The aim of this study is to investigate the interaction of ZnO/SiO₂ particles between the chloroprene rubber and its effect on the cure characteristics and mechanical properties of the cold vulcanizing adhesives. Curing efficiency and mechanical properties of ZnO/SiO₂ filled adhesives were compared with SiO₂ filled adhesives. ZnO nanoparticles were bounded to SiO₂ spherical nanoparticles by hydrolysis and condensation process. The morphology and elemental content of ZnO/SiO₂ particles were investigated by scanning electron microscopy and energy dispersive spectroscopy. The ZnO/SiO₂ particles were then blended with chloroprene rubber as accelerator during the vulcanization process. Cure characteristics, which are scorch time (t_{s2}), cure time (t_{c90}), maximum torque (M_{H}) and minimum torque (M_{L}) of the rubber compounds were determined at 190°C with a moving die rheometer. The fabric conveyor belt was used for measuring adhesive strength of the adhesives. The fabric conveyor belt was used for measuring adhesive strength of the adhesives. Application of the cold vulcanizing adhesives to the fabric conveyor belt was carried out at three different times (4, 8, and 24 h), 25°C temperature and 0.3 kg/cm² pressure. The results showed that ZnO/SiO₂ particles provided a higher adhesive strength than silica in the 4, 8, and 24 h of adhesion. ZnO/SiO₂ filled rubber blends gained superior vulcanization characteristics by the increasing cure rate index with the reducing cure time and scorch time. It has been concluded that ZnO/SiO₂ particles can be used as a new curing accelerator and simultaneously reinforcing filler.
The paper presents results of sintering proppants parameters and its influence on light ceramic proppants obtained by the mechanical granulation method. The proppants were prepared basing on a ceramic composition consisting of three raw materials such as kaolin, clay and bauxite mixed with poly(vinyl alcohol) binder with a molecular weight 26000 g/mol and hydrolysis degree of 88%, added in amount of 5 wt% with respect to the powder. Sintering temperature range oscillated between 1200 and 1225°C, kiln rotations were 1-2 rpm. Sintered proppants were characterized in compliance with PN-EN ISO 13503-2 norm and bulk density, sphericity coefficient, turbidity, solubility in acids and scanning electron microscopy observations have been estimated. The results demonstrated that sintering temperature and kiln rotation have an essential effect of the proppants parameters.
Conventional portland cement has found worldwide usage in the production of cementitious materials in recent years. Nevertheless, environmental problems such as high demand of raw materials, energy consumption and high amount of carbon dioxide emission take place before and during manufacturing process. The attempts have been made to seek alternative binders and develop supplementary materials for construction sector. Therefore, this study reports the results of an experimental program on the comparison of geopolymers with different compositions in terms of evaluating their physical and mechanical behavior. For that purpose, the effect of binder types and amount of binders and alkali activator (sodium hydroxide) was investigated. In addition, acidic pumice and waste aluminium particles were also used as fine aggregate and air entraining agent, respectively, in geopolymer production. The test results revealed that as the content of alkali activator increased, compressive and flexural strength decreased. Addition of waste aluminium particles decreased bulk density and strength owing to the some extent of entrained air.
Strontium titanate is a perovskite with a great potential to act as an anode material for solid oxide fuel cells. The requirements for these materials concern not only electrical but also microstructural properties. The strontium titanate with regular pore structure can exhibit lower flow resistance compared to random pore distributed materials. Several methods of synthesis (with addition of various organic agents) allowed obtaining materials with regular/irregular pore structure. Regardless of synthesis methods all materials showed high porosity (above 40 vol.%). Additionally it was found that three-dimensionally ordered macroporous structure collapsed after sintering at 1200°C whereas macro-mesoporous structure of P-123 modified strontium titanate had persisted.
Alpha brasses (in principle single-phase solid solution alloys containing less than 35% Zn) are usually processed by extrusion, forging or rolling. Although these materials are of widespread use, few detailed studies of the flow behavior of brass at high temperature are available. The hot workability of a CW602N brass (Cu-36.5%Zn-2%Pb) was thus investigated by torsion testing in the temperature range between 550 and 800°C, under equivalent strain rates ranging from 0.01 to 10 s^{-1}. The peak flow stress dependence on temperature and strain rate was described by the well-known Garofalo equation, with a stress exponent close to 4 and Q=220 kJ mol^{-1}. A considerably larger scatter of the experimental data was observed in the high temperature range. The detailed microstructural analysis of the deformed samples by scanning electron microscopy revealed substantial differences among the samples deformed in the low temperature regime and those torsioned at 750 and 800°C. These differences were analyzed and discussed to rationalize the different mechanical responses observed in the two hot-deformation regimes.
