5 C. B. Zheng, H. K. Jiang, Y. L. Huang, Hydrogen permeation
behaviour of X56 steel in simulated atmospheric environment under
loading, Corrosion Engineering Science & Technology, 46 (2011) 4,
365–367, doi:10.1179/147842209X12559428167689
6 C. Zheng, G. Yi, Temperature effect on hydrogen permeation of X56
steel, Materials Performance, 50 (2011) 4, 72–76
7 M. Schweda, T. Beck, J. Malzbender, Effect of support material
creep on the delamination failure of air plasma sprayed thermal
barrier coatings, Surface & Coatings Technology, 259 (2014) 5,
543–550, doi:10.1016/j.surfcoat.2014.10.033
8 L. Yang, Z. Shi, W. Yang, Enhanced capacitive deionization of lead
ions using air-plasma treated carbon nanotube electrode, Surface &
Coatings Technology, 251 (2014) 29, 122–127, doi:10.1016/
j.surfcoat.2014.04.012
9 X. Lu, X. Feng, Y. Zuo, C. Zheng, S. Lu, Evaluation of the micro-arc
oxidation treatment effect on the protective performance of a Mg-
rich epoxy coating on AZ91D magnesium alloy, Surface & Coatings
Technology, 270 (2015) 2, 227–235, doi:10.1016/j.surfcoat.2015.
02.052
10 Y. Wu, C. Han, J. Yang, Polypropylene films modified by air plasma
and feather keratin graft, Surface and Coatings Technology, 206
(2011) 3, 506–510, doi:10.1016/j.surfcoat.2011.07.073
11 F. Ghadami, M. H. Sohi, S. Ghadami, Effect of bond coat and
post-heat treatment on the adhesion of air plasma sprayed WC-Co
coatings, Surface & Coatings Technology, 261 (2015) 2, 289–294,
doi:10.1016/j.surfcoat.2014.11.016
12 M. Afzal, A. N. Khan, T. B. Mahmud T. I. Khan, M. Ajmal, Effect of
Laser Melting on Plasma Sprayed WC-12 wt.%Co Coatings, Surface
& Coatings Technology, 266 (2015) 1, 22–30, doi:10.1016/
j.surfcoat.2015.02.004
13 L. Yang, F. Yang, Y. Long, Y. Zhao, X. Xiong, Evolution of residual
stress in air plasma sprayed yttria stabilised zirconia thermal barrier
coatings after isothermal treatment, Surface & Coatings Technology,
251 (2014) 29, 98–105, doi:10.1016/j.surfcoat.2014.04.009
14 L. Wang, C. Lin, L. Yang, J. Zhang, J. Zheng, Preparation of nano/
micro-scale column-like topography on PDMS surfaces via vapor
deposition: Dependence on volatility solvents, Applied Surface
Science, 258 (2011) 1, 265–269, doi:10.1016/j.apsusc.2011.08.044
15 C. Riccardi, R. Barni, E. Selli, G. Mazzone, M. R. Massafra, Surface
modification of poly(ethylene terephthalate) fibers induced by radio
frequency air plasma treatment, Applied Surface Science, 211 (2003)
4, 386–397, doi:10.1016/s0169-4332(03)00265-4
16 C. B. Zheng, B. H. Yan, K. Zhang, Electrochemical investigation on
the hydrogen permeation behavior of 7075-T6 Al alloy and its
influence on stress corrosion cracking, International Journal of
Minerals Metallurgy and Materials, 22 (2015) 7, 729–737, doi:
10.1007/s12613-015-1128-5
17 A. E. Bolzán, L. M. Gassa, Comparative EIS study of the adsorption
and electro-oxidation of thiourea and tetramethylthiourea on gold
electrodes, Journal of Applied Electrochemistry, 44 (2014) 2,
279–292, doi:10.1007/s10800-013-0621-7
18 R. I. Tucceri, Deactivation of poly(o -aminophenol) film electrodes
by storage without use in the supporting electrolyte solution and its
comparison with other deactivation processes, A study employing
EIS, Journal of Applied Electrochemistry, 45 (2015) 10, 1123–1132,
doi:10.1007/s10800-015-0851-y
19 B. Ter-Ovanessian, C. Alemany-Dumont, B. Normand, Single freq-
uency electrochemical impedance investigation of zero charge
potential for different surface states of Cu–Ni alloys, Journal of
Applied Electrochemistry, 44 (2014) 3, 399–410, doi:10.1007/
s10800-013-0642-2
20 P. P. Deshpande, N. G. Jadhav, V. J. Gelling, D. Sazou, Conducting
polymers for corrosion protection: a review, Journal of Coatings
Technology and Research, 11 (2014) 4, 473–494, doi:10.1007/
s11998-014-9586-7
21 M. A. Domínguez-Crespo, A. M. Torres-Huerta, E. Onofre-Busta-
mante et al., Corrosion studies of PPy/Ni organic–inorganic hybrid
bilayer coatings on commercial carbon steel, Journal of Solid State
Electrochemistry, 19 (2015) 4, 1–17, doi:10.1007/s10008-014-
2712-8
22 F. Deflorian, S. Rossi, M. D. C. Vadillo, M. Fedel, Electrochemical
characterisation of protective organic coatings for food packaging,
Journal of Applied Electrochemistry, 39 (2009) 11, 2151–2157,
doi:10.1007/ s10800-009-9818-1
23 X. Pan, J. Wu, Y. Ge, K. Xiao, H. Luo, Preparation and characte-
rization of anticorrosion Ormosil sol–gel coatings for aluminum
alloy, Journal of Sol-Gel Science and Technology, 72 (2014) 1, 8–20,
doi:10.1007/s10971-014-3414-5
24 R. Rajamohan, S. K. Nayaki, M. Swaminathan, A Study on Host-
Guest Complexation of 5-Amino-2-Mercaptobenzimidazole with

-Cyclodextrin, Journal of Solution Chemistry, 40 (2011) 5, 803,
doi:10. 1007/s10953-011-9691-5
25 V. Prysiazhnyi, P. Vasina, N. R. Panyala, J. Havel, M. Cemak, Air
DCSBD plasma treatment of Al surface at atmospheric pressure,
Surface & Coatings Technology, 206 (2012) 12, 3011–3016,
doi:10.1016/j.surfcoat.2011.12.039
26 M. A. Samad, N. Satyanarayana, S. K. Sinha, Tribology of
UHMWPE film on air-plasma treated tool steel and the effect of
PFPE overcoat, Surface & Coatings Technology, 204 (2010) 9,
1330–1338, doi:10.1016/j.surfcoat.2009.09.011
C. B. ZHENG et al.: EIS AND SKP STUDY ON IMPROVEMENT OF THE PROTECTION PERFORMANCE ...
918 Materiali in tehnologije / Materials and technology 51 (2017) 6, 911–918
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
J. FOØT et al.: EFFECT OF THE MODE AND DYNAMICS OF THERMAL PROCESSES ...
919–924
EFFECT OF THE MODE AND DYNAMICS OF THERMAL
PROCESSES ON DSC-ACQUIRED PHASE-CHANGE
TEMPERATURE AND LATENT HEAT OF DIFFERENT KINDS
OF PCM
UGOTAVLJANJE VPLIVOV VRSTE IN DINAMIKE TERMI^NIH
PROCESOV NA RAZLI^NE PCM-MATERIALE S POMO^JO
DIFERENCIALNE VRSTI^NE KALORIMETRIJE (DSC)
Jan Foøt1, Zby{ek Pavlík1, Anton Trník1,2, Milena Pavlíková1, Robert ^erný1
1Czech Technical University Prague, Faculty of Civil Engineering, Department of Materials Engineering and Chemistry, Thákurova 7,
166 29 Prague 6, Czech Republic
2Constantine the Philosopher University in Nitra, Department of Physics, Faculty of Natural Sciences, A. Hlinku 1, 949 74 Nitra, Slovakia
pavlikz@fsv.cvut.cz
Prejem rokopisa – received: 2017-02-27; sprejem za objavo – accepted for publication: 2017-05-12
doi:10.17222/mit.2017.026
Thermal-energy-storage systems utilizing phase-change materials (PCMs) can find use in many fields, such as solar-energy
storage, waste-heat recovery or smart air conditioning in buildings. However, their incorporation into certain building elements
and possible utilization of thermal energy are related to the proper understanding of phase-change processes. In this paper,
thermophysical properties of five different PCMs were characterised in order to find suitable materials for incorporation into
lightweight plasters capable of moderating the interior microclimate of buildings. A DSC analysis as the main investigation
method was applied in the range of –10 °C to 55 °C, with the heating/cooling rates of (1, 5, 10 and 20) °C /min. Based on the
DSC data, the temperatures and enthalpies of the phase change were determined as functions of both the modes and dynamics of
the simulated thermal process. The obtained results were discussed and proper PCM candidates for an application in lightweight
interior plasters were identified.
