Agglomeration coordination number

An agglomerate coordination number. c, can be defined as the average number of contacts of a particle in an agglomerate siructure. The coordination number is important to understanding agglomerate mechanical and electronic proper ie.s. The value of can also... 

During thermal drying, or room temperature evaporation, capillary forces provoke stresses on the gel. This effect raises the coordination numbers of the particles, and produces collapse of the network, that is, particle agglomeration [153] (see Figure 2.28). 

This equation can only be integrated if the relationships are known between the coordination number and particle size kix) as well as between the adhesion force and particle size and distribution A [x, nix) ]. In most instances these are not available. To measure ate, agglomerate free of cracks must be uniformly stressed by tensile forces. This requires very sophisticated methods and experimental care (see Section 3.1.2.1). 

Normally, the particles within a system have different sizes. Therefore, a mean or average particle size characterizes the system only insufficiently. It is necessary to know the entire particle size distribution, particularly because the arrangement of particles in the system and, thus, the coordination number, which is very important for agglomeration, depend on the particle size distribution. 

The practical determination of coordination numbers in agglomerates is technically impossible, particularly because of the extreme smallness of the particles forming an agglomerate. Theoretically it is possible to determine the coordination number / (jc) of a spherical particle with diameter x which is surrounded by smaller spherical particles of size as... 

Fig.s 5.8 and 5.10 describe pictorially the binding mechanisms that were reviewed above. It should be pointed out that only the two-dimensional situation at one coordination point between two particles or solid surfaces is shown. In reality, each particle has many interaction sites (coordination points) with other particles in the three-dimensional structure. It should be further understood that in typical particulate bulk solids and agglomerates large numbers of particles are present per unit volume (see also Section 5.3.1) and participate in bonding due to the binding mechanisms presented above. 

Lubricants may be either liquid or solid additives (Tab. 5.3). They reduce the coefficient of friction between the particles of a bulk mass and, therefore, result in a somewhat higher agglomerate density or lower porosity, s. According to the relationship k s = K (see Section 5.2.1) additional adhesion sites (characterized by the coordination number, k) are activated by which increased agglomerate strength is expected. 

Porosity and Agglomerate Strength One of the equations that is most commonly used to describe the strength of agglomerates (see Section 5.2.1) connects the porosity, s, with the coordination number, k, the sum of all adhesion forces at each coordination point, Aj, and the particle size, (Eq. 5.8). 

Re H (CO) 2/ 90 also afforded small metal particles, but in this case agglomeration of the trimeric units to a mean of ca 15 atom particles was indicated by the Re-Re coordination number of 5.5. In this case the metal-metal distance was the same as that of the bulk metal. 

However, the coordination numbers were found to be lower than expected for such a material and so there may also be a high proportion (50%) of nickel in units too small to be evident in the electron micrograph. Further agglomeration was detected at higher activation temperatures after total decarbonylation. 

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