Journal of Thermal Analysis and [600560]

123
Journal of Thermal Analysis and
Calorimetry
An International Forum for Thermal
Studies

ISSN 1388-6150
Volume 118
Number 2

J Therm Anal Calorim (2014)
118:651-659
DOI 10.1007/s10973-014-3644-3Thermal behaviour and adsorption
properties of some benzothiazole
derivatives
Adriana Samide, Petre Rotaru, Cătălina
Ionescu, Bogdan Tutunaru, Anca
Moanță & Véronique Barragan-Montero

123
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Thermal behaviour and adsorption properties of some
benzothiazole derivatives
Adriana Samide •Petre Rotaru •Ca˘ta˘lina Ionescu •
Bogdan Tutunaru •Anca Moant ¸a˘•Ve´ronique Barragan-Montero
Received: 6 October 2013 / Accepted: 4 January 2014 / Published online: 31 January 2014
/C211Akade ´miai Kiado ´, Budapest, Hungary 2014
Abstract The thermal stability and the adsorption prop-
erties have been investigated for three benzothiazole com-
pounds: 2-mercaptobenzothiazole (MBT), N-cyclohexyl-2-
benzothiazole sulfenamide (NCBSA), and 2,20-dibenzo-
thiazole disulphide (BTD), reported in our early studies as
corrosion inhibitors for carbon steel in different media. Theelectrochemical results were used to calculate the degree of
surface coverage ( h). The adsorption mechanism of the three
inhibitors was discussed according to the free energy ofadsorption ( DG
/C14
ads) value obtained from Temkin adsorption
isotherm, this being the best way to quantitatively express
the adsorption process of their molecules on carbon steel
surface. Thus, a mixed type mechanism involving the syn-
ergism between physisorption and chemisorption was pro-posed. The thermal analysis curves showed that, for the
occurred events up to 470 /C176C, mass losses take place with
endothermic effects followed by the total oxidation of theresidue with an exothermic effect around 520 /C176C. Conse-
quently, their effectiveness follows the order: BTD [
NCBSA CMBT, while the thermal stability ranges as fol-
lows: NCBSA \BTD BMBT.Keywords Benzothiazole compounds /C1Thermal
behaviour /C1Adsorption properties
Introduction
The development of a modern industry at a high rate
implies the consumption of a huge amount of materials,
especially of metals and ferric alloys [ 1].
The destructive attack initiated by physical, chemical
and biological factors is manifested on all materials used in
various fields affecting the working life of the industrialplants. The corrosion in pipes, pumps, turbine blades,
coolers, water heaters, and other systems made of carbon
steel causes enormous industrial expenses due to produc-tion downtime, accidental injuries, and replacement costs
[1]. Carbon steel is an important material in industrial
applications, but it can be corroded in aqueous solutions,such as hydrochloric acid, because the Cl
-ions signifi-
cantly promote the corrosion process [ 1].
The treatments with organic compounds have been
proposed in order to improve anticorrosion protection
[2–20]. The available results show that most inhibitors
act by adsorption on the metal surface [ 3–13] involving
p-orbitals from inhibitor molecule and/or the interactions
between d-orbitals of the metal atoms and the lone pairs of
electrons from heteroatoms such as oxygen, nitrogen and
sulphur. The strength of adsorption, and hence, the extent
of inhibition is dependent on the nature of the organiccompounds and the nature of the metal and the corrosive
media [ 8–11].
The mass loss and the electrochemical measurements
have been used to evaluate the corrosion resistance of steel
in aqueous acid solutions [ 21–23], the composition and
thermal behaviour of the rust formed on the steel surfaceA. Samide ( &)/C1C. Ionescu /C1B. Tutunaru /C1A. Moant ¸a˘
Department of Chemistry, Faculty of Mathematics and Natural
Sciences, University of Craiova, 107i Calea Bucuresti, Craiova,Romaniae-mail: samide_adriana@yahoo.com
P. Rotaru
Department of Physics, Faculty of Mathematics and NaturalSciences, University of Craiova, 13 A.I. Cuza Street,200585 Craiova, Romania
V. Barragan-Montero
Equipe SyGReM, Institut des Biomole ´cules Max Mousseron
(IBMM), UMR 5247, CNRS-UM1-UM2, ENSCM, 8, rue del’Ecole Normale, 34296 Montpellier cedex 05, France
123J Therm Anal Calorim (2014) 118:651–659
DOI 10.1007/s10973-014-3644-3
Author's personal copy

being of great interest. The thermal analysis has been
applied by several workers in the study of the iron corro-sion products resulted in both uninhibited and inhibited
solutions [ 24–27]. The thermal behaviour of organic
compounds with different applications [ 28–34], including
as corrosion inhibitors [ 34], was successfully studied by
simultaneous TG/DSC/DTA analysis [ 28–34].
