Ing. Josef Sedláček, CSc.

Commercially available LaFeO3 powder was processed using the spark plasma sintering (SPS) technique. The results of the dielectric measurement showed high permittivity, but this was strongly frequency-dependent and was also accompanied by a high loss tangent. The chemical purity of the powder and changes induced by the SPS process influenced the stability of the dielectric parameters of the bulk compacts. A microstructure with a homogeneous grain size and a certain porosity was produced. The microhardness of the sintered LaFeO3 was rather high, about 8.3 GPa. All the results are in reasonable agreement with the literature related to the production of LaFeO3 using different techniques. At frequencies as low as 100 Hz, the material behaved like a colossal permittivity ceramic, but this character was lost with the increasing frequency. On the other hand, it exhibited persistent DC photoconductivity after illumination with a standard bulb.

Plasma spraying (PS) from liquid feedstocks is a promising alternative for fabricating the NiO-YSZ anodes for Solid Oxide Fuel Cell (SOFC). However, despite the inherent advantages of the PS process, the plasma sprayed anodes are still inferior to the conventional ones prepared by wet-ceramic techniques due to the difficulty of achieving the optimal porosity level. This study shows that due to recent development, the NiO-YSZ anode layers with desirable porosity and microstructure can now be effectively fabricated in a one-step process using PS equipment with a water-argon stabilized plasma torch. As a liquid feedstock, we utilized Ni nitrate (hexahydrate) solutions and YSZ suspensions with different ratios, using ethanol or water as solvents. We show that the ethanol-based feedstock provides a favorable microstructure and porosity of the resulted layers over the water-based one. In addition, apart from NiO and YSZ phases, the layers deposited with ethanol solvent contained even metallic Ni. Different ratios of Ni nitrate to YSZ in ethanol-based feedstocks greatly affected the layer's characteristics; when the content of Ni nitrate was high, the resulting layers had a non-uniform morphology with a very porous microstructure. On the contrary, the equal contents of Ni nitrate and YSZ in the feedstock resulted in the most optimal layer's microstructure, chemical composition, and thus sufficient electrical resistance, making such material potentially useful as anode for SOFC.

Yttrium aluminum garnet (YAG) with cerium admixture (Ce:YAG) was plasma sprayed using two different devices - gas-stabilized plasma (GSP) torch and water-stabilized plasma (WSP) torch. Coatings on stainless steel as well as self-standing plates were produced. Besides microstructure and crystallographic characterizations, dielectric tests were performed on these coatings. They included capacitance (i.e. relative permittivity), loss tangent and volume resistivity measurements. After spraying, the YAG crystal phase was preserved without any decomposition, but an amorphous fraction was detected in the as-sprayed coatings deposited by both processes. The dielectric behavior of the coatings was influenced by imperfections like splat boundaries, pores and thin cracks. The Ce:YAG samples were successfully plasma sprayed by both spray techniques. Selected aspects of wear were measured and compared with a single-crystal. The dielectric properties are comparable with the single-crystal and highly promising, particularly the loss tangent with values so low that they were not found in any other as-sprayed ceramic coating.

The high pressure forming at 300 MPa and room temperature was applied before firing of pure lithium fluoride powder. This material has very low sintering temperature, only about one half of typical oxide-ceramic dielectrics. Despite this fact, the resulting fired bulk was tested as dielectrics and showed very interesting characteristics. The best sample, fired at 750 °C and for 8 hours, had relative permittivity 12.1 and loss tangent 0.0006, frequency-and temperature-independent up to at least 150 °C. These parameters are comparable with oxide ceramics, fired at temperatures over 1500 °C, as for example alumina or YAG.

Various kinds of natural garnets belonging to the almandine type (3FeO·Al2O3·3SiO2) were sprayed by plasma spray technique to build coatings on metallic substrates. The experimental garnet powders came from different mines in the Czech Republic and Mongolia. After coating and cooling the substrates were removed. In this way, self-supporting plates were obtained and further studied with microscopy, X-ray diffraction, and dielectric spectroscopy. Mechanical properties were in our focus as well. Microhardness was measured on cross sections dedicated to microstructure observation. Wear resistance in wet conditions was tested in a slurry. Reflectance was measured applying visible and infrared (VIS-NIR) radiation. Dielectric properties of coatings were studied at low voltage capacitance, loss tangent and also under direct current (DC) resistance. The results show that garnet minerals are interesting candidates for various optical and electronic applications; they have similar dielectric behavior as, for example, aluminum oxide or similar high-purity synthetic oxides, and, simultaneously, they have extraordinarily low reflectance in VIS-NIR radiation. The differences between natural powders and resulting coatings are discussed in connection with their chemical and phase compositions.

