Volume 6 Preprint 22
Influence of Non-Isothermity on the General and Local Corrosion of Copper and Iron
S.A. Kaluzhina, A.V. Malygin, I.V. Sieber, V.I. Vigdorovitch
Keywords: Copper, iron, non-isothermal systems, sulphate, chloride, hydrocarbonate solutions, general and local corrosion
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INFLUENCE OF NON-ISOTHERMITY ON THE
AND LOCAL CORROSION OF COPPER AND IRON
S.A. Kaluzhina1, A.V. Malygin2, I.V. Sieber3, V.I. Vigdorovitch4
Voronezh State University, Dept. of Phys. Chem. University Sq.1,
394006 Voronezh, Russia, email@example.com
FGUP NIISK Voronezh Branch, Mendeleev St. 3b, 394014,
Voronezh, Russia, firstname.lastname@example.org
University of Erlangen-Nurnberg, Dept. for Mat. Sci. LKO.
Martensstr. 7. D-91058 Erlangen, Germany,
Derzhavin State University, Dept. of Analyt. Chem. & Ecol.
International St.33, 392622 Tambov, Russia, email@example.com
The effect of normal and tangential temperature gradients on
copper’s and iron’s behavior under conditions of active dissolution,
passive state and local depassivation was investigated. It was
established that the heat flux directed from metal to solution can:
a) to increase corrosion rate (Cu/NaCl); b) to reduce it (Fe/H2SO4);
c) to change the destruction’s nature (transition from passive state
to pit corrosion - Cu/NaHCO3 + NaCl, or transition from pit to spot
corrosion - Cu/NaHCO3 + Na2SO4). The appearance of tangential
temperature gradient on metal flat plate contacting with flowing
electrolyte is accompanying by the redistribution of destruction in
most heated (Fe/H2SO4; Cu/NaCl) or most cold (Fe/NaOH) zones
of the metal. Moreover nature of non-isothermal corroding surface
destruction and general metal losses depends not only from
temperature difference in system but also from change of
temperature distribution law along metal. The discussion of the
analyzed phenomenons reason was carried out.
Key words: Copper, iron, non-isothermal systems, sulphate,
chloride, hydrocarbonate solutions, general and local corrosion.
The heat-exchangers exploitation is accompanying by appearance
the tangential (along metal surface ) and normal ( on interface
metal/solution) temperature gradients [1-4]. In these conditions the
general corrosion process is including two types of damage:
thermogalvanic (TG) corrosion [1,2], connected with thermoelectric
effects, and corrosion initiated by thermal flux from metal to
aggressive liquid [3,4]. Both type of corrosion differ by specific
features and influence on a general metal losses and development
of local destruction. The detail analysis of these phenomenons in
corrosion active, passive metals and metals undergoing local
depassivation was carried out in the present work
Two types of complex plants, which permit to solve this problem,
are used: 1- a plant with non-isothermal plate and 2 – a plant with
heat-transferring rotation disk electrode[2,4,5].
The researches in conditions of tangential temperature gradient
were carried out on the plant type 1[2,5].The design of the plant
permits to measure simultaneously temperature distribution,
potentials and corrosion currents along metal surface. The basic
component of the plant is an electrolytic cell. The electrodes under
investigation (6 of them in the experiment) are cylinder-shaped
with working surface 1×10-4 m2 are pressed into the bottom of the
cell with electrode spacing 1×10-3m. The temperature of each
electrode is set by the out contact heating (soldering iron type) and
controlled by means of the special temperature meter device with
indicator transistor. The technique of electrode heating makes it
possible to obtain any temperature within the range of 30-90oC.
