Article
citation information:
Komsta, H., Vitenko, T., Buketov, А., Syzonenko, О., Bezbakh,
О., Torpakov, A., Kruglyj, D.,
Appazov, E., Popovych, P., Rybicka, I. Study of thermal stability and energy of activation of
epoxy composites with particles of synthesised powder
mixture for increasing reliability of vehicles. Scientific Journal of Silesian University of Technology. Series
Transport. 2021, 110, 73-86.
ISSN: 0209-3324. DOI: https://doi.org/10.20858/sjsutst.2021.110.6.
Henryk KOMSTA[1], Tetiana VITENKO[2], Аndrii BUKETOV[3], Оlha SYZONENKO[4], Оleh BEZBAKH[5], Andrii TORPAKOV[6], Dmytro KRUGLYJ[7], Eduard APPAZOV[8], Pavlo POPOVYCH[9], Iwona RYBICKA10
STUDY
OF THERMAL STABILITY AND ENERGY OF ACTIVATION OF EPOXY COMPOSITES WITH
PARTICLES OF SYNTHESISED POWDER MIXTURE FOR INCREASING RELIABILITY OF VEHICLES[10]
Summary. The prospective of the
application of new materials on a polymer base is shown in this work. Given
that developed composites can be efficiently used for protection of equipment
that is operated at elevated temperatures, the impact of the nature and
content of powder mixture, synthesised by high voltage electric discharge, on
the thermophysical properties of epoxy composites
were studied. Epoxy diane
oligomer was chosen as the main component of the binder during the formation
of the composites. Polyethylene polyamine hardener was used for cross-linking
of epoxy composites, which allows hardening of materials at room temperatures.
The selection of powder mixture, synthesised by high voltage electric
discharge, for increase of thermophysical properties
of developed materials was justified. More so, thermal stability and activation
energy of epoxy composites were studied. Permissible limits of the temperature,
at which developed materials can be used, were established based on the
conducted tests of thermophysical properties of
materials, filled by powder mixture, synthesised by high voltage electric
discharge.
Keywords: epoxy composite, thermal stability, activation
energy, filler
1. INTRODUCTION
The
problem of ensuring the reliability of parts of technological equipment during
their use in conditions under the impact of aggressive environments and
sign-alternating or increased temperatures is an urgent scientific and
technological problem. The use of polymer composite and protective coatings,
based on them, is a prospective way of solving this problem. Such materials are
notable due to increased values of physical, mechanical and thermophysical
properties, which is a determining factor in the fight against corrosion of
parts of technological equipment of modern industry in conditions of aggressive
environments impact.
It
is known [2, 5, 11-18, 23] that the increase of cohesion and especially of thermophysical properties of polymer composites is possible
by their modification, plasticisation or introduction
of nano- and micro- additives with homeopathic
content. The use of dispersion fillers is urgent from both economic and
ecological points of view. Authors of [4] have shown that the introduction of disperse
nanoparticles to the polymer matrix with insignificant content (from 0.05 up to
0.15%) ensures 2.2 – 2.8 times increase of cohesion properties of
protective coatings.
Thus,
it can be concluded that the development of new technologies of obtainment of
polymer composites and protective coatings, based on them, aimed at the
increase of the service life of technological equipment, is an urgent
industrial task. When solving this task, it is important to form
environment-friendly and cost-effective materials for parts repair. In this
context, the use of microadditives with insignificant
quantity in polymer composites is urgent from both scientific and practical
points of view.
In
previous works [4], the impact of the quantity of filler on the thermophysical properties of epoxy composites (thermal
stability, coefficient of thermal expansion, the glass transition temperature)
was experimentally studied. However, change of the structure of the composite,
including the destruction of physical and chemical bonds, under the impact of
thermal field is a multifaceted process [1, 3, 6-10, 14, 24].
Therefore,
the studies of thermal stability of developed materials using differential
thermal analysis (DTA) and thermal gravimetric
analysis (TGA) methods in the temperature range of ΔТ = 293
- 873 К is necessary to further establish the dependencies of
properties of developed materials on the temperature. During the studies of
materials thermal destruction processes, temperature rate was υ = 10 К/min.
