Carbon Suspensions Research Articles

Capacitive deionization concept based on suspension electrodes without ion exchange membranes

A new type of capacitive deionization (CDI) system, based on capacitive suspension electrodes (CSEs), was developed for the purpose of desalting brackish and seawater through the use of flowable carbon suspensions. CSEs derived from activated carbon and acetylene black demonstrated a specific capacitance of 92Fg−1 in a static mode in a 0.6M NaCl solution. The novel system introduced here is a proof of concept that capacitive suspension electrodes can be envisioned to desalt water without the aid of ion exchange membranes (IEMs).

Rheological properties of ginger-like amorphous carbon filled silicon oil suspensions

The rheological properties of amorphous carbon suspensions have attracted great attention, but they are still not fully understood due to the non-equilibrium nature of the structure. In this work, the linear and nonlinear rheological properties of ginger-like amorphous carbon (GC) filled silicon oil suspensions are investigated. The percolation threshold of GC/silicon oil suspensions is 1.2wt.% based on linear viscoelasticity and percolation theory. Moreover, a viscosity plateau and apparent negative normal stress differences are observed during pseudo-steady shear experiments for samples with GC concentration above 6wt.%. Furthermore, constant-rate shear flow confirms the evolution of structure as functions of shear rate and time. Additionally, strain softening of storage modulus and strain hardening of loss modulus are observed during strain sweep experiments for samples with GC concentration above the percolation threshold. Relating the rheological results with the structure observed by an in situ optical shearing cell, the change of viscosity and negative normal stress differences under pseudo-steady shear is supposed to result from the structure reorganization of GC networks.

Generation of cavitation luminescence by laser-induced exothermic chemical reaction

Absorption of high power laser radiation by aqueous carbon suspensions is known to result in the formation of highly compressed bubbles of hydrogen and carbon monoxide through the endothermic carbon-steam reaction. The bubbles expand rapidly, overreaching their equilibrium diameter, and then collapse tens to hundreds of microseconds after formation to give a flash of radiation. Here we report on the effects of laser-initiated exothermic chemical reaction on cavitation luminescence. Experiments with hydrogen peroxide added to colloidal carbon suspensions show that both the time of the light flash following the laser pulse and the intensity of luminescence increase with hydrogen peroxide concentration, indicating that large, highly energetic gas bubbles are produced. Additional experiments with colloidal carbon suspensions show the effects of high pressure on the luminescent intensity and its time of appearance following firing of the laser.

Photoinduced reactions occurring on activated carbons. A combined photooxidation and ESR study

This work demonstrates the ability of ash-free activated carbons to interact with UV light to promote the photooxidation of phenol in solution through the formation of radical species. Our results show that in the absence of inorganic impurities or semiconductor additives, the photodegradation efficiency of the studied activated carbons has to be ascribed to the carbon matrix itself. Hydroxyl radicals have been detected by spin trapping electron spin resonance spectroscopy upon UV irradiation of the activated carbon suspensions in aqueous solution. Although the ability to photogenerate radicals upon irradiation is well known in inorganic semiconductors (such as titanium dioxide) or carbon/semiconductor composites, we herein demonstrate the capacity of the carbon matrix alone to interact with UV light, generating reactive species that would be responsible for the observed photoinduced reaction using carbons alone in the absence of semiconductor additives. Thus, the conventional interpretation of the enhanced photodegradation efficiency of carbon/semiconductor photocatalysts -so far attributed to synergistic and confinement effects, and minimized surface recombination of the charge carriers- should be reconsidered to account for the radicals photogenerated when the carbons are exposed to UV light.

Obtaining carbon suspensions by the hydromechanical method

This paper presents the results of an investigation of the process of obtaining carbon suspensions with a fraction of carbon particles of size less than a micrometer by the hydromechanical method with the use of a gear-type pump and two rotor-type pulsation pulverizers.

An Optical Fiber Sensor for Measuring Light Absorption in Suspension Solutions

An optical fiber sensor based on attenuated total reflectance (ATR) for extraction chemical information from highly scattering turbid materials has been evaluated. The influence of particles on bulk absorption and ATR transmitted spectra of micron-sized graphite flakes and spherical glassy carbon suspensions were investigated. The ATR transmitted spectra of coiled fiber-optic sensor in those suspensions with various concentrations are insensitive to scattering of suspended particles, especially for graphite flake suspensions. The reason for different influence of graphite flakes and spherical glassy carbon particles suspensions on e ATR spectra analyzed. This study demonstrates that fiber-optic sensor based on ATR technique is a feasible technique in application for monitoring turbid suspensions.

Enhancement of the photoacoustic effect and sonoluminescence in carbon suspensions through exothermic chemical reaction.

