Structure and properties of plasma sprayed BaTiO3 coatings: Spray parameters versus structure and photocatalytic activity

Plasma spraying enables the creation of layers with thickness in a millimeter range adhering on various substrates. This paper provides a study of phase composition, optical properties and photocatalytic activity 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 optical properties and photocatalytic activity. The spraying was carried out by a direct current gas-stabilized plasma gun which normally utilizes spray distance (SD) in frames from 100 to 150 mm. Besides conventional SD 100 mm also extremely high SD 190 mm was used. The color of the sprayed coating is different for each SD and also differs from sintered BaTiO₃. X-ray diffraction and also SAD mode of HR-TEM show certain content of amorphous fraction in the coating. The hydrogen content in the coating was found to be higher in the coatings than in the sintered bulk. The diffuse reflectance was measured by UV–VIS spectrophotometry and corresponding band-gap energy was estimated. X-ray photoelectron spectroscopy confirms specific stoichiometric and structural disorder observed also at bang-gap evaluation and by Raman spectroscopy. HR-TEM images for crystalline and amorphous zones are given. Photocatalytic decomposition of acetone was tested and BaTiO₃ coatings compared with a sintered bulk.     

Preconsolidation, structural strength of soil, and its effect on subsoil upper structure interaction

When constructing a building, manufactured materials are used. That is the reason for their excellent material properties. In the case of the foundation, the natural condition of the soils must mostly always be respected. The geostatical stress plays a significant role on the subsoil behavior because it is the de facto natural form of the soil compaction. The soil has a memory of the highest stress that has ever been loaded on it. The soil can be considered incompressible if the magnitude of a surcharge is lower. In engineering practice the construction of higher buildings is founded in a deeper hole so that the depth of the influence zone achieves an acceptable value for the future surcharge of the upper structure. For very tall buildings, the deep hole foundation must be prolonged by piles. In particular, this article deals with laboratory testing that provides the preconsolidation. In Czech, we term it the structural strength of soil. The test provides the initial void ratio as well as the initial coefficient of fully saturated hydraulic conductivity. The isotropic consolidation test with the triaxial test apparatus and consequent knowledge of the pore pressure course was chosen to determine the initial soil properties, including the preconsolidation level. Derived theory together with the genetic algorithms provide an efficient tool for the determining parameters. Good knowledge of the influence zone is crucial when solving soil structure interaction. The progress of the influence zone was considered from the extensive research carried out at the University of Brasília, Brazil. Thus, using the measurements, the preconsolidation and its effect were verified in situ. The derived formulas and presented graphs for influence zone depth estimation have considerable importance for civil engineering practice. The Kantorovich method together with the strategy of convolution was used to reach dimensional reduction when deriving analytical formulas. Recommended results and formulas were verified against FEM code ADINA.     

脂肪酸酯分子结构对酯基钻井液性能的影响

脂肪酸酯的分子结构对酯基钻井液的性能具有重要的影响。在分析脂肪酸酯分子中酯基基团数、饱和度、分子构型、分子量大小以及分子间作用力的基础上,选取了6种饱和脂肪酸酯作为研究介质,测试了在不同温度条件下介质的粘度与密度,分析了影响介质粘度与密度的机理,得出了在低温下介质的粘度大小主要取决于脂肪酸酯中脂肪醇分子链的长度。介质密度的高低主要取决于脂肪酸酯的分子量,与脂肪酸酯中酯基的位置、α氢的活泼性以及分子间作用力大小无关。     

Plasma Spraying of Silica-Rich Calcined Clay Shale

Silica-rich clay shale is a viable candidate for replacement of mullite in many applications, especially when outstanding refractoriness and chemical resistance to various agents are desirable. In this contribution, instead of the commonly used synthetic mullite feedstock, the thermal stability of inexpensive calcined natural raw clay shale sprayed using water stabilized plasma system is reviewed. Phase stability and phase changes at elevated temperatures up to 1500 °C were studied by an array of experimental techniques ranging from measurements of thermal conductivity and the heat flow as functions of temperature, scanning electron microscopy, x-ray diffraction (XRD) of the annealed samples, and in situ high temperature XRD. The mostly amorphous as-sprayed coatings with less than 10 wt.% of mullite are temperature stable up to 800 °C and rapid crystallization occurs between 920 and 940 °C. Performed analyses gave evidence about the increase of mullite grain sizes for temperatures higher than 1200 °C and, moreover, certain saturation of crystallinity, not surpassing the threshold of 60 wt.% even for 1500 °C, is observed. The microstructure after annealing at 1500 °C is notable by clusters of fine needle-like mullite crystallites with sizes within the range of tens of nanometers in Si-rich amorphous matrix.     

