Showing 28 results for Activation
M.sh. Bafghi, A.h. Emami, A. Zakeri, J. Vahdati Khaki,
Volume 7, Issue 2 (6-2010)
Abstract
Abstract:
has been investigated. It has been shown that the mechanism of leaching reaction is diffusion through the product layer
and does not undergo any change as a result of mechanical activation in a wide range of experimental conditions.
Leaching rate is strongly influenced by milling intensity and the effect of ball to powder mass ratio is stronger than
milling time. Curve fitting of experimental data shows that leaching rate constant is approximately a linear function
of ball to powder mass ratio, while it obeys a power function with regard to the milling time.
The kinetics of chalcopyrite leaching in a ferric sulfate media for raw and mechanically activated samples
M. Sh. Bafghi, A. Yarahmadi, A. Ahmadi, H. Mehrjoo,
Volume 8, Issue 3 (9-2011)
Abstract
Abstract:
the reduction agent. Pellets of barite ore containing about 95% BaSO
temperature, time, ore grain size and the type and grain size of the carbon materials. Graphite, coke and charcoal have
been used as the reducing agent and the reduction experiments have been performed in the temperature range of 925-
1150 °C. Apart from conducting the experiments using pellets made of ore powder, kinetic analysis of the experimental
data by use of the reduced (dimensionless) time method has been another unique feature of the present study.
Experimental results show that grain size of either carbon material or barite ore has not appreciable effect on the
reaction rate. Kinetic analysis of the experimental data revealed the rate is strongly controlled by the chemical reaction
of carbon gasification (Boudouard reaction). The reaction rate is very considerably related to the type of carbon
material so that the activation energy varies from 15.6 kcal.mol
kcal.mol
gasification.
The present study deals with the reduction of barium sulfate (Barite) to barium sulfide by use of carbon as4 has been reduced under different conditions of-1 for charcoal to 26.3 kcal.mol-1 for graphite and 20.8-1 for coke. This behavior provides further support for the postulated reaction mechanism, i.e., carbon
M. M. Kashani Motlagh, A. A. Youzbashi, Z. Amiri Rigi,
Volume 8, Issue 4 (12-2011)
Abstract
A natural bentonite obtained from Khorasan, Iran, was submitted to acid activation with sulphuric acid. Sample aliquots (5gr)
were leached with 100 ml H2SO4 solutions of various concentrations (2–7N) at 80±2 oC for 2 hours. X–ray diffraction, chemical analysis, infrared spectroscopy and specific surface area measurements were performed in order to evaluate important structural modifications occurring as a result of acid attack. Octahedral sheet was affected by acid activation resulting into the dissolution of cations (Mg2+, Fe2+, Al3+) and consequent decomposition of montmorillonite structure. Bentonite samples were then tested in order to verify their capacity to bleach colza–soybean oil, and their performances were compared to that of a commercial bleaching clay. The bleaching ability of the natural clay was poor when compared with that of the industrial adsorbent. Acid activation of the bentonite sample with 7N sulphuric acid yielded an adsorbent material which was highly efficient in the bleaching of the oil functioned better than the commercial clay product under the same conditions.
Dr Ali Darehkordi, Mr Mohammad Sadegh Hosseini,
Volume 9, Issue 3 (9-2012)
Abstract
Montmorillonite modified is an efficient environmental friendly catalyst under one-pot-three-component synthesis of 3,4-dihydropyrimidine-2(1H) ones. The preparation was performed with an aldehyde, 1,3-dicarbonyl compounds, urea or thiourea under solvent-free conditions. In comparison with the other methods of Biginelli reaction, this new method has short reaction time inexpensive catalyst and in addition excellent yields were obtained.
M. S. Kaiser,
Volume 10, Issue 3 (9-2013)
Abstract
Precipitation behaviour of wrought Al-6Mg alloys with ternary scandium and quaternary zirconium and titanium has been studied. Hardness measurements and resistivity studies are employed to assess the precipitation behaviour of scandium doped Al-6Mg alloy without or with quaternary additions of zirconium and titanium. Further, the kinetics of precipitations are studied by differential scanning calorimetric technique. Scandium has been observed to form fine coherent Al3Sc precipitates during ageing and these are responsible for strengthening of the alloys. The precipitation kinetics of Al3Sc depends on the diffusion of scandium in aluminium. Presence of fine coherent precipitates of Al3Sc impedes the migration of dislocations and increase the recovery temperature. The kinetics of recrystallisation is also delayed.