Keywords: phase-change materials, differential scanning calorimetry, phase-change temperature
Sistemi za skladi{~enje toplotne energije, ki izkori{~ajo fazne spremembe v materialih (angl. PCMs; Phase Change Materials),
se uporabljajo na mnogih podro~jih, kot na primer pri pridobivanju in skladi{~enju son~ne energije, izkori{~anju odpadne
toplote, ali v inteligentnih prezra~evalnih sistemih stavb. Kakorkoli, njihova vgradnja v dolo~ene gradbene elemente in mo`no
izkori{~anje odpadne toplote, je povezana z ustreznim razumevanjem faznih sprememb. V tem prispevku so bile dolo~ene
termo-fizikalne lastnosti petih razli~nih PC materialov, da bi na{li ustrezne materiale za vklju~itev v lahke omete, ki bi bili
sposobni uravnavati notranjo mikroklimo stavb. Kot glavna preiskovalna metoda je bila uporabljena DSC (diferencialna vrsti~na
kalorimetrija) analiza v temperaturnem obmo~ju med –10 °C in 55 °C, s hitrostjo ogrevanja/hlajenja (1, 5, 10 in 20) °C/min.
Glede na podatke DSC-analize, so bile dolo~ene temperature in entalpije faznih sprememb v odvisnosti od obeh na~inov in
dinamike simuliranega termi~nega procesa. Dobljeni rezultati so bili pre{tudirani in najdeni so bili ustrezni PCM-materiali za
uporabo v lahkih notranjih ometih.
Klju~ne besede: materiali s faznimi spremembami, diferen~na dinami~na kalorimetrija, temperatura fazne spremembe
1 INTRODUCTION
The International Energy Agency noted in its World
Energy Outlook1 that the building sector is responsible
for approx. 30 % of the total energy consumption in the
US and Europe, whereas in developing countries, this
consumption is even higher, about 41 %. A substantial
part of energy is consumed by a building’s cooling and
heating in order to ensure a high living standard of the
building occupants. Nowadays, building energy efficien-
cy and a decrease in greenhouse-gas emissions are of
particular importance. Techniques known as passive
cooling are extensively studied and used in environ-
mentally friendly technologies for moderation of interior
climate.
Modern lightweight buildings bring many advantages
compared to the standard heavyweight constructions,
such as construction speed, economic benefits and archi-
tectural flexibility. Nevertheless, lightweight building
envelopes are more sensitive to the temperature fluc-
tuation because of their low thermal-storage capacity.2 A
decrease in the thermal-storage capacity leads to a higher
need for moderation of interior climate due to the exter-
nal and/or internal thermal load. Incorporation of PCMs
into the lightweight building envelopes can result in a
more stable interior temperature with lower requirements
on additional heating/cooling equipment.3 Latent-heat-
storage (LHS) systems can be utilized for the optimi-
zation of the ambient temperature, especially during
summer and winter temperature peaks or daily and
nightly fluctuations. These fluctuations are accompanied
by high energy consumption, creating demands on air-
conditioning systems in order to satisfy the requirements
on indoor comfort temperature.4 The efficiency of LHS
Materiali in tehnologije / Materials and technology 51 (2017) 6, 919–924 919
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
UDK 620.192.42:621.785.36:536:6 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(6)919(2017)
is strongly connected with the parameters of applied
PCMs which must comply with thermophysical, chemi-
cal and economic requirements.
PCM characteristics provided by manufacturers
without any exact information on the measurement
methodology can often be misrepresented, inaccurate, or
too optimistic, thus they require further study. Reliable
parameters of PCMs are essential for the design of build-
ing materials and components for latent-heat storage and
moderation of the interior climate. For a proper use of
PCMs, the temperature dependence of the enthalpy
around the phase transition has to be known with a good
accuracy. Analysis techniques used to study the phase
change are mainly conventional calorimetry, differential
scanning calorimetry (DSC) and differential thermal
analysis (DTA). However, other methods, e.g., the T-his-
tory method proposed by J. M. Marín5, also found use in
PCM tests. For the measurement of the PCM thermal
conductivity, the hot-disk method is often used.6 As
mentioned by B. Zalba,7 there is considerable uncertainty
about the property values provided by the manufacturers
(who give values of pure substances) and it is therefore
advisable to use DSC to obtain more accurate values. In
DSC, a reference sample is made to increase (or
decrease) its temperature at a constant rate and the PCM
sample is forced to follow this rate by changing the
power delivered to it. This allows one to extract the heat
capacity as a function of temperature. The transition heat
is then determined by integrating the heat-capacity
curve. The shape of the specific heat-capacity function
depends significantly on the heating and cooling rates
used in the measurements. Different scanning rates
ranging from 0.2 K/min to 10 K/min were employed in
DSC tests to investigate the thermophysical properties of
PCMs.8 Frequently, the enthalpy function or the apparent
heat capacity of a PCM is determined on the basis of
DSC measurements made at too high heating/cooling
rates.9 It was found that the standards used in calorimetry
designed for the materials other than PCMs are not
suitable for PCM testing due to the high heating rate,
affecting the melting/solidification range and stored heat.
When DSC runs at a higher scanning rate, it will give
design information that may not be sufficiently accurate.
In addition, the data on the measurements using different
scanning rates are not comparable.10 H. Mehling et al.11
proposed summarizing the standards for PCM testing, in
order to ensure the reproducibility and comparability of
PCM products. However, although many studies on the
PCM experimental characterization were conducted, no
universal methodology for the DSC tests of PCMs have
yet been developed. This is partially due to the variety of
PCM compositions as they are composed of paraffins,
fatty acids, hydrated salts, etc. For example, a charac-
teristic of most paraffins and salt hydrates is that the
phase change occurs in the temperature range, rather
than at a constant temperature as would be expected for
pure substances.
On this account, a detailed testing of five PCMs on a
paraffin basis was done in our research to describe the
materials’ thermal behaviour, taking into account the
temperature-change rate and the mode of the thermal
process (heating or cooling). The presented experimental
work aimed also at a comparison of two different groups
of PCMs prepared using microencapsulation and
dispersion in water.
