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RSM optimization of spray-coating parameters to enhance paper strength using cellulose nanocrystals extracted from young coconut husks
(2025-09-01)
Nuthongkum, Pilaipon
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Noonuruk, Russameeruk
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Bootchanont, Atipong
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Porjai, Porramain
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Wattanawikkam, Chakkaphan
This study optimizes spray-coating parameters for cellulose nanocrystals extracted from young coconut husks onto paper substrates using response surface methodology. CNCs were produced through acid hydrolysis and mechanical grinding, yielding nanocrystals with an average size of 116 nm and a crystallinity index increase from 28.89 % to 86.13 %. XRD and FTIR analyses confirmed high purity, while UV-vis revealed significant optical absorption in the UV range. Spray-coating parameters, including CNC concentration, volume, heating temperature, and heating duration, were optimized using a central composite design. The 2FI model revealed that CNC concentration and heating duration significantly affected film thickness, where higher CNC levels and longer heating durations produced thicker coatings. However, excessive CNC content led to agglomeration, compromising film quality. The quadratic model highlighted a significant relationship between coating parameters and tensile strength. Heat treatment notably enhanced mechanical properties, with optimal tensile strength reaching 26.15 ± 0.61 MPa-15 % higher than uncoated paper-under conditions of 4 % w/v CNC concentration, 1.5 ml volume, 75 °C heating temperature, and 35 min heating duration. This research highlights the potential of CNCs from young coconut husks as a sustainable reinforcement material, promoting agricultural waste valorization and enhancing paper properties.
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High-performance flexible thermoelectric generator based on silicone rubber and cover with graphite sheet
(2024-01-05)
Gobpant, Jakrit
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Klongratog, Bhanupol
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Rudradawong, Chalermpol
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Sakdanuphab, Rachsak
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Junlabhut, Prasopporn
Harvesting thermal energy through a flexible thermoelectric generator (FTEG) offers an excellent micro-power solution for energizing node sensors in the realm of Internet of Things (IoT) and wearable electronics. Nonetheless, current FTEG suffer from drawbacks including low efficiency, significant thermal resistance, and complex manufacturing procedures. In this study, a high-performance FTEG using silicone rubber was designed and fabricated using a straightforward process. The finite-element method was used to optimize the copper electrode thickness, and the bendable substrate layers with various thermal conductivity were studied for the first time. The copper electrode thickness of 0.1 mm was selected because it offers high flexibility and bendability while still providing a relatively high-power output. The 5 × 5 cm2 FTEG device was fabricated and covered with a bendable substrate. Silicon rubber (0.08 Wm−1K−1), silicon rubber added 5% graphene (0.14 Wm−1K−1), and graphite sheets (15 Wm−1K−1) were used as bendable substrates. The FTEG cover with graphite sheets has a maximum output voltage of 1.1 V under a temperature difference (ΔT) at 65 °C. Its maximum output power is 162.4 mW, corresponding to a power density of 6499.1 µW/cm2 under the same above ΔT. The experimental findings indicated that integrating a bendable substrate with high thermal conductivity and electrical insulation properties enhances the performance of the FTEG.
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Thickness Dependence of Thermoelectric Properties and Maximum Output Power of Single Planar Sb2Te3 Films
(2022-12-01)
Junlabhut, Prasopporn
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Nuthongkum, Pilaipon
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Harnwunggmoung, Adul
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Limsuwan, Pichet
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Hatayothai, Chanon
P-type Sb<inf>2</inf>Te<inf>3</inf> films with different thicknesses were deposited on polyimide substrates via heat treatment-assisted DC magnetron sputtering. The correlations between the thickness variance and the structure, dislocation density, surface morphology, thermoelectric properties and output power are investigated. As a result, it is clear that the film thickness and the heat treatment process during growth are related to the diffusion of deposited atoms on the substrate surface, leading to imperfection defects inside the films. The imperfections inside the films are affected by their properties. This work also presents the thermoelectric efficiency of a planar single leg of the deposited films with various thicknesses. The maximum power factor is 2.73 mW/mK2 obtained with a film thickness of 9.0 µm and an applied temperature of 100 °C. Planar Sb<inf>2</inf>Te<inf>3</inf> produced a maximum output power of 0.032 µW for a temperature difference of 58 K.
