Mimic alkoxide method: Well-sinterable nano-crystalline powder
    (Motivation)
    Aqueous precipitation:
    nanocrystal...
Example: Mimic Alkoxide Method
     Ex) CeO2
     - at high temperature
       4CeO2 → 2Ce2O3 + O2 (g)
      : retard the ...
Hydrothermal synthesis for MLCC
     (Strong points of Hydrothermal Synthesis in MLCC)
     1. The ability to produce soli...
Hydrothermal conversion from TiO2 into BaTiO3
     1.   TiCl4 (aq.) + alcohol + HPC (steric stabilizer)
     2.   Uniform ...
Hydrothermal
                                                            BaTiO3                          SrTiO3
          ...
Spray Pyrolysis
     What is Ultrasonic Spray Pyrolysis?
     A powder preparation process through the thermal decompositi...
Spray Pyrolysis: Concentration Effect
                                   TiO2/SnO2
                                   from...
Spray Pyrolysis: Microstructure 2
                                    Pb(Zr,Ti)O3 prepared from aqueous acetate-base
     ...
Composition analysis in one sphere




           1234




        J.-H.Lee and S.-J.Park, J.Mater.Sci.:Materials in Elect...
Hydrolysis: metal alkoxide
     Preparation of metal alkoxide
                   HgCl2
                                   ...
Hydrolysis of metal alkoxide: example


     Multi oxide
     1. The mixing between
        Ti(OC2H5)4 in EtOH
        Ta(...
Hydrolysis: example (ZrO2)




                                                                   pH decrease
            ...
Freeze Drying

                                               a. Solution droplets are sprayed
                           ...
Powders from Vapor-Phase Reactions




                                                                           Temperat...
Powders from Vapor-Phase Reactions

                                                         Log Kp = - ∆Go /(2.303RT)

