Isothermal Dilatometric Study of Sintering in Kaolin

Solid-state sintering for kaolin samples was studied by dilatometric measurements in the isothermal regime in the temperature range from 600 °C to 1100 °C. The relative expansion was measured for a period of 10h. For the temperatures up to 850 °C, we observed only a small shrinkage (less than 0.5 %), most of which took place within the first 3h of the measurements. For the temperatures above 850 °C, a significant shrinkage occurred for the whole measured time interval and reached up to 2.7 %. Anomalous behavior—a decrease in the shrinkage with the temperature—was observed in the range from 700 °C to 850 °C. The dilatometric measurements are supplemented by porosity distribution measurements. The standard spherical-grains microscopic model was applied to determine that for the initial stages of the sintering process, grain boundary diffusion was the dominant mechanism at lower temperatures (600 °C to 850 °C), whereas lattice diffusion was dominant at higher temperatures (900 °C, 1050 °C, and 1100 °C).     

Microstructure evolution and texture development during high-temperature uniaxial compression of magnesium alloy AZ31

Texture development in magnesium alloy AZ31 was studied by uniaxial compression tests at temperatures, strain rates and final strains ranging from 573 to 773 K, 1.0 × 10⁻³ to 5.0 × 10⁻⁵ s⁻¹ and −0.2 to −1.5, respectively. Fiber texture was formed in all of the deformation conditions. The main component of the texture varied depending on deformation conditions; it appeared about 33–38° away from the basal pole after the deformation at higher temperatures and lower strain rates. This can be attributed to the increased activity of the secondary pyramidal slip system. With a decrease in temperatures and an increase in strain rate, the tilting angle of the main component (compression plane) from the basal pole decreased down to about 20°. Construction of a basal fiber texture was detected after deformations at the lowest temperature and high strain rates.     

Built-in-self-test techniques for MEMS

As predicted by technology roadmaps, embedded micro-electro-mechanical-systems (MEMS) is yet another step in the continuous search for higher levels of integration and miniaturization. MEMS are analog components and the test paradigm is similar to the case of analog and mixed-signal circuits. However, given the fact that they work with signals other than electrical, the test of these embedded parts poses new challenges. In this paper, we will review some recent works in this field and we will present a complete approach to MEMS built-in-self-test (BIST) based on pseudorandom testing.     

Degree of Conversion of Dehydroxylation in a Large Electroceramic Body

The initial composition (36 mass% kaolin, 30 mass% alumina, 22 mass% feldspar, 12 mass% clay) and density of a body containing kaolinite is substantially altered during dehydroxylation which starts at a temperature of ~420 °C. Values of the degree of the dehydroxylation conversion of kaolinite into metakaolinite were experimentally obtained from a cylindrical sample with a radius of 80 mm from isothermal regimes at (450, 500, 550, 600, and 650) °C with heating times from 0 h to 10 h. The degree was determined for small samples (10 × 10 × 5 mm³) from different places of the cylindrical sample. This value was calculated from the mass loss caused by dehydroxylation. The dependencies of the degree of conversion on the small sample position, temperature, and time are presented.     

Acute and chronic toxicity effects of silver nanoparticles (NPs) on Drosophila melanogaster

The use of nanoscaled materials is rapidly increasing, however, their possible ecotoxicological effects are still not precisely known. This work constitutes the first complex study focused on in vivo evaluation of the acute and chronic toxic effects and toxic limits of silver nanoparticles (NPs) on the eukaryotic organism Drosophila melanogaster. For the purpose of this study, silver NPs were prepared in the form of solid dispersion using microencapsulation method, where mannitol was used as an encapsulation agent. This newly prepared solid dispersion with a high concentration of silver NPs was exploited to prepare the standard Drosophila culture medium at a silver concentration range from 10 mg·L(-1) to 100 mg·L(-1) of Ag in the case of the acute toxicity testing and at a concentration equal to 5 mg·L(-1) in the case of the chronic toxicity testing. The acute toxic effect of silver NPs on Drosophila melanogaster was observed for the silver concentration equal to 20 mg·L(-1). At this silver concentration, 50% of the tested flies were unable to leave the pupae, and they did not finish their developmental cycle. Chronic toxicity of silver NPs was assessed by a long-term exposure of overall eight filial generations of Drosophila melanogaster to silver NPs. The long-term exposure to silver NPs influenced the fertility of Drosophila during the first three filial generations, nevertheless the fecundity of flies in subsequent generations consequently increased up to the level of the flies from the control sample due to the adaptability of flies to the silver NPs exposure.     

A nanocrystalline hematite film prepared from iron(III) chloride precursor

This paper deals with a simple and low-cost method developed to deposit hematite (α-Fe₂O₃) layers on a fluorine-doped tin oxide (FTO/F:SnO₂) substrate by thermal decomposition of solid iron(III) chloride hexahydrate (FeCl₃⋅ 6H₂O). Deposition procedure takes place through chemical intermediate iron(III) oxide chloride (FeOCl) film. A crucial influence of atmosphere dynamics involved in the calcination process of FeOCl has been observed. As-deposited films were characterized by means of Conversion Electron Mössbauer Spectroscopy (CEMS), Grazing Angle X-Ray Diffractometry (GAXRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analysis. Final nanocrystalline hematite film with a cactus-field-like design consists of 20 nm thick porous crystal plates. A process of hematite doping by tin atoms from substrate coating is also discussed.     

A photosensitive polymer as recording material in holography

Summary A new reversible photochromic copolymer of maleic anhydride with styrene containing azo side groups was prepared. The system reacts to irradiation by a reversible trans-cis photoisomerization of light-sensitive azo groups. Irradiation also causes a change in the refractive index, so that the polymer may be employed in recording optical information in the form of phase hologram. The resolution of the material is higher than 2000 lines/mm.In spite of the large variability of organic compounds, according to available information only two groups of compounds have been utilized in the reversible recording of volume phase holograms. These are dimers of aromatic polycyclic hydrocarbons (Tomlinson et al. 1972) and stilbene derivatives (Anonym 1974). In this paper we describe a new reversible material for recording volume phase holograms (Matjka et al. 1978).     

A DC hybrid circuit breaker with ultra-fast contact opening and integrated gate-commutated thyristors (IGCTs)

Air-magnetic circuit breakers are widely used for short-circuit protection in dc electric railways or industrial plants. The well-known drawbacks of these breakers are mainly a slow breaking action, a short lifetime, and high maintenance costs due to the destructive effects of the arc. The use of power semiconductors in a full-static circuit breaker configuration allows the elimination of these disadvantages but is limited by excessive conduction losses. The paper will present the study of a so-called hybrid breaker, drawing its name from the combination of a high-speed mechanical switch and a bi-directional integrated gate-controlled thyristor assembly connected in parallel. The paper also includes experimental results from a prototype real scale.