Papers by Keyword: Activation

Abstract: Methods to increase travel distance of mine electric locomotive from one charging at the expense of fuel cells with proton-exchange membrane and to improve efficiency of the process as a result of using selective composite materials have been considered. It has been demonstrated that the use of activated natural materials will make it possible to increase membrane conductance up to 3.6·10⁻²Cm·cm⁻¹; that will allow increasing energy-efficiency of fuel cells for their operation in terms of mine electric locomotives.

Abstract: In this work, we analyze compensating defects which are formed after implantation of aluminum (Al) into n-type 4H-SiC epitaxial layers and subsequent thermal annealing. These defects reduce the expected free charge carrier density by 84% for a low doped layer with [Al]_impl ≈ 9ž·10¹⁶ cm^-3 and by 27 % for a high doped layer with [Al]_impl ≈ 2·ž10¹⁹ cm^-3. Furthermore, an electrical activation ratio of implanted aluminum ions of 100 % is calculated. The ionization energy of implanted aluminum as measured by Hall effect and admittance spectroscopy ranges from 101 meV to 305 meV depending on the doping concentration.

Abstract: We propose an empirical model to predict electrical activation ratios of aluminium- and boron-implanted silicon carbide with respect to various annealing temperatures. The obtained parameters and model extensions are implemented into Silvaco’s Victory Process simulator to enable accurate predictions of post-implantation process steps. The thus augmented simulator is used for numerous simulations to evaluate the activation behavior of p-type dopants as well as for the full process simulation of a pn-junction SiC diode to extract the carrier and acceptor depth profiles and compare the results with experimental findings.

Abstract: The Ti-Zr-V non-evaporable getter (NEG) films were grown on Aluminum (Al) alloy and CuCrZr alloy, which can be used to fabricate the vacuum chambers in the ultra-high vacuum status. The Al alloy and CuCrZr alloy samples with different surface roughness were prepared by the different manufacturing methods. We studied whether the behavior and the microstructure of the Ti-Zr-V getter films are influence by the surface roughness of the substrate. The surface morphologies of Ti-Zr-V NEG films appear distinct and the growth of the films follows the nature of the substrate surface. The Ti-Zr-V films have nanocrystalline structures and the grain sizes of the films become slightly larger with increasing the surface smoothness. In addition, it was found that the reduction of the Ti-Zr-V NEG films to the metallic state was affected by presence of surface defects on the films. The surface defects should result from the existence of micro-pores, pockmarks, and micro-cracks on the original substrate, which produced from the manufacturing process.

Abstract: The utilization of fly ash not only reduces the environmental impact but also improves some mechanical properties and durability of concrete. However, the early-age strength of fly ash concrete is sometimes lower than that of normal concrete due to the slow pozzolanic reaction of fly ash. In recent years, some researchers have suggested alkali or sulfate activation to accelerate the pozzolanic reaction. Some studies have used sodium hydroxide (NaOH) solution, while others have applied potassium sulfate (K₂SO₄) or sodium sulfate (Na₂SO₄) as activators which are effective in accelerating the pozzolanic reaction and increasing the strength at early age. On the other hand, the early-age strength of fly ash concrete is also improved by using porous ceramic aggregate (PCA) as an internal curing agent. Therefore, the present study aims at investigating the effect of an internal activating agent using PCA on hardness and pore structure of fly ash cement paste. In the experimental program, PCA immersed in two kinds of solution (K₂SO₄ and Na₂SO₄) was placed in the center of specimen with dimension of 21x21x20 mm. In addition, normal aggregate (NS) was used for reference. As a result, internal sulfate activation using PCA improved the hardness of interfacial transition zone (ITZ) between paste and PCA, and reduced the Ca(OH)₂ content in cement paste with 40% replacement with fly ash significantly at the age of 1 day, but negligibly at the ages of 7 and 28 days when compared with reference specimen. K₂SO₄ was more effective in improving hardness of ITZ as an internal activating agent than Na₂SO₄. Although the total pore volumes of the fly ash cement pastes using PCA imbibing sulfate activators were not reduced at the age of 28 days, their pore volumes with diameters less than 0.05 µm were increased.

