Kinetic for Corrosion

[snjaykdubey]

Dear Sir,

I need to develop a kinetic model in phreeqc  in order to calculate the corrosion rate for ferrous.
Whenever i try to run the simulation and try to plot the graph there is no change in concentration gradient of Fe.

Problem Statement : To determine the concentration of Fe during the corrosion until it form a magnetite. Graph : Fe conc vs Time


I hope if you can tell where i am making mistake?

SOLUTION 1

units   mol/L
pH      7.0
temp    25

Na 1.69e-1 #From BoundaryWater
Cl 1.60e-1 #From BoundaryWater


RATES
Corrosion


-start
rem PARM(1) = Time (s)
rem PARM(2) = Temperature (K)

10  Ea = 56e3 #JMol-1
20  Ec = 0    #JMol-1
30  ta = 1.578e7  #sec
40  MD = 7.87  #gm/cc
50  Atwt = 55.845 #IronAtomicWt
60  Ka = 1.58548e-12 #units cm/sec
70  Tref = 30+273   #In Kelvin
80  Kc = 1.585489e-14 #units cm/sec     
90  R=8.3144621 #JK−1mol−1
100 SA = 90300 #Surafce Area cm2


110 if (m <= 0) then goto 160
120 rate = -Ka*EXP(-PARM(1)/ta)*EXP[(-Ea/R)*(1/PARM(2) -1/Tref)]-Kc*1*EXP[(-Ec/R)*(1/PARM(2) -1/Tref)] #kinetic rate in cm/sec
130 rate = rate*(MD/Atwt) #kinetic rate in mol/cm2.s
140 rate = rate*SA   #kinetic rate in mol/s
150 moles  = rate*TIME
160 SAVE moles

-end

KINETICS

Corrosion

-m  0.140 
-formula Fe -1  Fe+2  1  e-  2
-parms 7.776e6 298
-step 7.776e6 in 100 steps
-tol 1e-15
INCREMENTAL_REACTIONS true

EQUILIBRIUM_PHASES
Magnetite

USER_GRAPH
-heading time Fe; -axis_titles days mol/L
10 graph_x total_time/86400
20 graph_y TOT("Fe")
-end

END

awaiting for your reply,

kind regards,
Sanjay Dubey

[dlparkhurst]

Your formula adds Fe and removes Fe, for a net change of zero.

The formula should be
-formula Fe