To provide laminar flux of electrolyte by the electrodes surface the
latter are located in the center of the cell bottom at the distance
twice as large as their common horizontal size. The above
described location of electrodes allows to consider the system of
different temperature gradient streamlined by the laminar flux of
The thermal and TG effects were estimated with help of special
electric and commutation transistor schemes permitting to
determine the distribution of temperature, potentials and corrosion
currents along non-isothermal surface with absence and presence
of the electric contact between it’s areas. The experiments were
carried out in the study of the TG corrosion of metals, contacting
with flowing electrolyte (v=27×10-4 m/s) in the temperature interval
20-70oC using of the different physic-chemical methods.
The influence of normal temperature gradient on electrochemical
and corrosion behavior of metals is studied on the original plant
type 2. The plant is made up of four blocks: 1 – electrode system;
2 – electrolytic cell; 3 – electronic control; 4 – motor speed control
The investigated non-isothermal systems
Systems with normal temperature gradient
0,05 M H2SO4
0,5 M NaCl
0,1 M NaHCO3 + 0,01 M NaCl
0,1 M NaHCO3 + 0,01 M
Systems with tangential temperature gradient
0,005 M H2SO4 + 0,045 M
0,1 M NaOH
0,5 M NaCl
The major element of the plant is a cylinder-shaped electrode
(D=5×10-3 m). From the inner side a hole is drilled for
thermoresistor which is placed at the distance of 1×10-3m from
boundary dividing the phases and used for control the temperature
on the disk surface. A regulated soldering iron-type heater heats
electrode. Control block compresses devices for: 1 – electrode
temperature control; 2 – electrode heater control; 3 – polarization;
4 – cell temperature regulation. The latter is a thermostatic glass
with capacity 1×10-3 m3. Hydrodynamic conditions in the system
are set by motor speed control block. The number of revolutions is
controlled by a specially calibrated voltmeter and may deviate
within the range of 120-2500 rpm.
The comparative data were received on the thermal equilibrium
metal with electrolyte (TEE) and on heat-transferring (HTE)
electrodes. Experiments were carried out at temperature ranging
from 20 to 80oC and positive thermal fluxes (PTF) (directed from
metal to solution) 14,0-56,8 kWt/m2 with using the complex physicchemical methods. The working electrode was an iron or copper.
The auxiliary electrode was a platinum spiral or grid. All the
electrode potentials were measured using saturated silver/silverchloride reference electrode held at 25oC, but all potentials were
reported versus the normal hydrogen scale (NHE).
RESULTS AND DISCUSSION
SYSTEMS WITH NORMAL TEMPERATURE GRADIENT
The detail researches were carried out in the systems where 1) the
active dissoluting metal corrodes with kinetic (Fe/H2SO4) or
diffusion (Cu/NaCl) control and 2) the passive metal undergoes of
local corrosion (LC) (Cu/NaHCO3+NaCl; Cu/NaHCO3+Na2SO4).
The experimental results have shown that at all investigated
systems heat transfer essentially influences as the general metal
corrosion stability as it’s ability to local destruction without
dependence from the nature of limiting process’s stage. Hence the
observed effects are differing under the system’s nature influence.
Thus, PTF can be considered as the method of corrosion
protection for system Fe/H2SO4 (Fig.1) where the free corrosion
rate HTE decreases in 1,5-1,7 times comparatively with TEE
having the corresponding temperature. The interpretation of this
effect was obtained at the series additional researches of iron’s
corrosion-electrochemical behavior under varying pH, sulphateions concentration, hydrodynamic and thermic conditions.
According to the experimental results in the analyzed system
Fe/H2SO4 corrosion process taking place with mixed oxygenhydrogen depolarization with the participation OH- and SO42--ions
in anodic reaction . PHF 1) reduces general rate of process
under parallel retarding of anodic and cathodic reactions at the
expense of decreasing temperature of the reaction’s zone and
change of the adsorption’s kinetic on the interface; 2) influences
the kinetic order of anodic process in connection with change of
adsorption properties of a surface; 3) changers the ratio of oxygen
and hydrogen components in cathodic process for the benefit of
the first because of intensive convective solution’s stirring in nearelectrode’s zone and oxygen thermodiffusion from the solution’s
volume to the metal surface.