The
aim of this work is the determination of dependence of thermal stability of
epoxy composite materials on heating temperature as well as the determination
of the energy of activation of the process of their destruction.
2. MATERIALS AND METHODS
Epoxy diane oligomer ED-20 (GOST 10587-84),
which is characterised by high adhesion and cohesion
strength, low shrinkage and processability when
applied to complex surface profile, was selected as the main binder component
for the formation of epoxy composite materials (CM).
Polyethylene polyamine (PEPA) (TS 6-05-241-202-78) hardener was used for cross-linking of
epoxy composites, which allows hardening of materials at room temperatures. PEPA is a low-molecule compound, which consists of
interconnected [-CH2-CH2-NH-]n
components. CM were polymerised by the introduction
of hardener in their composition at a stoichiometric ratio of components by
content (mass parts) – ED-20: PEPA – 100:
10.
Synthesised powder mixture (SPM) was used as microdisperse
filler for experimental studies, obtained with high voltage electric discharge
(HVED). Powder mixture of Fe (75%) + Ti (25%) initial mass composition was used as the initial
material for filler synthesis. During HVED-synthesis,
stored energy of single discharge (W1) was 1 kJ, while specific integral treatment
energy (Wsp)
was 25 MJ/kg [19-22]. The mean diameter of the initial powder mixture before HVED treatment was 45 µm while 90% of particles had a size higher than 10 µm.
Results of the
studies showed that HVED treatment leads to
dispersion of all treated particles and change of their phase composition with
the synthesis of high-modulus compounds of TiC and Fe3C (Table 1).
Tab. 1
Results of HVED
synthesis of the filler
|
Initial composition |
Composition after treatment |
Electrode system |
Diameter after treatment, d, μm |
||
|
dmin |
dmax |
dmean |
|||
|
Fe
(75%) + Ti (25%) |
Fe
(70%) + Ti (10%) + TiC
(15%) + Fe3C (5%) |
1 (point – plane) |
~1 |
112 |
11.5 |
Epoxy
composites were formed by the following technology [4]: resin was heated up to
the temperature of Т = 353 ± 2 К,
at which it was held during a time of τ = 20 ± 0,1 min;
oligomer and filler particles were hydrodynamically
merged during the time of τ = 10 ± 0.1 min;
composition underwent ultrasonic treatment (UST) during the time of τ = 1.5 ± 0.1 min;
the composition was cooled to room temperature during the time of τ = 60 ± 5 min;
the hardener was introduced and the composition was mixed during the time of τ = 5 ± 0.1 min.
Hardening of CM was performed according to the following regime: formation of
specimens and their holding during the time of 12.0 ± 0.1 h at
the temperature of Т = 293 ± 2 К,
heating with the rate of υ = 3 К/min
up to the temperature of Т = 393 ± 2 К,
holding during the time of τ = 2.0 ± 0.05
h, slow cooling to the temperature of Т = 293 ± 2
К. To achieve stabilisation of structure
processes in the composites, specimens were held during the time of τ = 24 h
on air at the temperature of Т = 293 ± 2 К,
and only after holding, experimental studies on these specimens were conducted.
TGA
and DTA analysis were carried out following these
standards:
1. ISO
8301:1991. International Organization for Standardization. Thermal insulation – Determination of steady-state
thermal resistance and related properties
– Heat flow meter
apparatus;
2. ISO
22007-2:2015, Plastics – Determination of thermal conductivity and
thermal diffusivity –
Part 2: Transient plane heat source (hot disc) method, International Organization for Standardization.
TGA
and DTA were performed after studies of the specimens
on «Thermoscan-2» derivatograph.
CM were studied in the temperature range of ∆Т = 298
- 773 К, using quartz crucibles for specimens with the volume of V = 0.5 cm3, and was heated at a rate υ = 10 K/min.
The Al2O3 powder (m = 0.5 g) was used as a
standard. Mass of specimens was m = 0.3 g.
