Trends Sci. 2025; 22(12): 11044

Introduction

The building construction sector accounts for approximately 40% of the total energy consumption worldwide. This share will increase as the energy consumption for space heating and cooling increases to 12% and 37%, respectively, in 2050. It has been reported that building construction and activities provided 36% of the global energy used in buildings and 39% of energy-related carbon dioxide emissions in 2018 [1,2]. Therefore, measures should be taken to limit this

consumption by introducing various renewable energy technologies and systems [3,4]. Thermal Energy Storage (TES) is one of the most important technologies for renewable energy storage that can manage heat, e.g., latent heat, sensible heat, and chemical heat [5]. TES systems can store excess heat energy using appropriate media; therefore, the stored energy can be withdrawn and reused when required in certain processes. Among these, latent heat storage using Phase Change Materials (PCM) is widely recognized for its high energy density and narrow operating temperature range, making it ideal for passive thermal regulation [6,7].

Thermal bonding agents, such as Phase Change Materials (PCM), can be utilized to improve thermal performance with less effect on existing structural properties. PCM are capable of changing phase at a given temperature, enabling latent heat absorption and release. This allows PCM to shift peak temperature loads and maintain indoor thermal comfort more effectively [8-10]. Many materials combining organic and inorganic substances have been used as PCM. The selection of PCM materials is typically based on thermal reliability, phase change temperature, chemical stability, and cost. Inorganic PCM have high latent heat capacity but are often corrosive. Organic PCM - such as paraffin - are non-toxic, chemically stable, and exhibit relatively high latent heat [11,12]. Paraffin, a saturated alkane with the empirical formula C_nH_2n+2, is widely used in thermal energy storage applications. It offers good chemical compatibility and a broad melting point range. However, its low thermal conductivity (< 0.3 W/m·K) is a limiting factor, particularly in applications requiring rapid heat exchange [13]. To overcome this, many researchers have explored the addition of thermally conductive materials into PCM.

A considerable number of studies have reported thermal enhancement achieved by dispersing metal nanoparticles in PCM, including Fe₃O₄ [14], TiO₂ [15], SiO₂ [16], Al₂O₃ and MgO [17]. Carbon-based materials such as carbon nanotubes (CNTs) [18], graphene [19], and carbon fibers [20] have also been used to increase conductivity. In Singh et al. [17], various nanomaterials (SiO₂, Al₂O₃ and MgO) at 0.1 - 0.5 vol% were added to paraffin, yielding significant increases in thermal conductivity (10.71% - 29.32%) and viscosity (up to 90%). In another study, Prabhu et al. [21] added 7.5 and 10 wt% of Al₂O₃ nanoparticles to paraffin, producing latent heat values of 203.89 and 187.44 kJ/kg and enhancing thermal conductivity by 42% and 57% compared to pure paraffin. However, high nanoparticle loading often compromises energy storage capacity due to volume displacement. He et al. [22]; He et al. [23] investigated the thermal and magnetic properties of Fe₃O₄-paraffin composites at 1 - 3 wt%. Thermal conductivity improved from 0.251 to 0.331 W/m·K, but latent heat declined with increasing Fe₃O₄ content. These results confirm that increasing filler content improves thermal conductivity but may reduce heat storage performance, emphasizing the need to optimize composition for target applications. Furthermore, carbon-based materials can be utilized to improve the thermal conductivity of PCM. Fikri et al. [18] investigated multi-walled carbon nanotubes (MWCNTs) as thermal enhancers and reported a 150.7% increase in thermal conductivity with the addition of 1 wt% MWCNTs - reaching 0.597 W/m·K compared to 0.238 W/m·K for pure A70 paraffin. Hu et al. [24] explored hybrid PCM composites using CNTs (2 wt%) and styrene-butadiene-styrene (SBS) at 18 - 8 wt%, processed at 180 °C. Although melting enthalpy decreased from 200.01 J/g (pure paraffin) to 142.28 - 157.70 J/g, the materials retained good morphological and mechanical integrity making them promising for TES. Sharshir et al. [25] examined paraffin doped with CuO, Co₃O₄, and CuO@Co₃O₄ (each 3 wt%). The synthesis involved magnetically assisted stirring at 60 °C and sonication. Morphological and EDX analyses confirmed uniform dispersion of the nanoparticles. Despite some reduction in melting enthalpy (11% - 20%), the nanocomposites exhibited improved thermal responsiveness and stability.

