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Properties of sintered cordierite ceramics obtained by sol-gel methods of powder synthesis
No full textCordierite (2MgO·2Al2O3·5SiO2) as a ceramic material has great importance in materials science and wide application in industry thanks to its low thermal expansion and dielectric constant, high chemical and thermal stability and high electrical resistivity. Cordierite ceramics is used for producing supports for electric heaters, ceramic fire resistant materials for furnaces, catalyst supports for the complete combustion of exhaust gases of internal combustion engines, insulation material in high frequency electronics, as well as substrates for integrated circuits and electronic modules. Properties of sintered cordierite ceramics, where cordierite powders were obtained by alkoxide hydrolitic and non-hydrolitic method, colloidal method and starting from silicic acid, were studied and compared. The properties of sintered materials were observed by SEM of the fracture surfaces and polished and thermally etched samples. The mechanical properties of obtained materials, microhardness and indentation fracture toughness, were determined by microindentation method. The best sinterability showed powder obtained by colloidal method (sintering temperature of 1370 °C for 2 h), and powder obtained by Si-acid method (sintering temperature of 1400 °C for 2h)
Calculation of local cleavage fracture stress in a medium-carbon V-microalloyed steel using finite element analysis
No full textCleavage fracture of commercial medium-carbon V-microalloyed forging steel with predominantly acicular ferrite structure was studied by means of fourpoint bending testing at liquid nitrogen temperature in conjunction with finite element analysis. Both two-dimensional and three-dimensional finite element models were used for the purpose of comparison. Cleavage fracture was initiated
by high plastic strains in the vicinity of notch tip. Strains calculated by threedimensional modeling were higher up to 80% than for two-dimensional model. Calculated local cleavage fracture stresses rendered effective surface energy
values of 49J/m2 and 60J/m2, for two-dimensional and three-dimensional numerical model, respectively. Both results are in good agreement with previously published data for medium carbon microalloyed steels
Structure–activity relationship of nanosized porous PEG-modified TiO2 powders in degradation of organic pollutants
No full textThis study aims to gain insights in structure–activity relationship of TiO2 photocatalysts. For this purpose photocatalysts were synthesized via classical sol–gel method using titanium isopropoxide as a precursor and polyethylene glycols (PEGs) of different molecular mass (Mn = 200, 600, 2000, 10,000) as a template agents. Incorporating PEG into TiO2 network enhanced not only catalyst porous structure, but also increased the fraction of anatase phase. The use of low-molecular-weight PEGs resulted in catalysts with increased anatase content and enlarged specific surface area. The catalyst photoactivity was estimated through degradation of organic pollutants: Reactive Black 5, arylazo pyridone dye and phenol. The results revealed that the photoactivity was following the same order independently of target pollutant: TiO2/P600 > TiO2/P200 > TiO2/P2000 > TiO2/P10000 > TiO2. BET surface area and anatase fraction, rather than pore diameter or pore volume, were found to be predominant catalyst property determining the activity for particular reaction system. The existence of synergistic effect between anatase and rutile phases was confirmed for the most active catalysts TiO2/P200 and TiO2/P600. These catalysts showed similar activity in dye degradation, while TiO2/P200 displayed significantly lower activity in phenol degradation, which was attributed to its lower sorption capacity and lower UV light utilization. The difference in the reactivity between investigated pollutants was discussed in relationship with their size, structure and sorption ability
Geobotanical and biogeochemical characterization of mine overburden in Bor and its potential for application in remediation
