Increasing Activation Time Research Articles

Electrical double layer capacitors with sucrose derived carbon electrodes in ionic liquid electrolytes

Activated carbons were prepared via a pyrolysis of sucrose followed by activation in the stream of CO 2 gas for 2–6 h at 900 °C to tune the pore size distribution (PSD) and increase the specific surface area (SSA). The porosity of the activated sucrose derived carbons (ASCs) has been characterized using N 2 sorption measurements. Increasing activation time led to the significant increase in SSA and pore volume of ASCs, among which sucrose derived carbon with 6 h activation time (ASC-6 h) exhibited the highest SSA of 1941 m 2 g −1 and the highest micropore volume of 0.87 cm 3 g −1. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge cycle tests have been applied to investigate the capacitive performance of the ASC electrodes in ionic liquids (ILs) at room and elevated temperatures. The ASC-6 h electrodes in ethyl-dimethyl-propyl-ammonium bis (trifluoromethylsulfonyl) imide (EdMPNTf 2N) showed specific capacitance in excess of 170 F g −1 at 60 °C, whereas the same electrodes in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF 4) showed slightly lower capacitance but significantly better rate performance.

The influence of positive polarity time on GTAW AC of aluminium

In this work, experiments were carried out to determine the welding behaviour of aluminium 1200 based on an increase in the activation time of the positive polarity for tungsten inert gas AC welding of this metal. To achieve this objective, a series of experiments was developed, in such a way that the intensity of the electrical current in the positive and negative polarities was the same; only the duration times in each polarity were modified. During the experiments, the current and voltage signals were acquired. In this way, the arc voltage and potential could be determined for each condition tested. In terms of the fusion behaviour, an increase in penetration and in welded areas was verified to the extent that longer positive polarity times were used. This behaviour is different from that commonly indicated in the literature about welding processes with non-consumable electrodes, which suggests a reduction in penetration with an increase in the positive polarity activation time. However, this trend grows constantly during the experiments from a determined point, where the positive polarity activity times are greater than 4.0 ms in a total period of 20.0 ms. The use of a minimum positive polarity time (1.3 ms) was shown to be effective for cathode cleaning, as it produced welds with satisfactory fusion characteristics and with minimum wear to the tungsten electrode. The good fusion capacity obtained in welds produced with long positive polarity times was attributed to phenomena arising from the emission of electrons due to the field effect that occurs during the positive electrode phases.

Sodium Channel NaV1.5 Expression is Enhanced in Cultured Adult Rat Skeletal Muscle Fibers

This study analyzes changes in the distribution, electrophysiological properties, and proteic composition of voltage-gated sodium channels (Na(V)) in cultured adult rat skeletal muscle fibers. Patch clamp and molecular biology techniques were carried out in flexor digitorum brevis (FDB) adult rat skeletal muscle fibers maintained in vitro after cell dissociation with collagenase. After 4 days of culture, an increase of the Na(V)1.5 channel type was observed. This was confirmed by an increase in TTX-resistant channels and by Western blot test. These channels exhibited increased activation time constant (tau(m)) and reduced conductance, similar to what has been observed in denervated muscles in vivo, where the density of Na(V)1.5 was increasing progressively after denervation. By real-time polymerase chain reaction, we found that the expression of beta subunits was also modified, but only after 7 days of culture: increase in beta(1) without beta(4) modifications. beta(1) subunit is known to induce a negative shift of the inactivation curve, thus reducing current amplitude and duration. At day 7, tau(h) was back to normal and tau(m) still increased, in agreement with a decrease in sodium current and conductance at day 4 and normalization at day 7. Our model is a useful tool to study the effects of denervation in adult muscle fibers in vitro and the expression of sodium channels. Our data evidenced an increase in Na(V)1.5 channels and the involvement of beta subunits in the regulation of sodium current and fiber excitability.

Clozapine does not require 5-HT1A receptors to block the locomotor hyperactivity induced by MK-801