LaFeO 3 commercial powder was fired by spark plasma sintering. Microstructure with homogeneous grain size and certain porosity was produced. Microhardness of the compact was rather high. The dielectric measurements showed high permittivity, but very frequency dependent, associated also with a high loss tangent. Analysis of the data showed high contribution of grain boundaries to the total impedance. The results roughly agree with the literature.

Barium titanate coatings were, for the first time, sprayed by a high feed-rate plasma torch with water stabilization of the plasma. Two power levels of the torch were applied for spraying to cover steel substrates. Various substrate preheating levels from 125 C to 377 C were used to modify cooling conditions. Microstructure and phase composition including crystallinity quantification were observed. Dielectric measurements proved that the relative permittivity between 300 and 400 coatings is too temperature sensitive over 170 C but fits the requirements of the EIA temperature coefficient between room temperature and 170 C. Simultaneously, the loss tangent remains rather low, between 0.02 and 0.07, in a broad range of temperatures and frequencies. Annealing was performed in air to heal the oxygen deficiency, but only modified the microstructure insignificantly. The dielectric properties of as-sprayed and annealed samples were discussed, with the main finding that the temperature coefficient of permittivity was improved by annealing. This study contributes to the search for the suitability of plasma-sprayed BaTiO3 coatings for application in the electrical industry, namely by the optimization of conditions for high feed-rate spraying.

Yttrium oxide was sprayed by a plasma torch using a coarse thermal spray powder, which must be in size range of tens of micrometers to ensure good penetration into the plasma stream. Thick coatings on steel substrates were produced with two sprays systems facilitating gas stabilized plasma (GSP) and hybrid water-argon stabilized plasma (WSP-H) techniques. Additionally, an ultra-fine yttrium oxide powder was sprayed from a suspension. Hybrid water-argon stabilized plasma system was used for this purpose. Markedly thinner compact coatings were produced this way. All three sorts of plasma sprayed deposits were studied by the same methods. Dielectric properties were studied in a broad range of frequencies and temperatures. The microstructure aspects as well as crystallite size were analyzed and discussed in relation to electrical properties. All coatings exhibited stable dielectric parameters versus changing frequency and temperature, comparable with literature values for various samples. Concerning sintered bulks, and especially their thermal stability of capacitance, the plasma sprayed coatings were slightly worse. However due to shape and size variability of the plasma spraying are yttria coatings prospective for technical applications.

Electrical components can fail during their function in an electrical circuit, especially in a harsh environment. One of the possible failure reasons is the electrochemical migration, which leads to a short circuit or change of electrical parameters of components. This paper focuses on electrochemical effects and explains mechanisms leading to the formation of a conductive path within a component molded in a plastic package. Appropriate diagnostic methods SEM/EDS and penetration tests have been chosen in order to find the root cause for short circuit creation. It was found that the conductive path appeared due to electrochemical migration of silver between the Electrically Conductive Adhesive (ECA) joints connecting the capacitor package. A tiny gap that was found between the molding compound and the leadframe of the package, showed to be the necessary condition for the electrochemical migration to appear. The main aim of this work was not just to identify the cause of an inadvertent conductive path creation, but also to identify the part of the manufacturing process, where similar problems can be prevented.

In this paper, we examined the dielectric properties of CaCu3Ti4O12 (CCTO) ceramics fabricated by various routes and discussed the most important conditions affecting their dielectric behavior. We prepared feedstock powder using a molten salt route and compared it with a commercial powder. Both powders were sintered using SPS. For some samples, annealing was applied after sintering. Other samples were obtained by high-pressure forming and conventional sintering, using both powders. Phase composition, porosity and microhardness were evaluated in comparison with the literature. The results showed that a sintering temperature just below or equal to 1000 C should be set for the SPS process. However, the best dielectric characteristics were obtained in samples prepared by high-pressure forming and conventional sintering, which showed a relative permittivity of 22,000 and a loss tangent of 0.13 at 1 MHz.

A series of samples was sintered from nanometric BaTiO3 powder by spark plasma sintering (SPS). Sintered tablets were polished, sputtered by aluminum to create electrode system and tested in DC and AC electric fields. The results were correlated with the SPS processing parameters and are discussed in connection with other BaTiO3 samples produced by SPS with or without additional heat treatment. Majority of our SPS fired samples had, even without subsequent thermal treatment, advantageous combination of high permittivity, DC resistivity and low loss factor, seldom reported for SPS technology. Samples were tested also in annealed state and compared with as-sintered ones.

