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13 pages, 40121 KiB

Open AccessArticle

Assessment of Manufacturing Parameters for New 3D-Printed Heating Circuits Based on CNT-Doped Nanocomposites Processed by UV-Assisted Direct Write

by Alejandro Cortés, Alberto Jiménez-Suárez, Mónica Campo, Alejandro Ureña and Silvia G. Prolongo

Appl. Sci. 2021, 11(16), 7534; https://doi.org/10.3390/app11167534 - 17 Aug 2021

Cited by 4 | Viewed by 2183

Abstract

This work consists of the development of an easy strategy to transform any structure into an efficient surface heater by the application of a low voltage over 3D printed nanocomposite circuits. To this end, the electrical conductivity and self-heating capabilities of UV-Assisted Direct [...] Read more.

This work consists of the development of an easy strategy to transform any structure into an efficient surface heater by the application of a low voltage over 3D printed nanocomposite circuits. To this end, the electrical conductivity and self-heating capabilities of UV-Assisted Direct Write 3D printed circuits doped with carbon nanotubes were widely explored as a function of the number of printed layers. Moreover, an optimization of the printing process was carried out by comparing the accuracy and printability obtained when printing with two different configurations: extruding and curing the ink in the same stage or curing the extruded ink in a second stage, after the whole layer was deposited. In this regard, the great homogeneity and repeatability of the heating showed by the four-layer printed circuits, together with their excellent performance for long heating times, proved their applicability to convert any structure to a surface heater. Finally, the deicing capability of the four-layer circuit was demonstrated, being able to remove a 2.5 mm thick ice layer in 4 min and 4 s. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in Materials)

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22 pages, 25815 KiB

Open AccessArticle

Machine Learning-Based Prediction and Optimisation System for Laser Shock Peening

by Jino Mathew, Rohit Kshirsagar, Suraiya Zabeen, Niall Smyth, Stratis Kanarachos, Kristina Langer and Michael E. Fitzpatrick

Appl. Sci. 2021, 11(7), 2888; https://doi.org/10.3390/app11072888 - 24 Mar 2021

Cited by 24 | Viewed by 4645

Abstract

Laser shock peening (LSP) as a surface treatment technique can improve the fatigue life and corrosion resistance of metallic materials by introducing significant compressive residual stresses near the surface. However, LSP-induced residual stresses are known to be dependent on a multitude of factors, [...] Read more.

Laser shock peening (LSP) as a surface treatment technique can improve the fatigue life and corrosion resistance of metallic materials by introducing significant compressive residual stresses near the surface. However, LSP-induced residual stresses are known to be dependent on a multitude of factors, such as laser process variables (spot size, pulse width and energy), component geometry, material properties and the peening sequence. In this study, an intelligent system based on machine learning was developed that can predict the residual stress distribution induced by LSP. The system can also be applied to “reverse-optimise” the process parameters. The prediction system was developed using residual stress data derived from incremental hole drilling. We used artificial neural networks (ANNs) within a Bayesian framework to develop a robust prediction model validated using a comprehensive set of case studies. We also studied the relative importance of the LSP process parameters using Garson’s algorithm and parametric studies to understand the response of the residual stresses in laser peening systems as a function of different process variables. Furthermore, this study critically evaluates the developed machine learning models while demonstrating the potential benefits of implementing an intelligent system in prediction and optimisation strategies of the laser shock peening process. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in Materials)

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13 pages, 5753 KiB

Open AccessArticle

Structural, Electronic, and Optical Properties of Group 6 Doped Anatase TiO₂: A Theoretical Approach

by Petros-Panagis Filippatos, Nikolaos Kelaidis, Maria Vasilopoulou, Dimitris Davazoglou and Alexander Chroneos

Appl. Sci. 2021, 11(4), 1657; https://doi.org/10.3390/app11041657 - 12 Feb 2021

Cited by 5 | Viewed by 2303

Abstract

Titania (TiO₂) is a key material used as an electron transport in dye-sensitized and halide perovskite solar cells due to its intrinsic n-type conductivity, visible transparency, low-toxicity, and abundance. Moreover, it exhibits pronounced photocatalytic properties in the ultra-violet part of the [...] Read more.

