1 / 13

Manganese oxide formation by heat treatment of MnCO 3 in air.

Manganese oxide formation by heat treatment of MnCO 3 in air. <500 C Reaction 1. MnCO 3 + ½ O 2 MnO 2 +CO 2. >500 C Reaction 2. 2 MnCO 3 + ½ O 2 Mn 2 O 3 + 2 CO 2. Note that in reaction 1, there is a net increase

elvis-mccormick
Download Presentation

Manganese oxide formation by heat treatment of MnCO 3 in air.

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Manganese oxide formation by heat treatment of MnCO3 in air. <500 C Reaction 1 MnCO3 + ½ O2MnO2+CO2 >500 C Reaction 2 2 MnCO3 + ½ O2Mn2O3 + 2 CO2 Note that in reaction 1, there is a net increase Of ½ mole of gas for each mole of Mn, and for reaction 2 there is a net increase of ¾ of a mole of gas for each mole of Mn. What can you say about the entropy change in each reaction? How does this help explain the temperature dependence between the two reactions?

  2. As the manganese oxide particles form from the carbonate salt, they begin to grow together, or ‘sinter’. The figure below is a TEM micrograph of neck formation during the sintering of Mn2O3 particles. Neck Pore 0.2 um Neck Why do the necks get larger and the pores get smaller as the heat treat time and or temperature increases?

  3. Powder Processing and the Problem with Porosity The idea of stress concentration at a ‘pore’

  4. L Tsint T B A A powder + B powder Liquid Phase Sintering A+B When we heat a powder pack of A powder + B powder to Tsint at the overall composition shown on the phase diagram, liquid fills the pores between the A particles. Why does the liquid spread to fill the pores?

  5. Hot Isostatic Pressing Ductile metal envelop subjected to high gas pressure

  6. Sintering Kinetics (shrinkage)

  7. Sintering Kinetics (density)

  8. ΔP

  9. ΔP σ=Patm + 2γ/r P=Patm r Flat surface Curved surface

  10. Two sphere model r2 r1 r The neck has a negative curvature component (-1/ρ), acting to reduce the pressure relative to the spherical surface.

  11. Sintering of Nickel powder. The time lapse photography illustrates Neck formation and coarsening.

  12. How does the driving force for sintering of cylindrical particles differ from that for sintering of spherical particles? Why do the ends of the cylindrical particles blunt during sintering?

More Related