The role of the van der Waals force in the agglomeration of powders containing submicron particles

Hartley, Paul; Parfitt, G. D.; Pollack, L.B.

doi:10.1016/0032-5910(85)80036-x

Cited by 118 publications

(45 citation statements)

References 22 publications

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“…The diameter of an individual spherical carbon black particle is 30 nm; 4,50 however, carbon black particles tend to merge into aggregates (∼ 1 μm) and agglomerates (∼10 μm), in which van der Waals forces are significant. [51][52][53] For example, Vivekanand et al 54 showed that van der Waals forces for CNTs were higher than that of graphite. Therefore, we propose that the attraction between the MWCNTs and carbon black particles are stronger than the attractive forces between carbon black particles.…”

Section: Implications Of Mwcnts In the Mpl-mwcnts In The Mplmentioning

confidence: 99%

Multiwall Carbon Nanotube-Based Microporous Layers for Polymer Electrolyte Membrane Fuel Cells

Lee

Banerjee

George

et al. 2017

J. Electrochem. Soc.

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The presence of multiwall carbon nanotubes (MWCNTs) corresponded to a dispersion of carbon black particles in the microporous layer (MPL) of the polymer electrolyte membrane (PEM) fuel cell. The gas diffusion layer (GDL) with a MWCNT-based MPL exhibited larger pores and a higher porosity compared to a conventional GDL, and less MPL intrusion into the GDL substrate was observed with the MWCNTs-based MPL. The GDLs were evaluated in operando in a fuel cell that was customized for concurrent liquid water visualization (synchrotron X-ray radiography) and electrochemical characterization. The MWCNT-based fuel cell exhibited higher power densities and lower mass transport resistances compared to the fuel cell with the conventional GDL; however, a higher liquid water saturation was observed for the MWCNT-based GDL. Although the liquid water saturation in the MWCNTbased GDL was higher, its higher effective porosity led to superior performance compared to the conventional fuel cell. The use of the MWCNTs-based MPL resulted in improved oxygen transport in the fuel cell, particularly at high current densities. The achievement of effective water management in the polymer electrolyte membrane (PEM) fuel cell remains a challenge. Excess liquid water accumulation in the gas diffusion layer (GDL) hinders the transport of oxygen in the fuel cell. Reduced oxygen diffusion in the liquid water saturated GDL leads to efficiency losses and unstable performance.1,2 However, the commonly used bi-layered GDL (containing a carbon fiber substrate and a microporous layer (MPL)) has been shown to enhance liquid water management and the overall performance of the fuel cell. [3][4][5][6][7][8] In recent years, significant effort has been devoted to developing novel carbon fiber substrates and MPLs.9-18 Thomas et al. 9 developed a novel method for preparing hydrophobic GDLs via the electrochemical reduction of diazonium salts. GDLs were prepared with homogenous hydrophobicity distributions in the absence of pore structure modifications. Nguyen et al. 10 introduced the direct fluorination of the GDL for providing homogenous hydrophobicity. Less liquid water content was observed in these novel GDLs compared to the conventional GDL (SGL 24 BC) when visualized with soft X-rays. In the works of Forner-Cuenca et al.,11,12 a patterning of wettability was applied to a Toray GDL through radiation grafting. Hydrophilic regions facilitated preferential pathways for liquid water transport, while hydrophobic regions facilitated gas transport. Chevalier et al.13 created a novel GDL via electrospinning and radiation grafting. Ko et al.14 proposed a novel GDL through the dry deposition of hydrophobic silicone nanolayer on carbon fibers. The longterm operational stability and dynamic response of the GDL were improved.On the other hand, a number of works have focused on MPL additives for improving water management in fuel cells.19-29 While conventional MPLs consist of carbon black particles and a hydrophobic agent, such as polytetrafluoroethylene (PTFE), recent ...

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Section: Implications Of Mwcnts In the Mpl-mwcnts In The Mplmentioning

confidence: 99%

Multiwall Carbon Nanotube-Based Microporous Layers for Polymer Electrolyte Membrane Fuel Cells

Lee

Banerjee

George

et al. 2017

J. Electrochem. Soc.

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“…of stability of carbon black dispersions (2)(3)(4)(5). The main cause of dispersion destabilization is the ubiquitous van der Waals force, which originates on an atomic scale from the interactions of induced dipole fluctuations via the electromagnetic field.…”

Section: Introductionmentioning

confidence: 99%

Calculations of van der Waals Forces in 2-Dimensionally Anisotropic Materials and Its Application to Carbon Black

Dagastine

Prieve

White

2002

Journal of Colloid and Interface Science

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“…It has been previously reported that TPA + can act as a scaffolding agent to help assembling these nano-sized crystallites [11,24]. Furthermore, since the size of the crystallites is smaller than 1 μm, van der Waals interaction can be particularly significant to keep the crystallites together in an aggregate [25]. This occurrence may enable the presence of mesopores through the voids between the smaller crystallites.…”

Section: Resultsmentioning

confidence: 99%

The Surface-to-volume Ratio of the Synthesis Reactor Vessel Governing the Low Temperature Crystallization of ZSM-5

et al. 2016

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Abstract. Zeolite ZSM-5 is one of the major catalysts in the petroleum and finechemical industries. The synthesis of zeolite ZSM-5 is usually carried out at a temperature above 100 °C using an immense amount of organic structuredirecting agents (OSDA). It is interesting to note that fine-tuning the initial gel mixture can be used to enhance the typical slow crystallization rate of ZSM-5. Herein, we report the effect of the surface-to-volume ratio of the reactor vessel on the crystallization of ZSM-5 at low temperature. The surface-to-volume ratio of the reactor vessel influences the heat-transfer during the synthesis, which further governs the crystallization of ZSM-5. It was found that the higher the surface-to-volume of the reactor, the more crystalline the resulting product. The products with the highest crystallinity exhibited a nearly spherical morphology composed of smaller ZSM-5 crystallites. This phenomenon allows the presence of inter-crystallite mesopores, which is an advantage for the catalytic reaction of bulky molecules. Keywords: low OSDA; low temperature; mesopores; surface-to-volume ratio; ZSM-5. IntroductionZeolite is a class of crystalline microporous (< 2 nm) aluminosilicate materials, arranged in a long-range order by TO4 (T = Si or Al) units. Zeolite is widely known for its application in particular fields such as sorption [1], catalysis [2,3] and ion-exchange [4]. Recently, its use has been extended to wider applications, including optical [5] and membrane technology [6]. Catalysis is the most known application of zeolite, for instance ZSM-5, especially for boosting the octane number in fluid catalytic cracking (FCC) units [7]. This is due to its peculiar structure comprising straight and zig-zag channels within sizes of around 5.5 Å and the presence of strong acid sites.

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The role of the van der Waals force in the agglomeration of powders containing submicron particles

Cited by 118 publications

References 22 publications

Multiwall Carbon Nanotube-Based Microporous Layers for Polymer Electrolyte Membrane Fuel Cells

Multiwall Carbon Nanotube-Based Microporous Layers for Polymer Electrolyte Membrane Fuel Cells

Calculations of van der Waals Forces in 2-Dimensionally Anisotropic Materials and Its Application to Carbon Black

The Surface-to-volume Ratio of the Synthesis Reactor Vessel Governing the Low Temperature Crystallization of ZSM-5

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