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The Processes for Stabilizing Suspensions for Ceramic Thermal Barrier Coatings (TBC)
Published in Navid Hosseinabadi, Hossein Ali Dehghanian, Suspension Plasma Spray Coating of Advanced Ceramics, 2022
Navid Hosseinabadi, Hossein Ali Dehghanian
Among stable suspensions, stable suspensions of Brownian hard spheres are the most convenient. As noted, such dispersions are difficult to realize in practice as the ubiquitous van der Waals attractive forces necessitate some explicit method of imparting stability. These stabilizing forces can be of electrostatic and/or steric origin, and when the interparticle interaction is repulsive at all but short separations and the barrier to aggregation is sufficiently large, the suspension is kinetically (sometimes referred to as colloidally) stable. Under these conditions, the microstructure and rheology have many similarities to the case of Brownian hard spheres. The strength of the Brownian force scales with kBT/a, which sets the scale for the elasticity of Brownian hard sphere suspensions. Imparting a significant electrostatic (charge), steric, or electrosteric stabilizing force can lead to much greater repulsive forces and, hence, larger elastic moduli. Furthermore, these forces can act over a significant range and, as a result, can drive crystallization and glass formation at much lower particle concentrations than those required for Brownian hard spheres.
Filtration
Published in Reid A. Peterson, Engineering Separations Unit Operations for Nuclear Processing, 2019
In addition to concentration, several other properties of the solids will affect filtration performance. These can include particle size distribution, density, morphology, speciation, interaction potentials, and hardness. Most models treat particles as hard spheres of a fixed size and density. Rarely are the solids in a nuclear waste suspension represented by a single component with a tight size distribution. In reality, the solid phase is a mixture of particles with various sizes, densities, shapes, and chemical composition. Particles will also undergo, to varying degrees, physicochemical changes such as aggregation, particle–particle interactions, chemisorption on the filter media, compaction, or attrition in the filter system. One crucial observation relevant to nuclear waste filtration is that distinct particles present in solution at a similar ϕb and possessing the same nominal size and density can have a different effect on the magnitude of the filter flux at the same operating conditions. The disparate impact on performance appears to occur solely because the particles are distinct chemical species, i.e., a Na3PO4 particle filters differently than an Fe(OH)3 particle of the same physical size (for a recent example of this, see Daniel et al. 2018). This type of behavior is not predicted by conventional filtration models. Consequently, the potential parameter space is vast, which is why nuclear waste suspensions are often thoroughly tested empirically to established expected performance.
Simulation of Crystalline Nanoporous Materials and the Computation of Adsorption/Diffusion Properties
Published in T. Grant Glover, Bin Mu, Gas Adsorption in Metal-Organic Frameworks, 2018
The united-atom approach is mostly used to make parametrization easier. There are several systems where coarse graining makes the simulation of large systems tractable. An example is the simulation of colloids which are dispersed-phase particles with a diameter between approximately 1 and 1000 nm. Colloids can be modeled as hard spheres of a particular diameter. The attractive forces between the particles are simplified and captured using, for example, square-well potentials. Deformable spheres are modeled as attractive spheres with mobile penetrable hard spheres as satellites. Using this approach, the cluster size and number of bonds can be analyzed and compared to experiments [66].
Shear viscosity of pseudo hard-spheres
Published in Molecular Physics, 2020
Faezeh Pousaneh, Astrid S. de Wijn
Hard Sphere (HS) models have been widely used as a basic approximation of a spherical atom or molecule (see, e.g. [1]), because of the simplicity of the interaction potential and the instantaneous elastic collision dynamics. Although the HS model is an idealized model, it still captures the essential physics of macroscopic behaviour of real fluids, both in and out of equilibrium. Consequenly, HS-based models are often used to study and understand the thermodynamics and transport properties of liquids. Nevertheless, because HS models are highly idealized, it is difficult to make quantitative predictions for more complex molecules based on purely theoretical calculations. This is why theory-based hard sphere models are often used as a basis for empirical approaches to fluid properties that go far beyond spherical molecules [2,3]. This type of approach, however, requires analytical theory that can be challenging to develop, especially for more complicated models.
Shape-controlled crystallisation pathways in dense fluids of ccp-forming hard polyhedra
Published in Molecular Physics, 2019
Richmond S. Newman, Samanthule Nola, Julia Dshemuchadse, Sharon C. Glotzer
Crystallisation is a fundamental and important process that is ubiquitous across many fields. Beyond the obvious relevance to chemistry and materials science, examples include biology (in proteins) [1], pharmaceuticals [2], manufacturing (e.g. silicon monocrystals) [3], geology (e.g. the solidification of magma) [4], and meteorology [5, 6]. While many ongoing efforts are leading to continuous advances in the field, our understanding of crystallisation at the microscopic level remains incomplete and many of its aspects remain to be explored. For this reason, simple models, like the hard sphere model, that permit the detailed study of crystallisation pathways have an important role to play in advancing our understanding of how crystals form. Hard shapes in particular serve as model systems for nanoparticle assemblies, which are the subject of intense investigations for numerous applications [7, 8], e.g. photonic materials [9], plasmonics [10, 11], drug delivery [12], catalysis [13], or sensing [14].
Bonding interactions between ligand-decorated colloidal particles
Published in Molecular Physics, 2018
Tine Curk, Urban Bren, Jure Dobnikar
We consider spherical hard-sphere particles of radius , each particle having N binders distributed over its surface, see Figure 1. Binders can be, e.g. ligands on the surface of the colloidal particles or single-stranded DNA segments grafted to it; throughout the text we use both ‘ligand’ or ‘binder’ to describe the same. These binders are attached to the grafting points on the colloid surface with a polymeric spacer. Two binders on different colloids can form a link (bond) whose free energy consists of a term due to the free energy of the bond formation, and a configurational penalty due to stretching of spacers with the hybridisation free energy of the two binders in solution. is the configurational contribution which only depends on the location of the grafting points of the two binders, respectively, under the assumption that does not depend on the presence of other binders. For ideal polymeric spacers, becomes a quadratic function of the distance . Bonding configurations are valence limited, every binder can attach to at most one other binder. There are no other interactions considered between binders and colloids. Inter-colloidal repulsion is described by a hard-sphere potential.