Review on micropore grade inorganic porous medium based form stable composite phase change materials: Preparation, performance improvement and effects on the properties of cement mortar

Construction and Building Materials 194 (2019) 287–310

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Construction and Building Materials
journal homepage: www.elsevier.com/locate/conbuildmat

Review

Review on micropore grade inorganic porous medium based form stable
composite phase change materials: Preparation, performance
improvement and effects on the properties of cement mortar
Min Li ⇑, Junbing Shi
Jiangsu Key Laboratory for Construction Materials, Southeast University, Nanjing 211189, China

h i g h l i g h t s
 The micropore grade inorganic porous medium are appropriate for the adsorption of PCMs.
 The performances of the inorganic porous medium based form-stable CPCMs were reviewed.
 The effects of the CPCMs on cement mortar were summarized.

a r t i c l e

i n f o

Article history:
Received 6 May 2018
Received in revised form 22 October 2018
Accepted 29 October 2018

Keywords:
Phase change materials

Micropore
Inorganic porous media
Thermal energy storage
Cement mortar

a b s t r a c t
Building energy consumption is an important part of energy consumption. Popularizing latent heat storage technology in building is beneficial to reducing building energy consumption. Phase change materials
(PCMs) are important carriers of latent heat energy storage technology. The application of PCMs in building materials is helpful in increasing the latent heat storage capacity of the building. The leakage of PCMs
can be prevented and the thermal conductivity of PCMs can be improved by incorporation of PCMs into
inorganic porous media. Among various types of inorganic porous materials, the materials containing
mainly micropores (0.1 lm–100 lm) such as expanded perlite (EP), expanded vermiculite (EV), diatomite
and expanded graphite (EG) have characteristics of high porosity, moderate pore diameter, low price and
wide sources. The four kinds of inorganic porous medium based composite PCMs are suitable for largescale usage in cement mortar. In this paper, the preparation, thermal properties, and performance
improvement of the four composite PCMs are reviewed. The effects of them on the properties of cement
mortar are also summarized.
Ó 2018 Elsevier Ltd. All rights reserved.

Contents
1.
2.
3.

4.

5.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The preparation method and characterization of micropore grade inorganic porous medium based FSCPCMs . . . . . . . . . . . . . . . . . . . . . . . . . .
Expanded vermiculite based FSCPCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.

Thermal properties of EV based FSCPCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.
Performance improvement of the EV based FSCPCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.1.
Improvement of the adsorption performance and heat storage performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.2.
Improvement of the thermal conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Expanded perlite based FSCPCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1.
Thermal properties of EP based FSCPCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2.
Performance improvement of the EP based FSCPCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2.1.
Improvement of the adsorption performance and heat storage performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2.2.
Improvement of the thermal conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Diatomite based FSCPCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

⇑ Corresponding author.
E-mail address: (M. Li).
/>0950-0618/Ó 2018 Elsevier Ltd. All rights reserved.

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5.1.
5.2.

Thermal properties of the diatomite based FSCPCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Performance improvement of the diatomite based FSCPCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2.1.
Improvement of the adsorption performance and heat storage performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2.2.
Improvement of the thermal conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.
Expanded graphite based FSCPCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.1.
Thermal properties of the EG based FSCPCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2.
Thermal conductivity of the EG based FSCPCM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.
The effect of the micropore grade inorganic porous medium based FSCPCMs on cement mortar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7.1.
Effect of the micropore grade inorganic porous medium based FSCPCMs on the heat storage performance of cement . . . . . . . . . . . . . .

7.2.
The influence of the micropore grade inorganic porous medium based FSCPCM on the strength of cement mortar . . . . . . . . . . . . . . . .
8.
Conclusions and outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conflict of interest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction
With the development of economy, the demand for energy is
increasing in all walks of life. However, due to the decrease of traditional fossil energy reserves and inefficient usage of existing
energy sources, the contradiction between supply and demand of
energy is becoming tense. Improving energy utilization and developing new energy have become an important way to ease this
contradiction.
At present, the thermal energy storage (TES) is regarded as an
important method to increase energy efficiency [1]. It includes sensible heat storage and latent heat storage. The sensible heat storage
can be implemented easily through heating or cooling the medium.
However, its utilization is limited by the low heat storage capacity
and large volume requirement [2]. The latent heat storage can be
realized through the phase change process (solid–solid, solid–liquid and gas–liquid) of the materials during which large amount
of heat can be utilized without a significant change of temperature
[3]. Because of the advantages of latent heat storage, the related
materials and technologies have become research hotspots in the
field of energy saving [4,5].
PCM is a kind of important latent heat storage material. The
PCMs can be divided into solid–solid PCMs, solid–liquid PCMs,
gas–solid PCMs and liquid–gas PCMs according to the type of phase
change. Besides, PCMs can be divided into inorganic PCMs, organic
PCMs and composite PCMs according to the chemical composition.
For solid–gas PCMs and liquid–gas PCMs, due to the generation of

gaseous substances during the phase change process, the volume
change of them is larger than that of the other kinds of PCMs. As
a result, even though the heat storage density of these PCMs is
higher than the other PCMs, the application of them was limited.
Solid-solid PCMs and solid–liquid PCMs were proved to have good
application potential in building energy conservation, solar energy
utilization, heat recovery, temperature control and other fields
[6–9]. Although PCMs have high thermal storage capacity, there
are still some problems in practical applications. The leakage during the solid–liquid phase change process and low thermal conductivity of the PCMS are considered to be the two outstanding issues
[10,11]. At present, incorporation techniques and macro/microencapsulating method are effective methods to prevent leakage.
The incorporation technique is to prepare composite PCMs by combining pure PCM with layered materials or porous materials.
Microencapsulation is a process of encapsulating pure PCM with
polymer or organic shell. [12,13]. Adding high thermal conductivity materials such as expanded graphite and nanometal can
improve the thermal conductivity of PCMs [14].
Inorganic porous medium, which has large surface area and
abundant pore structure, is an ideal supporting material to prepare
form stable composite phase change materials (FSCPCMs) [15,16].
In the inorganic porous medium based FSCPCM, the leakage issue

300
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302
302
303
304
304
306
307
308

308
308
308

can be effectively solved due to the micro capillary force and the
interfacial adsorption effect of inorganic porous medium. Moreover, the heat conduction of the PCMs can be improved because
of the high thermal conductivity of the inorganic materials [17].
The pore sizes of some inorganic porous materials [18–23] such
as zeolite, molecular sieve and porous silica are nanoscale (0–
100 nm). Such nanopores will hinder the phase transformation of
PCMs during adsorbing the PCMs. As a result, the adsorption capacity and heat storage capacity of the composite PCMs are decreased
[24]. However, the pore sizes of expanded perlite, expanded vermiculite, diatomite and expanded graphite are mainly microscale
(0.1 lm–100 lm). These micron scale pores have little interference
on the phase transition behavior of PCMs [25]. Besides, the four
porous materials have the advantages of wide sources and low
cost. [26,27]
Some reviewers have presented classifications, applications and
performance, however few reviewers focused on the micron pore
grade inorganic porous medium based FSCPCMs. The preparation,
characterization, thermal properties, and performance improvement of the EP based FSCPCM, EV based FSCPCM, diatomite based
FSCPCM and EG based FSCPCM are reviewed in this paper. The
effects of the four FSCMs on cement mortar are summarized.

2. The preparation method and characterization of micropore
grade inorganic porous medium based FSCPCMs
The preparation method of micropore grade inorganic porous
medium based FSCPCMs included direct impregnation method
and vacuum adsorption method [28,29]. The schematic diagram
of preparing FSCPCMs by direct impregnation method was shown
in Fig. 1 [28]. It included two kinds of mixing process. One was

Fig. 1. Schematic diagram of direct impregnation method [28].


M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

289

Fig. 2. Schematic diagram of vacuum adsorption method [29].

heating the PCMs to a molten state and then mixing them with the
supporting materials, the other was mixing the PCMs and supporting materials at solid state and then heating to a molten state. The
first mixing process was usually used to prepare composite materials with low phase change temperature and the second mixing
process was suitable for composites with high phase change temperature. The vacuum adsorption method was more complex than
the direct immersion method. The schematic diagram of preparing
PCMs by vacuum adsorption method was shown in Fig. 2 [29]. For
vacuum adsorption, except the capillary force and the surface tension of the porous materials, the pressure difference of the environment was also helpful to the adsorption of the liquid PCMs.
The characterization methods of micropore grade inorganic
porous medium based FSCPCMs mainly included differential thermal analysis (DSC), thermogravimetric analyzer (TG), Fourier
transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), thermal conductivity
analysis and thermal cycling test. Among them, DSC was used to
analyze the heat storage capacity of composite PCMs. The melting
temperature, freezing temperature and the latent heat of the composite PCMs could be calculated through the DSC curve. The DSC
curves of paraffin/expanded vermiculite based FSCPCM were
shown in Fig. 3 [30]. The FTIR was mainly used to determine
whether there were chemical reactions between PCMs and the
inorganic porous medium. The FTIR testing curves of capric acid/
expanded perlite based FSCPCM were revealed in Fig. 4 [31]. The
distribution of PCMs in supporting materials could be observed
by SEM [32]. The XRD was used to analyze the crystallinity of

the PCMs [33]. The thermal stability of composite PCMs was often
analyzed by TG and thermal cycling. The TG curves of Stearic acid/
Expanded vermiculite based FSCPCM were shown in Fig. 5 [34].

