Electrochemical behavior of exfoliated carbon fibers in H2SO4 electrolyte with different concentrations

Exfoliated carbon fibers (ExCFs) were prepared by the decomposition of intercalation compounds with nitric acid derived from pitch-based carbon fibers and used as electrodes of electrochemical capacitors in sulfuric acid electrolyte. The specific capacitance, which was estimated by cyclic voltammetry and galvanostatic charge-discharge (CD) measurements, increased gradually with the concentration of the electrolyte up to10 mol/dm³ and then rapidly to huge value in higher concentration of electrolyte. The capacitance obtained for a sample with the largest specific surface area (ca. 300 m²/g) was 450 F/g, which was calculated from the 50th discharge curve of CD experiment. The results suggest the possibility of pseudo-capacitance by the intercalation of sulfuric acid molecules into graphite gallery of ExCFs electrode.     

Effects of acid treatment duration and sulfuric acid molarity on purification of multi-walled carbon nanotubes

Multi-walled carbon nanotubes were synthesized using a Fe-Ni bimetallic catalyst supported by MgO using thermal chemical vapor deposition. Purification processes to remove unwanted carbon structures and other metallic impurities were carried out by boiling in sulfuric acid solution. Various analytical techniques such as TGA/DSC, Raman spectroscopy, SEM, HRTEM and EDAX were employed to investigate the morphology, graphitization and quality of the carbon nanotubes. The obtained results reveal the molarity of sulfuric acid and immersed time of the carbon nanotubes in the acid solution is very effective at purifying multi-walled carbon nanotubes. It was also found that 5 M concentration of boiling sulfuric acid for a 3 h treatment duration led to the highest removal of the impurities with the least destructive effect. Moreover, it was observed that acid treatment results in decreasing of CNTs’ diameter.     

Charge transfer in carbon composites based on fullerenes and exfoliated graphite

Physics of the Solid State - Kinetic processes have been studied in composites based on fullerenes and exfoliated graphite at the initial proportions of components from 1: 16 to 16: 1 in mass. The...     

Electrochemical capacitance from carbon nanotubes decorated with titanium dioxide nanoparticles in acid electrolyte

The electrochemical activity of an electrode of carbon nanotubes (CNTs) attached with TiO₂ nanoparticles was investigated. A chemical-wet impregnation was used to deposit different TiO₂ particle densities onto the CNT surface, which was chemically oxidized by nitric acid. Transmission electron microscopy showed that each TiO₂ nanoparticle has an average size of 30-50 nm. Nitrogen physisorption measurement indicated that the porosity of CNTs is partially hindered by some titania aggregations at high surface coverage. Cyclic voltammetry measurements in 1 M H₂SO₄ showed that (i) an obvious redox peak can be found after the introduction of TiO₂ and (ii) the specific peak current is proportional to the TiO₂ loading. This enhancement of electrochemical activity was attributed to the fact that TiO₂ particles act as a redox site for the improvement of energy storage. According to our calculation, the electrochemical capacitance of TiO₂ nanocatalysts in acid electrolyte was estimated to be 180 F/g. Charge-discharge cycling demonstrated that the TiO₂-CNT composite electrode maintains stable cycleability of over 200 cycles.     

硫酸中多气泡声致发光光谱

非线性声波方程与气泡脉动方程联立, 可以描述声空化云中的声场以及任何一个气泡的脉动过程,为数值计算空化场问题提供了理论框架.计算的声压分布变化可以用来计算单气泡动力学,了解任何位置处气泡发光过程以及气泡内气体温度和压强变化等. 对浓硫酸中氙气泡空化云的计算定性符合实验观测, 只有钠原子线谱的计算结果相比实验观测有些出入.     