Generation of the photoacoustic effect through chemical reaction of particulate carbon in chemically reactive solutions is presented. Experiments are carried out using a Q-switched Nd:YAG laser to heat carbon nanoparticles, initiating chemical reaction which results in sound production. The amplitude of the photoacoustic signal from a carbon suspension in H2O2–H2O mixtures is shown to increase dramatically as the percentage of H2O2 in solution increases. Laser induced chemical generation of sonoluminescence in aqueous carbon suspensions is also reported. Following irradiation and chemical reaction, highly compressed gas bubbles are formed. The expansion of the gas bubble past its equilibrium diameter results in oscillation of the bubble diameter. Tens of μs after the initial formation of the bubble, sonoluminescence is found to take place on collapse of the bubble. Experiments show that the sonoluminescent intensity is increased by a factor of more than 10 as the external pressure is increased from 1 to 6 atm. The time of appearance of optical radiation following the initial firing of the laser is found to decrease with increasing external pressure as well.

Endoscopic Tattooing: Complications Might Be Preventable with Careful Technique

Endoscopic tattooing was performed in the past using sterilized solutions of India ink, which often contained immunologically active proteins and occasionally caused complications that included sterile abscesses and even development of inflammatory bowel disease. Now, sterile suspensions of pure carbon black (Spot; GI Supply) are typically used and assumed to be inert and safe for injection. To investigate this assumption, researchers from a large center for endoscopic mucosal resection (EMR) of colonic lesions prospectively reviewed cases involving tattoo-related complications. Four cases were identified during 5 …

Optical transmittance of carbon suspensions in polymer matrixes under powerful pulsed laser irradiation

Optical transmittance of carbon suspensions in polymer matrixes under powerful pulsed laser irradiation

A Study on the Effects of Three Types of Deflocculants and the Increase in the pH on the Rheological Behavior of Nano Carbon Suspensions

In this study, the rheological behavior of carbon black suspension with different amounts of three deflocculants (Dispex G40, Dispex N40 and CMC) has been investigated. As the rheological behavior of carbon black is markedly dependent on pH, the effect of the increase in pH has been studied. Dispex G40 and Sodium carboxymethycellulose (CMC), are effective in promoting complete deflocculation of carbon black suspensions with 20, 30 and 40 wt% solids concentrations for Dispex G40, and 40 wt% for CMC. 40 wt% suspensions containing Dispex N40 exhibit a yield stress at all levels of deflocculant investigated. However, a minimum in the extrapolated yield stress and apparent viscosity curve indicates that there is an optimum deflocculation level. The addition of alkali enhances the deflocculating power of CMC and Dispex G40, reducing any existing yield stress to zero. However, it would appear that Dispex N40 is desorbed when the pH is increased as rapid coagulation of the system is apparent, arising from a reduction in the repulsive forces.

Noncovalent solubilization of nanoheterogeneous astralene-based structures The photochemical factor in optical limitation on carbon suspensions

Original composites consisting of suspensions of astralenes with luminescent solubilizers in various solvents have been synthesized for the first time by the method of noncovalent solubilization. The spectroluminescence characteristics of such composites have been measured. A band corresponding to the S11 transition between van Hove singularities has been detected in the 1800-nm region in the absorption spectrum of a suspension of astralenes in a liquid crystal. The effect of optical limitation of laser radiation has been investigated in certain composites. A discussion is given of the role of noncovalent solubilization and of the formation of an ion-radical pair in the photodynamics of optical limitation in. © 2005 Optical Society of America

Theoretical and computational studies of carbon nanotube composites and suspensions: Electrical and thermal conductivity

Monte Carlo simulations have been performed, aimed at finding a critical fractional volume (CFV) associated with the onset of percolation for randomly oriented nanotubes (or, indeed, any conductive particles with large aspect ratios) that are randomly dispersed in a low thermo- or electroconductive medium. The nanotubes were treated as capped interpenetrating conductive cylinders (``sticks'') with high (up to 2000) aspect ratio $a$. It has been found that for these aspect ratios the CFV is inversely proportional to $a$ resulting in surprisingly low filler volume loadings, of the order of 0.01%, required to achieve percolation in such systems. By studying fluctuations of the CFV and the density of the percolation clusters, various critical indices of the percolation theory have been calculated including the critical index of conductivity, $t$. For three-dimensional systems it has been found that $t$ decreases substantially with an increase in the aspect ratio. The calculated thermal and electrical conductivity of the nanotube suspensions and composites as functions of the nanotube loading is in good agreement with recent experimental data.

