The effects of residual stresses in thin W-C based coatings were investigated with the aim to find their influence on nanohardness and indentation modulus. Ten samples of W-C based coatings were deposited on microslide glass substrates using DC magnetron sputtering at the identical deposition parameters. Their thickness was in the range from 500 to 600 nm. The residual stresses in the coatings varied from 1.5 GPa up to 4.4 GPa. Increase of residual stress caused linear increase of HITfrom 16 to 19.5 GPa. This increase was only the result of the compressive stresses. EITof the studied coatings was not sensitive to residual stresses and corresponded to 185 GPa ± 15 GPa.

Several series of W-C based coatings were deposited by HiPIMS and HiTUS deposition technologies with different deposition parameters (power, frequency and pulse length in HiPIMS and pressure, acetylene content and RF bias in HiTUS). To investigate their effect on the hardness and tribological properties. The hardness of HiTUS coatings was up to 36 GPa and CoFs of these coatings were around 0.5, whereas the HiPIMS coatings exhibited lower hardness (18 – 20 GPa) but also lower CoFs (0.18 - 0.2).

The calcined gypsum–lime–metakaolin–water system and its subsystems consisting of two and three components are analyzed using the isothermal heat flow calorimetry, differential scanning calorimetry, and thermogravimetry. The hydration heat development in the initial hydration phase up to several hours is monitored in a common way, on the samples having a mass of about 1 g. In later time intervals up to 1 week when the values of the specific hydration heat power are very low, a large-volume calorimeter with better resolution is used for 300 g samples. The thermal analysis is carried out with the specimens undergoing hydration for the time periods of one to 8 days. The isothermal heat flow calorimetry shows that in the analyzed system and its subsystems, the majority of hydration heat is evolved during ~1.5 h after beginning of the hydration process. After 25 h, measurable amounts of hydration heat are produced in the gypsum–lime–metakaolin and metakaolin–lime mixes only, indicating a pozzolanic reaction in progress. In both these mixes, the differential scanning calorimetry reveals seven endothermic peaks corresponding to the thermal decomposition processes occurring during the heating up to 1000 °C. After 8 days of hydration, all Ca(OH)2 is found missing in the gypsum–lime–metakaolin and metakaolin–lime mixtures, which points to the completion of the pozzolanic reaction. The results obtained by the differential scanning calorimetry are well correlated with the mass changes measured by thermogravimetry and derivative thermogravimetry.

The temperature dependences of the electrical DC conductivity of calcite waste, kaolinite and illite based ceramics were measured in the temperature range of 20 - 1050oC. The ceramic mass that was used was a mixture of 60 wt. % kaolinitic-illitic clay, 20 - 40 wt. % of this clay was fired at 1000oC for 90 min and 0, 10 and 20 wt. % of calcite waste. During heating, several processes take place - the release of the physically bound water, the burning of organic impurities, the dehydroxylation of kaolinite and illite, the decomposition of calcite, and the creation of anorthite and mullite. All of these processes were checked by means of differential thermal analysis (DTA), derivative thermogravimetry (DTG) and thermodilatometry (TDA). At low temperatures (20 - 200oC), due to the release and decomposition of physically bound water, H+ and OH- are dominant charge carriers. After completion of release of physically bound water, up to the start of dehydroxylation at the temperature of ~ 450oC, the DC conductivity is dominated by a transport of Na+, K+, and Ca2+ ions. During dehydroxylation, H+ and OH- ions, which are released from kaolinite and illite lattices, contribute to the DC conductivity. Decomposition of calcite runs between ~ 700oC and 900oC. The glassy phase has a dominant influence on the DC conductivity in the fired ceramics. Its high conductivity is determined by the high mobility of Na+, K+, and Ca2+ ions.