M. Sheikhshab Bafghi, M. Karimi, M. Adeli,
Volume 10, Issue 4 (12-2013)
Abstract
In the present study, reduction of zinc oxide from the pellets made of steelmaking electric arc furnace dust has been investigated. Effects of such parameters as the type of carbon material (graphite, coke and charcoal) as well as time and temperature on the reduction reaction have been examined. The reduced (dimensionless) time method was applied to perform a kinetic analysis of the system. Experimental results showed that increasing the temperature in the range of 925-1150°C results in a remarkable increase in the reduction rate. It was also shown that the reduction process is controlled by chemical reaction. Meaningful difference in the activation energy values calculated for reduction with graphite (24.75 kcal/mol), coke (18.13 kcal/mol) and charcoal (11.52 kcal/mol) indicate the predominant role of chemical reaction (carbon gasification) in the overall reaction rate and its rate-controlling mechanism. Carbothermal reduction of pelletized EAF dust proved to be an efficient reduction method, so that above 90% reduction was achieved in about one hour at temperatures around 1100°C.
A Fattah-Alhosseini, M Asadi Asadabad,
Volume 11, Issue 4 (12-2014)
Abstract
Four compositions of austenitic Mn-Cr steels have been developed successfully for in-vessel component materials in power plant industry. The phase stability of these Mn-Cr steels was studied by and X-ray diffraction (XRD) patterns. XRD patterns have shown that the matrix of these Mn-Cr steels is a single γ-phase structure. The potentiodynamic polarisation curves suggested that these fabricated Mn-Cr steels showed passive behaviour in 0.1M H2SO 4solution. Therefore, semiconducting behaviour of passive film formed on these fabricated Mn-Cr steels in 0.1M H2SO 4 solution was evaluated by Mott–Schottky analysis. This analysis revealed that passive films behave as n-type and p-type semiconductors. Based on the Mott–Schottky analysis, it was also shown that donor and acceptor densities are in the order of 1021 cm -3 and are comparable for other austenitic stainless steels in acidic environments
S. Niksirat, Sh. Raygan, S. Moradi Ghiassabadi,
Volume 12, Issue 2 (6-2015)
Abstract
In this research, two different carbonaceous materials (Graphite:G and Petrocoke:P) were separately
compared in terms of the carbothermic reduction of hematite and anatase in order to synthesize Fe-TiC nanocrystalline composite by mechanically activated sintering method. Powders were activated in a planetary high-energy
ball mill under argon atmosphere for 0, 2, 5, 10,and 20 h. Then, the activated powders were analyzed by XRD and
SEM to investigate phase constituents and microstructure of the mixtures. Results proved that Fe
2
O
3
and TiO
2
were not
reduced by carbonaceous materials even after 20h of milling. SEM investigations showed that G-mixture was more
homogenous than P-mixture after 20h of milling, meaning that graphite-anatase-hematite was mixed satisfactorily.
Thermogravimetry analysis was done on 0 and 20h milled powders. TG and DTG curves showed that mechanical
activation led to almost 300°C decrease in the reduction temperature of hematite and anatase in both mixtures. In the
next step, the powders were sintered in a tube furnace under argon atmosphere. In the G-mixture, anatase was reduced
to titanium carbide at 1100°C but, in the P-mixture, temperature of 1200°C was essential for completely reducing
anatase to titanium carbide.Results of phase identification of the sintered powders showed that anano-crystalline ironbased composite with titanium carbide, as the reinforcement was successfully synthesized after 20 h high-energy
milling of the initial powders and subsequent sintering occurred at 1200˚C for 1h
N. Ghanbarpourabdoli, Sh. Raygan, H. Abdizadeh,
Volume 13, Issue 4 (12-2016)
Abstract
In this study, the adsorption of hexavalent chromium and zinc ions from the solution is investigated by raw red mud and mechanical-chemical activated red mud along with the possibility of selective reclamation of these ions from the solution. The mechanical-chemical activation of red mud was done by employing high-energy milling and subsequent acid treatment with HNO3. Raw red mud (RRM) and mechanical-chemical activated red mud (MCARM) adsorbents were characterized with Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), and Brunauer–Emmett–Teller (BET) methods. In order to determine the suitable adsorption conditions, effects of pH of the solution, amount of adsorption, temperature, and time of adsorption were investigated. It was found that the optimum pH for the adsorption of hexavalent chromium and zinc ions by MCARM adsorbent was 2 and 6, respectively. According to these pH values, MCARM had the ability to separately adsorb more than 95 and 79% of hexavalent chromium and zinc ions from the solution, respectively. Experimental results were in good agreement with Langmuir and Freundlich isotherms. By considering the kinetic models of adsorption, the kinetics of the adsorption of both ions followed the pseudo-second-order reaction model. It was also determined that almost 25.8 and 61.8% of the hexavalent chromium and zinc ions adsorbed in MCARM could be recovered
E. Mohammadi, M. Pourabdoli,
Volume 16, Issue 2 (6-2019)
Abstract