No full textPodručje rudarskog basena Bor smatra se 'crnom ekološkom tačkom' i jednim od najzagañenijih područja u Srbiji. Rudarske aktivnosti prisutne na ovom području duže od jednog veka ostavile su teške posledice po životnu sredinu i rezultovale obrazovanjem tehnogenih tvorevina u vidu jalovišnog materijala značajne površine, koje predstavljaju snažan izvor zagañenja čitave oblasti prašinom, dok prirodno luženje koje sa njih vrše atmosferilije ugrožava okolno zemljište i vodotokove. Sanacija borskih jalovišta smatra se zato jednim od prioriteta u zaštiti životne sredine na nacionalnom nivou. Biološka remedijacija smatra se jednim od ekonomski i ekološki najprihvatljivijih remedijacionih tehnologija za sanaciju degradiranih područja. Fitoremedijacija je prirodna tehnologija koja koristi biljke da ukloni, dezintegriše ili zadrži štetne hemijske materije koje se nalaze u različitim medijumima životne sredine. Petrološka, mineraloška i geohemijska karakterizacija rudničkog otpada pružaju informacije o sastavu otkrivke i njenom hemijskom ponašanju, predstavljajući polaznu osnovu za utvrñivanje stepena ugroženosti životne sredine i prioriteta za sanaciju odreñene lokacije. Geobotanička i biogeohemijska karakterizacija ukazuju na stepen povezanosti procesa u podlozi, deposolu i biljnom svetu, dajući okvir za odgovarajući obim i vrstu fitoremedijacije kao biotehnološkog rešenja za sanaciju borskog rudničkog otpada. Samonikle biljne vrste na području rudničkih jalovišta prilagoñene su na ekološke uslove ovih staništa, što ih čini prvim izborom kod istraživanja za potrebe fitoremedijacije. Na odlagalištima otkrivke u Boru, formiranim neselektivnim odlaganjem rudničke otkrivke, petrološko-mineraloškom i geohemijskom karakterizacijom izdvojeno je šest zasebnih litoloških grupa, od kojih su sve izuzev intenzivno orudnjenih stena selektivno kolonizovane od strane samoniklih biljnih vrsta. Na njima su izdvojena četiri inicijalna vegetacijska stadijuma povezana sa utvrñenim litološkim grupama, odnosno karakteristikama deposola koji su nastali njihovim razlaganjem. Ova povezanost je naročito izražena meñu grupama podloga koje svojom mineralogijom generišu kiselu, i onih koje generišu neutralnu do blago baznu reakciju deposola..
Application of raw peach shell particles for removal of methylene blue
No full textA possibility to apply raw, powdered peach shells ( PS) as a biosorbent for water purification was studied. The PSs are locally available as a solid waste in a fruit juice factory; methylene blue (MB) was chosen as representative of common pollutants in textile industry wastewater. The phase composition of prepared particles was identified by XRD. The particle morphology was characterized by FE-SEM, while the size distribution was measured by a laser light-scattering particle size analyzer. The BET specific surface area was determined from N-2 adsorption/desorption experiments. The effect of operating parameters: the biosorbent amount (50-1000 mg/100 mL), contact time (10-180 min), solution pH (2-12) and initial concentration (10-100 ppm) on biosorption efficiency was examined. Optimal conditions for MB removal were found to be: the biosorbent amount of 400 mg/100 mL and pH 5.5. A high efficiency of MB removal was established after 180 min: 99% for [MB](i) = 10 ppm and 76% for [MB](i) = 100 ppm. Biosorption is well described by the Freundlich- and BET-type isotherms, implicating heterogeneous adsorption sites and interconnections between adsorbed molecules. The FTIR spectroscopy results indicate hydrogen bonding between the dye and the biomass. The obtained results shown that raw peach shell particles could be used as an efficient low-cost biosorbent for dye removal from water
Ibuprofen sorption and release by modified natural zeolites as prospective drug carriers
No full textThe sorption of ibuprofen by modified natural zeolite composites at three concentration levels (10, 20 and 30 mmol/100 g) of cationic surfactants - benzalkonium chloride and cetylpyridinium chloride, in a buffer solution (pH 7.4), was studied. Characterization of the composites before and after ibuprofen sorption was performed by drug sorption and isotherm studies, zeta potential and Fourier Transform infrared spectroscopic analysis. The biopharmaceutical performance of cationic surfactant-modified zeolites as drug formulation excipients was evaluated by in vitro dissolution experiments from the composites with medium surfactant contents. The drug sorption was influenced by the surfactant type and amount used for the zeolite modification. Prolonged drug release over a period of 8 h (up to similar to 40%) was achieved with both groups of samples. The kinetic analysis showed that the drug release profiles were best fitted with the Higuchi and the Bhaskar models, indicating a combination of drug diffusion and ion exchange as the predominant release mechanisms
Application of apricot stone waste from fruit processing industry in environmental cleanup: copper biosorption study