The opposite effect of heat flux was established in system Cu/NaCl
where free corrosion rate for HTE exceeds corrosion rate for TEE
(with corresponding surface temperature) in 1,5-2,0 times (Fig. 1).
This effect have been stipulated by the parallel accelerating anodic
and cathodic reactions. According to the temperature-kinetic
analysis data copper corrosion passes with oxygen depolarization
under participation Cl--ions in anodic reaction . Moreover in the
both electrochemical reactions are taking place the diffusion limits.
It is necessary to take into account the following facts – change
Fig.1. The temperature dependence of the rates of the free
corrosion (a,b) and the local corrosion (c,d) of copper (a,c,d) in
0,5MNaCl (a), 0,1MNaHCO3 +0,01M Na2SO4 (c), 0,1MNaHCO3 +
of iron in 0,05MH2SO4 (b). 1-TEE; 2-HTE.
anodic product’s nature from CuCl to [CuCl2]- under temperature
rising TEE from 20 to 80oC and the stimulating PTF action not
only on diffusion stages but on kinetic stages. This effect can be
connected with change of composition and properties of the oxidesalt layer presenting on surface of heat electrode contacting with
. The presence of this films on copper surface
is confirmed by the established regularities of the cathodic process
oxygen reduce in which 1) role of kinetic limits is significant; 2)
Tafel coefficient value (bk = 0,20 B) is excessive; 3)
voltamperogramms measuring in direct and opposite directions
have the hysteresis. PTF, intensifying the oxygen transport from
solution to metal, increases the oxides ratio in oxide-salt film with
parallel raising it’s defectivity. Most essential acceleration of
cathodic process under PTF action was established in regime of
limit diffusion current which was increased in 2,1-2,8 times.
Because in most practical cases (75%) corrosion heat-transferring
surfaces have local character it was very interesting to estimate
the PTF role at these conditions. Two systems differing by the
mechanism of local corrosion (LC) were selected for investigation
– Cu/NaHCO3 + NaCl and Cu/NaHCO3 + Na2SO4 where copper is
undergoing LC at zone potentials 0,500-0,800 V (NHE) more
positive than steady state potential. The microscopic and
chronoamperometric data have shown that at 20oC the copper
surface destruction can be determined as spot corrosion
(electrolytes with Cl- -ions) or pit corrosion (solutions with SO4 2-ions) in dependence from ions activators nature. In addition the
character of temperature influence in this systems is essentially
differing. If the temperature of TEE is increased up to 80oC the
process copper LC completely ceases in the solution with the Cl-ions additives (Fig.1). However under PTF conditions this effect
didn’t observe and spot corrosion metal surface transfers to pit
corrosion (Fig.1). On the contrary, in the bicarbonate-sulphate
solutions the temperature raising TEE and HTE is accompanying
by the change copper surface destruction from pit corrosion to spot
corrosion. But under corresponding surface temperature the PTF
regime also reduces the LC rate at that case (Fig. 1).
The received inadequate effect of thermal conditions on the
susceptibility of copper to LC in the investigated electrolytes
stipulated by the different mechanism of pit initiation process [4,7]
and the different nature the particle-activators – in bicarbonatechloride solutions it is CuCl, in bicarbonate-sulphate it is SO42- –
ions. In connection with this the process of copper LC in the first
case starts with the primary formation of the nuclear of
crystallization CuCl on passive oxide-hydroxide film, which growing
to the metal surface, causes its local destruction. In the second
case, the ions-activators penetrate through the defects of oxidehydroxide film to the metal/oxide interface and interacts with metal
or with adsorption compound on its surface there. The increase of
the TEE temperature up to 80oC suppresses the development of
the LC in bicarbonate-chloride mediums as a result of the
intensification of the dissolving action of the heated electrolyte.