The effect of mechanical activation on the kinetics of ammoniacal thiosulfate leaching of a refractory oxide gold ore containing 2.8 ppm Au was investigated. The gold extraction of 99.81% was achieved by 16 h leaching of a sample mechanically activated for 60 minutes. The gold extraction observed for a similar reference sample without mechanical activation was only 55%. Studies revealed that leaching progresses at two different rates depending on the leaching time (0-2 h and 2-16 h). It was observed that diffusion through an ash layer as a dominant mechanism controls the leaching of samples mechanically activated up to 45 minutes during total leaching time, while reaction control and liquid film diffusion are dominant mechanisms for leaching of a sample mechanically activated for 60 minutes during 0-2 h and 2-16 h, respectively. The extraction observed during the ash diffusion step depends significantly upon mechanical activation time. Mechanical activation of 60 minutes results in high gold extraction in this step which when combined with subsequent chemical reaction gives close to 100% gold extraction in a 16 hour leach. Mechanical activation for up to 45 minutes leads to a modest improvement in overall gold extraction compared with the reference test without mechanical activation
A. R. Abbasian, M. R. Rahimipour, Z. Hamnabard,
Volume 16, Issue 4 (12-2019)
Abstract
In this work, lithium meta titanate (Li2TiO3) nanocrystallites were synthesized by hydrothermal method and subsequent heat treatment. The shrinkage of the powder compact was measured under constant heating rate in order to study the sintering behavior of the synthesized powders. Densification curves of the synthesized powders were also constructed via the dilatometry analysis and evaluated at several heating rates. Two separate methods of analytical procedure and master curve sintering were employed to determine the activation energy of the initial sintering stage. The activation energy values were estimated based on these two distinct methods as 229±14 and 230 kJ/mol respectively, consistenting with each other. Moreover, surface diffusion was determined as the dominant mechanism of densification on initial sintering of Li2TiO3 nanocrystallites.
A. Allahverdi, H. Hashemi, M. Mahinroosta,
Volume 17, Issue 1 (3-2020)
Abstract
This work evaluates the resistance of alkali-activated slag (AAS) mortar against sodium sulfate attack. The effects of immersion in 5% sodium sulfate solution under room temperature and wetting-drying cycles on the compressive strength of mortar specimens were considered for evaluating the extent of degradation. Mortar specimens prepared from type II and V Portland cements (PC2 and PC5) in accordance with ASTM standard were also used as reference. To characterize the chemical products of the degradation process due to sodium sulfate attack, the specimens were also studied by X-ray diffractometry, scanning electron microscopy, and the elemental analysis by energy dispersive X-ray spectroscopy. After 360 days of exposure to the sodium sulfate solution, PC2, PC5 and AAS cements showed 71, 52 and 45% reduction in compressive strength, respectively. According to the obtained results, AAS cement exhibits a higher sulfate resistance compared to PC2 and PC5.
A. Hasanvand, M. Pourabdoli, A. Ghaderi,
Volume 17, Issue 1 (3-2020)
Abstract
The main problem of cobalt oxide as a thermochemical heat storage material is its slow re-oxidation kinetics. In addition, redox (reduction and oxidation) behavior of as-received Co3O4 is degraded with increasing the number of redox cycles. To overcome this drawback, Al2O3 and Y2O3 were added to Co3O4 and effect of mechanical activation time (2, 4, 8, and 16 h) on the redox behavior (weight change value/rate, redox reversibility, reduction and re-oxidation values, and particle morphologies) of Co3O4-5 wt.% Al2O3 and Co3O4-5 wt. % Y2O3 composites was investigated using thermogravimetry method. The composites were studied by SEM, EDS, and X-ray map analyses before and after redox reactions. Results showed that increasing the mechanical activation time improves the redox kinetics of Co3O4-5wt. % Al2O3 in comparison with as-received Co3O4. Although, the alumina-containing samples, activated in short time showed the better redox kinetics than samples activated in long time. It was found that increasing the activation time to more than 8 h for alumina-containing samples reduces the redox kinetics due to decreasing the positive effect of Al2O3 in controlling the particle size growth and sintering. In the case of Co3O4-5wt. % Y2O3, an increase in activation time generally reduced the redox kinetics. As a result, redox reactions in a 16 h-activated Co3O4-5wt.% Y2O3 composite was completely stopped. In addition, results showed that weak performance of Co3O4-5 wt. % Y2O3 is related to intensive sintering and growth of cobalt oxide particles during redox reactions
Sara Ahmadi, Bijan Eftekhari Yekta, Hossein Sarpoolaky, Alireza Aghaei,
Volume 18, Issue 4 (12-2021)
Abstract
In the present work, monolithic gels were prepared through different drying procedures including
super critical, infrared wavelengths and traditional drying methods. Dense and transparent glasses
were obtained after controlled heat treatment of the dried porous xerogels in air atmosphere.
