Papers by Author: Petr Louda

Abstract: In this study, geopolymer samples were prepared by mixing metakaolin (MA) with activator solution made of potassium alkali silicate solution, potassium hydroxide flakes, and additional water. The aim of the experiment is to evaluate the mechanical strength of hardened samples based on four test variables including the SiO₂/K₂O molar ratios, K₂O concentration, H₂O/MA water coefficient, and curing temperature. The results reveal that K₂O concentration and H₂O/MA water coefficient impact strongly on the compressive strength, whereas varying of SiO₂/K₂O molar ratios in the range from 1.0 – 1.4 does not significantly change the compressive strength of geopolymer samples. On the other hand, high-temperature curing leads to higher mechanical strength of the samples in the early-age compared to curing at room temperature, due to the faster establishment of hard structure in the early-age of geo-polymerization process. However, curing at a temperature range of 80°C – 100°C contributes the non-linear strength development of the samples over the time.

Abstract: TiCN thin coatings with various different carbon contents were deposited using cathode arc evaporation of pure titanium in a mixture of N₂ and C₂H₂ gasses at a constant pressure of 1.5 Pa. The analyses show a transition from a stoichiometric to a non-stoichiometric coating structure with an increasing C₂H₂ content. Moreover, the increase in the acetylene in the gas mixture leads to a decrease in the crystal phase from pure polycrystalline to pure amorphous. Nanohardness changes from 30.4 to 4.4 GPa and the cohesive failure of the coatings is in the range of 61 - 72 N. The tribology is estimated by the Ball-on-Disc method and an Si₃N₄ ball as the counterpart. The measured coefficient of friction is in the range of 0.2 - 0.56.

Abstract: This paper is a continuation of our previous work. The article presents an investigation of the influence of coating deposition parameters, in particular a variation with 50% of both cathodic arc current and bias voltage, on the mechanical and tribological properties of TiCN coatings deposited by the cathodic arc evaporation of metals at a constant gas ratio. The thicknesses of the coatings are measured by the Calotest method using a 30-mm hard steel ball. The determined values are in the range of 734 – 1534 nm. Surface morphology and chemical composition are estimated by a Scanning Electron Microscope (SEM) and an Energy Dispersive Spectrometer (EDS) of SEM. The determined values of nanohardness are in the range of 10 - 23 GPa and adhesion values are in the range of 28 - 70 N. Tribology of the TiCN coatings is investigated with three different load forces (3N, 5N and 8N) by the CETR UMI Multi-Specimen Test System from Bruker with an Si3N4 ball counter-body. The friction coefficient is measured in the range of 0.19 - 0.23. Coating wear and wear of the counter-body are calculated, according to the standard EN1071-13:2010, wherein the values of the latter are in the range of (2.5 - 30) x 10-6 mm3.

Abstract: The article describes the effect of the pressure in the chamber during the deposition of thin layers on the basic mechanical properties of thin layers based on carbon. Monitoring parameters are mainly nanohardness, coefficient of friction and adhesion between the layer and substrate. This parameters are observed using nanohardness tester and scratch tester. All observed layers had the same thickens of layers. Carbon layers generally have poor adhesion to the substrate. To improve the adhesion, is used the interlayer of titanium which is between the substrate and carbon layer. Carbon layers are mostly used for their very good sliding properties especially in cases where can not be used process fluids or where is necessary to reduce the friction between the two materials. The carbon layer can also be used in medicine (for their biocompatibility), for machine tools (for their hardness and abrasion resistance) or as barriers layers (for their high chemical resistance).

Abstract: Chrome nitride (CrN) and CrN/Cr thin films were grown on EN ISO HS6-5-2 tool steel, which has been used as a substrate material. It is a high-speed Mo-W steel with high toughness. Chrome nitride thin films were deposited using a RF PA CVD/Magnetron Sputtering (MS) system at a gas flow ratio of 15/13 sccm of Ar/N₂. During the deposition process the pressure in the vacuum chamber was 0.9 Pa, the deposition Ubias and deposition time were different. The parameters of the process influence properties of the thin films were microstructure, hardness and adhesion to the substrate, etc. Optimal selection of process parameters is needed to achieve particular property combinations. The basis of the tribological measurements was the “ball-on-disc” testing method. Tribological testing (EN1071-13:2010) was conducted using a ball made from Si₃N₄ with a diameter of 6.350 mm, with a constant load of 3N at room temperature and humidity of 40±2 %. A Zeiss AXIO Imager M2 light optical microscope and a Dektak XT TM mechanical profilometer were used to evaluate the wear of the friction pairs at a load of 6mg and the size of the measured area of 200x1000 μm. The basis of the tribological measurements is the “ball-on-disc” testing method. Tribological testing (EN1071-13:2010) was conducted using a ball made from Si₃N₄ with a diameter of 6.350 mm, with a constant load of 3N at room temperature and humidity of 40±2 %. A Zeiss AXIO Imager M2 light optical microscope and a Dektak XT TM mechanical profilometer were used to evaluate the wear of the friction pairs at a load of 6mg and the size of the measured area of 200x1000 μm.

Abstract: A series of titanium carbonitride (TiCN) films with differing C content were deposited by cathodic arc evaporation of pure Ti in a gas composite environment of N₂ and C₂H₂. The increase of the C₂H₂ fraction in the gas environment leads to a continuous increase in the deposition rate of the TiCN thin films, as well as an increase in the adhesion of the films to the substrate. To evaluate the interaction of the material with the bacteria Escherichia coli CCM 3954 a method was used based on the ČSN EN ISO 56 0100 standard. The bacteria were inoculated in a liquid culture medium. It was observed that the monitored surfaces support the development of bacterial populations of E. coli depending on the type of TiCN thin films.

Abstract: Titanium carbonitride (TiCN) thin films with differing C content were deposited by cathodic arc evaporation of pure Ti in a gas composite environment of N₂ and C₂H₂. Scanning electron microscopy (SEM), scratch test, mechanical profilometer and “ball-on-disc” tribometer methods were used to characterize the surface, the coefficient of friction (CoF) of the TiCN thin films and the evaluated wear. An increase of the C₂H₂ fraction in the gas environment leads to a continuous increase in the deposition rate of the TiCN thin films, as well as an increase in the adhesion of the films to the substrate and the values of the CoF. Tribological test results (when tested against Si₃N₄ balls) show an increase in the friction coefficient of the TiCN from 0.08 to 0.32, with increasing carbon concentration in the film. The CoF decreases rapidly to 0.06 at a C content of 20.6 at.%, N 38.4 at.% and Ti 41.0 at.%.

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.