Titania (TiO₂) is a key material used as an electron transport in dye-sensitized and halide perovskite solar cells due to its intrinsic n-type conductivity, visible transparency, low-toxicity, and abundance. Moreover, it exhibits pronounced photocatalytic properties in the ultra-violet part of the solar spectrum. However, its wide bandgap (around 3.2 eV) reduces its photocatalytic activity in the visible wavelengths’ region and electron transport ability. One of the most efficient strategies to simultaneously decrease its bandgap value and increase its n-type conductivity is doping with appropriate elements. Here, we have investigated using the density functional theory (DFT), as well as the influence of chromium (Cr), molybdenum (Mo), and tungsten (W) doping on the structural, electronic, and optical properties of TiO₂. We find that doping with group 6 elements positively impacts the above-mentioned properties and should be considered an appropriate method for photocatalystic applications. In addition to the pronounced reduction in the bandgap values, we also predict the formation of energy states inside the forbidden gap, in all the cases. These states are highly desirable for photocatalytic applications as they induce low energy transitions, thus increasing the oxide’s absorption within the visible. Still, they can be detrimental to solar cells’ performance, as they constitute trap sites for photogenerated charge carriers. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in Materials)

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14 pages, 6535 KiB

Open AccessArticle

Defect Processes in Halogen Doped SnO₂

by Petros-Panagis Filippatos, Nikolaos Kelaidis, Maria Vasilopoulou, Dimitris Davazoglou and Alexander Chroneos

Appl. Sci. 2021, 11(2), 551; https://doi.org/10.3390/app11020551 - 8 Jan 2021

Cited by 10 | Viewed by 2669

Abstract

In the present study, we performed density functional theory calculations (DFT) to investigate structural changes and their impact on the electronic properties in halogen (F, Cl, Br, and I) doped tin oxide (SnO₂). We performed calculations for atoms intercalated either at [...] Read more.

In the present study, we performed density functional theory calculations (DFT) to investigate structural changes and their impact on the electronic properties in halogen (F, Cl, Br, and I) doped tin oxide (SnO₂). We performed calculations for atoms intercalated either at interstitial or substitutional positions and then calculated the electronic structure and the optical properties of the doped SnO₂. In all cases, a reduction in the bandgap value was evident, while gap states were also formed. Furthermore, when we insert these dopants in interstitial and substitutional positions, they all constitute a single acceptor and donor, respectively. This can also be seen in the density of states through the formation of gap states just above the valence band or below the conduction band, respectively. These gap states may contribute to significant changes in the optical and electronic properties of SnO₂, thus affecting the metal oxide’s suitability for photovoltaics and photocatalytic devices. In particular, we found that iodine (I) doping of SnO₂ induces a high dielectric constant while also reducing the oxide’s bandgap, making it more efficient for light-harvesting applications. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in Materials)

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17 pages, 4844 KiB

Open AccessArticle

Impact of Dy₂O₃ Substitution on the Physical, Structural and Optical Properties of Lithium–Aluminium–Borate Glass System

by Osama Bagi Aljewaw, Muhammad Khalis Abdul Karim, Halimah Mohamed Kamari, Mohd Hafiz Mohd Zaid, Noramaliza Mohd Noor, Iza Nurzawani Che Isa and Mohammad Hasan Abu Mhareb

Appl. Sci. 2020, 10(22), 8183; https://doi.org/10.3390/app10228183 - 19 Nov 2020

Cited by 38 | Viewed by 3774

Abstract

In this study, a series of Li₂O-Al₂O₃-B₂O₃ glasses doped with various concentrations of Dy₂O₃ (where x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 mol%) were prepared by using a conventional [...] Read more.

In this study, a series of Li₂O-Al₂O₃-B₂O₃ glasses doped with various concentrations of Dy₂O₃ (where x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 mol%) were prepared by using a conventional melt-quenching technique. The structural, physical and optical properties of the glasses were examined by utilising a variety of techniques instance, X-ray diffraction (XRD), UV–Vis-NIR spectrometer, Fourier transform infrared (FTIR) and photoluminescence (PL). The XRD spectra demonstrate the amorphous phase of all glasses. Furthermore, the UV-vis-NIR spectrometers have registered optical absorption spectra a numbers of peaks which exist at 1703, 1271, 1095, 902, 841, 802, 669, 458, 393 and 352 nm congruous to the transitions from the ground of state (⁶H_15/2) to different excited states, ⁶H_11/2, ⁶F_11/2 + ⁶H_9/2, ⁶F_9/2 + ⁶H_7/2, ⁶F_7/2, ⁶F_5/2, ⁶F_3/2, ⁴F_9/2, ⁴I_15/2, ⁴F_7/2 and ⁶P_7/2, respectively. The spectra of emission exhibit two strong emanation bands at 481 nm and 575 nm in the visible region, which correspond to the transitions ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2. All prepared glass samples doped with Dy₂O₃ show an increase in the emission intensity with an increase in the concentration of Dy³⁺. Based on the obtained results, the aforementioned glass samples may have possible applications, such as optical sensor and laser applications. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in Materials)