In this study, water stabilized plasma spraying (WSP) was used to prepare CaZrO3 coatings, whereas CaZrO3 bulk samples were fired using spark plasma sintering (SPS). The spraying feedstock was prepared from fine CaZrO3 powder by agglomeration (spray drying) and sintering. The initial fine CaZrO3 powder was used for SPS. In case of plasma sprayed materials, the influence of spraying process on the coating structure was studied. Differences in the structure of plasma sprayed thick coatings and SPS compacts were characterized using microscopy, density and porosity measurements. The deposits were striped-out from the substrate, ground and polished in order to produce samples in a shape of planparallel plates with a smooth surface. These samples - in principle monoblock capacitors were subjected to low voltage alternating electric field with a frequency range from 1 kHz to 1 MHz and their capacitance and loss factor were measured. Relative permittivity was calculated afterwards from the measured capacitance. Dependences of permittivity and losses were also studied for varying temperatures in a range 20-150 degrees C. Volume resistivity was measured in direct electric field at a room temperature. Influence of the SPS process and subsequent annealing on the microstructure and dielectric properties was studied as well. Decrease of porosity and rearrangement of grains after proper annealing brought improvements in the dielectric characteristics.

This paper aims to study various physical properties of lithium silicate ceramics. The work starts with the synthesis followed by characterization of the compounds. The samples are synthesized by reaction between SiO2 and Li2CO3 powders, compacted by spark plasma sintering (SPS) and then characterized by XRD, SEM and other techniques. The electrical properties are studied by dielectric spectroscopy. Dielectric and conductive properties of lithium silicate depend on the composition and microstructure, which factors are interconnected with the processing parameters. Li2 SiO3 and Li2Si2O5 were the major components present in the SPS bulk. The best combination of dielectric parameters is relative permittivity 6.41 and loss tangent 0.001 at frequency 0.9 MHz for the sample sintered at 950 °C for 30 min. Relative permittivity as well as loss tangent was monitored to increase with temperature up to 250 °C.

Various natural materials, namely ilmenite, diopside, tourmaline, olivine, garnet, and basalt, were plasma-sprayed and analyzed. This paper summarizes the various achievements of our earlier research and adds new results—mainly dielectric and optical characterizations. Plasma spraying of all of the materials was rather easy with a high feed-rate plasma system, which could process many kilograms of powder per hour. For easier characterizations, the coatings were detached from substrates in order to remain self-supporting. The plasma-sprayed layers that were coated from all studied materials acted as medium-permittivity and low-loss dielectrics, antireflective optical materials, and medium quality anti-abrasive barriers. Phase composition and microhardness were evaluated in addition to microstructure observations. Some coatings were amorphous and crystallized after further heating. As the melting points were well above 1000 C, all of them could also serve as thermal barriers for aluminum alloys and similar metals. The only material that was not easily sprayed was tourmaline, which gave very porous coatings without environmental barrier or dielectric characteristics.

Titanium dioxide (TiO2) was plasma sprayed using a high feed-rate spray system with hybrid water– argon stabilization torch (WSP-H). TiO2 powder agglom- erated from nanometric particles was used as the feedstock. The produced coating had thickness over 4 mm, to be comparable with bulk ceramic bodies. The deposit was removed from the substrate and annealed in air to reoxidize the oxygen deficient as-sprayed titania and to obtain material with a proper dielectric behavior. Besides the microstructure studies, radiofrequency dielectric spec- troscopy and microwave dielectric spectroscopy were in the focus of investigation. The approach to annealing of an extremely thick coating is studied: The significance of annealing of a large-area thick coating is discussed, as the role of grain interior and grain boundaries in the charge transport is influenced. Relative permittivity 94 and the Q*f product 12,800 GHz were reached at frequency 4 GHz, whereas the frequency response under 1 MHz was mapped continuously and the values (i.e., low and stable loss tangent) confirmed that a sprayed and air-an- nealed TiO2 is able to approach or also overperform dielectric parameters typical for TiO2 sintered bulk.

Tantalum pentoxide (Ta 2 O 5 ) was sintered with spark-plasma sintering (SPS) using a commercial powder with micometric particles composed of nanometric crystallites. The influence of the SPS process and subsequent annealing on the microstructure, phase composition and dielectric properties was studied. After the sintering, the product was oxygen deficient because of the low pressure in the sintering chamber. Evacuation was necessary for the process because of the carbon pistons and carbon die used for the powder compaction. After the subsequent annealing in air, the white color of Ta2O5 was restored, being a proper indication of a re-oxidation. Dielectric properties were studied in a broad range of frequencies and temperatures. As-sintered and also annealed samples exhibited a high relative permittivity in a range of 61–68, a loss factor of about 0.001 and a resistivity in the order of 10E11 Ohm m.