Abstract: We have demonstrated the possibility for epitaxial regrowth of crystalline SiC by laser melt annealing. The quality of the recrystallization is analyzed by XTEM, EELS, electron diffraction and XRD. The annealing guarantees a uniform activation achieved both in melting and solid phase. Carbon graphitization on the top surface and a crystallized silicon layer below is observed as an effect of the high temperature and the melting phase.

Abstract: This paper reports about results describing the mechanism of oxidation-reduction reactions occurring in the microwave plasma interaction with organic compounds solutions. Air and argon were used as the plasma gases in the experiments on disrupture of aqueous liquid organic compounds. Application of inversible redox indicator of methylene blue (MB) showed that disrupture of organic substances in microwave plasma was based on redox reactions. It was found that MB highest efficiency in the solution took place when air plasma-supporting gas was used.

Abstract: Permeable reactive barriers (PRBs) are passive, in-situ remediation systems that comprise the filtration of a contaminated groundwater through a reactive media able to degrade, adsorb or precipitate the pollutants. Selection of the reactive media depends on the nature of the contamination. While the majority of PRBs are used to treat groundwater contaminated with chlorinated volatile organic compounds or acid mine drainage, the present study is focused on heavy metals, namely Fe, Al, Cu, Ni, Zn, Mn and As. To remove such inorganic pollutants, four methodologies are usually implemented: a) redox reaction, b) adsorption and ion exchange, c) biological treatment (e.g. metal sulphides precipitation) and d) pH control and precipitation. The present paper deals with the last methodology in which an adjustment of pH by alkalinity-generating materials leads to the precipitation of metal hydroxides and the decrease in the concentration of dissolved species. As the solubility of metals depends on their valence, redox-potential, concentrations and kinetics of reaction, the target pH varies with respect to the considered metal. A pH of about 10 allows the precipitation of hydroxides of divalent ions (zinc, manganese, copper, lead, nickel, cobalt and cadmium), while a pH of around 6-7 is adapted to trivalent ions (iron, aluminium and chromium). However, the accumulation of precipitates in the pore spaces can cause clogging of the pores, hence decrease the porosity and hydraulic conductivity of the reactive media and alter its efficiency. To validate this assumption, the neutralizing ability of alkaline materials such as activated zeolite and magnesite were examined in a test column by monitoring the resultant pH with attention to impact of precipitates on the hydraulic properties of reactive materials. Based on the test results, both materialls are considered suitable to remove the groundwater contaminants with high efficiency (up to 99%) and suitable grain size to encourage flow through the PRB.

Abstract: The main chemical composition of waste brick is silicon dioxide,by means of chemical can stimulate its activity.In this experiment, gypsum, lime sodium hydroxide as activators,through the testing and research about the properties of compressive strength, dry density, water absorption of brick powder foam concrete,analyse the influence of three activators on the properties of foam concrete.The test results show that the:Mixing about 25% lime can guarantee the dry apparent density on the basis of compressive strength increases;Mixing 20% gypsum can make the strength and dry apparent density relatively stable;The incorporation of NaOH make the foam concrete appear quick setting,so it should not be used alone as activator.

Abstract: This paper reports the influence of light exposure (photodynamic) and magnetic field application on viability activation of anaerobic photosynthetic bacteria (rhodobacter sphaeroides). For photosynthetic process, the rhodobacter sphaeroides have bacteriochlorophyll and carotenoid as major and accessory pigments, respectively. A customized equipment was developed for investigating the effect of light and magnetic field applications on the growth of the bacterial colonies. It was consisted of three main parts, namely a sample holder, an array of light emitting diode (LED) as light source and Helmholtz coils as magnetic field source. The systems of this equipment were controlled by a microntroller of AVR ATMega-8535. Prior to the application in vitro, all LEDs were calibrated, both their intensity and wavelength. After the treatments, all bacteria substances were grown in photosynthetic media (PMS) for 48 hours followed by calculating the number bacterial colonies growth using a total plate count (TPC) method and Quebec colony counter. It was found that the growths of bacterial colonies were influenced by both light intensity and wavelength of LED array. At the same intensities, the wavelength of 430 nm showed highest effect on the growth of bacterial colonies. In addition, upon application of the optimum light combined with magnetic field, the highest growth of bacterial colonies was achieved more than 110% when the optimized light source of energy dose was 204 J/cm² and magnetic field was 1.8 mT.