Dendritic particles

It is difficult to evaluate the shape of such dendritic particles experimentally. However, some insight can be gained by atomic force microscopy (AFM) and transmission electron microscopy experiments (TEM). AFM experiments can give information about the overall size of the dendrimers, as shown by De Schryver [43], by spincoating very dilute solutions of dendrimers like 30 on mica, then visualizing single dendrimers. Their height measured in this manner corresponds very well to the diameters calculated by molecular mechanics simulations. First results from TEM measurements also confirm the expected dimensions [44]. Unfortunately, due to resolution limits, up to now direct visual information could not be obtained about the shape of the dendrimers. 

Amorphous tungsten oxide has been prepared by ultrasound irradiation of a solution of tungsten hexacarbonyl W(CO)6 in diphenylmethane (DPhM) in the presence of an Ar (80%) and O2 (20%) gaseous mixture at 90 °C [137]. Heating this amorphous powder at 550 °C under Ar yields snowflake-like dendritic particles consisting of a mixture of monodinic and orthorhombic WO2 crystals. Annealing... 

Figure 43. SEM photomicrographs of copper powder particles obtained by electrodeposition from 0.15 M CUSO4 in 0.50 MH2SO4, at an overpotential of700 mV (a) dendritic particle, and (b) the detail from Fig. 43a. (Reprinted from Ref. 80 with permission from Elsevier).

According to Wranglen,81 a dendrite consists of a stalk and branches (primary, secondary, etc.). It is obvious from Figs. 43 and 44 that the corncob-like elements forming the branches constitute the dendritic character of these particles. These corncob-like elements can be grouped in different forms of dendritic particles or alternatively can be formed individually at the electrode surface. This can easily be seen from Fig. 45, which shows disperse deposits immediately before they were tapped from the electrode surface. They were all obtained by electrodeposition processes when the... 

Snowfiakes are good examples of dendritic particles that contain branches or crystal structures emanating from a central point. Two dimensions are necessary to adequately characterize this particle type. Figure 9.3.d demonstrates a dendritic form of gold. 

Mica is an example of a material that forms very thin flakes. The characteristic dimensions are similar to the dendritic particles— thickness and width across the flake. Figure 9.3.e shows plate like structures of abhurite. 

Prevention of the Formation of Spongy Deposits and the Effect on Dendritic Particles... 

Hence, the larger the off period, the less dendritic particles are obtained. On the other hand, the current density during the on period on the tip of dendrites growing inside the diffusion layer is given by ... 

Fig. 8.4 Typical powder agglomerates detected in the powder electrodeposited at the Ni /Co = 0.67. (a) Agglomerate covered with fem-like dendrites, (b) Higher amount of dendritic particles around the agglomerates, (c) Compact agglomerate covered with small fem-like dendrites and the presence of cavities (Reprinted from Ref. [1] with kind permission from Springer)... 

Fig 15.12 Schematic of silicon/carbon nanocomposite granule formation through hierarchical bottom-up assembly, (a-c). Annealed carbon-black dendritic particles (a) are coated by silicon nanoparticles (b) and then assembled into rigid spheres with open interconnected internal channels during C deposition (c) (Reprinted with permission from Magasinsld et al. [89]. Copyright 2010)... 

Fig. 2.3 (a) Macrostructure of silver powdered deposits eiectrodeposited at an overpotential of 650 mV from 0.1 M AgNOs in both 0.5 M (NH4>2S04 and 0.5 M NH3 (b) dendritic particles obtained by tapping this silver deposit (c) and (d) the comcob-like elements of which dendrites are ctnnposed (Reprinted from [4] with permission from Electrochemical Society.)... 

Because of its application in the manufacturing of porous metaUo-ceramic bearings, of friction materials, parts for machineiy, various alloys, in chemical industry, in manufacture of rechargeable batteries, etc., Fe powder is an important industrial product [55]. Significant amount of Fe powder is produced by electrochemical technique and 20% of electrodeposited Fe powders have to be blended with Fe powders produced by other procedures. The main advantage of electrodeposited Fe powder is its volumetric mass (1.5-2.2 g cm ) and its suitability for pressing, due to dendritic particle shape. 

Dendrite particles varying in the size from about 5 pm to about 50 pm, as shown in Fig. 2.27a. 

The dendritic particle obtained by tapping of the copper deposit presented in Fig. 3.7a is shown in Fig. 3.8a. The dendritic character of this particle is made of the comcob-like elements as shown in Fig. 3.8b. The ultrasonic treatment of copper dendrites showed that the comcob-like forms were the basic elements of which copper dendrites are composed [32]. A further analysis of the comcob-like... 

Fig. 3.8 (a) Dendritic particle obtained by tapping of the copper deposit... 

In the dependence of concentration of Cu(II) ions, and hence the quantity of evolved hydrogen, the comcob-like elements can be grouped the different forms of dendritic particles from tree-like to those formed as flowers (Fig. 3.9a, b) or alternatively can be formed individually at the electrode surface (Fig. 3.9c) [31]. 

Fig. 3.13 Dendritic particle obtained by tapping of the powdered deposit electrodeposited by the pulsating overpotential (PO) regime with a deposition pulse of 3 ms (a) top view and (b) magnified part from (a). Pause duration 10 ms. Overpotential amplitude 1,000 mV. Solution 0.15 M CUSO4 in 0.50 M H2SO4...

Dendritic particle obtained by tapping of the powdered deposit obtained with a deposition pulse of 3 ms is shown in Fig. 3.13a. Copper dendrites are constmcted from comcob-like elements. Microanalysis of comcob-like elements revealed that they are composed of small agglomerates of copper grains (Fig. 3.13b). 

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