In prototyping and piece-production, stencil printing of the solder paste is expensive, and with the use of the stencil, it is not possible to react fast on changes in the design. Therefore, automatic or manual dispensers are used. This work aimed to develop a low-cost dispensing system based on a simple principle that uses torsion springs and its plastic construction is printable by a 3D printer. Unlike other dispensing systems, the presented dispenser allows continuous deposition of the solder paste. As the performance test showed, the deposition can be as good as with a commercial dispenser. Furthermore, the cost of the dispenser does not exceed 1€. In comparison with other commercial solutions, it is a negligible amount.

Příspevek popisuje koncepci dávkovačů pájecích past s velmi nízkými výrobními náklady.

Barium titanate coatings were first time sprayed by a high feed-rate plasma torch with water stabilization. Two power levels of the torch were applied. Two substrate materials were used—stainless steel and carbon steel. Various substrate preheating levels from 125 to 450 C were applied to change the cooling conditions. Microstructure, phase composition including crystallinity quantification, surface roughness and microhardness were evaluated. Dielectric measurements proved that coatings with medium-level relative permittivity and with stable loss factor course versus frequency of the AC electric field were fabricated by spraying. The cold substrates provided coatings with low reflectivity and visibly darker surface compare to the hot substrates. The coatings exhibited good dielectric properties - on the top of an expectable range for plasma-sprayed BaTiO3. This study is targeted to coatings prospective for electrical industry, namely via optimization of conditions at the high feed-rate spraying.

Tantalum pentoxide Ta2O5 was sintered by spark plasma sintering (SPS) using a commercial micrometric powder. Influence of the SPS process and subsequent annealing on microstructure, phase composition and dielectric properties was studied. After sintering the product is oxygen-deficient because of low pressure in the sintering chamber. The evacuation is necessary for the process because of carbon pistons and carbon die used for powder compaction. After subsequent annealing in air the color of the product Ta2O5 is restored that is proper indication of the re-oxidation. Dielectric properties were studied in a broad range of frequencies. Both as-sintered and annealed samples exhibit high relative permittivity about 61 to 68, loss factor about 0.001 and resistivity in order 10E11 Ωm.

Positron annihilation spectroscopy was employed for investigation of vacancy-like defects in plasma-sprayed barium titanate. Defect studies were combined with measurement of dielectric properties of barium titanate coatings. Samples prepared by gas-stabilized plasma spray (GSP) torch and by plasma torch with the hybrid water-argon stabilization (WSP-H) were studied. Processing parameters were selected so that GSP coatings were sprayed in reductive conditions, whereas WSP-H coatings were prepared in oxidizing environment. As-sprayed GSP coat- ing is dark, whereas WSP-H one is light. The dielectric properties of WSP-H coating are superior to those for GSP one. Defect studies revealed that both GSP and WSP-H coatings contain titanium vacancies. However, GSP coating contains in addition a considerable concentration of oxygen vacancies. Some fraction of oxygen vacancies in GSP coating is coupled with titanium vacancies forming par- tial Schottky defect. The structure of WSP-H coating is less disordered and con- tains only a low concentration of oxygen vacancies. This is consistent with reductive and oxidizing conditions in GSP and WSP-H spraying, respectively. Annealing at elevated temperatures in air leads to removal of oxygen vacancies which are filled by oxygen diffusing into the samples.

Several silicate materials were plasma sprayed and characterized by the authors in recent years from the point of view of their chemical and phase compositions, microstructure and mechanical as well as thermal properties. The present work is concerned with selected dielectric properties of these deposits. Synthetic mullite and steatite as well as natural olivine forsterite were plasma sprayed using the water - stabilized plasma system (WSP®). The deposits were striped-out, ground and polished to produce samples in form of plates with a smooth surface. Part of samples was later annealed in air. These samples-after coverage by metal electrodes functioning as monoblock capacitors were tested in the alternative low voltage electric field to measure capacity and loss factor in the frequency range from 200 Hz to 1 MHz. Relative permittivity was calculated from the measured capacity. Volume resistivity was measured in the direct electric field. It is shown that the relative permittivity of as-plasma sprayed silicates is less stable compared to bulk in the whole studied frequency range. However, thermal annealing modifies the structure much closer to the sintered bulk which is also reflected in dielectric properties. Insulating ability of plasma sprayed silicates with and without annealing is discussed in consequence with chemical changes and phase changes induced by annealing.