5-HT(1A) receptors mediate some effects of atypical antipsychotic drugs, such as the increase in cortical dopaminergic function, an effect likely related to the superior efficacy of these drugs on negative symptoms and cognitive deficits of schizophrenia. To examine whether 5-HT(1A) receptors are involved in the therapeutic action of clozapine (Clz) on positive symptoms, here we examined the ability of Clz to antagonize the behavioural syndrome induced by the non-competitive N-methyl-d-aspartate receptor antagonist, MK-801 in wild-type (WT) and 5-HT(1A)-receptor knockout (KO(1A)) mice. MK-801 administration induced hyperlocomotion, ataxia, stereotypies and an alteration of the locomotor pattern in both genotypes. However, some symptoms of the behavioural syndrome induced by MK-801 were less intense in KO(1A) mice compared with wild-type mice. Clz antagonized the majority of MK-801-induced effects in both strains of mice. No differences between genotypes were noted for the ability of Clz to antagonize the hyperlocomotion, yet Clz was more effective in preventing the increased activation time, short movements, circling behaviour and hind-limb abduction in KO(1A) mice. The present results indicate that 5-HT(1A) receptors do not play a critical role in Clz-induced antagonism of the main hyperactivity signs evoked by MK-801, suggesting that 5-HT(1A) receptors are not involved in the therapeutic action of Clz on positive symptoms of schizophrenia.

Preparation and Characterization of KOH-Activated Carbons Developed from Petroleum Coke

Potassium hydroxide activated carbons were prepared from Egyptian petroleum cokes with different KOH/coke ratios and at different activation temperatures and times. The textural properties were determined by adsorption of nitrogen at <TEX>$-196^{\circ}C$</TEX>. The adsorption of iodine and methylene blue was also investigated at <TEX>$30^{\circ}C$</TEX>. The surface area and the non-micropore volume increased whereas the micropore volume decreased with the increase of the ratio KOH/coke. Also the surface area and porosity increased with the rise of activation temperature from 500 to <TEX>$800^{\circ}C$</TEX>. Textural parameter considerably increased with the increase of activation time from 1 to 3 h. Further increasing of activation time from 3 to 4 h was associated with a less pronounced increase in textural parameters. The adsorption of iodine shows the same trend of surface area and porosity change exhibited by nitrogen adsorption, with KOH/coke ratio and temperature of activation. Adsorption of methylene blue follows pseudo-first-order kinetics and its equilibrium adsorption follows Langmuir and D-R models.

Preparation and characterization of activated carbon spheres from polystyrene sulphonate beads by steam and carbon dioxide activation

AbstractThe polymeric precursor polystyrene sulphonate beads were used to produce activated carbon spheres (ACSs). ACSs were prepared by carbonization of polymeric precursor at 800°C followed by activation of resultant char with steam and carbon dioxide activation processes. The resulting ACSs were characterized for N2 adsorption, Raman spectrometry, and scanning electron microscope (SEM). The adsorption properties such as, BET surface area (SBET), pore volume (Vpore), and micropore volume (Vmicro) of ACSs produced at different gasification time and temperature with steam and carbon dioxide activation were investigated in this study. It is found that porosity of ACSs produced from steam and carbon dioxide activation increases with increasing activation time. The results exhibited that ACSs produced from above carbon dioxide activation have shown high SBET and Vpore 1266 m2/g and 1.13 cm3/g respectively compared to ACSs from steam activation SBET 949 m2/g and Vpore 0.98 cm3/g, respectively. SEM study revealed that ACSs produced from carbon dioxide activation have exhibited a smooth surface and better microstructure as compared to ACSs from steam activation process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Influence of mechanical activation on the graft copolymerization of sugarcane bagasse and acrylic acid

Sugarcane bagasse (SCB) was mechanically activated by home-made high efficiency stirring mill. Graft copolymers (SCB–g–PAA) of SCB with different mechanical activation times ( t M) and acrylic acid (AA) have been synthesized by using ammonium persulfate/sodium sulfite redox pair as an initiator in aqueous solution. The effect of t M on the graft co-polymerization was evaluated by grafting ratio (GR) and grafting efficiency (GE). In addition, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to characterize the granular morphology, functional groups, crystal structure and thermal properties of the product. It was found that the mechanical activation could split fiber bundles and decrease significantly the crystallinity. SCB degraded after the mechanical activation (MA) and its thermal stability declined. Moreover, the graft copolymerization was enhanced obviously by MA processing. And GR and GE increased with the increase of activation time.

Effects of CO 2 activation on porous structures of coconut shell-based activated carbons

In this paper, textural characterization of an activated carbon derived from carbonized coconut shell char obtained at carbonization temperature of 600 °C for 2 h by CO 2 activation was investigated. The effects of activation temperature, activation time and flow rate of CO 2 on the BET surface area, total volume, micropore volume and yield of activated carbons prepared were evaluated systematically. The results showed that: (i) enhancing activation temperature was favorable to the formation of pores, widening of pores and an increase in mesopores; (ii) increasing activation time was favorable to the formation of micropores and mesopores, and longer activation time would result in collapsing of pores; (iii) increasing flow rate of CO 2 was favorable to the reactions of all active sites and formation of pores, further increasing flow rate of CO 2 would lead carbon to burn out and was unfavorable to the formation of pores. The degree of surface roughness of activated carbon prepared was measured by the fractal dimension which was calculated by FHH (Frenkel–Halsey–Hill) theory. The fractal dimensions of activated carbons prepared were greater than 2.6, indicating the activated carbon samples prepared had very irregular structures, and agreed well with those of average micropore size.

