Ball nulls

Fig. 3.29 Grain size of MgH in the ball-nulled MgH -l- Xwt%LiAlH composites as a function of the LiAlH, content...

Smear point and yield point are used to determine the binder needed to formulate a suitable millbase for grinding by dissolvers, roll mills, ball nulls, attritors, sand mills, and pearl mills. The amount of binder is given in volume or mass units. Apparatus rough glass plate, spatula with steel blade. 

Tbe aminoplast intended for extrusion must contain an insignificant amount of moisture and a large quantity of lubricant (to be added during crushing in the ball null) so as to have good plasticity. 

Particle Shape and Structure. Some materials exhibit particular properties owing to their particle shape or form, eg, the plate-hke minerals talcum and mica or acicular woUastonite. It is often desired to maintain particle shape in such cases, an impact-type mill is usually chosen rather than a ball null, as the latter tends to alter the original particle shape. 

Jorres M, Mersmann S, Raabe G, Bohn C. Organocatalytic solvent-free hydrogen bonding mediated asymmetric Michael additions under ball nulling conditions. Green Chem 2013 15 612-6. 

The minimum particle size possible by ball nulling is 0.1 puL... 

In vibratory milling the drum containing the media and powder is vigorously shaken. The collisions between the media are much more violent than they are in ball nulling and this can shorten milling times. Polymer balls can be used as media and this means any contamination can be burned off during subsequent firing. 

A composite from PPS and CNTs was prepared by a plastic pressure molding technique of a mixture of both compounds ntixed by ball null [84]. 

Values of breakage distribution function b(i, j) and specific rates of breakage Sj for a particular material in a ball null are shown in Table 12W2.1. To test the validity of these values, a sample of the material with the size distribution indicated in Table 12W2.2 is to be ground in a ball mill. Use the information in these tables to predict the size distribution of the product after one minute in the mill. (Note Sj values in Table 12W2.1 are based on 1 minute grinding time.)... 

The slurry weight concentration in a ball mill is 65-80%. Excessive concentration will cause the particles to stick to the balls and will decrease the effectiveness of grinding. The ball null may then freeze and spill out its contents, causing costly downtime to empty the null. For this reason, the weight concentration should not be allowed to exceed 80%. 

You have seen polished stones of hematite, quartz, etc. These are obtained by tumbling in the same type of null— the particle size is just bigger. The biggest ball null is the seashore, where pebbles are eventually changed into sand. 

The use of ball nulls to assist solvent-free asymmetric organocatalytic processes is stih very rare. In 2006 Bohn and coworkers [59] reported the first examples of such apphcations. This technique was used in a prohne catalyzed aldol reaction between ketones and aromatic aldehydes. The asymmetric organocatalytic aldol reaction was very intensively studied since the pioneering work by list and Barbas in 2000/2001 [21]. In the vast majority of cases it was performed in different organic solvents (e.g., DMSO, DMF), but in recent years several eco-friendly solvent-free, or using water, protocols have been reported. Such reactions, avoiding the use of organic solvents, are especiaUy preferred in industrial-scale processes and the synthesis of pharmaceuticals. 

If the process has undergone primary, secondary, and tertiary crushing, a process of screening is undertaken to separate the very coarse from finer particles. The particles are then further reduced in size by milling in rod nulls with the addition of water. The still dilute slurry is transported to a ball mill where steel balls achieve further reduction in size. The mixture of slurry and steel balls undergoes a separation at the exit from the ball mill (by using the difference in momentum between the two materials). Slurry is then diverted into a pump box. which is connected to slurry pumps. The slurry is pumped to cyclones, where the coarse particles are further separated from the fine particles. 

Zhang Z, Yang J, Null Y, Wang B, Xu J (2005) CoP synthesis and lithiation by ball-milling for anode materials of hthium ion cells. Solid State Ion 176 693-697... 

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