Solid oxide fuel cells (SOFCs) are electrochemical devices that convert the chemical energy of fuels directly into electricity with high conversion efficiency. A major advantage of SOFC systems compared to low-temperature fuel cells is that SOFCs can use humidified hydrocarbons as fuel. However, the use of hydrocarbons may lead to an undesirable carbon deposition as hydrocarbons are oxidized at the anode side in SOFCs. Such carbon deposits on the nickel–yttrium stabilized zirconia (Ni–YSZ) anode material are the most probable mode of deactivation of SOFCs. Therefore, commercially available NiO–YSZ anode material for high-temperature fuel cells was activated by a temperature-programmed reduction in a hydrogen atmosphere. In the next step, carbon was deliberately deposited on the reduced samples by isothermal deposition in a methane–argon atmosphere. The carbon deposits were then burned off with a temperature-programmed oxidation (TPO) in an oxygen–argon atmosphere at different heating rates using thermo-analytical equipment. The TPO was followed by TG, DTG, DTA and QMS measurements. The easiest way to distinguish among various types of deposited carbon was to follow the QMS curves. The obtained QMS curves were processed with Netzsch Peak Separation software in order to extract several peaks corresponding to various forms of carbon deposits. It was found that high amorphous and low amorphous carbon are burned off at relatively low temperatures (up to 650 °C), fibrous carbon is oxidized up to 750 °C, graphite is burned out up to 830 °C and finally, carbon diluted in nickel leaves the system in the 900–1000 °C range, depending on the oxidizing conditions. The isoconversional method was used to calculate activation energies of various carbon oxidation processes. The absolute values of the activation energies increase from amorphous carbon via fibrous carbon to graphite.
Among alternative anode materials for high-temperature fuel cells, the complex ceramic oxide La0,75Sr0,25Mn0,5Cr0,5O3 (LSCM) has recently shown good catalytic activity regarding fuel oxidation and sufficient stability in reductive environments at relatively low steam-to-carbon ratios. However, the electrical and ionic conductivities of LSCM are lower compared to some other perovskite materials. One of the possibilities to improve the conductivity of LSCM is in its composition variations, i.e., altering the Sr-content, doping on the A-site of the perovskite with other ions (Ba, Ca and Mg), and varying the Mn-to-Cr ratio on the B-site of the perovskite. In this paper, systems with the general formula La0.75SrxA0.25-xCr0.5Mn0.5O3 (A = Ba, Ca, Mg, x varies between 0 and 0.25) are described. Within the investigated system, prepared materials after synthesis contain the perovskite structure as a main crystallographic phase with relatively low additions of secondary phases. Any secondary phases are undesired, because they may substantially influence the electrical properties of the final materials. In samples with relatively high Sr-additions, a secondary Sr-rich phase Sr2CrO4 is also identified. Ca-doping may result in traces of CaCr2O4 phase in as-synthesized samples, while Ba-doping may lead to BaCrO4 or BaCO3 phases with higher Ba-additions. The quantity of the secondary phases may be controlled by calcination program or sintering conditions. Secondary phases, which may form additional grains or liquid phase, also influence the development of microstructures during sintering. Within the investigated compositions, the most promising materials are La0.75SrxCa0.25-xCr0.5Mn0.5O3 (x = 0.05–0.15), because they exhibit single-phase microstructure with fine grains after sintering at 1200 °C. Materials with Ba- or Mg-additions form precipitates of secondary phases at 1200 °C, which also remain present after sintering at higher temperatures.
The possibility of a dust explosion poses a high risk to industrial environments. According to some statistics in dust explosions as a combustible substance, wood dust is most often formed. The explosion properties and principles of burning wood are well researched; the main problem is the production growth and using of wood composites. These additives to the raw material represent completely different explosive hazards, which are poorly defined in professional literature sources. In this paper, it was presented the results of studies of the effects of the urea-formaldehyde adhesive in wood composites on explosion parameters. As part of the research, all input samples of powders were detailed in terms of particle size, particle shape, specific particle surface, pore particle size and moisture content. In the next step, the samples were determined by the explosive parameters, namely, the minimum ignition energy (MVE), the maximum explosive pressure (pmax) and the maximum pressure increase ((Δp / Δt) max). The parameter analysis showed that the parameter (Δp / Δt) max drops significantly when 9% of the urea-formaldehyde adhesive is added to the wood. The p(max) parameter and MVE, despite the addition of adhesive, maintains comparable values. In view of the observed effect on the explosion parameter (Δp / Δt)max, the inhibition mechanisms of the urea-formaldehyde adhesive were investigated. These were determined using thermogravimetric analysis (TG), differential thermogravimetric analysis (DTG), differential thermal analysis (DTA), and linear electron microscopy (SEM). It was found that at an increased temperature the urea-formaldehyde adhesive on wood particles forms a protective grease layer that changes the thermal properties of these particles and influences the flame temperature, and consequently also the burning rate in the particulate dispersion. In addition, the formation of said layers takes away the accessible heat from the reaction region because it is formed by an endothermic process.
The work deals with the field of powder dust explosion of aluminium powder. The characteristics and measured explosion parameters of three different aluminium powders (two powders and meals) are presented, produced in the company Kamnik-Schlenk d.o.o. The samples were determined by the size and distribution of the particle size, the specific surface and the thermal properties of the powder. The shape of the particles was determined by linear electron microscopy (SEM). The determination of sensitivity parameters of combustible dust (minimum ignition energy, MVE and minimum explosion concentrations, MEK) and parameters for the assessment of the consequences of a dust explosion (maximum explosion pressure (pmax), maximum pressure rise (Δp / Δt)max and Kst calculation) were carried out. Measured values make it easier to assess when choosing ways to prevent explosions and to determine effective safety measures in this kind of production, with the emphasis on the fact that every explosion, in addition to immediate effects on humans, equipment and the environment, leaves the long-term consequences that we do not even observe with current state of technology and measurements and regulate. Therefore, it is considered that the best way to prevent the negative effects of a dust explosion is to eliminate the conditions for its formation.