Tensile and fracture properties of an Mg-RE-Zn alloy at elevated temperatures

Magnesium alloy EZ10(Mg-RE-Zn) was deformed in tension at temperatures from 20 up to 520 °C. A rapid decrease of the yield and tensile strength with temperature was observed at temperatures higher than 300 °C. On the other hand, ductility of samples rapidly increased in the same temperature range. Light microscopy and scanning electron microscopy was used to reveal the reason for these behaviours. Intermetallic particles in grain boundaries are responsible for excellent mechanical properties at lower temperatures. Diffusional processes occurring at temperatures higher than 300 °C significantly influenced the deformation mechanism as well as the fracture character.     

InGaAs/GaAsSb/InP terahertz quantum cascade lasers

The development of In_0.53Ga_0.47As/GaAs_0.51Sb_0.49 terahertz quantum cascade lasers is reviewed, starting with the first demonstration, through growth direction dependent performance issues, to high performance devices. This InP-based material system is an attractive alternative to the almost exclusively used GaAs/Al_xGa_1-xAs. Devices achieve maximum operating temperatures of 142 K and exhibit broadband lasing over a range of 660 GHz. A special focus has to be put on the growth direction related interface asymmetry for this material system. Symmetric active region designs are an elegant technique to investigate such asymmetries. A significant impact on the device performance is observed and attributed to interface roughness scattering.     

Thermal stability and sorption properties of asphaltene sulfocathionites

Abstract

Using simultaneous thermogravimetry and differential scanning calorimetry, thermal stability and possible phase transitions of asphaltene sulfocationites and native asphaltenes have been evaluated; the kinetic characteristics of heating have been determined, namely, onset temperature of decomposition, stages of decomposition, and temperature ranges of stability. It has been determined that asphaltene sulfocationites retain structural-group features (IR spectroscopy method) and sorption characteristics while heating up to 350?°C.     

Gel based on modified chitosan for oil spill cleanup

A method has been developed for obtaining a polymer porous gel and coating based on nontoxic and environmentally friendly components: chitosan, citral, and glutaraldehyde. The chemical structure and morphology of the polymer gel were investigated by infrared spectroscopy and scanning electron microscopy, respectively. The contact angles were determined using a goniometer, and the water and oil absorption of the gel were determined by the gravimetric method based on changes in the gel mass. Measurement of the contact angle θ of transmission oil and water drops on the coating surface showed the hydrophobic nature of the coating (θ = 90° for water and θ = 0° for oil). Study of the sorption properties of the resulting gel showed high sorption capacity with respect to transmission oil (9.05 kg/kg) and low sorption capacity with respect to water (2.46 kg/kg). It was found that after oil desorption from the loaded aerogel, it can be reused. The potential possibility of recycling the spent gel through its biodegradation in the soil was shown. Because of the excellent sorption capacity, high porosity, low density, and soil degradability, the developed gel has a great potential for application in the field of environmental purification from oil pollution.     

Effect of a load shape on load acceleration at the start of an electric hoist

This contribution describes the effect of a load shape on load acceleration at the start of an electric hoist. The emphasis is on a comparison of acceleration course of loads. Two loads with entirely different shape-a load with a cuboid shape and one with a cylinder shape, were chosen. Improved mathematical theory for the start of an electric hoist with three degrees of freedom is used. Thus, we measured the acceleration of the electric hoist, the wire rope end and the load center of gravity for two loads with different shape.     

Silicon diffractive optical elements for high-power monochromatic terahertz radiation

This paper presents a fabrication technique and results of studies of silicon binary diffractive optical elements (DOEs): a diffractive lens and a 1 : 2 diffractive beam splitter with an aperture diameter of 30 mm for the terahertz spectral range. The elements were fabricated in two versions: with and without an antireflection coating of parylene C. The DOE characteristics were investigated in the beam of the Novosibirsk free electron laser at a wavelength of 141 μm. The results are given of a study of the radiation resistance of the coating, which remained intact upon exposure to an average radiation power density of 4 kW/cm²; the peak power in a 100 ps pulse was almost 8 MW/cm². Experimental estimates of the diffraction efficiency of the elements coated with the antireflection coating are in good agreement with theoretical estimates.