  ...
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Aem Lect4

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Aem Lect4

  1. 1. Mimic alkoxide method: Well-sinterable nano-crystalline powder (Motivation) Aqueous precipitation: nanocrystalline but hard agglomeration of ultra-fine particles - Powder calcined at 600oC - primary particle: ~ 15nm - secondary particle: ~50nm - ~37 primary particle within the secondary particle (Suggest Mimic alkoxide method) a. Ce(NO3)3•6H2O + 1-butanol : 0.1M b. DEA(diethylamine) (C2H5)2NH + 1-butanol : 1.0M c. Cerium source solution was dripped into precipitant solution(DEA) (C2H5)2NH + H2O → (C2H5)2NH2+ + OH- : OH - ions from the hydrolysis of molecular water of the cerium salt : involves minimum amount of water (better dispersion) J. -G. Li, T. Ikegami, J. -H. Lee, T. Mori, Acta mater. 49, 419-426 (2001) Advanced Electronic Ceramics I (2004) Example: Mimic Alkoxide method - maximize the driving force for the sintering (excess free energy of surface) - reduce the sintering temperature - provide fast densification kinetics (Herring’s scaling law: t2 =λn t1) Decrease T for full density Aggregate problem J. -G. Li, T. Ikegami, J. -H. Lee, T. Mori, Acta mater. 49, 419-426 (2001) Advanced Electronic Ceramics I (2004)
  2. 2. Example: Mimic Alkoxide Method Ex) CeO2 - at high temperature 4CeO2 → 2Ce2O3 + O2 (g) : retard the densification - Low-temperature sintering is desirable! - full density at 1000oC ( ~ 0.42 Tm) J. -G. Li, T. Ikegami, J. -H. Lee, T. Mori, Acta mater. 49, 419-426 (2001) Advanced Electronic Ceramics I (2004) Hydrothermal synthesis (Definition) The process using hot and pressurized water for precipitation of oxides (Driving force) The difference in solubility of the oxide phase from the least soluble precursor or intermediate A(OH) (s) + B(OH) (s)dissolution A(OH) (aq.) + B(OH) (aq.)PrecipitationABO3 (Characteristics) 1. Crystalline, anhydrous ceramic powder 2. Temperature : 100~370oC 3. Pressure : 6 ~ 15MPa 4. Do not need calcination and milling (avoid the contamination during the processing) 5. Employ relatively inexpensive raw materials From W.J.Dawson, Am.Ceram.Soc.Bull., 67(10), 1673 (1988) Advanced Electronic Ceramics I (2004)
  3. 3. Hydrothermal synthesis for MLCC (Strong points of Hydrothermal Synthesis in MLCC) 1. The ability to produce solid-solution particles of controlled size (can attain complex composition) cf) in poorly prepared co-precipitation - did not result solid solution - requires the calcination (and thereby ball milling) - large particle size ( d<1 µm is difficult by mall milling) - result higher sintering temperature (energy-consuming process) - result the coarse grain size (harmful for size reduction) 2. Well sinterable and small particles without any calcination - offers the energy-saving process to fabricate the integrated MLCC 3. Doping during the powder preparation is possible From W.J.Dawson, Am.Ceram.Soc.Bull., 67(10), 1673 (1988) Advanced Electronic Ceramics I (2004) Hydrothermal synthesis: BaTiO3 1. TiCl4 (aq.) + NH4OH → Ti-hydroxide. 2. Washing till No Cl- ions are detected. 3. Mixed with Ba(OH)2•6H2O (Ba/Ti = 1.5 in atomic ratio, concentration=0.5M ) 4. Treatment in 200oC for 5h in autoclave K.Abe and S. Matumoto, Ceramic Tracsaction, Vol.22, p.15 (1987) Advanced Electronic Ceramics I (2004)
  4. 4. Hydrothermal conversion from TiO2 into BaTiO3 1. TiCl4 (aq.) + alcohol + HPC (steric stabilizer) 2. Uniform heating using microwave oven formation of spherical gel 3. Adding NH4OH 4. Washing and separation using centrifugal J. Y. Choi, J. H. Kim and D. K. Kim, J. Am. Ceram. Soc., 81(5), 1353 (1998) Advanced Electronic Ceramics I (2004) Hydrothermal conversion from TiO2 into BaTiO3 Lead acetate trihydrate Barium hydroxide octahydrate Strontium hydroxide octahydrate J. Y. Choi, J. H. Kim and D. K. Kim, J. Am. Ceram. Soc., 81(5), 1353 (1998) Advanced Electronic Ceramics I (2004)