Previous studies have shown that conductive nanoparticles not only improve thermal conductivity but can also enhance thermal storage capacity [26,27]. However, most of these enhancements are studied at the material level, and their performance in real structural systems like concrete remains less explored. The integration of PCM into cementitious systems is gaining interest due to their potential in passive thermal regulation. Concrete, as a widely used building material, is an ideal carrier for PCM because of its formability, availability, and mechanical properties. Additional benefits include dampening thermal fluctuations and reducing freeze–thaw-related damage in cold climates [28]. PCM can be incorporated into concrete either directly or indirectly. In this study, an indirect approach is adopted [29], using microencapsulation.

This method places the PCM inside sealed containers (e.g., tubes or spheres) embedded into the concrete, preventing leakage and minimizing interference with the concrete’s structural function. It also improves both thermal and mechanical properties of the PCM-concrete composite [28]. Al-Yasiri et al. [30] investigated aluminum macroencapsulation in concrete and reported improved thermal behavior and extended retention times, especially under high outdoor temperatures. Thermal transfer rates increased with encapsulation surface area. In addition, Tetuko et al. [13] enhanced paraffin with 50% magnetite and showed that thermal conductivity rose from 0.32 to 0.53 W/m·K. The encapsulated system effectively stored and released heat during cyclic operation.

Comparatively, microencapsulation approaches such as those studied by Alsaadawi et al. [31] showed reduced peak temperatures (6.75 - 9.25 °C) when 1% - 10% microencapsulated PCM was added. However, compressive strength decreased, requiring higher target design strengths (~40 MPa). Despite some paraffin leakage upon shell breakage, PCM helped refine the interface between aggregate and cement paste. Ying et al. [32] implemented graded PCM aggregates to enable multi-stage latent heat release between 5 and −15 °C, mitigating frost heave in cold regions. Yet, as PCM content increased, compressive strength showed a declining trend-reinforcing the performance trade-off in structural applications. Although many advances have been made, few studies focus on natural fillers such as Fe₃O₄ from iron sand, or on scalable macroencapsulation systems embedded directly in concrete. This study aims to address both gaps.

In this research, paraffin is enhanced with natural Fe₃O₄ particles sourced from West Java, Indonesia. The composite is macroencapsulated in 4 copper tubes and embedded into concrete blocks. Copper was selected for its high thermal conductivity and compatibility with cementitious materials. The Fe₃O₄ content is varied at 20, 30, 40 and 50 vol% to evaluate its effect on thermal and magnetic behavior. The novelty of this study lies in 3 main aspects: (i) the use of natural, low-cost Fe₃O₄ as a thermally and magnetically active additive, (ii) the design of a practical copper-tube macroencapsulation system embedded in concrete, and (iii) the focus on real-world structural integration for building thermal energy management. The objective is to evaluate the thermophysical, magnetic, and structural performance of the PCM-concrete system and determine its feasibility as a passive energy storage solution.

Materials and methods

Materials

Paraffin with a nominal melting point of 50 - 60 C was used as the organic phase change material (PCM), which was acquired from a local supplier. An improvement in thermal conductivity was achieved by the addition of magnetite particles. The magnetite used in this research was obtained from the West Java region and mixed to form a paraffin-Fe₃O₄ composite phase change material (PCM). The physical and thermal properties of paraffin and Fe₃O₄ are summarized in Table 1 [33]. In addition, concrete was used to install the copper tube and encapsulate the PCM. The raw material of the concrete comprised cement, river sand, water and aggregates and its properties are given in Table 2 [34].

Table 1 Properties of paraffin and Fe₃O₄.

Table 2 Properties of aggregates.

Preparation of PCM

The preparation process of the PCM is shown in Figure 1. In this research, sonication heating was chosen because to its uniformity and rapid heating. The technique involves melting, stirring, sonication and solidification. Paraffin was first melted at 50 C and Fe₃O₄ was then added to the melting paraffin. Fe₃O₄ was added according to the compositions listed in Table 3. During sonication, the suspension was stirred in an ultrasonic bath for 15 min at 80 C, and ultrasonic frequency of 37 kHz was applied to achieve uniform dispersion and to avoid precipitation of nanoparticles. In the solidification step, the suspension was poured into a mold.

Table 3 Compositions of PCM samples.

Figure 1 Preparation of PCM composite with ultrasonic bath technique.

Preparation of concrete samples

The concrete was constructed with dimensions of 5×5×5 cm³. The concrete mix proportion was set to 0.7:2:1.5:1 (water: aggregates: river sand: cement). The concrete specimens were stored at room temperature for 28 days for the curing process. Four copper tubes with a diameter of 1.25 cm and length of 5 cm were used as the encapsulation media.