2 EXPERIMENTAL PART
For the evaluation of the PCM potential for the heat
storage in lightweight building elements, five types of
commercially produced PCMs were examined. Two of
them were polymethyl methacrylate microencapsulated
paraffin mixtures produced by BASF. They were in the
form of fine powders (a particle size of 50–300 μm)
having the solid content of 97–100 % (according to DIN
EN ISO 3251) and water content  3 %. According to
the data provided by BASF, the first product, Micronal
DS 5038 X, has a melting temperature of about 26 °C
and an enthalpy of fusion of 110 J/g. The second one,
Micronal DS 5040 X, has a slightly lower melting
temperature of 23 °C and an enthalpy of fusion of 100
J/g.12 The second group of the materials was produced by
Rubitherm. These materials were also based on a
paraffin mixture encapsulated in a polymer shell, but
they were delivered in the form of water dispersion with
the solid content of about 35 %. The company product
labels of these materials are RT 21 HC, RT 22 HC and
RT 25 HC. They have the main peak of the phase-change
temperature at (21, 22 and 25) °C, respectively. The
heat-storage-capacity values declared by the producer
are (190, 200 and 230) J/g.13
For the basic characterization of the tested PCMs,
measurements of bulk and powder densities were done.
The bulk and powder densities were obtained from the
measurement of the sample volume and mass. Powdered
materials were characterized by the powder density and
the PCMs in the form of water dispersion were charac-
terized by their bulk density. The relative expanded
uncertainty of these tests was 3.4 %.
Thermal conductivity was measured with an Isomet
2114 device (applied precision) which operates on a
transient-measurement principle. The measurement
range of the thermal conductivity was from 0.015 W/mK
to 6.0 W/mK with the accuracy of 5 % of the reading +
0.001 W/mK. For the measurement, a needle probe that
was inserted into the examined PCMS was used. The
expanded combined uncertainty was 4.3 %.
A DSC 822e (Mettler Toledo) device was employed
in the experiments, together with a Julabo FT 900
cooling device. Temperature and heat-flow calibrations
are very important for the accuracy of the data obtained
with DSC.14 The calibration of the measuring apparatus
was done according to ISO 11357-1.15 To avoid wasting
time while keeping the data accuracy satisfactory, we
J. FOØT et al.: EFFECT OF THE MODE AND DYNAMICS OF THERMAL PROCESSES ...
920 Materiali in tehnologije / Materials and technology 51 (2017) 6, 919–924
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
used "smart" temperature programs proposed by A.
Shimkin for the calibration.16 The samples (~10 mg for
the BASF materials and ~30 mg for the Rubitherm
PCMs) were placed into an aluminum crucible with a
volume of 40 mm3. During the measurement, the follow-
ing temperature regimes were applied: 5 min of the
isothermal regime, cooling at (1, 5, 10 and 20) °C/min
from 55 °C to –10 °C, 5 min of the isothermal regime,
heating at (1, 5, 10 and 20) °C/min from –10 °C to
55 °C, 5 min of the isothermal regime. All the experi-
ments were done in an air atmosphere with a flow rate of
40 mL/min. The enthalpy of fusion was obtained by
integrating the peak area between the start and end
temperatures of the peak. The measurement of the heat
capacity was carried out using sapphire as the reference
sample. Thus, the procedure for measuring the heat capa-
city consisted of three identical steps: 1. measurement of
the blank (the empty crucible), 2. measurement of the
sapphire, 3. measurement of the studied sample. Then,
the heat capacity was calculated with Equation (1):
C C
m H H
m H Hp pr
r s b
s r b
=
−
−
( )
( )
(1)
where Cpr (J/gK) is the heat capacity of the reference
sample (sapphire), mr (g) is the mass of the reference
sample (sapphire), ms (g) is the mass of the studied
sample, and Hb, Hr, and Hs (W/g) are the heat flows of
the blank, the reference sample (sapphire) and the
studied sample, respectively. The onset and endset
temperatures and the enthalpy of fusion were assessed
as the average of three independent measurements,
while the endset and onset temperatures were identified
according to ISO 11357-3:2011.17 According to this
ISO standard, the extrapolated onset temperature is
where the extrapolated baseline is intersected by the
tangent to the curve at the point of inflection and corres-
ponds to the start of the transition; the extrapolated
endset temperature is where the extrapolated baseline is
intersected by the tangent to the curve at the point of
inflection and corresponds to the end of the transition;
the peak temperature is the temperature, at which the
peak reaches the maximum (or minimum).
3 RESULTS AND DISCUSSION
The basic physical properties of the studied materials
are given in Table 1. The data represents the average
values from five measurements. The data was obtained in
laboratory conditions of 23.0 ± 2 °C and 30.0 ± 2 % RH.
Table 1: Basic physical properties and thermal conductivity of the
studied PCMS
PCM
Powder
density
Bulk
density
Thermal
conductivity
(kg/m3) (kg/m3) (W/m K)
Micronal DS 5038 X 361 – 0.080
Micronal DS 5040 X 365 – 0.079
Rubitherm RT 21 – 787 0.442
Rubitherm RT 22 – 789 0.445
Rubitherm RT 25 – 787 0.444
The powder densities of both BASF materials were
very similar, while the examined Rubitherm materials
exhibited almost identical values of the bulk density. For
both powdered BASF materials, the thermal conductivity
values were very low due to the presence of air gaps
between the particles. The assumed incorporation of the
PCM into the silicate matrix (cement or cement-lime
plasters) with almost no air between the PCM particles
is, of course, supposed to result in an increased thermal
conductivity as presented, for example, by Z. Wang et
al.18 On the other hand, the thermal conductivities of the
PCM dispersions were much higher. This was due to the
presence of more than 60 % of water in the dispersion.
From a practical point of view, a high thermal conduc-
tivity of PCMs ensures their effective thermal perfor-
mance, thus the optimum usage of the latent heat.
Figure 1 describes the results of the DSC analysis
used for the determination of the phase-change tem-
perature, the enthalpy of phase transition and the specific
heat capacity of the examined materials. A significant
effect of the heating and cooling rate on the monitored
temperature of the phase-change transition was observed
in all the cases. Generally, with the increasing heating/
cooling rate, the phase-change-transition range was more
spread; this feature was more remarkable for the mate-
rials based on dispersion. A similar PCM performance
with respect to the heating rate applied in a DSC analysis
was observed, e.g., by G. Feng et al.19 who analysed
capric acid of high purity ( 99.9 %) so that the
influence of the material impurity on DSC results was
J. FOØT et al.: EFFECT OF THE MODE AND DYNAMICS OF THERMAL PROCESSES ...
Materiali in tehnologije / Materials and technology 51 (2017) 6, 919–924 921
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 1: Heat flow during heating and cooling of: a) Micronal DS
5038 X, b) Micronal DS 5040 X, c) Rubitherm RT 21, d) Rubitherm
RT 22, e) Rubitherm RT 25
is strongly connected with the parameters of applied
PCMs which must comply with thermophysical, chemi-
cal and economic requirements.
PCM characteristics provided by manufacturers
without any exact information on the measurement
methodology can often be misrepresented, inaccurate, or
too optimistic, thus they require further study. Reliable
parameters of PCMs are essential for the design of build-
ing materials and components for latent-heat storage and
moderation of the interior climate. For a proper use of
PCMs, the temperature dependence of the enthalpy
around the phase transition has to be known with a good
accuracy. Analysis techniques used to study the phase
change are mainly conventional calorimetry, differential
scanning calorimetry (DSC) and differential thermal
analysis (DTA). However, other methods, e.g., the T-his-
tory method proposed by J. M. Marín5, also found use in
PCM tests. For the measurement of the PCM thermal
conductivity, the hot-disk method is often used.6 As
mentioned by B. Zalba,7 there is considerable uncertainty
about the property values provided by the manufacturers
(who give values of pure substances) and it is therefore
advisable to use DSC to obtain more accurate values. In
DSC, a reference sample is made to increase (or
decrease) its temperature at a constant rate and the PCM
sample is forced to follow this rate by changing the
power delivered to it. This allows one to extract the heat
capacity as a function of temperature. The transition heat
is then determined by integrating the heat-capacity
curve. The shape of the specific heat-capacity function
depends significantly on the heating and cooling rates
used in the measurements. Different scanning rates
ranging from 0.2 K/min to 10 K/min were employed in
DSC tests to investigate the thermophysical properties of
PCMs.8 Frequently, the enthalpy function or the apparent
heat capacity of a PCM is determined on the basis of
DSC measurements made at too high heating/cooling
rates.9 It was found that the standards used in calorimetry
designed for the materials other than PCMs are not
suitable for PCM testing due to the high heating rate,
affecting the melting/solidification range and stored heat.