Fig. 4. FTIR testing curves of capric acid/expandead perlite based FSCPCM [31].

Fig. 5. TG curve of Stearic acid/expanded vermiculite based FSCPCM [34].

Fig. 3. The DSC curve of paraffin/expanded vermiculite based FSCPCM [30].

The leakage of PCMs could be estimated by observing the oil
stains on filter papers after FSCPCMs were put on filter papers
and heated to the melting point, as shown in Fig. 6 [35]. The
thermal conductivity of FSCPCMs was characterized by thermal
conductivity analysis. The methods of thermal conductivity analy-


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skeleton and the magnesium hydroxide layer or the hydrogen oxygen aluminum layer. Moreover, there is a large amount of bound
water and free water existing among the unit layers of vermiculite.
The structure of vermiculite is shown in Fig. 8 [37]. The vermiculite
can expand more than ten times in the vertical direction during
calcination due to the loss of internal moisture. The structure varied to be layer structure of 2:1.
The bulk density of the vermiculite decreases and the porosity
increases after expansion. The EV mainly consists of two dimensional lamellar pores between 0.1 lm and 10 lm. Figs. 9 and 10 present the appearance of vermiculite and expanded vermiculite,
respectively [38]. Fig. 11 shows the pore distribution of EV [39]. EV
has many advantages such as wide source, high fire resistance,

non-toxic, sound absorption and low cost [40]. Especially, EV has
good adsorption properties because of the well-developed pore
structures. Fig. 12 showed the adsorption of mercury ions by EV [41].
3.1. Thermal properties of EV based FSCPCM

Fig. 6. Observation on leakage of the FSCPCM [35].

Fig. 7. Pores distribution of expanded graphite [25].

sis in literatures were different. Apart from the directly testing,
some researchers investigate the thermal conductivity by heating
and cooling rate. The pore structure of the inorganic porous materials was characterized by mercury intrusion method and low temperature nitrogen adsorption method. The mercury intrusion test
was more accurate for micropore grade inorganic porous medium.
The pore distribution of EG tested by mercury intrusion method
was shown in Fig. 7 [25].

The EV has been selected as the supporting material to prepare
the EV based FSCPCM by many researchers because of its good porous structure. The direct impregnation and vacuum adsorption
method were common preparation method. The prepared
FSCPCMs showed good thermal reliability and chemical stability.
Chung et al. [39] fabricated n-octadecane/EV FSCPCM via vacuum incorporation method and investigated the thermal properties and chemical stability of it. The highest mass percentage of
n-octadecane in the FSCPCM was 80.65%. Under this condition,
the melting temperature and latent heats of the FSCPCM were
26.1 °C and 142 J/g. The solidification temperature and latent heats
were 24.9 °C and 126.5 J/g. Moreover, the TG analysis and FIIR
analysis showed that the FSCPCM has good thermal stability and
chemical stability. The lauric acid/EV FSCPCM was prepared by
Wen et al. [42]. The content of the lauric acid (LA) in the composite
FSCPCM without leakage reached 70 wt%. The melting temperature
of the composite phase change material was 41.88 °C and the melting latent heat was 126.8 J/g. Thermal cycling test showed that the

FSCPCM still had good thermal reliability and chemical stability
after 200 times of melting/freezing cycling. The SEM morphology
in Fig. 13 showed that the EV empty interlayer spaces were largely
occupied by the impregnated LA. The results from FIIR analysis
showed that there was no chemical interaction between the EV
and the lauric acid.
The phase change temperatures can be adjusted to a proper
temperature by blending different PCMs when the phase change
temperature of pure PCMs are too high for building applications.
The Capric–myristic acid/EV FSCPCM was prepared by Karaipekli
[43] via vacuum incorporation. The capric acid (CA)–myristic acid

3. Expanded vermiculite based FSCPCM
The expanded vermiculite is obtained by calcination of mineral
vermiculite at high temperature [36]. The mineral vermiculite
belongs to the trioctahedron structure. Most of them are formed
by hydrothermal alteration or weathering of biotite, mica and chlorite. Vermiculite crystal consists of three structural unit layers. The
silicon oxygen skeleton exists between the structural unit layers.
The tetrahedron is formed by the combination of silicon oxygen

Fig. 8. Schematic diagram of vermiculite structure [37].


M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

291

Fig. 9. The appearance of vermiculite [38].

Fig. 10. The appearance of expanded vermiculite [38].

(MA) eutectic mixture was selected as PCMs. The phase change
temperature of the eutectic mixture was adjusted to 25 °C by controlling the mass ratio between capric acid and myristic acid at 3:7.
The eutectic acid was absorbed into the pore structures of the EV.
The maximum content of eutectic acid was 20% under the condition of no leakage. The melting and solidification temperature of
this FSCPCM were 19.8 °C and 17.1 °C and the latent heat was
27 J/g. The FSCPCM still had good thermal reliability and chemical
stability after 3000 thermal cycles. Wen et al. [44] used capric acid

(CA) – lauric acid (LA)eutectics mixture as PCM to prepare EV
based FSCPCM. The highest mass percentage of this eutectics mixture was 57.48%. Only physical combination existed between the
eutectics and the EV. The phase change temperature and latent
heat of this FSCPCM are 21–23 °C and 81.34 J/g. In addition, the
TG analysis and the 200 times melting/freezing cycling test
showed that this FSCPCM has good thermal stability. In the study
of Karaipekli et al. [45], a series of FSCPCMs were prepared by
incorporation of eutectic mixtures of fatty acids (capric–lauric,


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M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

Fig. 11. The pore distribution of the expanded vermiculite [39].

Fig. 12. Adsorption of mercury ions [41].

capric–palmitic and capric–stearic acids) and EV by vacuum
impregnation method. In order to meet the requirements of indoor
temperature controlling, the mass ratios of capric–lauric acids,

capric–palmitic acids and capric–stearic acids were adjusted to
64:36, 76.5:23.5 and 83:17, respectively. The maximum content
of these eutectic mixtures in the FSCPCMs were 40 wt%. The melting temperatures and latent heats of these FSCPCMs are in the
range of 19.09–25.64 8 °C and 61.03–72.05 J/g, respectively. Moreover, the results of the 5000 times heating and cooling cycle tests
showed that these FSCPCMs had good thermal reliability and

chemical stability. The capric(CA)–palmitic(PA)–stearic acid(SA)/
EV FSCPCM was prepared by Zhang et al. [29] via vacuum impregnation method. When the mass ratio of CA:PA:SA was 79.3:14.7:6,
the melting and freezing temperature was 19.3 °C and 17.1 °C,
respectively. The research showed that the CA–PA–SA was
sufficiently absorbed in the porous network of EV. There was no
chemical interaction between the expanded vermiculite and the
CA–PA–SA. The 70 wt% CA–PA–SA/EV sample melted at 19.3 °C
with a latent heat of 117.6 J/g and solidified at 17.1 °C with a latent
heat of 118.3 J/g. Moreover, the FSPCMs exhibited adequate stability even after being subjected to 200 melting–freezing cycles.
These literatures showed that the eutectic mixture was combined
with EV physically, which was similar to the pure PCM. The eutectic mixture/EV FSCPCM also showed good thermal reliability and
chemical stability.
Compared with organic PCMs, inorganic PCMs have larger thermal capacity, higher thermal conductivity, higher operating temperatures and the better compatibility with the micropore grade
inorganic porous media. The phase change temperature of the
inorganic PCMs is higher than that of the organic PCMs. The
sodium nitrate/EVFSCPCM was prepared by the incorporation of
sodium nitrate into EV with directing impregnation method [28].
The results showed that sodium nitrate and expanded vermiculite
in the composites only undergo physical combination, not a chemical reaction. The adsorptive capacity of the EV to sodium nitrate
was about 88%. The phase change temperature of the FSCPCM
was 300.9 °C and the latent heat was 157.2 J/g. In addition, after
200 h of heat treatment, the supercooling degree of the FSCPCM
were between 0.1 °C and 3.9 °C and the thermal enthalpy change
rate was lower than 5.0%. The thermal properties of the EV based

FSCPCMs were summarized and listed in Table 1.


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Fig. 13. SEM images of (a), (b) EV; (c) composite PCM (70 wt% LA/EV); (d) SEM image and EDS spectra of composite PCM(70 wt% LA/EV); Appearance photo of 70 wt% LA/EV
(e) at room temperature (f) after heating at 80 ◦C for 30 min [42].