The aim of the current study was to investigate the thermal
stability and the adsorption properties of three corrosion
inhibitors for carbon steel in 1.0 mol L
-1HCl solution. The
thermal behaviour and the adsorption properties of the fol-lowing benzothiazole compounds: 2-mercaptobenzothiazole,
N-cyclohexyl-2-benzothiazole sulfenamide (NCBSA), 2,2
0-
dibenzothiazole disulphide (BTD) were compared usingthermal analysis detailed as TG/DTG/DSC curves and elec-
trochemical measurements.
Experimental
Materials
Fluka products were used to study the thermal stability and
adsorption properties of some benzothiazole compounds.
Their chemical structures and purity are given in Table 1.
These compounds were investigated as corrosion inhibitorsfor carbon steel corrosion in different media, being reported in
our early studies [ 35–38]. The 2-mercaptobenzothiazole
(MBT) behaviour in hydrochloric solution was recentlyinvestigated using electrochemical measurements, and the
obtained results will be reported in the present paper. Note that
the thermal analysis was performed for all these compounds.Carbon steel plates with the following composition
(mass%): C =0.1 %; Si =0.035 %; Mn =0.4 %;
Cr=0.3 %; Ni =0.3 %; Fe in balance until 100 % were
used as working electrodes in electrochemical measure-
ments. The samples were mechanically polished withemery paper, degreased with acetone and dried in warm air.
MBT was investigated as corrosion inhibitor for carbon
steel in hydrochloric acid solution. HCl, analytical reagentgrade (AR), was obtained from Fluka. The appropriate
concentration of HCl was prepared using bidistilled water.
The corrosion tests were performed in 1.0 mol L
-1HCl
blank solution and in 1.0 mol L-1HCl solution containing
various concentrations of MBT: 0.06, 0.12, 0.25, and
0.5910-4mol L-1.
Methods and techniques
Electrochemical measurements
The potentiodynamic polarization was performed, in order
to determine the corrosion current density of carbon steel in
the presence and in the absence of MBT. The electro-
chemical measurements were carried out using a VoltaLab40 potentiostat/galvanostat with VoltaMaster 4 software. A
glass corrosion cell with three electrodes was used as fol-
lows: a platinum auxiliary electrode (area of 1.0 cm
2); a
saturated Ag/AgClsat reference electrode; and the carbon
steel samples as working electrodes (each area of 1.0 cm2).
The immersion time of the plates in the aggressive mediawas 4.0 min in open circuit, at room temperature
(23±2/C176C). The polarization curves were recorded with a
scan rate of 1.0 mV s
-1.Table 1 The chemical structures of inhibitors and their corresponding purity according to safety data sheet
Molecular structure IUPAC name Purity
NS
SH
MBT2-Mercaptobenzothiazole C95 remainder until 100 %: white mineral oil, moisture,
ash
NS
S
NH
NCBSAN-Cyclohexyl-2-
benzothiazole sulfenamideC95 remainder until 100 %: white mineral oil,
cyclohexylamine, BTD, moisture, ash
NS
S
S
NS
BTD2,20-Dibenzothiazole
disulphideC95 remainder until 100 %: white mineral oil, moisture,
ash652 A. Samide et al.
123
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Thermal analysis
Thermal analysis measurements (TG, DTG, and DSC) were
carried out in dynamic air atmosphere (150 cm3min-1),
under non-isothermal linear regime, using a horizontal
‘‘Diamond’’ Differential/Thermogravimetric Analyzer from
PerkinElmer Instruments. Samples from 1.281 to 3.058 mg,contained in alumina crucibles, were heated in the temper-
ature range of RT-600 /C176C. The employed heating rate was
10 K min
-1.