The chemical bonding as well as different properties of the prepared gels and the relevant glasses
were examined by means of Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmitt-
Teller (BET) and UV-Vis spectrometer. Based on the obtained results, different drying conditions
affect the average pore size and the total pore volume of the studied gels. The mean pore size was
found to be 8.7 nm, 2.4 nm and 3.2 nm for super critical, IR radiation and slow drying in air
atmosphere, respectively. The glass network structure was significantly changed by heat treatment temperature so that the B-O-Si bonds were formed only after 450 °C. It was found that the gel dried under super critical condition was unable to reach to its full density all over the selected sintering temperature interval.
Mojtaba Hosseini, Ali Allahverdi, Mohammad Jaafar Soltanian Fard,
Volume 19, Issue 1 (3-2022)
Abstract
The aim of the present research work is to evaluate the feasibility of processing and utilizing steel slag
in binary and ternary cement blends with limestone. The physical and microstructural properties of binary and
ternary composite cements produced by inter-grinding mixtures of ordinary Portland cement clinker, processed
steel slag and limestone in a laboratory ball mill with replacement levels varying from 0 wt.% to 30 wt.% were
studied. The effects of processed steel slag and limestone incorporation on density of dry cement mixes and water
consistency, setting time and volume stability of fresh and hardened cement pastes were investigated. Also,
density, water absorption, total open pore volume (%) and compressive strength of cement mortars were measured.
The mix with 15 wt.% limestone and 15 wt.% processed steel slag was selected as a typical ternary cement mix
for complementary studies including X-ray diffractometry, thermal gravimetry, Fourier-transform infrared
spectroscopy, and scanning electron microscopy analyses. The results show that removal of relatively high
metallic content of steel slag increases its grindability for mechanical activation and improves its hydraulic
properties effectively and makes it suitable for being recycled in cement industry. The results show that
mechanical activation of the cement mixes enhances the poor hydraulic activity of the processed steel slag and
compensates the strength loss to some extent. The physical and chemical properties of all studied composite
cement mixes comply with ASTM standard specifications, except the compressive strength of the cement mixes
at 28-days containing 20 wt.% or higher amounts of limestone ground to the relatively low Blaine specific surface
area of about 3000 cm2/g.
Nihel Hsouna, Mohsen Mhadhbi, Chaker Bouzidi,
Volume 19, Issue 1 (3-2022)
Abstract
Phosphate glass with different Al2O3 and Na2CO3 compositions [80NaH2PO4-(20-x) Na2CO3-xAl2O3 with a step from 0 to 4] were prepared through melt quenching technique furnace at 900 °C. In order to determine the structure and microstructure modification of the samples after heat treatment the IR and Raman spectroscopy were performed. The X-ray diffraction (XRD) result shows an amorphous character of the prepared glass. The result obtained by differential scanning calorimetry (DSC) reveals a good thermal stability in the temperature range of 25 to 400 °C. The impedance Nyquist diagrams were investigated and modeled by resistors and constant phase elements (CPE) equivalent circuits. These measurements show a non-Debye type dielectric relaxation. Both AC and DC conductivity, dielectric constant, and loss factors were determined. Thermal activation energies were also calculated. A changes in the electrical conductivity and activation energy depend upon the chemical composition were observed. Also, a transition in the conduction mechanism from ionic to mixed ionic polaronic was noted. In the same line, electrical modulus and dielectric loss parameters are also deduced. Their frequency and temperature dependency exhibited relaxation behavior. Likewise, activation energies value obtained from the analysis of M’’ and those obtained from the conductivity are closes, which proves the optimal character of the preparation conditions.