Table1
Thermal properties of EV based FSCPCMs.
EV based FSCPCMs

Adsorption
capacity (%)

Melting
temperature
(°C)

Latent heat
of melting
(J/g)

Freezing
temperature
(°C)

Latent heat

of freezing
(J/g)

Thermal
cycling
(times)

Decrease
percentage
of the latent heat

References

n-octadecane/EV
LA/EV
CA –LA/EV
CA – PA/EV
CA–SA/EV
CA–PA–SA/EV
sodium nitrate/EV

80.65
70
57.48
40
40
70
87.9

26.1

41.88
23.61
22.61
25.64
19.3
300.9

142
126.8
81.34
61.03
72.05
117.6
157.2

24.9
39.89
20.93
21.53
23.47
17.1
299.6

126.5
125.6
79.30
60.35
68.52
118.3
156.8

–
200
200
5000
5000
200
–

–
–
6.3%
2.8%
0.1%
3.4%
–

[39]
[42]
[44]
[45]
[45]
[29]
[28]

3.2. Performance improvement of the EV based FSCPCM
Until now, many kinds of EV based FSCPCM has been
developed. Although they exhibited good thermal stability
and chemical stability, the disadvantages such as limited

adsorption capacity and low thermal conductivity hindered
their application in thermal energy storage. To solve these
problems, some researchers have devoted to improve the
adsorption capacity, heat storage density and thermal
conductivity.


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3.2.1. Improvement of the adsorption performance and heat storage
performance
The latent heats of EV based FSCPCMs are mainly decided by
PCMs in the EV based FSCPCM because the expanded vermiculite
has no phase change ability. With the increase of the content of
PCMs, the adsorption capacity of the EV based FSCPCMs increased.
As a result, the thermal storage density is increased. Wei et al. [46]
conducted an experimental study of the performance improvement of the EV based FSCPCMs. The EV was modified by means
of acid treating method followed by loading Al2O3 particles as
shown in Fig. 14. Then, the Al2O3-loaded EV (aEV/AO) was used
as supporting matrix to absorb the lauric(LA)-myristic(MA)-stea
ric(SA) acid eutectic mixture (LA-MA-SA acid). Compared to the
EV, the adsorption capacity of aEV/AO to LA-MA-SA acid was
increased by 32.3 wt%. Due to the modification, the melting and
freezing latent heats of the FSCPM were increased by 51 J/g and
50.6 J/g, respectively. According to their study, the Si-OH groups
on the surface of EV were exposed after EV was partially delaminated and corroded by acid treatment, which was the reason for
the improvement of the adsorption capacity. Similar to the study
of Wei et al., Li et al. [47] treated titanium dioxide-loaded EV with

nitric acid firstly. Then the modified EV was used as stearic acid
(SA) supporting matrix to prepare a SA/modified EV FSCPCM via
vacuum impregnation method. The results showed that the

melting latent heat of the SA/modified expanded vermiculite
FSCPCM were increased by 69.2 J/g compared to the unmodified
FSCPCM.
Wei et al. [48] used methyl ammonium bromide and nitric acid
to modify the EV and obtained in-situ carbonation expanded vermiculite (EVC). The modification method was shown in Fig. 15.
The EVC was used as a carrier to adsorb capric acid(CA)–myristic
acid(MA)–stearic acid(SA) ternary eutectic acid to prepare FSCPCM.
It was found that the melting latent heat of the CA-MA-SA/
modified expanded vermiculite FSCPCM was 86.4 J/g, which was
39.1% higher than the unmodified EV based FSCPCM. The reason
for this improvement is the same with the explanation in Ref. [46].
3.2.2. Improvement of the thermal conductivity
Low thermal conductivity is a major drawback of the EV based
FSCPCM because it will lead to low heat transfer rate and heat storage efficiency. Researchers have done a great deal of work to
enhance the thermal conductivity. The thermal conductivity of
the EV based FSCPCM was increased by modifying the EV and adding high thermal conductivity components. Guan et al. [30] modified the EV with sucrose solution to form carbide film between the
layers of the EV. The EV was altered to the EV/carbon (EVC)
through this method. Then the paraffin/EMVC FSCPCM was prepared by vacuum impregnation method. The schematic diagram

Fig. 14. Schematic diagram of the preparation process of aEV/AO [46].

Fig. 15. Schematic diagram of the preparation process of EVC [48].


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M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

of the preparation process of the FSCPCM was shown in Fig. 16. The
results showed that the maximum content of paraffin in paraffin/
EMVC FSCPCM was 53.2 wt%. The thermal conductivity of the
paraffin/EMVC FSCPCM was increased by 193%. The authors
believed that the improvement was attributed to implanting high
thermal conductivity carbon network in vermiculite layers. Similarly, Zhang et al. [34] modified the EV by in situ carbonation with
starch solution. The result indicated that the maximum content of
stearic acid in the stearic/modified EV FSCPCM could reach
63.12 wt%. The thermal conductivity of FSCPCM prepared with
the modified EV was increased by 52.9% compared to unmodified
EV based FSCPCM.
In addition to the above modification methods, it was often
adopted to add thermal conductivity enhancement components
during the preparation process of the FSCPCM to improve the thermal conductivity. Deng et al. [49] developed a thermal conductivity enhanced FSCPCM with polyethylene glycol(PEG) as the phase
change material and the EV as the supporting material. The
nano-silicon carbide was used as the thermal conductivity
reinforcement material. The results revealed that the thermal
conductivity of this FSCPCM was 0.53 W/mÁK when the addition
of nano-silicon carbide was 3.29 wt%. The thermal conductivity
was increased by 96.2% compared to the FSCPCM without nanosilicon carbide. The authors contributed the enhancements to the
rapid heat transfer of nano-silicon and their effective dispersion
in the pore structures of EV. The same research group also studied
the effects of nano-silver wire on the thermal conductivity of the

PEG/EV FSCPCM [50]. The diameter of the nano-silver was 50–
100 nm and the length was 5–20 lm. It was founded that the
nano-silver wire could be well dispersed in the pore of expanded
vermiculite. After being added with 19.3 wt% of nano-silver wire,

the thermal conductivity of the PEG/EV FSCPCM was 0.68 W/mÁK,
which was increased by 172%. Deng et al. [51] used the Alumina
to enhance the thermal conductivity of the Na2HPO4Á12H2O/EV
FSCPCM. The thermal conductivity of the Na2HPO4Á12H2O/EV
FSCPCM was increased by 45.6%” after adding 5.3 wt% alumina.
Besides, the EG was commonly used as thermal conductivity
enhancement components in EV based FSCPCMs. The thermal conductivities of the EV based FSCPCM were provided in Table 2.

4. Expanded perlite based FSCPCM
Perlite is the acidic vitreous lava with a structure of pearl
cracks. About 95% of the perlite ore is glassy phase, in which the
amorphous quartz accounts for 65–75% and alkali metal oxides
accounts for about 8–9%.The internal moisture in the perlite is
about 2–6%. A porous EP with a low bulk density can be formed
after perlite is heated rapidly at the temperature of 700–1200 °C
[27,52].The pores in the EP range from 1 lm to 100 lm. The microscopic appearance of perlite before and after expansion was shown
in Fig. 17 [53]. The structure and distribution of the pores inside
the EP were shown in Figs. 18 and 19, respectively [39,54]. The
EP displayed good adsorption property due to the developed pores

Fig. 16. Schematic diagram of the preparation process of EVC composite materials [30].

Table 2
The thermal conductivities of the EV based FSCPCM.
EV based FSCPCMs

Thermal conductivity W/(mÁK)

Adding amount (wt%)

Increase ratio of the
thermal conductivity

References

Lauric acid/EV
Lauric acid/EV/EG

0.28
0.5

10

78.5%

[42]

Capric-myristic Acid/EV
Capric-myristic Acid/EV/EG

0.12
0.22

2

83.3%

[43]

Capric Acid – Lauric Acid/EV

Capric Acid – Lauric Acid/EV/EG

0.135
0.253

5

87.4%

[44]

Capric Acid – Palmitic Acid – Stearic Acid/EV
Capric Acid – Palmitic Acid – Stearic Acid/EV/Copper

0.242
0.362

5

49.6%

[29]

Polyethylene glycol/EV
Polyethylene glycol/EV/nano-silicon nitride

0.27
0.53

3.29

96.2%

[49]

Polyethylene glycol/EV
Polyethylene glycol/EV/nano-silver wire

0.25
0.68

19.3%

172%

[50]


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M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

Fig. 17. The micro-morphology of perlite before (a) and after expansion (b)[53].

and moderate pore size. The adsorption effect of EP on
p-nitrophenol was shown in Fig. 20 [55].
4.1. Thermal properties of EP based FSCPCM

Fig. 18. Internal pore structure of expanded perlite [54].

A series of form-stable EP based FSCPCMs have been prepared.
Organic materials with low phase change temperature are often
used as the phase change substance in the EP based FSCPCM. The
preparation methods of EP based FSCPCM mainly included vacuum
adsorption and melt impregnation. According to the research of
Takahiro et al. [56], the latent heat of the FSCPCM prepared by vacuuming was larger than the FSCPCM prepared without vacuuming,
as shown in Fig. 21. In the preparation process of EP based FSCPCM,
the liquid PCM was impregnated through capillary forces in EP.
However, the air pressure within the pores prevented the

Fig. 19. Internal pore distribution of expanded perlite [39].