Error of temperature determination was ∆Т = ±1 К.
Precision of thermal effects determination was 3 J/g. Precision of
determination of specimen’s mass was ∆m = 0.02 g.
3. RESULTS
AND DISCUSSION
At the first
stage of the studies, thermal stability of epoxy matrix was studied. Results of
this experiment and their justification are described in detail in this work
[3]. In particular, results of TGA showed absence of
the materials mass loss in the temperature range of ∆Т = 293 - 570 К (Fig. 1, curve 1
and Table 2). Further increase of the temperature leads to decrease of the
specimen’s mass. This occurs due to the excretion of volatile products
resulting from the destruction of chemical bonds between segments and lateral
groups of macromolecules of epoxy oligomer and active centres
on the surface of filler disperse particles. In addition, the beginning and
ending temperatures of the mass loss process, as well as the temperatures at
which the specimens’ mass was decreased by 5 - 20% were experimentally
found. It was established, that the temperature of the mass loss beginning for
epoxy matrix was Т0 = 588 К,
and the temperature at which the mass loss process ends was Тк = 710 К.
At this point, relative mass loss of matrix was εm = 80.7%
(Table 2).
On the further
stages of studies, similar parameters of thermal stability were determined for
the studied CM. It was discovered (Fig. 1 and Table 2), that the beginning of
thermal destruction for materials with fillers was observed in the temperature
range of Т = 616 - 627 К. Hence, it can be
stated that the thermal stability of the composites was increased when compared
to the thermal stability of the initial matrix, as the processes of thermal
destruction of studied materials occur at higher temperatures. First, this is
due to the increase of the quantity of chemical bonds on the unit of polymer
volume due to the presence of the disperse filler. Further, polymer around the
particles is in the state of outer surface layers, which increase the degree of
its cross-linking. Accordingly, it increases the values of composites thermal
stability.
Similar to
previous results, an increase of the value of the CM mass loss process ending
temperature when compared to the studied epoxy matrix, was observed, which characterises the end of materials thermal destruction
process. It was shown (Table 2), that introduction of SPM filler increases the
temperature of composites thermal destruction recorded at the end (in
comparison with matrix) from Тк = 710 К to Тк = 722
- 785 К. As noted above, this is due to the impact of physical and
chemical nature and topology of disperse particles surface on the passage of
the processes of interphase interaction during CM structure formation, which,
accordingly, is definitive for the formation of composites with increased
thermal stability and increased values of other thermophysical
properties.
Mass loss of
CM was additionally analysed by TGA
curves. It was shown (Table 2), that the relative mass loss of epoxy matrix was
εm = 80.7%.
Introduction of particles led to the decrease of the value from εm = 80.7%
(for epoxy matrix) to εm = 56.7
- 69.7%. It was shown (Table 2), that during the thermal destruction of CM, the
great impact was caused not only by the nature of the filler but also by its
quantity in the system. Analysis of the results of studies has shown that the
introduction of the particles leads to a significant decrease in CM mass loss
only in the case of fillers optimal content. In particular, the addition of SPM
in the quantity of q = 0.50
- 2.00 mass parts provides 1.4-times decrease of the value of relative
mass loss (from εm = 80.7%
(for epoxy matrix) to εm = 56.7
- 59.7%). Thus, it can be stated that particles of SPM significantly slow down
the processes of thermal destruction and, consequently, improve the durability
of epoxy composites that are used in the conditions of thermal field impact.
Tab. 2
Thermal stability of CM, filled by SPM particles
|
Filler content, q, mass parts |
Т0,
К |
Т5,
К |
Т10,
К |
Т20,
К |
Тк, К |
εm,% |
|
|
Matrix |
0 |
588 |
624 |
636 |
649 |
710 |
80.7 |
|
Synthesised powder mixture (SPM) |
0.05 |
627 |
634 |
640 |
656 |
785 |
69.7 |
|
0.50 |
621 |
629 |
636 |
650 |
722 |
56.7 |
|
|
2.00 |
616 |
626 |
633 |
647 |
737 |
59.7 |
|
Note: Т0 – temperature of mass loss
beginning (beginning of destruction); Т5, Т10, Т20
– temperature of mass losses (5%, 10% and 20%, respectively); Тк
– ending temperature of mass loss (end of destruction); εm
– relative mass loss.
