in connection with stationary heat flux”, so it can be assumed as well as verified by measuring that Ytong also has a higher thermal conductivity than that of polyurethane. From a physical point of view, the newly proposed material parameter “heat dissipation rate” generally indicates the “rate of heat loss to the external environment in connection with non-stationary heat flux”, so it may also be assumed and verified by measuring that the heat dissipation rate of Ytong will be higher than that of polyurethane.

Abstract: The article deals with the study of biocorrosion of concretes by sulphuric acid induced by oxidizing bacteria Acidithiobacillus thiooxidans. The concretes were prepared from reference cement CEM I 42,5 N, the mixtures of CEM I 42,5 N and antimicrobial ground granulated blastfurnace slag BIOLANOVA (GGBS) (with amount of GGBS 65 mass % - CEM III/A 32,5 N, 75 mass % - CEM III/B 32,5 N, 85 mass % - CEM III/C 32,5 N a 95 mass % - CEM III/C 32,5 N) and novel hybrid cement H-CEMENT (HC). The experiments were carried out in model laboratory conditions at 30 °C during 91 days. The degree of deterioration of concrete samples has been studied on the base of the pH changes of leachate, the concentrations of selected ions such as S, Ca and Si and the mass changes. It has been clearly confirmed, that in the presence of bacteria, the pronounced degradation of the samples occurred with exception of HC sample, which behaviour proved differences to the other samples. The HC concrete possessed more alkali leachate in comparison with the others. The concentration of sulphur S in leachate was increased by metabolic activity of bacteria due to biogenic H₂SO₄ formation. The increase of S concentration acidified leachate and so promoted leaching next substances from the samples. The concentration of silicon Si in leachate was promoted by metabolic activity of bacteria, as well. The development of Ca leaching concentration has been similar at all composite samples as in the case of reference CEM I 42,5 N concrete, however the smallest portion of leached Ca has been determined at HC concrete. The Ca leaching concentration has been increasing with the amount of GGBS being added to the composite CEM III concretes. The different tendency has been also observed at the HC samples in regards to the mass changes. The increase in mass has been measured at all concrete samples with exception of HC concrete, at which the mass decrease has been found out. The results confirmed the resistance of the concrete composite samples containing GGBS and HC to the sulphate attack and the HC sample showed the highest resistance to the sulphate biocorrosion.

Abstract: The motivation for this study was the increasing need of recycling waste plastics in the cleanest - separated form. Relatively inexpensive methods of physicochemical separation of plastics is based on the different wettability of their surfaces. Because most used polymers are relatively highly hydrophobic, which would lead to their collective flotation in water, the study was aimed for the selective suppression of the hydrophobic character - hydrophilization of one of the most common plastics, which is PET. XPS method gave interesting information about the actual mechanism of the chemical reactions at the PET surface, which was changed by the alkaline hydrolysis.