Ocena toplotne upornosti izbranih bentonitnih veziv

Bentonite is one of the most widely used clays associated with various applications. In the case of foundry technology, bentonite is primarily used as a binder for the mold manufacture. The thermal resistance of bentonite binders, also called the thermal stability, is a natural property of clay minerals, depending on the source, the mineralogical and chemical composition of clay and it is also closely connected to the bentonite structure (various interlayer ions, the level of ion substitution of montmorillonite). Generally, there are various methods for evaluating this property. This contribution describes various methods of determining the bentonite thermal stability based on the evaluation of the technological parameters of bentonite molding mixtures and their comparison. These methods were chosen on the basis of a background research and practical experiences. For the experiments the bentonites commonly used in the foundries of the Czech and Slovak region were selected.Web of Science49346946

Photocatalytic decomposition of nitrous oxide using TiO2 and Ag-TiO2 nanocomposite thin films

TiO2 and Ag-TiO2 (0.05, 0.25 and 1 wt% of Ag) thin films were prepared by the sol–gel method. The prepared films were characterized using SEM-EDAX, XRD, Raman spectroscopy, atomic force microscopy and UV–Vis spectrometry. Photocatalytic decomposition of N2O was performed in an annular batch reactor illuminated with an 8 W Hg lamp (254 nm wavelength). The photoreactivity of Ag-TiO2 increases with the Ag amount to 0.25 wt% Ag. Further increase of Ag loading to 1 wt% Ag did not change N2O conversion. The Ag particles deposited on the TiO2 surface can act as electron–hole separation centers. The presence of water vapor and oxygen in the reaction mixture slightly improved N2O conversion.Web of Science20917517

Photocatalytic degradation of selected pharmaceuticals using g-C3N4 and TiO2 nanomaterials

Exfoliated graphitic carbon nitride (g-C3N4) and two commercially available nanomaterials from titanium dioxide (P25 and CG300) were tested for the photocatalytic degradation of paracetamol (PAR), ibuprofen (IBU), and diclofenac (DIC). Prior to photocatalytic experiments, the nanomaterials were characterized by common methods, such as X-ray diffraction (XRD), UV-VIS diffuse reflectance spectroscopy (DRS), Fourier transformed infrared spectroscopy in attenuated total reflection mode (FTIR-ATR), transmission electron microscopy (TEM), physisorption of nitrogen, and dynamic vapor adsorption (DVS) of water. The sizes and specific surface area (SSA) of the TiO2 nanoparticles were 6 nm and 300 m(2)g(-1) for CG300 and 21 nm and 50 m(2)g(-1) for P25. The SSA of g-C3N4 was 140 m(2)g(-1). All photocatalytic experiments were performed under UV (368 nm), as well as VIS (446 nm) irradiation. TiO2 P25 was the most active photocatalyst under UV irradiation and g-C3N4 was the most active one under VIS irradiation. Photodegradation yields were evaluated by means of high performance liquid chromatography (HPLC) and reaction intermediates were identified using gas chromatography with mass detection (GC-MS). Paracetamol and ibuprofen were totally removed but the intermediates of diclofenac were observed even after 6 h of irradiation. Some intermediates, such as carbazole-1-acetic acid, 2,6-dichloraniline, and hydroxylated derivates of diclofenac were identified. This study showed that g-C3N4 is a promising photocatalyst for the degradation of pharmaceuticals in an aqueous environment, under visible light.Web of Science99art. no. 119

The effect of temperature and milling process on steel scale utilized as a pigment for ceramic glaze

This study is focused on the evaluation of the re-utilizability of scale originated during the steel casting and steel rolling processes as a pigment for glazes. Non-oiled scale with Fe3O4 as the major phase were used as a coloring component of transparent glaze matrix in: (i) as received state, (ii) thermally pre-treated at 700 and 900 degrees C, (iii) mechanically treated in planetary ball mill (60, 120 and 240 min) and (iv) mechanically treated in vibratory disc mill (60 and 120 min). Prepared glazes were applied on the surface of ceramic tiles prepared from a commercially available white ceramic slurry. The resulting tiles with given glaze were thermally treated at 800, 900 and 1060 degrees C. The pigments were characterized by X-ray powder diffraction method (XRD), X-ray fluorescence spectroscopy (XRF), granulometry (PSD), thermogravimetric analysis (TG) and differential thermal analysis (DTA), scanning electron microscopy (SEM/EDAX). The color of the samples was described by the coordinates L*a*b* from CIELAB color space. The results showed that the non-oiled scale is suitable as the pigment for ceramic glazes. Careful control of the scale treatment process (mechanical as well as thermal) together with the temperature of final glaze firing is necessary to obtain the glaze of desired color and quality.Web of Science138art. no. 181

Graphitic carbon nitride as a platform for the synthesis of silver nanoclusters

Graphitic carbon nitride (CN) synthetized by the thermal polycondensation of melamine at 550 degrees C for 4 h was further exfoliated by heating at 500 degrees C for 3 h. Silver cations were adsorbed on the exfoliated graphitic carbon nitride (CNE) and then reduced by sodium borohydride forming silver nanoclusters (NCs) with a size of less than 1 nm.The NCs were located on the CNE surface and did not change the CNE properties except for its pore size distribution and thereby specific surface area (SSA).The Ag NCs were able to collect the photoinduced electrons of CNE and thus reduce their recombination with the holes. It was also documented by the increase in the CNE photocatalytic activity in terms of the degradation of antibiotic Ofloxacin.This study demonstrates the ability of CNE to serve as a platform for a simple and fast synthesis of Ag NCs without any stabilizing compounds.Web of Science161art. no. 16