M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

Fig. 20. Effect of pH on the adsorption of Co and Pb onto EP [55]

Fig. 21. The Comparison between vacuum impregnation treatment and impregnation treatment for each porous material [56].

impregnation. It was difficult to evacuate the air within the pores
without vacuuming. As a result, the adsorption effect of the direct
impregnation was worse than the vacuum adsorption method.
Lu et al. [57] prepared a EP based FSCPCM in which paraffin was
used as PCM. The maximum content of paraffin can reach 60%
without leakage occurring. The phase change temperature is
27.56 °C and the latent heat of transformation is 80.9 J/g. The
results showed that paraffin and EP were physically combined,
which was the same as the EV based FSCPCM. Paraffin was distributed in the pores of the EP after impregnation. The FSCPCM still
maintain stable after 2000 times of heating and cooling cycles. The
thermal stability of the FSCPCM was shown in Fig. 22. Lauric acid/

EP FSCPCM was prepared by Sari et al. [58] via vacuum adsorption
method. The melting and solidification temperatures of the
composite were 44.13 °C and 40.97 °C, respectively. The latent heat
of fusion and latent heat of solidification were 93.36 J/g and
94.87 J/g, respectively. It was found that no chemical reaction
occurred between lauric acid and EP. In addition, the latent heat
value of melting reduced by 1.2% and the latent heat of freezing
reduced by 4.1% after 1000 times of thermal cycles. The decreases
in the latent heat capacity of the composite PCM were in a reasonable level for TES applications in buildings. The same authors [28]
also prepared capric acid/EP FSCPCM. The maximum adsorption
capacity of capric acid was up to 55%. The melting point was
31.8 °C and the latent heat of FSCPCM was 98.1 J/g. The latent heat
of melting decreased by 2.6% and the latent heat of freezing changed by 0.6% after 5000 times of thermal cycles. Liu et al. [59]

297

Fig. 22. DSC curves of paraffin/expanded perlite composites before and after hot
and cold cycles [57].

prepared a lauric acid/EP FSCPCM by the method of melting
impregnation. The maximum adsorption amount of lauric acid in
the EP can reach 70 wt%. The phase change temperature and latent
heat were 43.2 °C and 105.58 J/g, respectively.
In order to meet the demand of phase change temperature of
the PCMs, binary or multiple eutectic acids has been developed
by adjusting the content ratio of them. The preparing and thermal
properties of the EP based FSCPCMs with binary or multiple eutectic acids as PCM were investigated by some researchers. They drew
some similar conclusions with the EP based FSCPCMs with pure
PCM. Zhang et al. [60] prepared a capric acid-palmitic acid/EP
FSCPCM via vacuum adsorption. The maximum adsorption capacity of the EP to the eutectic acid was 65 wt%. The FSCPCM has a

melting temperature of 24.1 °C and a latent heat of 88.39 J/g. Jiao
et al. [61] used binary eutectic acid of capric acid and stearic acid
as the phase change material to prepare the EP based FSCPCM by
vacuum adsorption method. The content of the eutectic acid was
43.4%. The eutectic acid and the expanded perlite were simply
physically bonded. The melting temperature of the FSCPCM was
33 °C and the latent heat of phase transformation was 131.3 J/g.
The melting temperature and the latent heat of the specimen were
33.5 °C and 131.1 J/g after 1000 thermal cycles. Zhang et al. [62]
prepared lauric-palmitic-stearic acid/EP FSPCM using vacuum
impregnation method. The maximum adsorption amount of the
EP to the eutectic acid was 55 wt%. The melting temperature of
the FSCPCM was 31.8 °C, and the latent heat of melting was
81.5 J/g. The solidification temperature of the FSCPCM was
30.3 °C and the latent heat of solidification was 81.3 J/g. Moreover,
the melting and freezing latent heats of the FSCPCM dropped
slightly by 4.29% and 5.54%, respectively after 1000 times of thermal cycles. The FITR curves of the FSCPCM were shown in Fig. 23.
The infrared spectrum without significant new peaks indicated
that there were no chemical reactions between the lauricpalmitic-stearic acid and EP. The TG curves were shown in
Fig. 24. It can be seen that the 5% weight loss temperature of the
LA–PA–SA and LA–PA–SA/EP form-stable PCM were higher than
180 °C, which means that the LA–PA–SA/EP form-stable PCM had
a good thermal stability in the working temperature range which
was always designed as below 80 °C.
Considering the application of the EP based FSPCM under high
temperature, some researchers have attempted to prepare FSCPCM
by adsorbing inorganic PCMs into the pores of EP. Li et al. [63] used
sodium nitrate as the PCM to prepare sodium nitrate/EP FSCPCM.
The phase change temperature of the FSCPCM was 300 °C and
the latent heat of the FSCPCM increased with the content of

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M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

PPCM pD2 þ 4pcDcosh > Pair pD2
where P, D, c, and h represent the pressure, pore diameter, surface
tension of the PCM, and contact angle, respectively.
Liquid PCM was impregnated through capillary forces in a porous material, but the air pressure within the pores prevented the
impregnation. In contrast, the air within the pores was evacuated
before the impregnation treatment during the vacuum adsorption
process [56].
The prepared EP based FSCPCM have good thermal stability and
chemical stability. The thermal properties of the EP based FSCPCMs
were summarized and listed in Table 3.
4.2. Performance improvement of the EP based FSCPCM
Although the EP based FSCPM has excellent thermal properties,
some problems still should be solved to meet the requirement of
application. On the on hand, the thermal conductivity of the EP
based FSCPM is low due to the low thermal conductivity of EP
(0.07 W/(mÁK)). On the other hand, the leakage of the PCM would
be increased when the EP based FSCPM was used in cement. Until
now, the researchers have taken some measures to solve the two
problems.

Fig. 23. FT-IR spectra of LA–PA–SA, EP and LA–PA–SA/EP [62].

4.2.1. Improvement of the adsorption performance and heat storage
performance

Undesired adverse effects of the form-stable PCMs with the
cementitious composites have been reported when the PCM melting temperature was lower than the ambient temperature. That
was PCM leakage occurring during the mixing process with cementitious materials when water was added. Some measured had been
taken to avoid the leakage. Ramakrishnan et al. [64] covered the
surface of EP with a hydrophobic coating and then prepared
FSCPCM by vacuum adsorption using the hydrophobic EP as a support material. The maximum adsorption capacity of paraffin in the
hydrophobic EP was 50%. The paraffin adsorption ratio of the
hydrophobic EP was increased about 43% compared to the
uncoated EP. The latent heat of melting of the FSCPCM was
increased from 35.5 J/g to 60.9 J/g. The leakage of the FSCPCM
before and after modification was shown in Fig. 25. The reason
for the improvement was that the hydrophobic coated EP can prevent the contact between water molecules and porous EP due to
the hydrophobicity of EP.

Fig. 24. TG curves of the LA–PA–SA and LA–PA–SA/EP [62]

sodium nitrate. The results indicated that there was only a physical
combination between sodium nitrate and EP. The EP can absorb
90 wt% of sodium nitrate without leakage occurring.
In the EP based FSCPCMs, there was no chemical reactions
between EP and PCMs including pure organic PCMs, binary or multiple eutectic acid and inorganic PCMs. The vacuum adsorption was
beneficial for the adsorption of PCMs in EP. Under the impregnation treatment, the actual relationship was expressed by the following equation:

4.2.2. Improvement of the thermal conductivity
In the field of latent thermal energy storage, the heat transfer
technology that has to be employed to achieve high enough heat
charging/retrieval rates was the major cost. Therefore, it was a
key point in both energy and economic aspects to enhance the heat
transfer performance of the EP based FSCPCM. In order to increase
the thermal conductivity of EP based FSCPCM, researchers have

done a great deal of work. Zhang et al. [65] adopted in-situ car-

Table 3
Thermal properties of EP based FCPCMs.
EP based FSCPCMs

Adsorption
capacity(%)

Melting
temperature
(°C)

Latent heat
of melting
(J/g)

Freezing
temperature
(°C)

Latent heat
of freezing
(J/g)

Thermal
cycling
(times)

N-octadecane/EP

Paraffin/EP
Lauric acid/EP
Capric acid/EP
Capric – palmitic acid/EP
Capric – stearic acid/EP
Lauric – palmitic – stearic acid/EP
Sodium nitrate/EP

59.63
60
60
55
65
43.4
55
87.9

26.2
27.56
44.13
31.8
24.1
33
31.8
300.9

132.2
80.9
93.36
98.1

88.39
131.3
81.5
157.2

25.3
26.38
40.97
31.6
31
31
30.3
299,6

174.3
79.3
94.87
97.9
85.6
127.5
81.3
156.8

–
2000
1000
5000
–
1000
1000

–

Decrease
percentage
of the latent heat
3%
1.2%
2.6%
0.1%
4.29%

References

[39]
[57]
[58]
[31]
[60]
[61]
[62]
[63]


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M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

Fig. 25. Leakage of paraffin/expanded perlite composite before (a) and after
modification (b) [64].