A multifunctional material, strontium zirconate, SrZrO 3 , studied in literatures as a dielectric ceramics, thermal barrier coating, proton- conductor, and luminescent material was sprayed by a water-stabilized plasma torch WSP 500. Stainless steel and plain carbon steel were used as substrates. Coatings with thickness of 1 to 2 mm were produced, whereas the substrates were preheated over 450 °C. The torch working at 150 kW was able to spray SrZrO 3 with a spray rate of 10 kg per hour. Microstructure, phase composition, dielectric properties, and optical band gap were also investigated.

A series of samples was sintered from nanometric BaTiO3 powder by spark plasma sintering (SPS). Porosity on ultra-fine size scales, hardly accessible for quantification by conventional techniques, was measured by small angle neutron scattering (SANS). Band gap was estimated from diffuse reflectance measurements. Sintered tablets were polished, sputtered by aluminum to create electrode system and tested in DC and AC electric fields. The results were correlated with the SPS processing parameters and are discussed in connection with other BaTiO3 samples produced by SPS with or without additional heat treatment. Majority of our SPS fired samples had, even without subsequent thermal treatment, advantageous combination of high permittivity, DC resistivity and low loss factor, seldom reported for SPS technology.

An extremely thick TiO2 deposit was plasma sprayed using a water-stabilized spray system. Natural rutile TiO2 was used as feedstock powder. Reaching the required enormous thickness, 15 mm, was fast thanks to a high feed-rate WSP gun. The massive deposits were cut into slices aligned parallel with the substrate and studied. Their microstructure is lamellar with defects typical for plasma sprayed ceramics. Differences between the near-substrate slices, medium space slices and near-surface slices of the deposit were found namely in physical properties. Besides the microstructure, dielectric spectroscopy and electrochemical impedance spectroscopy were in the focus of investigation. The role of the grain interior and grain boundaries in the charge transport and the role of dipoles of various sizes are different near the substrate, in the middle and near the surface. The deposit was annealed to remove the oxygen sub-stoichiometry of the semiconductive as-sprayed titania. Various differences are present also in the annealed deposit since they are inherited from the as-sprayed state, which was not completely overlaid by annealing.

Zirconium-tin titanate ceramics (Zr,Sn)TiO4 was prepared by spark plasma sintering (SPS) technique. Resulting samples, low-height cylinders, were subjected to microstructural observations, immersion measurements of density and porosity and X-ray diffraction phase analysis. Dielectric parameters – relative permittivity and loss factor – were tested in the frequency range from 80 Hz to 1 MHz and volume DC resistivity was measured at 100 volts.

This paper studies calcium titanate (CaTiO3) dielectrics prepared by plasma spray technology. A water stabilized plasma gun (WSP) as well as a widely used gas stabilized plasma gun (GSP) were employed in this study to deposit three sample sets at different spray conditions. Prepared specimens were annealed in air at atmospheric pressure for 2 h at various temperatures from 530 to 1170 °C. X-ray diffraction (XRD), Raman spectroscopy and porosity measurements were used for sample characterization. Dielectric spectroscopy was applied to obtain relative permittivity, conductivity and loss factor frequency dependence. Band gap energy was estimated from reflectance measurements. The work is focused on the explanation of changes in microstructure and properties of a plasma sprayed deposit after thermal annealing. Obtained results show significant improvement of dielectric properties after thermal annealing.

Previously published results on electrical and mechanical properties of BaTiO3 coatings prepared by atmospheric plasma spraying showed anomalies in their dielectric response. This paper provides a study of electrical and mechanical properties of BaTiO3 coatings after thermal posttreatment. The spraying was carried out by a direct current gas-stabilized plasma gun. BaTiO3 was fed into the plasma jet as a feedstock powder prepared by reactive sintering of micrometer-sized powders of BaCO3 and TiO2. In the next step the coatings were annealed in air. Microstructure and phase composition are reported and discussed in relation to electric and mechanical properties. Dielectric properties are reported for the radio frequency (RF) range.

Natural diopside CaMgSi2O6 was processed by plasma spray technique into self-supporting plates.The experimental powder for spraying came fromas-mine natural diopside and was crushed and sieved to the proper size for plasma spraying with a water-stabilized plasma torch (WSP). These deposits were further studied with optical microscopy, SEM, X-raydiffraction, thermal analysis,mechanical tests and dielectric spectroscopy. Microhardness was measured on cross-sections prepared for microstructure observation. Dielectric properties of capacitor samples prepared from the self-supporting sprayed deposits were measured at low voltage.The results showed that diopside is an interesting candidate for various electrical applications as it has similar dielectric behavior as alumina or silicates.Thermal annealing of the SSP was done. Despite crystallization of theamorphous fraction (presentafterspraying)intoa fine-grained structure,annealing worsened slightly dielectric responses of diopside. Differences between diopside and other silicates sprayed by the author sinthepast are discussed.