Polyaniline/TiO2/kaolinite: The composite material with high electrical anisotropy

Kaolinite–TiO2 nanocomposite matrix (KATI) coated with polyaniline (PANI) layer has been prepared in powder form and pressed into tablets. The conductivity was studied in dependence on (1) wt.% of TiO2 in KATI matrix and (2) thermal pre-treatment of KATI matrix. The anisotropy factor α, i.e. the ratio of in-plane conductivity and conductivity in the direction perpendicular to the tablet plane, was found to be very high for PANI/KATI tablet (α is of the order of 103–104) in comparison with pure PANI tablet (α is of the order of 102). Structure has been studied using Raman spectroscopy, X-ray diffraction analysis, scanning electron microscopy and molecular modeling. The possibility of using the tablets as a load sensors have been tested and tablets pressed from composites containing calcined KATI seem to be promising material for this purpose.Web of Science1461-215214

A low-cost photoactive composite quartz sand/TiO2

The photoactive quartz sand/TiO2 composites were prepared by thermal hydrolysis of the suspension obtained by addition of quartz sand to a titanyl sulfate solution. The required amount of TiO2 in the prepared composites (i.e. 9, 22 and 45 wt.%, respectively) was achieved using a variable titanyl sulfate/quartz ratio. As reference materials, pure TiO2 was prepared using the thermal hydrolysis of the titanyl sulfate solution under the same condition as used during the preparation of composite quartz/TiO2. The composite samples, dried at 105 °C and calcined at temperatures of 500–900 °C, were investigated using X-ray fluorescence spectroscopy, X-ray powder diffraction analysis, transmission electron microscopy, and Fourier transform infrared spectroscopy. Structural ordering of TiO2 particles on the quartz surface was studied using atomistic simulations in a Material Studio modeling environment. Photodegradation activity of the composites was evaluated by the discoloration of Acid Orange 7 aqueous solution. The composite containing 22 wt.% of TiO2 and calcined at 800 °C exhibits the highest photoactivity. Higher and lower amounts of TiO2 led to worse results. The quartz/TiO2 composite is a promising material able to replace pure TiO2 in a wide range of building materials.Web of Science22249748

Identification of phase composition of binders from alkali-activated mixtures of granulated blast furnace slag and fly ash

The prepared alkali-activated binders (AAB) and composites using suitable latent hydraulic raw materials represent an alternative to materials based on Portland cements. This paper deals with ways how to influence the functional parameters of AAB by setting up mixtures of granulated blast furnace slag (GBFS) and fly ash with selected chemical compositions. In this way the course of hydration process is modified and the phase composition of products of alkali activation is changed as well as their final properties. The amorphous character of the hydration products makes evaluation of the phase composition of hardened AAB difficult and significantly limits the number of experimental techniques suitable to characterise their phase composition. It was observed that measuring the pH of water extracts obtained from the alkali-activated mixtures can give supplementary information about the process of hardening of alkali-activated mixtures of GBFS and fly ash.Web of Science581887

Electrically conductive aluminosilicate/graphene nanocomposite

Highly electrically conductive ceramic material based on aluminosilicate/graphene nanocomposite has been prepared by high pressure (400 MPa) compaction of montmorillonite intercalated with polyaniline followed with the high temperature (1400 °C) treatment in argon atmosphere. Tablets pressed from polyaniline/montmorillonite intercalate exhibits strong texture due to the disk-shaped montmorillonite particles and, consequently, the high anisotropy in conductivity. The high temperature induced phase transformation of montmorillonite into cristobalite and mullite preserved the aluminosilicate layered structure and created good conditions for formation of graphene sheets from polyaniline layers intercalated in montmorillonite. Therefore, the texture and anisotropy in conductivity remain preserved in resulting aluminosilicate/graphene tablets, while the in-plane conductivity in aluminosilicate/graphene tablets is 23,000× higher than the conductivity of uncalcined polyaniline/montmorillonite tablets. Simple fabrication method of aluminosilicate/graphene tablets is very promising for the manufacturing of the electrically conductive and tough ceramic material, which can be exposed to corrosive environment as well as to high temperatures.Web of Science34123117311

The role of graphitic carbon nitride in the formulation of copper-free friction composites designed for automotive brake pads

In this study, graphitic carbon nitride (g-C3N4, labelled as gCN) was tested in the formulation of copper-free (Cu-free) friction mixtures, which are potentially interesting for brake pad manufacturing. Three formulations of friction composites were prepared starting from a common Cu-free master batch: (i) without graphite, (ii) with graphite and (iii) with gCN. The mixtures were pressed in the form of pins by hot-press moulding. The friction-wear performance of the prepared pins was investigated using a pin-on-disc (PoD) test at room temperature (RT), high temperature (HT) (400 degrees C) and, again, at room temperature (H-RT). The values of the friction coefficient (mu) for the composites with gCN (or graphite) were as follows: (i) RT test, mu(RT) = 0.52 (0.47); (ii) HT test, mu(HT) = 0.37 (0.37); (iii) RT after the HT tests, mu(H-RT) = 0.49 (0.39). With respect to wear resistance, the samples with graphite performed better than the samples without this solid lubricant. To the best of our knowledge, this is the first report regarding the evaluation of the role of gCN in friction composites designed for automotive brake lining applications. The results indicate the main role of gCN as a soft abrasive.Web of Science121art. no. 12