Tetrahedral particles

Narayanan and El-Sayed investigated the effect of the electron-transfer reaction between ferricyanide and thiosulfate on the stability of particle shape [39,40]. The change in shape of the nanoparticle was time-dependent this change was in the form of a thermodynamic rounding of the particle into a sphere due to the dissolution of platinum atoms from the comers and edges of the tetrahedral and cubic platinum nanoparticles. Figure 18.3 demonstrates that the tetrahedral particle evolves into a distorted tetrahedral particle after one reaction cycle (Fig. 18.3a and b). For the cubic platinum nanoparticles (Fig. 18.3c), the rate of dissolution of platinum atoms was slower, and distorted cubic platinum nanoparticles (Fig. 18.3d) were dominant after two reaction cycles. 

Muinonen, K., 2003 Light scattering by tetrahedral particles in the kirchhoff approximation. In T. Wriedt, ed., Electromagnetic and Light Scattering — Theory and Applications VII, pp. 251-254. 

There is a problem of bound water both in hfeless nature and in biological systems at various levels of the stractural hierarchy. In this regard we can talk about the existence of the phenomenon of bound water with different from hulk water strac-tures and properties [17-19]. Let us consider a model of water associated with biopolymer. The basis of this model is the fact that water molecule can be represented as a distorted tetrahedron because an ideal tetrahedron bond angle is 109.28, and free water molecule bond angle is 104.5. The model assumes that the water may produce a continuous three-dimensional netwoik of tetrahedral particles. 

The basic stractural element of building twist-boat is chiral hexacycle that is composed of tetrahedral particles Twist-boat is chiral, that is, exists in the left and right form (Fig. 2.15). 

We will call a hexacycle stracture constructed only of twist-boats connected with each other as th-cycle [18], The th-cycle is a system of cycles that are built of tetrahedral particles (water molecules connected by H-bonds). The tetrahedral particles are arranged in a twist-boat hexacycles of the same chirality. The twist-boats are linked with each other in special way [18] and form a th-cycle. The main characteristics of th-cycle are ... 

A variety of flake or di-, tri-, and tetrahedral particle shapes are Obtained by this exclusive process. These unique shapes provide numrous functions including high surface area, permeability and reinforcement and have densities among the lowest of any of the mineral fillers. In addition to superior spatial loading, this property affords customers the added bonus of density control in their finished products. Oicalite Perlite fillers are off-white and do not interfere with the coloring of the products into which they are formulated. 

Fig. 13.8 Micrographs from TEM of the Pt/Si02 in situ treatment with increasing temperature, cubic and tetrahedral particles (Wang X., Zhuang J., Peng Q., Li Y., Nature, vol. 437, pp. 121-124, 2005, reproduced with permission)...

Talc and Pyrophyllite. Talc (qv) and pyrophjlhte are 2 1 layer clay minerals having no substitution in either the tetrahedral or octahedral layer. These are electrostatically neutral particles (x = 0) and may be considered ideal 2 1 layer hydrous phyUosiHcates. The stmctural formula of talc, the trioctahedral form, is Mg3Si402Q(0H)2 and the stmctural formula of pyrophylUte, the dioctahedral form, is Al2Si402Q (OH)2 (106). Ferripyrophyllite has the same stmcture as pyrophylUte, but has ferric iron instead of aluminum in the octahedral layer. Because these are electrostatically neutral they do not contain interlayer materials. These minerals are important in clay mineralogy because they can be thought of as pure 2 1 layer minerals (106). 

The essence of this idea is that there is a limit to which particles of like-size can occupy a given space, even when arranged in closely packed arrays (e.g., cubic or tetrahedral arrays). The voids that are left are usually smaller than the parent particles and may be filled by particles of smaller size to increase the concentrations of particles in space. Thus, polydispersity can give a lower viscosity at the same volume fraction or permit higher volume loading at the equivalent monodisperse viscosity. 

In NiFe204, an inverse spinel Fe +[Ni2+Fe3+]004, the spins of the octahedral sites are parallel with one another the same applies to the tetrahedral sites (Fig. 19.8). The interaction between the two kinds of sites is mediated by superexchange via the oxygen atoms. High-spin states being involved, Fe3+ (d5) has five unpaired electrons, and Ni2+ (ds) has two unpaired electrons. The coupled parallel spins at the octahedral sites add up to a spin of S = + =. It is opposed to the spin of S = of the Fe3+ particles at the tetrahedral sites. A total spin of S = 1 remains which is equivalent to two unpaired electrons per formula unit. 

The aluminum is incorporated in a tetrahedral way into the mesoporous structure, given place to Bronsted acidic sites which are corroborated by FTIR using pyridine as probe molecule. The presence of aluminum reduces the quantity of amorphous carbon produced in the synthesis of carbon nanotubes which does not happen for mesoporous silica impregnated only with iron. It was observed a decrease in thermal stability of MWCNTs due to the presence of more metal particles which help to their earlier oxidation process. 

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