Vlastimil Matějka

Preparation and characterization of photoactive composite kaolinite/TiO2

Preparation of nanocomposite kaolinite/TiO(2), using hydrolysis of titanyl sulfate in the presence of kaolin was addressed. A variable (kaolin)/(titanyl sulfate) ratio has been used in order to achieve the desired TiO(2) content in prepared nanocomposites. Calcination of the composites at 600 °C led to the transformation of the kaolinite to metakaolinite and to origination of metakaolinite/TiO(2) composites. The prepared samples were investigated using X-ray fluorescence spectroscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetry and diffuse reflectance spectroscopy in the UV-VIS region. Structural ordering of TiO(2) on the kaolinite particle surface was modeled using empirical force field atomistic simulations in the Material Studio modeling environment. Photodegradation activity of the composites prepared was evaluated by the discoloration of Acid Orange 7 aqueous solution.

Role of Al2O3 in Semi-Metallic Friction Materials and its Effects on Friction and Wear Performance

In this work the semi-metallic friction composites with moderately increased content of Al2O3 (0, 3.4, 5.6, 9.0, and 14.6 vol%) were successfully fabricated by casting technology and their tribological properties were evaluated. The character of friction surfaces was confirmed by SEM. The sample with 5.6 vol% of Al2O3 offers the best tribological property among the prepared formulations, and is characterized by high and steady friction coefficient (about 0.45) and low wear. With the temperature increasing, the stibnite patches population on friction surface increases and individual steel fibers spread due to their plastic deformation to form larger primary contact plateaus. The area covered by contact primary plateaus decreases with the alumina content increasing.

Semimetallic Brake Friction Materials Containing ZrSiO4: Friction Performance and Friction Layers Evaluation

The effect of ZrSiO4 (zircon) content on friction performance and friction surfaces of semimetallic brake friction materials is discussed. The experimental results indicate that the varying content of zircon affects the friction performance as well as plays crucial role in the iron film formation on the friction surfaces. The friction layers, formed during friction process, were carefully characterized using scanning electron microscopy with energy dispersive X-ray microanalysis, and X-ray diffraction methods. The phenomenon of two different types of iron film formation (film I and film II) on the friction surfaces is proposed and their formation and destruction mechanism is described. Despite the compositions of both iron films being similar, film I is formed by steel wool itself and film II by the debris from either disc or steel wool. The relationships among formulation, friction performance, and friction surfaces are summarized.

Towards the ranking of airborne particle emissions from car brakes – a system approach

Airborne particulate matter emitted from motor vehicle brakes is a contributor to urban air quality. Therefore, a method to rank brake pairs (pads and rotors) with respect to their particle emission factors in a reliable way is needed to develop a low-emission disc brake. A novel inertial disc brake dynamometer designed for brake particle emission studies, a modified SAE J 2707 cycle, an electrical low-pressure cascade impactor and a filter are used to test five different pad materials against cast-iron rotors. By changing only the pad materials, it is shown that the differences between the mass emission factor and the number emission factor of the the worst brake pair and those of the best brake pair decreases by more than four times and 19 times respectively. Furthermore, the results show that the material combination ranked the best in terms of the mass emission factor is ranked the worst in terms of the number emission factor. The results reveal that this combination of a test stand, a test cycle and particle instruments can discriminate between different brake pair materials in a reliable way in the case of the mass emission factors while more research has to be carried out in the case of the number emission factors.

EFFECT OF CALCINATION TEMPERATURE AND CALCINATION TIME ON THE KAOLINITE/TIO2 COMPOSITE FOR PHOTOCATALYTIC REDUCTION OF CO2 VLIV KALCINAČNÍ TEPLOTY A DOBY KALCINACE NA KOMPOZIT KAOLINIT/TIO2 PRO FOTOKATALYTICKOU REDUKCI CO2

Abstract The kaolinite/TiO2 composite (60 wt% of TiO2) was prepared by thermal hydrolysis of a raw kaolin suspension in titanyl sulphate and calcined at different temperatures (600, 650 and 700°C) and for different times (1, 2 and 3 h). The obtained samples were characterized by XRPD, N2 physical adsorption and SEM, and tested for photocatalytic reduction of CO2. The different calcination conditions did not influence TiO2 phase composition, only slightly changed the specific surface area, and significantly affected crystallite size of kaolinite/TiO2 composite. A higher temperature and longer duration of calcination lead to higher crystallinity of the powder. The photocatalytic results showed that the crystallite size determined the efficiency of kaolinite/TiO2 photocatalysts Abstrakt Kompozit kaolinit/TiO2 (60 hm% TiO2) byl připraven termální hydrolýzou suspenze surového kaolinu v síranu titanylu a kalcinován při různých teplotách (600, 650 a 700°C) a po různou dobu (1, 2 a 3 h). Získaný vzorek byl charakterizován pomocí XRPD, N2 fyzikální adsorpcí a SEM, a testován na fotokatalytickou redukci CO2. Rozdíl kalcinačních podmínek neovlivnil složení fáze TiO2, pouze se mírně pozměnila specifická povrchová plocha a výrazně byla ovlivněna velikost krystalitu kompozitu kaolinit/TiO2. Vyšší teplota a delší doba kalcinace vedly k vyšší krystalitě prášku. Fotokatalytické výsledky ukázaly, že velikost krystality určuje účinnost fotokatalyzítoru kaolinit/TiO2