A natural diopside CaMgSi2O6 was formed by plasma spray technique into coatings on magnesium substrates as well as self-standing plates. The powder for spraying came from as-mined natural diopside and was crushed and sieved to the proper size for plasma spraying by a water-stabilized plasma torch (WSP). By removing the substrates after cooling, self-supporting plates were obtained. These deposits as well as thinner coatings on Mg alloy were studied with optical microscopy, SEM, X-ray diffraction, thermal analysis, mechanical tests and dielectric spectroscopy. Microhardness was measured on cross-sections prepared for microstructure observation. Wear resistance at wet conditions was tested as well. Dielectric properties of monoblock capacitors prepared from the self standing deposits were measured at low voltage. The results showed that diopside is interesting candidate for various electrical applications; it has similar dielectric behavior as alumina or silicates. The differences between diopside and other silicates sprayed in the past are discussed in connection with their chemical and phase compositions.

This paper presents a study of dielectric properties, namely the relative permittivity and loss factor dependence on the frequency of a weak electric field. Perovskite CaTiO3 was studied in the form of coatings and self-supporting plates made by plasma spraying. A conventional gas stabilised plasma gun (GSP) as well as a water stabilised plasma gun (WSP) were employed. It was observed that plasma sprayed titanates exhibit a strong relaxation of permittivity and loss factor decrease with a frequency rise. These properties are influenced by spray technique and spraying parameters, but the relaxation character in general is preserved in all cases. The volume resistivity of the samples was studied as well. Several aspects of the structural features of plasma deposits, especially the phase composition, porosity character, and their influence on dielectric properties are discussed.

This paper presents a comparison of properties of BaTiO3 ceramics prepared by two different production methods:gas-stabilized plasma spraying (GSP) and spark plasma sintering (SPS).Samplesof both materials were evaluated by various techniques,the goal being to detect theCurie temperature of the ferroelectric transformation between the tetragonal and the cubic phase.All tests,resonant ultrasound spectroscopy,dielectric measurements,differential scanning calorimetry and temperature-resolvedX-ray diffraction (XRD), used in combination,proved the absence of this transformation in the case of GSPcoating up to 500 °C. Similarly,the tetragonal-to- orthorhombic transition temperature is shifted downwards,this transition probably taking place in a small fraction of the volume of coating. The SPS samples exhibit several anomalies, such as astrong anisotropy of relative permittivity, but their phase transformations were detected in the usual temperature ranges.

Lead zirconate titanate (PZT) was plasma sprayed onto various substrates of different character. Additionally, a free-standing body made by plasma spraying was investigated. X-ray diffraction analyses of a decomposition of the as-sprayed coating products detected components of the PT-PZ system as well as binary oxides-PbO and ZrO2. Due to the comparatively complex phase character, the Curie temperature monitored by DTA, had a smeared appearance without pronounced maxima. The corresponding electrical properties are comparable with those typically observed for CaTiO3, but are worse than the normal values of bulk PZT due to defective stoichiometry.

The aim of this work is an experimental study of lead-free solders. Ternary and binary alloys with different ratios of individual elements Ag, Al, Bi, Cu, In, Mg, Sb, Sn and Zn were prepared experimentally. The study of low-fusing solder alloys was performed with the aspect of observing their selected physical, chemical, structural and technological properties.

The aim of this work is an experimental study of lead-free solders. Ternary and binary alloys with different ratios of individual elements Ag, Al, Bi, Cu, In, Mg, Sb, Sn and Zn were prepared experimentally. The study of low-fusing solder alloys was performed with the aspect of observing their selected physical, chemical, structural and technological properties. The following characteristics were studied: temperatures and enthalpies of phase transformations (DTA, TG, DSC) of individual solders at the rates of re-heating and cooling of specimens of about 4 °C/min, macro- and micro-structural analysis (optical metallography), micro-hardness, chemical analysis: ICP-AES, optical emission spectrometry (OES), X-ray micro-analysis of individual phases in the structure of solders (WDX, EDX), measurement of density and electrical resistivity of selected solders in dependence on the temperature, test of wettability with or without use of fluxes, measurement of corrosion properties.