When DSC runs at a higher scanning rate, it will give
design information that may not be sufficiently accurate.
In addition, the data on the measurements using different
scanning rates are not comparable.10 H. Mehling et al.11
proposed summarizing the standards for PCM testing, in
order to ensure the reproducibility and comparability of
PCM products. However, although many studies on the
PCM experimental characterization were conducted, no
universal methodology for the DSC tests of PCMs have
yet been developed. This is partially due to the variety of
PCM compositions as they are composed of paraffins,
fatty acids, hydrated salts, etc. For example, a charac-
teristic of most paraffins and salt hydrates is that the
phase change occurs in the temperature range, rather
than at a constant temperature as would be expected for
pure substances.
On this account, a detailed testing of five PCMs on a
paraffin basis was done in our research to describe the
materials’ thermal behaviour, taking into account the
temperature-change rate and the mode of the thermal
process (heating or cooling). The presented experimental
work aimed also at a comparison of two different groups
of PCMs prepared using microencapsulation and
dispersion in water.
2 EXPERIMENTAL PART
For the evaluation of the PCM potential for the heat
storage in lightweight building elements, five types of
commercially produced PCMs were examined. Two of
them were polymethyl methacrylate microencapsulated
paraffin mixtures produced by BASF. They were in the
form of fine powders (a particle size of 50–300 μm)
having the solid content of 97–100 % (according to DIN
EN ISO 3251) and water content  3 %. According to
the data provided by BASF, the first product, Micronal
DS 5038 X, has a melting temperature of about 26 °C
and an enthalpy of fusion of 110 J/g. The second one,
Micronal DS 5040 X, has a slightly lower melting
temperature of 23 °C and an enthalpy of fusion of 100
J/g.12 The second group of the materials was produced by
Rubitherm. These materials were also based on a
paraffin mixture encapsulated in a polymer shell, but
they were delivered in the form of water dispersion with
the solid content of about 35 %. The company product
labels of these materials are RT 21 HC, RT 22 HC and
RT 25 HC. They have the main peak of the phase-change
temperature at (21, 22 and 25) °C, respectively. The
heat-storage-capacity values declared by the producer
are (190, 200 and 230) J/g.13
For the basic characterization of the tested PCMs,
measurements of bulk and powder densities were done.
The bulk and powder densities were obtained from the
measurement of the sample volume and mass. Powdered
materials were characterized by the powder density and
the PCMs in the form of water dispersion were charac-
terized by their bulk density. The relative expanded
uncertainty of these tests was 3.4 %.
Thermal conductivity was measured with an Isomet
2114 device (applied precision) which operates on a
transient-measurement principle. The measurement
range of the thermal conductivity was from 0.015 W/mK
to 6.0 W/mK with the accuracy of 5 % of the reading +
0.001 W/mK. For the measurement, a needle probe that
was inserted into the examined PCMS was used. The
expanded combined uncertainty was 4.3 %.
A DSC 822e (Mettler Toledo) device was employed
in the experiments, together with a Julabo FT 900
cooling device. Temperature and heat-flow calibrations
are very important for the accuracy of the data obtained
with DSC.14 The calibration of the measuring apparatus
was done according to ISO 11357-1.15 To avoid wasting
time while keeping the data accuracy satisfactory, we
J. FOØT et al.: EFFECT OF THE MODE AND DYNAMICS OF THERMAL PROCESSES ...
920 Materiali in tehnologije / Materials and technology 51 (2017) 6, 919–924
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
used "smart" temperature programs proposed by A.
Shimkin for the calibration.16 The samples (~10 mg for
the BASF materials and ~30 mg for the Rubitherm
PCMs) were placed into an aluminum crucible with a
volume of 40 mm3. During the measurement, the follow-
ing temperature regimes were applied: 5 min of the
isothermal regime, cooling at (1, 5, 10 and 20) °C/min
from 55 °C to –10 °C, 5 min of the isothermal regime,
heating at (1, 5, 10 and 20) °C/min from –10 °C to
55 °C, 5 min of the isothermal regime. All the experi-
ments were done in an air atmosphere with a flow rate of
40 mL/min. The enthalpy of fusion was obtained by
integrating the peak area between the start and end
temperatures of the peak. The measurement of the heat
capacity was carried out using sapphire as the reference
sample. Thus, the procedure for measuring the heat capa-
city consisted of three identical steps: 1. measurement of
the blank (the empty crucible), 2. measurement of the
sapphire, 3. measurement of the studied sample. Then,
the heat capacity was calculated with Equation (1):
C C
m H H
m H Hp pr
r s b
s r b
=
−
−
( )
( )
(1)
where Cpr (J/gK) is the heat capacity of the reference
sample (sapphire), mr (g) is the mass of the reference
sample (sapphire), ms (g) is the mass of the studied
sample, and Hb, Hr, and Hs (W/g) are the heat flows of
the blank, the reference sample (sapphire) and the
studied sample, respectively. The onset and endset
temperatures and the enthalpy of fusion were assessed
as the average of three independent measurements,
while the endset and onset temperatures were identified
according to ISO 11357-3:2011.17 According to this
ISO standard, the extrapolated onset temperature is
where the extrapolated baseline is intersected by the
tangent to the curve at the point of inflection and corres-
ponds to the start of the transition; the extrapolated
endset temperature is where the extrapolated baseline is
intersected by the tangent to the curve at the point of
inflection and corresponds to the end of the transition;
the peak temperature is the temperature, at which the
peak reaches the maximum (or minimum).
3 RESULTS AND DISCUSSION
The basic physical properties of the studied materials
are given in Table 1. The data represents the average
values from five measurements. The data was obtained in
laboratory conditions of 23.0 ± 2 °C and 30.0 ± 2 % RH.
Table 1: Basic physical properties and thermal conductivity of the
studied PCMS
PCM
Powder
density
Bulk
density
Thermal
conductivity
(kg/m3) (kg/m3) (W/m K)
Micronal DS 5038 X 361 – 0.080
Micronal DS 5040 X 365 – 0.079
Rubitherm RT 21 – 787 0.442
Rubitherm RT 22 – 789 0.445
Rubitherm RT 25 – 787 0.444
The powder densities of both BASF materials were
very similar, while the examined Rubitherm materials
exhibited almost identical values of the bulk density. For
both powdered BASF materials, the thermal conductivity
values were very low due to the presence of air gaps
between the particles. The assumed incorporation of the
PCM into the silicate matrix (cement or cement-lime
plasters) with almost no air between the PCM particles
is, of course, supposed to result in an increased thermal
conductivity as presented, for example, by Z. Wang et
al.18 On the other hand, the thermal conductivities of the
PCM dispersions were much higher. This was due to the
presence of more than 60 % of water in the dispersion.
From a practical point of view, a high thermal conduc-
tivity of PCMs ensures their effective thermal perfor-
mance, thus the optimum usage of the latent heat.