To
further study the processes of thermal destruction of matrix and epoxy
composites, materials underwent parallel study using DTA
method. Analysis of the DTA curve in the temperature
range of ∆Т = 273 - 373 К allowed detecting the
presence of exothermic effect (Fig. 1). Change of mass in this temperature
range in all studied specimens was not observed. It was considered that in this
case, the presence of exothermic effect is caused by the formation of
additional physical bonds in polymer materials due to their additional
hardening. More so, this leads to an additional increase in the degree of cross-linking
of developed materials.
Fig. 1. TGA curves of studied samples
Further, the exothermic effect in specimens
under the impact of the thermal field in the temperature range of ∆Т = 460
- 660 К was observed.
During the analysis of thermal destruction processes, the beginning and ending
temperatures of exoeffects are important. It was
shown (Fig. 1, curve 2 and Table 3), that the lowest temperature of exothermic
processes beginning (Тп = 460 К) was observed
for epoxy matrix. This indicates that at this temperature intensive relaxation
of physico-chemical bonds in polymer structure grid
starts. With further increase of the temperature, these bonds can disintegrate,
while the ending of the processes of structure rearrangement and matrix
destruction was observed at the ending temperature of exoeffect,
which was Тк = 649 К. It can be considered
that this is the limit at which matrix destruction was finished, that is, at
this temperature range, an intensive decrease of specimen’s mass was
observed (Fig. 1, curve 1).
Tab. 3
Temperature ranges of exoeffects of composites,
filled by SPM particles, according to DTA
|
Filler content, q, mass parts |
Temperature ranges of exoeffects |
Maximum value of exoeffects,
Тmax,
К |
||||
|
Тn,
К |
Тк, К |
∆Т1, К |
∆Т2, К |
|||
|
Matrix |
0 |
460 |
649 |
472 |
3,1 |
518 |
|
Synthesised powder mixture (SPM) |
0,05 |
479 |
655 |
177 |
2,0 |
530 |
|
0,50 |
461 |
656 |
195 |
2,4 |
528 |
|
|
2,00 |
462 |
651 |
189 |
2,4 |
531 |
|
Note: Тn
– beginning temperature of the exoeffect; Тк – ending temperature of
the exoeffect; ∆Т1 – temperature range of the exoeffect;
∆Т2
– difference of the temperatures between the specimen where
transformation occurs, and the standard, where no transformations take place.
Introduction of the filler increases the
beginning temperature of the materials thermal destruction from Тп = 460 К (for epoxy matrix) to Тп = 461 - 479 К. The temperature
recorded at the end of the thermal destruction was also moved to the right by
the abscissa axis and for all studied composites was in range of Тк = 651 - 656 К. These facts
indicate that the presence of dispersed particles leads to the formation of
materials with a strongly-stitched 3-dimensional polymer grid. This allows
extending the life of materials that operate at elevated temperatures.
Additionally,
the maximal value of the exoeffect temperature was
determined, which was Тmax = 518 К for matrix. It was
shown (Table 3), that introduction of the filler in different content ensures
increase of the maximum of exothermic processes peak to Тmax = 528 - 531 К, while the
highest value (Тmax = 531 К) was observed in
the case of addition of filler in the quantity of q = 2.00
mass parts for 100 mass parts of ED-20 epoxy oligomer. It can be concluded that
the movement of exoeffect peak to the area of high
temperatures indicates the increase of resistance of physico-chemical
bonds in the materials to destruction. It can be further concluded that these
conditions are the same for the formation of composite with the highest
resistance to destructive processes and micro-transformations in the structure
under the impact of the temperature.
