Ústav chemie materiálů

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CORROSION BEHAVIOUR OF AZ31 ALLOY IN AN ALKALINE ENVIRONMENT OF 0.1 M NACL IN THE PRESENCE OF LIGNITIC HUMIC ACID
(Tanger, 2024-01-08) Horák, Tomáš; Buchtík, Martin; Wasserbauer, Jaromír; Březina, Matěj; Doskočil, Leoš
Magnesium alloys are characterized by high corrosion rates. This undesirable phenomenon can be slowed down by corrosion inhibitors. Particularly environmentally friendly molecules are in the spotlight. A possible candidate for a green inhibitor may be humic acid isolated from lignite. In this work, the corrosion behavior of AZ31 was investigated in 0.1 M NaCl with and without humic acid at pH 9. Surface analysis was performed using a scanning electron microscope (SEM) with an energy dispersive X-ray spectroscope (EDS) and Fourier--transform infrared (FTIR) spectroscopy. Corrosion behavior was investigated using potentiodynamic polarization (PDP) measurements. The results showed that lignitic humic acid accelerates corrosion in 0.1 M NaCl at pH 9 and this effect was concentration dependent.
Filling of Chitosan Film with Wax/Halloysite Microparticles for Absorption of Hydrocarbon Vapors
(WILEY-V C H VERLAG GMBH, 2024-02-24) Caruso, Maria Rita; D’Agostino, Giulia; Wasserbauer, Jaromír; Šiler, Pavel; Cavallaro, Giuseppe; Milioto, Stefana; Lazzara, Giuseppe
The effect of the preparation protocol of chitosan (CHI) based films filled with wax microparticles stabilized by halloysite nanotubes (HNTs) in Pickering emulsions (PE) is investigated. The obtained results show that the addition of acetic acid (before or after the preparation of wax/HNT microspheres) affects the properties of the composite films as well as the colloidal stability of PE. The colloidal behavior of CHI/HNT/wax PE by optical microscopy and sedimentation tests are studied. On the other hand, the corresponding composite films (prepared by solvent casting method) are characterized through several techniques, including Scanning Electron Microscopy, UV-vis spectrometer, water permeability, and contact angle measurements. Dynamic Mechanical Analysis allows this to estimate the effect of wax microparticles on the tensile performances of CHI-based films. As a general consideration, the filling of the CHI matrix with wax/HNT improves the physicochemical properties of the films. Finally, the efficacy of the films as adsorbents of n-dodecane vapors is explored. Due to the presence of hydrophobic domains (wax embedded in CHI), the composite films possess higher adsorption efficiencies compared to pristine CHI. Accordingly, it can be stated that the combination of CHI with wax/HNT microparticles is promising to obtain biocompatible composite films useful for remediation purposes. Chitosan films filled with hydrophobic microparticles are successfully prepared by solvent casting of wax/halloysite Pickering emulsions. The addition of wax microparticles within chitosan generated the surface hydrophobization of the film. Due to hydrophobic attractions, the presence of microwax improved the absorption capacity toward n-dodecane vapors. The filled film is promising as a sustainable material for capturing organic pollutants, such as hydrocarbons. image
CONDUCTOMETRY ANALYSIS - BENEFICIAL METHOD FOR DETERMINING THE CHEMICAL COMPOSITION OF ALKALINE SILICATE SOLUTIONS
(Institute of Metals and Technology, 2024-04-12) Kalina, Lukáš; Bílek, Vlastimil; Flídrová, Michaela; Markusík, David; Topolář, Libor; Fládr, Josef
The study deals with the methodology for determining the chemical composition of alkaline silicate solutions. Nowadays, the most widely used method in industry is titration, using the color change of an acid -base indicator. This technique is very accurate for the determination of the total alkalinity (i.e., Na2O, K2O, or Li2O). However, a problem arises in the determination of the SiO2 content, since the color change of the methyl red indicator is very slow and therefore the equivalence point is unclear. The main aim of this work is to present the benefits of conductometric titration, where the equivalence point is indicated by a sudden change in the conductivity. The applicability of the method was verified with other analytical techniques, such as ICP-OES and gravimetric analyses. Their results confirmed the values of the obtained silicate module (the molar ratio of SiO2 and alkaline oxide) in the cases of sodium, potassium and lithium water glasses. Based on the obtained results, one can say that conductometry is a very promising method providing an accurate, fast and instrumentally undemanding chemical characterization of alkaline silicate solutions, usable even in a manufacturing process.