Characterizations

The crystalline paraffin and Fe₃O₄ phases of the PCM composite were determined using XRD (D/teX ultra250). The chemical structure of the PCM was analyzed using fourier transform infrared spectroscopy (FTIR; Thermoscientific Nicolet iS 10) in the range of 4,000 - 400 cm⁻¹. The morphology and microstructure of the shape-stabilized PCM were investigated using Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX; SEM Hitachi, SU3500). The thermal stability of the shape-stabilized PCM was evaluated using a differential scanning calorimeter (DSC 8000, Perkin Elmer) to determine the latent heat and phase change temperature, which was carried out in a N₂ atmosphere from 30 to 150 C at a heating/cooling rate of 10 C min⁻¹. The thermal conductivities of the PCM were measured using a QTM-500-thin film instrument.

Experimental set-up

In this study, concrete was installed with 4 copper tubes as PCM encapsulation media. Several thermocouples connected to a data logger were installed in the PCM encapsulated concrete to monitor temperature distribution. A heater at a constant temperature of 80 °C was applied to the PCM encapsulated concrete as the heat source. Rock wool was utilized as an insulation material to minimize heat loss. The experimental setup is illustrated in Figure 2. All prepared PCM specimens were poured into a copper tube inside the concrete (5×5×5 cm³). The samples consisted of 4 PCM specimens and were provided with an accurate calibrated measuring device to evaluate and compare their thermal performance. These devices use K-type thermocouples connected to an Arduino-based digital readout monitor. Temperature distribution measurements were conducted for 24 h per day. The temperature distribution experiment was conducted to test the thermal performance of PCM encapsulated in a concrete. The samples consisted of all PCM encapsulated concrete samples with different magnetite compositions.

Figure 2 Temperature distribution experimental set-up of PCM encapsulated concrete.

Results and discussion

Sturctural characterization of paraffin and Fe₃O₄

The analysis of the XRD spectra provided important information on the structural properties, that is, the phase and crystallite size (D) [35]. The X-ray diffraction (XRD) patterns of paraffin and Fe₃O₄ are shown in Figure 3. The XRD pattern data of paraffin are reported at 2 diffraction peaks: 21.46 and 23.84 which indicate diffraction from the (110) and (200) crystal planes, respectively. Paraffin also has a monoclinic crystalline phase based on the standard data of COD-96-434-3587. Although paraffin has monoclinic crystal characteristics at room temperature, an increase in paraffin temperature causes the β phase in paraffin to gradually change into the α phase and thus the crystal structure of paraffin becomes hexagonal or orthorhombic [36,37]. The XRD spectra of Fe₃O₄ showed diffraction peaks at 30.16 , 35.49 , 43.03 , 53.35 , 56.96 , 62.46 and 73.93 with phase crystallites of (220) (311) (400) (422) (511) (440) and (642) for the cubic phase structure, which were confirmed using COD-96-151-3305 standard data [35]. The general method for determining the crystallite size from the XRD spectra is the Scherrer method [35], as shown in Eq. (1). Where D is the crystallite size, k is a geometric factor (0.9), λ is the wavelength of a copper target of X-ray (λ = 1.79), β is the full width at half maximum (FWHM) of the diffraction peak and θ is the diffraction angle [35,38].

The presence of sharp and well-defined peaks indicates a highly ordered lattice structure. While detailed calculations of lattice constants and full width at half maximum (FWHM) are not included in this study, they represent important parameters for future work to assess the degree of crystallinity and potential lattice strain more precisely.

Based on the calculation, it was determined that the paraffin diameter was 3.93 nm while the Fe₃O₄ crystal size was 1.95 nm. However, due to the limitations of XRD in detecting low-angle grain boundaries or dislocation defects, further analysis using high-resolution TEM is recommended to investigate possible lattice imperfections and interfacial dislocations, which may play a role in phonon scattering and thermal conductivity behavior.

Figure 3 XRD patterns of paraffin and Fe₃O₄.