Preparation of microporous activated carbon and its electrochemical performance for electric double layer capacitor

Microporous activated carbons were prepared by microwave heating petroleum coke with potassium hydroxide as activation agent. Microporous activated carbons were characterized by infrared spectroscopy, X-ray diffraction and nitrogen adsorption/desorption isotherms. Electrochemical properties of an electric double layer capacitor using microporous activated carbon as electrode materials were investigated by constant current charge-discharge and electrochemical impedance spectroscopic techniques. The results show that the specific surface area and the pore volume of microporous activated carbon increase with increasing activation time before the activation time reaches 37 min. The microporous volume totals 94.0% in the microporous activated carbons and the average pore diameter of microporous activated carbon is 2.00 nm. Microporous activated carbons prepared in the activation time of 31, 35 and 37 min are named as AC-31, AC-35 and AC-37, respectively. Compared with AC-27 electrode, the internal resistance for ions transferring in AC-31, AC-35 or AC-37 electrode is relatively small. The specific capacitance of AC-31 is the biggest among the microporous activated carbons, and it retains 279.6 F g −1 maintaining 93.5% capacity after 200 recycling number.

Kinetics of specific surface area change using the Boltzmann model

During sintering of the 2MgO-2Al2O3-5SiO2 system, cordierite, an attractive ceramic material because of its properties, is obtained. Effects of mechanochemical activation of stoichiometric mixtures, performed to investigate possibilities of lowering cordierite formation temperature during sintering, were monitored by thermogravimetric and differential thermal analyses. Specific surface areas of the mechanically activated powder mixtures were determined by the BET method. Kinetics of the specific surface area increase was analyzed using the Boltzmann model. It was confirmed that with activation time increase, temperatures of phase transformations were shifted to lower values and, according to FTIR analysis no significant changes occurred during material aging. According to the obtained results, it may be concluded that since mechanochemical activation has an influence on the treated powder mixture, lowering of the cordierite formation temperature during the sintering process is expected.

Analysis of Various Experimental Methods and Preparation of Mesoporous Activated Carbon Powders from Sawdust Using Phosphoric Acid

A critical analysis of various reported experimental methods utilized for preparation of activated carbon using phosphoric acid was attempted to identify the right choice of experimental method. The various experimental methods were grouped into three major categories; of these, a two-stage activation process with the precursor exposed to preset furnace temperature in a self-generated atmosphere was identified to be a suitable method. Accordingly, activated carbon powders were prepared utilizing a two-stage activation process, covering the effect of activation time at 500°C with an impregnation ratio of 1.5. The samples were subjected to adsorption using methylene blue dye, and the adsorption capacity was found to increase with increase in activation time. An adsorption capacity greater than 400 mg/g of activated carbon shows highly developed pores, with pore size higher than 1.5 nm signifying its economical application to commercial liquid-phase adsorption processes. The adsorption isotherms were found to match well with the Langmuir isotherm model with correlation coefficient (r 2) greater than 0.95 as compared to the Freundlich isotherm model with r 2 less than 0.8.

Preparation and structure characterization of carbons prepared from resorcinol-formaldehyde resin by CO2 activation

In this work, carbon xerogels with a high pore volume and surface area (up to 2.58 cm3/g and 3200 m2/g respectively) have been synthesized using the sol-gel polycondensation of resorcinol (R) with formaldehyde (F) in a basic medium of monoethanolamine (MEA), followed by drying and pyrolysis. This medium (MEA) has not been used in previous investigations. The effect of activation with CO2 on the pore size distribution and the chemical functional groups has been investigated using N2 (77 K) adsorption, FTIR and elemental analysis techniques. A series of experiments has been conducted to investigate the effect of activation time and activation temperature. Activation of the samples was carried out at 850, 900 and 980 °C for times ranging from one to three hours. Within the range of activation conditions, an increase in activation time at 850 °C results in a continuous steady rise of the BET surface area and total pore volume. However, at the two higher temperatures, the surface area shows a maximum when plotted against activation time. FT-IR results show that the use of MEA as a catalyst leads to the formation of nitrogen functional groups in the surface of the resin.

