Chemical-Spectroscopic Determination of the Isotope Composition and Gravimetric Content of Uranium in Uranium–Aluminum Alloys and Products of Their Processing

Conditions of chemical separation of Al macroamounts and U microamounts, followed by atomic emission spectroscopic determination of the isotope composition and gravimetric content of U, were studied. An algorithm was developed for constructing calibration plots to determine the ²³⁵U/²³⁸U isotope ratio in various samples from nuclear fuel reprocessing. Optimum conditions of the spectral analysis for the U content were found by mathematical design of the experiment: NaCl content 2%, current 18 А, and exposure time 40 s. With the use of these conditions and of a specially developed form of carbon electrode, the uranium detection limit was decreased from 10^–3 to 10^–5%.     

Effect of Barothermal Processing on the Solid-State Formation of the Structure and Properties of 16 at % Si–Al Hypereutectic Alloy

We describe barothermal processing (hot isostatic pressing) of a 16 at % Si–Al binary alloy for 3 h at a temperature of 560°C and pressure of 100 MPa for 3 h, in combination with measurements of heat effects during cooling. The results demonstrate that this processing leads to the fragmentation of the silicon structural constituent and ensures a high degree of homogenization of the as-prepared alloy. Heat treatment of the 16 at % Si–Al alloy at 560°C and a pressure of 100 MPa leads to a thermodynamically driven enhanced silicon dissolution, up to ~10 at %, in the aluminum matrix, resulting in the formation of a supersaturated solid solution, which subsequently decomposes during cooling. We analyze the complete porosity elimination process, which makes it possible to obtain a material with 100% relative density. According to differential barothermal analysis, microstructural analysis, and scanning and transmission electron microscopy data, barothermal processing of the 16 at % Si–Al alloy produces a bimodal size distribution of the silicon phase constituent: microparticles 3.6 μm in average size and nanoparticles down to ~1 nm in diameter. The Al matrix has been shown to contain a high density of edge dislocations. Barothermal processing reduces the thermal expansion coefficient and microhardness of the hypereutectic alloy. We conclude that solid-state barothermal processing is an effective tool for completely eliminating microporosity from the 16 at % Si–Al alloy, reaching a high degree of homogenization, and controlling the microstructure of the alloy, in particular by producing high dislocation density in the aluminum matrix.     

Influence of the deposition pressure on the preparation of μc-Si:H thin films in hot-wire-assisted MWECR-CVD system

Considering the important influence of the deposition pressure on the growth of thin films, such as deposition rate, crystalline volume fraction and density, etc., and based on the analysis of the advantages and disadvantages on the mono-pressure method, we proposed a new method of high- and low-pressure combination to prepare hydrogenated microcrystalline silicon (μc-Si:H) films, i.e. at first we used high pressure to deposit film in 2 min in order to minish the thickness of incubation layer from the amorphous phase transition to crystalline phase, and then used low pressure to deposit film in 18 min to improve the density and decrease the oxidation of the film. The experimental results showed that using this new method the thin film with high crystalline volume fraction of 61% and low light-induced degradation ratio of 5.6% at 210 min was obtained, and meanwhile, it also possessed higher density and better photoelectronic properties than mono-pressure method.     

Effect of the substituent group in p-X-benzylidenemalononitrile on the optical and the electrical parameters of π-conjugated polymers based devices

Journal of Materials Science: Materials in Electronics - The effects of the substituent in p-substituent-benzylidenemalononitrile small molecules have been investigated. We found that the...     

Production of Carbopol® 974P and Carbopol® 971P Pellets by Extrusion‐Spheronization: Optimization of the Processing Parameters and Water Content

Pellets obtained by extrusion‐spheronization represent multiparticulate dosage forms whose interest in intestinal drug delivery can be potentiated and targeted through bioadhesive properties. However, adhesion itself makes the process difficult or even impossible. The problem of tackiness encountered with bioadhesive wet masses was previously eliminated by the use of electrolytes such as CaCl₂. This approach is known to reduce the viscosity of polyacrylic acids by disturbing the interactions between carboxylate groups on adjacent polymer molecules, thereby decreasing their bioadhesive properties. The present study aimed at producing pellets containing carbomers without addition of electrolytes in order to maintain their bioadhesive potentiality at its maximum. Carbopol® 974P (10%, 15% and 20%) and Carbopol® 971P (10%) were used in combination with Avicel® PH101. The extrusion speed (30, 45, 60, 90, and 150 rpm), spheronizer speed (350, 700, 960, 1000, and 1300 rpm), spheronization time (5, 10, 15, and 20 minutes) and amount of water (45%, 50%, 54%, and 58%) were optimized in order to obtain the highest yield of spherical pellets ranging 710–1000 µm in diameter. For pellets containing 10%, 15% Carbopol® 974P or 10% Carbopol® 971P and 45% water content, 30 rpm extrusion speed, 960 rpm, and 10 minutes spheronization speed and time led to the highest yields and sphericities, respectively, 72% and 0.91, 67% and 0.78, and 76% and 0.80. Production of pellets with 20% Carbopol® 974P could be achieved through the increase of the water content up to 58% and implementation of 30 rpm extrusion speed, 1300 rpm, and 10 minutes spheronization speed and time. The yield and sphericity were 42% and 0.78 respectively.     