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Improving the thermoelectric properties of thick Sb2Te3 film via Cu doping and annealing deposited by DC magnetron sputtering using a mosaic target
(2021-11-01)
Theekhasuk, Nattharika
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Sakdanuphab, Rachsak
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Nuthongkum, Pilaipon
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Pluengphon, Prayoonsak
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Harnwunggmoung, Adul
Thick Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films were deposited on flexible substrate by DC magnetron sputtering from a mosaic Cu–Sb<inf>2</inf>Te<inf>3</inf> target. The Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films were vacuum annealed to improve their thermoelectric properties. Density functional theory was used to clarify the internal mechanism of the Cu doped into the Sb<inf>2</inf>Te<inf>3</inf> system. The results showed that Cu substitution on a Sb site induced electronic states or impurity peaks of Sb<inf>2</inf>Te<inf>3</inf> at a valence band maximum. The carrier concentration of the Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films increased as the Cu-doped concentration increased. However, the crystallite size and Seebeck coefficient of the Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films decreased as the Cu-doped concentration increased. Post-annealing treatment improved the microstructure and thermoelectric properties of the Cu-doped Sb<inf>2</inf>Te<inf>3</inf> films. The maximum electrical conductivity and power factor values of 754.20 S/cm at 50 °C and 1.56 10−3 W/mK2 at 100 °C were obtained in the annealed film with a Cu-doped concentration of 3 at%.
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Influence of Sputtering Power Density on the Thermoelectric and Mechanical Properties of Flexible Thermoelectric Antimony Telluride Films Deposited by DC Magnetron Sputtering
(2020-05-01)
Junlabhut, Prasopporn
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Nuthongkum, Pilaipon
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Sakdanuphab, Rachsak
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Harnwunggmoung, Adul
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Sakulkalavek, Aparporn
Antimony telluride (Sb<inf>2</inf>Te<inf>3</inf>) films were deposited on flexible polyimide substrates by DC magnetron sputtering technique using a 99.9% alloy Sb<inf>2</inf>Te<inf>3</inf> target. We measured structural, electrical, thermoelectric and mechanical properties with sputtering power density in the range 30–50 W. X-ray diffraction confirmed that all Sb<inf>2</inf>Te<inf>3</inf> films have high crystallinity with a significant preferential growth along the (015) plane. Surface morphologies were verified by scanning electron microscope: deposited film grain size increased with sputtering power density. The elemental composition was determined by energy dispersive x-ray spectroscopy. Electrical transport properties, carrier concentration, was measured by Hall effect measurement at room temperature. Electrical conductivity and Seebeck coefficient were simultaneously measured by a DC four-terminal method (ZEM-3). The power factor was strongly dominated by electrical conductivity, leading to a maximum of 1.95 mW/K2m with sputtering power 45 W at 300°C. The wettability test, based on the contact angle, evaluated surface energy and hydrophilicity. Nanoindentation was measured on a NHT2 CSM Instrument with diamond Berkovich indenter (B-P 31) at room temperature. The hardness and elastic modulus of deposited Sb<inf>2</inf>Te<inf>3</inf> films increased with the power density.
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Enhancing the thermoelectric properties of sputtered Sb2Te3 thick films via post-annealing treatment
(2020-04-15)
Junlabhut, Prasopporn
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Nuthongkum, Pilaipon
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Sakulkalavek, Aparporn
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Harnwunggmoung, Adul
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Limsuwan, Pichet
Sb<inf>2</inf>Te<inf>3</inf> films of more than 10 μm in thickness were deposited on flexible polyimide substrates by heat treatment-assisted DC magnetron sputtering. The post-annealing parameters including the temperature (150–350 °C) and time (15–60 min) were varied to investigate the microstructure, chemical composition, porosity and thermoelectric properties of the thick films. X-ray diffraction showed that both the as-deposited and post-annealed films were polycrystalline with significant preferential growth along the (015) plane. The films showed slightly off-stoichiometric compositions after post-annealing treatment. Increasing the annealing temperature and annealing time led to an increase in crystalline size and a decrease in porosity of the thick films. This was related to grain growth, agglomeration and surface improvement. The electrical transport and thermoelectric properties including carrier concentration, carrier mobility, electrical conductivity and Seebeck coefficient were investigated using Hall effect measurements and a ZEM-3 apparatus. A maximum power factor of 1.7 mW/K2m was obtained following annealing at 350 °C for 30 min.
