Dispersion of Nano-Particle Clusters Using Mixed Flow and High Shear Impellers in Stirred Tanks

Xie, Liansong; Rielly, Chris D.; Eagles, W.; Özcan‐Taşkın, Gül

doi:10.1205/cherd06195

Cited by 39 publications

(26 citation statements)

References 9 publications

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“…36 Then, taking _ g c $ 10 4 s À1 , V ¼ 300 ml (as per the N-dependent study) and noting from Fig. 3F that N c ¼ 1800 rpm (30 s À1 ), we can estimate k 1 k 2 ¼ 75.…”

Section: Exfoliation Mechanismmentioning

confidence: 98%

“…the EkatoMizer and the LE-20 described in ref. 36). On a per unit liquid mass basis, P/M, is given by…”

Section: Graphene Concentration and Production Ratementioning

confidence: 99%

“…In fact, for a blade type similar to ours, k 2 $ 100 (ref. 36), so here k 1 k 2 should be $10 to 100. We expect exfoliation to stop once _ g max $ _ g c which manifests itself experimentally by N ¼ N c .…”

Section: Exfoliation Mechanismmentioning

confidence: 99%

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Turbulence-assisted shear exfoliation of graphene using household detergent and a kitchen blender

et al. 2014

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To facilitate progression from the lab to commercial applications, it will be necessary to develop simple, scalable methods to produce high quality graphene. Here we demonstrate the production of large quantities of defect-free graphene using a kitchen blender and household detergent. We have characterised the scaling of both graphene concentration and production rate with the mixing parameters: mixing time, initial graphite concentration, rotor speed and liquid volume. We find the production rate to be invariant with mixing time and to increase strongly with mixing volume, results which are important for scale-up. Even in this simple system, concentrations of up to 1 mg ml À1 and graphene masses of >500 mg can be achieved after a few hours mixing. The maximum production rate was $0.15 g h À1 , much higher than for standard sonication-based exfoliation methods. We demonstrate that graphene production occurs because the mean turbulent shear rate in the blender exceeds the critical shear rate for exfoliation.Over the last decade, graphene has become one of the most studied of all nano-materials due to its 2-dimensional structure and its unique set of physical properties. 1,2 During this period, the focus of much of the research community has been on mapping out and understanding the fundamental physics and chemistry of graphene. However, in recent years, the emphasis has started to shi slightly towards the demonstration of applications. 3 Over the next few years, we expect the emphasis to shi further as both academic and industrial researchers concentrate on fullling the applications potential of graphene, eventually leading to a range of graphene-enabled products.However, before this can be achieved, it will be critically important to develop industrially scalable production methods for graphene. While graphene can be produced by a range of techniques, many applications will require solution-processed 4 graphene. In particular, a number of applications will require access to large volumes of graphene dispersions or inks. Using standard solution deposition techniques such as inkjet printing 5,6 or spray coating, 7,8 such inks can be used to prepare a range of lms, coatings or patterned structures. In particular, applications in areas such as printed electronics will require the production of conductive lms or traces. Here, defect free graphene performs particularly well, giving high conductivity structures without high temperature post treatments. 5 Thus, it is clear that large scale production techniques for defect-free graphene are urgently required.Defect free graphene is generally produced by sonicating graphite powder either in certain solvents 9-16 or aqueous surfactant 17-23 solutions. The sonication tends to break up the graphite crystallites as well as exfoliating them to give large number of graphene nanosheets. 11 Raman spectroscopy 15,24,25 shows this method to produce negligible quantities of basal plane defects while XPS shows the akes to be un-oxidised. 14 While the graphene produced by this m...

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“…36 Then, taking _ g c $ 10 4 s À1 , V ¼ 300 ml (as per the N-dependent study) and noting from Fig. 3F that N c ¼ 1800 rpm (30 s À1 ), we can estimate k 1 k 2 ¼ 75.…”

Section: Exfoliation Mechanismmentioning

confidence: 98%

“…the EkatoMizer and the LE-20 described in ref. 36). On a per unit liquid mass basis, P/M, is given by…”