Results and discussion
Adsorption and inhibitory properties of MBT, NCBSA
and BTD
In our early studies, MBT, NCBSA and BTD have been
reported as corrosion inhibitors for carbon steel in differentmedia as follows: in ammonia media, MBT [ 35] and
NCBSA [ 36] have been shown to be effective inhibitors
which act by adsorption on metal surface, obtaining for thedegrees of the surface coverage ( h), values greater than 0.9
[35,36]; NCBSA [ 37] and BTD [ 38] were investigated in
1.0 mol L
-1HCl solution when the inhibition efficiency
(IE) value of 82 ±1 % was obtained [ 37,38]. The
research has shown that these act by adsorption on the
substrate surface. As an example, the IE values which werereported for NCBSA [ 37] and BTD [ 38] in 1.0 mol L
-1
HCl solution are listed in Table 2.
To complete the research and in order to discuss the
action mechanism of these compounds, the electrochemical
measurements were also performed for carbon steel in
1.0 mol L-1HCl blank solution and in 1.0 mol L-1HCl
solution containing various concentrations of MBT, such as
0.06, 0.12, 0.25, and 0.5 mmol L-1. The potentiodynamic
curves were recorded as Tafel and Stern diagrams in order
to calculate the corrosion current density ( icorr), as well as
the polarization resistance ( Rp), and consequently the IE of
MBT in acidic medium. The result of the electrochemical
measurements is shown in Fig. 1. From Fig. 1a, it can beobserved that the presence of MBT in 1.0 mol L-1HCl
solution shifts the corrosion potential ( Ecorr) to higher
values, while the polarization curves have been shifted to
lower current regions, showing the inhibition tendency ofthis compound that is more obvious with the increasing of
its concentration in hydrochloric acid solution.
Moreover, in the vicinity of E
corr, an appreciable
decrease in the current density is observed starting from the
concentration of 0.06 mmol L-1MBT in 1.0 mol L-1HCl
solution (Fig. 1b). The decrease in the anodic current is
more significant than that of the cathodic current, sug-
gesting that the addition of MBT in HCl solution reducesanodic dissolution in a considerable manner and also
delays the hydrogen evolution reaction. This indicates that
an anodic film on the carbon steel surface was formed [ 39]
implying that MBT acts as a corrosion inhibitor in
1.0 mol L
-1HCl solution by simultaneously suppressing
the cathodic and anodic processes, with the anodic pre-dominance, via adsorption on the carbon steel surface. This
suggests that, although inhibition is of mixed type, it is
predominantly anodic. The corrosion current density ( i
corr)
was calculated at intercept of the anodic and cathodic Tafel
lines to corrosion potential. The polarization resistance ( Rp)
was determined according to Eq. 1[39], where
di=dEðȚE!Ecorrrepresents the polarization conductance
obtained as the slopes of the tangent lines drawn to
polarization curves obtained in the vicinity of corrosion
potential (Fig. 1b).
1=Rp¼di=dEðȚE!Ecorr: ð1Ț
VoltaMaster 4 software was used to calculate the elec-
trochemical parameters listed in Table 3, such as the cor-
rosion potential ( Ecorr), the corrosion current density ( icorr),
the anodic and cathodic Tafel slopes ( baand bc), the
polarization resistance ( Rp). The inhibition efficiency per-
centage (IE) of MBT was determined from polarization
measurements according to the following equations, Eqs. 2
[35–42] and 3[39–41].
IE¼io
corr/C0icorr
io
corr/C2100 ; ð2Ț
where io
corrandicorrare the corrosion current densities of
carbon steel in 1.0 mol L-1HCl solution without and with
MBT, respectively.
IE¼Rp/C0Ro
p
Ro
p/C2100 ; ð3Ț
where RpandRo
prepresent the polarization resistances in
the presence and in the absence of MBT, respectively.
The results showed that the corrosion current density
decreased with the increase in MBT concentration, and
consequently, the IE increases, reaching a maximum valueTable 2 IE values obtained from electrochemical measurements for
carbon steel corrosion in 1.0 mol L-1HCl solution containing vari-
ous concentrations of NCBSA [ 37] and BTD [ 38]
C-inh/mmol L-1IE/%
NCBSA BTD
0.1 52.3 54.3
0.2 61.5 63.80.3 70.6 76.90.4 81.5 82.2Thermal behaviour and adsorption properties 653
123
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of 84 ±1 % at 0.5 mmol L-1of MBT. Also, the slopes of
the anodic and cathodic Tafel lines ( baandbc) were slightly
altered by increasing the tested compound concentration
(Table 3). The small change may be due to surface
blockage by MBT. This could be attributed to the fact that
the anodic carbon steel dissolution and the cathodic reac-
tion were both inhibited by MBT through merely blockingthe reaction sites of carbon steel surface without affecting
the anodic and cathodic reaction mechanism [ 42].
