Roman Jędrzejewski

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

AbstractDuring 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.

Determination of the Content of Promoters in Magnetite and Wustite Phases in the Fused Iron Catalyst

Taking advantage of differences in etching rates of crystallographic phases, forming an oxidized form of the fused iron catalyst, a content of promoters in main phases, magnetite and wustite, was determined. A calcium oxide content in magnetite and wustite was 0.54 wt% and 3.59 wt%, respectively. Aluminum oxide was found in the magnetite phase, and its content was 4.5 wt%. The third promoter, potassium oxide, was almost completely located outside these phases. XRD and ICP-OES instrumental methods were used in the investigations.

The activity of fused-iron catalyst doped with lithium oxide for ammonia synthesis

Abstract The iron catalyst precursor promoted with Al2O3, CaO, and Li2O was obtained applying the fusing method. Lithium oxide forms two phases in this iron catalyst: a chemical compound with iron oxide (Li2Fe3O4) and a solid solution with magnetite. The catalyst promoted with lithium oxide was not fully reduced at 773 K, while the catalyst containing potassium was easily reducible at the same conditions. After reduction at 873 K the activity of the catalyst promoted with lithium oxide was 41% higher per surface than the activity of the catalyst promoted with potassium oxide. The concentration of free active sites on the surface of the catalyst containing lithium oxide after full reduction was greater than the concentration of free active sites on the surface of the catalyst promoted with potassium oxide.

Preparation and characterization of catalyst mix Fe-Co/MgO for carbon nanotubes growth

Preparation and characterization of catalyst mix Fe-Co/MgO for carbon nanotubes growth Fe-Co/MgO is one of the most common catalyst mix applied to carbon nanotubes (CNTs) growth in chemical vapor deposition process. Therefore, here we present detailed study on the preparation and characterization of Fe-Co/MgO. The precursors of Fe and Co are iron (II) acetate and cobalt acetates, correspondingly. The molar ratio of the catalyst mix is Fe:Co:MgO=1:1:100. Initially, thermogravimetric analysis (TGA) of the mixture was performed. TGA analysis of it indicated the stepwise mass losses which pointed out the crucial thermal conditions for the changes in the elemental composition, morphology, crystallographic structure and vibrational properties. In current state of the art the lowest growth temperature for singlewalled carbon nanotubes is 550°C in CVD technique and here the characterization of the catalyst mix strongly suggest that this temperature can be decreased what would enhance the compatibility of CNT growth with current complementary metal-oxide-silicon (CMOS) technology for CNTs-based nanoelectronics. The morphology, crystallographic structure, elemental composition of the samples and its spectroscopic properties were performed via high resolution transmission electron microscopy (TEM), X-ray diffraction (XRD) and Infrared spectroscopy (IR), respectively.

Influence of substrate temperature and gas pressure on aluminum oxynitride coatings obtained by pulsed laser deposition

Abstract The paper presents results of the investigation on the influence of deposition parameters, such as substrate temperature, total gas pressure and reactive gas composition on the structure, chemical composition and mechanical properties of aluminum oxynitride coatings obtained by pulsed laser deposition (PLD) method. Selection of process parameter ranges, which could be promising for aluminum oxynitride (ALON) coatings deposition, was the main objective of the work. Two series of experiments were carried out with varied pressure and temperature. It was found that from the chemical composition viewpoint, the most promising are atmospheres containing 20 % to 40 % oxygen. The nitrogen to oxygen ratios in the coatings can be controlled by increasing the total pressure or substrate temperature. However, increasing the pressure has a negative effect on the O + N:Al ratio, mechanical properties and quality of the coatings. The influence of temperature is much less drastic and more controllable. Increasing the deposition temperature is much more beneficial since it improves the mechanical properties and can compensate to some extent the negative effect of the total pressure. From the coating quality viewpoint, it is possible to establish an optimum temperature range for which the coatings are characterized by a compact structure and a limited number of droplets.