Chemical stability analysis of PCM

Infrared spectrograms of the synthesized specimens were measured using a Thermoscientific Nicolet iS-10 instrument with has a scanning range of (4,000 - 400 cm⁻¹). Figure 4 shows the FTIR spectrum region of the PCM-A1 sample at 565.58 to 2,956.96 cm⁻¹ and PCM-A4 sample at 570.48 to 3,444.50 cm⁻¹. The spectrum of Fe₃O₄ occurs at wave numbers 570.48 and 565.58 cm⁻¹, which is characteristic of magnetite (Fe₃O₄) where the group formed is Fe-O [39]. While at a wave number of 719.40 and 719.47 cm⁻¹ are C-H functional groups, and 729 cm⁻¹ is CH₂ groups. At peak of 1,377.48 and 1,377.40 cm⁻¹ suggested the functional groups of CH₂ and O-H bonds [40]. The peak at 1,472 cm⁻¹ indicates a CH₂ rocking vibration [41]. At wave numbers of 2,848 and 2,917 cm⁻¹, CH₂ represents an asymmetrical stretching vibration [42]. The peak at 2,956 cm⁻¹ represents the O-H groups [43]. The comparison of FTIR the PCM-A1 and PCM-A4 samples showed no significant difference. This indicates that only physical mixing between paraffin and Fe₃O₄ occurred and did not damage the crystal structures of each other after the melting process. Thus, no new functional groups were formed in the PCM composites.

Figure 4 The results of FTIR spectra for PCM-A1 and PCM-A4 samples.

Morphology analysis of PCM

To determine the morphological structure of the PCM samples and the elemental content of the PCM, Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX) was used. SEM-EDX characterization was carried out at a magnification of 5k, samples were characterized as PCM-A1 and PCM-A4. The SEM-EDX morphology results at 5k magnification are shown in Figure 5. The magnetite particles had a suitable distribution range and were spherical, providing evidence that Fe₃O₄ was dispersed throughout the material. According to the results in Figures 5(a) - 5(b), magnetite (Fe₃O₄) is a bright particle that is uniformly distributed inside the paraffin-embedded layer, while some of it is concentrated in the layer facing down the paraffin [44]. In the case of the PCM-A4 sample, it can be seen that the ratio of paraffin to Fe₃O₄ is balanced. This is because the total mass compositions of paraffin and Fe₃O₄ were the same. For PCM with a composition of PCM-A1, the amount of paraffin dominated that of Fe₃O₄. In addition, the EDX analysis shown in Figures 5(c) - 5(d) confirmed the distribution of Fe₃O₄ between the paraffin layers and the formation of hybrid nano-Fe₃O₄ based PCM. Hence, shape-stabilized PCM have been developed [45]. This was confirmed by comparing the C, O, and Fe percentages. The EDX results are listed in Table 4.

Figure 5 (a) SEM images of PCM-A1, (b) SEM images of PCM-A4, (c) EDX analysis of PCM-A1, and (d) EDX analysis of PCM-A4.

Table 4 EDX Results of the PCM.

Magnentic analysis of PCM

The shape of the hysteresis curve of a particular material provides significant information regarding its magnetic behavior. The magnetic properties of the PCM measured using VSM250 are presented in Figure 6. The magnetization curve illustrates the saturation magnetization (Ms) versus magnetic field (H), confirming the presence of superparamagnetic iron oxide nanoparticles [46,47]. The saturation magnetization, coercivity, and retention values were derived from the hysteresis curves. The magnetic property parameters of the PCM are summarized in Table 5. The saturation magnetization (Ms) of the 50 vol% Fe₃O₄ PCM is 30.40 emu/g, which is lower than that reported by Hastak et al. who obtained a magnetization of 38.86 emu/g. This discrepancy was attributed to the presence of a non-magnetic paraffin mixture.

Subsequently, the magnetization value decreased by ~10% - 4% based on the amount of Fe₃O₄ added to the composite PCM. The hysteresis curve, resembling the letter S with a very small Hc value, indicates superparamagnetic properties. Another parameter of magnetic properties is the susceptibility value (χ). The susceptibility value quantifies the response of magnetic materials to an external magnetic field. Theoretically, M = χH; thus, the increase in χ is proportional to the increase in Ms [48]. Further investigation into the increase in Ms with the increase in Fe₃O₄ content in paraffin reveals that it can be related to the value of the magnetic moment and the size of the magnetic domain. Theoretically, the magnetization value is strongly correlated with the magnetic moment and magnetic domain size (Eq. (2)) [48].

The results of the VSM analysis on the composite PCM confirmed that the synthesized particles were soft magnetic. The minimal area of the hysteresis curve indicates that the synthesized particles were in close proximity to the superparamagnetic state. These magnetic values were comparable to those reported in previous studies. The addition of magnetite particles to PCM enhances its magnetic properties; however, the composite remains classified as a soft magnetic and superparamagnetic material. This material exhibits a favorable magnetic response and can be readily attracted by magnets [49,50].