X-ray diffraction and ^{57}Fe Mössbauer spectroscopy were applied as complementary methods in order to investigate the structure and hyperfine interactions of (BiFeO_3)_{1-x}-(BaTiO_3)_{x} solid solutions prepared by mechanical activation and subsequent heat treatment.
The crystallography and microstructure of eutectic carbides crystallizing in non-equilibrium conditions in hypoeutectic Fe24Cr0.8C have been studied by light microscopy, scanning electron microscopy, and transmission electron microscopy. The alloy was synthesized in an arc furnace in high purity argon atmosphere and crystallized on water-cooled copper mould. Greater thermal gradient in regions close to water-cooled, copper mould in comparison with top of the ingot gives a formation of eutectic carbides with two morphologies: large polygonal carbides and surrounding them much smaller, plate-like carbides instead of rod-like carbides, observed in top of the ingot. There was no evidence for influence of non-equilibrium crystallization to the formation of types of carbides different than M₂₃C₆.
The mechanical alloying process has been used to prepare nanocrystalline Cu_{70}Fe_{18}Co_{12} alloy from elemental Cu, Fe and Co powders in a planetary ball mill under argon atmosphere. The interdiffusion of Cu, Fe and Co leads to a heterogeneous solid solution with Cu-Fe-Co rich environments after 12 h of milling. The end product is a mixture of a highly disordered structure, fcc-Cu (Fe-Co), phase having different microstructural and structural parameters. For all the elaborate series, the evolution of coercive field and the remanence according to the time of milling is analyzed. The coercivity, H_{c}, decreases rapidly up to 8 h of milling to about 0.3 A/m and then the coercivity, increases to a maximum at 54 h. The influence of the time of milling at the resistivity of these alloys is shown.
The physical mechanisms of the deformation-induced structural transformations in molecular crystals, including morphological changes, amorphization and molecular polymorphous conversions in nano-dispersed bioinorganic compounds are discussed in this work. Integrated study using direct structural and structure-sensitive spectroscopic methods allowed obtaining the data on polymorphous transformations, taking place during mechanical activation in calcium gluconate monohydrate (CG). One of the possible reasons for lattice polymorphous transformations and amorphization, observed in the course of mechanical activation of low-symmetry molecular crystals, might be the spatial molecular isomerization. In this case, the disappearance of the translational invariance of the lattice is conditioned by the simultaneous coexistence of the reactants and reaction products, which have different stereo-organization of the molecular structure.
Although SiO₂ is produced mostly from mineral sources like quartz, it has recently been obtained from lignocellulosic natural resources, such as rice husk (hull). Several methods for extracting silica (SiO₂) from rice husks are available in the literature. These methods are based essentially on heat treatment and/or extraction. This study represents a thorough account of heat treatment and acid-base extraction, to obtain silica from rice husks with a high purity and to eliminate other inorganic impurities. Rice husks, considered to be a potential silica source, were pretreated with various acids, base and water and then thermally degraded in a fixed bed reactor under an inert gas atmosphere (N₂). The materials produced in these conditions were characterized by Brauner-Emmett-Teller analysis, for surface area and pore volume, by Fourier transform infrared spectroscopy, powder X-ray diffraction, X-ray fluorescence, and scanning electron microscopy.
Nanocrystalline powders of ZnAl_2O_4 and CdSe were prepared via mechanochemical synthesis. Powder slurries were coated as thin films on SiO_2 thin layer chromatography (TLC) sheet by capillary method. The photocatalytic activity of the film coating was tested in a self-made gas-phase flat-plate continuous-flow photocatalytic reactor with toluene as model air contaminant. The tested nanocrystalline ZnAl_2O_4 turned out to be poor oxidation photocatalyst under UV irradiation. CdSe displays considerable photocatalytic activity under visible light, where TiO_2 is inactive. The nonconventional one-step mechanochemical route to ZnAl_2O_4 and CdSe synthesis offers several advantages compared to traditional processing routes, including low-temperature solid state reactions at ambient temperature, absence of organic templates contamination and low expenses.