Influence of atmosphere composition on the structure and properties of aluminum oxynitride coatings deposited by PLD method

This work presents studies on the influence of oxygen content in reaction atmosphere during pulsed laser deposition on the structure and properties of aluminium oxynitride films. The coatings were grown on monocrystalline Si substrates. Aluminium nitride bulk disk was used as a target. The film deposition took place at room temperature and pressure of 0.5 Pa with varying content of oxygen and nitrogen. Thickness and roughness of the coatings were measured by profilometer. The X-ray diffractometer (XRD) was used for phase analysis of the coatings. Chemical composition was evaluated using X-ray microanalysis (EDS) by means of scanning electron microscopy (SEM). The surface topography was examined using an atomic force microscopy (AFM). Hardness of the coatings was measured by means of nanoindentation. Adhesion was evaluated in microscratch tests and the morphology of the residual scratch was characterized by AFM. Results showed that it was possible to obtain coatings composed of oxynitrides with different stoichiometry. Mechanical properties of the obtained coatings, however, were significantly different from those demonstrated by ALON ceramic. The content of oxygen in the coatings had an influence on the decreasing hardness and Young’s modulus and improved adhesion. There was no influence on thickness and roughness but the lowest number of droplets was noticed in the coatings obtained in pure oxygen.

The utilization of the mesoporous Ti-SBA-15 catalyst in the epoxidation of allyl alcohol to glycidol and diglycidyl ether in the water medium

Abstract This work presents the studies on the optimization the process of allyl alcohol epoxidation over the Ti-SBA-15 catalyst. The optimization was carried out in an aqueous medium, wherein water was introduced into the reaction medium with an oxidizing agent (30 wt% aqueous solution of hydrogen peroxide) and it was formed in the reaction medium during the processes. The main investigated technological parameters were: the temperature, the molar ratio of allyl alcohol/hydrogen peroxide, the catalyst content and the reaction time. The main functions the process were: the selectivity of transformation to glycidol in relation to allyl alcohol consumed, the selectivity of transformation to diglycidyl ether in relation to allyl alcohol consumed, the conversion of allyl alcohol and the selectivity of transformation to organic compounds in relation to hydrogen peroxide consumed. The analysis of the layer drawings showed that in water solution it is best to conduct allyl alcohol epoxidation in direction of glycidol (selectivity of glycidol 54 mol%) at: the temperature of 10–17°C, the molar ratio of reactants 0.5–1.9, the catalyst content 2.9–4.0 wt%, the reaction time 2.7–3.0 h and in direction of diglycidyl ether (selectivity of diglycidyl ether 16 mol%) at: the temperature of 18–33°C, the molar ratio of reactants 0.9–1.65, the catalyst content 2.0–3.4 wt%, the reaction time 1.7–2.6 h. The presented method allows to obtain two very valuable intermediates for the organic industry.

Stresses in the Surface Layer and Hydrogen Absorption and Diffusion in Cavitation Condition

Cavitation attack in liquids generated a various states of stresses in surface layers of metals. Differences in stress state effects on hydrogen absorption activated by the cavitation implosion. Results of XRD investigation and FEM modeling shows on inhomogenity of process.

Kinetics of the oxidation of iron carbide dispersed in a carbon matrix with water vapor.

The reaction of iron carbide embedded in a carbon matrix with water vapor was studied in the temperature range 300-500 degrees C and the partial pressure of water vapor p(H(2)O) = 0.63-3.26 kPa. At these conditions the superfine magnetite and hematite are the products of this reaction. High oxidation temperature and low partial pressure of water vapor are favorable conditions to obtain only magnetite phase dispersed in a carbon matrix. The oxidation rate of iron and iron carbide is the same for both of them in the initial, kinetic stage of the reaction. It was observed that carbon deposit caused an increase in the reaction rate as a result of spillover effect. The oxidation rate of iron carbide distributed in a carbon matrix increases linearly with the carburization degree of the sample. The reaction rate is also linearly dependent on the partial pressure of water vapor. The apparent activation energy was determined as 110 kJ/mol.