Effect of Grain Boundary on the Wettability and Interfacial Morphology in the Molten Bi／Cu System

The wetting behavior of molten Bi on polycrystalline Cu substrate and single crystal Cu substrate was studied by the sessile drop method in the temperature range from 673 to 873K. At low temperature the wetting behaviors of molten Bi on both types of Cu substrate were similar. However, at high temperature, the equilibrium contact angle of polycrystalline Cu substrate was lower than that of single crystal Cu substrate, because the preferred dissolution of grain boundaries leads to a smaller liquid/solid interracial energy for polycrystalline Cu substrate. The formation mechanism of arrow-shaped Cu grains at the Bi/single crystal Cu interface is also discussed.     

Effect of ZrB2 and Polyvinyl Butyral Content on the Oxidation Resistance of ZrB2–SiC Coatings Produced by Slurry Brushing Method

ZrB₂–SiC coatings are prepared on the surface of graphite by slurry brushing method to improve the oxidation resistance. Effects of ZrB₂ content and polyvinyl butyral (PVB)–ethanol solution concentration on microstructure and static oxidation behavior of the ZrB₂–SiC coatings are investigated at 1200 °C in air. The results indicate that increasing ZrB₂ content improves the oxidation resistance of the coatings. When ZrB₂ content increases from 30 to 45 wt%, weight loss rates of the coated samples after oxidation at 1200 °C for 120 min decrease from −0.92% to −1.67%. Increasing binder solution concentration raises component content in the coatings. As PVB–ethanol binder concentration increases from 0.025 to 0.075 g mL⁻¹, weight loss rates of the coated samples after oxidation at 1200 °C for 120 min decrease from 0.32% to −0.38%. Excellent oxidation resistance of ZrB₂–SiC coating is attributed to self-sealing ability of B₂O₃ and borosilicate glass. The composite glass can inhibit oxygen diffusion by filling defects in the coating promptly. The borosilicate glass phase can enhance the fluidity of the composite glass. ZrO₂ and ZrSiO₄ particles restrict the growth of the microcrack, which improves the oxidation resistance of ZrB₂–SiC coating.     

Radionuclides in Irradiated Graphite of Industrial Uranium–Graphite Reactors: Effect of Irradiation and Thermochemical Treatment on the Graphite Structure

The structure of irradiated graphite from decommissioned industrial uranium–graphite reactors was studied. The extent of disturbance of the graphite structure is closely correlated with temperature and integral neutral fluence. The perfection of the structure of graphite samples (data of X-ray diffraction and Raman spectroscopy) does not correlate with their radioactivity, which is due to low absolute concentration of the radionuclides. Mapping of the samples using Raman spectroscopy reveals spatial heterogeneity of the distribution of graphite lattice damages, which casts doubt on the representativeness of the spectra of individual points. The spatial distribution of domains differing in the crystal lattice perfection was studied for the first time and was compared with the radionuclide distribution. Satisfactory correlation between the radiographic and spectroscopic mapping data is observed for some samples. Irradiated graphite is strongly textured and contains amorphous microvolumes, which are probably radionuclide carriers. Thermochemical treatment (oxidation in O₂, thermal shock) leads to degradation of the irradiated graphite structure on the submicron level, accompanied by a drastic decrease in the mechanical strength of the samples.     

Effect of barothermal processing on the microstructure and properties of Al–10 at % Si hypoeutectic binary alloy

We describe barothermal processing (hot isostatic pressing) of an Al–10 at % Si binary alloy for 3 h at a temperature of 560°C and pressure of 100 MPa. The results demonstrate that this processing ensures a high degree of homogenization of the as-prepared alloy, which is chemically and structurally inhomogeneous. The morphology of the silicon microparticles in the material suggests that heat treatment of the Al–10 at % Si alloy at 560°C and a pressure of 100 MPa leads to a thermodynamically driven, essentially complete silicon dissolution in the aluminum matrix and the formation of a metastable, supersaturated solid solution, which subsequently decomposes during cooling. We analyze the associated porosity elimination process, which makes it possible to obtain a material with 100% relative density. Barothermal processing of the Al–10 at % Si alloy is shown to produce a bimodal size distribution of the silicon phase constituent: microparticles 1.6 µm in average size and nanoparticles 43 nm in average size. Barothermal processing is shown to reduce the thermal expansion coefficient of the alloy, and the microhardness of the two-phase alloy is determined. Based on the present results, we conclude that barothermal processing is an effective tool for eliminating microporosity from the Al–10 at % Si alloy, reaching a high degree of homogenization, and producing a near-optimal microstructure, which surpasses results of conventional heat treatment of the material at atmospheric and reduced pressures.     