Figure 6 Hysteresis curves of PCM-magnetite.

Table 5 VSM Results of PCM-magnetite composite.

DSC analyses of PCM

DSC characterizations were performed to analyze the thermal performance of the PCM and their phase-change behavior during the heating and cooling stages. The characterized samples consisted of PCM-A1 and PCM-A4 with sample weights of 5.6 and 5.8 mg, respectively. Characterization was performed according to ASTM D3418-15 test standards and measured using Perkin Elmer DSC 8000 test equipment in an aluminum cell with a nitrogen flow rate of 20 mL/min.

Figures 7(a) - 7(b) are the results of DSC characterization comparison between PCM-A1 and PCM-A2 samples at 1.5 cycles with an initial temperature of 30 °C and then heated to 100 °C with a temperature increase of 10 °C/min. In the first and fifth steps, PCM melting occurs, whereas in the third step, PCM solidification occurs. The coverage of the heat flow during the heat absorption and heat release process in the PCM-A1 sample, which contained 20 vol% Fe₃O₄ suggested a wider coverage than the PCM-A4 sample with the addition of 50 vol% Fe₃O₄. Figures 7(a) - 7(b) confirm that the PCM cycles can be repeated and do not exhibit a shift in the heat flow and thus remain stable [42]. The PCM melting process was found to be endothermic, as illustrated in Figure 7(c). Results indicate that the enthalpy values for the PCM-A4 and PCM-A1 samples were 17.13 and 55.28 J/g, respectively. The addition of Fe₃O₄ led to a decrease in the enthalpy and heat storage capacity of the PCM. However, this resulted in a significant increase in the thermal absorption region. The endothermic peak in the graph corresponds to the melting point of the PCM. In this study, the melting points for the PCM-A1 and PCM-A4 samples were found to be 56.67 and 56.81 ℃, respectively.

b

Figure 7 DSC results (a) 1.5 cycles of PCM-A1, (b) 1.5 cycles of PCM-A4, and (c) comparison of endothermic analysis of PCM-A1 and PCM-A4.

Thermal conductivity of PCM

The thermal conductivity of the PCM was investigated to determine their ability to transfer heat from a heat source. In this investigation, the thermal conductivity test of PCM was examined through tests conducted on the PCM-A4 and PCM-A1 samples. The results of the thermal conductivity characterization are shown in Table 6 and were comparedision with the results of previous research.

Thermal energy can be transmitted through solids in various ways, such as through electrical carriers (electrons or holes), lattice waves (phonons), spin waves, electromagnetic waves, and other excitations [51]. The addition of magnetite particles to paraffin can improve the thermal conductivity because magnetite contains iron (Fe), which allows thermal energy to flow through Fe electrons instead of the usual vibrations and rotations of the molecular chains in paraffin polymers. Some of the kinetic energy in the free electrons is transferred as vibrational energy to the atoms moving from the hot to cold regions. The magnetite particles in paraffin serve as fillers and act as heat carriers and thermal pathways during the melting and solidification of phase change materials (PCM). As a result, microconvection and thermophoresis can occur more quickly, and the heat transfer in paraffin-magnetite composites can be enhanced [52,53]. Magnetite particles can also boost the endothermic and exothermic reactions of PCM owing to their high thermal conductivities.

Table 6 Thermal conductivity of PCM at ambient temperature.

The following text provides an analysis of the thermal conductivities of PCM-A4 and PCM-A1, with the results indicating a higher thermal conductivity in PCM-A4 at 0.54 W/m.K compared to PCM-A1 at 0.37 W/mK. This increase in thermal conductivity is attributed to the addition of magnetite (Fe₃O₄) particles, compared to pure paraffin, which has a thermal conductivity of 0.23 W/m·K. Furthermore, the thermal conductivity obtained in this study aligns well with previous research [55]. It is important to note that a higher thermal conductivity in PCM is necessary to enhance the heat transfer from the heat source to the PCM in a shorter period of time, as suggested by previous studies [31,37].

Temperature distribution on concrete

The results obtained from the tests exhibit an exponential curve due to the endothermic process, which rises periodically and is directly proportional to the increase in temperature and time. As the solidification process takes place by gradually lowering the temperature to room temperature at 28 °C, the graph exhibits a decline due to the exothermic event, resulting in an exponential decrease. The temperature distribution results are shown in Figure 8. Heat is transferred from the heater, which serves as the heat source, to the concrete and copper tubes via conduction, which can be classified as sensible heat as the temperature changes. Conversely, in PCM, a phase change reaction occurs from solid to liquid (melting) without a change in temperature and can be classified as latent heat. When the heater was turned off during the cooling process, the PCM began to release latent heat, and another phase change transformation occurred (solidification) [13,56].