Application of adsorption isothermVarious adsorption isotherms were applied to fit the degree
of surface coverage ( h) values, but the good fit was found
to obey Temkin adsorption isotherm, which may be
expressed by Eq. 4[40,43,44]. Note that for NCBSA and
BTD, experimental data obtained in our previous studies[37,38] were used, according to the IE values listed in
Table 2.
h¼
1
f/C1lnKț1
f/C1lnC; ð4Ț–2.5–1.5–0.50.51.5
–700 –600 –500 –400E/mV vs. Ag/AgCllogi/A cm–21.0 M HCl blank 0.06 mM MBT
0.12 mM MBT 0.25 mM MBT
0.5 mM MBTa
–10–6–22610
–600 –550 –500 –450
E/mV vs. Ag/AgCli/mA cm–2
1.0 M HCl blank
0.06 mM MBT
0.12 mM MBT
0.25 mM MBT
0.5 mM MBTbFig. 1 Potentiodynamic curves
recorded with a scan rate of1.0 mV s
-1for carbon steel
corroded in 1.0 mol L-1HCl
blank solution and in1.0 mol L
-1HCl solution
containing various
concentrations of MBT: aTafel
diagram and bStern diagram
obtained in the vicinity of
corrosion potential ( Ecorr)
Table 3 Electrochemical parameters and IE obtained from electrochemical measurements for carbon steel corroded in 1.0 mol L-1HCl
solution in the absence and in the presence of various concentrations of MBT, at room temperature
C-MBT/mmol L-1Ecorr/mV versus Ag/AgCl icorr/mA cm-2ba/mV dec-1bc/mV dec-1Rp/Xcm2IE/%
From Eq. 2 From Eq. 3
0 -540 1.7 88 117 11.7 – –
0.06 -522 0.993 67 113 21.1 41.6 44.3
0.12 -509 0.882 63 98 25.4 48.1 53.9
0.25 -514 0.610 70 94 37.8 64.1 69.0
0.5 -508 0.284 66 87 78.2 83.3 85.0
MBT
y = 0.199 x + 2.3152
R2 = 0.9788
NCBSA
y = 0.2021 x + 2.3655
R2 = 0.9753
BTD
y = 0.2068 x + 2.4334
R2 = 0.9771
0.40.50.60.70.80.9
–10 –9 –8 –7lnCinh/mol L–1θMBT
NCBSA
BTD
Fig. 2 The plotted data as Temkin adsorption isotherm for corrosion
inhibition of carbon steel in 1.0 mol L-1HCl solution using: MBT,
NCBSA and BTD inhibitorsTable 4 Thermodynamic parameters calculated from Temkin iso-
therm for the adsorption of: MBT, NCBSA and BTD inhibitors on
carbon steel surface in 1.0 mol L-1HCl solution
Inhibitor Parameters
lnK/L mol-11/Slope DGads/C176/kJ mol-1BE/eV
MBT 11.63 5.02 -38.74 0.401
NCBSA 11.70 4.95 -38.92 0.403
BTD 11.76 4.84 -39.07 0.405654 A. Samide et al.
123
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where Cis the concentration (mol L-1) of inhibitor in the
bulk electrolyte, his the degree of surface coverage
(h=IE/100), Kis the adsorption–desorption equilibrium
constant and fis a heterogeneous factor of metal surface.
According to Eq. 4, from the graph hversus ln C, the
straight line relationship was obtained with regression
coefficient ( R2) reaching a value close to unity; the slope is
equal with 1/ fand the intercept from which the value of K
was calculated is represented by [(1/ f)/C1lnK]. Figure 2pre-
sents the Temkin adsorption isotherm attributed to MBT,NCBSA and BTD inhibitors of carbon steel corrosion in
1.0 mol L
-1HCl solution. The equilibrium constant of
adsorption–desorption ( K) was used to calculate the free
energy of adsorption ( DG/C14
ads) using Eq. 5[37–44]:
K¼1
55:5exp/C0DG/C14
ads
RT/C18/C19
; ð5Țwhere Ris the universal gas constant (8.31 J mol-1K-1),
Tis the temperature (298 K) and 55.5 is the molar con-
centration of water in the solution.