Brick clay from a locality Radobica, Central Slovakia, which was exploited for brick manufacturing in the past, was investigated for its possible reuse in the brick industry. The crystalline phases of the green sample were 48% of quartz, 37% of illite, 13%, of Na-feldspar and 2% of calcite. The measurements of Young's modulus of clay samples were performed during heating up to 1100 degrees C and also at room temperature on samples preheated at temperatures from 100 to 1100 degrees C. It was found during firing that 1) the physically bound water is released in 3 steps (up to 300 degrees C) and reaches 3 2.5 wt%. The thermal expansion is decelerated by setting the crystal closer at low temperatures. Young's modulus increases in its values (similar to 36%) which is a result of the closer structure that is created via release of the physically bound water. 2) The mass loss during dehydroxylation (450-750 degrees C) is similar to 3wt%. The superposition of dehydroxylation and alpha -> beta transformation of quartz creates a step similar to 3% of the relative thermal expansion. Young's modulus slightly decreases in its values, the dehydroxylation does not influence this trend. 3) Above 900 degrees C, the intensive contraction due to sintering is observed and a steep increase (250%) of Young's modulus takes place in this temperature interval. The irreversible changes of the Young's modulus measured at room temperature after firings at the temperatures from the interval 100-1100 degrees C give a different picture. Dehydroxylation affects Young's modulus very significantly decreasing its values from 7.8GPa (at 400 degrees C) to 4.3 GPa (at 700 degrees C). After dehydroxylation, the sintering increases Young's modulus. Since the porosity remains relatively high (similar to 30%) and a part of the glassy phase in the sample fired at 1100 degrees C is relatively low (25%), the Young's modulus is low even after firing at 1100 degrees C (9.3 GPa). (C) 2015 The Ceramic Society of Japan. All rights reserved.

The temperature dependences of the electrical DC conductivity of calcite waste, kaolinite and illite based ceramics were measured in the temperature range of 20 - 1050 degrees C. The ceramic mass that was used was a mixture of 60 wt. % kaolinitic-illitic clay, 20 - 40 wt. % of this clay was fired at 1000 degrees C for 90 min and 0, 10 and 20 wt. % of calcite waste. During heating, several processes take place the release of the physically bound water, the burning of organic impurities, the dehydroxylation of kaolinite and illite, the decomposition of calcite, and the creation of anorthite and mullite. All of these processes were checked by means of differential thermal analysis (DTA), derivative thermogravimetry (DTG) and thermodilatometry (TDA). At low temperatures (20 - 200 degrees C), due to the release and decomposition of physically bound water, H+ and OH- are dominant charge carriers. After completion of release of physically bound water, up to the start of dehydroxylation at the temperature of similar to 450 degrees C, the DC conductivity is dominated by a transport of Na+, K+ and Ca2+ ions. During dehydroxylation, H+ and OH- ions, which are released from kaolinite and illite lattices, contribute to the DC conductivity. Decomposition of calcite runs between similar to 700 degrees C and 900 degrees C. The glassy phase has a dominant influence on the DC conductivity in the fired ceramics. Its high conductivity is determined by the high mobility of Na+, K+, and Ca2+ ions.

The FIB/SEM investigations of the microstructure changes in the hard brittle W-C based coating deposited on softer steel substrate after nanoindentation tests revealed that a set of approximately equidistant circular cracks forms in the coating in a sink-in zone around the indent and single cracks appear under the indenter tip. Finite element modeling (FEM) indicated development and concentration of the highest principal tensile stresses in the sink-in zone and in the zone below the indenter, which are considered to be the reason for the experimentally observed cracking. The distance from the indenter tip to the first circular crack combined with the calibration curve obtained from the FEM of the location of tensile stress maxima in sink-in zone can be used as a simple method for the determination of the strength of the studied coatings.

The effect of accelerated climate ageing on historical bricks in the laboratory is investigated in the paper. Differences in thermal properties are experimentally determined and studied before and after bricks exposure to climate ageing, which consists of 60 freeze-thaw cycles. For measuring thermal conductivity, diffusivity and specific heat, pulse method is used.

The mechanical strength and Young’s modulus of green alumina porcelain (50 wt. % of kaolin, 25 wt. % of Al2O3, and 25 wt. % of feldspar) were measured during heating up to 900 °C and 1100 °C, respectively. To this end, we used the three point-bending method and modulated force thermomechanical analysis (mf-TMA). The loss liberation - of the physically bound water (20 – 250 °C) strengthens the sample and Young’s modulus increases its values significantly. The dehydroxylation that takes place in the range of 400 – 650 °C causes a slight decrease in Young’s modulus. On the other hand, the mechanical strength slightly increases in this temperature range, although it has a sudden drop at 420 °C. Beyond the dehydroxylation range, above 650 °C, both Young’s modulus and mechanical strength increase. Above 950 °C, a sharp increase of Young’s modulus is caused by the solid-state sintering and the new structure created by the high-temperature reactions in metakaolinite.