bonization method to modify EP. They conducted in-situ carbonation of the EP with sucrose solution to form a layer of carbonized
film on the surface of the EP and obtained an expanded perlite
composite with carbon layer (EPC). Then, they prepared a polyethylene glycol/EPC FSCPCM by vacuum impregnation. The schematic for the preparation of the EPC composite was shown in
Fig. 26. The results showed that the thermal conductivity of the
modified FSCPCM was 0.479 W/(mÁK), which was 2.9 times of the
unmodified FSCPCM. The high thermal conductivity of the carbonized film on surface of the EP was the reason for the improvement of the thermal conductivity of the composite PCM.
Besides, some researchers reported methods of adding thermal
conductivity enhancement components into the EP based FSCPCM.
The most commonly used thermal conductivity enhancement

Fig. 26. Schematic for the preparation of EPC composite [65].

component was expanded graphite (EG). Zhang et al. [62] conducted an experimental investigation on the EP based FSCPCM
with EG. It was found that the addition of 2 wt% EG would cause
an increase of 95% for the thermal conductivity of the ternary fatty
acid/EP FSCPCM. In addition to EG, graphene carbon nanotubes
were also used to enhance the thermal conductivity. Ramakrishnan
et al. [66] tested experimentally the heat enhancement of the EP
based FSCPCM by nano-graphene. The results indicated that a significant enhancement of the thermal conductivity was achieved.
The thermal conductivity was increased by 49% when the nanographene particles were added about 1 wt%. A similar study was
also conducted by Sun et al. [67]. They added graphite to the paraffin/EP FSCPCM to increase the thermal conductivity by 192% with
the addition of 5% of graphite. Karaipekli et al. [68] chose the carbon nanotubes(CNTs) as the thermal conductive reinforcement
component. It was found that the thermal conductivity of the
paraffin/EP FSCPCM was increased by 113.3% with the addition of
1 wt% CNTs. The improvement was attributed to the high thermal
conductivity (2000–6000 W/(mÁK)) of CNTs, which provided a
large heat transfer area for the paraffin/EP FSCPCM. Furthermore,
this phenomenon may be resulted from the reduction of void space
within the composite PCM and extension of contact surface area
between CNTs and the composite particles. The thermal conductivity improvement of the EP based FSCPCMs were shown in Table 4.

5. Diatomite based FSCPCM
Diatomite is formed by ancient diatoms after long geological
processes. The mineral composition of diatomite is amorphous
opal. The main chemical composition of diatomite is amorphous
silicon dioxide. There are a small amount of Al2O3, Fe2O3, CaO,
MgO, TiO2, Na2O and so on besides silicon dioxide. A lot of silicon
hydroxyl and hydrogen bonds exist in the surface and the micropores of diatomite, which is an important reason for having the
adsorption properties of diatomite. Because of the different shapes
of diatom before diagenesis, the micro-morphology of diatomite is
various including round sieve shape, banded shape and cylindrical
shape. The structure diagram and the microscopic morphology of
diatomite are shown in Figs. 27 and 28 respectively [69,70]. The
density of Chinese-made diatomite is usually in the range of 0.4–
0.9 g/cm3 and the pore radius is from 0.1 to 3 lm. The pore volume
is in the range of 0.45–0.98 cm3/g and the specific surface is in the
range of 33–65 m2/g. Roasting, pickling and other modifications
are helpful to increase the specific surface area and volume of
the pores. The pore size distribution of diatomaceous is shown in
Fig. 29 [71]. Diatomite has excellent adsorption capacity due to
its abundant pore structures. The influence of initial Cr (VI) concentration on the removal effect of Cr(VI) are shown in Fig. 30 [72].

Table 4
The thermal conductivity improvement of the EP based FSCPCM.
EP based FSCPCMs

Thermal ConductivityW/(mÁ K)

Adding amount(wt%)

Increase ratio of thermal conductivity

References

Laurie/EP
Laurie/EP/EG

0.07
0.13

10

85.7%

[58]

Capric Acid/EP
Capric Acid/EP/EG

0.087
0.143

10

64.3%

[31]

Capric Acid-Laurie/EP
Capric Acid – Lauric Acid/EP/EG

0.135
0.253

5

87.4%

[44]

Capric Acid – Palmitic Acid – Stearic Acid/EP
Capric Acid – Palmitic Acid – Stearic Acid/EP/EG

0.44
0.86

2

95.4%

[62]

Paraffin/EP
Paraffin/EP/Nano Graphene

0.35
0.52

1

48.6%

[66]

Paraffin/EP
Paraffin/EP/Carbon Nanotubes

0.15
0.32

1

113.3%

[68]


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M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

Fig. 27. The structure diagram of diatomite [69].

Fig. 28. SEM images of the diatomite [70].

Fig. 30. Influence of initial Cr (VI) concentration on the removal effect of Cr (VI)
(experimental conditions: catalyst amount = 2 g/L, UV light intensity = 500 W,
pH = 2.1) [72].

Fig. 29. The pore distribution of diatomite [71].

5.1. Thermal properties of the diatomite based FSCPCM
PCMs used for preparing diatomite based FSCPCM are abundant,
including paraffin, fatty acid, eutectic acids, polyethylene glycol,
sulfates, nitrates and so on. Phase change temperature of the
FSCPCM covers from low temperature to high temperature. The
prepared diatomite based FSCPCMs showed good thermal reliability and chemical stability.
Su et al. [73] prepared a series of diatomite based FSCPCMs by
vacuum absorption and investigated the structure of them. They
used n-hexadecane, n-octadecane and paraffin as PCM respectively. The results showed that the maximum content of the three
PCMs in the FSCPCM was 47%, 47% and 42%, respectively. The PCM
and the diatomite were physically combined. The microstructures
of the three FSCPCMs were shown in Fig. 31. Fu et al. [74] used diatomite to absorb capric acid by direct melt impregnation method

to prepare a diatomite based FSCPCM. The maximum adsorption
capacity to capric acid was 40%. The melting and solidification
temperatures were 40.9 °C and 38.7 °C, respectively. The latent
heat of melting and latent heat of freezing were 57.4 J/g and
57.2 J/g. The FSCPCM did not decompose when the surrounding
temperature was lower than 157 °C, which suggested the prepared
diatomite based FSCPCMs had good thermal stability. Karaman
et al. [75] prepared polyethylene glycol 1000 (PEG 1000)/diatomite
based FSCPCM by vacuum adsorption. The maximum content of
PEG 1000 could reach 50%. The melting temperature of the prepared FSCPCM was 27.7 °C and the latent heat of melting was
87.09 J/g. The result indicated that there was no chemical reaction
between PEG 1000 and diatomite. Similar to PEG1000/diatomite
based FSCPCPM. Qian et al. [76] prepared polyethylene glycol
2000/diatomite based FSCPCPM
In addition to pure PCM, Li et al. [77] prepared capric–lauric
acid/diatomite based FSCPCM by melting impregnation under ordinary pressure. The maximum of the eutectic acid in the FSCPCM
was 47%. The melting temperature of the FSCPCM was 16.74 °C

and the latent heat was 66.81 J/g. Tang et al. [78] carried out an
experimental study of preparing a carpic-palmic acid/diatomite
based FSCPCM. The maximum content of the eutectic acid in the
FSCPCM was 63.5%. The melting and solidification temperature of
the FSCPCM were 26.7 °C and 21.85 °C respectively. The latent heat
of melting was 98.3 J/g and the latent heat of freezing was 90.03 J/g.
Qian et al. [76] prepared two kinds of FSCPCMs by melting
impregnation with inorganic materials as phase change substance.
One was lithium nitrate/diatomite based FSCPCM and the other
was sodium sulfate/diatomite based FSCPCM. The results showed


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M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

Fig. 31. The microstructure of diatomite and diatomite based FSCPCM [72].

that the highest content of lithium nitrate and sodium sulfate in
the FSCPCMs were 60% and 65%, respectively. The melting temperature and the latent heat of the lithium nitrate/diatomite based
FSCPCM were 250.7 °C and 215.6 J/g. For sodium sulfate/diatomite
based FSCPCM, the melting temperature was 887.61 °C and the
latent heat of melting was 101.59 J/g. Compared with the pure
PCM, the supercooling extents of the prepared FSCPCMs were
reduced by 23.7% and 19.9%, respectively. The results suggested
that the supercooling extent of PCMs can be favorably reduced
by impregnation with diatomite supporter. After 200 thermal
cycling, the melting latent heat value of these two kinds of
FSCPCMs changed by 9.3% and 1.7%, which were acceptable in
application. The potassium nitrate/diatomite based FSCPCM was

prepared by Deng et al. [79] via melt impregnation. The melting

temperature of the FSCPCM was 330.23 °C and the latent heat of
melting was 60.52 J/g. The solidification temperature and the
latent heats were 332.9 °C and 47.3 J/g. The melting point for of
the FSCPCM varied from 330.23 °C to 330.11 °C and the latent heats
varied from 60.52 J/g to 54.64 J/g after 50 times of thermal cycles.
Xu et al. [80] prepared sodium nitrate/diatomite based FSCPCM.
The maximum content of sodium nitrate in FSCPCM was 70%.
The melting temperature of the FSCPCM was 307.8 °C and the
melting latent heat was 115.79 J/g. The above researches showed
that there was no chemical interaction between the inorganic
PCMs and diatomite. The FSCPMCs all showed good thermal reliability and good form stable due to the capillary force and the surface tension force of the diatomite. The thermal properties of the
diatomite based FSCPCMs were shown in Table 5.

