Powder quality

Schreiner etal. (2001) modelled the precipitation process of CaC03 in the SFTR via direct solution of the coupled mass and population balances and CFD in order to predict flow regimes, induction times and powder quality. The fluid dynamic conditions in the mixer-segmenter were predicted using CFX 4.3 (Flarwell, UK). 

Wood powder is a kind of upgraded fuel that is burned in large-scale combustion plants for heat production. However, it is possible to use wood powder for power generation as well. It is a biofuel made of sawdust, shavings and bark. The raw material is crushed, dried and milled to tine particles in order to obtain the best fuel properties. There are many different wood powder qualities dependant on different physical properties such as particle size distribution, particle shape and also moisture content. The powder is usually handled in a closed system from milling to storing in silos to avoid the risk of dust explosions. The raw materials and type of mill used determine the properties of the wood powder (Paulrud et al, 2002). 

Table 1. Relationship between water volume of hydrolysis and powder quality.

Table 2. Relationship between solvent and powder quality.

Over the years, guidelines that have to do with processing conditions, process control, powder quality, and material properties have been defined to optimize the process. A great deal of study has been carried out by Crawford s group, resulting in a number of... 

Oxidation of Tungsten Metal Powder. Tungsten powder, of average grain size > 1 pm, reacts like bulk tungsten. Finer powder qualities, depending on grain size and preparation method, can be pyrophoric. 

Tungsten carbide powder can be prepared from different raw materials and by various production methods, as outlined in Fig. 9.3. Only methods used today on a technical or pilot plant scale are considered. The conventional procedure covers the widest range of powder qualities in regard to particle size (0.15 12 pm), and consequently the biggest... 

The choice of the correct mill and milling conditions depends on the hardmetal grade produced, mainly on the WC grain size. Attritors are used today for most powder qualities (1-12 pm). They have become increasingly popular because of the significantly shorter milling times. Optimized ball mills are still preferred for submicron qualities, which are very sensitive to all types of heterogeneities. 

Typical scrap materials for hydrometallurgical treatment are grinding sludges, floor sweepings, contaminated powder qualities, tungsten-copper, and solid pieces, which can be dissolved by electrolysis. 

Caric, M. and Kalab, M. 1987. Effects of drying techniques on milk powders quality and microstructure A review. Food Microstruct. 6, 171-180. 

Introduced for additional drying and cooling to improve drying efficiency and powder quality... 

In the production practice, interrelated variation of the different process parameters is applied to obtain the desired leady oxide powder quality. When the leady oxide powder is too coarse to he used directly in battery manufacture, it is subjected to further grinding in a mill. 

Molybdenum delays, also of the above U.S. patent,extend over the seconds as well as the millisecond range with proper selection of the metal powder qualities. In loose powder form, the fast mixtures burn very violently. 

These preliminary results show that polyimide-alumina composites combine together some properties that are very useful in cryogenic technology In the specific case of the TORE II project, alumina does not give a sufficiently low value of thermal conductivity on the other hand, A2 alumina seems to be limited by mechanical considerations An intermediate powder quality could be the best compromise ... 

Pellet, Powder, Quality Control, brochure by Optical Control Systems, GmbH (www. ocsgmbh.com)... 

In summary, the experiments of Barringer and Bowen demonstrate clearly that substantial benefits can be achieved in sintering and microstructure control when the powder quality is carefully controlled and the powder packing is homogeneous, i.e., when careful attention is paid to the processing steps that precede firing. However, this fabrication route is not currently used in many industrial applications where mass production and low cost are important considerations. 

Powder preparation by solid-state reactions generally has an advantage in terms of production cost, but as outlined earlier, the powder quality is also an important consideration for advanced ceramics. The powders are normally agglomerated and a grinding step is almost always required to produce powders with better characteristics. Grinding in ball mills leads to the contamination of the powder with impmities. Incomplete reactions, especially in poorly mixed powders, may produce undesirable phases. Furthermore, the particle shape of ground powders is usually difficult to control. 

The powder quality may be varied, to an extent, by modifying both the conditions of electrolysis, electrolyte composition and the nature of the electrode surface. 

The choice given to the production engineer or research powder technologist is thus dependent upon the level of information required. In the design of mass flow hoppers there tends to be a greater need for knowledge on yield loci, stresses and failure criteria than that possibly needed for routine powder quality control. 

In Fig. 18a typical PSDs of powders are shwon. The narrow PSD in Fig. 18a, with APS 43 pm, is a typical distribution for good powder quality. In contrast, although average particles are smaller, 3 pm, the long tail between 6 and 20 pm represents an unacceptable powder. Fig. 18b. Finally, in Fig. 18c, a bimodal example is given. Generally, APS 4—5 p and narrow PSD 90% below 10 pm, 96% below 15 and 100% below 20 pm, respresents a typical high quality zeolite powder. 

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