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11 pages, 2389 KiB

Open AccessArticle

CQDs@NiO: An Efficient Tool for CH₄ Sensing

by Marilena Carbone

Appl. Sci. 2020, 10(18), 6251; https://doi.org/10.3390/app10186251 - 9 Sep 2020

Cited by 22 | Viewed by 2727

Abstract

A composite material based on carbon quantum dots (CQDs) and NiO was prepared and tested for methane sensing. The synthesis procedure is simple and foresees the preparation of the CQDs by citric acid pyrolysis and NiO by hydrothermal synthesis. A phase sonication and [...] Read more.

A composite material based on carbon quantum dots (CQDs) and NiO was prepared and tested for methane sensing. The synthesis procedure is simple and foresees the preparation of the CQDs by citric acid pyrolysis and NiO by hydrothermal synthesis. A phase sonication and stirring procedure yielded the composite CQDs@NiO at different loads. The composites were characterized by X-ray diffraction, ultraviolet–visible light (UV–Vis) spectroscopy, SEM microscopy, energy-dispersive spectroscopy (EDS) mapping, and surface area, porosity, and impedance measurements. A gas sensor was built in-house and used to probe the response of the synthesized samples to CH₄ detection, at constant environmental humidity. The CQDs@NiO at 1% weight load displayed excellent performances in terms of gas response both vs. temperature and vs. concentration, whereas higher loads resulted in CQD aggregation and diminished output. Response/recovery times of the 1%CQDs@NiO sample were good, as well as the selectivity and the stability over time and for variable environmental humidity. The estimated limit of detection was 0.1 ppm. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in Materials)

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17 pages, 5105 KiB

Open AccessArticle

Flexural Performance of Novel Nail-Cross-Laminated Timber Composite Panels

by Yannian Zhang, Moncef L. Nehdi, Xiaohan Gao and Lei V. Zhang

Appl. Sci. 2020, 10(17), 5983; https://doi.org/10.3390/app10175983 - 29 Aug 2020

Cited by 7 | Viewed by 2904

Abstract

Cross-laminated timber (CLT) is an innovative wood panel composite that has been attracting growing interest worldwide. Apart from its economic benefits, CLT takes full advantage of both the tensile strength parallel to the wood grain and its compressive strength perpendicular to the grain, [...] Read more.

Cross-laminated timber (CLT) is an innovative wood panel composite that has been attracting growing interest worldwide. Apart from its economic benefits, CLT takes full advantage of both the tensile strength parallel to the wood grain and its compressive strength perpendicular to the grain, which enhances the load bearing capacity of the composite. However, traditional CLT panels are made with glue, which can expire and lose effectiveness over time, compromising the CLT panel mechanical strength. To mitigate such shortcomings of conventional CLT panels, we pioneer herein nail-cross-laminated timber (NCLT) panels with more reliable connection system. This study investigates the flexural performance of NCLT panels made with different types of nails and explores the effects of key design parameters including the nail incidence angle, nail type, total number of nails, and number of layers. Results show that NCLT panels have better flexural performance than traditional CLT panels. The failure mode of NCLT panels depends on the nail angle, nail type, and quantity of nails. A modified formula for predicting the flexural bearing capacity of NCLT panels was proposed and proven accurate. The findings could blaze the trail for potential applications of NCLT panels as a sustainable and resilient construction composite for lightweight structures. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in Materials)

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11 pages, 2596 KiB

Open AccessArticle

Air Pressure, Gas Exposure and Electron Beam Irradiation of 2D Transition Metal Dichalcogenides

by Antonio Di Bartolomeo, Aniello Pelella, Alessandro Grillo, Francesca Urban and Filippo Giubileo

Appl. Sci. 2020, 10(17), 5840; https://doi.org/10.3390/app10175840 - 23 Aug 2020

Cited by 5 | Viewed by 2618

Abstract

In this study, we investigate the electrical transport properties of back-gated field-effect transistors in which the channel is realized with two-dimensional transition metal dichalcogenide nanosheets, namely palladium diselenide (PdSe₂) and molybdenum disulfide (MoS₂). The effects of the environment (pressure, [...] Read more.