Surface-charge-governed electrolyte transport in carbon nanotubes

The transport behavior of pressure-driven aqueous electrolyte solution through charged carbon nanotubes(CNTs) is studied by using molecular dynamics simulations. The results reveal that the presence of charges around the nanotube can remarkably reduce the flow velocity as well as the slip length of the aqueous solution, and the decreasing of magnitude depends on the number of surface charges and distribution. With 1-M KCl solution inside the carbon nanotube, the slip length decreases from 110 nm to only 14 nm when the number of surface charges increases from 0 to 12 e. This phenomenon is attributed to the increase of the solid–liquid friction force due to the electrostatic interaction between the charges and the electrolyte particles, which can impede the transports of water molecules and electrolyte ions. With the simulation results,we estimate the energy conversion efficiency of nanofluidic battery based on CNTs, and find that the highest efficiency is only around 30% but not 60% as expected in previous work.     

Percolation transition in carbon composite on the basis of fullerenes and exfoliated graphite

The electrical conductivity of a carbon composite on the basis of C₆₀ fullerenes and exfoliated graphite is investigated in the range of relative contents of components from 0 to 100%. The samples are obtained by the thermal treatment of the initial dispersed mixtures in vacuum in the diffusion–adsorption process and their further cold pressing. The resistivity of the samples gradually increases with an increase in the fraction of fullerenes, and a sharp transition from the conductive state to the dielectric one is observed after achieving certain concentrations of C₆₀. The interpretation of the results within the percolation theory makes it possible to evaluate the percolation threshold (expressed as a relative content of graphite) as equal to 4.45 wt % and the critical conductivity index as equal to 1.85 (which is typical for three-dimensional twocomponent disordered media including those having pores).

     

Dynamics of a sonoluminescing bubble in sulfuric acid

The spectral shape and observed sonoluminescence emission from Xe bubbles in concentrated sulfuric acid is consistent only with blackbody emission from a spherical surface that fills the bubble. The interior of the observed 7000 K blackbody must be at least 4 times hotter than the emitting surface in order that the equilibrium light-matter interaction length be smaller than the radius. Bright emission is correlated with long emission times (approximately 10 ns), sharp thresholds, unstable translational motion, and implosions that are sufficiently weak that contributions from the van der Waals hard core are small.     

Tunable passively Q-switched ytterbium-doped fiber laser with mechanically exfoliated GaSe saturable absorber

A tunable passively Q-switched ytterbium-doped fiber laser using few-layer gallium selenide(GaSe) as a saturable absorber(SA) is demonstrated.The few-layer GaSe SA,which is fabricated by the mechanical exfoliation method,is able to generate a Q-switched fiber laser that has a maximum repetition rate of 92.6 kHz and a minimum pulsed width of 2.3 μs.The highest pulse energy exhibited by the generated pulse is 18.8 nJ with a signal to noise ratio of ~40 dB.The tunability of the proposed laser covers from 1042 to 1082 nm,giving a tuning range of 40 nm.     

Q-switched fiber laser using carbon platinum saturable absorber on side-polished fiber

A 1550 nm Q-switched fiber laser using a carbon platinum saturable absorber deposited on side-polished fiber(SPF) is proposed and demonstrated. The SPF is approximately 2 mm with a polarization-dependent loss(PDL)of 0.4 dB and an insertion loss of 2.5 dB. A stable Q-switched output spectrum is obtained at 1559.34 nm with a peak power of ~6 mW, a pulse width of 1.02 μs, pulse energy of 5.8 nJ, average output power of 0.76 mW, and a repetition rate of 131.6 kHz taken at a pump power of 230.0 mW. A signal-to-noise ratio of 49.62 d B indicates that the Q-switched pulse is highly stable.     

Interphase formation and fiber matrix adhesion in carbon fiber reinforced epoxy resin: influence of carbon fiber surface chemistry

The chemistry and morphology of the carbon fiber surface are important parameters which govern the properties of the interfacial region and the adhesion between carbon fibers and polymeric matrix in carbon fiber reinforced polymers. In the presented paper the surface chemistry of the fibers is varied while the surface morphology is left unchanged. We analyze chemical functionality and morphology of carbon fiber surfaces showing different degrees of activation, together with the adhesion of these fibers to an epoxy matrix and the width of the interfacial region between fiber and matrix. An increase of the oxygen and nitrogen concentration of the fiber surface, in particular in form of carboxyl functional groups, results in a significant increase of interfacial shear strength. Also the width of the interphase, as determined by scanning force microscopy in nanomechanical mode, depends on the activation degree of the carbon fibers. However, no direct correlation between interphase width, surface chemistry and fiber matrix adhesion is found, suggesting no direct influence of interphase width on adhesion properties.     