Sonali Wagh, Umesh Tupe, Anil Patil, Arun Patil,
Volume 19, Issue 4 (12-2022)
Abstract
Temperature is one of the key factor that affecting the electrical, physical, structural, and morphological properties as well as the crystallinity of the nanomaterials. The current study investigates the effect of annealing temperature on the structural and electrical properties of lanthanum oxide (La2O3) thick films. La2O3 thick films were prepared on a glass substrate using a conventional screen printing technique. In this work, T1 is an unannealed prepared film, whereas T2 and T3 are annealed in a muffle furnace for 3 hours at 350°C and 450°C, respectively. XRD technique was exploited to investigate the crystallization behavior of the films. It was found that the crystal structure of La2O3 thick films are pure hexagonal phase. The annealing temperatures were revealed to have influence on the crystallite sizes of the films. SEM and EDS was used to study the morphology and elemental analysis of the films respectively. The electrical properties of the films were explored by measuring resistivity, temperature coefficient of resistivity (TCR), and activation energy at lower and higher temperatures regions. The film annealed at 450°C has high resistivity, a high TCR, and small crystallite size. The thickness of the La2O3 thick films was also found to decrease as the annealing temperature increased.
Ekaterina Dmitrieva, Ivan Korchunov, Ekaterina Potapova, Sergey Sivkov, Alexander Morozov,
Volume 19, Issue 4 (12-2022)
Abstract
The article discusses the effect of calcined clays on the properties of Portland cement. An optimal method for calcining clays is proposed, which makes it possible to reduce the proportion of Portland cement clinker in cement to 60% and increase the strength characteristics from 55 MPa to 79 MPa. The study of the composition and structure of clays made it possible to select the optimal heat treatment parameters, at which the calcination products are characterized by the highest pozzolanic activity. It is shown that the use of alkali-activated calcined clays significantly increases the strength and durability of hardened cement binders compared to the composition without additives. In addition, calcined clays increase the frost resistance of cement in a 5% NaCl solution. The obtained experimental data are confirmed by thermodynamic calculations and the results of scanning electron microscopy.
Bijan Eftekhari Yekta, Omid Banapour Ghafari,
Volume 20, Issue 4 (12-2023)
Abstract
Glasses in the B2O3-Li2 (O, Cl2, I2) system were prepared through the conventional melt-quenching method. Then, the conductivity of the molten and glassy states of these compositions was evaluated. Furthermore, the thermal and crystallization behavior of the glasses was determined using simultaneous thermal analysis (STA) and X-ray diffractometry (XRD). The electrical conductivity of the melts was measured at temperatures ranging from 863 to 973 K, and the activation energy of the samples was calculated using the data obtained from ion conduction in the molten state and found to be in the vicinity of 32 kcal/mol. In glassy states, electrical conductivity was also measured. To determine this property, the electrochemical impedance spectroscopy method (EIS) was used. In the molten state, temperature played an important role in the ion conductivity; however, at lower temperatures, other factors became important. Based on the results, the addition of LiI and LiCl to the B2O3-Li2O base glass system (75 B2O3, 10 Li2O, 7.5 LiI, 7.5 LiCl) (mol%) increases the ionic conductivity of the glass from 3.2 10-8 S.cm-1 to 1.4 10-7 S.cm-1 at 300 K.
Zahra Rezayi, Mostafa Mirjalili, Jalil Vahdati Khaki,
Volume 21, Issue 0 (3-2024)
Abstract
Celestite ore, the primary mineral for producing strontium compounds, particularly strontium carbonate, is processed using the black ash method, which involves carbothermic reduction, water leaching, and carbonation. This study aims to investigate the combined effect of mechanical activation and additional graphite on the recovery rate and purity of strontium carbonate. Celestite ore with a strontium sulfate content of 79% was obtained from the Dasht-e-Kavir mine. Acid washing with 10% hydrochloric acid significantly reduced carbonate impurities, resulting in a celestite purity of 96.9%. Mixtures of celestite and graphite with varying amounts of graphite were prepared with and without milling. The mixtures were roasted at 900 °C for 1 hour to form strontium sulfide, followed by hot water leaching. After filtration, sodium carbonate was added to the leachate containing SrS, resulting in the formation and precipitation of white strontium carbonate crystals. The results showed that the addition of graphite increased the recovery rate in unmilled specimens. However, the recovery rate decreased significantly when 1 and 10 hours of milling were applied in the presence of excess graphite. Conversely, in the absence of additional graphite, milling for 1 and 10 hours increased the strontium recovery rate to over 95%. Furthermore, the analysis of strontium carbonate obtained from the sample with the highest recovery rate showed a purity of over 99.9%.