Figure 1 describes the results of the DSC analysis
used for the determination of the phase-change tem-
perature, the enthalpy of phase transition and the specific
heat capacity of the examined materials. A significant
effect of the heating and cooling rate on the monitored
temperature of the phase-change transition was observed
in all the cases. Generally, with the increasing heating/
cooling rate, the phase-change-transition range was more
spread; this feature was more remarkable for the mate-
rials based on dispersion. A similar PCM performance
with respect to the heating rate applied in a DSC analysis
was observed, e.g., by G. Feng et al.19 who analysed
capric acid of high purity ( 99.9 %) so that the
influence of the material impurity on DSC results was
J. FOØT et al.: EFFECT OF THE MODE AND DYNAMICS OF THERMAL PROCESSES ...
Materiali in tehnologije / Materials and technology 51 (2017) 6, 919–924 921
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 1: Heat flow during heating and cooling of: a) Micronal DS
5038 X, b) Micronal DS 5040 X, c) Rubitherm RT 21, d) Rubitherm
RT 22, e) Rubitherm RT 25
neglected. G. Feng et al.19 applied heating rates of (10, 5,
1, 0.5 and 0.1) °C/min. When the heating/cooling rate
increased from 0.1 °C/min to 10 °C/min, the biggest
deviations in solid- and liquid-transition temperatures
were 1.1 °C and 6.4 °C, respectively.
In our case, when the heating or cooling rate in-
creased from 1 °C/min to 20 °C/min, the biggest diffe-
rence in the onset of the liquid-transition temperature
was 1.9 °C (measured for Rubitherm RT 21) and it was
2.8 °C for the onset of the solidification temperature (for
Rubitherm RT 25). On the other hand, sharp boundaries
of the phase-change transition were found for the lower
rates of the heating. In this case, it was easy to identify
the onset and endset temperatures of the phase change
and to calculate its corresponding enthalpy.
The onset and endset temperatures used for the
assessment of the enthalpy of the phase transition are
given in Table 2. Comparing the measured onset and
endset temperatures with the phase-change temperatures
declared by the producers, the mean values measured for
the lower heating/cooling rates corresponded to those
provided on PCM product sheets.
Table 2: Phase-change temperatures
PCM
Temperature-
change rate
(°C/min)
Heating (°C) Cooling (°C)
Onset Endset Onset Endset
Micronal
DS 5038 X
1 23.3 27.8 23.7 19.5
5 23.2 32.8 24.7 14.0
10 22.9 37.4 24.6 6.2
20 22.8 44.1 24.2 –1.7
Micronal
DS 5040 X
1 19.6 25.5 22.7 15.9
5 19.5 30.4 22.4 17.0
10 19.4 34.5 22.1 4.7
20 19.3 41.1 21.6 –3.5
Rubitherm
RT 21 HC
1 19.6 25.7 22.5 16.2
5 19.9 33.2 21.9 8.4
10 20.1 37.0 21.5 12.6
20 21.5 46.2 19.9 –10.1
Rubitherm
RT 22 HC
1 20.4 26.4 22.7 16.9
5 20.7 32.5 22.3 9.9
10 20.7 38.3 21.0 2.0
20 21.0 43.7 20.6 –4.9
Rubitherm
RT 25 HC
1 22.7 27.6 24.9 18.7
5 22.0 33.1 23.5 12.0
10 21.7 36.9 23.8 8.7
20 21.0 44.3 22.1 1.7
Considering the DSC plots, we can see that during
the heating process all the measured heat flux vs.
temperature curves exhibited a unimodal character. On
the other hand, during the cooling, bimodal or even
trimodal shapes were obtained for materials Micronal
DS 5038 X and Rubitherm RT 21 HC. In the past,
bimodal shapes of DSC curves were found by other
investigators as well. J. Jeon et al.20 reported on two
phase-change peaks of paraffin. The first phase-change
peak in the cooling process was high, corresponding to
the liquid-solid transition of paraffin, but the second
peak was much lower. As it was analysed in detail by
N. Ukrainczyk et al.21, this smaller endotherm corres-
ponds to the solid-solid transition when the close-packed
hexagonal system of paraffin transforms into the ortho-
rhombic or monoclinic (depending on the number of
carbon atoms in a molecule) crystalline structure.
Considering the findings of the other investigators
mentioned above, the shapes of the DSC plots of Micro-
nal DS 5038 X and Rubitherm RT 21 in the cooling
phase can be explained with two main effects. First, the
paraffin underwent two phase transitions.20,21 Second,
due to the high cooling rate adopted for the DSC anal-
ysis, the super-cooling phenomena could also contribute
to the appearance of the bimodal (or/and trimodal) shape
of the DSC plots.22
In Table 3, the enthalpies of fusion and crystalliza-
tion in dependence on the heating and cooling rate are
presented. The PCMs produced by BASF exhibited
substantially lower enthalpies, as compared to the values
obtained for the materials delivered by Rubitherm. While
the enthalpy values of the BASF products varied from
93 J/g to 103 J/g, the Rubitherm materials yielded the
enthalpy in a range of 113–183 J/g. Enthalpy values
similar to those shown in Table 4 were obtained, e.g., by
J. Jeon et al.20 and X. Liu at al.23 who obtained, for
paraffinic waxes, enthalpies of fusion of 144.6 J/g and
153.5 J/g, respectively. Comparing the measured data
with the enthalpy values provided on product sheets, the
values obtained in our case were lower, especially for the
Rubitherm materials.
Table 3: Phase-change enthalpies
PCM
Temperature-
change rate
(°C/min)
Enthalpy (J/g)
Heating Cooling
Micronal DS
5038 X
1 99.5 102.6
5 101.2 103.4
10 98.9 103.6
20 97.9 103.9
Micronal DS
5040 X
1 97.7 100.3
5 94.0 96.1
10 95.2 98.8
20 96.0 103.2
Rubitherm RT
21 HC
1 124.3 131.6
5 125.5 128.8
10 126.9 131.3
20 113.0 119.0
Rubitherm RT
22 HC
1 134.0 128.2
5 131.9 134.2
10 126.0 130.6
20 125.8 131.3
Rubitherm RT
25 HC
1 175.0 166.8
5 177.3 167.8
10 178.5 171.1
20 174.9 183.2
J. FOØT et al.: EFFECT OF THE MODE AND DYNAMICS OF THERMAL PROCESSES ...
922 Materiali in tehnologije / Materials and technology 51 (2017) 6, 919–924
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
The heating/cooling-rate change resulted in only
small differences between the measured enthalpies of
fusion and crystallization (< 7 %) up to 10 °C/min. For
20 °C/min, the differences were higher in some cases
(Rubitherm RT 21 HC for both the heating and cooling
phase, Rubitherm RT 25 HC for the cooling phase)
which could be attributed to the higher uncertainty of the
measurement of higher temperature-change rates and the
difficulty to distinguish the endset and onset tempera-
tures of the phase change. The differences between the
enthalpies of fusion and crystallization of particular
tested materials were small in all the cases, up to 6 %;
they were well within the measurement uncertainty.
Figure 2 shows the specific-heat-capacity plots ob-
tained from the DSC tests. The data represents the
average values of three measurements. All the tested
materials exhibited an increase in the specific-heat
capacity during the melting. Similar to the heat-flow
plots shown in Figures 1 to 5, a remarkable increase in
the specific-heat capacity with the decreasing tempera-
ture-change rate was observed in the temperature ranges
corresponding to the solid-liquid phase transitions. For
instance, for the heating rate of 1 °C/min, the specific-
heat-capacity function of Micronal DS 5038 X reached
the maximum at 30.1 J/g K. When the heating rate of 20
°C/min was used, the specific-heat-capacity maximum
was only 8.5 J/g K. This finding can have significant
consequences for the practical capabilities of particular
PCMs to moderate the interior climate of a building
exposed to different exterior climatic loads as well as to
moderate technological processes, energy recuperation,
etc.
From a quantitative point of view, the measured
values of the specific-heat capacity corresponding to
melting are very high, making the studied PCMs well
applicable for effective heat storage in building and
construction elements. For lower temperatures, for
example 10 °C, the measured specific-heat capacity
dropped and reached values of 1.4–2.6 J/g K. Similar
results for paraffin E53 were reported by E. M. Anghel et
al.24 who obtained, at 10 °C, a specific heat capacity of
1.6 J/g K. Similarly, D. Zhou et al.25 reported on the spe-
cific-heat capacity of Rubitherm 25 that was 2.1 J/g K.