Ultrasonic-assisted ozone degradation of organic pollutants in industrial sulfuric acid

In this work, a combination of ozone (O₃) and ultrasound (US) has been firstly used to decolorize black concentrated sulfuric acid with high organic content. The effect of different reaction factors on the transparency, extent of decolorization, H₂SO₄ mass fraction, and organic pollutants removal is studied. In addition, the systematic interaction between ultrasound and ozone on the decolorization process is reviewed through comparative experiments of O₃, US and US/O₃. A sulfuric acid product that meets the requirements for first-class products in national standards, with an extent of decolorization of 74.07%, transparency of 70 mm, and a mass fraction of 98.04%, is obtained under the optimized conditions. Under the same conditions, it has been established that the treatment time can be saved by 25% using the US/O₃ process compared to using O₃. Further, the production of oxidative free radicals (•OH) in a concentrated sulfuric acid system is enhanced using the US/O₃ process compared with O₃. In addition, the degree of effectiveness of different oxidizing components on the decolorization process is revealed by adding different free radical shielding agents when the US/O₃ process is used.     

Sonoluminescence and dynamics of cavitation bubble populations in sulfuric acid

The detailed link of liquid phase sonochemical reactions and bubble dynamics is still not sufficiently known. To further clarify this issue, we image sonoluminescence and bubble oscillations, translations, and shapes in an acoustic cavitation setup at 23 kHz in sulfuric acid with dissolved sodium sulfate and xenon gas saturation. The colour of sonoluminescence varies in a way that emissions from excited non-volatile sodium atoms are prominently observed far from the acoustic horn emitter (“red region”), while such emissions are nearly absent close to the horn tip (“blue region”). High-speed images reveal the dynamics of distinct bubble populations that can partly be linked to the different emission regions. In particular, we see smaller strongly collapsing spherical bubbles within the blue region, while larger bubbles with a liquid jet during collapse dominate the red region. The jetting is induced by the fast bubble translation, which is a consequence of acoustic (Bjerknes) forces in the ultrasonic field. Numerical simulations with a spherical single bubble model reproduce quantitatively the volume oscillations and fast translation of the sodium emitting bubbles. Additionally, their intermittent stopping is explained by multistability in a hysteretic parameter range. The findings confirm the assumption that bubble deformations are responsible for pronounced sodium sonoluminescence. Notably the observed translation induced jetting appears to serve as efficient mixing mechanism of liquid into the heated gas phase of collapsing bubbles, thus potentially promoting liquid phase sonochemistry in general.     

Mechanism of dc conduction in polyaniline doped with sulfuric acid

A temperature variation of dc conductivity in the range 77–300 K has been carried out in order to explore the mechanism of charge transport in polyaniline (PAN) doped with sulfuric acid. The variable range hopping (VRH) exponent changes as the transition of the PAN lattice takes place in a narrow pH range thereby indicating that the charge transport is crucially composition dependent. A decrease in activation energy has been observed as the doping level is increased. Spin concentration of charge carriers determined by electron spin resonance spectroscopy has also been found to depend on the doping level of the specimen. Polarons and bipolarons formed during the doping process are the charge carriers in this system. The temperature dependence of dc conductivity and activation energy data are indicative of existence of both VRH and mixed conduction for various doping levels in these samples.     

Comparison between the single-bubble sonoluminescences in sulfuric acid and in water

Single-bubble sonoluminescence (SBSL) is achieved with strong stability in sulfuric acid solutions. Bubble dynamics and the SBSL spectroscopy in the sulfuric acid solutions with different concentrations are studied with phase-locked integral stroboscopic photography method and a spectrograph, respectively. The experimental results are compared with those in water. The SBSL in sulfuric acid is brighter than that in water. One of the most important reasons for that is the larger viscosity of sulfuric acid, which results in the larger ambient radius and thus the more contents of luminous material inside the bubble. However, sonoluminescence bubble’s collapse in sulfuric acid is less violent than that in water, and the corresponding blackbody radiation temperature of the SBSL in sulfuric acid is lower than that in water. Supported by the National Natural Science Foundation of China (Grant Nos. 10434070 and 10704037) and the Ministry of Education Priorities Project of China (Grant No. 103078)     