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Comparison of thermoelectric properties of flexible bismuth telluride thin films deposited via DC and RF magnetron sputtering
(2019-11-18)
Jitthamapirom, Piya
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Wanarattikan, Pornsiri
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Nuthongkum, Pilaipon
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Sakdanuphab, Rachsak
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Sakulkalavek, Aparporn
Bi<inf>2</inf>Te<inf>3</inf> thin films were deposited onto polyamide sheets with direct current (DC) or radio frequency (RF) magnetron sputtering techniques. The films were prepared using a Bi<inf>2</inf>Te<inf>3</inf> target at a varying pre-heating temperature from 150 to 350 °C. It was observed that the type of plasma excitation and pre-heating temperature can significantly change the composition, preferred orientation, crystallinity, and thermoelectric properties of the films. The pre-heat treatment significantly affected the non-stoichiometric composition. In addition, it was shown that crystallinity and (0 0 l) planes were enhanced in the DC sputtered coatings at a high pre-heating temperature. The maximum power factor of 3.5 × 10−3 W/m K2 at 285 °C was obtained for the films deposited using DC magnetron sputtering and a pre-heating temperature of 350 °C. The carrier concentration and mobility of the film were 5.40 × 1020 cm−3 and 13.04 cm2/V s, respectively. Compared with an ordinary Bi<inf>2</inf>Te<inf>3</inf> film, the power factor of such film has been greatly increased. The results indicated that DC magnetron sputtering can enhance the (0 0l) plane orientation in the Bi<inf>2</inf>Te<inf>3</inf> film.
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[Bi]:[Te] Control, Structural and Thermoelectric Properties of Flexible BixTey Thin Films Prepared by RF Magnetron Sputtering at Different Sputtering Pressures
(2017-11-01)
Nuthongkum, Pilaipon
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Sakdanuphab, Rachsak
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Horprathum, Mati
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Sakulkalavek, Aparporn
In this work, flexible Bi<inf>x</inf>Te<inf>y</inf> thin films were prepared by radio frequency (RF) magnetron sputtering using a Bi<inf>2</inf>Te<inf>3</inf> target on polyimide substrate. The effects of sputtering pressures, which ranged between 0.6 Pa and 1.6 Pa on the [Bi]:[Te] ratio, and structural and thermoelectric properties were investigated. The [Bi]:[Te] ratio of thin film was determined by energy-dispersive spectrometry (EDS). The EDS spectra show the variation of the [Bi]:[Te] ratio as the sputtering pressure is varied. The film deposited at 1.4 Pa almost has a stoichiometric composition. The selective films with different [Bi]:[Te] ratios and sputtering pressures were characterized by their surface morphologies, crystal and chemical structures by field emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD) and Raman spectroscopy, respectively. Electrical transport properties, including carrier concentration and mobility, were measured by Hall effect measurements. Seebeck coefficients and electrical conductivities were simultaneously measured by a direct current four-terminal method (ZEM-3). The XRD and Raman spectroscopy results show a difference in microstructure between BiTe and Bi<inf>2</inf>Te<inf>3</inf> depending on the [Bi]:[Te] ratio. Electrical conductivity and Seebeck coefficient are related to the crystal and chemical structures. The maximum power factor of the Bi<inf>2</inf>Te<inf>3</inf> thin film is 9.5 × 10−4 W/K2 m at room temperature, and it increases to 12.0 × 10−4 W/K2 m at 195°C.
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RSM Base Study of the Effect of Argon Gas Flow Rate and Annealing Temperature on the [Bi]:[Te] Ratio and Thermoelectric Properties of Flexible Bi-Te Thin Film
(2017-05-01)
Nuthongkum, Pilaipon
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Sakulkalavek, Aparporn
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Sakdanuphab, Rachsak
Bismuth telluride (Bi-Te) thin films coated on a flexible substrate were prepared by RF (radio frequency) magnetron sputtering technique. A response surface methodology based on a central composite design was used to optimize deposition parameters, including the amount of Ar gas flow rate (100.5–106.5 sccm) in the sputtering process and the annealing temperature (250–320°C) for stoichiometric Bi<inf>2</inf>Te<inf>3</inf> thin films. The mathematical model was validated and proven to be statistically sufficient and accurate in predicting a response (Te content). The stoichiometric Bi<inf>2</inf>Te<inf>3</inf> thin films can be prepared on terms appropriate to the Ar flow rate and annealing temperature under several conditions, such as at the Ar flow rate of 103.5 sccm followed by an annealing temperature of 285°C. The characterization of the crystal structure and surface morphology of selected samples with different [Bi]:[Te] content were analyzed by x-ray diffraction (XRD) and a field emission scanning electron microscope, respectively. The XRD spectra showed Bi-Te and Bi<inf>2</inf>Te<inf>3</inf> structures that corresponded with the ratio of [Bi]:[Te]. The Seebeck coefficient and electrical conductivity were simultaneously measured at room temperature and up to 300°C by a direct current four-terminal method. The maximum power factor of the stoichiometric Bi<inf>2</inf>Te<inf>3</inf> thin film was 61×10−5 W/K2m at 243°C.

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