4 CONCLUSIONS
A thermophysical analysis of several different PCMs
in the form of a fine powder and water dispersion was
done, taking into account the effects of the mode and
dynamics of a DSC-simulated thermal process on
phase-change characteristics.
The main results of the experimental work can be
summarized in the following points:
• The choice of a proper heating/cooling mode of the
DSC test was of particular importance for the eva-
luation and generalization of the PCM thermal
performance. In this respect, it was found that a
universal methodology for testing PCMs with an
assumed application in the construction industry is
actually missing although the low-temperature
change rate looks promising for a detailed description
of phase-change processes.
• A significant effect of the heating and cooling rate on
the monitored temperature of the phase-change
transition was observed for all the studied PCMs.
Generally, with the increasing rate of the temperature
change, the phase-change-transition range was more
spread; this feature was more remarkable for the
materials based on dispersion.
• The temperature-rate change resulted in only small
differences between the measured enthalpies of
fusion and crystallization up to 10 °C/min.
• The powdered PCMs produced by BASF exhibited
substantially lower phase-change enthalpies, when
compared to the water-dispersed PCMs delivered by
Rubitherm. This was in agreement with the data
provided by PCM producers. However, all the studied
materials were found to be suitable candidates for
application in lightweight interior plasters.
• An increase in the heating rate led to a decrease in
the maximum specific-heat capacity in the desired
operational range of the examined PCMs. From the
point of view of their assumed application for the
moderation of a building’s interior climate, their
effectiveness is better for slower temperature
changes, as in common climatic conditions.
• Based on the findings presented above, it can be
concluded that from a practical point of view, aiming
at an effective use of PCMs in the conditioning of a
J. FOØT et al.: EFFECT OF THE MODE AND DYNAMICS OF THERMAL PROCESSES ...
Materiali in tehnologije / Materials and technology 51 (2017) 6, 919–924 923
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 2: Specific-heat capacity during heating: a) Micronal DS 5038
X, b) Micronal DS 5040 X, c) Rubitherm RT 21, d) Rubitherm RT 22,
e) Rubitherm RT 25
neglected. G. Feng et al.19 applied heating rates of (10, 5,
1, 0.5 and 0.1) °C/min. When the heating/cooling rate
increased from 0.1 °C/min to 10 °C/min, the biggest
deviations in solid- and liquid-transition temperatures
were 1.1 °C and 6.4 °C, respectively.
In our case, when the heating or cooling rate in-
creased from 1 °C/min to 20 °C/min, the biggest diffe-
rence in the onset of the liquid-transition temperature
was 1.9 °C (measured for Rubitherm RT 21) and it was
2.8 °C for the onset of the solidification temperature (for
Rubitherm RT 25). On the other hand, sharp boundaries
of the phase-change transition were found for the lower
rates of the heating. In this case, it was easy to identify
the onset and endset temperatures of the phase change
and to calculate its corresponding enthalpy.
The onset and endset temperatures used for the
assessment of the enthalpy of the phase transition are
given in Table 2. Comparing the measured onset and
endset temperatures with the phase-change temperatures
declared by the producers, the mean values measured for
the lower heating/cooling rates corresponded to those
provided on PCM product sheets.
Table 2: Phase-change temperatures
PCM
Temperature-
change rate
(°C/min)
Heating (°C) Cooling (°C)
Onset Endset Onset Endset
Micronal
DS 5038 X
1 23.3 27.8 23.7 19.5
5 23.2 32.8 24.7 14.0
10 22.9 37.4 24.6 6.2
20 22.8 44.1 24.2 –1.7
Micronal
DS 5040 X
1 19.6 25.5 22.7 15.9
5 19.5 30.4 22.4 17.0
10 19.4 34.5 22.1 4.7
20 19.3 41.1 21.6 –3.5
Rubitherm
RT 21 HC
1 19.6 25.7 22.5 16.2
5 19.9 33.2 21.9 8.4
10 20.1 37.0 21.5 12.6
20 21.5 46.2 19.9 –10.1
Rubitherm
RT 22 HC
1 20.4 26.4 22.7 16.9
5 20.7 32.5 22.3 9.9
10 20.7 38.3 21.0 2.0
20 21.0 43.7 20.6 –4.9
Rubitherm
RT 25 HC
1 22.7 27.6 24.9 18.7
5 22.0 33.1 23.5 12.0
10 21.7 36.9 23.8 8.7
20 21.0 44.3 22.1 1.7
Considering the DSC plots, we can see that during
the heating process all the measured heat flux vs.
temperature curves exhibited a unimodal character. On
the other hand, during the cooling, bimodal or even
trimodal shapes were obtained for materials Micronal
DS 5038 X and Rubitherm RT 21 HC. In the past,
bimodal shapes of DSC curves were found by other
investigators as well. J. Jeon et al.20 reported on two
phase-change peaks of paraffin. The first phase-change
peak in the cooling process was high, corresponding to
the liquid-solid transition of paraffin, but the second
peak was much lower. As it was analysed in detail by
N. Ukrainczyk et al.21, this smaller endotherm corres-
ponds to the solid-solid transition when the close-packed
hexagonal system of paraffin transforms into the ortho-
rhombic or monoclinic (depending on the number of
carbon atoms in a molecule) crystalline structure.
Considering the findings of the other investigators
mentioned above, the shapes of the DSC plots of Micro-
nal DS 5038 X and Rubitherm RT 21 in the cooling
phase can be explained with two main effects. First, the
paraffin underwent two phase transitions.20,21 Second,
due to the high cooling rate adopted for the DSC anal-
ysis, the super-cooling phenomena could also contribute
to the appearance of the bimodal (or/and trimodal) shape
of the DSC plots.22
In Table 3, the enthalpies of fusion and crystalliza-
tion in dependence on the heating and cooling rate are
presented. The PCMs produced by BASF exhibited
substantially lower enthalpies, as compared to the values
obtained for the materials delivered by Rubitherm. While
the enthalpy values of the BASF products varied from
93 J/g to 103 J/g, the Rubitherm materials yielded the
enthalpy in a range of 113–183 J/g. Enthalpy values
similar to those shown in Table 4 were obtained, e.g., by
J. Jeon et al.20 and X. Liu at al.23 who obtained, for
paraffinic waxes, enthalpies of fusion of 144.6 J/g and
153.5 J/g, respectively. Comparing the measured data
with the enthalpy values provided on product sheets, the
values obtained in our case were lower, especially for the
Rubitherm materials.
Table 3: Phase-change enthalpies
PCM
Temperature-
change rate
(°C/min)
Enthalpy (J/g)
Heating Cooling
Micronal DS
5038 X
1 99.5 102.6
5 101.2 103.4
10 98.9 103.6
20 97.9 103.9
Micronal DS
5040 X
1 97.7 100.3
5 94.0 96.1
10 95.2 98.8
20 96.0 103.2
Rubitherm RT
21 HC
1 124.3 131.6
5 125.5 128.8
10 126.9 131.3
20 113.0 119.0
Rubitherm RT
22 HC
1 134.0 128.2
5 131.9 134.2
10 126.0 130.6
20 125.8 131.3
Rubitherm RT
25 HC
1 175.0 166.8
5 177.3 167.8
10 178.5 171.1
20 174.9 183.2
J. FOØT et al.: EFFECT OF THE MODE AND DYNAMICS OF THERMAL PROCESSES ...
922 Materiali in tehnologije / Materials and technology 51 (2017) 6, 919–924
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
The heating/cooling-rate change resulted in only
small differences between the measured enthalpies of
fusion and crystallization (< 7 %) up to 10 °C/min. For
20 °C/min, the differences were higher in some cases
(Rubitherm RT 21 HC for both the heating and cooling
phase, Rubitherm RT 25 HC for the cooling phase)
which could be attributed to the higher uncertainty of the
measurement of higher temperature-change rates and the
difficulty to distinguish the endset and onset tempera-
tures of the phase change. The differences between the
enthalpies of fusion and crystallization of particular
tested materials were small in all the cases, up to 6 %;
they were well within the measurement uncertainty.