Porous structure and liquid‐phase adsorption properties of activated carbon aerogels

AbstractIn this article, activated carbon aerogels (ACAs) were prepared by CO2 activation. Their pore structures were investigated by N2 adsorption–desorption analysis. ACAs have excellent microporosity (e.g. 0.36 cm3/g) and mesoporosity (e.g. 1.72 cm3/g). Adsorption characteristics of phenol, methylene blue, I2, and VB12 on ACAs in the liquid phase were studied by static adsorption experiments. Results showed that CO2 activation process is an effective way to introduce micropores in carbon aerogels, which is enhanced with the increase of activation time. As a result, the adsorption capacities of the four mentioned adsorbates on ACAs were improved gradually with the increase of activation time. However, mesopore volume is also a factor on improving adsorption properties for the relatively giant molecules methylene blue and VB12. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Surface Immobilization of Catalytic Beacons Based on Ratiometric Fluorescent DNAzyme Sensors: A Systematic Study

DNAzyme-based catalytic beacons have the potential for sensing a large number of relevant analytes. Thus, a systematic investigation of factors affecting their performance when immobilized into gold-coated nanocapillary array membranes (NCAMs) was undertaken. Enzyme immobilization times were varied to determine that as little as 15 min was sufficient for ratiometric detection of Pb2+-specific activity, while immobilization density saturated after 1.5 h. Immobilization of the DNAzymes into NCAMs with 600 nm pore size resulted in higher immobilization efficiency and higher enzymatic activity than that with 200 nm pore size. A poly-T linker length between the tethering thiol and first oligonucleotide, used to extend the DNAzyme above the backfilling mercaptohexanol (MCH) monolayer, had no effect on DNAzyme activity. The backfilling method of immobilization, involving backfilling followed by hybridization, was found most effective for DNAzyme activity compared to immobilization of hybridized DNAzyme complex (a 67% loss of activity) or concurrent enzyme and MCH immobilization (75% loss of activity). The backfilling MCH monolayer provided approximately 3.5 times increase in activity compared to DNAzyme assembled without MCH, and was over 5 times more active than shorter and longer backfilling molecules tested. The immobilized DNAzyme retained its optimized performance at 50 mM NaCl. Finally, the generalized immobilization and ratiometric procedure was employed for a uranyl-specific DNAzyme with 25 +/- 15 times increase in ratio observed. These findings form a firm basis on which practical applications of catalytic beacons can be realized, including sensors for both Pb2+ and UO22+ ions.

Porous properties of activated carbon produced from Eucalyptus and Wattle wood by carbon dioxide activation

This work focused on the preparation of activated carbon from eucalyptus and wattle wood by physical activation with CO2. The preparation process consisted of carbonization of the wood samples under the flow of N2 at 400°C and 60 min followed by activating the derived chars with CO2. The activation temperature was varied from 600 to 900°C and activation time from 60 to 300 min, giving char burn-off in the range of 20/2-83%. The effect of CO2 concentration during activation was also studied. The porous properties of the resultant activated carbons were characterized based on the analysis of N2 adsorption isotherms at −196°C. Experimental results showed that surface area, micropore volume and total pore volume of the activated carbon increased with the increase in activation time and temperature with temperature exerting the larger effect. The activated carbons produced from eucalyptus and wattle wood had the BET surface area ranging from 460 to 1,490 m2/g and 430 to 1,030 m2/g, respectively. The optimum activation conditions that gave the maximum in surface area and total pore volume occurred at 900°C and 60 min for eucalyptus and 800°C and 300 min for wattle wood. Under the conditions tested, the obtained activated carbons were dominated with micropore structure (∼80% of total pore volume).

Optimization of antibody immobilization for sensing using piezoelectrically excited-millimeter-sized cantilever (PEMC) sensors

The effectiveness of antibody immobilization on sensor performance was evaluated using a piezoelectric-excited millimeter-sized cantilever (PEMC) sensor and a model protein, bovine serum albumin (BSA). The immobilization parameters—antibody and activation reagent concentration and reaction time were systematically varied and the resultant sensor response to 1 pg/mL BSA was measured. The highest frequency shift due to BSA attachment (1931 ± 60 Hz) was obtained when 100 μg/mL antibody solution was activated with EDC (2 mM) and sulfo-NHS (5 mM) for 30 min prior to reaction with primary amine on the sensor surface. Increasing activation time from 30 to 60 min resulted in an 8% decrease in sensor response, while activation at 0.2 mM EDC and 0.5 mM NHS resulted in a 65% decrease. The logarithmic correlation between antibody concentration and sensor response suggests that a lower antibody concentration of 10 μg/mL is sufficient for BSA at 1 pg/mL. With 10 μg/mL antibody, the PEMC sensor response was 725 ± 50 Hz ( n = 2) for 1 pg/mL BSA with a signal to noise ratio of 41.

