Water Vapour Adsorption on the Iron(111) Surface Studied by LEED and WFC

In a sample isolation and gas inlet system for aggressive gases saturation states of adsorption as a function of water vapour pressure were generated on the Fe(111)-surface at room temperature and analyzed quantitatively under ultra-high vacuum conditions using the methods LEED and WFC. There is a random adsorption layer emerging passing over into a p(1 × 1) structure when heated between 200°C and 400°C. This structure is more resistent to heat and oxygen treatment than an oxygen adsorption or oxide layer, respectively. The adsorption velocity for oxygen on the p(1 × 1)–H₂O structure amounts to only about 15% of the adsorption velocity on the p(1 × 1)–O structure. The adsorption isotherm measured can be described through a theoretical model.     

Validation of a complex urban noise model close to a road

The adequacy of a model for the sound level close to a road is investigated by comparing resulting predictions for the sound level over a building façade with measurements. The road model involves the road geometry (the number and positions of traffic lanes), the traffic structure (vehicle flow rates and their average speeds in each lane) and equivalent omnidirectional point sources representing the vehicles. It is found that the assumed road traffic noise source model is adequate only for predicting levels over the higher part of the façade. However the investigation has allowed definition of what improvements are needed in the road source modelling to enable adequate predictions over the whole of the building façade.     

The effect of aluminium oxide on the reduction of cobalt oxide and thermostabillity of cobalt and cobalt oxide

During precipitation and calcination at 200°C nanocrystalline Co₃O₄ was obtained with average size crystallites of 13 nm and a well developed specific surface area of 44 m² g^?1. A small addition of a structural promoter, e.g. Al₂O₃, increases the specific surface area of the cobalt oxide (54 m² g^?1) and decreases the average size of crystallites (7 nm). Al₂O₃ inhibits the reduction process of Co₃O₄ by hydrogen. Reduction of cobalt oxide with aluminium oxide addition runs by equilibrium state at all the respective temperatures. The apparent activation energy of the recrystallization process of the nanocrystalline cobalt promoted by the aluminium oxide is 85 kJ mol^?1. Aluminium oxide improves the thermostability of both cobalt oxide and the cobalt obtained as a result of oxide phase reduction.      

Zur Quantentheorie der Néel-Wände in dünnen ferromagnetischen Schichten

Using a general quantum mechanical method earlier developed by the author it is shown, that the periodic domain structure of thin ferromagnetic single-crystal films (thickness below 500 Å) as well as the rotation of the magnetization vector in theNéel wall can be obtained by a simple minimalisation procedure based on a variational principle. As an example some calculations and results for a unixial film are presented.     

The effect of iron nanocrystallites’ size in catalysts for ammonia synthesis on nitriding reaction and catalytic ammonia decomposition

Iron catalyst for ammonia synthesis of various mean sizes of iron nanocrystallites were nitrided with ammonia in a differential reactor equipped with systems that made it possible to conduct both thermogravimetric measurements and hydrogen concentration analyses in the reacting gas mixture. The nitriding process was investigated under atmospheric pressure at the temperature of 475°C. It was found that along with an increase of mean size of iron nanocrystallites, with a decrease of specific surface area of the samples, nitriding degree of solid samples increased. At the same time the rate of surface reaction of catalytic ammonia decomposition decreased. Along with an increase of the samples’ specific surface area an increase of the catalyst’s activity was observed. However, it was also observed that the concentration of active sites on the catalysts’ surface decreased along with an increase of specific surface area.     

Geometrical analysis of large elastic deflections of axially compressed cylindrical and conical shells

This paper presents an analysis of the post-buckling behaviour of isotropic cylindrical and conical shells under axial compression. The starting point of the paper is Lagrange's variational principle, the application of which consists in assuming a kinematically admissible strain and displacement field. The field is determined considering the geometry of quasi-isometric deformations of the shell after buckling. That permits solving the problem with no limitation on the magnitude of the displacements.     

Surface and catalytic properties of potassium-modified cobalt molybdenum catalysts for ammonia synthesis

The influence of potassium addition on the structural, catalytic and surface properties of the cobalt molybdenum nitride was studied. The measurements of the catalytic activity and the specific surface area as well as the phase analysis with the use of X-ray diffraction were performed. The mixtures of Co₃Mo₃N and Co₂Mo₃N phases have been found to constitute the samples. The concentration ratio between the Co₂Mo₃N and Co₃Mo₃N phases is notably influenced by potassium admixture. The specific surface area of the catalysts changes also with the Co₂Mo₃N/Co₃Mo₃N ratio. The catalytic activity of the catalysts in the ammonia synthesis carried out at 400 °C and under the pressure of 10 MPa can be increased up to 2.4 times by the addition of potassium compounds. There is the optimal range of potassium concentration between 0.8 and 1.2 wt.%.     

Nucleation in a gas‐solid state reaction

A nucleation in a reaction of a gas with a solid state where one of the products is solid (GSR‐S) has been discussed. It was pointed out that the phenomenon observed for nanopowders, i.e. nucleation in sequence of the crystallites sizes, should be valid in case of defected monocrystals. However in such a case the constituents of a monocrystal, i.e. mosaic domains separated by structural defects, should undergo phase transition in sequence of size or, in other words, the time needed for the initiation of a nucleus in the case of a small domain is shorter than in the case of big one. Finally the less defected the crystal is, the bigger domains are, and thus the longer nucleation time is needed.     

Solid-gas reaction with adsorption as the rate limiting step

The model of nucleation where adsorption of reactant is a rate-limiting step has been considered. Assuming the adsorption range model, a numerical simulation has been made. The dependency of bulk concentration and surface coverage versus time and thermogravimetric curves are presented. The crystallite size is suggested to be the key factor of the nucleation rate. Theoretical considerations have been compared with the experimental results of the iron nitriding reaction.