Table 5
The thermal properties of the diatomite based FSCPCM.
Diatomite based FSCPCMs

Adsorption
capacity(%)

Melting
temperature
(°C)

Latent heat
of melting
(J/g)

Freezing
temperature
(°C)

Latent heat
of freezing
(J/g)

Thermal
cycling
(Times)

Decrease ratio
of the latent heat

References

N-octadecane/Diatomite
Paraffin/Diatomite
Hexadecane/Diatomite
lauric Acid/Diatomite
Polyethylene Glycol 1000/Diatomite
Polyethylene Glycol 2000/Diatomite
Capric Acid – Lauric Acid/Diatomite
Capric Acid – palmic Acid/Diatomite
Lithium Nitrate/Diatomite
Sodium Sulfate/Diatomite
Potassium Nitrate/Diatomite

47

42
47
40
50
58
47
63.5
60
60
65

31.29
57.09
23.68
40.9
27.7
57.92
16.74
26.7
250.7
887.61
330.23

116.8
61.96
120.1
57.4
87.09
105.7
66.81

98.3
215.6
101.59
60.52

23.65
50.23
13.17
38.7
32.2
46.03
–
21.85
243.58
887.61
332.9

112.9
59.74
118.0
57.2
87.05
95.46
–
90.03
190.3
102.34
47.3

–

–
–
–
1000
200
–
–
200
200
50

–
–
–
–
1.1%
2.2%
–
–
9.3%
1.7%
9.7%

[73]
[73]
[73]
[74]
[75]
[76]
[77]

[78]
[76]
[76]
[79]


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5.2. Performance improvement of the diatomite based FSCPCM
Although the thermal stability and chemical stability of the diatomite based FSCPCM are good, the adsorption performance, storage capacity and thermal conductivity are unsatisfactory. So far,
researchers have made some efforts to improve these properties.
5.2.1. Improvement of the adsorption performance and heat storage
performance
Like the EV based FSCPCM and the EP based FSCPCM, the latent
heats of the diatomite based FSCPCM were also mainly decided by
the content of PCMs in the FSCPCM. The heat storage performance
of the diatomite based FSCPCM are enhanced with the increase of
the adsorption capacity of the diatomite. Modifying diatomite by
grinding, calcinations and surface treatment is helpful to improve
its adsorption capacity. Sun et al. [81] investigated the effects of
calcination conditions including calcination temperature and calcination time on specific surface area of diatomite. The results were
shown in Fig. 32. It demonstrated that the specific surface area of
the diatomite increased initially with increasing the calcination
temperature and the specific surface became stable when the calcination temperature reached 450 °C. For diatomite, higher specific
surface leaded to better adsorption capacity, so the optimum calcinations temperature was 450 °C. Li et al. [82] studied the adsorption capacity of diatomite with different particle sizes. The
results showed that the adsorption capacity of diatomite to paraf-

fin was increased from 35% to 50% with the decreasing of particle

size. The latent heat of the FSCPCM was increased accordingly from
45.96 J/g to 63.98 J/g. Qian et al. [83] treated diatomite with
sodium hydroxide and then prepared polyethylene glycol/diatomite FSCPCM using the modified diatomite as the supporting
material. The results indicated that the maximum content of polyethylene glycol in FSCPCM was increased from 48% to 70%. The
melting and freezing latent heats of the FSCPCM were increased
by 40.8 J/g and 35.2 J/g, respectively. The author reported that soluble silicates SiO2À
formed after the treatment with sodium
3
hydroxide, which resulted in the creation of larger pores, flaws,
cracks and a larger surface area. Therefore, the adsorption capacity
of the diatomite was increased.
5.2.2. Improvement of the thermal conductivity
When the diatomite based FSCPCMs were used in the thermal
energy storage systems, the high thermal conductivity was an
important parameter, which could assure the high heater transfer
efficiency. For diatomite based FSCPCMs, the mainly method to
improve the thermal conductivity was adding high thermal conductivity components such as Ag nanoparticles, carbon nanotubes
and expanded graphite. Xu et al. [84] developed a thermal conductivity enhanced diatomite based FSCPCM with multi-walled carbon
nanotubes. The thermal conductivity of the modified FSCPCM was
1.8 W/mÁK with the addition of 0.26 wt% multi-walled carbon nanotubes. The promotion percentage of the thermal conductivity was
42.5% compared to the FSCPCM without multi-walled carbon nanotubes. Qian et al. [85] chose the Ag nanoparticles as the thermal
conductivity components. They found that the thermal conductivity of the FSCPCM was increased by 127% after the addition of
7.2 wt% of Ag nanoparticles. The authors contributed the improvement of the thermal conductivity to the Ag nanoparticles. The
same group also studied the improvement effect of the singlewalled carbon nanotubes [86]. The result indicated that the thermal conductivity of the FSCPCM was increased by 180% when the
addition of the single-walled carbon nanotubes was 2%. The thermal conductivities of the diatomite based FSCPCMs were shown
in Table 6.
6. Expanded graphite based FSCPCM

Fig. 32. Variation of specific surface area of diatomite with different calcination
temperature and time [81].

Expanded graphite (EG) is a kind of carbonaceous raw materials
obtained from natural flake graphite, which is treated by chemical
or electrochemical intercalation and then been heated instantaneously to produce high-temperature expansion. Graphite is consisted of multiple ‘‘microcells”. There are many tiny pores within
the micro-cells to form abundant pore structures of EG. The figure
schematic structural and magnification image of EG were shown in
Figs. 33 and 34, respectively [87,88]. After the expansion, mainly

Table 6
The thermal conductivities of the diatomite based FSCPCM.
Diatomite based FSCPCMs

Thermal Conductivity
W/(mÁK)

Adding amount
(wt%)

Increase ratio of the
thermal conductivity

References

Polyethylene Glycol 1000/Diatomite
Polyethylene Glycol 1000/Diatomite/EG

0.32
0.67

10

109.3%

[75]

Capric Acid – Palmitic Acid/Diatomite
Capric Acid – Palmitic Acid/Diatomite/EG

0.19
0.292

5

53.7%

[78]

Paraffin/Diatomite
Paraffin/Diatomite/Multi-walled Carbon Nanotubes

1.3
1.8

0.26

42.5%

[84]

Polyethylene Glycol 2000/Diatomite

Polyethylene glycol 2000/Diatomite/Ag nanoparticles

0.35
0.82

7.2

127%

[85]

Polyethylene glycol 2000/diatomite
Polyethylene glycol 2000/Diatomite/Single-walled Carbon Nanotubes

0.35
0.87

2

180%

[86]


M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

Fig. 33. The structure diagram of expanded graphite [87].

10 lm–100 lm two-dimensional layered pores are formed in the
EG, as shown in Fig. 35 [89]. EG not only retained many advantages

of natural graphite, but also possesses the features that natural
graphite does not possess such as porous structure, high reactivity,
large specific surface area, high compressibility and high elastic
modulus. Due to these characteristics, EG has excellent adsorption
capacity. Fig. 36 showed the adsorption capacity of the EG to oil
[90].

Fig. 35. The pore size distribution of expanded graphite [89].

6.1. Thermal properties of the EG based FSCPCM
The preparation process of expanded graphite is simple and the
cost of EG is low. So, expanded graphite is often used as inorganic
porous media to adsorb PCMs. The excellent adsorption capacity of
EG comes from the interconnected open pores and good compatibility with many surfaces.
The research results suggested that the adsorption capacity of
EG to PCMs was much better than that of EP, EV and diatomite.
The adsorption capacity of EG varied from 80 wt% to 93 wt%,
whereas the adsorption capacity of the EP and EV was about
60 wt%. The adsorption capacity of the diatomite was much lower,
which was about 50 wt%. Accordingly, the heat storage capacity of
the EG based FSCPCM was much better than that of the EP, EV and
diatomite based FSCPCM. The adsorption capacity and the latent
heat of EP, EV, diatomite and EG based FSCPCM with paraffin as
the phase change substance were compared in Table 7.
Zhang et al. [91] used EG with thermal treatment to prepare
EG/paraffin FSCPCM. The mass content of paraffin in the FSCPCM

Fig. 36. The adsorption result of expanded graphite to oil [90].