Conclusively, it should be noted that analysis
of DTA and TGA curves as
well as previously conducted studies of CM thermophysical
properties (thermal stability, coefficient of thermal expansion, the glass
transition temperature), indicates the following; Developed materials,
especially the composite with filler content of q = 2.00 mass
parts for 100 mass parts of ED-20 epoxy oligomer, are advisable to operate in
the temperature range of ΔТ = 273 - 473 К, as the further
increase of thermal field impact intensity leads to the beginning of thermal
destruction processes, which cause the premature destruction of materials.
On the next stage of the studies, the energy of
activation of thermal destruction of epoxy matrix and developed composite
materials with particles of CPM with different content was determined. Analysis
of TGA curves allowed the determination of the
destruction temperature and relative mass loss of specimens during the heating
of epoxy composites. Energy of CM activation was calculated using this data. In
addition, analysis of thermal effects that occur in CM during the heating was
performed in the context of results of DTA and TGA studies.
TGA curves allow determination of energy of
activation of thermal-oxidation destruction Еа, calculated using Broido’s method based on double logarithmization
[1]. The condition for the application of Broido’s
method is the determination of the first order of decomposition, which is
relevant for a wide range of polymers [4]. Polymers mass loss is a prove of 1st
order (n = 1) provided that there is a linear dependency ln(100/(100 – Δm) from reversed temperature
1000/Т, К-1. Given the mass loss (Δm) of
the specimen at given temperature T, a line was drawn, and the
activation energy was determined through the tangent of the slope of the
logarithmic dependence Δm on reversed temperature T. Further,
the value of destruction activation energy, kJ/mol,
was found according to the expression:
Еа = – R·tg(φ). (1)
During the graphical determination of activation energy, a graph was built
as a direct line, by tangent of the slope φ
of which Еа
was determined (Fig. 2). Then:
– tg(φ) = yi/xi, (2)
Е = R·yi/xi, (3)
where xi=
xbegin
– xend
– length of the line along the axis of the abscissa; yi= ybegin
– yend
– the length of the line along the vertical axis; [xbegin;
ybegin]
and [xend;
yend]
– coordinates of beginning and end of the line, respectively.
Fig. 2. Method of graphic determination of activation energy
Given the above, Broido's
method can be represented analytically in the form of an equation [1]:
(4)
where:
– specimens
mass loss at every studied temperature in the range of materials
decomposition,%;
– energy
of activation, kJ/mol;
– universal
gas constant, R = 8.31 J/(mol·K);
– temperature,
К
Mass of the specimens was
determined according to the derivatograms (Fig. 1) in
range of temperatures of ∆Т = 573
- 713 К with the step of ∆Т = 10 К.
Obtained values of the specimen’s mass (expressed in grams) were
transformed to percents according to the expression:
,
(5)
where:
– initial
mass of the specimen at the initial temperature of studies Т1 = 573 К,
(
= const), g;
– specimens
mass loss, g.
Mass of the specimens at the
initial temperature of studies Т1 = 573 К according
to this method was considered as 100%.
Using the equation (4), values
of the double logarithm of the specimen’s mass change were evaluated.
Results of this evaluation are given in Table 4.