The contact of oxidized copper with a cold solution under PTF
condition promotes the formation of the nuclear of crystallization
CuCl critical sizes on passive film surface, that stimulates the
development of the LC. In solutions with SO42- – ions additives the
concentration of the ions-activators does not change with the
increase of the temperature, but its activity grows. This together
with the increase of the passive layers defects results in the strong
etching of the metal surface. On the HTE the main role is playing
the last factor and the LC intensity decreases in comparison with
TEE at the appropriate surface temperature.
Thus the established inadequate action of temperature and nonisothermity in investigated systems is permitting to estimate the
thermic factor as additional criteria for identification of general and
local corrosion mechanism.
SYSTEMS WITH TANGENTIAL TEMPERATURE GRADIENT
The model with non-isothermal plate is permitting to program the
different temperature distribution along metal surface. At this case
temperature gradient’s variation can be by two methods: 1) by the
changing of plate’s ends temperature under linear distribution of
temperature along metal surface and 2) under the fixed the
temperature difference in system by the varying the law of
temperature distribution along metal surface. The second method
was selected for present work under the estimation of TG effects
role in general corrosion damage of iron in acid sulphate and
alkaline solutions and of copper in neutral chloride electrolytes.
The comparative data were received under linear (LTD), parabolic
(PTD) and exponential (ETD) temperature distribution. (Fig. 2 )
Earlier it was shown that at the all investigated systems tangential
temperature gradient due to potential gradient (dE/dl) providing of
TG corrosion development. Under this the temperature increase
induces the linear change of steady state potential but the value
and sign dE/dT essentially depends from the metal nature and the
solution’s composition. dE/dT = -1,6×10-3 (Fe/H2SO4), -0,8×10-3
(Cu/NaCl) and +2,0×10-3 V/deg (Fe/NaOH).Thus at zone of
variable temperature at the first two cases (active metals) had to
act TG elements with the heat anodes but on the passive iron case
had to act TG elements with the cold anodes. The results of the
present research have shown (Fig.2) that the distribution of steady
state potentials along plate from iron and copper in analyzed
electrolytes is reproducing of the corresponding temperature
distribution. According it under all thermic regimes the steady state
potentials of iron in acid sulphate solution and copper in neutral
chloride solution is displaced to the negative side in direction from
cold to heat end of the plate and consequently the heat areas have
to fulfill the anodic function under thermoelectric contacts
conditions. The passive iron in alkaline solution demonstrates
another behavior – it’s steady state potential is displaced to
positive direction at temperature increase and in the thermoelectric
contact zone had to work TG elements with the cold anodes.
Fig.2.Distribution of the temperature (a) and steady state potential
(b,c) along the copper (b) and iron (c) under parabolic (1,1’), linear
(2,2’), and exponential (3,3’) laws. Solutions- 0,5MNaCl (b);
0,005MH2SO4 +0,45MNa2SO4 (c –1,2,3); 0,1MNaOH (c-1’, 2’, 3’)
In addition the changing of law temperature distribution produces
the gradient temperature changing. Thus under LTD temperature
gradient remains constant for all non-isothermal plate and under
PTD it decreases from cold end to heat end of plate (at 10,0 time
for copper, at 3,2 time for active iron and at 5,0 time for passive
iron) but under ETD it increases at that direction (at 6,7; 1,7 and
3,5 times consequently for enumerated above systems. It’s
naturally to assume that this effect has to be reflected at the
character of non-isothermal metal surface destruction. For
confirming this supposition the additional experiments and
calculations were carried out [2, 5]. The obtained results have
shown that a location of a point of a polarity inversion (lo) (in which
electrode potential coincides with a mixed potential of shortcircuited system with tangential temperature gradient (E*) and
which divides non-isothermal metal plate on anodic and cathodic
zones  at all investigated systems is displacing to the heat end
of plate direction under transfer from PTD to LTD and ETD. Thus
only under PTD TG corrosion of active metals (Fe/H2SO4;
Cu/NaCl) passes in conditions of commensurable squares of
anodic (Sa) and cathodic (Sc) zones (Fig. 3). For LTD and ETD the
most part of non-isothermal plate is situating under cathode
protection and the summary square of cathodic zones exceeds the
anode’s square at 1,9 (LTD); 4,5 (ETD) – Cu/NaCl and at
2,1(LTD); 5,0 (ETD) – Fe/H2SO4.