Fig. 34. Low (a) and high (b) magnification image of expanded graphite [88]

303


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M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

Table 7
The adsorption capacity and the latent heat of FSCPCMs with paraffin as the phase change substance.
Samples

Adsorption capacity
(%)

Melting temperature
(°C)

Latent heat of melting
(J/g)

Freezing temperature
(°C)

Latent heat of freezing
(J/g)

References

Paraffin/EG

Paraffin/EG
Paraffin/EV
Paraffin/EP
Paraffin/diatomite

85.56
92
67
60
42

48.79
52.2
48.0
27.56
57.09

161.45
170.3
135.5
80.9
61.96

–
–
52.5
26.38
50.23

–

–
137.6
79.3
59.74

[91]
[92]
[93]
[56]
[72]

was 85.56%. The melting temperature and latent heats of this
FSCPCM were 48.79 °C and 161.45 J/g, respectively. Due to the
paraffin was held by the strong capillary force and the strong surface tension force of the EG, no leakage was occurred while paraffin
was performing the phase change from solid to liquid in spite of
the high content of paraffin. The capric acid(CA)/EG FSCPCM, lauric
acid(LA)/EG FSCPCM and myristic acid(MA)/EG FSCPCM were prepared by Sari et al. [94]. The maximum content of these fatty acids
in the FSCPCMs were 80 wt%. The melting latent heats of CA/EG
FSCPCM, LA/EG FSCPCM and MA/EG FSCPCM were 132.64 J/g,
138.43 J/g and 145.64 J/g respectively. The freezing latent heats
of these FSCPCMs were 134.21 J/g, 139.16 J/g and 146.22 J/g
respectively. The leakage did not occur when the FSCPCMs melted,
the reason for which was the same with the Ref. [91].
EG could be obtained after microwave treatment of graphite.
Compared with the high temperature heating process, microwave
irradiation could be performed at room temperature in a very short
time with less energy-consuming. Zhang et al. [92] prepared a
paraffin/EG FSCPCM. The graphite powder was dried in a vacuum
oven at 70 °C for 20 h, followed by irradiating using a domestic
microwave oven with an overall power of 800 W to yield the EG.

The maximum content of paraffin in this FSCPCM was 92 wt%
and the latent heat of the FSCPCM was 173.1 J/g. The octadecane/
EG FSCPCM was prepared by Li et al. [95] and Kim et al. [96]. The
EG they used was obtained after microwave treatment. It was
founded that there was no chemical reactions between the PCMs
and the EG. The tetradecyl alcohol(TD)/EG FSCPCM was developed
by Zeng et al. [97]. In the preparation process, a certain amount of
ethanol was added to improve the uniformity of the FSCPCM. The
results revealed that the maximum content of TD could reach up
to 93 wt% in the FSCPCM. The melting temperature and latent
heats were 35.35 °C and 202.6 J/g, respectively. It was observed
from the SEM images that the pores of the EG were not fully occupied by TD. The form-stability of the TD/EG composite form-stable
PCMs under certain pressure comes from these partially occupied
pores. The SEM images of natural flake graphite, EG and TD/EG-2
was shown in Fig. 37. No liquid D-Mannitol was observed on the
surface of the FSCPCM during the solid–liquid phase change process when the mass content of the D-Mannitol was 85%. The author
believed the reason was that D-Mannitol was hold by the tension
force and capillary force of the porous EG [98].
The adsorption of the binary or multiple eutectic fatty acids in
EG was studied by some researches. The results showed that the
preparation process and the properties of the prepared composite
PCMs were similar with those using pure PCM as the phase change
substance. The succinic- adipic/EG FSCPCM was prepared by Liu
et al. [99]. The mass content of eutectic acid was 90 wt%. There
were no chemical reactions between them. The melting temperature and latent heats of the FSCPCM was 135 °C and 206 J/g respectively. After 100 times of thermal cycles, the latent heat of the
FSCPCM only decreased by 1.3%. For the palmitic- stearic acid
eutectic mixture/EG FSCPCM obtained by Yuan et al. [100], the
mass ratio of eutectic acid and expanded graphite was13:1. The
melting temperature and melting latent heats of the FSCPCM was
53.89 °C and166.27 J/g, respectively. After 720 times of thermal

cycles, the latent heats of the FSCPCM changed slightly to
161.4 J/g, which showed the FSCPCM has good thermal reliability.
Except the above FSCPCMs, Capric-Palmitic-Stearic acid/EG
FSCPCM [101], Luaric-Myristic-Palmitic acid/EG FSCPCM [102],
Myristic-Palmitic-Stearic acid/EG FSCPCM [103] and CapricMyristic-Palmitic acid/EG FSCPCM [104] were also been prepared.
The results showed that the eutectic acid and EG were all combined by physical bonding. The thermal cycling tests and TG analysis showed that these PCMs all have good thermal stability and
chemical stability. Inorganic PCMs such as sodiumnitrate, potassium nitrate, and their eutectic mixture [105] were also used in
the EG based FSCPCMs. The thermal properties of the EG based
FSCPCMs were shown in Table 8.
6.2. Thermal conductivity of the EG based FSCPCM
The thermal conductivity of the EG based FSCPCM was much
higher than the EP, EV and diatomite based FSCPCM because EG
was used as not only the supporting material but also the heat conduction reinforced material. Xia et al. [110] researched the influence of the content of EG on the thermal conductivity of paraffin/
EG FSCPCM. The results indicated that the thermal conductivity
of the FSCPCM increased with the content of EG. When the content
of the EG was 10 wt%, the thermal conductivity of the FSCPCM was
3.83 W/mÁK, which was more than 10-fold higher than that of pure
paraffin (0.305 W/mÁK). Mills et al. [111] prepared EG based
FSCPCM through capillary forces between liquid RT-24 paraffin
and the EG. The thermal conductivity of the FSCPCM (16.6 W/mÁK)
was roughly 8200% higher than the thermal conductivity of the
RT-24 paraffin (0.2 W/mÁK). The study of Xu et al. [98] showed that
the D-mannitol/EG FSCPCM loading 15 wt% EG has a thermal conductivity of 7.31 W/mÁK, which was increased by approximately 12
times compared with the thermal conductivity of pure D-Mannitol
(0.60 W/mÁK). The thermal conductivity of FSCPCM of the
palmitate-stearic acid/EG FCPCM [100] was 2.51 W/mÁK, which
was 865% of the eutectic fatty acid. Li et al. [106] mixed EG and
the lithium nitrate-potassium nitrate to prepare FSCPCM. When
the content of EG was 10 wt%, the thermal conductivity of the

FSCPCM was up to 8.5–9.5 W/mÁK, which was more than 8 times
of the pure PCM. The improvement of the thermal conductivity
came from the high thermal conductivity of EG and the spatial network structure of EG, which caused an increase of the contact areas
with the PCM.
7. The effect of the micropore grade inorganic porous medium
based FSCPCMs on cement mortar
Cement mortar as the common building materials was used in
walls, floors, ceilings and other parts. The current studies showed
that adding micropore grade inorganic porous medium based
FSCPCM into cement mortar would make the cement mortar possessing the ability of thermal storage and temperature-control.
The building energy could be saved consequently. However, it
would cause the decrease of the strength of the cement mortar.


305

M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

Fig. 37. SEM images of natural flake graphite (a and b), EG (c and d) and TD/EG-2 (e and f) [97].

Table 8
Thermal properties of EG based FSCPCMs.
EG based FSCPCMs

Adsorption
capacity (%)

Melting
temperature
(°C)

Paraffin/EG
Capric acid/EG
Lauric acid/EG
Myristic acid/EG
Tetradecyl alcohol/EG
D-Mannitol/EG

92
80
80
80
93
85

52. 2
27. 8
41. 21
51. 6
35. 35
151. 82

Succinic – Adipic acid/EG
Palmitic – Stearic acid/EG
Capric – Palmitic – Stearic acid/EG

90
92. 9
90

136. 6
53. 89
21. 33

Lithium nitrate-potassium nitrate/EG
sodium sulfate decahydrate-sodium
phosphate dibasic dodecahydrate/EG
Calcium chloride hexahydrate/EG
Lithium nitrate- potassium chlorid/EG

90
87

126.1
32.05

90
90

309.92
165.5

Latent heat
of melting
(J/g)

Freezing
temperature
(°C)

Latent heat
of Freezing
(J/g)

Thermal
cycling
(times)

Decrease ratio of
the latent heat

References

Single organic PCMs
170. 3
132. 64
28. 52
138. 43
40. 30
145. 64
50. 70
202. 6
34. 93
267. 7
–

134.
139.
146.
201.

–

–
–
–
–
–
–

–
–
–
–
–
–

[92]
[94]
[94]
[94]
[97]
[98]

Organic eutectic acid
207. 6
134. 5
166. 27
54. 37
131. 7
19. 01

203. 6
166. 13
127. 2

100
720
500

1%
0.7%
5.6%

[99]
[100]
[101]

152.4
140.8

100
100

0.8%
5.69%

[106]
[107]

–

–

–
–

–
–

[108]
[109]

Inorganic PCMs
149.1
114.1
172.3
17.11
160.9
178.1

–
–

21
16
22
2


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M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

7.1. Effect of the micropore grade inorganic porous medium based
FSCPCMs on the heat storage performance of cement
The effects of paraffin/expanded perlite FSCPCM on thermal
properties of cement were studied by Li et al. [112]. They reported
details of a testing device used to investigate the heat storage efficiency of a cement board with EP based FSCPCM. The thermal
behavior testing scheme was shown in Fig. 38. The thermal behaviors of cement with and without EP based FSCPCM were shown in
Fig. 39. The results indicated that the maximum temperature difference between top and bottom surfaces of the panels (point A
and B) for the cement board without EP based FSCPCM was 1 °C
and the maximum temperature difference for the cement board
cement with EP based FSCPCM was 1.5 °C. A higher temperature
difference means greater thermal inertia. This means the thermal
inertia of the cement with EP based FSCPCM was improved compared to the cement without EP based FSCPCM. The same authors
also studied the effects of the paraffin/diatomite FSCPCM on the
thermal property of the cement [81]. The proportion of raw materials, the size of the cement board and the testing device were
same with Ref. [112]. The thermal inertia of cement panels was
shown in Fig. 40. For R0, the temperature difference increases at
certain rate before point 1. After point 1, the difference stays nearly
constant at 1 °C. For D30, the temperature difference develops similarly with R0 before point 1. However, after point 1, the temperature differences of D30 increases sharply compared with R0. The
results showed that the thermal inertia of cement panel was
improved after addition of paraffin/diatomite FSCPCM in cement
panel.
Ramakrishnan [113] developed a setup to measure the heat
storage capacity of the cement with EP based FSCPCM, which
was shown in Fig. 41. The indoor temperature variation during
two consecutive days was shown in Fig. 42. The results illustrated

Fig. 38. thermal behavior testing scheme [112].

