Measurement of linear dimensions of pattern elements of micro- and nano-structures under high- and low-voltage scanning electron microscopes

Measurements of the line width of one and the same test object under high- and low-voltage scanning electron microscopes are performed. Translated from Izmeritel’naya Tekhnika, No. 1, pp. 15–17, January, 2009.     

Void Nucleation and Growth in Dual-Phase Steel 600 during Uniaxial Tensile Testing

Commercial dual-phase (DP) steel in sheet form and comprised of ferrite, martensite, and bainite was subjected to uniaxial tension up to fracture. The damage characteristics were studied through extensive quantitative metallography and scanning electron microscope (SEM) observations of polished sections and fracture surfaces of failed specimens. The observed void nucleation mechanisms include nucleation at the martensite/ferrite interface or triple junction (most predominant), nucleation due to the cracking of martensite particles, and nucleation at the inclusions. The void characteristics in terms of area fraction, void density, void size ranges, and void orientations were analyzed as a function of thickness strain from various regions of the different uniaxial tensile test specimens taken to fracture. The damage analysis suggests that the void nucleation occurs during the entire deformation process with an almost constant rate and this rate reduces before fracture. A nucleation strain of 0.15 has been estimated for this material.     

Life Expectancy Evaluation of the Wood Poles Which Support the Hellenic Electrical Distribution Network

The Hellenic electrical distribution lines have been basically supported with the use of wood poles. Outages due to aging, degradation, or broken wood poles may infer significant costs due to repair and loss of energy to consumers. Lifetime estimation of wood poles is significant for maintenance and replacement decisions at the power utility. The paper presents a methodology, based on a statistical analysis, for the evaluation of the life expectancy and the production of a survival curve of a typical Hellenic distribution wood pole in-service. The proposed methodology intends to minimize the life-cycle cost of inspection and refurbishment of wood poles in the distribution network of Hellas, something that is really important in the new competitive and liberating Hellenic electrical energy market.     

The Critical Temperature of Aluminum

The critical temperature, T _c, of metals is a fundamental point when vaporization due to high energy exchanges occurs. Although aluminum is a metal often studied as a benchmark for theories, its critical temperature is not known with a high degree of accuracy. Its determination by experiment is difficult as a result of its high value. This paper reviews the existing data and proposes new ones resulting from recent measurements of particular physical properties and recent theoretical approaches. These new estimates lead to the recommended value of T _c = (6700 ± 800) K.     

Surface Cu depletion of Cu(In,Ga)Se2 films: An investigation by hard X-ray photoelectron spectroscopy

The origin of surface Cu depletion of polycrystalline chalcopyrite thin films and its consequences for the physics of related solar cells have been discussed for the past 15 years. In order to shed light on the composition and thickness of this Cu-depleted surface layer, depth-dependent compositional analysis by hard X-ray photoelectron spectroscopy was performed. The data from Cu-poor grown Cu(In,Ga)Se₂ samples point to a surface layer in the sub-nanometer regime, which is completely depleted of Cu. This result supports the surface reconstruction model proposed by first-principles calculations by other authors. Analysis of the surface morphology of the investigated samples confirms the conjunction of Cu depletion and faceting of the surface. Theoretical considerations show that the apparent surface concentration ratio of [Cu]/([In] + [Ga]) = 1/3 found by conventional photoelectron spectroscopy studies can be explained by the surface reconstruction model.     

The Influence of Corrosion and Cross-Section Diameter on the Mechanical Properties of B500c Steel

Corrosion is a negative contributor on the structural integrity of concrete structures and leads to degradation of the mechanical properties of steel rebar. Exposure to chloride, seawater, salt and saltwater and deicing chemical environments influences the concrete-steel bond and weakens it. A considerable strength factor of the two-phase steel B500_c (martensitic, ferritic-perlitic) is considered to be the outer martensitic cortex thickness, which varies according to the area of the rebar cross section. In order to evaluate the influence of corrosion and the size of the area on the mechanical properties of B500_c steel, an experimental investigation was conducted on B500_c ribbed steel rebar of 8, 12, 16, and 18 mm diameter, and which were artificially corroded for 10, 20, 30, 45, 60, 90, and 120 days. The laboratory tests suggest that corrosion duration and rebar cross-sectional area size had a significant impact on the strength and ductility degradation of the specimens. The tensile mechanical properties before and after corrosion indicated progressive variation and drastic drop in their values. The extended salt spray exposure enhanced the damage and created pits and notches, resulting in stress concentration points and progressive reduction of ductility and available energy. Anti-seismic design and codes that ignore the influence of the size of the cross-section area and the level of corrosion and mechanical behavior of reinforcing steel could lead to unpredictable performance during severe ground motion.     

Growth and morphology manipulation of carbon nanostructures on porous supports

Structural polymorphism of carbon grown on porous supports by chemical vapor deposition (CVD) is demonstrated. Combining three different supports (activated carbon, macroporous polymeric beads, and microporous aluminophosphate molecular sieves), with two catalysts (Ni and Fe), yielded a variety of carbon nanostructures ranging from coils and belts to fibers and tubes, without changing CVD temperature, time, and precursor composition and flow rate. Ion exchange between ammonium-impregnated supports and the metals was necessary in order to achieve a fine dispersion of the catalyst over the support surface. Metal-support interactions and the balance between ammonium and metal concentrations were investigated and found to considerably affect catalyst dispersion, shape, and crystallographic orientation, which in turn determined the morphological and structural characteristics, and yield of the carbon product. The catalyst-loaded supports and the resulting carbon materials were characterized by scanning and transmission electron microscopy, thermogravimetic analysis, X-ray diffraction, and Raman spectroscopy, while nitrogen and mercury porosimetry were used to characterize the supports and evaluate the degree of support pore blocking by the carbon deposits.