Hydration kinetics of C3A: effect of lithium, copper and sulfur-based mineralizers
(Springer Nature, 2024-09-16) Bartoníčková, Eva; Ptáček, Petr; Novotný, Radoslav; Palovčík, Jakub; Másilko, Jiří; Švec, Jiří; Sedlačík, Martin; Koplík, Jan; Staněk, Theodor; Hemzal, Dušan
Calcium aluminate phases have a particular effect on the early heat release during setting initiation and have a substantial influence on the further workability of ordinary Portland cement. The nature of the calcium aluminate hydration products and its kinetics strongly depends on sulfate content and humidity. The effect of mineralisers on melt formation and viscosity is well described for calcium silicate systems, but information is still lacking for calcium aluminates. Therefore, the synergistic effect on the crystal structure and hydration mechanism of the tricalcium aluminate phase of the addition of mineralizers, i.e. Li2O, CuO, SO3 to the raw meal is here investigated. Co-doped calcium aluminate structures were formed during high-temperature treatment. Thermal analysis (TG-DTA and heating microscopy) was used to describe the ongoing high-temperature reaction. Resulting phase composition was dependent on the concentration of the mineralizer. While phase pure system was prepared with low mineralizer concentrations, with increasing mineralizer content the secondary phases were formed. Raman spectroscopy and XPS analysis were used to investigate the cation substitution and to help describe the cations bonding in co-doped calcium aluminate system. Prepared powders have been hydrated in a controlled manner at different temperatures (288, 298, 308 K). The resulting calorimetric data have been used to investigate the hydration kinetics and determine the rate constant of hydration reaction. First-order reaction (FOR) model was here applied for the activation energy and frequency factor calculations. The metastable and stable calcium aluminate hydrates were formed according to initial phase composition. In phase pure systems with low S content, the formation of stable and metastable hydrates was depended on the reaction temperature. Conversely, in systems with secondary phases and higher S content, the hydration mechanism resembled that which appears in calcium sulfoaluminates.
Internal hydrophobic treatment for mortar containing supplementary cementitious materials: thermal analysis of kinetics and products of hydration
(SPRINGER, 2024-09-30) Materak, Kalina; Wieczorek, Alicja; Chałupka-Śpiewak, Karolina; Koniorczyk, Marcin; Kalina, Lukáš; Bílek, Vlastimil
The presented research investigates the application of the organosilicon admixtures based on triethoxyoctylsilane (OTES) on the hydration of the cement-based material with addition of supplementary cementitious materials (SCM) such as blast furnace slag and microsilica. The influence of silane-based admixtures on the kinetics of hydration was investigated by isothermal calorimetry. The calorimetric results disclosed that applied admixtures affect the hydration process of cement paste with SCM. The DTA/TG analysis provided the information about impact of triethoxyoctylsilane on the composition and formation of the mineral phases. The DTA/TG measurements showed noticeable changes in the thermal decomposition of the tested materials and amount of bounded water. The impact of OTES on the microstructure and pore size distribution of pastes was examined by mercury intrusion porosimetry. The result showed significant changes in the range of pore diameters. The influence of organosilicon admixtures on the compressive strength of mortars after 2, 7, 28, 56 and 90 days was also investigated. The effect depended on the mineral additive used. In case of blast furnace slag, the development of compressive strength was only delayed, however, in the case of microsilica, it was stopped.

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