Structural analysis of sheet nickel welded joints

The paper presents an analysis of structure nickel sheet welded joints made by applying Gas Tungsten Arc Welding (GTAW) method. Based on results of metallographic examination, HV5 hardness measurements, Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis of the welds it was found that the joints were characterized with a three-zone structure with large columnar dendrites in the welds. Columnar dendrites show a mosaic substructure with uniformly distributed carbides of M3C type rich in nickel

Theoretical investigation of the electronic structure of Fe(II) complexes at spin-state transitions

The electronic structure relevant to low spin (LS)high spin (HS) transitions in Fe(II) coordination compounds with a FeN6 core are studied. The selected [Fe(tz)6]2+(1) (tz=1H-tetrazole), [Fe(bipy)3]2+(2) (bipy=2,2’-bipyridine) and [Fe(terpy)2]2+ (3) (terpy=2,2’:6’,2’’-terpyridine) complexes have been actively studied experimentally, and with their respective mono-, bi-, and tridentate ligands, they constitute a comprehensive set for theoretical case studies. The methods in this work include density functional theory (DFT), time-dependent DFT (TD-DFT) and multiconfigurational second order perturbation theory (CASPT2). We determine the structural parameters as well as the energy splitting of the LS-HS states (ΔEHL) applying the above methods, and comparing their performance. We also determine the potential energy curves representing the ground and low-energy excited singlet, triplet, and quintet d6 states along the mode(s) that connect the LS and HS states. The results indicate that while DFT is well suited for the prediction of structural parameters, an accurate multiconfigurational approach is essential for the quantitative determination of ΔEHL. In addition, a good qualitative agreement is found between the TD-DFT and CASPT2 potential energy curves. Although the TD-DFT results might differ in some respect (in our case, we found a discrepancy at the triplet states), our results suggest that this approach, with due care, is very promising as an alternative for the very expensive CASPT2 method. Finally, the two dimensional (2D) potential energy surfaces above the plane spanned by the two relevant configuration coordinates in [Fe(terpy)2]2+ were computed both at the DFT and CASPT2 levels. These 2D surfaces indicate that the singlet-triplet and triplet-quintet states are separated along different coordinates, i.e. different vibration modes. Our results confirm that in contrast to the case of complexes with mono- and bidentate ligands, the singlet-quintet transitions in [Fe(terpy)2]2+ cannot be described using a single configuration coordinate

Projektowanie przegród budowlanych poprzez obliczenia higrotermiczne - doświadczenia i wytyczne

In the past simple steady-state calculation methods were employed to assess the risk of interstitial condensation in wall and roof constructions. Today the hygrothermal performance of building envelope system s may accurately be predicted by validated simulation tools whose practical application is going to be standardized in Europe. Balancing diurnal and seasonal moisture fluxes by hygrothermal simulations instead of striving for a perfect seal helps to design more moisture tolerant and hence more durable building components. Simulation studies may even trigger the search for innovative products such as the smart vapour retarder whose d evelopmen t is summerized in this paper.Dla oszacowania stopnia ryzyka wewnętrznego zawilgocenia ścian i dachów były dotychczas stosowane proste, stacjonarne metody obliczeniowe. Obecnie, procesy cieplno -wilgotnościowe zachodzące w przegrodach, mogą być dokładnie przewidywane za pomocą zweryfiko- wanych narzędzi obliczeniowych, których praktyczne zastosowanie jest w Europie normalizowane. Zamiast dążyć do uzyskania idealnie szczelnych izolacji przeciwwilgocio- wych można, poprzez zbilansowanie dobowych i sezonowych przepływów wilgoci za pomocą symulacji higrotermicznych, projektować bardziej tolerancyjne wilgotnościowo a przez to trwalsze komponenty budowlane. Badania symulacyjne mogą nawet spowodować poszukiwania innowacyjnych materiałów jak inteligentna folia adaptacyjna, której rozwój przedstawiono w tym artykule