In this study, we investigate the electrical transport properties of back-gated field-effect transistors in which the channel is realized with two-dimensional transition metal dichalcogenide nanosheets, namely palladium diselenide (PdSe₂) and molybdenum disulfide (MoS₂). The effects of the environment (pressure, gas type, electron beam irradiation) on the electrical properties are the subject of an intense experimental study that evidences how PdSe₂-based devices can be reversibly tuned from a predominantly n-type conduction (under high vacuum) to a p-type conduction (at atmospheric pressure) by simply modifying the pressure. Similarly, we report that, in MoS₂-based devices, the transport properties are affected by pressure and gas type. In particular, the observed hysteresis in the transfer characteristics is explained in terms of gas absorption on the MoS₂ surface due to the presence of a large number of defects. Moreover, we demonstrate the monotonic (increasing) dependence of the width of the hysteresis on decreasing the gas adsorption energy. We also report the effects of electron beam irradiation on the transport properties of two-dimensional field-effect transistors, showing that low fluences of the order of few e^-/nm² are sufficient to cause appreciable modifications to the transport characteristics. Finally, we profit from our experimental setup, realized inside a scanning electron microscope and equipped with piezo-driven nanoprobes, to perform a field emission characterization of PdSe₂ and MoS₂ nanosheets at cathode–anode separation distances as small as 200 nm. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in Materials)

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11 pages, 22220 KiB

Open AccessArticle

Piezoelectric Sensor with a Helical Structure on the Thread Core

by Cheoleon Park, Hojoon Kim and Youngsu Cha

Appl. Sci. 2020, 10(15), 5073; https://doi.org/10.3390/app10155073 - 23 Jul 2020

Cited by 5 | Viewed by 3474

Abstract

In this paper, we introduce a piezoelectric sensor curled on a thread core in a helical structure. In particular, a polyvinylidene fluoride film was curled and fixed on a thread core. A series of experiments were designed to deliver flexural loading to the [...] Read more.

In this paper, we introduce a piezoelectric sensor curled on a thread core in a helical structure. In particular, a polyvinylidene fluoride film was curled and fixed on a thread core. A series of experiments were designed to deliver flexural loading to the piezoelectric sensor, to study its sensing characteristics. The experimental results show that the sensing output of the sensor is in phase with the applied flexural loading. In addition, the output voltage of the textile-based piezoelectric sensor was measured according to various flexural loadings. The flexural bending angle applied to the piezoelectric sensor is expected to be a power function of the voltage output. In addition, we demonstrate a smart textile by weaving the piezoelectric sensor. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in Materials)

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15 pages, 7102 KiB

Open AccessFeature PaperArticle

Influence of Loading Orientation and Knitted Versus Woven Transversal Connections in 3D Textile Reinforced Cement (TRC) Composites

by Michael El Kadi, Panagiotis Kapsalis, Danny Van Hemelrijck, Jan Wastiels and Tine Tysmans

Appl. Sci. 2020, 10(13), 4517; https://doi.org/10.3390/app10134517 - 29 Jun 2020

Cited by 14 | Viewed by 2967

Abstract

As previous research has shown, the use of 3D textiles does not only facilitate the manufacturing process of Textile Reinforced Cement (TRC) composites but also influences the mechanical properties of the TRC. A fundamental understanding of the contribution of the transversal connections in [...] Read more.