Variations of sorption moisture in the capillary porous materials result in strong fluid-skeleton interactions due to molecular and surface forces, which produce moisture-induced deformation. The effect of moisture sorption on the non-linear elastic behavior of hygroscopic porous building materials has been experimentally investigated showing strong influence of moisture especially in the lower moisture content range. In the framework poroelasticity moisture influence on elastic behavior is described by two poroelastic coefficients, which present the fluid-skeleton coupling. This paper presents an application of the procedure for the determination of the coupling coefficients for medieval brick.

Baroque bricks were investigated by DTA, TG, EGA, TDA, and XRD. The analyses showed that the brick consisted of dehydroxylated illite, quartz, and calcite. Dehydroxylation as a consequence of the former rehydroxylation was not found probably because of protection of the bricks by plaster. Between the temperatures 600 and 800 °C, (a) intensive mass loss in TG, (b) endothermic minimum in DTA, (c) intensive escape of CO2 in EGA, and (d) contraction of the sample in TDA were observed. All these events belong to decomposition of calcite. As follows from these results, the maximum firing temperature was about 700 °C. The bricks have relatively high porosity ~43 % and specific surface area ~18.6 m2 g−1.

During the heating stage of the firing of a ceramic material, the mass \(m\), length \(l\), and diameter \(d\) of the sample alter their values depending on the temperature \(t\). Young’s modulus \(E(f,m,l,d)\) measured by a sonic resonance method is also a function of the resonance frequency \(f\). Therefore, three thermal analyses (TGA, TDA, modulated force TMA) must be performed to obtain correct values of Young’s modulus. The calculation of Young’s modulus can be simplified if TGA and/or TDA are omitted. This necessarily leads to partly incorrect results. If TGA is not performed, we have \(E[f(t),m_0 ,l(t),d(t)]\) and the relative difference \((\{E[f(t),m(t),l(t),d(t)]-E[f(t),m_0 ,l(t),d(t)]\}/E[f(t),m(t),l(t),d(t)])\) reaches 7 % for \(t> 650\,^\circ \text{ C}\) and less than 2 % for \(t< 500\,^\circ \text{ C}\). If TDA is not performed, we have \(E[f(t),m(t),l_0 ,d_0 ]\) and the relative difference (\(\{E[f(t),m(t),l(t),d(t)]-E[f(t),m(t),l_0 ,d_0 ]\}/E[f(t),m(t),l(t),d(t)])\) is less than 0.6 % for \(t < 1000\,^\circ \text{ C}\). For the simplest case, we have \(E[f(t),m_0 ,l_0 ,d_0 ]\) and the relative difference (\(\{E[f(t),m(t),l(t),d(t)]-E[f(t),m_0 ,l_0 ,d_0 ]\}/E[f(t),m(t),l(t),d(t)])\) is 7.5 % for \(t > 600\,^\circ \text{ C}\) and less than 2 % for \(t<500\,^\circ \text{ C}\).

The samples from kaolin Sedlec were investigated by the help of DTA, TG, and temperature dependences of DC conductivity using Pt wire electrodes and linear heating up to 1,050 °C. After drying, the samples contained ~1.5 mass% of the physically bound water. DTA and TG reflected generally known facts about a release of the physically bound water, dehydroxylation, and metakaolinite → Si–Al spinel transformation. The results of electrical measurements showed the electric current passed over the maximum at 60 °C. The self-ionization of water results in the process H2O → H+ + OH− in the water layers on the crystal surfaces; consequently, OH− and H+ are the main charge carriers in the low-temperature region. The water molecules simultaneously evaporate from the sample which decreases the number of the charge carriers. When the physically bound water evaporates, the current is carried mostly by K+ and Na+ ions. During dehydroxylation, the hydroxyls OH− split into H+ and O2−. The ions H+ jump to the neighboring OH− groups creating the water molecules. The ions O2−remain bounded to the newly created metakaolinite lattice. Therefore, mobile protons contribute to the electric current. At the same time, this contribution gradually decreases because of the escape of H2O from the sample. The sharp current peak and DTA peak at 970 °C imply relatively fast metakaolinite → Si–Al spinel transformation. This DC current peak results from the shift of Al3+ and O2− ions into new positions.

The paper briefly summarizes the basic problems in physics of disordered materials, namely in physics of noncrystalline semiconductors. Although there was much attention devoted to the research in this area, many questions about the nature of processes taking place in these substances still remain unanswered. This article familiarizes the readers with the barrier-cluster-heating model of disordered semiconductors and discusses the possibility of explanations of the mentioned phenomena on its base. This article offers the explanation of the mid-gap absorption and mid-gap photoluminescence on the base of the barrier-cluster-heating model.