No full textIntroduction. Apricots (Prunus armeniaca L.) have an important role in Serbia's fruit production. Average annual production of 25,035 t generates approximately 1,577 t apricot stone (AS) waste and most of it ends up in landfill sites. In order to minimize the environmental impact, an investigation of the possible use of AS was done by developing a biosorbent for wastewater treatment. Materials and methods. AS waste from the fruit processing industry was used to remove Cu(II) ions from water solution by batch adsorption techniques. This solid waste residue was characterized by FTIR, SEM and EDX. The effects of pH, contact time, metal concentration and biosorbent dosage on the process of biosorption were studied. Results and discussion. Obtained FTIR results confirm that the uptake of Cu(II) ions from aqueous solution involves carboxylate moieties from lignin and fatty acids. Also, the presence of seeds in the AS blend significantly increased biosorption performance providing active sites important for the sorption process. The ion exchange mechanism was also confirmed. The best fitting adsorption model is the Langmuir model and the maximum biosorption capacity (qmax) is 4.45mg L-1 at pH 5.0. Biosorption of the Cu(II) ions follows a pseudo second-order kinetic model. According to thermodynamic parameters the biosorption process is endothermic and spontaneous. Conclusion. Numerous biosorbents were investigated for biosorption of Cu(II) ions from aqueous solution, but no report on application of untreated AS waste has been found in literature. This preliminary study confirmed that this material can successfully and rapidly remove dissolved copper ions from dilute solutions
The nano-wetting aspect at the liquid-metal/sic interface
No full textThe wetting process on the nano-scale, as an initial and essential step in liquid metal/ceramic joining, is discussed here. Thanks to recent breakthroughs in experimental techniques with nanometre resolution, questions posed several decades ago are being looked at again. Despite recorded facts on acting mechanisms, the published results are very diverse due to the variety of materials and their structures, as well as experimental conditions, so the modeling is inevitable for process development and to overcome the multi-scale influencing parameters issues. A nano-scale wetting model have been proposed and tested on results obtained in a liquid-metal/SiC system that was published in the literature
Usefulness of ANN-based model for copper removal from aqueous solutions using agro industrial waste materials
No full textU radu je ispitana mogućnost upotrebe lokalno dostupnih lignoceluloznih materijala kao potencijalnih biosorbenata u svrhu uklanjanja jona bakra iz vodenih rastvora. Ispitivani materijali predstavljaju čvrst otpad koji nastaje nakon prerade kukuruza (oklasak kukuruza) i nakon prerade voća (koštice kajsije). Ovakav otpad ima malu ekonomsku vrednost a njegovo odlaganje predstavlja ekološki problem. U šaržnom sistemu ispitani su uticaj inicijalne koncentracije Cu(II) jona (Ci), količine biomase (m) i zapremine rastvora (V) na efikasnost biosorpcije i vrednost biosorpcionog kapaciteta. Utvrđeni su optimalni procesni parametri. Eksperimentalni rezultati su poređeni sa dva modela: SOP (second order polynomial regression models) i ANN (artificial neural networks), pri čemu je SOP model pokazao prihvatljiv determinacioni koefijent (0,842-0,997), dok je ANN pokazao visoku tačnost prognoze (0,980-0,986) u odnosu na eksperimentalne rezultate.The purpose of this study was to investigate the adsorption properties of locally available lignocellulose biomaterials as biosorbents for the removal of copper ions from aqueous solution. Materials are generated from juice production (apricot stones) and from the corn milling process (corn cob). Such solid wastes have little or no economic value and very often present a disposal problem. Using batch adsorption techniques the effects of initial Cu(II) ions concentration (Ci), amount of biomass (m) and volume of metal solution (V) on biosorption efficiency and capacity were studied for both materials, without any pre-treatments. The optimal parameters for both biosorbents were selected depending on the highest sorption capability of biosorbent in removal of Cu(II). Experimental data were compared with second order polynomial regression models (SOPs) and artificial neural networks (ANNs). SOPs showed acceptable coefficients of determination (0.842-0.997), while ANNs performed with high prediction accuracy (0.980-0.986) in comparison to experimental results