  5. 5. Hydrothermal BaTiO3 SrTiO3 conversion from TiO2 into BaTiO3 Spherical morphology TiO2 (from precursor TiO2 or ZrO2) PbZrO3 PbTiO3 ZrO2 Crystallinity and phase BZT (from hydrothermal treatment) PZT ZrTiO4 J. Y. Choi, J. H. Kim and D. K. Kim, J. Am. Ceram. Soc., 81(5), 1353 (1998) Advanced Electronic Ceramics I (2004) Hydrothermal synthesis Advanced Electronic Ceramics I (2004)
  6. 6. Spray Pyrolysis What is Ultrasonic Spray Pyrolysis? A powder preparation process through the thermal decomposition of the droplet generated by ultrasonic transducion. The Advantage of Spray Pyrolysis Process. 1. spherical morphology. 2. narrow particle size distribution. 3. easy preparation of the powder with the complex composition. 4. relatively homogeneous composition. : compositional heterogeneity is restricted within a spherical secondary powder. 5. Easy manipulation of particle size 6. No calcination 7. Successive processing The Shortcoming of Spray Pyrolysis Process. 1. Energy-consuming process. 2. makes hollow structures frequently. [Jong-Heun Lee, Ph.D. Thesis, Seoul National University, 1993] Advanced Electronic Ceramics I (2004) Spray Pyrolysis: Schematic 8πγ 1/3 Ddroplet = 0.34 ρf2 Ddroplet : droplet size γ : surface tension of solution ρ: density of solution f: resonance frequency for the ultrasonic transducer (1.67 MHz) - typical droplet size for aqueous solution ranges ~ 3µm Advanced Electronic Ceramics I (2004)
  7. 7. Spray Pyrolysis: Concentration Effect TiO2/SnO2 from TiCl4(aq.) +SnCl4(aq.) at 800oC Size manipulation comes from the mechanism, “one particle from one droplet” [Jong-Heun Lee, Ph.D. Thesis, Seoul National University, 1993] Advanced Electronic Ceramics I (2004) Spray Pyrolysis: Microstructure 1 TiO2 prepared from 0.19M TiCl4 aqueous solution at 600oC. [J.-H.Lee, H.-J.Cho, and S.-J.Park, Ceramic Transaction Vol.22, pp39-44(1991)] SnO2 prepared from 0.2M SnCl4 aqueous solution at 800oC. [J.-H.Lee and S.-J.Park, J.Am.Ceram.Soc., 76(3), 777-780, (1993)] TiO2-SnO2 prepared from 0.2M TiCl4-SnCl4 aqueous solution at 800oC. [J.-H.Lee and S.-J.Park, J.Mater.Sci.:Materials in Electronics, 4, 254-258 (1993)] Advanced Electronic Ceramics I (2004)
  8. 8. Spray Pyrolysis: Microstructure 2 Pb(Zr,Ti)O3 prepared from aqueous acetate-base solution at 700oC. [H.-B.Kim, J.-H.Lee, and S.-J.Park, J. Mater. Sci. :Materials in Electronics, 6, 84-89 (1995)] Zr0.8Sn0.2TiO4 prepared from ZrO(CH3COO)2- TiCl4 -SnCl4 aqueous solution at 800oC. [S.-Y.Cho, J.-H.Lee, S.-J.Park, J.Mater.Sci., 30, 3274-3278 (1995)] Advanced Electronic Ceramics I (2004) Observation of the inner part of sphere epoxy particle Dimpling and ion-thinning Fig. Inner structure of SnO2 spheres prepared at 800oC from 0.2M SnCl4 solution. Ring patterns of (C) and (D) were obtained in the area of inner and crust(see arrow) layer of the secondary sphere, respectively. J.-H.Lee and S.-J.Park, J.Am.Ceram.Soc., 76(3), 777-780, (1993) Advanced Electronic Ceramics I (2004)
  9. 9. Composition analysis in one sphere 1234 J.-H.Lee and S.-J.Park, J.Mater.Sci.:Materials in Electronics, 4, 254-258 (1993) Advanced Electronic Ceramics I (2004) Spray Pyrolysis: Application Easy manipulation of particle size : manipulation of pore and/or grain size (ceramic humidity sensor, ZnO varistor, and the control of the electric properties related to the grain boundary) : Sintering study Narrow size distribution, spherical and good flowability : Screen printing of luminescent materials in display applications : Controlled compaction Advanced Electronic Ceramics I (2004)