Tab. 4
Results
of the evaluation of the double value of the
logarithm of specimen’s mass change
|
T, К |
10³/T,К |
ln{ln[100/(100-Δm)]} |
|||
|
SPM filler content, q, mass parts |
|||||
|
0 |
0.05 |
0.50 |
2.00 |
||
|
573 |
1.745 |
– |
– |
– |
– |
|
583 |
1.715 |
– |
– |
– |
– |
|
593 |
1.686 |
– |
– |
– |
– |
|
603 |
1.658 |
– |
– |
– |
– |
|
613 |
1.631 |
– |
– |
– |
– |
|
623 |
1.605 |
– |
– |
–3.712 |
–3.712 |
|
633 |
1.580 |
– |
–3.287 |
–2.287 |
–2.180 |
|
643 |
1.555 |
– |
–2.118 |
–1.710 |
–1.600 |
|
653 |
1.531 |
–3.547 |
–1.538 |
–1.337 |
–1.320 |
|
663 |
1.508 |
–2.528 |
–1.200 |
–1.045 |
–1.004 |
|
673 |
1.486 |
–2.142 |
–1.004 |
–0.800 |
–0.752 |
|
683 |
1.464 |
–1.855 |
–0.705 |
–0.551 |
–0.530 |
|
693 |
1.443 |
–1.624 |
–0.435 |
–0.367 |
–0.327 |
|
703 |
1.422 |
–1.429 |
–0.216 |
–0.278 |
–0.192 |
|
713 |
1.403 |
–1.259 |
–0.060 |
–0.163 |
–0.106 |
Given the specimen’s
mass loss (∆m) at the
temperature of T, a
line was drawn, and the activation energy E was determined through the
tangent of slope of the logarithmic dependence Δm
on reversed temperature T. Processing of the experimental results, which
consists in the mathematical transformation of mass loss curve, was performed
in the MS-Excel software. Graphs of logarithmic dependence of specimen’s mass loss
∆m on reversed temperature 103/Т
are shown on Fig. 3.
Analysis of destruction rates (Fig. 3) of studied
composites allowed to derivate of the equation of the dependence of specimen’s mass loss ∆m on reversed temperature 103/Т for epoxy matrix and CM with
different content of SPM disperse particles. Based on obtained equations, the
values of energy of activation E
of thermal-oxidation destruction of developed materials were calculated (Table
5).
Fig. 3. Graphic
dependency of destruction ration of CM with SPM particles:
♦ - matrix; ■
– 0,05%; ▲ – 0,5%; × - 2,00%
Tab. 5
Results of the graphical determination of energy
of activation Ea of thermal-oxidation destruction of
CM with SPM particles
|
q, mass
parts |
Xbegin |
Xend |
Xi |
Ybegin. |
Yend |
Yi |
tq(φ) |
E, kJ/mol |
|
0 |
1.531 |
1.403 |
0.128 |
– 1.053 |
– 3.108 |
2.055 |
16.057 |
133.5 |
|
0.05 |
1.605 |
1.403 |
0.202 |
0.204 |
– 3.066 |
3.270 |
16.190 |
134.6 |
|
0.50 |
1.605 |
1.403 |
0.202 |
0.204 |
– 2.815 |
3.052 |
15.108 |
135.6 |
|
2.00 |
1.605 |
1.403 |
0.202 |
0.290 |
– 2.763 |
3.053 |
15.116 |
135.7 |
It was considered, that the increase of activation energy indicates the
decrease of thermal destruction processes rate. The value of activation energy
for epoxy matrix was discovered as E = 133.5 kJ/mol (Table 5).
Introduction of particles of SPM filler in the quantity of q = 0.05
- 2.00 mass parts for 100 mass parts of ED-20 epoxy oligomer ensures increase, yet
insignificant, of this characteristic up to E = 134.6 - 135.7 kJ/mol. This additionally confirms the
results of studies shown above and indicates the durability of physico-chemical bonds in CM under the impact of the
temperature.
Therefore, the results of the studies allowed to establish the values of
activation energy, which causes the onset of reactions of thermal destruction
of epoxy composites. It can be stated that the material, which contains
particles of synthesised powder mixture in the
quantity of q = 2.00 mass parts for 100 mass parts
of ED-20 epoxy oligomer was characterised by the highest
complex values of thermophysical properties.
Formation of such composite ensures the increase of the values of not only the
beginning and ending temperatures of thermal destruction, but also the increase
of activation energy from E = 133.5 kJ/mol (for epoxy matrix) to E = 135.7 kJ/mol for the
processes of thermal destruction of materials. This indicates the increase of complex values of the thermophysical properties of CM and confirms the
reliability of the results of the conducted studies as well.
