Showing 9 results for Porous
S. Yaghmaei, A. A. Seifkordi and H. Shirzadi,
Volume 21, Issue 1 (7-2002)
Abstract
A mathematical model has been analyzed for in-situ bioremediation with the purpose of remediating organic contaminated soil. Oxygen rich water when passed through the porous media of soil activates the aerobic microorganisms, leading to the biodegradation of the organic content. The model equations comprise three convection-dispersion partial differential solution of these equations has been conducted using the finite difference method. The effects of insufficient oxygen supply, growth of biomass and resistance to contaminant migration on the rate of biodegradation have been analyzed by numerically solving the equations.
The results from the numerical simulation indicate that the rate of biodegradation of contaminants in soil may be constrained not only by insufficient oxygen supply, but also by resistance to contaminant migration within the pore network.
Keywords: Bioremediation, Soil, Porous media, modeling
H. R. Sheibani and H. Bayyat,
Volume 26, Issue 1 (7-2007)
Abstract
A physical model of gabion overflow dams was studied to determine the velocity profile and Reynolds shear stress. Physical tests were done under two different conditions of dam crest, overflow dams with impermeable and with permeable crests. Instantaneous velocity components over dam crest were measured by an ADV (Acoustic Doppler Velocimeter) instrument. This instrument is capable of measuring instantaneous velocity components with frequencies up to 25 Hz. Average velocity components and bed shear stress were extracted from ADV measurements. The results of this research show the effect of crest permeability on velocity and Reynolds shear stress. The magnitude of Reynolds shear stresses, horizontal velocity components, and absolute value of vertical velocity components under the permeable scenario are bigger than those of the impermeable scenario. Velocity distribution over the dam crest is different from the universal logarithmic profile.
Z. Taherian, M. A. Yousefpour, M. A. Faghihi Sani, A. Nemati,
Volume 31, Issue 1 (6-2012)
Abstract
The aim of this work was synthesis of MCM-41/HA nanocomposite and biodegradation behavior of pure silica-mesoporous in attendance of hydroxyapatite crystals. These materials were synthsized by sol-gel method and ageing at 100°C for 24hr. A surfactant was used as template. The pores were formed after removal of surfactant by calcination at 550°C. FTIR results demonstrated formation of silanol and siloxan groups of silica network and hydroxyl and phosphate groups of HA network. Also SEM, TEM and EDS results confirmed presence of HA crystals within MCM-41 structure. Finally biodegradation behavior was examined by ICP and FTIR analysis. The results indicated biodegradable HA phase in the nanocomposite (with release of Ca2+ inos in water and the increasing of the pH value) can increase non-bridging oxygens of the silica network and therefore, it improves biodegradation behavior of silica network.
Sadrnezhad, S. Katiraei,
Volume 33, Issue 2 (3-2015)
Abstract
Mechanical property of porous nickel-titanium alloy produced by volumetric combustion synthesis (VCS) for bone surgery applications is reported in this paper. Stress-strain behavior of the alloy is determined by uniaxial tension test. Superelastic diagram of the porous alloy is compared with that of the solid material cooled from austenite stability temperature. Due to movements of the dislocations, growth of the nucleation sites and thinning of the martensite plates during cooling, plastic deformation and necking behavior of these materials are principally different from that of the ordinary materials. Elastic
modulus and yield stress of the material have nonlinear relationship with porosity percentage and obey the following correlations
and
The stress-strain curves of the alloy show more than 6 percent elongation before rupture, even with 30 percent porosity. A comparison of the cleavage surfaces of the combustion synthesis samples with those of the powder metallurgical ones indicate great influence of production process on fracture mechanism.
M.a. Yousefpour, F. Safari Kooshali, B. Khoshandam,
Volume 34, Issue 3 (12-2015)
Abstract
The purpose of this work was to study the hydrogen adsorption on the surface of mesoporous materials based on silica (SBA-16) modified with palladium via temperature. Since mesoporous silica materials have a high specific surface area, and the ordered mesoporous size of 2-10nm, they are suitable for adsorption and storage of hydrogen. SBA-16 is suitable for this purpose due to its cubic crystalstructure and open pores. Single-stage sol-gel method was used to produce nanostructure composite from salt of palladium (PdCl3) and mesoporous silica precursor. The aging time was selected as 12 hr at 80˚C. Furthermore, the obtained materials were heated at 550˚C for 6 hr to remove surfactant and to form pores. Then the materials were characterized by large angle and small angle x-ray diffraction analysis, and hydrogen absorption analysis at upto 200kPa pressure at three different temperatures of -196˚C (77 K), -123˚C (150 K) and 30˚C (303 K). Furthermore, adsorption-desorption of nitrogen gas was studied. The surface morphology was observed by field emission scanning electron microscope (FESEM). In addition, the amount of palladium, oxygen, and silicon were measured by using energy dispersive spectroscopy) EDS ). Finally, the functional groups on the surface of mesoporous silica materials were evaluated using Fourier transform infrared spectroscopy (FTIR). The results of XRD and EDS analyses confirmed the presence of palladium and palladium oxide in mesoporous amorphous silica. In addition, BET results showed that addition of palladium in SBA-16 decreased the surface area, and produced 791 and 538m2/g for SBA-16 and SBA-16/Pd, respectively. Hydrogen absorption in nano structure composite was decreasing with temperatur in comparison with SAB-16. On the other hand, the maximum hydrogen absorption in the nano structure composite containing palladium was obtained at -196˚C (77 K).