Figure 8 Temperature distribution results (a) PCM-A1, (b) PCM-A2, (c) PCM-A3, (d) and PCM-A4.

In the PCM-A1 and PCM-A3 samples, the thermal absorption was greater than that of the other samples, because the addition of a large amount of paraffin affected the phase changes process [57,58]. The results of the thermal distribution test prove that the PCM-encapsulated concrete can withstand heat and store thermal energy. Furthermore, the maximum stress that the concrete can withstand is reduced as the fraction of PCM increases. The low intensity of PCM reduces the global intensity of concrete. According to the Chinese national standard GB/T 20473-2006 (insulation and mortar in buildings), the maximum tolerable stress of concrete blocks should be higher than 0.4 MPa to meet the demand of a building material. Thus, 15% of PCM was the optimal mass fraction when concrete-based PCM was produced [54,59,60]. Figure 8 suggests that PCM from the 4 compositions have an average critical temperature value of 56.7 ℃ with different crisis times. This occurs because of the large amount of magnetite added to PCM, which that affects the longer melting-liquid phase process [61,62]. The longest critical time in the PCM-A4 PCM is 28,951 s.

Conclusions

Paraffin-magnetite (Fe₃O₄) PCM encapsulated in tubes embedded in concrete was prepared and analyzed. XRD characterization showed that Fe₃O₄ and paraffin had cubic and monoclinic crystal phases. The FTIR results showed that magnetite (Fe₃O₄) was successfully distributed on the paraffin filler in the PCM. In addition, magnetite particles were evenly distributed inside the PCM, confirmed by the SEM-EDX morphology results. In contrast, VSM analysis showed that the addition of magnetite increased the saturation magnetization. DSC analysis suggested that the endothermic peak occurred at the highest temperature of 56.81 ℃ for PCM-A4 and PCM were confirmed to be stable as thermal energy storage. The highest thermal conductivity was obtained for PCM-A4 composition of 0.54 W/m·K. Additionally, the results of the thermal distribution analysis confirmed that the PCM could store and transmit heat. Moreover, the paraffin-magnetite composites studied in this investigation have potential applications in thermal energy storage owing to the thermal properties of the composites. These results demonstrate that the composite has potential as a thermal energy storage medium in building materials. However, this study has certain limitations that warrant further investigation. The long-term thermal stability and cycling reliability of the composite remain underexplored, particularly in relation to repeated phase transitions and environmental exposure. To address potential agglomeration and improve dispersion uniformity, future studies should consider surface tension modification strategies, such as the incorporation of surfactants. Additionally, while this research focused on Fe₃O₄ due to its natural abundance and magnetic responsiveness, alternative filler materials - such as metal oxides and carbon-based nanomaterials - may offer improved thermal performance. Future research should investigate these advanced materials and evaluate their structural integrity, scalability, and integration potential in real-world building thermal management systems.

Acknowledgements

The authors would like to thank the Research Center for Advanced Materials, National Research and Innovation Agency (BRIN), Indonesia for the facilities used in this research. The authors also acknowledge the PMDSU (Master to Doctoral Education) Batch VIII scholarship program from the Ministry of Education, Culture, Research and Technology of Indonesia for financial support, and the Postgraduate Physics Program at Universitas Sumatera Utara, Indonesia for their support and encouragement.

Declaration of Generative AI in Scientific Writing

The authors acknowledge the use of ChatGPT (OpenAI) in the preparation of this manuscript, specifically for language editing and grammar correction. No content generation, scientific idea creation, or data interpretation was performed by AI. The authors take full responsibility for the content and conclusions of this work.

Credit author statement

Widya Sonita Gultom: Writing - original draft; Investigation; Formal analysis; Project administration. Timbangen Sembiring: Writing - review & editing; Validation; Supervision; Conceptualization; Funding acquisition. Anggito Pringgo Tetuko: Validation; Supervision; Conceptualization; Resources; Muhammad Fauzi: Methodology; Data curation; Investigation. Amdy Fachredzy: Project administration. Eko Arief Setiadi: Validation. Nining Sumawati Asri: Validation. Ayu Yuswita Sari: Validation. Martha Rianna: Validation. Erna Frida: Validation. Achmad Maulana Soehada Sebayang: Validation.

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