Loading in 5 sec....

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

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

- 208 Views
- Uploaded on

Download Presentation
## PowerPoint Slideshow about ' Manganese oxide formation by heat treatment of MnCO 3 in air.' - manton

**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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

Manganese oxide formation by heat treatment of MnCO3 in air.

<500 C Reaction 1

MnCO3 + ½ O2MnO2+CO2

>500 C Reaction 2

2 MnCO3 + ½ O2Mn2O3 + 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?

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?

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

Δ illustrates Neck formation and coarsening.P

P illustrates Neck formation and coarsening.

σ=Patm + 2γ/r

P=Patm

r

Flat surface

Curved surface

ΔP=2γ/r

‘Master’ Equation of Thermodynamics illustrates Neck formation and coarsening.

For an isothermal process with no change in composition

Divide both sides by the number of atoms in the system=N

ΔP=2γ/r for inside a spherical particle.

Positive and Negative Curvature illustrates Neck formation and coarsening.

Corrugated Surface Example (2D)

vapor

ΔP=-γ/r

Negative Curvature

Atoms move from

high free energy to low.

solid

ΔP=γ/r

Positive Curvature

Two sphere model illustrates Neck formation and coarsening.

r2

r1

r

The neck has a negative curvature component (-1/ρ), acting to reduce the pressure relative to the spherical surface.

Download Presentation

Connecting to Server..