Distinct nonequilibrium plasma chemistry of C2 affecting the synthesis of nanodiamond thin films from C2H2 (1%)/H2/Ar-rich plasmas

6 pages, 5 figures, 6 tables.We show that the concentrations of the species C2 (X 1Σg+), C2 (a 3Πu), and C2H exhibit a significant increase when the argon content grows up to 95% in medium pressure (0.75 Torr) radio frequency (rf) (13.56 MHz) produced C2H2 (1%)/H2/Ar plasmas of interest for the synthesis of nanodiamond thin films within plasma enhanced chemical vapor deposition devices. In contrast, the concentrations of CH3 and C2H2 remain practically constant. The latter results have been obtained with an improved quasianalytic space–time-averaged kinetic model that, in addition, has allowed us to identify and quantify the relative importance of the different underlying mechanisms driving the nonequilibrium plasma chemistry of C2. The results presented here are in agreement with recent experimental results from rf CH4/H2/Ar-rich plasmas and suggest that the growth of nanodiamond thin films from hydrocarbon/Ar-rich plasmas is very sensitive to the contribution of C2 and C2H species from the plasma.This work was partially funded by CICYT (Spain) under a Ramón y Cajal project and under Project No. TIC2002- 03235. One of the authors (F.J.G.V.) acknowledges a Ramón y Cajal contract from the Spanish Ministry of Science and Technology (MCYT). One of the authors (J.M.A.) acknowledges partial support from CICYT (Spain) under Project No. MAT 2002-04085-C02-02.Peer reviewe

Long term behaviour of the resistivity of concrete

Against the background of immense costs of repair or replacement of concrete structures degraded by reinforcement corrosion, a strong interest in industry and research can nowadays be found in the underlying processes and in possibilities to influence them. As a part of the reinforcement corrosion circuit, the resistivity of concrete is a decisive material parameter with regard to corrosion propagation, which itself is a time-dependent process of many years of length. For this reason, a picture of the long term behaviour of the resistivity of concrete could be of great value. This paper presents resistivity data of concrete specimens up to an age of 17 year. An investigation was carried out of their development throughout the years in dependence of all main aspects influencing the magnitude and the development of the resistivity (climate, cement type, water/cement-ratio).Structural EngineeringCivil Engineering and Geoscience

Mechanical and Surface Geometric Properties of Reinforcing Bars and Their Significance for the Development of Near-Surface Notch Stresses

Due to the production process, reinforcing steel bars possess an inhomogeneous microstructure associated with different material properties over the cross-section (e.g., hardness, ductility or strength). Furthermore, the surface required for the bond has a negative effect on the fatigue behavior. The first investigations were carried out in the 1970s and detected the fillet radius r as a key influencing factor. Until now, few studies had been carried out that investigate the quantification of the surface properties on the fatigue behavior, and none of them compared these properties with the local strengths of the material. The current paper presents the first results of a reverse-engineered reinforcing steel bar based on a previously performed laser scanning process. The rebar models were used to calculate the notch stress factors for different diameters based on von Mises stresses taken from FEM simulations. The notch stress factors showed a functional relationship with the fillet radius, which was already shown in the literature. Further experimental investigations on the fatigue and tensile behavior of the structural components in the investigated Tempcore® rebars were carried out on microstructure specimens eroded by WEDM. The results of the tensile tests were used to derive a yield and tensile strength distribution in the cross-section. Depending on the microstructure, a yield strength between 415 N/mm2 (ferrite/pearlite core) and 690 N/mm2 (tempered martensite surface) was found. The acting notch stresses show a logarithmic dependency of the fillet radius, but do not reach the material strength of the surface

За кадры. 1978. № 44 (2115)

Старейшая кузница инженерных кадров Сибири1. Химико-технологический 2. Инженерной химии и химической кибернетикиАвтоматика и вычислительной техникиТеплоэнергетическийГеологоразведочныйФизико-техническийЭлектро-энергетическийЭлектрофизическийМашиностроительныйМатематика / В. РожковаПонять и усвоить. Физика / Л. ГригорукУсловия прием

Bond Behavior of WAAM Reinforcements in Comparison to Conventional Steel Reinforcements

Additive manufacturing is becoming increasingly important in the construction industry. Wire arc additive manufacturing (WAAM) can be integrated into the selective paste intrusion (SPI) to enable the simultaneous printing of reinforced concrete. The bond behavior of a WAAM reinforcement was investigated with pull-out tests and compared to alternative reinforcement types to analyze the stress transfer between the different components. In the first step, the surface of all the reinforcement types was recorded using a laser-based line scan measuring system. This permits the evaluation of the surface parameters, such as the surface roughness Rq, or the related rib area fR. The WAAM reinforcement showed a bond behavior in the pull-out tests that was comparable to a reinforcing steel bar. Both the bond stresses achieved, and the occurring scatter of the measurement results at the characteristic slip values were almost the same. Even without existing transverse ribs, the WAAM reinforcement reached maximum bond stresses similar to the reinforcing steel. An evaluation of the surface roughness revealed a linear relationship with the maximum bond stress achieved with a logarithmic scaling of Rq. The bond work Wτ, which is a measure of the system stiffness, showed that WAAM reinforcements and reinforcing steel bars have approximately similar behavior