Agglomerations, 108 high-efficiency

The major consumer of tantalum is the capacitor production industry. About 60% of the total amount of tantalum currently produced is in the form of fine, agglomerated high purity powder of capacitor grade. Tantalum capacitors have high volumetric efficiency and reliability. A basic description of tantalum capacitor technology is presented in overview [19]. 

The authors of [37] confirmed high efficiency of the activation of a mixture of aluminium hydroxide with silicic acid. Monophase mullite was obtained. It was free from iron impurities by treating in weak hydrochloric acid solution. In order to improve agglomeration, the powder, synthesized at 1200°C, was subjected to additional activation for 10 min. Mullite with the density of 3 g/cm was obtained. 

Most of the powder is discharged directly from the bottom of the chamber. Spent drying air containing fine powder particles is cleaned in highly efficient cyclones and in some cases further cleaned in a bag filter or a wet scrubber. Powder from the cyclone may be discharged separately or it may be returned to the drying chamber in the vicinity of the atomizer where it will adhere to new droplets and form agglomerates. 

In the hot gas clean-up system of a coal-burning fluidized bed power plant, acoustic agglomeration could be installed after the first cleaning cyclones and followed by a high efficiency cyclone. The power required to operate the acoustic agglomerator is about 0.02-0.5<7o of the power plant output. This means that for a 250 MW power plant several hundred kilowatts of acoustic power are needed. Compared with the acoustic power output of a four-engine jet aircraft... 

The organic melt is emulsified in water with the aid of a suitable nonionic agent and stabilized by a protective colloid, e.g. potato starch gelatinized with water. The system is crystallized by cooling, and the crystals are separated from the emulsion and washed with water. The operation may be repeated if required. A typical example is shown in Figure 8.57 where five or six emulsion-crystallization cycles yield an almost pure naphthalene at an overall yield of 70 per cent compared with a less pure product at a 2 per cent yield by seven conventional fractional crystallization steps. The high efficiency of the emulsion crystallization is apparently due to the fact that crystal agglomeration does... 

A second form of desolvation chamber relies on diffusion of small vapor molecules through pores in a Teflon membrane in preference to the much larger droplets (molecular agglomerations), which are held back. These devices have proved popular with thermospray and ultrasonic nebulizers, both of which produce large quantities of solvent and droplets in a short space of time. Bundles of heated hollow polyimide or Naflon fibers have been introduced as short, high-surface-area membranes for efficient desolvation. 

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