Effect of the TiN content in the Pd-TiN seed layer on the microstructure and magnetic properties of Co∕Pd multilayered media

[Co(0.2 nm)∕Pd(0.8 nm)](20) multilayered films on 15 nm Pd-TiN seed layers were fabricated by dc magnetron sputtering without heating the substrate. The effects of TiN content on microstructure and magnetic properties of the [Co∕Pd] multilayered media were studied. By increasing the TiN content in the Pd-TiN seed layer to an optimum level, coercivity of the [Co∕Pd] multilayered media increased to 6.7 kOe. However, further increase of TiN content beyond 22 vol % reduced coercivity (Hc), implying that there exists a critical TiN concentration to enhance the magnetic property of the [Co∕Pd] multilayered media. Transmission electron microscopic observations revealed that well-isolated [Co∕Pd] multilayered grains with apparent grain boundaries were achieved by controlling the TiN content in the Pd-TiN seed layer. The average grain diameter was 8 nm with a dispersion of 11.2%, grown on the Pd-TiN seed layer with TiN content of 22 vol %.     

Effect of Film Thickness on the Optical Parameters and Electrical Conductivity of Te10Ge10Se77Sb3 Chalcogenide Glass

Several thin films of Te10Ge10Se77Sb3 chalcogenide glass of different thicknesses (250 nm to 400 nm) were prepared by thermalevaporation under vacuum of 133×10-6 Pa (10-6torr). X- ray diffraction analysis showed the amorphicity of the preparedfilms which become partially crystalline by annealing. Transmittance and reflectance measurements in the spectral range of200 nm to 2500 nm have been carried out at normal incidence. The analysis of the absorption coefficient data showed theexistence of indirect transition for the photon energy E in the range 1~3 eV and direct transition for E >3 eV. From thedetermination of the optical constants (n, k), the dispersion of the refractive index has anomalous behaviour in the region ofthe fundamental absorption edge, and followed by the single- effective oscillator approach.The investigated optical parameterssuch as the optical energy gap Eopt, the high frequency dielectric constant εoo, the oscillator position λo, and the oscillatorstrength So, were significantly     

Effect of doping- and field-induced charge carrier density on the electron transport in nanocrystalline ZnO

The charge transport properties of thin films of sol-gel processed undoped and Al-doped zinc oxide nanoparticles with variable doping level between 0.8 and 10?at.% were investigated. The x-ray diffraction studies revealed a decrease of the average crystallite sizes in highly doped samples. We provide estimates of the conductivity and the resulting charge carrier densities with respect to the doping level. The increase of charge carrier density due to extrinsic doping was compared to the accumulation of charge carriers in field effect transistor structures. This allowed us to assess the scattering effects due to extrinsic doping on the electron mobility. The latter decreases from 4.6 × 10(-3) to 4.5 × 10(-4)?cm(2)?V(-1)?s(-1) with increasing doping density. In contrast, the accumulation leads to an increasing mobility up to 1.5 × 10(-2)?cm(2)?V(-1)?s(-1). The potential barrier heights related to grain boundaries between the crystallites were derived from temperature dependent mobility measurements. The extrinsic doping initially leads to a grain boundary barrier height lowering, followed by an increase due to doping-induced structural defects. We conclude that the conductivity of sol-gel processed nanocrystalline ZnO:Al is governed by an interplay of the enhanced charge carrier density and the doping-induced charge carrier scattering effects, achieving a maximum at 0.8?at.% in our case.     

Effect of addition of Ce in Sn–30Zn solder on the structure and properties of the Mg/Al-brazed joint

AZ31B Mg alloy and 6061 Al alloy are joined using low-temperature soldering with Sn–30Zn–xCe solder alloy. The effect of Ce content in Sn–30Zn–xCe solders on microstructure evolution and mechanical properties of the different brazed joints are investigated. The experimental results show that adding appropriate amount of Ce into Sn–30Zn solder is conducive to decreasing the amount of Mg₂Sn intermetallic compounds and increasing the amount of Al–Sn–Zn solid solutions in the soldering zone of the brazed joint, which restricts the drawback of the formation of hard and brittle Mg₂Sn intermetallic compounds and enhances the mechanical property of soldered joint. The average shear strength of the Mg/Sn–30Zn–0.05Ce/Al-brazed joint can reach 77.48 MPa. Results also indicate that the excessive content of Ce leads to the formation of some Ce–Zn and Ce–Sn intermetallic compounds in soldering zone and subsequently decreases the strength of soldered joint.     