As previous research has shown, the use of 3D textiles does not only facilitate the manufacturing process of Textile Reinforced Cement (TRC) composites but also influences the mechanical properties of the TRC. A fundamental understanding of the contribution of the transversal connections in the 3D textile to the loadbearing behavior of 3D TRCs is, however, still lacking in the literature. Therefore, this research experimentally investigates two different parameters of 3D TRCs; firstly, the 3D textile typology, namely knitted versus woven transversal connections, is investigated. Secondly, the influence of the stress direction with respect to the orientation of these connections (parallel or perpendicular) is studied. A clear influence of the orientation is witnessed for the woven 3D TRC system while no influence is observed for the knitted 3D TRC. Both woven and knitted 3D TRC systems show an increased post-cracking bending stiffness compared to an equivalent 2D system (with the same textiles but without transversal connections), yet the woven 3D TRC clearly outperforms the knitted 3D TRC. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in Materials)

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Review

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41 pages, 2333 KiB

Open AccessReview

Can Sustainable Packaging Help to Reduce Food Waste? A Status Quo Focusing Plant-Derived Polymers and Additives

by Imke Korte, Judith Kreyenschmidt, Joana Wensing, Stefanie Bröring, Jan Niklas Frase, Ralf Pude, Christopher Konow, Thomas Havelt, Jessica Rumpf, Michaela Schmitz and Margit Schulze

Appl. Sci. 2021, 11(11), 5307; https://doi.org/10.3390/app11115307 - 7 Jun 2021

Cited by 8 | Viewed by 6351

Abstract

The promotion of sustainable packaging is part of the European Green Deal and plays a key role in the EU’s social and political strategy. One option is the use of renewable resources and biomass waste as raw materials for polymer production. Lignocellulose biomass [...] Read more.

The promotion of sustainable packaging is part of the European Green Deal and plays a key role in the EU’s social and political strategy. One option is the use of renewable resources and biomass waste as raw materials for polymer production. Lignocellulose biomass from annual and perennial industrial crops and agricultural residues are a major source of polysaccharides, proteins, and lignin and can also be used to obtain plant-based extracts and essential oils. Therefore, these biomasses are considered as potential substitute for fossil-based resources. Here, the status quo of bio-based polymers is discussed and evaluated in terms of properties related to packaging applications such as gas and water vapor permeability as well as mechanical properties. So far, their practical use is still restricted due to lower performance in fundamental packaging functions that directly influence food quality and safety, the length of shelf life, and thus the amount of food waste. Besides bio-based polymers, this review focuses on plant extracts as active packaging agents. Incorporating extracts of herbs, flowers, trees, and their fruits is inevitable to achieve desired material properties that are capable to prolong the food shelf life. Finally, the adoption potential of packaging based on polymers from renewable resources is discussed from a bioeconomy perspective. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in Materials)

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12 pages, 1861 KiB

Open AccessReview

A Palette of Efficient and Stable Far-Red and NIR Dye Lasers

by Edurne Avellanal-Zaballa, Leire Gartzia-Rivero, Jorge Bañuelos, Inmaculada García-Moreno, Antonia R. Agarrabeitia, Eduardo Peña-Cabrera and Maria Jose Ortiz

Appl. Sci. 2020, 10(18), 6206; https://doi.org/10.3390/app10186206 - 7 Sep 2020

Cited by 6 | Viewed by 3080

Abstract

The disposal of long-wavelength-emitting sources is of paramount relevance in technology and biophotonics due to the low interference with the surroundings that these kinds of far-red and near-infrared radiations hold. As a result of the continued efforts carried out during the last few [...] Read more.

The disposal of long-wavelength-emitting sources is of paramount relevance in technology and biophotonics due to the low interference with the surroundings that these kinds of far-red and near-infrared radiations hold. As a result of the continued efforts carried out during the last few years by our research group to design new boron-dipyrromethene (BODIPY) dyes with improved photonic performance, two approaches were tested to develop a new generation of organic dyes able to display efficient and long-lasting laser emission in both target spectral regions. On the one hand, the annulation of aromatic benzofuran at the dipyrrin backbone leads to conformationally restricted dyes yielding photostable and bright laser emission beyond 600 nm at the far-red spectral region. On the other hand, a more pronounced shift to longer wavelengths reaching 725 nm at the near-infrared region is feasible, while keeping a reasonably high laser efficiency and tolerance to prolonged and intense pumping, based on aza-BODIPYs bearing peripheral aryl rings. These two complementary strategies yield a library of laser-emitting compounds comprising the 600–725 nm spectral region. Moreover, their laser performance is better than the commercially available dye lasers active in this spectral window. Full article

(This article belongs to the Special Issue 10th Anniversary of Applied Sciences: Invited Papers in Materials)

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