Milling rate

Figure 7.19 Effect of solids content in the milling of an alumina slurry on milling rate, expressed as cumulative mass percent fines. From J. S. Reed, Principles of Ceramics Processing, 2nd ed. Copyright 1995 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

Ion milling is a more widely applicable etching technique in that all materials may be sputtered away anisotropically. The ion milling rate typically does not vary more than a factor of 100. Redeposition of material from the substrate or surrounding fixtures can lead to undesirable cross-contamination. Hosaka et al. (39) used SIMS to show that redeposition of ionic impurities can occur during ion etching of SiO layers on Si when using a... 

Specimens that contain materials with very different ion-milling rates, such as metallic multilayers grown on silicon substrates, often tend to form bridges of material across the perforated area. Ion-milling at very low angles of incidence ( 1-2°) in a direction parallel to the interface can sometimes be used to overcome or at least alleviate these bridging problems. Finally, it should be noted that the use of a crystalline substrate such as silicon provides a convenient reference material for specimen orientation purposes in the TEM. Examination of the substrate EDP can be used to ensure that the substrate normal is aligned exactly perpendicular to the electron beam direction. The thin-film microstructure can then be easily determined. 

Crop Projection. To establish the mill-rated throughput, it is first necessary to have details of the projected crop over say a 10-year period depending on the planting program. The general practice is to consider the peak month crop at 12.5% of the annual crop and that the mill will operate at 20 hr per day for 25 days during the peak month. 

One important parameter contributing to different breakage mechanisms is solids concentration or density in the mill. This directly influences the number of particle-particle or particle-wall collisions and the force of those collisions. Particle density in the mill is controlled not only by feed rate to the mill, but also by mill residence time. Depending on the type of equipment and how it is operated, solids density in the mill can impact both the milling rate and its efficiency so understanding and control of this parameter are important for scale-up. 

Rotor speed Increasing tip speed increases milling rate and produces smaller particles. Typical ranges 10-50 m/sec ... 

Rotor/stator gap (gap width) Smaller gap increases shear forces, increases milling rate, and produces smaller particles. 

Rotor/stator design (number of teeth) Mainly affects milling rate, but can affect steady-state particle size achieved... 

Slurry density Higher solids concentration increases milling rate but does not typically affect steady-state particle size. 

Slurry density or solids concentration will affect milling efficiency and therefore cycle time. Generally speaking, the higher the slurry density, the faster the milling rate, although there is a practical limit to the solids concentration that can be milled without plugging or flow problems. 

Agitator speed Higher linear velocity at the agitator tip increases milling rate... 

Figure 4. Fine resist dot and magnetic column arrays before and after ion-milling for 5 min at 200 V (a) and (b)before ion milling, (c) and (d) after ion milling (milling rates 4.0 and 4.6 nm/s in resist and PtCo layer, respectively).

Daily milling Aimual cane processing Milling rate... 

Recently there has been a report of the use of Ar+ ion milling (500 eV) to open the bottom cap in the anodized alumina using a normal ion milling machine. The rate of milling can be controlled by the ion beam current density (generally <1 mA cm ) and also the incident angle. The nominal milling rate is 100 A min at normal incidence for a current density of 1 mA cm [12]. 

The milling rates observed to date demonstrate that it is possible to obtain increased production rates for SCF-produced products. The milling rates for SCF-produced products are three to four times faster with 35% less energy requirements than that observed with the same materials produced from conventional methods. SCF-produced products have a foam-like character that, when milled, yield a finer particle size distribution for the finished product than that achieved via flake milling of conventional, melt-mixed material. 

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