Content of Long-Lived Radionuclides of Carbon-14 and Chlorine-36 in Reactor Graphite and in the Biosphere (Is there a Problem with Carbon-14 and Chlorine-36 when It Comes to the Processing of Reactor Graphite?)

Radiochemistry - The amounts of technogenic carbon and chlorine contained in reactor graphite and in the biosphere are compared. The total amount of 14C on Earth and in the atmosphere, according to...     

Biocomposites based on cellulose acetate and short curauá fibers: Effect of plasticizers and chemical treatments of the fibers

Biocomposites based on cellulose acetate and short curauá fibers were prepared by extrusion on a laboratory scale. The influence on the mechanical and thermal properties of the biocomposites caused by three different plasticizers, dioctyl phthalate (DOP), triethyl acetate (TEC) and glycerol triacetate (GTA), and the chemical treatment of the fibers was evaluated. The fibers were mercerized or extracted with acetone. The efficiency of the plasticizers was determined by their molecular features, however, for some applications DOP can be replaced by less hazardous plasticizers, such as TEC and GTA. The biocomposites presented morphology of fibrils uniformly dispersed in the polymer matrices and higher Young’s modulus, higher thermal dimensional stability and lower thermal conductivity in comparison with the properties of the corresponding plasticized polymer matrices. Moreover, these biocomposites combine mechanical and dimensional properties of dense materials with thermal conductivities of porous and thermally insulating polymers.     

Investigation on the Static Fatigue Mechanism and Effect of Specimen Thickness on the Static Fatigue Lifetime in WC–Co Cemented Carbides

The static fatigue mechanism and effect of specimen thickness on static fatigue lifetime for four WC–Co cemented carbides were studied with different binder contents and carbide grain sizes. Static fatigue tests under three-point bend loading were conducted on different sized specimens. The fracture surfaces of rupture specimens were examined by scanning electron microscopy to investigate the static fatigue micromechanisms. Experimental results show that microcracks nucleate from defects or inhomogeneities and the connection of microcracks produces a main crack. The main crack propagates rapidly, resulting in the fracture of specimens. The extension of static fatigue lifetime with the increase of specimen thickness is due to the decrease of plastic zone size near the crack tip and relevant energy change during the crack growth. The effect of specimen thickness on static fatigue lifetime is much greater for cemented carbides with larger WC grain size or higher cobalt content, which is attributed to operative toughening mechanisms.     

Effect of moisture on the mechanical properties of CFRP–wood composite: An experimental and atomistic investigation

Adhesive bonding of fiber-reinforced polymers (FRP) to wood has been proven as a general way to achieve reinforcement and rehabilitation for wood structures. Although a significant mechanical enhancement can be acquired by using such approach, there exists a big concern about the long-term performance of the FRP–wood composite, especially under the effect of moisture. In this paper, both experimental and atomistic approaches are adopted for investigating the moisture effect on the entire FRP–wood composite system. Macroscopic mechanical tests show that its mechanical properties and its fracture behaviors notably change at different levels of ambient humidity. From an atomistic perspective, molecular dynamics (MD) simulations reveal that water molecules significantly reduce the adhesion energy between wood and epoxy. Results from experimental and numerical studies imply that the strength of the FRP–wood interface critically determines the mechanical performance of the entire system. The water molecules absorbed at the interface are crucial to the durability of multi-layer systems and a general mechanism governing the failure modes of such systems is found.     

Effect of mendable polymer stitch density on the toughening and healing of delamination cracks in carbon–epoxy laminates

This paper presents an investigation into the effect of stitch density on the delamination toughening and self-healing properties of carbon–epoxy laminates. The stitches provide the laminate with the synergistic combination of high mode I interlaminar fracture toughness to resist delamination cracking and healing properties to repair delamination damage. The results show that the fracture toughness of the laminate increased with stitch density, due to higher traction (crack closure) loads exerted by the stitches bridging the delamination. During the healing process these bridging stitches first melt and then flow into the delamination, leading to self-healing with full restoration of the mode I fracture toughness. Furthermore, the stitches were capable of repairing delamination cracks many times larger than the original size of the stitches. The effect of stitch density on the healing process of delamination cracks and restoration of fracture toughness was found to remain approximately the same under multiple repair operations.