Sonochemical decolorization of acid black 210 in the presence of exfoliated graphite

The decolorization of acid black 210 by ultrasonic irradiation in the presence of exfoliated graphite was investigated. Low pH value and large exfoliation volume of exfoliated graphite favored the ultrasonic decolorization of acid black 210. The combination method of ultrasonic waves and exfoliated graphite achieved better results than either exfoliated graphite or ultrasound alone. Improved decolorization efficiency has been observed in the present system compared to the process using a combination of ultrasound and activated carbon. In the combination method of ultrasonic waves and exfoliated graphite, approximately 99.5% of acid black 210 was removed using 0.8 g/l exfoliated graphite at a pH of 1 within 120 min at 51 degrees C.     

Investigation on ultrasonic cavitation erosion of TiMo and TiNb alloys in sulfuric acid solution

Two kinds of Ti-alloys, i.e., TiMo and TiNb alloys are manufactured in this paper, and their ultrasonic cavitation erosion behaviors in 0.1 M H₂SO₄ solution are evaluated by the mean depth erosion (MDE), SEM and white light photograph. The results show that MDE of TiMo and TiNb alloys obviously increase with increasing the cavitation erosion time, however, they evidently decrease with the increment of Mo or Nb content at each fixed cavitation erosion time, and even some large blank areas (uneroded areas) still exist on the sample surface after ultrasonic cavitation erosion for 2 h in the case of Ti10Mo and Ti20Nb samples, implying the enhanced anti-cavitation erosion property of Ti-alloy by adding Mo or Nb element. The MDE of Ti10Mo or Ti20Nb sample is lower than that of TC4 sample in the case of each cavitation erosion time, indicating the better cavitation erosion resistance of of Ti10Mo or Ti20Nb sample. The influences of Mo and Nb on the passivity of TiMo and TiNb alloys during the ultrasonic cavitation erosion are detected by potentiodynamic curves. The results display that Ti, TC4, TixMo (x = 1, 5, 10) and TixNb (x = 5, 10, 20) samples are all almost in the passive state within the potential region from 0V_SCE to 1.5V_SCE during ultrasonic cavitation erosion, and the passive current density evidently decreases with increasing Mo or Nb content, indicating the enhanced passive characteristic by adding Mo or Nb alloys during the ultrasonic cavitation erosion.     

Comparison of Xe single bubble sonoluminescence in water and sulfuric acid

Using the equations of fluid mechanics with proper boundary conditions and taking account of the gas properties, we can numerically simulate the process of single bubble sonoluminescence, in which electron-neutral atom bremsstrahlung, electron-ion bremsstrahlung and recombination radiation, and the radiative attachment of electrons to atoms and molecules contribute to the light emission. The calculation can quantitatively or qualitatively interpret the experimental results. We find that the accumulated heat energy inside the compressed gas bubble is mostly consumed by the chemical reaction, therefore, the maximum degree of ionization inside Xe bubble in water is much lower than that in sulfuric acid, of which the vapour pressure is very low. In addition, in sulfuric acid much larger pa and R0 are allowed which makes the bubbles in it much brighter than that in water.     

Effects of plasma surface modification on the mechanical properties of carbon fiber and carbon fiber/epoxy composite

_The effect of surface treatment on mechanical properties of carbon fibers has been investigated by application of plasma polymerization of selected monomers in the vapor phase. The role of the fiber-matrix interface on carbon fiber-reinforced epoxy resin composites has also been studied. Composites have been prepared separately by the use of plasma-modified and unmodified carbon fibers in the epoxy resin matrix. The mechanical properties of carbon fibers (Hercules and Grafil) as well as of fiber/epoxy composites were examined by using single filament and three-point bending tests, respectively. It was observed that plasma polymerization treatment at selected plasma conditions led to significant improvement of interlaminar shear and flexural strength values of composites.