Figure 2 shows the specific-heat-capacity plots ob-
tained from the DSC tests. The data represents the
average values of three measurements. All the tested
materials exhibited an increase in the specific-heat
capacity during the melting. Similar to the heat-flow
plots shown in Figures 1 to 5, a remarkable increase in
the specific-heat capacity with the decreasing tempera-
ture-change rate was observed in the temperature ranges
corresponding to the solid-liquid phase transitions. For
instance, for the heating rate of 1 °C/min, the specific-
heat-capacity function of Micronal DS 5038 X reached
the maximum at 30.1 J/g K. When the heating rate of 20
°C/min was used, the specific-heat-capacity maximum
was only 8.5 J/g K. This finding can have significant
consequences for the practical capabilities of particular
PCMs to moderate the interior climate of a building
exposed to different exterior climatic loads as well as to
moderate technological processes, energy recuperation,
etc.
From a quantitative point of view, the measured
values of the specific-heat capacity corresponding to
melting are very high, making the studied PCMs well
applicable for effective heat storage in building and
construction elements. For lower temperatures, for
example 10 °C, the measured specific-heat capacity
dropped and reached values of 1.4–2.6 J/g K. Similar
results for paraffin E53 were reported by E. M. Anghel et
al.24 who obtained, at 10 °C, a specific heat capacity of
1.6 J/g K. Similarly, D. Zhou et al.25 reported on the spe-
cific-heat capacity of Rubitherm 25 that was 2.1 J/g K.
4 CONCLUSIONS
A thermophysical analysis of several different PCMs
in the form of a fine powder and water dispersion was
done, taking into account the effects of the mode and
dynamics of a DSC-simulated thermal process on
phase-change characteristics.
The main results of the experimental work can be
summarized in the following points:
• The choice of a proper heating/cooling mode of the
DSC test was of particular importance for the eva-
luation and generalization of the PCM thermal
performance. In this respect, it was found that a
universal methodology for testing PCMs with an
assumed application in the construction industry is
actually missing although the low-temperature
change rate looks promising for a detailed description
of phase-change processes.
• A significant effect of the heating and cooling rate on
the monitored temperature of the phase-change
transition was observed for all the studied PCMs.
Generally, with the increasing rate of the temperature
change, the phase-change-transition range was more
spread; this feature was more remarkable for the
materials based on dispersion.
• The temperature-rate change resulted in only small
differences between the measured enthalpies of
fusion and crystallization up to 10 °C/min.
• The powdered PCMs produced by BASF exhibited
substantially lower phase-change enthalpies, when
compared to the water-dispersed PCMs delivered by
Rubitherm. This was in agreement with the data
provided by PCM producers. However, all the studied
materials were found to be suitable candidates for
application in lightweight interior plasters.
• An increase in the heating rate led to a decrease in
the maximum specific-heat capacity in the desired
operational range of the examined PCMs. From the
point of view of their assumed application for the
moderation of a building’s interior climate, their
effectiveness is better for slower temperature
changes, as in common climatic conditions.
• Based on the findings presented above, it can be
concluded that from a practical point of view, aiming
at an effective use of PCMs in the conditioning of a
J. FOØT et al.: EFFECT OF THE MODE AND DYNAMICS OF THERMAL PROCESSES ...
Materiali in tehnologije / Materials and technology 51 (2017) 6, 919–924 923
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 2: Specific-heat capacity during heating: a) Micronal DS 5038
X, b) Micronal DS 5040 X, c) Rubitherm RT 21, d) Rubitherm RT 22,
e) Rubitherm RT 25
building’s interior climate, the most crucial is the
monitoring of temperature fluctuations in the interior
and the performance of a DSC analysis according to
the measured indoor-temperature-rate change. In this
way, the choice of a proper PCM will consider the
actual conditions of a building, and the thermal enve-
lope with the incorporated PCM will be "tailor-
made".
Acknowledgment
Authors gratefully acknowledge the financial support
of the Czech Science Foundation, under project No
P105/12/G059.
5 REFERENCES
1 World Energy Outlook 2010, OECD/IEA, SOREGRAPH, Paris
Cedex 2010, 731
2 Y. Zhang, S. Zhuang, Q. Wang, J. He, Experimental research on the
thermal performance of composite PCM hollow block walls and
validation of phase transition heat transfer models, Adv. Mater. Sci.
Eng., (2016), doi:10.1155/2016/6359414
3 A. G. Entrop, H. J. H. Brouwers, A. H. M. E. Reinders, Experimental
research on the use of micro-encapsulated phase change materials to
store solar energy in concrete floors and to save energy in Dutch
houses, Sol. Energy, 85 (2011), doi:10.1016/j.solener.2011.02.017
4 F. Agyenim, N. Hewitt, P. Eames, M. Smyth, A review of materials,
heat transfer and phase change problem formulation for latent heat
thermal storage systems (LHTESS), Renew. Sust. Energ. Rev., 14
(2010), doi:10.1016/j.rser.2009.10.015
5 J. M. Marín, B. Zalba, L. F. Cabeza, H. Mehling, Determination of
enthalpy–temperature curves of phase change materials with the
temperature-history method: improvement to temperature dependent
properties, Measurement Sci. Technol., 14 (2003), doi:10.1088/
0957-0233/14/2/305
6 L. Gao, J. Zhao, Q. An, D. Zhao, F. Meng, X. Liu, Experiments on
thermal performance of erythritol/expanded graphite in a direct
contact thermal energy storage container, Appl. Therm. Eng., 113
(2017), doi:10.1016/j.applthermaleng.2016.11.073
7 B. Zalba, J. M. Marín, L. F. Cabeza, H. Mehling, Review on thermal
energy storage with phase change: materials, heat transfer analysis
and applications, Appl. Therm. Eng., 23 (2003), doi:10.1016/S1359-
4311(02)00192-8
8 P. Losada-Pérez, C. S. P. Tripathi, J. Leyes, G. Cordoyiannis, C.
Glorieux, J. Thoen, Measurement of heat capacity and enthalpy of
phase change materials by adiabatic scanning calorimetry, Int. J.
Thermophys., 32 (2011), doi:0.1007/s10765-011-0984-0
9 C. Arkar, S. Medved, Influence of accuracy of thermal property data
of a phase change material on the result of a numerical model of a
packed bed latent heat storage with spheres, Thermochim. Acta, 438
(2005), doi:10.1016/j.tca.2005.08.032
10 B. He, V. Martin, F. Setterwall, Phase transition temperature ranges
and storage density of paraffin wax phase change materials, Energy,
29 (2004), doi:10.1016/j.energy.2004.03.002
11 H. Mehling, H. P. Ebert, P. Schossig, Development of standards for
materials testing and quality control of PCM, 7th IIR Conference on
Phase Change Materials and Slurries for Refrigeration and Air
Conditioning, Dinan 2006, 1–9
12 Product Overview, BASF company, http://product-finder.basf.com,
6.4.2017
13 PCM RT-Line, Rubitherm, https://www.rubitherm.eu, 6.4.2017
14 E. Gmelin, S. M. Sarge, Temperature, heat and heat flow rate
calibration of differential scanning calorimeters, Thermochim. Acta,
347 (2000), doi:10.1016/S0040-6031(99)00424-4
15 ISO 11357-1:2016 Plastics – Differential scanning calorimetry
(DSC) – Part 1: General principles, ISO Committee, Geneve
16 A. Shimkin, Optimization of DSC calibration procedure, Thermo-
chim. Acta, 566 (2013), doi:10.1016/j.tca.2013.04.039
17 ISO 11357-3:2011 Plastics – Differential scanning calorimetry
(DSC) – Part 3: Determination of temperature and enthalpy of
melting and crystallization, ISO Committee, Geneve
18 Z. Wang, H. Su, S. Zhao, N. Zhao, Influence of phase change ma-
terial on mechanical and thermal properties of clay geopolymer
mortar, Constr. Build. Mater., 120 (2016), doi:10.1016/j.conbuild-
mat.2016.05.091
19 G. Feng, K. Huang, H. Xie, H. Li, X. Liu, S. Liu, DSC test error of
phase change material (PCM) and its influence on the simulation of
the PCM floor, Renew. Energy, 87 (2016), doi:10.1016/j.renene.