The thermodynamic parameters for the adsorption of
these inhibitors according to Temkin adsorption isotherm
are presented in Table 4.
The low and negative value of DG/C14
adsindicates the
spontaneous adsorption of inhibitors on the carbon steel
surface. The DG/C14
adsvalue obtained from Temkin adsorption
isotherm leads to the conclusion that the assumption of a
mixed action mechanism involving physical and chemical
adsorption is the most truthful. The DG/C14
adsvalue is rela-
tively close to -40 kJ mol-1that is usually accepted as a
threshold value between chemical and physical adsorption
[39,41,43,45]. This kind of values may indicate that the
chemisorption dominates the physical adsorption. It is
100.04 0.05
0.00
–0.05
–0.10
–0.15
–0.20
–0.25
–0.30Derivative mass/mg min–1
–0.35
–0.4090
80
70
60
50
40Mass/%
30
20
10
–0.5
10 50 100 150 200 250 300
Temperature/°C350 400 450DTG
DSC
TG
500 550 60054
Heat flow Endo up/mW3210–1–2
Fig. 3 Thermoanalytical
curves of MBT
100.05 0.05
0.00
–0.05
–0.10
–0.15
–0.20
–0.25
–0.30Derivative mass/mg min–1
–0.35
–0.4090
80
70
60
50
40Mass/%
30
20
10
–0.5
10 50 100 150 200 250 300
Temperature/°C350 400 450DTG
DSC
TG
500 550 6004
6
8
10
Heat flow Endo up/mW20–2–4–6–8–10 Fig. 4 Thermoanalytical
curves of NCBSAThermal behaviour and adsorption properties 655
123
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noticed that the value of fis more than unity, that is, a
single molecule of inhibitor disables several active sites
from the metal surface [ 40,41]. This can be explained
taking into consideration the basic concept of adsorption. Itis apparent from the molecular structure that the inhibitors
can be adsorbed on the carbon steel surface through the
lone pairs of electrons of nitrogen and/or sulphur atomsfrom thiazole ring and/or from lateral chain and/or by de-
localized p-electrons of benzene ring. Based on these data,
it can be concluded that these inhibitors act by adsorption
on carbon steel surface; the mixed mechanism of physi-sorption and chemisorption of their molecules is proposed.
Apparently, their effectiveness as corrosion inhibitors of
carbon steel varies as follows: BTD [NCBSA CMBT.
100.02Derivative mass/mg min–1900.1
0.0
–0.1
–0.2
–0.3
–0.4
–0.5
–0.6
–0.7–0.8
–0.9
–1.0
–1.1
–1.280
70
60
50
40Mass/%
30
20
10
–1.5
10 50 100 150 200 250 300
Temperature/°C350 400 450DTG
DSC
TG
500 550 600
Heat flow Endo up/mW–22
–20
–15
–10
–5
0
5
10
15
20
Fig. 5 Thermoanalytical
curves of BTD
Table 5 Characteristics of the thermodegradation steps of corrosion inhibitors
Inhibitor Step Temperature
range/ /C176CThermal
effectMaximum/ /C176C Mass loss/% Associated process
MBT 1 128–150 Endo 141.5 1.6 Loss of adsorbed water and/or adsorbed
gases
2 150–203 Endo 176 – Melting point3 203–268 Endo 249 81.5 MBT decomposition in different by-
products
4 268–304 Endo 283.5 12.4 Decomposition of some by-products5 304–458 – – 2.7 Thermal degradation resulting NO
x,S O 2
6 458–530 Exo 522 1.8 Burning resulting CO 2
NCBSA 1 76.5–135 Endo 113.5 6.3 Loss of adsorbed water overlapped with
cyclohexylamine loss
2 135–170 Endo 149 – Melting point3 170–285 Endo 267 52.3 NCBSA decomposition in different by-
products
4 285–337 Endo 308 33.6 BTD decomposition overlapped with
decomposition of some by-products
5 337–465 – – 2.9 Thermal degradation resulting NO
x,S O 2
6 465–565 Exo 520 5.0 Burning resulting CO 2
BTD 1 118–153 – – 1.4 –
2 153–178 Endo 162 – Melting point3 178–345 Endo 308 88.6 BTD decomposition4 345–457 – – 3.8 Thermal degradation resulting NO
x,S O 2
5 457–589 Exo 522 6.2 Burning resulting CO 2656 A. Samide et al.
