Nanomaterials as Flow Regulators in Dry Powders

Zimmermann, Ingfried; Eber, M.; Meyer, Kristin

doi:10.1524/zpch.218.1.51.25388

Cited by 70 publications

(50 citation statements)

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“…6d) [26][27][28]. As an enhancement of Rumpf's [11] and Eber's [25] models, all distances between two carrier particles and a spherical guest particle have been added (mean radius R 1,2 ) according to Eq.…”

Section: Models Of Functional Principles Of One Asperity In Contact Wmentioning

confidence: 99%

“…Therefore, this distance can be neglected and for the van der Waals forces, Eber obtained Eq. (12):The Sandwich-model of Zimmermann [26] describes the interparticle adhesion between two spherical carrier particles and one guest particle in the contact zone, Fig. 6d) …”

mentioning

confidence: 99%

“…(14) and setting it to zero, the radius of the asperity at minimum adhesion force can be calculated by the approximation given by Eq. (15):Meyer [30] developed a 3-point-model as an extension of Zimmermann's sandwich-model [26], where a mechanically instable contact is obtained. In this 3-point-model, both carrier particles are bonded by three guest particles, Fig.…”

mentioning

confidence: 99%

“…In addition to the above mentioned regions, the 3-point-model [25], the distance between the carrier particles calculated at the same asperity or guest particle size is twice as large as the value from the Rumpf model. A lower adhesion force is calculated using the Sandwich-model of Zimmermann [26]. The reason for this is the lower van der Waals interaction between two spheres, Eq.…”

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confidence: 99%

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Improvement of Flowability of Fine Cohesive Powders by Flow Additives

Tomas

Kleinschmidt

2009

Chem Eng & Technol

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Most minerals and concentrates, auxiliaries, agricultural and synthetic particulate solid products are produced with particle sizes of less than 100 lm. These fine powders show similar problematic product properties. Their interparticle adhesion forces, especially van der Waals forces, exceed the gravitational forces by orders of magnitude. Thus, the trouble-free treatment of these products presents large problems as well as scientific and technological challenges. The physical properties of such materials, especially flowability, are essential for many industrial applications including product generation, processing, application and consumption, e.g., in the pharmaceutical, chemical, food and manufacturing industries or plant engineering. In recent decades, one of the most frequently used solutions to this problem has been to add small amounts of flow additives that improve the flowability of these fine cohesive powders. This paper provides an overview of the physico-chemically active principles of flow additives, model approaches and useful flowability evaluation methods. The efficiency of several flow additives, i.e., nanoparticles and surfactants, is critically discussed by the provision of selected test results from the literature. Conclusions are drawn with respect to the application of this flow additive method in process industries. Introduction and Problem DescriptionThere are many branches of the global economy, in which particulate solids, i.e., bulk solids and powders, are produced, transported, handled, converted or consumed. This include collections of particle of all sizes, usually classified as bulk solids (d > 100 lm), as well as fine (d < 100 lm), ultrafine (d < 10 lm) and nanoscale (d < 100 nm) powders 1) . Frequently, the term "bulk solids" is also used for all heaped particle collectives independent of particle sizes.Many raw materials, additives, agricultural and synthetic particulate solids are produced with particle sizes smaller than 100 lm. These materials show a number of problematic product properties [1]. Their interparticle forces, especially van der Waals forces, exceed the gravitational forces by several orders of magnitude. Thus, the trouble-free handling of these products is a serious problem as well as presenting a scientific and technological challenge. However, their physical properties, especially the flowability, are essential in several industrial applications, e.g., in the pharmaceutical, food, and chemical industries as well as in mechanical and plant engineering.Flowing or yielding means that a powder is brought to irreversible deformation, and therefore, to the desired level of flow by an external mechanical stressing event which can be a force or energy. According to this method, only the trouble-free discharge of a powder out off a storage container by its dead weight is considered as good flowability. In contrast, powders that show flow problems are classified as poorly flowing or non-flowing. Such flow problems are very frequent in the case of cohesive powders with...

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Section: Models Of Functional Principles Of One Asperity In Contact Wmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Improvement of Flowability of Fine Cohesive Powders by Flow Additives

Tomas

Kleinschmidt

2009

Chem Eng & Technol

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“…For a straightforward development of freely flowing powders an understanding of the forces controlling the powder flow on the particulate level is required. In a series of papers, Zimmermann et al [1][2][3][4] explained the mechanism by which flow-regulating agents such as hydrophilic and hydrophobic fumed silicas, precipitated silicas, carbon black, and titanium dioxide control the cohesiveness of powders.…”

Section: Introductionmentioning

confidence: 99%

Efficiency of Nanoscaled Flow Regulators

2010

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In dry powders the particle flow is mainly determined by van der Waals forces. It was proved in systematic studies that in addition to the hydrophilic silica Aerosil® 200 also hydrophobic silicas, various types of carbon black, or precipitated silicas are able to act as flow regulators if these highly aggregated nanomaterials can be broken down into smaller fragments comprising only a few primary particles. To characterize the ability of a given nanomaterial to act as flow regulator, the two terms effectiveness and efficiency were introduced. Effectiveness describes the maximum achievable reduction of the tensile strength by a given concentration of the nanomaterial. The parameter efficiency expresses the mixing time required to achieve the maximum reduction of tensile strength. The efficiency, however, is strongly dependent on the energy brought up by the mixing procedure. This energy is needed to desagglomerate the highly aggregated nanomaterials. Since up to now there is no method to measure these forces directly and methods allowing their indirect determination were looked for.

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