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Aem Lect7

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  • 1. Ball Milling Equipment http://www.pauloabbe.com/ Advanced Electronic Ceramics I (2004) Critical mill speed Gravity = centrifugal force mg = mRω 2 ω = (g/R)1/2 critical mill speed = (g/R)1/2 /2π (rotation/sec.) where g = gravitational coefficient R : mill radius Proper mill speed = 0.6 ~ 0.7 x critical mill speed Advanced Electronic Ceramics I (2004)
  • 2. Milling media: ball 1. The highest density for the highest kinetic energy at the impact (1/2mv2) 2. Cost 3. Wear resistance 4. Contamination from the ball Advanced Electronic Ceramics I (2004) Milling Good Bad Advanced Electronic Ceramics I (2004)
  • 3. Milling Advanced Electronic Ceramics I (2004) Mechanochemical synthesis: BaTiO3 1. The starting materials : BaO and TiO2 (particle size: 2-4 µm) 2. Powder mixture was loaded into a cylindrical vial (diameter and length: 40 mm), together with a milling ball 12.7 mm in diameter. 3. The vial was placed into a nitrogen glove box and sealed with an elastomer quot;Oquot;-ring. 4. High-energy shaker mill was operated at 900 rpm for 5, 10, and 15 h. TiO2 TiO2 TiO2 J. Xue, J. Wang, and D. Wan, J. Am. Ceram. Soc., 83(1), 232 (2000) Advanced Electronic Ceramics I (2004)
  • 4. Mechanochemical synthesis: Cr2O3 Na2Cr2O7+S ⇒ Cr2O3+Na2SO4 Experimental 1. anhydrous Na2Cr2O7 grains (99.6%, ~1 mm), S powder (98%, -100 mesh), 2. Na2SO4 granules (99+%, ~0.3 mm), and NaCl beads (99.8%, ~0.3 mm). were used as inert diluents and added to the starting powders. 3. The sealing of starting powders in a hardened steel vial under a high purity Ar gas atmosphere. 4. Milling 5. Heat treatments of the as-milled powder under vacuum in a fused silica tube for 1 h. 6. Removal of the salt by-product by washing 7. Drying in an oven (60°C) T. Tsuzuki and P. G. McCormick, Acta Materialia, 48(11), 2795 (2000) Advanced Electronic Ceramics I (2004) Mechanochemical synthesis: Cr2O3 Fig.TEM images of the powder heat-treated at: (a) 450°C; (b) 550°C; (c) 600°C. Fig. XRD patterns of the washed powders after heat treatment at: (a) 450°C; (b) 600°C. T. Tsuzuki and P. G. McCormick, Acta Materialia, 48(11), 2795 (2000) Advanced Electronic Ceramics I (2004)
  • 5. Mechanochemical synthesis: CeO2 CeCl3 + 3NaOH → Ce(OH)3 + 3NaCl Solid-state displacement reaction during milling Experimental 1. Anhydrous CeCl3(99.9% pure, 20 mesh) NaOH powders, NaCl diluents 2. The sealing of starting powders in a hardened steel vial under a high purity Ar gas atmosphere. 3. Milling 4. Removal of by-product, NaCl, by washing with de-ionized water 5. Drying in an oven (60°C) T. Tsuzuki and P. G. McCormick, J.Am.Ceram.Soc., 84(7), 1453 (2001) Advanced Electronic Ceramics I (2004) Mechanochemical synthesis: CeO2 Figure XRD patterns of the CeCl3 + 3NaOH powder mixture without NaCl diluent ((a) as-milled powder after combustion, (b) powder calcined at 500°C, and (c) powder washed after calcining). T. Tsuzuki and P. G. McCormick, J.Am.Ceram.Soc., 84(7), 1453 (2001) Advanced Electronic Ceramics I (2004)
  • 6. Planetary Ball Mill - Planet-like movement - Reduce milling time - employ for mechanical alloying* - size reduction to ~ 1µm Grinding vial and balls: agate, silicon nitride, sintered corundum, zirconia, chrome steel, Cr-Ni steel, tungsten carbide, and plastic polyamide. *Mechanical alloying (MA) is a solid-state powder processing technique involving repeated welding, fracturing, and rewelding of powder particles in a high- energy ball mill. Originally developed to produce oxide- dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. http://www.lavallab.com/ Advanced Electronic Ceramics I (2004) Attrition Mill The powder to be milled is placed in a stationary tank with the grinding media. This mixture is then agitated by a shaft with arms, rotating at a high speed of about 250 rpm - lifetime of blade is short - abrasion produces metal impurity C. Suryanarayana, Progress in http://www.netzschusa.com/Dry_Gri Materials Science, 46 (2001) 1- nding/Lab_PE075-PR1Satt.htm 184 Advanced Electronic Ceramics I (2004)
  • 7. Jet Mill Jet Fluid Energy Mill is designed for fine grinding of most industrial powders including abrasives, ceramics, glass, powder coatings, and toners. The particle on particle impaction allows for extremely hard materials to be pulverized economically. Incorporation of a centrifugal air classifier efficiently recycles oversize particles back to the pulverizing zone and produces consistent products in the size range of 90% less than 75 μm to 90% less than 5 μm. - Precise Product Top Size Control - Lab to Production Sizes - Narrow Product Size Distributions - Abrasion Resistant Linings - Independent Use of Classifier - Simple Design for Cleaning 1. Supersonic jet of particles shot at each other 2. Own grinding medium 3. High cost http://www.ccetech.thomasregister.com/olc/ccetech/opjetmil.htm Advanced Electronic Ceramics I (2004)

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