XRD measurements were carried out on plasma sprayed titanates BaTiO3, CaTiO3, MgTiO3 and a mixture of last two. Samples were tested as dielectrics and volume resistivities of the materials were also summarized. Microwave microscopy was used for mapping of the dielectric response of selected samples. The results exhibit differences in the crystal structure between plasma sprayed coatings and feedstock powders.

Titanium dioxide coatings were sprayed by WSP gun to form self-supporting bodies with a photocatalytically active surface. Prepared bodies were studied by XRD, HR-TEM, XPS, Raman spectroscopy, UV-VIS spectrophotometry and photocatalytic tests.Porosity was studied by image analysis also microhardness was measured.

Monografie podává ucelený přehled o výsledcích studia fázových rovnovah materiálů pájek určených pro vysokoteplotní aplikace. Monografie rozšiřuje experimentální a teoretické poznatky o materiálech vhodných zejména pro bezolovnaté pájky pro aplikace za zvýšených teplot.

Spark-plasma-sintering (SPS) process uses of microscopic electrical discharge between sintered particles under pressure. BaTiO3 samples were manufactured using SPS process at sintering temperature 1300°C, pressure 80 MPa, sintering time 20 min and controlled cooling rate. Dielectric properties of BaTiO3 samples were measured in the frequency range from 9 kHz to 1 MHz. Measured samples exhibit extremely high value of relative permittivity and anisotropy of dielectric properties.

This work deals with impedance and conductivity analysis of carbon black - polystyrene composite layers prepared from the solution of polystyrene in toluene. The aim of the work was comparison of the results obtained by different methods of measurements. The samples were prepared with carbon black concentrations from 1%w to 7%w by coating into Petri dishes. The measurements of impedance and conductivity were carried out after toluene evaporation at room temperature in the frequency region from 0 Hz (DC) up to 100 kHz. The data of three terminal measurement system and Van der Pauw method are presented. It was shown that electrical properties are similar in planar and normal directions. The resistivity was observed as a function of measuring voltage.

Raman and infrared spectroscopic measurements were carried out on plasma sprayed titanates CaTiO3, MgTiO3 and their mixture. Samples were tested in comparison with sintered analogs. Microwave microscopy was used for mapping of the dielectric response of the as-sprayed as well as annealed samples. The results show differences in the crystal lattice between plasma sprayed and sintered sample in the case of MgTiO3 whereas CaTiO3 is identical with its sintered bulk analog. The reason can be found in sensitivity of MgTiO3 to the reductive conditions at plasma spraying whereas CaTiO3 seems to be rather inert from this viewpoint.

The anisotropy and inhomogeneity of electrical properties of polystyrene - carbon black composite films prepared from solution were studied by the methods of Van der Pauw and dielectric spectroscopy in the frequency region 0,1Hz up to 100 MHz.

The work deals with dielectric properties of carbon black-polystyrene composite plates prepared by evaporation of toluene from solution. The samples with carbon black and de-ionized carbon black with lower amount of ions which were extracted in water were studied.

This work deals with electrical and dielectrical properties of polymer - carbon black composites prepared from the solution directly poured into Petri dishes and by the method of spin coating. The solutions of polystyrene in toluene were used for polymer matrix. The carbon black agglomerates were pulverized and dispersed by mechanical rotational homogenizer and by ultrasonic homogenizer. Two kinds of carbon black were used for the samples preparation. 1. Dry carbon black. 2. Carbon black without ions which were extracted in water. Measurements were carried out on the samples with the thickness 0,05 - 0,2 mm with carbon black content from 2 w% to 8 w%. Electrical measurements were carried out at temperatures 20 - 100 C by the method of impedance analysis in the frequency region 102 - 106 Hz both in normal and planar direction and by the method of van der Pauw. The carbon black agglomerate structures were studied by optical and AFM microscopy.

This work deals with electrical and dielectrical properties of polymer - carbon black composites prepared from the solution directly poured into Petri dishes and by the method of spin coating. The solutions of polystyrene in toluene were used for polymer matrix. The carbon black agglomerates were pulverized and dispersed by mechanical rotational homogenizer and by ultrasonic homogenizer. Two kinds of carbon black were used for the samples preparation. 1. Dry carbon black. 2. Carbon black without ions which were extracted in water. Measurements were carried out on the samples with the thickness 0,05 - 0,2 mm with carbon black content from 2 w% to 8 w%. Electrical measurements were carried out at temperatures 20 - 100 C by the method of impedance analysis in the frequency region 102 - 106 Hz both in normal and planar direction and by the method of van der Pauw. The carbon black agglomerate structures were studied by optical and AFM microscopy.