Nonlinear-optical limiters of laser radiation based on suspensions of carbon and fulleroid nanoparticles

The mechanisms of nonlinear-optical limitation in suspensions of carbon and fulleroid nanoparticles have been studied experimentally and theoretically. The study was carried out in the wide spectral range of 300-1064 nm. Suspensions of fulleroid nanoparticles - astralenes - have proven to be more promising in a number of parameters (the limitation efficiency, the possibility of multiple use). © 2004 Optical Society of America

Rheological and Electrical Properties of Oxidized Carbon Black Suspensions in Vaseline Oil under Shear and Vibration

The results of investigations of the rheological characteristics and electrical resistance of the suspensions of carbon black in vaseline oil under the effects of shear and vibration were presented. The investigations are carried out on an original unit that allowed one to simultaneously subject the suspensions to shear deformation and orthogonal vibration. The electrical resistance was also measured in an ac pulsed low-voltage mode. Possible mechanisms of the suspension conductivity were considered depending on the regime of dynamic action.

Laser-Initiated Chemical Reactions in Carbon Suspensions

We report on laser-initiated chemical reactions in colloidal carbon suspensions. Irradiation of carbon particles ranging in size from 13 to 75 nm in diameter suspended in water, toluene, and benzen...

Optical limiting threshold in carbon suspensions and reverse saturable absorber materials

I report on the measurement of threshold energy fluence for optical limiting of nanosecond and microsecond pulses in a high-performance carbon suspension known as Defence Research Establishment Valcartier carbon black suspension (CBS)-100. Thresholds as low as 24-mJ/cm(2) (nanosecond regime) and 100-mJ/cm(2) (microsecond regime) have been obtained. The measurement technique, based on an f/20 optical system and a small analysis aperture, has been tested by measurement of reverse saturable absorber materials and other carbon suspensions whose properties can be found in the technical literature. A factor of merit has emerged from these measurements that could be used to order by limiting performance the different types of carbon suspension. In this ordering, CBS-100 appears as the best choice in the set of suspensions tested for short and long pulses.

CROSS-FLOW FILTRATION OF β-LACTOGLOBULIN SOLUTIONS LOADED WITH ADSORBENT PARTICLES

The influence of adsorbent particles on the characteristics of protein solution filtration was studied. Three media, activated carbon suspensions, β-lactoglobulin solutions, and a mixture of both, were filtered on a 0.2-μm pore alumina membrane. Moreover, the adsorption of protein on microparticles was studied and 1 isotherm was determined. Comparison of permeate fluxes, apparent retention coefficients, and hydraulic resistance values at steady state conditions highlights the existence of adsorbent-protein interactions. Permeability and retention seems to depend on cross-flow velocity. Correlations are proposed to express steady state fluxes versus operating parameters: cross-flow velocity, transmembrane pressure, and adsorbent and protein concentrations.

OPTICAL LIMITING WITH CARBON SUSPENSIONS AT SELECTED WAVELENGTHS AND PULSE LENGTHS

High-performance liquid suspensions of fine carbon particles have been developed at DREV over the last 10 years to fulfil requirements regarding eye protection against laser radiation over a wide range of wavelengths and pulse lengths. This paper reports on the single-pulse characteristics of DREV's best limiting suspension named CBS-100 at wavelengths of 532, 751 and 1064 nm, and at pulse lengths of 0.01, 0.1, 1 and 100 μs. Some results at higher repetition rate (6 pps) and a comparison with recent retinal damage threshold data are included also.

Photoacoustic shock generation in carbon suspensions

This letter discusses photoacoustic shock wave generation and the origin of nonlinear sound wave generation in carbon suspensions. The Burgers equation for an inviscid fluid is solved for an exponential acoustic wave. The solution shows an increasingly steep wave form that gradually coalesces into a shock front. Large dynamic range measurements of photoacoustic waves generated by a pulsed-laser beam in carbon suspensions show the pressure in the wave to depart significantly from the predictions of linear response theory. Acoustic sound speed and amplitude measurements indicate that weak shocks are produced from the photoacoustic sound generation process rather than from nonlinear propagational effects.

Nonaqueous UFC suspensions, used as conductive additive in cathodes for lithium batteries

Abstract Three nonaqueous ultrafine carbon suspensions (UFC) were explored as conductive additives in LiMn2O4 cathodes for Li cell. The specific surface areas, pore volume distributions of the pure materials and of the cathode mixtures were measured. The results were compared with these obtained using TAB2 alone. A considerable decreasing of the specific resistivity and pore volume increasing of the UFC pellets after sintering was established. The electrochemical cycling test showed 5 to 10% higher discharge capacity of the cathodes containing 20% UFC+TAB2 at a ratio from 1:3 to 1:1, than that of the cathodes with only 20% TAB2. It is proposed the better results are due to the two physical chemical properties: pore volume and specific resistivity.