Utilization of Photoactive Kaolinite/TiO2 Composite in Cement-Based Building Materials

Titanium dioxide (TiO2) is the most studied photocatalyst with application potential in many branches of industry. Building industry represent the sector, where the photoactive TiO2 have been already successfully utilized. Concretes, plasters, paints are building materials where the photoactive TiO2 is widely tested. However the amount of TiO2 in these materials is limited with respect to their final properties. If the TiO2 replaces the certain amount of cement in concretes, the resulting compressive strength decreases when this photocatalyst is added in non-adequate content. The surface of kaolinite particles can serve as a matrix for nanosized TiO2 growing what results in photoactive composite – kaolin/TiO2 formation. After the calcination of this composite the process of kaolinite dehydroxylation is responsible for metakaolinite formation and composite metakaolinite/TiO2 with latently hydraulic properties originates. If the metakoline/TiO2 is used for partial cement replacement the compressive strength of resulting samples is notably increased and its surface shows photodegradation ability against rhodamine B.

Structure and properties of kaolinite intercalated with potassium acetate and their nanocomposites with polyamide 1010

The intercalation complex marked as KAA was a modified kaolinite (KA) with potassium acetate as an intercalating agent, which was used as a reinforcement to prepare polyamide 1010 (PA1010) matrix nanocomposites (PKAA) by melt compounding. X-Ray diffraction results indicated that the interlayer basal spacing increased from 0.720 nm (KA) to 1.411 nm (KAA), after an intercalation process with an intercalation ratio of 99.7%. The nanocomposite with 2 wt% KAA exhibited the best comprehensive mechanical properties, including tensile strength, elongation at break, and notched impact strength. Furthermore, the thermal performance of these nanocomposites could be effectively improved, which manifested as the elevated glass transition temperature and thermal decomposition temperature in the test results of the dynamic mechanical thermal analysis and thermogravimetric analysis (TGA). The melting point and crystallization behavior of PKAA were also increased due to results from the differential scanning calorimetry. Besides, the bilayer inserting model was simulated by Materials Studios software to further understand the structure-function relationship of PKAA.

Functional nanostructures of montmorillonite with conducting polyaniline

Abstract The present work describes the effect of montmorillonite (MMT) particles on the alignment of conducting polyaniline (PANI) chains in a PANI/MMT composite. The composite was prepared both as a powder, pressed into pellets, and as thin films deposited on glass surfaces. For comparison, pure PANI was also prepared in these two forms. A combination of X-ray powder diffraction analysis and molecular modelling confirmed the successful intercalation of the PANI into theMMT, while Raman spectroscopy confirmed the presence of the conducting form of PANI (i.e. the emeraldine salt) in all samples. Scanning electron microscopy, transmission electron microscopy and atomic force microscopy were used to study the morphologies of all samples. Conductivity measurements showed that the presence of the MMT particles in the PANI/MMT composites contributes to a significant increase in the electrical conductivity in comparison with the pure PANI samples. Moreover, in the pressed pellets the presence of theMMT particles led to an extremely high electrical anisotropy. TheUV-VIS spectroscopy results showed that the PANI/MMT thin film exhibited a selective transmittance in the range 450-650 nm; therefore, the PANI/MMT thin film is not only conductive, but also suitable for use in various optical applications.

Scaling effects of measuring disc brake airborne particulate matter emissions – A comparison of a pin-on-disc tribometer and an inertia dynamometer bench under dragging conditions

An important contributor to non-exhaust emissions in urban areas is airborne particulate matter originating from brake systems. A well-established way to test such systems in industry is to use inertia dynamometer benches; although they are quite expensive to run. Pin-on-disc tribometers, on the other hand, are relatively cheap to run, but simplify the real system. The literature indicates promising correlations between these two test stands with regard to measured airborne number distribution. Recent studies also show a strong dependency between the airborne number concentration and the disc temperature. However, a direct comparison that also takes into account temperature effects is missing. The aim of this paper is, therefore, to investigate how the transition temperature is affected by the different test scales, under dragging conditions, and the effects on total concentration and size distribution. New and used low-steel pins/pads were tested against cast iron discs/rotors on both the aforementioned test stands, appositely designed for particulate emission studies. A constant normal load and constant rotational velocity were imposed in both test stands. Results show that a transition temperature can always be identified. However, it is influenced by the test scale and the frictional pair status. Nevertheless, emissions are assessed similarly when an equivalent frictional pair status is analysed (e.g. run-in). Further investigations for fully run-in samples on the pin-on-disc should be performed in order to finally assess the possibility of using the tribometers for the initial assessment of different friction materials.

Biotic Attack in Claddings of Prefabricated Buildings

Problems biotic attack facades of prefabricated buildings takes particular with regard to given increasing demands and requirements of thermal technique and energy. In the last twenty years, increased demands on thermal properties of exterior walls, increasing the thickness of thermal insulation, additional insulation contact changes prefabricated walls on multilayer circuit design, but at the same time claddings prefab evident adverse side effects in the form of color change in outer surface rendering locally and globally. In this paper are discussed laboratory tests on the sample confirmed the presence of external plaster façade panel biotic attach building, which is equipped with additional contact system.