Z. Talebi, Mahin Karimi, Negar Habibi,
Volume 37, Issue 1 (6-2018)
Abstract
In the present study, silica aerogel was evaluated by a two-step catalytic process at the ambient pressure drying, under different synthesis conditions. The effects of the catalyst and water content in the hydrolysis step on the physical properties of silica aerogel, including density, porosity and shrinkage, were investigated. The results showed that increasing the water content in the hydrolysis step increased the shrinkage of gel network and density of obtained aerogel. Moreover, in the presence of insufficient water, NH4OH as the condensation catalyst in the gel formation step was more effective on the physical properties of silica aerogel, as compared to HCl as thehydrolysis catalyst; Moreover, the increase in the NH4OH content led to lower density and higher porosity. On the other hand, NH4OH effect on the physical properties of silica aerogel was not noticeable in the presence of enough water content. In the NH4OH/HCl molar ratio of 6, the best silica aerogel sample was obtained with the density of 0.214 g/cm3, porosity of 90% and shrinkage of 23%
M. Haghshenas Gorgani, M. Mirkazemi, F. Golestanifard,
Volume 37, Issue 4 (3-2019)
Abstract
In this research, the rheological behavior and stability of suspensions containing Si3N4, Al2O3, Y2O3 and starch were investigated in order to use them in the starch consolidation casting of porous silicon nitride. Dolapix CE64 was used as the dispersant. Then, the effect of some parameters such as Si3N4 surface oxidation, dispersant content, solid loading and starch content on the viscosity and rheological behavior of Si3N4-starch slurry was determined. Surface oxidation of Si3N4 powder at 800°C for 2 hours reduced the viscosity of the slurry, effectively. The best dispersant content was 0.4 wt. %, relative to ceramic powders. Slurries containing 30 to 40 vol. % and 7.5 to 25 vol. % starch, relative to total solid loading, had the suitable viscosity and the sufficient stability for casting by the starch consolidation method.
A. R. Parvanian, H. R. Salimijazi, M. H. Fathi,
Volume 38, Issue 4 (1-2020)
Abstract
The concentrated solar power (CSP) is one of the renewable energy sources in which solar irradiation heat energy will be used in a steam turbine to generate electrical grid. Solar radiation is absorbed by a solar receiver reactor on the surface of a porous solar absorber. In this survey, synthesis and mechanical/thermal characterization of micro-porous silicon carbide (SiC) absorber to be used in solar reactor is carried out. SiC foams were synthesized and categorized based on three different pore sizes i.e. 5, 12 and 75 ppi. Mechanical behavior and thermal shock resistance of porous foams in the working temperature range for absorber (25-1200 °C) were evaluated. Results revealed that the specific compressive strength (σc/ρ) of foams increase exponentially by a decrement in the porosity percentage and the average pore size. Moreover, for foams with smaller pore size, a considerable decrease in mechanical strength due to thermal shock was observed. This could be due to increase in the number of struts per unit volume i.e. more weak struts to withstand the mechanical loading. So, porous foams with coarser pore sizes were distinguished to be more capable of tolerating thermal shock while serving as solar absorbers.
F. Mofid Nakhae, M. Rajabi, H. R. Bakhsheshi-Rad,
Volume 40, Issue 3 (11-2021)
Abstract
Development of bioactive ceramic composite scaffold materials with enhanced mechanical strength has been a topic of great interest in bone tissue engineering. In the present study, β-tricalcium phosphate scaffolds with various amounts of bredigite and an interconnected pore network suitable for bone regeneration were fabricated by the space holder method. The effect of high concentrations of bredigite on the structure, mechanical properties (compressive strength), and in vitro bioactivity was investigated. According to the results, immersion in simulated body fluid (SBF) led to the apatite formation on the surface of the scaffold, but increasing the bredigite content caused the agglomeration of the bredigite phase at the grain boundaries and deteriorated the mechanical properties.