CO 2 capture by activated and impregnated anthracites

Porous materials are being proposed as suitable candidates for CO 2 capture due to their highly developed porous structure. Although anthracites are known to produce high surface area activated carbons, there are very limited studies on the application of activated anthracites. Accordingly, in this work, high surface area activated anthracites were prepared by steam activation and their CO 2 capacities were investigated. The activated anthracites are mainly microporous. The increase in activation time results in a continuous steady rise of the mesopore area and volume, while the micropore and total pore area and volume reach a maximum at 3 h. The surface areas go through a maximum with increasing solid yields. The adsorption capacity of the activated anthracites decreases rapidly with increasing adsorption temperature, probably due to the adsorption being a physisorption process. The anthracite with the highest CO 2 adsorption capacity is the sample activated at 800 °C for 2 h, whose surface area was only 540 m 2/g, and the adsorbed amount of CO 2 was 65.7 mg-CO 2/g-adsorbent. This is probably due to a relationship between microporosity and CO 2 physisorption processes. Several surface treatment methods, including NH 3 heat treatment and polyethylenimine (PEI) impregnation, were used to modify the surface properties of the activated anthracites in an attempt to increase their CO 2 capture capacity at higher temperatures. The surface treatment methods investigated change the porous structure and surface chemistry of the anthracites, and therefore, affect their CO 2 capacities.

Preparation and characterization of activated carbons from rice husks and shells of palm fruits

Activated carbons from palm fruit shells (PFS) and rice husks (RH) were prepared using physical and chemical activation processes, respectively. The influence of activation time and temperature (in the case of PFS) and impregnation ratio and carbonization temperature (in the case of RH) on the properties of the resultant carbons were studied. In the case of PFS carbons, there were an increase in adsorption capacity and surface areas with increase in activation time and temperature. The surface area ranged between 292 and 642 m2g-1 at temperature range of between 1000 and 1200 K. In the case of RH carbons, surface areas and adsportion capacity also increased with increase in impregnation ratio and carbonization temperature. However, at temperatures above 1100 K there was a decrease in both surface area and adsorption capacity. The surface areas ranged between 146 m2g-1 and 526 m2g-1 at a temperature range of 1000 to 1100 K for the later carbons. Tanz. J. Sci. Vol. 28(2) 2002: 131-142

Cerium silicates formation from mechanically activated oxide mixtures

Reactions of cerium silicate formation in mechanically activated oxide powders of CeO2 and SiO2 (quarz) were studied. Three different mixtures were prepared, the compositions of which corresponded to Ce2Si2O7, Ce4.67(SiO4)3O and Ce2SiO5. Oxide mixtures were mechanically activated in vibratory mill up to 120 min. X-ray analysis performed on activated mixtures showed that the CeO2 crystallite size decreased with increasing activation time. However, CeO2 lattice distortions passed through a maximum after 30 min of activation. The results obtained after heating showed that reactions proceeded via formation of intermediate compounds. Evidence of the existence of a liquid phase at 1550°C is given.

Reduction of ST elevation in repeated coronary occlusion model depends on both altered metabolic response and conduction property

The aim of this study was to elucidate the mechanisms of altered electrical response to ischemia in repeated coronary occlusion model. To test its dependence on metabolic response, extracellular K + concentration (eKC), myocardial pH and P co 2 were simultaneously measured with epicardial ECG during three consecutive 4 min of left anterior descending coronary artery (LAD) occlusion separated by 15 min of reperfusion in canine hearts. ECG changes induced by infusion of high K +-buffer (10 mM) into the coronary arterial bed via carotid artery–LAD bypass (referred to as high K +-challenges: HKC) were also tested prior to (the first HKC), and during each reperfusion period (the second to the fourth HKC). ST elevation was significantly reduced in subsequent occlusions (3.14±0.48 and 2.98±0.47 mV in the second and third occlusion, both P<0.05, compared to 4.91±0.78 mV in the first). This was accompanied by significant attenuation of the changes in eKC, tissue pH and P co 2. ST elevation induced by HKC also significantly reduced after repeated occlusion (4.09±0.79 mV in the fourth HKC vs. 5.64±0.68 mV in the first, P<0.05) in spite of the identical changes in eKC during HKC. This progressive decrease in ST changes by HKC was rather consistent with augmented conduction delay (86.4±7.1% increase in activation time in the fourth vs. 54.3±3.4% in the first, P<0.01). These findings indicate that repeated ischemia induces altered electrical response to subsequent ischemia based on both attenuated metabolic response and altered conduction property.