Fig. 40. Thermal inertia of cement panels: Ordinary cement (R0), Cement with
paraffin/diatomite FSCPCM (D30) [81].

that the peak temperature in the PCM enhanced test cell was
2.67 °C lower than that in the cement test cell over two consecutive days. This meant the heat storage capacity of the cement with
this EP based FSCPCM was improved.
In order to avoid leakage in the cement, He et al. [114] coated
the EP based FSCPCM with sealing materials. They first prepared
fatty acid/expanded perlite FSCPCM, and then coated the FSCPCM
with paraffin. Finally, the coated FSCPCM was added in cement
to prepare heat storage mortar. The results showed that the delay
time of air temperature was 0 min for the normal mortar, whereas
the delay time of the heat storage mortar was 24 min. This suggested that the heat storage performance of the mortar was
increased with the addition of this EP based FSCPCM. Similarly,
Sun et al. [115] developed a method of coating the paraffin/expanded perlite FSCPCM with epoxy resin. They added the coated
paraffin/expanded perlite FSCPCM in the cement mortar. It was
founded that the absorb/release heat time of cement mortar with
paraffin/EP FSCPCM was approximately double compared to the
ordinary cement mortar. Xu et al. [116] studied the influence of
this FSCPCM on the heat storage performance of mortar. The
results revealed that the thermal energy storage capacity of the
mortar with paraffin/diatomite FSCPCM was increased by 5.438 J/g
compared to the mortar without FSCPCM. The same authors also
prepared lightweight mortar with heat storage capacity by replacing river sand with paraffin/EV FSCPCM [117]. The results indicated
that the elapsed time of the mortar with paraffin/EV FSCPCM was
increased by 174.6% compared to the mortar without paraffin/EV
FSCPCM. The air temperature inside the holder box was reduced
4.3%. Zhang et al. [118] prepared a FSCPCM with high thermal conductivity and analyzed the influence of the FSCPCM on cement

Fig. 39. Thermal behaviors of R0 and E30 under low temperature change rate: Ordinary cement (R0), Cement with EP based FSCPCM (E30) [112].

M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

307

Fig. 41. Prototype experiment set up (a) schematic diagram of test cell [units: mm] (b) physical set up [113].

Fig. 42. Indoor temperature variation during summer design days [113].

Fig. 43. SEM image of broken piece of cement/EPOP paste [115].

mortar. It was founded that, with the addition of this FSCPCM, the
effective thermal value of cement mortar was decreased. Moreover, the onset time of temperature peak was delayed and the cooling amplitude was increased, which means the mortar with this
FSCPCM showed proper temperature controlling effects.

mortar was decreased by 66.7% compared to the ordinary mortar.
The similar results were obtained by Li et al. [112]. In the study
of Xu et al. [116], 30 wt% cement was replaced by paraffin/diatomite FSCPCM. The results indicated that, compared with the
mortar before replacement, the maximum 28 day compressive
strength and flexural strength of the new mortar were decreased
by 48.7% and 47.5%, respectively. The compressive strength of
cement with FSCPCM (TESC) and cement without FSCPCM (NC)
at 7 and 28 days was shown in Fig. 44. They also prepared the

7.2. The influence of the micropore grade inorganic porous medium
based FSCPCM on the strength of cement mortar
It should be paid attention to that adding the EP based FSCPCM,
EV based FSCPCM, diatomite based FSCPCM and EG based FSCPCM
PCM into the cement mortar would reduce the compressive

strength of the cement mortar. In order to make FSCPCM acceptable for application in building, the content of the FSCPCM should
be controlled appropriately to balance the demands between the
heat storage performance and the strength and make. Sun et al.
[115] used epoxy resin to coat the paraffin/EP FSCPCM firstly,
and then studied the effect of the coated FSCPCM on the compressive strength of the cement mortar. It was found that the compressive strength and flexural strength of mortar decreased with the
increasing of the FSCPCM. When 30% of cement was replaced by
the FSCPCM, the compressive strength of the mortar decreased
from 23.88 MPa to 9.27 MPa. In the authors’ opinion, this was
because the strength of paraffin/EP FSCPCM was obviously lower
than that of sand and cement. With more ‘‘soft” paraffin/EP based
FSCPCM being added into cement mortar, the mechanical properties of the cement mortar became lower. The broken FSCPCMs
were visible on the failure surfaces, as shown in Fig. 43. Ramakrishnan [113] replaced 80% of volume quartz sand with paraffin/
hydrophobic EP FSCPCM to prepare the heat storage mortar. It
was found that the 28 day compressive strength of the prepared

Fig. 44. Compressive strength of NC and various TESCs at 7 and 28 days [116].


308

M. Li, J. Shi / Construction and Building Materials 194 (2019) 287–310

lightweight mortar with heat storage capacity by replacing the
river sand with the paraffin/expanded vermiculite FSCPCM completely [117]. The 28 day compressive strength of the lightweight
mortar was 18.1 MPa, which was reduced by 56.5% compared to
the mortar with river sand. The lower stiffness of the fabricated
FSCPCM compared to the river sand was the major reason for the
mechanical strength reductions. Zhang et al. [119] carried out an
investigation of the compressive strength of cement mortar containing the octadecane/EG FSCPCM. The compressive strength of
the mortar decreased from 23.7 MPa to 10.5 MPa when the content

of the FSCPCM reached 2.5%.

2. The influence of the micropore grade inorganic porous medium
based FSCPCM on the microstructure and hydration products of
cement mortar should be further studied in order to get the
mechanism of the strength decrease.
3. The influence of the micropore grade inorganic porous medium
based FSCPCM on the durability of cement mortar, which was
unclear presently, should be studied for the application in the
field of the building.
Conflict of interest
None.

8. Conclusions and outlook
This paper reviewed the structure, morphology, pore size distribution and application characteristics of four micropore grade
inorganic porous materials: expanded vermiculite, expanded perlite, expanded graphite and diatomite. The preparation of FSCPCMs
with these four kinds of materials as the supporting material was
reported. The thermal properties, performance improvement of
the EP based FSCPCM, EV based FSCPCM, diatomite based FSCPCM
and EG based FSCPCM was summarized. The effect of the four
FSCPCM on the cement mortar was also analyzed. The conclusions
were drawn as follow:
1. Expanded vermiculite, expanded perlite, diatomite and
expanded graphite with mainly micropore grade pores have
abundant pore structures and appropriate pore size distribution
for the adsorption of PCMs. EG presented outstanding adsorption property among the four micropore grade inorganic porous
materials, the adsorption capacity of which to PCM was up to
93%. The more the adsorption capacity to PCM, the higher heat
storage capacity the FSCPCMs had.
2. The EP based FSCPCM, EV based FSCPCM, diatomite based

FSCPCM and EG based FSCPCM have the advantage of simple
preparation process, wide source of raw materials and good
thermal properties. Especially, the EG based FSCPCM showed
prominent thermal property.
3. For EP based FSCPCM, EV based FSCPCM, diatomite based
FSCPCM and EG based FSCPCM, PCMs were stabilized in the
pore structure of the supporting materials by the capillary force
and surface tension. The supporting material and the PCM were
all combined physically.
4. The adsorption property, heat storage property and thermal
conductivity of the EP based FSCPCM, EV based FSCPCM and
diatomite based FSCPCM was enhanced by adding the thermal
enhancement components and modifying EP, EV and diatomite.
The EG based FSCPCM itself showed outstanding properties
because EG was used as not only the supporting material but
also the thermal enhancement component.
5. The content of the FSCPCM in cement mortar should be controlled because the addition of the four FSCPCM into cement
mortar would reduce the strength of the cement mortar
although it endowed the cement mortar with the thermal storage property.
Based on the research status of the micropore grade inorganic
porous medium based FSCPCM, the following aspects that should
be researched further in the future was put forward.
1. The effect of the pore structure of the micropore grade inorganic porous medium on the heat transfer and phase change
behavior of phase change materials needs to be further
explored. New methods to improve the thermal storage capacity and the thermal conductivity should be developed.

Acknowledgements
The work was supported by the National Natural Science Foundation of China (51178102) and the key project of National Natural
Science Foundation of China (51738003), which are financed by the
National Natural Science Fund Committee.

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