The passive iron’s TG behavior in alkaline solutions, where the
steady state potential of metal linearly shifts to the region of
Fig.3. Corrosion destruction profile of the non-isothermal plate from
copper in 0,5M NaCl (a,b,c) and iron in 0,005MH2SO4 + O,045M
Na2SO4 (d,e,f) and in 0,1MNaOH (g, h,i) under the free corrosion
(1) and TG corrosion (2) conditions. (a, d, g – LTD, b, e, h – PTD,
c, f, i –ETD).
differs from iron’s TG behavior in acid electrolyte. It results the
appearance TG elements with cold anodes in the thermoelectric
contact zone [2,5] and thus thermal and TG effects have the
opposite direction (Fig. 3). The TG effects predominant role due to
the redistribution of destruction along non-isothermal surface with
it’s localization on cold sites under final accounting. In addition at
line PTD→LTD→ETD the square of heat cathodic zone is
decreasing. For example, relation Sc/Sa=2,0 ( PTD); 7,3 (LTD) and
Obviously, that described change of the corrosion damage profile
of the investigated metal’s non-isothermal plate is reflected on the
general mass losses under thermoelectric contact conditions. In
addition the important role plays as the nature of system so the
temperature distribution law. Thus the development of TG
corrosion on copper almost does not change the general losses
under PTD, increases it at 3,0 times under LTD and decreases at
3,0 times under ETD. The behavior of active and passive iron is
similar under LTD – TG corrosion causes the common increasing
of mass losses in 3,2 and 12,6 times respectively. However under
the two another laws of temperature distribution for active and
passive metal was observed the opposite effects. Thus under ETD
TG corrosion does not influence on general mass losses of active
iron but sharply at 15,0 times increases it on passive metal. At
PTD TG corrosion causes the decrease of general mass losses in
1,9 times for iron in alkaline solution under parallel strengthening of
dangerous character of destruction, localized on small cold anode
region. Under analogic conditions TG corrosion of active iron is
accompanied the increase the general losses of metal in 7,0 times.
- Influences of normal and tangential temperature gradient on the
general and local corrosion copper and iron in the electrolytes
with different pH and anion composition were investigated.
- The positive heat fluxes on the interface metal/solution can to
stimulate (Cu/NaCl) or to inhibite (Fe/H2SO4) corrosion process
for active dissoluting metals but don’t influence on it’s
- The heat-transfer action on copper LC intensity
hydrocarbonate solutions depends from nature of aggressive
anions additives.In the presence chloride-ions LC intensity
increases under heat fluxes, but in the presence sulphate-ions
was observed the opposite effect.
- At the non-isothermal systems with tangential temperature
gradients thermal and thermogalvanic (TG) effects can to
enhance the action one another (Fe/H2SO4; Cu/NaCl) or on the
contrary to relax it (Fe/NaOH).In the first case the zones of
primary damage are being the heat areas, it the second – the
- The commensurability of losses from thermal both TG effects and
essentially dependence of non-isothermal metal surface
destruction’s nature from the law of temperature distribution are
This research was partially supported by the competitive Center of
Fundamental Natural Sciences by the Ministry of Education of
Russian Federation (Grant E02-5.0-51).
The authors are very grateful Organizing Committee of
International Symposium “Corrosion Science in the 21st Century”
and personally Prof. Dr.P.Jordan and Dr.G.Shannon for attention.
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