Spin and electron density redistribution upon binding of non-innocent ligand by iron in enzymatic environment: challenges for quantum chemistry

The quality of the description of a chemical bond between the metal (active site) and the ligand (substrate) critically depends on the electronic processes accompanying the bond formation. However, as far as transition metal centers (TM) in enzymes are considered, most of the properties related to their electronic structure are extremely challenging for quantum chemistry. Especially severe problems appear for the bonding of NO to ferrous sites, e.g. in myoglobin or non-heme enzymes. Therefore, special care has to be shown in the assessment of a quantum chemical method employed with respect to its power in describing the properties of interest. In this work we discuss spin-resolved Fe-NO charge transfers and their relation to the metal spin state, with special attention paid to the interpretation of the bonding between NO and the transition metal center in terms of dative or covalent contributions; furthermore, the impact of spin and the electron transfer on the reactivity of the center is discussed. The stress is put on the role of the coordinating environment in controlling the reaction mechanism via fine-tuning of the spin and the oxidation status of the metal core. This goes in line with the high significance of spin in enzymatic reaction mechanisms (cf. multi-state reactivity proposed for iron enzymes)

Morphology and Material Properties of Carbides in High (24%) Chromium Cast Iron

The present paper is a presentation of results of a study on morphology, chemical composition, material properties (HVIT, HIT, EIT), and nanoindentation elastic and plastic work for carbide precipitates in chromium cast iron containing 24% Cr. It has been found that the carbides differ in chemical composition, as well as in morphology and values characterizing their material properties. The carbides containing the most chromium which had the shape of thick and long needles were characterized with highest values of the analyzed material properties

The Effect of Structure on Thermal Power of Cast-iron Heat Exchangers

The objective of the study reported in this paper was to determine the effect of structure on thermal power of cast-iron heat exchangers which in this case were furnace chambers constituting the main component of household fireplace-based heating systems and known commonly as fireplace inserts. For the purpose of relevant tests, plate-shaped castings were prepared of gray iron with flake graphite in pearlitic matrix (the material used to date typically for fireplace inserts) as well as similar castings of gray cast iron with vermicular graphite in pearlitic, ferritic-pearlitic, and ferritic matrix. For all the cast iron variants of different structures (graphite precipitate shapes and matrix type), calorimetric measurements were carried out consisting in determining the heat power which is quantity representing the rate of heat transfer to the ambient environment. It has been found that the value of the observed heat power was affected by both the shape of graphite precipitates and the type of alloy matrix. Higher thermal power values characterize plate castings of gray iron with vermicular graphite compared to plates cast of the flake graphite gray iron. In case of plates made of gray cast iron with vermicular graphite, the highest values of thermal power were observed for castings made of iron with ferritic matrix

Improvement of Resistance of Cast-iron Heat Exchangers to High-temperature Corrosion

The paper discusses the possibility of improving resistance of heat exchangers made of gray cast iron with flake graphite to high-temperature corrosion by providing them with metallic coatings. A metallic coating containing 76.9% Ni, 19.8% Cr, 1.7% Si, 0.9% Fe, and 0.9% Mn was applied by means of the plasma spraying method and subjected to cyclically variable thermal loads in the atmosphere of solid fuels combustion products (oxygen, sulfur, chlorine, and sodium). In a 30-day thermal load test held at temperature 500°C it has been found that thickness of the metallic coating decreased from the initial (240 ± 6) μm to (231 ± 6) μm. The depth to which sulfur, chlorine, and sodium penetrated the coating was about 30 μm. Increased oxygen content occurred along the whole coating depth. In the coating area adjacent to the substrate surface, the content was twice as high compared to this observed in the initial coating material. Although presence of oxygen was found within the whole depth of the coating, i.e. (231 ± 6) μm, no signs of susceptibility of the sprayed metallic layer to separation from substrate of gray cast iron with flake graphite were found