  10. 10. Hydrolysis: metal alkoxide Preparation of metal alkoxide HgCl2 Al(OC3H7)3 + 3/2H2↑ Al + 3C3H7OH ∆ HgI Mg(OC2H5)2 + 2H2↑ Mg + 2C2H5OH ∆ 2 SiCl4 + 4C2H5OH Si(OC2H5)4 + 4HCl↑ TiCl4 + 4ROH Ti(OR)4 + 4NH4Cl Hydrolysis of metal alkoxide Ti(OCnH2n+1)4 + 2H2O → TiO2 + 4(CnH2n+1)OH Advanced Electronic Ceramics I (2004) Hydrolysis of metal alkoxide: example Single oxide 1. 0.1-0.2M Ti(iOC3H7)4 : titanium tetraisopropoxide in isopropanol, + the mixture between water and isopropanol (0.3-1.5M water) 2. 0.1-0.2M Ti(OC2H5)4 : titanium tetraethoxide in ethanol, + the mixture between water and ethanol (0.3-1.5M water) - the molar ratio (water/alcohol > 0.3) - yields mono-disperse, spherical titanium hydroxide From isopropoxide From ethoxide 0.07 - 0.3 µm 0.3 - 0.6 µm Avg. particle size range Shape equiaxed spherical Substructures multinuclear particles mostly singlet E.A.Barringer and H.K.Bowen, J.Am.Ceram.Soc., Dec., C199, (1982) Advanced Electronic Ceramics I (2004)
  11. 11. Hydrolysis of metal alkoxide: example Multi oxide 1. The mixing between Ti(OC2H5)4 in EtOH Ta(OC2H5)5 in EtOH Nb(OC2H5)5 in EtOH 2. Adding the mixture between water and ethanol 3. Hydrolysis reaction in N2 4. Washing with de-ionized water 5. Re-dispersion in a dilute aqueous solution of SrCl2 6. Adding aqueous solution of (NH4)2CO3 to precipitate the Sr on the surface of TiO2 surface (B. Fegley, Jr., E.A.Barringer and H.K.Bowen, J.Am.Ceram.Soc., June, C113 (1984) Advanced Electronic Ceramics I (2004) Hydrolysis Stirring Thermocouple Cooling water Source solution Heating mantle Advanced Electronic Ceramics I (2004)
  12. 12. Hydrolysis: example (ZrO2) pH decrease ZrOCl2 + (n+1) H2O → ZrO2•nH2O + 2H+ + 2Cl- K.Matsui and M.Ohagai, J.Ceram.Soc.Jpn., 106(9), 883-887 (1998) Advanced Electronic Ceramics I (2004) Hydrolysis: example (ZrO2) Control parameter 1. Starting and ending pH - adding NH4OH or HCl * the measurement of highly acidic oH - measure the pH of the diluted solution and calculate the pH 2. The [ZrO2+] in the clear solution as a function of reaction time 3. The temperature of solution 4. Boiling time K.Matsui and M.Ohagai, J.Am.Ceram.Soc., 80(8),1949-56 (1997) Advanced Electronic Ceramics I (2004)
  13. 13. Freeze Drying a. Solution droplets are sprayed into a bath of immiscible liquid (hexane) or directly into liquid N2 b. The frozen product is skimmed from the top of the refrigerant (the diameter of the frozen beads: 0.01 ~ 0.5 mm) c. Frozen sample is introduced into a vacuum chamber (P:~1torr) ⇒ sublimation of solvent 4. Calcination J. S. Reed, “Principles of Ceramic Processings,” Advanced Electronic Ceramics I (2004) Powders from Vapor-Phase Reactions 1. Sub-micron size (good) 2. Well-dispersed particles (good) 3. Narrow particle-size distribution (good) 4. Formation of non-oxide powder due to easy control of atmosphere 5. Requires large volume of gases for reaction (disadvantage) 6. Energy-consuming process(heat) (disadvantage) 7. Requires relatively expensive equipment for reaction (disadvantage) 8. Restriction in the choice of reactor materials (to avoid corrosion by reactant gases) (ex.) 1. TiCl4(g) + 2H2O(g) → TiO2(s) + 4HCl(g) 2. SiCl4(g) + 4NH3(g) → Si3N4(s) + 12HCl(g) 3. Thermal decomposition of (CH3)2SiCl2 and CH3SiH5 Advanced Electronic Ceramics I (2004)
  14. 14. Powders from Vapor-Phase Reactions Temperature(K) Japanese Ceramics Society, Ceramic Processing, Powder Preparation and Forming, (1984) Advanced Electronic Ceramics I (2004) Powders from Vapor-Phase Reactions 44000x4.2/(2.303X8.3144X773) Log Kp = - ∆Go /(2.303RT) Japanese Ceramics Society, Ceramic Processing, Powder Preparation and Forming, (1984) Advanced Electronic Ceramics I (2004)
  15. 15. Powders from Vapor-Phase Reactions Log Kp = - ∆Go /(2.303RT) Powder Powder formation at Log Kp> 3 formation (homogeneous nucleation) The formation of thin film, powder, Thin film, Powder, and fiber on substrate at 2>Log Kp> 0 and fiber on substrate (heterogeneous nucleation) Powder Thin film fiber Japanese Ceramics Society, Ceramic Processing, Powder Preparation and Forming, (1984) Advanced Electronic Ceramics I (2004)

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