The paper deals with the problem of decreasing level of knowledge of university students due to the changes of the school system in Slovakia. As the commonly repeated words connected with education in 21st.century are key competencies, we tried to look at the problems and challenges in teaching physics from this point of view. The role of classical experiments in our computerized world is also discussed.

The paper deals with thermodilatometry of green and fired ceramic samples. Problems connected with the measurements in dilatometric practice are described in detail, namely a) the influence of the pressing force of the push-rod, b) the effect of an improperly placed sample and improper measuring range, c) the influence of the volume of a sample, d) the influence of the heating rate, and e) the influence of the grounding and AD transducer on the results of the thermodilatometric analysis.

An upgraded version of the TGA/DTA analyzer Derivatograph 1100° is described.A linear variable differential transformer (LVDT) is used as a sensor of the balance movement to register changes in the sample mass.The furnace temperature measured by a Pt-PtRh10 thermocouple located in its original position is controlled using the temperature programmer TLK 38.Thermocouples for DTA and their connections are left in the original state.Electrical signals from LVDT and thermocouples are sent to multimeter AGILENT 34972A which is connected to a PC.The program records the time of the measurement, furnace temperature, difference between the temperatures of the measured and the reference samples, and mass of the sample.The program's output is a graph with continuous TGA and DTA curves.

A pavement brick taken from a Romanesque part of the church in Pác, in the Trnava County, Slovakia, was investigated by x-ray diffraction analysis (XRD) and thermal analyses as differential thermal analysis (DTA), thermogravimetry (TG) and thermodilatometry (TD). It was found that the brick contained dehydroxylated illitic clay, calcite and quartz. As revealed, dehydroxylation was completely finished and no redehydroxylation was observed. Partial decomposition of calcite was also found. The estimated firing temperature is between 600 °C and 700 °C.

Green ceramic material is a mixture of 60 wt % of clay, 10 wt % of calcite waste and 30 wt % of the clay fired at 1000 degrees C for 90 min. The clay consists of 83 wt % of phyllosicates. The samples were undergone to XRD analysis, DTA, TGA, TDA and mf-TMA during heating 5 degrees C/min. The mf-TMA was based on the measuring Young's modulus by resonant method. The samples pass over several changes release of the physically bounded water, burning of the organic impurities, dehydroxylation of kaolinite and illite, decomposition of calcite and creation of anorthite and mullite. The first visible increasing of Young's modulus, which runs from room temperature to similar to 300 degrees C, is a consequence of the release of the physically bounded water from pores, micropores and faces of crystals. In a temperature interval 450-650 degrees C dehydroxylation of kaolinite and Mite takes place, then decomposition of calcite runs between similar to 700 and 900 degrees C. These three processes produce new structures which are mechanically weak because of significant part of micropores. In spite of that, Young's modulus tends to slightly increase from 500 to 750 degrees C and decreases only in a small extent during heating from 750 to 850 degrees C. Then a steep increase of Young's modulus values is recorded which can be ascribed to superposition of the solid-state sintering and creation of anortitc at similar to 950 degrees C and mullite above 950 degrees C. (c) 2012 The Ceramic Society of Japan. All rights reserved.

Electrical dc conductivity of kaolin and ceramic material consisting of 50 wt.% of kaolin and clay, 25 wt.% of quartz and 25 wt.% of feldspar was measured in the temperature range of 20-600 °C.At low temperatures (20-200 °C), charge carriers are H + and OH -ions released from defects located on crystal surfaces and polar water molecules in the pores.In this temperature region, the conduction activation energy is 0.3-0.35eV.Upon releasing physically bound water, up to start of dehydroxylation at temperature ∼450 °C, dc conductivity is determined by transport of Na + , Ca 2+ and K + ions.The conduction activation energy in this region is 1.03 eV.During dehydroxylation, the charge carriers associate into neutral complexes with OH -ions, which are released from kaolinite lattice.The result is a temporary decrease in the dc conductivity.Temperature dependences of the dc conductivity show a slight anisotropy.Conductivity is higher in the direction parallel with the basic faces of kaolinite crystals.In fired ceramics, the glassy phase has a dominant influence on the dc conductivity, which is determined by the concentration and mobility of Na + and K + ions.The conduction activation energy is 0.78 eV.Above 300 °C, fired kaolin-based ceramics can be considered fast ionic conductors.