Plasma spraying enables to create layers with thickness in a millimeter range adhering on various substrates. This paper provides a study of electric and mechanical properties of BaTiO3 coatings prepared by atmospheric plasma spraying. The spraying was carried out by a direct current gas-stabilized plasma gun. BaTiO3 was fed into the plasma jet as a feedstock powder prepared by a reactive sintering of micrometer-sized powders of BaCO3 and TiO2. Microstructure and phase composition are reported and discussed in connection with electric and mechanical properties.

Předmět Nanotechnologie je ve studijním programu Elektrotechnika a informatika zařazen do inženýrského bloku Elektronika a fotonika oboru Elektronika. Cílem předmětu je seznámení studentů se současnými nanotechnologiemi pro potřebu kvalifikovaného řešení problémů spojených s další miniaturizací systémů a prvků zejména v elektronice. Předmět je tématicky velice rozsáhlý. Vychází z aplikací kvantové fyziky, růstu fraktálů, koloidních systémů a samovolného růstu nanostruktur. Cvičení navazují na přednášky a vhodně je doplňují. Cvičení jsou laboratorní a mají demonstrační charakter. Do osnov jsou také včleněny dvě exkurze. Jedná se o exkurzi na pracoviště MBE a MO VPE ve FÚ AV ČR a na pracoviště výroby nanovláken firmy ELMARCO v Liberci (letos Euronanoforum 2009, Praha).

The aim of our work was to test electrical and optical properties (especially surface resistivity and optical absorbance) of laboratory prepared Al susceptors and to determine the relationships between them and to find the optimum thickness of metallization from the point of view of maximum microwave energy absorption in the film. Set of Al layers of varying thickness (from just about 3 to 30 nm) were deposited onto PET films by vacuum evaporation. Prepared susceptors have non-uniform, perforated structure as resulted from microscopic and AFM observation. DC surface resistivity was measured by classical four point method. Optical absorbance of susceptors was measured by UV/VIS Spectrometer Perkin Elmer Lambda 11 at the wave length 626 nm. A set of susceptors was tested in measurement waveguide at the frequency 2.45 GHz and the applied microwave power of 1.8 mW. The maximum microwave energy absorption at 2.45 GHz was found to occur in susceptor of optical absorbance of about 0.22.

Work is concentrated on electric conductivity of plasma sprayed tungsten-based cermets and their comparison with their analogs made pressure-assisted sintering.

Copper and copper-tungsten composite coatings were produced by high velocity oxy fuel spraying. After initial optimization of the spraying parameters, coatings of various compositions were made and their structure, composition, mechanical, thermal and electrical properties were characterized. The HVOF technique was to able to produce rather dense coatings with minimal oxide content and relatively good mechanical and thermal properties compared, for example, to plasma sprayed coatings, however, the achievecdtungsten content was quite low.

The subject Nanotechnology - acquirement of basic knowledge in the sphere of up-to-date nanotechnologies for demands of solving of qualified problems concerning further systems and elements miniaturization, namely in electronics.

Several silicate materials were plasma sprayed and characterized by the authors from the viewpoint of their sprayability, chemical and phase composition, microstructure and mechanical as well as thermal properties. Samples were then tested to measure their permittivity and loss factor in frequency range from 200 Hz to 1 MHz.

The article is concerned with selected dielectric properties of zirconium silicate was plasma sprayed. The deposits were tested to measure permittivity and loss factor in the frequency range from 300 Hz to 1 MHz. Dielectric strength was measured in DC regime. The results reveal that also after heating almost to 1000°C the difference between samples, caused by various plasma setup parameters, will manifest itself.

The contribution reported plasma spraying of zirconium silicate, heat after-treatment and its dielectric characterization.

Contribution is concentrated on electric resistivity understoichiometric TiO2 prepared by plasma spraing. There is described the influence of spraying conditions on electric resistivity of plasma deposit.

An electromagnetic brake for rail vehicles has to produce the maximum drag force at the lowest field current and highest possible efficiency. This can be achieved only by simultaneous high-level optimization of its magnetic circuit and arrangement of the field coils. The paper presents the complete electromechanical solution of the problem. The first part is aimed at a more detailed specification of the technical problem with respect to the principal requirements and limitations concerning technical aspects of the device. The next step is aimed at forming the mathematical model that is solved by the finite element method. The main part of the paper contains a typical example in several variants (even with respecting abrasion) with illustrative results. Properties of the suggested variants are compared with the properties of the up to now manufactured device that was designed by the classical method based on solution of discrete magnetic circuits.

Dielectric properties of plasma sprayed silicates

Urychlená krystalizace z roztoku v tavenině.