123
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By estimation, the binding energy (BE) values for the
molecules of each inhibitor, the same value of 0.4 eV was
obtained for all inhibitors (Table 4). These BE values
confirm that the chemical adsorption mechanism prevailson physisorption one, being higher than 0.1 eV, but less
than 1.0 eV, thus indicating a moderate to strong anchoring
of molecules on carbon steel surface [ 46].
Thermal behaviour of the inhibitorsThermal analysis is detailed as TG/DTG/DSC curves
which are shown in Figs. 3(MBT), 4(NCBSA) and 5
(BTD).
It can be observed that for all inhibitors, up to 470 /C176C,
mass losses take place, with endothermic effects; it meansthat thermooxidative decomposition occurs; after 470 /C176C,
the residue of combustion is evidenced with an exothermic
effect. The inhibitors events involve their decomposition indifferent by-products such as amines, H
2S and by-products
of mercaptans, followed by total oxidation to CO, CO 2,
NO xand SO 2. The characteristics and the interpretation of
the decomposition steps are systematized in Table 5.
The associated events of MBT (Fig. 3) or BTD (Fig. 5)
decomposition do not involve other outstanding remarksthan those listed in Table 5. The melting points which are
indicated in Table 5are very close to those given in liter-
ature data [ 47,48]. TG/DTG/DSC curves of NCBSA
(Fig. 4) imply several comments. At low temperature,
successive and parallel with the loss of moisture, other
events take place such as the evaporation and/or decom-position of cyclohexylamine (this is an impurity from the
manufacturing process). An accurate assignment of the
endothermic peaks from this temperature range is difficult,especially that on the DTG curve many fluctuations are
notified. Thus, the presence of an endothermic peak at
308/C176C shows that NCBSA is contaminated with BTD (the
same maximum for BTD may be observed in Fig. 5). This
was expected, knowing from the beginning that NCBSA
contains some amount of BTD, but it cannot be preciselycalculated. As a consequence, the melting point of NCBSA
shifts toward a higher value than that specified by the lit-
erature [ 49].
Based on these data, it can be concluded that the
NCBSA purity is smaller than that was expected. Cyclo-
hexylamine and BTD, as impurities, have no influence onthe mechanism of inhibition, and there is no risk to use this
compound as corrosion inhibitor. Concerning the thermal
stability of these inhibitors, referring to the degradation ofthe product itself, we may conclude that this ranges as
follows NCBSA \BTD BMBT. Moreover, these sub-
stances are not recommended to be used as corrosioninhibitors in an organic medium, which works as heat-
transfer agent, but there is no risk for their application inaqueous solutions, because until 90 /C176C all studied com-
pounds present a very good thermal stability.
Conclusions
The thermal stability and the effectiveness of three ben-
zothiazole compounds applied as corrosion inhibitors of
carbon steel surface in 1.0 mol L
-1HCl solution were
discussed.
Temkin adsorption isotherm fitted well with the exper-
imental data obtained for electrochemical measurements ofcarbon steel in 1.0 mol L
-1HCl blank solution and in
1.0 mol L-1HCl solution containing various concentra-
tions of each inhibitor: MBT, NCBSA and BTD. These actby adsorption on substrate through the lone pairs of elec-
trons of nitrogen and/or sulphur atoms from thiazole ring
and/or from lateral chain and/or by delocalized p-electrons
of benzene ring. The mixed mechanism of physisorption
and chemisorption of their molecules was proposed, with
the effectiveness as corrosion inhibitors of carbon steelranging as follows: BTD [NCBSA CMBT.
The thermal analysis for all inhibitors indicated that, up
to 470 /C176C, mass losses take place, with endothermic effects
and, after 470 /C176C, the combustion of residue is obvious
with an exothermic effect, the thermal stability of these
inhibitors ranging as follows: NCBSA \BTD BMBT.
There is no risk, concerning their degradation for the
applications of these benzothiazole compounds as corro-
sion inhibitors in aqueous solutions until 90 /C176C, but they
are not recommended to be used in organic heating transfer
agents.
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