X-ray diffraction and ^{57}Fe Mössbauer spectroscopy were applied as complementary methods to investigate the structure and hyperfine interactions of the Aurivillius compounds prepared by mechanical activation and subsequent heat treatment. Preliminary milling of precursors enhanced the diffusion process and pure Aurivillius compounds were obtained at lower temperature as compared with conventional solid-state sintering technology (lower at least by 50 K). All the investigated Aurivillius compounds are paramagnetic materials at room temperature.
Bimetal composites are a group of promising engineering materials with high developing and service potential. Especially in many fields they can be a powerful low cost alternative to metal-ceramic composites. The most commonly encountered type of these composites is steel reinforced aluminium matrix composites which stand out with high wear and abrasion resistance. Significant fabrication processes of metal/metal composites are based on liquid metal techniques. In this study, Al/steel composite specimens were produced by using vacuum assisted solid mould investment casting technique. A7075 wrought aluminium alloy were infiltrated into steel preforms, which were produced with 304 stainless steel and H13 hot-work tool steel turnings, in the plaster based solid investment casting moulds. Microstructure observations, HV microhardness measurements, scanning electron microscopy and energy dispersive X-ray spectroscopy analysis were carried out for characterization.
A nonferroelectric high permittivity compound with the perovskite structure, Bi_{2/3}Cu_3Ti_4O_{12}, was synthesized at 900°C. The ceramic powder and appropriate organic additives were used for preparation of a slurry for tape casting. The obtained green tapes were smooth, flexible, and with a uniform thickness of 25 μm after drying at 50°C. Ag electrodes were screen printed on green rectangular sheets cut by a laser. Subsequent operations were screen printing of Ag internal electrodes, stacking of green sheets, isostatic lamination, cutting, deposition of external terminations and co-firing of dielectric and conductive layers at 850°C. Scanning electron microscopy observations showed well sintered, dense, fine-grained microstructure of ceramic layers and good cooperation with the electrodes made of commercial Ag paste. Capacitance and dissipation factor of multilayer capacitors were examined in the temperature range from - 55 to 330C at frequencies 10 Hz-2 MHz. The fabricated multilayer capacitors exhibit high capacitance and relatively low temperature coefficient of capacitance in the temperature range from - 55 to 110°C. The obtained lead-free high permittivity nonferroelectric material Bi_{2/3}Cu_3Ti_4O_{12} is a spontaneously formed internal barrier capacitor. This material seems to be a promising alternative for conventional lead-based relaxor dielectrics in multilayer ceramic capacitors.
A new perovskite material Nd_{2/3}CuTa_4O_{12} was applied as a naturally formed internal barrier layer capacitor. The powder prepared by solid state synthesis and ball milling was pressed into pellets and sintered at 1180-1220°C. Dielectric properties of ceramic samples were characterized by impedance spectroscopic studies carried out in the temperature range from - 55 to 700C at frequencies 10 Hz ÷ 2 MHz. Two types of the dielectric response were revealed - a high frequency response attributed to grains which occurred at low temperatures, and a low frequency one related to grain boundaries which dominated at higher temperatures. Resistances and capacitances of grains were found to be two orders lower than those of grain boundaries. Two plateaus were observed in the dielectric permittivity versus frequency plots - a low frequency step corresponding to a high value of 10^4 and a high frequency step at a level of 40. Scanning electron microscopy observations and energy dispersive spectroscopy analysis confirmed that Nd_{2/3}CuTa_4O_{12} ceramics were composed of semiconducting grains and insulating oxygen-enriched grain boundaries. The formation of such an electrically heterogeneous system during the one step fabrication process in air leads to spontaneous internal barrier layer capacitance effects responsible for a high and relatively stable dielectric permittivity of the developed material.