2015.07.085
20 J. Jeon, S. G. Jeong, J. H. Lee, J. Seo, S. Kim, High thermal
performance composite PCMs loading xGnP for application to
building using radiant floor heating system, Sol. Energ. Mater. Sol.
C., 101 (2012), doi:10.1016/j.solmat.2012.02.028
21 N. Ukrainczyk, S. Kurajica, J. Sipusic, Thermophysical comparison
of five commercial paraffin waxes as latent heat storage materials,
Chem. Biochem. Eng. Q., 24 (2010)
22 Z. Pavlík, J. Foøt, M. Pavlíková, J. Pokorný, A. Trník, R. ^erný,
Modified lime-cement plasters with enhanced thermal and hygric
storage capacity for moderation of interior climate, Energ. Buildings,
126 (2016), doi:10.1016/j.enbuild.2016.05.004
23 X. Liu, H. Liu, S. Wang, L. Zhang, H. Cheng, Preparation and
thermal properties of form stable paraffin phase change material
encapsulation, Energ. Convers. Manage., 47 (2006), doi:10.1016/
j.enconman.2005.10.031
24 E. M. Anghel, A. Georgiev, S. Petrescu, R. Popov, M. Constanti-
nescu, Thermo-physical characterization of some paraffins used as
phase change materials for thermal energy storage, J. Therm. Anal.
Calorim., 117 (2014), doi:10.1007/s10973-014-3775-6
25 D. Zhou, C. Y. Zhao, Y. Tian, Review on thermal energy storage with
phase change materials (PCMs) in building applications, Appl.
Energ. 92 (2012), doi:10.1016/j.apenergy.2011.08.025
J. FOØT et al.: EFFECT OF THE MODE AND DYNAMICS OF THERMAL PROCESSES ...
924 Materiali in tehnologije / Materials and technology 51 (2017) 6, 919–924
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
M. BUCHTÍK et al.: CHARACTERIZATION OF Ni-P COATING PREPARED ON A WROUGHT AZ61 ...
925–931
CHARACTERIZATION OF Ni-P COATING PREPARED ON A
WROUGHT AZ61 MAGNESIUM ALLOY VIA ELECTROLESS
DEPOSITION
KARAKTERIZACIJA Ni-P PREVLEKE, PRIPRAVLJENE Z
NEELEKTRI^NO DEPOZICIJO NA KOVANI MAGNEZIJEVI
ZLITINI AZ61
Martin Buchtík1, Petr Kosár1, Jaromír Wasserbauer1, Pavel Dole`al1,2
1Brno University of Technology, Faculty of Chemistry, Purkyòova 464/118, 602 00 Brno, Czech Republic
2Brno University of Technology, Faculty of Mechanical Engineering, Technická 2896/2, 602 00 Brno, Czech Republic
xcbuchtik@fch.vutbr.cz
Prejem rokopisa – received: 2017-03-08; sprejem za objavo – accepted for publication: 2017-04-20
doi:10.17222/mit.2017.029
A low-phosphorous Ni-P coating was prepared on a wrought AZ61 magnesium alloy via electroless deposition for 1 h after an
adequate substrate-surface pre-treatment. The prepared coating with a thickness of 10 μm was characterized by the uniform
distribution of Ni (95.4 % mass fraction) and P (4.6 % mass fraction) in the cross-section. Microcavities present in the coating
resulted in quite a low corrosion resistance of the coated magnesium alloy in a 0.1 M NaCl solution. On the other hand, the
coating exhibits a high degree of adhesion, as evidenced by a scratch test, and significantly improves the AZ61
magnesium-alloy microhardness.
Keywords: electroless nickel, magnesium alloy, AZ61, characterization of Ni-P coatings
Malo porozna Ni-P prevleka je bila pripravljena na povr{ini kovane AZ61 magnezijeve zlitine. Prevleka je bila pripravljena z
enourno neelektri~no depozicijo na predhodno ustrezno obdelani povr{ini zlitine. Pripravljena prevleka debeline 10 μm je imela
v pre~nem prerezu enakomerno porazdelitev Ni (95,4 % masnih odstotkov) in P (4,6 % masnih odstotkov). Zaradi prisotnosti
mikropraznin v izdelani prevleki je korozijska odpornost prevle~ene magnezijeve zlitine v 0,1 M NaCl raztopini slaba. Preizkusi
razenja prevleke pa so po drugi strani pokazali zelo dober oprijem izdelane prevleke s povr{ino zlitine in znatno izbolj{anje
mikrotrdote AZ61 magnezijeve zlitine.
Klju~ne besede: brezelektri~no nikljanje, magnezijeva zlitina, AZ61, karakterizacija Ni-P prevlek
1 INTRODUCTION
Due to their low density, magnesium alloys are
ranked among the lightest constructional metallic mate-
rials. Magnesium alloys concurrently have a high
specific strength, toughness and good casting properties.
They find their application in the automotive and aero-
space industry.1–4 A high chemical reactivity, low corro-
sion resistance and low hardness are their negative
properties.4 Therefore, it is necessary to protect magne-
sium alloys against the effects of external environment.
There are several ways of protecting magnesium alloys
such as galvanic or electroless deposition of coatings,
conversion coatings, organic coatings and varnishing.
Electroless-deposited Ni-P coatings improve the
coated-material resistance to corrosive environments and
material mechanical and wear resistance. Deposited Ni-P
coatings have a higher corrosion resistance, physico-
mechanical and tribological properties compared to
non-treated magnesium alloys.5–7 Generally, the industry
identifies three groups of electroless Ni-P coatings
according to their phosphorus contents. Low-phosphorus
coatings contain 2–5 % mass fractions of phosphorus,
medium-phosphorus Ni-P coatings contain 6–9 % mass
fractions of phosphorus and high-phosphorus Ni-P
coatings contain 10–13 % mass fractions of phosphorus.8
Low-phosphorus Ni-P coatings are predominantly used
to increase the hardness of the coated substrate.1 In gene-
ral, the hardness, crystallinity and density of electroless
Ni-P coatings decrease with the increasing content of
phosphorus in the coatings. However, the corrosion
resistance of Ni-P coatings increases with the increasing
content of phosphorus.1,9
The hardness of deposited low-phosphorus Ni-P coat-
ings can be additionally increased by heat treatment.5
During heat treatment, the deposited coating consisting
of an amorphous Ni-P phase decomposes due to a
gradual increase in the temperature to form crystalline
particles of phosphide (Ni3P). Fine crystalline particles
of phosphide (Ni3P) are formed simultaneously, predo-
minantly in the form of precipitates.9 The highest value
of the hardness of Ni-P coatings is reached after the heat
treatment at 400 °C for 1 h, when the hardness reaches a
value of up to 1300 HV.10 The hardness of Ni-P coatings
can also be increased by reducing the phosphorus con-
tent by changing the ratio of the components contained
in the nickel bath and by changing the coating-process
Materiali in tehnologije / Materials and technology 51 (2017) 6, 925–931 925
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
UDK 67.017:621.793.3:669.721.5 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(6)925(2017)