4. ENGINEERING
USE OF DEVELOPED COMPOSITES TO INCREASE THE RELIABILITY OF VEHICLES
Based on the conducted
studies, the materials and regimens of forming of epoxy compositions for
protective coatings were developed. Among the developed polymer-composite coatings
that match the high requirements of operation belongs anti-corrosion
polymer-composite coating (APСС). The
main purpose of the coating is to improve the physical and mechanical, thermophysical and anticorrosive properties of marine and
river transport equipment. APCC is a material based
on epoxy matrix and dispersed and fibrous discrete fillers. The material
developed contains SPM filler to improve the thermophysical
properties and corrosion resistance of the equipment parts. The developed
material has high rates of thermophysical and
anticorrosive properties, and its service life is 4 - 6 years. The low cost of
the ingredients of the polymer composition, in comparison with known materials,
is ensured by improving the quality and increasing the service life and
inter-service periods.
The technological process of
forming APCC consists of the following operations:
surface preparation, preparation of compositions, coating, and polymerisation of the composite.
The quality of the preparation
of the protective surface largely determines the reliability and durability of APCC. Surface preparation consists of degreasing and
removing various contaminants, scale, and rust by sandblasting.
The application of developed
protective coating based on APCC on ship structures
is performed via pneumatic spraying of the composition with a thickness of
0.2-0.4 mm, which allows to significantly increase the thermophysical
properties and corrosion durability of protective coatings.
The filler is added to the
epoxy resin in appropriate proportions and hydrodynamically
combined. After mixing the components, the hardener is introduced immediately
before the composition is applied to the workpiece surface.
The composite material,
coatings and technology of its formation and application have been implemented
at the Kherson Shipyard (Kherson, Ukraine), which allows increasing the
operational characteristics of the protective coatings of shafts and heat
exchangers of an engine department on ships. These parts are operated at elevated
temperatures and under the influence of corrosive environments. For this
purpose, it is necessary to increase both thermophysical
properties and corrosion resistance.
The implementation of the
developed protective coating allows:
·
to increase the indices
of the thermophysical properties by 1.4 - 1.6 times;
·
to increase the performance of
anticorrosive properties in 2.1 - 2.3 times.
5.
CONCLUSIONS
According
to the results of studies of the destruction processes of the epoxy composites
structure, the following points can be drawn.
1.
Thermal stability of composite materials, characterised by the beginning and ending temperature of
the mass loss was studied using methods of thermal gravimetric analysis and
differential thermal analysis. It was discovered that the introduction of
powder mixture filler in the quantity of q = 0.05 - 2.00 mass parts by 100 mass parts of ED-20 epoxy
oligomer ensures increase of the beginning temperature of materials thermal
destruction from Тп = 460 К (for epoxy matrix) to Тп = 461 - 479 К. The temperature
of the thermal destruction ending was moved to the right by the abscissa axis
and all studied composites were in range of Тк = 651 - 656 К.
2.
Analysis of the results of studies shows that
introduction of particles leads to a significant decrease of CM mass loss only
in the case of fillers optimal content. In particular, the addition of SPM in
the quantity of q = 0.50 -
2.00 mass parts for 100
mass parts of ED-20 epoxy oligomer provides 1.4-times decrease of
the value of relative mass loss (from εm = 80.7% (for epoxy matrix) to εm = 56.7
- 59.7%). Hence, it can be stated that particles of active filler significantly
slow down the process of thermal destruction and, consequently, improve the
durability of epoxy composites, which are operated under the influence of the
thermal field.
3.
Results
of studies allowed to establish the values of activation energy,
which causes the onset of reactions of thermal destruction of epoxy composites.
It was shown that the material, which contains particles of synthesised
powder mixture in the quantity of q = 2.00 mass parts for 100 mass parts of ED-20 epoxy
oligomer was characterised by the highest complex
values of thermophysical properties. Formation of
such composite ensures the increase of the values of not only the beginning and
ending temperatures of thermal destruction, but also the increase of activation
energy from E = 133.5 kJ/mol (for epoxy
matrix) to E = 135.7 kJ/mol for the
processes of thermal destruction of materials. This indicates the increase of complex values of these CM thermophysical
properties and similarly confirms the reliability of the results of the
conducted studies.
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Received 11.07.2020; accepted in revised form 25.10.2020
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