Tungsten carbide (WC) powder having a crystallite size around 55 nm and the Brunauer-Emmett-Teller specific surface area 2.75 m^2/g was sintered using the field assisted sintering/spark plasma sintering technique. Sintered samples were investigated using different analytical methods providing detailed information on the microstructure and mechanical properties of materials. Density and porosity of specimens were determined using the Archimedes principle and optical and scanning electron micrographs. The X-ray diffraction investigations provided the information on the crystal real structure and crystallite sizes. The electron backscatter diffraction measurements yielded the details about the grain size, frequency, and distributions of grain boundaries. Finally, the essential mechanical properties of sintered samples were obtained from the hardness and fracture toughness measurements. The influences of individual sintering conditions: sintering temperature and sintering time especially, on the microstructure and mechanical properties of sintered specimens were derived. Fully compact samples having the Vickers hardness HV10 around 29 GPa and fracture toughness K_{Ic} approximately 7.2 MPa m^{1/2} were sintered from temperatures of 1800C and holding times 1 min. Specimens sintered at lower temperatures showed lower density which resulted in a significant drop in the sample hardness.
Soft magnetic composite was prepared by coating the commercial FeSi powder by Mn_{0.8}Zn_{0.2}Fe₂O₄ (MnZn) ferrite, which serves as a potential dielectric phase. MnZn ferrite was prepared by the sol-gel method followed by the auto-self combustion process. The spinel structure of MnZn ferrite was analyzed by X-ray diffraction technique. The composite material was prepared by uniaxial compaction technique and sintered either by conventional or unconventional microwave method. The microwave sintering was applied in order to reduce a grain growth and decrease the overall sintering time. The microstructure of FeSi powder is formed by grains of different diameter. Magnetic force microscopy and scanning electron microscopy were used for an investigation of the correlation between the grain size, grain boundaries and magnetic domains. Magnetic force microscopy visualization of magnetic domains in the prepared soft magnetic composite brings insight into how the magnetically active coating (MnZn ferrite) influences the soft magnetic (FeSi) powder under the influence of the external magnetic field.
Depth distribution of implanted species and microstructure of oxygen-containing Czochralski grown silicon (Cz-Si) implanted with light ions (such as H^{+}) are strongly influenced by hydrostatic pressure applied during the post-implantation treatment. Composition and structure of Si:H prepared by implantation of Cz-Si with H_{2}^{+}; fluence D = 1.7 × 10^{17} cm^{-2}, energy E = 50 keV (projected range of H_{2}^{+}, R_{p}(H) = 275 nm), processed at up to 923 K under Ar pressure up to 1.2 GPa for up to 10 h, were investigated by elastic recoil detection Rutherford backscattering methods and the depths distributions of implanted hydrogen and also carbon, oxygen and silicon in the near surface were determined for all samples. The defect structure of Si:H was also investigated by synchrotron diffraction topography at HASYLAB (Germany). High sensitivity to strain associated with small inclusions and dislocation loops was provided by monochromatic (λ = 0.1115 nm) beam topography. High resolution X-ray diffraction was also used.
Composites and nanocomposites as commercially used engineering materials with continuous development, are important for rising market and industry needs. Significant role is played by polymers, whose consumption increases every year, thanks to low cost of production, economical processing and broad scope of material composition possibilities, including nanomaterials and basing on them nanocomposites. Nanocomposites, using power of nanotechnology, may improve physical, chemical and mechanical properties, comparing to composites. Investigation of structure and properties of such materials is necessary to obtain knowledge about phenomena at micro and nanoscale and gives opportunity to design and control structure, because the properties of any material depend on its matter. Polymer matrix nanocomposites are interesting and very promising class of polymer composites. Investigation of structure development due to different heat treatment and under different processing condition of injection molded specimens of polypropylene and montmorillonite composition has been performed. Dispersion of nanoreinforcement, in the shape of 2:1 layer silicates, was observed under transmission and scanning electron microscope. Application of advanced technology of multiplication of oriented layer mostly reinforcing and orienting micro and nanoparticles along polymeric specimen, allowed to obtain several layers and significantly reinforced material. Light microscope has been used for observation layered zone, visible just in polarization mode.
Multilayer amorphous TiB_{x}/TiSi_{y}C_{z} coatings were formed by duplex treatment: dual beam ion beam assisted deposition and pulsed laser deposition. Post-deposition heating was applied to activate crystallization in the coating. In situ transmission electron microscopy heating experiments were conducted in the temperature range 20-600°C. Crystallization of TiB₂ phase in TiB_{x} layers begun at 450°C, while TiSi_{y}C_{z} layers retained nearly amorphous up to 600°C.
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.