Download - Pourbaix Diagram Hendriyanto W
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Diagram PourbaixIron E-pH diagram
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Diagram Pourbaix
• Kegunaan:– Mengetahui reaksi yang terjadi secara
Termodinamika (korosi atau ekstraksi)– Mengetahui bentuk stabil dari logam pada kondisi
tertentu
• Kekurangan:– Dalam aplikasi dibidang korosi, tidak dapat
digunakan untuk memprediksi laju korosi yang terjadi. Hanya
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Diagram Pourbaix
• Nernst Eq. :aA + bB cC +dD
E = E0 - lnDimana: ln K = 2.303 log K RT/F = 0.0592 (T=25o)
RT[A]a [B]bnF[C]c [D]d
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Diagram Pourbaix
• Energi bebas gibbs:G = - nFE
∆G = RT ln K
G = Energi bebas Gibbsn = Jumlah elektron terlibatF = konstanta Faraday 96500E = Potensial
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Diagram Pourbaix
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Equation
pH tinggi
pH rendah
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Equation
• E = E0 – log
= 1
0.0592
2[H2 ][H+ ]2
[H2 ]
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Equation
pH tinggi
pH rendah
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Prinsipnya adalah
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Pourbaix diagram for iron-water system at 250C
1
4
3
2
5
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1. Fe2+ + 2e- Fe
E = E0 - log
E = - 0,44 + log
E = - 0,44 + 0,0296 log
nFRT
[Fe2+]1
RT 2F [Fe2+]
[Fe2+]
Back
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2. Fe3+ + e- Fe2+
•
Back
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3. 2Fe3+ + 3H2O Fe2O3 + 6H+
∆G = - 8420 J/mol
K =
log K = 6 log - 2 logLog K = - 6pH – 2 log
∆G = - RT ln KSo, log K =
Log K = 1,431,43 = - 6pH – 2log
pH = - 0,238 – 0,33 log
[H+]6
[Fe3+]2
[H+] [Fe3+]
[Fe3+]
- 8420 - RT
[Fe3+][Fe3+]Back
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4. Fe2O3 + 6H+ + 2e- 2Fe2+ + 3H2O
•
Back
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5. Fe3O4 + 8H+ + 2e- 3Fe2+ + 4H2O
•
Back