Section: Graphene Concentration and Production Ratementioning

confidence: 99%

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Turbulence-assisted shear exfoliation of graphene using household detergent and a kitchen blender

et al. 2014

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“…Other process devices used by previous researchers include the sawtooth impeller (Xie et al, 2007), batch rotor-stator (Xie et al, 2007;Pacek et al, 2007), high pressure devices Sauter and Schuchmann, 2012), stirred bead mills (Kowalski et al, 2008, Schilde et al, 2011 and ultrasonicators (Sauter et al, 2006(Sauter et al, , 2008. Some of the studies included numerical modelling to develop both an understanding of the flows within process devices which are not accessible for measurements and also models describing the deagglomeration process (Baldyga et al, 2006(Baldyga et al, , 2007(Baldyga et al, , 2008(Baldyga et al, , 2009.…”

Section: Introductionmentioning

confidence: 99%

Comparative performance of in-line rotor-stators for deagglomeration processes

Özcan-Taşkın

Padron

Kubicki

2016

Chemical Engineering Science

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In-line rotor-stators are used for a wide range of power intensive dispersion applications, including the breakup of immiscible liquid droplets or agglomerates. This study, performed within the DOMINO project at BHR Group, aimed at studying the performance of three different rotor-stator head designs for deagglomeration processes. A given test system, nanoscale silica particles-in-water, was used to identify the mechanism and kinetics of break-up and determine the smallest attainable size. Three rotorstator head designs used were the GPDH-SQHS and EMSC screens from Silverson and Ytron Z-Lab from Ytron. These in-line rotor-stators were used in the recirculation loop of a stirred tank with a total dispersion volume of 100 litres. Power input and residence time were varied by changing the rotor speed and dispersion flow rate. Breakup was found to occur through erosion regardless of the operating conditions or rotor-stator design. The smallest fragments obtained were aggregates, rather than primary particles, and these were of a mean diameter of 150-200 nm; also independent of the operating conditions or rotor-stator head design. With a given rotor-stator operated at a given flow rate, increasing the rotor speed and hence the power input increased the break up kinetics. For a given design at a given specific power input, whilst the break up rate per tank turnover decreased when the flow rate was increased, the total processing time could be reduced. There were differences in the volume of the mixer head and chamber volumes; in addition, a smaller flow rate range could be covered with the Ytron design. Comparison of the different designs was therefore not straightforward. It could however be shown that the rotor-stator designs with a high number and small size of holes and/or gaps have a faster break up rate.

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“…Consequently, a study has been carried out to investigate the flow field and turbulence properties generated by an EkatoMizer, which is a type of sawtooth impeller. Recently, studies have been carried out to investigate the dispersion of nano-particle agglomerates by a sawtooth impeller (Xie et al, 2007;Xie et al, 2008), but the present contribution focuses on the local hydrodynamics of the flow close to the rotating blades.…”

Section: Introductionmentioning

confidence: 99%

PIV study of the flow field generated by a sawtooth impeller

Unadkat

Rielly

Nagy

2011

Chemical Engineering Science

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Stereoscopic and high-speed particle image velocimetry (PIV) techniques have been employed to study the flow field induced by a sawtooth (EkatoMizer) impeller, operated in the fully turbulent flow regime at an impeller speed of 1500 rpm.Ensemble-averaged mean flow fields and turbulence quantities were calculated for a region close to the impeller blades. The flow was found to be anisotropic near the impeller and exhibited return-to-isotropy behaviour further away from it. Macroinstabilities were found to have a high probability of occurrence in the discharge stream. All three velocity components from the stereo-PIV measurements were used to estimate the dissipation rate, by adopting a large eddy simulation (LES) analogy.Spurious vectors distorting the dissipation rate calculation were identified, and various standard deviation filters were applied for vector validation. By evaluating the filtered dissipation rate profiles against the multi-fractal intermittency model of Meneveau and Sreenivasan (1991), the global standard deviation filter was found to be the most suitable type. The ratio of the maximum to the mean dissipation rate for the EkatoMizer discharge stream was found to be similar to that reported for Rushton disk turbine and pitched-blade turbine impellers in the literature, raising questions about the reported high-shear advantage of sawtooth impellers.

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Dispersion of Nano-Particle Clusters Using Mixed Flow and High Shear Impellers in Stirred Tanks

Cited by 39 publications

References 9 publications

Turbulence-assisted shear exfoliation of graphene using household detergent and a kitchen blender

Turbulence-assisted shear exfoliation of graphene using household detergent and a kitchen blender

Comparative performance of in-line rotor-stators for deagglomeration processes

PIV study of the flow field generated by a sawtooth impeller

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